Connexin 43 dephosphorylation contributes to arrhythmias and cardiomyocyte apoptosis in ischemia/reperfusion hearts

Dexmedetomidine and Perioperative Arrhythmias

The highly selective α2-adrenoceptor agonist dexmedetomidine is a commonly used sedative drug for patients undergoing anesthesia and intensive care treatment. Several studies have indicated that dexmedetomidine may have a potential role in preventing and treating perioperative tachyarrhythmias. However, the specific effect and mechanism of action of dexmedetomidine in this context remain unclear. Dexmedetomidine is known to regulate the electrophysiologic function of the myocardium by inhibiting the function of the sinus node and atrioventricular node, as well as affecting myocardial repolarization. This paper aims to provide a theoretical basis for the prevention and treatment of perioperative arrhythmias by summarizing the effects of dexmedetomidine on myocardial electrophysiologic function and its impact on different types of arrhythmias.

Intrathecal Anesthesia Prevents Ventricular Arrhythmias in Rats with Myocardial Ischemia/Reperfusion

INTRODUCTION

Ventricular arrhythmia is commonly provoked by acute cardiac ischemia through sympathetic exaggeration and is often resistant to anti-arrhythmic therapies. Thoracic epidural anesthesia has been reported to terminate fatal ventricular arrhythmia; however, its underlying mechanism is unknown.

METHODS

Rats were randomly divided into four groups: sham, sham plus bupivacaine, ischemia/reperfusion (IR), and IR plus bupivacaine groups. Bupivacaine (1 mg/mL, 0.05 mL/100 g body weight) was injected intrathecally into the L5-L6 intervertebral space prior to establishing a myocardial IR rat model. Thereafter, cardiac arrhythmia, cardiac function, myocardial injury, and electrical activities of the heart and spinal cord were evaluated.

RESULTS

Intrathecal bupivacaine inhibited spinal neural activity, improved heart rate variability, reduced ventricular arrhythmia score, and ameliorated cardiac dysfunction in IR rats. Furthermore, intrathecal bupivacaine attenuated cardiac injury and myocardial apoptosis and regulated cardiomyocyte autophagy and connexin-43 distribution during myocardial IR.

CONCLUSION

Our results indicate that intrathecal bupivacaine blunts spinal neural activity to prevent cardiac arrhythmia and dysfunction induced by IR and that this anti-arrhythmic activity may be associated with regulation of autonomic balance, myocardial apoptosis and autophagy, and cardiac gap junction function.

IL6/adiponectin/HMGB1 feedback loop mediates adipocyte and macrophage crosstalk and M2 polarization after myocardial infarction

Background

Differences in border zone contribute to different outcomes post-infarction, such as left ventricular aneurysm (LVA) and myocardial infarction (MI). LVA usually forms within 24 h of the onset of MI and may cause heart rupture; however, LVA surgery is best performed 3 months after MI. Few studies have investigated the LVA model, the differences in border zones between LVA and MI, and the mechanism in the border zone.

Methods

The LVA, MI, and SHAM mouse models were used. Echocardiography, Masson's trichrome staining, and immunofluorescence staining were performed, and RNA sequencing of the border zone was conducted. The adipocyte-conditioned medium-treated hypoxic macrophage cell line and LVA and MI mouse models were employed to determine the effects of the hub gene, adiponectin (ADPN), on macrophages. Quantitative polymerase chain reaction (qPCR), Western blot analysis, transmission electron microscopy, and chromatin immunoprecipitation (ChIP) assays were conducted to elucidate the mechanism in the border zone. Human subepicardial adipose tissue and blood samples were collected to validate the effects of ADPN.

Results

A novel, simple, consistent, and low-cost LVA mouse model was constructed. LVA caused a greater reduction in contractile functions than MI owing to reduced wall thickness and edema in the border zone. ADPN impeded cardiac edema and promoted lymphangiogenesis by increasing macrophage infiltration post-infarction. Adipocyte-derived ADPN promoted M2 polarization and sustained mitochondrial quality via the ADPN/AdipoR2/HMGB1 axis. Mechanistically, ADPN impeded macrophage HMGB1 inflammation and decreased interleukin-6 (IL6) and HMGB1 secretion. The secretion of IL6 and HMGB1 increased ADPN expression via STAT3 and the co-transcription factor, YAP, in adipocytes. Based on ChIP and Dual-Glo luciferase experiments, STAT3 promoted ADPN transcription by binding to its promoter in adipocytes. In vivo, ADPN promoted lymphangiogenesis and decreased myocardial injury after MI. These phenotypes were rescued by macrophage depletion or HMGB1 knockdown in macrophages. Supplying adipocytes overexpressing STAT3 decreased collagen disposition, increased lymphangiogenesis, and impaired myocardial injury. However, these effects were rescued after HMGB1 knockdown in macrophages. Overall, the IL6/ADPN/HMGB1 axis was validated using human subepicardial tissue and blood samples. This axis could serve as an independent factor in overweight MI patients who need coronary artery bypass grafting (CABG) treatment.

Conclusion

The IL6/ADPN/HMGB1 loop between adipocytes and macrophages in the border zone contributes to different clinical outcomes post-infarction. Thus, targeting the IL6/ADPN/HMGB1 loop may be a novel therapeutic approach for cardiac lymphatic regulation and reduction of cell senescence post-infarction.

Post translational modifications of connexin 43 in ventricular arrhythmias after myocardial infarction

Ventricular arrhythmias are the leading cause of sudden cardiac death in patients after myocardial infarction (MI). Connexin43 (Cx43) is the most important gap junction channel-forming protein in cardiomyocytes. Dysfunction of Cx43 contributes to impaired myocardial conduction and the development of ventricular arrhythmias. Following an MI, Cx43 undergoes structural remodeling, including expression abnormalities, and redistribution. These alterations detrimentally affect intercellular communication and electrical conduction within the myocardium, thereby increasing the susceptibility to post-infarction ventricular arrhythmias. Emerging evidence suggests that post-translational modifications play essential roles in Cx43 regulation after MI. Therefore, Cx43-targeted management has the potential to be a promising protective strategy for the prevention and treatment of post infarction ventricular arrhythmias. In this article, we primarily reviewed the regulatory mechanisms of Cx43 mediated post-translational modifications on post-infarction ventricular arrhythmias. Furthermore, Cx43-targeted therapy have also been discussed, providing insights into an innovative treatment strategy for ventricular arrhythmias after MI.

TRPV4 blockade alleviates endoplasmic reticulum stress mediated apoptosis in hypoxia-induced cardiomyocyte injury

BACKGROUND

Hypoxia-induced myocardial injury remains to be a huge health issue worldwide. Transient receptor potential vanilloid 4 (TRPV4) is a high-flux Ca2+ channel that is involved in numerous cardiovascular diseases. However, the role of TRPV4 in myocardial hypoxic injury remains unclear. Accordingly, this study aimed to investigate the antiapoptotic activity of TRPV4 inhibition and elucidate the underlying mechanisms in myocardial hypoxic injury.

METHODS

The ability of TRPV4 to modulate the endoplasmic reticulum stress (ERS) and apoptosis was assessed in vitro through the administration of the TRPV4 antagonist HC-067047 or the agonist GSK1016790A. Additionally, intracellular Ca2+ concentration was measured by Fluo-4 AM.

RESULTS

TRPV4 expression was significantly upregulated in hypoxic H9c2 cells compared with that in normoxic cardiomyocytes, accompanied with increased intracellular Ca2+ levels. Conversely, TRPV4 inhibition alleviated ERS in hypoxic H9c2 cells and prevented apoptosis, whereas TRPV4 agonist exacerbated such events. Furthermore, H9c2 cell apoptosis was attenuated with the administration of 4-PBA, an ERS inhibitor.

CONCLUSION

TRPV4 inhibition alleviates hypoxia-induced H9c2 cell apoptosis by mitigating ERS.

FGF21 protects against doxorubicin-induced cardiotoxicity by inhibiting connexin 43 ubiquitination

BACKGROUND

Fibroblast growth factor 21 (FGF21) regulates glycolipid metabolism and insulin homeostasis and acts as a cardioprotective factor by protecting against myocardial ischemia/reperfusion injury, hypertension, and vascular dysfunction. FGF21 has been reported to prevent Doxorubicin (Dox)-induced cardiotoxicity, and the related signaling pathway is worthy of further study. Connexin43 (Cx43) protein was reduced by Dox treatment, especially low phosphorylated form of Cx43. Thus the aim of study is to explore the protection effect of FGF21 on Dox induced cardiotoxicity by improving the expression of Cx43 and the involved signaling pathway.

METHODS AND RESULTS

FGF21 inhibited apoptosis in Dox-treated mice and cardiomyocytes. FGF21 increased the levels of connexin43 phosphorylated at serine (S) 282 (p-Cx43 S282) and total Cx43 to inhibit Dox-induced apoptosis. By RNA sequencing, we found that deubiquitinase monocyte chemoattractant protein-induced protein 1 (MCPIP1) expression was increased by FGF21. We further found that FGF21 induced the phosphorylation of fibroblast growth factor receptor 1 (FGFR1), extracellular signal-regulated kinase 1 and 2 (Erk1/2), and Elk. Phosphorylated Elk translocated to the nucleus and increased the expression of MCPIP1. Then, MCPIP1 bound neural precursor cell expressed developmentally downregulated protein 4 (Nedd4), an E3 ubiquitination ligase, as shown by co-immunoprecipitation (Co-IP), and suppressed Cx43 ubiquitination and degradation, competitively inhibiting the binding of Cx43 with Nedd4. Thus Nedd4 could not bind and ubiquitinate Cx43, leading to the up-regulation of Cx43 and phosphorylation of Cx43 at S282.

CONCLUSIONS

FGF21 inhibited the effects of Dox on cardiomyocytes by elevating the phosphorylation of Cx43 at S282 and total Cx43 expression. This study suggests a previously unknown mechanism for the FGF21-mediated enhancement of cardiomyocyte survival and provides an effective approach to protect against the adverse cardiac effects of Dox.

The potential roles of stress-induced phosphoprotein 1 and connexin 43 in rats with reperfusion arrhythmia

OBJECTIVE

Connexin 43 (Cx43) is a critical gene for maintaining myocardial homeostasis. Interestingly, Cx43 and stress-induced phosphoprotein 1 (STIP1) were recorded to be lowly expressed in ischemia/reperfusion (I/R). However, their impacts on reperfusion arrhythmia (RA) remain to be explored. Our study aimed to find out the related underlying mechanisms.

METHODS

After the establishment of an isolated heart model through Langendorff perfusion, the heart rate, conduction activation time, conduction velocity, and conduction direction of the left ventricle were evaluated, along with the apoptotic rate detection in the collected myocardial tissues. After the construction of a hypoxia/reoxygenation (H/R)-induced cellular model, cell apoptosis, intercellular communication, cell viability, and the content of reactive oxygen species, superoxide dismutase, malondialdehyde, and lactic dehydrogenase were measured. The expression of Cx43 and STIP1 was determined in both rat heart and cell models. The bindings of STIP3 and Cx43 to  heat shock protein 90 (HSP90) and heat shock protein 70 (HSP70) were verified.

RESULTS

Relative to the corresponding controls, Cx43 and STIP1 were decreased in myocardial tissues of RA rats and H/R-stimulated H9C2 cells, where Cx43-binding HSP70 and HSP90 were respectively increased and decreased, and ubiquitination level of Cx43 was enhanced. STIP1 overexpression promoted protein expression of Cx43, intercellular communication, and cell viability, and reduced cell apoptosis and oxidative stress in H/R-stimulated H9C2 cells.

CONCLUSION

STIP1 promoted Cx43 expression to improve intercellular communication and reduce oxidative stress in H/R-stimulated H9C2 cells.

Insulin-Like Growth Factor 1 Receptor Deficiency Alleviates Angiotensin II-Induced Cardiac Fibrosis Through the Protein Kinase B/Extracellular Signal-Regulated Kinase/Nuclear Factor-κB Pathway

Background The renin-angiotensin system plays a crucial role in the development of heart failure, and Ang II (angiotensin II) acts as the critical effector of the renin-angiotensin system in regulating cardiac fibrosis. However, the mechanisms of cardiac fibrosis are complex and still not fully understood. IGF1R (insulin-like growth factor 1 receptor) has multiple functions in maintaining cardiovascular homeostasis, and low-dose IGF1 treatment is effective in relieving Ang II-induced cardiac fibrosis. Here, we aimed to investigate the molecular mechanism of IGF1R in Ang II-induced cardiac fibrosis. Methods and Results Using primary mouse cardiac microvascular endothelial cells and fibroblasts, in vitro experiments were performed. Using C57BL/6J mice and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9)-mediated IGF1R heterozygous knockout (Igf1r+/-) mice, cardiac fibrosis mouse models were induced by Ang II for 2 weeks. The expression of IGF1R was examined by quantitative reverse transcription polymerase chain reaction, immunohistochemistry, and Western blot. Mice heart histologic changes were evaluated using Masson and picro sirius red staining. Fibrotic markers and signal molecules indicating the function of the Akt (protein kinase B)/ERK (extracellular signal-regulated kinase)/nuclear factor-κB pathway were detected using quantitative reverse transcription polymerase chain reaction and Western blot. RNA sequencing was used to explore IGF1R-mediated target genes in the hearts of mice, and the association of IGF1R and G-protein-coupled receptor kinase 5 was identified by coimmunoprecipitation. More important, blocking IGF1R signaling significantly suppressed endothelial-mesenchymal transition in primary mouse cardiac microvascular endothelial cells and mice in response to transforming growth factor-β1 or Ang II, respectively. Deficiency or inhibition of IGF1R signaling remarkably attenuated Ang II-induced cardiac fibrosis in primary mouse cardiac fibroblasts and mice. We further observed that the patients with heart failure exhibited higher blood levels of IGF1 and IGF1R than healthy individuals. Moreover, Ang II treatment significantly increased cardiac IGF1R in wild type mice but led to a slight downregulation in Igf1r+/- mice. Interestingly, IGF1R deficiency significantly alleviated cardiac fibrosis in Ang II-treated mice. Mechanistically, the phosphorylation level of Akt and ERK was upregulated in Ang II-treated mice, whereas blocking IGF1R signaling in mice inhibited these changes of Akt and ERK phosphorylation. Concurrently, phosphorylated p65 of nuclear factor-κB exhibited similar alterations in the corresponding group of mice. Intriguingly, IGF1R directly interacted with G-protein-coupled receptor kinase 5, and this association decreased ≈50% in Igf1r+/- mice. In addition, Grk5 deletion downregulated expression of the Akt/ERK/nuclear factor-κB signaling pathway in primary mouse cardiac fibroblasts. Conclusions IGF1R signaling deficiency alleviates Ang II-induced cardiac fibrosis, at least partially through inhibiting endothelial-mesenchymal transition via the Akt/ERK/nuclear factor-κB pathway. Interestingly, G-protein-coupled receptor kinase 5 associates with IGF1R signaling directly, and it concurrently acts as an IGF1R downstream effector. This study suggests the promising potential of IGF1R as a therapeutic target for cardiac fibrosis.

Dapagliflozin ameliorates sepsis-induced heart injury by inhibiting cardiomyocyte apoptosis and electrical remodeling through the PI3K/Akt pathway

BACKGROUND

Sepsis-induced heart injury is one of the leading causes of circulation disorders worldwide. Dapagliflozin, a sodium-glucose cotransporter 2 inhibitor mainly used for controlling blood glucose, has been shown to exert a protective effect on cardiomyocytes. However, the protective effect of dapagliflozin against sepsis-induced cardiac injury and the underlying mechanism needs to be studied.

AIM

This study aims to investigate the effect of dapagliflozin on sepsis-induced cardiomyopathy and the potential mechanisms involved.

METHODS

The rat model of sepsis was constructed by intraperitoneal injection of lipopolysaccharide. Echocardiography and electrophysiological studies were performed to detect changes in cardiac function and electrical activity. Cardiac pathological alternation and cardiomyocyte apoptosis were measured by H&E staining, serological analysis, immunohistochemical, immunofluorescence, and TUNEL assays. Western blot and qRT-PCR were performed to elucidate the underlying mechanism of dapagliflozin. Additionally, corresponding experiments in H9c2 cells were performed to further validate the mechanisms in vitro.

RESULTS

Dapagliflozin improved cardiac dysfunction and reduced the susceptibility to ventricular arrhythmias in sepsis rats by ameliorating cardiac inflammation, suppressing cardiomyocyte apoptosis, and alleviating ventricular electrical remodeling. The PI3K/Akt signaling pathway inhibitor inhibited the anti-apoptotic effect of dapagliflozin, indicating that the protective effect was related to the activation of the PI3K/Akt pathway.

CONCLUSION

Dapagliflozin ameliorated sepsis-induced cardiac injury by suppressing electrical remodeling and cardiomyocyte apoptosis, which could be attributed to the PI3K/Akt pathway.

Phloretin ameliorates heart function after myocardial infarction via NLRP3/Caspase-1/IL-1β signaling

OBJECTIVES/AIMS

Inflammation is crucial in structural and electrical remodeling after myocardial infarction (MI), affecting cardiac pump function and conduction pathways. Phloretin possesses an anti-inflammation role by inhibiting the NLRP3/Caspase-1/IL-1β pathway. However, the effects of Phloretin on cardiac contractile and electrical conduction function after MI remained unclear. Therefore, we aimed to investigate the potential role of Phloretin in a rat model of MI.

METHODS

Rats were assigned into four groups: Sham, Sham+Phloretin, MI and MI+Phloretin, with ad libitum food and water. In the MI and MI+Phloretin groups, the left anterior descending coronary artery was occluded for 4 weeks, while the Sham and Sham+Phloretin groups received sham operation. The Sham+Phloretin group and the MI+Phloretin group received oral administration of Phloretin. In vitro, H9c2 cells were subjected to hypoxic conditions to simulate an MI model, with Phloretin for 24 h. Cardiac electrophysiological properties were assessed following MI, including the effective refractory period (ERP), action potential duration (APD)90 and ventricular fibrillation (VF) incidence. Echocardiography evaluated left ventricular ejection fraction (LVEF), left ventricular fraction shortening (LVFS), left ventricular internal diameter at end-diastole (LVIDd), left ventricular internal diameter at end-systole (LVIDs), left ventricular end-systolic volume (LVESV) and left ventricular end-diastolic volume (LVEDV) to assess cardiac function. Serum type B natriuretic peptide (BNP) level was applied to evaluate the degree of Heart failure (HF). The fibrosis area and severity were assessed by Masson staining and protein expression levels of collagen 3, collagen 1, TGF-β and α-SMA. Western blot analysis estimated the protein expression levels of NLRP3, Pro Caspase-1, Caspase-1, ASC, IL-18, IL-1β, pp38, p38, and Connexin43(Cx43) to elucidate the influence of inflammation on electrical remodeling after MI.

RESULTS

Our findings demonstrate that Phloretin inhibits the NLRP3/Caspase-1/IL-1β pathway, leading to the upregulation of Cx43 by limiting p38 phosphorylation, which further decreases susceptibility to ventricular arrhythmias (VAs). Additionally, Phloretin attenuated fibrosis by inhibiting inflammation to prevent HF. In vitro experiments also provided strong evidence supporting the inhibitory effects of Phloretin on the NLRP3/Caspase-1/IL-1β pathway.

CONCLUSION

Our results suggest that Phloretin could suppress the NLRP3/Caspase-1/IL-1β pathway to reverse structural and electrical remodeling after MI to prevent the occurrence of VAs and HF.

CCR2 inhibitor strengthens the adiponectin effects against myocardial injury after infarction

Little evidence demonstrated the effects of nitric oxide (NO) hydrogel with adipocytes in vivo. We aimed to investigate the effects of adiponectin (ADPN) and CCR2 antagonist on cardiac functions and macrophage phenotypes after myocardial infarction (MI) using chitosan caged nitric oxide donor (CSNO) patch with adipocytes. 3T3-L1 cell line was induced to adipocytes and ADPN expression was knocked down. CSNO was synthesized and patch was constructed. MI model was constructed and patch was placed on the infarcted area. ADPN knockdown adipocytes or control was incubated with CSNO patch, and CCR2 antagonist was also used to investigate the ADPN effects on myocardial injury after infarction. On day 7 after operation, cardiac functions of the mice using CSNO with adipocytes or ADPN knockdown adipocytes improved more than in mice only using CSNO for treatment. Lymphangiogenesis increased much more in the MI mice using CSNO with adipocytes. After treating with CCR2 antagonist, Connexin43+ CD206+ cells and ZO-1+ CD206+ cells increased, suggesting that CCR2 antagonist promoted M2 polarization after MI. Besides, CCR2 antagonist promoted ADPN expression in adipocytes and cardiomyocytes. ELISA was also used and CKMB expression was much lower than other groups at 3 days after operation. On day 7 after operation, the VEGF and TGFβ expressions were high in the adipocytes CSNO group, illustrating that higher ADPN led to better treatment. In all, CCR2 antagonist enhanced the ADPN effects on macrophage M2 polarization and cardiac functions. The combination used in border zone and infarcted areas may help improve patients' prognosis in surgery, such as CABG.

Biological Modification of Arrhythmogenic Substrates by Cell-Free Therapeutics

Ventricular arrhythmias (VAs) represent a major cause of sudden cardiac death and afflict patients with heart failure from both ischaemic and non-ischaemic origins, and inherited cardiomyopathies. Current VA management, including anti-arrhythmic medications, autonomic modulation, implantable cardioverter-defibrillator implantation, and catheter ablation, remains suboptimal. Catheter ablation may even cause significant cardiomyocyte loss. Cell-based therapies and exosome treatment have been proposed as promising strategies to lessen cardiomyocyte death, modulate immune reaction, and reduce myocardial scarring, and, therefore, are potentially beneficial in treating VAs. In this review, we summarise the current cornerstones of VA management. We also discuss recent advances and ongoing evidence regarding cell-based and exosome therapy, with special attention to VA treatment.

Downregulation of cardiac PIASy inhibits Cx43 SUMOylation and ameliorates ventricular arrhythmias in a rat model of myocardial ischemia/reperfusion injury

BACKGROUND

Dysfunction of the gap junction channel protein connexin 43 (Cx43) contributes to myocardial ischemia/reperfusion (I/R)-induced ventricular arrhythmias. Cx43 can be regulated by small ubiquitin-like modifier (SUMO) modification. Protein inhibitor of activated STAT Y (PIASy) is an E3 SUMO ligase for its target proteins. However, whether Cx43 is a target protein of PIASy and whether Cx43 SUMOylation plays a role in I/R-induced arrhythmias are largely unknown.

METHODS

Male Sprague-Dawley rats were infected with PIASy short hairpin ribonucleic acid (shRNA) using recombinant adeno-associated virus subtype 9 (rAAV9). Two weeks later, the rats were subjected to 45 min of left coronary artery occlusion followed by 2 h reperfusion. Electrocardiogram was recorded to assess arrhythmias. Rat ventricular tissues were collected for molecular biological measurements.

RESULTS

Following 45 min of ischemia, QRS duration and QTc intervals statistically significantly increased, but these values decreased after transfecting PIASy shRNA. PIASy downregulation ameliorated ventricular arrhythmias induced by myocardial I/R, as evidenced by the decreased incidence of ventricular tachycardia and ventricular fibrillation, and reduced arrythmia score. In addition, myocardial I/R statistically significantly induced PIASy expression and Cx43 SUMOylation, accompanied by reduced Cx43 phosphorylation and plakophilin 2 (PKP2) expression. Moreover, PIASy downregulation remarkably reduced Cx43 SUMOylation, accompanied by increased Cx43 phosphorylation and PKP2 expression after I/R.

CONCLUSION

PIASy downregulation inhibited Cx43 SUMOylation and increased PKP2 expression, thereby improving ventricular arrhythmias in ischemic/reperfused rats heart.

Rhodiola wallichiana var.cholaensis protects against myocardial ischemia-reperfusion injury by attenuating oxidative stress-mediated apoptosis via enhancing Nrf2 signaling

The present study aimed to explore the cardioprotective effects of Rhodiola wallichiana var.cholaensis (RW) against hypoxia/reoxygenation (H/R)-induced H9c2 cell injury and ischemia/reperfusion (I/R)-induced myocardial injury. Following treatment with RW, H9c2 cells were subjected to 4 h of hypoxia/3 h of reoxygenation. MTT assay, LDH assay, and flow cytometry were employed to detect cell viability and changes of ROS and mitochondrial membrane potential. Moreover, after RW treatment, rats underwent 30 min of ischemia, followed by 120 min of reperfusion. Masson and TUNEL staining were performed to measure myocardial damage and apoptosis, respectively. The changes in the levels of proteins were detected by ELISA and western blot. The results showed that RW attenuated the H/R-induced increase in LDH release and loss of the mitochondrial membrane potential, as well as the apoptosis in H9c2 cells. Meanwhile, RW significantly reduces the ST-segment elevation and improves cardiomyocytes' injury, inhibit the apoptosis induced by I/R in rats. Furthermore, RW could decrease the levels of MDA and increase the levels of SOD, T-AOC. GSH-Px and GSH both in vivo and in vitro. Besides, RW increased the expressions of Nrf2, HO-1, ARE and NQO1, and decreased the expressions of Keap1, activating the Nrf2 signaling pathway. Taken together, these results suggested that RW exerts cardioprotection on H/R injury in H9c2 cells and I/R injury in rats by attenuating oxidative stress-mediated apoptosis via enhancing Nrf2 signaling.

Connexin 43 dephosphorylation at serine 282 induces spontaneous arrhythmia and increases susceptibility to ischemia/reperfusion injury

Background

Connexin 43 (Cx43), the predominant gap junction protein in hearts, is modified by specific (de)phosphorylation events under physiological and pathological states to affect myocardium function and structure. Previously we found that deficiency in Cx43 S282 phosphorylation could impair intercellular communication and contribute to cardiomyocyte apoptosis by activating p38 mitogen-activated protein kinase (p38 MAPK)/factor-associated suicide (Fas)/Fas-associating protein with a novel death domain (FADD) pathway, which is involved in myocardium injury in ischemia/reperfusion (I/R) heart. In addition, mutant at Cx43 S282 substituted with alanine heterozygous mice (S282A+/-) exhibited different degrees of ventricular arrhythmias and only some underwent myocardium apoptosis. In this study, we aimed to investigate the role of Cx43 pS282 in different cardiac pathological phenotypes.

Methods

We examined cardiac function, structure, and relevant protein expression in S282A+/- mice (aged 2, 10 and 30 weeks) by electrocardiograph, echocardiography, histological staining, and co-immunoprecipitation followed by Western blot. Intraperitoneal isoprenaline injection and I/R surgery were applied in S282A+/- mice as external stimulus. 2,3,5-triphenyltetrazolium chloride staining was used for myocardium infarction evaluation.

Results

Adult S282A+/- mice (aged 10 and 30 weeks) still exhibited spontaneous arrhythmia. Unlike neonatal stage (aged around 2 weeks), no apoptosis-related manifestations and the activation of p38 MAPK-Fas-FADD apoptotic pathway were observed in adult S282A+/- hearts. S282A+/- neonatal mice with cardiomyocytes apoptosis exhibited more than 60% dephosphorylation at Cx43 S282 than WT mice, while less than 40% S282 dephosphorylation were found in adult S282A+/- mice. In addition, although S282A+/- mice displayed normal cardiac function, they were highly susceptible to isoproterenol-induced ECG alternans and prone to cardiac injury and deaths upon I/R attack.

Conclusions

These results reinforce that Cx43 S282 dephosphorylation acts as a susceptibility factor in regulating cardiomyocyte survival and cardiac electrical homeostasis in basal conditions and contributes to myocardium injury in the setting of I/R. Cx43 S282 phosphorylation was competent to induce spontaneous arrhythmias, cardiomyocyte apoptosis and deaths based on the degree of S282 dephosphorylation.

Ginsenoside Rb1 promotes the activation of PPARα pathway via inhibiting FADD to ameliorate heart failure

PURPOSE

Ginsenoside Rb1 (GRb1), a dammarane-type triterpene saponin compound mainly distributed in ginseng (Panax ginseng), has been demonstrated to ameliorate cardiovascular diseases. However, it remains unclear whether GRb1 alleviates heart failure (HF) by maintaining cardiac energy metabolism balance. Therefore, this work aimed to investigate the cardiac benefits of GRb1 against cardiac energy deficit and explore its mechanism of action.

METHODS AND RESULTS

Isoproterenol (ISO) induced HF Sprague-Dawley rats were administrated with GRb1 or fenofibrate for 6 weeks. ISO-induced primary neonatal rat cardiomyocytes (NRCMs) were used as the in vitro model. In vivo, GRb1 significantly improved the structural and metabolic disorder, as demonstrated by the restoration of cardiac function, inhibition of cardiac hypertrophy and fibrosis, and increased adenosine triphosphate (ATP) generation. In vitro, GRb1 effectively protected mitochondrial function and scavenged excessive reactive oxygen species. Moreover, in ISO-induced NRCMs, GRb1 significantly inhibited the abnormal upregulation of Fas-associated death domain (FADD), promoted transcriptional activation of peroxisome proliferator-activated receptor-alpha (PPARα), improved the aberrant expression of cardiac energy metabolism-related enzymes and cardiac fatty acid oxidation, and subsequently increased the synthesis of ATP. Noticeably, GRb1 could inhibit the increased binding between FADD and PPARα, which contributed to the activation of PPARα. Furthermore, GRb1 strengthened the thermal stabilization of FADD and might bind to FADD directly.

CONCLUSIONS

Collectively, it's part of the in-depth mechanism of GRb1's cardio-protection that GRb1 could directly bind to FADD and counteract its negative role in the transcription of PPARα thus ameliorating cardiac energy derangement and HF.

MiR-130a-3p regulates FUNDC1-mediated mitophagy by targeting GJA1 in myocardial ischemia/reperfusion injury

Understanding the complex pathogenesis in myocardial ischemia/reperfusion (I/R) injury (IRI) is an urgent problem in clinical trials. Increasing pieces of evidence have suggested that miRNAs are involved in the occurrence and development of heart diseases by regulating mitochondria-related gene expression. Mitochondria have been acknowledged as the key triggers of cardiac I/R injury. However, the potential impact of miR-130a on mitochondria remains unclear in myocardial IRI. Exploring the regulatory mechanism of miR-130a on mitochondria may provide a new target for IRI therapy. In the present study, we found that miR-130a significantly increased in acute myocardial infarction (AMI) patients and myocardial I/R rats. MiR-130a could downregulate the viability of cardiomyocytes and the knockdown of miR-130a could protect the viability of cardiomyocytes under hypoxia-reoxygenation (HR). Over-expression of miR-130a resulted in mitochondrial dysfunction. It was evidenced by decreases in mitochondrial ATP production, mitochondrial membrane potential (MMP), and an increase in reactive oxygen species (ROS) production. However, suppression of miR-130a could protect against mitochondrial damage, show elevation of mitochondrial ATP production rate and MMP, and reduce ROS production. We further explored the effect of miR-130a on the mitochondrial quality control (QMC) system by determining mitochondrial-protein-specific proteases and analyzed mitochondrial morphology by fluorescence imaging and electron microscopy, respectively. It was noted that miR-130a could suppress mitochondrial fusion and FUNDC1-mediated mitophagy to accelerate myocardial IRI. Moreover, we investigated the potential miR-130a targeted mitochondria-related genes to understand the regulatory mechanism of miR-130a in the setting of myocardial IRI. It was revealed that miR-130a targeted GJA1, and GJA1 rescued IRI by enhancing ATP production rate and oxidative phosphorylation, meanwhile protecting cell viability, MMP, and activating mitophagy. In addition, the knockdown of miR-130a significantly activated FUNDC1-mediated mitophagy, while the knockdown of GJA1 reversed the relevant response. Collectively, our findings suggest that miR-130a regulates FUNDC1-mediated mitophagy by targeting GJA1 in myocardial IRI.

Panax ginseng against myocardial ischemia/reperfusion injury: A review of preclinical evidence and potential mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Panax ginseng C. A. Meyer (P. ginseng) is effective in the prevention and treatment of myocardial ischemia-reperfusion (I/R) injury. The mechanism by which P. ginseng exerts cardioprotective effects is complex. P. ginseng contains many pharmacologically active ingredients, such as molecular glycosides, polyphenols, and polysaccharides. P. ginseng and each of its active components can potentially act against myocardial I/R injury. Myocardial I/R was originally a treatment for myocardial ischemia, but it also induced irreversible damage, including oxygen-containing free radicals, calcium overload, energy metabolism disorder, mitochondrial dysfunction, inflammation, microvascular injury, autophagy, and apoptosis.

AIM OF THE STUDY

This study aimed to clarify the protective effects of P. ginseng and its active ingredients against myocardial I/R injury, so as to provide experimental evidence and new insights for the research and application of P. ginseng in the field of myocardial I/R injury.

MATERIALS AND METHODS

This review was based on a search of PubMed, NCBI, Embase, and Web of Science databases from their inception to February 21, 2022, using terms such as "ginseng," "ginsenosides," and "myocardial reperfusion injury." In this review, we first summarized the active ingredients of P. ginseng, including ginsenosides, ginseng polysaccharides, and phytosterols, as well as the pathophysiological mechanisms of myocardial I/R injury. Importantly, preclinical models with myocardial I/R injury and potential mechanisms of these active ingredients of P. ginseng for the prevention and treatment of myocardial disorders were generally summarized.

RESULTS

P. ginseng and its active components can regulate oxidative stress related proteins, inflammatory cytokines, and apoptosis factors, while protecting the myocardium and preventing myocardial I/R injury. Therefore, P. ginseng can play a role in the prevention and treatment of myocardial I/R injury.

CONCLUSIONS

P. ginseng has a certain curative effect on myocardial I/R injury. It can prevent and treat myocardial I/R injury in several ways. When ginseng exerts its effects, should be based on the theory of traditional Chinese medicine and with the help of modern medicine; the clinical efficacy of P. ginseng in preventing and treating myocardial I/R injury can be improved.

The Characteristic of Resident Macrophages and their Therapeutic Potential for Myocardial Infarction

Resident macrophages (R-mac) are a subset of macrophages with self-renewal functions, which play a pivotal role in the homeostasis, inflammation, injury, and repair of the heart. In this paper, we summarize the knowledge related to cardiac R-mac and describe their dominating functions in myocardial infarction, such as inhibiting fibrosis and adverse remodeling, promoting revascularization and improving arrhythmia, etc. In the last, we sketch out the extended application of R-mac in tissue engineering, providing a novel direction of research and application for the therapy in the future.

Role of cardiac mitofusins in cardiac conduction following simulated ischemia-reperfusion

Mitochondrial dysfunction induced by acute cardiac ischemia-reperfusion (IR), may increase susceptibility to arrhythmias by perturbing energetics, oxidative stress production and calcium homeostasis. Although changes in mitochondrial morphology are known to impact on mitochondrial function, their role in cardiac arrhythmogenesis is not known. To assess action potential duration (APD) in cardiomyocytes from the Mitofusins-1/2 (Mfn1/Mfn2)-double-knockout (Mfn-DKO) compared to wild-type (WT) mice, optical-electrophysiology was conducted. To measure conduction velocity (CV) in atrial and ventricular tissue from the Mfn-DKO and WT mice, at both baseline and following simulated acute IR, multi-electrode array (MEA) was employed. Intracellular localization of connexin-43 (Cx43) at baseline was evaluated by immunohistochemistry, while Cx-43 phosphorylation was assessed by Western-blotting. Mfn-DKO cardiomyocytes demonstrated an increased APD. At baseline, CV was significantly lower in the left ventricle of the Mfn-DKO mice. CV decreased with simulated-ischemia and returned to baseline levels during simulated-reperfusion in WT but not in atria of Mfn-DKO mice. Mfn-DKO hearts displayed increased Cx43 lateralization, although phosphorylation of Cx43 at Ser-368 did not differ. In summary, Mfn-DKO mice have increased APD and reduced CV at baseline and impaired alterations in CV following cardiac IR. These findings were associated with increased Cx43 lateralization, suggesting that the mitofusins may impact on post-MI cardiac-arrhythmogenesis.

Ventricular arrhythmias in acute myocardial ischaemia-Focus on the ageing and sex

Annually, approximately 17 million people die from cardiovascular diseases worldwide, half of them suddenly. The most common direct cause of sudden cardiac death is ventricular arrhythmia triggered by an acute coronary syndrome (ACS). The study summarizes the knowledge of the mechanisms of arrhythmia onset during ACS in humans and in animal models and factors that may influence the susceptibility to life-threatening arrhythmias during ACS with particular focus on the age and sex. The real impact of age and sex on the arrhythmic susceptibility within the setting of acute ischaemia is masked by the fact that ACSs result from coronary artery disease appearing with age much earlier among men than among women. However, results of researches show that in ageing process changes with potential pro-arrhythmic significance, such as increased fibrosis, cardiomyocyte hypertrophy, decrease number of gap junction channels, disturbances of the intracellular Ca²⁺ signalling or changes in electrophysiological parameters, occur independently of the development of cardiovascular diseases and are more severe in male individuals. A review of the literature also indicates a marked paucity of research in this area in female and elderly individuals. Greater awareness of sex differences in the aging process could help in the development of personalized prevention methods targeting potential pro-arrhythmic factors in patients of both sexes to reduce mortality during the acute phase of myocardial infarction. This is especially important in an era of aging populations in which women will predominate due to their longer lifespan.

Benefits of SGLT2 inhibitors in arrhythmias

Some studies have shown that sodium-glucose cotransporter (SGLT) 2 inhibitors can definitively attenuate the occurrence of cardiovascular diseases such as heart failure (HF), dilated cardiomyopathy (DCM), and myocardial infarction. With the development of research, SGLT2 inhibitors can also reduce the risk of arrhythmias. So in this review, how SGLT2 inhibitors play a role in reducing the risk of arrhythmia from the perspective of electrical remodeling and structural remodeling are explored and then the possible mechanisms are discussed. Specifically, we focus on the role of SGLT2 inhibitors in Na+ and Ca2 + homeostasis and the transients of Na+ and Ca2 +, which could affect electrical remodeling and then lead to arrythmia. We also discuss the protective role of SGLT2 inhibitors in structural remodeling from the perspective of fibrosis, inflammation, oxidative stress, and apoptosis. Ultimately, it is clear that SGLT2 inhibitors have significant benefits on cardiovascular diseases such as HF, myocardial hypertrophy and myocardial infarction. It can be expected that SGLT2 inhibitors can reduce the risk of arrhythmia.

Connexin 43 hyper-phosphorylation at serine 282 triggers apoptosis in rat cardiomyocytes via activation of mitochondrial apoptotic pathway

Cx43 is the major connexin in ventricular gap junctions, and plays a pivotal role in control of electrical and metabolic communication among adjacent cardiomyocytes. We previously found that Cx43 dephosphorylation at serine 282 (pS282) caused cardiomyocyte apoptosis, which is involved in cardiac ischemia/reperfusion injury. In this study we investigated whether Cx43-S282 hyper-phosphorylation could protect cardiomyocytes against apoptosis. Adenovirus carrying rat full length Cx43 gene (Cx43-wt) or a mutant gene at S282 substituted with aspartic acid (S282D) were transfected into neonatal rat ventricular myocytes (NRVMs) or injected into rat ventricular wall. Rat abdominal aorta constriction model (AAC) was used to assess Cx43-S282 phosphorylation status. We showed that Cx43 phosphorylation at S282 was increased over 2-times compared to Cx43-wt cells at 24 h after transfection, while pS262 and pS368 were unaltered. S282D-transfected cells displayed enhanced gap junctional communication, and increased basal intracellular Ca²⁺ concentration and spontaneous Ca²⁺ transients compared to Cx43-wt cells. However, spontaneous apoptosis appeared in NRVMs transfected with S282D for 34 h. Rat ventricular myocardium transfected with S282D in vivo also exhibited apoptotic responses, including increased Bax/Bcl-xL ratio, cytochrome c release as well as caspase-3 and caspase-9 activities, while factor-associated suicide (Fas)/Fas-associated death domain expression and caspase-8 activity remained unaltered. In addition, AAC-induced hypertrophic ventricles had apoptotic injury with Cx43-S282 hyper-phosphorylation compared with Sham ventricles. In conclusion, Cx43 hyper-phosphorylation at S282, as dephosphorylation, also triggers cardiomyocyte apoptosis, but through activation of mitochondrial apoptosis pathway, providing a fine-tuned Cx43-S282 phosphorylation range required for the maintenance of cardiomyocyte function and survival.

Macrophages-Related Genes Biomarkers in the Deterioration of Atherosclerosis

Background

The macrophages are involved in all stages of cardiovascular diseases, demonstrating the correlation between inflammation, atherosclerosis, and myocardial infarction (MI). Here, we aim to investigate macrophages-related genes in the deterioration of atherosclerosis.

Methods

GSE41571 was downloaded and the abundance of immune cells was estimated by utilizing the xCell. By utilizing the limma test and correlation analysis, differentially expressed macrophages-related genes (DEMRGs) were documented. The functional pathways and the protein–protein interaction (PPI) network were analyzed and the hub DEMRGs were obtained. The hub DEMRGs and their interactions were analyzed using NetworkAnalyst 3.0 and for validation, the expressions of hub DEMRGs were analyzed using the GSE135055 and GSE116250 datasets as well as atherosclerosis and MI mice model.

Results

A total of 509 differentially expressed genes (DEGs) were correlated with the abundance of macrophages and were identified as DEMRGs (Pearson correlation coefficients (PCC) > 0.6), which were mainly enriched in extracellular structure organization, lysosomal membrane, MHC protein complex binding, and so on. After screening out, 28 hub DEMRGs were obtained with degrees ≥20, including GNAI1 (degree = 113), MRPS2 (degree = 56), HCK (degree = 45), SOCS3 (degree = 40), NET1 (degree = 28), and so on. After validating using Gene Expression Omnibus (GEO) datasets and the atherosclerosis and MI mice model, eight proteins were validated using ApoE-/- and C57 mice. The expression levels of proteins, including SYNJ2, NET1, FZD7, LCP2, HCK, GNB2, and PPP4C were positively correlated to left ventricular ejection fraction (LVEF), while that of EIF4EBP1 was negatively correlated to LVEF.

Conclusion

The screened hub DEMRGs, SYNJ2, NET1, FZD7, LCP2, HCK, GNB2, EIF4EBP1, and PPP4C, may be therapeutic targets for treatment and prediction in the patients with plaque progression and MI recurrent events. The kit of the eight hub DEMRGs may test plaque progression and MI recurrent events and help in the diagnosis and treatment of MI-induced heart failure (HF), thus decreasing mortality and morbidity.

Src-homology domain 2 containing protein tyrosine phosphatase-1 (SHP-1) directly binds to proto-oncogene tyrosine-protein kinase Src (c-Src) and promotes the transcriptional activation of connexin 43 (Cx43)

The prevalence of atrial fibrillation (AF), which is one of the common arrhythmias in clinics, is increasing sharply and has affected millions of patients, which is expected to triple by 2050. The purpose of the study was to explore the regulatory relationship between Src-homology domain 2 containing protein tyrosine phosphatase-1 (SHP-1) and proto-oncogene tyrosine-protein kinase Src (c-Src) and the regulation of Connexins 43 (Cx43), and its effect on AF was also studied. Mouse atrial myocyte line (HL-1 cell line) was used as the research object. After overexpression of SHP-1, the expressions of p-c-Src, Cx43, and SHP-1 were detected by Western blot and cellular immunofluorescence, respectively. The location and interaction of SHP-1 and c-Src in the cells were detected by immunofluorescence co-localization and co-immunoprecipitation (Co-IP). The regulation of c-Src and Cx43 was detected by DNA pull down, chromatin co-immunoprecipitation (CHIP), and dual-luciferase reporter system. The results revealed that overexpression of SHP-1 could inhibit the phosphorylation and activation of c-Src and increase the expression of Cx43. Moreover, there was a direct binding between SHP-1 and c-Src, and c-Src could bind to the promoter region of Cx43 and inhibit the transcription of Cx43. In conclusion, SHP-1 could bind to c-Src and inhibit the activity of c-Src, thus enhancing the transcriptional activation of Cx43 and improving the function of gap junction.

Caveolin-3 and Arrhythmias: Insights into the Molecular Mechanisms

Caveolin-3 is a muscle-specific protein on the membrane of myocytes correlated with a variety of cardiovascular diseases. It is now clear that the caveolin-3 plays a critical role in the cardiovascular system and a significant role in cardiac protective signaling. Mutations in the gene encoding caveolin-3 cause a broad spectrum of clinical phenotypes, ranging from persistent elevations in the serum levels of creatine kinase in asymptomatic humans to cardiomyopathy. The influence of Caveolin-3(CAV-3) mutations on current density parallels the effect on channel trafficking. For example, mutations in the CAV-3 gene promote ventricular arrhythmogenesis in long QT syndrome 9 by a combined decrease in the loss of the inward rectifier current (I_K1) and gain of the late sodium current (I_Na-L). The functional significance of the caveolin-3 has proved that caveolin-3 overexpression or knockdown contributes to the occurrence and development of arrhythmias. Caveolin-3 overexpression could lead to reduced diastolic spontaneous Ca²⁺ waves, thus leading to the abnormal L-Type calcium channel current-induced ventricular arrhythmias. Moreover, CAV-3 knockdown resulted in a shift to more negative values in the hyperpolarization-activated cyclic nucleotide channel 4 current (I_HCN4) activation curve and a significant decrease in I_HCN4 whole-cell current density. Recent evidence indicates that caveolin-3 plays a significant role in adipose tissue and is related to obesity development. The role of caveolin-3 in glucose homeostasis has attracted increasing attention. This review highlights the underlining mechanisms of caveolin-3 in arrhythmia. Progress in this field may contribute to novel therapeutic approaches for patients prone to developing arrhythmia.

Advances of Traditional Chinese Medicine Regulating Connexin43 in the Prevention and Treatment of Myocardial Infarction

Gap junctions are the main form of interaction between cardiomyocytes, through which the electrochemical activities between cardiomyocytes can be synchronized to maintain the normal function of the heart. Connexins are the basis of gap junctions. Changes in the expression, structural changes (e.g., phosphorylation and dephosphorylation), and distribution of connexins can affect the normal electrophysiological activities of the heart. Myocardial infarction (MI) and concurrent arrhythmia, shock, or heart failure can endanger life. The structural and functional damage of connexin (Cx) 43 in cardiomyocytes is a central part of the pathological progression of MI and is one of the main pathological mechanisms of arrhythmia after MI. Therefore, increasing Cx43 expression has become one of the main measures to prevent MI. Also, intervention in Cx43 expression can improve the structural and electrical remodeling of the myocardium to improve MI prognosis. Here, research progress of Cx43 in MI and its prevention and treatment using Traditional Chinese Medicine formulations is reviewed.

Serine-threonine protein phosphatase regulation of Cx43 dephosphorylation in arrhythmogenic disorders

Regulation of cell-to-cell communication in the heart by the gap junction protein Connexin43 (Cx43) involves modulation of Cx43 phosphorylation state by protein kinases, and dephosphorylation by protein phosphatases. Dephosphorylation of Cx43 has been associated with impaired intercellular coupling and enhanced arrhythmogenesis in various pathologic states. While there has been extensive study of the protein kinases acting on Cx43, there has been limited studies of the protein phosphatases that may underlie Cx43 dephosphorylation. The focus of this review is to introduce serine-threonine protein phosphatase regulation of Cx43 phosphorylation state and cell-to-cell communication, and its impact on arrhythmogenesis in the setting of chronic heart failure and myocardial ischemia, as well as on atrial fibrillation. We also discuss the therapeutic potential of modulating protein phosphatases to treat arrhythmias in these clinical settings.

Mechanisms of Connexin Regulating Peptides

Gap junctions (GJ) and connexins play integral roles in cellular physiology and have been found to be involved in multiple pathophysiological states from cancer to cardiovascular disease. Studies over the last 60 years have demonstrated the utility of altering GJ signaling pathways in experimental models, which has led to them being attractive targets for therapeutic intervention. A number of different mechanisms have been proposed to regulate GJ signaling, including channel blocking, enhancing channel open state, and disrupting protein-protein interactions. The primary mechanism for this has been through the design of numerous peptides as therapeutics, that are either currently in early development or are in various stages of clinical trials. Despite over 25 years of research into connexin targeting peptides, the overall mechanisms of action are still poorly understood. In this overview, we discuss published connexin targeting peptides, their reported mechanisms of action, and the potential for these molecules in the treatment of disease.

Remodeling of Cardiac Gap Junctional Cell-Cell Coupling

The heart works as a functional syncytium, which is realized via cell-cell coupling maintained by gap junction channels. These channels connect two adjacent cells, so that action potentials can be transferred. Each cell contributes a hexameric hemichannel (=connexon), formed by protein subuntis named connexins. These hemichannels dock to each other and form the gap junction channel. This channel works as a low ohmic resistor also allowing the passage of small molecules up to 1000 Dalton. Connexins are a protein family comprising of 21 isoforms in humans. In the heart, the main isoforms are Cx43 (the 43 kDa connexin; ubiquitous), Cx40 (mostly in atrium and specific conduction system), and Cx45 (in early developmental states, in the conduction system, and between fibroblasts and cardiomyocytes). These gap junction channels are mainly located at the polar region of the cardiomyocytes and thus contribute to the anisotropic pattern of cardiac electrical conductivity. While in the beginning the cell–cell coupling was considered to be static, similar to an anatomically defined structure, we have learned in the past decades that gap junctions are also subject to cardiac remodeling processes in cardiac disease such as atrial fibrillation, myocardial infarction, or cardiomyopathy. The underlying remodeling processes include the modulation of connexin expression by e.g., angiotensin, endothelin, or catecholamines, as well as the modulation of the localization of the gap junctions e.g., by the direction and strength of local mechanical forces. A reduction in connexin expression can result in a reduced conduction velocity. The alteration of gap junction localization has been shown to result in altered pathways of conduction and altered anisotropy. In particular, it can produce or contribute to non-uniformity of anisotropy, and thereby can pre-form an arrhythmogenic substrate. Interestingly, these remodeling processes seem to be susceptible to certain pharmacological treatment.

MiR-23a Is Involved in Myocardial Ischemia/Reperfusion Injury by Directly Targeting CX43 and Regulating Mitophagy

Activation of CX43 signaling protects myocardial cells from myocardial ischemia/reperfusion (I/R) injury. However, the underlying mechanism remains unclear. MicroRNAs (miRNAs) are well known to play important roles in the progression of diverse diseases. Here, we first confirmed the expression profile of CX43 in rat heart tissues with I/R injury. Then, microRNAs (miRNAs) that target CX43 were predicted using miRDB, miRWalk, and TargetScan. The candidate miR-23a was selected, and its expression level in I/R samples was investigated. To determine the role of miR-23a, rat primary myocardial cells were transfected with miR-23a mimics after they were subjected to hypoxia-reoxygenation (H/R) injury. Transfection of miR-23a mimics stimulated mitophagy through the PINK1/Parkin pathway and downregulated the protein level of CX43. Treatment of miR-23a-transfected cells with NF-kB inhibitors completely abolished miR-23a-mediated mitophagy after H/R. Moreover, miR-23a transfection significantly suppressed CX43 expression and enhanced mitophagy in the model heart in vivo. Therefore, miR-23a plays a detrimental role in myocardial I/R injury by enhancing mitophagy and inhibiting CX43 mRNA.

The roles of PKC-δ and PKC-ε in myocardial ischemia/reperfusion injury

Ischemia and reperfusion (I/R) cause a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, opening of mitochondrial permeability transition pores (mPTPs) and promotion of cell death (apoptosis or necrosis). PKC-δ and PKC-ε, belonging to a family of serine/threonine kinases, have been demonstrated to play important roles during I/R injury in cardiovascular diseases. However, the cardioprotective mechanisms of PKC-δ and PKC-ε in I/R injury have not been elaborated until now. This article discusses the roles of PKC-δ and PKC-ε during myocardial I/R in redox regulation (redox signaling and oxidative stress), cell death (apoptosis and necrosis), Ca²⁺ overload, and mitochondrial dysfunction.

Pathogenesis of arrhythmogenic cardiomyopathy: role of inflammation

Arrhythmogenic cardiomyopathy (AC) is an inherited disease characterized by progressive breakdown of heart muscle, myocardial tissue death, and fibrofatty replacement. In most cases of AC, the primary lesion occurs in one of the genes encoding desmosomal proteins, disruption of which increases membrane fragility at the intercalated disc. Disrupted, exposed desmosomal proteins also serve as epitopes that can trigger an autoimmune reaction. Damage to cell membranes and autoimmunity provoke myocardial inflammation, a key feature in early stages of the disease. In several preclinical models, targeting inflammation has been shown to blunt disease progression, but translation to the clinic has been sparse. Here we review current understanding of inflammatory pathways and how they interact with injured tissue and the immune system in AC. We further discuss the potential role of immunomodulatory therapies in AC.

Effects of Hypothermic Hypoxia/Reoxygenation Fibroblast Culture Medium Containing Sevoflurane on Cardiomyocytes

We established a model of hypothermic hypoxia/reoxygenation injury of fibroblasts, simulated the process of ischemia/reperfusion injury during cardiopulmonary bypass, and studied the effects of cardiac fibroblasts on cardiomyocyte activity, connexin 43 (Cx43), and calmodulin kinase II (CaMKII) expression. Furthermore, the effects of sevoflurane-treated fibroblast culture medium on cardiac activity, Cx43 protein, and CaMKII expression were observed. The results showed that the fibroblast culture medium damaged by hypothermic hypoxia/reoxygenation could reduce the beating frequency of cardiomyocytes, increase the mortality of cardiomyocytes, decrease the relative expression of Cx43, and increase the relative expression of CaMKII. However, sevoflurane containing hypothermic hypoxia/reoxygenation injury fibroblast culture medium can increase the beating frequency of cardiomyocytes, reduce the mortality of cardiomyocytes, increase the relative expression of Cx43 protein, and decrease the relative expression of CaMKII. The results suggest that the antiarrhythmic effects of sevoflurane on the expression of Cx43 and CaMKII are related to fibroblasts.

LncRNA CRNDE inhibits cardiomyocytes apoptosis by YAP1 in myocardial ischaemia/reperfusion injury

BACKGROUND

Cardiomyocytes apoptosis is the basic pathological process of myocardial ischaemia/reperfusion (MI/R) injury, so inhibiting apoptosis of cardiomyocytes can effectively improve MI/R injury. Long non-coding RNA colorectal neoplasia differentially expressed (lncRNA CRNDE) can inhibit cell apoptosis, but its specific role in MI/R injury has not been studied. The aim of this study is to explore the specific effect of lncRNA CRNDE on cardiomyocytes apoptosis.

METHODS

MI/R model in vivo and hypoxia/re-oxygenation (H/R) model in vitro were constructed. Apoptotic levels were assessed by TUNEL staining assay. QRT-PCR was used to validate lncRNA CRNDE level in myocardial tissues and HL-1 cells. The protein expressions of YAP1, Bcl-2 and cleaved caspase-3 were detected by western blot analysis. Flow cytometry was used to determine the apoptosis rate of cardiomyocytes. RIP assay was used to detect the interaction between lncRNA CRNDE and YAP1.

RESULTS

The extent of cardiomyocytes apoptosis was significantly increased, and the levels of lncRNA CRNDE, YAP1 and Bcl-2 were down-regulated, while cleaved caspase-3 expression was up-regulated in MI/R mice and H/R-treated HL-1 cells. The expressions of YAP1 and Bcl-2 were decreased, while the expression of cleaved caspase-3 was increased after the knockdown of lncRNA CRNDE. Furthermore, lncRNA CRNDE could bind to YAP1 and regulated the protein level of YAP1 by ubiquitination and proteasomal degradation pathway. After transfection of Si-YAP1 in the H/R-treated HL-1 cells transfected with pc-DNA CRNDE, the protein level of Bcl-2 was decreased, while cleaved caspase-3 expression and the apoptosis rate were increased.

CONCLUSION

Our study suggested that lncRNA CRNDE could regulate YAP1 level by ubiquitination and proteasomal degradation pathway, thus inhibiting cardiomyocytes apoptosis in MI/R injury.

Connexins in the Heart: Regulation, Function and Involvement in Cardiac Disease

Connexins are a family of transmembrane proteins that play a key role in cardiac physiology. Gap junctional channels put into contact the cytoplasms of connected cardiomyocytes, allowing the existence of electrical coupling. However, in addition to this fundamental role, connexins are also involved in cardiomyocyte death and survival. Thus, chemical coupling through gap junctions plays a key role in the spreading of injury between connected cells. Moreover, in addition to their involvement in cell-to-cell communication, mounting evidence indicates that connexins have additional gap junction-independent functions. Opening of unopposed hemichannels, located at the lateral surface of cardiomyocytes, may compromise cell homeostasis and may be involved in ischemia/reperfusion injury. In addition, connexins located at non-canonical cell structures, including mitochondria and the nucleus, have been demonstrated to be involved in cardioprotection and in regulation of cell growth and differentiation. In this review, we will provide, first, an overview on connexin biology, including their synthesis and degradation, their regulation and their interactions. Then, we will conduct an in-depth examination of the role of connexins in cardiac pathophysiology, including new findings regarding their involvement in myocardial ischemia/reperfusion injury, cardiac fibrosis, gene transcription or signaling regulation.

Intercellular Communication in the Heart: Therapeutic Opportunities for Cardiac Ischemia

The maintenance of tissue, organ, and organism homeostasis relies on an intricate network of players and mechanisms that assist in the different forms of cell-cell communication. Myocardial infarction, following heart ischemia and reperfusion, is associated with profound changes in key processes of intercellular communication, involving gap junctions, extracellular vesicles, and tunneling nanotubes, some of which have been implicated in communication defects associated with cardiac injury, namely arrhythmogenesis and progression into heart failure. Therefore, intercellular communication players have emerged as attractive powerful therapeutic targets aimed at preserving a fine-tuned crosstalk between the different cardiac cells in order to prevent or repair some of harmful consequences of heart ischemia and reperfusion, re-establishing myocardial function.

Hongjingtian injection protects against myocardial ischemia reperfusion-induced apoptosis by blocking ROS induced autophagic- flux

BACKGROUND

Hongjingtian injection (HJT) has been widely used in the clinic to treat coronary heart disease in China. However, the underlying mechanisms of therapies still need to be illustrated. The present study aims to determine whether HJT protects against myocardial ischemia reperfusion injury via Reactive Oxygen Species (ROS)-induced autophagic flux and apoptosis and, if so, to explore the underlying mechanisms.

METHODS

In vivo myocardial protection and autophagy regulation of HJT in myocardial ischemia reperfusion injury in C57BL/6 J and CAG-RFP-EGFP-LC3 transgenic C57BL/6 J mice were investigated. In vitro, the effects of HJT on apoptosis, autophagic flux, oxidative stress and mitochondrial function were observed in H2O2-induced H9c2 cells. In addition, apoptosis-related proteins and autophagy-related proteins were assessed to explore the underlying mechanisms.

RESULTS

HJT significantly decreased the infarct area and cell apoptosis after myocardial ischemia reperfusion injury in C57BL/6 J mice. Autophagic flux was reduced by HJT treatment after myocardial ischemia reperfusion injury in CAG-RFP-EGFP-LC3 transgenic C57BL/6 J mice. HJT inhibited H2O2-induced cell apoptosis by significantly decreasing the levels of cleaved caspase 3 and increasing the Bcl-2/Bax ratio. HJT inhibited autophagic flux after H2O2 stimulation by significantly decreasing LC3-Ⅱ and p-AMPK expression and increasing p-mTOR. HJT inhibited ROS production and improved mitochondrial function in H2O2-induced cells by significantly increasing the mitochondrial membrane potential, intracellular ATP contents and oxygen consumption.

CONCLUSION

The beneficial effects of HJT in treating myocardial ischemia reperfusion are partially due to improved mitochondrial function and regulated autophagy to inhibit cell apoptosis through the AMPK/mTOR pathway.

Knockout of MYOM1 in human cardiomyocytes leads to myocardial atrophy via impairing calcium homeostasis

Myomesin-1 (encoded by MYOM1 gene) is expressed in almost all cross-striated muscles, whose family (together with myomesin-2 and myomesin-3) helps to cross-link adjacent myosin to form the M-line in myofibrils. However, little is known about its biological function, causal relationship and mechanisms underlying the MYOM1-related myopathies (especially in the heart). Regrettably, there is no MYMO1 knockout model for its study so far. A better and further understanding of MYOM1 biology is urgently needed. Here, we used CRISPR/Cas9 gene-editing technology to establish an MYOM1 knockout human embryonic stem cell line (MYOM1-/- hESC), which was then differentiated into myomesin-1 deficient cardiomyocytes (MYOM1-/- hESC-CMs) in vitro. We found that myomesin-1 plays an important role in sarcomere assembly, contractility regulation and cardiomyocytes development. Moreover, myomesin-1-deficient hESC-CMs can recapitulate myocardial atrophy phenotype in vitro. Based on this model, not only the biological function of MYOM1, but also the aetiology, pathogenesis, and potential treatments of myocardial atrophy caused by myomesin-1 deficiency can be studied.

p38 MAPK Pathway in the Heart: New Insights in Health and Disease

The p38 mitogen-activated kinase (MAPK) family controls cell adaptation to stress stimuli. p38 function has been studied in depth in relation to cardiac development and function. The first isoform demonstrated to play an important role in cardiac development was p38α; however, all p38 family members are now known to collaborate in different aspects of cardiomyocyte differentiation and growth. p38 family members have been proposed to have protective and deleterious actions in the stressed myocardium, with the outcome of their action in part dependent on the model system under study and the identity of the activated p38 family member. Most studies to date have been performed with inhibitors that are not isoform-specific, and, consequently, knowledge remains very limited about how the different p38s control cardiac physiology and respond to cardiac stress. In this review, we summarize the current understanding of the role of the p38 pathway in cardiac physiology and discuss recent advances in the field.

Melatonin as a therapy in cardiac ischemia-reperfusion injury: Potential mechanisms by which MT2 activation mediates cardioprotection

Introduction

Previous studies reported the beneficial effects of pretreatment with melatonin on the heart during cardiac ischemia/reperfusion (I/R) injury. However, the effects of melatonin given after cardiac ischemia, as well as its comparative temporal effects are unknown. These include pretreatment, during ischemia, and at the onset of reperfusion. Also, the association between melatonin receptors and cardiac arrhythmias, mitochondrial function and dynamics, autophagy, and mitophagy during cardiac I/R have not been investigated.

Objectives

We tested two major hypotheses in this study. Firstly, the temporal effect of melatonin administration exerts different cardioprotective efficacy during cardiac I/R. Secondly, melatonin provides cardioprotective effects via MT2 activation, leading to improvement in cardiac mitochondrial function and dynamics, reduced excessive mitophagy and autophagy, and decreased cardiac arrhythmias, resulting in improved LV function.

Methods

Male rats were subjected to cardiac I/R, and divided into 4 intervention groups: vehicle, pretreatment with melatonin, melatonin given during ischemia, and melatonin given at the onset of reperfusion. In addition, either a non-specific melatonin receptor (MT) blocker or specific MT2 blocker was given to rats.

Results

Treatment with melatonin at all time points alleviated cardiac I/R injury to a similar extent, quantified by reduction in infarct size, arrhythmia score, LV dysfunction, cardiac mitochondrial dysfunction, imbalance of mitochondrial dynamics, excessive mitophagy, and a decreased Bax/Bcl2 ratio. In H9C2 cells, melatonin increased %cell viability by reducing mitochondrial dynamic imbalance and a decrease in Bax protein expression. The cardioprotective effects of melatonin were dependent on MT2 activation.

Conclusion

Melatonin given before or after ischemia exerted equal levels of cardioprotection on the heart with I/R injury, and its beneficial effects on cardiac arrhythmias, cardiac mitochondrial function and dynamics were dependent upon the activation of MT2.

Caduet enhances connexin 43 phosphorylation in left ventricular and thoracic aorta of SH model rats

Caduet, also known as amlodipine besylate and atorvastatin calcium (AM + AT) tablet, can improve cardiac and vascular remodeling in patients with spontaneous hypertension (SH), but the underlying mechanism remains unknown. The present study aimed to explore whether AM + AT improved hypertensive left ventricular and thoracic aortic remodeling by regulating connexin 43 (Cx43) phosphorylation. A total of 32 male spontaneous hypertension model rats (SHR) were randomly divided into four groups: SHR control group, amlodipine-alone group (SHR-AM), atorvastatin-alone (SHR-AT) and AM + AT group (SHR-AM + AT); 8 Wistar-Kyoto (WKY) rats with normal blood pressure were used as the normal control. Drugs were orally administered for 8 weeks; subsequently, body weight, heart rate (HR), left ventricular mass index (LVMI), blood pressure (BP), plasma lipid levels and morphological changes of myocardial tissue in each group were analyzed. The expression of total (T)-Cx43 and phosphorylated (P)-Cx43 protein in the left ventricular and thoracic aortic tissues was determined using western blotting and immunofluorescence double labeling. The results revealed that AM + AT significantly decreased LVMI and cardiomyocyte cross-sectional area compared with SHR-AM and SHR-AT group. The western blotting results demonstrated that AM + AT could inhibit the expression of T-Cx43 protein, but increased the expression of P-Cx43 in the left ventricular and thoracic aorta. Moreover, immunofluorescence results indicated AM + AT could also decrease the expression T-Cx43, and increase that of P-Cx43 in the left ventricular and thoracic aorta compared with AM and AT alone. Therefore, it was concluded that AM + AT may mitigate left ventricular and thoracic aorta remodeling in SH rats by enhancing Cx43 phosphorylation, and the efficacy of AM + AT was superior to that of AM and AT alone.

Connexin 43 plays a role in proliferation and migration of pulmonary arterial fibroblasts in response to hypoxia

Pulmonary hypertension (PH) is a disease associated with vasoconstriction and remodelling of the pulmonary vasculature. Pulmonary artery fibroblasts (PAFs) play an important role in hypoxic-induced remodelling. Connexin 43 (Cx43) is involved in cellular communication and regulation of the pulmonary vasculature. Using both in vitro and in vivo models of PH, the aims of this study were to (i) investigate the role of Cx43 in hypoxic-induced proliferation and migration of rat PAFs (rPAFs) and rat pulmonary artery smooth muscle cells (rPASMCs) and (ii) determine whether Cx43 expression is dysregulated in the rat sugen5416/hypoxic model of PH. The role of Cx43 in hypoxic-induced proliferation and migration was investigated using Gap27 (a pharmacological inhibitor of Cx43) or genetic knockdown of Cx43 using siRNA. Cx43 protein expression was increased by hypoxia in rPAFs but not rPASMCs. Hypoxic exposure, in the presence of serum, resulted in an increase in proliferation of rPAFs but not rPASMCs. Hypoxic exposure caused migration of rPAFs but not rPASMCs. Phosphorylation of p38 mitogen-activated protein kinase (MAPK) and ERK1/2 were increased by hypoxia in rPAFs. The effects of hypoxia on proliferation, migration and MAPK phosphorylation in rPAFs were attenuated in the presence of Gap27 or Cx43 siRNA. Cx43 protein expression was increased in sugen5416/hypoxic rat lung; this increased expression was not observed in sugen5416/hypoxic rats treated with the MAPK pathway inhibitor GS-444217. In conclusion, Cx43 is involved in the proliferation and migration of rPAFs in response to hypoxia via the MAPK signalling pathway.

Cardiac remodeling and arrhythmogenesis are ameliorated by administration of Cx43 mimetic peptide Gap27 in heart failure rats

Alterations in connexins and specifically in 43 isoform (Cx43) in the heart have been associated with a high incidence of arrhythmogenesis and sudden death in several cardiac diseases. We propose to determine salutary effect of Cx43 mimetic peptide Gap27 in the progression of heart failure. High-output heart failure was induced by volume overload using the arterio-venous fistula model (AV-Shunt) in adult male rats. Four weeks after AV-Shunt surgery, the Cx43 mimetic peptide Gap27 or scrambled peptide, were administered via osmotic minipumps (AV-Shunt_Gap27 or AV-Shunt_Scr) for 4 weeks. Cardiac volumes, arrhythmias, function and remodeling were determined at 8 weeks after AV-Shunt surgeries. At 8^th week, AV-Shunt_Gap27 showed a marked decrease in the progression of cardiac deterioration and showed a significant improvement in cardiac functions measured by intraventricular pressure-volume loops. Furthermore, AV-Shunt_Gap27 showed less cardiac arrhythmogenesis and cardiac hypertrophy index compared to AV-Shunt_Scr. Gap27 treatment results in no change Cx43 expression in the heart of AV-Shunt rats. Our results strongly suggest that Cx43 play a pivotal role in the progression of cardiac dysfunction and arrhythmogenesis in high-output heart failure; furthermore, support the use of Cx43 mimetic peptide Gap27 as an effective therapeutic tool to reduce the progression of cardiac dysfunction in high-output heart failure.

New insights into the role of mitochondria in cardiac microvascular ischemia/reperfusion injury

As reperfusion therapies have become more widely used in acute myocardial infarction patients, ischemia-induced myocardial damage has been markedly reduced, but reperfusion-induced cardiac injury has become increasingly evident. The features of cardiac ischemia-reperfusion (I/R) injury include microvascular perfusion defects, platelet activation and sequential cardiomyocyte death due to additional ischemic events at the reperfusion stage. Microvascular obstruction, defined as a no-reflow phenomenon, determines the infarct zone, myocardial function and peri-operative mortality. Cardiac microvascular endothelial cell injury may occur much earlier and with much greater severity than cardiomyocyte injury. Endothelial cells contain fewer mitochondria than other cardiac cells, and several of the pathological alterations during cardiac microvascular I/R injury involve mitochondria, such as increased mitochondrial reactive oxygen species (mROS) levels and disturbed mitochondrial dynamics. Although mROS are necessary physiological second messengers, high mROS levels induce oxidative stress, endothelial senescence and apoptosis. Mitochondrial dynamics, including fission, fusion and mitophagy, determine the shape, distribution, size and function of mitochondria. These adaptive responses modify extracellular signals and orchestrate intracellular processes such as cell proliferation, migration, metabolism, angiogenesis, permeability transition, adhesive molecule expression, endothelial barrier function and anticoagulation. In this review, we discuss the involvement of mROS and mitochondrial morphofunction in cardiac microvascular I/R injury.

Butyrate improves cardiac function and sympathetic neural remodeling following myocardial infarction in rats

Increased inflammation is found in cardiac sympathetic neural remodeling with malignant ventricular arrhythmia (VA) following myocardial infarction (MI). Butyrate, as a microbiota-derived short-chain fatty acid, can inhibit inflammation and myocardial hypertrophy. However, the role of butyrate in sympathetic neural remodeling after MI is unknown. This study aimed to investigate whether butyrate could improve cardiac dysfunction and VA following MI by regulating inflammation and sympathetic neural remodeling. MI rats were randomized to administrate the butyrate or vehicle through intraperitoneal injection to undergo the study. Our data demonstrated that butyrate treatment preserved the partial cardiac function at 7 days post-MI. Butyrate downregulated the expression of essential for inflammatory response in the infarct border zone at 3 days post-MI. Particularly, butyrate promoted expression of M2 macrophage markers. Increased expressions of nerve growth factor and norephinephrine at 7 days after MI were inhibited in butyrate-treated rats. Furthermore, butyrate significantly decreased the density of nerve fibers for growth-associated protein-43 and tyrosine hydroxylase and resulted in fewer episodes of inducible VA. In conclusion, butyrate administration ameliorated cardiac function and VA after MI possibly through promoting M2 macrophage polarization to suppress inflammatory responses and inhibit sympathetic neural remodeling and may present an effective pharmacological strategy for the prevention of MI-related remodeling.

Fibroblast growth factor 21 inhibited ischemic arrhythmias via targeting miR-143/EGR1 axis

Ventricular arrhythmia is the most common cause of sudden cardiac death in patients with myocardial infarction (MI). Fibroblast growth factor 21 (FGF21) has been shown to play an important role in cardiovascular and metabolic diseases. However, the effects of FGF21 on ventricular arrhythmias following MI have not been addressed yet. The present study was conducted to investigate the pharmacological action of FGF21 on ventricular arrhythmias after MI. Adult male mice were administrated with or without recombinant human basic FGF21 (rhbFGF21), and the susceptibility to arrhythmias was assessed by programmed electrical stimulation and optical mapping techniques. Here, we found that rhbFGF21 administration reduced the occurrence of ventricular tachycardia (VT), improved epicardial conduction velocity and shorted action potential duration at 90% (APD90) in infarcted mouse hearts. Mechanistically, FGF21 may improve cardiac electrophysiological remodeling as characterized by the decrease of INa and IK1 current density in border zone of infarcted mouse hearts. Consistently, in vitro study also demonstrated that FGF21 may rescue oxidant stress-induced dysfunction of INa and IK1 currents in cultured ventricular myocytes. We further found that oxidant stress-induced down-regulation of early growth response protein 1 (EGR1) contributed to INa and IK1 reduction in post-infarcted hearts, and FGF21 may recruit EGR1 into the SCN5A and KCNJ2 promoter regions to up-regulate NaV1.5 and Kir2.1 expression at transcriptional level. Moreover, miR-143 was identified as upstream of EGR1 and mediated FGF21-induced EGR1 up-regulation in cardiomyocytes. Collectively, rhbFGF21 administration effectively suppressed ventricular arrhythmias in post-infarcted hearts by regulating miR-143-EGR1-NaV1.5/Kir2.1 axis, which provides novel therapeutic strategies for ischemic arrhythmias in clinics.

Emerging Function of Cardiac Macrophages Ushers in a New Era for the Electrophysiology of the Heart

Maintaining a coordinated heart rhythm is essential for maintaining the heart’s pumping function and blood circulation. Every heartbeat is generated by electrical impulse propagation that is passing through gap junctions, which are composed of connexin proteins. In mammalian hearts, Cx43, Cx40, Cx45, and Cx30.2 are expressed and regulated by post-translational modification. Cardiac macrophages account for only a small number of total heart cells, but they reside all around the heart. They are primarily established prenatally, and they arise from embryonic yolk sac progenitors. Recently, increasing attention has been directed toward novel roles for cardiac resident macrophages, especially in the heart’s electrical impulse conduction. Here, we provide an overview of the recent findings on connexins, with a focus on the emerging function of cardiac macrophages, and we discuss the future directions of treatment for heart disease.