Recovery of pancreatic beta-cells from nitric oxide-induced damage

Proinflammatory cytokines inhibit pancreatic beta-cell function and induce damage to beta-cell DNA, ultimately resulting in beta-cell death and the development of type I diabetes. While nitric oxide mediates the damaging effects of cytokines on beta-cells, nitric oxide also activates a DNA repair process. This dissertation explores the mechanisms regulating the repair of nitric oxide-damaged DNA. First, we demonstrate that beta-cells have the ability to repair DNA that is damaged following 24 h incubation with IL-1 (when beta-cells can recover function); however, cytokine-induced DNA damage becomes irreversible following 36 h incubation with IL-1. This irreversible DNA damage correlates with the induction of apoptosis as measured by caspase-3 cleavage and activity.;Next, we sought to identify pathways activated by nitric oxide in the beta-cell which mediate DNA repair. Similar to the recovery of metabolic function, we found that nitric oxide-induced JNK activation plays a central role in the repair process through the p53-independent upregulation of GADD45alpha.;Finally, we demonstrate that the activation of FoxO1 by nitric oxide is required for the induction of GADD45alpha and repair of nitric oxide-damaged DNA. Additionally, we demonstrate that the inhibition of SIRT-1 attenuates the repair of nitric oxide-damaged DNA and drives FoxO1-dependent apoptosis in response to proinflammatory cytokines. These results demonstrate that SIRT-1 promotes the repair of nitric oxide-damaged DNA and protects beta-cells from nitric oxide-induced apoptosis through the regulation of FoxO1.;Overall, this study uncovers pathways initiated by nitric oxide in pancreatic beta-cells which activate the repair of DNA damage-induced by nitric oxide and protect beta-1 cells from cytokine-induced death. The identification of mediators of repair could have therapeutic potential in the setting of islet transplantation. There are currently many limitations of islet transplantation including beta-cell availability, loss of beta-cell mass during isolation, and islet rejection. The activation of recovery pathways could be used to preserve islet mass during islet isolation procedures and prevent islet destruction by the immune system following transplantation.