Reserpine maintains photoreceptor survival in retinal ciliopathy by resolving proteostasis imbalance and ciliogenesis defects

Abstract

Ciliopathies manifest from sensory abnormalities to syndromic disorders with multi-organ pathologies, with retinal degeneration a highly penetrant phenotype. Photoreceptor cell death is a major cause of incurable blindness in retinal ciliopathies. To identify drug candidates to maintain photoreceptor survival, we performed an unbiased, high-throughput screening of over 6,000 bioactive small molecules using retinal organoids differentiated from induced pluripotent stem cells (iPSC) of rd16 mouse, which is a model of Leber congenital amaurosis (LCA) type 10 caused by mutations in the cilia-centrosomal gene CEP290. We identified five non-toxic positive hits, including the lead molecule reserpine, which maintained photoreceptor development and survival in rd16 organoids. Reserpine also improved photoreceptors in retinal organoids derived from induced pluripotent stem cells of LCA10 patients and in rd16 mouse retina in vivo. Reserpine-treated patient organoids revealed modulation of signaling pathways related to cell survival/death, metabolism, and proteostasis. Further investigation uncovered dysregulation of autophagy associated with compromised primary cilium biogenesis in patient organoids and rd16 mouse retina. Reserpine partially restored the balance between autophagy and the ubiquitin-proteasome system at least in part by increasing the cargo adaptor p62, resulting in improved primary cilium assembly. Our study identifies effective drug candidates in preclinical studies of CEP290 retinal ciliopathies through cross-species drug discovery using iPSC-derived organoids, highlights the impact of proteostasis in the pathogenesis of ciliopathies, and provides new insights for treatments of retinal neurodegeneration.

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“…Among the drugs tested, reserpine showed the best output in terms of photoreceptor survival, which was also confirmed in organoids derived from affected patients and in vivo animal models. The authors also found that reserpine modulates two pathways that are critical for protein homeostasis, which is mainly regulated through the degradative activity of autophagy and ubiquitin-proteasome system, cited previously [89]. Clinical trials will be necessary to evaluate the real efficacy of reserpine in retinal diseases.…”

“…Even though pharmaceutical research still relies on animal models, progress has been made to identify in vitro cell cultures that can be used in pre-clinical studies. For example, the organoids obtained from retinal iPSC derived from patients [89] were shown to be a valid system for drug screening, and it allowed the identification of reserpine as a possible treatment for retinal disease.…”

“…Retinal ciliopathies [88] cause irreversible blindness from a young age; hence, many researchers are focused on finding new drugs and therapies. In 2023, Chen and co-authors [89] published the results of a screening of over 6000 existing drugs for their ability to improve photoreceptor survival in the retinal organoids derived from a mice model for ciliopathy [90]. Among the drugs tested, reserpine showed the best output in terms of photoreceptor survival, which was confirmed in organoids derived from affected patients and in vivo animal models.…”

Pathways controlling neurotoxicity and proteostasis in mitochondrial complex I deficiency

“…Alterations in the ubiquitin/proteasome and autophagy/lysosome systems have been documented in various genetic forms of retinal degeneration and in other aging-dependent ocular diseases [ 54 , 55 ], as has oxidative stress and mitochondrial dysfunction [ 42 , 43 ], suggesting fundamental connections among these pathways. A functionally important relationship between altered proteostasis and photoreceptor vulnerability was recently suggested by a chemical screening approach in an induced pluripotent stem cell-derived model of retinal degeneration caused by genetic ciliary dysfunction, which identified reserpine as both promoting photoreceptor survival and normalizing proteostasis [ 56 ].…”

Cell type-focused compound screen in human organoids reveals molecules and pathways controlling cone photoreceptor death

“…These two objectives rely on efficient and large-scale production of human organoids, as well as the comprehensive recording and analysis of phenotypic changes within 3D tissues. Noteworthy progress has been made in screening for compounds using mouse intestinal organoids 10 and dissociated cells from mouse retinal organoids 11 , contributing to our understanding of organ biology and allowing for potential therapy development. However, therapies developed in mice do not always translate to humans due to variation in cell types and molecular pathways between the two species [12][13][14] .…”