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N. Caporale, K. D. Kolstad, I. Tochitsky, D. Dalkara, T. Huang, D. Trauner, R. H. Kramer, Y. Dan, E. Y. Isacoff, J. G. Flannery; LiGluR-Mediated Visual Responses in the Rodent Models of Inherited Blinding Diseases. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2524.
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© ARVO (1962-2015); The Authors (2016-present)
An alternative therapy for late stage blinding diseases, where the retina lacks photoreceptors, is to restore light responsiveness by expressing light-activated channels in the remaining neurons. To test this strategy, we used adeno-associated virus (AAV2) to deliver the engineered light-activated glutamate receptor, LiGluR, to retinal ganglion cells (RGCs) in the rd1 mouse model and in the tra-/-, cnga3-/-, opn4-/- triple knockout mouse. We then examined the restored visual responses at the level of the retina, visual cortex and behavior.
Either LiGluR or channelrhodopsin2 (ChR2) was cloned into an AAV-2 vector backbone. The virus (1012-1013 vg/mL) was injected into the vitreous of 6-month old mice. Experiments were conducted >3-weeks post-injection to allow for maximal expression. Recordings from RGCs were conducted in vitro, using multielectrode arrays. Recordings of cortical population responses were conducted in vivo, using low-impedance glass electrodes. Visual and behavioral responses were assessed with light at 380 and 500nm.
Expression of LiGluR in the RGCs restored visual responses in degenerated retinas. The spiking responses of individual RGCs were robust and reliable across trials. At the cortical level, visual responses were maximal at ~380nm (the peak sensitivity of LiGluR). Peak LiGluR-mediated cortical responses to a 300ms full-field flash were 50% of wild type amplitude and were significantly larger than those mediated by ChR2. Importantly, LiGluR also restored the pupillary reflex in the triple knockout mice.
Expression of the engineered light-sensitive channel, LiGluR, in RGCs can reinstate retinal and cortical visual responses, as well as the pupillary reflex, in animal models of inherited blinding diseases. In particular, the restoration of the pupillary reflex has important implications for the recovery of circadian rhythms. These results suggest that LiGluR is a promising candidate for therapeutics aimed at restoring visual function to patients in late stage retinal degeneration.
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