Peripheral-type Myelin Research Articles

Transplantation of human bone marrow stromal cell-derived Schwann cells reduces cystic cavity and promotes functional recovery after contusion injury of adult rat spinal cord

The aim of this study was to evaluate whether transplantation of human bone marrow stromal cell-derived Schwann cells (hBMSC-SC) promotes functional recovery after contusive spinal cord injury of adult rats. Human bone marrow stromal cells (hBMSC) were cultured from bone marrow of adult human patients and induced into Schwann cells (hBMSC-SC) in vitro. Schwann cell phenotype was confirmed by immunocytochemistry. Growth factors secreted from hBMSC-SC were detected using cytokine antibody array. Immunosuppressed rats were laminectomized and their spinal cords were contused using NYU impactor (10 g, 25 mm). Nine days after injury, a mixture of Matrigel and hBMSC-SC (hBMSC-SC group) was injected into the lesioned site. Five weeks after transplantation, cresyl-violet staining revealed that the area of cystic cavity was smaller in the hBMSC-SC group than that in the control group. Immunohistochemistry revealed that the number of anti-growth-associated protein-43-positive nerve fibers was significantly larger in the hBMSC-SC group than that in the control group. At the same time, the number of tyrosine hydroxylase- or serotonin-positive fibers was significantly larger at the lesion epicenter and caudal level in the hBMSC-SC group than that in the control group. In electron microscopy, formation of peripheral-type myelin was recognized near the lesion epicenter in the hBMSC-SC group. Hind limb function recovered significantly in the hBMSC-SC group compared with the control group. In conclusion, the functions of hBMSC-SC are comparable to original Schwann cells in rat spinal cord injury models, and are thus potentially useful treatments for patients with spinal cord injury.

Schwann cell-like remyelination following transplantation of human umbilical cord blood (hUCB)-derived mesenchymal stem cells in dogs with acute spinal cord injury

Human umbilical cord blood derived mesenchymal stem cells (hUCB-MSCs) have significant therapeutic potential in cell-based therapies following spinal cord injury (SCI). To evaluate this potential, we conducted our preliminary investigations on the remyelination of injured spinal cords with hUCB-MSC transplantations and we observed its long term effects on dogs with SCI. Of the ten injured dogs, seven were transplanted with hUCB-MSCs 1 week after SCI, whereas the remaining three dogs were not transplanted. Two transplanted dogs died over the first month after transplantation because of urinary tract infection, bedsores and sepsis. The SCI dogs showed no improvement in motor and sensory functions and their urinary dysfunction persisted until they were euthanized (from 3 months to 1 year) while hind-limb recovery in 4 dogs among the five transplanted dogs was significantly improved. In the recovered dogs, functional recovery was sustained for three years following transplantation. Histological results from five transplanted dogs showed that many axons were remyelinated by P0-postive myelin sheaths after transplantation. Our results suggest that transplantation of hUCB-derived MSCs may have beneficial therapeutic effects. Furthermore, histological results provided the first in vivo evidence that hUCB-MSCs are able to enhance the remyelination of peripheral-type myelin sheaths following SCI.

Convergence of Cells from the Progenitor Fraction of Adult Olfactory Bulb Tissue to Remyelinating Glia in Demyelinating Spinal Cord Lesions

BackgroundProgenitor cells isolated from adult brain tissue are important tools for experimental studies of remyelination. Cells harvested from neurogenic regions in the adult brain such as the subependymal zone have demonstrated remyelination potential. Multipotent cells from the progenitor fraction have been isolated from the adult olfactory bulb (OB) but their potential to remyelinate has not been studied.Methodology/Principal FindingsWe used the buoyant density gradient centrifugation method to isolate the progenitor fraction and harvest self-renewing multipotent neural cells grown in monolayers from the adult green-fluorescent protein (GFP) transgenic rat OB. OB tissue was mechanically and chemically dissociated and the resultant cell suspension fractionated on a Percoll gradient. The progenitor fraction was isolated and these cells were plated in growth media with serum for 24 hrs. Cells were then propagated in N2 supplemented serum-free media containing b-FGF. Cells at passage 4 (P4) were introduced into a demyelinated spinal cord lesion. The GFP+ cells survived and integrated into the lesion, and extensive remyelination was observed in plastic sections. Immunohistochemistry revealed GFP+ cells in the spinal cord to be glial fibrillary acidic protein (GFAP), neuronal nuclei (NeuN), and neurofilament negative. The GFP+ cells were found among primarily P0+ myelin profiles, although some myelin basic protein (MBP) profiles were present. Immuno-electron microscopy for GFP revealed GFP+ cell bodies adjacent to and surrounding peripheral-type myelin rings.Conclusions/SignificanceWe report that neural cells from the progenitor fraction of the adult rat OB grown in monolayers can be expanded for several passages in culture and that upon transplantation into a demyelinated spinal cord lesion provide extensive remyelination without ectopic neuronal differentiation.

Myelination and nodal formation of regenerated peripheral nerve fibers following transplantation of acutely prepared olfactory ensheathing cells

Transplantation of olfactory ensheathing cells (OECs) into injured spinal cord results in improved functional outcome. Mechanisms suggested to account for this functional improvement include axonal regeneration, remyelination and neuroprotection. OECs transplanted into transected peripheral nerve have been shown to modify peripheral axonal regeneration and functional outcome. However, little is known of the detailed integration of OECs at the transplantation site in peripheral nerve. To address this issue, cell populations enriched in OECs were isolated from the olfactory bulbs of adult green fluorescent protein (GFP)-expressing transgenic rats and transplanted into a sciatic nerve crush lesion which transects all axons. Five weeks to 6 months after transplantation, the nerves were studied histologically. GFP-expressing OECs survived in the lesion and distributed longitudinally across the lesion zone. The internodal regions of individual teased fibers distal to the transection site were characterized by GFP expression in the cytoplasmic and nuclear compartments of cells surrounding the axons. Immunoelectron microscopy for GFP indicated that the transplanted OECs formed peripheral type myelin. Immunostaining for sodium channel and Caspr revealed a high density of Na v1.6 at the newly formed nodes of Ranvier which were flanked by paranodal Caspr staining. These results indicate that transplanted OECs extensively integrate into transected peripheral nerve and form myelin on regenerated peripheral nerve fibers, and that nodes of Ranvier of these axons display proper sodium channel organization.

Transplanted Schwann cells, not olfactory ensheathing cells, myelinate optic nerve fibres

In a previous study we found that olfactory ensheathing cells transplanted into complete retrobulbar transections of the rat optic nerve mediated regeneration of severed retinal ganglion cell axons through the graft region. Although the regenerating axons were ensheathed by the transplanted cells, none of the regenerating axons became myelinated by either central or peripheral type myelin. In the present study we used the same operative procedure but transplanted Schwann cells instead of olfactory ensheathing cells. As with the olfactory ensheathing cell transplants the Schwann cells transplants also induced regeneration of the severed retinal ganglion cell axons into the graft region. In contrast to the situation with the olfactory ensheathing cell transplants, however, a considerable number of the regenerating axons became myelinated by peripheral type myelin produced by the transplanted Schwann cells. This observation identifies a further distinction between these two cell types which are phenotypically similar in many ways, but which have been shown to have major functional differences with regard to regeneration in spinal cord lesions.

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.

SCIP/Oct-6, Krox-20, and desert hedgehog mRNA expression during CNS remyelination by transplanted olfactory ensheathing cells.

Olfactory ensheathing cells (OECs), although having a separate developmental origin to Schwann cells, are able to generate myelin sheaths following transplantation into areas of CNS demyelination that are remarkably similar to those made by Schwann cells. The transcriptional control of Schwann cell myelination has been well documented, in particular the role of SCIP/Oct-6 and Krox-20. It is not known, however, whether these transcription factors are also expressed when OECs assume a myelinating phenotype. In this study, we addressed this question by using a transplantation approach to generate myelinating OECs and then examined the expression of SCIP/Oct-6 and Krox-20 mRNA by in situ hybridization using oligonucleotide probes. We also examined the expression of desert hedgehog (Dhh), a Schwann cell-derived signaling molecule that is responsible for regulating the development of the connective tissue elements in peripheral nerve, which bear similarities to the morphologies adopted by nonmyelinating transplanted cells. Our results indicate that both Krox-20 and Dhh mRNA are strongly expressed by transplanted OECs, with SCIP mRNA present at much lower levels. The expression of Krox-20 relative to the expression of P0 mRNA by the transplanted OECs is consistent with its playing a similar role in OEC myelination to that in Schwann cell myelination, while the expression of Dhh suggests a possible mechanism for the diverse morphologies that cells adopt following OEC transplantation into the damaged CNS. Taken together, our results provide further evidence for the close similarity of OECs and Schwann cells and suggest that, despite their separate origins, the manner in which they generate a peripheral-type myelin sheath involves similar regulatory mechanisms.

Spinal cord lesions of multiple sclerosis

The neuropathological findings of the spinal cord lesions of six human multiple sclerosis cases are described. The spinal cord was extensively necrotic and occasionally cystic in five remitting and relapsing cases. The lesions became more severe as the disease course prolonged and relapses increased. The spinal cords of two cases in particular, with a duration of illness of more than 5 years, were severely atrophic. In these cases, peripheral type remyelination was prominent, although central type remyelination was minimal. In contrast, in mouse spinal cords, in which experimental demyelination and remyelination were induced by ethidium bromide, the degree of central type remyelination and peripheral type remyelination was almost the same. Longitudinal sections of the transitional zone between the areas of central type remyelination and peripheral type remyelination contrained Ranvier nodes, in which central type myelin and peripheral type myelin were situated side by side around a central type axon. These transitional zones were similar to those of the normal transitional zone between the central nervous system and peripheral nervous system of the nerve roots. One chronic progressive case, despite the very long duration of illness, showed classical sharply demarcated demyelinated lesions with marked fibrillary gliosis. The spinal cord of this case was not atrophic and axons were well preserved.

Schwann cell-like myelination following transplantation of an olfactory bulb-ensheathing cell line into areas of demyelination in the adult CNS.

In this study we have transplanted a clonal olfactory bulb-ensheathing cell line into focal areas of the rat spinal cord which contain demyelinated axons but neither oligodendrocytes nor astrocytes. The cell line was created by retroviral incorporation of the temperature-sensitive Tag gene into FACS-sorted 04+ cells from 7-day-old rat pup olfactory bulb. The spinal cord lesions were obtained by injecting small volumes of ethidium bromide into the dorsal white matter of spinal cord previously exposed to 40 Grays of X-irradiation. Many of the axons were remyelinated by PO+ myelin sheaths 21 days after transplantation. Light and electron microscopy revealed cells engaging and myelinating axons in a manner highly reminiscent of Schwann cells within similar lesions. GFAP+ cells were also present within the lesion. This study provides the first in vivo evidence that olfactory bulb-ensheathing cells are able to produce peripheral-type myelin sheaths around axons of the appropriate diameter.

Extensive proliferation of peripheral type myelin in necrotic spinal cord lesions of multiple sclerosis

Peripheral type “remyelination” in the spinal cord was investigated in a 34-year-old woman with relapsing multiple sclerosis (MS) over 7 years following her initial presentation with myelopathy. Confined to the large necrotizing cord lesions involving the gray matter, there was prominent proliferation of peripheral type myelin, measuring up to one-third of the cross-sectional field of the cord. These nerve bundles with peripheral type myelin, which was devoid of glial fibrillary acidic protein immunoreactivity, consisted of relatively monotonous, small-caliber nerve fibers arranged in parallel along the long axis of the cord. The ratio of the myelin thickness to axonal diameter was not as small as that of the ordinary remyelination. Co-existing abundant neuroma formation indicated exuberant regenerative activity of the peripheral nerves. These findings suggest that the peripheral nerve fibers with their axons originating from nerve roots may enter the necrotic MS cord lesions in such a way as to manifest in spinal cord trauma. Relatively frequent occurrence of this extensive proliferation of peripheral type myelin in Japanese MS subjects appears to be related to the severity of tissue destruction experienced in Japanese as compared with that of occidental MS.

Autoradiographic and ultrastructural studies of areas of spinal cord occupied by Schwann cells and Schwann cell myelin

Schwann cells, peripheral-type myelin and connective tissue elements develop within the dorsal portion of the X-irradiated spinal cord in immature rats. Factors controlling the distribution of these elements within the irradiated site are not fully understood. In the present study [ 3H]thymidine autoradiography was used to examine proliferative activities of cells in these areas occupied by peripheral nervous system components, and correlative ultrastructural evaluations were made. At 15 and 20 days post-irradiation (P-I), the Schwann cells occupied the dorsolateral portions of the dorsal funiculi, and heavily labeled cells occurred throughout these areas. By 25 days P-I the Schwann cells extended ventrally into the depths of the dorsal funiculi and into the dorsal gray matter, and labeled cells were concentrated in the deeper portions of these areas. Ultrastructurally, the Schwann cells and peripheral-type myelin were more mature in the superficial portions where proliferative activity was diminished. In contrast, much less mature, peripheral-type myelin occurred in the depths where the labeled cells were concentrated. At 30 and 45 days P-I, labeled cells were much less frequent but usually occurred in the depths when observed. Similarly, a dorsal-ventral gradient in maturity of peripheral-type myelin was evident ultrastructurally. By 60 and 90 days P-I, labeling was rare, and mature Schwann cell myelin was present throughout the areas. Astrocytes and their processes were less numerous in regions invaded by Schwann cells, as compared to controls, and studies are in progress to evaluate the relationships between these glial elements and intraspinal peripheral nervous system components.

Remyelination in multiple sclerosis with peripheral type myelin.

Unusually large areas of remyelination occurred in demyelinated plaques within the spinal cord of a patient with longstanding multiple sclerosis (MS). The regenerated myelin was indistinguishable from that of the peripheral nerves by optical and electron microscopy. The myelinforming cells within the spinal cord, morphologically identical to the Schwann cells, could be traced to the spinal nerve roots. At the periphery of the remyelinated zones, astrocytic processes were present adjacent to the regenerated peripheral type myelinated fibers similar to those normally seen in the nerve roots close to the spinal cord. In addition, Rosenthal fibers were frequently seen in such zones. There was no appreciable clinical improvement in this patient attributable to the remyelination. The mechanism of such focal remyelination in this otherwise typical case of MS remains obscure.