👤 J van der Velden

Increased levels of α-tubulin and its post-translational modifications (PTMs) are found in human heart failure and could initiate diastolic dysfunction by modulating cardiomyocyte stiffness. How these modifications occur and how they may underlie cardiac dysfunction remains unknown. Upstream kinases may play a critical role, but this has not been explored. Here we address this question by, for the first time ever, determining levels of the enzymes involved in microtubule (MT) detyrosination and acetylation (αTAT1, HDAC6) in a well-characterized cohort of patients with hypertrophic cardiomyopathy (HCM). In HCM patients (N=10-11), protein levels of detyrosination enzymes remain unaltered, whilst levels of αTAT1 and HDAC6 were decreased and increased, respectively. Phosphoproteomics in HCM (N=24) and control (N=8) myocardium identified significant differences in over 1900 serine/threonine and 160 tyrosine phosphosites, in addition to increased EGFR/IGF1R-MAPK signaling in HCM. We subsequently showed that MT repolymerization was increased in HCM We show that the altered HCM MT code cannot be attributed to levels of key MT-modifying enzymes. By combining kinome analyses in human HCM hearts with hiPSC-CM studies on MT dynamics, PTMs and contractility we unveiled a regulatory role for MTs in the cardiomyocyte response to beta-adrenergic receptor stimulation. Disease-mediated changes in the MT code thereby exert both a direct, and indirect effect on cardiac function via mediating the response to adrenergic activation. Show less

Hypertrophic cardiomyopathy (HCM) is a prevalent inherited cardiac disorder marked by left ventricular hypertrophy and hypercontractility. This excessive mechanical workload creates an energetic mismatch in which consumption exceeds production, leading to myocardial energy depletion. Although CK (creatine kinase) plays a key role in cardiac energy homeostasis, its involvement in HCM remains unclear. This study investigates how hypercontractility-driven mitochondrial stress and the resulting increase in mitochondrial H CK function was analyzed using myocardial left ventricular tissue from 92 patients with HCM (with and without pathogenic sarcomere variants) and 30 non-failing human controls. Myofilament and mitochondrial CK isoforms were measured using mRNA analysis, protein immunoblotting, enzyme activity assays, mass spectrometry, and redox-sensitive proteomics. To explore links between hypercontractility, mitochondrial reactive oxygen species, and CK dysfunction, we used isolated cardiomyocytes from wild-type, mitochondrial-targeted catalase-overexpressing, CK knockout (myofilament and mitochondrial CK deletion), HCM-associated Our analysis revealed significant reductions in myofilament and mitochondrial CK protein levels, as well as CK activity, in myocardium of patients with HCM, primarily because of oxidative modifications of CK. In isolated mouse cardiomyocytes from wild-type and CK knockouts, hypercontractility induced by EMD-57033 elevated mitochondrial H This study reveals a mechanistic link between hypercontractility, mitochondrial reactive oxygen species, and CK dysfunction in HCM, perpetuating a cycle of energetic dysfunction. Targeting hypercontractility and oxidative stress through myosin inhibition offers a strategy to restore energy balance and reduce arrhythmic risk in HCM. Show less

Previous studies have shown that individuals with a hypertrophic cardiomyopathy (HCM) pathogenic variant (PV) or likely pathogenic variant (LPV) without a HCM phenotype (PV/LPV carrier) have decreased myocardial external efficiency (MEE), which is thought to be a key pathomechanism in the onset and progression of HCM. Metabolic treatments improved exercise capacity in HCM patients, but evidence that such drugs correct reduced MEE is lacking. The ENERGY trial is a double-blind, placebo-controlled randomized clinical trial to define if the metabolic drug trimetazidine (TMZ) corrects reduced MEE in PV/LPV carriers for HCM. 51 MYBPC3 or MYH7 PV/LPV carriers were screened after which 40 were included and randomized into a treatment group (n = 20) or placebo group (n = 20) stratified for sex. Participants were treated with TMZ 20 mg or placebo three times daily during 8 weeks. The main outcome of this study was MEE as measured by [11C]-acetate positron emission tomography/computed tomography (PET/CT) and cardiac magnetic resonance (CMR) scan. Secondary outcomes were exercise parameters as measured by cardio-pulmonary exercise testing (CPET). Drug safety was monitored by (serious) adverse event registration. Treatment groups were comparable in terms of age, sex, body mass index, P/LP gene variant, and echocardiographic parameters without significant differences. Baseline CMR parameters and MEE were not significantly different between treatment groups. Eight weeks of treatment with TMZ did not significantly alter MEE compared to placebo. The mean MEE changed from 30.3 ± 3.8 to 29.8 ± 4.3% in the placebo group and from 30.1 ± 4 to 29.1 ± 4% in the TMZ group. Compared to placebo, the TMZ group did not have a significantly different MEE (difference -0.44, 95% interaction CI, -2.863 to 1.986, P = 0.68). The mean V'O2max as a percentage of predicted V'O2max (V'O2max %pred) changed from 108 ± 17 to 111 ± 19 (95% CI, -6 to 10, P = 0.84) percent in the placebo group and from 105 ± 17 to 113 ± 14 (95% CI, 1 to 16, P = 0.03) percent in the TMZ group. After adjustment for baseline, the TMZ group had a significantly increased V'O2max %pred (difference 6.37, 95% interaction CI, -3 to 16, P = 0.04). The ENERGY trial is the first proof-of-concept randomized controlled trial to test the hypothesis that TMZ improves MEE in MYBPC3 or MYH7 PV/LPV carriers. We conclude that metabolic therapy with TMZ may not correct the P/LP gene variant-related decrease in MEE. Netherlands Trial Register NL7492 (URL https://onderzoekmetmensen.nl/nl/trial/25078). Show less

Hypertrophic cardiomyopathy (HCM) is often caused by pathogenic or likely pathogenic variants, of which 30-50 % involve a variant in the gene encoding cardiac myosin-binding protein-C (MYBPC3). We generated human induced pluripotent stem cell lines from five individuals from two families carrying a pathogenic Dutch MYBPC3 founder variant: c.2373insG (n = 2) and c.2827C > T (n = 3), with highly variable disease expression. Peripheral blood mononuclear cells were reprogrammed using episomal plasmids. All cell lines express pluripotent markers, exhibit a normal karyotype, and could differentiate into derivatives of each germ layers in vitro. These cell lines can serve as disease model to investigate HCM pathogenesis. Show less

Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and associated with left ventricular hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with the findings that microtubule detyrosination (dTyr-MT) is markedly elevated in heart failure. Acute reduction of dTyr-MT by inhibition of the detyrosinase (VASH [vasohibin]/SVBP [small VASH-binding protein] complex) or activation of the tyrosinase (TTL [tubulin tyrosine ligase]) markedly improved contractility and reduced stiffness in human failing cardiomyocytes and thus posed a new perspective for HCM treatment. In this study, we tested the impact of chronic tubulin tyrosination in an HCM mouse model ( Adeno-associated virus serotype 9-mediated TTL transfer was applied in neonatal wild-type rodents, in 3-week-old knock-in mice, and in HCM human induced pluripotent stem cell-derived cardiomyocytes. We show (1) TTL for 6 weeks dose dependently reduced dTyr-MT and improved contractility without affecting cytosolic calcium transients in wild-type cardiomyocytes; (2) TTL for 12 weeks reduced the abundance of dTyr-MT in the myocardium, improved diastolic filling, compliance, cardiac output, and stroke volume in knock-in mice; (3) TTL for 10 days normalized cell area in HCM human induced pluripotent stem cell-derived cardiomyocytes; (4) TTL overexpression activated transcription of tubulins and other cytoskeleton components but did not significantly impact the proteome in knock-in mice; (5) SVBP-deficient EHTs exhibited reduced dTyr-MT levels, higher force, and faster relaxation than TTL-deficient and wild-type EHTs. RNA sequencing and mass spectrometry analysis revealed distinct enrichment of cardiomyocyte components and pathways in SVBP-deficient versus TTL-deficient EHTs. This study provides the first proof of concept that chronic activation of tubulin tyrosination in HCM mice and in human EHTs improves heart function and holds promise for targeting the nonsarcomeric cytoskeleton in heart disease. Show less

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in the cardiac myosin binding protein-C (cMyBP-C) encoding gene MYBPC3. In the Netherlands, approximately 25% of patients carry the MYBPC3 Show less

Phenotypic expression of hypertrophic cardiomyopathy (HCM) and disease course are associated with unfavorable metabolic health. We investigated if Western diet (WD) feeding is sufficient to trigger cardiac hypertrophy and dysfunction in heterozygous (HET) Wild-type (WT) and HET mice (3-months-old) were fed a WD or normal chow (NC) for 8 weeks. Metabolomic analyses on serum revealed systemic metabolic derailment in WD-fed WT and HET mice. Strikingly, only WD-fed HET mice developed cardiac hypertrophy and dysfunction, which was not driven by aggravated cardiac myosin binding protein-C haploinsufficiency. WD reduced oxidative phosphorylation and increased toxic lipids in the heart irrespective of genotype. Cardiac proteomic analyses revealed higher abundance of proteins involved in fatty acid oxidation in WD-fed mice, however this increase was blunted in HET compared to WT mice. Accordingly, cardiac metabolomic and lipidomic analyses showed accumulation of acylcarnitines in WD-fed HET vs WT mice. WD feeding triggered cardiac dysfunction and hypertrophy in otherwise phenotype-negative HET Show less

Employing animal models to study heart failure (HF) has become indispensable to discover and test novel therapies, but their translatability remains challenging. Although cytoskeletal alterations are linked to HF, the tubulin signature of common experimental models has been incompletely defined. Here, we assessed the tubulin signature in a large set of human cardiac samples and myocardium of animal models with cardiac remodeling caused by pressure overload, myocardial infarction or a gene defect. We studied levels of total, acetylated, and detyrosinated α-tubulin and desmin in cardiac tissue from hypertrophic (HCM) and dilated cardiomyopathy (DCM) patients with an idiopathic (n = 7), ischemic (n = 7) or genetic origin (n = 59), and in a pressure-overload concentric hypertrophic pig model (n = 32), pigs with a myocardial infarction (n = 28), mature pigs (n = 6), and mice (n = 15) carrying the HCM-associated MYBPC3 Show less

Diastolic dysfunction is central to diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy (HCM). However, therapies that improve cardiac relaxation are scarce, partly due to a limited understanding of modulators of cardiomyocyte relaxation. We hypothesized that cardiac relaxation is regulated by multiple unidentified proteins and that dysregulation of kinases contributes to impaired relaxation in patients with HCM. We optimized and increased the throughput of unloaded shortening measurements and screened a kinase inhibitor library in isolated adult cardiomyocytes from wild-type mice. One hundred fifty-seven kinase inhibitors were screened. To assess which kinases are dysregulated in patients with HCM and could contribute to impaired relaxation, we performed a tyrosine and global phosphoproteomics screen and integrative inferred kinase activity analysis using HCM patient myocardium. Identified hits from these 2 data sets were validated in cardiomyocytes from a homozygous Screening of 157 kinase inhibitors in wild-type (N=33) cardiomyocytes (n=24 563) resulted in the identification of 17 positive inotropes and 21 positive lusitropes, almost all of them novel. The positive lusitropes formed 3 clusters: cell cycle, EGFR (epidermal growth factor receptor)/IGF1R (insulin-like growth factor 1 receptor), and a small Akt (α-serine/threonine protein kinase) signaling cluster. By performing phosphoproteomic profiling of HCM patient myocardium (N=24 HCM and N=8 donors), we demonstrated increased activation of 6 of 8 proteins from the EGFR/IGFR1 cluster in HCM. We validated compounds from this cluster in mouse HCM (N=12) cardiomyocytes (n=2023). Three compounds from this cluster were able to improve relaxation in HCM cardiomyocytes. We showed the feasibility of screening for functional modulators of cardiomyocyte relaxation and contraction, parameters that we observed to be modulated by kinases involved in EGFR/IGF1R, Akt, cell cycle signaling, and FoxO (forkhead box class O) signaling, respectively. Integrating the screening data with phosphoproteomics analysis in HCM patient tissue indicated that inhibition of EGFR/IGF1R signaling is a promising target for treating impaired relaxation in HCM. Show less

Hypertrophic cardiomyopathy (HCM) is a relatively common genetic heart disease characterised by myocardial hypertrophy. HCM can cause outflow tract obstruction, sudden cardiac death and heart failure, but severity is highly variable. In this exploratory cross-sectional study, circulating acylcarnitines were assessed as potential biomarkers in 124 MYBPC3 founder variant carriers (59 with severe HCM, 26 with mild HCM and 39 phenotype-negative [G + P-]). Elastic net logistic regression identified eight acylcarnitines associated with HCM severity. C3, C4, C6-DC, C8:1, C16, C18 and C18:2 were significantly increased in severe HCM compared to G + P-, and C3, C6-DC, C8:1 and C18 in mild HCM compared to G + P-. In multivariable linear regression, C6-DC and C8:1 correlated to log-transformed maximum wall thickness (coefficient 5.01, p = 0.005 and coefficient 0.803, p = 0.007, respectively), and C6-DC to log-transformed ejection fraction (coefficient -2.50, p = 0.004). Acylcarnitines seem promising biomarkers for HCM severity, however prospective studies are required to determine their prognostic value. Show less

Transcriptional bursting is a common expression mode for most genes where independent transcription of alleles leads to different ratios of allelic mRNA from cell to cell. Here we investigated burst-like transcription and its consequences in cardiac tissue from Hypertrophic Cardiomyopathy (HCM) patients with heterozygous mutations in the sarcomeric proteins cardiac myosin binding protein C (cMyBP-C, Show less

Glucose-dependent insulinotropic polypeptide (GIP) and its receptor (GIPR) are part of the incretin system that regulates glucose homeostasis. A series of GIPR residues putatively important for ligand binding and receptor activation were mutated and pharmacologically evaluated using GIPR selective agonists in cAMP accumulation, ERK1/2 phosphorylation (pERK1/2) and β-arrestin 2 recruitment assays. The impact of mutation on ligand efficacy was determined by operational modelling of experimental data for each mutant, with results mapped onto the full-length, active-state GIPR structure. Two interaction networks, comprising transmembrane helix (TM) 7, TM1 and TM2, and extracellular loop (ECL) 2, TM5 and ECL3 were revealed, respectively. Both networks were critical for Gα Show less

The glucose-dependent insulinotropic polypeptide (GIP) is a 42-residue metabolic hormone that is actively being targeted for its regulatory role of glycemia and energy balance. Limited structural data of its receptor has made ligand design tedious. This study investigates the structure and function of the GIP receptor (GIPR), using a homology model based on the GLP-1 receptor. Molecular dynamics combined with in vitro mutational data were used to pinpoint residues involved in ligand binding and/or receptor activation. Significant differences in binding mode were identified for the naturally occurring agonists GIP(1-30)NH Show less

The heart muscle diseases hypertrophic (HCM) and dilated (DCM) cardiomyopathies are leading causes of sudden death and heart failure in young, otherwise healthy, individuals. We conducted genome-wide association studies and multi-trait analyses in HCM (1,733 cases), DCM (5,521 cases) and nine left ventricular (LV) traits (19,260 UK Biobank participants with structurally normal hearts). We identified 16 loci associated with HCM, 13 with DCM and 23 with LV traits. We show strong genetic correlations between LV traits and cardiomyopathies, with opposing effects in HCM and DCM. Two-sample Mendelian randomization supports a causal association linking increased LV contractility with HCM risk. A polygenic risk score explains a significant portion of phenotypic variability in carriers of HCM-causing rare variants. Our findings thus provide evidence that polygenic risk score may account for variability in Mendelian diseases. More broadly, we provide insights into how genetic pathways may lead to distinct disorders through opposing genetic effects. Show less

Hypertrophic cardiomyopathy (HCM) patients are at increased risk of ventricular arrhythmias and sudden cardiac death, which can occur even in the absence of structural changes of the heart. HCM mouse models suggest mutations in myofilament components to affect Ca Show less

Hypertrophic cardiomyopathy (HCM) is the most common genetic disease of the cardiac muscle, frequently caused by mutations in MYBPC3. However, little is known about the upstream pathways and key regulators causing the disease. Therefore, we employed a multi-omics approach to study the pathomechanisms underlying HCM comparing patient hearts harboring MYBPC3 mutations to control hearts. Using H3K27ac ChIP-seq and RNA-seq we obtained 9310 differentially acetylated regions and 2033 differentially expressed genes, respectively, between 13 HCM and 10 control hearts. We obtained 441 differentially expressed proteins between 11 HCM and 8 control hearts using proteomics. By integrating multi-omics datasets, we identified a set of DNA regions and genes that differentiate HCM from control hearts and 53 protein-coding genes as the major contributors. This comprehensive analysis consistently points toward altered extracellular matrix formation, muscle contraction, and metabolism. Therefore, we studied enriched transcription factor (TF) binding motifs and identified 9 motif-encoded TFs, including KLF15, ETV4, AR, CLOCK, ETS2, GATA5, MEIS1, RXRA, and ZFX. Selected candidates were examined in stem cell-derived cardiomyocytes with and without mutated MYBPC3. Furthermore, we observed an abundance of acetylation signals and transcripts derived from cardiomyocytes compared to non-myocyte populations. By integrating histone acetylome, transcriptome, and proteome profiles, we identified major effector genes and protein networks that drive the pathological changes in HCM with mutated MYBPC3. Our work identifies 38 highly affected protein-coding genes as potential plasma HCM biomarkers and 9 TFs as potential upstream regulators of these pathomechanisms that may serve as possible therapeutic targets. Show less

We recently showed more severe diastolic dysfunction at the time of myectomy in female compared to male patients with obstructive hypertrophic cardiomyopathy. Early recognition of aberrant cardiac contracility using cardiovascular magnetic resonance (CMR) imaging may identify women at risk of cardiac dysfunction. To define myocardial function at an early disease stage, we studied regional cardiac function using CMR imaging with tissue tagging in asymptomatic female gene variant carriers. CMR imaging with tissue tagging was done in 13 MYBPC3, 11 MYH7 and 6 TNNT2 gene carriers and 16 age-matched controls. Regional peak circumferential strain was derived from tissue tagging images of the basal and midventricular segments of the septum and lateral wall. Left ventricular wall thickness and global function were comparable between MYBPC3, MYH7, TNNT2 carriers and controls. MYH7 gene variant carriers showed a different strain pattern as compared to the other groups, with higher septal peak circumferential strain at the basal segments compared to the lateral wall, whereas MYBPC3, TNNT2 carriers and controls showed higher strain at the lateral wall compared to the septum. Only subtle gene-specific changes in strain pattern occur in the myocardium preceding development of cardiac hypertrophy. Overall, our study shows that there are no major contractile deficits in asymptomatic females carrying a pathogenic gene variant, which would justify the use of CMR imaging for earlier diagnosis. Show less

Hypertrophic cardiomyopathy (HCM) is the most prevalent monogenic heart disease, commonly caused by truncating variants in the MYBPC3 gene. HCM is an important cause of sudden cardiac death; however, overall prognosis is good and penetrance in genotype-positive individuals is incomplete. The underlying mechanisms are poorly understood and risk stratification remains limited. To create a nationwide cohort of carriers of truncating MYBPC3 variants for identification of predictive biomarkers for HCM development and progression. In the multicentre, observational BIO FOr CARe (Identification of BIOmarkers of hypertrophic cardiomyopathy development and progression in Dutch MYBPC3 FOunder variant CARriers) cohort, carriers of the c.2373dupG, c.2827C > T, c.2864₂₈₆₅delCT and c.3776delA MYBPC3 variants are included and prospectively undergo longitudinal blood collection. Clinical data are collected from first presentation onwards. The primary outcome constitutes a composite endpoint of HCM progression (maximum wall thickness ≥ 20 mm, septal reduction therapy, heart failure occurrence, sustained ventricular arrhythmia and sudden cardiac death). So far, 250 subjects (median age 54.9 years (interquartile range 43.3, 66.6), 54.8% male) have been included. HCM was diagnosed in 169 subjects and dilated cardiomyopathy in 4. The primary outcome was met in 115 subjects. Blood samples were collected from 131 subjects. BIO FOr CARe is a genetically homogeneous, phenotypically heterogeneous cohort incorporating a clinical data registry and longitudinal blood collection. This provides a unique opportunity to study biomarkers for HCM development and prognosis. The established infrastructure can be extended to study other genetic variants. Other centres are invited to join our consortium. Show less

Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disease. While ≈50% of patients with HCM carry a sarcomere gene mutation (sarcomere mutation-positive, HCM A proteomics screen was performed in cardiac tissue from 39 HCM In all HCM patient samples, we found lower levels of metabolic pathway proteins and higher levels of extracellular matrix proteins. Levels of total and detyrosinated α-tubulin were markedly higher in HCM Our findings indicate that microtubules and especially its detyrosination contribute to the pathomechanism of patients with HCM Show less

Tirzepatide (LY3298176) is a dual GIP and GLP-1 receptor agonist under development for the treatment of type 2 diabetes mellitus (T2DM), obesity, and nonalcoholic steatohepatitis. Early phase trials in T2DM indicate that tirzepatide improves clinical outcomes beyond those achieved by a selective GLP-1 receptor agonist. Therefore, we hypothesized that the integrated potency and signaling properties of tirzepatide provide a unique pharmacological profile tailored for improving broad metabolic control. Here, we establish methodology for calculating occupancy of each receptor for clinically efficacious doses of the drug. This analysis reveals a greater degree of engagement of tirzepatide for the GIP receptor than the GLP-1 receptor, corroborating an imbalanced mechanism of action. Pharmacologically, signaling studies demonstrate that tirzepatide mimics the actions of native GIP at the GIP receptor but shows bias at the GLP-1 receptor to favor cAMP generation over β-arrestin recruitment, coincident with a weaker ability to drive GLP-1 receptor internalization compared with GLP-1. Experiments in primary islets reveal β-arrestin1 limits the insulin response to GLP-1, but not GIP or tirzepatide, suggesting that the biased agonism of tirzepatide enhances insulin secretion. Imbalance toward GIP receptor, combined with distinct signaling properties at the GLP-1 receptor, together may account for the promising efficacy of this investigational agent. Show less

Enzymatic cleavage of endogenous peptides is a commonly used principle to initiate, modulate and terminate action for instance among cytokines and peptide hormones. The incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and the related hormone glucagon-like peptide-2 (GLP-2) are all rapidly N-terminally truncated with severe loss of intrinsic activity. The most abundant circulating form of full length GIP(1-42) is GIP(3-42) (a dipeptidyl peptidase-4 (DPP-4) product). GIP(1-30)NH Show less

In patients with type 2 diabetes mellitus (T2DM), the insulinotropic action of the GIP system is desensitized, whereas this is not the case for the GLP-1 system. This has raised an interesting discussion of whether GIP agonists or antagonists are most suitable for future treatment of T2DM together with GLP-1-based therapies. Homozygous carriers of the GIP receptor (GIPR) variant, [E354Q], display lower bone mineral density, increased bone fracture risk and slightly increased blood glucose. Here, we present an in-depth molecular pharmacological phenotyping of GIPR-[E354Q]. In silico modelling suggested similar interaction of the endogenous agonist GIP(1-42) to [E354Q] as to GIPR wt. This was supported by homologous competition binding in COS-7 cells revealing GIPR wt-like affinities of GIP(1-42) with K Show less

Mutations in MYBPC3 are the most common cause of hypertrophic cardiomyopathy (HCM). These mutations produce dysfunctional protein that is quickly degraded and not incorporated in the myofilaments. Most patients are heterozygous and allelic expression differs between cells. We hypothesized that this would lead to cell-to-cell variation in cardiac myosin binding protein-C (cMyBP-C, encoded by MYBPC3 gene) protein levels. Twelve HCM patients were included (six had no sarcomere mutations (HCM Protein and mRNA analysis revealed significantly reduced cMyBP-C levels in MYBPC3 This is the first study to demonstrate intercellular variation of myofilament cMyBP-C protein expression within the myocardium from HCM patients with heterozygous MYBPC3 mutations. Show less

Alterations in autophagy have been reported in hypertrophic cardiomyopathy (HCM) caused by Danon disease, Vici syndrome, or LEOPARD syndrome, but not in HCM caused by mutations in genes encoding sarcomeric proteins, which account for most of HCM cases. We evaluated autophagy in patients with HCM carrying Altogether, we found that (1) autophagy is altered in patients with HCM carrying Show less

The study included 680 subjects: 271 FG+ carriers, 132 G+ probands with HCM, and 277 G- probands with HCM. FG+ carriers included 134 FG+ probands with HCM, 54 FG+ relatives diagnosed with HCM after family screening, 74 FG+/phenotype-negative relatives, and 9 with noncompaction or dilated cardiomyopathy. The clinical phenotype of FG+ and G+ probands with HCM was similar. FG+ and G+ probands were younger with less left ventricular outflow tract obstruction than G- probands, however, had more hypertrophy, and nonsustained ventricular tachycardia. FG+ relatives with HCM had less hypertrophy, smaller left atria, and less systolic and diastolic dysfunction than FG+ probands with HCM. After 8±6 years, cardiovascular mortality in FG+ probands with HCM was similar to G+ HCM (22% versus 14%; log-rank Clinical phenotype and outcome of FG+ HCM was similar to G+ HCM but worse than G- HCM and FG+ HCM diagnosed in the context of family screening. These findings indicate the need for more intensive follow-up of FG+ and G+ HCM versus G- HCM and FG+ HCM in relatives. Show less

The "super-relaxed state" (SRX) of myosin represents a 'reserve' of motors in the heart. Myosin heads in the SRX are bound to the thick filament and have a very low ATPase rate. Changes in the SRX are likely to modulate cardiac contractility. We previously demonstrated that the SRX is significantly reduced in mouse cardiomyocytes lacking cardiac myosin binding protein-C (cMyBP-C). Here, we report the effect of mutations in the cMyBP-C gene (MYBPC3) using samples from human patients with hypertrophic cardiomyopathy (HCM). Left ventricular (LV) samples from 11 HCM patients were obtained following myectomy surgery to relieve LV outflow tract obstruction. HCM samples were genotyped as either MYBPC3 mutation positive (MYBPC3mut) or negative (HCMsmn) and were compared to eight non-failing donor hearts. Compared to donors, only MYBPC3mut samples display a significantly diminished SRX, characterised by a decrease in both the number of myosin heads in the SRX and the lifetime of ATP turnover. These changes were not observed in HCMsmn samples. There was a positive correlation (p < 0.01) between the expression of cMyBP-C and the proportion of myosin heads in the SRX state, suggesting cMyBP-C modulates and maintains the SRX. Phosphorylation of the myosin regulatory light chain in MYBPC3mut samples was significantly decreased compared to the other groups, suggesting a potential mechanism to compensate for the diminished SRX. We conclude that by altering both contractility and sarcomeric energy requirements, a reduced SRX may be an important disease mechanism in patients with MYBPC3 mutations. Show less