Different factors promote axonal regeneration of adult rat retinal ganglion cells after lens injury and intravitreal peripheral nerve grafting

We have investigated the differential mediators of the neurotrophic effects of intravitreal peripheral nerve grafting and lens injury on adult rat retinal ganglion cells (RGC). Lens injury and intravitreal peripheral nerve grafting both stimulated RGC neurite growth in vitro and axon regeneration past the optic nerve lesion site in vivo concomitant with activation of retinal glia and invasion of macrophages into the eye. These observations, together with the results of coculture studies using a macrophage-free intact peripheral nerve segment, a macrophage-free intact lens, a macrophage-rich peripheral nerve segment, or a macrophage-rich injured lens in retinal cultures suggest that the stimulation of RGC axon regeneration by lens injury and intravitreal peripheral nerve grafting share a common macrophage-derived component overlain by distinct lens-derived and peripheral nerve-derived neurotrophic factors, respectively. RGC axon regeneration following lens injury and intravitreal peripheral nerve grafting was similar in vivo, correlating with similar retinal glia activation whereas, in vitro, the level of RGC neurite outgrowth was significantly higher following intravitreal peripheral nerve grafting compared with lens injury, concomitant with the presence of increased numbers of activated retinal glia. This suggests that in vivo RGC axon regeneration induced by lens injury and peripheral nerve grafting may be limited, in part, by factors derived from activated retinal glia.