42-OR: Effects of Oxidative Phosphorylation Complexes Defects on Beta-Cell Function

Background: The pancreatic beta cell is a highly metabolic cell type relying on mitochondrial metabolism for stimulus-secretion coupling. Specifically, the ATP-producing oxidative phosphorylation (OXPHOS) pathway is central to insulin secretion. Although disruptions in ATP production occur in beta cell dysfunction, the exact mechanisms remain unknown. We generated beta cell specific inducible knockout mouse models of OXPHOS Complex I, III, and IV to determine the direct effects of each OXPHOS complex on beta cell function. We hypothesize that individual complexes contribute distinctly to beta cell function.

Methods: Male OXPHOS^f/f - MIPcre^ERT mice were administered tamoxifen (150mg/kg) or vehicle by I.P. injection for 5 days. Glucose and insulin tolerance were assessed 3 weeks after induction. Mice were anesthetized with ketamine/xylazine and perfused with PBS followed by 4% PFA. Pancreata were dissected, embedded in OCT, and cut for islet hormone staining. To determine mitochondrial respiration, Seahorse Bioenergetic Flux analysis was performed on isolated islets from all groups.

Results: Complex III knockout mice developed severe hyperglycemia and glucose intolerance at 3 weeks post-induction, while insulin tolerance remained the same. The other two models showed a trend towards hyperglycemia starting at 5 weeks, but retained their ability to regulate glucose at 3 weeks. Interestingly, no changes in islet cytoarchitecture were observed in any of the groups. Western blot analyses on islet lysates confirmed a marked, and comparable knockdown of the targeted complex in all 3 models. Defects were seen in glucose-stimulated mitochondrial respiration for all knockout models at 3 weeks.

Conclusions: Mice with Complex III deficient beta cells showed a robust diabetic phenotype compared to Complexes I and IV models despite all models having significant knockdown of the targeted complex. This supports the hypothesis that specific OXPHOS complexes contribute differentially to beta cell function.