System χ_c- overexpression prevents 2-deoxy-d-ribose-induced β-cell damage

Pancreatic β-cells are vulnerable to oxidative stress, which promotes β-cell failure in type 2 diabetes. System χ_c- is a sodium-independent, cystine/glutamate antiporter that mediates the exchange of extracellular l-cystine and intracellular l-glutamate. The import of l-cystine through this transporter is the rate-limiting step in the glutathione (GSH) biosynthesis pathway that plays a significant role in antioxidative defense. Previously, we reported that 2-deoxy-d-ribose (dRib) induces oxidative damage through GSH depletion in pancreatic β-cells. In the current study, we elucidated the mechanism underlying the oxidative stress-induced β-cell damage. We measured the intracellular l-[¹⁴C]cystine uptake, GSH content, reactive oxygen species (ROS) levels, cytotoxicity, and apoptosis in rat insulinoma cell line, RINm5F. Treatment of dRib decreased the intracellular l-[¹⁴C]cystine uptake and GSH content and increased the intracellular ROS levels, cytotoxicity, and apoptosis in a time- and dose-dependent manner. Conversely, 2-mercaptoethanol (2-ME), a cystine uptake enhancer, recovered the dRib-induced decrease in l-[¹⁴C]cystine uptake, GSH content, and cell viability in a Na⁺-independent manner. In the case of isolated islets, dRib dose-dependently decreased the intracellular l-[¹⁴C]cystine uptake and cell viability; however, dRib-induced cytotoxicity was completely recovered by adding N-acetyl cysteine (NAC). To confirm that system χ_c- mediates the oxidative stress-induced β-cell damage, we overexpressed xCT (the substrate-specific subunit of system χ_c-) using a lentiviral vector in RINm5F cells. Overexpression of xCT fully recovered the dRib-induced decrease in l-[¹⁴C]cystine uptake and GSH content and prevented the dRib-induced increase in ROS levels, cytotoxicity, and apoptosis. The overexpression of xCT showed a protective effect against dRib-induced oxidative damage in RINm5F cells. Our study showed that dRib depletes intracellular GSH content through inhibition of cystine transport via system χ_c- in β-cells.