Metabolic Control of Sensory Neuron Survival by the p75 Neurotrophin Receptor in Schwann Cells.

We report that the neurotrophin receptor p75 contributes to sensory neuron survival through the regulation of cholesterol metabolism in Schwann cells. Selective deletion of p75 in mouse Schwann cells of either sex resulted in a 30% loss of dorsal root ganglia (DRG) neurons and diminished thermal sensitivity. P75 regulates Schwann cell cholesterol biosynthesis in response to BDNF, forming a co-receptor complex with ErbB2 and activating ErbB2-mediated stimulation of sterol regulatory element binding protein 2 (SREBP2), a master regulator of cholesterol synthesis. Schwann cells lacking p75 exhibited decreased activation of SREBP2 and a reduction in 7-dehydrocholesterol (7-DHC) reductase (DHCR7) expression, resulting in accumulation of the neurotoxic intermediate, 7-dehyrocholesterol in the sciatic nerve. Restoration of DHCR7 in p75 null Schwann cells in mice significantly attenuated DRG neuron loss. Together, these results reveal a mechanism by which the disruption of lipid metabolism in glial cells negatively influences sensory neuron survival, which has implications for a wide range of peripheral neuropathies.SIGNIFICANCE STATEMENT Although expressed in Schwann cells, the role of p75 in myelination has remained unresolved in part because of its dual expression in sensory neurons that Schwann cells myelinate. When p75 was deleted selectively among Schwann cells, myelination was minimally affected, while sensory neuron survival was reduced by 30%. The phenotype is mainly due to dysregulation of cholesterol biosynthesis in p75-deficient Schwann cells, leading to an accumulation of neurotoxic cholesterol precursor, 7-dehydrocholesterol (7-DHC). Mechanism-wise, we discovered that in response to BDNF, p75 recruits and activates ErbB2 independently of ErbB3, thereby stimulating the master regulator, sterol regulatory element binding protein 2 (SREBP2). These results together highlight a novel role of p75 in Schwann cells in regulating DRG neuron survival by orchestrating proper cholesterol metabolism.

SoxD transcription factor deficiency in Schwann cells delays myelination in the developing peripheral nervous system.

The three SoxD proteins, Sox5, Sox6 and Sox13, represent closely related transcription factors with important roles during development. In the developing nervous system, SoxD proteins have so far been primarily studied in oligodendroglial cells and in interneurons of brain and spinal cord. In oligodendroglial cells, Sox5 and Sox6 jointly maintain the precursor state, interfere with terminal differentiation, and thereby ensure the proper timing of myelination in the central nervous system. Here we studied the role of SoxD proteins in Schwann cells, the functional counterpart of oligodendrocytes in the peripheral nervous system. We show that Schwann cells express Sox5 and Sox13 but not Sox6. Expression was transient and ceased with the onset of terminal differentiation. In mice with early Schwann cell-specific deletion of both Sox5 and Sox13, embryonic Schwann cell development was not substantially affected and progressed normally into the promyelinating stage. However, there was a mild and transient delay in the myelination of the peripheral nervous system of these mice. We therefore conclude that SoxD proteins-in stark contrast to their action in oligodendrocytes-promote differentiation and myelination in Schwann cells.

TNF-mimetic peptide mixed with fibrin glue improves peripheral nerve regeneration.

Surgical intervention is necessary following nerve trauma. Tubular prostheses can guide growing axons and inserting substances within these prostheses can be positive for the regeneration, making it an alternative for the current standard tools for nerve repair. Our aim was to investigate the effects of fibrin glue BthTL when combined with a synthetic TNF mimetic-action peptide on nerve regeneration. Male Wistar rats suffered left sciatic nerve transection. For repairing, we used empty silicon tubes (n = 10), tubes filled with fibrin glue BthTL (Tube + Glue group, n = 10) or tubes filled with fibrin glue BThTL mixed with TNF mimetic peptide (Tube + Glue + Pep group, n = 10). Animals were euthanized after 45 days. We collected nerves to perform immunostaining (neurofilament, GAP43, S100-ß, NGFRp75 and Iba-1), light and transmission electron microscopy (for counting myelinated, unmyelinated and degenerated fibers; and for the evaluation of morphometric aspects of regenerated fibers) and collagen staining. All procedures were approved by local ethics committee (protocol 063/17). Tube + Glue + Pep group showed intense inflammatory infiltrate, higher Iba-1 expression, increased immunostaining for NGFRp75 receptor (which characterizes Schwann cell regenerative phenotype), higher myelin thickness and fiber diameter and more type III collagen deposition. Tube + Glue group showed intermediate results between empty tube and Tube + Glue + Pep groups for anti-NGFRp75 immunostaining, inflammation and collagen; on fiber counts, this group showed more degenerate fibers and fewer unmyelinated axons than others. Empty tube group showed superiority only in GAP43 immunostaining. A combination of BthTL glue and TNF mimetic peptide induced greater axonal regrowth and remyelination.

Microtopographical patterns promote different responses in fibroblasts and Schwann cells: A possible feature for neural implants.

The chronic reliability of bioelectronic neural interfaces has been challenged by foreign body reactions (FBRs) resulting in fibrotic encapsulation and poor integration with neural tissue. Engineered microtopographies could alleviate these challenges by manipulating cellular responses to the implanted device. Parallel microchannels have been shown to modulate neuronal cell alignment and axonal growth, and Sharklet™ microtopographies of targeted feature sizes can modulate bio-adhesion of an array of bacteria, marine organisms, and epithelial cells due to their unique geometry. We hypothesized that a Sharklet™ micropattern could be identified that inhibited fibroblasts partially responsible for FBR while promoting Schwann cell proliferation and alignment. in vitro cell assays were used to screen the effect of Sharklet™ and channel micropatterns of varying dimensions from 2 to 20 µm on fibroblast and Schwann cell metrics (e.g., morphology/alignment, nuclei count, metabolic activity), and a hierarchical analysis of variance was used to compare treatments. In general, Schwann cells were found to be more metabolically active and aligned than fibroblasts when compared between the same pattern. 20 µm wide channels spaced 2 µm apart were found to promote Schwann cell attachment and alignment while simultaneously inhibiting fibroblasts and warrant further in vivo study on neural interface devices. No statistically significant trends between cellular responses and geometrical parameters were identified because mammalian cells can change their morphology dependent on their environment in a manner dissimilar to bacteria. Our results showed although surface patterning is a strong physical tool for modulating cell behavior, responses to micropatterns are highly dependent on the cell type.

Deletion of the Gene Encoding the NMDA Receptor GluN1 Subunit in Schwann Cells Causes Ultrastructural Changes in Remak Bundles and Hypersensitivity in Pain Processing.

Abnormalities in interactions between sensory neurons and Schwann cells (SCs) may result in heightened pain processing and chronic pain states. We previously reported that SCs express the NMDA receptor (NMDA-R), which activates cell signaling in response to glutamate and specific protein ligands, such as tissue-type plasminogen activator. Herein, we genetically targeted grin1 encoding the essential GluN1 NMDA-R subunit, conditionally in SCs, to create a novel mouse model in which SCs are NMDA-R-deficient (GluN1- mice). These mice demonstrated increased sensitivity to light touch, pinprick, and thermal hyperalgesia in the absence of injury, without associated changes in motor function. Ultrastructural analysis of adult sciatic nerve in GluN1- mice revealed increases in the density of Aδ fibers and Remak bundles and a decrease in the density of Aß fibers, without altered g-ratios. Abnormalities in adult Remak bundle ultrastructure were also present including aberrant C-fiber ensheathment, distances between axons, and increased poly-axonal pockets. Developmental and post radial sorting defects contributed to altered nerve fiber densities in adult. Uninjured sciatic nerves in GluN1- mice did not demonstrate an increase in neuroinflammatory infiltrates. Transcriptome profiling of dorsal root ganglia (DRGs) revealed 138 differentially regulated genes in GluN1- mice. One third of the regulated genes are known to be involved in pain processing, including sprr1a, npy, fgf3, atf3, and cckbr, which were significantly increased. The intraepidermal nerve fiber density (IENFD) was significantly decreased in the skin of GluN1- mice. Collectively, these findings demonstrate that SC NMDA-R is essential for normal PNS development and for preventing development of pain states.SIGNIFICANCE STATEMENT Chronic unremitting pain is a prevalent medical condition; however, the molecular mechanisms that underlie heightened pain processing remain incompletely understood. Emerging data suggest that abnormalities in Schwann cells (SCs) may cause neuropathic pain. We established a novel mouse model for small fiber neuropathy (SFN) in which grin1, the gene that encodes the NMDA receptor (NMDA-R) GluN1 subunit, is deleted in SCs. These mice demonstrate hypersensitivity in pain processing in the absence of nerve injury. Changes in the density of intraepidermal small fibers, the ultrastructure of Remak bundles, and the transcriptome of dorsal root ganglia (DRGs) provide possible explanations for the increase in pain processing. Our results support the hypothesis that abnormalities in communication between sensory nerve fibers and SCs may result in pain states.

CMTM6 expressed on the adaxonal Schwann cell surface restricts axonal diameters in peripheral nerves.

The velocity of nerve conduction is moderately enhanced by larger axonal diameters and potently sped up by myelination of axons. Myelination thus allows rapid impulse propagation with reduced axonal diameters; however, no myelin-dependent mechanism has been reported that restricts radial growth of axons. By label-free proteomics, STED-microscopy and cryo-immuno electron-microscopy we here identify CMTM6 (chemokine-like factor-like MARVEL-transmembrane domain-containing family member-6) as a myelin protein specifically localized to the Schwann cell membrane exposed to the axon. We find that disruption of Cmtm6-expression in Schwann cells causes a substantial increase of axonal diameters but does not impair myelin biogenesis, radial sorting or integrity of axons. Increased axonal diameters correlate with accelerated sensory nerve conduction and sensory responses and perturbed motor performance. These data show that Schwann cells utilize CMTM6 to restrict the radial growth of axons, which optimizes nerve function.

Neuronal activity disrupts myelinated axon integrity in the absence of NKCC1b.

Through a genetic screen in zebrafish, we identified a mutant with disruption to myelin in both the CNS and PNS caused by a mutation in a previously uncharacterized gene, slc12a2b, predicted to encode a Na+, K+, and Cl- (NKCC) cotransporter, NKCC1b. slc12a2b/NKCC1b mutants exhibited a severe and progressive pathology in the PNS, characterized by dysmyelination and swelling of the periaxonal space at the axon-myelin interface. Cell-type-specific loss of slc12a2b/NKCC1b in either neurons or myelinating Schwann cells recapitulated these pathologies. Given that NKCC1 is critical for ion homeostasis, we asked whether the disruption to myelinated axons in slc12a2b/NKCC1b mutants is affected by neuronal activity. Strikingly, we found that blocking neuronal activity completely prevented and could even rescue the pathology in slc12a2b/NKCC1b mutants. Together, our data indicate that NKCC1b is required to maintain neuronal activity-related solute homeostasis at the axon-myelin interface, and the integrity of myelinated axons.

Ultrastructural characterization of mitochondrial damage in experimental autoimmune neuritis.

Data are sparse about mitochondrial damage in GBS and in its most frequently employed animal model, experimental autoimmune neuritis (EAN). We here characterized changes in mitochondrial content and morphology at different time points during EAN by use of ultrastructural imaging and immunofluorescent labelling. Histological examination revealed that demyelinated axons and their adjacent Schwann cells showed reduced mitochondrial content and remaining mitochondria appeared swollen with greater diameter in Schwann cells and unmyelinated axons. Our findings indicate that in EAN, particularly mitochondria in Schwann cells are damaged. Further studies are warranted to address whether these changes are amenable to novel, mitoprotective treatments.

Elmo1 function, linked to Rac1 activity, regulates peripheral neuronal numbers and myelination in zebrafish.

Peripheral nervous system development involves a tight coordination of neuronal birth and death and a substantial remodelling of the myelinating glia cytoskeleton to achieve myelin wrapping of its projecting axons. However, how these processes are coordinated through time is still not understood. We have identified engulfment and cell motility 1, Elmo1, as a novel component that regulates (i) neuronal numbers within the Posterior Lateral Line ganglion and (ii) radial sorting of axons by Schwann cells (SC) and myelination in the PLL system in zebrafish. Our results show that neuronal and myelination defects observed in elmo1 mutant are rescued through small GTPase Rac1 activation. Inhibiting macrophage development leads to a decrease in neuronal numbers, while peripheral myelination is intact. However, elmo1 mutants do not show defective macrophage activity, suggesting a role for Elmo1 in PLLg neuronal development and SC myelination independent of macrophages. Forcing early Elmo1 and Rac1 expression specifically within SCs rescues elmo1-/- myelination defects, highlighting an autonomous role for Elmo1 and Rac1 in radial sorting of axons by SCs and myelination. This uncovers a previously unknown function of Elmo1 that regulates fundamental aspects of PNS development.

Behind the pathology of macrophage-associated demyelination in inflammatory neuropathies: demyelinating Schwann cells.

In inflammatory peripheral demyelinating disorders, demyelination represents segmental demyelination in which the myelin sheath of a myelinating Schwann cell (SC) is completely removed by macrophages or a partial myelin degeneration in the paranode occurring due to autoantibodies attacking the node/paranode. For the segmental demyelination from living myelin-forming SCs, macrophages infiltrate within the endoneurium and insinuate between myelin lamellae and the cytoplasm of SCs, and the myelin is then removed via phagocytosis. During the macrophage invasion into the SC cytoplasm from the node of Ranvier and internodal areas, the attacked SCs do not remain quiescent but transdifferentiate into inflammatory demyelinating SCs (iDSCs), which exhibit unique demyelination pathologies, such as myelin uncompaction from Schmidt-Lanterman incisures with myelin lamellae degeneration. The longitudinal extension of this self-myelin clearance process of iDSCs into the nodal region is associated with the degeneration of nodal microvilli and paranodal loops, which provides a potential locus for macrophage infiltration. In addition to the nodal intrusion, macrophages appear to be able to invade fenestrated internodal plasma membrane or the degenerated outer mesaxon of iDSC. These SC demyelination morphologies indicate that the SC reprogramming to iDSCs may be a prerequisite for macrophage-mediated inflammatory demyelination. In contrast, paranodal demyelination caused by autoantibodies to nodal/paranodal antigens does not result in iDSC-dependent macrophage infiltration and subsequent segmental demyelination. In the context of inflammatory demyelination, the novel perspective of iDSCs provides an important viewpoint to understand the pathophysiology of demyelinating peripheral neuropathies and establish diagnostic and therapeutic strategies.

Matrix metalloproteinase 7 promoted Schwann cell migration and myelination after rat sciatic nerve injury.

Schwann cells experience de-differentiation, proliferation, migration, re-differentiation and myelination, and participate in the repair and regeneration of injured peripheral nerves. Our previous sequencing analysis suggested that the gene expression level of matrix metalloproteinase 7 (MMP7), a Schwann cell-secreted proteolytic enzyme, was robustly elevated in rat sciatic nerve segments after nerve injury. However, the biological roles of MMP7 are poorly understood. Here, we exposed primary cultured Schwann cells with MMP7 recombinant protein and transfected siRNA against MMP7 into Schwann cells to examine the effect of exogenous and endogenous MMP7. Meanwhile, the effects of MMP7 in nerve regeneration after sciatic nerve crush in vivo were observed. Furthermore, RNA sequencing and bioinformatic analysis of Schwann cells were conducted to show the molecular mechanism behind the phenomenon. In vitro studies showed that MMP7 significantly elevated the migration rate of Schwann cells but did not affect the proliferation rate of Schwann cells. In vivo studies demonstrated that increased level of MMP7 contributed to Schwann cell migration and myelin sheaths formation after peripheral nerve injury. MMP7-mediated genetic changes were revealed by sequencing and bioinformatic analysis. Taken together, our current study demonstrated the promoting effect of MMP7 on Schwann cell migration and peripheral nerve regeneration, benefited the understanding of cellular and molecular mechanisms underlying peripheral nerve injury, and thus might facilitate the treatment of peripheral nerve regeneration in clinic.

Nicotine-induced oxidative stress alters sciatic nerve barriers in rat through modulation of ZO-1 & VEGF expression.

This study aimed to evaluate the histopathological and ultrastructural changes in sciatic nerve barriers after exposure to different doses of nicotine. Twenty-seven adult male rats were divided into 2 groups; group I served as control (n = 9) and group II that received nicotine (n = 18) was subdivided into two equal subgroups; group IIa and group IIb that were injected subcutaneously daily for one month with nicotine at a dose of 3 mg/kg and 6 mg/kg body weight, respectively. Specimens of sciatic nerve were processed for light and electron microscopy. Immunohistochemical expression of ZO-1 and vascular endothelium growth factor (VEGF) were investigated. Abundance of mRNA for VEGF was determined via qRT-PCR. Total antioxidant capacity (TAC), malondialdehyde (MDA), alanine transaminase (ALT) and aspartate transaminase (AST) were measured. Group IIb showed increased perineural fibrosis and myelin abnormalities. ZO-1 expression was significantly decreased. Schwann cells showed features of apoptosis and blood capillaries showed disrupted lining. High statistical difference in the level of mRNA expression of VEGF between group IIb and group I was found. There was decreased level of TAC and increased MDA, ALT and AST. A dose-dependent nicotine-induced oxidative stress on the sciatic nerve occurred via disruption of nerve barriers, altered VEGF and ZO-1 levels.

Peptide nanostructures on nanofibers for peripheral nerve regeneration.

Self-assembled peptide nanofibrous scaffolds with designer sequences, similar to neurite growth promoting molecules enhance the differentiation of neural stem cells. However, self-assembled peptide nanofibrous scaffolds lack the required mechanical strength to suffice to bridge long critical-sized peripheral nerve defects. Hence, there is a demand for a potential neural substrate, which could be biomimetic coupled with bioactive nanostructures to regrow the denuded axons towards the distal end. In the present study, we developed designer self-assembling peptide-based aligned poly(lactic-co-glycolic acid) (PLGA) nanofibrous scaffolds by simple surface coating of peptides or coelectrospinning. Retention of secondary structures of peptides in peptide-coated and cospun fibers was confirmed by circular dichroism spectroscopy. The rod-like peptide nanostructures enhance the typical bipolar morphology of Schwann cells. Although the peptide-coated PLGA scaffolds exhibited significant increase in Schwann cell proliferation than pristine PLGA and PLGA-peptide cospun scaffolds (p < .05), peptide cospun scaffolds demonstrated better cellular infiltration and significantly higher gene expression of neural cell adhesion molecule, glial fibrillary acidic protein, and peripheral myelin protein22 compared to the pristine PLGA and PLGA-peptide-coated scaffolds. Our results demonstrate the positive effects of aligned peptide coelectrospun scaffolds with biomimetic cell recognition motifs towards functional proliferation of Schwann cells. These scaffolds could subsequently repair peripheral nerve defects by augmenting axonal regeneration and functional nerve recovery.

NRG1 type I dependent autoparacrine stimulation of Schwann cells in onion bulbs of peripheral neuropathies.

In contrast to acute peripheral nerve injury, the molecular response of Schwann cells in chronic neuropathies remains poorly understood. Onion bulb structures are a pathological hallmark of demyelinating neuropathies, but the nature of these formations is unknown. Here, we show that Schwann cells induce the expression of Neuregulin-1 type I (NRG1-I), a paracrine growth factor, in various chronic demyelinating diseases. Genetic disruption of Schwann cell-derived NRG1 signalling in a mouse model of Charcot-Marie-Tooth Disease 1A (CMT1A), suppresses hypermyelination and the formation of onion bulbs. Transgenic overexpression of NRG1-I in Schwann cells on a wildtype background is sufficient to mediate an interaction between Schwann cells via an ErbB2 receptor-MEK/ERK signaling axis, which causes onion bulb formations and results in a peripheral neuropathy reminiscent of CMT1A. We suggest that diseased Schwann cells mount a regeneration program that is beneficial in acute nerve injury, but that overstimulation of Schwann cells in chronic neuropathies is detrimental.

Characteristic clinical and ultrastructural findings in nesprinopathies.

AIMS: To define the neurological and neuropathological alterations caused by SYNE1 mutations. METHODS: We describe 5 patients (3 males, 2 females; age 3-24 years) from 3 families. The diagnostic work-up included three muscle biopsies and two nerve biopsies in three of the cases. RESULTS: Three different phenotypes were discerned. Two patients showed progressive ataxia, mental retardation, neuropathy and radially deviated thumbs (spinocerebellar ataxia, SCAR, type 8 phenotype). Two patients had mild congenital myopathy with restrictive lung disease, clubfeet and thumb anomalies (myopathic arthrogryposis). One patient had congenital myopathy with dilated cardiomyopathy and adducted thumbs (Emery-Dreifuss Muscular Dystrophy, EDMD, type 4). Light microscopy of the three muscle biopsies revealed chronic non-necrotizing myopathy without rimmed vacuoles in all cases combined with neurogenic atrophy in one case. The two nerve biopsies showed predominantly axonal neuropathy with demyelinating features. Nuclear alterations, most notably lobulation and focal widening of the space between inner and outer leaflet of the nuclear envelope, were a prominent consistent feature of myonuclei and Schwann cell nuclei in each of the three muscle specimens and one nerve specimen that could be examined by electron microscopy. CONCLUSION: Thumb abnormalities and nuclear envelope alterations are characteristic for SYNE 1 mutations. Schwann cell nuclei are affected, indicating that such nuclear envelope changes in glial cells contribute to the neurodegenerative phenotype in human nesprinopathies.

Protective Effect of Baicalein on Oxidative Stress-induced DNA Damage and Apoptosis in RT4-D6P2T Schwann Cells.

Background: Due to its high antioxidant activity, baicalein, a kind of flavonoid present in Radical Scutellariae, has various pharmacological effects. However, the protective effect against oxidative stress in Schwann cells, which plays an important role in peripheral neuropathy, has not yet been studied. In this study, the effects of baicalein on hydrogen peroxide (H2O2)-induced DNA damage and apoptosis in RT4-D6P2T Schwann cells were evaluated. Methods: Cell viability assay was performed using MTT assay and colony formation assay. Apoptosis was assessed by flow cytometry analysis and DNA fragmentation assay. The effects on DNA damage and ATP content were analyzed by comet method and luminometer. In addition, changes in protein expression were observed by Western blotting. Results: Our results show that baicalein significantly inhibits H2O2-induced cytotoxicity through blocking reactive oxygen species (ROS) generation. We also demonstrate that baicalein is to block H2O2-induced DNA damage as evidenced by inhibition of DNA tail formation and γH2AX phosphorylation. Moreover, baicalein significantly attenuated H2O2-induced apoptosis and mitochondrial dysfunction, and restored inhibition of ATP production. The suppression of apoptosis by baicalein in H2O2-stimulated cells was associated with reduction of increased Bax/Bcl-2 ratio, activation of caspase-9 and -3, and degradation of poly (ADP-ribose) polymerase. Conclusions: These results demonstrate that baicalein eliminates H2O2-induced apoptosis through conservation of mitochondrial function by the removal of ROS. Therefore, it is suggested that baicalein protects Schwann cells from oxidative stress, and may be beneficial for the prevention and treatment of peripheral neuropathy induced by oxidative stress.

Direct conversion of adult human skin fibroblasts into functional Schwann cells that achieve robust recovery of the severed peripheral nerve in rats.

Direct conversion is considered a promising approach to obtain tissue-specific cells for cell therapies; however, this strategy depends on exogenous gene expression that may cause undesired adverse effects such as tumorigenesis. By optimizing the Schwann cell induction system, which was originally developed for trans-differentiation of bone marrow mesenchymal stem cells into Schwann cells, we established a system to directly convert adult human skin fibroblasts into cells comparable to authentic human Schwann cells without gene introduction. Serial treatments with beta-mercaptoethanol, retinoic acid, and finally a cocktail of basic fibroblast growth factor, forskolin, platelet-derived growth factor-AA, and heregulin-ß1 (EGF domain) converted fibroblasts into cells expressing authentic Schwann cell markers at an efficiency of approximately 75%. Genome-wide gene expression analysis suggested the conversion of fibroblasts into the Schwann cell-lineage. Transplantation of induced Schwann cells into severed peripheral nerve of rats facilitated axonal regeneration and robust functional recovery in sciatic function index comparable to those of authentic human Schwann cells. The contributions of induced Schwann cells to myelination of regenerated axons and re-formation of neuromuscular junctions were also demonstrated. Our data clearly demonstrated that cells comparable to functional Schwann cells feasible for the treatment of neural disease can be induced from adult human skin fibroblasts without gene introduction. This direct conversion system will be beneficial for clinical applications to peripheral and central nervous system injuries and demyelinating diseases.

The conceptual introduction of the "demyelinating Schwann cell" in peripheral demyelinating neuropathies.

Myelinating Schwann cells undergo irreversible demyelination in many demyelinating neuropathies that show complete demyelination of the internode. Dedifferentiation, reprogramming, and myelin clearance processes-which are specifically discussed in this article-appear to be shared by various demyelinating peripheral conditions, such as Wallerian degeneration, immune-mediated, and toxic demyelinating diseases. We propose to introduce the concept of the "demyelinating Schwann cell (DSC)" as a novel cell phenotype, which has specific properties required for myelin sheath clearance. We anticipate that the introduction of the DSC concept will provide a significant advance in understanding the pathophysiological mechanisms of demyelinating peripheral neuropathies.

Molecularly engineered metal-based bioactive soft materials - Neuroactive magnesium ion/polymer hybrids.

The development of bioactive soft materials that can guide cell behavior and have biomimetic mechanical properties is an active and challenging topic in regenerative medicine. A common strategy to create a bioactive soft material is the integration of biomacromolecules with polymers. However, limited by their complex structures and sensitivity to temperature and chemicals, it is relatively difficult to maintain the bioactivity of biomacromolecules during their preparation, storage, and application. Here, a new kind of bioactive soft material based on the molecular integration of metal ions and polymers is designed and exemplified by a hybrid of magnesium ion (Mg2+) and poly(glycerol-sebacate-maleate) (PGSM-Mg). Mg2+ was firmly incorporated into PGSM molecules through a complexation interaction as evidenced by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The PGSM matrix provided the soft nature and facile processing of the hybrid, which could serve as an injectable material and be fabricated into elastic porous three-dimensional (3D) scaffolds. The Mg2+ immobilized in the PGSM chain conferred neuroactivity to the resultant hybrid. PGSM-Mg exhibited adequate biodegradability and a sustained release of Mg2+. PGSM-Mg 3D scaffolds promoted the adhesion and proliferation of Schwann cells (SCs) more effectively than poly(lactic-co-glycolic acid) (PLGA) scaffolds. Furthermore, SCs on PGSM-Mg scaffolds expressed significantly more neural specific genes than those on PLGA, PGS, and PGSM, including nerve growth factor (NGF) and neurotrophic factor-3 (NTF3). All these results indicated that Mg2+ immobilized through molecular integration could efficiently regulate the bioactivity of polymers. In view of the wide availability, diverse bioactivity, and high stability of metal ions, the strategy of molecular coupling of metal ions and polymers is expected to be a new general approach to construct bioactive soft materials. STATEMENT OF SIGNIFICANCE: Bioactive soft materials are designed on the basis of the molecular integration of metal ions and polymers. Immobilized metal ions offer a new way to endow bioactivity to polymers. Different from biomolecules such as proteins and genes, metal ions are quite stable and can resist harsh processing conditions. Further, the polymeric matrix provides the soft nature and facile processing of the hybrid. Different from stiff metal-containing inorganic materials, the hybrid is a biomimetic soft material and can be readily processed just like its polymer precursor under mild conditions. In view of the diversity of metal ions and polymers, this strategy is expected to be a new powerful and general approach to construct bioactive soft materials for a wide range of biomedical applications.

Modified PLGA nanofibers as a nerve regenerator with Schwann cells.

Polylactide-co-glycolide acid (PLGA) is known as a biodegradable and biocompatible polymer. This polymer has been highly used in tissue engineering. In this study, the biological behavior of Schwann cells (Rat) was investigated in co-culture with L lysine/gelatine coated PLGA nano-fiber. In this study, PLGA was dissolved in a hexafluoro propanol based solvent and nanofiber prepared by an electronic method. They were coated with gelatin and poly-L-lysine individually. These polymer properties were investigated by Scanning Electron Microscopy (SEM) analysis and contact angle measurement. After extraction of rat Schwann cells, the cells were cultured in three groups of nano-fiber; nano-fiber PLGA, nano-fiber gelatine coated PLGA and nano-fiber poly-L-lysine coated PLGA. Cell death and Cell proliferation were evaluated by Acridine orange staining (living cell with a green nucleus and dead cell with an orange nucleus) and morphology was investigated by SEM in 2, 4 and 6 days. The diameter of electronic nanofiber PLGA was between 270 to 700 nm. Average contact angles of PLGA, PLGA coated with gelatine, coated with poly-L-lysine and PLGA were 40.12, 64.58 and 107.66degrees, respectively. The findings showed a significant reduction of cell proliferation in PLGA nanofiber ( it was important than PLGA without nano-fiber (P <0.05)). But, this amount was increased in nanofiber which coated with poly-L-lysine and gelatine. PLGA nanofiber-poly-L-lysine was more biocompatible than PLGA nanofiber-gelatine and this comparison was done with rat Schwann cells.