The study shows that palmitic acid, a common saturated fat, can worsen eye damage in diabetes by triggering a type of cell death called ferroptosis through a chemical change (palmitoylation) of a protein called Keap1. This effect was seen in mouse models and human retinal cells, and blocking Keap1 reduced the damage.

Retinal microvascular endothelial cells (RMECs) injury caused by sustained hyperglycemia was the initial factor in diabetic retinopathy (DR). Here, we explored a novel mechanism by which palmitic acid (PA) contributed to RMEC damage in DR. Diabetic rats and high glucose (HG)-treated human RMECs (HRMECs) were used for the in vivo and in vitro experiments. The pathological changes of retinal tissues were evaluated by hematoxylin & eosin staining; mannose receptor (CD206) and B7-2 (CD86) expression were detected by immunohistochemical staining and flow cytometry; cell viability was measured using Cell Counting Kit-8; the protein levels were detected by Western blot. Ferroptosis was induced in the retinal tissues of diabetic rats and HG-treated HRMECs, which was verified by increased kelch-like ECH-associated protein 1 (Keap1), acyl-CoA synthetase long-chain family member 4 (ACSL4), malondialdehyde (MDA), and reactive oxygen species (ROS) levels, whereas glutathione (GSH), nuclear factor erythroid 2-related factor 2 (Nrf2), and glutathione peroxidase 4 (GPX4) levels were decreased. PA exhibited the similar promotion effect on ferroptosis in HRMECs, which was reversed by 2-bromohexadecanoic acid and further enhanced by Palmostatin B. The palmitoylation modification of Keap1 in HRMECs was confirmed, and si-Keap1 reversed the increased Keap1, ACSL4, MDA and ROS, decreased Nrf2, GPX4 and GSH induced by PA. The in vivo experiments further revealed that si-Keap1 alleviated DR and reduced ferroptosis. These results suggested that PA induced Keap1 palmitoylation to upregulate Keap1 levels to inhibit Nrf2/GPX4 pathway, thus enhancing ferroptosis in HRMECs and aggravating DR.