Gene therapy with constitutively active MEK protects retinal ganglion cells in experimental glaucoma.

Abstract

Abstract: : Purpose: We recently demonstrated that stimulation of the mitogen activated protein kinase (MAPK) pathway is critical for neurotrophin–induced retinal ganglion cell (RGC) survival. Here we tested if gene transfer of a constitutively active form of MEK, an upstream activator of MAPK, protected RGCs in experimental glaucoma. 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 chamber of adult male Brown Norway rats. Two weeks later, animals received an injection of hypertonic saline into episcleral veins to induce chronic intraocular pressure (IOP) elevation. RGC survival was assessed at 2 and 4 weeks after IOP increase using two complementary methods: i) quantification of RGCs backlabeled with diI, a long–lasting fluorescent marker, and ii) quantification of axonal profiles in optic nerves. Activation of the MAPK pathway and c–fos expression were examined by imunocytochemistry and Western blot analysis. Results: MEK–ca gene transfer markedly increased RGC survival in glaucomatous rats. For example, 2 weeks after IOP elevation AAV.MEK–ca protected 60% of RGCs in the entire retina whereas administration of AAV.MEK–wt or AAV.GFP promoted 34% or 36% survival, respectively. More importantly, up to 89% of RGCs were protected in the superior retinal quadrant, the site of viral vector administration. This survival effect correlated with selective activation of the MAPK pathway and c–fos expression in RGCs following MEK–ca gene delivery. Conclusions: Our data indicate that constitutive stimulation of the MAPK pathway, via MEK–ca gene transfer, is an effective neuroprotective strategy for injured RGCs in experimental glaucoma.

Keywords: gene transfer/gene therapy • ganglion cells • signal transduction