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.

'Hot phase' clinical presentation in arrhythmogenic cardiomyopathy.

AIMS: The aim of this study is to evaluate the clinical features of patients affected by arrhythmogenic cardiomyopathy (AC), presenting with chest pain and myocardial enzyme release in the setting of normal coronary arteries ('hot phase'). METHODS AND RESULTS: We collected detailed anamnestic, clinical, instrumental, genetic, and histopathological findings as well as follow-up data in a series of AC patients who experienced a hot phase. A total of 23 subjects (12 males, mean age at the first episode 27 ± 16 years) were identified among 560 AC probands and family members (5%). At first episode, 10 patients (43%) already fulfilled AC diagnostic criteria. Twelve-lead electrocardiogram recorded during symptoms showed ST-segment elevation in 11 patients (48%). Endomyocardial biopsy was performed in 11 patients, 8 of them during the acute phase showing histologic evidence of virus-negative myocarditis in 88%. Cardiac magnetic resonance was performed in 21 patients, 12 of them during the acute phase; oedema and/or hyperaemia were detected in 7 (58%) and late gadolinium enhancement in 11 (92%). At the end of follow-up (mean 17 years, range 1-32), 12 additional patients achieved an AC diagnosis. Genetic testing was positive in 77% of cases and pathogenic mutations in desmoplakin gene were the most frequent. No patient complained of sustained ventricular arrhythmias or died suddenly during the 'hot phase'. CONCLUSION: 'Hot phase' represents an uncommon clinical presentation of AC, which often occurs in paediatric patients and carriers of desmoplakin gene mutations. Tissue characterization, family history, and genetic test represent fundamental diagnostic tools for differential diagnosis.

Recent Advances in CRISPR/Cas9-Based Genome Editing Tools for Cardiac Diseases.

In the past two decades, genome editing has proven its value as a powerful tool for modeling or even treating numerous diseases. After the development of protein-guided systems such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), which for the first time made DNA editing an actual possibility, the advent of RNA-guided techniques has brought about an epochal change. Based on a bacterial anti-phage system, the CRISPR/Cas9 approach has provided a flexible and adaptable DNA-editing system that has been able to overcome several limitations associated with earlier methods, rapidly becoming the most common tool for both disease modeling and therapeutic studies. More recently, two novel CRISPR/Cas9-derived tools, namely base editing and prime editing, have further widened the range and accuracy of achievable genomic modifications. This review aims to provide an overview of the most recent developments in the genome-editing field and their applications in biomedical research, with a particular focus on models for the study and treatment of cardiac diseases.

Modeling Cardiovascular Diseases with hiPSC-Derived Cardiomyocytes in 2D and 3D Cultures.

In the last decade, the generation of cardiac disease models based on human-induced pluripotent stem cells (hiPSCs) has become of common use, providing new opportunities to overcome the lack of appropriate cardiac models. Although much progress has been made toward the generation of hiPSC-derived cardiomyocytes (hiPS-CMs), several lines of evidence indicate that two-dimensional (2D) cell culturing presents significant limitations, including hiPS-CMs immaturity and the absence of interaction between different cell types and the extracellular matrix. More recently, new advances in bioengineering and co-culture systems have allowed the generation of three-dimensional (3D) constructs based on hiPSC-derived cells. Within these systems, biochemical and physical stimuli influence the maturation of hiPS-CMs, which can show structural and functional properties more similar to those present in adult cardiomyocytes. In this review, we describe the latest advances in 2D- and 3D-hiPSC technology for cardiac disease mechanisms investigation, drug development, and therapeutic studies.

Arrhythmogenic Ventricular Cardiomyopathy Associated With Fibromuscular Dysplasia of Ostial Right Main Coronary Artery.

In this article, we report the autopsy findings of a 23-year-old woman, who was found unconscious at home by her relatives. During the transportation to the hospital, the woman was handed over to the ambulance personnel, who were the first to provide cardiopulmonary resuscitation. In the hospital, after an hour-lasting asystole, the heart activity was restored. Prolonged cardiac arrest led to hypoxic brain injury, which resulted in a persistent coma. Examinations carried out during hospitalization detected hypokinetic interventricular septum, frequent ventricular extrasystoles and ventricular fibrillation. The patient died within 35 hours of admission to the hospital. Gross findings of the heart included a noticeable increase of the adipose tissue in the right ventricular wall, where histologically focal myocardial atrophy with focal transmural lipomatosis reaching endocardium were detected. Death was attributed to arrhythmogenic ventricular cardiomyopathy. Pathogenic variants in JUP gene and KCNH2 gene confirmed the diagnosis. Other finding of note was fibromuscular dysplasia of ostial right main coronary artery causing a significant luminal narrowing.

Phenotypic expression is a prerequisite for malignant arrhythmic events and sudden cardiac death in arrhythmogenic right ventricular cardiomyopathy.

AIMS: Whether a desmosomal (DS)-gene defect may in itself induce life-threatening ventricular arrhythmias regardless of phenotypic expression of arrhythmogenic right ventricular cardiomyopathy (ARVC) is still debated. This prospective study evaluated the long-term outcome of DS-gene mutation carriers in relation to the ARVC phenotypic expression. METHODS AND RESULTS: The study population included 116 DS-gene mutation carriers [49% males; median age 33 years (16-48 years)] without prior sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). The incidence of the arrhythmic endpoint, including sudden cardiac death (SCD), aborted SCD, sustained VT, and appropriate implantable cardioverter-defibrillator (ICD) intervention was evaluated prospectively and stratified by the presence of ARVC phenotype and risk factors (syncope, ventricular dysfunction, and non-sustained VT). At enrolment, 40 of 116 (34%) subjects fulfilled the criteria for definite ARVC while the remaining were either borderline or phenotype negatives. During a median follow-up of 8.5 (5-12) years, 10 patients (9%) had arrhythmic events (0.9%/year). The event rate was 2.3%/year among patients with definite ARVC and 0.2%/year among borderline or phenotype negative patients (P = 0.002). In patients with definite ARVC, the incidence of arrhythmias was higher in those with ≥1 risk factors (4.1%/year) than in those with no risk factors (0.4%/year, P = 0.02). Mortality was 0.2%/year (1 heart failure death and 1 SCD). CONCLUSIONS: The ARVC phenotypic expression is a prerequisite for the occurrence of life-threatening arrhythmias in DS-gene mutation carriers. The vast majority of malignant arrhythmic events occurred in patients with an overt disease phenotype and major risk factors suggesting that this subgroup most benefits from ICD therapy.

A founder MYBPC3 mutation results in HCM with a high risk of sudden death after the fourth decade of life.

BACKGROUND: Mutations in the cardiac myosin binding protein C (MYBPC3) gene account for a significant proportion of patients affected with hypertrophic cardiomyopathy (HCM). The aim of this study was to evaluate the penetrance and the impact of a frequent founder MYBPC3 mutation on HCM clinical expression and prognosis. METHODS AND RESULTS: Mutation screening of MYBPC3 gene was performed in 97 HCM probands. Nineteen (19.5%) resulted to be carriers of the founder p.F305Pfs*27 mutation and other 45 mutation carriers were identified during the evaluation of 14 families. Eleven (38%) mutation carriers were diagnosed between ages 30 years and 40 years. Disease penetrance was incomplete (64.4%), age-related and was greater in men than women (85% vs 48%, p=0.009). Probands carrying the founder mutation exhibited highest prevalence of non-sustained ventricular tachycardia (63% vs 22%, p=0.003; 63% vs 23%, p=0.01) and implantable cardioverter-defibrillator (58% vs 17%, p=0.001; 58% vs 18%, p=0.005) when compared with probands without MYBPC3 mutations or carrying other MYBPC3 mutations. Reduced survival due to sudden cardiac death (SCD) or aborted SCD occurred more frequently after the fourth decade of life in probands carrying p.F305Pfs*27 mutation than those without MYBPC3 mutations (32% vs 15%, p=0.01). CONCLUSIONS: p.F305Pfs*27 mutation carriers have a high probability to develop the disease between ages 30 years and 40 years with a significant major risk if they are men. This founder mutation is associated with an increase of SCD/aborted SCD events after the fourth decade of life.These findings are of relevant importance for management and clinical decision-making in patients with HCM.

Genetics meets epigenetics: Genetic variants that modulate noncoding RNA in cardiovascular diseases.

After the recent description of the human genome by the ENCODE and the FANTOM consortia, major attention has been addressed to the so-called "genomic noise", which mainly consists of noncoding RNAs (ncRNAs). Among them, microRNAs and long non-coding RNAs have been demonstrated to modulate gene expression and to be involved in several human diseases. Since ncRNAs and their targets are encoded in the genome, genetic principles apply. Common variants are supposed to influence the expression level and the functionality of ncRNAs, with subsequent differential regulation of their target genes. Moreover, several reports showed that polymorphisms in ncRNA or their target genes play a role in the development of cardiovascular adverse phenotype. Here, we provide an overview of the effects of these variations in cardiovascular diseases.