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Circulation Research Jun 2020The adult human heart is an organ with low regenerative potential. Heart failure following acute myocardial infarction is a leading cause of death due to the inability...
RATIONALE
The adult human heart is an organ with low regenerative potential. Heart failure following acute myocardial infarction is a leading cause of death due to the inability of cardiomyocytes to proliferate and replenish lost cardiac muscle. While the zebrafish has emerged as a powerful model to study endogenous cardiac regeneration, the molecular mechanisms by which cardiomyocytes respond to damage by disassembling sarcomeres, proliferating, and repopulating the injured area remain unclear. Furthermore, we are far from understanding the regulation of the chromatin landscape and epigenetic barriers that must be overcome for cardiac regeneration to occur.
OBJECTIVE
To identify transcription factor regulators of the chromatin landscape, which promote cardiomyocyte regeneration in zebrafish, and investigate their function.
METHODS AND RESULTS
Using the Assay for Transposase-Accessible Chromatin coupled to high-throughput sequencing (ATAC-Seq), we first find that the regenerating cardiomyocyte chromatin accessibility landscape undergoes extensive changes following cryoinjury, and that activator protein-1 (AP-1) binding sites are the most highly enriched motifs in regions that gain accessibility during cardiac regeneration. Furthermore, using bioinformatic and gene expression analyses, we find that the AP-1 response in regenerating adult zebrafish cardiomyocytes is largely different from the response in adult mammalian cardiomyocytes. Using a cardiomyocyte-specific dominant negative approach, we show that blocking AP-1 function leads to defects in cardiomyocyte proliferation as well as decreased chromatin accessibility at the and loci, which regulate sarcomere disassembly and cardiomyocyte protrusion into the injured area, respectively. We further show that overexpression of the family members and can promote changes in mammalian cardiomyocyte behavior in vitro.
CONCLUSIONS
AP-1 transcription factors play an essential role in the cardiomyocyte response to injury by regulating chromatin accessibility changes, thereby allowing the activation of gene expression programs that promote cardiomyocyte dedifferentiation, proliferation, and protrusion into the injured area.
Topics: Animals; Cells, Cultured; Chromatin; Myocytes, Cardiac; Protein Serine-Threonine Kinases; Rats; Rats, Sprague-Dawley; Regeneration; Sarcomeres; Transcription Factor AP-1; Zebrafish; Zebrafish Proteins
PubMed: 32312172
DOI: 10.1161/CIRCRESAHA.119.316167 -
European Journal of Heart Failure Sep 2014Although genetic testing has been recommended in patients with hypertrophic cardiomyopathy (HCM) in current clinical practice, its utility in prognostic prediction...
AIMS
Although genetic testing has been recommended in patients with hypertrophic cardiomyopathy (HCM) in current clinical practice, its utility in prognostic prediction remains to be ascertained. We assessed the dosage effect of rare variants in sarcomere genes on the long-term outcomes of HCM.
METHODS AND RESULTS
A total of 529 unrelated HCM patients were prospectively recruited and followed for 4.7 ± 3.2 years. Eight sarcomere genes were screened with targeted resequencing and identified variants were validated through Sanger sequencing. After polymorphisms and likely neutral rare variants were excluded, the patients were segregated into three groups based on the dosage of rare variants: no rare variant, a single rare variant, and multiple rare variants. Multiple rare variants were identified in 7.2% (38/529) of the study patients. Patients with multiple rare variants were younger at diagnosis, and had greater maximum LV wall thicknesses and larger left atria. The risk for cardiovascular death in patients with multiple rare variants was higher than in those without rare variants (P =10⁻⁵) or in those with a single rare variant (P = 2 × 10⁻⁵). Multivariable analysis revealed that multiple rare variants were a risk factor for cardiovascular death [hazard ratio (HR) 3.74, 95% confidence interval (CI) 1.84-7.58, P = 0.0003], as well as sudden cardiac death (HR 3.57, 95% CI 1.23-10.35, P = 0.019) and heart failure-related death (HR 4.62, 95% CI 1.67-12.76, P = 0.003).
CONCLUSIONS
The presence of multiple rare variants in sarcomere genes is a risk factor for malignant outcomes in HCM, and may be appropriate to consider as a criterion in the risk stratification of HCM patients.
Topics: Adult; Cardiomyopathy, Hypertrophic; China; DNA; Female; Follow-Up Studies; Gene Frequency; Genetic Testing; Genetic Variation; Genotype; Humans; Male; Middle Aged; Mutation; Prospective Studies; Risk Factors; Sarcomeres; Survival Rate; Time Factors
PubMed: 25132132
DOI: 10.1002/ejhf.144 -
The Journal of Clinical Investigation Feb 2022A sarcomere is the contractile unit of the myofibril in striated muscles such as cardiac and skeletal muscles. The assembly of sarcomeres depends on multiple molecules...
A sarcomere is the contractile unit of the myofibril in striated muscles such as cardiac and skeletal muscles. The assembly of sarcomeres depends on multiple molecules that serve as raw materials and participate in the assembly process. However, the mechanism of this critical assembly process remains largely unknown. Here, we found that the cell fate determinant Numb and its homolog Numblike regulated sarcomere assembly and maintenance in striated muscles. We discovered that Numb and Numblike are sarcomeric molecules that were gradually confined to the Z-disc during striated muscle development. Conditional knockout of Numb and Numblike severely compromised sarcomere assembly and its integrity and thus caused organelle dysfunction. Notably, we identified that Numb and Numblike served as sarcomeric α-Actin-binding proteins (ABPs) and shared a conserved domain that can bind to the barbed end of sarcomeric α-Actin. In vitro fluorometric α-Actin polymerization assay showed that Numb and Numblike also played a role in the sarcomeric α-Actin polymerization process. Last, we demonstrate that Numb and Numblike regulate sarcomeric α-Actinin-dependent (ACTN-dependent) Z-disc consolidation in the sarcomere assembly and maintenance. In summary, our studies show that Numb and its homolog Numblike regulate sarcomere assembly and maintenance in striated muscles, and demonstrate a molecular mechanism by which Numb/Numblike, sarcomeric α-Actin, and ACTN cooperate to control thin filament formation and Z-disc consolidation.
Topics: Actin Cytoskeleton; Actins; Animals; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Mice; Mice, Transgenic; Muscle Development; Nerve Tissue Proteins; Sarcomeres
PubMed: 35104799
DOI: 10.1172/JCI139420 -
Circulation Research Jul 2023Increasing cardiomyocyte contraction during myocardial stretch serves as the basis for the Frank-Starling mechanism in the heart. However, it remains unclear how this...
BACKGROUND
Increasing cardiomyocyte contraction during myocardial stretch serves as the basis for the Frank-Starling mechanism in the heart. However, it remains unclear how this phenomenon occurs regionally within cardiomyocytes, at the level of individual sarcomeres. We investigated sarcomere contractile synchrony and how intersarcomere dynamics contribute to increasing contractility during cell lengthening.
METHODS
Sarcomere strain and Ca were simultaneously recorded in isolated left ventricular cardiomyocytes during 1 Hz field stimulation at 37 °C, at resting length and following stepwise stretch.
RESULTS
We observed that in unstretched rat cardiomyocytes, differential sarcomere deformation occurred during each beat. Specifically, while most sarcomeres shortened during the stimulus, ≈10% to 20% of sarcomeres were stretched or remained stationary. This nonuniform strain was not traced to regional Ca disparities but rather shorter resting lengths and lower force production in systolically stretched sarcomeres. Lengthening of the cell recruited additional shortening sarcomeres, which increased contractile efficiency as less negative, wasted work was performed by stretched sarcomeres. Given the known role of titin in setting sarcomere dimensions, we next hypothesized that modulating titin expression would alter intersarcomere dynamics. Indeed, in cardiomyocytes from mice with titin haploinsufficiency, we observed greater variability in resting sarcomere length, lower recruitment of shortening sarcomeres, and impaired work performance during cell lengthening.
CONCLUSIONS
Graded sarcomere recruitment directs cardiomyocyte work performance, and harmonization of sarcomere strain increases contractility during cell stretch. By setting sarcomere dimensions, titin controls sarcomere recruitment, and its lowered expression in haploinsufficiency mutations impairs cardiomyocyte contractility.
Topics: Rats; Mice; Animals; Sarcomeres; Connectin; Myocytes, Cardiac; Myocardial Contraction; Myocardium
PubMed: 37401464
DOI: 10.1161/CIRCRESAHA.123.322588 -
Cells & Development Dec 2021Muscles generate forces for animal locomotion. The contractile apparatus of muscles is the sarcomere, a highly regular array of large actin and myosin filaments linked... (Review)
Review
Muscles generate forces for animal locomotion. The contractile apparatus of muscles is the sarcomere, a highly regular array of large actin and myosin filaments linked by gigantic titin springs. During muscle development many sarcomeres assemble in series into long periodic myofibrils that mechanically connect the attached skeleton elements. Thus, ATP-driven myosin forces can power movement of the skeleton. Here we review muscle and myofibril morphogenesis, with a particular focus on their mechanobiology. We describe recent progress on the molecular structure of sarcomeres and their mechanical connections to the skeleton. We discuss current models predicting how tension coordinates the assembly of key sarcomeric components to periodic myofibrils that then further mature during development. This requires transcriptional feedback mechanisms that may help to coordinate myofibril assembly and maturation states with the transcriptional program. To fuel the varying energy demands of muscles we also discuss the close mechanical interactions of myofibrils with mitochondria and nuclei to optimally support powerful or enduring muscle fibers.
Topics: Animals; Biophysics; Morphogenesis; Myofibrils; Myosins; Sarcomeres
PubMed: 34863916
DOI: 10.1016/j.cdev.2021.203760 -
International Journal of Molecular... Dec 2022The cardiac sarcomere is a triumph of biological evolution wherein myriad contractile and regulatory proteins assemble into a quasi-crystalline lattice to serve as the... (Review)
Review
The cardiac sarcomere is a triumph of biological evolution wherein myriad contractile and regulatory proteins assemble into a quasi-crystalline lattice to serve as the central point upon which cardiac muscle contraction occurs. This review focuses on the many signaling components and mechanisms of regulation that impact cardiac sarcomere function. We highlight the roles of the thick and thin filament, both as necessary structural and regulatory building blocks of the sarcomere as well as targets of functionally impactful modifications. Currently, a new focus emerging in the field is inter-myofilament signaling, and we discuss here the important mediators of this mechanism, including myosin-binding protein C and titin. As the understanding of sarcomere signaling advances, so do the methods with which it is studied. This is reviewed here through discussion of recent live muscle systems in which the sarcomere can be studied under intact, physiologically relevant conditions.
Topics: Sarcomeres; Myocardium; Heart; Connectin; Myofibrils; Myocardial Contraction
PubMed: 36555864
DOI: 10.3390/ijms232416223 -
The Journal of Physiology Jun 2017The ubiquitin-proteasome system (UPS) plays a critical role in removing unwanted intracellular proteins and is involved in protein quality control, signalling and cell... (Review)
Review
The ubiquitin-proteasome system (UPS) plays a critical role in removing unwanted intracellular proteins and is involved in protein quality control, signalling and cell death. Because the heart is subject to continuous metabolic and mechanical stress, the proteasome plays a particularly important role in the heart, and proteasome dysfunction has been suggested as a causative factor in cardiac dysfunction. Proteasome impairment has been detected in cardiomyopathies, heart failure, myocardial ischaemia, and hypertrophy. Proteasome inhibition is also sufficient to cause cardiac dysfunction in healthy pigs, and patients using a proteasome inhibitor for cancer therapy have a higher incidence of heart failure. In this Topical Review we discuss the experimental data which suggest UPS dysfunction is a common feature of cardiomyopathies, with an emphasis on hypertrophic cardiomyopathy caused by sarcomeric mutations. We also propose potential mechanisms by which cardiomyopathy-causing mutations may lead to proteasome impairment, such as altered calcium handling and increased oxidative stress due to mitochondrial dysfunction.
Topics: Animals; Cardiomyopathy, Hypertrophic; Heart; Heart Failure; Humans; Proteasome Endopeptidase Complex; Sarcomeres; Ubiquitin
PubMed: 28181243
DOI: 10.1113/JP273607 -
Cells Jul 2021With the advent of super-resolution microscopy, we gained a powerful toolbox to bridge the gap between the cellular- and molecular-level analysis of living organisms.... (Review)
Review
With the advent of super-resolution microscopy, we gained a powerful toolbox to bridge the gap between the cellular- and molecular-level analysis of living organisms. Although nanoscopy is broadly applicable, classical model organisms, such as fruit flies, worms and mice, remained the leading subjects because combining the strength of sophisticated genetics, biochemistry and electrophysiology with the unparalleled resolution provided by super-resolution imaging appears as one of the most efficient approaches to understanding the basic cell biological questions and the molecular complexity of life. Here, we summarize the major nanoscopic techniques and illustrate how these approaches were used in model systems to revisit a series of well-known cell biological phenomena. These investigations clearly demonstrate that instead of simply achieving an improvement in image quality, nanoscopy goes far beyond with its immense potential to discover novel structural and mechanistic aspects. With the examples of synaptic active zones, centrosomes and sarcomeres, we will explain the instrumental role of super-resolution imaging pioneered in in understanding fundamental subcellular constituents.
Topics: Animals; Centrosome; Drosophila; Microscopy, Fluorescence; Models, Biological; Sarcomeres; Single Molecule Imaging
PubMed: 34440693
DOI: 10.3390/cells10081924 -
International Journal of Molecular... Jan 2020Sarcomere assembly and maintenance are essential physiological processes required for cardiac and skeletal muscle function and organism mobility. Over decades of... (Review)
Review
Sarcomere assembly and maintenance are essential physiological processes required for cardiac and skeletal muscle function and organism mobility. Over decades of research, components of the sarcomere and factors involved in the formation and maintenance of this contractile unit have been identified. Although we have a general understanding of sarcomere assembly and maintenance, much less is known about the development of the thin filaments and associated factors within the sarcomere. In the last decade, advancements in medical intervention and genome sequencing have uncovered patients with novel mutations in sarcomere thin filaments. Pairing this sequencing with reverse genetics and the ability to generate patient avatars in model organisms has begun to deepen our understanding of sarcomere thin filament development. In this review, we provide a summary of recent findings regarding sarcomere assembly, maintenance, and disease with respect to thin filaments, building on the previous knowledge in the field. We highlight debated and unknown areas within these processes to clearly define open research questions.
Topics: Actin Cytoskeleton; Animals; Humans; Muscle Contraction; Muscle Proteins; Muscle, Skeletal; Muscular Diseases; Mutation; Sarcomeres; Whole Genome Sequencing
PubMed: 31952119
DOI: 10.3390/ijms21020542 -
International Journal of Molecular... Oct 2021Inherited cardiomyopathies form a heterogenous group of disorders that affect the structure and function of the heart. Defects in the genes encoding sarcomeric proteins... (Review)
Review
Inherited cardiomyopathies form a heterogenous group of disorders that affect the structure and function of the heart. Defects in the genes encoding sarcomeric proteins are associated with various perturbations that induce contractile dysfunction and promote disease development. In this review we aimed to outline the functional consequences of the major inherited cardiomyopathies in terms of myocardial contraction and kinetics, and to highlight the structural and functional alterations in some sarcomeric variants that have been demonstrated to be involved in the pathogenesis of the inherited cardiomyopathies. A particular focus was made on mutation-induced alterations in cardiomyocyte mechanics. Since no disease-specific treatments for familial cardiomyopathies exist, several novel agents have been developed to modulate sarcomere contractility. Understanding the molecular basis of the disease opens new avenues for the development of new therapies. Furthermore, the earlier the awareness of the genetic defect, the better the clinical prognostication would be for patients and the better the prevention of development of the disease.
Topics: Animals; Cardiomyopathies; Humans; Myocardial Contraction; Myocardium; Myocytes, Cardiac; Sarcomeres
PubMed: 34681814
DOI: 10.3390/ijms222011154