Distinct Cardiac Connexin-43 Expression in Hypertrophied and Atrophied Myocardium May Impact the Vulnerability of the Heart to Malignant Arrhythmias. A Pilot Study

Our and other studies suggest that myocardial hypertrophy in response to hypertension and hyperthyroidism increases propensity of the heart to malignant arrhythmias, while these are rare in conditions of hypothyroidism or type-1 diabetes mellitus associated with myocardial atrophy. One of the crucial factors impacting the susceptibility of the heart to life-threatening arrhythmias is gap junction channel protein connexin-43 (Cx43), which ensure cell-to-cell coupling for electrical signal propagation. Therefore, we aimed to explore Cx43 protein abundance and its topology in hypertrophic and hypotrophic cardiac phenotype. Analysis were performed in left ventricular tissue of adult male spontaneously hypertensive rat (SHR), Wistar Kyoto rats treated for 8-weeks with L-thyroxine, methimazol or strepotozotocin to induce hyperthyroid, hypothyroid and type-1 diabetic status as well as non-treated animals. Results showed that comparing to healthy rats there was a decrease of total myocardial Cx43 and its variant phosphorylated at serine368 in SHR and hyperthyroid rats. Besides, enhanced localization of Cx43 was demonstrated on lateral sides of hypertrophied cardiomyocytes. In contrast, total Cx43 protein and its serine368 variant were increased in atrophied left ventricle of hypothyroid and type-1 diabetic rats. It was associated with less pronounced alterations in Cx43 topology. In parallel, the abundance of PKCepsilon, which phosphorylates Cx43 at serine368 that stabilize Cx43 function and distribution was reduced in hypertrophied heart while enhanced in atrophied once. Findings suggest that differences in the abundance of cardiac Cx43, its variant phosphorylated at serine368 and Cx43 topology may explain, in part, distinct propensity of hypertrophied and atrophied heart to malignant arrhythmias.

Increased thermogenesis in hairless SHR is associated with enhanced myocardial connexin-43 signaling and suppression of pro-fibrotic signaling

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic VEGA 2/0158/19, 2/0002/20 and Slovak Research and Development Agency APVV 18-0548,19-0317

Background

We have previously shown that downregulation of myocardial gap junction channel protein, connexin-43 (Cx43), and up-regulation of extracellular matrix (ECM) proteins in spontaneously hypertensive rats (SHR) hearts promote occurrence of lethal arrhythmia. Cold acclimation has a potential for reducing cardiovascular risk but there is a gap of knowledge concern the heart response to adaptive thermogenesis.

Purpose

To explore myocardial Cx43 and ECM proteins in genetically hairless strain of SHR, that represents rewarding model of increased adaptive thermogenesis.

Methods

Adult hairless males and females SHRM strain that harbors mutated desmoglein-4 gene and their wild type SHR were housed at standard 22 °C (that is below thermo-neutrality for these animals) and 12:12 hour light: dark cycle. WKY control rats were used as reference normotensive strain. Heart samples of the left ventricular tissue from euthanatized rats were used for the proteomics of Cx43, protein kinases, which phosphorylates Cx43, and for ECM markers TGF-β, SMAD2/3, MMP-2, collagen-1. Immunofluoresence detection of Cx43 was performed to examine its myocardial topology.

Key Results

Cx43 protein and its phosphorylatetd status was reduced in males and females SHR vs WKY rat hearts. In contrast, adaptive thermogenesis resulted in increased both parameters in SHRM regardless the sex. Moreover, pathological topology of Cx43 attributed to its enhanced localization at lateral sides of the cardiomyocytes in SHR was attenuated in SHRM. In addition, there were gentle differences in protein levels of PKA, PKG, PKCε, MAPK, Akt between SHR and SHRM. Protein level of TGF-β and SMAD2/3 were increased in SHR vs WKY rat hearts but decreased in SHRM unlike collagen-1 that was not altered in SHRM vs SHR.

Conclusion

Findings revealed beneficial up-regulation of myocardial Cx43 along with down-regulation of extracellular matrix proteins in response of hairless SHR to increased thermogenesis.

Artificial light pollution and obesity as a risk factors of malignant cardiac arrhythmias - antiarrhythmogenic effect of omacor

Funding Acknowledgements

Type of funding sources: None.

Light pollution disrupts circadian rhythms and increases the development of obesity, but their connection to cardiovascular disease, in particular to malignant arrhythmias, is not well known.

Herein, we investigated if female rats exposed to continuous light and high-sucrose diet had altered myocardial gene transcripts and/or protein expression which affects arrhythmogenesis. We then assessed if Omacor® supplementation benefitted affected rats.

In a first experiment, adult female spontaneously hypertensive (SHR) and normotensive Wistar rats (WR) were housed under standard 12 h/12 h light/dark cycles or exposed to 6-weeks continuous 300 lux light for 24 h. In a second experiment, adult female WR rats received sucrose diet (30% sucrose solution) continuously (24 h) performed for 8 weeks. Half the rats from both experiments were throughout the experiment treated with 200 mg/100g b.w. Omacor®.

Continuous light resulted in higher rat vulnerability to malignant ventricular fibrillation (VF). This was linked with myocardial connexin-43 (Cx43) down-regulation and deteriorated intercellular electrical coupling, due in part to increased pro-inflammatory NF-κB and iNOS transcripts and decreased sarcoplasmic reticulum Ca 2+ ATPase transcripts. Omacor® treatment increased the electrical threshold to induce the VF linked with amelioration of myocardial Cx43 mRNA and Cx43 protein levels and the suppression of NF-κB and iNOS.

8 weeks lasting intake of 30% sucrose solution downregulated Cx43 and PKCε signaling along with an upregulation of myocardial PKCδ and miR-30a rendering the heart prone to ventricular arrhythmias. There was a clear benefit of Omacor® supplementation due to their antiarrhythmic effects associated with the attenuation of myocardial Cx43, PKC, and miR-30a abnormalities.

This indicates that rat exposure to continuous light and high-sucrose result in deleterious cardiac alterations jeopardizing intercellular Cx43 channel-mediated electrical communication, thereby increasing the risk of malignant arrhythmias. The adverse effects were attenuated by treatment with Omacor®, thus supporting its potential benefit and the relevance of monitoring omega-3 index in human populations at risk.

Cardiac hypertrophy as a response to volume overload in normotension and hypertension, and possible cardioprotection with angiotensin (1–7)

 

The extracellular matrix (ECM) is a highly dynamic structure that affects the proper functioning of various tissues. ECM is involved in cell signaling, participates in the origin and development of pathology and its positive influence can result in improved disease. The pathophysiology of ECM also affects intercellular communication, which results in various arrhythmias in the heart. In the present work, we focused on the signaling pathways involved in cardiac structural remodeling due to volume overload, and at the same time, we tested the possibilities of the cardioprotective effect of angiotensin (1–7) (Ang (1–7)). As an experimental model of volume overload, we chose the aortocaval fistula (ACF) model, where we focused on the compensatory phase of heart failure. Male, 8 weeks old rats, from the normotensive Hannover Spraque-Dawley (HSD), the hypertensive Ren-2 of transgenic rats (TGR), and transgenic rats expressing the Ang (1–7) producing a fusion protein (TGR(A1–7)3292), we operationally created the ACF. 5 weeks after operation, the animals were decapitated and cardiac tissue samples were taken. The ratio of cardiac weight to tibial length did not show differences between normotensive HSD and hypertensive subjects after ACF, but TGR(A1–7)3292 rats had significantly less hypertrophy compared to HSD and TGR after ACF. Hydroxyproline was increased in the TGR ACF group in both ventricles and in the right ventricle it was significantly reduced by Ang (1–7) compared to TGR ACF. In our selected proteins, the group of protein kinases C (PKC) α, δ, ε, matrix metalloproteinase 2 (MMP-2), SMAD2/3, connexin 43 (Cx43) and its phosphorylated form (pCx43) there were changes in protein levels, either due to hypertension after ACF, and in several cases the cardioprotective effect of Ang (1–7) was confirmed. PKCα and PKCδ showed a decrease in the TGR ACF group compared to HSD ACF and a decrease in the TGR(A1–7)3292 ACF group compared to HSD and TGR after ACF in both chambers. MMP-2 activity in the left and right ventricles had a reduced trend in the TGR and TGR(A1–7)3292 groups after ACF compared to HSD ACF. The same change occurred in MMP-2 protein expression in the right ventricle, in contrast to the left ventricle, where no change occurred. In the right ventricle, there was a decrease in SMAD2/3 protein expression in the TGR(A1–7)3292 group of ACFs compared to HSD and TGR after ACF. HSP70 protein expression was also reduced in both chambers in the (TGR(A1–7)3292) ACF group compared to HSD and TGR after ACF. Cx43 and pCx43 showed a very similar trend in both chambers, with an increase in the TGR ACF group versus HSD ACF, and the TGR(A1–7)3292 ACF versus HSD and TGR after ACF. Based on the obtained results, it can be stated that the right ventricle is more significantly affected by ACF and the endogenous production of Ang (1–7) alleviated the changes of the monitored proteins and the remodeling of the ECM caused by volume overload.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic VEGA 2/0158/19, 2/0002/20Slovak Research and Development Agency APVV 15-0119, APVV-19-0317