Role of connexin-43 in protective PI3K-Akt-GSK-3β signaling in cardiomyocytes

Abstract

Sarcolemmal connexin-43 (Cx43) and mitochondrial Cx43 play distinct roles: formation of gap junctions and production of reactive oxygen species (ROS) for redox signaling. In this study, we examined the hypothesis that Cx43 contributes to activation of a major cytoprotective signal pathway, phosphoinositide 3-kinase (PI3K)-Akt-glycogen synthase kinase-3β (GSK-3β) signaling, in cardiomyocytes. A δ-opioid receptor agonist {[d-Ala(2),d-Leu(5)]enkephalin acetate (DADLE)}, endothelin-1 (ET-1), and insulin-like growth factor-1 (IGF-1) induced phosphorylation of Akt and GSK-3β in H9c2 cardiomyocytes. Reduction of Cx43 protein to 20% of the normal level by Cx43 small interfering RNA abolished phosphorylation of Akt and GSK-3β induced by DADLE or ET-1 but not that induced by IGF-1. DADLE and IGF-1 protected H9c2 cells from necrosis after treatment with H(2)O(2) or antimycin A. The protection by DADLE or ET-1, but not that by IGF-1, was lost by reduction of Cx43 protein expression. In contrast to Akt and GSK-3β, PKC-ε, ERK and p38 mitogen-activated protein kinase were phosphorylated by ET-1 in Cx43-knocked-down cells. Like diazoxide, an activator of the mitochondrial ATP-sensitive K(+) channel, DADLE and ET-1 induced significant ROS production in mitochondria, although such an effect was not observed for IGF-1. Cx43 knockdown did not attenuate the mitochondrial ROS production by DADLE or ET-1. Cx43 was coimmunoprecipitated with the β-subunit of G protein (Gβ), and knockdown of Gβ mimicked the effect of Cx43 knockdown on ET-1-induced phosphorylation of Akt and GSK-3β. These results suggest that Cx43 contributes to activation of class I(B) PI3K in PI3K-Akt-GSK-3β signaling possibly as a cofactor of Gβ in cardiomyocytes.

Vinculin directly binds zonula occludens-1 and is essential for stabilizing connexin 43 containing gap junctions in cardiac Myocytes

“…A recent study describes that interference with Akt1 signaling in all cells in vivo, reduced cardiac dysfunction, hypertrophy and cardiac fibrosis, thereby improving survival in a mouse model of spontaneous myocardial infarction ( Kerr et al, 2013). Most relevant for our study here is that Cx43 was shown to contribute to the activation of the PI3K/Akt signaling pathway in cardiac myocytes (Ishikawa et al, 2012).…”

Targeted disruption of PDE3B, but not PDE3A, protects murine heart from ischemia/reperfusion injury

“…It also has been suggested that mitochondrial connexin-43 translocates to IMM through the HSP90-dependent translocase complex of the outer mitochondrial membrane (TOM) pathway (36) and plays a crucial role in cardioprotection associated with the PI3K/Akt/GSK-3β pathways (55). In PDE3B −/− heart the improved postischemic recovery of RPP was inhibited significantly by blocking the PKAdependent mitoK Ca channel opening by paxilline (Fig.…”

Type 2 diabetes induces subendocardium-predominant reduction in transient outward K+ current with downregulation of Kv4.2 and KChIP2

“…RNA was extracted from tissue samples and analyzed as previously reported (9,35). In brief, Endo and Epi tissues were carefully sampled with sharp scissors in cold (4°C) Tyrode solution in a refrigerator room.…”