Cardiac Myosin-Binding Protein C Is Required for Complete Relaxation in Intact Myocytes

Pohlmann, Lutz; Kröger, Irena; Vignier, Nicolas; Schlossarek, Saskia; Krämer, Elisabeth; Coirault, Catherine; Sultan, Karim R.; El‐Armouche, Ali; Winegrad, Saul; Eschenhagen, Thomas; Carrier, Lucie

doi:10.1161/circresaha.107.158774

Cited by 116 publications

(106 citation statements)

References 49 publications

(47 reference statements)

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“…The cMyBP-C dependence of myofilament Ca 2+ sensitivity is controversial, which is possibly due to differences in models and experimental conditions. At short SL (1.8-2.1 μm), Ca 2+ sensitivity is increased after partial extraction of cMyBP-C [28], replacement by a truncated form [50], and in cMyBP-C Knockout mouse model [10,41]. As have other groups, we recently observed that at long SL (>2.2 μm) Ca 2+ sensitivity is not affected by ablation of cMyBP-C [10,23,46].…”

Section: Myosin-binding Protein-c Modulationsupporting

confidence: 65%

Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch

Mou

Guennec

Mosca

et al. 2008

Pflugers Arch - Eur J Physiol

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The present study examined the contribution of myofilament contractile proteins to regional function in guinea pig myocardium. We investigated the effect of stretch on myofilament contractile proteins, Ca 2+ sensitivity, and cross-bridge cycling kinetics (K tr ) of force in single skinned cardiomyocytes isolated from the sub-endocardial (ENDO) or sub-epicardial (EPI) layer. As observed in other species, ENDO cells were stiffer, and Ca 2+ sensitivity of force at long sarcomere length was higher compared with EPI cells. Maximal K tr was unchanged by stretch, but was higher in EPI cells possibly due to a higher α-MHC content. Submaximal Ca 2+ -activated K tr increased only in ENDO cells with stretch. Stretch of skinned ENDO muscle strips induced increased phosphorylation in both myosinbinding protein C and myosin light chain 2. We concluded that transmural MHC isoform expression and differential regulatory protein phosphorylation by stretch contributes to regional differences in stretch modulation of activation in guinea pig left ventricle.

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Section: Myosin-binding Protein-c Modulationsupporting

confidence: 65%

Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch

Mou

Guennec

Mosca

et al. 2008

Pflugers Arch - Eur J Physiol

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“…Loss of cMyBP-C accelerates crossbridge cycling and impairs kinetics of contraction and relaxation. 24,25,27 Complete knockout of cMyBP-C resulted in profound cardiac hypertrophy and impaired contractile function in mice. 29,30 Surprisingly, transgenic mice harboring only 40% of the normally expressed full-length cMyBP-C did not have LV hypertrophy and showed preserved cardiac function.…”

Section: Discussionmentioning

confidence: 99%

“…43,44 Similarly, a greater myofilament Ca 2ϩ sensitivity was found in skinned myocytes at short sarcomere length from cMyBP-C knockout mice, 45 and a greater sensitivity to external Ca 2ϩ was found in cMyBP-C knockout intact atrial tissue. 25 Hence, the frameshift MYBPC3 mutations inducing cMyBP-C haploinsufficiency may directly increase Ca 2ϩ sensitivity. On the other hand, increased myofilament Ca 2ϩ sensitivity has also been found in end-stage failing human myocardium (idiopathic dilated cardiomyopathy) without known mutations in sarcomeric proteins.…”

Section: Discussionmentioning

confidence: 99%

Cardiac Myosin-Binding Protein C Mutations and Hypertrophic Cardiomyopathy

et al. 2009

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Background-Mutations in the MYBPC3 gene, encoding cardiac myosin-binding protein C (cMyBP-C), are a frequent cause of familial hypertrophic cardiomyopathy. In the present study, we investigated whether protein composition and function of the sarcomere are altered in a homogeneous familial hypertrophic cardiomyopathy patient group with frameshift mutations in MYBPC3 (MYBPC3 mut ). Methods and Results-Comparisons were made between cardiac samples from MYBPC3 mutant carriers (c.2373dupG, nϭ7; c.2864_2865delCT, nϭ4) and nonfailing donors (nϭ13). Western blots with the use of antibodies directed against cMyBP-C did not reveal truncated cMyBP-C in MYBPC3 mut . Protein expression of cMyBP-C was significantly reduced in MYBPC3 mut by 33Ϯ5%. Cardiac MyBP-C phosphorylation in MYBPC3 mut samples was similar to the values in donor samples, whereas the phosphorylation status of cardiac troponin I was reduced by 84Ϯ5%, indicating divergent phosphorylation of the 2 main contractile target proteins of the ␤-adrenergic pathway. Force measurements in mechanically isolated Triton-permeabilized cardiomyocytes demonstrated a decrease in maximal force per crosssectional area of the myocytes in MYBPC3 mut (20.2Ϯ2.7 kN/m 2 ) compared with donor (34.5Ϯ1.1 kN/m 2 ). Moreover, Ca 2ϩ sensitivity was higher in MYBPC3 mut (pCa 50 ϭ5.62Ϯ0.04) than in donor (pCa 50 ϭ5.54Ϯ0.02), consistent with reduced cardiac troponin I phosphorylation. Treatment with exogenous protein kinase A, to mimic ␤-adrenergic stimulation, did not correct reduced maximal force but abolished the initial difference in Ca 2ϩ sensitivity between MYBPC3 mut (pCa 50 ϭ5.46Ϯ0.03) and donor (pCa 50 ϭ5.48Ϯ0.02). Conclusions-Frameshift MYBPC3 mutations cause haploinsufficiency, deranged phosphorylation of contractile proteins, and reduced maximal force-generating capacity of cardiomyocytes. The enhanced Ca 2ϩ sensitivity in MYBPC3 mut is due to hypophosphorylation of troponin I secondary to mutation-induced dysfunction.

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“…This is indeed observed in cMyBP-C KO mice with a HCM phenotype, where crossbridge cycling is accelerated in membrane-permeabilized cardiomyocytes (43,44), consistent with impaired relaxation of intact cardiomyocytes (48). Pohlmann et al (48) observed that cardiomyocytes with total cMyBP-C ablation contracted at very low Ca 2+ levels and had lower diastolic sarcomere length, which was associated with high actin-myosin interactions (i.e., diastolic length was partially normalized to controls following addition of the crossbridge inhibitor BDM). This is also consistent with the augmented sarcomere stiffness observed in MYBPC3 mutations (Fig.…”

Section: Discussionmentioning

confidence: 99%

ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease

Sequeira

Najafi

Wijnker

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Diastolic dysfunction is general to all idiopathic dilated (IDCM) and hypertrophic cardiomyopathy (HCM) patients. Relaxation deficits may result from increased actin-myosin formation during diastole due to altered tropomyosin position, which blocks myosin binding to actin in the absence of Ca 2+ . We investigated whether ADP-stimulated force development (without Ca 2+ ) can be used to reveal changes in actin-myosin blockade in human cardiomyopathy cardiomyocytes. Cardiac samples from HCM patients, harboring thick-filament (MYH7 mut , MYBPC3 mut ) and thin-filament (TNNT2 mut , TNNI3 mut ) mutations, and IDCM were compared with sarcomere mutation-negative HCM (HCM smn ) and nonfailing donors. Myofilament ADP sensitivity was higher in IDCM and HCM compared with donors, whereas it was lower for MYBPC3. Increased ADP sensitivity in IDCM, HCM smn , and MYH7 mut was caused by low phosphorylation of myofilament proteins, as it was normalized to donors by protein kinase A (PKA) treatment. Troponin exchange experiments in a TNNT2 mut sample corrected the abnormal actin-myosin blockade. In MYBPC3 trunc samples, ADP sensitivity highly correlated with cardiac myosin-binding protein-C (cMyBP-C) protein level. Incubation of cardiomyocytes with cMyBP-C antibody against the actin-binding N-terminal region reduced ADP sensitivity, indicative of cMyBP-C's role in actin-myosin regulation. In the presence of Ca 2+ , ADP increased myofilament force development and sarcomere stiffness. Enhanced sarcomere stiffness in sarcomere mutation-positive HCM samples was irrespective of the phosphorylation background. In conclusion, ADP-stimulated contraction can be used as a tool to study how protein phosphorylation and mutant proteins alter accessibility of myosin binding on actin. In the presence of Ca 2+ , pathologic [ADP] and low PKA-phosphorylation, high actin-myosin formation could contribute to the impaired myocardial relaxation observed in cardiomyopathies.H eart failure (HF) is a syndrome clinically defined as the inability of the heart to sufficiently supply blood to organs and tissues (1). Systolic dysfunction is present in approximately one-half of the HF population, whereas diastolic dysfunction is a common feature in almost all HF patients (2). Moreover, in hypertrophic cardiomyopathy (HCM), which is caused by mutations in genes encoding thinand thick-filament proteins, impaired diastolic function is frequently observed (3). Impaired relaxation of the heart may be caused by high myofilament Ca 2+ sensitivity. This increased sensitivity for Ca 2+ would result in residual myofilament activation at diastolic [Ca 2+ ], which may delay the onset of ventricular relaxation and limit proper filling of the heart. High myofilament Ca 2+ sensitivity has been observed in both acquired and genetic forms of cardiomyopathy (3, 4). In human idiopathic dilated cardiomyopathy (IDCM), high myofilament Ca 2+ sensitivity has been associated with reduced β-adrenergic receptor-mediated phosphorylation by protein kinase A (PKA) (4). Reduced PKA phospho...

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Cardiac Myosin-Binding Protein C Is Required for Complete Relaxation in Intact Myocytes

Cited by 116 publications

References 49 publications

Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch

Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch

Cardiac Myosin-Binding Protein C Mutations and Hypertrophic Cardiomyopathy

ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease

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