Perturbed Length-Dependent Activation in Human Hypertrophic Cardiomyopathy with Missense Sarcomeric Gene Mutations
Rationale: High myofilament Ca2+-sensitivity has been proposed as trigger of disease pathogenesis in familial hypertrophic cardiomyopathy (HCM) based on in vitro and transgenic mice studies. However, myofilament Ca2+-sensitivity depends on protein phosphorylation and muscle length and at present data in human are scarce.
Objective:To investigate if high myofilament Ca2+-sensitivity and perturbed length-dependent activation is characteristic for human HCM with mutations in thick and thin filament proteins.
Methods and Results:: Cardiac samples from HCM patients harboring mutations in genes encoding thick (MYH7, MYBPC3) and thin (TNNT2, TNNI3, TPM1) filament proteins were compared with sarcomere mutation-negative HCM (HCMsmn) and non-failing donors. Cardiomyocyte force measurements showed higher myofilament Ca2+-sensitivity in all HCM samples and low phosphorylation of protein kinase A (PKA)-targets compared to donors. After exogenous PKA treatment, myofilamentCa2+-sensitivity was either similar (MYBPC3mut, TPM1mut, HCMsmn), higher (MYH7mut, TNNT2mut) or even significantly lower (TNNI3mut) compared to donors. Length-dependent activation was significantly smaller in all HCM than in donor samples. PKA treatment increased phosphorylation of PKA-targets in HCM myocardium and normalized length-dependent activation to donor values in HCMsmn and HCM with truncating MYBPC3 mutations, but not in HCM with missense mutations. Replacement of mutant by wild-type troponin in TNNT2mu and TNNI3mut corrected length-dependent activation to donor values.
Conclusions: High myofilament Ca2+-sensitivity is a common characteristic of human HCM and partly reflects hypophosphorylation of PKA-targets compared to donors. Length-dependent sarcomere activation is perturbed by missense mutations, possibly via post-translational modifications other than PKA-hypophosphorylation or altered protein-protein interactions, and represents a common pathomechanism in HCM.
- Received October 31, 2012.
- Revision received March 13, 2013.
- Accepted March 18, 2013.