AMP-Activated Protein Kinase α1 Regulates Cardiac Gap Junction Protein Connexin 43 and Electrical Remodeling Following Pressure Overload

Background/Aims: Adenosine 5'-monophosphate (AMP)-activated protein kinase (Ampk) modulates a wide array of cellular functions and regulates various ion channels and transporters. In failing human hearts an increased Ampk alpha 1 activity was observed. The present study aimed to uncover the impact of Ampk alpha 1 on cardiac electrical remodeling. Methods: Gene-targeted mice lacking functional Ampk alpha 1 (Ampk alpha 1(-/-)) and corresponding wild-type mice were exposed to pressure overload by "transverse aortic constriction" (TAC). In vivo electrophysiology was performed with a single catheter technique, myocardial conduction velocities and conduction characteristics investigated in isolated hearts, transcript levels quantified by RTPCR and protein abundance determined by Western blotting. Moreover, connexin 43 (Cx43) was expressed in Xenopus oocytes with or without coexpression of wild-type or mutant AMPK and Cx43 protein abundance quantified utilizing confocal microscopy. Results: TAC treatment increased Ampk alpha 1 protein expression in cardiac tissue from wild-type mice. TAC further increased left ventricular conduction inhomogeneity and triggered conduction blocks, effects blunted in the Ampk alpha 1(-/-) mice. TAC treatment decreased Cx43 protein abundance in cardiac tissue, an effect significantly blunted in the Ampk alpha 1(-/-) mice. TAC treatment did not modify Cx43 mRNA levels but increased ubiquitination of Cx43 protein, an effect mitigated by Ampk alpha 1 deficiency. As shown in Xenopus oocytes, Cx43 cell membrane protein abundance was significantly downregulated by wild-type AMPKWT and constitutively active AMPK(gamma R70Q), but not by catalytically inactive AMPK(alpha K45R). Conclusion: Ampk alpha 1 stimulates ubiquitination of the gap junction protein Cx43, thereby contributing to gap junction remodeling following pressure overload. Copyright (C) 2015 S. Karger AG, Basel