Mitochondrial network fragmentation has been associated with metabolic dysregulation, although the underlying mechanisms remain unknown. Herein, using multiple cellular models where the physiological relevance of fatty acid is well-established, we show that mitochondrial fragmentation is highly associated with increased fatty acid oxidation (FAO) rates. Through confocal imaging and stable isotope tracing analysis, forced mitochondrial elongation using Mfn2 over-expression or Drp1 depletion significantly decreased FAO rates, while Mfn2 knockout leads to enhanced FAO rates (P-value =0.0003) , suggesting that mitochondrial morphology regulates fatty acid utilization. To determine the mechanism by which mitochondrial architecture controls fatty acid utilization we studied the effects of mitochondrial fragmentation and elongation on CPT1 activity. Remarkably, we find that CPT1 sensitivity to its main regulator, malonyl-CoA is strongly affected by molecular interventions that inhibit mitochondrial fusion and fission. Notably, the reduction in hepatic FAO rates upon mitochondrial elongation is attributed to a 14 fold increase in CPT1 sensitivity to malonyl-CoA. Consistent with this mechanism we show that the inhibition of FAO imposed by mitochondrial elongation can be overcome using CPT1 pharmacological activator that is malonyl-CoA-independent, but not by the malonyl-CoA-sensitive activator. Furthermore, we tested the functional implications of this mechanism in hepatocytes and beta cells. In hepatocytes we show that forced elongation by the inhibition of fission reduced gluconeogenesis by 30-70%. Whereas in islets, forced mitochondrial fragmentation through molecular inhibition of fusion, resulted in a 2.5 fold increase in insulin secretion at basal glucose concentrations, a phenomenon associated with prediabetes and obesity. Taken together, our study provides a biochemical and mechanistic explanation by which changes to mitochondrial architecture affects fuel utilization and lipid metabolism.
J. Ngo: None. D. Choi: None. L. Stiles: None. A. S. Divakaruni: None. M. Liesa: None. N. N. Danial: None. O. Shirihai: None.
American Diabetes Association (1-19-IBS-049)