Melatonin reprograms antioxidant defenses to suppress ferroptosis via Homer1a/mGluR1-Nrf2/xCT signaling after retinal ischemia-reperfusion.

Melatonin (Mel) exerts antioxidant and anti-ferroptosis effects not only via the canonical receptors Mt1/Mt2 but also via metabotropic glutamate receptor 1 (mGluR1)/glutamate-mediated signaling. Nevertheless, the regulatory mechanism by which Mel modulates mGluR1/glutamate signaling in retinal ischemia-reperfusion (I/R) injury and its downstream effects on ferroptosis and oxidative stress remain poorly understood. Here, bulk RNA sequencing identified that the Mel receptors Mt1/Mt2 and ferroptosis/iron-redox regulators (Gpx4, Fth1, and xCT) were significantly downregulated after retinal I/R. Mel improved retinal structural and visual function, visual-guidance behavior, and electrophysiological responses following I/R while concurrently reducing ferroptotic and inflammatory injury markers. These benefits were largely abolished by Mel membrane receptor antagonists. Mechanistically, Mel upregulated Homer1a in vivo and in vitro in a receptor-dependent manner. Conditional deletion of Homer1a in transgenic mice, as well as Homer1a knockdown in retinal ganglion cells (RGCs), abolished the protective effects of Mel on visual function, along with its anti-ferroptotic and anti-inflammatory activities. Molecular docking and immunoprecipitation assays demonstrated that Mel restored the interaction between Homer1a and mGluR1 and activated the xCT/GSH/Gpx4 antioxidant axis. Pharmacologic inhibition of xCT with the buthionine sulfoximine (BSO) simulation pr genetic interference with xCT expression counteracted the protective effects of Mel. Mel also enhanced Nrf2-mediated transcriptional expression of cCT in a Homer1a/mGluR1-dependent manner. Collectively, our results define a Mel-Homer1a/mGluR1-Nrf2/xCT signaling cascade that promotes RGCs survival after I/R by suppressing ferroptosis/iron-redox reactions, thereby providing a potential translatable strategy for receptor-targeted intervention in I/R-related retinal damage.