Remodelling of myocardial intercalated disc protein connexin 43 causes increased susceptibility to malignant arrhythmias in ARVC/D patients

Arrhythmogenic Right Ventricular Cardiomyopathy Post-Mortem Assessment: A Systematic Review

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disorder characterized by the progressive fibro-fatty replacement of the right ventricular myocardium, leading to myocardial atrophy. Although the structural changes usually affect the right ventricle, the pathology may also manifest with either isolated left ventricular myocardium or biventricular involvement. As ARVC shows an autosomal dominant pattern of inheritance with variable penetrance, the clinical presentation of the disease is highly heterogeneous, with different degrees of severity and patterns of myocardial involvement even in patients of the same familiar group with the same gene mutation: the pathology spectrum ranges from the absence of symptoms to sudden cardiac death (SCD) sustained by ventricular arrhythmias, which may, in some cases, be the first manifestation of an otherwise silent pathology. An evidence-based systematic review of the literature was conducted to evaluate the state of the art of the diagnostic techniques for the correct post-mortem identification of ARVC. The research was performed using the electronic databases PubMed and Scopus. A methodological approach to reach a correct post-mortem diagnosis of ARVC was described, analyzing the main post-mortem peculiar macroscopic, microscopic and radiological alterations. In addition, the importance of performing post-mortem genetic tests has been underlined, which may lead to the correct identification and characterization of the disease, especially in those ARVC forms where anatomopathological investigation does not show evident morphostructural damage. Furthermore, the usefulness of genetic testing is not exclusively limited to the correct diagnosis of the pathology, but is essential for promoting targeted screening programs to the deceased's family members. Nowadays, the post-mortem diagnosis of ARVC performed by forensic pathologist remains very challenging: therefore, the identification of a clear methodological approach may lead to both a reduction in under-diagnoses and to the improvement of knowledge on the disease.

Management of arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a disease characterised by fibrofatty replacement of the ventricular myocardium due to specific mutations, leading to ventricular arrhythmias and sudden cardiac death. Treating this condition can be challenging due to progressive fibrosis, phenotypic variations and small patient cohorts limiting the feasibility of conducting meaningful clinical trials. Although widely used, the evidence base for anti-arrhythmic drugs is limited. Beta-blockers are theoretically sound, yet their efficacy in reducing arrhythmic risk is not robust. Additionally, the impact of sotalol and amiodarone is inconsistent with studies reporting contradictory results. Emerging evidence suggests that combining flecainide and bisoprolol may be efficacious.Radiofrequency ablation has shown some potential in disrupting ventricular tachycardia circuits, with combined endo and epicardial ablation yielding better results which could be considered at the index procedure. In addition, stereotactic radiotherapy may be a future option that can decrease arrhythmias beyond simple scar formation by altering levels of Nav1.5 channels, Connexin 43 and Wnt signalling, potentially modifying myocardial fibrosis.Future therapies, such as adenoviruses and GSk3b modulation, are still in early-stage research. While implantable cardioverter-defibrillator implantation is a key intervention for reducing arrhythmic death, the risks of inappropriate shocks and device complications must be carefully considered.

Humanized Dsp ACM Mouse Model Displays Stress-Induced Cardiac Electrical and Structural Phenotypes

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder characterized by fibro-fatty infiltration with an increased propensity for ventricular arrhythmias and sudden death. Genetic variants in desmosomal genes are associated with ACM. Incomplete penetrance is a common feature in ACM families, complicating the understanding of how external stressors contribute towards disease development. To analyze the dual role of genetics and external stressors on ACM progression, we developed one of the first mouse models of ACM that recapitulates a human variant by introducing the murine equivalent of the human R451G variant into endogenous desmoplakin (DspR451G/+). Mice homozygous for this variant displayed embryonic lethality. While DspR451G/+ mice were viable with reduced expression of DSP, no presentable arrhythmogenic or structural phenotypes were identified at baseline. However, increased afterload resulted in reduced cardiac performance, increased chamber dilation, and accelerated progression to heart failure. In addition, following catecholaminergic challenge, DspR451G/+ mice displayed frequent and prolonged arrhythmic events. Finally, aberrant localization of connexin-43 was noted in the DspR451G/+ mice at baseline, becoming more apparent following cardiac stress via pressure overload. In summary, cardiovascular stress is a key trigger for unmasking both electrical and structural phenotypes in one of the first humanized ACM mouse models.

Cardiac features in a patient with erythrokeratodermia cardiomyopathy syndrome

Patients with erythrokeratodermia cardiomyopathy syndrome exhibit congenital, generalised erythrokeratoderma and dilated cardiomyopathy during early childhood. We report a case of erythrokeratodermia cardiomyopathy syndrome in a 15-year-old male patient and focus this report on cardiac features that were present.

Decreased Expression of Plakophilin-2 and αT-Catenin in Arrhythmogenic Right Ventricular Cardiomyopathy: Potential Markers for Diagnosis

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a hereditary disease of the heart muscle. Clinical challenges remain, however, in identifying patients with ARVC in the early or concealed stages with subtle clinical manifestations. Therefore, we wanted to identify potential targets by immunohistochemical (IHC) analysis in comparison with controls. Pathogenic mutations were identified in 11 of 37 autopsied patients with ARVC. As observed from IHC analysis of the RV, expression of αT-catenin and plakophilin-2 is significantly decreased in autopsied patients with ARVC as compared to controls, and the decreased expression is consistent in patients with and without pathogenic mutations. Furthermore, ARVC specimens demonstrated a reduced localization of αT-catenin, desmocollin-2, desmoglein-2, desmoplakin, and plakophilin-2 on intercalated discs. These findings have been validated by comparing RV specimens obtained via endomyocardial biopsy between patients with ARVC and those without. The pathogenic mutation was present in 3 of 5 clinical patients with ARVC. In HL-1 myocytes, siRNA was used to knockdown CTNNA3, and western blotting analysis demonstrated that the decline in αT-catenin expression was accompanied by a significant decline in the expression of plakophilin-2. The aforementioned effect was directed towards protein degradation rather than mRNA stability. Plakophilin-2 expression decreases concurrently with the decline in CTNNA3 expression. Therefore, the expression of αT-catenin and plakophilin-2 could be potential surrogates for the diagnosis of ARVC.

Buccal Mucosa Cells as a Potential Diagnostic Tool to Study Onset and Progression of Arrhythmogenic Cardiomyopathy

In arrhythmogenic cardiomyopathy (ACM) pathogenic variants are found in genes encoding desmosomal proteins and in non-desmosomal genes, such as phospholamban (PLN, p.Arg14del variant). Previous research showed that plakoglobin protein levels and localization in the cardiac tissue of ACM patients, and PLN p.Arg14del patients diagnosed with an ACM phenotype, are disturbed. Moreover, the effects of pathogenic variants in desmosomal genes are reflected in non-cardiac tissues like buccal mucosa cells (BMC) which could serve as a promising new and non-invasive tool to support diagnosis. We collected the BMC of 33 ACM patients, 17 PLN p.Arg14del patients and 34 controls, labelled the BMC with anti-plakoglobin antibodies at different concentrations, and scored their membrane labelling. We found that plakoglobin protein levels were significantly reduced in BMC obtained from diagnosed ACM patients and preclinical variant carriers when compared to controls. This effect was independent from age and sex. Moderate to strong correlations were found with the revised 2010 Task Force Criteria score which is commonly used for ACM diagnosis (r_s = −0.67, n = 64, p < 0.0001 and r_s = −0.71, n = 64, p < 0.0001). In contrast, plakoglobin scores in PLN p.Arg14del patients were comparable to controls (p > 0.209), which suggests differences in underlying etiology. However, for the individual diagnosis of the ‘classical’ ACM patient, this method might not be discriminative enough to distinguish true patients from variant carriers and controls, because of the high interindividual variability.

Immunofluorescent Localization of Plakoglobin Is Altered in Endomyocardial Biopsy Samples from Dogs with Clinically Relevant Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

Diagnosing the early stages of canine Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is complicated by day-to-day arrhythmia variability, and absence of reliable, transthoracic echocardiographic features. Definitive diagnosis requires histopathologic identification of transmural fibrofatty replacement of the right ventricle. Reduction of immunofluorescent signal for plakoglobin (PG) at the intercalated disc (ID) is reported in ARVC-affected humans and boxers. Our objective was to determine whether reduced immunofluorescent signal for PG in endomyocardial biopsy samples (EMBs) correspond with a histopathologic diagnosis of ARVC. Here, 49 dogs were evaluated: 43 with advanced cardiac disease and 6 non-clinical boxers with mild to moderate ventricular arrhythmia (VA) burden. EMBs were obtained from all dogs; samples were prepared with antibodies recognizing cadherin (PC) and PG and evaluated with confocal microscopy. Investigators were blinded to breed and clinical status. ARVC was histopathologically diagnosed in 8 out of 49 dogs. Of these, three out of eight had clinical signs consistent with ARVC (two boxers, one English bulldog) and reduced PG signal at ID; five out of eight were non-clinical boxers with moderate VA and no reduction in PG. A total of 41 out of 49 dogs were histopathologically diagnosed with non-ARVC cardiac disease; 1 out of 41 showed reduction of PG at ID, while 40 out of 41 had no PG reduction. These results suggest that EMB PG signal is reduced in dogs with advanced ARVC, but not in the occult phase of the disease. Additionally, presence of PG at ID supports a diagnosis of non-ARVC cardiac disease in dogs with clinical signs. These results may offer an additional test that helps differentiate advanced ARVC from other myocardial diseases.

Brugada syndrome and arrhythmogenic cardiomyopathy: overlapping disorders of the connexome?

Arrhythmogenic cardiomyopathy (ACM) and Brugada syndrome (BrS) are inherited diseases characterized by an increased risk for arrhythmias and sudden cardiac death. Possible overlap between the two was suggested soon after the description of BrS. Since then, various studies focusing on different aspects have been published pointing to similar findings in the two diseases. More recent findings on the structure of the cardiac cell-cell junctions may unite the pathophysiology of both diseases and give further evidence to the theory that they may in part be variants of the same disease spectrum. In this review, we aim to summarize the studies indicating the pathophysiological, genetic, structural, and electrophysiological overlap between ACM and BrS.

Molecular mechanisms of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy is a genetic disorder characterized by the risk of life-threatening arrhythmias, myocardial dysfunction and fibrofatty replacement of myocardial tissue. Mutations in genes that encode components of desmosomes, the adhesive junctions that connect cardiomyocytes, are the predominant cause of arrhythmogenic cardiomyopathy and can be identified in about half of patients with the condition. However, the molecular mechanisms leading to myocardial destruction, remodelling and arrhythmic predisposition remain poorly understood. Through the development of animal, induced pluripotent stem cell and other models of disease, advances in our understanding of the pathogenic mechanisms of arrhythmogenic cardiomyopathy over the past decade have brought several signalling pathways into focus. These pathways include canonical and non-canonical WNT signalling, the Hippo-Yes-associated protein (YAP) pathway and transforming growth factor-β signalling. These studies have begun to identify potential therapeutic targets whose modulation has shown promise in preclinical models. In this Review, we summarize and discuss the reported molecular mechanisms underlying the pathogenesis of arrhythmogenic cardiomyopathy.

PAR2 promotes M1 macrophage polarization and inflammation via FOXO1 pathway

Macrophages polarization plays essential but different roles in most diseases such as atherosclerosis, adipose tissue inflammation, and insulin resistance. Our previous study revealed that protease-activated receptor 2 (PAR2), a G-protein coupled receptor influenced macrophage function, but little is known regarding the regulation of macrophage polarization process and its potential mechanisms. In the present study, bone marrow-derived macrophages (BMDM) isolated from C57/BL6 mice and cultured with L929-conditional medium and murine macrophage cell line RAW264.7 were used to study the function of PAR2 activation in vitro. BMDM was stimulated by the small molecular PAR2 agonist, 2-furoyl-LIGRLO-amide trifluoroacetate salt, followed by transcription factor microarray to screen the significantly activated signaling pathways under PAR2 activation. Western blot analysis, quantitative real-time polymerase chain reaction (qRT-PCR) was used to evaluate the expression of targeted genes and transcription factors. Immunofluorescence was used to observe the subcellular distribution of transcription factors. Our results demonstrated that M1-like polarization was presented by PAR2 agonist treatment with significant upregulation of interleukin-1β, interleukin-6, monocyte chemotactic protein-1, and tumor necrosis factor-α in BMDM and RAW264.7. Microarray identified forkhead box protein O1 (FOXO1) was significantly increased under PAR2 agonist stimulation, which was confirmed by qPCR and Western blot analysis. Immunofluorescence demonstrated that increased FOXO1 accumulated in the nucleus, which is necessary to promote transcription for targeted genes. We further knocked down FOXO1 expression using small interfering RNA, which alleviated PAR2-induced proinflammatory gene expression. The PAR2/FOXO1 pathway mediated stimulation of proinflammatory genes was further confirmed by tryptase, an endogenous ligand of PAR2. In conclusion, this study demonstrated that PAR2 activation-induced M1 polarization and inflammation through the FOXO1-dependent pathway.

Astragalus Root dry extract restores connexin43 expression by targeting miR-1 in viral myocarditis

BACKGROUND

Viral myocarditis is defined as viral infection of myocardial tissue leading to impaired heart function and heart failure. Accumulating evidences have shown that arrhythmia is one of important complicating diseases of viral myocarditis causing increased mortality and morbidity. There are no effective treatment for the viral infection and complicating arrhythmia.

PURPOSE

This study investigated the effect and mechanism of Astragalus Root dry extract (ARDE) on arrhythmia induced by CVB3 in mice.

METHODS

The mice and HL-1 cells were treated with CVB3 and ARDE. Reciprocal regulation of Cx43 and miR-1 were observed in the CVB3 infected mouse myocardium and culture HL-1 cells.

RESULTS

CVB3 IP injection increased immune cell infiltration in mouse left ventricle and caused irregular arrhythmia. ARDE treatment prevented the increase of immune cell infiltration and arrhythmia. Overexpression of miR-1 significantly inhibited both endogenous Cx43 expression and Cx43 3'UTR luciferase activity in HL-1 cells. Mutation of census binding site of +1586-1593 bp not +465-472 bp in Cx43 3'UTR luciferase resulted in abolishment of miR-1 inhibitory effects in HL-1 cells. Loss-of- function of miR-1 restored CVB3-induced Cx43 expression reduction in cultured HL-1 cells. The presence of ARDE attenuated the augmented miR-1 induced by CVB3 infection in vivo and in vitro.

CONCLUSION

This study identified that CVB3 infection reduced Cx43 expression by elevating miR-1 level in mouse viral myocarditis. For the first time, ARDE was shown to prevent arrhythmia, and rescue CVB3-induced endogenous Cx43 expression by regulating miR-1 level.

A founder homozygous DSG2 variant in East Asia results in ARVC with full penetrance and heart failure phenotype

BACKGROUND

Variants in the desmoglein-2 (DSG2) gene account for a significant proportion of patients with Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC). The aim of this study was to evaluate the genetic epidemiology of DSG2 and the impact of a frequent homozygous DSG2 variant in East Asia.

METHODS

Genetic screening of 14 ARVC related genes was performed in 118 unrelated index patients using next-generation sequencing. Following that, family screening, clinical evaluation and haplotype analysis were performed among eight probands who carry the same homozygous DSG2 variant. We also examined the histopathology and protein expression using immunofluorescence staining on the myocardial tissue of two probands undergoing heart transplant.

RESULTS

Eighteen (15.2%) patients bear rare putatively deleterious variants in DSG2, among which 8 patients shared the homozygous DSG2 p.Phe531Cys variant. Family screening demonstrated that only homozygous variant carriers exhibited definite ARVC phenotype with 100% penetrance, while heterozygous variant carriers were either unaffected or only presented mild ARVC related symptoms in 25% relatives. Left ventricular involvement and bi-ventricular failure were common among homozygous p. Phe531Cys variant patients even at early age. Haplotype analysis demonstrated p. Phe531Cys was a founder variant in East Asia population with an allele frequency of 0.12%.

CONCLUSIONS

We identified, for the first time, a homozygous founder variant of DSG2 in East Asia, which was at surprisingly high frequency of 8.47% among Chinese ARVC patients with a full penetrance. This result suggested an urgent demand of genetic counseling for the probands and their relatives with heterozygous variant.

Comprehensive Myocardial Proteogenomics Profiling Reveals C/EBPα as the Key Factor in the Lipid Storage of ARVC

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is hereditary cardiomyopathy characterized by the fibro-fatty replacement of the myocardium. A small number of noncomprehensive profiling studies based on human cardiac tissues have been conducted and reported; consequently, ARVC's gene expression pattern characteristics remain largely undocumented. Our study applies large-scaled, quantitative proteomics based on TMT-labeled LC-MS/MS to analyze the left and right ventricular myocardium of four ARVC and four DCM explanted hearts to compare them with normal hearts. Our objective is to reveal the characteristic proteome pattern in ARVC compared with DCM as well as nondiseased heart. We also conducted the RNA sequencing of 10 right ventricles from ARVC hearts paired with four nondiseased donor hearts to validate the proteome results. In a manner similar to that of the well-defined DCM heart failure model, the ARVC model demonstrates the downregulation of mitochondrial function proteins and the effects of many heart failure regulators such as TGFB, RICTOR, and KDM5A. In addition, the inflammatory signaling, especially the complement system, was activated much more severely in ARVC than in DCM. Our most significant discovery was the lipid metabolism reprogramming of both ARVC ventricles in accordance with the upregulation of lipogenesis factors such as FABP4 and FASN. We identified the key upstream regulator of lipogenesis as C/EBPα. Transcriptome profiling verified the consistency with proteome alterations. This comprehensive proteogenomics profiling study reveals that an activation of C/EBPα, along with the upregulation of its lipogenesis targets, accounts for lipid storage and acts as a hallmark of ARVC.