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    Vitellogenin 2 promotes muscle development and stimulates the browning of white fat. Li Yilei,Sun Xiaoli,Bai Yun,Ji Yunyan,Ren Huawei,Yu Xiuju,Yan Yi,He Xiaoyan,Dong Yanjun,Zhang Liping,Luo Xiaomao,Wang Haidong Aging Eggs are rich in nutrients and contain a lot of protein. Although eggs have proved to accelerate the growth of C2C12 cells, the regulatory and mechanism of fertilized egg yolk extract (FEYE) on skeletal muscle development and fat metabolism remains unclearly. The mice were treated with FEYE by gavage for 24 d, we found that FEYE can inhibit the expression of skeletal muscle atrophy genes such as MSTN and Murf-1, and up-regulate the expression levels of MYOD, MYOG and Irisin. In addition, the treatment of FEYE induced UCP1 and PGC1α high expression in WAT, thereby causing WAT browning reaction. In order to confirm the composition of FEYE, we performed protein full spectrum identification (LC MS/MS) analysis and found the most enriched component is vitellogenin 2 (VTG2). Therefore, we added the recombinant protein VTG2 to C2C12 cells and found that VTG2 promoted the proliferation and differentiation of C2C12 cells. After that, we further proved that VTG2 inhibited the expression of MSTN and improved the expression of MYOD and Irisin. Finally, the dual luciferase test proved that VTG2 directly inhibited the transcriptional activity of MSTN. Our results conclude that FEYE inhibits the expression of MSTN in muscle tissues by delivering VTG2, thereby promoting skeletal muscle development, and can also promote the expression level of FNDC5 in serum. Then, FNDC5 acts on the fat through the serum, stimulating the browning reaction of white adipocytes. Therefore, VTG2 can be used to stop muscle consumption, improve skeletal muscle aging, and prevent obesity. 10.18632/aging.203590
    Extracellular lipidome change by an SGLT2 inhibitor, luseogliflozin, contributes to prevent skeletal muscle atrophy in db/db mice. Bamba Ryo,Okamura Takuro,Hashimoto Yoshitaka,Majima Saori,Senmaru Takafumi,Ushigome Emi,Nakanishi Naoko,Asano Mai,Yamazaki Masahiro,Takakuwa Hiroshi,Hamaguchi Masahide,Fukui Michiaki Journal of cachexia, sarcopenia and muscle BACKGROUND:Diabetes mellitus increases the excretion of urinary glucose from the renal glomeruli due to elevated blood glucose levels. In the renal tubules, SGLT2 is expressed and reabsorbs the excreted urinary glucose. In the pathogenesis of diabetes mellitus, glucose reabsorption by SGLT2 is increased, and SGLT2 inhibitors improve hyperglycaemia by inhibiting this reabsorption. When urinary glucose excretion is enhanced, glucose supply to skeletal muscle may be insufficient and muscle protein catabolism may be accelerated. On the other hand, SGLT2 inhibitors not only ameliorate hyperglycaemia but also improve fatty acid metabolism in muscle, which may prevent muscle atrophy. METHODS:Eight-week-old male db/m mice or db/db mice were fed a standard diet with or without the SGLT2i luseogliflozin (0.01% w/w in chow) for 8 weeks. Mice were sacrificed at 16 weeks of age, and skeletal muscle and serum lipidomes, as well as skeletal muscle transcriptome, were analysed. RESULTS:Administration of SGLT2i led to not only decreased visceral fat accumulation (P = 0.004) but also increased soleus muscle weight (P = 0.010) and grip strength (P = 0.0001). The levels of saturated fatty acids, especially palmitic acid, decreased in both muscles (P = 0.017) and sera (P = 0.041) upon administration of SGLT2i, while the content of monosaturated fatty acids, especially oleic acid, increased in both muscle (P < 0.0001) and sera (P = 0.009). Finally, the accumulation of transcripts associated with fatty acid metabolism, such as Scd1, Fasn, and Elovl6, and of muscle atrophy-associated transcripts, such as Foxo1, Mstn, Trim63, and Fbxo32, decreased following SGLT2i administration. CONCLUSIONS:Intramuscular fatty acid metabolism and gene expression were influenced by the extracellular lipidome, which was modified by SGLT2i. Hence, secondary effects, other than the hypoglycaemic effects of SGLT2i, might lead to the alleviation of sarcopenia. 10.1002/jcsm.12814
    Identification and Small Molecule Inhibition of an Activating Transcription Factor 4 (ATF4)-dependent Pathway to Age-related Skeletal Muscle Weakness and Atrophy. Ebert Scott M,Dyle Michael C,Bullard Steven A,Dierdorff Jason M,Murry Daryl J,Fox Daniel K,Bongers Kale S,Lira Vitor A,Meyerholz David K,Talley John J,Adams Christopher M The Journal of biological chemistry Aging reduces skeletal muscle mass and strength, but the underlying molecular mechanisms remain elusive. Here, we used mouse models to investigate molecular mechanisms of age-related skeletal muscle weakness and atrophy as well as new potential interventions for these conditions. We identified two small molecules that significantly reduce age-related deficits in skeletal muscle strength, quality, and mass: ursolic acid (a pentacyclic triterpenoid found in apples) and tomatidine (a steroidal alkaloid derived from green tomatoes). Because small molecule inhibitors can sometimes provide mechanistic insight into disease processes, we used ursolic acid and tomatidine to investigate the pathogenesis of age-related muscle weakness and atrophy. We found that ursolic acid and tomatidine generate hundreds of small positive and negative changes in mRNA levels in aged skeletal muscle, and the mRNA expression signatures of the two compounds are remarkably similar. Interestingly, a subset of the mRNAs repressed by ursolic acid and tomatidine in aged muscle are positively regulated by activating transcription factor 4 (ATF4). Based on this finding, we investigated ATF4 as a potential mediator of age-related muscle weakness and atrophy. We found that a targeted reduction in skeletal muscle ATF4 expression reduces age-related deficits in skeletal muscle strength, quality, and mass, similar to ursolic acid and tomatidine. These results elucidate ATF4 as a critical mediator of age-related muscle weakness and atrophy. In addition, these results identify ursolic acid and tomatidine as potential agents and/or lead compounds for reducing ATF4 activity, weakness, and atrophy in aged skeletal muscle. 10.1074/jbc.M115.681445
    Sarcopenia in Elderly Diabetic Patients: Role of Dipeptidyl Peptidase 4 Inhibitors. Rizzo Maria Rosaria,Barbieri Michelangela,Fava Ilaria,Desiderio Manuela,Coppola Carla,Marfella Raffaele,Paolisso Giuseppe Journal of the American Medical Directors Association BACKGROUND:Our study aimed to investigate the effect of dipeptidyl peptidase 4 inhibitors (DPP4-I) on sarcopenic parameters in elderly type 2 diabetic patients. DESIGN:All elderly diabetic patients were invited to present themselves at our outpatient Geriatric Centre to undergo to evaluation of glycemic, inflammatory, and sarcopenic parameters and to perform a meal test for glucagon-like peptide-1 analogue (GLP-1) activity evaluation. SETTING:According to European Working Group on Sarcopenia in Older People (EWGSOP) criteria, sarcopenic parameters were assessed by bioelectrical impedance analysis (BIA) and Kern dynamometer and 4-m gait speed tests. All patients received standardized meals for the assessment of postprandial levels of GLP-1 activity. PARTICIPANTS, MEASUREMENTS:Data of 80 elderly diabetic patients treated with oral glucose-lowering drugs (DPP4-I or Sulfonylureas Group) for at least 24 months before enrollment were analyzed. RESULTS:The DPP4-I Group showed appropriate glycemic control, lower levels of inflammatory parameters, a significant and greater increase, during interprandial periods, of GLP-1 activity, and better sarcopenic parameters (fat-free mass, skeletal muscle mass, and related indices, muscle strength, and gait speed) compared with the Sulfonylureas Group. Univariate analysis showed that sarcopenic parameters correlated with glycemic control and with GLP-1 area under the curve values. Multivariate analysis confirms these relationships. CONCLUSION:The results are consistent with the hypothesis that DPP4-I use might have a positive effect on the loss of muscle mass and its function. 10.1016/j.jamda.2016.04.016
    Dulaglutide improves muscle function by attenuating inflammation through OPA-1-TLR-9 signaling in aged mice. Khin Phyu Phyu,Hong Yeonhee,Yeon MyeongHoon,Lee Dae Ho,Lee Jong Han,Jun Hee-Sook Aging Dulaglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, is widely used to treat diabetes. However, its effects on muscle wasting due to aging are poorly understood. In the current study, we investigated the therapeutic potential and underlying mechanism of dulaglutide in muscle wasting in aged mice. Dulaglutide improved muscle mass and strength in aged mice. Histological analysis revealed that the cross-sectional area of the tibialis anterior (TA) in the dulaglutide-treated group was thicker than that in the vehicle group. Moreover, dulaglutide increased the shift toward middle and large-sized fibers in both young and aged mice compared to the vehicle. Dulaglutide increased myofiber type I and type IIa in young (18.5% and 8.2%) and aged (1.8% and 19.7%) mice, respectively, compared to the vehicle group. Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, decreased but increased by dulaglutide in aged mice. The expression of atrophic factors such as myostatin, atrogin-1, and muscle RING-finger protein-1 was decreased in aged mice, whereas that of the myogenic factor, MyoD, was increased in both young and aged mice following dulaglutide treatment. In aged mice, optic atrophy-1 (OPA-1) protein was decreased, whereas Toll-like receptor-9 (TLR-9) and its targeting inflammatory cytokines (interleukin-6 [IL-6] and tumor necrosis factor-α [TNF-α]) were elevated in the TA and quadriceps (QD) muscles. In contrast, dulaglutide administration reversed this expression pattern, thereby significantly attenuating the expression of inflammatory cytokines in aged mice. These data suggest that dulaglutide may exert beneficial effects in the treatment of muscle wasting due to aging. 10.18632/aging.203546
    Amelioration of muscle wasting by glucagon-like peptide-1 receptor agonist in muscle atrophy. Hong Yeonhee,Lee Jong Han,Jeong Kwang Won,Choi Cheol Soo,Jun Hee-Sook Journal of cachexia, sarcopenia and muscle BACKGROUND:Skeletal muscle atrophy is defined as a reduction of muscle mass caused by excessive protein degradation. However, the development of therapeutic interventions is still in an early stage. Although glucagon-like peptide-1 receptor (GLP-1R) agonists, such as exendin-4 (Ex-4) and dulaglutide, are widely used for the treatment of diabetes, their effects on muscle pathology are unknown. In this study, we investigated the therapeutic potential of GLP-1R agonist for muscle wasting and the mechanisms involved. METHODS:Mouse C2C12 myotubes were used to evaluate the in vitro effects of Ex-4 in the presence or absence of dexamethasone (Dex) on the regulation of the expression of muscle atrophic factors and the underlying mechanisms using various pharmacological inhibitors. In addition, we investigated the in vivo therapeutic effect of Ex-4 in a Dex-induced mouse muscle atrophy model (20 mg/kg/day i.p.) followed by injection of Ex-4 (100 ng/day i.p.) for 12 days and chronic kidney disease (CKD)-induced muscle atrophy model. Furthermore, we evaluated the effect of a long-acting GLP-1R agonist by treatment of dulaglutide (1 mg/kg/week s.c.) for 3 weeks, in DBA/2J-mdx mice, a Duchenne muscular dystrophy model. RESULTS:Ex-4 suppressed the expression of myostatin (MSTN) and muscle atrophic factors such as F-box only protein 32 (atrogin-1) and muscle RING-finger protein-1 (MuRF-1) in Dex-treated C2C12 myotubes. The suppression effect was via protein kinase A and protein kinase B signalling pathways through GLP-1R. In addition, Ex-4 treatment inhibited glucocorticoid receptor (GR) translocation by up-regulating the proteins of GR inhibitory complexes. In a Dex-induced muscle atrophy model, Ex-4 ameliorated muscle atrophy by suppressing muscle atrophic factors and enhancing myogenic factors (MyoG and MyoD), leading to increased muscle mass and function. In the CKD muscle atrophy model, Ex-4 also increased muscle mass, myofiber size, and muscle function. In addition, treatment with a long-acting GLP-1R agonist, dulaglutide, recovered muscle mass and function in DBA/2J-mdx mice. CONCLUSIONS:GLP-1R agonists ameliorate muscle wasting by suppressing MSTN and muscle atrophic factors and enhancing myogenic factors through GLP-1R-mediated signalling pathways. These novel findings suggest that activating GLP-1R signalling may be useful for the treatment of atrophy-related muscular diseases. 10.1002/jcsm.12434
    Long acting GLP-1 analog liraglutide ameliorates skeletal muscle atrophy in rodents. Gurjar Anagha Ashok,Kushwaha Sapana,Chattopadhyay Sourav,Das Nabanita,Pal Subhashis,China Shyamsundar Pal,Kumar Harish,Trivedi Arun Kumar,Guha Rajdeep,Chattopadhyay Naibedya,Sanyal Sabyasachi Metabolism: clinical and experimental BACKGROUND:Skeletal muscle atrophy is characterized by muscle wasting with partial or complete functional loss. Skeletal muscle atrophy severely affects the quality of life and currently, there is no available therapy except for spinal muscular atrophy. OBJECTIVE:Drug repositioning is a promising strategy that reduces cost and time due to prior availability of safety and toxicity details. Here we investigated myogenic and anti-atrophy effects of glucagon-like peptide-1 (GLP-1) analog liraglutide. METHODS:We used several in vitro atrophy models in C2C12 cells and in vivo models in Sprague Dawley rats to study Liraglutide's efficacy. Western blotting was used to assess cAMP-dependent signaling pathways specifically activated by liraglutide. Therapeutic efficacy of liraglutide was investigated by histological analysis of transverse muscle sections followed by morphometry. Myogenic capacity was investigated by immunoblotting for myogenic factors. RESULTS:Liraglutide induced myogenesis in C2C12 myoblasts through GLP-1 receptor via a cAMP-dependent complex network of signaling events involving protein kinase A, phosphoinositide 3-kinase/protein kinase B, p38 mitogen-activated protein kinase and extracellular signal-regulated kinase. Liraglutide imparted protection against freeze injury, denervation, and dexamethasone -induced skeletal muscle atrophy and improved muscular function in all these models. In a therapeutic model, liraglutide restored myofibrillar architecture in ovariectomy-induced atrophy. Anti-atrophy actions of liraglutide involved suppression of atrogene expression and enhancement in expression of myogenic factors. CONCLUSION:Liraglutide imparted protection and restored myofibrillar architecture in diverse models of muscle atrophy. Given its potent anti-atrophy, and recently reported osteoanabolic effects, we propose liraglutide's clinical evaluation in skeletal muscle atrophy and musculoskeletal disorders associated with diverse pathologies. 10.1016/j.metabol.2019.154044
    Muscle weakness and selective muscle atrophy in osteoprotegerin-deficient mice. Hamoudi Dounia,Bouredji Zineb,Marcadet Laetitia,Yagita Hideo,Landry Louis-Bénédict,Argaw Anteneh,Frenette Jérôme Human molecular genetics Bone and muscle are tightly coupled and form a functional unit under normal conditions. The receptor-activator of nuclear factor κB/receptor-activator of nuclear factor κB ligand/osteoprotegerin (RANK/RANKL/OPG) triad plays a crucial role in bone remodeling. RANKL inhibition by OPG prevents osteoporosis. In contrast, the absence of OPG results in elevated serum RANKL and early onset osteoporosis. However, the impacts of OPG deletion on muscle structure and function are unknown. Our results showed that 1-, 3- and 5-month-old Opg-/- mice have reduced tibial and femoral bone biomechanical properties and higher levels of circulating RANKL. OPG-deficient mice displayed reduced locomotor activity and signs of muscle weakness at 5 months of age. Furthermore, OPG deficiency did not affect the skeletal muscles in 1- and 3-month-old mice. However, it impaired fast-twitch EDL but not slow-twitch Sol muscles in 5-month-old Opg-/- mice. Moreover, 5-month-old Opg-/- mice exhibited selective atrophy of fast-twitch-type IIb myofibers, with increased expression of atrophic proteins such as NF-kB, atrogin-1 and MuRF-1. We used an in vitro model to show that RANKL-stimulated C2C12 myotubes significantly increased the expression of NF-kB, atrogin-1 and MuRF-1. A 2-month anti-RANKL treatment starting at 3 months of age in Opg-/- mice improved voluntary activity, the ex vivo maximum specific force (sP0) of EDL muscles, and whole limb grip force performance and rescued the biomechanical properties of bone. In conclusion, the deletion of OPG and the disruption of the RANKL/OPG balance induced osteoporosis as well as the selective weakness and atrophy of the powerful fast-twitch IIb myofibers, which was partly alleviated by an anti-RANKL treatment. 10.1093/hmg/ddz312
    Denosumab, a fully human monoclonal antibody to RANKL, inhibits bone resorption and increases BMD in knock-in mice that express chimeric (murine/human) RANKL. Kostenuik Paul J,Nguyen Hung Q,McCabe James,Warmington Kelly S,Kurahara Carol,Sun Ning,Chen Ching,Li Luke,Cattley Russ C,Van Gwyneth,Scully Shelia,Elliott Robin,Grisanti Mario,Morony Sean,Tan Hong Lin,Asuncion Frank,Li Xiaodong,Ominsky Michael S,Stolina Marina,Dwyer Denise,Dougall William C,Hawkins Nessa,Boyle William J,Simonet William S,Sullivan John K Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research RANKL is a TNF family member that mediates osteoclast formation, activation, and survival by activating RANK. The proresorptive effects of RANKL are prevented by binding to its soluble inhibitor osteoprotegerin (OPG). Recombinant human OPG-Fc recognizes RANKL from multiple species and reduced bone resorption and increased bone volume, density, and strength in a number of rodent models of bone disease. The clinical development of OPG-Fc was discontinued in favor of denosumab, a fully human monoclonal antibody that specifically inhibits primate RANKL. Direct binding assays showed that denosumab bound to human RANKL but not to murine RANKL, human TRAIL, or other human TNF family members. Denosumab did not suppress bone resorption in normal mice or rats but did prevent the resorptive response in mice challenged with a human RANKL fragment encoded primarily by the fifth exon of the RANKL gene. To create mice that were responsive to denosumab, knock-in technology was used to replace exon 5 from murine RANKL with its human ortholog. The resulting "huRANKL" mice exclusively express chimeric (human/murine) RANKL that was measurable with a human RANKL assay and that maintained bone resorption at slightly reduced levels versus wildtype controls. In young huRANKL mice, denosumab and OPG-Fc each reduced trabecular osteoclast surfaces by 95% and increased bone density and volume. In adult huRANKL mice, denosumab reduced bone resorption, increased cortical and cancellous bone mass, and improved trabecular microarchitecture. These huRANKL mice have potential utility for characterizing the activity of denosumab in a variety of murine bone disease models. 10.1359/jbmr.081112
    RANKL inhibition improves muscle strength and insulin sensitivity and restores bone mass. Bonnet Nicolas,Bourgoin Lucie,Biver Emmanuel,Douni Eleni,Ferrari Serge The Journal of clinical investigation Receptor activator of Nfkb ligand (RANKL) activates, while osteoprotegerin (OPG) inhibits, osteoclastogenesis. In turn a neutralizing Ab against RANKL, denosumab improves bone strength in osteoporosis. OPG also improves muscle strength in mouse models of Duchenne's muscular dystrophy (mdx) and denervation-induce atrophy, but its role and mechanisms of action on muscle weakness in other conditions remains to be investigated. We investigated the effects of RANKL inhibitors on muscle in osteoporotic women and mice that either overexpress RANKL (HuRANKL-Tg+), or lack Pparb and concomitantly develop sarcopenia (Pparb-/-). In women, denosumab over 3 years improved appendicular lean mass and handgrip strength compared to no treatment, whereas bisphosphonate did not. HuRANKL-Tg+ mice displayed lower limb force and maximal speed, while their leg muscle mass was diminished, with a lower number of type I and II fibers. Both OPG and denosumab increased limb force proportionally to the increase in muscle mass. They markedly improved muscle insulin sensitivity and glucose uptake, and decrease anti-myogenic and inflammatory gene expression in muscle, such as myostatin and protein tyrosine phosphatase receptor-γ. Similarly, in Pparb-/-, OPG increased muscle volume and force, while also normalizing their insulin signaling and higher expression of inflammatory genes in skeletal muscle. In conclusions, RANKL deteriorates, while its inhibitor improves, muscle strength and insulin sensitivity in osteoporotic mice and humans. Hence denosumab could represent a novel therapeutic approach for sarcopenia. 10.1172/JCI125915
    RANKL Mediates Muscle Atrophy and Dysfunction in a Cigarette Smoke-induced Model of Chronic Obstructive Pulmonary Disease. Xiong Jing,Le Yanqing,Rao Yafei,Zhou Lu,Hu Yuhan,Guo Suliang,Sun Yongchang American journal of respiratory cell and molecular biology Skeletal muscle dysfunction is one of the important comorbidities of chronic obstructive pulmonary disease (COPD); however, the underlying mechanisms remain largely unknown. RANKL (receptor activator of nuclear factor κB ligand), a key mediator in osteoclast differentiation, was also found to play a role in skeletal muscle pathogenesis. Whether RANKL is involved in COPD-related skeletal muscle dysfunction is as-of-yet unknown. We examined the expression of RANKL/RANK in skeletal muscles from mice exposed to cigarette smoke (CS) for 24 weeks. Grip strength and exercise capacity as well as muscular morphology were evaluated in CS-exposed mice with or without anti-RANKL treatment. The expressions of protein synthesis- or muscle growth-related molecules (IGF-1, myogenin, and myostatin), muscle-specific ubiquitin E3 ligases (MuRF1 and atrogin-1), and the NF-κb inflammatory pathway were also evaluated in skeletal muscles. The effect of CS extract on RANKL/RANK expression and that of exogenous RANKL on the ubiquitin-proteasome pathway in C2C12 myotubes were investigated . Long-term CS exposure induced skeletal muscle dysfunction and atrophy together with upregulation of RANKL/RANK expression in a well-established mouse model of COPD. RANKL neutralization prevented skeletal muscle dysfunction and atrophy. RANKL inhibition decreased expressions of myostatin and MuRF1/Atrogin1 and suppressed the NF-κb pathway in skeletal muscles from CS-exposed mice. In experiments with C2C12 myotubes, CS extract induced expression of RANKL/RANK, and exogenous RANKL induced activation of the ubiquitin-proteasome pathway and NF-κb pathway via RANK. Our results revealed an important role of the RANKL/RANK pathway in muscle atrophy induced by CS exposure, suggesting that RANKL may be a potential therapeutic target in COPD-related skeletal muscle dysfunction. 10.1165/rcmb.2020-0449OC
    Muscle RANK is a key regulator of Ca2+ storage, SERCA activity, and function of fast-twitch skeletal muscles. Dufresne Sébastien S,Dumont Nicolas A,Boulanger-Piette Antoine,Fajardo Val A,Gamu Daniel,Kake-Guena Sandrine-Aurélie,David Rares Ovidiu,Bouchard Patrice,Lavergne Éliane,Penninger Josef M,Pape Paul C,Tupling A Russell,Frenette Jérôme American journal of physiology. Cell physiology Receptor-activator of nuclear factor-κB (RANK), its ligand RANKL, and the soluble decoy receptor osteoprotegerin are the key regulators of osteoclast differentiation and bone remodeling. Here we show that RANK is also expressed in fully differentiated myotubes and skeletal muscle. Muscle RANK deletion has inotropic effects in denervated, but not in sham, extensor digitorum longus (EDL) muscles preventing the loss of maximum specific force while promoting muscle atrophy, fatigability, and increased proportion of fast-twitch fibers. In denervated EDL muscles, RANK deletion markedly increased stromal interaction molecule 1 content, a Ca(2+)sensor, and altered activity of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) modulating Ca(2+)storage. Muscle RANK deletion had no significant effects on the sham or denervated slow-twitch soleus muscles. These data identify a novel role for RANK as a key regulator of Ca(2+)storage and SERCA activity, ultimately affecting denervated skeletal muscle function. 10.1152/ajpcell.00285.2015
    RANKL Blockade Reduces Cachexia and Bone Loss Induced by Non-Metastatic Ovarian Cancer in Mice. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research Tumor- and bone-derived soluble factors have been proposed to participate in the alterations of skeletal muscle size and function in cachexia. We previously showed that mice bearing ovarian cancer (OvCa) exhibit cachexia associated with marked bone loss, whereas bone-targeting agents, such as bisphosphonates, are able to preserve muscle mass in animals exposed to anticancer drugs. De-identified CT images and plasma samples from female patients affected with OvCa were used for body composition assessment and quantification of circulating cross-linked C-telopeptide type I (CTX-I) and receptor activator of NF-kB ligand (RANKL), respectively. Female mice bearing ES-2 tumors were used to characterize cancer- and RANKL-associated effects on muscle and bone. Murine C2C12 and human HSMM myotube cultures were used to determine the OvCa- and RANKL-dependent effects on myofiber size. To the extent of isolating new regulators of bone and muscle in cachexia, here we demonstrate that subjects affected with OvCa display evidence of cachexia and increased bone turnover. Similarly, mice carrying OvCa present high RANKL levels. By using in vitro and in vivo experimental models, we found that elevated circulating RANKL is sufficient to cause skeletal muscle atrophy and bone resorption, whereas bone preservation by means of antiresorptive and anti-RANKL treatments concurrently benefit muscle mass and function in cancer cachexia. Altogether, our data contribute to identifying RANKL as a novel therapeutic target for the treatment of musculoskeletal complications associated with RANKL-expressing non-metastatic cancers. © 2021 American Society for Bone and Mineral Research (ASBMR). 10.1002/jbmr.4480
    An anti-RANKL treatment reduces muscle inflammation and dysfunction and strengthens bone in dystrophic mice. Hamoudi Dounia,Marcadet Laetitia,Piette Boulanger Antoine,Yagita Hideo,Bouredji Zineb,Argaw Anteneh,Frenette Jérôme Human molecular genetics Duchenne muscular dystrophy (DMD) is the most severe form of muscular dystrophy which leads to progressive muscle degeneration and inflammation. The receptor activator of nuclear factor NF-κB ligand (RANKL) and its receptor (RANK), which are expressed in bone and skeletal and cardiac muscles, form a signaling network upstream from nuclear factor-kappa B (NF-κB). We thus hypothesized that prolonged silencing RANKL/RANK signaling would significantly improve DMD. We showed that RANK and RANKL protein levels were increased in the microenvironment of myofibers of 5-month-old utrophin haploinsufficient mdx (mdx/utrn+/-) mice and that a 4 mg/kg dose of anti-RANKL antibody every 3 d for 28 days is optimal and more effective than 1 mg/kg every 3 d for improving the ex vivo maximum specific force (sP0) of dystrophic EDL muscles from mdx/utrn+/- mice. This functional improvement was associated with a reduction in muscle edema, damage, and fibrosis and a marked reduction in serum CK levels. The anti-RANKL treatment inhibited the NF-κB pathway, increased the proportion of anti-inflammatory and non-cytotoxic M2 macrophages, and reduced the number of centrally-nucleated myofibers and the frequency of small myofibers, suggesting that anti-RANKL inhibits the cycle of degeneration/regeneration in dystrophic mice. A three-point bending test showed that a 28-d anti-RANKL treatment increases the mechanical properties of bone in mdx/utrn+/- dystrophic mice. In conclusion, the anti-RANKL treatment protected against skeletal muscle dysfunctions while enhancing bone mechanical properties, filling two needs with one deed in the context of muscular dystrophy. 10.1093/hmg/ddz124
    Reactive oxygen species play an essential role in IGF-I signaling and IGF-I-induced myocyte hypertrophy in C2C12 myocytes. Handayaningsih Anastasia-Evi,Iguchi Genzo,Fukuoka Hidenori,Nishizawa Hitoshi,Takahashi Michiko,Yamamoto Masaaki,Herningtyas Elizabeth-Henny,Okimura Yasuhiko,Kaji Hidesuke,Chihara Kazuo,Seino Susumu,Takahashi Yutaka Endocrinology IGF-I induces skeletal muscle hypertrophy by stimulating protein synthesis and suppressing the protein degradation pathway; the downstream signaling pathways Akt-mammalian target of rapamycin (mTOR)-p70-kDA-S6-kinase (p70S6K), and Forkhead box O1 (FoxO1) play essential roles in this regulation. Reactive oxygen species (ROS) modulate the signaling of various growth factors via redox regulation. However, the role of ROS in IGF-I signaling is not fully understood. In this study, we investigated whether ROS regulate the signaling and biological action of IGF-I in C2C12 myocytes. We found that IGF-I induces ROS in C2C12 myocytes. While treatment with H(2)O(2) significantly enhanced IGF-I-induced phosphorylation of the IGF-I receptor (IGF-IR), IGF-IR phosphorylation was markedly attenuated when cells were treated with antioxidants. The downstream signaling pathway, Akt-mTOR-p70S6K was subsequently down-regulated. Furthermore, the phosphorylation of FoxO1 by IGF-I decreased concomitantly with the restoration of the expression of its target genes, Atrogin-1 and muscle RING finger 1, which are related to muscle atrophy. Nox4 knockdown, which is reportedly to produce ROS in insulin signaling, attenuated IGF-I-induced IGF-IR phosphorylation, indicating that Nox4 is involved in the regulation of IGF-I signaling. Importantly, antioxidant treatments inhibited IGF-I-induced myocyte hypertrophy, demonstrating that ROS are necessary for IGF-I-induced myocyte hypertrophy in vitro. These results indicate that ROS play an essential role in the signaling and biological action of IGF-I in C2C12 myocytes. 10.1210/en.2010-0981
    High parathyroid hormone levels are associated with osteosarcopenia in older individuals with a history of falling. Suriyaarachchi Pushpa,Gomez Fernando,Curcio Carmen L,Boersma Derek,Murthy Lavanya,Grill Vivian,Duque Gustavo Maturitas OBJECTIVES:The combination of osteopenia/osteoporosis and sarcopenia (osteosarcopenia) defines a diagnostic subset of individuals at higher risk of falls, fractures and institutionalization. In this study we aimed to assess the potential role of high serum levels of parathyroid hormone (PTH) in osteosarcopenia. We hypothesized that a high PTH level is one of the major determinants of this syndrome. STUDY DESIGN:Cross-sectional study in 400 subjects (mean age = 79, 65% women) assessed between 2009 and 2014 at the Falls and Fractures Clinic, Nepean Hospital (Penrith, Australia). MAIN OUTCOME MEASURES:Medical history, physical examination, bone densitometry, body composition, posturography, grip strength, gait parameters, and blood tests for nutrition and secondary causes of sarcopenia and osteoporosis. Patients were assigned to one of four groups: 1) osteopenic/osteoporotic; 2) sarcopenic; 3) osteosarcopenic; or 4) non-sarcopenic/non-osteopenic. Patients with abnormal corrected calcium levels were excluded from analysis. Between-group differences were assessed using one-way analysis of variance and chi-squared tests. Multivariable linear regression was used to evaluate the association between the groups and PTH levels adjusted for age, vitamin D, renal function and albumin. RESULTS:24% of the subjects had a high serum PTH level with normal corrected calcium level. These subjects were older, reported more falls per year, and had lower grip strength, limits of stability, BMD, and gait velocity. Subjects with high PTH levels were more likely to be in the osteosarcopenia group than in the non-sarcopenic/non-osteopenic group (OR 6.88; CI: 1.9-9.2). CONCLUSIONS:We reported an independent association between high PTH levels and osteosarcopenia. Our results suggest an important role of PTH in osteosarcopenia that deserves further exploration. 10.1016/j.maturitas.2018.04.006
    Preventing muscle wasting by osteoporosis drug alendronate in vitro and in myopathy models via sirtuin-3 down-regulation. Chiu Hsien-Chun,Chiu Chen-Yuan,Yang Rong-Sen,Chan Ding-Cheng,Liu Shing-Hwa,Chiang Chih-Kang Journal of cachexia, sarcopenia and muscle BACKGROUND:A global consensus on the loss of skeletal muscle mass and function in humans refers as sarcopenia and cachexia including diabetes, obesity, renal failure, and osteoporosis. Despite a current improvement of sarcopenia or cachexia with exercise training and supportive therapies, alternative and specific managements are needed to discover for whom are unable or unwilling to embark on these treatments. Alendronate is a widely used drug for osteoporosis in the elderly and postmenopausal women. Osteopenic menopausal women with 6 months of alendronate therapy have been observed to improve not only lumbar bone mineral density but also handgrip strength. However, the effect and mechanism of alendronate on muscle strength still remain unclear. Here, we investigated the therapeutic potential and the molecular mechanism of alendronate on the loss of muscle mass and strength in vitro and in vivo. METHODS:Mouse myoblasts and primary human skeletal muscle-derived progenitor cells were used to assess the effects of low-dose alendronate (0.1-1 μM) combined with or without dexamethasone on myotube hypertrophy and myogenic differentiation. Moreover, we also evaluated the effects of low-dose alendronate (0.5 and 1 mg/kg) by oral administration on the limb muscle function and morphology of mice with denervation-induced muscle atrophy and glycerol-induced muscle injury. RESULTS:Alendronate inhibited dexamethasone-induced myotube atrophy and myogenic differentiation inhibition in mouse myoblasts and primary human skeletal muscle-derived progenitor cells. Alendronate significantly abrogated dexamethasone-up-regulated sirtuin-3 (SIRT3), but not SIRT1, protein expression in myotubes. Both SIRT3 inhibitor AKG7 and SIRT3-siRNA transfection could also reverse dexamethasone-up-regulated atrogin-1 and SIRT3 protein expressions. Animal studies showed that low-dose alendronate by oral administration ameliorated the muscular malfunction in mouse models of denervation-induced muscle atrophy and glycerol-induced muscle injury with a negative regulation of SIRT3 expression. CONCLUSIONS:The putative mechanism by which muscle atrophy was improved with alendronate might be through the SIRT3 down-regulation. These findings suggest that alendronate can be a promising therapeutic strategy for management of muscle wasting-related diseases and sarcopenia. 10.1002/jcsm.12289
    TNF Receptor-Associated Factor 6 Mediates TNFα-Induced Skeletal Muscle Atrophy in Mice During Aging. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research During aging, muscle mass decreases, leading to sarcopenia, associated with low-level chronic inflammation (inflammaging), which induces sarcopenia by promoting proteolysis of muscle fibers and inhibiting their regeneration. Patients with a variety of pathologic conditions associated with sarcopenia, including rheumatoid arthritis (RA), have systemically elevated TNFα serum levels, and transgenic mice with TNFα overexpression (TNF-Tg mice, a model of RA) develop sarcopenia between adolescence and adulthood before they age. However, if and how TNFα contributes to the pathogenesis of sarcopenia during the normal aging process and in RA remains largely unknown. We report that TNFα levels are increased in skeletal muscles of aged WT mice, associated with muscle atrophy and decreased numbers of satellite cells and Type IIA myofibers, a phenotype that we also observed in adult TNF-Tg mice. Aged WT mice also have increased numbers of myeloid lineage cells in their skeletal muscles, including macrophages and granulocytes. These cells have increased TNFα expression, which impairs myogenic cell differentiation. Expression levels of TNF receptor-associated factor 6 (TRAF6), an E3 ubiquitin ligase, which mediates signaling by some TNF receptor (TNFR) family members, are elevated in skeletal muscles of both aged WT mice and adult TNF-Tg mice. TRAF6 binds to TNFR2 in C2C12 myoblasts and mediates TNFα-induced muscle atrophy through NF-κB-induced transcription of the muscle-specific E3 ligases, Atrogen1 and Murf1, which promote myosin heavy-chain degradation. Haplo-deficiency of TRAF6 prevents muscle atrophy and the decrease in numbers of satellite cells, Type IIA myofibers, and myogenic regeneration in TRAF6 ;TNF-Tg mice. Our findings suggest that pharmacologic inhibition of TRAF6 signaling in skeletal muscles during aging could treat/prevent age- and RA-related sarcopenia by preventing TNFα-induced proteolysis and inhibition of muscle fiber regeneration. © 2020 American Society for Bone and Mineral Research. 10.1002/jbmr.4021
    The Role of TGFβ in Bone-Muscle Crosstalk. Regan Jenna N,Trivedi Trupti,Guise Theresa A,Waning David L Current osteoporosis reports PURPOSE OF REVIEW:The role of bone-derived factors in regulation of skeletal muscle function is an important emerging aspect of research into bone-muscle crosstalk. Implications for this area of research are far reaching and include understanding skeletal muscle weakness in cancer, osteoporosis, cachexia, rare diseases of bone, and aging. RECENT FINDINGS:Recent research shows that bone-derived factors can lead to changes in the skeletal muscle. These changes can either be anabolic or catabolic, and we focus this review on the role of TGFβ in driving oxidative stress and skeletal muscle weakness in the setting of osteolytic cancer in the bone. The bone is a preferred site for breast cancer metastasis and leads to pathological bone loss. Osteolytic cancer in the bone leads to release of TGFβ from the bone via osteoclast-mediated bone destruction. Our appreciation of crosstalk between the muscle and bone has recently expanded beyond mechanical force-driven events to encompass a variety of signaling factors originating in one tissue and communicating to the other. This review summarizes some previously known mediators of bone-to-muscle signaling and also recent work identifying a new role for bone-derived TGFβ as a cause of skeletal muscle weakness in the setting of osteolytic cancer in the bone. Multiple points of potential therapeutic intervention are discussed. 10.1007/s11914-017-0344-5
    Metformin induces muscle atrophy by transcriptional regulation of myostatin via HDAC6 and FoxO3a. Kang Min Ju,Moon Ji Wook,Lee Jung Ok,Kim Ji Hae,Jung Eun Jeong,Kim Su Jin,Oh Joo Yeon,Wu Sang Woo,Lee Pu Reum,Park Sun Hwa,Kim Hyeon Soo Journal of cachexia, sarcopenia and muscle BACKGROUND:Skeletal muscle atrophy is a severe condition that involves loss of muscle mass and quality. Drug intake can also cause muscle atrophy. Biguanide metformin is the first-line and most widely prescribed anti-diabetic drug for patients with type 2 diabetes. The molecular mechanism of metformin in muscle is unclear. METHODS:Myostatin expression was investigated at the protein and transcript levels after metformin administration. To investigate the pathways associated with myostatin signalling, we used real-time polymerase chain reaction, immunoblotting, luciferase assay, chromatin immunoprecipitation assay, co-immunoprecipitation, immunofluorescence, primary culture, and confocal microscopy. Serum analysis, physical performance, and immunohistochemistry were performed using our in vivo model. RESULTS:Metformin induced the expression of myostatin, a key molecule that regulates muscle volume and triggers the phosphorylation of AMPK. AMPK alpha2 knockdown in the background of metformin treatment reduced the myostatin expression of C2C12 myotubes (-49.86 ± 12.03%, P < 0.01) and resulted in increased myotube diameter compared with metformin (+46.62 ± 0.88%, P < 0.001). Metformin induced the interaction between AMPK and FoxO3a, a key transcription factor of myostatin. Metformin also altered the histone deacetylase activity in muscle cells (>3.12-fold ± 0.13, P < 0.001). The interaction between HDAC6 and FoxO3a induced after metformin treatment. Confocal microscopy revealed that metformin increased the nuclear localization of FoxO3a (>3.3-fold, P < 0.001). Chromatin immunoprecipitation revealed that metformin induced the binding of FoxO3a to the myostatin promoter. The transcript-level expression of myostatin was higher in the gastrocnemius (GC) muscles of metformin-treated wild-type (WT) (+68.9 ± 10.01%, P < 0.001) and db/db mice (+55.84 ± 6.62%, P < 0.001) than that in the GC of controls (n = 4 per group). Average fibre cross-sectional area data also showed that the metformin-treated C57BL/6J (WT) (-31.74 ± 0.75%, P < 0.001) and C57BLKS/J-db/db (-18.11 ± 0.94%, P < 0.001) mice had decreased fibre size of GC compared to the controls. The serum myoglobin level was significantly decreased in metformin-treated WT mice (-66.6 ± 9.03%, P < 0.01). CONCLUSIONS:Our results demonstrate that metformin treatment impairs muscle function through the regulation of myostatin in skeletal muscle cells via AMPK-FoxO3a-HDAC6 axis. The muscle-wasting effect of metformin is more evident in WT than in db/db mice, indicating that more complicated mechanisms may be involved in metformin-mediated muscular dysfunction. 10.1002/jcsm.12833
    Metformin limits ceramide-induced senescence in C2C12 myoblasts. Jadhav Kavita S,Dungan Cory M,Williamson David L Mechanisms of ageing and development UNLABELLED:High lipid and ceramide concentrations are hallmarks of obese and/or insulin resistant skeletal muscle, yet little is known about its role on cell cycle and senescence. The purpose of this study was to examine the role of ceramide on muscle senescence, and whether metformin limited this response. METHODS:Low passage, proliferating C2C12 myoblasts were treated with a control, 50μM C2-ceramide (8h), and/or 2mM metformin, then examined for insulin sensitivity, cell senescence, cell proliferation, cell cycle, protein expression of cell cycle regulators. RESULTS:Ceramide treatment caused a dephosphorylation (p<0.05) of Akt and 4E-BP1, regardless of the presence of insulin. The ceramide treated myoblasts displayed higher β-galactosidase staining (p<0.05), reduced BrDu incorporation and total number of cells (p<0.05), and an increased proportion of cells in G2-phase (p<0.05) versus control cultures. Ceramide treatment also upregulated (p<0.05) p53 and p21 protein expression, that was reversed by either pifithrin-α or shRNA for p53. Metformin limited (p<0.05) ceramide's effects on insulin signaling, senescence, and cell cycle regulation. CONCLUSIONS:High ceramide concentrations reduced myoblast proliferation that was associated with aberrant cell cycle regulation and a senescent phenotype, which could provide an understanding of skeletal muscle cell adaptation during conditions of high intramuscular lipid deposition and/or obesity. 10.1016/j.mad.2013.11.002
    Metformin and leucine increase satellite cells and collagen remodeling during disuse and recovery in aged muscle. Petrocelli Jonathan J,Mahmassani Ziad S,Fix Dennis K,Montgomery Jessie A,Reidy Paul T,McKenzie Alec I,de Hart Naomi M,Ferrara Patrick J,Kelley Joshua J,Eshima Hiroaki,Funai Katsuhiko,Drummond Micah J FASEB journal : official publication of the Federation of American Societies for Experimental Biology Loss of muscle mass and strength after disuse followed by impaired muscle recovery commonly occurs with aging. Metformin (MET) and leucine (LEU) individually have shown positive effects in skeletal muscle during atrophy conditions but have not been evaluated in combination nor tested as a remedy to enhance muscle recovery following disuse atrophy in aging. The purpose of this study was to determine if a dual treatment of metformin and leucine (MET + LEU) would prevent disuse-induced atrophy and/or promote muscle recovery in aged mice and if these muscle responses correspond to changes in satellite cells and collagen remodeling. Aged mice (22-24 months) underwent 14 days of hindlimb unloading (HU) followed by 7 or 14 days of reloading (7 or 14 days RL). MET, LEU, or MET + LEU was administered via drinking water and were compared to Vehicle (standard drinking water) and ambulatory baseline. We observed that during HU, MET + LEU resolved whole body grip strength and soleus muscle specific force decrements caused by HU. Gastrocnemius satellite cell abundance was increased with MET + LEU treatment but did not alter muscle size during disuse or recovery conditions. Moreover, MET + LEU treatment alleviated gastrocnemius collagen accumulation caused by HU and increased collagen turnover during 7 and 14 days RL driven by a decrease in collagen IV content. Transcriptional pathway analysis revealed that MET + LEU altered muscle hallmark pathways related to inflammation and myogenesis during HU. Together, the dual treatment of MET and LEU was able to increase muscle function, satellite cell content, and reduce collagen accumulation, thus improving muscle quality during disuse and recovery in aging. 10.1096/fj.202100883R
    Muscle wasting in disease: molecular mechanisms and promising therapies. Cohen Shenhav,Nathan James A,Goldberg Alfred L Nature reviews. Drug discovery Atrophy occurs in specific muscles with inactivity (for example, during plaster cast immobilization) or denervation (for example, in patients with spinal cord injuries). Muscle wasting occurs systemically in older people (a condition known as sarcopenia); as a physiological response to fasting or malnutrition; and in many diseases, including chronic obstructive pulmonary disorder, cancer-associated cachexia, diabetes, renal failure, cardiac failure, Cushing syndrome, sepsis, burns and trauma. The rapid loss of muscle mass and strength primarily results from excessive protein breakdown, which is often accompanied by reduced protein synthesis. This loss of muscle function can lead to reduced quality of life, increased morbidity and mortality. Exercise is the only accepted approach to prevent or slow atrophy. However, several promising therapeutic agents are in development, and major advances in our understanding of the cellular mechanisms that regulate the protein balance in muscle include the identification of several cytokines, particularly myostatin, and a common transcriptional programme that promotes muscle wasting. Here, we discuss these new insights and the rationally designed therapies that are emerging to combat muscle wasting. 10.1038/nrd4467
    FOXO3a mediates signaling crosstalk that coordinates ubiquitin and atrogin-1/MAFbx expression during glucocorticoid-induced skeletal muscle atrophy. Zheng Bin,Ohkawa Sakae,Li Haiyan,Roberts-Wilson Tiffany K,Price S Russ FASEB journal : official publication of the Federation of American Societies for Experimental Biology Muscle atrophy is a consequence of chronic diseases (e.g., diabetes) and glucocorticoid-induced insulin resistance that results from enhanced activity of the ubiquitin-proteasome pathway. The PI3K/Akt pathway inhibits the FOXO-mediated transcription of the muscle-specific E3 ligase atrogin-1/MAFbx (AT-1), whereas the MEK/ERK pathway increases Sp1 activity and ubiquitin (UbC) expression. The observations raise a question about how the transcription of these atrogenes is synchronized in atrophic muscle. We tested a signaling model in which FOXO3a mediates crosstalk between the PI3K/Akt and MEK/ERK pathways to coordinate AT-1 and UbC expression. In rat L6 myotubes, dexamethasone (> or = 24 h) reduced insulin receptor substrate (IRS)-1 protein and PI3K/Akt signaling and increased AT-1 mRNA. IRS-2 protein, MEK/ERK signaling, Sp1 phosphorylation, and UbC transcription were simultaneously increased. Knockdown of IRS-1 using small interfering RNA or adenovirus-mediated expression of constitutively activated FOXO3a increased IRS-2 protein, MEK/ERK signaling, and UbC expression. Changes in PI3K/Akt and MEK/ERK signaling were recapitulated in rat muscles undergoing atrophy due to streptozotocin-induced insulin deficiency and concurrently elevated glucocorticoid production. IRS-1 and Akt phosphorylation were decreased, whereas MEK/ERK signaling and expression of IRS-2, UbC and AT-1 were increased. We conclude that FOXO3a mediates a reciprocal communication between the IRS-1/PI3K/Akt and IRS-2/MEK/ERK pathways that coordinates AT-1 and ubiquitin expression during muscle atrophy. 10.1096/fj.09-151480
    Inducible depletion of satellite cells in adult, sedentary mice impairs muscle regenerative capacity without affecting sarcopenia. Fry Christopher S,Lee Jonah D,Mula Jyothi,Kirby Tyler J,Jackson Janna R,Liu Fujun,Yang Lin,Mendias Christopher L,Dupont-Versteegden Esther E,McCarthy John J,Peterson Charlotte A Nature medicine A key determinant of geriatric frailty is sarcopenia, the age-associated loss of skeletal muscle mass and strength. Although the etiology of sarcopenia is unknown, the correlation during aging between the loss of activity of satellite cells, which are endogenous muscle stem cells, and impaired muscle regenerative capacity has led to the hypothesis that the loss of satellite cell activity is also a cause of sarcopenia. We tested this hypothesis in male sedentary mice by experimentally depleting satellite cells in young adult animals to a degree sufficient to impair regeneration throughout the rest of their lives. A detailed analysis of multiple muscles harvested at various time points during aging in different cohorts of these mice showed that the muscles were of normal size, despite low regenerative capacity, but did have increased fibrosis. These results suggest that lifelong reduction of satellite cells neither accelerated nor exacerbated sarcopenia and that satellite cells did not contribute to the maintenance of muscle size or fiber type composition during aging, but that their loss may contribute to age-related muscle fibrosis. 10.1038/nm.3710
    Mfn2 deficiency links age-related sarcopenia and impaired autophagy to activation of an adaptive mitophagy pathway. Sebastián David,Sorianello Eleonora,Segalés Jessica,Irazoki Andrea,Ruiz-Bonilla Vanessa,Sala David,Planet Evarist,Berenguer-Llergo Antoni,Muñoz Juan Pablo,Sánchez-Feutrie Manuela,Plana Natàlia,Hernández-Álvarez María Isabel,Serrano Antonio L,Palacín Manuel,Zorzano Antonio The EMBO journal Mitochondrial dysfunction and accumulation of damaged mitochondria are considered major contributors to aging. However, the molecular mechanisms responsible for these mitochondrial alterations remain unknown. Here, we demonstrate that mitofusin 2 (Mfn2) plays a key role in the control of muscle mitochondrial damage. We show that aging is characterized by a progressive reduction in Mfn2 in mouse skeletal muscle and that skeletal muscle Mfn2 ablation in mice generates a gene signature linked to aging. Furthermore, analysis of muscle Mfn2-deficient mice revealed that aging-induced Mfn2 decrease underlies the age-related alterations in metabolic homeostasis and sarcopenia. Mfn2 deficiency reduced autophagy and impaired mitochondrial quality, which contributed to an exacerbated age-related mitochondrial dysfunction. Interestingly, aging-induced Mfn2 deficiency triggers a ROS-dependent adaptive signaling pathway through induction of HIF1α transcription factor and BNIP3. This pathway compensates for the loss of mitochondrial autophagy and minimizes mitochondrial damage. Our findings reveal that Mfn2 repression in muscle during aging is a determinant for the inhibition of mitophagy and accumulation of damaged mitochondria and triggers the induction of a mitochondrial quality control pathway. 10.15252/embj.201593084
    Crosstalk between MLO-Y4 osteocytes and C2C12 muscle cells is mediated by the Wnt/β-catenin pathway. Huang Jian,Romero-Suarez Sandra,Lara Nuria,Mo Chenglin,Kaja Simon,Brotto Leticia,Dallas Sarah L,Johnson Mark L,Jähn Katharina,Bonewald Lynda F,Brotto Marco JBMR plus We examined the effects of osteocyte secreted factors on myogenesis and muscle function. MLO-Y4 osteocyte-like cell conditioned media (CM) (10%) increased soleus muscle contractile force by ~25%. MLO-Y4 and primary osteocyte CM (1-10%) stimulated myogenic differentiation of C2C12 myoblasts, but 10% osteoblast CMs did not enhance C2C12 cell differentiation. Since WNT3a and WNT1 are secreted by osteocytes, and the expression level of is increased in MLO-Y4 cells by fluid flow shear stress, both were compared, showing WNT3a more potent than WNT1 in inducing myogenesis. Treatment of C2C12 myoblasts with WNT3a at concentrations as low as 0.5ng/mL mirrored the effects of both primary osteocyte and MLO-Y4 CM by inducing nuclear translocation of β-catenin with myogenic differentiation, suggesting that Wnts might be potential factors secreted by osteocytes that signal to muscle cells. Knocking down in MLO-Y4 osteocytes inhibited the effect of CM on C2C12 myogenic differentiation. Sclerostin (100ng/mL) inhibited both the effects of MLO-Y4 CM and WNT3a on C2C12 cell differentiation. RT-PCR array results supported the activation of the Wnt/β-catenin pathway by MLO-Y4 CM and WNT3a. These results were confirmed by qPCR showing up-regulation of myogenic markers and two Wnt/β-catenin downstream genes, and . We postulated that MLO-Y4 CM/WNT3a could modulate intracellular calcium homeostasis as the trigger mechanism for the enhanced myogenesis and contractile force. MLO-Y4 CM and WNT3a increased caffeine-induced Ca release from the sarcoplasmic reticulum (SR) of C2C12 myotubes and the expression of genes directly associated with intracellular Ca signaling and homeostasis. Together, these data show that and , osteocytes can stimulate myogenesis and enhance muscle contractile function and suggest that Wnts could be mediators of bone to muscle signaling, likely via modulation of intracellular Ca signaling and the Wnt/β-Catenin pathway. 10.1002/jbm4.10015
    Mechanically loaded myotubes affect osteoclast formation. Juffer Petra,Jaspers Richard T,Klein-Nulend Jenneke,Bakker Astrid D Calcified tissue international In response to mechanical loading skeletal muscle produces numerous growth factors and cytokines that enter the circulation. We hypothesized that myotubes produce soluble factors that affect osteoclast formation and aimed to identify which osteoclastogenesis-modulating factors are differentially produced by mechanically stimulated myotubes. C2C12 myotubes were subjected to mechanical loading by cyclic strain for 1 h, and postincubated with or without cyclic strain for 24 h. The effect of cyclic strain on gene expression in myotubes was determined by PCR. Conditioned medium (CM) was collected from cultures of unloaded and loaded myotubes and from MLO-Y4 osteocytes. CM was added to mouse bone marrow cells containing osteoclast precursors, and after 6 days osteoclasts were counted. Compared to unconditioned medium, CM from unloaded osteocytes increased osteoclast formation, while CM from unloaded myotubes decreased osteoclast formation. Cyclic strain strongly enhanced IL-6 expression in myotubes. CM from cyclically strained myotubes increased osteoclast formation compared to CM from unloaded myotubes, but this effect did not occur in the presence of an IL-6 antibody. In conclusion, mechanically loaded myotubes secrete soluble factors, among others IL-6, which affect osteoclast formation. These results suggest that muscle could potentially affect bone homeostasis in vivo via production of growth factors and/or cytokines. 10.1007/s00223-013-9813-8
    Relative abundance of mature myostatin rather than total myostatin is negatively associated with bone mineral density in Chinese. Wu Long-Fei,Zhu Dong-Cheng,Wang Bing-Hua,Lu Yi-Hua,He Pei,Zhang Yun-Hong,Gao Hong-Qin,Zhu Xiao-Wei,Xia Wei,Zhu Hong,Mo Xing-Bo,Lu Xin,Zhang Lei,Zhang Yong-Hong,Deng Fei-Yan,Lei Shu-Feng Journal of cellular and molecular medicine Myostatin is mainly secreted by skeletal muscle and negatively regulates skeletal muscle growth. However, the roles of myostatin on bone metabolism are still largely unknown. Here, we recruited two large populations containing 6308 elderly Chinese and conducted comprehensive statistical analyses to evaluate the associations among lean body mass (LBM), plasma myostatin, and bone mineral density (BMD). Our data revealed that total myostatin in plasma was mainly determined by LBM. The relative abundance of mature myostatin (mature/total) was significantly lower in high versus low BMD subjects. Moreover, the relative abundance of mature myostatin was positively correlated with bone resorption marker. Finally, we carried out in vitro experiments and found that myostatin has inhibitory effects on the proliferation and differentiation of human osteoprogenitor cells. Taken together, our results have demonstrated that the relative abundance of mature myostatin in plasma is negatively associated with BMD, and the underlying functional mechanism for the association is most likely through inhibiting osteoblastogenesis and promoting osteoclastogenesis. 10.1111/jcmm.13438
    Myostatin regulates the production of fibroblast growth factor 23 (FGF23) in UMR106 osteoblast-like cells. Ewendt Franz,Feger Martina,Föller Michael Pflugers Archiv : European journal of physiology Myostatin is a signaling molecule produced by skeletal muscle cells (myokine) that inhibits muscle hypertrophy and has further paracrine and endocrine effects in other organs including bone. Myostatin binds to activin receptor type 2B which forms a complex with transforming growth factor-β type I receptor (TGF-βRI) and induces intracellular p38MAPK and NFκB signaling. Fibroblast growth factor 23 (FGF23) is a paracrine and endocrine mediator produced by bone cells and regulates phosphate and vitamin D metabolism in the kidney. P38MAPK and NFκB-dependent store-operated Ca entry (SOCE) are positive regulators of FGF23 production. Here, we explored whether myostatin influences the synthesis of FGF23. Fgf23 gene expression was determined by qRT-PCR and FGF23 protein by ELISA in UMR106 osteoblast-like cells. UMR106 cells expressed activin receptor type 2A and B. Myostatin upregulated Fgf23 gene expression and protein production. The myostatin effect on Fgf23 was significantly attenuated by TGF-βRI inhibitor SB431542, p38MAPK inhibitor SB202190, and NFκB inhibitor withaferin A. Moreover, SOCE inhibitor 2-APB blunted the myostatin effect on Fgf23. Taken together, myostatin is a stimulator of Fgf23 expression in UMR106 cells, an effect at least partially mediated by downstream TGF-βRI/p38MAPK signaling as well as NFκB-dependent SOCE. 10.1007/s00424-021-02561-y
    Skeletal Response to Soluble Activin Receptor Type IIB in Mouse Models of Osteogenesis Imperfecta. Jeong Youngjae,Daghlas Salah A,Xie Yixia,Hulbert Molly A,Pfeiffer Ferris M,Dallas Mark R,Omosule Catherine L,Pearsall R Scott,Dallas Sarah L,Phillips Charlotte L Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research Osteogenesis imperfecta (OI) is a heritable connective tissue disorder primarily due to mutations in the type I collagen genes (COL1A1 and COL1A2), leading to compromised biomechanical integrity in type I collagen-containing tissues such as bone. Bone is inherently mechanosensitive and thus responds and adapts to external stimuli, such as muscle mass and contractile strength, to alter its mass and shape. Myostatin, a member of the TGF-β superfamily, signals through activin receptor type IIB to negatively regulate muscle fiber growth. Because of the positive impact of myostatin deficiency on bone mass, we utilized a soluble activin receptor type IIB-mFc (sActRIIB-mFc) fusion protein in two molecularly distinct OI mouse models (G610C and oim) and evaluated their bone properties. Wild-type (WT), +/G610C, and oim/oim mice were treated from 2 to 4 months of age with either vehicle (Tris-buffered saline) or sActRIIB-mFc (10 mg/kg). Femurs of sActRIIB-mFc-treated mice exhibited increased trabecular bone volume regardless of genotype, whereas the cortical bone microarchitecture and biomechanical strength were only improved in WT and +/G610C mice. Dynamic histomorphometric analyses suggest the improved cortical bone geometry and biomechanical integrity reflect an anabolic effect due to increased mineral apposition and bone formation rates, whereas static histomorphometric analyses supported sActRIIB-mFc treatment also having an anti-catabolic impact with decreased osteoclast number per bone surface on trabecular bone regardless of sex and genotype. Together, our data suggest that sActRIIB-mFc may provide a new therapeutic direction to improve both bone and muscle properties in OI. © 2018 American Society for Bone and Mineral Research. 10.1002/jbmr.3473
    Activin receptor type 2A (ACVR2A) functions directly in osteoblasts as a negative regulator of bone mass. Goh Brian C,Singhal Vandana,Herrera Angelica J,Tomlinson Ryan E,Kim Soohyun,Faugere Marie-Claude,Germain-Lee Emily L,Clemens Thomas L,Lee Se-Jin,DiGirolamo Douglas J The Journal of biological chemistry Bone and skeletal muscle mass are highly correlated in mammals, suggesting the existence of common anabolic signaling networks that coordinate the development of these two anatomically adjacent tissues. The activin signaling pathway is an attractive candidate to fulfill such a role. Here, we generated mice with conditional deletion of activin receptor (ACVR) type 2A, ACVR2B, or both, in osteoblasts, to determine the contribution of activin receptor signaling in regulating bone mass. Immunohistochemistry localized ACVR2A and ACVR2B to osteoblasts and osteocytes. Primary osteoblasts expressed activin signaling components, including ACVR2A, ACVR2B, and ACVR1B (ALK4) and demonstrated increased levels of phosphorylated Smad2/3 upon exposure to activin ligands. Osteoblasts lacking ACVR2B did not show significant changes However, osteoblasts deficient in ACVR2A exhibited enhanced differentiation indicated by alkaline phosphatase activity, mineral deposition, and transcriptional expression of osterix, osteocalcin, and dentin matrix acidic phosphoprotein 1. To investigate activin signaling in osteoblasts , we analyzed the skeletal phenotypes of mice lacking these receptors in osteoblasts and osteocytes (osteocalcin-Cre). Similar to the lack of effect , ACVR2B-deficient mice demonstrated no significant change in any bone parameter. By contrast, mice lacking ACVR2A had significantly increased femoral trabecular bone volume at 6 weeks of age. Moreover, mutant mice lacking both ACVR2A and ACVR2B demonstrated sustained increases in trabecular bone volume, similar to those in ACVR2A single mutants, at 6 and 12 weeks of age. Taken together, these results indicate that activin receptor signaling, predominantly through ACVR2A, directly and negatively regulates bone mass in osteoblasts. 10.1074/jbc.M117.782128
    Myostatin/Activin Receptor Ligands in Muscle and the Development Status of Attenuating Drugs. Endocrine reviews Muscle wasting disease indications are among the most debilitating and often deadly noncommunicable disease states. As a comorbidity, muscle wasting is associated with different neuromuscular diseases and myopathies, cancer, heart failure, chronic pulmonary and renal diseases, peripheral neuropathies, inflammatory disorders, and, of course, musculoskeletal injuries. Current treatment strategies are relatively ineffective and can at best only limit the rate of muscle degeneration. This includes nutritional supplementation and appetite stimulants as well as immunosuppressants capable of exacerbating muscle loss. Arguably, the most promising treatments in development attempt to disrupt myostatin and activin receptor signaling because these circulating factors are potent inhibitors of muscle growth and regulators of muscle progenitor cell differentiation. Indeed, several studies demonstrated the clinical potential of "inhibiting the inhibitors," increasing muscle cell protein synthesis, decreasing degradation, enhancing mitochondrial biogenesis, and preserving muscle function. Such changes can prevent muscle wasting in various disease animal models yet many drugs targeting this pathway failed during clinical trials, some from serious treatment-related adverse events and off-target interactions. More often, however, failures resulted from the inability to improve muscle function despite preserving muscle mass. Drugs still in development include antibodies and gene therapeutics, all with different targets and thus, safety, efficacy, and proposed use profiles. Each is unique in design and, if successful, could revolutionize the treatment of both acute and chronic muscle wasting. They could also be used in combination with other developing therapeutics for related muscle pathologies or even metabolic diseases. 10.1210/endrev/bnab030
    Muscles, exercise and obesity: skeletal muscle as a secretory organ. Pedersen Bente K,Febbraio Mark A Nature reviews. Endocrinology During the past decade, skeletal muscle has been identified as a secretory organ. Accordingly, we have suggested that cytokines and other peptides that are produced, expressed and released by muscle fibres and exert either autocrine, paracrine or endocrine effects should be classified as myokines. The finding that the muscle secretome consists of several hundred secreted peptides provides a conceptual basis and a whole new paradigm for understanding how muscles communicate with other organs, such as adipose tissue, liver, pancreas, bones and brain. However, some myokines exert their effects within the muscle itself. Thus, myostatin, LIF, IL-6 and IL-7 are involved in muscle hypertrophy and myogenesis, whereas BDNF and IL-6 are involved in AMPK-mediated fat oxidation. IL-6 also appears to have systemic effects on the liver, adipose tissue and the immune system, and mediates crosstalk between intestinal L cells and pancreatic islets. Other myokines include the osteogenic factors IGF-1 and FGF-2; FSTL-1, which improves the endothelial function of the vascular system; and the PGC-1α-dependent myokine irisin, which drives brown-fat-like development. Studies in the past few years suggest the existence of yet unidentified factors, secreted from muscle cells, which may influence cancer cell growth and pancreas function. Many proteins produced by skeletal muscle are dependent upon contraction; therefore, physical inactivity probably leads to an altered myokine response, which could provide a potential mechanism for the association between sedentary behaviour and many chronic diseases. 10.1038/nrendo.2012.49
    Insulin receptor signaling in osteoblasts regulates postnatal bone acquisition and body composition. Fulzele Keertik,Riddle Ryan C,DiGirolamo Douglas J,Cao Xuemei,Wan Chao,Chen Dongquan,Faugere Marie-Claude,Aja Susan,Hussain Mehboob A,Brüning Jens C,Clemens Thomas L Cell Global energy balance in mammals is controlled by the actions of circulating hormones that coordinate fuel production and utilization in metabolically active tissues. Bone-derived osteocalcin, in its undercarboxylated, hormonal form, regulates fat deposition and is a potent insulin secretagogue. Here, we show that insulin receptor (IR) signaling in osteoblasts controls osteoblast development and osteocalcin expression by suppressing the Runx2 inhibitor Twist2. Mice lacking IR in osteoblasts have low circulating undercarboxylated osteocalcin and reduced bone acquisition due to decreased bone formation and deficient numbers of osteoblasts. With age, these mice develop marked peripheral adiposity and hyperglycemia accompanied by severe glucose intolerance and insulin resistance. The metabolic abnormalities in these mice are improved by infusion of undercarboxylated osteocalcin. These results indicate the existence of a bone-pancreas endocrine loop through which insulin signaling in the osteoblast ensures osteoblast differentiation and stimulates osteocalcin production, which in turn regulates insulin sensitivity and pancreatic insulin secretion. 10.1016/j.cell.2010.06.002
    Chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport. Yaspelkis B B,Ansari L,Ramey E L,Holland G J,Loy S F Metabolism: clinical and experimental Leptin, the product of the ob gene, has been shown to reduce fat mass, food intake, hyperglycemia, and hyperinsulinemia and to increase whole-body glucose disposal. However, it is unknown if leptin improves insulin action in skeletal muscle. Therefore, the purpose of this investigation was to determine if chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport. Sixty-nine female Sprague-Dawley rats (240 to 250 g) were randomly assigned to one of three groups: (1) control, (2) pair-fed, and (3) leptin. All animals were subcutaneously implanted with miniosmotic pumps that delivered 0.5 mg leptin/kg/d to the leptin animals and vehicle to the control and pair-fed animals for 14 days. Following this 14-day period, all animals were subjected to hindlimb perfusion to determine the rates of skeletal muscle glucose uptake and 3-O-methyl-D-glucose (3-MG) transport under basal, submaximal (500 microU/mL), and maximal (10,000 microU/mL) insulin concentrations. Chronic leptin treatment significantly increased (P < .05) the rate of glucose uptake across the hindlimb by 27%, 32%, and 47% under basal, submaximal, and maximal insulin, respectively, compared with the control and pair-fed condition. However, when the submaximal rate of glucose uptake was expressed as a percentage of maximal insulin-stimulated glucose uptake, no differences existed among the groups, indicating that leptin treatment does not increase insulin sensitivity. Rates of 3-MG transport in the soleus, plantaris, and white and red portions of the gastrocnemius (WG and RG) were significantly increased (P < .05) in leptin animals under all perfusion conditions. 3-MG transport was not different between control and pair-fed animals. Collectively, these findings suggest that improvements in insulin-stimulated skeletal muscle glucose uptake and transport following chronic leptin treatment result from increased insulin responsiveness.
    Leptin increases skeletal muscle lipoprotein lipase and postprandial lipid metabolism in mice. Donahoo William T,Stob Nicole R,Ammon Stefen,Levin Nancy,Eckel Robert H Metabolism: clinical and experimental The ability of leptin to preserve lean tissue during weight loss may be in part due to differences in nutrient partitioning. Because lipoprotein lipase (LPL) plays a key role in partitioning lipid nutrients, this study was conducted to test the hypothesis that leptin would modify the tissue-specific regulation of LPL and result in increased lipid oxidation and decreased storage. The effects of daily intraperitoneal leptin injections (2 mg/kg body weight) over 2 weeks on LPL activity and postprandial lipid metabolism were tested in both wild-type (WT), leptin-deficient ob/ob obese mice and mice pair fed to the leptin-treated mice. On the experimental day, mice were given food by gavage, blood was drawn periodically, and adipose tissue and skeletal muscle were harvested for measurements of LPL activity at 240 minutes. After 2 weeks of leptin administration, skeletal muscle LPL (SMLPL) activity was increased in leptin-treated compared with pair-fed (P = .012) and WT (P = .002) mice. There was no effect of leptin or pair feeding on postprandial adipose tissue LPL activity. In ob/ob mice, leptin treatment normalized the decrease in postprandial free fatty acid concentration (P = .066). Leptin had no effect on either the area under the triglyceride (TG) excursion or the integrated area under the TG excursion in WT mice. In ob/ob mice, however, the TG excursion was lower in the leptin-treated than the pair-fed mice by area under the TG excursion (P = .012) and was lower than in the WT mice by integrated area under the TG excursion (P = .027). As expected, 2 weeks of leptin treatment decreased body weight in both the WT and ob/ob mice (-2.6% and -10.4%, respectively). Leptin treatment increased SMLPL, an effect that may have contributed to the leptin-induced weight loss. The leptin-induced decreased postprandial TG excursion in ob/ob mice suggests that leptin acts to augment clearance of postprandial TG-rich lipoprotein lipid and that this increase may in part be secondary to the increased activity of SMLPL. The trend for decreased postprandial free fatty acid may indicate that leptin decreases adipose tissue lipid stores without increasing lipolysis. 10.1016/j.metabol.2010.03.016
    Leptin is a physiological regulator of skeletal muscle angiogenesis and is locally produced by PDGFRα and PDGFRβ expressing perivascular cells. Nwadozi Emmanuel,Ng Andrew,Strömberg Anna,Liu Hsin-Yi,Olsson Karl,Gustafsson Thomas,Haas Tara L Angiogenesis Skeletal muscle capillarity is characteristically reduced in mature leptin receptor-deficient (Lepr) mice, which has been attributed to the capillary loss that occurs secondary to metabolic dysfunction. Despite wide recognition of leptin as a pro-angiogenic molecule, the contribution of this adipokine has largely been overlooked in peripheral tissues. Moreover, prior documentation of leptin production within skeletal muscle indicates a potential paracrine role in maintaining local tissue homeostasis. Thus, we hypothesized that leptin is a physiological local paracrine regulator of skeletal muscle angiogenesis and that its production may be modulated by nutrient availability. Lepr mice exhibited impaired angiogenesis during normal developmental maturation of skeletal myocytes, corresponding with an inability to increase vascular endothelial growth factor-A (VEGFA) mRNA and protein levels between 4 and 13 weeks. In cultured murine and human skeletal myocytes, recombinant leptin increased VEGFA mRNA levels. Leptin mRNA was detectable in skeletal muscle, increasing with prolonged high-fat feeding in mice, and with adiposity in human subjects. Platelet-derived growth factor receptor (PDGFR)α- and PDGFRβ- expressing perivascular cell populations were identified as leptin producing within skeletal muscle of mice and humans. Furthermore, in response to 2 weeks of high-fat feeding, PDGFRβ+ but not PDGFRα+ cells increased leptin production. We conclude that leptin is a physiological regulator of the capillary network in skeletal muscle and stimulates VEGFA production by skeletal myocytes. PDGFRβ expressing perivascular cells exhibit the capacity to act as local "nutrient-sensors" that couple nutrient status to leptin production in skeletal muscle. 10.1007/s10456-018-9641-6
    Hallmarks of frailty and osteosarcopenia in prematurely aged PolgA mice. Scheuren Ariane C,D'Hulst Gommaar,Kuhn Gisela A,Masschelein Evi,Wehrle Esther,De Bock Katrien,Müller Ralph Journal of cachexia, sarcopenia and muscle BACKGROUND:Frailty is a geriatric syndrome characterized by increased susceptibility to adverse health outcomes. One major determinant thereof is the gradual weakening of the musculoskeletal system and the associated osteosarcopenia. To improve our understanding of the underlying pathophysiology and, more importantly, to test potential interventions aimed at counteracting frailty, suitable animal models are needed. METHODS:To evaluate the relevance of prematurely aged PolgA mice as a model for frailty and osteosarcopenia, we quantified the clinical mouse frailty index in PolgA and wild-type littermates (PolgA , WT) with age and concertedly assessed the quantity and quality of bone and muscle tissue. Lastly, the anabolic responsiveness of skeletal muscle, muscle progenitors, and bone was assessed. RESULTS:PolgA accumulated health deficits at a higher rate compared with WT, resulting in a higher frailty index at 40 and 46 weeks of age (+166%, +278%, P < 0.0001), respectively, with no differences between genotypes at 34 weeks. Concomitantly, PolgA displayed progressive musculoskeletal deterioration such as reduced bone and muscle mass as well as impaired functionality thereof. In addition to lower muscle weights (-14%, P < 0.05, -23%, P < 0.0001) and fibre area (-20%, P < 0.05, -22%, P < 0.0001) at 40 and 46 weeks, respectively, PolgA showed impairments in grip strength and concentric muscle forces (P < 0.05). PolgA mutation altered the acute response to various anabolic stimuli in skeletal muscle and muscle progenitors. While PolgA muscles were hypersensitive to eccentric contractions as well as leucine administration, shown by larger downstream signalling response of the mechanistic target of rapamycin complex 1, myogenic progenitors cultured in vitro showed severe anabolic resistance to leucine and robust impairments in cell proliferation. Longitudinal micro-computed tomography analysis of the sixth caudal vertebrae showed that PolgA had lower bone morphometric parameters (e.g. bone volume fraction, trabecular, and cortical thickness, P < 0.05) as well as reduced remodelling activities (e.g. bone formation and resorption rate, P < 0.05) compared with WT. When subjected to 4 weeks of cyclic loading, young but not aged PolgA caudal vertebrae showed load-induced bone adaptation, suggesting reduced mechanosensitivity with age. CONCLUSIONS:PolgA mutation leads to hallmarks of age-related frailty and osteosarcopenia and provides a powerful model to better understand the relationship between frailty and the aging musculoskeletal system. 10.1002/jcsm.12588
    Metabolomics Study of Whole-body Vibration on Lipid Metabolism of Skeletal Muscle in Aging Mice. Jiang Dingwen,Liu Chang,Chen Ye,Xing Xuejiao,Zheng Danmeng,Guo Zhanpeng,Lin Sen International journal of sports medicine Ageing increases the occurrence and development of many diseases. Exercise is believed to be an effective way to improve ageing and skeletal muscle atrophy. However, many elderly people are unable to engage in active exercise. Whole-body vibration is a passive way of moving that is especially suitable for the elderly and people who find it inconvenient to exercise. Metabolomics is the systematic study of metabolic changes in small molecules. In this study, metabolomics studies were performed to investigate the regulatory effect of whole-body vibration on the skeletal muscles of ageing mice. After 12 weeks, we found that whole-body vibration had the most obvious effect on lipid metabolism pathways (such as linoleic acid, α-linolenic acid metabolism, glycerophospholipid metabolism pathways) in skeletal muscle of ageing mice. Through further research we found that whole-body vibration decreased the levels of triglycerides, total cholesterol, low-density lipoprotein cholesterol and very low-density lipoprotein in blood; decreased the lipid deposition in skeletal muscle; decreased the protein expression of monocyte chemoattractant protein-1 and interleukin-6; improved the protein levels of phosphorylated insulin receptor substrate-1, phosphate phosphoinositide 3-kinase and p-AKT; improved the protein levels of klotho; and decreased the protein expression of p53. These findings reveal that whole-body vibration might postpone senility by attenuating lipid deposition and reducing chronic inflammation and the insulin resistance of skeletal muscle. 10.1055/a-1268-8458
    Camphene Attenuates Skeletal Muscle Atrophy by Regulating Oxidative Stress and Lipid Metabolism in Rats. Baek Suji,Kim Jisu,Moon Byung Seok,Park Sun Mi,Jung Da Eun,Kang Seo Young,Lee Sang Ju,Oh Seung Jun,Kwon Seung Hae,Nam Myung Hee,Kim Hye Ok,Yoon Hai Jeon,Kim Bom Sahn,Lee Kang Pa Nutrients Sarcopenia- or cachexia-related muscle atrophy is due to imbalanced energy metabolism and oxidative stress-induced muscle dysfunction. Monoterpenes play biological and pharmacological reactive oxygen species (ROS) scavenging roles. Hence, we explored the effects of camphene, a bicyclic monoterpene, on skeletal muscle atrophy in vitro and in vivo. We treated L6 myoblast cells with camphene and then examined the ROS-related oxidative stress using Mito Tracker Red FM and anti-8-oxoguanine antibody staining. To investigate lipid metabolism, we performed real-time polymerase chain reactions, holotomographic microscopy, and respiratory gas analysis. Rat muscle atrophy in in vivo models was observed using F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography and immunocytochemistry. Camphene reversed the aberrant cell size and muscle morphology of L6 myoblasts under starvation and in in vivo models. Camphene also attenuated E3 ubiquitin ligase muscle RING-finger protein-1, mitochondrial fission, and 8-oxoguanine nuclear expression in starved myotubes and hydrogen peroxide (HO)-treated cells. Moreover, camphene significantly regulated lipid metabolism in HO-treated cells and in vivo models. These findings suggest that camphene may potentially affect skeletal muscle atrophy by regulating oxidative stress and lipid metabolism. 10.3390/nu12123731
    FGF-2 targets sclerostin in bone and myostatin in skeletal muscle to mitigate the deleterious effects of glucocorticoid on musculoskeletal degradation. Adhikary Sulekha,Choudhary Dharmendra,Tripathi Ashish Kumar,Karvande Anirudha,Ahmad Naseer,Kothari Priyanka,Trivedi Ritu Life sciences AIM:Myokines are associated with regulation of bone and muscle mass. However, limited information is available regarding the impact of myokines on glucocorticoid (GC) mediated adverse effects on the musculoskeletal system. This study investigates the role of myokine fibroblast growth factor-2 (FGF-2) in regulating GC-induced deleterious effects on bone and skeletal muscle. METHODS:Primary osteoblast cells and C2C12 myoblast cell line were treated with FGF-2 and then exposed to dexamethasone (GC). FGF-2 mediated attenuation of the inhibitory effect of GC on osteoblast and myoblast differentiation and muscle atrophy was assessed through quantitative PCR and western blot analysis. Further, FGF-2 was administered subcutaneously to dexamethasone treated mice to collect bone and skeletal muscle tissue for in vivo analysis of bone microarchitecture, mechanical strength, histomorphometry and for histological alterations in treated tissue samples. KEY FINDINGS:FGF-2 abrogated the dexamethasone induced inhibitory effect on osteoblast differentiation by modulating BMP-2 pathway and inhibiting Wnt antagonist sclerostin. Further, dexamethasone induced atrophy in C2C12 cells was mitigated by FGF-2 as evident from down regulation of atrogenes expression. FGF-2 prevented GC-induced impairment of mineral density, biomechanical strength, trabecular bone volume, cortical thickness and bone formation rate in mice. Additionally, skeletal muscle tissue from GC treated mice displayed weak myostatin immunostaining and reduced expression of atrogenes following FGF-2 treatment. SIGNIFICANCE:FGF-2 mitigated GC induced effects through inhibition of sclerostin and myostatin expression in bone and muscle respectively. Taken together, this study exhibited the role of exogenous FGF-2 in sustaining osteoblastogenesis and inhibiting muscle atrophy in presence of glucocorticoid. 10.1016/j.lfs.2019.05.022
    Soluble Klotho causes hypomineralization in Klotho-deficient mice. Minamizaki Tomoko,Konishi Yukiko,Sakurai Kaoru,Yoshioka Hirotaka,Aubin Jane E,Kozai Katsuyuki,Yoshiko Yuji The Journal of endocrinology The type I transmembrane protein αKlotho (Klotho) serves as a coreceptor for the phosphaturic hormone fibroblast growth factor 23 (FGF23) in kidney, while a truncated form of Klotho (soluble Klotho, sKL) is thought to exhibit multiple activities, including acting as a hormone, but whose mode(s) of action in different organ systems remains to be fully elucidated. FGF23 is expressed primarily in osteoblasts/osteocytes and aberrantly high levels in the circulation acting via signaling through an FGF receptor (FGFR)-Klotho coreceptor complex cause renal phosphate wasting and osteomalacia. We assessed the effects of exogenously added sKL on osteoblasts and bone using Klotho-deficient () mice and cell and organ cultures. sKL induced FGF23 signaling in bone and exacerbated the hypomineralization without exacerbating the hyperphosphatemia, hypercalcemia and hypervitaminosis D in mice. The same effects were seen in rodent bone models , in which we also detected formation of a sKL complex with FGF23-FGFR and decreased (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression. Further, sKL-FGF23-dependent hypomineralization was rescued by soluble PHEX. These data suggest that exogenously added sKL directly participates in FGF23 signaling in bone and that PHEX is a downstream effector of the sKL-FGF23-FGFR axis in bone. 10.1530/JOE-17-0683
    Metformin alleviates dexamethasone-induced apoptosis by regulating autophagy via AMPK/mTOR/p70S6K in osteoblasts. Experimental cell research Glucocorticoid (GC)-induced osteoporosis (GIOP) is the most common type of secondary osteoporosis. Osteoblast apoptosis induced by GCs is now considered as a crucial factor for GIOP. Many clinical, in vivo, and in vitro studies have shown that metformin has a beneficial effect on bone metabolism and bone formation. To investigate whether metformin could be used to treat GIOP, we explored the influence of metformin on dexamethasone (Dex)-induced apoptosis of osteoblasts and its underlying mechanisms. In this study, the CCK8 assay was used to determine the optimal metformin concentration and processing time. The expression levels of target proteins were examined by Western blot and immunofluorescence; the expression levels of target genes were tested by quantitative PCR. Apoptotic cells were detected using flow cytometry. Characteristics of autophagy were observed by transmission electron microscopy. An autophagy inhibitor was administered to investigate whether autophagy decreases apoptosis. Sh-AMPK transfection and an mTOR activator were used to investigate the role of AMPK/mTOR signaling in metformin-induced autophagy. The results showed that metformin alleviated Dex-induced apoptosis of osteoblasts accompanied by increased autophagy. Treatment with the autophagy inhibitor 3-methyladenine (3-MA) attenuated the effect of metformin on apoptosis, autophagy, and the AMPK/mTOR/p70S6K signaling pathway. The anti-apoptotic effect of metformin on osteoblasts is associated with the promotion of autophagy. Furthermore, sh-AMPK transfection and the mTOR activator MHY1485 impaired metformin-mediated inhibition of osteoblast apoptosis and promotion of autophagy. The AMPK/mTOR/p70S6K signaling pathway plays a role in metformin-mediated apoptosis suppression and autophagy promotion. In conclusion, metformin can alleviate Dex-induced osteoblast apoptosis by inducing autophagy via the AMPK/mTOR/p70S6K pathway. This study highlights the potential value of metformin in the treatment of GIOP. 10.1016/j.yexcr.2022.113120
    Counteracting age-related VEGF signaling insufficiency promotes healthy aging and extends life span. Grunewald M,Kumar S,Sharife H,Volinsky E,Gileles-Hillel A,Licht T,Permyakova A,Hinden L,Azar S,Friedmann Y,Kupetz P,Tzuberi R,Anisimov A,Alitalo K,Horwitz M,Leebhoff S,Khoma O Z,Hlushchuk R,Djonov V,Abramovitch R,Tam J,Keshet E Science (New York, N.Y.) Aging is an established risk factor for vascular diseases, but vascular aging itself may contribute to the progressive deterioration of organ function. Here, we show in aged mice that vascular endothelial growth factor (VEGF) signaling insufficiency, which is caused by increased production of decoy receptors, may drive physiological aging across multiple organ systems. Increasing VEGF signaling prevented age-associated capillary loss, improved organ perfusion and function, and extended life span. Healthier aging was evidenced by favorable metabolism and body composition and amelioration of aging-associated pathologies including hepatic steatosis, sarcopenia, osteoporosis, "inflammaging" (age-related multiorgan chronic inflammation), and increased tumor burden. These results indicate that VEGF signaling insufficiency affects organ aging in mice and suggest that modulating this pathway may result in increased mammalian life span and improved overall health. 10.1126/science.abc8479
    Combination of inflammation-related cytokines promotes long-term muscle stem cell expansion. Fu Xin,Xiao Jun,Wei Yuning,Li Sheng,Liu Yan,Yin Jie,Sun Kun,Sun Hao,Wang Huating,Zhang Zongkang,Zhang Bao-Ting,Sheng Chun,Wang Hongyan,Hu Ping Cell research Muscle stem cells (MuSCs, satellite cells) are the major contributor to muscle regeneration. Like most adult stem cells, long-term expansion of MuSCs in vitro is difficult. The in vivo muscle regeneration abilities of MuSCs are quickly lost after culturing in vitro, which prevents the potential applications of MuSCs in cell-based therapies. Here, we establish a system to serially expand MuSCs in vitro for over 20 passages by mimicking the endogenous microenvironment. We identified that the combination of four pro-inflammatory cytokines, IL-1α, IL-13, TNF-α, and IFN-γ, secreted by T cells was able to stimulate MuSC proliferation in vivo upon injury and promote serial expansion of MuSCs in vitro. The expanded MuSCs can replenish the endogenous stem cell pool and are capable of repairing multiple rounds of muscle injuries in vivo after a single transplantation. The establishment of the in vitro system provides us a powerful method to expand functional MuSCs to repair muscle injuries. 10.1038/cr.2015.58
    Dkk3 dependent transcriptional regulation controls age related skeletal muscle atrophy. Yin Jie,Yang Lele,Xie Yangli,Liu Yan,Li Sheng,Yang Wenjun,Xu Bo,Ji Hongbin,Ding Lianghua,Wang Kun,Li Gang,Chen Lin,Hu Ping Nature communications Age-related muscle atrophy (sarcopenia) is the leading cause for disability in aged population, but the underlying molecular mechanisms are poorly understood. Here we identify a novel role for the secreted glycoprotein Dickkopf 3 (Dkk3) in sarcopenia. Forced expression of Dkk3 in muscles in young mice leads to muscle atrophy. Conversely, reducing its expression in old muscles restores both muscle size and function. Dkk3 induces nuclear import of β-catenin and enhances its interaction with FoxO3, which in turn activates the transcription of E3 ubiquitin ligase Fbxo32 and Trim63, driving muscle atrophy. These findings suggest that Dkk3 may be used as diagnostic marker and as therapeutic target for age-related muscle atrophy, and reveal a distinct transcriptional control of Fbxo32 and Trim63. 10.1038/s41467-018-04038-6
    Identification of the shared gene signatures and pathways between sarcopenia and type 2 diabetes mellitus. PloS one BACKGROUND:Sarcopenia is characterized by the age-associated loss of skeletal muscle mass and strength that develops progressively and plays an important role in the disability of the elderly. It has received growing attention over the last decade and has been implicated as both a cause and consequence of type 2 diabetes mellitus (T2DM). The existence of T2DM could increase the risk of developing sarcopenia through multiple mechanisms including advanced glycation end-product accumulation. Meanwhile, sarcopenia would alter glucose disposal and may contribute to the development and progression of T2DM due to reduced muscle mass. METHODS:We implemented transcriptomic analysis of skeletal muscle biopsy specimens in sarcopenia patients and proliferating myoblasts or differentiated myotubes from individuals with T2DM. Related microarray data were selected from Gene Expression Omnibus (GEO) to screen the genes, which were differentially expressed for sarcopenia and T2DM. Multiple combinatorial statistical methods and bioinformatics tools were used to analyze the common DEGs. Meanwhile, functional enrichment analysis was also carried out. Furthermore, we constructed the protein-protein interaction (PPI), as well as transcription factor (TF)-gene interactions network and TF-miRNA coregulatory network. Finally, based on the common DEGs, drug compounds were speculated using the Drug Signatures database (DSigDB). RESULTS:A total of 1765 and 2155 DEGs of sarcopenia and T2DM were screened, respectively. 15 common genes (LXN, CIB2, PEA15, KANK2, FGD1, NMRK1, PLCB1, SEMA4G, ADARB1, UPF3A, CSTB, COL3A1, CD99, ETV3, FJX1) correlated with sarcopenia and T2DM simultaneously were then identified, and 3 genes (UPF3A, CSTB and PEA15) of them were regarded as hub genes. Functional enrichment analysis revealed several shared pathways between two diseases. In addition, according to the TF-gene interactions network and TF-miRNA coregulatory network, part of TF and miRNA may be identified as key regulator in sarcopenia and T2DM at the same time (e.g., CREM and miR-155). Notably, drug compounds for T2DM and sarcopenia were also suggested, such as coenzyme Q10. CONCLUSION:This study revealed that sarcopenia and T2DM may share similar pathogenesis and provided new biological targets and ideas for early diagnosis and effective treatment of sarcopenia and T2DM. 10.1371/journal.pone.0265221
    Urolithin A suppresses RANKL-induced osteoclastogenesis and postmenopausal osteoporosis by, suppresses inflammation and downstream NF-κB activated pyroptosis pathways. Tao Huaqiang,Li Wenming,Zhang Wei,Yang Chen,Zhang Chun,Liang Xiaolong,Yin Juan,Bai Jiaxiang,Ge Gaoran,Zhang Haifeng,Yang Xing,Li Hongxia,Xu Yaozeng,Hao Yuefeng,Liu Yu,Geng Dechun Pharmacological research Osteoporosis (OP) is characterized by decreased trabecular bone volume and microarchitectural deterioration in the medullary cavity. Urolithin A (UA) is a biologically active metabolite generated by the gut microbiota. UA is the measurable product considered the most relevant urolithin as the final metabolic product of polyphenolic compounds. Considering that catabolic effects mediated by the intestinal microbiota are highly involved in pathological bone disorders, exploring the biological influence and molecular mechanisms by which UA alleviates OP is crucial. Our study aimed to investigate the effect of UA administration on OP progression in the context of estrogen deficiency-induced bone loss. The in vivo results indicated that UA effectively reduced ovariectomy-induced systemic bone loss. In vitro, UA suppressed Receptor Activator for Nuclear Factor-κB Ligand (RANKL)-triggered osteoclastogenesis in a concentration-dependent manner. Signal transduction studies and sequencing analysis showed that UA significantly decreased the expression of inflammatory cytokines (e.g., IL-6 and TNF-α) in osteoclasts. Additionally, attenuation of inflammatory signaling cascades inhibited the NF-κB-activated NOD-like receptor signaling pathway, which eventually led to decreased cytoplasmic secretion of IL-1β and IL-18 and reduced expression of pyroptosis markers (NLRP3, GSDMD, and caspase-1). Consistent with this finding, an NLRP3 inflammasome inhibitor (MCC950) was employed to treat OP, and modulation of pyroptosis was found to ameliorate osteoclastogenesis and bone loss in ovariectomized (OVX) mice, suggesting that UA suppressed osteoclast formation by regulating the inflammatory signal-dependent pyroptosis pathway. Conceivably, UA administration may be a safe and promising therapeutic strategy for osteoclast-related bone diseases such as OP. 10.1016/j.phrs.2021.105967
    Butyrate ameliorates skeletal muscle atrophy in diabetic nephropathy by enhancing gut barrier function and FFA2-mediated PI3K/Akt/mTOR signals. Tang Gang,Du Yi,Guan Haochen,Jia Jieshuang,Zhu Nan,Shi Yuping,Rong Shu,Yuan Weijie British journal of pharmacology BACKGROUND AND PURPOSE:Muscle protein catabolism in patients with diabetic nephropathy (DN) results in striking loss of muscle proteins, which increases morbidity and mortality risks. Evidence shows that short-chain fatty acids (SCFAs) play an important role in health maintenance and disease development. Recently, the connection between butyrate (a SCFA) and DN has been revealed, although the relationship between butyrate and muscle atrophy remains unclear. EXPERIMENTAL APPROACH:We studied changes in serum butyrate levels in DN patients using metabolomic analyses. In db/db mice, protective effects of butyrate on DN-induced muscle atrophy. were explored. Inhibition of muscle atrophy by butyrate and the underlying mechanism(s) were studied in C2C12 cells exposed to high glucose/lipopolysaccharide (HG/LPS). KEY RESULTS:Butyrate levels in DN patients were significantly decreased. In db/db mice, supplementing normal diet with butyrate improved intestinal barrier function. Concurrently, butyrate alleviated muscle atrophy, promoted PI3K/Akt/mTOR signalling, and suppressed oxidative stress and autophagy in skeletal muscle of db/db mice, and in HG/LPS-exposed C2C12 cells. Further, FFA2 receptors, key components of SCFA signalling, were decreased in skeletal muscle of db/db mice and in HG/LPS-exposed C2C12 cells. Overexpression of FFA2 receptors activated PI3K/Akt/mTOR signalling and inhibited oxidative stress and autophagy in HG/LPS-exposed C2C12 cells. Silencing of FFA2 blocked PI3K/Akt/mTOR signalling that was improved by butyrate, as well as the suppression of oxidative stress and reduction of autophagy. CONCLUSION AND IMPLICATION:Butyrate exerts protective effects on muscle atrophy induced by DN by enhancing intestinal barrier function and activating the FFA2 receptor-mediated PI3K/Akt/mTOR pathway. 10.1111/bph.15693
    Reduced Physical Activity Alters the Leucine-Stimulated Translatome in Aged Skeletal Muscle. Mahmassani Ziad S,McKenzie Alec I,Petrocelli Jonathan J,de Hart Naomi M,Fix Dennis K,Kelly Joshua J,Baird Lisa M,Howard Michael T,Drummond Micah J The journals of gerontology. Series A, Biological sciences and medical sciences Periods of inactivity experienced by older adults induce nutrient anabolic resistance creating a cascade of skeletal muscle transcriptional and translational aberrations contributing to muscle dysfunction. The purpose of this study was to identify how inactivity alters leucine-stimulated translation of molecules and pathways within the skeletal muscle of older adults. We performed ribosomal profiling alongside RNA sequencing from skeletal muscle biopsies taken from older adults (n = 8; ~72 years; 6 F/2 M) in response to a leucine bolus before (Active) and after (Reduced Activity) 2 weeks of reduced physical activity. At both visits, muscle biopsies were taken at baseline, 60 minutes (early response), and 180 minutes (late response) after leucine ingestion. Previously identified inactivity-related gene transcription changes (PFKFB3, GADD45A, NMRK2) were heightened by leucine with corresponding changes in translation. In contrast, leucine also stimulated translational efficiency of several transcripts in a manner not explained by corresponding changes in mRNA abundance ("uncoupled translation"). Inactivity eliminated this uncoupled translational response for several transcripts, and reduced the translation of most mRNAs encoding for ribosomal proteins. Ingenuity Pathway Analysis identified discordant circadian translation and transcription as a result of inactivity such as translation changes to PER2 and PER3 despite unchanged transcription. We demonstrate inactivity alters leucine-stimulated "uncoupled translation" of ribosomal proteins and circadian regulators otherwise not detectable by traditional RNA sequencing. Innovative techniques such as ribosomal profiling continues to further our understanding of how physical activity mediates translational regulation, and will set a path toward therapies that can restore optimal protein synthesis on the transcript-specific level to combat negative consequences of inactivity on aging muscle. 10.1093/gerona/glab077
    FNDC5/irisin facilitates muscle-adipose-bone connectivity through ubiquitination-dependent activation of runt-related transcriptional factors RUNX1/2. The Journal of biological chemistry In the past decade, the cleavage protein irisin derived from fibronectin type III domain-containing protein 5 (FNDC5) in exercise-stimulated skeletal muscle has increasingly become a biomarker associated with metabolic syndrome and osteoporosis in humans. However, it is unclear how this protein facilitates muscle-adipose-bone connectivity in metabolic and skeletal homeostasis. In this study, we unexpectedly observed that the FNDC5 gene can be markedly activated during the differentiation of brown adipocytes but not white adipocytes, and that FNDC5 is specifically expressed in mouse brown adipose tissues (BATs). But unlike it in the skeletal muscles, the expression of FNDC5/irisin in BAT is promoted by cold exposure rather than exercise in mice. Analysis of promoter activity and chromatin immunoprecipitation further showed that peroxisome proliferator-activated receptor γ coactivator-1α and thyroid hormone receptors cooperate on the FNDC5 gene promoter to induce its transcription. We found that FNDC5/irisin stimulates the runt-related transcriptional factors RUNX1/2 via a focal adhesion kinase-dependent pathway in both bone and subcutaneous white adipose tissues. Mechanistically, focal adhesion kinase is stimulated by FNDC5/irisin and then facilitates E3 ubiquitin-protein ligase WW domain-containing protein 2 to ubiquitinate and subsequently activate RUNX1/2, culminating in the activation of osteoblast-related or thermogenesis-related genes. Interestingly, the PR domain containing protein 16 that is crucial for subcutaneous white adipose "browning" and skeletal development was found to form a complex with RUNX1/2 in a WW domain-containing protein 2-dependent manner. These findings elucidate a signaling mechanism by which FNDC5/irisin supports the muscle-adipose-bone connectivity, especially BAT-bone connectivity. 10.1016/j.jbc.2022.101679
    Epoxymicheliolide inhibits osteoclastogenesis and resists OVX-induced osteoporosis by suppressing ERK1/2 and NFATc1 signaling. International immunopharmacology The hyperactivity of osteoclasts caused by postmenopausal estrogen deficiency plays an imperative role in the progression of osteoporosis. Although osteoporosis-related drugs have been widely used to alleviate this disorder, there is an urgent need for drugs with fewer side effects. In this study, we found that epoxymicheliolide (EMCL), a derivative of parthenolide, has a high affinity to ERK1/2, but the treatment and mechanism of osteoporosis using EMCL have not been explored. Therefore, we intended to figure out the effects and potential mechanisms of EMCL on RANKL-stimulated osteoclast formation and function in vitro, construct an OVX murine model to simulate the therapeutic effects of EMCL on estrogen-deficient bone loss subsequently. EMCL restrained the phosphorylation of ERK1/2 in the RANKL-stimulated MAPK pathway, which in sequence inhibited the transcription and expression of the main osteoclast transcription factor NFATc1, resulting in the suppression of osteoclastogenesis and bone resorption. However, the same concentration of EMCL did not affect the proliferation and differentiation of osteoblasts. In vivo experiments showed that EMCL can significantly resist osteoporosis caused by estrogen deficiency, alleviate bone loss, and reduce the number of osteoclasts. These results suggest that EMCL can reduce osteoclast production and bone resorption by inhibiting ERK1/2 phosphorylation and NFATc1 entering the nucleus, and could be used in the treatment of osteoporosis caused by estrogen deficiency and hyperactivity of osteoclasts. 10.1016/j.intimp.2022.108632
    Role of microRNA-19b-3p on osteoporosis after experimental spinal cord injury in rats. Archives of biochemistry and biophysics Osteoporosis is a common complication accompanied by spinal cord injury (SCI) occurrence. MicroRNAs (miRNAs) have been proved to play a crucial role in the progression of osteoporosis, but their regulating mechanism is unclear. The present study investigated miRNA-19b-3p level in SCI rats induced by modified Allen method, as well as the role of miRNA-19b-3p in osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). MiRNA-19b-3p expression and bone mineral density (BMD) of femurs were measured at day 21 and day 60 after SCI in rats. Obvious miRNA-19b-3p up-regulation and aggravated bone loss were observed. MiRNA-19b-3p overexpression suppressed BMSC-derived osteoblast differentiation, which was confirmed by the decrease in alkaline phosphatase (ALP) activity, EBF2 expression, osteoprotegrin (OPG) to receptor activator of nuclear factor kappa-B ligand (RANKL) ratio and cell mineralization degree. Besides, MiRNA-19b-3p knockdown could reverse this phenomenon. Dual-luciferase reporter assays verified the targeting relationship between miRNA-19b-3p and EBF2. The in vivo experiments confirmed miRNA-19b-3p down-regulation could significantly attenuate osteoporosis after SCI, which was verified by increased BMD, collagen content, femur mineralization degree, EBF2 protein, and OPG-to-RANKL ratio. The results show that miRNA-19b-3p plays an important role in the osteoporosis process after SCI through regulating EBF2 expression. 10.1016/j.abb.2022.109134
    The regulative effect and repercussion of probiotics and prebiotics on osteoporosis: involvement of brain-gut-bone axis. Zhang Yuan-Wei,Cao Mu-Min,Li Ying-Juan,Dai Guang-Chun,Lu Pan-Pan,Zhang Ming,Bai Li-Yong,Chen Xiang-Xu,Zhang Cheng,Shi Liu,Rui Yun-Feng Critical reviews in food science and nutrition Osteoporosis (OP) is a systemic disease characterized by decreased bone mass and degeneration of bone microstructure. In recent years, more and more researches have focused on the close relationship between gut microbiota (GM) and the occurrence and progression of OP, and the regulation of probiotics and prebiotics on bone metabolism has gradually become a research hotspot. Based on the influence of brain-gut-bone axis on bone metabolism, this review expounds the potential mechanisms of probiotics and prebiotics on OP from next perspectives: regulation of intestinal metabolites, regulation of intestinal epithelial barrier function, involvement of neuromodulation, involvement of immune regulation and involvement of endocrine regulation, so as to provide a novel and promising idea for the prevention and treatment of OP in the future. 10.1080/10408398.2022.2047005
    1,25(OH)2vitamin D3 stimulates myogenic differentiation by inhibiting cell proliferation and modulating the expression of promyogenic growth factors and myostatin in C2C12 skeletal muscle cells. Garcia Leah A,King Keisha K,Ferrini Monica G,Norris Keith C,Artaza Jorge N Endocrinology Skeletal muscle wasting is an important public health problem associated with aging, chronic disease, cancer, kidney dialysis, and HIV/AIDS. 1,25-Dihydroxyvitamin D (1,25-D3), the active form of vitamin D, is widely recognized for its regulation of calcium and phosphate homeostasis in relation to bone development and maintenance and for its calcemic effects on target organs, such as intestine, kidney, and parathyroid glands. Emerging evidence has shown that vitamin D administration improves muscle performance and reduces falls in vitamin D-deficient older adults. However, little is known of the underlying mechanism or the role 1,25-D3 plays in promoting myogenic differentiation at the cellular and/or molecular level. In this study, we examined the effect of 1,25-D3 on myoblast cell proliferation, progression, and differentiation into myotubes. C(2)C(12) myoblasts were treated with 1,25-D3 or placebo for 1, 3, 4, 7, and 10 d. Vitamin D receptor expression was analyzed by quantitative RT-PCR, Western blottings and immunofluorescence. Expression of muscle lineage, pro- and antimyogenic, and proliferation markers was assessed by immunocytochemistry, PCR arrays, quantitative RT-PCR, and Western blottings. Addition of 1,25-D3 to C(2)C(12) myoblasts 1) increased expression and nuclear translocation of the vitamin D receptor, 2) decreased cell proliferation, 3) decreased IGF-I expression, and 4) promoted myogenic differentiation by increasing IGF-II and follistatin expression and decreasing the expression of myostatin, the only known negative regulator of muscle mass, without changing growth differentiation factor 11 expression. This study identifies key vitamin D-related molecular pathways for muscle regulation and supports the rationale for vitamin D intervention studies in select muscle disorder conditions. 10.1210/en.2011-0159
    The transient receptor potential channel TRPV6 is dynamically expressed in bone cells but is not crucial for bone mineralization in mice. van der Eerden Bram C J,Weissgerber Petra,Fratzl-Zelman Nadja,Olausson Jenny,Hoenderop Joost G J,Schreuders-Koedam Marijke,Eijken Marco,Roschger Paul,de Vries Teun J,Chiba Hideki,Klaushofer Klaus,Flockerzi Veit,Bindels René J M,Freichel Marc,van Leeuwen Johannes P T M Journal of cellular physiology Bone is the major store for Ca(2+) in the body and plays an important role in Ca(2+) homeostasis. During bone formation and resorption Ca(2+) must be transported to and from bone by osteoblasts and osteoclasts, respectively. However, little is known about the Ca(2+) transport machinery in these bone cells. In this study, we examined the epithelial Ca(2+) channel TRPV6 in bone. TRPV6 mRNA is expressed in human and mouse osteoblast-like cells as well as in peripheral blood mononuclear cell-derived human osteoclasts and murine tibial bone marrow-derived osteoclasts. Also other transcellular Ca(2+) transport genes, calbindin-D(9k) and/or -D(28K), Na(+)/Ca(2+) exchanger 1, and plasma membrane Ca(2+) ATPase (PMCA1b) were expressed in these bone cell types. Immunofluorescence and confocal microscopy on human osteoblasts and osteoclasts and mouse osteoclasts revealed TRPV6 protein at the apical domain and PMCA1b at the osteoidal domain of osteoblasts, whereas in osteoclasts TRPV6 was predominantly found at the bone-facing site. TRPV6 was dynamically expressed in human osteoblasts, showing maximal expression during mineralization of the extracellular matrix. 1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) did not change TRPV6 expression in both mineralizing and non-mineralizing SV-HFO cultures. Lentiviral transduction-mediated overexpression of TRPV6 in these cells did not alter mineralization. Bone microarchitecture and mineralization were unaffected in Trpv6(D541A/D541A) mice in which aspartate 541 in the pore region was replaced with alanine to render TRPV6 channels non-functional. In summary, TRPV6 and other proteins involved in transcellular Ca(2+) transport are dynamically expressed in bone cells, while TRPV6 appears not crucial for bone metabolism and matrix mineralization in mice. 10.1002/jcp.22923
    The calcium channel TRPV6 is a novel regulator of RANKL-induced osteoclastic differentiation and bone absorption activity through the IGF-PI3K-AKT pathway. Ma Jun,Zhu Lei,Zhou Zhibin,Song Tengfei,Yang Lei,Yan Xu,Chen Aimin,Ye Tian Wen Cell proliferation OBJECTIVES:Calcium ion signals are important for osteoclast differentiation. Transient receptor potential vanilloid 6 (TRPV6) is a regulator of bone homeostasis. However, it was unclear whether TRPV6 was involved in osteoclast formation. Therefore, the aim of this study was to evaluate the role of TPRV6 in bone metabolism and to clarify its regulatory role in osteoclasts at the cellular level. MATERIALS AND METHODS:Bone structure and histological changes in Trpv6 knockout mice were examined using micro-computed tomography and histological analyses. To investigate the effects of Trpv6 on osteoclast function, we silenced or overexpressed Trpv6 in osteoclasts via lentivirus transfection, respectively. Osteoclast differentiation and bone resorption viability were measured by tartrate-resistant acid phosphatase (TRAP) staining and pit formation assays. The expression of osteoclast marker genes, including cathepsin k, DC-STAMP, Atp6v0d2 and TRAP, was measured by qRT-PCR. Cell immunofluorescence and Western blotting were applied to explore the mechanisms by which the IGF-PI3K-AKT pathway was involved in the regulation of osteoclast formation and bone resorption by Trpv6. RESULTS:We found that knockout of Trpv6 induced osteoporosis and enhanced bone resorption in mice, but did not affect bone formation. Further studies showed that Trpv6, which was distributed on the cell membrane of osteoclasts, acted as a negative regulator for osteoclast differentiation and function. Mechanistically, Trpv6 suppressed osteoclastogenesis by decreasing the ratios of phosphoprotein/total protein in the IGF-PI3K-AKT signalling pathway. Blocking of the IGF-PI3K-AKT pathway significantly alleviated the inhibitory effect of Trpv6 on osteoclasts formation. CONCLUSIONS:Our study confirmed the important role of Trpv6 in bone metabolism and clarified its regulatory role in osteoclasts at the cellular level. Taken together, this study may inspire a new strategy for the treatment of osteoporosis. 10.1111/cpr.12955
    Decreased bioavailability of vitamin D in obesity. Wortsman J,Matsuoka L Y,Chen T C,Lu Z,Holick M F The American journal of clinical nutrition BACKGROUND:Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism. OBJECTIVE:This study assessed whether obesity alters the cutaneous production of vitamin D(3) (cholecalciferol) or the intestinal absorption of vitamin D(2) (ergocalciferol). DESIGN:Healthy, white, obese [body mass index (BMI; in kg/m(2)) > or = 30] and matched lean control subjects (BMI </= 25) received either whole-body ultraviolet radiation or a pharmacologic dose of vitamin D(2) orally. RESULTS:Obese subjects had significantly lower basal 25-hydroxyvitamin D concentrations and higher parathyroid hormone concentrations than did age-matched control subjects. Evaluation of blood vitamin D(3) concentrations 24 h after whole-body irradiation showed that the incremental increase in vitamin D(3) was 57% lower in obese than in nonobese subjects. The content of the vitamin D(3) precursor 7-dehydrocholesterol in the skin of obese and nonobese subjects did not differ significantly between groups nor did its conversion to previtamin D(3) after irradiation in vitro. The obese and nonobese subjects received an oral dose of 50000 IU (1.25 mg) vitamin D(2). BMI was inversely correlated with serum vitamin D(3) concentrations after irradiation (r = -0.55, P: = 0.003) and with peak serum vitamin D(2) concentrations after vitamin D(2) intake (r = -0.56, P: = 0.007). CONCLUSIONS:Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments. 10.1093/ajcn/72.3.690
    Identification of morphological markers of sarcopenia at early stage of aging in skeletal muscle of mice. Sayed Ramy K A,de Leonardis Erika Chacin,Guerrero-Martínez José A,Rahim Ibtissem,Mokhtar Doaa M,Saleh Abdelmohaimen M,Abdalla Kamal E H,Pozo María J,Escames Germaine,López Luis C,Acuña-Castroviejo Darío Experimental gerontology The gastrocnemius muscle (GM) of young (3months) and aged (12months) female wild-type C57/BL6 mice was examined by light and electron microscopy, looking for the presence of structural changes at early stage of the aging process. Morphometrical parameters including body and gastrocnemius weights, number and type of muscle fibers, cross section area (CSA), perimeter, and Feret's diameter of single muscle fiber, were measured. Moreover, lengths of the sarcomere, A-band, I-band, H-zone, and number and CSA of intermyofibrillar mitochondria (IFM), were also determined. The results provide evidence that 12month-old mice had significant changes on skeletal muscle structure, beginning with the reduction of gastrocnemius weight to body weight ratio, compatible with an early loss of skeletal muscle function and strength. Moreover, light microscopy revealed increased muscle fibers size, with a significant increase on their CSA, perimeter, and diameter of both type I and type II muscle fibers, and a reduction in the percentage of muscle area occupied by type II fibers. Enhanced connective tissue infiltrations, and the presence of centrally nucleated muscle fibers, were also found in aged mice. These changes may underlie an attempt to compensate the loss of muscle mass and muscle fibers number. Furthermore, electron microscopy discovered a significant age-dependent increase in the length of sarcomeres, I and H bands, and reduction on the overlapped actin/myosin length, supporting contractile force loss with age. Electron microscopy also showed an increased number and CSA of IFM with age, which may reveal more endurance at 12months of age. Together, mice at early stage of aging already show significant changes in gastrocnemius muscle morphology and ultrastructure that are suggestive of the onset of sarcopenia. 10.1016/j.exger.2016.07.007
    A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Attie Kenneth M,Borgstein Niels G,Yang Yijun,Condon Carolyn H,Wilson Dawn M,Pearsall Amelia E,Kumar Ravi,Willins Debbie A,Seehra Jas S,Sherman Matthew L Muscle & nerve INTRODUCTION:ACE-031 is a soluble form of activin receptor type IIB (ActRIIB). ACE-031 promotes muscle growth by binding to myostatin and other negative regulators of muscle mass. METHODS:This double-blind, placebo-controlled study evaluated the safety, pharmacokinetics, and pharmacodynamics of ACE-031 in 48 healthy, postmenopausal women randomized to receive 1 dose of ACE-031 (0.02-3 mg/kg s.c.) or placebo (3:1). RESULTS:ACE-031 was generally well-tolerated. Adverse events included injection site erythema. Mean ACE-031 AUC(0-∞) and C(max) increased linearly with dose; mean T(½) was 10-15 days. Statistically significant increases in mean total body lean mass (3.3%; P = 0.03, by DXA) and thigh muscle volume (5.1%; P = 0.03, by MRI) were observed at day 29 in the 3 mg/kg group. Statistically significant changes in serum biomarkers suggest ACE-031 also improved bone and fat metabolism. CONCLUSIONS:Single-dose ACE-031 treatment was generally well-tolerated and resulted in increases in muscle mass in healthy postmenopausal women. 10.1002/mus.23539
    Determinants of Muscle and Bone Aging. Curtis Elizabeth,Litwic Anna,Cooper Cyrus,Dennison Elaine Journal of cellular physiology Loss of bone and muscle with advancing age represent a huge threat to loss of independence in later life. Osteoporosis represents a major public health problem through its association with fragility fractures, primarily of the hip, spine and distal forearm. Sarcopenia, the age related loss of muscle mass and function, may add to fracture risk by increasing falls risk. In the context of muscle aging, it is important to remember that it is not just a decline in muscle mass which contributes to the deterioration of muscle function. Other factors underpinning muscle quality come into play, including muscle composition, aerobic capacity and metabolism, fatty infiltration, insulin resistance, fibrosis and neural activation. Genetic, developmental, endocrine and lifestyle factors, such as physical activity, smoking and poor diet have dual effects on both muscle and bone mass in later life and these will be reviewed here. Recent work has highlighted a possible role for the early environment. Inflammaging is an exciting emerging research field that is likely to prove relevant to future work, including interventions designed to retard to reverse bone and muscle loss with age. 10.1002/jcp.25001
    Insulin-like growth factor-I-coupled mitogenic signaling in primary cultured human skeletal muscle cells and in C2C12 myoblasts. A central role of protein kinase Cdelta. Czifra Gabriella,Tóth István Balázs,Marincsák Rita,Juhász István,Kovács Ilona,Acs Péter,Kovács László,Blumberg Peter M,Bíró Tamás Cellular signalling In this study, we have investigated the effects of insulin-like growth factor-I (IGF-I) on cellular responses of primary human skeletal muscle cells and mouse C2C12 myoblasts. In human muscle, IGF-I stimulated proliferation and fusion of the cells and the expression of the differentiation marker desmin. These effects were completely inhibited by Rottlerin, the inhibitor of the protein kinase C (PKC)delta, but were not affected by the inhibition of the mitogen-activated protein kinase (MAPK) or the phosphatidylinositide 3-kinase (PI-3K) pathways. Furthermore, IGF-I initiated the selective translocation of PKCdelta to the nucleus. In C2C12 myoblasts, the growth-promoting effects of IGF-I were abrogated by inhibition of PKCdelta, but not by the inhibition of the PI-3K system. However, in contrast to the human data, the MAPK inhibitor PD098059 partially (yet significantly) also inhibited the action of IGF-I and, furthermore, IGF-I induced phosphorylation of the MAPK Erk-1/2. In addition, overexpression of constitutively active form of PKCdelta in C2C12 cells fully mimicked, whereas overexpression of kinase inactive mutant of the isoform prevented the action of IGF-I. Finally, the inhibition of PKCdelta suspended the IGF-I-induced phosphorylation of Erk-1/2 and, moreover, the inhibition of the MAPK pathway partially (yet significantly) inhibited the accelerated growth of C2C12 cells overexpressing PKCdelta. Taken together, these results demonstrate a novel, central and exclusive involvement of PKCdelta in mediating the action of IGF-I on human skeletal muscle cells, with an additional yet PKCdelta-dependent contribution of the MAPK pathway on C2C12 myoblasts. 10.1016/j.cellsig.2005.11.007
    Ligand-independent activation of the androgen receptor by insulin-like growth factor-I and the role of the MAPK pathway in skeletal muscle cells. Kim Hye Jin,Lee Won Jun Molecules and cells In this study, the roles of the p38 MAPK, ERK1/2 and JNK signaling pathway in IGF-I-induced AR induction and activation were examined. C2C12 cells were treated with IGF-I in the absence or presence of various inhibitors of p38 MAPK (SB203580), ERK1/2 (PD98059), and JNK (SP600125). Inhibition of the MAPK pathway with SB203580, PD98059, or SP600125 significantly decreased IGF-I-induced AR phosphorylation and total AR protein expression. IGF-I-induced nuclear fraction of total AR and phosphorylated AR were significantly inhibited by SB203580, PD98059, or SP600125. Furthermore, IGF-I-induced AR mRNA and skeletal alpha-actin mRNA were blocked by those inhibitors in dose-dependent manner. Confocal images showed that IGF-I-induced AR nuclear translocation from cytosol was significantly blocked by SB203580, PD98059, or SP600125, suggesting that the MAPK pathway regulates IGF-I-induced AR nuclear localization in skeletal muscle cells. The present results suggest that the MAPK pathways are required for the ligand-independent activation of AR by IGF-I in C2C12 skeletal muscle cells. 10.1007/s10059-009-0167-z
    Pretreatment with insulin-like growth factor I protects skeletal muscle cells against oxidative damage via PI3K/Akt and ERK1/2 MAPK pathways. Yang Shi Yu,Hoy Michael,Fuller Barry,Sales Kevin M,Seifalian Alexander M,Winslet Marc C Laboratory investigation; a journal of technical methods and pathology Oxidative stress has an important role in the pathogenesis of many muscle diseases. The major contributors to oxidative stress in muscle tissue are reactive oxygen species such as oxygen ions, free radicals, and peroxides. Insulin-like growth factor I (IGF-I) has been shown to increase muscle mass and promote muscle cell proliferation, differentiation, and survival. We, therefore, hypothesized that IGF-I might also be cytoprotective for muscle cells during oxidative stress. Exogenous hydrogen peroxide (H(2)O(2)) was used to induce oxidative stress/damage in two types of skeletal muscle cells. Apoptotic pathways were assessed after the oxidative damage and the effects of IGF-I on oxidative stress in muscle cells were examined. Different IGF-I sub-pathways were analyzed with measurement of the expression of pro-and anti-apoptotic proteins. It was found that H(2)O(2) diminishes muscle cell viability and induces a caspase-independent apoptotic cell death. Pretreatment with IGF-I protects muscle cells from H(2)O(2)-induced cell death and enhances muscle cells survival. This effect appears to result from the promotion of the anti-apoptotic protein, Bcl2. Further investigation shows that protection is via an IGF-I sub-pathway: PI3K/Akt and ERK1/2 MAPK pathways. Protecting muscle cells from oxidative damage presents a potential application in the treatment of the muscle wasting, which appears in many muscle pathologies including Duchenne muscle dystrophy and sarcopenia. 10.1038/labinvest.2009.139
    Fibroblast growth factor 9 (FGF9) inhibits myogenic differentiation of C2C12 and human muscle cells. Huang Jian,Wang Kun,Shiflett Lora A,Brotto Leticia,Bonewald Lynda F,Wacker Michael J,Dallas Sarah L,Brotto Marco Cell cycle (Georgetown, Tex.) Osteoporosis and sarcopenia (osteosarcopenia (OS)) are twin-aging diseases. The biochemical crosstalk between muscle and bone seems to play a role in OS. We have previously shown that osteocytes produce soluble factors with beneficial effects on muscle and . Recently, enhanced FGF9 production was observed in the OmGFP66 osteogenic cell line. To test its role in myogenic differentiation, C2C12 myoblasts were treated with recombinant FGF9. FGF9 as low as 10 ng/mL inhibited myogenic differentiation, suggesting that FGF9 might be a potential inhibitory factor produced from bone cells with effects on muscle cells. FGF9 (10-50 ng/mL) significantly decreased mRNA expression of and while increasing the expression of . Consistent with the phenotype, RT-qPCR array revealed that FGF9 (10 ng/mL) increased the expression of while decreased the expression of and decreased, respectively. FGF9 decreased caffeine-induced Ca release from the sarcoplasmic reticulum (SR) of C2C12 myotubes and reduced the expression of genes (i.e. ) directly associated with intracellular Ca homeostasis. Myogenic differentiation in human skeletal muscle cells was similarly inhibited by FGF9 but required higher doses of 200 ng/mL FGF9. FGF9 was also shown to stimulate C2C12 myoblast proliferation. FGF2 and the FGF9 subfamily members FGF16 and FGF20 also inhibited C2C12 myoblast differentiation and enhanced proliferation. Intriguingly, the differentiation inhibition was independent of proliferation enhancement. These findings suggest that FGF9 may modulate myogenesis via a complex signaling mechanism. 10.1080/15384101.2019.1691796
    Shared and distinct mechanisms of skeletal muscle atrophy: A narrative review. Wilburn Dylan,Ismaeel Ahmed,Machek Steven,Fletcher Emma,Koutakis Panagiotis Ageing research reviews Maintenance of skeletal muscle mass and function is an incredibly nuanced balance of anabolism and catabolism that can become distorted within different pathological conditions. In this paper we intend to discuss the distinct intracellular signaling events that regulate muscle protein atrophy for a given clinical occurrence. Aside from the common outcome of muscle deterioration, several conditions have at least one or more distinct mechanisms that creates unique intracellular environments that facilitate muscle loss. The subtle individuality to each of these given pathologies can provide both researchers and clinicians with specific targets of interest to further identify and increase the efficacy of medical treatments and interventions. 10.1016/j.arr.2021.101463