Abstract 449: The H2 Domain in the Connexin43 Carboxyl Terminus Regulates Cardioprotection From Ischemia Reperfusion Injury

Abstract

Cardiac ischemia-reperfusion (IR) injury occurs in patients with acute coronary syndromes undergoing percutaneous intervention to re-establish blood flow in blocked or narrowed arteries. Presently, there are no therapies approved to prevent the loss of heart muscle, scar tissue formation and contractile dysfunction that result from IR injury. We have previously reported that α CT1, a Connexin 43 (Cx43) mimetic peptide currently in Phase III testing in humans (GAIT1; NCT02667327) as a therapy for chronic skin wounds (PMID:27856288; 25072595), improves contractile function of mouse hearts following injury in association with increases in PKCε-mediated phosphorylation of Cx43 at serine 368 (S368) (PMID: 21273554). Here, we report that induction of S368 phosphorylation and cardioprotection from IR injury by α CT1 involves direct protein-protein interaction of α CT1 with a short alpha-helical sequence within the Cx43 carboxyl terminus (CT) termed the H2 domain. The interacting protein domains involved in Cx43 S368 phosphorylation were identified and validated by a combination of techniques including tandem mass spectroscopy, surface plasmon resonance, immunoprecipitation and thermal shift assays. These studies indicated that α CT1 induced S368 phosphorylation (pS368) via a novel mechanism involving interaction between a pair of positively charged lysines (K344, K345) in the Cx43 CT H2 domain and a cluster of negatively charged amino acids i α CT1. It is further shown that the known ability of α CT1 to interact with Zonula Occludens-1 (ZO-1), has no direct role in either the induction of S368 phosphorylation or protection from IR injury. Finally, we identify a small, novel variant of α CT1 ( α CT11 - RPRPDDLEI, Mr 1110) that penetrates myocyte membranes, induces S368 phosphorylation and robustly preserves ventricular contractile function and cardiac muscle when administered after ischemic injury. Data on Cx43 hemichannel dependence of α CT11 uptake by cells will be presented. Our results indicate that selective targeting of the secondary structure and phospho-status of the Cx43 CT by small peptidergic drugs may provide a novel and potent pharmacological approach to preservation of cardiac muscle following IR injury.