Drug screening in iPSC-derived retinal organoids identifies reserpine to maintain photoreceptor survival through restoration of proteostasis

Abstract

Purpose : Loss of vision in early-onset inherited retinal diseases is primarily associated with degeneration of the light-sensing photoreceptors. A common cause of photoreceptor degeneration is the disruption of biogenesis and/or function of the outer segment (OS). How a compromised OS leads to photoreceptor cell death remains largely unclear, and a better understanding of this process is essential for developing effective treatments. As a specialized primary cilium of photoreceptors, the OS senses external environment and modulates diverse signaling pathways. Therefore, we hypothesize that: (1) loss of the OS disrupts signaling pathway(s) and results in photoreceptor cell death; and (2) restoration of compromised pathway(s) should maintain photoreceptor survival.

Methods : We performed an unbiased screening of over 6000 small-molecule drugs for maintaining photoreceptor survival in retinal organoids differentiated from induced pluripotent stem cells of the rd16 mouse, a model of Leber congenital amaurosis (LCA) caused by CEP290 mutations. Positive hits were validated in CEP290-LCA patient organoids and in in vivo rd16 mouse retina by morphological and/or functional assays. The mechanism of action of the lead compound was interrogated by transcriptomics, immunostaining, and immunoblotting.

Results : The lead compound reserpine, identified in the primary screens, could partially rescue photoreceptors in CEP290-LCA patient organoids and rd16 mouse retina in vivo. Reserpine treatment resulted in modulation of signaling pathways related to cell death/survival, metabolism, and proteostasis. Our studies uncovered misregulation of autophagy in patient organoids and rd16 mouse retina and its association with compromised OS biogenesis. Reserpine partially restored the balance between autophagy and the ubiquitin-proteasome system, at least in part through the common cargo adaptor p62, resulting in improved OS biogenesis.

Conclusions : We identified an effective drug candidate to rescue CEP290-LCA photoreceptors in vitro and in vivo. The drug action is mediated at least in part through modulation of the misregulated autophagy pathway. Our study highlights a key role of loss of proteostasis in photoreceptor degeneration and suggests druggable targets for treatments of inherited retinal diseases.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.