Final Report Summary - OPTOGENRET (Microbial opsins for mammalian vision: Optogenetics in the retina)
Optogenetic reactivation of surviving retinal neurons using microbial opsins has the potential to re store vision independent of patient's specific mutations. One challenge of microbial opsin based vision restoration is the high light intensity requirement of these opsins. Blue light sensitive opsins therefore pose a safety risk to the retina. We lifted this challengge by using a novel red-shifted channelrhodopsin variant, called ReaChR and have shown the potential of photochemical damage is much lower for red-shifted wavelengths of light. Our results demonstrated, for the first time, that it is possible to trigger spike responses in the human retina with an optogenetic technique. Moreover, our data provides a first proof of principle that with an optogenetic approach it should be possible to stimulate the dendritic fields of midget ganglion cell separately, exploiting the central human retina's innate high-acuity circuitry. This method targeting the output neurons of the retina (retinal ganglion cells) is already predicted to give rise to above acuity above the legal threshold for blindness as we calculated in a recent collaboration.
Another major challenge of an optogenetic approach, just like any other approach aiming to restore vision- it is to restore a vision as close to natural vision as possible. We have contributed to this, by targeting microbial opsins to remaining degenerated cone photoreceptors in mice and primates as well second-order neurons (ON bipolar cells) which are still present at late stages of disease. These strategies utilize neural circuits upstream of ganglion cells. Although the cone directed approach is the most compelling in terms of restoring high acuity and natural like vision, it is limited by the life span of the remaining cones. Indeed, in some patients these 'dormant cones' stay alive for a very long time but in others, they end up disappearing at the latest stages of disease. ln collaboration with two teams of my host institute, we proposed a creative solution to this problem by combining optogenetics and regenerative medicine. We engineered stem cells to express microbial opsins. lndeed A major challenge in the treatment of retinal degenerative diseases, with the transplantation of replacement photoreceptors, is the difficulty in inducing the grafted cells to grow and maintain light sensitive outer segments (OS) in the host retina, which depends on proper interaction with the underlying retinal pigment epithelium (RPE). For a RPE-independent treatment approach, we introduced a hyperpolarizing microbial opsin into photoreceptor precursors from new-born mice and transplanted them into blind mice lacking the photoreceptor layer. These optogenetically-transformed photoreceptors were light responsive and their transplantation lead to the recovery of visual function, as shown by ganglion cell recordings and behavioral tests. Subsequently, we confirmed translational potential of this strategy by generating cone photoreceptors from human induced pluripotent stem cells (hiPSCs), expressing the chloride pump Jaws. After transplantation into blind mice, we observed light-driven responses at the photoreceptor and ganglion cell level. These results demonstrate that structural and functional retinal repair is possible by combining stem cell therapy and optogenetics opening new avenues for high acuity vision restoration.
Another major challenge of an optogenetic approach, just like any other approach aiming to restore vision- it is to restore a vision as close to natural vision as possible. We have contributed to this, by targeting microbial opsins to remaining degenerated cone photoreceptors in mice and primates as well second-order neurons (ON bipolar cells) which are still present at late stages of disease. These strategies utilize neural circuits upstream of ganglion cells. Although the cone directed approach is the most compelling in terms of restoring high acuity and natural like vision, it is limited by the life span of the remaining cones. Indeed, in some patients these 'dormant cones' stay alive for a very long time but in others, they end up disappearing at the latest stages of disease. ln collaboration with two teams of my host institute, we proposed a creative solution to this problem by combining optogenetics and regenerative medicine. We engineered stem cells to express microbial opsins. lndeed A major challenge in the treatment of retinal degenerative diseases, with the transplantation of replacement photoreceptors, is the difficulty in inducing the grafted cells to grow and maintain light sensitive outer segments (OS) in the host retina, which depends on proper interaction with the underlying retinal pigment epithelium (RPE). For a RPE-independent treatment approach, we introduced a hyperpolarizing microbial opsin into photoreceptor precursors from new-born mice and transplanted them into blind mice lacking the photoreceptor layer. These optogenetically-transformed photoreceptors were light responsive and their transplantation lead to the recovery of visual function, as shown by ganglion cell recordings and behavioral tests. Subsequently, we confirmed translational potential of this strategy by generating cone photoreceptors from human induced pluripotent stem cells (hiPSCs), expressing the chloride pump Jaws. After transplantation into blind mice, we observed light-driven responses at the photoreceptor and ganglion cell level. These results demonstrate that structural and functional retinal repair is possible by combining stem cell therapy and optogenetics opening new avenues for high acuity vision restoration.