Protein Kinase C-Mediated Hyperphosphorylation and Lateralization of Connexin 43 Are Involved in Autoimmune Myocarditis-Induced Prolongation of QRS Complex

Translationally controlled tumor protein interacts with connexin 43 and facilitates intercellular coupling between cardiomyocytes

Introduction

Connexins are gap junction proteins that play pivotal roles in intercellular communication. Connexin 43 (Cx43) is one of the most ubiquitously expressed connexin isoforms in human. Cx43 has been demonstrated to be involved in the pathological process of various diseases, including arrhythmias. Recently, translationally controlled tumor protein (TCTP), a highly conserved anti-apoptotic protein, has been shown to play an important role in protecting against the development of heart failure. However, its role in arrhythmogenesis remains unclear. In this study, we aimed to examine the interaction between TCTP and Cx43 and investigate the roles of TCTP in the formation of Cx43 gap junction channels and gap junctional intercellular communication (GJIC) in cardiomyocytes.

Methods and results

We found that TCTP was predominantly expressed in the intercalated discs of mouse heart tissue. Cx43 in adult mouse hearts was coimmunoprecipitated using a TCTP-specific antibody. Additionally, co-localization of TCTP and Cx43 was demonstrated using a proximity ligation assay in iPS cell-derived human cardiomyocytes. TCTP silencing reduced the formation of Cx43 gap junction channels at the intercellular contacts between cardiomyocytes. Moreover, TCTP silencing significantly attenuated GJIC among cardiomyocytes. Interestingly, the development of ventricular arrhythmia was attenuated in cardiomyocyte-specific TCTP-overexpressing mice.

Conclusion

These findings indicate that TCTP regulates GJIC. Thus, TCTP may be a therapeutic target for preventing Cx43-related pathogenesis.

Cardiac Fibroblasts Enhance MMP2 Activity to Suppress Gap Junction Function in Cardiomyocytes

Although it is crucial to promptly restore blood perfusion to revive the ischemic myocardium, reperfusion itself can paradoxically contribute to the electrical instability and arrhythmias of the myocardium. Several studies have revealed that cardiac fibroblasts can impact cardiac electrophysiology through various mechanisms including the deposition of extracellular matrix, release of chemical mediators, and direct electrical coupling with myocytes. Previously, we have shown that hypoxia/reoxygenation (H/R)-treated rat fibroblasts conditional medium (H/R-FCM) could decrease the spontaneous beating frequency of rat neonatal cardiomyocytes and downregulate the expression of gap junction proteins. However, the specific mechanism by which H/R-FCM affects the gap junctions requires further investigation. H/R-FCM was obtained by culturing confluent rat cardiac fibroblasts (RCF) for 4 h under hypoxic conditions. Gap junction function, hemichannel activity, and expression of Cx43 were examined upon treatment with H/R-FCM. Gelatin zymography was performed to detect matrix metalloproteinase (MMP) activity in the conditioned medium. The effect of H/R-FCM and MMP2 inhibitors on cardiac electrophysiology and arrhythmias was investigated with an isolated rat ischemia/reperfusion (I/R) model. H/R-FCM treatment impaired gap junction function, downregulated Cx43 expression, and increased hemichannel activity in rat cardiomyocytes (H9c2). The adverse effect of H/R-FCM on gap junction, which was confirmed by the cardiomyocyte H/R model, was involved in the activation of MMP2. MMP2 inhibition could partially attenuate the detrimental effects of I/R on myocardial electrophysiological indices and arrhythmia susceptibility. Our study indicates that inhibition of MMP2 may be a promising therapeutic target for the treatment of reperfusion arrhythmia.

The activation of P38MAPK Signaling Pathway Impedes the Delivery of the Cx43 to the Intercalated Discs During Cardiac Ischemia-Reperfusion Injury

Ischemic heart disease is caused by coronary artery occlusion. Despite the increasing number and success of interventions for restoring coronary artery perfusion, myocardial ischemia-reperfusion (I/R) injury remains a significant cause of morbidity and mortality worldwide. Inspired by the impact of I/R on the Cx43 trafficking to the intercalated discs (ICDs), we aim to explore the potential mechanisms underlying the downregulation of Cx43 in ICDs after myocardial I/R. Gene set enrichment analysis (GSEA), Western blotting, and immunofluorescence experiments showed that Myocardial I/R activated the P38MAPK signaling pathway and promoted microtubule depolymerization. Inhibition of P38MAPK signaling pathway activation attenuated I/R-induced microtubule depolymerization. The ability of SB203580 to recover the distribution of Cx43 and electrophysiological parameters in I/R myocardium depended on microtubule stability. Our study suggests that microtubule depolymerization caused by the activation of the P38MAPK signaling pathway is an important mechanism underlying the downregulation of Cx43 in ICDs after myocardial I/R.

Role of Connexin 43 phosphorylation on Serine-368 by PKC in cardiac function and disease

Intercellular communication mediated by gap junction channels and hemichannels composed of Connexin 43 (Cx43) is vital for the propagation of electrical impulses through cardiomyocytes. The carboxyl terminal tail of Cx43 undergoes various post-translational modifications including phosphorylation of its Serine-368 (S368) residue. Protein Kinase C isozymes directly phosphorylate S368 to alter Cx43 function and stability through inducing conformational changes affecting channel permeability or promoting internalization and degradation to reduce intercellular communication between cardiomyocytes. Recent studies have implicated this PKC/Cx43-pS368 circuit in several cardiac-associated diseases. In this review, we describe the molecular and cellular basis of PKC-mediated Cx43 phosphorylation and discuss the implications of Cx43 S368 phosphorylation in the context of various cardiac diseases, such as cardiomyopathy, as well as the therapeutic potential of targeting this pathway.

COVID-19 is associated with the risk of cardiovascular disease death: A two-sample Mendelian randomization study

Objective

This study aimed to estimate the causal effects of Coronavirus disease 2019 susceptibility and hospitalization on cardiovascular disease death using two-sample Mendelian randomization analysis.

Methods

We used statistics from a genome-wide association study. A total of 2,568,698 participants were assessed in this study, including 1,299,010 in Coronavirus disease 2019 susceptibility databases, 908,494 in Coronavirus disease 2019 hospitalization database, and 361,194 in a cardiovascular disease death database. We performed two-sample Mendelian randomization analysis using the inverse variance weighted method. As sensitivity analysis techniques, Mendelian randomization-Egger regression, heterogeneity analyses, and Leave-one-out analysis were employed. Reverse Mendelian randomization analysis was used to detect reverse causality. Statistical significance was defined as P < 0.05.

Results

Coronavirus disease 2019 susceptibility may be a causal factor for cardiovascular disease death (β = 2.188 × 10^–3, P = 0.002), which involves five common single nucleotide polymorphisms. Similarly, Coronavirus disease 2019 hospitalization may also be a causal factor for cardiovascular disease death (β = 8.626 × 10^–4, P = 0.010), which involves nine common single nucleotide polymorphisms. Furthermore, sensitivity and reverse Mendelian randomization analysis suggested that no heterogeneity, horizontal pleiotropy or reverse causality was found between Coronavirus disease 2019 and cardiovascular disease death.

Conclusion

Our bidirectional Mendelian randomization analysis showed a causal relationship between Coronavirus disease 2019 susceptibility and hospitalization associated with an increased risk of cardiovascular disease death.