2-Deoxy-d-ribose induces ferroptosis in renal tubular epithelial cells via ubiquitin-proteasome system-mediated xCT protein degradation

Ferroptosis is a novel form of cell death triggered by iron-dependent lipid peroxidation. Recent findings suggest that inhibiting system χc-induces ferroptosis by reducing intracellular cystine levels, and that ferroptosis in renal tubular epithelial cells (RTECs) contributes to acute kidney injury (AKI) and diabetic nephropathy. Moreover, 2-deoxy-d-ribose (dRib) has been shown to inhibit cystine uptake through xCT, the functional unit of system χc-, in β-cells. This study aimed to investigate if dRib induces ferroptosis in RTECs and identify the underlying mechanisms. dRib treatment reduced cystine uptake and glutathione (GSH) content, and increased intracellular levels of malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), lipid reactive oxygen species (ROS), and cell death in both NRK-52E cells and primary cultured RTECs. However, treatment with inhibitors of ferroptosis, such as deferoxamine (DFO), ferrostatin-1 (Fer-1), and liproxstatin-1 (Lip-1), counteracted the effects of dRib on GSH, MDA, 4-HNE, and lipid ROS levels, as well as cell death. Additionally, 2-mercaptoethanol (2-ME) treatment or xCT gene overexpression protected against dRib-induced changes. Moreover, transmission electron microscopy revealed dRib-induced mitochondrial shrinkage, decrease in cristae number, and outer membrane rupture. Furthermore, dRib treatment upregulated the expression of genes associated with ferroptosis, and downregulated xCT protein expression. The decrease in xCT protein caused by dRib was consistently observed even when treated with the protein synthesis inhibitor cycloheximide. However, treatment with the proteasome inhibitor MG132 reversed the dRib-induced decrease in xCT protein expression. Additionally, dRib increased xCT protein ubiquitination. Overall, dRib induces ferroptosis in RTECs by degrading xCT protein through ubiquitin-proteasome system (UPS), resulting in reduced intracellular cystine uptake. Therefore, targeting the regulation of system χc-through UPS could be a potential therapeutic approach for AKI and diabetic nephropathy.