Regeneration of ganglion cell axons into a peripheral nerve graft alters retinal expression of glial markers and decreases vulnerability to re-axotomy

Abstract

Purpose: To compare the effect of cutting the optic nerve versus replacing the cut optic nerve with a peripheral nerve (PN) graft on retinal glial markers, and to determine whether the PN graft can stabilize regenerating retinal ganglion cells (RGCs), thus preventing their death following re-axotomy.

Methods: Retinas harvested after ganglion cell regeneration into a sciatic nerve graft were compared to untreated control retinas and retinas obtained following optic nerve axotomy. Glial-specific proteins such as glial fibrillary acidic protein (GFAP), Bcl-2 and complement-3 receptor (Ox-42) were examined using immunohistochemistry. Ganglion cells that survived the second axotomy were quantified on retinal flat mounts by retrograde labeling from the graft.

Results: GFAP expression in astrocytes and Muller cells was elevated in axotomized retinas when compared to controls, and an additional up-regulation in Muller cells was found in retinas following ganglion cell regeneration. Increased GFAP expression in retinas containing regenerated neurons was accompanied by increased Bcl-2 expression with latter being confined to Muller cells. Moreover, re-axotomy of the regenerated axons within the graft did not result in significant retrograde degeneration of RGCs within 28 days.

Conclusions: The data suggest that the graft stabilizes the regenerating RGCs to an extent reminiscent of peripheral neurons, a process that may involve the interaction between neuronal and glial elements.