In vitro high-content screening reveals miR-429 as a protective molecule in photoreceptor degeneration

Inherited retinal diseases (IRDs) are clinically and genetically heterogeneous disorders characterized by progressive photoreceptor degeneration and irreversible vision loss. MicroRNAs (miRNAs), a class of endogenous non-coding RNAs with post-transcriptional regulatory properties, are known to play a major role in retinal function, both in physiological and pathological conditions. Given their ability to simultaneously modulate multiple molecular pathways, miRNAs represent promising therapeutic tools for disorders with high genetic heterogeneity, such as IRDs. In the present study, we performed high-content imaging (HCI) screening to assess the impact of miRNA overexpression on a photoreceptor cell line undergoing light-induced degeneration. More than 1,200 miRNAs were assayed for putative protective effects in light-stressed 661W photoreceptor-like cells, and the top-performing miRNAs were further validated in independent in vitro assays. miR-429 showed the strongest cell-protective effect in vitro. Adeno-associated viral vector-mediated subretinal delivery of miR-429 in the Rho ^P23H/+ IRD mouse model preserved electrophysiological responses and was associated with reduced inflammatory processes in the retina. We demonstrate that the HCI in vitro assay we devised is a reliable screening method to select candidate molecules for mutation-independent therapeutic approaches for retinal disorders. Moreover, our data indicate that miR-429 represents a potential therapeutic target against photoreceptor degeneration.