A missense mutation in a ubiquitously expressed protein, vinculin, confers susceptibility to hypertrophic cardiomyopathy

Focal Adhesion's Role in Cardiomyocytes Function: From Cardiomyogenesis to Mechanotransduction

Mechanotransduction refers to the ability of cells to sense mechanical stimuli and convert them into biochemical signals. In this context, the key players are focal adhesions (FAs): multiprotein complexes that link intracellular actin bundles and the extracellular matrix (ECM). FAs are involved in cellular adhesion, growth, differentiation, gene expression, migration, communication, force transmission, and contractility. Focal adhesion signaling molecules, including Focal Adhesion Kinase (FAK), integrins, vinculin, and paxillin, also play pivotal roles in cardiomyogenesis, impacting cell proliferation and heart tube looping. In fact, cardiomyocytes sense ECM stiffness through integrins, modulating signaling pathways like PI3K/AKT and Wnt/β-catenin. Moreover, FAK/Src complex activation mediates cardiac hypertrophic growth and survival signaling in response to mechanical loads. This review provides an overview of the molecular and mechanical mechanisms underlying the crosstalk between FAs and cardiac differentiation, as well as the role of FA-mediated mechanotransduction in guiding cardiac muscle responses to mechanical stimuli.

The intercalated disc: a unique organelle for electromechanical synchrony in cardiomyocytes

The intercalated disc (ID) is a highly specialized structure that connects cardiomyocytes via mechanical and electrical junctions. Although described in some detail by light microscopy in the 19th century, it was in 1966 that electron microscopy images showed that the ID represented apposing cell borders and provided detailed insight into the complex ID nanostructure. Since then, much has been learned about the ID and its molecular composition, and it has become evident that a large number of proteins, not all of them involved in direct cell-to-cell coupling via mechanical or gap junctions, reside at the ID. Furthermore, an increasing number of functional interactions between ID components are emerging, leading to the concept that the ID is not the sum of isolated molecular silos but an interacting molecular complex, an "organelle" where components work in concert to bring about electrical and mechanical synchrony. The aim of the present review is to give a short historical account of the ID's discovery and an updated overview of its composition and organization, followed by a discussion of the physiological implications of the ID architecture and the local intermolecular interactions. The latter will focus on both the importance of normal conduction of cardiac action potentials as well as the impact on the pathophysiology of arrhythmias.

Chemical hazard of robotic hull in-water cleaning discharge on coastal embryonic fish

In-water cleaning (IWC) involves the removal of biofilms and foulants from the hull of a ship using brush or water jet. During IWC, several factors associated with the harmful chemical contaminants release to the marine environment, which can create "hotspots" of chemical contamination in coastal areas. To elucidate the potential toxic effects of IWC discharge, we investigated developmental toxicity in embryonic flounder, which are sensitive life stage to chemical exposure. Zinc and copper were the dominant metals, while zinc pyrithione was the most abundant biocide associated with IWC discharge in two remotely operated IWC. Discharge from IWC carried by both remotely operated vehicles (ROVs) produced developmental malformations including pericardial edema, spinal curvature, and tail-fin defects. In an analyses of differential gene expression profiles (fold-change of genes with a cutoff < 0.05) as assessed by high-throughput RNA sequencing, genes associated with muscle development were commonly and significantly changed. The gene ontology (GO) of embryos exposed to IWC discharge from ROV A activities highly enriched muscle and heart development, while cell signaling and transport were evident in embryos exposed to IWC discharge of ROV B. We analyzed the gene network by significant GO terms. In the network, TTN, MYOM1, CASP3, and CDH2 genes appeared to be key regulators of the toxic effects on muscle development. In embryos exposed to ROV B discharge, HSPG2, VEGFA, and TNF genes related to the nervous system pathway were affected. These results shed light on the potential impacts of muscle and nervous system development in non-target coastal organisms exposed to contaminants found in IWC discharge.

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

Targeted exome analysis of Russian patients with hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM), described as the presence of hypertrophy of left ventricular, is the most prevalent heritable cardiovascular disease with predominantly an autosomal dominant type of inheritance. However, pathogenic alleles are not identified in at least 25% of patients with HCM, and the spectrum of pathogenic variants that contribute to the development of HCM in Russia has not been fully described. Therefore, the goal of our study was to identify genetic variants associated with the etiopathogenesis of HCM in Russian patients.

Methods

The study cohort included 98 unrelated adult patients with HCM. We performed targeted exome sequencing, an analysis using various algorithms for prediction of the impact of variants on protein structure and the prediction of pathogenicity using ACMG Guidelines.

Results

The frequency of pathogenic and likely pathogenic variants in all HCM‐related genes was 8% in our patients. We also identified 20 variants of uncertain significance in all HCM‐related genes.

Conclusions

The prevalence of individual pathogenic variants in HCM‐related genes in Russian population appears to be lower than in general European population, which could be explained by ethnic features of Russian population, age characteristics of our sample, or unidentified pathogenic variants in genes previously not linked with HCM.

Clinical prediction of genotypes in hypertrophic cardiomyopathy: A systematic review

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac condition and the most common cause of sudden cardiac death (SCD) in patients below the age of 35. Genetic testing is a vital part of HCM diagnostics, yet correlation with clinical phenotypes remains complex. Identifying clinical predictors of informative genetic testing may prevent unnecessary investigations and improve cost-effectiveness of services. This article reviews the current literature pertinent to identifying such predictors.

METHODS

Five literature databases were screened using a suitably designed search strategy. Studies investigating the correlation between having a positive genetic test for HCM and a range of clinical and radiological parameters were included in the systematic review.

RESULTS

Twenty-nine observational studies of a total of 9,486 patients were included. The main predictors of informative genetic testing were younger age, higher septal thickness, reverse septal curvature, family history of HCM and SCD and the absence of hypertension. Two externally validated scoring systems have also been developed: the Mayo and Toronto scores. Novel imaging markers and complex algorithmic models are emerging predictors.

CONCLUSION

Using clinical predictors to decide whom to test is a feasible alternative to investigating all comers. Nonetheless, currently there is not enough evidence to unequivocally recommend for or against this strategy. Further validation of current predictors and identification of new ones remain open research avenues.

Loss-of-function or gain-of-function variations in VINCULIN (VCL) are risk factors of human neural tube defects

Background

Neural tube defects (NTDs) are severe birth defects resulting from the failure of neural tube closure during embryogenesis. Both genetic and environmental factors contribute to the occurrence of NTDs and the heritability of NTDs is approximately 70%. As a key component of focal adhesions, Vinculin (VCL) plays pivotal roles in cell skeleton remodeling and signal transduction. Vcl deficient mice displayed NTD, but how VCL variants contribute to human NTDs has not been addressed yet.

Methods

We screened VCL variants in a Chinese cohort of 387 NTDs and 244 controls by targeted next‐generation sequencing.

Results

We identified four case‐specific VCL variations (p.M209L, p.D256fs, p.L555V and p.R586Q). VCL p.D256fs and p.L555V are novel variations that have never been reported. Our analysis revealed that p.D256fs is a loss‐of‐function variant, while p.L555V showed a gain of function in planner cell polarity (PCP) pathway regulation and cell migration, probably due to its enhanced protein stability.

Conclusion

Our study reports human NTD specific novel variations in VCL and provides the functional evaluation of VCL variants related to the etiology of human NTDs.

The Cryogenic Electron Microscopy Structure of the Cell Adhesion Regulator Metavinculin Reveals an Isoform-Specific Kinked Helix in Its Cytoskeleton Binding Domain

Vinculin and its heart-specific splice variant metavinculin are key regulators of cell adhesion processes. These membrane-bound cytoskeletal proteins regulate the cell shape by binding to several other proteins at cell-cell and cell-matrix junctions. Vinculin and metavinculin link integrin adhesion molecules to the filamentous actin network. Loss of both proteins prevents cell adhesion and cell spreading and reduces the formation of stress fibers, focal adhesions, or lamellipodia extensions. The binding of talin at cell-matrix junctions or of α-catenin at cell-cell junctions activates vinculin and metavinculin by releasing their autoinhibitory head-tail interaction. Once activated, vinculin and metavinculin bind F-actin via their five-helix bundle tail domains. Unlike vinculin, metavinculin has a 68-amino-acid insertion before the second α-helix of this five-helix F-actin-binding domain. Here, we present the full-length cryogenic electron microscopy structure of metavinculin that captures the dynamics of its individual domains and unveiled a hallmark structural feature, namely a kinked isoform-specific α-helix in its F-actin-binding domain. Our identified conformational landscape of metavinculin suggests a structural priming mechanism that is consistent with the cell adhesion functions of metavinculin in response to mechanical and cellular cues. Our findings expand our understanding of metavinculin function in the heart with implications for the etiologies of cardiomyopathies.

An assessment of the role of vinculin loss of function variants in inherited cardiomyopathy

The ACMG/AMP variant classification framework was intended for highly penetrant Mendelian conditions. While it is appreciated that clinically relevant variants exhibit a wide spectrum of penetrance, accurately assessing and expressing the pathogenicity of variants with lower penetrance can be challenging. The vinculin (VCL) gene illustrates these challenges. Model organism data provide evidence that loss of function of VCL may play a role in cardiomyopathy and aggregate case-control studies suggest low penetrance. VCL loss of function variants, however, are rarely identified in affected probands and therefore there is a paucity of family studies clarifying the clinical significance of individual variants. This study, which aggregated data from >18,000 individuals who underwent gene panel or exome testing for inherited cardiomyopathies, identified 32 probands with VCL loss-of-function variants and confirmed enrichment in probands with dilated cardiomyopathy (odds ratio [OR] = 9.01; confidence interval [CI] = 4.93-16.45). Our data revealed that the majority of these individuals (89.5%) had pediatric onset of disease. Family studies demonstrated that heterozygous loss of function of VCL alone is insufficient to cause cardiomyopathy but that these variants do contribute to disease risk. In conclusion, VCL loss-of-function variants should be reported in a diagnostic setting but need to be clearly distinguished as having lower penetrance.

Analysis of cardiac magnetic resonance imaging in 36,000 individuals yields genetic insights into dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is an important cause of heart failure and the leading indication for heart transplantation. Many rare genetic variants have been associated with DCM, but common variant studies of the disease have yielded few associated loci. As structural changes in the heart are a defining feature of DCM, we report a genome-wide association study of cardiac magnetic resonance imaging (MRI)-derived left ventricular measurements in 36,041 UK Biobank participants, with replication in 2184 participants from the Multi-Ethnic Study of Atherosclerosis. We identify 45 previously unreported loci associated with cardiac structure and function, many near well-established genes for Mendelian cardiomyopathies. A polygenic score of MRI-derived left ventricular end systolic volume strongly associates with incident DCM in the general population. Even among carriers of TTN truncating mutations, this polygenic score influences the size and function of the human heart. These results further implicate common genetic polymorphisms in the pathogenesis of DCM.

Hypertrophic Cardiomyopathy: An Overview of Genetics and Management

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous cardiac muscle disorder with a diverse natural history, characterized by unexplained left ventricular hypertrophy (LVH), with histopathological hallmarks including myocyte enlargement, myocyte disarray and myocardial fibrosis. Although these features can cause significant cardiac symptoms, many young individuals with HCM are asymptomatic or mildly symptomatic. Sudden cardiac death (SCD) may occur as the initial clinical manifestation. Over the past few decades, HCM has been considered a disease of sarcomere, and typically as an autosomal dominant disease with variable expressivity and incomplete penetrance. Important insights into the genetic landscape of HCM have enhanced our understanding of the molecular pathogenesis, empowered gene-based diagnostic testing to identify at-risk individuals, and offered potential targets for the development of therapeutic agents. This article reviews the current knowledge on the clinical genetics and management of HCM.

Hypertrophic Cardiomyopathy: An Overview of Genetics and Management

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous cardiac muscle disorder with a diverse natural history, characterized by unexplained left ventricular hypertrophy (LVH), with histopathological hallmarks including myocyte enlargement, myocyte disarray and myocardial fibrosis. Although these features can cause significant cardiac symptoms, many young individuals with HCM are asymptomatic or mildly symptomatic. Sudden cardiac death (SCD) may occur as the initial clinical manifestation. Over the past few decades, HCM has been considered a disease of sarcomere, and typically as an autosomal dominant disease with variable expressivity and incomplete penetrance. Important insights into the genetic landscape of HCM have enhanced our understanding of the molecular pathogenesis, empowered gene-based diagnostic testing to identify at-risk individuals, and offered potential targets for the development of therapeutic agents. This article reviews the current knowledge on the clinical genetics and management of HCM.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic cardiomyopathies.

Exploring the Continuum of Hypertrophic Cardiomyopathy-From DNA to Clinical Expression

The concepts underlying hypertrophic cardiomyopathy (HCM) pathogenesis have evolved greatly over the last 60 years since the pioneering work of the British pathologist Donald Teare, presenting the autopsy findings of “asymmetric hypertrophy of the heart in young adults”. Advances in human genome analysis and cardiac imaging techniques have enriched our understanding of the complex architecture of the malady and shaped the way we perceive the illness continuum. Presently, HCM is acknowledged as “a disease of the sarcomere”, where the relationship between genotype and phenotype is not straightforward but subject to various genetic and nongenetic influences. The focus of this review is to discuss key aspects related to molecular mechanisms and imaging aspects that have prompted genotype–phenotype correlations, which will hopefully empower patient-tailored health interventions.

Reprint of: Proteomics in cardiovascular diseases: Unveiling sex and gender differences in the era of precision medicine

Cardiovascular diseases (CVDs) represent the most important cause of mortality in women and in men. Contrary to the long-standing notion that the effects of the major risk factors on CVD outcomes are the same in both sexes, recent evidence recognizes new, potentially independent, sex/gender-related risk factors for CVDs, and sex/gender-differences in the clinical presentation of CVDs have been demonstrated. Furthermore, some therapeutic options may not be equally effective and safe in men and women. In this context, proteomics offers an extremely useful and versatile analytical platform for biomedical researches that expand from the screening of early diagnostic and prognostic biomarkers to the investigation of the molecular mechanisms underlying CDVs. In this review, we summarized the current applications of proteomics in the cardiovascular field, with emphasis on sex and gender-related differences in CVDs.

SIGNIFICANCE

Increasing evidence supports the profound effect of sex and gender on cardiovascular physio-pathology and the response to drugs. A clear understanding of the mechanisms underlying sexual dimorphisms in CVDs would not only improve our knowledge of the etiology of these diseases, but could also inform health policy makers and guideline committees in tailoring specific interventions for the prevention, treatment and management of CVDs in both men and women.

Proteomics in cardiovascular diseases: Unveiling sex and gender differences in the era of precision medicine

Cardiovascular diseases (CVDs) represent the most important cause of mortality in women and in men. Contrary to the long-standing notion that the effects of the major risk factors on CVD outcomes are the same in both sexes, recent evidence recognizes new, potentially independent, sex/gender-related risk factors for CVDs, and sex/gender-differences in the clinical presentation of CVDs have been demonstrated. Furthermore, some therapeutic options may not be equally effective and safe in men and women. In this context, proteomics offers an extremely useful and versatile analytical platform for biomedical researches that expand from the screening of early diagnostic and prognostic biomarkers to the investigation of the molecular mechanisms underlying CDVs. In this review, we summarized the current applications of proteomics in the cardiovascular field, with emphasis on sex and gender-related differences in CVDs.

SIGNIFICANCE

Increasing evidence supports the profound effect of sex and gender on cardiovascular physio-pathology and the response to drugs. A clear understanding of the mechanisms underlying sexual dimorphisms in CVDs would not only improve our knowledge of the etiology of these diseases, but could also inform health policy makers and guideline committees in tailoring specific interventions for the prevention, treatment and management of CVDs in both men and women.

Whole gene sequencing identifies deep-intronic variants with potential functional impact in patients with hypertrophic cardiomyopathy

BACKGROUND

High throughput sequencing technologies have revolutionized the identification of mutations responsible for genetic diseases such as hypertrophic cardiomyopathy (HCM). However, approximately 50% of individuals with a clinical diagnosis of HCM have no causal mutation identified. This may be due to the presence of pathogenic mutations located deep within the introns, which are not detected by conventional sequencing analysis restricted to exons and exon-intron boundaries.

OBJECTIVE

The aim of this study was to develop a whole-gene sequencing strategy to prioritize deep intronic variants that may play a role in HCM pathogenesis.

METHODS AND RESULTS

The full genomic DNA sequence of 26 genes previously associated with HCM was analysed in 16 unrelated patients. We identified likely pathogenic deep intronic variants in VCL, PRKAG2 and TTN genes. These variants, which are predicted to act through disruption of either splicing or transcription factor binding sites, are 3-fold more frequent in our cohort of probands than in normal European populations. Moreover, we found a patient that is compound heterozygous for a splice site mutation in MYBPC3 and the deep intronic VCL variant. Analysis of family members revealed that carriers of the MYBPC3 mutation alone do not manifest the disease, while family members that are compound heterozygous are clinically affected.

CONCLUSION

This study provides a framework for scrutinizing variation along the complete intronic sequence of HCM-associated genes and prioritizing candidates for mechanistic and functional analysis. Our data suggest that deep intronic variation contributes to HCM phenotype.

An East Asian Common Variant Vinculin P.Asp841His Was Associated With Sudden Unexplained Nocturnal Death Syndrome in the Chinese Han Population

Background

We have identified the cardiomyopathy‐susceptibility gene vinculin (VCL) mutation M94I may account for a sudden unexplained nocturnal death syndrome (SUNDS) case. We addressed whether VCL common variant D841H is associated with SUNDS.

Methods and Results

In 8 of 120 SUNDS cases, we detected an East Asian common VCL variant p.Asp841His (D841H). Comparing the H841 allele frequency of the general population in the local database (15 of 1818) with SUNDS victims (10 of 240) gives an odds ratio for SUNDS of 5.226 (95% CI, 2.321, 11.769). The VCL‐D841H variant was engineered and either coexpressed with cardiac sodium channel (SCN5A) in HEK293 cells or overexpressed in human induced pluripotent stem‐cell–derived cardiomyocytes to examine its effects on sodium channel function using the whole‐cell patch‐clamp method. In HEK293 cells, under physiological pH conditions (pH 7.4), D841H caused a 29% decrease in peak I_Na amplitude compared to wild type (WT), whereas under acidotic conditions (pH 7.0), D841H decreased further to 43% along with significant negative shift in inactivation compared to WT at pH 7.4. In induced pluripotent stem‐cell‐derived cardiomyocytes, similar effects of D841H on I_Na were observed. VCL colocalized with SCN5A at the intercalated disk in human cardiomyocytes. VCL was also confirmed to directly interact with SCN5A, and VCL‐D841H did not disrupt the association of VCL and SCN5A.

Conclusions

A VCL common variant was genetically and biophysically associated with Chinese SUNDS. The aggravation of loss of function of SCN5A caused by VCL‐D841H under acidosis supports that nocturnal sleep respiratory disorders with acidosis may play a key role in the pathogenesis of SUNDS.

Genomic Insights into Cardiomyopathies: A Comparative Cross-Species Review

In the global human population, the leading cause of non-communicable death is cardiovascular disease. It is predicted that by 2030, deaths attributable to cardiovascular disease will have risen to over 20 million per year. This review compares the cardiomyopathies in both human and non-human animals and identifies the genetic associations for each disorder in each species/taxonomic group. Despite differences between species, advances in human medicine can be gained by utilising animal models of cardiac disease; likewise, gains can be made in animal medicine from human genomic insights. Advances could include undertaking regular clinical checks in individuals susceptible to cardiomyopathy, genetic testing prior to breeding, and careful administration of breeding programmes (in non-human animals), further development of treatment regimes, and drugs and diagnostic techniques.

Vinculin variant M94I identified in sudden unexplained nocturnal death syndrome decreases cardiac sodium current

Sudden unexplained nocturnal death syndrome (SUNDS) remains an autopsy negative disorder with unclear etiology. Vinculin (VCL) was linked to sudden arrhythmia death in VCL knockout mice prior to the appearance of cardiomyopathy. We hypothesized VCL mutations underlie risk for SUNDS. A rare heterozygous variant VCL-M94I was found in a SUNDS victim who suffered sudden nocturnal tachypnea and lacked pathogenic variants in known arrhythmia-causing genes. VCL was identified to interact with SCN5A in vitro/vivo. The VCL-M94I was co-expressed with the cardiac sodium channel in HEK293 cells and also overexpressed in induced pluripotent stem cells derived cardiomyocytes (iPSCs-CM). In HEK293 cells with pH 7.4, VCL-M94I caused ~30% decrease in peak sodium current (I_Na) amplitude compared to WT; under acidotic conditions (pH 7.0) typically found with hypoxia during sleep apnea, M94I resulted in 37% reduction in peak I_Na compared to WT and the combination of VCL-M94I and pH 7.0 decreased peak I_Na by ~56% compared to WT at pH 7.4. In iPSCs-CM, similar effects of M94I on reduction of peak I_Na were observed. This study initially shows both physical and functional interaction between VCL and cardiac sodium channel, and suggests an important role for respiratory acidosis in triggering the fatal arrhythmia underlying SUNDS.

Amplified pathogenic actions of angiotensin II in cysteine-rich LIM-only protein 4-negative mouse hearts

LIM domain proteins have been identified as essential modulators of cardiac biology and pathology; however, it is unclear which role the cysteine-rich LIM-only protein (CRP)4 plays in these processes. In studying CRP4 mutant mice, we found that their hearts developed normally, but lack of CRP4 exaggerated multiple parameters of the cardiac stress response to the neurohormone angiotensin II (Ang II). Aiming to dissect the molecular details, we found a link between CRP4 and the cardioprotective cGMP pathway, as well as a multiprotein complex comprising well-known hypertrophy-associated factors. Significant enrichment of the cysteine-rich intestinal protein (CRIP)1 in murine hearts lacking CRP4, as well as severe cardiac defects and premature death of CRIP1 and CRP4 morphant zebrafish embryos, further support the notion that depleting CRP4 is incompatible with a proper cardiac development and function. Together, amplified Ang II signaling identified CRP4 as a novel antiremodeling factor regulated, at least to some extent, by cardiac cGMP.-Straubinger, J., Boldt, K., Kuret, A., Deng, L., Krattenmacher, D., Bork, N., Desch, M., Feil, R., Feil, S., Nemer, M., Ueffing, M., Ruth, P., Just, S., Lukowski, R. Amplified pathogenic actions of angiotensin II in cysteine-rich LIM-only protein 4 negative mouse hearts.

Landscape of Pleiotropic Proteins Causing Human Disease: Structural and System Biology Insights

Pleiotropy is the phenomenon by which the same gene can result in multiple phenotypes. Pleiotropic proteins are emerging as important contributors to rare and common disorders. Nevertheless, little is known on the mechanisms underlying pleiotropy and the characteristic of pleiotropic proteins. We analyzed disease-causing proteins reported in UniProt and observed that 12% are pleiotropic (variants in the same protein cause more than one disease). Pleiotropic proteins were enriched in deleterious and rare variants, but not in common variants. Pleiotropic proteins were more likely to be involved in the pathogenesis of neoplasms, neurological, and circulatory diseases and congenital malformations, whereas non-pleiotropic proteins in endocrine and metabolic disorders. Pleiotropic proteins were more essential and had a higher number of interacting partners compared with non-pleiotropic proteins. Significantly more pleiotropic than non-pleiotropic proteins contained at least one intrinsically long disordered region (P < 0.001). Deleterious variants occurring in structurally disordered regions were more commonly found in pleiotropic, rather than non-pleiotropic proteins. In conclusion, pleiotropic proteins are an important contributor to human disease. They represent a biologically different class of proteins compared with non-pleiotropic proteins and a better understanding of their characteristics and genetic variants can greatly aid in the interpretation of genetic studies and drug design.

Targeted next-generation sequencing helps to decipher the genetic and phenotypic heterogeneity of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is mainly associated with myosin, heavy chain 7 (MYH7) and myosin binding protein C, cardiac (MYBPC3) mutations. In order to better explain the clinical and genetic heterogeneity in HCM patients, in this study, we implemented a target-next generation sequencing (NGS) assay. An Ion AmpliSeq™ Custom Panel for the enrichment of 19 genes, of which 9 of these did not encode thick/intermediate and thin myofilament (TTm) proteins and, among them, 3 responsible of HCM phenocopy, was created. Ninety-two DNA samples were analyzed by the Ion Personal Genome Machine: 73 DNA samples (training set), previously genotyped in some of the genes by Sanger sequencing, were used to optimize the NGS strategy, whereas 19 DNA samples (discovery set) allowed the evaluation of NGS performance. In the training set, we identified 72 out of 73 expected mutations and 15 additional mutations: the molecular diagnosis was achieved in one patient with a previously wild-type status and the pre-excitation syndrome was explained in another. In the discovery set, we identified 20 mutations, 5 of which were in genes encoding non-TTm proteins, increasing the diagnostic yield by approximately 20%: a single mutation in genes encoding non-TTm proteins was identified in 2 out of 3 borderline HCM patients, whereas co-occuring mutations in genes encoding TTm and galactosidase alpha (GLA) altered proteins were characterized in a male with HCM and multiorgan dysfunction. Our combined targeted NGS-Sanger sequencing-based strategy allowed the molecular diagnosis of HCM with greater efficiency than using the conventional (Sanger) sequencing alone. Mutant alleles encoding non-TTm proteins may aid in the complete understanding of the genetic and phenotypic heterogeneity of HCM: co-occuring mutations of genes encoding TTm and non-TTm proteins could explain the wide variability of the HCM phenotype, whereas mutations in genes encoding only the non-TTm proteins are identifiable in patients with a milder HCM status.

Quantitative Non-canonical Amino Acid Tagging (QuaNCAT) Proteomics Identifies Distinct Patterns of Protein Synthesis Rapidly Induced by Hypertrophic Agents in Cardiomyocytes, Revealing New Aspects of Metabolic Remodeling

Cardiomyocytes undergo growth and remodeling in response to specific pathological or physiological conditions. In the former, myocardial growth is a risk factor for cardiac failure and faster protein synthesis is a major factor driving cardiomyocyte growth. Our goal was to quantify the rapid effects of different pro-hypertrophic stimuli on the synthesis of specific proteins in ARVC and to determine whether such effects are caused by alterations on mRNA abundance or the translation of specific mRNAs. Cardiomyocytes have very low rates of protein synthesis, posing a challenging problem in terms of studying changes in the synthesis of specific proteins, which also applies to other nondividing primary cells. To study the rates of accumulation of specific proteins in these cells, we developed an optimized version of the Quantitative Noncanonical Amino acid Tagging LC/MS proteomic method to label and selectively enrich newly synthesized proteins in these primary cells while eliminating the suppressive effects of pre-existing and highly abundant nonisotope-tagged polypeptides. Our data revealed that a classical pathologic (phenylephrine; PE) and the recently identified insulin stimulus that also contributes to the development of pathological cardiac hypertrophy (insulin), both increased the synthesis of proteins involved in, e.g. glycolysis, the Krebs cycle and beta-oxidation, and sarcomeric components. However, insulin increased synthesis of many metabolic enzymes to a greater extent than PE. Using a novel validation method, we confirmed that synthesis of selected candidates is indeed up-regulated by PE and insulin. Synthesis of all proteins studied was up-regulated by signaling through mammalian target of rapamycin complex 1 without changes in their mRNA levels, showing the key importance of translational control in the rapid effects of hypertrophic stimuli. Expression of PKM2 was up-regulated in rat hearts following TAC. This isoform possesses specific regulatory properties, so this finding indicates it may be involved in metabolic remodeling and also serve as a novel candidate biomarker. Levels of translation factor eEF1 also increased during TAC, likely contributing to faster cell mass accumulation. Interestingly those two candidates were not up-regulated in pregnancy or exercise induced CH, indicating PKM2 and eEF1 were pathological CH specific markers. We anticipate that the methodologies described here will be valuable for other researchers studying protein synthesis in primary cells.

SCN5A(K817E), a novel Brugada syndrome-associated mutation that alters the activation gating of NaV1.5 channel

BACKGROUND

Brugada syndrome (BrS) is an inherited lethal arrhythmic disorder characterized by syncope and sudden cardiac death from ventricular tachyarrhythmias. Here we identified a novel K817E mutation of SCN5A gene in a man with type 1 BrS electrocardiogram pattern using next-generation sequencing targeted for 73 cardiac disorder-related genes. SCN5A encodes the α-subunit of NaV1.5 voltage-gated Na(+) channel, and some of its mutations are linked to BrS. The proband had no mutation in any of the other arrhythmia-related genes sequenced.

OBJECTIVE

We investigated whether the K817E mutation causes a functional change of NaV1.5 channel responsible for the BrS phenotype.

METHODS

We compared the electrophysiological properties of the whole-cell currents mediated by wild-type and mutant channels heterologously expressed in human embryonic kidney 293 cells by using a voltage-clamp technique.

RESULTS

The K817E mutation reduced the Na(+) current density by 39.0%-91.4% at membrane potentials from -55 to -5 mV. This reduction resulted from a ~24-mV positive shift in the voltage dependence of activation. The mutation also decelerated recovery from both fast and intermediate inactivation, whereas it had little effect on the cell surface expression, single-channel conductance, voltage-dependence of fast inactivation, entry into intermediate inactivation, use-dependent loss of channel availability, or closed-state inactivation.

CONCLUSION

The K817E mutation of SCN5A gene leads to loss of function of NaV1.5 channel and may underlie the BrS phenotype of the proband.

Mechanosensitive components of integrin adhesions: Role of vinculin

External forces play a key role in shaping development and normal physiology. Aberrant responses to forces, or changes in the nature of such forces, are implicated in a variety of diseases. Cells contain several types of adhesions, linking them to their external environment. It is through these adhesions that forces are both sensed (from the outside inwards) and applied (from inside to out). Furthermore, several adhesion-based proteins are sensitive to changes in intracellular forces, utilising them for activation and regulation. Here, we outline how vinculin, a key component of integrin-mediated adhesions linking the actin cytoskeleton to the extracellular matrix (ECM), is regulated by force and acts as force transducing protein. We discuss the role of vinculin in vivo and its place in health and disease; summarise the proposed mechanisms by which vinculin is recruited to and activated at integrin-ECM adhesions; and discuss recent findings that place vinculin as the major force sensing and transmitting component of cell–matrix adhesion complexes. Finally, we discuss the role of vinculin in regulating the cellular responses to both the physical properties of the external environment and to externally applied physical stimuli.

Sex-specific association of rs4746172 of VCL gene with hypertension in two Han populations from Southern China

Hypertension is the most common and lethal risk factor for cardiovascular disease (CVD). Numerous variants have been associated with hypertension, however, most of which failed to get replication due to ethnic differences. In this study, we analyzed associations of 10 newly reported single nucleotide polymorphisms (SNPs) in Europeans with hypertension in Chinese. A total of 1766 samples consisting of 880 subjects with hypertension and 886 controls were collected and the SNPs were genotyped using multiple assays based on the SNaPshot mini-sequencing approach. Our results revealed a significant genotypic association of rs4746172 of VCL with hypertension with a lower frequency of minor allele in male subjects (OR = 0.70, 95% CI: 0.54-0.92, p = 0.011) but not in females. To validate the result, we genotyped the SNPs in another Chinese population with 546 individuals, and got a consistent association for the rs4746172 (OR = 0.56, 95% CI: 0.38-0.82, p = 2.4 × 10(-3)) in males. The VCL-encoding protein was involved in cardiomyopathy that associated with hypertension, therefore our results suggest the rs4746172 of VCL may be a novel target for clinical interventions to reduce CVD risk by regulating blood pressure in male Chinese.

Molecular genetics and pathogenesis of cardiomyopathy

Cardiomyopathy is defined as a disease of functional impairment in the cardiac muscle and its etiology includes both extrinsic and intrinsic factors. Cardiomyopathy caused by the intrinsic factors is called as primary cardiomyopathy of which two major clinical phenotypes are hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Genetic approaches have revealed the disease genes for hereditary primary cardiomyopathy and functional studies have demonstrated that characteristic functional alterations induced by the disease-associated mutations are closely related to the clinical types, such that increased and decreased Ca(2+) sensitivities of muscle contraction are associated with HCM and DCM, respectively. In addition, recent studies have suggested that mutations in the Z-disc components found in HCM and DCM may result in increased and decreased stiffness of sarcomere, respectively. Moreover, functional analysis of mutations in the other components of cardiac muscle have suggested that the altered response to metabolic stresses is associated with cardiomyopathy, further indicating the heterogeneity in the etiology and pathogenesis of cardiomyopathy.

Costamere proteins and their involvement in myopathic processes

Muscle fibres are very specialised cells with a complex structure that requires a high level of organisation of the constituent proteins. For muscle contraction to function properly, there is a need for not only sarcomeres, the contractile structures of the muscle fibre, but also costameres. These are supramolecular structures associated with the sarcolemma that allow muscle adhesion to the extracellular matrix. They are composed of protein complexes that interact and whose functions include maintaining cell structure and signal transduction mediated by their constituent proteins. It is important to improve our understanding of these structures, as mutations in various genes that code for costamere proteins cause many types of muscular dystrophy. In this review, we provide a description of costameres detailing each of their constituent proteins, such as dystrophin, dystrobrevin, syntrophin, sarcoglycans, dystroglycans, vinculin, talin, integrins, desmin, plectin, etc. We describe as well the diseases associated with deficiency thereof, providing a general overview of their importance.

Vinculin network-mediated cytoskeletal remodeling regulates contractile function in the aging heart

The human heart is capable of functioning for decades despite minimal cell turnover or regeneration, suggesting that molecular alterations help sustain heart function with age. However, identification of compensatory remodeling events in the aging heart remains elusive. We present the cardiac proteomes of young and old rhesus monkeys and rats, from which we show that certain age-associated remodeling events within the cardiomyocyte cytoskeleton are highly conserved and beneficial rather than deleterious. Targeted transcriptomic analysis in Drosophila confirmed conservation and implicated vinculin as a unique molecular regulator of cardiac function during aging. Cardiac-restricted vinculin overexpression reinforced the cortical cytoskeleton and enhanced myofilament organization, leading to improved contractility and hemodynamic stress tolerance in healthy and myosin-deficient fly hearts. Moreover, cardiac-specific vinculin overexpression increased median life span by more than 150% in flies. A broad array of potential therapeutic targets and regulators of age-associated modifications, specifically for vinculin, are presented. These findings suggest that the heart has molecular mechanisms to sustain performance and promote longevity, which may be assisted by therapeutic intervention to ameliorate the decline of function in aging patient hearts.

Between Rho(k) and a hard place: the relation between vessel wall stiffness, endothelial contractility, and cardiovascular disease

Vascular stiffness is a mechanical property of the vessel wall that affects blood pressure, permeability, and inflammation. As a result, vascular stiffness is a key driver of (chronic) human disorders, including pulmonary arterial hypertension, kidney disease, and atherosclerosis. Responses of the endothelium to stiffening involve integration of mechanical cues from various sources, including the extracellular matrix, smooth muscle cells, and the forces that derive from shear stress of blood. This response in turn affects endothelial cell contractility, which is an important property that regulates endothelial stiffness, permeability, and leukocyte-vessel wall interactions. Moreover, endothelial stiffening reduces nitric oxide production, which promotes smooth muscle cell contraction and vasoconstriction. In fact, vessel wall stiffening, and microcirculatory endothelial dysfunction, precedes hypertension and thus underlies the development of vascular disease. Here, we review the cross talk among vessel wall stiffening, endothelial contractility, and vascular disease, which is controlled by Rho-driven actomyosin contractility and cellular mechanotransduction. In addition to discussing the various inputs and relevant molecular events in the endothelium, we address which actomyosin-regulated changes at cell adhesion complexes are genetically associated with human cardiovascular disease. Finally, we discuss recent findings that broaden therapeutic options for targeting this important mechanical signaling pathway in vascular pathogenesis.

The role of clinical, genetic and segregation evaluation in sudden infant death

Sudden infant death syndrome (SIDS) is the leading cause of death in the first year of life. Several arrhythmogenic genes have been associated with cardiac pathologies leading to infant sudden cardiac death (SCD). Our aim was to take advantage of next generation sequencing (NGS) technology to perform a thorough genetic analysis of a SIDS case. A SIDS case was referred to our institution after negative autopsy. We performed a genetic analysis of 104 SCD-related genes using a custom panel. Confirmed variants in index case were also analyzed in relatives. Clinical evaluation of first-degree family members was performed. Relatives did not show pathology. NGS identified seven variants. Two previously described as pathogenic. Four previously catalogued without clinical significance. The seventh variation was novel. Familial segregation showed that the index case's mother carried all same genetic variations except one, which was inherited from the father. The sister of the index case carried three variants. We believe that molecular autopsy should be included in current forensic protocols after negative autopsy. In addition to NGS technologies, familial genetic testing should be also performed to clarify potential pathogenic role of new variants and to identify genetic carriers at risk of SCD.

The integrin adhesome: from genes and proteins to human disease

The adhesive interactions of cells with their environment through the integrin family of transmembrane receptors have key roles in regulating multiple aspects of cellular physiology, including cell proliferation, viability, differentiation and migration. Consequently, failure to establish functional cell adhesions, and thus the assembly of associated cytoplasmic scaffolding and signalling networks, can have severe pathological effects. The roles of specific constituents of integrin-mediated adhesions, which are collectively known as the 'integrin adhesome', in diverse pathological states are becoming clear. Indeed, the prominence of mutations in specific adhesome molecules in various human diseases is now appreciated, and experimental as well as in silico approaches provide insights into the molecular mechanisms underlying these pathological conditions.

Integrins and integrin-associated proteins in the cardiac myocyte

Integrins are heterodimeric, transmembrane receptors that are expressed in all cells, including those in the heart. They participate in multiple critical cellular processes including adhesion, extracellular matrix organization, signaling, survival, and proliferation. Particularly relevant for a contracting muscle cell, integrins are mechanotransducers, translating mechanical to biochemical information. Although it is likely that cardiovascular clinicians and scientists have the highest recognition of integrins in the cardiovascular system from drugs used to inhibit platelet aggregation, the focus of this article will be on the role of integrins specifically in the cardiac myocyte. After a general introduction to integrin biology, the article will discuss important work on integrin signaling, mechanotransduction, and lessons learned about integrin function from a range of model organisms. Then we will detail work on integrin-related proteins in the myocyte, how integrins may interact with ion channels and mediate viral uptake into cells, and also play a role in stem cell biology. Finally, we will discuss directions for future study.

Vinculin directly binds zonula occludens-1 and is essential for stabilizing connexin-43-containing gap junctions in cardiac myocytes

Vinculin (Vcl) links actin filaments to integrin- and cadherin-based cellular junctions. Zonula occludens-1 (ZO-1, also known as TJP1) binds connexin-43 (Cx43, also known as GJA1), cadherin and actin. Vcl and ZO-1 anchor the actin cytoskeleton to the sarcolemma. Given that loss of Vcl from cardiomyocytes causes maldistribution of Cx43 and predisposes cardiomyocyte-specific Vcl-knockout mice with preserved heart function to arrhythmia and sudden death, we hypothesized that Vcl and ZO-1 interact and that loss of this interaction destabilizes gap junctions. We found that Vcl, Cx43 and ZO-1 colocalized at the intercalated disc. Loss of cardiomyocyte Vcl caused parallel loss of ZO-1 from intercalated dics. Vcl co-immunoprecipitated Cx43 and ZO-1, and directly bound ZO-1 in yeast two-hybrid studies. Excision of the Vcl gene in neonatal mouse cardiomyocytes caused a reduction in the amount of Vcl mRNA transcript and protein expression leading to (1) decreased protein expression of Cx43, ZO-1, talin, and β1D-integrin, (2) reduced PI3K activation, (3) increased activation of Akt, Erk1 and Erk2, and (4) cardiomyocyte necrosis. In summary, this is the first study showing a direct interaction between Vcl and ZO-1 and illustrates how Vcl plays a crucial role in stabilizing gap junctions and myocyte integrity.

Fermitins, the orthologs of mammalian Kindlins, regulate the development of a functional cardiac syncytium in Drosophila melanogaster

The vertebrate Kindlins are an evolutionarily conserved family of proteins critical for integrin signalling and cell adhesion. Kindlin-2 (KIND2) is associated with intercalated discs in mice, suggesting a role in cardiac syncytium development; however, deficiency of Kind2 leads to embryonic lethality. Morpholino knock-down of Kind2 in zebrafish has a pleiotropic effect on development that includes the heart. It therefore remains unclear whether cardiomyocyte Kind2 expression is required for cardiomyocyte junction formation and the development of normal cardiac function. To address this question, the expression of Fermitin 1 and Fermitin 2 (Fit1, Fit2), the two Drosophila orthologs of Kind2, was silenced in Drosophila cardiomyocytes. Heart development was assessed in adult flies by immunological methods and videomicroscopy. Silencing both Fit1 and Fit2 led to a severe cardiomyopathy characterised by the failure of cardiomyocytes to develop as a functional syncytium and loss of synchrony between cardiomyocytes. A null allele of Fit1 was generated but this had no impact on the heart. Similarly, the silencing of Fit2 failed to affect heart function. In contrast, the silencing of Fit2 in the cardiomyocytes of Fit1 null flies disrupted syncytium development, leading to severe cardiomyopathy. The data definitively demonstrate a role for Fermitins in the development of a functional cardiac syncytium in Drosophila. The findings also show that the Fermitins can functionally compensate for each other in order to control syncytium development. These findings support the concept that abnormalities in cardiomyocyte KIND2 expression or function may contribute to cardiomyopathies in humans.

Evolving form to fit function: cardiomyocyte intercalated disc and transverse-tubule membranes

The vertebrate cardiac myocyte has evolved a highly organized cellular membrane architecture and cell-cell contacts in order to effectively transmit precisely timed and homogeneous depolarizing waves without failure (>2 billion times/human life span). Two unique specialized membrane domains, the intercalated disc and the transverse tubule (T-tubule), function to ensure the rapid and coordinated propagation of the action potential throughout the heart. Based on their critical roles in structure, signaling, and electric inter- and intracellular communication, it is not surprising that dysfunction in these membrane structures is associated with aberrant vertebrate physiology, resulting in potentially fatal congenital and acquired disease. This chapter will review the fundamental components of cardiomyocyte intercalated disc and transverse-tubule membranes with a focus on linking dysfunction in these membranes with human cardiovascular disease.

Metavinculin: New insights into functional properties of a muscle adhesion protein

Metavinculin is a muscle-specific splice variant of the ubiquitously expressed cytoskeletal adaptor protein vinculin. Both proteins are thought to be co-expressed in all muscle types where they co-localize to microfilament-associated adhesion sites. It has been shown that a metavinculin-specific insertion of 68 amino acids alters the biochemical properties of the five-helix bundle in the tail domain. Here, we demonstrate that the metavinculin-specific helix H1' plays an important role for protein stability of the tail domain, since a point mutation in this helix, R975W, which is associated with the occurrence of dilated cardiomyopathy in man, further decreases thermal stability of the metavinculin tail domain. In striated muscle progenitor cells (myoblasts), both, metavinculin and the R975W mutant show significantly reduced, albeit distinctive residency and exchange rates in adhesion sites as compared to vinculin. In contrast to previous studies, we show that metavinculin is localized in a muscle fiber type-dependent fashion to the costameres of striated muscle, reflecting the individual metabolic and physiological status of a given muscle fiber. Metavinculin expression is highest in fast, glycolytic muscle fibers and virtually absent in M. diaphragmaticus, a skeletal muscle entirely lacking fast, glycolytic fibers. In summary, our data suggest that metavinculin enrichment in attachment sites of muscle cells leads to higher mechanical stability of adhesion complexes allowing for greater shear force resistance.

A mild form of SLC29A3 disorder: a frameshift deletion leads to the paradoxical translation of an otherwise noncoding mRNA splice variant

We investigated two siblings with granulomatous histiocytosis prominent in the nasal area, mimicking rhinoscleroma and Rosai-Dorfman syndrome. Genome-wide linkage analysis and whole-exome sequencing identified a homozygous frameshift deletion in SLC29A3, which encodes human equilibrative nucleoside transporter-3 (hENT3). Germline mutations in SLC29A3 have been reported in rare patients with a wide range of overlapping clinical features and inherited disorders including H syndrome, pigmented hypertrichosis with insulin-dependent diabetes, and Faisalabad histiocytosis. With the exception of insulin-dependent diabetes and mild finger and toe contractures in one sibling, the two patients with nasal granulomatous histiocytosis studied here displayed none of the many SLC29A3-associated phenotypes. This mild clinical phenotype probably results from a remarkable genetic mechanism. The SLC29A3 frameshift deletion prevents the expression of the normally coding transcripts. It instead leads to the translation, expression, and function of an otherwise noncoding, out-of-frame mRNA splice variant lacking exon 3 that is eliminated by nonsense-mediated mRNA decay (NMD) in healthy individuals. The mutated isoform differs from the wild-type hENT3 by the modification of 20 residues in exon 2 and the removal of another 28 amino acids in exon 3, which include the second transmembrane domain. As a result, this new isoform displays some functional activity. This mechanism probably accounts for the narrow and mild clinical phenotype of the patients. This study highlights the 'rescue' role played by a normally noncoding mRNA splice variant of SLC29A3, uncovering a new mechanism by which frameshift mutations can be hypomorphic.

Familial dilated cardiomyopathy associated with congenital defects in the setting of a novel VCL mutation (Lys815Arg) in conjunction with a known MYPBC3 variant

Idiopathic dilated cardiomyopathy (DCM) is a primary myocardial disorder characterized by ventricular chamber enlargement and systolic dysfunction. Twenty to fifty percent of idiopathic DCM cases are thought to have a genetic cause. Of more than 30 genes known to be associated with DCM, rare variants in the VCL and MYBPC3 genes have been reported in several cases of DCM. In this report, we describe a family with DCM and congenital abnormalities who carry a novel missense mutation in the VCL gene. More severely affected family members also possess a second missense variant in MYBPC3, raising the possibility that this variant may be a disease modifier. Interestingly, many of the affected individuals also have congenital defects, including two with bicuspid aortic valve with aortic regurgitation. We discuss the implications of the family history and genetic information on management of at-risk individuals with aortic regurgitation.

[Advances in the molecular pathogenesis of hypertrophic cardiomyopathy]

Hypertrophic Cardiomyopathy (HCM) is a primary cardiac disorder characterized by asymmetric thickening of the septum and left ventricular wall. HCM affects 1 in 500 individuals in the general population, and it is the most common cause of sudden death in the young and athletes. The clinic phenotype of HCM is highly variable with respect to age at onset, degree of symptoms, and risk of sudden death. HCM is usually inherited as a Mendelian autosomal dominant trait. To date, over 900 mutations have been reported in HCM, which were mainly located in 13 genes encoding cardiac sarcomere protein, e.g., MYH7, MYBPC3, and TnT. In addition, more and more mitochondrial DNA mutations were reported to be associated with the pathogenesis of HCM. Based on the description of the clinical phenotype and morphological characteristics, this review focuses on the research in the molecular pathogenic mechanism of HCM and its recent advances.

Vinculin and talin: focus on the myocardium

Cardiomyopathy is a heart muscle disease caused by decreased contractility of the ventricles leading to heart failure and premature death. Multiple conditions like ischemic heart disease (atherosclerosis), hypertension, diabetes, viral infection, alcohol abuse, obesity and genetic mutations can lead to cardiomyopathy. Single gene mutations in sarcomeric proteins, Z-disk-associated proteins, membrane/associated proteins, intermediate filaments, calcium cycle proteins as well as in modifier genes have been linked to cardiomyopathy. Clinical practice guidelines have been formulated by the American Heart Association and the Heart Failure Association of America on how to genetically evaluate patients with cardiomyopathy. To illustrate the concept that alterations in genes cause cardiovascular disease, this review will focus on two membrane-associated proteins, vinculin and talin. We will discuss the general function of vinculin/metavinulin as well as talin1 and talin2, with emphasis on what is understood about their role in the cardiac myocyte and in whole heart.

Identifying sarcomere gene mutations in hypertrophic cardiomyopathy: a personal history

This review provides an historical and personal perspective on the discovery of genetic causes for hypertrophic cardiomyopathy (HCM). Extraordinary insights by physicians who initially detailed remarkable and varied manifestations of the disorder, collaboration among multidisciplinary teams with skills in clinical diagnostics and molecular genetics, and hard work by scores of trainees solved the etiologic riddle of HCM and unexpectedly demonstrated mutations in sarcomere protein genes as the cause of disease. In addition to celebrating 20 years of genetic research in HCM, this article serves as an introductory overview to a thematic review series that will present contemporary advances in the field of hypertrophic heart disease. Through the continued application of advances in genetic methodologies, combined with biochemical and biophysical analyses of the consequences of human mutations, fundamental knowledge about HCM and sarcomere biology has emerged. Expanding research to elucidate the mechanisms by which subtle genetic variation in contractile proteins remodel the human heart remains an exciting opportunity, one with considerable promise to provide new strategies to limit or even prevent HCM pathogenesis.

New insights into vinculin function and regulation

Vinculin is a cytoplasmic actin-binding protein enriched in focal adhesions and adherens junctions that is essential for embryonic development. Much is now known regarding the role of vinculin in governing cell-matrix adhesion. In the past decade that the crystal structure of vinculin and the molecular details for how vinculin regulates adhesion events have emerged. The recent data suggests a critical function for vinculin in regulating integrin clustering, force generation, and strength of adhesion. In addition to an important role in cell-matrix adhesion, vinculin is also emerging as a regulator of apoptosis, Shigella entry into host cells, and cadherin-based cell-cell adhesion. A close inspection of this work reveals that there are similarities between vinculin's role in focal adhesions and these processes and also some intriguing differences.

Mutation type is not clinically useful in predicting prognosis in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), or clinically unexplained hypertrophy of the heart, is a common genetic cardiovascular disorder marked by genetic and phenotypic heterogeneity. As the genetic mutations underlying the pathogenesis of this disease have been identified, investigators have attempted to link mutations to clearly defined alterations in survival in hopes of identifying prognostically relevant biomarkers of disease. While initial studies labeling particular MYH7 -encoded beta myosin heavy chain and TNNT2 -encoded cardiac troponin T mutations as “malignant” or “benign” raised hopes for mutation-specific risk stratification in HCM, a series of subsequent investigations identified mutations in families with contradictory disease phenotypes. Furthermore, subsequent proband-based cohort studies indicated that the clinical prognostic relevance of individual mutations labeled as “malignant” or “benign” in large referral centers is negligible. Herein, we seek to summarize the controversy and dispute the notion that mutation-specific risk stratification in HCM is possible at the present time. We provide evidence for clinicians and basic scientists alike to move beyond simple mutation descriptors to a more nuanced understanding of HCM mutations that fully captures the multi-factorial nature of HCM disease expression.

[Molecular mechanisms of genetic damages of the myocardium in cardiomyopathy]

The review highlighted problems of reorganization of myocardical contractile and cytoskeletal proteins in cardiomyopathy (CM). The role of the genetic factors coding contractile proteins, proteins of thin and thick filaments, and also extracellular matrix proteins in processes of formation and development of hypertrophic (HCM) and dilated (DCM) cardiomyopathy are analyzed. The mechanisms responsible for the changes in cardiac proteins on regulation involved into force generation, its transfer, recycling ATP, impairments in transmembranal signals, that finally lead to cardiac cell dysfunction determining various manifestations of CM are considered.

The vinculin-DeltaIn20/21 mouse: characteristics of a constitutive, actin-binding deficient splice variant of vinculin

Background

The cytoskeletal adaptor protein vinculin plays a fundamental role in cell contact regulation and affects central aspects of cell motility, which are essential to both embryonal development and tissue homeostasis. Functional regulation of this evolutionarily conserved and ubiquitously expressed protein is dominated by a high-affinity, autoinhibitory head-to-tail interaction that spatially restricts ligand interactions to cell adhesion sites and, furthermore, limits the residency time of vinculin at these sites. To date, no mutants of the vinculin protein have been characterized in animal models.

Methodology/Principal Findings

Here, we investigate vinculin-ΔEx20, a splice variant of the protein lacking the 68 amino acids encoded by exon 20 of the vinculin gene VCL. Vinculin-ΔEx20 was found to be expressed alongside with wild type protein in a knock-in mouse model with a deletion of introns 20 and 21 (VCL-ΔIn20/21 allele) and shows defective head-to-tail interaction. Homozygous VCL-ΔIn20/21 embryos die around embryonal day E12.5 showing cranial neural tube defects and exencephaly. In mouse embryonic fibroblasts and upon ectopic expression, vinculin-ΔEx20 reveals characteristics of constitutive head binding activity. Interestingly, the impact of vinculin-ΔEx20 on cell contact induction and stabilization, a hallmark of the vinculin head domain, is only moderate, thus allowing invasion and motility of cells in three-dimensional collagen matrices. Lacking both F-actin interaction sites of the tail, the vinculin-ΔEx20 variant unveils vinculin's dynamic binding to cell adhesions independent of a cytoskeletal association, and thus differs from head-to-tail binding deficient mutants such as vinculin-T12, in which activated F-actin binding locks the protein variant to cell contact sites.

Conclusions/Significance

Vinculin-ΔEx20 is an active variant supporting adhesion site stabilization without an enhanced mechanical coupling. Its presence in a transgenic animal reveals the potential of splice variants in the vinculin gene to alter vinculin function in vivo. Correct control of vinculin is necessary for embryonic development.

Cell-cell connection to cardiac disease

Intercalated disks (ICDs) are highly organized cell-cell adhesion structures, which connect cardiomyocytes to one another. They are composed of three major complexes: desmosomes, fascia adherens, and gap junctions. Desmosomes and fascia adherens junction are necessary for mechanically coupling and reinforcing cardiomyocytes, whereas gap junctions are essential for rapid electrical transmission between cells. Because human genetics and mouse models have revealed that mutations and/or deficiencies in various ICD components can lead to cardiomyopathies and arrhythmias, considerable attention has focused on the biologic function of the ICD. This review will discuss recent scientific developments related to the ICD and focus on its role in regulating cardiac muscle structure, signaling, and disease.