Internalization and Dephosphorylation of Connexin43 in Hypertrophied Right Ventricles of Rats With Pulmonary Hypertension

Abstract

ap junctions are specialized membrane regions consisting of groups of channels that directly connect the cytoplasmic components of adjacent cells and enable intercellular communication with respect to the exchange of ions and small (<1 kDa) molecules. 1 Gap junctions are composed of transmembrane proteins that belong to the connexin family. The principal gap junctional protein expressed in ventricles of the mammalian heart is connexin43 (Cx43), although connexin40, connexin45 and connexin 30.2 (and its human ortholog, connexin31.9) are also expressed in other regions of the heart. [2][3][4] Remodeling of gap junction in the heart is an important feature of the structural substrates for conduction disturbance and arrhythmogenesis under various pathological conditions including myocardial ischemia, infarction and hypertrophy. [2][3][4][5][6][7][8] In our previous immunohistochemical studies on rats with pressure overload-induced ventricular hypertrophy, we have shown that the cellular distribution of gap junctions are altered; in normal ventricles Cx43 gap junctions are largely confined to the intercalated disks at the cell termini, but in hypertrophied ventricles, Cx43 gap junctions are displaced from the intercalated disks and widely distributed. 9,10 Cx43 is a phosphoprotein, and the phosphorylation/dephosphorylation of Cx43 plays important roles in the regulation of protein turnover dynamics (trafficking, plaque assembly, internalization and degradation) as well as channels gating properties. 1,[11][12][13][14] In the hearts subjected to acute ischemia, [15][16][17] and in non-ischemic heart failure, 18 as well as in dilated cardiomyopathy, 19 dephosphorylation of Cx43 was shown to play an important role in its disorganization and electrical uncoupling of ventricular cells under the pathological conditions. It is well known that ventricular hypertrophy is associated with the activation or inhibition of various types of protein kinases and/or phosphatases. We, therefore, hypothesized that phosphorylation/dephosphorylation of Cx43 could also be involved in the disorganization of Cx43 gap junctions in the pressure-overload ventricular hypertrophy.In the present study, we have investigated the expression and distribution of Cx43 and its phosphorylation state in hypertrophied ventricles of rats with monocrotaline (MCT)-induced pulmonary hypertension by immunoconfocal and electron microscopy, as well as immunoblotting using isoform-specific antibodies. Background Altered expression and distribution of gap junctions might provide substrates for abnormal conduction and arrhythmogenesis in the heart, but little is known about the regulation of gap junctions under pathological conditions. The organization and phosphorylation state of connexin43 (Cx43) in ventricular hypertrophy will be investigated. Methods and ResultsRight ventricular (RV) hypertrophy was induced in rats by treatment with monocrotaline. Subcellular Cx43 distribution was assessed by immunoconfocal and electron microscopy. Immunolabeling of Cx43 was conf...

Antioxidant, EUK-8, Prevents Murine Dilated Cardiomyopathy

“…25,26,34 In human studies, downregulation of the principal gap junction protein, Cx43, was implicated in arrhythmia in ischemic heart disease and heart failure caused by DCM. 25,35 In this study, we showed that Cx43 was downregulated in H/MSod2 −/− hearts and when EUK-8 was administered to the mutant mice, the Cx43 level significantly improved without transcriptional restoration.…”

“…Cx43 is a major gap junction protein that regulates cardiac conduction. 25,26 It is speculated that Cx43 downregulation causes the development or progression of heart failure in H/M-Sod2 −/− mice, so to test this, we investigated levels of Cx43 in H/M-Sod2 -/-mice. As shown in Figure 6, the levels of Cx43 were markedly reduced in the hearts of salinetreated H/M-Sod2 −/− mice (P<0.01).…”

Ischemia Enhances Translocation of Connexin43 and Gap Junction Intercellular Communication, Thereby Propagating Contraction Band Necrosis After Reperfusion

“…It is accepted that Cx43 undergoes trafficking from the sarcoplasmic reticulum and Golgi apparatus to GJs and endocytosis-mediated degradation in lysosomes or proteasomes. 33,34 It has also been shown that Cx43 translocates to mitochondria and affords protection in ischemic preconditioning. 26,35 The P1 fraction contained marker proteins for the sarcoplasmic reticulum, Golgi apparatus, lysosomes, and mitochondria (data not shown).…”

Connexin-43 Redistribution and Gap Junction Activation During Forced Restraint Protects Against Sudden Arrhythmic Death in Rats

“…[15][16][17] In the hypertrophied right ventricles of rats with pulmonary hypertension, Cx43 underwent internalization, dephosphorylation, and degradation. 18 In Cx43-deficient mice, GJ uncoupling induced a sharp (>80%) reduction in Cx43 expression and a moderate (~40%) decrease in CV, 19,20 as well as regional heterogeneity in repolarization current. 21 This mutation resulted in high (~80%) mortality due to spontaneous arrhythmias in 1 study, 19 whereas other groups have documented inducible arrhythmias in the same model.…”