Variable cardiac myosin binding protein-C expression in the myofilaments due to MYBPC3 mutations in hypertrophic cardiomyopathy

Background: 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. Methods: Twelve HCM patients were included (six had no sarcomere mutations (HCMsmn) and served as the control group and six harbored mutations in the MYBPC3 gene (MYBPC3mut). Western blot and RNA sequencing analysis of cardiac tissue lysates were performed to detect overall cMyBP-C protein and mRNA levels. Cellular expression of cMyBP-C and α-actin was obtained by immunofluorescence staining. Quantification of cell-to-cell variation of cMyBP-C expression between cardiomyocytes was measured by determining the ratio of cMyBP-C:α-actin stained area of each cell. Results: Protein and mRNA analysis revealed significantly reduced cMyBP-C levels in MYBPC3mutpatients compared with HCMsmnpatients (0.73 ± 0.09 vs. 1.0 ± 0.15, p <.05; 162.3 ± 16.4 vs. 326.2 ± 41.9 RPKM, p =.002), without any sign of truncated proteins. Immunofluorescence staining of individual cardiomyocytes in HCMsmnpatients demonstrated homogenous and equal cMyBP-C:α-actin staining ratio. In contrast, MYBPC3mutpatients demonstrated inhomogeneous staining patterns with a large intercellular variability per patient. Coefficient of variance for cMyBP-C/α-actin staining for each patient showed a significant difference between both groups (17.30 ± 4.08 vs. 5.18 ± 0.65% in MYBPC3mutvs. HCMsmn, p =.02). Conclusion: 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

Development of a new therapeutic technique to direct stem cells to the infarcted heart using targeted microbubbles: StemBells

Successful stem cell therapy after acute myocardial infarction (AMI) is hindered by lack of engraftment of sufficient stem cells at the site of injury. We designed a novel technique to overcome this problem by assembling stem cell-microbubble complexes, named 'StemBells'.StemBells were assembled through binding of dual-targeted microbubbles (~ 3 μm) to adipose-derived stem cells (ASCs) via a CD90 antibody. StemBells were targeted to the infarct area

Variable cardiac myosin binding protein-C expression in the myofilaments due to MYBPC3 mutations in hypertrophic cardiomyopathy

Background: 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. Methods: Twelve HCM patients were included (six had no sarcomere mutations (HCMsmn) and served as the control group and six harbored mutations in the MYBPC3 gene (MYBPC3mut). Western blot and RNA sequencing analysis of cardiac tissue lysates were performed to detect overall cMyBP-C protein and mRNA levels. Cellular expression of cMyBP-C and α-actin was obtained by immunofluorescence staining. Quantification of cell-to-cell variation of cMyBP-C expression between cardiomyocytes was measured by determining the ratio of cMyBP-C:α-actin stained area of each cell. Results: Protein and mRNA analysis revealed significantly reduced cMyBP-C levels in MYBPC3mut patients compared with HCMsmn patients (0.73 ± 0.09 vs. 1.0 ± 0.15, p <.05; 162.3 ± 16.4 vs. 326.2 ± 41.9 RPKM, p =.002), without any sign of truncated proteins. Immunofluorescence staining of individual cardiomyocytes in HCMsmn patients demonstrated homogenous and equal cMyBP-C:α-actin staining ratio. In contrast, MYBPC3mut patients demonstrated inhomogeneous staining patterns with a large intercellular variability per patient. Coefficient of variance for cMyBP-C/α-actin staining for each patient showed a significant difference between both groups (17.30 ± 4.08 vs. 5.18 ± 0.65% in MYBPC3mut vs. HCMsmn, p =.02). Conclusion: 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

Don't judge the myocardium by its cover : The incremental value of cardiac magnetic resonance imaging in left ventricular hypertrophy

Contains fulltext : 190547.pdf (publisher's version ) (Open Access

Increased Myocardial Oxygen Consumption Precedes Contractile Dysfunction in Hypertrophic Cardiomyopathy Caused by Pathogenic TNNT2 Gene Variants

BACKGROUND: Hypertrophic cardiomyopathy is caused by pathogenic sarcomere gene variants. Individuals with a thin-filament variant present with milder hypertrophy than carriers of thick-filament variants, although prognosis is poorer. Herein, we defined if decreased energetic status of the heart is an early pathomechanism in TNNT2 (troponin T gene) variant carriers. METHODS AND RESULTS: Fourteen individuals with TNNT2 variants (genotype positive), without left ventricular hypertrophy (G+/LVH−; n=6) and with LVH (G+/LVH+; n=8) and 14 healthy controls were included. All participants underwent cardiac magnetic resonance and [11C]-acetate positron emission tomography imaging to assess LV myocardial oxygen consumption, contractile parameters and myocardial external efficiency. Cardiac efficiency was significantly reduced compared with controls in G+/LVH− and G+/LVH+. Lower myocardial external efficiency in G+/LVH− is explained by higher global and regional oxygen consumption compared with controls without changes in contractile parameters. Reduced myocardial external efficiency in G+/LVH+ is explained by the increase in LV mass and higher oxygen consumption. Septal oxygen consumption was significantly lower in G+/LVH+ compared with G+/LVH−. Although LV ejection fraction was higher in G+/LVH+, both systolic and diastolic strain parameters were lower compared with controls, which was most evident in the hypertrophied septal wall. CONCLUSIONS: Using cardiac magnetic resonance and [11C]-acetate positron emission tomography imaging, we show that G+/LVH− have an initial increase in oxygen consumption preceding contractile dysfunction and cardiac hypertrophy, followed by a decline in oxygen consumption in G+/LVH+. This suggests that high oxygen consumption and reduced myocardial external efficiency characterize the early gene variant–mediated disease mechanisms that may be used for early diagnosis and development of preventive treatments

Regional myocardial function at preclinical disease stage of hypertrophic cardiomyopathy in female gene variant carriers

International audienceAbstract 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

Disease Stage-Dependent Changes in Cardiac Contractile Performance and Oxygen Utilization Underlie Reduced Myocardial Efficiency in Human Inherited Hypertrophic Cardiomyopathy

Background— Reduced myocardial efficiency represents a target for therapy in hypertrophic cardiomyopathy although therapeutic benefit may depend on disease stage. Here, we determined disease stage–dependent changes in myocardial efficiency and effects of myectomy surgery. Methods and Results— Myocardial external efficiency (MEE) was determined in 27 asymptomatic mutation carriers (genotype positive/phenotype negative), 10 patients with hypertrophic obstructive cardiomyopathy (HOCM), 10 patients with aortic valve stenosis, and 14 healthy individuals using [ 11 C]-acetate positron emission tomography and cardiovascular magnetic resonance imaging. Follow-up measurements were performed in HOCM and aortic valve stenosis patients 4 months after surgery. External work did not differ in HOCM compared with controls, whereas myocardial oxygen consumption was lower in HOCM. Because of a higher cardiac mass, total cardiac oxygen consumption was significantly higher in HOCM than in controls and genotype positive/phenotype negative. MEE was significantly lower in genotype positive/phenotype negative than in controls (28±6% versus 42±6%) and was further decreased in HOCM (22±5%). In contrast to patients with aortic valve stenosis, MEE was not improved in patients with HOCM after surgery, which was explained by opposite changes in the septum (decrease) and lateral (increase) wall. Conclusions— Different mechanisms underlie reduced MEE at the early and advanced stage of hypertrophic cardiomyopathy. The initial increase and subsequent reduction in myocardial oxygen consumption during disease progression indicates that energy deficiency is a primary mutation-related event, whereas mechanisms secondary to disease remodeling underlie low MEE in HOCM. Our data highlight that the benefit of therapies to improve energetic status of the heart may vary depending on the disease stage and that treatment should be initiated before cardiac remodeling. </jats:sec

Variable cardiac myosin binding protein-C expression in the myofilaments due to MYBPC3 mutations in hypertrophic cardiomyopathy

BACKGROUND: 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. METHODS: Twelve HCM patients were included (six had no sarcomere mutations (HCMsmn) and served as the control group and six harbored mutations in the MYBPC3 gene (MYBPC3mut). Western blot and RNA sequencing analysis of cardiac tissue lysates were performed to detect overall cMyBP-C protein and mRNA levels. Cellular expression of cMyBP-C and α-actin was obtained by immunofluorescence staining. Quantification of cell-to-cell variation of cMyBP-C expression between cardiomyocytes was measured by determining the ratio of cMyBP-C:α-actin stained area of each cell. RESULTS: Protein and mRNA analysis revealed significantly reduced cMyBP-C levels in MYBPC3mut patients compared with HCMsmn patients (0.73 ± 0.09 vs. 1.0 ± 0.15, p < .05; 162.3 ± 16.4 vs. 326.2 ± 41.9 RPKM, p = .002), without any sign of truncated proteins. Immunofluorescence staining of individual cardiomyocytes in HCMsmn patients demonstrated homogenous and equal cMyBP-C:α-actin staining ratio. In contrast, MYBPC3mut patients demonstrated inhomogeneous staining patterns with a large intercellular variability per patient. Coefficient of variance for cMyBP-C/α-actin staining for each patient showed a significant difference between both groups (17.30 ± 4.08 vs. 5.18 ± 0.65% in MYBPC3mut vs. HCMsmn, p = .02). CONCLUSION: 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