Anti-arrhythmic Cardiac Phenotype Elicited by Chronic Intermittent Hypoxia Is Associated With Alterations in Connexin-43 Expression, Phosphorylation, and Distribution.

Jana Kohutova,Narcis Tribulova,Ondrej Sebesta,Frantisek Kolar,Barbara Szeiffova Bacova,Pavel Vebr,Jitka M Zurmanova,Barbara Elsnicova,Marek Vecka,Daniela Hornikova,Marketa Hlavackova,Jana Jezkova,Jan Neckar,Kristyna Holzerova,Tamara Egan Benova,Olga Novakova

doi:10.3389/fendo.2018.00789

Abstract

Remodeling of the cellular distribution of gap junctions formed mainly by connexin-43 (Cx43) can be related to the increased incidence of cardiac arrhythmias. It has been shown that adaptation to chronic intermittent hypobaric hypoxia (IHH) attenuates the incidence and severity of ischemic and reperfusion ventricular arrhythmias and increases the proportion of anti-arrhythmic n-3 polyunsaturated fatty acids (n−3 PUFA) in heart phospholipids. Wistar rats were exposed to simulated IHH (7,000 m, 8-h/day, 35 exposures) and compared with normoxic controls (N). Cx43 expression, phosphorylation, localization and n−3 PUFA proportion were analyzed in left ventricular myocardium. Compared to N, IHH led to higher expression of total Cx43, its variant phosphorylated at Ser368 [p-Cx43(Ser368)], which maintains “end to end” communication, as well as p-Cx43(Ser364/365), which facilitates conductivity. By contrast, expression of non-phosphorylated Cx43 and p-Cx43(Ser278/289), attenuating intercellular communication, was lower in IHH than in N. IHH also resulted in increased expression of protein kinase A and protein kinase G while casein kinase 1 did not change compared to N. In IHH group, which exhibited reduced incidence of ischemic ventricular arrhythmias, Cx43 and p-Cx43(Ser368) were more abundant at “end to end” gap junctions than in N group and this difference was preserved after acute regional ischemia (10 min). We further confirmed higher n-3 PUFA proportion in heart phospholipids after adaptation to IHH, which was even further increased by ischemia. Our results suggest that adaptation to IHH alters expression, phosphorylation and distribution of Cx43 as well as cardioprotective n-3PUFA proportion suggesting that the anti-arrhythmic phenotype elicited by IHH can be at least partly related to the stabilization of the “end to end” conductivity between cardiomyocytes during brief ischemia.

Highlights

Proper intercellular communication is essential for normal electrical activation of the myocardium and synchronized contraction of the heart for [review see [1]]
Total Cx43 expression (t-Cx43) increased by 48% (Figure 1B) and, in parallel, the level of high-phosphorylated P1+P2 forms of t-Cx43 increased by 56 % (Figures 1A,C) in intermittent hypobaric hypoxia (IHH) myocardium compared to normoxic group
In the present study we demonstrated the association of antiarrhythmic phenotype of IHH rats with increased myocardial t-Cx43 protein level and its phosphorylation, as well as enhanced location of both t-Cx43 and p-Cx43(Ser368) at “end to end” junctions; the latter effect persisted even after 10-min ischemia

Summary

Introduction

Proper intercellular communication is essential for normal electrical activation of the myocardium and synchronized contraction of the heart for [review see [1]]. Various pathological states may lead to rhythm disturbances due to altered intercellular communication resulting in changes of conduction properties, expression and distribution of connexin-43 (Cx43), as a main component of gap junction (GJ) channels within ventricular myocardium [2, 3]. Reduction of GJ number and conductance increases susceptibility to spontaneous and inducible ventricular arrhythmias both under control conditions and during ischemia and reperfusion (I/R) [4, 5]. GJ permeability and conductivity are controlled by complex and multifactorial processes. These events are generally influenced by changes of intracellular environment under physiological and pathological conditions, e.g., pH and Ca2+ concentration [8,9,10]. The GJ conductivity is strongly influenced by Cx43 expression levels, its posttranslational modifications, protein-protein interactions, e.g., dimerization and interaction with Zona Occludens (ZO-1), Cx43 assembly and last but not least, the size of GJ plaques and their localization within cardiomyocytes [for review see [11]]

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