Preserved cross-bridge kinetics in human hypertrophic cardiomyopathy patients with MYBPC3 mutations

Abstract

Mutations in the MYBPC3 gene, encoding cardiac myosin binding protein C (cMyBP-C) are frequent causes of hypertrophic cardiomyopathy (HCM). Previously, we have presented evidence for reduced cMyBP-C expression (haploinsufficiency), in patients with a truncation mutation in MYBPC3. In mice, lacking cMyBP-C cross-bridge kinetics was accelerated. In this study, we investigated whether cross-bridge kinetics was altered in myectomy samples from HCM patients harboring heterozygous MYBPC3 mutations (MYBPC3mut). Isometric force and the rate of force redevelopment (k tr) at different activating Ca(2+) concentrations were measured in mechanically isolated Triton-permeabilized cardiomyocytes from MYBPC3mut (n = 18) and donor (n = 7) tissue. Furthermore, the stretch activation response of cardiomyocytes was measured in tissue from eight MYBPC3mut patients and five donors to assess the rate of initial force relaxation (k 1) and the rate and magnitude of the transient increase in force (k 2 and P 3, respectively) after a rapid stretch. Maximal force development of the cardiomyocytes was reduced in MYBPC3mut (24.5 ± 2.3 kN/m(2)) compared to donor (34.9 ± 1.6 kN/m(2)). The rates of force redevelopment in MYBPC3mut and donor over a range of Ca(2+) concentrations were similar (k tr at maximal activation: 0.63 ± 0.03 and 0.75 ± 0.09 s(-1), respectively). Moreover, the stretch activation parameters did not differ significantly between MYBPC3mut and donor (k 1: 8.5±0.5 and 8.8 ± 0.4 s(-1); k 2: 0.77 ± 0.06 and 0.74 ± 0.09 s(-1); P 3: 0.08 ± 0.01 and 0.09 ± 0.01, respectively). Incubation with protein kinase A accelerated k 1 in MYBPC3mut and donor to a similar extent. Our experiments indicate that, at the cMyBP-C expression levels in this patient group (63 ± 6 % relative to donors), cross-bridge kinetics are preserved and that the depressed maximal force development is not explained by perturbation of cross-bridge kinetics.

Contractile Defect Caused by Mutation in MYBPC3 Revealed under Conditions Optimized for Human PSC-Cardiomyocyte Function

“…This result was also observed following shRNA-mediated MYBPC3 knockdown in otherwise normal cells. Our results are supported by measurements in adult patient-derived cells assessed in vitro where a 30%–40% decrease in maximum Ca 2+ -activated force development has been observed in cells with the c.2373insG mutation, and a mechanism of haploinsufficiency suggested ( van Dijk et al., 2009 , van Dijk et al., 2014 , Witjas-Paalberends et al., 2013 ). Importantly, the force generation defects we observed here were in non-hypertrophic cells, suggesting a primary event not consequential to hypertrophy and related maladaptive processes.…”

The Genetic Landscape of Cardiomyopathy and Its Role in Heart Failure

“…HCM-associated MYBPC3 mutations, especially those that reduce the amount of cMyBP-C, promote a loss of cross-bridge cycling inhibition. The loss of cMyBP-C regulation has been shown to decrease maximal force development in samples of human tissue from mutation carriers (van Dijk et al, 2014) and in mouse models of disease (Barefield et al, 2014a; Harris et al, 2002). However, these MYBPC3 mutations have been shown to increase the energetic cost of contraction similar to MYH7 mutations (Witjas-Paalberends et al, 2014b).…”

The Sydney Heart Bank: improving translational research while eliminating or reducing the use of animal models of human heart disease

“…They showed that, although maximal force development was reduced, the rates of force redevelopment, stretch activation and cross-bridge kinetics did not differ significantly. This suggested that cross-bridge kinetics were not altered, a finding that was consistent with haploinsufficiency (van Dijk et al 2013). In another paper, Kuster et al (2013) hypothesized that microRNAs played a role in HCM.…”