Reversible insulin resistance in non-insulin-dependent diabetes mellitus.
Karam J H
Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme
Insulin resistance is a major component of non-insulin-dependent diabetes mellitus (NIDDM). While a genetic contribution is likely, as yet none of several proposed candidate genes have been incriminated in the typically obese patient with NIDDM to explain their insulin resistance. Accordingly, this review focuses on some recent advances in understanding three acquired factors contributing to insulin resistance: visceral obesity, glucotoxicity and lipotoxicity. Newer computerized tomography scans allow quantitation of fat accumulating in visceral organs including the mesentery and omentum. This visceral fat relates much more to the insulin resistance syndrome than does subcutaneous fat. Moreover, exercise, as performed by active Sumo wrestlers, is associated with low visceral fat, absent hyperglycemia and absent dyslipidemia despite massive subcutaneous obesity. It remains to be seen whether exercise programs more moderate than Sumo wrestling will also mobilize visceral fat. A new metabolic pathway has recently been described whereby hexosamines are formed by an increased flux of glucose into fat and muscle. These hexosamine products appear to explain how glucotoxicity results in insulin resistance. They act as a negative feedback system to limit further glucose transport by insulin target tissue during hyperglycemia. Lipotoxicity has previously been implicated in insulin resistance by its inhibitory effect on glucose uptake by muscle because of the Randle-fatty acid cycle. Recently the role of elevated fatty acids in producing "hepatic" resistance to insulin in NIDDM has also been documented, but the site of insulin resistance may be the fat cell rather than the hepatocyte. Therapy consists mainly of hygienic measures, including caloric restriction and exercise, which can reverse all three of these acquired forms of insulin resistance. In addition, pharmacologic measures to reduce hyperglycemia can reduce the glucotoxicity and lipotoxicity. The use of insulin-sparing antihyperglycemia drugs may be particularly useful in the insulin-resistant patient to avoid weight gain while correcting the hyperglycemia.
Analysis of human skeletal muscle after 48 h immobilization reveals alterations in mRNA and protein for extracellular matrix components.
Urso Maria L,Scrimgeour Angus G,Chen Yi-Wen,Thompson Paul D,Clarkson Priscilla M
Journal of applied physiology (Bethesda, Md. : 1985)
We examined the effects of 48 h of knee immobilization on alterations in mRNA and protein in human skeletal muscle. We hypothesized that 48 h of immobilization would increase gene expression and respective protein products for ubiquitin-proteasome pathway (UPP) components. Also, we used microarray analysis to identify novel pathways. Biopsies were taken from the vastus muscle of five men (20.4 +/- 0.5 yr) before and after 48-h immobilization. Global changes in gene expression were analyzed by use of Affymetrix GeneChips. Candidate genes were confirmed via quantitative RT-PCR. Western blotting (WB) was used to quantify protein products of candidate genes and to assess Akt pathway activation. Immunohistochemistry was used to localize proteins found to be altered when assessed via WB. The greatest percentage of genes showing altered expression with the GeneChip included genes involved in the UPP, metallothionein function, and extracellular matrix (ECM) integrity. Quantitative RT-PCR analysis confirmed increases in mRNA for UPP components [USP-6, small ubiquitin-related modifier (SUMO-1)] and the metallothioneins (MT2A, MT1F, MT1H, MT1X) and decreases in mRNA content for matrix metalloproteinases (MMP-28, TIMP-1) and ECM structural components [collagen III (COLIII) and IV (COLIV)]. Only phosphorylated Akt (Ser473, Thr308), COLIII and COLIV protein levels were significantly different postimmobilization (25, 10, 88, and 28% decrease, respectively). Immunohistochemistry confirmed WB showing decreased staining for collagens postimmobilization. Our results suggest that 48 h of immobilization increases mRNA content for components of the UPP and metallothionein function while decreasing mRNA and protein for ECM components as well as decreased phosphorylation of Akt.
In vitro PCNA modification assays.
Parker Joanne L,Ulrich Helle D
Methods in molecular biology (Clifton, N.J.)
Modification of the replicative sliding clamp, PCNA, by monoubiquitin, polyubiquitin, and SUMO contributes to the processing of DNA damage during replication. In order to investigate the properties of the relevant conjugation enzymes, their interactions, substrate recognition, and the regulation of their activities, reconstitution of the modification reactions from purified components in vitro is an instructive exercise. Here we describe the purification of the relevant enzymes and accessory proteins from E. coli or S. cerevisiae as well as protocols for setting up small-scale ubiquitylation and sumoylation reactions with budding yeast PCNA. In addition, we provide a method for the purification of monoubiquitylated PCNA for further biochemical studies.
Disrupting SUMOylation enhances transcriptional function and ameliorates polyglutamine androgen receptor-mediated disease.
Chua Jason P,Reddy Satya L,Yu Zhigang,Giorgetti Elisa,Montie Heather L,Mukherjee Sarmistha,Higgins Jake,McEachin Richard C,Robins Diane M,Merry Diane E,Iñiguez-Lluhí Jorge A,Lieberman Andrew P
The Journal of clinical investigation
Expansion of the polyglutamine (polyQ) tract within the androgen receptor (AR) causes neuromuscular degeneration in individuals with spinobulbar muscular atrophy (SBMA). PolyQ AR has diminished transcriptional function and exhibits ligand-dependent proteotoxicity, features that have both been implicated in SBMA; however, the extent to which altered AR transcriptional function contributes to pathogenesis remains controversial. Here, we sought to dissociate effects of diminished AR function from polyQ-mediated proteotoxicity by enhancing the transcriptional activity of polyQ AR. To accomplish this, we bypassed the inhibitory effect of AR SUMOylation (where SUMO indicates small ubiquitin-like modifier) by mutating conserved lysines in the polyQ AR that are sites of SUMOylation. We determined that replacement of these residues by arginine enhances polyQ AR activity as a hormone-dependent transcriptional regulator. In a murine model, disruption of polyQ AR SUMOylation rescued exercise endurance and type I muscle fiber atrophy; it also prolonged survival. These changes occurred without overt alterations in polyQ AR expression or aggregation, revealing the favorable trophic support exerted by the ligand-activated receptor. Our findings demonstrate beneficial effects of enhancing the transcriptional function of the ligand-activated polyQ AR and indicate that the SUMOylation pathway may be a potential target for therapeutic intervention in SBMA.
Irisin Ameliorates Hypoxia/Reoxygenation-Induced Injury through Modulation of Histone Deacetylase 4.
Zhao Yu Tina,Wang Hao,Zhang Shouyan,Du Jianfeng,Zhuang Shougang,Zhao Ting C
Irisin is a recently identified myokine which brings increases in energy expenditure and contributes to the beneficial effects of exercise through the browning of white adipose tissues. However, its effects in the heart remains unknown. This study sought to determine the effects of irisin on hypoxia/reoxygenation injury and its relationship with HDAC4. Wild type and stable HDAC4-overexpression cells were generated from H9c2 cardiomyoblasts. HDAC4 overexpression cells and wild type H9c2 cells were exposed to 24 hours of hypoxia followed by one hour of reoxygenation in vitro in the presence or absence of irisin (5 ng/ml). Cell cytotoxicity, apoptosis, mitochondrial respiration, and mitochondrial permeability transition pore (mPTP) were determined. Western blotting was employed to determine active-caspase 3, annexin V, and HDAC4 expression. As compared to wild type H9c2 group, HDAC4 overexpression remarkably led to a great increase in cell death as evident by the increased lactate dehydrogenase (LDH) leakage, ratio of caspase-3-positive cells as well as the upregulated levels of active-caspase 3 and annexin V shown by western blot analysis. In addition, HDAC4 overexpression also induced much severe mitochondrial dysfunction, as indicated by apoptotic mitochondria and increased mPTP. However, irisin treatment significantly attenuated all of these effects. Though irisin treatment did not influence the expression of HDAC4 at the transcriptional level, western blot analysis showed that HDAC4 protein levels decreased in a time-dependent way after administration of irisin, which is associated with the degradation of HDAC4 mediated by small ubiquitin-like modification (SUMO). Our results are the first to demonstrate that the protective effects of irisin in cardiomyoblasts exposed to hypoxia/reoxygenation might be associated with HDAC4 degradation.
Effects of aerobic exercise on hippocampal SUMOylation in APP/PS1 transgenic mice.
Chenfei Zhang,Haizhen Yu,Jie Xia,Na Zhao,Bo Xu
Alzheimer's disease (AD) is the most common neurodegenerative disease. SUMOylation, a post-translational modification, has been found to be dysregulated in the AD brain and to exacerbate learning and memory disabilities and increase amyloid beta (Aβ) expression further. To investigate whether exercise-induced alleviation of AD was associated with SUMOylation, which still remains unknown, 3-month-old C57BL/6 mice and APP/PS1 transgenic mice were randomly divided into the wild-type control (WC), wild-type exercise (WE), APP/PS1 control (AC), and APP/PS1 exercise (AE) groups. Mice in the exercise groups underwent a 3-month treadmill exercise regimen. We observed impaired learning and memory abilities in APP/PS1 mice, but the 3-month treadmill exercise regimen improved spatial learning and memory abilities in wild-type and APP/PS1 mice. In addition, senile plaques, SUMO1 mRNA, and SENP1 mRNA levels increased in the hippocampi of APP/PS1 mice. However, 3-month treadmill exercise decreased the levels of senile plaques, SUMO1 mRNA and SENP1 mRNA as well as may reduce SUMO1 modification in 6-month-old APP/PS1 mice, but SUMO2 mRNA expression, SUMO2/3 modification, and overall SUMOylation levels did not significantly change. Our results suggest that the impaired learning and memory abilities and aggregations of Aβ may relate to increased hippocampal SUMO1 transcription levels; the beneficial effects of treadmill exercise on learning and memory performances and AD pathogenesis may associated with the abatement of SUMO1 modification, but may not with SUMO2/3 modification.
Intense Resistance Exercise Promotes the Acute and Transient Nuclear Translocation of Small Ubiquitin-Related Modifier (SUMO)-1 in Human Myofibres.
Gehlert Sebastian,Klinz Franz Josef,Willkomm Lena,Schiffer Thorsten,Suhr Frank,Bloch Wilhelm
International journal of molecular sciences
Protein sumoylation is a posttranslational modification triggered by cellular stress. Because general information concerning the role of small ubiquitin-related modifier (SUMO) proteins in adult skeletal muscle is sparse, we investigated whether SUMO-1 proteins will be subjected to time-dependent changes in their subcellular localization in sarcoplasmic and nuclear compartments of human type I and II skeletal muscle fibers in response to acute stimulation by resistance exercise (RE). Skeletal muscle biopsies were taken at baseline (PRE), 15, 30, 60, 240 min and 24 h post RE from 6 male subjects subjected to a single bout of one-legged knee extensions. SUMO-1 localization was determined via immunohistochemistry and confocal laser microscopy. At baseline SUMO-1 was localized in perinuclear regions of myonuclei. Within 15 and up to 60 min post exercise, nuclear SUMO-1 localization was significantly increased (p < 0.01), declining towards baseline levels within 240 min post exercise. Sarcoplasmic SUMO-1 localization was increased at 15 min post exercise in type I and up to 30 min post RE in type II myofibres. The changing localization of SUMO-1 proteins acutely after intense muscle contractions points to a role for SUMO proteins in the acute regulation of the skeletal muscle proteome after exercise.