Removing the Requirement for Subretinal Injection: Intravitreal Delivery of Engineered AAV-GDNF Can Provide Sustained Photoreceptor Protection Without Retinal Detachement

Abstract

Purpose: : Gene therapy via secretion of neurotrophic factors (NFs) has significant potential for treating many retinal degenerations without requiring knowledge of the specific disease mechanism. In retinal degenerations, Müller glia (MG) survive late in the disease, and their close physical contact with all retinal cell types makes them strong candidates for secreting NF or anti-angiogenic factors. In addition, MG extend radially through the retina, allowing viral transduction from their vitreal endfeet, which avoids the detachment-related trauma of subretinal injections. Furthermore, intravitreal injection yields broad pan-retinal expression not available with a focal subretinal ‘bleb’. We engineered a MG-specific AAV vector capable of high-efficiency MG transduction from the vitreous and explored its therapeutic potential. This AAV vector promotes secretion of the neurotrophin GDNF from MG in a transgenic rat model of retinitis pigmentosa.

Methods: : The GDNF protein concentration in retinal homogenates and vitreal fluid of injected animals was ~2500 pg/ml, (10-fold greater than previous studies of GDNF-induced rescue). Furthermore, significant anatomic and functional improvement was observed by histopathology and ERG in eyes treated with ShHY10- GDNF. Moreover, this rescue persisted for a significantly longer duration (>5 months post-injection) than previous studies.

Results: : The GDNF protein concentration in retinal homogenates and vitreal fluid of injected animals was ~2500 pg/ml, (10-fold greater than previous studies of GDNF-induced rescue). Furthermore, significant anatomic and functional improvement was observed by histopathology and ERG in eyes treated with ShHY10- GDNF. Moreover, this rescue persisted for a significantly longer duration (>5 months post-injection) than previous studies.

Conclusions: : Neuroprotection of photoreceptors by GDNF overexpression from MG is a highly promising strategy to slow retinal degeneration. The use of MG-specific AAV from the vitreous is advantageous in terms of safety, efficacy, and longevity. Therefore, the less invasive intravitreal approach has potential for the treatment of retinal degenerations of known and unknown etiology

Keywords: degenerations/dystrophies • gene transfer/gene therapy • Muller cells