ADORA2A activation restores lysosomal function and photoreceptor outer segment degradation in stressed retinal pigment epithelium

Abstract

Background Age-related macular degeneration (AMD) involves early retinal pigment epithelium (RPE) dysfunction and impaired processing of photoreceptor outer segments (POS). We investigated whether ADORA2A regulates post-ingestive POS handling and lysosomal recovery under AMD-relevant stress. Methods A2E-stressed ARPE-19 cells, primary porcine RPE cells, and a sodium iodate-induced mouse model were studied. ADORA2A was activated with CGS21680 and inhibited with ZM241385. POS handling, LC3B/Rubicon association with POS, lysosomal function, Rubicon depletion, chronic stress phenotypes, and retinal protection were assessed. Results A2E increased ADORA2A expression while preserving receptor-dependent cAMP responsiveness. CGS21680 had modest effects on early POS binding and uptake but enhanced post-ingestive POS clearance and rhodopsin degradation; these effects were attenuated by ZM241385 and ADORA2A knockdown. CGS21680 increased LC3B and Rubicon association with POS-containing structures, improved lysosomal acidification, and restored DQ Green BSA processing, Cathepsin D activity, and V-ATPase-associated assembly. Bafilomycin A1 increased LC3-II and p62 accumulation and impaired CGS21680-associated POS clearance, supporting lysosome-dependent turnover. Rubicon depletion attenuated CGS21680-associated improvements in POS clearance and lysosomal acidification. CGS21680 also reduced chronic stress-associated autofluorescence, oxidative stress, apoptosis, and junctional disruption. These protective effects were reproduced in primary RPE cells. In sodium iodate-injured mice, CGS21680 preserved outer retinal structure, reduced FITC-BSA leakage, improved electroretinographic responses, and was accompanied by increased CREB phosphorylation and recovery of Cathepsin D proteolytic competence. Conclusion ADORA2A activation promotes Rubicon-associated, lysosome-dependent LC3 processing of internalized POS and restores lysosomal degradative competence, supporting ADORA2A as a potential therapeutic target for early AMD.