15-OR: Mitochondrial NRF2 in ß-cell Oxidative Stress Response

Abstract

β-cells are highly metabolic and vulnerable to a variety of exogenous stressors, including excess glucose and proinflammatory cytokines. Many of these stressors elicit the accumulation of reactive oxygen species (ROS) , which can cause oxidative damage and lead to cell death. To restore homeostasis in the face of accumulating ROS, all cells, including β-cells, are equipped with adaptive stress response mechanisms such as the antioxidant response and autophagy. The antioxidant response is primarily driven by nuclear translocation of the transcription factor, NRF2. However, recently we observed a pool of NRF2 in the mitochondria that is associated with both the antioxidant response and a selective form of autophagy, known as mitophagy. We therefore hypothesized that NRF2 mediates coupling of mitophagy with the antioxidant response in the β-cell and is essential for restoration of β-cell homeostasis under conditions of increased ROS. We first asked whether loss of murine NRF2 was associated with increased susceptibility to β-cell damage induced by the toxic glucose analog, streptozotocin (STZ) . Multiple low dose STZ injections (45mg/kg for 5 consecutive days) rendered whole-body NRF2 knockout mice diabetic more quickly than wild type controls. To study the role of β-cell NRF2 in autophagy/antioxidant response coupling, we then generated a β-cell specific NRF2 knockout mouse (NRF2Δβ) by breeding NRF2 floxed mice with mice bearing the Ins1Cre/wt allele. NRF2Δβ mice appear to be phenotypically normal until at least 20 weeks of age and do not develop spontaneous diabetes. We then set out to determine how loss of β-cell NRF2 affects the mitochondria by both immunofluorescence analysis and transmission electron microscopy of isolated pancreata. We observed rounded β-cell mitochondrial morphology in the absence of NRF2. Collectively, our data are consistent with a role for NRF2 in β-cell mitochondrial function and suggest that NRF2 is required for proper response to β-cell damage. Disclosure A.Novak: n/a. J.Crowder: None. M.Marasco: Other Relationship; Eli Lilly and Company. A.K.Linnemann: Consultant; Janssen Research & Development, LLC. Funding NIDDK (R01DK124380)