The E3 ubiquitin ligase parkin is dispensable for metabolic homeostasis in murine pancreatic cells and adipocytes

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