Comparative analysis of Schwann cell lines as model systems for myelin gene transcription studies

Evolution of glial cells: a non-bilaterian perspective

Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.

Influence of Magnesium Degradation on Schwannoma Cell Responses to Nerve Injury Using an In Vitro Injury Model

Nerve guidance conduits for peripheral nerve injuries can be improved using bioactive materials such as magnesium (Mg) and its alloys, which could provide both structural and trophic support. Therefore, we investigated whether exposure to Mg and Mg-1.6wt%Li thin films (Mg/Mg-1.6Li) would alter acute Schwann cell responses to injury. Using the RT4-D6P2T Schwannoma cell line (SCs), we tested extracts from freeze-killed cells (FKC) and nerves (FKN) as in vitro injury stimulants. Both FKC and FKN induced SC release of the macrophage chemoattractant protein 1 (MCP-1), a marker of the repair SC phenotype after injury. Next, FKC-stimulated cells exposed to Mg/Mg-1.6Li reduced MCP-1 release by 30%, suggesting that these materials could have anti-inflammatory effects. Exposing FKC-treated cells to Mg/Mg-1.6Li reduced the gene expression of the nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), and myelin protein zero (MPZ), but not the p75 neurotrophin receptor. In the absence of FKC, Mg/Mg-1.6Li treatment increased the expression of NGF, p75, and MPZ, which can be beneficial to nerve regeneration. Thus, the presence of Mg can differentially alter SCs, depending on the microenvironment. These results demonstrate the applicability of this in vitro nerve injury model, and that Mg has wide-ranging effects on the repair SC phenotype.

Neuron-Schwann cell interactions in peripheral nervous system homeostasis, disease, and preclinical treatment

Schwann cells (SCs) have a critical role in the peripheral nervous system. These cells are able to support axons during homeostasis and after injury. However, mutations in genes associated with the SCs repair program or myelination result in dysfunctional SCs. Several neuropathies such as Charcot-Marie-Tooth (CMT) disease, diabetic neuropathy and Guillain-Barré syndrome show abnormal SC functions and an impaired regeneration process. Thus, understanding SCs-axon interaction and the nerve environment in the context of homeostasis as well as post-injury and disease onset is necessary. Several neurotrophic factors, cytokines, and regulators of signaling pathways associated with proliferation, survival and regeneration are involved in this process. Preclinical studies have focused on the discovery of therapeutic targets for peripheral neuropathies and injuries. To study the effect of new therapeutic targets, modeling neuropathies and peripheral nerve injuries (PNIs) in vitro and in vivo are useful tools. Furthermore, several in vitro protocols have been designed using SCs and neuron cell lines to evaluate these targets in the regeneration process. SCs lines have been used to generate effective myelinating SCs without success. Alternative options have been investigated using direct conversion from somatic cells to SCs or SCs derived from pluripotent stem cells to generate functional SCs. This review will go over the advantages of these systems and the problems associated with them. In addition, there have been challenges in establishing adequate and reproducible protocols in vitro to recapitulate repair SC-neuron interactions observed in vivo. So, we also discuss the mechanisms of repair SCs-axon interactions in the context of peripheral neuropathies and nerve injury (PNI) in vitro and in vivo. Finally, we summarize current preclinical studies evaluating transgenes, drug, and novel compounds with translational potential into clinical studies.

Modification of hyaluronic acid to enable click chemistry photo-crosslinking of hydrogels with tailorable degradation profiles

Hyaluronic acid (HA) is a naturally occurring mucopolysaccharide that, due to its inherent bioactivity and extracellular matrix-like structure, has the potential to be utilised extensively in tissue engineering. However, this glycosaminoglycan lacks the properties required for cellular adhesion and photo-crosslinking by UV light, which significantly hinders this polymers applicability. This research presents a method for modifying hyaluronic acid via thiolation and methacrylation to generate a novel photo-crosslinkable polymer with improved physicochemical properties, biocompatibility and the potential to customize biodegradability according to the ratio of monomers used. A decrease in stiffness proportional to increasing thiol concentration was observed when testing the compressive strength of hydrogels. Conversely, it was noted that the storage moduli of hydrogels increased proportionally to thiol concentration indicating a greater degree of cross-linking with the addition of thiol. The addition of thiol to HA increased the biocompatibility of the material in both neuronal and glial cell lines and improved the degradability of methacrylated HA. Due to the enhanced physicochemical properties and biocompatibility imparted by the introduction of thiolated HA, this novel hydrogel system could have numerous bioengineering applications.

Designing a Prolonged Method of Therapeutic Delivery to Support Rehabilitation From Ototoxic Damage in a Schwann Cell Model

HYPOTHESIS

The ototoxicity of gentamicin and cisplatin can be evaluated with a Schwann cell model to screen for otoprotective agents that can be encapsulated into poly (lactic-co-glycolic acid) (PLGA) microparticles for drug delivery to the inner ear.

BACKGROUND

Aminoglycosides and cisplatin are widely prescribed but known to cause ototoxicity. There is strong evidence that compromise to Schwann cells ensheathing inner ear afferent neurons results in inner ear dysfunction mimicking drug-induced ototoxicity. There is a need for a model for ototoxic demyelination to screen medications for protective potential and to subsequently target and tune the delivery of any promising agents.

METHODS

RT4-D6P2T rat schwannoma cells were used as a Schwann cell model to assess gentamicin and cisplatin toxicity and to screen for protective agents. Cell viability was evaluated with the MTT cell proliferation assay. N -acetylcysteine (NAC) was encapsulated into a PLGA microparticle, and its elution profile was determined.

RESULTS

The estimated 50% lethal concentration dose for gentamicin was 805.6 μM, which was 46-fold higher than that for cisplatin (17.5 μM). In several trials, cells dosed with NAC and cisplatin demonstrated a 22.6% ( p < 0.001) increase in cell viability when compared with cisplatin alone. However, this protective effect was not consistent across all trials. NAC was encapsulated into a PLGA microparticle and elution plateaued at 5 days.

CONCLUSION

When dosed at their respective therapeutic ranges, cisplatin is more likely than gentamicin to induce damage to the Schwann cell model. Although NAC demonstrates an uncertain role in protecting against cisplatin-induced Schwann cell cytotoxicity, this study establishes a method to screen for other otoprotective medications to encapsulate into a tunable microparticle for localized drug delivery.

Electroceutical approach ameliorates intracellular PMP22 aggregation and promotes pro-myelinating pathways in a CMT1A in vitro model

Charcot-Marie-Tooth disease subtype 1A (CMT1A) is one of the most prevalent demyelinating peripheral neuropathies worldwide, caused by duplication of the peripheral myelin protein 22 (PMP22) gene, which is expressed primarily in Schwann cells (SCs). PMP22 overexpression in SCs leads to intracellular aggregation of the protein, which eventually results in demyelination. Unfortunately, previous biochemical approaches have not resulted in an approved treatment for CMT1A disease, compelling the pursuit for a biophysical approach such as electrical stimulation (ES). However, the effects of ES on CMT1A SCs have remained unexplored. In this study, we established PMP22-overexpressed Schwannoma cells as a CMT1A in vitro model, and investigated the biomolecular changes upon applying ES via a custom-made high-throughput ES platform, screening for the condition that delivers optimal therapeutic effects. While PMP22-overexpressed Schwannoma exhibited intracellular PMP22 aggregation, ES at 20 Hz for 1 h improved this phenomenon, bringing PMP22 distribution closer to healthy condition. ES at this condition also enhanced the expression of the genes encoding myelin basic protein (MBP) and myelin-associated glycoprotein (MAG), which are essential for assembling myelin sheath. Furthermore, ES altered the gene expression for myelination-regulating transcription factors Krox-20, Oct-6, c-Jun and Sox10, inducing pro-myelinating effects in PMP22-overexpressed Schwannoma. While electroceuticals has previously been applied in the peripheral nervous system towards acquired peripheral neuropathies such as pain and nerve injury, this study demonstrates its effectiveness towards ameliorating biomolecular abnormalities in an in vitro model of CMT1A, an inherited peripheral neuropathy. These findings will facilitate the clinical translation of an electroceutical treatment for CMT1A.

Acetyl-L-carnitine improves erectile function in bilateral cavernous nerve injury rats via promoting cavernous nerve regeneration

BACKGROUND

Neurogenic erectile dysfunction (NED) caused by cavernous nerve (CN) injury is a typical complication after pelvic surgery, which lacks efficient treatments. Acetyl-L-carnitine (ALCAR) has been proven to promote nerve repair.

OBJECTIVES

To investigate the effect and potential mechanism of ALCAR in the treatment of NED.

MATERIALS AND METHODS

Thirty-two rats were randomly divided into bilateral cavernous nerve injury (BCNI) group, BCNI + lower-dose ALCAR (50 mg/kg/day) group, BCNI + higher-dose (100 mg/kg/day) group and sham-operated group. Erectile function was assessed 14 days after daily intraperitoneal injection of ALCAR or placebo. The penile tissues were gathered for subsequent histological and molecular biological analysis. Rat Schwann cell (SC) line S16 was used to verify the mechanism of ALCAR in vitro.

RESULTS

We found that the erectile function of the rats in BCNI group was severely impaired, which was improved considerably in both BCNI+ALCAR-LD and BCNI+ALCAR-HD groups. Also, we observed decreased smooth muscle and increased collagen content in corpus cavernosum in BCNI group. The expressions of fibrosis markers TGF-β, CTGF, and Smad 2/3 were significantly up-regulated in the BCNI group. The above changes were alleviated after the administration of lower and higher-dose ALCAR. Meanwhile, the NO/cGMP pathway was promoted and the RhoA/ROCK pathway was inhibited in the corpus cavernosum of BCNI rats after ALCAR treatment, accompanied by increased nNOS and down-regulated Tyrosine Hydroxylase. In vitro, ALCAR promoted the migration and proliferation of SC, and increased the expression of Pmp22 and NGF. Further, rats treated with ALCAR had high expression of ATF3 and S100 in the distal nerve tissues of the CN extrusion site.

DISCUSSION AND CONCLUSION

ALCAR could promote nerve repair and regeneration, inhibit penile fibrosis and improve penile erection by promoting the proliferation and migration of SC and the secretion of NGF. Our study confirms that ALCAR may be a potential treatment strategy for NED. This article is protected by copyright. All rights reserved.

Genome-Edited Coincidence and PMP22-HiBiT Fusion Reporter Cell Lines Enable an Artifact-Suppressive Quantitative High-Throughput Screening Strategy for PMP22 Gene-Dosage Disorder Drug Discovery

Charcot-Marie-Tooth 1A (CMT1A) is the most common form of hereditary peripheral neuropathies, characterized by genetic duplication of the critical myelin gene Peripheral Myelin Protein 22 (PMP22). PMP22 overexpression results in abnormal Schwann cell differentiation, leading to axonal loss and muscle wasting. Since regulation of PMP22 expression is a major target of therapeutic discovery for CMT1A, we sought to establish unbiased approaches that allow the identification of therapeutic agents for this disease. Using genome editing, we generated a coincidence reporter assay that accurately monitors Pmp22 transcript levels in the S16 rat Schwann cell line, while reducing reporter-based false positives. A quantitative high-throughput screen (qHTS) of 42 577 compounds using this assay revealed diverse novel chemical classes that reduce endogenous Pmp22 transcript levels. Moreover, some of these classes show pharmacological specificity in reducing Pmp22 over another major myelin-associated gene, Mpz (Myelin protein zero). Finally, to investigate whether compound-mediated reduction of Pmp22 transcripts translates to reduced PMP22 protein levels, we edited the S16 genome to generate a reporter assay that expresses a PMP22-HiBiT fusion protein using CRISPR/Cas9. Overall, we present a screening platform that combines genome edited cell lines encoding reporters that monitor transcriptional and post-translational regulation of PMP22 with titration-based screening (e.g., qHTS), which could be efficiently incorporated into drug discovery campaigns for CMT1A.

Intraoperative visualization of nerves using a myelin protein-zero specific fluorescent tracer

BACKGROUND

Surgically induced nerve damage is a common but debilitating side effect in oncological surgery. With the aim to use fluorescence guidance to enable nerve-sparing interventions in future surgery, a fluorescent tracer was developed that specifically targets myelin protein zero (P0).

RESULTS

Truncated homotypic P0 protein-based peptide sequences were C-terminally functionalized with the far-red cyanine dye Cy5. The lead compound Cy5-P0101-125 was selected after initial solubility, (photo)physical and in vitro evaluation (including P0-blocking experiments). Cy5-P0101-125 (KD = 105 ± 17 nM) allowed in vitro and ex vivo P0-related staining. Furthermore, Cy5-P0101-125  enabled in vivo fluorescence imaging of the Sciatic nerve in mice after local intravenous (i.v.) administration and showed compatibility with a clinical fluorescence laparoscope during evaluation in a porcine model undergoing robot-assisted surgery. Biodistribution data revealed that i.v. administered [111In]In-DTPA-P0101-125 does not enter the central nervous system (CNS).

CONCLUSION

P0101-125 has proven to be a potent nerve-specific agent that is able to target P0/myelin under in vitro, ex vivo, and in vivo conditions without posing a threat for CNS-related toxicity.

In vitro, In vivo and Ex vivo Models for Peripheral Nerve Injury and Regeneration

Peripheral Nerve Injuries (PNI) frequently occur secondary to traumatic injuries. Recovery from these injuries can be expectedly poor, especially in proximal injuries. In order to study and improve peripheral nerve regeneration, scientists rely on peripheral nerve models to identify and test therapeutic interventions. In this review, we discuss the best described and most commonly used peripheral nerve models that scientists have and continue to use to study peripheral nerve physiology and function.

N-Formylated Peptide Induces Increased Expression of Both Formyl Peptide Receptor 2 (Fpr2) and Toll-Like Receptor 9 (TLR9) in Schwannoma Cells-An In Vitro Model for Early Inflammatory Profiling of Schwann Cells

Following nerve injury, disintegrated axonal mitochondria distal to the injury site release mitochondrial formylated peptides and DNA that can induce activation and inflammatory profiling of Schwann cells via formyl peptide receptor 2 (Fpr2) and toll-like receptor 9 (TLR9), respectively. We studied RT4 schwannoma cells to investigate the regulation of Fpr2 and TLR9 after stimulation with fMLF as a prototypical formylated peptide. RT4 cells were treated with fMLF at various concentrations and times with and without pretreatment with inhibitors (chloroquine for activated TLR9, PBP10 for Fpr2). Western blots of Fpr2, TLR9, p-p38, p-NFκB, and IL-6 were compared in relation to inflammatory profiling of RT4 cells and chemokine receptors (CCR2, CXCR4) as potential co-receptors of Fpr2. fMLF stimulation upregulated Fpr2 in RT4 cells at low concentrations (10 nM and 100 nM) but higher concentrations were required (10 µM and 50 µM) when the cells were pretreated with an activated TLR9 inhibitor. Moreover, the higher concentrations of fMLF could modulate TLR9 and inflammatory markers. Upregulation of Fpr2 triggered by 10 nM and 100 nM fMLF coincided with higher levels of chemokine receptors (CCR2, CXCR4) and PKCβ. Treating RT4 cells with fMLF, as an in vitro model of Schwann cells, uncovered Schwann cells’ complex responses to molecular patterns of release from injured axonal mitochondria.

Fibulin 5, a human Wharton's jelly-derived mesenchymal stem cells-secreted paracrine factor, attenuates peripheral nervous system myelination defects through the Integrin-RAC1 signaling axis

In the peripheral nervous system (PNS), proper development of Schwann cells (SCs) contributing to axonal myelination is critical for neuronal function. Impairments of SCs or neuronal axons give rise to several myelin-related disorders, including dysmyelinating and demyelinating diseases. Pathological mechanisms, however, have been understood at the elementary level and targeted therapeutics has remained undeveloped. Here, we identify Fibulin 5 (FBLN5), an extracellular matrix (ECM) protein, as a key paracrine factor of human Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) to control the development of SCs. We show that co-culture with WJ-MSCs or treatment of recombinant FBLN5 promotes the proliferation of SCs through ERK activation, whereas FBLN5-depleted WJ-MSCs do not. We further reveal that during myelination of SCs, FBLN5 binds to Integrin and modulates actin remodeling, such as the formation of lamellipodia and filopodia, through RAC1 activity. Finally, we show that FBLN5 effectively restores the myelination defects of SCs in the zebrafish model of Charcot-Marie-Tooth (CMT) type 1, a representative demyelinating disease. Overall, our data propose human WJ-MSCs or FBLN5 protein as a potential treatment for myelin-related diseases, including CMT.

Biofabrication of nerve fibers with mimetic myelin sheath-like structure and aligned fibrous niche

Nerve tissues contain hierarchically ordered nerve fibers, while each of the nerve fibers has nano-oriented fibrous extracellular matrix and a core-shell structure of tubular myelin sheath with elongated axons encapsulated. Here, we report, for the first time, a ready approach to fabricate biomimetic nerve fibers which are oriented and have a core-shell structure to spatially encapsulate two types of cells, neurons and Schwann cells. A microfluidic system was designed and assembled, which contained a coaxial triple-channel chip and a stretching loading device. Alginate was used first to assist the fabrication, which was washed away afterwards. The orientation of the biomimetic nerve fibers was optimized by the control of the compositions of methacrylate hyaluronan and fibrin, together with the parameters of microfluidic shearing and external stretching. Also, neurons and Schwann cells, which were respectively located in the core and shell of the fibers, displayed advanced biologic functions, including neurogenesis and myelinating maturation. We demonstrate that the neural performance is relatively good, compared to that resulted from individually encapsulated in single-layer microfibers. The present study brings insights to fabricate biomimetic nerve fibers for their potential in neuroscience research and nerve regeneration. Moreover, the present methodology on the fabrication of oriented fibers with different types of cells separately encapsulated should be applicable to biomimetic constructions of various tissues.

Sox2 controls Schwann cell self-organization through fibronectin fibrillogenesis

The extracellular matrix is known to modulate cell adhesion and migration during tissue regeneration. However, the molecular mechanisms that fine-tune cells to extra-cellular matrix dynamics during regeneration of the peripheral nervous system remain poorly understood. Using the RSC96 Schwann cell line, we show that Sox2 directly controls fibronectin fibrillogenesis in Schwann cells in culture, to provide a highly oriented fibronectin matrix, which supports their organization and directional migration. We demonstrate that Sox2 regulates Schwann cell behaviour through the upregulation of multiple extracellular matrix and migration genes as well as the formation of focal adhesions during cell movement. We find that mouse primary sensory neurons and human induced pluripotent stem cell-derived motoneurons require the Sox2-dependent fibronectin matrix in order to migrate along the oriented Schwann cells. Direct loss of fibronectin in Schwann cells impairs their directional migration affecting the alignment of the axons in vitro. Furthermore, we show that Sox2 and fibronectin are co-expressed in proregenerative Schwann cells in vivo in a time-dependent manner during sciatic nerve regeneration. Taken together, our results provide new insights into the mechanisms by which Schwann cells regulate their own extracellular microenvironment in a Sox2-dependent manner to ensure the proper migration of neurons.

Regulating PMP22 expression as a dosage sensitive neuropathy gene

Structural variation in the human genome has emerged as a major cause of disease as genomic data have accumulated. One of the most common structural variants associated with human disease causes the heritable neuropathy known as Charcot-Marie-Tooth (CMT) disease type 1A. This 1.4 Mb duplication causes nearly half of the CMT cases that are genetically diagnosed. The PMP22 gene is highly induced in Schwann cells during development, although its precise role in myelin formation and homeostasis is still under active investigation. The PMP22 gene can be considered as a nucleoprotein complex with enzymatic activity to produce the PMP22 transcript, and the complex is allosterically regulated by transcription factors that respond to intracellular signals and epigenomic modifications. The control of PMP22 transcript levels has been one of the major therapeutic targets of therapy development, and this review summarizes those approaches as well as efforts to characterize the regulation of the PMP22 gene.

Regulation of the neuropathy-associated Pmp22 gene by a distal super-enhancer

Peripheral nerve myelination is adversely affected in the most common form of the hereditary peripheral neuropathy called Charcot-Marie-Tooth Disease. This form, classified as CMT1A, is caused by a 1.4 Mb duplication on chromosome 17, which includes the abundantly expressed Schwann cell myelin gene, Peripheral Myelin Protein 22 (PMP22). This is one of the most common copy number variants causing neurological disease. Overexpression of Pmp22 in rodent models recapitulates several aspects of neuropathy, and reduction of Pmp22 in such models results in amelioration of the neuropathy phenotype. Recently we identified a potential super-enhancer approximately 90-130 kb upstream of the Pmp22 transcription start sites. This super-enhancer encompasses a cluster of individual enhancers that have the acetylated histone H3K27 active enhancer mark, and coincides with smaller duplications identified in patients with milder CMT1A-like symptoms, where the PMP22 coding region itself was not part of the duplication. In this study, we have utilized genome editing to create a deletion of this super-enhancer to determine its role in Pmp22 regulation. Our data show a significant decrease in Pmp22 transcript expression using allele-specific internal controls. Moreover, the P2 promoter of the Pmp22 gene, which is used in other cell types, is affected, but we find that the Schwann cell-specific P1 promoter is disproportionately more sensitive to loss of the super-enhancer. These data show for the first time the requirement of these upstream enhancers for full Pmp22 expression.

Surface functionalization of TiO2 nanotubes with minocycline and its in vitro biological effects on Schwann cells

Background

Minocycline has been widely used in central nervous system disease. However, the effect of minocycline on the repairing of nerve fibers around dental implants had not been previously investigated. The aim of the present study was to evaluate the possibility of using minocycline for the repairing of nerve fibers around dental implants by investigating the effect of minocycline on the proliferation of Schwann cells and secretion of neurotrophic factors nerve growth factor and glial cell line-derived neurotrophic factor in vitro.

Methods

TiO₂ nanotubes were fabricated on the surface of pure titanium via anodization at the voltage of 20, 30, 40 and 50 V. The nanotubes structure were characterized by scanning electron microscopy and examined with an optical contact angle. Then drug loading capability and release behavior were detected in vitro. The TiO₂ nanotubes loaded with different concentration of minocycline were used to produce conditioned media with which to treat the Schwann cells. A cell counting kit-8 assay and cell viability were both selected to study the proliferative effect of the specimens on Schwann cell. Reverse transcription-quantitative PCR and western blot analyses were used to detect the related gene/protein expression of Schwann cells.

Results

The results showed that the diameter of TiO₂ nanotubes at different voltage varied from 100 to 200 nm. The results of optical contact angle and releasing profile showed the nanotubes fabricated at the voltage of 30 V met the needs of the carrier of minocycline. In addition, the TiO₂ nanotubes loaded with the concentration of 20 μg/mL minocycline increased Schwann cells proliferation and secretion of neurotrophic factors in vitro.

Conclusions

The results suggested that the surface functionalization of TiO₂ nanotubes with minocycline was a promising candidate biomaterial for the peripheral nerve regeneration around dental implants and has potential to be applied in improving the osseoperception of dental implant.

A genome-wide assessment of conserved SNP alleles reveals a panel of regulatory SNPs relevant to the peripheral nerve

Background

Identifying functional non-coding variation is critical for defining the genetic contributions to human disease. While single-nucleotide polymorphisms (SNPs) within cis-acting transcriptional regulatory elements have been implicated in disease pathogenesis, not all cell types have been assessed and functional validations have been limited. In particular, the cells of the peripheral nervous system have been excluded from genome-wide efforts to link non-coding SNPs to altered gene function. Addressing this gap is essential for defining the genetic architecture of diseases that affect the peripheral nerve. We developed a computational pipeline to identify SNPs that affect regulatory function (rSNPs) and evaluated our predictions on a set of 144 regions in Schwann cells, motor neurons, and muscle cells.

Results

We identified 28 regions that display regulatory activity in at least one cell type and 13 SNPs that affect regulatory function. We then tailored our pipeline to one peripheral nerve cell type by incorporating SOX10 ChIP-Seq data; SOX10 is essential for Schwann cells. We prioritized 22 putative SOX10 response elements harboring a SNP and rapidly validated two rSNPs. We then selected one of these elements for further characterization to assess the biological relevance of our approach. Deletion of the element from the genome of cultured Schwann cells—followed by differential gene expression studies—revealed Tubb2b as a candidate target gene. Studying the enhancer in developing mouse embryos revealed activity in SOX10-positive cells including the dorsal root ganglia and melanoblasts.

Conclusions

Our efforts provide insight into the utility of employing strict conservation for rSNP discovery. This strategy, combined with functional analyses, can yield candidate target genes. In support of this, our efforts suggest that investigating the role of Tubb2b in SOX10-positive cells may reveal novel biology within these cell populations.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4692-z) contains supplementary material, which is available to authorized users.

Neurofibromatosis type 2 tumor suppressor protein is expressed in oligodendrocytes and regulates cell proliferation and process formation

The neurofibromatosis type 2 (NF2) tumor suppressor protein Merlin functions as a negative regulator of cell growth and actin dynamics in different cell types amongst which Schwann cells have been extensively studied. In contrast, the presence and the role of Merlin in oligodendrocytes, the myelin forming cells within the CNS, have not been elucidated. In this work, we demonstrate that Merlin immunoreactivity was broadly distributed in the white matter throughout the central nervous system. Following Merlin expression during development in the cerebellum, Merlin could be detected in the cerebellar white matter tract at early postnatal stages as shown by its co-localization with Olig2-positive cells as well as in adult brain sections where it was aligned with myelin basic protein containing fibers. This suggests that Merlin is expressed in immature and mature oligodendrocytes. Expression levels of Merlin were low in oligodendrocytes as compared to astrocytes and neurons throughout development. Expression of Merlin in oligodendroglia was further supported by its identification in either immortalized cell lines of oligodendroglial origin or in primary oligodendrocyte cultures. In these cultures, the two main splice variants of Nf2 could be detected. Merlin was localized in clusters within the nuclei and in the cytoplasm. Overexpressing Merlin in oligodendrocyte cell lines strengthened reduced impedance in XCELLigence measurements and Ki67 stainings in cultures over time. In addition, the initiation and elongation of cellular projections were reduced by Merlin overexpression. Consistently, cell migration was retarded in scratch assays done on Nf2-transfected oligodendrocyte cell lines. These data suggest that Merlin actively modulates process outgrowth and migration in oligodendrocytes.

Miconazole enhances nerve regeneration and functional recovery after sciatic nerve crush injury

INTRODUCTION

Improving axonal outgrowth and remyelination is crucial for peripheral nerve regeneration. Miconazole appears to enhance remyelination in the central nervous system. In this study we assess the effect of miconazole on axonal regeneration using a sciatic nerve crush injury model in rats.

METHODS

Fifty Sprague-Dawley rats were divided into control and miconazole groups. Nerve regeneration and myelination were determined using histological and electrophysiological assessment. Evaluation of sensory and motor recovery was performed using the pinprick assay and sciatic functional index. The Cell Counting Kit-8 assay and Western blotting were used to assess the proliferation and neurotrophic expression of RSC 96 Schwann cells.

RESULTS

Miconazole promoted axonal regrowth, increased myelinated nerve fibers, improved sensory recovery and walking behavior, enhanced stimulated amplitude and nerve conduction velocity, and elevated proliferation and neurotrophic expression of RSC 96 Schwann cells.

DISCUSSION

Miconazole was beneficial for nerve regeneration and functional recovery after peripheral nerve injury. Muscle Nerve 57: 821-828, 2018.

Class IIa histone deacetylases link cAMP signaling to the myelin transcriptional program of Schwann cells

Schwann cells respond to cyclic adenosine monophosphate (cAMP) halting proliferation and expressing myelin proteins. Here we show that cAMP signaling induces the nuclear shuttling of the class IIa histone deacetylase (HDAC)-4 in these cells, where it binds to the promoter and blocks the expression of c-Jun, a negative regulator of myelination. To do it, HDAC4 does not interfere with the transcriptional activity of MEF2. Instead, by interacting with NCoR1, it recruits HDAC3 and deacetylates histone 3 in the promoter of c-Jun, blocking gene expression. Importantly, this is enough to up-regulate Krox20 and start Schwann cell differentiation program-inducing myelin gene expression. Using conditional knockout mice, we also show that HDAC4 together with HDAC5 redundantly contribute to activate the myelin transcriptional program and the development of myelin sheath in vivo. We propose a model in which cAMP signaling shuttles class IIa HDACs into the nucleus of Schwann cells to regulate the initial steps of myelination in the peripheral nervous system.

The formation of lipid droplets favors intracellular Mycobacterium leprae survival in SW-10, non-myelinating Schwann cells

Leprosy is a chronic infectious disease that is caused by the obligate intracellular pathogen Mycobacterium leprae (M.leprae), which is the leading cause of all non-traumatic peripheral neuropathies worldwide. Although both myelinating and non-myelinating Schwann cells are infected by M.leprae in patients with lepromatous leprosy, M.leprae preferentially invades the non-myelinating Schwann cells. However, the effect of M.leprae infection on non-myelinating Schwann cells has not been elucidated. Lipid droplets (LDs) are found in M.leprae-infected Schwann cells in the nerve biopsies of lepromatous leprosy patients. M.leprae-induced LD formation favors intracellular M.leprae survival in primary Schwann cells and in a myelinating Schwann cell line referred to as ST88-14. In the current study, we initially characterized SW-10 cells and investigated the effects of LDs on M.leprae-infected SW-10 cells, which are non-myelinating Schwann cells. SW-10 cells express S100, a marker for cells from the neural crest, and NGFR p75, a marker for immature or non-myelinating Schwann cells. SW-10 cells, however, do not express myelin basic protein (MBP), a marker for myelinating Schwann cells, and myelin protein zero (MPZ), a marker for precursor, immature, or myelinating Schwann cells, all of which suggests that SW-10 cells are non-myelinating Schwann cells. In addition, SW-10 cells have phagocytic activity and can be infected with M. leprae. Infection with M. leprae induces the formation of LDs. Furthermore, inhibiting the formation of M. leprae-induced LD enhances the maturation of phagosomes containing live M.leprae and decreases the ATP content in the M. leprae found in SW-10 cells. These facts suggest that LD formation by M. leprae favors intracellular M. leprae survival in SW-10 cells, which leads to the logical conclusion that M.leprae-infected SW-10 cells can be a new model for investigating the interaction of M.leprae with non-myelinating Schwann cells.

Leprosy is a chronic infectious disease that is caused by the obligate intracellular pathogen Mycobacterium leprae (M.leprae). Leprosy is the leading cause of all non-traumatic peripheral neuropathies worldwide. Both myelinating and non-myelinating Schwann cells are infected by M.leprae in lepromatous leprosy, but the non-myelinating Schwann cells show greater susceptibility to M.leprae invasion. However, the effect of M.leprae infection on non-myelinating Schwann cells has not been elucidated. Our results show that SW-10 cells are non-myelinating Schwann cells. Infection with M. leprae induces lipid droplet (LD) formation. Furthermore, inhibition of M. leprae-induced LD formation enhances the maturation of phagosomes containing live M.leprae and decreases the ATP content of M. leprae in SW-10 cells, suggesting that LD formation by M. leprae favors M. leprae survival in SW-10 cells. Based on these findings, it should be clear that M.leprae-infected SW-10 cells can serve as a new model for investigating the interaction of M.leprae with non-myelinating Schwann cells.

Biofunctionalization of Nerve Interface via Biocompatible Polymer-Roughened Pt Black on Cuff Electrode for Chronic Recording

Peripheral nerve cuff electrodes with roughened Pt black (BPt) are coated with polyethylene glycol (PEG) and Nafion (NF). Although the influence of coated PEG and Nafion on roughened BPt on the electrical properties is weak, the cuff electrode with BPt/PEG and BPt/Nafion exhibits some very important properties. For example, it markedly decreases interfacial impedance, increases charge storage capacity (CSC) due to retaining the BPt surface structure, good stability without exfoliation in repetitive cyclic voltammetry scanning because it is protected by PEG or Nafion coating. In cell viability test, Nafion-coated BPt does not show cytotoxicity to rat Schwann cell line (S16) at 24 and 72 h with the Nafion coating ranging from 0.1 to 10 mg cm^-2 . In addition, real-time polymerase chain reaction (PCR) analysis indicates that Schwann cell differentiation (S100 calcium-binding protein B, myelin basic protein, peripheral myelin protein 22), proliferation (proliferating cell nuclear antigen, cyclin-dependent kinase 1 (CDK1)), and adhesion molecules (neural cell adhesion molecule, laminin, fibronectin) are upregulated up to 5 mg cm^-2 of Nafion. In animal study, the BPt/Nafion reduces infiltration of fibrotic tissue with high axonal maintenance with upregulation of proliferation (CDK1), adhesion (laminin, neuronal cell adhesion molecule), and neurotrophic factor receptor-related (gdnf family receptor alpha 1) mRNA expressions.

Dual specificity phosphatase 15 regulates Erk activation in Schwann cells

Schwann cells and oligodendrocytes are the myelinating cells of the peripheral and central nervous system, respectively. Despite having different myelin components and different transcription factors driving their terminal differentiation there are shared molecular mechanisms between the two. Sox10 is one common transcription factor required for several steps in development of myelinating glia. However, other factors are divergent as Schwann cells need the transcription factor early growth response 2/Krox20 and oligodendrocytes require Myrf. Likewise, some signaling pathways, like the Erk1/2 kinases, are necessary in both cell types for proper myelination. Nonetheless, the molecular mechanisms that control this shared signaling pathway in myelinating cells remain only partially characterized. The hypothesis of this study is that signaling pathways that are similarly regulated in both Schwann cells and oligodendrocytes play central roles in coordinating the differentiation of myelinating glia. To address this hypothesis, we have used genome-wide binding data to identify a relatively small set of genes that are similarly regulated by Sox10 in myelinating glia. We chose one such gene encoding Dual specificity phosphatase 15 (Dusp15) for further analysis in Schwann cell signaling. RNA interference and gene deletion by genome editing in cultured RT4 and primary Schwann cells showed Dusp15 is necessary for full activation of Erk1/2 phosphorylation. In addition, we show that Dusp15 represses expression of several myelin genes, including myelin basic protein. The data shown here support a mechanism by which early growth response 2 activates myelin genes, but also induces a negative feedback loop through Dusp15 to limit over-expression of myelin genes.

Bupivacaine Induces Apoptosis via ROS in the Schwann Cell Line

Local anesthetics have been generally accepted as being safe. However, recent clinical trials and basic studies have provided strong evidence for the neurotoxicity of local anesthetics, especially through apoptosis. We hypothesized that local anesthetics cause neural complications through Schwann cell apoptosis. Among local anesthetics tested on the Schwann cell line, RT4-D6P2T, bupivacaine significantly induced cell death, measured by the methyl tetrazolium (MTT) assay, in a dose- (LD50 = 476 μM) and time-dependent manner. The bupivacaine-induced generation of reactive oxygen species (ROS), which was initiated within 5 hrs and preceded the activation of caspase-3 and poly ADP-ribose polymerase (PARP) degradation, was suggested to trigger apoptosis, exhibited by Hoechst 33258 nuclear staining and DNA fragmentation. Furthermore, concomitant block of ROS by anti-oxidants significantly inhibited bupivacaine-induced apoptosis. Among the local anesthetics for peripheral neural blocks, bupivacaine induced apoptosis in the Schwann cell line, which may be associated with ROS production.

Stringent comparative sequence analysis reveals SOX10 as a putative inhibitor of glial cell differentiation

Background

The transcription factor SOX10 is essential for all stages of Schwann cell development including myelination. SOX10 cooperates with other transcription factors to activate the expression of key myelin genes in Schwann cells and is therefore a context-dependent, pro-myelination transcription factor. As such, the identification of genes regulated by SOX10 will provide insight into Schwann cell biology and related diseases. While genome-wide studies have successfully revealed SOX10 target genes, these efforts mainly focused on myelinating stages of Schwann cell development. We propose that less-biased approaches will reveal novel functions of SOX10 outside of myelination.

Results

We developed a stringent, computational-based screen for genome-wide identification of SOX10 response elements. Experimental validation of a pilot set of predicted binding sites in multiple systems revealed that SOX10 directly regulates a previously unreported alternative promoter at SOX6, which encodes a transcription factor that inhibits glial cell differentiation. We further explored the utility of our computational approach by combining it with DNase-seq analysis in cultured Schwann cells and previously published SOX10 ChIP-seq data from rat sciatic nerve. Remarkably, this analysis enriched for genomic segments that map to loci involved in the negative regulation of gliogenesis including SOX5, SOX6, NOTCH1, HMGA2, HES1, MYCN, ID4, and ID2. Functional studies in Schwann cells revealed that: (1) all eight loci are expressed prior to myelination and down-regulated subsequent to myelination; (2) seven of the eight loci harbor validated SOX10 binding sites; and (3) seven of the eight loci are down-regulated upon repressing SOX10 function.

Conclusions

Our computational strategy revealed a putative novel function for SOX10 in Schwann cells, which suggests a model where SOX10 activates the expression of genes that inhibit myelination during non-myelinating stages of Schwann cell development. Importantly, the computational and functional datasets we present here will be valuable for the study of transcriptional regulation, SOX protein function, and glial cell biology.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3167-3) contains supplementary material, which is available to authorized users.

Schwann Cells Increase Prostate and Pancreatic Tumor Cell Invasion Using Laminin Binding A6 Integrin

Human pancreatic and prostate cancers metastasize along nerve axons during perineural invasion. The extracellular matrix laminin class of proteins is an abundant component of both myelinated and non-myelinated nerves. Analysis of human pancreatic and prostate tissue revealed both perineural and endoneural invasion with Schwann cells surrounded or disrupted by tumor, respectively. Tumor and nerve cell co-culture conditions were used to determine if myelinating or non-myelinating Schwann cell (S16 and S16Y, respectively) phenotype was equally likely to promote integrin-dependent cancer cell invasion and migration on laminin. Conditioned medium from S16 cells increased tumor cell (DU145, PC3, and CFPAC1) invasion into laminin approximately 1.3-2.0 fold compared to fetal bovine serum (FBS) treated cells. Integrin function (e.g., ITGA6p formation) increased up to 1.5 fold in prostate (DU145, PC3, RWPE-1) and pancreatic (CFPAC1) cells, and invasion was dependent on ITGA6p formation and ITGB1 as determined by function-blocking antibodies. In contrast, conditioned medium isolated from S16Y cells (non-myelinating phenotype) decreased constitutive levels of ITGA6p in the tumor cells by 50% compared to untreated cells and decreased ITGA6p formation 3.0 fold compared to S16 treated cells. Flow cytometry and western blot analysis revealed loss of ITGA6p formation as reversible and independent of overall loss of ITGA6 expression. These results suggest that the myelinating phenotype of Schwann cells within the tumor microenvironment increased integrin-dependent tumor invasion on laminin.

SOX10 regulates an alternative promoter at the Charcot-Marie-Tooth disease locus MTMR2

Schwann cells are the myelinating glia of the peripheral nervous system and dysfunction of these cells causes motor and sensory peripheral neuropathy. The transcription factor SOX10 is critical for Schwann cell development and maintenance, and many SOX10 target genes encode proteins required for Schwann cell function. Loss-of-function mutations in the gene encoding myotubularin-related protein 2 (MTMR2) cause Charcot-Marie-Tooth disease type 4B1 (CMT4B1), a severe demyelinating peripheral neuropathy characterized by myelin outfoldings along peripheral nerves. Previous reports indicate that MTMR2 is ubiquitously expressed making it unclear how loss of this gene causes a Schwann cell-specific phenotype. To address this, we performed computational and functional analyses at MTMR2 to identify transcriptional regulatory elements important for Schwann cell expression. Through these efforts, we identified an alternative, SOX10-responsive promoter at MTMR2 that displays strong regulatory activity in immortalized rat Schwann (S16) cells. This promoter directs transcription of a previously unidentified MTMR2 transcript that is enriched in mouse Schwann cells compared to immortalized mouse motor neurons (MN-1), and is predicted to encode an N-terminally truncated protein isoform. The expression of the endogenous transcript is induced in a heterologous cell line by ectopically expressing SOX10, and is nearly ablated in Schwann cells by impairing SOX10 function. Intriguingly, overexpressing the two MTMR2 protein isoforms in HeLa cells revealed that both localize to nuclear puncta and the shorter isoform displays higher nuclear localization compared to the longer isoform. Combined, our data warrant further investigation of the truncated MTMR2 protein isoform in Schwann cells and in CMT4B1 pathogenesis.

Tead1 regulates the expression of Peripheral Myelin Protein 22 during Schwann cell development

Schwann cells are myelinating glia in the peripheral nervous system that form the myelin sheath. A major cause of peripheral neuropathy is a copy number variant involving the Peripheral Myelin Protein 22 (PMP22) gene, which is located within a 1.4-Mb duplication on chromosome 17 associated with the most common form of Charcot-Marie-Tooth Disease (CMT1A). Rodent models of CMT1A have been used to show that reducing Pmp22 overexpression mitigates several aspects of a CMT1A-related phenotype. Mechanistic studies of Pmp22 regulation identified enhancers regulated by the Sox10 (SRY sex determining region Y-box 10) and Egr2/Krox20 (Early growth response protein 2) transcription factors in myelinated nerves. However, relatively little is known regarding how other transcription factors induce Pmp22 expression during Schwann cell development and myelination. Here, we examined Pmp22 enhancers as a function of cell type-specificity, nerve injury and development. While Pmp22 enhancers marked by active histone modifications were lost or remodeled after injury, we found that these enhancers were permissive in early development prior to Pmp22 upregulation. Pmp22 enhancers contain binding motifs for TEA domain (Tead) transcription factors of the Hippo signaling pathway. We discovered that Tead1 and co-activators Yap and Taz are required for Pmp22 expression, as well as for the expression of Egr2 Tead1 directly binds Pmp22 and Egr2 enhancers early in development and Tead1 binding is induced during myelination, correlating with Pmp22 expression. The data identify Tead1 as a novel regulator of Pmp22 expression during development in concert with Sox10 and Egr2.

Involvement of the Tyro3 receptor and its intracellular partner Fyn signaling in Schwann cell myelination

During early development of the peripheral nervous system, Schwann cell precursors proliferate, migrate, and differentiate into premyelinating Schwann cells. After birth, Schwann cells envelop neuronal axons with myelin sheaths. Although some molecular mechanisms underlying myelination by Schwann cells have been identified, the whole picture remains unclear. Here we show that signaling through Tyro3 receptor tyrosine kinase and its binding partner, Fyn nonreceptor cytoplasmic tyrosine kinase, is involved in myelination by Schwann cells. Impaired formation of myelin segments is observed in Schwann cell neuronal cultures established from Tyro3-knockout mouse dorsal root ganglia (DRG). Indeed, Tyro3-knockout mice exhibit reduced myelin thickness. By affinity chromatography, Fyn was identified as the binding partner of the Tyro3 intracellular domain, and activity of Fyn is down-regulated in Tyro3-knockout mice, suggesting that Tyro3, acting through Fyn, regulates myelination. Ablating Fyn in mice results in reduced myelin thickness. Decreased myelin formation is observed in cultures established from Fyn-knockout mouse DRG. Furthermore, decreased kinase activity levels and altered expression of myelination-associated transcription factors are observed in these knockout mice. These results suggest the involvement of Tyro3 receptor and its binding partner Fyn in Schwann cell myelination. This constitutes a newly recognized receptor-linked signaling mechanism that can control Schwann cell myelination.

Biocompatibility and characterization of a peptide amphiphile hydrogel for applications in peripheral nerve regeneration

Peripheral nerve injury is a debilitating condition for which new bioengineering solutions are needed. Autografting, the gold standard in treatment, involves sacrifice of a healthy nerve and results in loss of sensation or function at the donor site. One alternative solution to autografting is to use a nerve guide conduit designed to physically guide the nerve as it regenerates across the injury gap. Such conduits are effective for short gap injuries, but fail to surpass autografting in long gap injuries. One strategy to enhance regeneration inside conduits in long gap injuries is to fill the guide conduits with a hydrogel to mimic the native extracellular matrix found in peripheral nerves. In this work, a peptide amphiphile (PA)-based hydrogel was optimized for peripheral nerve repair. Hydrogels consisting of the PA C₁₆GSH were compared with a commercially available collagen gel. Schwann cells, a cell type important in the peripheral nerve regenerative cascade, were able to spread, proliferate, and migrate better on C₁₆GSH gels in vitro when compared with cells seeded on collagen gels. Moreover, C₁₆GSH gels were implanted subcutaneously in a murine model and were found to be biocompatible, degrade over time, and support angiogenesis without causing inflammation or a foreign body immune response. Taken together, these results help optimize and instruct the development of a new synthetic hydrogel as a luminal filler for conduit-mediated peripheral nerve repair.

PACAP interacts with PAC1 receptors to induce tissue plasminogen activator (tPA) expression and activity in schwann cell-like cultures

Regeneration of peripheral nerves depends on the abilities of rejuvenating axons to migrate at the injury site through cellular debris and altered extracellular matrix, and then grow along the residual distal nerve sheath conduit and reinnervate synaptic targets. Considerable evidence suggest that glial cells participate in this process, although the mechanisms remain to be clarified. In cell culture, regenerating neurites secrete PACAP, a peptide shown to induce the expression of the protease tissue plasminogen activator (tPA) in neural cell types. In the present studies, we tested the hypothesis that PACAP can stimulate peripheral glial cells to produce tPA. More specifically, we addressed whether or not PACAP promoted the expression and activity of tPA in the Schwann cell line RT4-D6P2T, which shares biochemical and physical properties with Schwann cells. We found that PACAP dose- and time-dependently stimulated tPA expression both at the mRNA and protein level. Such effect was mimicked by maxadilan, a potent PAC1 receptor agonist, but not by the PACAP-related homolog VIP, suggesting a PAC1-mediated function. These actions appeared to be mediated at least in part by the Akt/CREB signaling cascade because wortmannin, a PI3K inhibitor, prevented peptide-driven CREB phosphorylation and tPA increase. Interestingly, treatment with BDNF mimicked PACAP actions on tPA, but acted through both the Akt and MAPK signaling pathways, while causing a robust increase in PACAP and PAC1 expression. PACAP6-38 totally blocked PACAP-driven tPA expression and in part hampered BDNF-mediated effects. We conclude that PACAP, acting through PAC1 receptors, stimulates tPA expression and activity in a Akt/CREB-dependent manner to promote proteolytic activity in Schwann-cell like cultures.

3D in vitro modeling of the central nervous system

There are currently more than 600 diseases characterized as affecting the central nervous system (CNS) which inflict neural damage. Unfortunately, few of these conditions have effective treatments available. Although significant efforts have been put into developing new therapeutics, drugs which were promising in the developmental phase have high attrition rates in late stage clinical trials. These failures could be circumvented if current 2D in vitro and in vivo models were improved. 3D, tissue-engineered in vitro systems can address this need and enhance clinical translation through two approaches: (1) bottom-up, and (2) top-down (developmental/regenerative) strategies to reproduce the structure and function of human tissues. Critical challenges remain including biomaterials capable of matching the mechanical properties and extracellular matrix (ECM) composition of neural tissues, compartmentalized scaffolds that support heterogeneous tissue architectures reflective of brain organization and structure, and robust functional assays for in vitro tissue validation. The unique design parameters defined by the complex physiology of the CNS for construction and validation of 3D in vitro neural systems are reviewed here.

Polytherapy with a combination of three repurposed drugs (PXT3003) down-regulates Pmp22 over-expression and improves myelination, axonal and functional parameters in models of CMT1A neuropathy

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited sensory and motor peripheral neuropathy. It is caused by PMP22 overexpression which leads to defects of peripheral myelination, loss of long axons, and progressive impairment then disability. There is no treatment available despite observations that monotherapeutic interventions slow progression in rodent models. We thus hypothesized that a polytherapeutic approach using several drugs, previously approved for other diseases, could be beneficial by simultaneously targeting PMP22 and pathways important for myelination and axonal integrity. A combination of drugs for CMT1A polytherapy was chosen from a group of authorised drugs for unrelated diseases using a systems biology approach, followed by pharmacological safety considerations. Testing and proof of synergism of these drugs were performed in a co-culture model of DRG neurons and Schwann cells derived from a Pmp22 transgenic rat model of CMT1A. Their ability to lower Pmp22 mRNA in Schwann cells relative to house-keeping genes or to a second myelin transcript (Mpz) was assessed in a clonal cell line expressing these genes. Finally in vivo efficacy of the combination was tested in two models: CMT1A transgenic rats, and mice that recover from a nerve crush injury, a model to assess neuroprotection and regeneration. Combination of (RS)-baclofen, naltrexone hydrochloride and D-sorbitol, termed PXT3003, improved myelination in the Pmp22 transgenic co-culture cellular model, and moderately down-regulated Pmp22 mRNA expression in Schwannoma cells. In both in vitro systems, the combination of drugs was revealed to possess synergistic effects, which provided the rationale for in vivo clinical testing of rodent models. In Pmp22 transgenic CMT1A rats, PXT3003 down-regulated the Pmp22 to Mpz mRNA ratio, improved myelination of small fibres, increased nerve conduction and ameliorated the clinical phenotype. PXT3003 also improved axonal regeneration and remyelination in the murine nerve crush model. Based on these observations in preclinical models, a clinical trial of PTX3003 in CMT1A, a neglected orphan disease, is warranted. If the efficacy of PTX3003 is confirmed, rational polytherapy based on novel combinations of existing non-toxic drugs with pleiotropic effects may represent a promising approach for rapid drug development.

Cyclic mechanical stress modulates neurotrophic and myelinating gene expression of Schwann cells

OBJECTIVES

This study aimed to investigate the response of Schwann cells to cyclic compressive and tensile stresses of different durations of stimulation.

MATERIALS AND METHODS

RSC96 cells were subjected to cyclic tensile stress or compressive stress; for either, cells in five groups were treated for 0, 1, 2, 24 and 48 h respectively. Enzyme-linked immunosorbent assay was conducted to detect secretion of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 and neurotrophin-4 in the culture medium. Real-time PCR was conducted to quantify mRNA expression of neurotrophins including NGF, BDNF, neurotrophin-3 and neurotrophin-4, and myelin-related genes including Sox10, Krox20, neuregulin 1, NCAM, N-cadherin, P0, MAG and MBP. Immunofluorescent staining was performed to visualize Krox20 and F-actin in the tensile groups.

RESULTS

Within 24 h, cells treated with cyclic tensile stress expressed and secreted significantly more BDNF, while cyclic compression down-regulated BDNF expression. Cells treated with both tensile and compressive stress down-regulated expression of NRG1, NCAM, Krox20 and Sox10 at all time points. Expression of N-cadherin was not affected by either stretch or compression. F-actin was down-regulated by tensile stress.

CONCLUSIONS

Both tensile and compressive loading down-regulated expression of several important myelin-related Schwann cells genes and thus facilitated demyelination. Tensile stress meanwhile promoted secretion of BDNF by Schwann cells within 24 h, which may contribute to maintenance and repair of damaged axons. These effects of mechanical stress might have been mediated by the actin cytoskeleton.

Haplotype-specific modulation of a SOX10/CREB response element at the Charcot-Marie-Tooth disease type 4C locus SH3TC2

Loss-of-function mutations in the Src homology 3 (SH3) domain and tetratricopeptide repeats 2 (SH3TC2) gene cause autosomal recessive demyelinating Charcot-Marie-Tooth neuropathy. The SH3TC2 protein has been implicated in promyelination signaling through axonal neuregulin-1 and the ERBB2 Schwann cell receptor. However, little is known about the transcriptional regulation of the SH3TC2 gene. We performed computational and functional analyses that revealed two cis-acting regulatory elements at SH3TC2-one at the promoter and one ∼150 kb downstream of the transcription start site. Both elements direct reporter gene expression in Schwann cells and are responsive to the transcription factor SOX10, which is essential for peripheral nervous system myelination. The downstream enhancer harbors a single-nucleotide polymorphism (SNP) that causes an ∼80% reduction in enhancer activity. The SNP resides directly within a predicted binding site for the transcription factor cAMP response element binding protein (CREB), and we demonstrate that this regulatory element binds to CREB and is activated by CREB expression. Finally, forskolin induces Sh3tc2 expression in rat primary Schwann cells, indicating that SH3TC2 is a CREB target gene. These findings prompted us to determine if SNP genotypes at SH3TC2 are associated with differential phenotypes in the most common demyelinating peripheral neuropathy, CMT1A. Interestingly, this revealed several associations between SNP alleles and disease severity. In summary, our data indicate that SH3TC2 is regulated by the transcription factors CREB and SOX10, define a regulatory SNP at this disease-associated locus and reveal SH3TC2 as a candidate modifier locus of CMT disease phenotypes.

Quercetin alleviates high glucose-induced Schwann cell damage by autophagy

Quercetin can reverse high glucose-induced inhibition of neural cell proliferation, and therefore may have a neuroprotective effect in diabetic peripheral neuropathy. It is difficult to obtain primary Schwann cells and RSC96 cells could replace primary Schwann cells in studies of the role of autophagy in the mechanism underlying diabetic peripheral neuropathy. Here, we show that under high glucose conditions, there are fewer autophagosomes in immortalized rat RSC96 cells and primary rat Schwann cells than under control conditions, the proliferative activity of both cell types is significantly impaired, and the expression of Beclin-1 and LC3, the molecular markers for autophagy, is significantly lower. After intervention with quercetin, the autophagic and proliferative activity of both cell types is rescued. These results suggest that quercetin can alleviate high glucose-induced damage to Schwann cells by autophagy.

Characterization of glial cell models and in vitro manipulation of the neuregulin1/ErbB system

The neuregulin1/ErbB system plays an important role in Schwann cell behavior both in normal and pathological conditions. Upon investigation of the expression of the neuregulin1/ErbB system in vitro, we explored the possibility to manipulate the system in order to increase the migration of Schwann cells, that play a fundamental role in the peripheral nerve regeneration. Comparison of primary cells and stable cell lines shows that both primary olfactory bulb ensheathing cells and a corresponding cell line express ErbB1-ErbB2 and neuregulin1, and that both primary Schwann cells and a corresponding cell line express ErbB2-ErbB3, while only primary Schwann cells express neuregulin1. To interfere with the neuregulin1/ErbB system, the soluble extracellular domain of the neuregulin1 receptor ErbB4 (ecto-ErbB4) was expressed in vitro in the neuregulin1 expressing cell line, and an unexpected increase in cell motility was observed. In vitro experiments suggest that the back signaling mediated by the transmembrane neuregulin1 plays a role in the migratory activity induced by ecto-ErbB4. These results indicate that ecto-ErbB4 could be used in vivo as a tool to manipulate the neuregulin1/ErbB system.

Role of connexin 32 hemichannels in the release of ATP from peripheral nerves

Extracellular purines elicit strong signals in the nervous system. Adenosine-5'-triphosphate (ATP) does not spontaneously cross the plasma membrane, and nervous cells secrete ATP by exocytosis or through plasma membrane proteins such as connexin hemichannels. Using a combination of imaging, luminescence and electrophysiological techniques, we explored the possibility that Connexin 32 (Cx32), expressed in Schwann cells (SCs) myelinating the peripheral nervous system could be an important source of ATP in peripheral nerves. We triggered the release of ATP in vivo from mice sciatic nerves by electrical stimulation and from cultured SCs by high extracellular potassium concentration-evoked depolarization. No ATP was detected in the extracellular media after treatment of the sciatic nerve with Octanol or Carbenoxolone, and ATP release was significantly inhibited after silencing Cx32 from SCs cultures. We investigated the permeability of Cx32 to ATP by expressing Cx32 hemichannels in Xenopus laevis oocytes. We found that ATP release is coupled to the inward tail current generated after the activation of Cx32 hemichannels by depolarization pulses, and it is sensitive to low extracellular calcium concentrations. Moreover, we found altered ATP release in mutated Cx32 hemichannels related to the X-linked form of Charcot-Marie-Tooth disease, suggesting that purinergic-mediated signaling in peripheral nerves could underlie the physiopathology of this neuropathy.

PACAP and VIP increase the expression of myelin-related proteins in rat schwannoma cells: involvement of PAC1/VPAC2 receptor-mediated activation of PI3K/Akt signaling pathways

PACAP and its cognate peptide VIP participate in various biological functions, including myelin maturation and synthesis. However, defining whether these peptides affect peripheral expression of myelin proteins still remains unanswered. To address this issue, we assessed whether PACAP or VIP contribute to regulate the expression of three myelin proteins (MAG, MBP and MPZ, respectively) using the rat schwannoma cell line (RT4-P6D2T), a well-established model to study myelin gene expression. In addition, we endeavored to partly unravel the underlying molecular mechanisms involved. Expression of myelin-specific proteins was assessed in cells grown either in normal serum (10% FBS) or serum starved and treated with or without 100 nM PACAP or VIP. Furthermore, through pharmacological approach using the PACAP/VIP receptor antagonist (PACAP6-38) or specific pathway (MAPK or PI3K) inhibitors we defined the relative contribution of receptors and/or signaling pathways on the expression of myelin proteins. Our data show that serum starvation (24h) significantly increased both MAG, MBP and MPZ expression. Concurrently, we observed increased expression of endogenous PACAP and related receptors. Treatment with PACAP or VIP further exacerbated starvation-induced expression of myelin markers, suggesting that serum withdrawal might sensitize cells to peptide activity. Stimulation with either peptides increased phosphorylation of Akt at Ser473 residue but had no effect on phosphorylated Erk-1/2. PACAP6-38 (10 μM) impeded starvation- or peptide-induced expression of myelin markers. Similar effects were obtained after pretreatment with the PI3K inhibitor (wortmannin, 10 μM) but not the MAPKK inhibitor (PD98059, 50 μM). Together, the present finding corroborate the hypothesis that PACAP and VIP might contribute to the myelinating process preferentially via the canonical PI3K/Akt signaling pathway, providing the basis for future studies on the role of these peptides in demyelinating diseases.

The ATP-binding cassette transporter-2 (ABCA2) regulates esterification of plasma membrane cholesterol by modulation of sphingolipid metabolism

The ATP-binding cassette transporters are a large family (~48 genes divided into seven families A-G) of proteins that utilize the energy of ATP-hydrolysis to pump substrates across lipid bilayers against a concentration gradient. The ABC "A" subfamily is comprised of 13 members and transport sterols, phospholipids and bile acids. ABCA2 is the most abundant ABC transporter in human and rodent brain with highest expression in oligodendrocytes, although it is also expressed in neurons. Several groups have studied a possible connection between ABCA2 and Alzheimer's disease as well as early atherosclerosis. ABCA2 expression levels have been associated with changes in cholesterol and sphingolipid metabolism. In this paper, we hypothesized that ABCA2 expression level may regulate esterification of plasma membrane-derived cholesterol by modulation of sphingolipid metabolism. ABCA2 overexpression in N2a neuroblastoma cells was associated with an altered bilayer distribution of the sphingolipid ceramide that inhibited acylCoA:cholesterol acyltransferase (ACAT) activity and cholesterol esterification. In contrast, depletion of endogenous ABCA2 in the rat schwannoma cell line D6P2T increased esterification of plasma membrane cholesterol following treatment with exogenous bacterial sphingomyelinase. These findings suggest that control of ABCA2 expression level may be a key locus of regulation for esterification of plasma membrane-derived cholesterol through modulation of sphingolipid metabolism.

A derivative of ascorbic acid modulates cAMP production

We reported, in previous experiments, that AA is a global regulator of cAMP pools. In this study, we demonstrate that K873, an analog of AA we synthesized and presenting antiproliferative properties, has also an impact on cAMP production. However, K873 has no antioxidant activity, at the contrary of AA. It definitively demonstrates that action of AA on the cAMP production is not linked to antioxidant activity. These data suggest that AA, and derivatives of this molecule, could be promising drug acting on biological processes that are under the control of cAMP dependent pathway.

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.