MicroRNA-182-5p attenuates cerebral ischemia-reperfusion injury by targeting Toll-like receptor 4.
Wang Ji,Xu Zhimin,Chen Xiufen,Li Yan,Chen Chen,Wang Chongwu,Zhu Jianwei,Wang Zhaotao,Chen Wenjin,Xiao Zongyu,Xu Ruxiang
Biochemical and biophysical research communications
Cerebral ischemia-reperfusion-induced microglial activation causes neuronal death through the release of inflammatory cytokines. Increasing evidence suggests that microRNAs (miRNAs) exert a neuroprotective effect by modulating the inflammatory process in cerebral ischemia-reperfusion injury. Furthermore, Toll-like receptor 4 (TLR4) is increasingly being considered to have a significant role in the regulation of inflammation. However, whether miRNAs mediate their neuroprotective effects by regulating TLR4-mediated inflammatory responses remains unknown. To explore this gap in the literature, we conducted both in vitro and in vivo experiments. In vitro: BV2 cells were activated by oxygen-glucose deprivation (OGD). TLR4 and inflammatory cytokine (TNF-a, IL-6, and IL-1β) transcription and translation expression levels were assessed using RT-PCR, ELISA, and western blot. BV2 cells were transfected with miR-182-5p mimics, inhibitors, siTLR4, or negative control (NC) using lipofectamine 2000 reagent. To confirm whether TLR4 is a direct target of miR-182-5p, we performed a luciferase reporter assay. In BV2 cells, we observed that OGD upregulated TLR4 expression, but downregulated miR-182-5p expression. We determined that miR-182-5p inhibited TLR4 by directly binding to its 3'-UTR. Furthermore, miR-182-5p suppressed the release of TNF-a, IL-6, and IL-1β. In vivo: A middle cerebral artery occlusion (MCAO) rat model was used to mimic cerebral ischemia-reperfusion. Iba1 and TLR4 double staining was used to demonstrate that the target of miR-182-5p in microglial cells, and the mediator of the anti-inflammatory effect, is TLR4. TTC staining was performed to evaluate the infarct volume. Compared to the animals treated with miR-182-5p NC and normal saline, rats treated with miR-182-5p mimics demonstrated significantly enhanced neurological functions. TTC staining results were consistent with neurological function test findings. In summary, our data suggested that miR-182-5p exhibits potential neuroprotective effects in the cerebral ischemia-reperfusion injury via the regulation of the TLR4-mediated inflammatory response.
Toll-Like Receptor 4 Knockdown Attenuates Brain Damage and Neuroinflammation After Traumatic Brain Injury via Inhibiting Neuronal Autophagy and Astrocyte Activation.
Jiang Hongsheng,Wang Yanzhou,Liang Xin,Xing Xiaofeng,Xu Xiuzhen,Zhou Caifeng
Cellular and molecular neurobiology
Toll-like receptor 4 (TLR4) has been linked to various pathophysiological conditions, such as traumatic brain injury (TBI). It is reported that posttraumatic neuroinflammation is an essential event in the progression of brain injury after TBI. Recent evidences indicate that TLR4 mediates glial phagocytic activity and inflammatory cytokines production. Thus, TLR4 may be an important therapeutic target for neuroinflammatory injury post-TBI. This study was designed to explore potential effects and underlying mechanisms of TLR4 in rats suffered from TBI. TBI model was induced using a controlled cortical impact in rats, and application of TLR4 shRNA silenced TLR4 expression in brain prior to TBI induction. Elevated TLR4 was specifically observed in the hippocampal astrocytes and neurons posttrauma. Interestingly, TLR4 shRNA decreased the concentrations of interleukin (IL)-1β, IL-6, and tissue necrosis factor-α; alleviated hippocampal neuronal damage; reduced brain edema formation; and improved neurological deficits after TBI. Meanwhile, to further explore underlying molecular mechanisms of this neuroprotective effects of TLR4 knockdown, our results showed that TLR4 knockdown significantly inhibited the upregulation of autophagy-associated proteins caused by TBI. More importantly, an autophagy inducer, rapamycin pretreated, could partially abolish neuroprotective effects of TLR4 knockdown on TBI rats. Furthermore, TLR4 silencing markedly suppressed GFAP upregulation and improved cell hypertrophy to attenuate TBI-induced astrocyte activation. Taken together, these findings suggested that TLR4 knockdown ameliorated neuroinflammatory response and brain injury after TBI through suppressing autophagy induction and astrocyte activation.
Pentraxin-3 is upregulated in the central nervous system during MS and EAE, but does not modulate experimental neurological disease.
Ummenthum Kimberley,Peferoen Laura A N,Finardi Annamaria,Baker David,Pryce Gareth,Mantovani Alberto,Bsibsi Malika,Bottazzi Barbara,Peferoen-Baert Regina,van der Valk Paul,Garlanda Cecilia,Kipp Markus,Furlan Roberto,van Noort Johannes M,Amor Sandra
European journal of immunology
Pentraxin-3 (PTX3), an acute-phase protein released during inflammation, aids phagocytic clearance of pathogens and apoptotic cells, and plays diverse immunoregulatory roles in tissue injury. In neuroinflammatory diseases, like MS, resident microglia could become activated by endogenous agonists for Toll like receptors (TLRs). Previously we showed a strong TLR2-mediated induction of PTX3 in cultured human microglia and macrophages by HspB5, which accumulates in glia during MS. Given the anti-inflammatory effects of HspB5, we examined the contribution of PTX3 to these effects in MS and its animal model EAE. Our data indicate that TLR engagement effectively induces PTX3 expression in human microglia, and that such expression is readily detectable in MS lesions. Enhanced PTX3 expression is prominently expressed in microglia in preactive MS lesions, and in microglia/macrophages engaged in myelin phagocytosis in actively demyelinating lesions. Yet, we did not detect PTX3 in cerebrospinal fluid of MS patients. PTX3 expression is also elevated in spinal cords during chronic relapsing EAE in Biozzi ABH mice, but the EAE severity and time course in PTX3-deficient mice did not differ from WT mice. Moreover, systemic PTX3 administration did not alter the disease onset or severity. Our findings reveal local functions of PTX3 during neuroinflammation in facilitating myelin phagocytosis, but do not point to a role for PTX3 in controlling the development of autoimmune neuroinflammation.
E6020, a synthetic TLR4 agonist, accelerates myelin debris clearance, Schwann cell infiltration, and remyelination in the rat spinal cord.
Church Jamie S,Milich Lindsay M,Lerch Jessica K,Popovich Phillip G,McTigue Dana M
Oligodendrocyte progenitor cells (OPCs) are present throughout the adult brain and spinal cord and can replace oligodendrocytes lost to injury, aging, or disease. Their differentiation, however, is inhibited by myelin debris, making clearance of this debris an important step for cellular repair following demyelination. In models of peripheral nerve injury, TLR4 activation by lipopolysaccharide (LPS) promotes macrophage phagocytosis of debris. Here we tested whether the novel synthetic TLR4 agonist E6020, a Lipid A mimetic, promotes myelin debris clearance and remyelination in spinal cord white matter following lysolecithin-induced demyelination. In vitro, E6020 induced TLR4-dependent cytokine expression (TNFα, IL1β, IL-6) and NF-κB signaling, albeit at ∼10-fold reduced potency compared to LPS. Microinjection of E6020 into the intact rat spinal cord gray/white matter border induced macrophage activation, OPC proliferation, and robust oligodendrogenesis, similar to what we described previously using an intraspinal LPS microinjection model. Finally, a single co-injection of E6020 with lysolecithin into spinal cord white matter increased axon sparing, accelerated myelin debris clearance, enhanced Schwann cell infiltration into demyelinated lesions, and increased the number of remyelinated axons. In vitro assays confirmed that direct stimulation of macrophages by E6020 stimulates myelin phagocytosis. These data implicate TLR4 signaling in promoting repair after CNS demyelination, likely by stimulating phagocytic activity of macrophages, sparing axons, recruiting myelinating cells, and promoting remyelination. This work furthers our understanding of immune-myelin interactions and identifies a novel synthetic TLR4 agonist as a potential therapeutic avenue for white matter demyelinating conditions such as spinal cord injury and multiple sclerosis.
A presumed antagonistic LPS identifies distinct functional organization of TLR4 in mouse microglia.
Döring Christin,Regen Tommy,Gertig Ulla,van Rossum Denise,Winkler Anne,Saiepour Nasrin,Brück Wolfgang,Hanisch Uwe-Karsten,Janova Hana
Microglia as principle innate immune cells of the central nervous system (CNS) are the first line of defense against invading pathogens. They are capable of sensing infections through diverse receptors, such as Toll-like receptor 4 (TLR4). This receptor is best known for its ability to recognize bacterial lipopolysaccharide (LPS), a causative agent of gram-negative sepsis and septic shock. A putative, naturally occurring antagonist of TLR4 derives from the photosynthetic bacterium Rhodobacter sphaeroides. However, the antagonistic potential of R. sphaeroides LPS (Rs-LPS) is no universal feature, since several studies suggested agonistic rather than antagonistic actions of this molecule depending on the investigated mammalian species. Here we show the agonistic versus antagonistic potential of Rs-LPS in primary mouse microglia. We demonstrate that Rs-LPS efficiently induces the release of cytokines and chemokines, which depends on TLR4, MyD88, and TRIF, but not CD14. Furthermore, Rs-LPS is able to regulate the phagocytic capacity of microglia as agonist, while it antagonizes Re-LPS-induced MHC I expression. Finally, to our knowledge, we are the first to provide in vivo evidence for an agonistic potential of Rs-LPS, as it efficiently triggers the recruitment of peripheral immune cells to the endotoxin-challenged CNS. Together, our results argue for a versatile and complex organization of the microglial TLR4 system, which specifically translates exogenous signals into cellular functions. Importantly, as demonstrated here for microglia, the antagonistic potential of Rs-LPS needs to be considered with caution, as reactions to Rs-LPS not only differ by cell type, but even by function within one cell type.
Mitochondrial Damage-Associated Molecular Patterns of Injured Axons Induce Outgrowth of Schwann Cell Processes.
Korimová Andrea,Klusáková Ilona,Hradilová-Svíženská Ivana,Kohoutková Marcela,Joukal Marek,Dubový Petr
Frontiers in cellular neuroscience
Activated Schwann cells put out cytoplasmic processes that play a significant role in cell migration and axon regeneration. Following nerve injury, axonal mitochondria release mitochondrial damage-associated molecular patterns (mtDAMPs), including formylated peptides and mitochondrial DNA (mtDNA). We hypothesize that mtDAMPs released from disintegrated axonal mitochondria may stimulate Schwann cells to put out cytoplasmic processes. We investigated RT4-D6P2T schwannoma cells (RT4) treated with N-formyl-L-methionyl-L-leucyl-phenylalanine (fMLP) or cytosine-phospho-guanine oligodeoxynucleotide (CpG ODN) for 1, 6 and 24 h. We also used immunohistochemical detection to monitor the expression of formylpeptide receptor 2 (FPR2) and toll-like receptor 9 (TLR9), the canonical receptors for formylated peptides and mtDNA, in RT4 cells and Schwann cells distal to nerve injury. RT4 cells treated with fMLP put out a significantly higher number of cytoplasmic processes compared to control cells. Preincubation with PBP10, a selective inhibitor of FPR2 resulted in a significant reduction of cytoplasmic process outgrowth. A significantly higher number of cytoplasmic processes was also found after treatment with CpG ODN compared to control cells. Pretreatment with inhibitory ODN (INH ODN) resulted in a reduced number of cytoplasmic processes after subsequent treatment with CpG ODN only at 6 h, but 1 and 24 h treatment with CpG ODN demonstrated an additive effect of INH ODN on the development of cytoplasmic processes. Immunohistochemistry and western blot detected increased levels of tyrosine-phosphorylated paxillin in RT4 cells associated with cytoplasmic process outgrowth after fMLP or CpG ODN treatment. We found increased immunofluorescence of FPR2 and TLR9 in RT4 cells treated with fMLP or CpG ODN as well as in activated Schwann cells distal to the nerve injury. In addition, activated Schwann cells displayed FPR2 and TLR9 immunostaining close to GAP43-immunopositive regenerated axons and their growth cones after nerve crush. Increased FPR2 and TLR9 immunoreaction was associated with activation of p38 and NFkB, respectively. Surprisingly, the growth cones displayed also FPR2 and TLR9 immunostaining. These results present the first evidence that potential mtDAMPs may play a key role in the induction of Schwann cell processes. This reaction of Schwann cells can be mediated via FPR2 and TLR9 that are canonical receptors for formylated peptides and mtDNA. The possible role for FPR2 and TLR9 in growth cones is also discussed.
CD200 restrains macrophage attack on oligodendrocyte precursors via toll-like receptor 4 downregulation.
Hayakawa Kazuhide,Pham Loc-Duyen D,Seo Ji Hae,Miyamoto Nobukazu,Maki Takakuni,Terasaki Yasukazu,Sakadžić Sava,Boas David,van Leyen Klaus,Waeber Christian,Kim Kyu-Won,Arai Ken,Lo Eng H
Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism
There are numerous barriers to white matter repair after central nervous system injury and the underlying mechanisms remain to be fully understood. In this study, we propose the hypothesis that inflammatory macrophages in damaged white matter attack oligodendrocyte precursor cells via toll-like receptor 4 signaling thus interfering with this endogenous progenitor recovery mechanism. Primary cell culture experiments demonstrate that peritoneal macrophages can attack and digest oligodendrocyte precursor cells via toll-like receptor 4 signaling, and this phagocytosis of oligodendrocyte precursor cells can be inhibited by using CD200-Fc to downregulate toll-like receptor 4. In an in vivo model of white matter ischemia induced by endothelin-1, treatment with CD200-Fc suppressed toll-like receptor 4 expression in peripherally circulating macrophages, thus restraining macrophage phagocytosis of oligodendrocyte precursor cells and leading to improved myelination. Taken together, these findings suggest that deleterious macrophage effects may occur after white matter ischemia, whereby macrophages attack oligodendrocyte precursor cells and interfere with endogenous recovery responses. Targeting this pathway with CD200 may offer a novel therapeutic approach to amplify endogenous oligodendrocyte precursor cell-mediated repair of white matter damage in mammalian brain.
Intrathecal triamcinolone acetonide exerts anti-inflammatory effects on Lewis rat experimental autoimmune neuritis and direct anti-oxidative effects on Schwann cells.
Pitarokoili Kalliopi,Sgodzai Melissa,Grüter Thomas,Bachir Hussein,Motte Jeremias,Ambrosius Björn,Pedreiturria Xiomara,Yoon Min-Suk,Gold Ralf
Journal of neuroinflammation
BACKGROUND:Corticosteroids dominate in the treatment of chronic autoimmune neuropathies although long-term use is characterized by devastating side effects. METHODS:We introduce the intrathecal application of the synthetic steroid triamcinolone (TRIAM) as a novel therapeutic option in experimental autoimmune neuritis in Lewis rats RESULTS: After immunization with neuritogenic P2 peptide, we show a dose-dependent therapeutic effect of one intrathecal injection of 0.3 or 0.6 mg/kg TRIAM on clinical and electrophysiological parameters of neuritis with a lower degree of inflammatory infiltrates (T cells and macrophages) and demyelination in the sciatic nerve. In vitro studies in Schwann cell cultures showed an increased expression of IL-1 receptor antagonist and reduced expression of Toll-like receptor 4 after incubation with TRIAM as well as a protective effect of TRIAM against oxidative stress after HO exposure. CONCLUSION:Intrathecal TRIAM application could be a novel immunomodulatory and potentially neuroprotective option for autoimmune neuropathies with a direct effect on Schwann cells.
Therapeutic implications of toll-like receptors in peripheral neuropathic pain.
Thakur Krishan K,Saini Jyoti,Mahajan Kanika,Singh Dhyanendra,Jayswal Dinkar P,Mishra Srishti,Bishayee Anupam,Sethi Gautam,Kunnumakkara Ajaikumar B
Neuropathic pain is a state of chronic pain arising after peripheral or central nerve injury. These injuries can be mediated through the activation of various cells (astrocytes, microglia and Schwann cells), as well as the dissolution of distal axons. Recent studies have suggested that after nerve injury, Toll-like receptors (TLRs) involved in Wallerian degeneration and generation of neuropathic pain. Furthermore, these TLRs are responsible for the stimulation of astrocytes and microglia that can cause induction of the proinflammatory mediators and cytokines in the spinal cord, thereby leading to the generation and maintenance of neuropathic pain. Indeed considering the prevalence of neuropathic pain and suffering of the affected patients, insights into the diverse mechanism(s) of activation of TLR signaling cascades may open novel avenues for the management of this chronic condition. Moreover, existing therapies like antidepressants, anticonvulsants, opiates and other analgesic are not sufficiently effective in reducing the pain. In this review, we present substantial evidences highlighting the diverse roles of TLRs and their signaling pathways involved in the progression of neuropathic pain. Furthermore, an elaborate discussion on various existing treatment regimens and future targets involving TLRs has also been included.
Toll-Like Receptor 3 Contributes to Wallerian Degeneration after Peripheral Nerve Injury.
Lee Hyunkyoung,Baek Jiyeon,Min Hyunjung,Cho Ik-Hyun,Yu Seong-Woo,Lee Sung Joong
OBJECTIVE:It is well known that Schwann cells play an important role in Wallerian degeneration after peripheral nerve injury. Previously, we reported that toll-like receptor 3 (TLR3) is expressed on Schwann cells, implicating its role in Schwann cell activation during Wallerian degeneration. In this study, we tested this possibility using TLR3 knock-out mice. METHODS:Sciatic nerve-crush injury was induced in wild-type and TLR3 knock-out mice. Histological sections of the sciatic nerve were analyzed for Wallerian degeneration on days 3 and 7 after injury. The level of macrophage infiltration was measured by real-time RT-PCR, flow cytometry and immunohistochemistry. The macrophage-recruiting chemokine gene expressions in the injured nerve were determined by real-time RT-PCR. RESULTS:In TLR3 knock-out mice, the nerve injury-induced axonal degeneration and subsequent axonal debris clearance were reduced compared to in wild-type mice. In addition, nerve injury-induced macrophage infiltration into injury sites was attenuated in TLR3 knock-out mice and was accompanied by reduced expression of macrophage-recruiting chemokines such as CC-chemokine ligands (CCL)2/MCP-1, CCL4/MIP-1β and CCL5/RANTES. These macrophage-recruiting chemokines were induced in primary Schwann cells upon TLR3 stimulation. Finally, intraneural injection of polyinosinic-polycytidylic acid, a synthetic TLR3 agonist, induced macrophage infiltration into the sciatic nerve in vivo. CONCLUSION:These data show that TLR3 signaling contributes to Wallerian degeneration after peripheral nerve injury by affecting Schwann cell activation and macrophage recruitment to injured nerves.
Knockout of toll-like receptor impairs nerve regeneration after a crush injury.
Hsieh Ching-Hua,Rau Cheng-Shyuan,Kuo Pao-Jen,Liu Shu-Hsuan,Wu Chia-Jung,Lu Tsu-Hsiang,Wu Yi-Chan,Lin Chia-Wei
Background:Toll-like receptors (TLRs) are involved in the initiation of Schwann cell activation and subsequent recruitment of macrophages for clearance of degenerated myelin and neuronal debris after nerve injury. The present study was designed to investigate the regenerative outcome and expression of myelination-related factors in -knockout mice following a sciatic nerve crush injury. Materials and methods:A standard sciatic nerve crush injury, induced by applying constant pressure to the nerve with a No. 5 jeweler's forceps for 30 s, was performed in C57BL/6, , , , , and mice. Quantitative histomorphometric analysis of toluidine blue-stained nerve specimens and walking track analysis were performed to evaluate nerve regeneration outcomes. PCR Arrays were used to detect the expression of neurogenesis-related genes of dorsal root ganglia as well as of myelination-related genes of the distal nerve segments. Results:Worse nerve regeneration after nerve crush injury was found in all knockout mice than in C57BL/6 mice. Delayed expression of myelin genes and a different expression pattern of myelination-related neurotrophin genes and transcription factors were found in -knockout mice in comparison to C57BL/6 mice. In these TLR-mediated pathways, insulin-like growth factor 2 and brain-derived neurotrophic factor, as well as early growth response 2 and N-myc downstream-regulated gene 1, were significantly decreased in the early and late stages, respectively, of nerve regeneration after a crush injury. Conclusions:Knockout of genes decreases the expression of myelination-related factors and impairs nerve regeneration after a sciatic nerve crush injury.
Toll-Like Receptor 4 (TLR4) Expression Affects Schwann Cell Behavior in vitro.
Zhang Huanhuan,Shao Zhiwei,Zhu Yun,Shi Lingyu,Li Zhihao,Hou Rui,Zhang Chunwang,Yao Dengbing
Peripheral nerve injury can result in the decreased quality of life and bring us economic burden on society and individuals. Wallerian degeneration (WD) is critical for nerve degeneration and regeneration, but the mechanisms of WD are still elusive. Here, we report the effect of Toll-like receptor 4 (TLR4) on cultured Schwann cells (SCs) in vitro. The data showed that TLR4 expression was up-regulated after sciatic nerve injury of rat. TLR4 was expressed in cultured SCs. Enhanced or silenced expression of TLR4 affected SC proliferation, migration, apoptosis and relative gene expression. Furthermore, altered expression of TLR4 resulted in expression changes in c-Jun, ERK and catenin but not AKT and c-Fos pathways in SCs. These results suggested that TLR4 may be an important effective target in peripheral nerve degeneration and/or regeneration during WD in future investigations.
Schwann cell differentiation inhibits interferon-gamma induction of expression of major histocompatibility complex class II and intercellular adhesion molecule-1.
Lisak Robert P,Bealmear Beverly,Benjamins Joyce A
Journal of neuroimmunology
Interferon-gamma (IFN-γ) upregulates major histocompatibility complex class II (MHC class II) antigens and intercellular adhesion molecule-1 (ICAM-1) on Schwann cells (SC) in vitro, but in nerves of animals and patients MHC class II is primarily expressed on inflammatory cells. We investigated whether SC maturation influences their expression. IFN-γ induced MHC class II and upregulated ICAM-1; the axolemma-like signal 8-bromo cyclic adenosine monophosphate (8 Br cAMP) with IFN-γ inhibited expression. Delaying addition of 8 Br cAMP to SC already exposed to IFN-γ inhibited ongoing expression; addition of IFN-γ to SC already exposed to 8 Br cAMP resulted in minimal expression. Variability of cytokine-induced MHC class II and ICAM-1 expression by SC in vivo may represent the variability of signals from axolemma.
Inflammaging impairs peripheral nerve maintenance and regeneration.
Büttner Robert,Schulz Alexander,Reuter Michael,Akula Asha K,Mindos Thomas,Carlstedt Annemarie,Riecken Lars B,Baader Stephan L,Bauer Reinhard,Morrison Helen
The regenerative capacity of peripheral nerves declines during aging, contributing to the development of neuropathies, limiting organism function. Changes in Schwann cells prompt failures in instructing maintenance and regeneration of aging nerves; molecular mechanisms of which have yet to be delineated. Here, we identified an altered inflammatory environment leading to a defective Schwann cell response, as an underlying mechanism of impaired nerve regeneration during aging. Chronic inflammation was detected in intact uninjured old nerves, characterized by increased macrophage infiltration and raised levels of monocyte chemoattractant protein 1 (MCP1) and CC chemokine ligand 11 (CCL11). Schwann cells in the old nerves appeared partially dedifferentiated, accompanied by an activated repair program independent of injury. Upon sciatic nerve injury, an initial delayed immune response was followed by a persistent hyperinflammatory state accompanied by a diminished repair process. As a contributing factor to nerve aging, we showed that CCL11 interfered with Schwann cell differentiation in vitro and in vivo. Our results indicate that increased infiltration of macrophages and inflammatory signals diminish regenerative capacity of aging nerves by altering Schwann cell behavior. The study identifies CCL11 as a promising target for anti-inflammatory therapies aiming to improve nerve regeneration in old age.
mTORC1 Is Transiently Reactivated in Injured Nerves to Promote c-Jun Elevation and Schwann Cell Dedifferentiation.
Norrmén Camilla,Figlia Gianluca,Pfistner Patrick,Pereira Jorge A,Bachofner Sven,Suter Ueli
The Journal of neuroscience : the official journal of the Society for Neuroscience
Schwann cells (SCs) are endowed with a remarkable plasticity. When peripheral nerves are injured, SCs dedifferentiate and acquire new functions to coordinate nerve repair as so-called repair SCs. Subsequently, SCs redifferentiate to remyelinate regenerated axons. Given the similarities between SC dedifferentiation/redifferentiation in injured nerves and in demyelinating neuropathies, elucidating the signals involved in SC plasticity after nerve injury has potentially wider implications. c-Jun has emerged as a key transcription factor regulating SC dedifferentiation and the acquisition of repair SC features. However, the upstream pathways that control c-Jun activity after nerve injury are largely unknown. We report that the mTORC1 pathway is transiently but robustly reactivated in dedifferentiating SCs. By inducible genetic deletion of the functionally crucial mTORC1-subunit Raptor in mouse SCs (including male and female animals), we found that mTORC1 reactivation is necessary for proper myelin clearance, SC dedifferentiation, and consequently remyelination, without major alterations in the inflammatory response. In the absence of mTORC1 signaling, c-Jun failed to be upregulated correctly. Accordingly, a c-Jun binding motif was found to be enriched in promoters of genes with reduced expression in injured mutants. Furthermore, using cultured SCs, we found that mTORC1 is involved in c-Jun regulation by promoting its translation, possibly via the eIF4F-subunit eIF4A. These results provide evidence that proper c-Jun elevation after nerve injury involves also mTORC1-dependent post-transcriptional regulation to ensure timely dedifferentiation of SCs. A crucial evolutionary acquisition of vertebrates is the envelopment of axons in myelin sheaths produced by oligodendrocytes in the CNS and Schwann cells (SCs) in the PNS. When myelin is damaged, conduction of action potentials along axons slows down or is blocked, leading to debilitating diseases. Unlike oligodendrocytes, SCs have a high regenerative potential, granted by their remarkable plasticity. Thus, understanding the mechanisms underlying SC plasticity may uncover new therapeutic targets in nerve regeneration and demyelinating diseases. Our work reveals that reactivation of the mTORC1 pathway in SCs is essential for efficient SC dedifferentiation after nerve injury. Accordingly, modulating this signaling pathway might be of therapeutic relevance in peripheral nerve injury and other diseases.
GSK3β inhibition accelerates axon debris clearance and new axon remyelination.
Chen Yixun,Weng Jian,Han Duanyang,Chen Bo,Ma Mingtai,Yu Youlai,Li Ming,Liu Zhongdi,Zhang Peixun,Jiang Baoguo
American journal of translational research
Glycogen synthase kinase 3β (GSK3β) inhibitors, especially the mood stabilizer lithium chloride, are also used as neuroprotective or anti-inflammatory agents. We studied the influence of LiCl on inducing early myelin clearance and on regulating the remyelination following peripheral nerves injury. We showed that the oral administration of adult mice with LiCl after sciatic nerve crush injury accelerated in vivo myelin debris clearance stimulated the expression of myelin proteins, restored the myelin structure, and accelerated the recovery of sciatic functions. LiCl treatment also promoted remyelination of the sciatic nerve after crush. Furthermore, we also demonstrated that LiCl exerts its action in Schwann cells by increasing the amount of β-catenin and provoking its nuclear localization in vivo. We showed by ChIP experiments that LiCl treatment drives β-catenin to bind to T-cell factor/lymphoid-enhancer factor response elements identified in myelin-related genes. Taken together, our results provide the first evidence that the GSK3β could be considered as an important drug in inducing early myelin debris clearance and regulating the expression of myelin genes, which open new approaches in the clinical treatment of nerve injuries by utilizing GSK3β inhibitors such as lithium.
Inflammatory cytokine receptor blockade in a rodent model of mild traumatic brain injury.
Perez-Polo J R,Rea H C,Johnson K M,Parsley M A,Unabia G C,Xu G-Y,Prough D,DeWitt D S,Paulucci-Holthauzen A A,Werrbach-Perez K,Hulsebosch C E
Journal of neuroscience research
In rodent models of traumatic brain injury (TBI), both Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) levels increase early after injury to return later to basal levels. We have developed and characterized a rat mild fluid percussion model of TBI (mLFP injury) that results in righting reflex response times (RRRTs) that are less than those characteristic of moderate to severe LFP injury and yet increase IL-1α/β and TNFα levels. Here we report that blockade of IL-1α/β and TNFα binding to IL-1R and TNFR1, respectively, reduced neuropathology in parietal cortex, hippocampus, and thalamus and improved outcome. IL-1β binding to the type I IL-1 receptor (IL-1R1) can be blocked by a recombinant form of the endogenous IL-1R antagonist IL-1Ra (Kineret). TNFα binding to the TNF receptor (TNFR) can be blocked by the recombinant fusion protein etanercept, made up of a TNFR2 peptide fused to an Fc portion of human IgG1. There was no benefit from the combined blockades compared with individual blockades or after repeated treatments for 11 days after injury compared with one treatment at 1 hr after injury, when measured at 6 hr or 18 days, based on changes in neuropathology. There was also no further enhancement of blockade benefits after 18 days. Given that both Kineret and etanercept given singly or in combination showed similar beneficial effects and that TNFα also has a gliotransmitter role regulating AMPA receptor traffic, thus confounding effects of a TNFα blockade, we chose to focus on a single treatment with Kineret.
Oligodendrocyte precursor cells present antigen and are cytotoxic targets in inflammatory demyelination.
Kirby Leslie,Jin Jing,Cardona Jaime Gonzalez,Smith Matthew D,Martin Kyle A,Wang Jingya,Strasburger Hayley,Herbst Leyla,Alexis Maya,Karnell Jodi,Davidson Todd,Dutta Ranjan,Goverman Joan,Bergles Dwight,Calabresi Peter A
Oligodendrocyte precursor cells (OPCs) are abundant in the adult central nervous system, and have the capacity to regenerate oligodendrocytes and myelin. However, in inflammatory diseases such as multiple sclerosis (MS) remyelination is often incomplete. To investigate how neuroinflammation influences OPCs, we perform in vivo fate-tracing in an inflammatory demyelinating mouse model. Here we report that OPC differentiation is inhibited by both effector T cells and IFNγ overexpression by astrocytes. IFNγ also reduces the absolute number of OPCs and alters remaining OPCs by inducing the immunoproteasome and MHC class I. In vitro, OPCs exposed to IFNγ cross-present antigen to cytotoxic CD8 T cells, resulting in OPC death. In human demyelinated MS brain lesions, but not normal appearing white matter, oligodendroglia exhibit enhanced expression of the immunoproteasome subunit PSMB8. Therefore, OPCs may be co-opted by the immune system in MS to perpetuate the autoimmune response, suggesting that inhibiting immune activation of OPCs may facilitate remyelination.
Prednisone alleviates demyelination through regulation of the NLRP3 inflammasome in a C57BL/6 mouse model of cuprizone-induced demyelination.
Yu Hao,Wu Mingfeng,Lu Geng,Cao Tingting,Chen Nan,Zhang Yijia,Jiang Zhiguo,Fan Hongbin,Yao Ruiqin
Myelin abnormalities, oligodendrocyte damage, and concomitant glia activation are common in demyelinating diseases of the central nervous system (CNS). Increasing evidence has demonstrated that the inflammatory response triggers demyelination and gliosis in demyelinating disorders. Numerous clinical interventions, including those used to treat multiple sclerosis (MS), have confirmed prednisone (PDN) as a powerful anti-inflammatory drug that reduces the inflammatory response and promotes tissue repair in multiple inflammation sites. However, the underlying mechanism of PDN in ameliorating myelin damage is not well understood. In our study, a cuprizone (CPZ)-induced demyelinated mouse model was used to explore the mechanism of the protection provided by PDN. Open-field tests showed that CPZ-treated mice exhibited significantly increased anxiety and decreased exploration. However, PDN improved emotional behavior, as evidenced by an increase in the total distance traveled, and central distance traveled as well as the mean amount of time spent in the central area. CPZ-induced demyelination was observed to be alleviated in PDN-treated mice based on luxol fast blue (LFB) staining and myelin basic protein (MBP) expression analyses. In addition, PDN reduced astrocyte and microglia activation in the corpus callosum. Furthermore, we demonstrated that PDN inhibited the Nod-like receptor pyrin domain containing 3 (NLRP3) inflammasome signaling pathway and related inflammatory cytokines and chemokines, including TNF-α, CCL8, CXCL10 and CXCL16. PDN also reduced the serum corticosterone levels in the CPZ-treated mice. Taken together, these results suggest that inhibition of the NLRP3 signaling pathway may be a novel mechanism by which PDN exerts its protective actions in demyelinating diseases.
Prostaglandin D2 synthase modulates macrophage activity and accumulation in injured peripheral nerves.
Forese Maria Grazia,Pellegatta Marta,Canevazzi Paolo,Gullotta Giorgia S,Podini Paola,Rivellini Cristina,Previtali Stefano C,Bacigaluppi Marco,Quattrini Angelo,Taveggia Carla
We have previously reported that prostaglandin D2 Synthase (L-PGDS) participates in peripheral nervous system (PNS) myelination during development. We now describe the role of L-PGDS in the resolution of PNS injury, similarly to other members of the prostaglandin synthase family, which are important for Wallerian degeneration (WD) and axonal regeneration. Our analyses show that L-PGDS expression is modulated after injury in both sciatic nerves and dorsal root ganglia neurons, indicating that it might play a role in the WD process. Accordingly, our data reveals that L-PGDS regulates macrophages phagocytic activity through a non-cell autonomous mechanism, allowing myelin debris clearance and favoring axonal regeneration and remyelination. In addition, L-PGDS also appear to control macrophages accumulation in injured nerves, possibly by regulating the blood-nerve barrier permeability and SOX2 expression levels in Schwann cells. Collectively, our results suggest that L-PGDS has multiple functions during nerve regeneration and remyelination. Based on the results of this study, we posit that L-PGDS acts as an anti-inflammatory agent in the late phases of WD, and cooperates in the resolution of the inflammatory response. Thus, pharmacological activation of the L-PGDS pathway might prove beneficial in resolving peripheral nerve injury.
Targeting toll-like receptor-4 (TLR4)-an emerging therapeutic target for persistent pain states.
Bruno Kelly,Woller Sarah A,Miller Yury I,Yaksh Tony L,Wallace Mark,Beaton Graham,Chakravarthy Krishnan
Toll-like receptors (TLRs) are a family of pattern recognition receptors that initiate signaling in innate and adaptive immune pathways. The highly conserved family of transmembrane proteins comprises an extracellular domain that recognizes exogenous and endogenous danger molecules and an ectodomain that activates downstream pathways in response. Recent studies suggest that continuous activation or dysregulation of TLR signaling may contribute to chronic disease states. The receptor is located not only on inflammatory cells (meningeal and peripheral macrophages) but on neuraxial glia (microglia and astrocytes), Schwann cells, fibroblasts, dorsal root ganglia, and dorsal horn neurons. Procedures blocking TLR functionality have shown pronounced effects on pain behavior otherwise observed in models of chronic inflammation and nerve injury. This review addresses the role of TLR4 as an emerging therapeutic target for the evolution of persistent pain and its role in noncanonical signaling, mediating anomalous pro-algesic actions of opiates. Accordingly, molecules targeting inhibition of this receptor have promise as disease-modifying and opioid-sparing alternatives for persistent pain states.
miRNA-155 silencing reduces sciatic nerve injury in diabetic peripheral neuropathy.
Chen Ji,Li Chao,Liu Wenjie,Yan Bin,Hu Xiaoling,Yang Fengrui
Journal of molecular endocrinology
Neuropathic pain represents one of the most common complications associated with diabetes mellitus (DM) that impacts quality of life. Accumulating studies have highlighted the involvement of miRNAs in DM. Thus, the current study aimed to investigate the roles of miR-155 in diabetic peripheral neuropathy (DPN). In vitro DPN models were established using rat Schwann cells (SCs) by treatment with 5.5 mM glucose. Gain- or loss-of-function studies were conducted to determine the effect of miR-155 on Nrf2, cellular function, reactive oxygen species and inflammation. Rat DNP models were established by streptozotocin injection and damage of sciatic nerve. Next, miR-155 antagomir or agomir was employed to investigate the effects associated with miR-155 on motor and sciatic nerve conduction velocity (MNCV, SNCV), angiogenesis and inflammatory response in vivo. Nrf2 was identified to be a target of miR-155 by dual-luciferase reporter gene assay. Silencing of miR-155 or restoration of Nrf2 promoted cell proliferation, inhibited apoptosis and alleviated inflammation in vitro. miR-155 antagomir-induced inhibition increased MNCV and SNCV, strengthened angiogenesis and alleviated inflammation in DPN rats. Additionally, the effects exerted by miR-155 were reversed when Nrf2 was restored both in vitro and in vivo. Taken together, the key findings of our study provide evidence indicating that miR-155 targeted and suppressed Nrf2 in DPN. miR-155 silencing was found to alleviate sciatic nerve injury in DPN, highlighting its potential as a therapeutic target for DPN.
Dynamic impact of brief electrical nerve stimulation on the neural immune axis-polarization of macrophages toward a pro-repair phenotype in demyelinated peripheral nerve.
McLean Nikki A,Verge Valerie M K
Demyelinating peripheral nerves are infiltrated by cells of the monocyte lineage, including macrophages, which are highly plastic, existing on a continuum from pro-inflammatory M1 to pro-repair M2 phenotypic states. Whether one can therapeutically manipulate demyelinated peripheral nerves to promote a pro-repair M2 phenotype remains to be elucidated. We previously identified brief electrical nerve stimulation (ES) as therapeutically beneficial for remyelination, benefits which include accelerated clearance of macrophages, making us theorize that ES alters the local immune response. Thus, the impact of ES on the immune microenvironment in the zone of demyelination was examined. Adult male rat tibial nerves were focally demyelinated via 1% lysophosphatidyl choline (LPC) injection. Five days later, half underwent 1 hour 20 Hz sciatic nerve ES proximal to the LPC injection site. ES had a remarkable and significant impact, shifting the macrophage phenotype from predominantly pro-inflammatory/M1 toward a predominantly pro-repair/M2 one, as evidenced by an increased incidence of expression of M2-associated phenotypic markers in identified macrophages and a decrease in M1-associated marker expression. This was discernible at 3 days post-ES (8 days post-LPC) and continued at the 5 day post-ES (10 days post-LPC) time point examined. ES also affected chemokine (C-C motif) ligand 2 (CCL2; aka MCP-1) expression in a manner that correlated with increases and decreases in macrophage numbers observed in the demyelination zone. The data establish that briefly increasing neuronal activity favorably alters the immune microenvironment in demyelinated nerve, rapidly polarizing macrophages toward a pro-repair phenotype, a beneficial therapeutic concept that may extend to other pathologies. GLIA 2016;64:1546-1561.
A silver lining of neuroinflammation: Beneficial effects on myelination.
Goldstein Evan Z,Church Jamie S,Hesp Zoe C,Popovich Phillip G,McTigue Dana M
Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.
Neuregulin-1 promotes remyelination and fosters a pro-regenerative inflammatory response in focal demyelinating lesions of the spinal cord.
Kataria Hardeep,Alizadeh Arsalan,Shahriary Ghazaleh M,Saboktakin Rizi Shekoofeh,Henrie Ryan,Santhosh Kallivalappil T,Thliveris James A,Karimi-Abdolrezaee Soheila
Oligodendroglial cell death and demyelination are hallmarks of neurotrauma and multiple sclerosis that cause axonal damage and functional impairments. Remyelination remains a challenge as the ability of endogenous precursor cells for oligodendrocyte replacement is hindered in the unfavorable milieu of demyelinating conditions. Here, in a rat model of lysolecithin lysophosphatidyl-choline (LPC)-induced focal demyelination, we report that Neuregulin-1 (Nrg-1), an important factor for oligodendrocytes and myelination, is dysregulated in demyelinating lesions and its bio-availability can promote oligodendrogenesis and remyelination. We delivered recombinant human Nrg-1β1 (rhNrg-1β1) intraspinally in the vicinity of LPC demyelinating lesion in a sustained manner using poly lactic-co-glycolic acid microcarriers. Availability of Nrg-1 promoted generation and maturation of new oligodendrocytes, and accelerated endogenous remyelination by both oligodendrocyte and Schwann cell populations in demyelinating foci. Importantly, Nrg-1 enhanced myelin thickness in newly remyelinated spinal cord axons. Our complementary in vitro studies also provided direct evidence that Nrg-1 significantly promotes maturation of new oligodendrocytes and facilitates their transition to a myelinating phenotype. Nrg-1 therapy remarkably attenuated the upregulated expression chondroitin sulfate proteoglycans (CSPGs) specific glycosaminoglycans in the extracellular matrix of demyelinating foci and promoted interleukin-10 (IL-10) production by immune cells. CSPGs and IL-10 are known to negatively and positively regulate remyelination, respectively. We found that Nrg-1 effects are mediated through ErbB2 and ErbB4 receptor activation. Our work provides novel evidence that dysregulated levels of Nrg-1 in demyelinating lesions of the spinal cord pose a challenge to endogenous remyelination, and appear to be an underlying cause of myelin thinning in newly remyelinated axons.
Sustained Local Release of NGF from a Chitosan-Sericin Composite Scaffold for Treating Chronic Nerve Compression.
Zhang Lei,Yang Wen,Tao Kaixiong,Song Yu,Xie Hongjian,Wang Jian,Li Xiaolin,Shuai Xiaoming,Gao Jinbo,Chang Panpan,Wang Guobin,Wang Zheng,Wang Lin
ACS applied materials & interfaces
Chronic nerve compression (CNC), a common form of peripheral nerve injury, always leads to chronic peripheral nerve pain and dysfunction. Current available treatments for CNC are ineffective as they usually aim to alleviate symptoms at the acute phase with limited capability toward restoring injured nerve function. New approaches for effective recovery of CNC injury are highly desired. Here we report for the first time a tissue-engineered approach for the repair of CNC. A genipin cross-linked chitosan-sericin 3D scaffold for delivering nerve growth factor (NGF) was designed and fabricated. This scaffold combines the advantages of both chitosan and sericin, such as high porosity, adjustable mechanical properties and swelling ratios, the ability of supporting Schwann cells growth, and improving nerve regeneration. The degradation products of the composite scaffold upregulate the mRNA levels of the genes important for facilitating nerve function recovery, including glial-derived neurotrophic factor (GDNF), early growth response 2 (EGR2), and neural cell adhesion molecule (NCAM) in Schwann cells, while down-regulating two inflammatory genes' mRNA levels in macrophages, tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β). Importantly, our tissue-engineered strategy achieves significant nerve functional recovery in a preclinical CNC animal model by decreasing neuralgia, improving nerve conduction velocity (NCV), accelerating microstructure restoration, and attenuating gastrocnemius muscles dystrophy. Together, this work suggests a promising clinical alternative for treating chronic peripheral nerve compression injury.
Interleukin-1β Promotes Schwann Cells De-Differentiation in Wallerian Degeneration via the c-JUN/AP-1 Pathway.
Chen Gang,Luo Xiaohe,Wang Wenjin,Wang Yimei,Zhu Fei,Wang Wei
Frontiers in cellular neuroscience
Schwann cells (SCs) de-differentiate in Wallerian degeneration (WD) following nerve injury and, by doing so, can actively promote nerve repair and functional recovery. An innate-immune response is an important component of the complex of events referred to as WD. Damaged peripheral nervous system SCs produce IL-1β and other inflammatory cytokines. We hypothesized that, in addition to a role in immune responses, IL-1β participates in de-differentiation and proliferation of SCs. qPCR and ELISA demonstrated that expression of IL-1β mRNAs and protein increased after nerve injury. Immunofluorescent staining and western blotting demonstrated that expression of the p75 neurotrophin receptor (p75NTR) was significantly increased and levels of myelin protein zero (MPZ) were significantly decreased after IL-1β exposure compared with control groups WD. Additionally, qPCR demonstrated that IL-1β elevated expression of the de-differentiation gene p75NTR and decreased expression of myelination locus MPZ and promoted SCs de-differentiation. Furthermore, immunofluorescent staining, western blotting, qPCR and ELISA revealed that IL-1β promoted c-JUN expression and activation of AP-1 activity of SCs in an WD model. Finally, Immunofluorescent staining illustrated that IL-1β elevated expression of Ki67 in SCs nuclei, the apoptosis of SCs were detected by TUNEL. SCs of WD produce IL-1β which promotes SCs de-differentiation and proliferation.
Immunoglobulins stimulate cultured Schwann cell maturation and promote their potential to induce axonal outgrowth.
Tzekova Nevena,Heinen André,Bunk Sebastian,Hermann Corinna,Hartung Hans-Peter,Reipert Birgit,Küry Patrick
Journal of neuroinflammation
BACKGROUND:Schwann cells are the myelinating glial cells of the peripheral nervous system and exert important regenerative functions revealing them as central repair components of many peripheral nerve pathologies. Intravenous immunoglobulins (IVIG) are widely used to treat autoimmune and inflammatory diseases including immune-mediated neuropathies. Nevertheless, promotion of peripheral nerve regeneration is currently an unmet therapeutical goal. We therefore examined whether immunoglobulins affect glial cell homeostasis, differentiation, and Schwann cell dependent nerve regenerative processes. METHODS:The responses of different primary Schwann cell culture models to IVIG were investigated: immature or differentiation competent Schwann cells, myelinating neuron/glial cocultures, and dorsal root ganglion explants. Immature or differentiating Schwann cells were used to study cellular proliferation, morphology, and gene/protein expression. Myelination rates were determined using myelinating neuron/glia cocultures, whereas axonal outgrowth was assessed using non-myelinating dorsal root ganglion explants. RESULTS:We found that IVIG specifically bind to Schwann cells and detected CD64 Fc receptor expression on their surface. In response to IVIG binding, Schwann cells reduced proliferation rates and accelerated growth of cellular protrusions. Furthermore, we observed that IVIG treatment transiently boosts myelin gene expression and myelination-related signaling pathways of immature cells, whereas in differentiating Schwann cells, myelin expression is enhanced on a long-term scale. Importantly, myelin gene upregulation was not detected upon application of IgG1 control antibodies. In addition, we demonstrate for the first time that Schwann cells secrete interleukin-18 upon IVIG stimulation and that this cytokine instructs these cells to promote axonal growth. CONCLUSIONS:We conclude that IVIG can positively influence the Schwann cell differentiation process and that it enhances their regenerative potential.
Apolipoprotein E isoform-specific effects on cytokine and nitric oxide production from mouse Schwann cells after inflammatory stimulation.
Zhang Ke-Jia,Zhang Hong-Liang,Zhang Xing-Mei,Zheng Xiang-Yu,Quezada Hernan Concha,Zhang Duo,Zhu Jie
Previously, we reported that apolipoprotein E (apoE) deficiency increased the susceptibility to experimental autoimmune neuritis (EAN), an inflammatory autoimmune disorder of the peripheral nervous system (PNS) and an animal model for human Guillain-Barré syndrome (GBS) by affecting the antigen-presenting function of Schwann cells (SCs) via influence upon IL-6 production. To further elucidate the role of apoE in inflammation of the PNS, here we studied the effect of different isoforms of apoE on SCs in response to inflammatory stimulation. SCs from apoE2, E3 and E4 transgenic (Tg) and wild type (WT) mice were cultured, and their responses to stimulation by lipopolysaccharide (LPS) plus interferon (IFN)-γ were compared. Upon stimulation, the morphology of cultured SCs changed. Pronounced production of interleukin (IL)-6 and IL-10 within SCs, and of IL-6 and nitric oxide (NO) in the supernatants were found in an isoform-dependent manner (apoE3>apoE2≈apoE4). Further results indicated that both nuclear factor (NF) κB and Akt signaling pathways were involved in the process by the same isoform-dependent pattern. However, the expression of co-stimulatory molecules as showing the antigen-presenting capacity of SCs was not significantly different among these groups. In conclusion, SCs respond to inflammatory insults accompanied by increased productions of IL-6, IL-10 and NO in an apoE-isoform-dependent manner. SCs from apoE2 and apoE4 Tg mice seem to bear some dysfunction in producing cytokines (IL-6 and IL-10) and NO as compared with their apoE3 counterparts, probably resulting from their insufficiency to suppress the activation of NFκB and Akt pathways. Our findings may help to understand the role of different isoforms of apoE in inflammatory disorders of the PNS.
Macrophage polarization in nerve injury: do Schwann cells play a role?
Stratton Jo Anne,Shah Prajay T
Neural regeneration research
In response to peripheral nerve injury, the inflammatory response is almost entirely comprised of infiltrating macrophages. Macrophages are a highly plastic, heterogenic immune cell, playing an indispensable role in peripheral nerve injury, clearing debris and regulating the microenvironment to allow for efficient regeneration. There are several cells within the microenvironment that likely interact with macrophages to support their function - most notably the Schwann cell, the glial cell of the peripheral nervous system. Schwann cells express several ligands that are known to interact with receptors expressed by macrophages, yet the effects of Schwann cells in regulating macrophage phenotype remains largely unexplored. This review discusses macrophages in peripheral nerve injury and how Schwann cells may regulate their behavior.
Local production of serum amyloid a is implicated in the induction of macrophage chemoattractants in Schwann cells during wallerian degeneration of peripheral nerves.
Jang So Young,Shin Yoon Kyung,Lee Ha Young,Park Joo Youn,Suh Duk Joon,Kim Jong Kuk,Bae Yoe-Sik,Park Hwan Tae
The elevation of serum levels of serum amyloid A (SAA) has been regarded as an acute reactive response following inflammation and various types of injuries. SAA from the liver and extrahepatic tissues plays an immunomodulatory role in a variety of pathophysiological conditions. Inflammatory cytokines in the peripheral nerves have been implicated in the Wallerian degeneration of peripheral nerves after injury and in certain types of inflammatory neuropathies. In the present study, we found that a sciatic nerve axotomy could induce an increase of SAA1 and SAA3 mRNA expression in sciatic nerves. Immunohistochemical staining showed that Schwann cells are the primary sources of SAA production after nerve injury. In addition, interleukin-6-null mice, but not tumor necrosis factor-α-null mice showed a defect in the production of SAA1 in sciatic nerve following injury. Dexamethasone treatment enhanced the expression and secretion of SAA1 and SAA3 in sciatic nerve explants cultures, suggesting that interleukin-6 and corticosteroids might be major regulators for SAA production in Schwann cells following injury. Moreover, the stimulation of Schwann cells with SAA1 elicited the production of the macrophage chemoattractants, Ccl2 and Ccl3, in part through a G-protein coupled receptor. Our findings suggest that locally produced SAA might play an important role in Wallerian degeneration after peripheral nerve injury.
Expression of antigen processing and presenting molecules by Schwann cells in inflammatory neuropathies.
Meyer Zu Horste Gerd,Heidenreich Holger,Lehmann Helmar C,Ferrone Soldano,Hartung Hans-Peter,Wiendl Heinz,Kieseier Bernd C
Schwann cells are the myelinating glia cells of the peripheral nervous system (PNS) and can become targets of an autoimmune response in inflammatory neuropathies like the Guillain-Barré syndrome (GBS). Professional antigen presenting cells (APCs) are known to promote autoimmune responses in target tissues by presenting self-antigens. Other cell types could participate in local autoimmune responses by acting as nonprofessional APCs. Using a combined approach of immunocytochemistry, immunohistochemistry, and flow cytometry analysis we demonstrate that human Schwann cells express the antigen processing and presenting machinery (APM) in vitro and in vivo. Moreover, cultured human Schwann cells increase the expression of proteasome subunit delta (Y), antigen peptide transporter TAP2, and HLA Class I and HLA Class II complexes in an inflammatory environment. In correlation with this observation, Schwann cells in sural nerve biopsies from GBS patients show increased expression of antigen processing and presenting molecules. Furthermore, cultured human Schwann cells can proteolytically digest fluorescently-labeled nonmammalian antigen ovalbumin. Taken together, our data suggest antigen processing and presentation as a possible function of Schwann cells that may contribute to (auto)immune responses within peripheral nerves.
Schwann Cell Transplantation Subdues the Pro-Inflammatory Innate Immune Cell Response after Spinal Cord Injury.
Pearse Damien D,Bastidas Johana,Izabel Sarah S,Ghosh Mousumi
International journal of molecular sciences
The transplantation of Schwann cells (SCs) has been shown to provide tissue preservation and support axon growth and remyelination as well as improve functional recovery across a diverse range of experimental spinal cord injury (SCI) paradigms. The autologous use of SCs has progressed to Phase 1 SCI clinical trials in humans where their use has been shown to be both feasible and safe. The contribution of immune modulation to the protective and reparative actions of SCs within the injured spinal cord remains largely unknown. In the current investigation, the ability of SC transplants to alter the innate immune response after contusive SCI in the rat was examined. SCs were intraspinally transplanted into the lesion site at 1 week following a thoracic (T8) contusive SCI. Multicolor flow cytometry and immunohistochemical analysis of specific phenotypic markers of pro- and anti-inflammatory microglia and macrophages as well as cytokines at 1 week after SC transplantation was employed. The introduction of SCs significantly attenuated the numbers of cluster of differentiation molecule 11B (CD11b)⁺, cluster of differentiation molecule 68 (CD68)⁺, and ionized calcium-binding adapter molecule 1 (Iba1)⁺ immune cells within the lesion implant site, particularly those immunoreactive for the pro-inflammatory marker, inducible nitric oxide synthase (iNOS). Whereas numbers of anti-inflammatory CD68⁺ Arginase-1 (Arg1⁺) iNOS cells were not altered by SC transplantation, CD68⁺ cells of an intermediate, Arg1⁺ iNOS⁺ phenotype were increased by the introduction of SCs into the injured spinal cord. The morphology of Iba1⁺ immune cells was also markedly altered in the SC implant, being elongated and in alignment with SCs and in-growing axons versus their amoeboid form after SCI alone. Examination of pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and anti-inflammatory cytokines, interleukin-4 (IL-4) and interleukin-10 (IL-10), by multicolor flow cytometry analysis showed that their production in CD11b⁺ cells was unaltered by SC transplantation at 1 week post-transplantation. The ability of SCs to subdue the pro-inflammatory iNOS⁺ microglia and macrophage phenotype after intraspinal transplantation may provide an important contribution to the neuroprotective effects of SCs within the sub-acute SCI setting.