Faculty Bibliography

BACKGROUND:Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy associated with a high risk of ventricular arrhythmia (VA). Several animal models have been used to postulate a therapeutic role of the inhibition of the ryanodine 2 receptor via the use of flecainide for this disease. Clinical data describing its use are scarce, however, especially in patients without implantable cardioverter-defibrillators or with left ventricular (LV) involvement. OBJECTIVES/OBJECTIVE:This study sought to report safety and effectiveness long-term, multicenter data on the impact of flecainide therapy on arrhythmic outcomes in patients with a definite diagnosis of ARVC. METHODS:Patients with definite ARVC receiving flecainide at 12 academic institutions were enrolled in the study. Baseline was defined as the time of flecainide initiation. Premature ventricular complex burdens, nonsustained ventricular tachycardia (NSVT) rates, and sustained VA yearly/rates were collected and compared while on and off flecainide. Side effects and flecainide discontinuation were tracked. Analyses were performed in the overall cohort as well as stratifying for genotype (gene positive vs negative; plakohpillin-2 [PKP-2] vs non PKP-2) and for LV involvement. RESULTS:; LV ejection fraction 55.9 ± 7.3%; right ventricular ejection fraction 44.5 ± 10.5% at baseline) were enrolled, with 66 patients (34.6%) showing LV involvement. The median dose of flecainide was 200 mg/d [150-200 mg/d], with 166 patients (86.9%) also taking a beta-blocker. The median follow-up time on flecainide was 4.2 years [1.9-6.3 years]. Flecainide was well tolerated, with a low (7.9%) discontinuation rate. After flecainide initiation, a significant reduction in the 24-hour premature ventricular complex burden and in the rate of nonsustained ventricular tachycardia was observed (2,190 vs 418; P < 0.001; 35.1% vs 21.5%; P = 0.003). For patients with prior VA events, a significant reduction in the amount of VA episodes/y (1.1 [0.4-1.6] episodes/y vs 0 [0-0.3] episodes/y; P < 0.001) was observed. These safety and effectiveness findings were consistent across genotype subgroups, as well as in patients with and without LV involvement. CONCLUSIONS:Flecainide use had a favorable safety profile and was associated with an observed to a significant reduction in arrhythmic burden in patients with ARVC, irrespective of the underlying genotype or LV involvement.

Desmosomes are adhesive cell contacts abundant in tissues exposed to mechanical strain, such as the stratified and simple epithelia of the epidermis and mucous membranes, as well as the myocardium. Besides their role in mechanical cell cohesion, desmosomes also modulate pathways important for tissue differentiation, wound healing and immune responses. Dysfunctional desmosomes, resulting from pathogenic variants in genes encoding desmosomal components, autoantibodies targeting desmosomal adhesion molecules or inflammation, cause the life-threatening diseases arrhythmogenic cardiomyopathy and pemphigus and contribute to the pathogenesis of inflammatory bowel diseases. The Alpine Desmosome Disease Meeting 2024 (ADDM 2024), held in Grainau, Germany in October 2024, connected international researchers from basic sciences with clinical experts from dermatology, cardiology, gastroenterology and surgery. The participants discussed recent advances, identified hot topics in desmosome biology and disease and provided new concepts for pathogenesis and treatment approaches.

Arrhythmogenic cardiomyopathy (ACM) is a genetically heterogeneous inherited cardiomyopathy with an estimated prevalence of 1:5000-10 000 that predisposes patients to life-threatening ventricular arrhythmias (VA) and sudden cardiac death (SCD). ACM diagnostic criteria and risk prediction models, particularly for arrhythmogenic right ventricular cardiomyopathy (ARVC), the most common form of ACM, are typically genotype-agnostic, but numerous studies have established clinically meaningful genotype-phenotype associations. Early signs of ACM onset differ by genotype indicating the need for genotype-specific diagnostic criteria and family screening paradigms. Likewise, risk factors for SCD vary by genetic subtype, indicating that genotype-specific guidelines for management are also warranted. Of particular importance, genotype-specific therapeutic approaches are being developed. Results from a randomized controlled trial for flecainide use in ARVC patients are currently pending. Research in a plakophilin-2-deficient mouse model suggests this antiarrhythmic drug may be particularly useful for patients with likely pathogenic or pathogenic (LP/P) PKP2 variants. Additionally, the first gene therapy clinical trials in ARVC patients harboring LP/P PKP2 variants are currently underway. This review aims to provide clinicians caring for ACM patients with an up-to-date overview of the current literature in genotype-specific natural history of disease and management of ACM patients and describe scientific advances that have led to upcoming clinical trials.

BACKGROUND/UNASSIGNED:gene to an adult mammalian heart deficient in PKP2 can arrest disease progression and significantly prolong survival. METHODS/UNASSIGNED:Experiments were performed using a PKP2-cKO (cardiac-specific, tamoxifen-activated deletion of plakophilin-2). The potential therapeutic, adeno-associated virus vector of serotype rh.74 (AAVrh.74)-PKP2a (PKP2 variant A; RP-A601) is a recombinant AAVrh.74 gene therapy viral vector encoding the human PKP2a. AAVrh.74-PKP2a was delivered to adult mice by a single tail vein injection either before or after tamoxifen-activated PKP2-cKO. PKP2 expression was confirmed by molecular and histopathologic analyses. Cardiac function and disease progression were monitored by survival analyses, echocardiography, and electrocardiography. RESULTS/UNASSIGNED:Consistent with prior findings, loss of PKP2 expression caused 100% mortality within 50 days after tamoxifen injection. In contrast, AAVrh.74-PKP2a-mediated PKP2a expression resulted in 100% survival for >5 months (at study termination). Echocardiographic analysis revealed that AAVrh.74-PKP2a prevented right ventricle dilation, arrested left ventricle functional decline, and mitigated arrhythmia burden. Molecular and histological analyses showed AAVrh.74-PKP2a-mediated transgene mRNA and protein expression and appropriate PKP2 localization at the cardiomyocyte intercalated disc. Importantly, the therapeutic benefit was shown in mice receiving AAVrh.74-PKP2a after disease onset. CONCLUSIONS/UNASSIGNED:These preclinical data demonstrate the potential for AAVrh.74-PKP2a (RP-A601) as a therapeutic for PKP2-related arrhythmogenic right ventricular cardiomyopathy in both early and more advanced stages of the disease.

Protein"“protein interactions are essential for normal cellular processes and signaling events. Defining these interaction networks is therefore crucial for understanding complex cellular functions and interpretation of disease-associated gene variants. We need to build a comprehensive picture of the interactions, their affinities and interdependencies in the specific organ to decipher hitherto poorly understood signaling mechanisms through ion channels. Here we report the experimental identification of the ensemble of protein interactors for 13 types of ion channels in murine cardiac tissue. Of these, we validated the functional importance of ten interactors on cardiac electrophysiology through genetic knockouts in zebrafish, gene silencing in mice, super-resolution microscopy and patch clamp experiments. Furthermore, we establish a computational framework to reconstruct human cardiomyocyte ion channel networks from deep proteome mapping of human heart tissue and human heart single-cell gene expression data. Finally, we integrate the ion channel interactome with human population genetics data to identify proteins that influence the electrocardiogram (ECG). We demonstrate that the combined channel network is enriched for proteins influencing the ECG, with 44% of the network proteins significantly associated with an ECG phenotype. Altogether, we define interactomes of 13 major cardiac ion channels, contextualize their relevance to human electrophysiology and validate functional roles of ten interactors, including two regulators of the sodium current (epsin-2 and gelsolin). Overall, our data provide a roadmap for our understanding of the molecular machinery that regulates cardiac electrophysiology.

Connexins are crucial cardiac proteins that form hemichannels and gap junctions. Gap junctions are responsible for the propagation of electrical and chemical signals between myocardial cells and cells of the specialized conduction system in order to synchronize the cardiac cycle and steer cardiac pump function. Gap junctions are normally open, while hemichannels are closed, but pathological circumstances may close gap junctions and open hemichannels, thereby perturbing cardiac function and homeostasis. Current evidence demonstrates an emerging role of hemichannels in myocardial ischemia and arrhythmia, and tools are now available to selectively inhibit hemichannels without inhibiting gap junctions as well as to stimulate hemichannel incorporation into gap junctions. We review available experimental evidence for hemichannel contributions to cellular pro-arrhythmic events in ventricular and atrial cardiomyocytes, and link these to insights at the level of molecular control of connexin-43-based hemichannel opening. We conclude that a double-edged approach of both preventing hemichannel opening and preserving gap junctional function will be key for further research and development of new connexin-based experimental approaches for treating heart disease.

Recent advances in volume electron microscopy (vEM) allow unprecedented visualization of the electron-dense structures of cells, tissues and model organisms at nanometric resolution in three dimensions (3D). Light-based microscopy has been widely used for specific localization of proteins; however, it is restricted by the diffraction limit of light, and lacks the ability to identify underlying structures. Here, we describe a protocol for ultrastructural detection, in three dimensions, of a protein (Connexin 43) expressed in the intercalated disc region of adult murine heart. Our protocol does not rest on the expression of genetically encoded proteins and it overcomes hurdles related to pre-embedding and immunolabeling, such as the penetration of the label and the preservation of the tissue. The pre-embedding volumetric immuno-electron microscopy (pre-embedding vIEM) protocol presented here combines several practical strategies to balance sample fixation with antigen and ultrastructural preservation, and penetration of labeling with blocking of non-specific antigen binding sites. The small 1.4 nm gold along with surrounded silver used as a detection marker buried in the sample also serves as a functional conductive resin that significantly reduces the charging of samples. Our protocol also presents strategies for facilitating the successful cutting of the samples during serial block-face scanning electron microscopy (SBF-SEM) imaging. Our results suggest that the small gold-based pre-embedding vIEM is an ideal labeling method for molecular localization throughout the depth of the sample at subcellular compartments and membrane microdomains.

Brugada syndrome is a heritable channelopathy characterized by a peculiar electrocardiogram (ECG) pattern and increased risk of cardiac arrhythmias and sudden death. The arrhythmias originate because of an imbalance between the repolarizing and depolarizing currents that modulate the cardiac action potential. Even if an overt structural cardiomyopathy is not typical of Brugada syndrome, fibrosis and structural changes in the right ventricle contribute to a conduction slowing, which ultimately facilitates ventricular arrhythmias. Currently, Mendelian autosomal dominant transmission is detected in less than 25% of all clinical confirmed cases. Although 23 genes have been associated with the condition, only SCN5A, encoding the cardiac sodium channel, is considered clinically actionable and disease causing. The limited monogenic inheritance has pointed toward new perspectives on the possible complex genetic architecture of the disease, involving polygenic inheritance and a polygenic risk score that can influence penetrance and risk stratification. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.