Cortactin's Influence on Mitochondrial Bioenergetics in the Diabetic Heart: A Novel Viewpoint

Abstract

Cortactin, a protein which controls the cytoskeleton, has been suggested to impact mitochondrial function by influencing the outer mitochondrial membrane during fusion and fission. Cortactin has been shown to interact directly with Coronin 1b by affecting Arp 2/3 during actin formation and branching, but it is currently unknown how cortactin dynamics affect the structure and function of mitochondria in the heart during type 2 diabetes mellitus. The goal of the study was to visualize changes in cytoskeletal proteins in the type 2 diabetic heart, and determine whether genetic alteration of cortactin levels impacts the mitochondrion on a molecular level. We hypothesized that cytoskeletal proteins associated with mitochondrial dynamics would be significantly altered in the type 2 diabetic state, and that specific changes in cortactin would have a direct effect on mitochondrial bioenergetics and function. Western blots were utilized to visualize cortactin, coronin1b and phosphor‐coronin1b levels in type 2 diabetic human patient heart and db/db mouse cardiac tissue. Results indicated that in both type 2 diabetic human patient and db/db cardiac tissue, cortactin and coronin1b levels are dysregulated. Cortactin levels were significantly increased (P<0.05) as were coronin1b levels in db/db mouse cardiac tissue (P<0.05). Phosphorylated coronin1b was significantly decreased in human type 2 diabetic cardiac tissue (P<0.05). To determine whether increased cortactin levels observed in the type 2 diabetic state can influence the mitochondrion, we utilized an HL‐1 cardiomyocyte model in which cortactin was either knocked down or overexpressed. Mitochondria were isolated post transfection with an expression vector for cortactin and analyzed via flow cytometry for size and internal complexity, JC‐1 staining for membrane potential, electron transport chain complex activities, and bioenergetics using the Seahorse. Cortactin overexpression and knockdown significantly altered the membrane potential of the mitochondria (P<0.05). Further, in cells overexpressing cortactin, exogenous fatty acid utilization was decreased (P<0.05), and cells appeared to be completely dependent of endogenous free fatty acids (FFA) for respiration (P<0.05). Taken together, our data indicate that cortactin is significantly increased in the type 2 diabetic heart of both human patient and mouse cardiac tissue. Further, these data indicate that increased cortactin levels associated with the type 2 diabetic heart may contribute to changes in mitochondrial function by influencing membrane potential and their capacity to utilize FFA during respiration.Support or Funding InformationSupport: NIH R01 HL128485; AHA 17PRE33660333This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.