Schwann Cell Apoptosis Research Articles

Glycolaldehyde induces endoplasmic reticulum stress and apoptosis in Schwann cells.

Schwann cell injury is caused by diabetic neuropathy. The apoptosis of Schwann cells plays a pivotal role in diabetic nerve dysfunction. Glycolaldehyde is a precursor of advanced glycation end products that contribute to the pathogenesis of diabetic neuropathy. In this study, we examined whether glycolaldehyde induces endoplasmic reticulum (ER) stress and apoptosis in rat Schwann cells. Schwann cells treated with 500μM glycolaldehyde showed morphological changes characteristic of apoptosis. Glycolaldehyde activated apoptotic signals, such as caspase-3 and caspase-8. Furthermore, it induced ER stress response involving RNA-dependent protein kinase-like ER kinase (PERK), inositol-requiring ER-to-nucleus signal kinase 1α (IRE1α), and eukaryotic initiation factor 2α (eIF2α). In addition, glycolaldehyde activated CCAAT/enhancer-binding homologous protein (CHOP), an ER stress response factor crucial to executing apoptosis. Knockdown of nuclear factor E2-related factor 2 (Nrf2), which is involved in the promotion of cell survival following ER stress, enhanced glycolaldehyde-induced cytotoxicity, indicating that Nrf2 plays a protective role in the cytotoxicity caused by glycolaldehyde. Taken together, these findings indicate that glycolaldehyde is capable of inducing apoptosis and ER stress in Schwann cells. The ER stress induced by glycolaldehyde may trigger the glycolaldehyde-induced apoptosis in Schwann cells. This study demonstrated for the first time that glycolaldehyde induced ER stress.

Third-degree hindpaw burn injury induced apoptosis of lumbar spinal cord ventral horn motor neurons and sciatic nerve and muscle atrophy in rats.

Background. Severe burns result in hypercatabolic state and concomitant muscle atrophy that persists for several months, thereby limiting patient recovery. However, the effects of burns on the corresponding spinal dermatome remain unknown. This study aimed to investigate whether burns induce apoptosis of spinal cord ventral horn motor neurons (VHMNs) and consequently cause skeletal muscle wasting. Methods. Third-degree hindpaw burn injury with 1% total body surface area (TBSA) rats were euthanized 4 and 8 weeks after burn injury. The apoptosis profiles in the ventral horns of the lumbar spinal cords, sciatic nerves, and gastrocnemius muscles were examined. The Schwann cells in the sciatic nerve were marked with S100. The gastrocnemius muscles were harvested to measure the denervation atrophy. Result. The VHMNs apoptosis in the spinal cord was observed after inducing third-degree burns in the hindpaw. The S100 and TUNEL double-positive cells in the sciatic nerve increased significantly after the burn injury. Gastrocnemius muscle apoptosis and denervation atrophy area increased significantly after the burn injury. Conclusion. Local hindpaw burn induces apoptosis in VHMNs and Schwann cells in sciatic nerve, which causes corresponding gastrocnemius muscle denervation atrophy. Our results provided an animal model to evaluate burn-induced muscle wasting, and elucidate the underlying mechanisms.

The Role of Oxidative Stress in Diabetic Neuropathy: Generation of Free Radical Species in the Glycation Reaction and Gene Polymorphisms Encoding Antioxidant Enzymes to Genetic Susceptibility to Diabetic Neuropathy in Population of Type I Diabetic Patients.

Diabetic neuropathy (DN) represents the main cause of morbidity and mortality among diabetic patients. Clinical data support the conclusion that the severity of DN is related to the frequency and duration of hyperglycemic periods. The presented experimental and clinical evidences propose that changes in cellular function resulting in oxidative stress act as a leading factor in the development and progression of DN. Hyperglycemia- and dyslipidemia-driven oxidative stress is a major contributor, enhanced by advanced glycation end product (AGE) formation and polyol pathway activation. There are several polymorphous pathways that lead to oxidative stress in the peripheral nervous system in chronic hyperglycemia. This article demonstrates the origin of oxidative stress derived from glycation reactions and genetic variations within the antioxidant genes which could be implicated in the pathogenesis of DN. In the diabetic state, unchecked superoxide accumulation and resultant increases in polyol pathway activity, AGEs accumulation, protein kinase C activity, and hexosamine flux trigger a feed-forward system of progressive cellular dysfunction. In nerve, this confluence of metabolic and vascular disturbances leads to impaired neural function and loss of neurotrophic support, and over the long term, can mediate apoptosis of neurons and Schwann cells, the glial cells of the peripheral nervous system. In this article, we consider AGE-mediated reactive oxygen species (ROS) generation as a pathogenesis factor in the development of DN. It is likely that oxidative modification of proteins and other biomolecules might be the consequence of local generation of superoxide on the interaction of the residues of L-lysine (and probably other amino acids) with α-ketoaldehydes. This phenomenon of non-enzymatic superoxide generation might be an element of autocatalytic intensification of pathophysiological action of carbonyl stress. Glyoxal and methylglyoxal formed during metabolic pathway are detoxified by the glyoxalase system with reduced glutathione as co-factor. The concentration of reduced glutathione may be decreased by oxidative stress and by decreased in situ glutathione reductase activity in diabetes mellitus. Genetic variations within the antioxidant genes therefore could be implicated in the pathogenesis of DN. In this work, the supporting data about the association between the -262T > C polymorphism of the catalase (CAT) gene and DN were shown. The -262TT genotype of the CAT gene was significantly associated with higher erythrocyte catalase activity in blood of DN patients compared to the -262CC genotype (17.8 ± 2.7 × 10(4) IU/g Hb vs. 13.5 ± 3.2 × 10(4) IU/g Hb, P = 0.0022). The role of these factors in the development of diabetic complications and the prospective prevention of DN by supplementation in formulations of transglycating imidazole-containing peptide-based antioxidants (non-hydrolyzed carnosine, carcinine, n-acetylcarcinine) scavenging ROS in the glycation reaction, modifying the activity of enzymic and non-enzymic antioxidant defenses that participate in metabolic processes with ability of controlling at transcriptional levels the differential expression of several genes encoding antioxidant enzymes inherent to DN in Type I Diabetic patients, now deserve investigation.

TGF-β1 is critical for Wallerian degeneration after rat sciatic nerve injury

Wallerian degeneration (WD) is a process of axonal degeneration distal to the injury site followed by a robust regenerative response. It involves degeneration and regeneration which can be directly induced by nerve injury and activated by transcription factors. Although WD has been studied extensively, the precise mechanisms of transcription factors regulating WD are still elusive. In this study, we reported the effect of transforming growth factor-β1 (TGF-β1) on WD after rat sciatic nerve injury. The data showed that TGF-β1 may express in injured rat sciatic nerve and cultured Schwann cells (SCs). Knock down of TGF-β1 expressions resulted in the reduction of SC proliferation and apoptosis, up regulation of cytokines and Smad2, 4. Enhanced expression of TGF-β1 could promote SC proliferation and apoptosis, down regulation of cytokines and Smad2, 4. Altered expressions of TGF-β1 may affect Smad and AKT but not c-Jun and extracellular regulated protein kinase (ERK) pathways. Our results revealed the role of TGF-β1 on WD and provided the basis for the molecular mechanisms of TGF-β1-regulated nerve degeneration and/or regeneration.

MiR-204 promotes apoptosis in oxidative stress-induced rat Schwann cells by suppressing neuritin expression

Neuritin (Nrn1) is a neurotrophin that plays an important role in nervous system plasticity and repair following nerve injury. MicroRNAs (miRNAs) are a type of small non-coding RNA that regulate nearly all aspects of nerve development and survival, including apoptosis. Here it was found that miR-204 negatively regulates Nrn1 protein expression through direct interaction with Nrn1 transcript. Moreover, miR-204 activates cleaved caspase-3, enhancing the sensitivity of RSC96 Schwann cells to H2O2-induced oxidative stress and apoptosis. Thus, miR-204 expressed at a low level may create a microenvironment suitable for the repair of injured nerves by relieving the inhibition of Nrn1 transcription and stimulating the anti-apoptotic function of Schwann cells. These results provide novel insights into the roles of miR-204 in nerve injury and repair.

Neuroprotective effects of carboxymethylated chitosan on hydrogen peroxide induced apoptosis in Schwann cells

The protective and promotion effects of Carboxymethylated chitosan (CMCS) on peripheral nerve and cultured Schwann cells (SCs) have been demonstrated, but few studies discussed the protective roles of CMCS on SCs apoptosis. We explored the anti-apoptotic activities of CMCS in SCs to enhance cells survival in this present study. Rat SCs were isolated and cultured in vitro, hydrogen peroxide (H2O2) was used to establish the apoptosis models of SCs. Cells proliferative activity was assessed by CCK-8 assay. The apoptosis of SCs was detected by flow cytometry (FCM) analysis. Superoxide dismutase (SOD) and malondialdehyde (MDA) activities were detected by the corresponding assay kit. The nuclear appearance of apoptotic SCs was observed by nuclear staining with Hoechst 33342. The real-time PCR was performed to detect the levels of Bcl-2, Bax, Caspase-3 and -9 mRNA. Detection of caspase-3 and -9 was fulfilled by using Western blot analysis. FCM assay and Hoechst33342 staining results indicated that CMCS could protect SCs from apoptosis with dose and time-dependent manner. SOD and MDA analysis results indicated that CMCS could promote SOD activity and reduce the MDA levels in H2O2 induced SCs. The decreased caspase-3, -9 and Bax activities and increased Bcl-2 activity were observed in CMCS treated SCs. The present study indicates CMCS has the neuroprotective effect on peripheral nerves and inhibit SCs apoptosis.

SorCS2 regulates dopaminergic wiring and is processed into an apoptotic two-chain receptor in peripheral glia.

Balancing trophic and apoptotic cues is critical for development and regeneration of neuronal circuits. Here we identify SorCS2 as a proneurotrophin (proNT) receptor, mediating both trophic and apoptotic signals in conjunction with p75(NTR). CNS neurons, but not glia, express SorCS2 as a single-chain protein that is essential for proBDNF-induced growth cone collapse in developing dopaminergic processes. SorCS2- or p75(NTR)-deficient in mice caused reduced dopamine levels and metabolism and dopaminergic hyperinnervation of the frontal cortex. Accordingly, both knockout models displayed a paradoxical behavioral response to amphetamine reminiscent of ADHD. Contrary, in PNS glia, but not in neurons, proteolytic processing produced a two-chain SorCS2 isoform that mediated proNT-dependent Schwann cell apoptosis. Sciatic nerve injury triggered generation of two-chain SorCS2 in p75(NTR)-positive dying Schwann cells, with apoptosis being profoundly attenuated in Sorcs2(-/-) mice. In conclusion, we have demonstrated that two-chain processing of SorCS2 enables neurons and glia to respond differently to proneurotrophins.

Erythropoietin attenuates oxidative stress and apoptosis in Schwann cells isolated from streptozotocin-induced diabetic rats

High glucose-evoked oxidative stress and apoptosis within Schwann cells (SCs) are mechanisms facilitating the procession of diabetic peripheral neuropathy (DPN). Although erythropoietin (EPO) was demonstrated to have neuroprotective effects in neurodegenerative diseases, the effects of EPO on glucose-evoked oxidative stress and apoptosis of SCs remain unknown. Primary cultured SCs isolated from streptozotocin (STZ)-induced diabetic peripheral neuropathic rats and normal control rats were exposed to high or normal glucose condition with or without EPO incubation for 72 h. Cell viability, apoptotic rate, cellular reactive oxygen species (ROS) level, total glutathione (GSH) level, EPO mRNA and erythropoietin receptor (EPOR) mRNA levels were assayed. SCs from diabetic rats showed a lower cell viability and a higher apoptotic rate. High glucose culture condition elevated ROS level and diminished total GSH level of SCs. EPO improved cell viability and decreased cell apoptotic rate of SCs. EPO also elevated total GSH level and decreased intracellular ROS level. SCs from diabetic rats exhibited higher EPO mRNA and EPOR mRNA levels than SCs from normal control rats. The data of this study offered fresh viewpoints for interpreting the pathogenesis of DPN and novel pharmacological principles implicit in the therapeutic effect of EPO.

The effects of claudin 14 during early Wallerian degeneration after sciatic nerve injury.

Claudin 14 has been shown to promote nerve repair and regeneration in the early stages of Wallerian degeneration (0–4 days) in rats with sciatic nerve injury, but the mechanism underlying this process remains poorly understood. This study reported the effects of claudin 14 on nerve degeneration and regeneration during early Wallerian degeneration. Claudin 14 expression was up-regulated in sciatic nerve 4 days after Wallerian degeneration. The altered expression of claudin 14 in Schwann cells resulted in expression changes of cytokines in vitro. Expression of claudin 14 affected c-Jun, but not Akt and ERK1/2 pathways. Further studies revealed that enhanced expression of claudin 14 could promote Schwann cell proliferation and migration. Silencing of claudin 14 expression resulted in Schwann cell apoptosis and reduction in Schwann cell proliferation. Our data revealed the role of claudin 14 in early Wallerian degeneration, which may provide new insights into the molecular mechanisms of Wallerian degeneration.

Effect of serum containing Jinmaitong Capsule (筋脉通胶囊) on Rats’ Schwann cell apoptosis induced by high glucose concentration

To evaluate the effect of serum containing Jinmaitong Capsule (JMT) on apoptosis of Schwann cells (SCs) that are cultured in high glucose at the cellular and molecular levels. SCs were cultured in Dulbecco's modified Eagle's medium (control group), high glucose (50 mmol/L) medium supplemented with 20% rat serum (HG group), and 50 mmol/L glucose medium supplemented with serum containing JMT (JMT group). SC apoptosis was detected using a terminal deoxynucleotidyl transferase dUTP nick end labeling kit. The expression of Bcl-2 and the caspase-3 p20 subunit in SCs were detected by realtime fluorogenic quantitative polymerase chain reaction and confocal laser scanning microscopy, respectively. No apoptosis was detected in SCs that were cultured in the control group. The percentage of apoptosis of SCs cultured in the HG group was much higher than that in the control group. The apoptosis of SCs in the JMT group was lower than that in the HG group. Fluorescence intensity of Bcl-2 and the expression of Bcl-2 mRNA in SCs that were cultured in the HG group were much lower than those in the control group and much higher than those in the JMT group (P<0.01). The fluorescence intensity of caspase-3 p20 and the expression of caspase-3 p20 mRNA in SCs that were cultured in the HG group were much higher than those in the control group (P<0.01), and they were remarkably lower in the JMT group (P<0.01). JMT effectively prevents SC apoptosis that is induced by high glucose. This effect may be because of increased expression of Bcl-2 mRNA and protein and decreased expression of caspase-3 p20 mRNA and protein.

Intracellular reactive oxidative stress, cell proliferation and apoptosis of Schwann cells on carbon nanofibrous substrates

Despite considerable research to develop carbon based materials for biomedical applications, the toxicity of carbon remains a major concern. In order to address this issue as well as to investigate the cell fate processes of neural cells from the perspective of neural tissue engineering applications, the in vitro cytocompatibility of polyacrylonitrile (PAN) derived continuous carbon nanofibers and PAN derived carbon thin films were investigated both quantitatively and qualitatively using in vitro biochemical assays followed by extensive flow cytometry analysis. The experimental results of Schwann cell fate, i.e. cell proliferation, cell metabolic activity and cell apoptosis on amorphous carbon substrates are discussed in reference to the time dependent evolution of intracellular oxidative stress. Apart from providing evidence that an electrospun carbon nanofibrous substrate can physically guide the cultured Schwann cells, this study suggested that continuous carbon nanofibers and amorphous carbon films are not cytotoxic in vitro and do not significantly induce apoptosis of Schwann cells, but in fact even facilitate their proliferation and growth.

The effect of exercise on mobilization of hematopoietic progenitor cells involved in the repair of sciatic nerve crush injury [RETRACTED

Object Mobilization of hematopoietic progenitor cells (HPCs) from bone marrow involved in the process of peripheral nerve regeneration occurs mostly through deposits of CD34(+) cells. Treadmill exercise, with either differing intensity or duration, has been shown to increase axon regeneration and sprouting, but the effect of mobilization of HPCs on peripheral nerve regeneration due to treadmill exercise has not yet been elucidated. Methods Peripheral nerve injury was induced in Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The animals were categorized into 2 groups: those with and without treadmill exercise (20 m/min for 60 minutes per day for 7 days). Cytospin and flow cytometry were used to determine bone marrow progenitor cell density and distribution. Neurobehavioral analysis, electrophysiological study, and regeneration marker expression were investigated at 1 and 3 weeks after exercise. The accumulation of HPCs, immune cells, and angiogenesis factors in injured nerves was determined. A separate chimeric mice study was conducted to assess CD34(+) cell distribution according to treadmill exercise group. Results Treadmill exercise significantly promoted nerve regeneration. Increased Schwann cell proliferation, increased neurofilament expression, and decreased Schwann cell apoptosis were observed 7 days after treadmill exercise. Elevated expression of S100 and Luxol fast blue, as well as decreased numbers of vacuoles, were identified in the crushed nerve 3 weeks after treadmill exercise. Significantly increased numbers of mononuclear cells, particularly CD34(+) cells, were induced in bone marrow after treadmill exercise. The deposition of CD34(+) cells was abolished by bone marrow irradiation. In addition, deposits of CD34(+) cells in crushed nerves paralleled the elevated expressions of von Willebrand factor, isolectin B4, and vascular endothelial growth factor. Conclusions Bone marrow HPCs, especially CD34(+) cells, were able to be mobilized by low-intensity treadmill exercise, and this effect paralleled the significant expression of angiogenesis factors. Treadmill exercise stimulation of HPC mobilization during peripheral nerve regeneration could be used as a therapy in human beings.

Nerve Injury-related Autoimmunity Activation Leads to Chronic Inflammation and Chronic Neuropathic Pain

Peripheral nerve injuries that provoke neuropathic pain are associated with chronic inflammation and nervous lesions. The authors hypothesized that chronic neuropathic pain might be caused by chronic inflammation resulting from a nervous autoimmune reaction triggered by nerve injury. The authors observed chronic inflammation and neuropathic behaviors for up to 12 weeks after nerve injury in T lymphocyte-deficient nude mice and their heterozygous littermates. Lymphocyte proliferation and Schwann cell apoptosis were examined after coculture of each population with various neural tissues from normal rats and those with nerve injury. Nude mice recovered faster and exhibited less thermal hyperalgesia after nerve injury compared to their heterozygous littermates. A large number of IL-17 cells indicative of lymphocyte activation were found in the injured sciatic nerve and spinal cord (L4-6) of heterozygous littermates, but far fewer of these populations were found in nude mice. In vitro lymphocyte proliferation was enhanced after coculture with nerve tissues from normal rats compared to nerve tissue-free phosphate-buffered saline controls. In particular, coculture with sciatic nerve tissue enhanced proliferation by 80%, dorsal root ganglion by 46%, and spinal cord by 14%. Moreover, neural tissues from rats with nerve injury markedly increased the lymphocyte proliferation compared to coculture with tissues from corresponding normal rats. Schwann cell apoptosis was triggered in vitro when cocultured with lymphocytes from neuropathic rats. Our study suggests that chronic neuropathic pain might be caused by chronic inflammation resulting from a nervous autoimmune reaction triggered by nerve injury.

CD8+ T Cell-Mediated Cytotoxicity toward Schwann Cells Promotes Diabetic Peripheral Neuropathy

Background: Damage to Schwann cells has been reported in the development of diabetic peripheral neuropathy (DPN), but how Schwann cells are damaged has not been elucidated. Methods: The highly expressed proteins in the PBMC of DPN patients were identified through MALDI-TOF/TOF and SELDI protein chip technology. The expression levels of CXCR3 were detected by qPCR and flow cytometric analysis. Transwell migration assay was to investigate the migration of CD8⁺ T cells. Western-blot analysis was to detect the levels of p38 MAP kinases pathway related proteins and TNF-α, FasL, and PDL1. Results: Two highly expressed proteins, CXCR3 and p38, were identified. Under high glucose conditions, CXCR3 was elevated in CD8⁺ T cells via the activation of p38 MAP kinases. Moreover, CXCL9, CXCL10, and CXCL11 expression were induced in Schwann cells, leading to the recruitment and infiltration of CD8⁺ T cells into DPN tissues. Further study demonstrated that Schwann cells promoted activation of CD8⁺ T cells and induced expression of TNF-α, FasL, and PDL1 on CD8⁺ T cells, in return, CD8⁺ T cells induced obvious apoptosis of Schwann cells. Conclusion: Our study indicates that CD8⁺ T cells mediate cytotoxicity toward Schwann cells and play an important role in the development of DPN.

The Beneficial Effect of Ginsenoside Rg1 on Schwann Cells Subjected to Hydrogen Peroxide Induced Oxidative Injury

Ginsenoside Rg1 (GRg1) has been considered to have therapeutic potential in promoting peripheral nerve regeneration and functional recovery after sciatic nerve injuries. However, the mechanism underlying the beneficial effect of GRg1 on peripheral nerve regeneration is currently unclear. The possible effect of GRg1 on Schwann cells (SCs), which were subjected to oxidative injury after nerve injury, might contribute to the beneficial effect of GRg1 on nerve regeneration. The present study was designed to investigate the potential beneficial effect of GRg1 on SCs exposed to oxidative injury. The oxidative injury to SCs was induced by hydrogen peroxide. The effect of GRg1 (50 μM) on SCs exposed to oxidative injury was measured by the levels of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT) in SCs. The cell number and cell viability of SCs were evaluated through fluorescence observation and MTT assay. The apoptosis of SCs induced by oxidative injury was evaluated by an apoptosis assay. The expression and secretion of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were evaluated using RT-PCR, Western blotting, and an ELISA method. We found that GRg1 significantly up-regulated the level of SOD, GSH and CAT, and decreased the level of MDA in SCs treated with hydrogen peroxide. In addition, GRg1 has been shown to be able to inhibit the proapoptotic effect of hydrogen peroxide, as well as inhibit the detrimental effect of hydrogen peroxide on cell number and cell viability. Furthermore, GRg1 also increased the mRNA levels, protein levels and secretion of NGF and BDNF in SCs after incubation of hydrogen peroxide. Further study showed that preincubation with H89 (a PKA inhibitor) significantly inhibited the effects induced by hydrogen peroxide, indicating that the PKA pathway might be involved in the antioxidant effect and neurotrophic factors (NTFs) promoting effect of GRg1. In addition, a short-term in vivo study was performed to confirm and validate the antioxidant effect and nerve regeneration-promoting effect of GRg1 in a sciatic crush injury model in rats. We found that GRg1 significantly increased SOD, CAT and GSH, decreased MDA, as well as promoted nerve regeneration after crush injury. In conclusion, the present study showed that GRg1 is capable of helping SCs recover from the oxidative insult induced by hydrogen peroxide, which might account, at least in part, for the beneficial effect of GRg1 on nerve regeneration.

Puerarin prevents high glucose-induced apoptosis of Schwann cells by inhibiting oxidative stress.

Oxidative stress may be the unifying factor for the injury caused by hyperglycemia in diabetic peripheral neuropathy. Puerarin is the major isoflavonoid derived from Radix puerariae and has been shown to be effective in increasing superoxide dismutase activity. This study sought to investigate the neuroprotective effect of puerarin on high glucose-induced oxidative stress and Schwann cell apoptosis in vitro. Intracellular reactive oxygen radicals and mitochondrial transmembrane potential were detected by flow cytometry analysis. Apoptosis was confirmed by TUNEL and oxidative stress was monitored using an enzyme-linked immunosorbent assay for the DNA marker 8-hydroxy-2-deoxyguanosine. The expression levels of bax and bcl-2 were analyzed by quantitative real-time reverse transcriptase-PCR, while protein expression of cleaved caspase-3 and -9 were analyzed by means of western blotting. Results suggested that puerarin treatment inhibited high glucose-induced oxidative stress, mitochondrial depolarization and apoptosis in a dose-dependent manner. Furthermore, puerarin treatment downregulated Bax expression, upregulated bcl-2 expression and attenuated the activation of caspase-3 and -9. Overall, our results indicated that puerarin antagonized high glucose-induced oxidative stress and apoptosis in Schwann cells.

Neuritin is expressed in Schwann cells and down-regulated in apoptotic Schwann cells under hyperglycemia

We aimed to explore neuritin expression in Schwann cells under different glucose conditions. Expression of neuritin at the levels of transcription and translation in purified Schwann cells was detected and measured using reverse transcriptase (RT) (quantitative) polymerase chain reaction (PCR) and western blot. Apoptosis of Schwann cells was measured by flow cytometry using Fluorescence Activated Cell Sorter (FACS) analysis and caspase fluorometric assay. Neuritin mRNA and protein were detected in cultured primary Schwann cells. Neuritin was identified as cell membrane form of protein and predominately as secreted or solube form of protein. Neuritin was significantly lower in 150 mM glucose condition, and more significantly lower in 300 mM glucose, than 5.6 mM glucose condition at 36 hours and especially at 48 hours of the culture, respectively (P < 0.05–0.01). In contrast to 5.6 mM glucose, obvious apoptosis of Schwann cells was demonstrated at 42 hours in 300 mM glucose condition and at 48 hours in 150 mM glucose, respectively (P < 0.05–0.01). Neuritin and apoptosis were correlated in a power regression (P < 0.01). 5.6 mM glucose cultured cells did not show these obvious changes during the experiment. It is concluded that neuritin mRNA and protein were expressed and down-regulated in Schwann cells under high-glucose concentration and the down-regulation may contribute to apopotosis of Schwann cells.

Fingolimod Impedes Schwann Cell–Mediated Myelination

Fingolimod (FTY720), a first-in-class sphingosine-1-phosphate (S1P) receptor agonist, is a recently approved drug for treating relapsing multiple sclerosis. Experimental evidence suggests that FTY720 not only exhibits anti-inflammatory properties but also promotes myelination in the central nervous system by direct interaction with oligodendrocytes. To assess the effects of FTY720 on Schwann cells (SCs) and peripheral nerve myelination. Receptor expression studies and myelination were investigated in primary rat SCs and rat neuronal/SC cocultures. Cells were treated with physiologically relevant concentrations of the active phosphorylated form of FTY720 (FTY720P). In addition, S1P receptor expression was corroborated in human and rat peripheral nerve tissue sections. Schwann cells express all known S1P receptors on the RNA level, not altered by FTY720P. In the myelination model, treatment with FTY720P resulted in a significant reduction of quantitative myelin formation. FTY720P induced reactive oxygen species in SCs associated with apoptosis of these cells, as demonstrated by the detection of cysteine aspartic acid–specific protease 3 and 7, as well as terminal deoxynucleotidyl transferase dUTP nick-end labeling. This effect was dependent of S1P signaling because the blocking of S1P receptors ameliorated reactive oxygen species production, SC apoptosis, and myelin loss. FTY720P at greater concentrations induces apoptosis in SCs and may interfere with peripheral nerve myelination.

The protective effect of Alpha lipoic acid on Schwann cells exposed to constant or intermittent high glucose

Diabetic peripheral neuropathy (DPN) is one of the most common and costly microvascular complications of diabetes, and no effective therapy exists. Previous studies have demonstrated that oxidative stress may be the unifying factor for the damaging effect of hyperglycemia. The aim of this study was to examine the impact of treatment with Alpha lipoic acid (ALA) on the intermittent high glucose (IHG) or high glucose (HG)-induced oxidative stress-induced mitochondrial pathway activation and Schwann cells (SCs) apoptosis in vitro. Our results suggested that IHG and HG induced SCs apoptosis in both caspase-dependent and caspase-independent pathways related to oxidative stress. More importantly, the cytotoxic effect of IHG was significantly more potent than that of HG. Treatment with ALA inhibited the IHG and HG-induced oxidative stress and apoptosis in SCs. Furthermore, treatment with ALA down-regulated the Bax expression and the release of cytochrome c and AIF translocation, but up-regulated the Bcl-2 expression in SCs. Treatment with ALA attenuated the activation of caspase-3 and caspase-9 and minimized the cleavage of PARP in SCs. These findings suggest that variability in glycemic control could be more deleterious than a constant HG and ALA antagonized the IHG-induced oxidative stress, activation of mitochondrial pathway and apoptosis in SCs.

The RNA-Binding Protein Human Antigen R Controls Global Changes in Gene Expression during Schwann Cell Development

An important prerequisite to myelination in peripheral nerves is the establishment of one-to-one relationships between axons and Schwann cells. This patterning event depends on immature Schwann cell proliferation, apoptosis, and morphogenesis, which are governed by coordinated changes in gene expression. Here, we found that the RNA-binding protein human antigen R (HuR) was highly expressed in immature Schwann cells, where genome-wide identification of its target mRNAs in vivo in mouse sciatic nerves using ribonomics showed an enrichment of functionally related genes regulating these processes. HuR coordinately regulated expression of several genes to promote proliferation, apoptosis, and morphogenesis in rat Schwann cells, in response to NRG1, TGFβ, and laminins, three major signals implicated in this patterning event. Strikingly, HuR also binds to several mRNAs encoding myelination-related proteins but, contrary to its typical function, negatively regulated their expression, likely to prevent ectopic myelination during development. These functions of HuR correlated with its abundance and subcellular localization, which were regulated by different signals in Schwann cells.