Retinal pigment epithelium (RPE) cell damage is implicated in the pathogenesis of age‐related macular degeneration (AMD). An increase of interferon‐γ (IFN‐γ) levels was observed in patients with AMD, but whether inflammatory factors are causally related to AMD progression is unclear. Here, we demonstrate a direct causal relationship between IFN‐γ and RPE cell death. IFN‐γ induced human retinal pigment epithelial cell (ARPE‐19) death accompanied by increases in Fe²⁺, reactive oxygen species, lipid peroxidation, and glutathione (GSH) depletion, which are main characteristics of ferroptosis. Mechanistically, IFN‐γ upregulates the level of intracellular Fe²⁺ through inhibiting Fe²⁺ efflux protein SLC40A1 and induces GSH depletion by blocking cystine/glutamate antiporter, System xc‐. At the same time, treatment with IFN‐γ decreases the level of glutathione peroxidase 4 (GPx4), rendering the cells more sensitive to ferroptosis. JAK1/2 and STAT1 inhibitors could reverse the reduction of SLC7A11, GPx4 and GSH expression induced by IFN‐γ, indicating IFN‐γ induces ARPE‐19 cell ferroptosis via activation of the JAK1‐2/STAT1/SLC7A11 signaling pathway. The above results were largely confirmed in IFN‐γ‐treated mice in vivo. Finally, we used sodium iodate (NaIO₃)‐induced retinal degeneration to further explore the role of ferroptosis in AMD in vivo. Consistent with the role of IFN‐γ, treatment with NaIO₃ decreased SLC7A11, GPx4 and SLC40A1 expressions. NaIO₃‐induced RPE damage was accompanied by increased iron, lipid peroxidation products (4‐hydroxynonenal, malondialdehyde), and GSH depletion, and ferroptosis inhibitors could reverse the above phenomenon. Taken together, our findings suggest that inhibiting ferroptosis or reducing IFN‐γ may serve as a promising target for AMD.

Diabetic retinopathy (DR) is a serious and relatively under-recognized complication of diabetes. Müller glial cells extend throughout the retina and play vital roles in maintaining retinal homeostasis. Previous studies have demonstrated that TGR5, a member of the bile acid-activated GPCR family, could ameliorate DR. However, the role of TGR5 in regulating Müller cell function and the underlying mechanism remains to be ascertained. To address this, high glucose (HG)-treated human Müller cells and streptozotocin-treated Sprague-Dawley rats were used in the study. The IP3R1-GRP75-VDAC1 axis and mitochondrial function were assessed after TGR5 ablation or agonism. Cytosolic mitochondrial DNA (mtDNA)-mediated cGAS-STING activation was performed. The key markers of retinal vascular leakage, apoptosis, and inflammation were examined. We found that mitochondrial Ca²⁺ overload and mitochondrial dysfunction were alleviated by TGR5 agonist. Mechanically, TGR5 blocked the IP3R1-GRP75-VDAC1 axis mediated Ca²⁺ efflux from the endoplasmic reticulum into mitochondria under diabetic condition. Mitochondrial Ca²⁺ overload led to the opening of the mitochondrial permeability transition pore and the release of mitochondrial DNA (mtDNA) into the cytosol. Cytoplasmic mtDNA bound to cGAS and upregulated 2’3’ cyclic GMP-AMP. Consequently, STING-mediated inflammatory responses were activated. TGR5 agonist prevented retinal injury, whereas knockdown of TGR5 exacerbated retinal damage in DR rats, which was rescued by the STING inhibitor. Based on the above results, we propose that TGR5 might be a novel therapeutic target for the treatment of DR.

Cellular senescence is a hallmark of aging and has been linked to age-related diseases. Age-related macular degeneration (AMD), the most common aging-related retinal disease, is prospectively associated with retinal pigment epithelial (RPE) senescence. However, the mechanism of RPE cell senescence remains unknown. In this study, tert-butyl hydroperoxide (TBH)-induced ARPE-19 cells and D-galactose-treated C57 mice were used to examine the cause of elevated iron in RPE cell senescence. Ferric ammonium citrate (FAC)-treated ARPE-19 cells and C57 mice were used to elucidated the mechanism of iron overload-induced RPE cell senescence. Molecular biology techniques for the assessment of iron metabolism, cellular senescence, autophagy, and mitochondrial function in vivo and in vitro. We found that iron level was increased during the senescence process. Ferritin, a major iron storage protein, is negatively correlated with intracellular iron levels and cell senescence. NCOA4, a cargo receptor for ferritinophagy, mediates degradation of ferritin and contributes to iron accumulation. Besides, we found that iron overload leads to mitochondrial dysfunction. As a result, mitochondrial DNA (mtDNA) is released from damaged mitochondria to cytoplasm. Cytoplasm mtDNA activates the cGAS-STING pathway and promotes inflammatory senescence-associated secretory phenotype (SASP) and cell senescence. Meanwhile, iron chelator Deferoxamine (DFO) significantly rescues RPE senescence and retinopathy induced by FAC or D-gal in mice. Taken together, these findings imply that iron derived from NCOA4-mediated ferritinophagy causes cellular senescence via the cGAS-STING pathway. Inhibiting iron accumulation may represent a promising therapeutic approach for age-related diseases such as AMD.

Endoplasmic reticulum (ER) and mitochondrial dysfunction play fundamental roles in the pathogenesis of diabetic retinopathy (DR). However, the interrelationship between the ER and mitochondria are poorly understood in DR. Here, we established high glucose (HG) or advanced glycosylation end products (AGE)-induced human retinal vascular endothelial cell (RMEC) models in vitro, as well as a streptozotocin (STZ)-induced DR rat model in vivo. Our data demonstrated that there was increased ER–mitochondria coupling in the RMECs, which was accompanied by elevated mitochondrial calcium ions (Ca²⁺) and mitochondrial dysfunction under HG or AGE incubation. Mechanistically, ER–mitochondria coupling was increased through activation of the IP3R1–GRP75–VDAC1 axis, which transferred Ca²⁺ from the ER to the mitochondria. Elevated mitochondrial Ca²⁺ led to an increase in mitochondrial ROS and a decline in mitochondrial membrane potential. These events resulted in the elevation of mitochondrial permeability and induced the release of cytochrome c from the mitochondria into the cytoplasm, which further activated caspase-3 and promoted apoptosis. The above phenomenon was also observed in tunicamycin (TUN, ER stress inducer)-treated cells. Meanwhile, BAPTA-AM (calcium chelator) rescued mitochondrial dysfunction and apoptosis in DR, which further confirmed of our suspicions. In addition, 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, was shown to reverse retinal dysfunction in STZ-induced DR rats in vivo. Taken together, our findings demonstrated that DR fueled the formation of ER–mitochondria coupling via the IP3R1–GRP75–VDAC1 axis and accelerated Ca²⁺-dependent cell apoptosis. Our results demonstrated that inhibition of ER–mitochondrial coupling, including inhibition of GRP75 or Ca²⁺ overload, may be a potential therapeutic target in DR.

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus. Abnormal energy metabolism in microvascular endothelium is involved in the progression of diabetic retinopathy. Bile Acid G‐Protein‐Coupled Membrane Receptor (TGR5) has emerged as a novel regulator of metabolic disorders. However, the role of TGR5 in diabetes mellitus‐induced microvascular dysfunction in retinas is largely unknown. Herein, enzyme‐linked immunosorbent assay was used for analyzing bile acid (BA) profiles in diabetic rat retinas and retinal microvascular endothelial cells (RMECs) cultured in high glucose medium. The effects of TGR5 agonist on streptozotocin (STZ)‐induced diabetic retinopathy were evaluated by HE staining, TUNEL staining, retinal trypsin digestion, and vascular permeability assay. A pharmacological inhibitor of RhoA was used to study the role of TGR5 on the regulation of Rho/Rho‐associated coiled‐coil containing protein kinase (ROCK) and western blot, immunofluorescence and siRNA silencing were performed to study the related signaling pathways. Here we show that bile acids were downregulated during DR progression in the diabetic rat retinas and RMECs cultured in high glucose medium. The TGR5 agonist obviously ameliorated diabetes‐induced retinal microvascular dysfunction in vivo, and inhibited the effect of TNF‐α on endothelial cell proliferation, migration, and permeability in vitro. In contrast, knockdown of TGR5 by siRNA aggravated TNF‐α‐induced actin polymerization and endothelial permeability. Mechanistically, the effects of TGR5 on the improvement of endothelial function was due to its regulatory role on the ROCK signaling pathway. An inhibitor of RhoA significantly reversed the loss of tight junction protein under TNF‐α stimulation. Taken together, our findings suggest that insufficient BA signaling plays an important pathogenic role in the development of DR. Upregulation or activation of TGR5 may inhibit RhoA/ROCK‐dependent actin remodeling and represent an important therapeutic intervention for DR.