Abstract
Abstract: :
Purpose: We previously demonstrated that brain–derived neurotrophic factor and its receptor, TrkB, promote the survival of retinal ganglion cells (RGC) via the mitogen–activated protein kinase (MAPK) pathway. The goal of the present study was to determine the effect of constitutive activation of MAPK on RGC survival and axon regeneration after acute optic nerve lesion. Methods: Adeno–associated virus (AAV) containing genes that encoded constitutively active MEK (AAV.MEK–ca), wild–type MEK (AAV.MEK–wt) or green fluorescent protein (AAV.GFP) were injected into the vitreous of adult female Sprague–Dawley rats. For analysis of cell survival, RGCs were backlabeled with FluoroGold and quantified on whole–mounted retinas at 1, 2 and 4 weeks after optic nerve transection. To investigate nerve regeneration, RGC axons were labeled with the anterograde tracer cholera–toxin ß–subunit (CTß) and regenerating axons were quantified in optic nerve sections at 2 weeks after micro–crush lesion. Results: MEK–ca gene delivery markedly increased RGC survival at all times examined. In the superior retinal quadrant, the site of vector administration, MEK–ca expression protected up to 93% of RGCs at 2 weeks after axotomy and 40% of RGCs at 4 weeks post–injury. Importantly, we found a tight correlation between MAPK activation and neuronal survival: an average of 86% of surviving RGCs also expressed AAV.MEK–ca at 4 weeks after axotomy. The number of RGC axons extending distal to the lesion site in retinas treated with AAV.MEK–ca was not significantly different from controls. Conclusions:Our data indicate that selective activation of neuroprotective signaling pathways, such as the MAPK, is an effective strategy to promote RGC survival. While the MAPK pathway is directly involved in RGC neuroprotection, other signaling components appear to be required for RGC axon regeneration.
Keywords: gene transfer/gene therapy • ganglion cells • neuroprotection