Extracellular matrix stiffness modulates angiogenic properties of the retinal pigment epithelium

Physiological and pathological processes, such as aging and basal deposit aggregation in degenerative retinal diseases like age-related macular degeneration (AMD), alter the mechanical properties of Bruch's membrane (BrM). These mechanical changes in the extracellular matrix (ECM) significantly affect retinal pigment epithelial (RPE) cells, influencing their morphology, transcriptome and angiogenic behavior. ARPE-19 cells were cultured on hydrogels of physiological stiffness (30 and 80 kPa) and on conventional tissue culture plastic (TCP) for comparison. Gene expression was analyzed by droplet digital PCR (ddPCR), while protein-level changes were examined using immunofluorescence (IF), Western blotting (WB) and enzyme-linked immunosorbent assays (ELISA). Stiffness-dependent modulation of endothelial cells by RPE-conditioned media was investigated using in vitro angiogenesis assays. RPE cells cultured on softer substrates exhibited enhanced angiogenic properties, including increased expression of CD44 and vascular endothelial growth factor (VEGF). In contrast, stiffer substrates promoted antiangiogenic responses, associated with altered distribution of thrombospondin 1 (THBS1). These findings underscore the importance of ECM mechanics in modulating angiogenic signaling and highlight their potential relevance in retinal pathologies such as AMD. Local disruptions in adhesion or mechanical cues, potentially caused by basal deposits, may contribute to proangiogenic behavior even in the context of globally increased tissue stiffness with age.