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The Journal of Physiology Aug 2022The force-pCa (F-pCa) curve is used to characterize steady-state contractile properties of cardiac muscle cells in different physiological, pathological and...
The force-pCa (F-pCa) curve is used to characterize steady-state contractile properties of cardiac muscle cells in different physiological, pathological and pharmacological conditions. This provides a reduced preparation in which to isolate sarcomere mechanisms. However, it is unclear how changes in the F-pCa curve impact emergent whole-heart mechanics quantitatively. We study the link between sarcomere and whole-heart function using a multiscale mathematical model of rat biventricular mechanics that describes sarcomere, tissue, anatomy, preload and afterload properties quantitatively. We first map individual cell-level changes in sarcomere-regulating parameters to organ-level changes in the left ventricular function described by pressure-volume loop characteristics (e.g. end-diastolic and end-systolic volumes, ejection fraction and isovolumetric relaxation time). We next map changes in the sarcomere-regulating parameters to changes in the F-pCa curve. We demonstrate that a change in the F-pCa curve can be caused by multiple different changes in sarcomere properties. We demonstrate that changes in sarcomere properties cause non-linear and, importantly, non-monotonic changes in left ventricular function. As a result, a change in sarcomere properties yielding changes in the F-pCa curve that improve contractility does not guarantee an improvement in whole-heart function. Likewise, a desired change in whole-heart function (i.e. ejection fraction or relaxation time) is not caused by a unique shift in the F-pCa curve. Changes in the F-pCa curve alone cannot be used to predict the impact of a compound on whole-heart function. KEY POINTS: The force-pCa (F-pCa) curve is used to assess myofilament calcium sensitivity after pharmacological modulation and to infer pharmacological effects on whole-heart function. We demonstrate that there is a non-unique mapping from changes in F-pCa curves to changes in left ventricular (LV) function. The effect of changes in F-pCa on LV function depend on the state of the heart and could be different for different pathological conditions. Screening of compounds to impact whole-heart function by F-pCa should be combined with active tension and calcium transient measurements to predict better how changes in muscle function will impact whole-heart physiology.
Topics: Animals; Calcium; Myocardial Contraction; Myocytes, Cardiac; Myofibrils; Rats; Sarcomeres
PubMed: 35737959
DOI: 10.1113/JP283352 -
Journal of the American Heart... Dec 2019Background A genetic cause can be identified in 30% of noncompaction cardiomyopathy patients (NCCM) with clinical features ranging from asymptomatic cardiomyopathy to... (Comparative Study)
Comparative Study
Background A genetic cause can be identified in 30% of noncompaction cardiomyopathy patients (NCCM) with clinical features ranging from asymptomatic cardiomyopathy to heart failure with major adverse cardiac events (MACE). Methods and Results To investigate genotype-phenotype correlations, the genotypes and clinical features of genetic NCCM patients were collected from the literature. We compared age at diagnosis, cardiac features and risk for MACE according to mode of inheritance and molecular effects for defects in the most common sarcomere genes and NCCM subtypes. Geno- and phenotypes of 561 NCCM patients from 172 studies showed increased risk in children for congenital heart defects (<0.001) and MACE (<0.001). In adult NCCM patients the main causes were single missense mutations in sarcomere genes. Children more frequently had an X-linked or mitochondrial inherited defect (=0.001) or chromosomal anomalies (<0.001). was involved in 48% of the sarcomere gene mutations. and mutations had lower risk for MACE than and (=0.001). The NCCM/dilated cardiomyopathy cardiac phenotype was the most frequent subtype (56%; =0.022) and was associated with an increased risk for MACE and high risk for left ventricular systolic dysfunction (<0.001). In multivariate binary logistic regression analysis , arrhythmia -, non-sarcomere non-arrhythmia cardiomyopathy-and X-linked genes were genetic predictors for MACE. Conclusions Sarcomere gene mutations were the most common cause in adult patients with lower risk of MACE. Children had multi-systemic disorders with severe outcome, suggesting that the diagnostic and clinical approaches should be adjusted to age at presentation. The observed genotype-phenotype correlations endorsed that DNA diagnostics for NCCM is important for clinical management and counseling of patients.
Topics: Adolescent; Adult; Age Factors; Cardiomyopathies; Child; Child, Preschool; Female; Genetic Association Studies; Heart Diseases; Humans; Infant; Male; Risk Assessment; Sarcomeres; Young Adult
PubMed: 31771441
DOI: 10.1161/JAHA.119.012993 -
Archives of Biochemistry and Biophysics Feb 2019Current inotropic therapies improve systolic function in heart failure patients but also elicit undesirable side effects such as arrhythmias and increased intracellular... (Review)
Review
Current inotropic therapies improve systolic function in heart failure patients but also elicit undesirable side effects such as arrhythmias and increased intracellular Ca transients. In order to maintain myocyte Ca homeostasis, the increased cytosolic Ca needs to be actively transported back to sarcoplasmic reticulum leading to depleted ATP reserves. Thus, an emerging approach is to design sarcomere-based treatments to correct impaired contractility via a direct and allosteric modulation of myosin's intrinsic force-generating behavior -a concept that potentially avoids the "off-target" effects. To achieve this goal, various biophysical approaches are utilized to investigate the mechanistic impact of sarcomeric modulators but information derived from diverse approaches is not fully integrated into therapeutic applications. This is in part due to the lack of information that provides a coherent connecting link between biophysical data to in vivo function. Hence, our ability to clearly discern the drug-mediated impact on whole-heart function is diminished. Reducing this translational barrier can significantly accelerate clinical progress related to sarcomere-based therapies by optimizing drug-dosing and treatment duration protocols based on information obtained from biophysical studies. Therefore, we attempt to link biophysical mechanical measurements obtained in isolated cardiac muscle and in vivo contractile function.
Topics: Animals; Cardiotonic Agents; Heart Failure; Humans; Myocardial Contraction; Myocardium; Sarcomeres; Translational Research, Biomedical
PubMed: 30576628
DOI: 10.1016/j.abb.2018.12.021 -
Disease Markers 2020The sarcomeric proteins control the movement of cells in diverse species, whereas the deregulation can induce tumours in model organisms and occurs in human carcinomas.... (Review)
Review
The sarcomeric proteins control the movement of cells in diverse species, whereas the deregulation can induce tumours in model organisms and occurs in human carcinomas. Sarcomeric proteins are recognized as oncogene and related to tumor cell metastasis. Recent insights into their expressions and functions have led to new cancer therapeutic opportunities. In this review, we appraise the evidence for the sarcomeric proteins as cancer genes and discuss cancer-relevant biological functions, potential mechanisms by which sarcomeric proteins activity is altered in cancer.
Topics: Gene Expression Regulation, Neoplastic; Humans; Muscle Proteins; Neoplasm Metastasis; Neoplasms; Sarcomeres
PubMed: 32670437
DOI: 10.1155/2020/8885286 -
The Journal of Clinical Investigation Jan 2024Heterozygous (HET) truncating variant mutations in the TTN gene (TTNtvs), encoding the giant titin protein, are the most common genetic cause of dilated cardiomyopathy...
Heterozygous (HET) truncating variant mutations in the TTN gene (TTNtvs), encoding the giant titin protein, are the most common genetic cause of dilated cardiomyopathy (DCM). However, the molecular mechanisms by which TTNtv mutations induce DCM are controversial. Here, we studied 127 clinically identified DCM human cardiac samples with next-generation sequencing (NGS), high-resolution gel electrophoresis, Western blot analysis, and super-resolution microscopy in order to dissect the structural and functional consequences of TTNtv mutations. The occurrence of TTNtv was found to be 15% in the DCM cohort. Truncated titin proteins matching, by molecular weight, the gene sequence predictions were detected in the majority of the TTNtv+ samples. Full-length titin was reduced in TTNtv+ compared with TTNtv- samples. Proteomics analysis of washed myofibrils and stimulated emission depletion (STED) super-resolution microscopy of myocardial sarcomeres labeled with sequence-specific anti-titin antibodies revealed that truncated titin was structurally integrated into the sarcomere. Sarcomere length-dependent anti-titin epitope position, shape, and intensity analyses pointed at possible structural defects in the I/A junction and the M-band of TTNtv+ sarcomeres, which probably contribute, possibly via faulty mechanosensor function, to the development of manifest DCM.
Topics: Humans; Cardiomyopathy, Dilated; Connectin; Heart; Sarcomeres
PubMed: 37962957
DOI: 10.1172/JCI169753 -
Biochimica Et Biophysica Acta.... Aug 2017Pre-mRNA splicing is an important biological process that allows production of multiple proteins from a single gene in the genome, and mainly contributes to protein... (Review)
Review
Pre-mRNA splicing is an important biological process that allows production of multiple proteins from a single gene in the genome, and mainly contributes to protein diversity in eukaryotic organisms. Alternative splicing is commonly governed by RNA binding proteins to meet the ever-changing demands of the cell. However, the mis-splicing may lead to human diseases. In the heart of human, mis-regulation of alternative splicing has been associated with heart failure. In this short review, we focus on alternative splicing of sarcomeric genes and review mis-splicing related heart failure with relatively well studied Sarcomeric genes and splicing mechanisms with identified regulatory factors. The perspective of alternative splicing based therapeutic strategies in heart failure has also been discussed.
Topics: Alternative Splicing; Animals; Heart Failure; Humans; Myocardium; RNA Precursors; RNA-Binding Proteins; Sarcomeres
PubMed: 27825848
DOI: 10.1016/j.bbadis.2016.11.008 -
Current Protocols in Human Genetics Jan 2018Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful cellular platform for illuminating mechanisms of human cardiovascular disease...
Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful cellular platform for illuminating mechanisms of human cardiovascular disease and for pharmacological screening. Recent advances in CRISPR/Cas9-mediated genome editing technology underlie this profound utility. We have generated hiPSC-CMs harboring fluorescently-tagged sarcomeric proteins, which provide a tool to non-invasively study human sarcomere function and dysfunction. In this unit, we illustrate methods for conducting high-efficiency, small molecule-mediated differentiation of hiPSCs into cardiomyocytes, and for performing non-invasive contractile analysis through direct sarcomere tracking of GFP-sarcomere reporter hiPSC-CMs. We believe that this type of analysis can overcome sensitivity problems found in other forms of contractile assays involving hiPSC-CMs by directly measuring contractility at the fundamental contractile unit of the hiPSC-CM, the sarcomere. © 2018 by John Wiley & Sons, Inc.
Topics: Cell Differentiation; Green Fluorescent Proteins; Humans; Induced Pluripotent Stem Cells; Myocytes, Cardiac; Sarcomeres
PubMed: 29364522
DOI: 10.1002/cphg.53 -
Cytoskeleton (Hoboken, N.J.) Apr 2018Cloning and sequencing of various tropomyosin isoforms expressed in chickens have been described since the early 1980s. However, to the best of our knowledge, this is...
Cloning and sequencing of various tropomyosin isoforms expressed in chickens have been described since the early 1980s. However, to the best of our knowledge, this is the first report on the molecular characterization and the expression of the sarcomeric isoform of the TPM3 gene in cardiac and skeletal muscles from developing as well as adult chickens. Expression of TPM3α was performed by conventional RT-PCR as well as qRT-PCR using relative expression (by ΔC as well as ΔΔC methods) and by determining absolute copy number. The results employing all these methods show that the expression level of TPM3α is maximum in embryonic (10-day/15-day old) skeletal muscle and can barely be detected in both cardiac and skeletal muscles from the adult chicken. Our various RT-PCR analyses suggest that the expression of high molecular weight TPM3 isoforms are regulated at the transcription level from the proximal promoter at the 5'-end of the TPM3 gene.
Topics: Amino Acid Sequence; Animals; Base Sequence; Chick Embryo; Chickens; Embryonic Development; Gene Expression Regulation, Developmental; Muscle, Skeletal; Myocardium; Protein Isoforms; Sarcomeres; Tropomyosin
PubMed: 29220867
DOI: 10.1002/cm.21426 -
Expert Opinion on Drug Discovery Apr 2020: Heart failure remains one of the largest clinical challenges in the United States. Researchers have continually searched for more effective heart failure treatments... (Review)
Review
: Heart failure remains one of the largest clinical challenges in the United States. Researchers have continually searched for more effective heart failure treatments that target the cardiac sarcomere but have found few successes despite numerous expensive cardiovascular clinical trials. Among many reasons, the high failure rate of cardiovascular clinical trials may be partly due to incomplete characterization of a drug candidate's complex interaction with cardiac physiology.: In this review, the authors address the issue of preclinical cardiovascular studies of sarcomere-targeting heart failure therapies. The authors consider inherent tradeoffs made between mechanistic transparency and physiological fidelity for several relevant preclinical techniques at the atomic, molecular, heart muscle fiber, whole heart, and whole-organism levels. Thus, the authors suggest a comprehensive, bottom-up approach to preclinical cardiovascular studies that fosters scientific rigor and hypothesis-driven drug discovery.: In the authors' opinion, the implementation of hypothesis-driven drug discovery practices, such as the bottom-up approach to preclinical cardiovascular studies, will be imperative for the successful development of novel heart failure treatments. However, additional changes to clinical definitions of heart failure and current drug discovery culture must accompany the bottom-up approach to maximize the effectiveness of hypothesis-driven drug discovery.
Topics: Animals; Cardiovascular Agents; Drug Development; Drug Discovery; Drug Evaluation, Preclinical; Heart Failure; Humans; Sarcomeres
PubMed: 32067508
DOI: 10.1080/17460441.2020.1722637 -
Cardiovascular Research Apr 2015Over the past decade, our understanding of cardiomyopathies has improved dramatically, due to improvements in screening and detection of gene defects in the human genome... (Review)
Review
Over the past decade, our understanding of cardiomyopathies has improved dramatically, due to improvements in screening and detection of gene defects in the human genome as well as a variety of novel animal models (mouse, zebrafish, and drosophila) and in silico computational models. These novel experimental tools have created a platform that is highly complementary to the naturally occurring cardiomyopathies in cats and dogs that had been available for some time. A fully integrative approach, which incorporates all these modalities, is likely required for significant steps forward in understanding the molecular underpinnings and pathogenesis of cardiomyopathies. Finally, novel technologies, including CRISPR/Cas9, which have already been proved to work in zebrafish, are currently being employed to engineer sarcomeric cardiomyopathy in larger animals, including pigs and non-human primates. In the mouse, the increased speed with which these techniques can be employed to engineer precise 'knock-in' models that previously took years to make via multiple rounds of homologous recombination-based gene targeting promises multiple and precise models of human cardiac disease for future study. Such novel genetically engineered animal models recapitulating human sarcomeric protein defects will help bridging the gap to translate therapeutic targets from small animal and in silico models to the human patient with sarcomeric cardiomyopathy.
Topics: Animals; Cardiomyopathies; Cats; Computer Simulation; Dogs; Drosophila; Genetic Markers; Genetic Predisposition to Disease; Humans; Mice, Transgenic; Models, Animal; Models, Cardiovascular; Mutation; Phenotype; Sarcomeres; Zebrafish
PubMed: 25600962
DOI: 10.1093/cvr/cvv006