Hyperactivation of ATF4/TGF-ß1 signaling contributes to the progressive cardiac fibrosis in Arrhythmogenic cardiomyopathy caused by DSG2 Variant.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterized with progressive cardiac fibrosis and heart failure. However, the exact mechanism driving the progression of cardiac fibrosis and heart failure in ACM remains elusive. This study aims to investigate the underlying mechanisms of progressive cardiac fibrosis in ACM caused by newly identified Desmoglein-2 (DSG2) variation. METHODS: We identified homozygous DSG2F531C variant in a family with 8 ACM patients using whole-exome sequencing and generated Dsg2F536C knock-in mice. Neonatal and adult mouse ventricular myocytes isolated from Dsg2F536C knock-in mice were used. We performed functional, transcriptomic and mass spectrometry analyses to evaluate the mechanisms of ACM caused by DSG2F531C variant. RESULTS: All eight patients with ACM were homozygous for DSG2F531C variant. Dsg2F536C/F536C mice displayed cardiac enlargement, dysfunction, and progressive cardiac fibrosis in both ventricles. Mechanistic investigations revealed that the variant DSG2-F536C protein underwent misfolding, leading to its recognition by BiP within the endoplasmic reticulum, which triggered endoplasmic reticulum stress, activated the PERK-ATF4 signaling pathway and increased ATF4 levels in cardiomyocytes. Increased ATF4 facilitated the expression of TGF-ß1 in cardiomyocytes, thereby activating cardiac fibroblasts through paracrine signaling and ultimately promoting cardiac fibrosis in Dsg2F536C/F536C mice. Notably, inhibition of the PERK-ATF4 signaling attenuated progressive cardiac fibrosis and cardiac systolic dysfunction in Dsg2F536C/F536C mice. CONCLUSIONS: Hyperactivation of the ATF4/TGF-ß1 signaling in cardiomyocytes emerges as a novel mechanism underlying progressive cardiac fibrosis in ACM. Targeting the ATF4/TGF-ß1 signaling may be a novel therapeutic target for managing ACM.

In Vivo Approaches to Understand Arrhythmogenic Cardiomyopathy: Perspectives on Animal Models.

Arrhythmogenic cardiomyopathy (AC) is a hereditary cardiac disorder characterized by the gradual replacement of cardiomyocytes with fibrous and adipose tissue, leading to ventricular wall thinning, chamber dilation, arrhythmias, and sudden cardiac death. Despite advances in treatment, disease management remains challenging. Animal models, particularly mice and zebrafish, have become invaluable tools for understanding AC's pathophysiology and testing potential therapies. Mice models, although useful for scientific research, cannot fully replicate the complexity of the human AC. However, they have provided valuable insights into gene involvement, signalling pathways, and disease progression. Zebrafish offer a promising alternative to mammalian models, despite the phylogenetic distance, due to their economic and genetic advantages. By combining animal models with in vitro studies, researchers can comprehensively understand AC, paving the way for more effective treatments and interventions for patients and improving their quality of life and prognosis.

Animal Models and Molecular Pathogenesis of Arrhythmogenic Cardiomyopathy Associated with Pathogenic Variants in Intercalated Disc Genes.

Arrhythmogenic cardiomyopathy (ACM) is a rare genetic cardiac disease characterized by the progressive substitution of myocardium with fibro-fatty tissue. Clinically, ACM shows wide variability among patients; symptoms can include syncope and ventricular tachycardia but also sudden death, with the latter often being its sole manifestation. Approximately half of ACM patients have been found with variations in one or more genes encoding cardiac intercalated discs proteins; the most involved genes are plakophilin 2 (PKP2), desmoglein 2 (DSG2), and desmoplakin (DSP). Cardiac intercalated discs provide mechanical and electro-metabolic coupling among cardiomyocytes. Mechanical communication is guaranteed by the interaction of proteins of desmosomes and adheren junctions in the so-called area composita, whereas electro-metabolic coupling between adjacent cardiac cells depends on gap junctions. Although ACM has been first described almost thirty years ago, the pathogenic mechanism(s) leading to its development are still only partially known. Several studies with different animal models point to the involvement of the Wnt/ß-catenin signaling in combination with the Hippo pathway. Here, we present an overview about the existing murine models of ACM harboring variants in intercalated disc components with a particular focus on the underlying pathogenic mechanisms. Prospectively, mechanistic insights into the disease pathogenesis will lead to the development of effective targeted therapies for ACM.

Generation of an induced pluripotent stem cell line from a patient with arrhythmogenic right ventricular cardiomyopathy harboring a TMEM43 splice-site variant.

Arrhythmogenic cardiomyopathy (ACM) is a cardiomyopathy that is predominantly inherited and characterized by cardiac arrhythmias and structural abnormalities. TMEM43 (transmembrane protein 43) is one of the well-known genetic culprits behind ACM. In this study, we successfully generated an induced pluripotent stem cell (iPSC) line, YCMi010-A, derived from a male patient diagnosed with ACM. Although these iPSCs harbored a heterozygous intronic splice variant, TMEM43 c.443-2A > G, they still displayed normal cellular morphology and were confirmed to express pluripotency markers. YCMi010-A iPSC line is a promising model for investigating the pathomechanisms associated with ACM and exploring potential therapeutic strategies.

Targeting arrhythmogenic macrophages: lessons learned from arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac condition characterized by cardiac remodeling and life-threatening ventricular arrhythmias. In this issue of the JCI, Chelko, Penna, and colleagues mechanistically addressed the intricate contribution of immune-mediated injury in ACM pathogenesis. Inhibition of nuclear factor κ-B (NF-κB) and infiltration of monocyte-derived macrophages expressing C-C motif chemokine receptor-2 (CCR2) alleviated the phenotypic ACM features (i.e., fibrofatty replacement, contractile dysfunction, and ventricular arrhythmias) in desmoglein 2-mutant (Dsg2mut/mut) mice. These findings pave the way for efficacious and targetable immune therapy for patients with ACM.

NFĸB signaling drives myocardial injury via CCR2+ macrophages in a preclinical model of arrhythmogenic cardiomyopathy.

Nuclear factor κ-B (NFκB) is activated in iPSC-cardiac myocytes from patients with arrhythmogenic cardiomyopathy (ACM) under basal conditions, and inhibition of NFκB signaling prevents disease in Dsg2mut/mut mice, a robust mouse model of ACM. Here, we used genetic approaches and single-cell RNA-Seq to define the contributions of immune signaling in cardiac myocytes and macrophages in the natural progression of ACM using Dsg2mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2mut/mut mice. NFκB signaling in cardiac myocytes mobilizes macrophages expressing C-C motif chemokine receptor-2 (CCR2+ cells) to affected areas within the heart, where they mediate myocardial injury and arrhythmias. Contractile dysfunction in Dsg2mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA-Seq and cellular indexing of transcriptomes and epitomes (CITE-Seq) studies revealed marked proinflammatory changes in gene expression and the cellular landscape in hearts of Dsg2mut/mut mice involving cardiac myocytes, fibroblasts, and CCR2+ macrophages. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2mut/mut mice were dependent on CCR2+ macrophage recruitment to the heart. These results highlight complex mechanisms of immune injury and regulatory crosstalk between cardiac myocytes, inflammatory cells, and fibroblasts in the pathogenesis of ACM.

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.

Arrhythmogenic left ventricular cardiomyopathy caused by a novel likely pathogenic DSP mutation, p.K1165Rfs*8, in a family with sudden cardiac death.

OBJECTIVE: We conducted an investigation into the clinical and molecular characteristics of Arrhythmogenic left ventricular cardiomyopathy (ALVC) caused by a novel likely pathogenic mutation in an Iranian pedigree with sudden cardiac death (SCD). BACKGROUND: ALVC is a genetically inherited myocardial disease characterized by the substitution of fibro-fatty tissue in the left ventricular myocardium, predominantly inherited in an autosomal dominant pattern and is commonly associated with genes involved in encoding desmosomal proteins, specifically Desmoplakin (DSP). METHODS: The patient and available family members underwent a comprehensive clinical assessment, including Cardiac magnetic resonance (CMR) imaging, along with Whole-exome sequencing (WES). The identified variant was confirmed and segregated by Polymerase chain reaction (PCR) and Sanger sequencing in the family members. RESULTS: A novel likely pathogenic heterozygous variant, DSP (NM_004415.4), c.3492_3498del, p.K1165Rfs*8 was discovered in the proband. This variant is likely to be the primary reason for ALVC in this specific family. This variant was confirmed by Sanger sequencing and segregated in other affected members of the family. CONCLUSION: We identified a novel likely pathogenic variant in the DSP gene, which has been identified as the cause of ALVC in an Iranian family. Our investigation underscores the importance of genetic testing, specifically WES, for individuals suspected of ALVC and have a family history of SCD.

Increase of Epicardial Adipose Tissue (EAT) With Fat Infiltration of Right Ventricular Myocardium: Is it Always a High-Risk Stigmata or a Worrisome Feature?

Incidental epicardial adipose tissue (EAT) and subepicardial fat infiltration on CT scans are not uncommon and the differential diagnosis can be a challenge. Considering the vastness of the possible disorders, it is important to differentiate physiologic age-related condition from pathologic disease. We present a case of an asymptomatic 81-year-old woman in which according to ECG and CMR findings we considered as possible differential diagnoses arrhythmogenic cardiomyopathy (ACM) dominant-right variant, lipomatosis and physiological growth of epicardial fat. We focus on patient characteristics, location of the fat replacement, heart morphovolumetry, wall motion of the ventricles and absence of late gadolinium enhancement to diagnose pericardial fat hypertrophy and physiological fatty infiltration. The role of EAT is unclear and it could play a part in the development of atherosclerosis and atrial fibrillation. Therefore, the clinicians should not underestimate this condition even if it would be an incidental finding in asymptomatic patients.

Role of microRNAs in arrhythmogenic cardiomyopathy: translation as biomarkers into clinical practice.

Arrhythmogenic cardiomyopathy is a rare inherited entity, characterized by a progressive fibro-fatty replacement of the myocardium. It leads to malignant arrhythmias and a high risk of sudden cardiac death. Incomplete penetrance and variable expressivity are hallmarks of this arrhythmogenic cardiac disease, where the first manifestation may be syncope and sudden cardiac death, often triggered by physical exercise. Early identification of individuals at risk is crucial to adopt protective and ideally personalized measures to prevent lethal episodes. The genetic analysis identifies deleterious rare variants in nearly 70% of cases, mostly in genes encoding proteins of the desmosome. However, other factors may modulate the phenotype onset and outcome of disease, such as microRNAs. These small noncoding RNAs play a key role in gene expression regulation and the network of cellular processes. In recent years, data focused on the role of microRNAs as potential biomarkers in arrhythmogenic cardiomyopathy have progressively increased. A better understanding of the functions and interactions of microRNAs will likely have clinical implications. Herein, we propose an exhaustive review of the literature regarding these noncoding RNAs, their versatile mechanisms of gene regulation and present novel targets in arrhythmogenic cardiomyopathy.

[A case of arrhythmogenic right ventricular cardiomyo-pathy associated with myocardial inflammation].

Recent years have been marked by a number of published reports that have shown a high frequency of signs of myocardial inflammation in patients with confirmed arrhythmogenic right ventricular cardiomyopathy (ARVC). This article presents a clinical case of typical phenotypic manifestations of ARVC associated with morphometric signs of subacute myocarditis. A 66-year-old man presented to the emergency department with signs of arrhythmogenic shock caused by ventricular tachycardia. Examination detected electrocardiographic signs of (ARVC), visualized signs of right ventricular dilatation, increased trabeculation, and wall fibrosis. Endomyocardial biopsy of the right ventricular wall showed degenerative alterations of cardiomyocytes with perivascular lymphocytic infiltration and areas of granulation tissue. New facts that evidence inflammatory alterations of the myocardium will still require specifying and reconsidering positions of expert consensuses on diagnostics and treatment of ARVC.

Activation of PPARα Ameliorates Cardiac Fibrosis in Dsg2-Deficient Arrhythmogenic Cardiomyopathy.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is a genetic heart muscle disease characterized by progressive fibro-fatty replacement of cardiac myocytes. Up to now, the existing therapeutic modalities for ACM are mostly palliative. About 50% of ACM is caused by mutations in genes encoding desmosomal proteins including Desmoglein-2 (Dsg2). In the current study, the cardiac fibrosis of ACM and its underlying mechanism were investigated by using a cardiac-specific knockout of Dsg2 mouse model. METHODS: Cardiac-specific Dsg2 knockout (CS-Dsg2-/-) mice and wild-type (WT) mice were respectively used as the animal model of ACM and controls. The myocardial collagen volume fraction was determined by histological analysis. The expression levels of fibrotic markers such as α-SMA and Collagen I as well as signal transducers such as STAT3, SMAD3, and PPARα were measured by Western blot and quantitative real-time PCR. RESULTS: Increased cardiac fibrosis was observed in CS-Dsg2-/- mice according to Masson staining. PPARα deficiency and hyperactivation of STAT3 and SMAD3 were observed in the myocardium of CS-Dsg2-/- mice. The biomarkers of fibrosis such as α-SMA and Collagen I were upregulated after gene silencing of Dsg2 in HL-1 cells. Furthermore, STAT3 gene silencing by Stat3 siRNA inhibited the expression of fibrotic markers. The activation of PPARα by fenofibrate or AAV9-Pparα improved the cardiac fibrosis and decreased the phosphorylation of STAT3, SMAD3, and AKT in CS-Dsg2-/- mice. CONCLUSIONS: Activation of PPARα alleviates the cardiac fibrosis in ACM.

Defective Desmosomal Adhesion Causes Arrhythmogenic Cardiomyopathy by Involving an Integrin-αVß6/TGF-ß Signaling Cascade.

BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is characterized by progressive loss of cardiomyocytes with fibrofatty tissue replacement, systolic dysfunction, and life-threatening arrhythmias. A substantial proportion of ACM is caused by mutations in genes of the desmosomal cell-cell adhesion complex, but the underlying mechanisms are not well understood. In the current study, we investigated the relevance of defective desmosomal adhesion for ACM development and progression. METHODS: We mutated the binding site of DSG2 (desmoglein-2), a crucial desmosomal adhesion molecule in cardiomyocytes. This DSG2-W2A mutation abrogates the tryptophan swap, a central interaction mechanism of DSG2 on the basis of structural data. Impaired adhesive function of DSG2-W2A was confirmed by cell-cell dissociation assays and force spectroscopy measurements by atomic force microscopy. The DSG2-W2A knock-in mouse model was analyzed by echocardiography, ECG, and histologic and biomolecular techniques including RNA sequencing and transmission electron and superresolution microscopy. The results were compared with ACM patient samples, and their relevance was confirmed in vivo and in cardiac slice cultures by inhibitor studies applying the small molecule EMD527040 or an inhibitory integrin-αVß6 antibody. RESULTS: The DSG2-W2A mutation impaired binding on molecular level and compromised intercellular adhesive function. Mice bearing this mutation develop a severe cardiac phenotype recalling the characteristics of ACM, including cardiac fibrosis, impaired systolic function, and arrhythmia. A comparison of the transcriptome of mutant mice with ACM patient data suggested deregulated integrin-αVß6 and subsequent transforming growth factor-ß signaling as driver of cardiac fibrosis. Blocking integrin-αVß6 led to reduced expression of profibrotic markers and reduced fibrosis formation in mutant animals in vivo. CONCLUSIONS: We show that disruption of desmosomal adhesion is sufficient to induce a phenotype that fulfils the clinical criteria to establish the diagnosis of ACM, confirming the dysfunctional adhesion hypothesis. Deregulation of integrin-αVß6 and transforming growth factor-ß signaling was identified as a central step toward fibrosis. A pilot in vivo drug test revealed this pathway as a promising target to ameliorate fibrosis. This highlights the value of this model to discern mechanisms of cardiac fibrosis and to identify and test novel treatment options for ACM.

Loss of Nuclear Envelope Integrity and Increased Oxidant Production Cause DNA Damage in Adult Hearts Deficient in PKP2: A Molecular Substrate of ARVC.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by high propensity to life-threatening arrhythmias and progressive loss of heart muscle. More than 40% of reported genetic variants linked to ARVC reside in the PKP2 gene, which encodes the PKP2 protein (plakophilin-2). METHODS: We describe a comprehensive characterization of the ARVC molecular landscape as determined by high-resolution mass spectrometry, RNA sequencing, and transmission electron microscopy of right ventricular biopsy samples obtained from patients with ARVC with PKP2 mutations and left ventricular ejection fraction >45%. Samples from healthy relatives served as controls. The observations led to experimental work using multiple imaging and biochemical techniques in mice with a cardiac-specific deletion of Pkp2 studied at a time of preserved left ventricular ejection fraction and in human induced pluripotent stem cell-derived PKP2-deficient myocytes. RESULTS: Samples from patients with ARVC present a loss of nuclear envelope integrity, molecular signatures indicative of increased DNA damage, and a deficit in transcripts coding for proteins in the electron transport chain. Mice with a cardiac-specific deletion of Pkp2 also present a loss of nuclear envelope integrity, which leads to DNA damage and subsequent excess oxidant production (O2.- and H2O2), the latter increased further under mechanical stress (isoproterenol or exercise). Increased oxidant production and DNA damage is recapitulated in human induced pluripotent stem cell-derived PKP2-deficient myocytes. Furthermore, PKP2-deficient cells release H2O2 into the extracellular environment, causing DNA damage and increased oxidant production in neighboring myocytes in a paracrine manner. Treatment with honokiol increases SIRT3 (mitochondrial nicotinamide adenine dinucleotide-dependent protein deacetylase sirtuin-3) activity, reduces oxidant levels and DNA damage in vitro and in vivo, reduces collagen abundance in the right ventricular free wall, and has a protective effect on right ventricular function. CONCLUSIONS: Loss of nuclear envelope integrity and subsequent DNA damage is a key substrate in the molecular pathology of ARVC. We show transcriptional downregulation of proteins of the electron transcript chain as an early event in the molecular pathophysiology of the disease (before loss of left ventricular ejection fraction <45%), which associates with increased oxidant production (O2.- and H2O2). We propose therapies that limit oxidant formation as a possible intervention to restrict DNA damage in ARVC.

Spectrum of Rare and Common Genetic Variants in Arrhythmogenic Cardiomyopathy Patients.

Arrhythmogenic cardiomyopathy (ACM) is a rare inherited disorder, whose genetic cause is elusive in about 50-70% of cases. ACM presents a variable disease course which could be influenced by genetics. We performed next-generation sequencing on a panel of 174 genes associated with inherited cardiovascular diseases on 82 ACM probands (i) to describe and classify the pathogenicity of rare variants according to the American College of Medical Genetics and Genomics both for ACM-associated genes and for genes linked to other cardiovascular genetic conditions; (ii) to assess, for the first time, the impact of common variants on the ACM clinical disease severity by genotype-phenotype correlation and survival analysis. We identified 15 (likely) pathogenic variants and 66 variants of uncertain significance in ACM-genes and 4 high-impact variants in genes never associated with ACM (ABCC9, APOB, DPP6, MIB1), which deserve future consideration. In addition, we found 69 significant genotype-phenotype associations between common variants and clinical parameters. Arrhythmia-associated polymorphisms resulted in an increased risk of arrhythmic events during patients' follow-up. The description of the genetic framework of our population and the observed genotype-phenotype correlation constitutes the starting point to address the current lack of knowledge in the genetics of ACM.

Histopathological diagnosis of arrhythmogenic right ventricular cardiomyopathy: A review of three autopsy cases.

INTRODUCTION: Arrhythmogenic right ventricular cardiomyopathy is an underdiagnosed myocardial disease which commonly presents with sudden cardiac death in young people. It is considered as a challenge for forensic pathologist due to its pathological changes. Here, we presented three cases of postmortem diagnosis of arrhythmogenic right ventricular cardiomyopathy with involvement of other subtypes. CASE REPORT: Here, we report autopsy cases of sudden cardiac death as the first clinical manifestation observed in three patients with different ages and with no medical history, nor previous family history of sudden death or heart diseases. The postmortem investigations were performed and the diagnosis of arrhythmogenic cardiomyopathy with three expression forms was later confirmed by histopathological examination, this latter showed fibroadipose tissue infiltrations of the myocardium. The diagnosis of arrhythmogenic cardiomyopathy was discussed with review through the literature. CONCLUSION: We presented special characteristic and histopathology features of arrhythmogenic cardiomyopathy cases, discovered in our usual forensic practice. This may be helpful for forensic pathologists to make a reliable diagnosis even in the absence of clinical history.

A Drosophila melanogaster model for TMEM43-related arrhythmogenic right ventricular cardiomyopathy type 5.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a severe cardiac disease that leads to heart failure or sudden cardiac death (SCD). For the pathogenesis of ARVC, various mutations in at least eight different genes have been identified. A rare form of ARVC is associated with the mutation TMEM43 p.S358L, which is a fully penetrant variant in male carriers. TMEM43 p.S358 is homologous to CG8111 p.S333 in Drosophila melanogaster. We established CRISPR/Cas9-mediated CG8111 knock-out mutants in Drosophila, as well as transgenic fly lines carrying an overexpression construct of the CG8111 p.S333L substitution. Knock-out flies developed normally, whereas the overexpression of CG8111 p.S333L caused growth defects, loss of body weight, cardiac arrhythmias, and premature death. An evaluation of a series of model mutants that replaced S333 by selected amino acids proved that the conserved serine is critical for the physiological function of CG8111. Metabolomic and proteomic analyses revealed that the S333 in CG8111 is essential to proper energy homeostasis and lipid metabolism in the fly. Of note, metabolic impairments were also found in the murine Tmem43 disease model, and fibrofatty replacement is a hallmark of human ARVC5. These findings contribute to a more comprehensive understanding of the molecular functions of CG8111 in Drosophila, and can represent a valuable basis to assess the aetiology of the human TMEM43 p.S358L variant in more detail.

GCN5 contributes to intracellular lipid accumulation in human primary cardiac stromal cells from patients affected by Arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is a genetic disease associated with sudden cardiac death and cardiac fibro-fatty replacement. Over the last years, several works have demonstrated that different epigenetic enzymes can affect not only gene expression changes in cardiac diseases but also cellular metabolism. Specifically, the histone acetyltransferase GCN5 is known to facilitate adipogenesis and modulate cardiac metabolism in heart failure. Our group previously demonstrated that human primary cardiac stromal cells (CStCs) contribute to adipogenesis in the ACM pathology. Thus, this study aims to evaluate the role of GCN5 in ACM intracellular lipid accumulation. To do so, CStCs were obtained from right ventricle biopsies of ACM patients and from samples of healthy cadaveric donors (CTR). GCN5 expression was increased both in ex vivo and in vitro ACM samples compared to CTR. When GCN5 expression was silenced or pharmacologically inhibited by the administration of MB-3, we observed a reduction in lipid accumulation and a mitigation of reactive oxygen species (ROS) production in ACM CStCs. In agreement, transcriptome analysis revealed that the presence of MB-3 modified the expression of pathways related to cellular redox balance. Altogether, our findings suggest that GCN5 inhibition reduces fat accumulation in ACM CStCs, partially by modulating intracellular redox balance pathways.

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.