Primary Schwann Cells Research Articles

PAR-1 activation affects the neurotrophic properties of rat Schwann cells

PAR-1 (Protease-activated receptor–1) is a G-protein-coupled receptor that elicits cellular responses to extracellular proteases such as thrombin. In the peripheral nervous system (PNS), the expression and/or the role of PAR-1 are still poorly investigated. Several authors speculated that many functions in PNS, such as motor, secretory, vascular, nociceptive, inflammatory or regenerative processes, may be regulated by PARs (Vergnolle et al. 2003; Shavit et al., 2008; Wang et al., 2013). The present study was aimed to determine if PAR-1 activation affects neurotrophic properties of Schwann cells. By double immunofluorescence experiments we observed a specific staining for PAR-1 in S100β-positive cells of rat sciatic nerve and sciatic teased fibres. Moreover, PAR-1 was highly expressed in Schwann cell cultures obtained from both neonatal and adult rat sciatic nerves. When PAR-1 specific agonists were added to these cultures a higher proliferation rate was observed. Moreover, conditioned medium from primary Schwann cells treated with PAR-1 agonists increased cell survival and neurite outgrowth of PC12 cells. Therefore synthesis and secretion of several factors by Schwann cells treated with PAR-1 agonist peptides were investigated by RT-PCR, western blot and proteomics analysis. By these experiments some molecules, including extracellular matrix components and adhesion molecules, were identified as putative neurotrophic candidates.

Basic Fibroblast Growth Factor (bFGF) Facilitates Differentiation of Adult Dorsal Root Ganglia-Derived Neural Stem Cells Toward Schwann Cells by Binding to FGFR-1 Through MAPK/ERK Activation

Considerable research has been devoted to unraveling the regulation of neural stem cell (NSC) differentiation. The responses of NSCs to various differentiation-inducing stimuli, however, are still difficult to estimate. In this study, we aimed to search for a potent growth factor that was able to effectively induce differentiation of NSCs toward Schwann cells. NSCs were isolated from dorsal root ganglia (DRGs) of adult rats and identified by immunostaining. Three different growth factors were used to stimulate the differentiation of DRG-derived NSCs (DRG-NSCs). We found that among these three growth factors, bFGF was the strongest inducer for the glial differentiation of DRG-NSCs, and bFGF induced the generation of an increased number of Schwann cell-like cells as compared to nerve growth factor (NGF) and neuregulin1-β (NRG). These Schwann cell-like cells demonstrated the same characteristics as those of primary Schwann cells. Furthermore, we noted that bFGF-induced differentiation of DRG-NSCs toward Schwann cells might be mediated by binding to fibroblast growth factor receptor-1 (FGFR-1) through activation of MAPK/ERK signal pathway.

Low-Density Lipoprotein Receptor Related protein-1 (LRP1)-Dependent Cell Signaling Promotes Neurotrophic Activity in Embryonic Sensory Neurons

Developing sensory neurons require neurotrophic support for survival, neurite outgrowth and myelination. The low-density lipoprotein receptor-related protein-1 (LRP1) transactivates Trk receptors and thereby functions as a putative neurotrophin. Herein, we show that LRP1 is abundantly expressed in developing dorsal root ganglia (DRG) and that LRP1-dependent cell signaling supports survival, neurite extension and receptivity to Schwann cells even in the absence of neurotrophins. Cultured embryonic DRG neurons (E15) were treated with previously characterized LRP1 ligands, LRP1-receptor binding domain of α2-macroglobulin (RBD), hemopexin domain of MMP-9 (PEX) or controls (GST) for two weeks. These structurally diverse LRP1 ligands significantly activated and sustained extracellular signal-regulated kinases (ERK1/2) 5-fold (p<0.05), increased expression of growth-associated protein-43(GAP43) 15-fold (P<0.01), and increased neurite outgrowth 20-fold (P<0.01). Primary sensory neurons treated with LRP1 ligands survived > 2 weeks in vitro, to an extent equaling NGF, a finding associated with canonical signaling mechanisms and blockade of caspase-3 cleavage. LRP1 ligand-induced survival and sprouting were blocked by co-incubation with the LRP1 antagonist, receptor associated protein (RAP), whereas RAP had no effect on NGF-induced activity. Site directed mutagenesis of the LRP1 ligand, RBD, in which Lys1370 and Lys1374 are converted to alanine to preclude LRP1 binding, were ineffective in promoting cell signaling, survival or inducing neurite extension in primary sensory neurons, confirming LRP1 specificity. Furthermore, LRP1-induced neurite sprouting was mediated by Src-family kinase (SFK) activation, suggesting transactivation of Trk receptors. Co-cultures of primary embryonic neurons and Schwann cells showed that LRP1 agonists promoted axonal receptivity to myelination to Schwann cells. Collectively, these findings identify LRP1 as a novel and perhaps essential trophic molecule for sensory neuronal survival and development.

Transplantation of Schwann cells co-cultured with brain-derived neurotrophic factor for the treatment of experimental autoimmune neuritis

The aim of this study was to investigate the effects of transplantation of Schwann cells (SCs) co-cultured with brain-derived neurotrophic factor (BDNF) for the treatment of experimental autoimmune neuritis (EAN). Primary SCs were co-cultured with various BDNF concentrations, and the optimum concentration was determined by cell proliferation, and NGF and FGF levels. A rat model of EAN was established by immunization with 400μg of P2 peptide dissolved in Freund's complete adjuvant. SCs were labeled with CFSE and injected into the cisterna magna 14days after immunization. We found proliferation of SCs, and NGF and FGF levels were highest at a BDNF concentration of 50ng/mL. Compared with EAN group, SCs+BDNF group showed the lower paralysis scores from day 34 to day 45, and in sciatic nerves showed a significant decrease in inflammatory cell infiltration (involved CD4-, CD8- and CD68-positive cells) at days 25 and 35, an alleviated demyelination at days 35 and 45, and an increase in S-100-positive cells and a decrease in NGF-positive cells at each time point (P<0.05). Compared with the EAN group, the SCs+BDNF group showed, in sciatic nerves, the mRNA level of NGF was significantly decreased but that of S-100 was increased at day 25, the mRNA level of CCL3 was also remarkably reduced at day 35, and the mRNA level of CD11a, CCL3 and NGF was reduced but that of S-100 was elevated at day 45 (P<0.05). There were no differences in results between the SCs group and EAN group. In the end, we draw the conclusions that the exogenous SCs injected through cisterna magna can migrate to the injured peripheral nerves, BDNF promotes the proliferation and secretory function of SCs in vitro, and BDNF-treated SCs in vivo can reduce paralysis, inflammation, and demyelination and improve the self-repair capability of body in EAN.

AQP1 expression alterations affect morphology and water transport in Schwann cells and hypoxia-induced up-regulation of AQP1 occurs in a HIF-1α-dependent manner

Aquaporin-1 (AQP1) is the principle water channel in the peripheral nervous system (PNS) and is specifically localized to Schwann cells in the PNS. However, the pathophysiological role of AQP1 in peripheral nerves is poorly understood. Here, we utilized RNA interference by lentiviral transduction to specifically down-regulate AQP1 expression and a lentiviral overexpression protocol to up-regulate AQP1 expression, in primary Schwann cell cultures. AQP1 gene silencing resulted in a cell shrinkage phenotype, while AQP1 gene overexpression caused a cell swelling phenotype, as validated by cell volume determinations. Secondly, we utilized an in vitro hypoxia model in Schwann cells to mimic in vivo facial nerve injury. We demonstrated that AQP1 expression was induced within 8h following hypoxia injury in vitro, and that AQP1 knockdown (KD) caused the cells to resist edema following hypoxia. Finally, we investigated the hypoxic regulation of the AQP1 gene, as well as the involvement of Hypoxia-inducible factor-1α (HIF-1α) in AQP1 modulation and we found that KD of HIF-1α decreased hypoxia-dependent induction of endogenous AQP1 expression at both the mRNA and protein levels. Taken together, these results indicate that (1) AQP1 is an important factor responsible for the fast water transport of cultured Schwann cells and is involved in cell plasticity; (2) AQP1 alterations may be a primary factor in hypoxia-induced peripheral nerve edema; (3) HIF-1α participates in the hypoxic induction of the AQP1 gene; (4) AQP1 inhibition might provide a new therapeutic alternative for the treatment of some forms of peripheral nerve edema.

The fetal endothelium of the human placenta: advantages and perils of phenotypic plasticity

Successful regeneration of injured peripheral nerves is mainly attributed to the plastic behavior of Schwann cells. Upon loss of axons, these cells trans-differentiate into regeneration promoting repair cells which provide trophic support to regrowing axons. Among others, activation of cJun was revealed to be involved in this process, initiating the stereotypic pattern of Schwann cell phenotype alterations during Wallerian degeneration. Nevertheless, the ability of Schwann cells to adapt and therefore the nerve's potential to regenerate can be limited in particular after long term denervation or in neuropathies leading to incomplete regeneration only and thus emphasizing the need for novel therapeutic approaches. Here we stimulated primary neonatal and adult rat Schwann cells with Fingolimod/FTY720P and investigated its impact on the regeneration promoting phenotype. FTY720P activated a number of de-differentiation markers including cJun and interfered with maturation marker and myelin expression. Functionally, FTY720P treated Schwann cells upregulated growth factor expression and these cells enhanced dorsal root ganglion neurite outgrowth on inhibitory substrates. Our results therefore provide strong evidence that FTY720P application supports the generation of a repair promoting cellular phenotype and suggest that Fingolimod could be used as treatment for peripheral nerve injuries and diseases.

NTRK1/TrkA expression is a potential regulator of neuroblastoma cross-talk with the schwannian stroma

Schwann cells (SC) are the predominant morphological feature of neuroblastomas (NB) with good prognosis. High-level NTRK1/TrkA expression, which is known to mediate tumor cell differentiation, is characteristic of this NB subgroup. We hypothesized that Schwannian stromal development and neuroblastic differentiation is based on bidirectional interaction of NB and SC. Reanalysis of microarray data from SY5Y NB cells stably transfected with NTRK1, NTRK2 or the empty vector revealed that upregulation of genes influencing motility and growth of SC is restricted to NTRK1-positive cells. Incubation of primary SC with supernatants of NTRK1-expressing NB cells significantly enhanced SC proliferation and migration. SC-conditioned medium also induced differentiation of NTRK1-expressing cells. Finally, NTRK1 induction in NB xenografts mixed with primary SC significantly reduced tumor growth in vivo. In addition to effects on angiogenesis, immunogenicity and apoptosis, NTRK1 expression in NB might attract adjacent SC that then induce neuroblastic differentiation by secreting the NTRK1-specific ligand, nerve growth factor, and thus, contributing to a mature and less malignant NB phenotype.

Oxydative phosphorylation in sciatic nerve myelin and its impairment in a model of dysmyelinating peripheral neuropathy

Myelin sheath is the proteolipid membrane wrapping the axons of CNS and PNS. We have shown data suggesting that CNS myelin conducts oxidative phosphorylation (OXPHOS), challenging its role in limiting the axonal energy expenditure. Here, we focused on PNS myelin. Samples were: (i) isolated myelin vesicles (IMV) from sciatic nerves, (ii) mitochondria from primary Schwann cell cultures, and (iii) sciatic nerve sections, from wild type or Charcot-Marie-Tooth type 1A (CMT1A) rats. The latter used as a model of dys-demyelination. O₂ consumption and activity of OXPHOS proteins from wild type (Wt) or CMT1A sciatic nerves showed some differences. In particular, O₂ consumption by IMV from Wt and CMT1A 1-month-old rats was comparable, while it was severely impaired in IMV from adult affected animals. Mitochondria extracted from CMT1A Schwann cell did not show any dysfunction. Transmission electron microscopy studies demonstrated an increased mitochondrial density in dys-demyelinated axons, as to compensate for the loss of respiration by myelin. Confocal immunohistochemistry showed the expression of OXPHOS proteins in the myelin sheath, both in Wt and dys-demyelinated nerves. These revealed an abnormal morphology. Taken together these results support the idea that also PNS myelin conducts OXPHOS to sustain axonal function.

Mutation of SIMPLE in Charcot–Marie–Tooth 1C alters production of exosomes

Charcot-Marie-Tooth (CMT) disease is an inherited neurological disorder. Mutations in the small integral membrane protein of the lysosome/late endosome (SIMPLE) account for the rare autosomal-dominant demyelination in CMT1C patients. Understanding the molecular basis of CMT1C pathogenesis is impeded, in part, by perplexity about the role of SIMPLE, which is expressed in multiple cell types. Here we show that SIMPLE resides within the intraluminal vesicles of multivesicular bodies (MVBs) and inside exosomes, which are nanovesicles secreted extracellularly. Targeting of SIMPLE to exosomes is modulated by positive and negative regulatory motifs. We also find that expression of SIMPLE increases the number of exosomes and secretion of exosome proteins. We engineer a point mutation on the SIMPLE allele and generate a physiological mouse model that expresses CMT1C-mutated SIMPLE at the endogenous level. We find that CMT1C mouse primary embryonic fibroblasts show decreased number of exosomes and reduced secretion of exosome proteins, in part due to improper formation of MVBs. CMT1C patient B cells and CMT1C mouse primary Schwann cells show similar defects. Together the data indicate that SIMPLE regulates the production of exosomes by modulating the formation of MVBs. Dysregulated endosomal trafficking and changes in the landscape of exosome-mediated intercellular communications may place an overwhelming burden on the nervous system and account for CMT1C molecular pathogenesis.

Signaling through Arf6 guanine-nucleotide exchange factor cytohesin-1 regulates migration in Schwann cells

During development of the peripheral nervous system (PNS), Schwann cells migrate along neuronal axons before initiating myelination of the axons. While intercellular signals controlling migration, between Schwann cells and peripheral neurons, are established, how their intracellular transduction of the signals into Schwann cells still remains to be clarified. Here, we show that cytohesin-1, a guanine-nucleotide exchange factor (GEF), and the effector Arf6 are required for migration of primary Schwann cells. Knockdown of cytohesin-1 or Arf6 in Schwann cells, as well as treatment with the chemical cytohesin inhibitor SecinH3 or knockout of cytohesin-1, inhibits peripheral neuronal conditioned medium-mediated migration. Similar effects are also observed following stimulation with each of growth factors contained in a conditioned medium, suggesting that cytohesin-1 plays a role in transducing soluble ligand signals from neurons. Reintroduction of small interfering (si)RNA-resistant cytohesin-1 into Schwann cells reverses blunted migration in the siRNA-transfected Schwann cells, illustrating the importance of cytohesin-1 in migration. On the other hand, introduction of cytohesin-1 that harbors the Tyr-382 mutation, which is an amino acid that is important for its activation, failed to reverse the reduction in primary Schwann cell migration. These results suggest that signaling through cytohesin-1 is required for Schwann cell migration, revealing a novel mechanism for Schwann cell migration.

The Neuregulin‐Rac‐MKK7 pathway regulates antagonistic c‐jun/Krox20 expression in Schwann cell dedifferentiation

Schwann cells respond to nerve injury by dedifferentiating into immature states and producing neurotrophic factors, two actions that facilitate successful regeneration of axons. Previous reports have implicated the Raf-ERK cascade and the expression of c-jun in these Schwann cell responses. Here we used cultured primary Schwann cells to demonstrate that active Rac1 GTPase (Rac) functions as a negative regulator of Schwann cell differentiation by upregulating c-jun and downregulating Krox20 through the MKK7-JNK pathway, but not through the Raf-ERK pathway. The activation of MKK7 and induction of c-jun in sciatic nerves after axotomy was blocked by Rac inhibition. Microarray experiments revealed that the expression of regeneration-associated genes, such as glial cell line-derived neurotrophic factor and p75 neurotrophin receptor, after nerve injury was dependent on Rac but not on ERK. Finally, the inhibition of ErbB2 signaling prevented MKK7 activation, c-jun induction, and Rac-dependent gene expression in sciatic nerve explant cultures. Taken together, our results indicate that the neuregulin-Rac-MKK7-JNK/c-jun pathway regulates Schwann cell dedifferentiation following nerve injury.

Cell Type- and Isotype-Specific Expression and Regulation of β-Tubulins in Primary Olfactory Ensheathing Cells and Schwann Cells In Vitro

Olfactory ensheathing cells (OECs) and Schwann cells (SCs) are closely-related cell types with regeneration-promoting properties. Comparative gene expression analysis is particularly relevant since it may explain cell type-specific effects and guide the use of each cell type into special clinical applications. In the present study, we focused on β-tubulin isotype expression in primary adult canine glia as a translational large animal model. β-tubulins so far have been studied mainly in non-neuronal tumors and implied in tumorigenic growth. We show here that primary OECs and SCs expressed βII-V isotype mRNA. Interestingly, βIII-tubulin mRNA and protein expression was high in OECs and low in SCs, while fibroblast growth factor-2 (FGF-2) induced its down-regulation in both cell types to the same extent. This was in contrast to βV-tubulin mRNA which was similarly expressed in both cell types and unaltered by FGF-2. Immunocytochemical analysis revealed that OEC cultures contained a higher percentage of βIII-tubulin-positive cells compared to SC cultures. Addition of FGF-2 reduced the number of βIII-tubulin-positive cells in both cultures and significantly increased the percentage of cells with a multipolar morphology. Taken together, we demonstrate cell type-specific expression (βIII) and isotype-specific regulation (βIII, βV) of β-tubulin isotypes in OECs and SCs. While differential expression of βIII-tubulin in primary glial cell types with identical proliferative behaviour argues for novel functions unrelated to tumorigenic growth, strong βIII-tubulin expression in OECs may help to explain the specific properties of this glial cell type.

Glial differentiation of human adipose-derived stem cells: Implications for cell-based transplantation therapy

Increasing evidence has shown that adipose-derived stem cells (ASCs) could transdifferentiate into Schwann cell (SC)-like cells to enhance nerve regeneration, suggesting potential new cell-based transplantation therapy for peripheral nerve injuries and neurodegenerative disorders. For the implementation of these results to the clinical setting, it is of great importance to establish the differentiation of human ASCs (hASCs) into a SC phenotype. In this study, we studied hASCs obtained from subcutaneous fat tissue of healthy donors. By a mixture of glial growth factors we differentiated them into Schwann cell-like cells (dhASCs). We then assessed their ability to act as Schwann cells in vitro and in vivo and also compared them with primary human Schwann cells (hSCs). Enzyme-linked immunosorbent assay showed that dhASCs secreted brain-derived neurotrophic factor (BDNF)/nerve growth factor (NGF) at a comparable level, and glial cell-derived neurotrophic factor (GDNF) at a level even higher than hSCs, whereas undifferentiated hASCs (uhASCs) secreted low levels of these neurotrophic factors. In co-culture with NG108-15 neuronal cells we found that both dhASCs and hSCs significantly increased the percentage of cells with neurites, the neurite length, and the number of neurites per neuron, whereas uhASCs increased only the percentage of cells with neurites. Finally, we transplanted green fluorescent protein (GFP)-labeled hASCs into the crushed tibial nerve of athymic nude rats. The transplanted hASCs showed a close association with PGP9.5-positive axons and myelin basic protein (MBP)-positive myelin at 8weeks after transplantation. Quantitative analysis revealed that dhASCs transplantation resulted in significantly improved survival and myelin formation rates (a 7-fold and a 10-fold increase, respectively) as compared with uhASCs transplantation. These findings suggest that hASCs took part in supporting and myelinating regenerating axons, and thus have achieved full glial differentiation in vivo. In conclusion, hASCs can differentiate into SC-like cells that possess a potent capacity to secrete neurotrophic factors as well as to form myelin in vivo. These findings make hASCs an interesting prospect for cell-based transplantation therapy for various peripheral nerve disorders.

Involvement of Src in the membrane skeletal complex, MPP6–4.1G, in Schmidt–Lanterman incisures of mouse myelinated nerve fibers in PNS

Schmidt-Lanterman incisures (SLIs) are a specific feature of myelinated nerve fibers in the peripheral nervous system (PNS). In this study, we report localization of a signal transduction protein, Src, in the SLIs of mouse sciatic nerves, and its phosphorylation states in Y527 and Y418 (P527 and P418, respectively) under normal conditions or deletion of a membrane skeletal protein, 4.1G. In adult mouse sciatic nerves, Src was immunolocalized in SLIs as a cone-shape, as well as in paranodes and some areas of structures reminiscent of Cajal bands. By immunostaining in normal nerves, P527-Src was strongly detected in SLIs, whereas P418-Src was much weaker. Developmentally, P418-Src was detected in SLIs of early postnatal mouse sciatic nerves. The staining patterns for P527 and P418 in normal adult nerve fibers were opposite to those in primary culture Schwann cells and a Schwannoma cell line, RT4-D6P2T. In 4.1G-deficient nerve fibers, which had neither 4.1G nor the membrane protein palmitoylated 6 (MPP6) in SLIs, the P418-Src immunoreactivity in SLIs was clearly detected at a stronger level than that in the wild type. An immunoprecipitation study revealed Src interaction with MPP6. These findings indicate that the Src-MPP6-4.1G protein complex in SLIs has a role in signal transduction in the PNS.

Blockade of IL-6 receptor accelerates nerve regeneration in experimental sciatic nerve crush injury

IL-6 is known as a multifunctional cytokine regulating immune response and inflammation. Many studies have shown that IL-6 affects the nervous system. However, the involvement of IL-6 in the nervous system, particularly in the peripheral nervous system (PNS), remains incompletely understood. Here, we assessed the effect of rat anti-mouse IL-6 receptor monoclonal antibody (MR16-1) in the treatment of experimental sciatic nerve crush injury in mice. The mice were given a single intraperitoneal injection (2 mg/head) of MR16-1 or Rat IgG as a control antibody the day before nerve crush injury. Treatment with MR16-1 significantly promoted sciatic functional recovery, and histological remyelination was greater than that by Rat IgG treatment. Furthermore, IL-6 expression was confirmed in the nerve after nerve crush injury in the Rat IgG group, but not in the MR16-1 group. MR16-1 also decreased the number of infiltrating macrophages. Additionally, IL-6 decreased the expression of nerve growth factor (NGF) mRNA in cultured primary mouse Schwann cells, and this decrease in NGF expression by IL-6 was reversed with MR16-1. These findings suggest that MR16-1 may inhibit the infiltration of macrophages and the decrease of NGF in Schwann cells, resulting in the acceleration of nerve regeneration. Rec.10/30/2012, Acc.1/24/2013, pp156-163

Secretion of ATP from Schwann cells through lysosomal exocytosis during Wallerian degeneration

The present study demonstrates that adenosine triphosphate (ATP) is released from Schwann cells through lysosomal exocytosis during Wallerian degeneration and in response to stimulation. In primary Schwann cell cultures, ATP was stored in lysosomal vesicles. ATP could then induce Ca(2+)-dependent lysosomal exocytosis. Among three stimulants of lysosomal exocytosis (glutamate, NH(4)Cl and zymosan), only NH(4)Cl was sufficient to induce ATP release from ex vivo sciatic nerve explants at 3 days in vitro. Lysosomal exocytosis inhibitors (metformin, chlorpromazine and vacuolin-1) reversed the effect of NH(4)Cl-enhanced ATP release, replicating the state of explants treated with NH(4)Cl in the absence of lysosomal exocytosis inhibitors. Furthermore, we observed ATP release through lysosomal exocytosis during Wallerian degeneration in sciatic explant cultures using the recently identified vesicular nucleotide transporter (VNUT). From these experiments, we conclude that the exocytosis of lysosomes in Schwann cells during Wallerian degeneration is Ca(2+)-dependent, and that it induces ATP release from 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.

Extracellular Matrix Molecules Enhance the Neurotrophic Effect of Schwann Cell-Like Differentiated Adipose-Derived Stem Cells and Increase Cell Survival Under Stress Conditions

Since the first reports of induction of adipose-derived stem cells (ASC) into neuronal and glial cell phenotypes, expectations have increased regarding their use in tissue engineering applications for nerve repair. Cell adhesion to extracellular matrix (ECM) is a basic feature of survival, differentiation, and migration of Schwann cells (SC) during nerve regeneration, and fibronectin and laminin are two key molecules of this process. Interaction between ECM and SC-like differentiated ASC (dASC) could potentially improve the neurotrophic potential of the stem cells. We have investigated the effect of ECM molecules on SC-like dASC in terms of proliferation, adhesion, and cell viability. Fibronectin and laminin did not affect the proliferation of dASC when compared with cell adherent tissue culture plastic, but significantly improved viability and cell attachment when dASC were exposed to apoptotic conditions. To assess the influence of the ECM molecules on dASC neurotrophic activity, dASC were seeded onto ECM-coated culture inserts suspended above dorsal root ganglia (DRG) sensory neurons. Neurite outgrowth of DRG neurons was enhanced when dASC were seeded on fibronectin and laminin when compared with controls. When DRG neurons and dASC were in direct contact on the various surfaces there was significantly enhanced neurite outgrowth and coculture with laminin-conditioned dASC produced the longest neurites. Compared with primary SCs, dASC grown on laminin produced similar levels of neurite outgrowth in the culture insert experiments but neurite length was shorter in the direct contact groups. Anti β1 integrin blocking antibody could inhibit baseline and dASC evoked neurite elongation but had no effect on outgrowth mediated by laminin-conditioned dASC. ECM molecules had no effect on the levels of nerve growth factor and brain-derived neurotrophic factor secretion from dASC. The results of the study suggest that ECM molecules can significantly improve the potential of dASC for nerve regeneration.

Enzymatic Engineering of Polysialic Acid on Cells in Vitro and in Vivo Using a Purified Bacterial Polysialyltransferase

In vertebrates, polysialic acid (PSA) is typically added to the neural cell adhesion molecule (NCAM) in the Golgi by PST or STX polysialyltransferase. PSA promotes plasticity, and its enhanced expression by viral delivery of the PST or STX gene has been shown to promote cellular processes that are useful for repair of the injured adult nervous system. Here we demonstrate a new strategy for PSA induction on cells involving addition of a purified polysialyltransferase from Neisseria meningitidis (PST(Nm)) to the extracellular environment. In the presence of its donor substrate (CMP-Neu5Ac), PST(Nm) synthesized PSA directly on surfaces of various cell types in culture, including Chinese hamster ovary cells, chicken DF1 fibroblasts, primary rat Schwann cells, and mouse embryonic stem cells. Similarly, injection of PST(Nm) and donor in vivo was able to produce PSA in different adult brain regions, including the cerebral cortex, striatum, and spinal cord. PSA synthesis by PST(Nm) requires the presence of the donor CMP-Neu5Ac, and the product could be degraded by the PSA-specific endoneuraminidase-N. Although PST(Nm) was able to add PSA to NCAM, most of its product was attached to other cell surface proteins. Nevertheless, the PST(Nm)-induced PSA displayed the ability to attenuate cell adhesion, promote neurite outgrowth, and enhance cell migration as has been reported for endogenous PSA-NCAM. Polysialylation by PST(Nm) occurred in vivo in less than 2.5 h, persisted in tissues, and then decreased within a few weeks. Together these characteristics suggest that a PST(Nm)-based approach may provide a valuable alternative to PST gene therapy.