A critical role for mitochondrial dynamics in cigarette smoke condensate-induced RPE senescence

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Its pathogenesis remains incompletely understood, partly due to the complex interplay of genetic risk, aging, and environmental stressors. Cigarette smoking (CS) is a major modifiable risk factor for AMD, yet the mechanism linking CS to disease progression remains unclear. We hypothesized that CS accelerates AMD pathogenesis by exacerbating cellular senescence in the retinal pigment epithelium (RPE), thereby driving age-related RPE dysfunction and degeneration. In this study, differentiated ARPE-19 cells or mice were exposed to low-dose cigarette smoke condensate (CSC) to model stress-induced RPE senescence. CSC induced senescence-associad RPE phenotypes characterized by increased senescence markers, mitochondrial dysfunction, and retinal functional impairment. RPE senescence phenotypes were also detected in mice exposed to 6 months of CS in the smoking chamber. CSC-induced RPE senescence was associated with a biphasic alteration in mitochondrial morphology, progressing from early mitochondrial fragmentation to late mitochondrial hyperfusion, as well as impaired mitophagy flux, reduced mitochondrial turnover, and decreased mitochondrial biogenesis. Mechanistically, CSC increased dynamin-related protein 1 (DRP1) phosphorylation and promoted cleavage of the mitochondrial phosphatase PGAM5, linking reduced DRP1-dependent fission to mitochondrial remodeling, elevated mitochondrial oxidative stress, and activation of mTOR signaling. Notably, overexpression of a DRP1 activity mutant (K38A) mimics the CSC-induced RPE senescence, while overexpression of the phosphodeficient DRP1-S637A mutant significantly attenuates both mTOR signaling and CSC-induced RPE senescence by restoring mitochondrial fission balance, improving mitochondrial quality-control responses, and reducing mitochondrial oxidative stress. Collectively, these findings identify impaired DRP1-dependent mitochondrial remodeling as a key mechanism linking CSC exposure to RPE senescence. While we confirmed the RPE senescence phenotype in mice after chronic CS exposure, the specific mechanisms observed in this study require further validation in a chronic CS model. These findings encourage future research into mitochondrial dynamics and RPE senescence in AMD, suggesting that modulating RPE mitochondrial dynamics holds therapeutic potential for delaying AMD progression.