Ochratoxin A induces mitochondrial apoptosis and ferroptosis by inhibiting Sigma-1 receptor to disrupt redox and cholesterol homeostasis

Ochratoxin A (OTA), a secondary fungal metabolite known for its nephrotoxic effects, is widespread in various foods and animal feeds. Our recent investigation suggests a correlation between OTA-induced nephrotoxicity and Sigma-1 receptor (Sig-1R)-mediated mitochondrial apoptosis in human proximal tubule epithelial-originated kidney-2 (HK-2) cells. However, the involvement of Sig-1R in OTA-induced nephrotoxicity, encompassing other forms of regulated cell death like ferroptosis, remains unexplored. In this research, cell viability, apoptotic rate, cholesterol levels, mitochondrial glutathione (mGSH) levels, reactive oxygen species (ROS) levels, and protein expressions in HK-2 cells treated with OTA and/or blarcamesine hydrochloride (Anavex 2-73) were evaluated. The results suggest that OTA induces mitochondrial apoptosis and ferroptosis by inhibiting Sig-1R, subsequently promoting sterol regulatory element-binding protein 2 (SREBP2), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), GRAM domain-containing protein 1B (GRAMD1B), steroidogenic acute regulatory protein, mitochondrial (StARD1), 78 kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), cyclophilin D (CypD), Cleaved-Caspase-3, B-cell lymphoma-2-associated X protein (BAX), and long-chain fatty acid-CoA ligase 4 (ACSL4), inhibiting tumor necrosis factor receptor-associated protein 1 (TRAP1), mitochondrial 2-oxoglutarate/malate carrier protein (SLC25A11), B-cell lymphoma-2-like protein 1 (BCL-XL), and glutathione peroxidase 4 (GPX4), reducing mGSH levels, and increasing total cholesterol, mitochondrial cholesterol, and ROS levels. In conclusion, OTA induces mitochondrial apoptosis and ferroptosis by inhibiting Sig-1R, thereby disrupting redox and cholesterol homeostasis in vitro. The regulation of cholesterol homeostasis by Sig-1R and its involvement in OTA-induced mitochondrial apoptosis and ferroptosis are reported here for the first time.