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.

Secreted PDZD2 exerts an insulinotropic effect on INS-1E cells by a PKA-dependent mechanism.

Secreted PDZD2 (sPDZD2) is a signaling molecule generated upon proteolytic processing of the multi-PDZ-containing protein PDZD2. Previous analysis of gene-trap mice deficient in the synthesis of full-length PDZD2, but not the secreted form, revealed a role of PDZD2 in the regulation of glucose-stimulated insulin secretion. Here, using the pancreatic INS-1E ß cells as in vitro model, we showed that depletion of PDZD2/sPDZD2 by RNA interference suppressed the expression of ß-cell genes Ins1, Glut2 and MafA whereas treatment with recombinant sPDZD2 rescued the suppressive effect. Similar to GLP-1, sPDZD2 stimulated intracellular cAMP levels, activated ß-cell gene expression in a PKA-dependent manner and induced the phosphorylation and nuclear localization of PDX1. Depletion of PDX1 inhibited the sPDZD2 insulinotropic effect, which could also be demonstrated in mouse islets. In summary, our findings are consistent with sPDZD2 serving a signaling function in regulating ß-cell gene expression.