Involvement of FSP1-CoQ₁₀-NADH and GSH-GPx-4 pathways in retinal pigment epithelium ferroptosis

Retinal pigment epithelium (RPE) degeneration plays an important role in a group of retinal disorders such as retinal degeneration (RD) and age-related macular degeneration (AMD). The mechanism of RPE cell death is not yet fully elucidated. Ferroptosis, a novel regulated cell death pathway, participates in cancer and several neurodegenerative diseases. Glutathione peroxidase 4 (GPx-4) and ferroptosis suppressor protein 1 (FSP1) have been proposed to be two main regulators of ferroptosis in these diseases; yet, their roles in RPE degeneration remain elusive. Here, we report that both FSP1-CoQ₁₀-NADH and GSH-GPx-4 pathways inhibit retinal ferroptosis in sodium iodate (SIO)-induced retinal degeneration pathologies in human primary RPE cells (HRPEpiC), ARPE-19 cell line, and mice. GSH-GPx-4 signaling was compromised after a toxic injury caused by SIO, which was aggravated by silencing GPx-4, and ferroptosis inhibitors robustly protected RPE cells from the challenge. Interestingly, while inhibition of FSP1 caused RPE cell death, which was aggravated by SIO exposure, overexpression of FSP1 effectively protected RPE cells from SIO-induced injury, accompanied by a significant down-regulation of CoQ₁₀/NADH and lipid peroxidation. Most importantly, in vivo results showed that Ferrostatin-1 not only remarkably alleviated SIO-induced RPE cell loss, photoreceptor death, and retinal dysfunction but also significantly ameliorated the compromised GSH-GPx-4 and FSP1-CoQ₁₀-NADH signaling in RPE cells isolated from SIO-induced RPE degeneration. These data describe a distinct role for ferroptosis in controlling RPE cell death in vitro and in vivo and may provide a new avenue for identifying treatment targets for RPE degeneration.