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K. D. Kolstad, K. P. Greenberg, K. I. Guerin, I. Zolfaghar, J. G. Flannery; Targeted Expression of GDNF to Retinal Müller Cells Slows Degeneration in the S334-4 Rat Model of RP. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4609.
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Sustained secretion of neurotrophic factors from Müller glia holds promise for slowing photoreceptor degeneration in the diseased retina. Previous gene therapy studies have targeted epithelia and neurons for expression of trophic factors. In earlier studies, human GDNF ( hGDNF) has been shown to be a potent neuroprotective agent in the retina. Müller glia span the entire retina and provide endogenous trophic support by secreting survival factors to photoreceptors. Thus, we expect that overexpression of hGDNF by gene transfer to retinal glia will enhance these protective affects.
hGDNF and hGDNF-GFP fusion constructs driven by the mouse GFAP promoter were cloned into a lentiviral vector and packaged with the VSV-G envelope glycoprotein. High titer (109-10 10 TU/mL) mGFAP.GDNF/GDNF-GFP fusion and control mGFAP.GFP vectors were injected (3µl) into the superior subretinal space of S334 rats at p15. The S334 transgenic rat model exhibits retinal degeneration resulting from expression of a truncated form of rhodopsin. We are evaluating the rescue effect of Müller cell specific secretion of GDNF by ERG and histopathology in lenti-GDNF injected and lenti-GFP control animals. Cell specificity of transduction has been assessed by immunochemistry and direct visualization of GFP expression in fusion and control injected eyes.
In glial cell cultures, lentivirus carrying the hGDNF.GFP fusion gene drives robust GFP expression. Following in vivo injection of LV mGFAP.GFP and mGFAP.GDNF.GFP fusion vectors, expression is seen in retinal Müller cells and few RPE cells. Secretion and function of the GDNF-GFP fusion protein is currently being assessed. ERG data at one month post injection indicates a preservation of the a and b-wave amplitudes in LV-GDNF injected eyes compared to LV-GFP injected controls.
LV vectors facilitate targeted gene transfer to RMCs. Preliminary data indicates that LV mediated delivery of hGDNF to Müller cells slows retinal degeneration in an animal model of ADRP, showing promise as a potential clinical therapy.
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