FSP1 controls retinal pigment epithelium degeneration: role of ferroptosis

Abstract

Purpose : Retinal pigment epithelium (RPE) degeneration is central in the pathogenesis of age-related macular degeneration. Ferroptosis is an iron-dependent novel regulated cell death pathway attributed to lipid peroxidation and plays an important role in eye diseases. This study aimed to elucidate the role of ferroptosis suppressor protein-1 (FSP1) in RPE degeneration. Methods : Primary human retinal pigment epithelial cells (HRPEpiC) and ARPE-19 exposed to sodium iodate (SI) were used as the in vitro RPE degeneration model. C57BL/6J mice receiving intraperitoneal injection of SI were chosen as the in vivo RPE degeneration model. Ferroptosis inhibitors and glutathione peroxidase-4 (GPx-4) silencing RNAs were used to test the involvement of ferroptosis. Levels of intracellular labile iron, lipid peroxidation, glutathione, coenzyme Q10 (CoQ10), and nicotinamide adenine dinucleotide hydrogen (NADH) were measured. Protein expressions were assessed by immunohistochemistry and Western blot. Retinal function was assessed by electroretinography (ERG). Statistical analysis was performed using SPSS. Results : SI triggered RPE cell damage, accompanied by increased levels of intracellular labile iron, glutathione disulfide (GSSG), and lipid peroxidation but decreased amount of cytoplasmic glutathione and GPx-4. Ferroptosis inhibitors significantly alleviated SI-induced cell damage, with the restoration of the aforementioned markers. However, silencing GPx-4 aggravated SI-induced cell damage. Although inhibition of FSP1 aggravated SI-induced cell damage, overexpression of FSP1 ameliorated cell damage with decreased lipid peroxidation accompanied by recovery of CoQ10 and NADH. Additionally, SI induced a dramatic reduction in retinal function, retinal thickness, and levels of ferroptosis suppressors, with significantly elevated RPE labile iron, GSSG, and lipid peroxidation in mice. Most notably, ferrostatin-1 markedly restored retinal thickness and ERG function, along with elevated levels of ferroptosis suppressors such as GPx-4 and FSP1. These data further confirmed the distinct role of ferroptosis in RPE degeneration. Conclusions : FSP1 plays an important role in SI-induced RPE degeneration models in vitro and in vivo. Activation of either FSP1/CoQ10/NADH or GSH/GPx-4 pathway effectively protected SI-induced damages in HRPEpiC cells, ARPE-19 cells, and mouse retina, supporting ferroptosis as a novel target for future AMD treatment.