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• W2960691256 abstract "HCM is a prevalent and complex disease governed by multiple molecular mechanisms, and there is currently no efficient cure. New treatment strategies are under development, and several drugs are reaching the final stages of clinical trials, with partial efficacy.HCM disease models vary in complexity. Furthermore, they are limited by sample availability, demanding logistics, preparation artefacts, oversimplicity, and species-differences relative to the human cardiovascular physiology, often producing conflicting results.Application of genome-editing technology to hPSCs enables unlimited isogenic sets of heart cells in which the primary mutation is the only change, allowing elucidation of disease phenotypes and genetic causation.Uncovering new disease mechanisms and targets will pave the way to more efficient HCM therapeutics. Hypertrophic cardiomyopathy (HCM) is a prevalent and complex cardiovascular disease where cardiac dysfunction often associates with mutations in sarcomeric genes. Various models based on tissue explants, isolated cardiomyocytes, skinned myofibrils, and purified actin/myosin preparations have uncovered disease hallmarks, enabling the development of putative therapeutics, with some reaching clinical trials. Newly developed human pluripotent stem cell (hPSC)-based models could be complementary by overcoming some of the inconsistencies of earlier systems, whilst challenging and/or clarifying previous findings. In this article we compare recent progress in unveiling multiple HCM mechanisms in different models, highlighting similarities and discrepancies. We explore how insight is facilitating the design of new HCM therapeutics, including those that regulate metabolism, contraction and heart rhythm, providing a future perspective for treatment of HCM. Hypertrophic cardiomyopathy (HCM) is a prevalent and complex cardiovascular disease where cardiac dysfunction often associates with mutations in sarcomeric genes. Various models based on tissue explants, isolated cardiomyocytes, skinned myofibrils, and purified actin/myosin preparations have uncovered disease hallmarks, enabling the development of putative therapeutics, with some reaching clinical trials. Newly developed human pluripotent stem cell (hPSC)-based models could be complementary by overcoming some of the inconsistencies of earlier systems, whilst challenging and/or clarifying previous findings. In this article we compare recent progress in unveiling multiple HCM mechanisms in different models, highlighting similarities and discrepancies. We explore how insight is facilitating the design of new HCM therapeutics, including those that regulate metabolism, contraction and heart rhythm, providing a future perspective for treatment of HCM. Cardiomyopathies constitute a heterogeneous group of diseases that represent the major cause of heart failure (HF), and are defined by structural or functional perturbations of the myocardium [1.Elliott P.M. et al.2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy. The Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC).Eur. Heart J. 2014; 35: 2733-2779Crossref PubMed Scopus (6) Google Scholar]. HCM is the most prevalent cardiac genetic disease, often leading to sudden cardiac death at a young age [2.Harris K.M. et al.Prevalence, clinical profile, and significance of left ventricular remodeling in the end-stage phase of hypertrophic cardiomyopathy.Circulation. 2006; 114: 216-225Crossref PubMed Scopus (397) Google Scholar]. Although described by increased left ventricle (LV) wall thickness in the absence of abnormal loading conditions (see Clinician’s Corner), HCM shares many hallmarks with other cardiomyopathies [3.Harvey P.A. Leinwand L.A. The cell biology of disease: cellular mechanisms of cardiomyopathy.J. Cell Biol. 2011; 194: 355-365Crossref PubMed Scopus (159) Google Scholar] and progresses to a compensatory phase. However, a sustained hypertrophic response leads to HF as a result of energy and functional imbalance [4.Ashrafian H. et al.Hypertrophic cardiomyopathy: a paradigm for myocardial energy depletion.Trends Genet. 2003; 19: 263-268Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar]. Although classically associated with preserved to hyperdynamic ejection fraction (EF), burn-out HCM with systolic dysfunction is also part of the HCM spectrum [1.Elliott P.M. et al.2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy. The Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC).Eur. Heart J. 2014; 35: 2733-2779Crossref PubMed Scopus (6) Google Scholar]. Approximately half of HCM patients bear mutations in one or more of >20 genes encoding sarcomeric proteins and associated myofilament elements that are responsible for regulating cardiomyocyte contraction and ultimately cardiac function [5.Keren A. et al.Hypertrophic cardiomyopathy: the genetic determinants of clinical disease expression.Nat. Clin. Pract. Cardiovasc. Med. 2008; 5: 158-168Crossref PubMed Scopus (140) Google Scholar, 6.Marston S.B. How do mutations in contractile proteins cause the primary familial cardiomyopathies?.J. Cardiovasc. Transl. Res. 2011; 4: 245-255Crossref PubMed Scopus (77) Google Scholar, 7.Maron B.J. et al.Genetics of hypertrophic cardiomyopathy after 20 years: clinical perspectives.J. Am. Coll. Cardiol. 2012; 60: 705-715Crossref PubMed Scopus (344) Google Scholar]. However, genetic causation is very complex because HCM typically shows variable penetrance (see Glossary) and expressivity, even in the same family [8.Cahill T.J. et al.Genetic cardiomyopathies causing heart failure.Circ. Res. 2013; 113: 660-675Crossref PubMed Scopus (0) Google Scholar] (Figure 1). This implies that factors beyond the single pathogenic mutation (e.g., genetic/epigenetic background, environmental modifiers) influence the phenotype, as verified in nonfamilial HCM patients [9.Ingles J. et al.Nonfamilial hypertrophic cardiomyopathy - prevalence, natural history, and clinical implications.Circ. Cardiovasc. Genet. 2017; 10e001620Crossref PubMed Scopus (18) Google Scholar]. Overall, the clinical and genetic complexity of HCM and its manifold molecular mechanisms have hindered the development of effective treatment options. Although noninvasive monitoring of cardiac function in patients has generated diagnostic tools for determining the progression of HCM [10.Jenni R. et al.Echocardiographic and pathoanatomical characteristics of isolated left ventricular non-compaction: a step towards classification as a distinct cardiomyopathy.Heart. 2001; 86: 666-671Crossref PubMed Google Scholar], this approach cannot characterize disease mechanisms. Such understanding would allow progress towards better therapeutics. In this regard, several HCM models that enable more refined analyses of cardiac physiology have been generated. These include; (i) intact heart muscle strips, (ii) isolated cardiomyocytes, (iii) myofibrils derived from skinned hearts, and (iv) purified actin/myosin sarcomeric proteins, as well as (v) in silico approaches [11.Duncker D.J. et al.Animal and in silico models for the study of sarcomeric cardiomyopathies.Cardiovasc. Res. 2015; 105: 439-448Crossref PubMed Scopus (0) Google Scholar, 12.Romero L. et al.In silico screening of the impact of hERG channel kinetic abnormalities on channel block and susceptibility to acquired long QT syndrome.J. Mol. Cell. Cardiol. 2015; 87: 271-282Abstract Full Text Full Text PDF PubMed Google Scholar, 13.Passini E. et al.Human in silico drug trials demonstrate higher accuracy than animal models in predicting clinical pro-arrhythmic cardiotoxicity.Front. Physiol. 2017; 8: 668Crossref PubMed Scopus (51) Google Scholar]. Although these models have contributed greatly to dissecting the hallmarks of HCM (the reader is directed to [14.Eschenhagen T. et al.Modelling sarcomeric cardiomyopathies in the dish: from human heart samples to iPSC cardiomyocytes.Cardiovasc. Res. 2015; 105: 424-438Crossref PubMed Scopus (38) Google Scholar] for an exhaustive analysis), they still pose several challenges such as sample availability, preparation artefacts, and species differences (Figure 2, Key Figure). The recent application of genome editing to human pluripotent stem cell (hPSC)-derived cardiomyocytes (hPSC-CMs) has enabled multifaceted investigation of the genetic causation of HCM, complementing previous models (comprehensively reviewed in [15.Eschenhagen T. Carrier L. Cardiomyopathy phenotypes in human-induced pluripotent stem cell-derived cardiomyocytes – a systematic review.Pflügers Arch. 2018; 471: 755-768Crossref PubMed Scopus (1) Google Scholar, 16.Sewanan L.R. Campbell S.G. Modelling sarcomeric cardiomyopathies with human cardiomyocytes derived from induced pluripotent stem cells.J. Physiol. 2019; (Published online January 9, 2019. https://doi.org/10.1113/JP276753)Crossref PubMed Scopus (0) Google Scholar]). In the following, we evaluate the pros and cons of different HCM models, and critically explore recently uncovered discrepancies obtained from their study, to consolidate current knowledge of disease mechanisms with a view towards future therapeutics. Initial studies to dissect the mechanisms underlying HF were performed in cardiac muscle strips from explanted human hearts [17.Sonnenblick E.H. et al.The contractile properties of human heart muscle: studies on myocardial mechanics of surgically excised papillary muscles.J. Clin. Invest. 1965; 44: 966-977Crossref PubMed Google Scholar], unveiling hallmarks of HCM. Post-mortem histological analysis of cardiac tissue revealed extensive areas of interstitial fibrosis, myocyte enlargement, and chaotic spatial arrangement in HCM patients [18.Varnava A.M. et al.Hypertrophic cardiomyopathy: the interrelation of disarray, fibrosis, and small vessel disease.Heart. 2000; 84: 476Crossref PubMed Google Scholar]. Further investigations showed 2–2.5-fold increased polyploidy in HCM, with inconsistent changes in multinucleation [19.Schneider R. Pfitzer P. Number of nuclei in isolated human myocardial cells.Virchows Arch. B Cell Pathol. 1972; 12: 238-258Google Scholar, 20.Vliegen H.W. et al.Myocardial changes in pressure overload-induced left ventricular hypertrophy. A study on tissue composition, polyploidization and multinucleation.Eur. Heart J. 1991; 12: 488-494Crossref PubMed Google Scholar, 21.Olivetti G. et al.Aging, cardiac hypertrophy and ischemic cardiomyopathy do not affect the proportion of mononucleated and multinucleated myocytes in the human heart.J. Mol. Cell. Cardiol. 1996; 28: 1463-1477Abstract Full Text PDF PubMed Scopus (156) Google Scholar]. Isolated mitochondria from human hypertrophied hearts exhibited about twofold higher oxygen consumption relative to healthy controls [22.Lindenmayer G.E. et al.Some biochemical studies on subcellular systems isolated from fresh recipient human cardiac tissue obtained during transplantation.Am. J. Cardiol. 1971; 27: 277-283Abstract Full Text PDF PubMed Scopus (0) Google Scholar]. Preservation of an intact sarcolemma in whole tissue preparations is advantageous for the recapitulation of cardiac tissue architecture and pharmacology in vitro. This led to characterization of HCM pathophysiology by the identification of abnormal drug responses, including an attenuated increase in contraction force induced by β-adrenergic agonists [23.Bristow M.R. et al.Decreased catecholamine sensitivity and β-adrenergic-receptor density in failing human hearts.N. Engl. J. Med. 1982; 307: 205-211Crossref PubMed Google Scholar], and perturbed calcium handling leading to prolonged relaxation during diastole [24.Gwathmey J.K. et al.Abnormal intracellular calcium handling in myocardium from patients with end-stage heart failure.Circ. Res. 1987; 61: 70-76Crossref PubMed Google Scholar]. However, cardiac tissue biopsies are often derived from HF patients who have undergone myectomy to reduce muscle thickening, and therefore require demanding logistics of sample handling (e.g., immediate processing). Mechanical and enzymatic dissociation of human endocardial tissue generates viable cardiomyocytes that have been used for electrophysiology studies and pharmacological responses [25.Coppini R. et al.Altered Ca2+ and Na+ homeostasis in human hypertrophic cardiomyopathy: implications for arrhythmogenesis.Front. Physiol. 2018; 9: 1391Crossref PubMed Scopus (0) Google Scholar], revealing arrhythmias (sixfold higher early after-depolarizations) and ~50% higher diastolic Ca2+ concentrations. Single-cell transcriptome investigations revealed highly variable mutant versus wild-type (WT) sarcomeric gene expression in heterozygous HCM patients, underlying heterogeneous cell contractility and Ca2+ sensitivity [26.Montag J. et al.Burst-like transcription of mutant and wildtype MYH7-alleles as possible origin of cell-to-cell contractile imbalance in hypertrophic cardiomyopathy.Front. Physiol. 2018; 9: 359Crossref PubMed Scopus (6) Google Scholar]. However, isolated human cardiomyocytes dedifferentiate almost immediately after explant and do not proliferate in culture [27.Bird S.D. et al.The human adult cardiomyocyte phenotype.Cardiovasc. Res. 2003; 58: 423-434Crossref PubMed Scopus (110) Google Scholar]. Thus, human cardiac tissue and its derivatives offer an important, but rarely available, biological source, and this greatly reduces the scope of the physiological parameters that can be investigated. Subcellular structures have also been used to model HCM by placing tissue/cell-derived skinned myofibril preparations between a force transducer and length motor, and immersing in solutions with different Ca2+ concentrations to stimulate contraction/relaxation [28.van der Velden J. et al.Isometric tension development and its calcium sensitivity in skinned myocyte-sized preparations from different regions of the human heart.Cardiovasc. Res. 1999; 42: 706-719Crossref PubMed Scopus (0) Google Scholar]. This method enables direct access to myofilament function to quantify isometric tension, Ca2+ sensitivity, and ATP consumption (Figure 2). Most reports using this methodology show decreased contractile force in human HCM samples. For instance, cardiac explants from patients bearing different mutations in MYH7 and MYBPC3 genes [encoding β‐myosin heavy chain (β-MHC), and myosin-binding protein C, respectively] have consistently revealed lower tension forces relative to healthy controls (21 vs 36 kN/m2), with MYH7-mutant samples showing the lowest values when normalized to myofibril density (73 vs 113 kN/m2) [29.Witjas-Paalberends E.R. et al.Mutations in MYH7 reduce the force generating capacity of sarcomeres in human familial hypertrophic cardiomyopathy.Cardiovasc. Res. 2013; 99: 432-441Crossref PubMed Scopus (52) Google Scholar]. In addition, Kraft et al. showed a modest increase in Ca2+ sensitivity of skinned myofibers from human cardiac explants bearing the R723G-β-MHC mutation, relative to healthy controls, that was dependent on the hyperphosphorylation state of several sarcomeric proteins [cardiac troponin I/T (cTnI/T), MYBPC, and myosin light chain 2 (MLC2] [30.Kraft T. et al.Familial hypertrophic cardiomyopathy: functional effects of myosin mutation R723G in cardiomyocytes.J. Mol. Cell. Cardiol. 2013; 57: 13-22Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar]. Simultaneous measurement of force development and ATPase activity in tissue-extracted myofibrils can be used to quantify the energy cost of contraction. This revealed significant increases for tissues from MYBPC3-mutant and MYH7-mutant patients, compared with sarcomere mutation-negative (SMN) HCM patients, at saturating Ca2+ concentrations [31.Witjas-Paalberends E.R. et al.Gene-specific increase in the energetic cost of contraction in hypertrophic cardiomyopathy caused by thick filament mutations.Cardiovasc. Res. 2014; 103: 248-257Crossref PubMed Scopus (46) Google Scholar]. This was corroborated in multicellular cardiac myofibrils of human R403Q-β-MHC, showing ~50% lower tension generation relative to SMN-HCM patients, as well as maximum ATPase activity [32.Witjas-Paalberends E.R. et al.Faster cross-bridge detachment and increased tension cost in human hypertrophic cardiomyopathy with the R403Q MYH7 mutation.J. Physiol. 2014; 592: 3257-3272Crossref PubMed Scopus (37) Google Scholar]. This results in a higher cost of contraction, indicating inefficient ATP utilization that causes higher cardiac workload, often leading to HF (termed the ‘energy depletion model’ [4.Ashrafian H. et al.Hypertrophic cardiomyopathy: a paradigm for myocardial energy depletion.Trends Genet. 2003; 19: 263-268Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar]). However, this difference was not observed in single myofibrils derived from the same tissues, indicating that sample preparation affects the endpoint assay [33.Piroddi N. et al.Tension generation and relaxation in single myofibrils from human atrial and ventricular myocardium.Pflugers Arch. - Eur. J. Physiol. 2007; 454: 63-73Crossref PubMed Scopus (0) Google Scholar]. Nevertheless, myofibrils derived from skinned cardiac muscle offer simpler handling logistics because samples can be frozen in a relaxation solution that preserves their functionality for several months. Remarkably, higher energy cost in HCM muscle strips appears to be a feature shared by different mutations. This was recently corroborated in homozygous K280N-troponin T samples, which showed 24–72% higher values than three different control groups, that was ascribed to faster cross-bridge detachment [34.Piroddi N. et al.The homozygous K280N troponin T mutation alters cross-bridge kinetics and energetics in human HCM.J. Gen. Physiol. 2019; 151: 18Crossref PubMed Scopus (2) Google Scholar]. Addressing the low sample availability limitations of whole-cell/tissue preparations, in vitro motility assays were developed by recording the movement of fluorescently labeled actin filaments over a layer of randomly oriented myosin molecules immunoadsorbed to an antibody-coated surface [35.Warshaw D.M. The in vitro motility assay: a window into the myosin molecular motor.News Physiol. Sci. 1996; 11: 1-7Google Scholar]. Tethering an ultracompliant microneedle to actin filaments enables measurement of average force per crossbridge, facilitating direct assessment of sarcomeric mutations and interactions at the molecular level. However, studies performed using this technique have produced results conflicting with whole-tissue/cell analysis. For instance, rat tissues with heterologous expression of R403Q-α-MHC showed a fourfold decrease in ATPase activity and a fivefold reduction in motility compared with controls [36.Sweeney H.L. et al.Heterologous expression of a cardiomyopathic myosin that is defective in its actin interaction.J. Biol. Chem. 1994; 269: 1603-1605PubMed Google Scholar], whereas the same mutation in myosin isolated from mouse explants led to 2.3-fold higher ATPase activity and 60% higher velocity than WT myosin tissue [37.Tyska M.J. et al.Single-molecule mechanics of R403Q cardiac myosin isolated from the mouse model of familial hypertrophic cardiomyopathy.Circ. Res. 2000; 86: 737-744Crossref PubMed Google Scholar]. These discrepancies extended to human biopsies. Although tissues from patients harboring β-MHC mutations displayed consistently lower sliding velocities (0.11–0.29 μm/s) than healthy controls (0.48 μm/s) [38.Cuda G. et al.The in vitro motility activity of beta-cardiac myosin depends on the nature of the beta-myosin heavy chain gene mutation in hypertrophic cardiomyopathy.J. Muscle Res. Cell Motil. 1997; 18: 275-283Crossref PubMed Scopus (0) Google Scholar], another report showed the opposite in R403Q- and L908V-βMHC, which had 30% higher velocities [39.Palmiter K.A. et al.R403Q and L908V mutant beta-cardiac myosin from patients with familial hypertrophic cardiomyopathy exhibit enhanced mechanical performance at the single molecule level.J. Muscle Res. Cell Motil. 2000; 21: 609-620Crossref PubMed Scopus (100) Google Scholar]. These differences highlight the main drawback of this method: technical artefacts derived from protein purification procedures. Tissue biopsies contain limited concentrations of myosins that are further degraded by freezing and tissue handling procedures. Alternatively, heterologous production of recombinant proteins often result in changes in structure and expression levels relative to endogenous systems, with functional consequences for the endpoint assay [14.Eschenhagen T. et al.Modelling sarcomeric cardiomyopathies in the dish: from human heart samples to iPSC cardiomyocytes.Cardiovasc. Res. 2015; 105: 424-438Crossref PubMed Scopus (38) Google Scholar]. These limitations are evidenced when analyzing the same protein interactions by different techniques. Laser-trap assays can be used for direct molecular analysis of actin–myosin interactions by measuring the force and displacement resulting from the interaction of a single myosin molecule with an optically trapped actin filament [40.Finer J.T. et al.Single myosin molecule mechanics: piconewton forces and nanometre steps.Nature. 1994; 368: 113-119Crossref PubMed Scopus (1405) Google Scholar]. The same group has shown significant differences between myosin extracted from mice bearing the R403Q-β-MHC mutation vs WT when performing in vitro motility assays (2.3-fold higher ATPase activity, 2.2-fold greater force generation, and 1.6-fold faster actin filament sliding), but no changes in force and displacement in the same samples when using the optical trap assay [37.Tyska M.J. et al.Single-molecule mechanics of R403Q cardiac myosin isolated from the mouse model of familial hypertrophic cardiomyopathy.Circ. Res. 2000; 86: 737-744Crossref PubMed Google Scholar]. Taken together, these differences suggest that more reductionist models, where isolated proteins are investigated under unloaded conditions, tend to generate less robust conclusions due to technical constraints and the absence of physiological complexity that is characteristic of highly organized sarcomeres. Animal models of heart disease have been crucial in advancing knowledge of pathophysiology towards new therapeutics because the basic principles of cardiac excitation and contraction in the species used are relatively conserved [41.Milani-Nejad N. Janssen P.M.L. Small and large animal models in cardiac contraction research: advantages and disadvantages.Pharmacol. Ther. 2014; 141: 235-249Crossref PubMed Scopus (122) Google Scholar]. Although some naturally occurring cardiomyopathies have been detected in animals (e.g., Portuguese waterdogs), transgenic animal models enable detailed physiological and molecular analysis of disease [11.Duncker D.J. et al.Animal and in silico models for the study of sarcomeric cardiomyopathies.Cardiovasc. Res. 2015; 105: 439-448Crossref PubMed Scopus (0) Google Scholar, 42.Longeri M. et al.Myosin-binding protein C DNA variants in domestic cats (A31P, A74T, R820W) and their association with hypertrophic cardiomyopathy.J. Vet. Intern. Med. 2013; 27: 275-285Crossref PubMed Scopus (30) Google Scholar]. Rodents (e.g., Syrian hamsters [43.Sakamoto A. et al.Both hypertrophic and dilated cardiomyopathies are caused by mutation of the same gene, δ-sarcoglycan, in hamster: an animal model of disrupted dystrophin-associatedglycoproteincomplex.Proc. Natl. Acad. Sci. 1997; 94: 13873-13878Crossref PubMed Scopus (0) Google Scholar]) in particular have been extensively employed to model HCM because they overcome cell source limitations and facilitate whole-organism investigation of disease progression over time. Primary cardiomyocytes isolated from transgenic rats and mice have been integrated into fibrin-based engineered heart tissues (EHTs) that enable assessment of contractility by measuring the displacement of silicon posts to which they are attached [44.Eder A. et al.Human engineered heart tissue as a model system for drug testing.Adv. Drug Deliv. Rev. 2016; 96: 214-224Crossref PubMed Scopus (44) Google Scholar]. Analysis of the contractile force of rat cardiomyocytes transduced with adeno-associated virus expressing FLH1 variants containing single-nucleotide polymorphisms (SNPs) identified in HCM patients revealed hyper- or hypocontractile phenotypes depending on the mutation (K455fs-Fhl1, 27% higher force; C276S-Fhl1, 23% lower force vs WT controls). Evaluation of the beating kinetics of these tissues showed prolonged contraction and relaxation times in both variants (~18% and ~30% longer, respectively) [45.Friedrich F.W. et al.Evidence for FHL1 as a novel disease gene for isolated hypertrophic cardiomyopathy.Hum. Mol. Genet. 2012; 21: 3237-3254Crossref PubMed Scopus (76) Google Scholar]. The same approach was applied to Ankrd1 in rat, showing ~50% higher contractile force as well as contraction and relaxation velocities in T123M-Ankrd1 EHTs versus controls, but no discernible phenotypes in P52A and I280V variants [46.Crocini C. et al.Impact of ANKRD1 mutations associated with hypertrophic cardiomyopathy on contraction parameters of engineered heart tissue.Basic Res. Cardiol. 2013; 108: 349Crossref PubMed Scopus (29) Google Scholar]. This reinforces the notion that HCM phenotypes are mutation-specific because different mutations in the same locus elicit variable effects on contraction. Furthermore, data from transgenic mouse models have clearly linked mutations in sarcomeric genes with impaired Ca2+ handling. Knollmann and colleagues studied isolated cardiomyocytes, perfused hearts, and whole mice bearing the human I79N-cTnT mutation, showing shortened ventricular action potentials at 70% repolarization (14 ms in I79N-cTnT, vs 23 ms in control). Ca2+ transients of electrically stimulated ventricular I79N-cTnT myocytes were measured using a fluorescent Ca2+ indicator dye (Fura-2-AM) and showed reduced intensity (half the fluorescent amplitude in I79N-cTnT vs control) and twofold slower decay kinetics, consistent with increased Ca2+ sensitivity of I79N-cTnT mutant fibers [47.Knollmann B.C. et al.Familial hypertrophic cardiomyopathy-linked mutant troponin T causes stress-induced ventricular tachycardia and calcium-dependent action potential remodeling.Circ. Res. 2003; 92: 428-436Crossref PubMed Scopus (0) Google Scholar]. Moreover, EHTs made from Mybpc3-mutant mice displayed higher sensitivity to Ca2+, as evidenced by lower Ca2+ EC50 values for force generation relative to the WT (0.34 mM for homozygous, 0.48 mM for heterozygous, vs 0.66 mM for WT) [48.Stöhr A. et al.Contractile abnormalities and altered drug response in engineered heart tissue from Mybpc3-targeted knock-in mice.J. Mol. Cell. Cardiol. 2013; 63: 189-198Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar, 49.Carrier L. et al.Asymmetric septal hypertrophy in heterozygous cMyBP-C null mice.Cardiovasc. Res. 2004; 63: 293-304Crossref PubMed Scopus (98) Google Scholar]. This methodology has also shown differences in Ca2+ EC50 values for contraction between species (0.15, 0.39, and 1.05 mM Ca2+ for rat, mouse, and human EHTs, respectively [50.Stoehr A. et al.Automated analysis of contractile force and Ca2+ transients in engineered heart tissue.Am. J. Physiol. Heart Circ. Physiol. 2014; 306: H1353-H1363Crossref PubMed Scopus (49) Google Scholar]). The variation in Ca2+ EC50 values for contraction between species highlights the main drawback of animal models – the existence of striking dissimilarities in cardiovascular physiology relative to humans. These are particularly prominent in the mouse: mice have ~10-fold faster beat rates (500 bpm vs 60 bpm) and 5–10-fold shorter electrocardiogram duration (50–100 ms vs 450 ms) relative to humans [41.Milani-Nejad N. Janssen P.M.L. Small and large animal models in cardiac contraction research: advantages and disadvantages.Pharmacol. Ther. 2014; 141: 235-249Crossref PubMed Scopus (122) Google Scholar]. Changes in gene expression are also abundant, such as those pertaining to α/β-MHC expression: whereas in humans the α isoform is mainly located to the atria and the β to the ventricles [51.Morano I. Tuning the human heart molecular motors by myosin light chains.J. Mol. Med. 1999; 77: 544-555Crossref PubMed Scopus (0) Google Scholar], in the mouse the α-MHC is highly expressed in both compartments [52.Lyons G.E. et al.Developmental regulation of myosin gene expression in mouse cardiac muscle.J. Cell Biol. 1990; 111: 2427-2436Crossref PubMed Scopus (296) Google Scholar]. Despite sharing >90% sequence homology, this discrepancy in α versus β-MHC expression is reflected in the animal models generated. Knock-in R403Q-α-MHC mice exhibited a significant enhancement in ATPase activity and transient kinetics (e.g., 20% increase in ADP release rate) relative to WT littermates, whereas R403Q-β-MHC animals displayed opposite or nonsignificant changes [53.Lowey S. et al.Functional effects of the hypertrophic cardiomyopathy R403Q mutation are different in an α- or β-myosin heavy chain backbone.J. Biol. Chem. 2008; 283: 20579-20589Crossref PubMed Scopus (51) Google Scholar, 54.Lowey S. et al.Transgenic mouse α- and β-cardiac myosins containing the R403Q mutation show isoform-dependent transient kinetic differences.J. Biol. Chem. 2013; 288: 14780-14787Crossref PubMed Scopus (0) Google Scholar]. These inconsistencies are further exacerbated when comparing the same mutation in different animals. A recent report characterizing a transgenic rabbit model of the same mutation R403Q-β-MHC showed ~20% lower force generation in comparison with WT littermates in single myofibril analysis by atomic force microscopy [55.Lowey S. et al.Hypertrophic cardiomyopathy R403Q mutation in rabbit β-myosin reduces contractile function at the molecular and myofibrillar leve" @default.
• W2960691256 created "2019-07-23" @default.
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• W2960691256 date "2019-09-01" @default.
• W2960691256 modified "2023-10-17" @default.
• W2960691256 title "Modeling Hypertrophic Cardiomyopathy: Mechanistic Insights and Pharmacological Intervention" @default.
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