Genetic Reactivation of Cone Photoreceptors Restores Complex Visual Responses in Retinitis pigmentosa - Part 1

Abstract

Purpose: : In retinal degenerative diseases like Retinitis pigmentosa (RP) rod photoreceptors die early whereas light-insensitive, morphologically altered cone photoreceptors persist. Here we show a "single gene" therapeutic intervention to cones in RP that is independent of the primary genetic lesion in rods.

Methods: : We use adeno-associated-virus (AAV)-mediated gene transfer to express an archaebacterial halorhodopsin (eNpHR) specifically in cones in two mouse models of RP (rd1 and Cnga3^-/-; Rho^-/- double-knockout mice). Photoreceptor-specific promoters restricted eNpHR-expression to cones. Resensitized retinas were analyzed by molecular biological, imaging and electrophysiological techniques. Furthermore, we could translate our approach to postmortem ex vivo human retinas.

Results: : We show that the targeted expression of archaebacterial halorhodopsin (enhanced NpHR) to cones can substitute for the native phototransduction cascade and restore their light sensitivity. Resensitized photoreceptors activate all retinal cone pathways (the natural ON and OFF pathway), drive sophisticated retinal circuit functions (poster part 2) including directional selectivity, activate cortical circuits and mediate visually guided behaviors (poster part 3). Using human ex vivo retinas we show that halorhodopsin can reactivate light-insensitive human photoreceptors.

Conclusions: : Our results demonstrate that, despite the diverse genetic origin of RP, the targeted expression of a single gene can restore significant functionality to the visual system following degenerative changes.

Keywords: gene transfer/gene therapy • retinal degenerations: cell biology • photoreceptors