Downregulation of the SREBP pathways and disruption of redox status by 25-hydroxycholesterol predispose cells to ferroptosis

Enzymatically formed side-chain oxysterols function as signaling molecules regulating cholesterol homeostasis and act as intermediates in the biosynthesis of bile acids. In addition to these physiological functions, an imbalance in oxysterol homeostasis has been implicated in pathophysiology. Cholesterol 25-hydroxylase (CH25H) and its product 25-hydroxycholesterol (25-OHC), also formed by autoxidation, are associated with amyotrophic lateral sclerosis. However, the effects of 25-OHC on cell viability in glial cells remain unclear. This study demonstrates that 25-OHC induces ferroptosis, an iron-dependent programmed cell death, in mouse Schwann IMS32 cells. Mechanistically, 25-OHC suppressed the expression of selenoprotein glutathione peroxidase 4 (GPX4) at both the transcriptional and translational levels by inhibiting the processing of sterol regulatory element-binding proteins (SREBPs). In addition, 25-OHC upregulated the expression of NADH-cytochrome b5 reductase 1 (CYB5R1) and NADPH-cytochrome P450 reductase (POR), enzymes that promote lipid peroxidation. We further found that 25-OHC increases the expression of glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) and decreases glutathione levels. Importantly, non-cytotoxic concentrations of 25-OHC enhanced cellular sensitivity to ferroptosis inducers by downregulating GPX4 expression. These findings reveal a multifaceted approach whereby 25-OHC induces ferroptosis through SREBP pathway suppression and redox imbalance in mouse Schwann IMS32 cells.