2013-P: Parkin Is Dispensable in Pancreatic Beta Cells and Adipocytes for Metabolic Homeostasis

The E3 ligase parkin is a critical regulator of mitophagy and has been identified as a susceptibility gene for type 2 diabetes (T2D), but its role in metabolically active tissues to modulate the development of T2D is unknown. Pancreatic β-cells and adipocytes both rely heavily on mitochondrial function to regulate optimal glycemic control to prevent T2D, but the role of parkin to modulate β-cell or adipocyte mitochondrial quality control is unclear. Despite the reported importance of parkin to control mitophagy, here we report that parkin surprisingly is dispensable in both β-cells and adipocytes for glucose homeostasis during diet-induced insulin resistance. We observe that insulin secretion, β-cell formation, and islet architecture were preserved in parkin deficient β-cells and islets, suggesting parkin is not necessary for control of β-cell function and islet compensation for diet-induced obesity. While transient parkin deficiency mildly impaired mitochondrial turnover in β-cell lines, parkin deletion in primary β-cells yielded no deficits in mitochondrial clearance. In adipocyte-specific deletion models, lipid uptake and β-oxidation were increased in cultured cells, while adipose tissue morphology, glucose homeostasis, or the beige-to-white adipocyte transition were unaffected in vivo. In key metabolic tissues where mitochondrial dysfunction is implicated in the development of T2D, our studies unexpectedly demonstrate that parkin is not an essential regulator of glucose tolerance, whole-body energy metabolism, or mitochondrial quality control. These findings highlight a novel role for parkin-independent processes to maintain β-cell and adipocyte mitochondrial quality control with diet-induced obesity.