Gatekeeper Connexin43 Phosphorylation Events Regulate Cardiac Gap Junction Coupling During Stress

Abstract

Rapid and well-orchestrated action potential propagation through the myocardium is essential to each heartbeat. Gap junctions comprising primarily Cx43 reside within the intercalated discs connecting cardiomyocytes, effecting not only direct intercellular electrical coupling, but the localization of other junctional structures and ion channels. Alterations in Cx43 expression occur in essentially all forms of heart disease and is therefore a topic of intense study. Posttranslational modification of Cx43 is understood to impact trafficking, conduction, and stability. Altered Cx43 phosphorylation is well described during pathological remodeling of gap junctions in response to cellular stress. Research has revealed how phosphorylation of specific residues elicit specific effects on Cx43, but the complexity of this process has left much unknown. In particular, the role phosphorylation of a triplet of double serine residues, Ser365, Ser368, and Ser373, plays in GJ function and Cx43/14-3-3 interaction has been called into question. Using an ex vivo whole heart ischemia model we find a decrease in pS368 in mice lacking the ability to phosphorylate S365 and S373 while under stress. In vitro transfection of human induced pluripotent stem cell-derived cardiomyocytes when stressed with PMA were also carried out. These data allow us to piece together the exquisite interplay of gatekeeper phosphorylation events upstream of channel closure, altered protein-protein interactions, and gap junction internalization and degradation. It is hoped that our increasing understanding of this important area of gap junction biology will facilitate better understanding of arrhythmogenesis, and potential therapeutic strategies to restore or preserve normal electrical coupling in diseased hearts.