The Role of c-fos in Cell Death and Regeneration of Retinal Ganglion Cells

PURPOSE. To investigate the effect of c-fos on apoptotic cell death and regeneration of damaged retinal ganglion cells (RGCs) in tissue culture of retinal explants. METHODS. Retinas from transgenic mice carrying the exogenous c-fos gene under the control of the interferon (IFN)-␣/␤ inducible Mx-promoter (Mx-c-fos), c-fos-deficient mice, and littermate control mice were dissected and cultured in a threedimensional collagen gel culture system, followed by an analysis of TdT-dUTP terminal nick-end labeling (TUNEL) staining and measurement of neurites that emerged from explants. RESULTS. Compared with littermate control mice, Mx-c-fos transgenic animals showed a higher ratio of TUNEL positivity in the RGC layer from early in the culture period that correlated with the small number of regenerating neurites. In contrast, the c-fos-null mutated mice showed a still-lower ratio of TUNEL-positive cells. Nevertheless, the number of regenerating neurites was significantly lower in the initial phase, although the drastic increase in density of neurite regeneration was observed in the late period of culture. CONCLUSIONS. These findings suggest that c-fos is involved in both apoptotic cell death and regeneration of damaged RGCs. Elucidation of the precise c-fos-mediated cascade involved in RGC apoptosis and regeneration is significant in realizing neuronal survival and regeneration. (Invest Ophthalmol Vis Sci

The Role of Schwann Cells During Retinal Ganglion Cell Regeneration Induced by Peripheral Nerve Transplantation

Purpose. To investigate the key role of Schwann cells in retinal ganglion cell regeneration elicited by peripheral nerve autotransplantation. Methods. Three kinds of autografts, Schwann-cell graft (intact sciatic nerve, consisting of living Schwann cells and their basal laminae), Schwann-cell-eliminated graft (consisting mainly of Schwann cell basal laminae) and partial Schwann-cell graft (consisting of basal laminae and diffusible factors secreted by Schwann cells) were prepared and autotransplanted to the adult rat optic nerve. The membrane specialization between regenerating axons and Schwann cells was observed by electron microscopy. The expression of cell adhesion molecules was demonstrated by Western blot analysis and immunohistochemistry. Results. Retinal ganglion cell axons were observed to regenerate into the Schwann-cell graft, in contact with Schwann cells but not into the Schwann-cell-eliminated graft. The regeneration was not observed in the empty basal laminae of the partial Schwann-cell graft. Most of regenerating axons contacted astrocytes in the optic nerve segment, and Schwann cells in the graft. At the interface of regenerating axon and Schwann cell, in addition to immunoreactivity of N-CAM and LI, short focal tight junctions were observed. Conclusions. These results suggested that viable Schwann cells are good substrate for retinal ganglion cell regeneration, the intimate contact with viable Schwann cell surface plays an important role in retinal ganglion cell regeneration, tight junctions, and cell adhesion molecules (LI, N-CAM) are observed between the regenerating axon and Schwann cell. Invest Ophthalmol Vis Sci. 1997;38:140T-1410. At is well known that the injured retinal ganglion cell (RGC) is incapable of regeneration. This inability appears to be related to the glial environment, in that RGC axons are known to regenerate into the autotransplanted peripheral nerve graft, providing evidence of the intrinsic capacity of RGC axons to regenerate when provided with a permissive environment. 1 " Although increasingly more is known about the factors and conditions that contribute to a successful regeneration in vitro, precise interactions between regenerating RGC axons and glial cells including Schwann cells in vivo are poorly understood. To observe the association of these factors with RGC regeneration in vivo, we transplanted three kinds of peripheral nerve autografts (Schwann-cell graft, Schwann-cell eliminated graft, and partial Schwanncell graft) into the cut end of the adult rat optic nerve. An intact fresh sciatic nerve segment was used for a Schwann-cell (SC) graft, which contains viable Schwann cells and their basal laminae for the entire length, so that diffusible factors, extracellular matrix molecules, and cell adhesion molecules on Schwann cell surfaces are thought to be present. Schwann-cell eliminated (SCE) grafts containing mainly Schwann cell basal laminae (i.e., extracellular matrix) were prepared by compressing sciatic nerve segments, which eliminates living Schwann cells. Particularly, we prepared partial Schwann cell (PSC) grafts, in which the Schwann-cell containing cellular and the Schwann-cell Investigative Ophthalmology & Visual Sci