GRP75-mediated ER-mitochondria coupling Promotes RPE Ferroptosis via GPX4 degradation in Age-related Macular Degeneration

Age-related macular degeneration (AMD) is a common threat to vision among the elderly, which is marked by retinal pigment epithelium (RPE) degeneration and geographic atrophy. Progressive loss of RPE cells is a defining hallmark of dry AMD, and although ferroptosis has emerged as a key pathogenic mechanism, its upstream triggers remain poorly understood. Here, we identify an organelle crosstalk-based mechanism that drives ferroptosis in RPE. We demonstrate that glucose-regulated protein 75 (GRP75), a critical protein in forming mitochondria-associated endoplasmic reticulum membranes (MAMs), was an upstream signal modulator of ferroptosis in RPE cells. GRP75 expression was significantly upregulated in NaIO₃-induced AMD models. Mechanistically, GRP75 upregulation enhanced calcium transfer from endoplasmic reticulum to mitochondria via the IP3R1-GRP75-VDAC1 complex, leading to mitochondrial Ca²⁺ overload, triggering mitochondrial permeability transition pore (mPTP) opening, and subsequent mtDNA leakage. Released mtDNA activated the cGAS-STING signaling and lead to the recruitment and activation of TBK1. Subsequently, TBK1 phosphorylated p62/SQSTM1 and initiated GPX4 degradation via both autophagy-lysosome and ubiquitin-proteasome systems. As a key negative regulator of ferroptosis, GPX4 degradation markedly accelerates RPE cell ferroptosis and promotes AMD progression. Knockdown of GRP75 effectively preserved GPX4 stability, attenuated lipid peroxidation, and restored retinal neurodegeneration in vivo. These findings establish GRP75 as a central mediator in ferroptosis and define a new ferroptosis suppression mechanism which may represent new strategies for therapeutic intervention in AMD and other ferroptosis-associated diseases.