Antibody-mediated CNS demyelination II. Focal spinal cord lesions induced by implantation of an IgM antisulfatide-secreting hybridoma

We showed previously that spinal cord implants of hybridoma cells (O1) that secrete an IgM antigalactocerebroside cause focal multiple-sclerosis-like plaques of demyelination followed by remyelination to form “shadow plaques” (Rosenbluth et al., 1999). The antibody in that case was directed against a glycolipid present in mature oligodendrocytes and myelin but not in precursor cells. We now report the effects of implanting a different hybridoma (O4) that secretes IgM antibodies directed against sulfatide, a constituent not only of mature myelin and oligodendrocytes but also of late precursor cells, in order to determine whether this hybridoma too would generate focal demyelination and would, in addition, block remyelination. Our results show that focal plaques of demyelination indeed appear after O4 implantation, and that remyelination does occur, but only in cases where the hybridoma cells have degenerated, probably through host rejection. The occurrence of remyelination suggests that oligodendrocyte precursor cells are capable of migrating in rapidly from adjacent areas or that early precursors, not yet expressing sulfatide, remain undamaged within the lesions. In cases where intact hybridoma cells persist at lesion sites, remyelination does not occur. Failure of remyelination in this model thus appears to result from the continuing presence of antimyelin antibodies rather than from depletion of oligodendrocyte precursors.     

Inhibition of Epidermal Growth Factor Receptor Improves Myelination and Attenuates Tissue Damage of Spinal Cord Injury

Preventing demyelination and promoting remyelination of denuded axons are promising therapeutic strategies for spinal cord injury (SCI). Epidermal growth factor receptor (EGFR) inhibition was reported to benefit the neural functional recovery and the axon regeneration after SCI. However, its role in de- and remyelination of axons in injured spinal cord is unclear. In the present study, we evaluated the effects of EGFR inhibitor, PD168393 (PD), on the myelination in mouse contusive SCI model. We found that expression of myelin basic protein (MBP) in the injured spinal cords of PD treated mice was remarkably elevated. The density of glial precursor cells and oligodendrocytes (OLs) was increased and the cell apoptosis in lesions was attenuated after PD168393 treatment. Moreover, PD168393 treatment reduced both the numbers of OX42 + microglial cells and glial fibrillary acidic protein + astrocytes in damaged area of spinal cords. We thus conclude that the therapeutic effects of EGFR inhibition after SCI involves facilitating remyelination of the injured spinal cord, increasing of oligodendrocyte precursor cells and OLs, as well as suppressing the activation of astrocytes and microglia/macrophages.     

ULTRASTRUCTURAL STUDY OF REMYELINATION IN AN EXPERIMENTAL LESION IN ADULT CAT SPINAL CORD

This report presents ultrastructural observations on the cytological events that attend myelin formation occurring in the wake of demyelination in adult cat spinal cord. Lesions were induced in subpial cord by cerebrospinal fluid (c.s.f.) exchange (1, 2). Tissue from eleven cats at nine intervals from 19 to 460 days was fixed in situ by replacing c.s.f. with buffered OsO₄ and embedded in Araldite. After demyelination, axons are embraced by sheet-like glial processes. An occasional myelin sheath is first seen at 19 days; by 64 days, all axons are at least thinly myelinated. The cytoplasm of the myelin-forming cells, unlike that of either oligodendrocyte or fibrous astrocyte in normal cord, is dense with closely packed organelles and fine fibrils. Many of the myelinogenic cells become scarring astrocytes and at 460 days the lesion teems with their fibril-filled processes. Oligodendrocytes appear in the lesion after remyelination is under way. Phagocytes disappear gradually. A myelin sheath is formed by spiral wrapping of a sheet-like glial process around an axon. Where the first turn of the spiral is completed, a mesaxon is formed. As cytoplasm is lost from the process, the plasma membrane comes together along its outer and cytoplasmic surfaces to form compact myelin. Only a small amount of cytoplasm is retained; it is confined to the paramesaxonal region and, on the sheath exterior, to a longitudinal ridge which appears in profile as a small loop. This outer loop has the same rotational orientation as the inner mesaxon. These vestiges of spiral membrane wrapping are also found in normal adult and new-born cat cord. Nodes are present in all stages of remyelination and in normal adult cat and kitten cord. These observations suggest that myelin is reformed in the lesion in the same way it is first formed during normal development. The mechanism of myelin formation is basically similar to that proposed for peripheral nerve and amphibian and mammalian optic nerve; it does not agree with present views on the mechanism of myelinogenesis in mammalian brain and cord. This is the first demonstration of remyelination in adult mammalian central nervous tissue.     

Use of a rat Y chromosome probe to determine the long-term survival of glial cells transplanted into areas of CNS demyelination

A lack of suitable markers for cells which undergo division following transplantation has hindered studies assessing the long-term survival of glial cell grafts in the CNS. A probe specific to the rat Y chromosome was used to identify male glial cells grafted into an area of ethidium bromide-induced demyelination in syngeneic adult female rat spinal cord 4 weeks, 6 months and 12 months post-transplantation. At all time points there was extensive oligodendrocyte remyelination of transplanted lesions, and graft-derived cells were present within the lesion up to 12 months post-transplantation. In order to demonstrate graft-derived oligodendrocytes in the remyelinated region at 6 and 12 months, double-labelling studies were performed using the oligodendrocyte-specific antibodies carbonic anhydrase II or phosphatidyl ethanolamine-binding protein in combination with the Y chromosome probe. It was found that the majority of oligodendrocytes in the transplanted region were graft-derived. Graft-mediated remyelination was associated with a reduction in myelin sheath thickness and increase in nodal frequency similar to that observed in spontaneous remyelination, suggesting that, like axons remyelinated spontaneously, axons remyelinated by grafted cells will be capable of secure conduction. An alteration in the immunoreactivity of oligodendrocytes from carbonic anhydrase II-negative in the unlesioned dorsal funiculus to carbonic anhydrase II-positive in the remyelinated dorsal funiculus was considered to reflect a reduction in the amount of myelin supported by each oligodendrocyte, leading to the proposal that carbonic anhydrase II immunoreactivity may provide a means of identifying areas of remyelination in normally carbonic anhydrase II-negative white matter tracts.     

Failure of Schwann cells as supporting cells for adult neural progenitor cell grafts in the acutely injured spinal cord

Adult neural progenitor cells (NPC) co-grafted with fibroblasts replace cystic lesion defects and promote cell-contact-mediated axonal regeneration in the acutely injured spinal cord. Fibroblasts are required as a platform to maintain NPC within the lesion; however, they are suspected to create an inhospitable milieu for regenerating central nervous system (CNS) axons. Therefore, we thought to replace fibroblasts by primary Schwann cells, which might serve as a superior scaffold to maintain NPC within the lesion and might further enhance axon regrowth and remyelination following spinal cord injury. Adult rats underwent a cervical dorsal column transection immediately followed by transplantation of either NPC/Schwann cell or NPC/Schwann cell/fibroblast co-grafts. Animals receiving Schwann cell or fibroblast grafts alone, or Schwann cell/fibroblast co-grafts served as controls. At 3 weeks after injury/transplantation, histological analysis revealed that only fibroblast-containing grafts were able to replace the cystic lesion defect. In both co-cultures and co-grafts, Schwann cells and NPC were segregated. Almost all NPC migrated out of the graft into the adjacent host spinal cord. As a consequence, only peripheral-type myelin, but no CNS-type myelin, was detected within co-grafts containing NPC/Schwann cells. Corticospinal axon regeneration into Schwann-cell-containing co-grafts was reduced. Taken together, Schwann cells within NPC grafts contribute to remyelination. However, Schwann cells fail as a supporting platform to maintain NPC within the graft and impair CNS axon regeneration; this makes them an unfavorable candidate to support/augment NPC grafts following spinal cord injury.This work was supported by the Institute International de Recherche en Paraplégie Geneva, on behalf of an anonymous donation, and ReForM-Program, University of Regensburg, School of Medicine.     

Mediators of oligodendrocyte differentiation during remyelination

Myelin, a dielectric sheath that wraps large axons in the central and peripheral nervous systems, is essential for proper conductance of axon potentials. In multiple sclerosis (MS), autoimmune-mediated damage to myelin within the central nervous system (CNS) leads to progressive disability primarily due to limited endogenous repair of demyelination with associated axonal pathology. While treatments are available to limit demyelination, no treatments are available to promote myelin repair. Studies examining the molecular mechanisms that promote remyelination are therefore essential for identifying therapeutic targets to promote myelin repair and thereby limit disability in MS. Here, we present our current understanding of the critical extracellular and intracellular pathways that regulate the remyelinating capabilities of oligodendrocyte precursor cells (OPCs) within the adult CNS.     

Xenotransplantation of transgenic pig olfactory ensheathing cells promotes axonal regeneration in rat spinal cord

Here we describe transplantation of olfactory ensheathing cells (OECs) or Schwann cells derived from transgenic pigs expressing the human complement inhibitory protein, CD59 (hCD59), into transected dorsal column lesions of the spinal cord of the immunosuppressed rat to induce axonal regeneration. Non-transplanted lesion-controlled rats exhibited no impulse conduction across the transection site, whereas in animals receiving transgenic pig OECs or Schwann cells impulse conduction was restored across and beyond the lesion site for more than a centimeter. Cell labeling indicated that the donor cells migrated into the denervated host tract. Conduction velocity measurements showed that the regenerated axons conducted impulses faster than normal axons. By morphological analysis, the axons seemed thickly myelinated with a peripheral pattern of myelin expected from the donor cell type. These results indicate that xenotranplantation of myelin-forming cells from pigs genetically altered to reduce the hyperacute response in humans are able to induce elongative axonal regeneration and remyelination and restore impulse conduction across the transected spinal cord.     

Electron Microscopic Study of Demyelination in an Experimentally Induced Lesion in Adult Cat Spinal Cord

Plaques of subpial demyelination were induced in adult cat spinal cords by repeated withdrawal and reinjection of cerebrospinal fluid. Peripheral cord was fixed by replacing cerebrospinal fluid available at cisternal puncture with 3 per cent buffered OsO₄. Following extirpation, surface tissue was further fixed in 2 per cent buffered OsO₄, dehydrated in ethanol, and embedded in araldite. Normal subpial cord consists mainly of myelinated axons and two types of macroglia, fibrous astrocytes and oligodendrocytes. Twenty-nine hours after lesion induction most myelin sheaths are deteriorating and typical macroglia are no longer visible. Phagocytosis of myelin debris has begun. In 3-day lesions, axons are intact and their mitochondria and neurofibrils appear normal despite continued myelin breakdown. All axons are completely demyelinated by 6 days. They lack investments only briefly, however, for at 10 and 14 days, macroglial processes appear and embrace them. These macroglia do not resemble either one of the normally occurring glia; their dense cytoplasm contains fibrils in addition to the usual organelles. It is proposed that these macroglia, which later accomplish remyelination, are the hypertrophic or swollen astrocytes of classical neuropathology. The suggestion that these astrocytes possess the potential to remyelinate axons in addition to their known ability to form cicatrix raises the possibility of pharmacological control of their expression.     

Remyelination induced by a DNA aptamer in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a debilitating inflammatory disease of the central nervous system (CNS) characterized by local destruction of the insulating myelin surrounding neuronal axons. With more than 200 million MS patients worldwide, the absence of treatments that prevent progression or induce repair poses a major challenge. Anti-inflammatory therapies have met with limited success only in preventing relapses. Previous screening of human serum samples revealed natural IgM antibodies that bind oligodendrocytes and promote both cell signaling and remyelination of CNS lesions in an MS model involving chronic infection of susceptible mice by Theiler's encephalomyelitis virus and in the lysolecithin model of focal demyelination. This intriguing result raises the possibility that molecules with binding specificity for oligodendrocytes or myelin components may promote therapeutic remyelination in MS. Because of the size and complexity of IgM antibodies, it is of interest to identify smaller myelin-specific molecules with the ability to promote remyelination in vivo. Here we show that a 40-nucleotide single-stranded DNA aptamer selected for affinity to murine myelin shows this property. This aptamer binds multiple myelin components in vitro. Peritoneal injection of this aptamer results in distribution to CNS tissues and promotes remyelination of CNS lesions in mice infected by Theiler's virus. Interestingly, the selected DNA aptamer contains guanosine-rich sequences predicted to induce folding involving guanosine quartet structures. Relative to monoclonal antibodies, DNA aptamers are small, stable, and non-immunogenic, suggesting new possibilities for MS treatment.     

Immunoglobulins and complement in demyelination induced in mice by Theiler's virus

Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) produces chronic demyelination and persistent infection in the central nervous system (CNS) of susceptible SJL mice. This series of experiments examined the contribution of humoral immunity and C to myelin destruction. As in multiple sclerosis, mice persistently infected with TMEV had elevated levels of IgG and oligoclonal bands in the cerebrospinal fluid (CSF). Immunoblot studies revealed that even in animals exhibiting profound demyelination, IgG in the serum and CSF was directed primarily at virus antigen rather than at normal myelin components. Inflammatory cells positive for Ig were distributed mainly around blood vessels, but occasionally they infiltrated the spinal cord parenchyma. Rare examples of myelin sheaths positive for IgG were found by immunoelectron microscopy in spinal cord sections from infected mice; the third component of complement (C3) was commonly found in the walls of CNS blood vessels but not on myelin. Neither serum nor CSF IgG from infected mice bound to myelin sheaths or other CNS components in sections of normal syngeneic spinal cord. There were significantly more demyelinating lesions in infected mice depleted of C components with cobra venom factor. These data do not support a humoral autoimmune basis for the CNS demyelination that occurs in association with persistent TMEV infection. However, the humoral immune response directed at TMEV antigens may either limit virus spread or promote virus persistence.     

Promotion of Remyelination by Sulfasalazine in a Transgenic Zebrafish Model of Demyelination

Most of the axons in the vertebrate nervous system are surrounded by a lipid-rich membrane called myelin, which promotes rapid conduction of nerve impulses and protects the axon from being damaged. Multiple sclerosis (MS) is a chronic demyelinating disease of the CNS characterized by infiltration of immune cells and progressive damage to myelin and axons. One potential way to treat MS is to enhance the endogenous remyelination process, but at present there are no available treatments to promote remyelination in patients with demyelinating diseases.Sulfasalazine is an anti-inflammatory and immune-modulating drug that is used in rheumatology and inflammatory bowel disease. Its anti-inflammatory and immunomodulatory properties prompted us to test the ability of sulfasalazine to promote remyelination. In this study, we found that sulfasalazine promotes remyelination in the CNS of a transgenic zebrafish model of NTR/MTZ-induced demyelination. We also found that sulfasalazine treatment reduced the number of macrophages/microglia in the CNS of demyelinated zebrafish larvae, suggesting that the acceleration of remyelination is mediated by the immunomodulatory function of sulfasalazine. Our data suggest that temporal modulation of the immune response by sulfasalazine can be used to overcome MS by enhancing myelin repair and remyelination in the CNS.     

Multiple sclerosis - remyelination failure as a cause of disease progression

Multiple sclerosis (MS) is the most frequent demyelinating disease of the central nervous system (CNS) that affects worldwide about 2.5 million people. The morphological correlates of the disease are multiple lesions in brain and spinal cord which are characterized by demyelination, inflammation, gliosis and axonal damage. The underlying cause for the permanent neurological deficits in MS patients is axonal loss. Demyelinated axons are prone to damage due to the lack of trophic support by myelin sheaths and oligodendrocytes, as well as the increased vulnerability to immune mediated attacks. Remyelination occurs, but especially in chronic lesions is frequently limited to a small rim at the lesion border. Current treatment strategies are based on anti-inflammatory or immunomodulatory drugs and have the potential to reduce the numbers of newly evolving lesions, although as yet no treatment strategy exists to influence or prevent the progressive disease phase. Therefore, the development of neuroprotective treatment options, such as the promotion of endogenous remyelination is an attractive strategy. A prerequisite for the development of such new treatments is the understanding of the mechanisms leading to remyelination and the reasons for insufficient endogenous repair in chronic MS. This review will therefore provide an overview of the current concepts regarding remyelination in the rodent and human CNS. We will also summarize a selected number of inhibitory pathways and non-disease related factors which may contribute to remyelination failure in chronic MS.     

Probing the influence of myelin and glia on the tensile properties of the spinal cord

Although glia have been historically classified as the structurally supporting cells of the central nervous system, their role in tissue mechanics is still largely unstudied. The influence of myelin and glia on the mechanical properties of spinal cord tissue was examined by testing embryonic day 18 chick embryo spinal cords in uniaxial tension following disruption of the glial matrix using either ethidium bromide (EB) or an antibody against galactocerebroside (αGalC) in the presence of complement. Demyelination was confirmed by myelin basic protein immunoreactivity and quantified using osmium tetroxide staining. A substantial loss of astrocytes and oligodendrocytes concurrent with demyelination was observed following EB injection but not αGalC injection. No morphological changes were observed following injection of saline or IgG with complement as controls for EB and αGalC. Demyelinated spinal cords demonstrated significantly lower stiffness and ultimate tensile stress than myelinated spinal cords. No significant differences were observed in the tensile response between the two demyelinating protocols. The results demonstrate that the glial matrix provides significant mechanical support to the spinal cord, and suggests that myelin and cellular coupling of axons via the glial matrix in large part dictates the tensile response of the tissue.     

The demonstration by transplantation of the very restricted remyelinating potential of post-mitotic oligodendrocytes

To examine the remyelinating ability of post-mitotic oligodendrocytes, we subjected cell preparations derived from neonatal and adult rats to 40 Grays of X-irradiation to remove mitotically active cells and injected them into areas of demyelination in which the inherent ability to generate remyelinating cells had been inhibited. The extensive remyelination seen following implantation of non-irradiated neonatal and adult cells was almost completely abolished when the transplanted cell suspension was exposed to 40 Grays of X-irradiation, demonstrating that effective remyelination requires the generation of cells by mitosis. Radiation-resistant and therefore non-dividing oligodendrocytes were detected in areas of demyelination following transplantation of neonatal cultures and oligodendrocyte preparations derived from the adult nervous system. However, the pattern of myelin formation associated with the radiation-resistant oligodendrocytes from the two sources was different. Following implantation of X-irradiated neonatal cultures, a small number of oligodendrocytes could be found within the area of demyelination, and although these cells formed sheets of myelin membrane, they did not form myelin sheaths. After implantation of X-irradiated adult cells, in addition to the aberrant myelin formation seen with the neonatal cells, some myelin sheaths were observed. Our findings confirm that effective remyelination requires cell division and suggest that there may be diverse populations of radiation-resistant oligodendrocytes in the adult nervous system, some of which can form myelin sheaths and others of which can only make myelin sheets. Important for the interpretation of our previous studies is the demonstration here that 40 Grays of X-irradiation per se does not inhibit oligodendrocytes from remyelinating axons.     

Detection of sodium channel distribution in rat sciatic nerve following lysophosphatidylcholine-induced demyelination

Summary In vivo application of lysophosphatidylcholine (LPC) to rat sciatic nerve induces impaired hind leg movement within 2 days which is recovered by 6 days. Segmental demyelination was seen at 2 days after LPC application, and remyelination had barely started in a few axons by 6 days. Using sodium channel-specific monoclonal antibodies and immunofluorescence microscopy, we observed altered distribution of sodium channels in demyelinated axons. Bright fluorescent labeling was found along the segmentally demyelinated axolemma at 6 days in contrast to the dim staining of the demyelinated nerve found at 2 days. In addition, radioimmunoassays detected an elevated number of antibody binding sites on sciatic nerve trunk from the sixth day. Our data provide the immunocytochemical evidence for the assumption that recruitment of sodium channels into demyelinated axolemma contributes to the recovery of function following axon demyelination by LPC.     

The response of NG2-expressing oligodendrocyte progenitors to demyelination in MOG-EAE and MS

Remyelination of primary demyelinated lesions is a common feature of experimental models of multiple sclerosis (MS) and is also suggested to be the normal response to demyelination during the early stages of MS itself. Many lines of evidence have shown that remyelination is preceded by the division of endogenous oligodendrocyte precursor cells (OPCs) in the lesion and its borders. It is suggested that this rapid response of OPCs to repopulate the lesion site and their subsequent differentiation into new oligodendrocytes is the key to the rapid remyelination. Antibodies to the NG2 chondroitin sulphate proteoglycan have proved exceedingly useful in following and quantitating the response of endogenous OPCs to demyelination. Here we review the literature on the response of NG2-expressing OPCs to demyelination and provide some new evidence on their response to the chronic inflammatory demyelinating environment seen in recombinant myelin oligodendrocyte glycoprotein (MOG) induced experimental allergic encephalomyelitis (EAE) in the DA rat. NG2-expressing OPCs responded to the inflammatory demyelination in this model by becoming reactive and increasing in number in a very focal manner. Evidence of NG2⁺OPCs in lesioned areas beginning to express the oligodendrocyte marker CNP was also seen. The response of OPCs appeared to occur following successive relapses but did not always lead to remyelination, with areas of chronic demyelination observed in the spinal cord. The presence of OPCs in the adult human CNS is clearly of vital importance for repair in multiple sclerosis (MS). As in rat tissue, the antibody labels an evenly distributed cell population present in both white and grey matter, distinct from HLA-DR⁺microglia. NG2⁺cells are sparsely distributed in the centre of chronic MS lesions. These cells apparently survive demyelination and exhibit a multi-processed or bipolar morphology in the very hypocellular environment of the lesion.     

Prostacyclin promotes oligodendrocyte precursor recruitment and remyelination after spinal cord demyelination

Adult oligodendrocyte precursor cells (OPCs) are located adjacent to demyelinated lesion and contribute to myelin repair. The crucial step in remyelination is the migration of OPCs to the demyelinated area; however, the mechanism of OPC migration remains to be fully elucidated. Here we show that prostacyclin (prostaglandin I₂, PGI₂) promotes OPC migration, thereby promoting remyelination and functional recovery in mice after demyelination induced by injecting lysophosphatidylcholine (LPC) into the spinal cord. Prostacyclin analogs enhanced OPC migration via a protein kinase A (PKA)-dependent mechanism, and prostacyclin synthase expression was increased in the spinal cord after LPC injection. Notably, pharmacological inhibition of prostacyclin receptor (IP receptor) impaired remyelination and motor recovery, whereas the administration of a prostacyclin analog promoted remyelination and motor recovery after LPC injection. Our results suggest that prostacyclin could be a key molecule for facilitating the migration of OPCs that are essential for repairing demyelinated areas, and it may be useful in treating disorders characterized by demyelination.     

Glial grafting for demyelinating disease

Remyelination of demyelinated central nervous system (CNS) axons is considered as a potential treatment for multiple sclerosis, and it has been achieved in experimental models of demyelination by transplantation of pro-myelinating cells. However, the experiments undertaken have not addressed the need for tissue-type matching in order to achieve graft-mediated remyelination since they were performed in conditions in which the chance for graft rejection was minimized. This article focuses on the factors determining survival of allogeneic oligodendrocyte lineage cells and their contribution to the remyelination of demyelinating CNS lesions. The immune status of the CNS as well as the suitability of different models of demyelination for graft rejection studies are discussed, and ways of enhancing allogeneic oligodendrocyte-mediated remyelination are presented. Finally, the effects of glial graft rejection on host remyelination are described, highlighting the potential benefits of the acute CNS inflammatory response for myelin repair.     

Experimental Demyelination and Remyelination of Murine Spinal Cord by Focal Injection of Lysolecithin

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system characterized by plaque formation containing lost oligodendrocytes, myelin, axons, and neurons. Remyelination is an endogenous repair mechanism whereby new myelin is produced subsequent to proliferation, recruitment, and differentiation of oligodendrocyte precursor cells into myelin-forming oligodendrocytes, and is necessary to protect axons from further damage. Currently, all therapeutics for the treatment of multiple sclerosis target the aberrant immune component of the disease, which reduce inflammatory relapses but do not prevent progression to irreversible neurological decline. It is therefore imperative that remyelination-promoting strategies be developed which may delay disease progression and perhaps reverse neurological symptoms. Several animal models of demyelination exist, including experimental autoimmune encephalomyelitis and curprizone; however, there are limitations in their use for studying remyelination. A more robust approach is the focal injection of toxins into the central nervous system, including the detergent lysolecithin into the spinal cord white matter of rodents. In this protocol, we demonstrate that the surgical procedure involved in injecting lysolecithin into the ventral white matter of mice is fast, cost-effective, and requires no additional materials than those commercially available. This procedure is important not only for studying the normal events involved in the remyelination process, but also as a pre-clinical tool for screening candidate remyelination-promoting therapeutics.     

Delayed Nerve Stimulation Promotes Axon-Protective Neurofilament Phosphorylation,Accelerates Immune Cell Clearance and Enhances Remyelination In Vivo in Focally Demyelinated Nerves

Rapid and efficient axon remyelination aids in restoring strong electrochemical communication with end organs and in preventing axonal degeneration often observed in demyelinating neuropathies. The signals from axons that can trigger more effective remyelination in vivo are still being elucidated. Here we report the remarkable effect of delayed brief electrical nerve stimulation (ES; 1 hour @ 20 Hz 5 days post-demyelination) on ensuing reparative events in a focally demyelinated adult rat peripheral nerve. ES impacted many parameters underlying successful remyelination. It effected increased neurofilament expression and phosphorylation, both implicated in axon protection. ES increased expression of myelin basic protein (MBP) and promoted node of Ranvier re-organization, both of which coincided with the early reappearance of remyelinated axons, effects not observed at the same time points in non-stimulated demyelinated nerves. The improved ES-associated remyelination was accompanied by enhanced clearance of ED-1 positive macrophages and attenuation of glial fibrillary acidic protein expression in accompanying Schwann cells, suggesting a more rapid clearance of myelin debris and return of Schwann cells to a nonreactive myelinating state. These benefits of ES correlated with increased levels of brain derived neurotrophic factor (BDNF) in the acute demyelination zone, a key molecule in the initiation of the myelination program. In conclusion, the tremendous impact of delayed brief nerve stimulation on enhancement of the innate capacity of a focally demyelinated nerve to successfully remyelinate identifies manipulation of this axis as a novel therapeutic target for demyelinating pathologies.