Exploration of the P1 residue in 3CL protease inhibitors leading to the discovery of a 2-tetrahydrofuran P1 replacement.

The virally encoded 3C-like protease (3CLpro) is a well-validated drug target for the inhibition of coronaviruses including Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). Most inhibitors of 3CLpro are peptidomimetic, with a γ-lactam in place of Gln at the P1 position of the pseudopeptide chain. An effort was pursued to identify a viable alternative to the γ-lactam P1 mimetic which would improve physicochemical properties while retaining affinity for the target. Discovery of a 2-tetrahydrofuran as a suitable P1 replacement that is a potent enzymatic inhibitor of 3CLpro in SARS-CoV-2 virus is described herein.

Severe Cardiac Dysfunction and Death Caused by Arrhythmogenic Right Ventricular Cardiomyopathy Type 5 Are Improved by Inhibition of Glycogen Synthase Kinase-3ß.

BACKGROUND: Arrhythmogenic cardiomyopathy/arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiac disease characterized by fibrofatty replacement of the myocardium, resulting in heart failure and sudden cardiac death. The most aggressive arrhythmogenic cardiomyopathy/ARVC subtype is ARVC type 5 (ARVC5), caused by a p.S358L mutation in TMEM43 (transmembrane protein 43). The function and localization of TMEM43 are unknown, as is the mechanism by which the p.S358L mutation causes the disease. Here, we report the characterization of the first transgenic mouse model of ARVC5. METHODS: We generated transgenic mice overexpressing TMEM43 in either its wild-type or p.S358L mutant (TMEM43-S358L) form in postnatal cardiomyocytes under the control of the α-myosin heavy chain promoter. RESULTS: We found that mice expressing TMEM43-S358L recapitulate the human disease and die at a young age. Mutant TMEM43 causes cardiomyocyte death and severe fibrofatty replacement. We also demonstrate that TMEM43 localizes at the nuclear membrane and interacts with emerin and ß-actin. TMEM43-S358L shows partial delocalization to the cytoplasm, reduced interaction with emerin and ß-actin, and activation of glycogen synthase kinase-3ß (GSK3ß). Furthermore, we show that targeting cardiac fibrosis has no beneficial effect, whereas overexpression of the calcineurin splice variant calcineurin Aß1 results in GSK3ß inhibition and improved cardiac function and survival. Similarly, treatment of TMEM43 mutant mice with a GSK3ß inhibitor improves cardiac function. Finally, human induced pluripotent stem cells bearing the p.S358L mutation also showed contractile dysfunction that was partially restored after GSK3ß inhibition. CONCLUSIONS: Our data provide evidence that TMEM43-S358L leads to sustained cardiomyocyte death and fibrofatty replacement. Overexpression of calcineurin Aß1 in TMEM43 mutant mice or chemical GSK3ß inhibition improves cardiac function and increases mice life span. Our results pave the way toward new therapeutic approaches for ARVC5.

Animal models of arrhythmogenic right ventricular cardiomyopathy: what have we learned and where do we go? Insight for therapeutics.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare genetically-determined cardiac heart muscle disorder characterized by fibro-fatty replacement of the myocardium that results in heart failure and sudden cardiac death (SCD), predominantly in young males. The disease is often caused by mutations in genes encoding proteins of the desmosomal complex, with a significant minority caused by mutations in non-desmosomal proteins. Existing treatment options are based on SCD prevention with the implantable cardioverter defibrillator, antiarrhythmic drugs, and anti-heart failure medication. Heart transplantation may also be required and there is currently no cure. Several genetically modified animal models have been developed to characterize the disease, assess its progression, and determine the influence of potential environmental factors. These models have also been very valuable for translational therapeutic approaches, to screen new treatment options that prevent and/or reverse the disease. Here, we review the available ARVC animal models reported to date, highlighting the most important pathophysiological findings and discussing the effect of treatments tested so far in this setting. We also describe gaps in our knowledge of the disease, with the goal of stimulating research and improving patient outcomes.

Clonal analysis identifies hemogenic endothelium as the source of the blood-endothelial common lineage in the mouse embryo.

The first blood and endothelial cells of amniote embryos appear in close association in the blood islands of the yolk sac (YS). This association and in vitro lineage analyses have suggested a common origin from mesodermal precursors called hemangioblasts, specified in the primitive streak during gastrulation. Fate mapping and chimera studies, however, failed to provide strong evidence for a common origin in the early mouse YS. Additional in vitro studies suggest instead that mesodermal precursors first generate hemogenic endothelium, which then generate blood cells in a linear sequence. We conducted an in vivo clonal analysis to determine the potential of individual cells in the mouse epiblast, primitive streak, and early YS. We found that early YS blood and endothelial lineages mostly derive from independent epiblast populations, specified before gastrulation. Additionally, a subpopulation of the YS endothelium has hemogenic activity and displays characteristics similar to those found later in the embryonic hemogenic endothelium. Our results show that the earliest blood and endothelial cell populations in the mouse embryo are specified independently, and that hemogenic endothelium first appears in the YS and produces blood precursors with markers related to definitive hematopoiesis.

Early Preventive Treatment With Enalapril Improves Cardiac Function and Delays Mortality in Mice With Arrhythmogenic Right Ventricular Cardiomyopathy Type 5.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy type 5 (ARVC5) is an inherited cardiac disease with complete penetrance and an aggressive clinical course caused by mutations in TMEM43 (transmembrane protein 43). There is no cure for ARVC5 and palliative treatment is started once the phenotype is present. A transgenic mouse model of ARVC5 expressing human TMEM43-S358L (TMEM43mut) recapitulates the human disease, enabling the exploration of preventive treatments. The aim of this study is to determine whether preventive treatment with heart failure drugs (ß-blockers, ACE [angiotensin-converting enzyme] inhibitors, mineralocorticoid-receptor antagonists) improves the disease course of ARVC5 in TMEM43mut mice. METHODS: TMEM43mut male/female mice were treated with metoprolol (ß-blockers), enalapril (ACE inhibitor), spironolactone (mineralocorticoid-receptor antagonist), ACE inhibitor + mineralocorticoid-receptor antagonist, ACE inhibitor + mineralocorticoid-receptor antagonist + ß-blockers or left untreated. Drugs were initiated at 3 weeks of age, before ARVC5 phenotype, and serial ECG and echocardiograms were performed. RESULTS: TMEM43mut mice treated with enalapril showed a significantly increased median survival compared with untreated mice (26 versus 21 weeks; P=0.003). Enalapril-treated mice also exhibited increased left ventricular ejection fraction at 4 months compared with controls (37.0% versus 24.9%; P=0.004), shorter QRS duration and reduced left ventricle fibrosis. Combined regimens including enalapril also showed positive effects. Metoprolol decreased QRS voltage prematurely and resulted in a nonsignificant decrease in left ventricular ejection fraction compared with untreated TMEM43mut mice. CONCLUSIONS: Preventive enalapril-based regimens reduced fibrosis, improved ECG, echocardiographic parameters and survival of ARVC5 mice. Early metoprolol did not show positive effects and caused premature ECG abnormalities. Our findings pave the way to consider prophylactic enalapril in asymptomatic ARVC5 genetic carriers.

Conformational modification of serpins transforms leukocyte elastase inhibitor into an endonuclease involved in apoptosis.

The best-characterized biochemical feature of apoptosis is degradation of genomic DNA into oligonucleosomes. The endonuclease responsible for DNA degradation in caspase-dependent apoptosis is caspase-activated DNase. In caspase-independent apoptosis, different endonucleases may be activated according to the cell line and the original insult. Among the known effectors of caspase-independent cell death, L-DNase II (LEI [leukocyte elastase inhibitor]-derived DNase II) has been previously characterized by our laboratory. We have thus shown that this endonuclease derives from the serpin superfamily member LEI by posttranslational modification (A. Torriglia, P. Perani, J. Y. Brossas, E. Chaudun, J. Treton, Y. Courtois, and M. F. Counis, Mol. Cell. Biol. 18:3612-3619, 1998). In this work, we assessed the molecular mechanism involved in the change in the enzymatic activity of this molecule from an antiprotease to an endonuclease. We report that the cleavage of LEI by elastase at its reactive center loop abolishes its antiprotease activity and leads to a conformational modification that exposes an endonuclease active site and a nuclear localization signal. This represents a novel molecular mechanism for a complete functional conversion induced by changing the conformation of a serpin. We also show that this molecular transformation affects cellular fate and that both endonuclease activity and nuclear translocation of L-DNase II are needed to induce cell death.

Leukocyte Elastase Inhibitor, the precursor of L-DNase II, inhibits apoptosis by interfering with caspase-8 activation.

LEI (Leukocyte Elastase Inhibitor), the precursor of the pro-apoptotic molecule L-DNase II, belongs to the ovalbumin subgroup of serpins. Several serpins can inhibit apoptosis: the viral serpin Crm A inhibits Fas or TNFalpha-induced apoptosis, and overexpression of PAI-2 or PI-9 protects cells from TNFalpha or granzyme B induced apoptosis. We have previously shown that LEI overexpression protects cells from etoposide-induced apoptosis. The molecular reason of this anti-apoptotic activity is now investigated. We show that, in BHK-21 and HeLa cells, LEI anti-protease activity is essential for its anti-apoptotic effect. The protease inhibited is cathepsin D, released from the lysosome during etoposide treatment. Cathepsin D enhances caspase activity in the cell by cleaving procaspase-8 and LEI overexpression slows down this cleavage, protecting cells from apoptosis. This let us presume that high expression of LEI in tumor cells may reduce the efficiency of etoposide as a chemotherapeutic agent.

Correction to: Usefulness of Genetic Testing in Hypertrophic Cardiomyopathy: an Analysis Using Real-World Data.

The name of author M. Alejandra Restrepo-Cordoba was parsed incorrectly (in such a way as to suggest that her surname is "Alejandra Restrepo-Cordoba") in this article as published.

Activation of Serine One-Carbon Metabolism by Calcineurin Aß1 Reduces Myocardial Hypertrophy and Improves Ventricular Function.

BACKGROUND: In response to pressure overload, the heart develops ventricular hypertrophy that progressively decompensates and leads to heart failure. This pathological hypertrophy is mediated, among others, by the phosphatase calcineurin and is characterized by metabolic changes that impair energy production by mitochondria. OBJECTIVES: The authors aimed to determine the role of the calcineurin splicing variant CnAß1 in the context of cardiac hypertrophy and its mechanism of action. METHODS: Transgenic mice overexpressing CnAß1 specifically in cardiomyocytes and mice lacking the unique C-terminal domain in CnAß1 (CnAß1Δi12 mice) were used. Pressure overload hypertrophy was induced by transaortic constriction. Cardiac function was measured by echocardiography. Mice were characterized using various molecular analyses. RESULTS: In contrast to other calcineurin isoforms, the authors show here that cardiac-specific overexpression of CnAß1 in transgenic mice reduces cardiac hypertrophy and improves cardiac function. This effect is mediated by activation of serine and one-carbon metabolism, and the production of antioxidant mediators that prevent mitochondrial protein oxidation and preserve ATP production. The induction of enzymes involved in this metabolic pathway by CnAß1 is dependent on mTOR activity. Inhibition of serine and one-carbon metabolism blocks the beneficial effects of CnAß1. CnAß1Δi12 mice show increased cardiac hypertrophy and declined contractility. CONCLUSIONS: The metabolic reprogramming induced by CnAß1 redefines the role of calcineurin in the heart and shows for the first time that activation of the serine and one-carbon pathway has beneficial effects on cardiac hypertrophy and function, paving the way for new therapeutic approaches.

Genetic Etiology for Alcohol-Induced Cardiac Toxicity.

BACKGROUND: Alcoholic cardiomyopathy (ACM) is defined by a dilated and impaired left ventricle due to chronic excess alcohol consumption. It is largely unknown which factors determine cardiac toxicity on exposure to alcohol. OBJECTIVES: This study sought to evaluate the role of variation in cardiomyopathy-associated genes in the pathophysiology of ACM, and to examine the effects of alcohol intake and genotype on dilated cardiomyopathy (DCM) severity. METHODS: The authors characterized 141 ACM cases, 716 DCM cases, and 445 healthy volunteers. The authors compared the prevalence of rare, protein-altering variants in 9 genes associated with inherited DCM. They evaluated the effect of genotype and alcohol consumption on phenotype in DCM. RESULTS: Variants in well-characterized DCM-causing genes were more prevalent in patients with ACM than control subjects (13.5% vs. 2.9%; p = 1.2 ×10-5), but similar between patients with ACM and DCM (19.4%; p = 0.12) and with a predominant burden of titin truncating variants (TTNtv) (9.9%). Separately, we identified an interaction between TTN genotype and excess alcohol consumption in a cohort of DCM patients not meeting ACM criteria. On multivariate analysis, DCM patients with a TTNtv who consumed excess alcohol had an 8.7% absolute reduction in ejection fraction (95% confidence interval: -2.3% to -15.1%; p < 0.007) compared with those without TTNtv and excess alcohol consumption. The presence of TTNtv did not predict phenotype, outcome, or functional recovery on treatment in ACM patients. CONCLUSIONS: TTNtv represent a prevalent genetic predisposition for ACM, and are also associated with a worse left ventricular ejection fraction in DCM patients who consume alcohol above recommended levels. Familial evaluation and genetic testing should be considered in patients presenting with ACM.

Usefulness of Genetic Testing in Hypertrophic Cardiomyopathy: an Analysis Using Real-World Data.

This study sought to determine the usefulness of genetic testing to predict evolution in hypertrophic cardiomyopathy (HCM) and to assess the role of genetic testing in clinical practice. Genetic results of 100 HCM patients tested for mutations in ≥10 HCM-causing genes were evaluated. Patients were classified as with poor (group A) or favourable (group B) clinical course. Forty-five pathogenic mutations (PM) were identified in 28 patients (56 %) from group A and in 23 (46 %) from group B (p = 0.317). Only 40 patients (40 %) exhibited PM that had been previously reported and only 15 (15 %) had PM reported in ≥10 individuals. PM associated with poor prognosis were identified in just five patients from group A (10 %). Genetic findings are not useful to predict prognosis in most HCM patients. By contrast, real-world data reinforce the usefulness of genetic testing to provide genetic counselling and to enable cascade genetic screening.

Lung ultrasound as a translational approach for non-invasive assessment of heart failure with reduced or preserved ejection fraction in mice.

AIMS: Heart failure (HF) has become an epidemic and constitutes a major medical, social, and economic problem worldwide. Despite advances in medical treatment, HF prognosis remains poor. The development of efficient therapies is hampered by the lack of appropriate animal models in which HF can be reliably determined, particularly in mice. The development of HF in mice is often assumed based on the presence of cardiac dysfunction, but HF itself is seldom proved. Lung ultrasound (LUS) has become a helpful tool for lung congestion assessment in patients at all stages of HF. We aimed to apply this non-invasive imaging tool to evaluate HF in mouse models of both systolic and diastolic dysfunction. METHODS AND RESULTS: We used LUS to study HF in a mouse model of systolic dysfunction, dilated cardiomyopathy, and in a mouse model of diastolic dysfunction, diabetic cardiomyopathy. LUS proved to be a reliable and reproducible tool to detect pulmonary congestion in mice. The combination of LUS and echocardiography allowed discriminating those mice that develop HF from those that do not, even in the presence of evident cardiac dysfunction. The study showed that LUS can be used to identify the onset of HF decompensation and to evaluate the efficacy of therapies for this syndrome. CONCLUSIONS: This novel approach in mouse models of cardiac disease enables for the first time to adequately diagnose HF non-invasively in mice with preserved or reduced ejection fraction, and will pave the way to a better understanding of HF and to the development of new therapeutic approaches.

Additional value of screening for minor genes and copy number variants in hypertrophic cardiomyopathy.

INTRODUCTION: Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited heart disease. Next-generation sequencing (NGS) is the preferred genetic test, but the diagnostic value of screening for minor and candidate genes, and the role of copy number variants (CNVs) deserves further evaluation. METHODS: Three hundred and eighty-seven consecutive unrelated patients with HCM were screened for genetic variants in the 5 most frequent genes (MYBPC3, MYH7, TNNT2, TNNI3 and TPM1) using Sanger sequencing (N = 84) or NGS (N = 303). In the NGS cohort we analyzed 20 additional minor or candidate genes, and applied a proprietary bioinformatics algorithm for detecting CNVs. Additionally, the rate and classification of TTN variants in HCM were compared with 427 patients without structural heart disease. RESULTS: The percentage of patients with pathogenic/likely pathogenic (P/LP) variants in the main genes was 33.3%, without significant differences between the Sanger sequencing and NGS cohorts. The screening for 20 additional genes revealed LP variants in ACTC1, MYL2, MYL3, TNNC1, GLA and PRKAG2 in 12 patients. This approach resulted in more inconclusive tests (36.0% vs. 9.6%, p<0.001), mostly due to variants of unknown significance (VUS) in TTN. The detection rate of rare variants in TTN was not significantly different to that found in the group of patients without structural heart disease. In the NGS cohort, 4 patients (1.3%) had pathogenic CNVs: 2 deletions in MYBPC3 and 2 deletions involving the complete coding region of PLN. CONCLUSIONS: A small percentage of HCM cases without point mutations in the 5 main genes are explained by P/LP variants in minor or candidate genes and CNVs. Screening for variants in TTN in HCM patients drastically increases the number of inconclusive tests, and shows a rate of VUS that is similar to patients without structural heart disease, suggesting that this gene should not be analyzed for clinical purposes in HCM.

Genetic basis of familial dilated cardiomyopathy patients undergoing heart transplantation.

BACKGROUND: Dilated cardiomyopathy (DCM) is the most frequent cause of heart transplantation (HTx). The genetic basis of DCM among patients undergoing HTx has been poorly characterized. We sought to determine the genetic basis of familial DCM HTx and to establish the yield of modern next generation sequencing (NGS) technologies in this setting. METHODS: Fifty-two heart-transplanted patients due to familial DCM underwent NGS genetic evaluation with a panel of 126 genes related to cardiac conditions (59 associated with DCM). Genetic variants were initially classified as pathogenic mutations or as variants of uncertain significance (VUS). Final pathogenicity status was determined by familial cosegregation studies. RESULTS: Initially, 24 pathogenic mutations were found in 21 patients (40%); 25 patients (48%) carried 19 VUS and 6 (12%) did not show any genetic variant. Familial evaluation of 220 relatives from 36 of the 46 families with genetic variants confirmed pathogenicity in 14 patients and allowed reclassification of VUS as pathogenic in 17 patients, and as non-pathogenic in 3 cases. At the end of the study, the DCM-causing mutation was identified in 38 patients (73%) and 5 patients (10%) harbored only VUS. No genetic variants were identified in 9 cases (17%). CONCLUSIONS: The genetic spectrum of familial DCM patients undergoing HTx is heterogeneous and involves multiple genes. NGS technology plus detailed familial studies allow identification of causative mutations in the vast majority of familial DCM cases. Detailed familial studies remain critical to determine the pathogenicity of underlying genetic defects in a substantial number of cases.

Truncating FLNC Mutations Are Associated With High-Risk Dilated and Arrhythmogenic Cardiomyopathies.

BACKGROUND: Filamin C (encoded by the FLNC gene) is essential for sarcomere attachment to the plasmatic membrane. FLNC mutations have been associated with myofibrillar myopathies, and cardiac involvement has been reported in some carriers. Accordingly, since 2012, the authors have included FLNC in the genetic screening of patients with inherited cardiomyopathies and sudden death. OBJECTIVES: The aim of this study was to demonstrate the association between truncating mutations in FLNC and the development of high-risk dilated and arrhythmogenic cardiomyopathies. METHODS: FLNC was studied using next-generation sequencing in 2,877 patients with inherited cardiovascular diseases. A characteristic phenotype was identified in probands with truncating mutations in FLNC. Clinical and genetic evaluation of 28 affected families was performed. Localization of filamin C in cardiac tissue was analyzed in patients with truncating FLNC mutations using immunohistochemistry. RESULTS: Twenty-three truncating mutations were identified in 28 probands previously diagnosed with dilated, arrhythmogenic, or restrictive cardiomyopathies. Truncating FLNC mutations were absent in patients with other phenotypes, including 1,078 patients with hypertrophic cardiomyopathy. Fifty-four mutation carriers were identified among 121 screened relatives. The phenotype consisted of left ventricular dilation (68%), systolic dysfunction (46%), and myocardial fibrosis (67%); inferolateral negative T waves and low QRS voltages on electrocardiography (33%); ventricular arrhythmias (82%); and frequent sudden cardiac death (40 cases in 21 of 28 families). Clinical skeletal myopathy was not observed. Penetrance was >97% in carriers older than 40 years. Truncating mutations in FLNC cosegregated with this phenotype with a dominant inheritance pattern (combined logarithm of the odds score: 9.5). Immunohistochemical staining of myocardial tissue showed no abnormal filamin C aggregates in patients with truncating FLNC mutations. CONCLUSIONS: Truncating mutations in FLNC caused an overlapping phenotype of dilated and left-dominant arrhythmogenic cardiomyopathies complicated by frequent premature sudden death. Prompt implantation of a cardiac defibrillator should be considered in affected patients harboring truncating mutations in FLNC.

[Lineage tracing of epicardial cells during development and regeneration]. / Estudios de linaje del epicardio durante el desarrollo y la regeneración cardiaca.

Tracing the history of individual cells during embryonic morphogenesis in a structure as complex as the cardiovascular system is one of the major challenges of developmental biology. It involves determining the relationships between the various lineages of cells forming an organ at different stages, describing the topological rearrangements tissues undergo during morphogenesis, and characterizing the interactions between cells in different structures. However, despite the great expectations raised in the field of regenerative medicine, only limited progress has been made in using regenerative therapy to repair the cardiovascular system. Recent research has highlighted the role of the epicardium during cardiac regeneration, but it is still unclear whether it is important for molecular signaling or acts as a source of progenitor cells during this process. Consequently, increasing knowledge about the origin, diversification and potential of epicardial cells during development and homeostasis and under pathological conditions is of fundamental importance both for basic research and for the development of effective cellular therapies. The aims of this article were to provide a general overview of the classical techniques used for tracing cell lineages, including their potential and limitations, and to describe novel techniques for studying the origin and differentiation of the epicardium and its role in cardiac regeneration.

Clonal analysis in mice underlines the importance of rhombomeric boundaries in cell movement restriction during hindbrain segmentation.

BACKGROUND: Boundaries that prevent cell movement allow groups of cells to maintain their identity and follow independent developmental trajectories without the need for ongoing instructive signals from surrounding tissues. This is the case of vertebrate rhombomeric boundaries. Analysis in the developing chick hindbrain provided the first evidence that rhombomeres are units of cell lineage. The appearance of morphologically visible rhombomeres requires the segment restricted expression of a series of transcription factors, which position the boundaries and prefigure where morphological boundaries will be established. When the boundaries are established, when the cells are committed to a particular rhombomere and how they are organized within the hindbrain are important questions to our understanding of developmental regionalization. METHODOLOGY/PRINCIPAL FINDINGS: Sophisticated experimental tools with high-resolution analysis have allowed us to explore cell lineage restriction within the hindbrain in mouse embryos. This novel strategy is based on knock-in alleles of ubiquitous expression and allows unrestricted clonal analysis of cell lineage from the two-cell stage to the adult mouse. Combining this analysis with statistical and mathematical tools we show that there is lineage compartmentalization along the anteroposterior axis from very early stages of mouse embryonic development. CONCLUSIONS: Our results show that the compartment border coincides with the morphological boundary in the mouse hindbrain. The restriction of the cells to cross rhombomeric boundaries seen in chick is also observed in mouse. We show that the rhombomeric boundaries themselves are involved in cell movement restriction, although an underlying pre-pattern during early embryonic development might influence the way that cell populations organize.

Molecular mechanism of L-DNase II activation and function as a molecular switch in apoptosis.

The discovery of caspase activation counts as one of the most important finds in the biochemistry of apoptosis. However, targeted disruption of caspases does not impair every type of apoptosis. Other proteases can replace caspases and several so called "caspase independent" pathways are now described. Here we review our current knowledge on one of these pathways, the LEI/L-DNase II. It is a serine protease-dependent pathway and its key event is the transformation of LEI (leukocyte elastase inhibitor, a serine protease inhibitor) into L-DNase II (an endonuclease). The molecular events leading to this change of enzymatic function as well as the cross-talk and interactions of this molecule with other apoptotic pathway, including caspases, are discussed.