Genetic Reactivation of Cone Photoreceptors Restores Complex Visual Responses in Retinitis pigmentosa - Part 2

Abstract

Purpose: : The loss of photoreceptor function in retinal degeneration like Retinitis pigmentosa (RP) leads to incurable blindness. We evaluated the potential of a red-light sensitive chloride pump, eNpHR (enhanced Natronomonas pharaonis Halorhodopsin), to restore light evoked activity of cones in two mouse models of RP (rd1 and Cnga3^-/-; Rho^-/- double-knockout mice).

Methods: : eNpHR was delivered to photoreceptors using Adeno-Associated-Viruses (poster part 1). To test if eNpHR is functional in treated retinas we recorded light responses from photoreceptors, ganglion cells and the visual cortex, and performed behavioral experiments (poster part 3). We also tested if eNpHR is functional in photoreceptors of cultured human retinas using lentiviral vectors.

Results: : Red-light stimulation induced a robust hyperpolarizing current in eNpHR-expressing photoreceptors. Light responses could be recorded in ON, OFF and ON-OFF ganglion cells in the eNpHR treated retinas, confirming that both ON and OFF pathways are functional. Resensitized photoreceptors drove sophisticated retinal circuit functions including center-surround receptive fields and directional selectivity. These retinal pathways activated cortical circuits and mediated visually guided behavior (poster part 3). In the parafoveal region of human ex vivo retinas, brightly labeled photoreceptors displayed large photocurrents and photovoltages with spectral tuning reflecting eNpHR activation.

Conclusions: : We have demonstrated that the targeted expression of eNpHR in photoreceptor cells is able to restore light sensitivity and the image processing capability of the retina in the absence of functional photoreceptors. Light-induced activity was observed at the ganglion cell level, in the visual cortex and at the behavioral level. Using human ex vivo retinas we showed that Halorhodopsin can reactivate light-insensitive human photoreceptors.

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