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. 2013 Jan 15;8(2):177-85.
doi: 10.3969/j.issn.1673-5374.2013.02.011.

Role of Endogenous Schwann Cells in Tissue Repair After Spinal Cord Injury

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Free PMC article

Role of Endogenous Schwann Cells in Tissue Repair After Spinal Cord Injury

Shu-Xin Zhang et al. Neural Regen Res. .
Free PMC article

Abstract

Schwann cells are glial cells of peripheral nervous system, responsible for axonal myelination and ensheathing, as well as tissue repair following a peripheral nervous system injury. They are one of several cell types that are widely studied and most commonly used for cell transplantation to treat spinal cord injury, due to their intrinsic characteristics including the ability to secrete a variety of neurotrophic factors. This mini review summarizes the recent findings of endogenous Schwann cells after spinal cord injury and discusses their role in tissue repair and axonal regeneration. After spinal cord injury, numerous endogenous Schwann cells migrate into the lesion site from the nerve roots, involving in the construction of newly formed repaired tissue and axonal myelination. These invading Schwann cells also can move a long distance away from the injury site both rostrally and caudally. In addition, Schwann cells can be induced to migrate by minimal insults (such as scar ablation) within the spinal cord and integrate with astrocytes under certain circumstances. More importantly, the host Schwann cells can be induced to migrate into spinal cord by transplantation of different cell types, such as exogenous Schwann cells, olfactory ensheathing cells, and bone marrow-derived stromal stem cells. Migration of endogenous Schwann cells following spinal cord injury is a common natural phenomenon found both in animal and human, and the myelination by Schwann cells has been examined effective in signal conduction electrophysiologically. Therefore, if the inherent properties of endogenous Schwann cells could be developed and utilized, it would offer a new avenue for the restoration of injured spinal cord.

Keywords: Schwann cells; astrocytes; axonal regeneration; bone marrow stromal cell; cell transplantation; grant-supported paper; myelination; neural regeneration; neuroregeneration; olfactory ensheathing cells; rat; rose Bengal; scar ablation; spinal cord injury; tissue repair.

Conflict of interest statement

Conflicts of interest: None declared.

Figures

Figure 1
Figure 1
Endogenous repaired tissue in cross section from injury epicenter of a rat (6 weeks after 25 mm contusion; hematoxylin-eosin staining). (A) The repaired tissue located at the dorsal part of damaged cord, connects bilaterally to the spared tissue, and neighbors the lesion cavity, which is surrounded by the glial scar (arrows) and spared tissue. (B) Under higher magnification, the repaired tissue can be divided into three different zones: fibrotic, cellular and axonal. The fibrotic zone is surrounded by a U-shape cellular zone. The axonal zone does not appear clearly due to its small amount of axons at this moment. (C) The cellular zone, connecting to both spared tissue (*) and fibrotic zone, consists mainly of Schwann cells migrating from dorsal root (arrowheads). (D) Regenerating axons (myelinated fibers) with hematoxylin-eosin staining are difficult to identify at the axonal zone (arrowheads), cellular zone and fribrotic zone (arrows). DR: Dorsal root; VR: ventral root. Magnifications: 4 × (A), 10 × (B), 20 × (C), 40 ×(D). Replicated from reference [18] with permission.
Figure 2
Figure 2
Fluorescent images of Schwann cells and axons. Neighboring cross paraffin sections of injury epicenter from a rat 14 weeks after contusion were immunostained with antibodies against p75NTR (Schwann cells), neurofilament and glial fibrillary acidic protein (A) and routinely stained with hematoxylin-eosin (B) as comparison. A’ and B’ are the local magnifications of A and B, respectively. Schwann cells derived from the dorsal root are distributed in three zones of the repaired tissue (with higher density in the cellular zone) and spared tissue. Axons are also present in three zones of the repaired tissue and spared tissue, but the axonal zone (regenerating axons) and spared tissue (spared or regenerating axons) have a higher density of axons. ST: Spared tissue. Magnifications: 4 × (A, B), 40 × (A’, B’). Replicated from reference [18] with permission.
Figure 3
Figure 3
P0-positive myelin sheaths in different areas of rats with chronically contused spinal cord (P0 immunostaining; A–D, cross section; E, F: horizontal section). (A) In the fibrotic zone, P0-positive myelin sheaths (myelinated fibers, dark brown in color) form small fascicles encircled by a layer of fibroblasts (arrowheads), showing the PNS style. (B) P0-positive myelin sheaths in the cellular zone do not form fascicles but scatter among densely compacted Schwann cells. (C) In the axonal zone, numerous P0-positive myelin sheaths are aggregated and are dense in appearance. (D) In the spared tissue, the P0-positive myelin sheaths (regenerating or demyelinated axons) are distributed unevenly. (E) P0-positive myelin sheaths found 15 mm caudal to the injury site. They are distributed along with a small longitudinal cyst (*) in the dorsal funiculus. The arrows indicate the direction of Schwann cell movement. DR: Dorsal root. (F) The local magnification of E, clearly showing the P0-positive myelin sheaths. The node of Ranvier is pointed by arrowheads. Nuclei of both Schwann cells and other cells of spinal cord were stained in purple with hematoxylin. Magnifications: 4 × (E), 40 × (A–D, F). Replicated from reference [18] with permission.

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