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Journal of the American College of... Aug 2020Predictive genetic screening of relatives of patients with hypertrophic cardiomyopathy (HCM) caused by sarcomere protein (SP) gene mutations is current standard of care,...
BACKGROUND
Predictive genetic screening of relatives of patients with hypertrophic cardiomyopathy (HCM) caused by sarcomere protein (SP) gene mutations is current standard of care, but there are few data on long-term outcomes in mutation carriers without HCM.
OBJECTIVES
The aim of this study was to determine the incidence of new HCM diagnosis in SP mutation carriers.
METHODS
This was a retrospective analysis of adult and pediatric SP mutation carriers identified during family screening who did not fulfill diagnostic criteria for HCM at first evaluation.
RESULTS
The authors evaluated 285 individuals from 156 families (median age 14.2 years [interquartile range: 6.8 to 31.6 years], 141 [49.5%] male individuals); 145 (50.9%) underwent cardiac magnetic resonance (CMR). Frequency of causal genes was as follows: MYBPC3 n = 123 (43.2%), MYH7 n = 69 (24.2%), TNNI3 n = 39 (13.7%), TNNT2 n = 34 (11.9%), TPM1 n = 9 (3.2%), MYL2 n = 6 (2.1%), ACTC1 n = 1 (0.4%), multiple mutations n = 4 (1.4%). Median follow-up was 8.0 years (interquartile range: 4.0 to 13.3 years) and 86 (30.2%) patients developed HCM; 16 of 50 (32.0%) fulfilled diagnostic criteria on CMR but not echocardiography. Estimated HCM penetrance at 15 years of follow-up was 46% (95% confidence interval [CI]: 38% to 54%). In a multivariable model adjusted for age and stratified for CMR, independent predictors of HCM development were male sex (hazard ratio [HR]: 2.91; 95% CI: 1.82 to 4.65) and abnormal electrocardiogram (ECG) (HR: 4.02; 95% CI: 2.51 to 6.44); TNNI3 variants had the lowest risk (HR: 0.19; 95% CI: 0.07 to 0.55, compared to MYBPC3).
CONCLUSIONS
Following a first negative screening, approximately 50% of SP mutation carriers develop HCM over 15 years of follow-up. Male sex and an abnormal ECG are associated with a higher risk of developing HCM. Regular CMR should be considered in long-term screening.
Topics: Adolescent; Adult; Cardiac Myosins; Cardiomyopathy, Hypertrophic; Child; DNA; DNA Mutational Analysis; Echocardiography; Female; Follow-Up Studies; Genetic Testing; Heterozygote; Humans; Male; Mutation; Pedigree; Retrospective Studies; Sarcomeres; Young Adult
PubMed: 32731933
DOI: 10.1016/j.jacc.2020.06.011 -
Circulation Dec 2023Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic...
BACKGROUND
Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic cardiomyopathy (HCM), a disease caused by sarcomere gene mutations. We hypothesized that microvascular dysfunction in HCM was secondary to abnormal microvascular growth and could occur independent of ventricular hypertrophy.
METHODS
We used multimodality imaging methods to track the temporality of microvascular dysfunction in HCM mouse models harboring mutations in the sarcomere genes (cardiac myosin binding protein C3) or (myosin heavy chain 6). We performed complementary molecular methods to assess protein quantity, interactions, and post-translational modifications to identify mechanisms regulating this response. We manipulated select molecular pathways in vivo using both genetic and pharmacological methods to validate these mechanisms.
RESULTS
We found that microvascular dysfunction in our HCM models occurred secondary to reduced myocardial capillary growth during the early postnatal time period and could occur before the onset of myocardial hypertrophy. We discovered that the E3 ubiquitin protein ligase MDM2 (murine double minute 2) dynamically regulates the protein stability of both HIF1α (hypoxia-inducible factor 1 alpha) and HIF2α (hypoxia-inducible factor 2 alpha)/EPAS1 (endothelial PAS domain protein 1) through canonical and noncanonical mechanisms. The resulting HIF imbalance leads to reduced proangiogenic gene expression during a key period of myocardial capillary growth. Reducing MDM2 protein levels by genetic or pharmacological methods normalized HIF protein levels and prevented the development of microvascular dysfunction in both HCM models.
CONCLUSIONS
Our results show that sarcomere mutations induce cardiomyocyte MDM2 signaling during the earliest stages of disease, and this leads to long-term changes in the myocardial microenvironment.
Topics: Mice; Animals; Proto-Oncogene Proteins c-mdm2; Cardiomyopathy, Hypertrophic; Myocardium; Myocytes, Cardiac; Sarcomeres; Mutation; Hypertrophy; Myosin Heavy Chains
PubMed: 37886847
DOI: 10.1161/CIRCULATIONAHA.123.064332 -
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 -
Current Cardiology Reports Jun 2023The pace of identifying cardiomyopathy-associated mutations and advances in our understanding of sarcomere function that underlies many cardiomyopathies has been... (Review)
Review
PURPOSE OF REVIEW
The pace of identifying cardiomyopathy-associated mutations and advances in our understanding of sarcomere function that underlies many cardiomyopathies has been remarkable. Here, we aim to synthesize how these advances have led to the promising new treatments that are being developed to treat cardiomyopathies.
RECENT FINDINGS
The genomics era has identified and validated many genetic causes of hypertrophic and dilated cardiomyopathies. Recent advances in our mechanistic understanding of sarcomere pathophysiology include high-resolution molecular models of sarcomere components and the identification of the myosin super-relaxed state. The advances in our understanding of sarcomere function have yielded several therapeutic agents that are now in development and clinical use to correct contractile dysfunction-mediated cardiomyopathy. New genes linked to cardiomyopathy include targets with limited clinical evidence and require additional investigation. Large portions of cardiomyopathy with family history remain genetically undiagnosed and may be due to polygenic disease.
Topics: Humans; Cardiomyopathy, Hypertrophic; Sarcomeres; Cardiomyopathies; Cardiomyopathy, Dilated; Mutation
PubMed: 37060436
DOI: 10.1007/s11886-023-01876-9 -
The American Journal of Cardiology Sep 2022Hypertrophic cardiomyopathy (HCM) is a global and relatively common cause of patient morbidity and mortality and is among the first reported monogenic cardiac diseases.... (Review)
Review
Hypertrophic cardiomyopathy (HCM) is a global and relatively common cause of patient morbidity and mortality and is among the first reported monogenic cardiac diseases. For 30 years, the basic etiology of HCM has been attributed largely to variants in individual genes encoding cardiac sarcomere proteins, with the implication that HCM is fundamentally a genetic disease. However, data from clinical and network medicine analyses, as well as contemporary genetic studies show that single gene variants do not fully explain the broad and diverse HCM clinical spectrum. These transformative advances place a new focus on possible novel interactions between acquired disease determinants and genetic context to produce complex HCM phenotypes, also offering a measure of caution against overemphasizing monogenics as the principal cause of this disease. These new perspectives in which HCM is not a uniformly genetic disease but likely explained by multifactorial etiology will also unavoidably impact how HCM is viewed by patients and families in the clinical practicing community going forward, including relevance to genetic counseling and access to healthcare insurance and psychosocial wellness.
Topics: Cardiomyopathy, Hypertrophic; Heart; Humans; Mutation; Phenotype; Sarcomeres
PubMed: 35843734
DOI: 10.1016/j.amjcard.2022.06.017 -
Circulation Sep 2023In hypertrophic cardiomyopathy (HCM), myocyte disarray and microvascular disease (MVD) have been implicated in adverse events, and recent evidence suggests that these...
BACKGROUND
In hypertrophic cardiomyopathy (HCM), myocyte disarray and microvascular disease (MVD) have been implicated in adverse events, and recent evidence suggests that these may occur early. As novel therapy provides promise for disease modification, detection of phenotype development is an emerging priority. To evaluate their utility as early and disease-specific biomarkers, we measured myocardial microstructure and MVD in 3 HCM groups-overt, either genotype-positive (G+LVH+) or genotype-negative (G-LVH+), and subclinical (G+LVH-) HCM-exploring relationships with electrical changes and genetic substrate.
METHODS
This was a multicenter collaboration to study 206 subjects: 101 patients with overt HCM (51 G+LVH+ and 50 G-LVH+), 77 patients with G+LVH-, and 28 matched healthy volunteers. All underwent 12-lead ECG, quantitative perfusion cardiac magnetic resonance imaging (measuring myocardial blood flow, myocardial perfusion reserve, and perfusion defects), and cardiac diffusion tensor imaging measuring fractional anisotropy (lower values expected with more disarray), mean diffusivity (reflecting myocyte packing/interstitial expansion), and second eigenvector angle (measuring sheetlet orientation).
RESULTS
Compared with healthy volunteers, patients with overt HCM had evidence of altered microstructure (lower fractional anisotropy, higher mean diffusivity, and higher second eigenvector angle; all <0.001) and MVD (lower stress myocardial blood flow and myocardial perfusion reserve; both <0.001). Patients with G-LVH+ were similar to those with G+LVH+ but had elevated second eigenvector angle (<0.001 after adjustment for left ventricular hypertrophy and fibrosis). In overt disease, perfusion defects were found in all G+ but not all G- patients (100% [51/51] versus 82% [41/50]; =0.001). Patients with G+LVH- compared with healthy volunteers similarly had altered microstructure, although to a lesser extent (all diffusion tensor imaging parameters; <0.001), and MVD (reduced stress myocardial blood flow [=0.015] with perfusion defects in 28% versus 0 healthy volunteers [=0.002]). Disarray and MVD were independently associated with pathological electrocardiographic abnormalities in both overt and subclinical disease after adjustment for fibrosis and left ventricular hypertrophy (overt: fractional anisotropy: odds ratio for an abnormal ECG, 3.3, =0.01; stress myocardial blood flow: odds ratio, 2.8, =0.015; subclinical: fractional anisotropy odds ratio, 4.0, =0.001; myocardial perfusion reserve odds ratio, 2.2, =0.049).
CONCLUSIONS
Microstructural alteration and MVD occur in overt HCM and are different in G+ and G- patients. Both also occur in the absence of hypertrophy in sarcomeric mutation carriers, in whom changes are associated with electrocardiographic abnormalities. Measurable changes in myocardial microstructure and microvascular function are early-phenotype biomarkers in the emerging era of disease-modifying therapy.
Topics: Humans; Hypertrophy, Left Ventricular; Sarcomeres; Diffusion Tensor Imaging; Genetic Predisposition to Disease; Mutation; Cardiomyopathy, Hypertrophic; Phenotype; Biomarkers; Fibrosis
PubMed: 37463608
DOI: 10.1161/CIRCULATIONAHA.123.063835 -
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 -
JCI Insight Jan 2020Mutations in cardiac myosin binding protein C (MyBP-C, encoded by MYBPC3) are the most common cause of hypertrophic cardiomyopathy (HCM). Most MYBPC3 mutations result in...
Mutations in cardiac myosin binding protein C (MyBP-C, encoded by MYBPC3) are the most common cause of hypertrophic cardiomyopathy (HCM). Most MYBPC3 mutations result in premature termination codons (PTCs) that cause RNA degradation and a reduction of MyBP-C in HCM patient hearts. However, a reduction in MyBP-C has not been consistently observed in MYBPC3-mutant induced pluripotent stem cell cardiomyocytes (iPSCMs). To determine early MYBPC3 mutation effects, we used patient and genome-engineered iPSCMs. iPSCMs with frameshift mutations were compared with iPSCMs with MYBPC3 promoter and translational start site deletions, revealing that allelic loss of function is the primary inciting consequence of mutations causing PTCs. Despite a reduction in wild-type mRNA in all heterozygous iPSCMs, no reduction in MyBP-C protein was observed, indicating protein-level compensation through what we believe is a previously uncharacterized mechanism. Although homozygous mutant iPSCMs exhibited contractile dysregulation, heterozygous mutant iPSCMs had normal contractile function in the context of compensated MyBP-C levels. Agnostic RNA-Seq analysis revealed differential expression in genes involved in protein folding as the only dysregulated gene set. To determine how MYBPC3-mutant iPSCMs achieve compensated MyBP-C levels, sarcomeric protein synthesis and degradation were measured with stable isotope labeling. Heterozygous mutant iPSCMs showed reduced MyBP-C synthesis rates but a slower rate of MyBP-C degradation. These findings indicate that cardiomyocytes have an innate capacity to attain normal MyBP-C stoichiometry despite MYBPC3 allelic loss of function due to truncating mutations. Modulating MyBP-C degradation to maintain MyBP-C protein levels may be a novel treatment approach upstream of contractile dysfunction for HCM.
Topics: Alleles; Cardiomyopathy, Hypertrophic; Carrier Proteins; Cell Line; Codon, Nonsense; Frameshift Mutation; Gene Editing; Genetic Predisposition to Disease; Heterozygote; Humans; Muscle Development; Mutation; Myocytes, Cardiac; RNA, Messenger; Sarcomeres; Transcriptome
PubMed: 31877118
DOI: 10.1172/jci.insight.133782 -
Circulation Research May 2021Our insight into the diverse and complex nature of dilated cardiomyopathy (DCM) genetic architecture continues to evolve rapidly. The foundations of DCM genetics rest on... (Review)
Review
Our insight into the diverse and complex nature of dilated cardiomyopathy (DCM) genetic architecture continues to evolve rapidly. The foundations of DCM genetics rest on marked locus and allelic heterogeneity. While DCM exhibits a Mendelian, monogenic architecture in some families, preliminary data from our studies and others suggests that at least 20% to 30% of DCM may have an oligogenic basis, meaning that multiple rare variants from different, unlinked loci, determine the DCM phenotype. It is also likely that low-frequency and common genetic variation contribute to DCM complexity, but neither has been examined within a rare variant context. Other types of genetic variation are also likely relevant for DCM, along with gene-by-environment interaction, now established for alcohol- and chemotherapy-related DCM. Collectively, this suggests that the genetic architecture of DCM is broader in scope and more complex than previously understood. All of this elevates the impact of DCM genetics research, as greater insight into the causes of DCM can lead to interventions to mitigate or even prevent it and thus avoid the morbid and mortal scourge of human heart failure.
Topics: Alleles; Cardiomyopathy, Dilated; Cohort Studies; Connectin; Cross-Sectional Studies; Gene-Environment Interaction; Genetic Loci; Genetic Variation; Humans; Models, Statistical; Phenotype; Sarcomeres
PubMed: 33983834
DOI: 10.1161/CIRCRESAHA.121.318157 -
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