HCM-causing mutations increased maximal force-generating capacity by 50% and 80% compared to wild type, whereas DCM-causing mutations led to depressed function.
Do HCM and DCM mutations differentially affect the molecular force generation of mouse α-cardiac myosin?
HCM-causing mutations lead to enhanced molecular force generation, whereas DCM-causing mutations lead to depressed function, suggesting distinct mechanical alterations initiate disparate phenotypic responses.
Point mutations in cardiac myosin, the heart's molecular motor, produce distinct clinical phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathy. Do mutations alter myosin's molecular mechanics in a manner that is predictive of the clinical outcome? We have directly characterized the maximal force-generating capacity (F(max)) of two HCM (R403Q, R453C) and two DCM (S532P, F764L) mutant myosins isolated from homozygous mouse models using a novel load-clamped laser trap assay. F(max) was 50% (R403Q) and 80% (R453C) greater for the HCM mutants compared with the wild type, whereas F(max) was severely depressed for one of the DCM mutants (65% S532P). Although F(max) was normal for the F764L DCM mutant, its actin-activated ATPase activity and actin filament velocity (V(actin)) in a motility assay were significantly reduced (Schmitt JP, Debold EP, Ahmad F, Armstrong A, Frederico A, Conner DA, Mende U, Lohse MJ, Warshaw D, Seidman CE, Seidman JG. Proc Natl Acad Sci USA 103: 14525-14530, 2006.). These F(max) data combined with previous V(actin) measurements suggest that HCM and DCM result from alterations to one or more of myosin's fundamental mechanical properties, with HCM-causing mutations leading to enhanced but DCM-causing mutations leading to depressed function. These mutation-specific changes in mechanical properties must initiate distinct signaling cascades that ultimately lead to the disparate phenotypic responses observed in HCM and DCM.
Debold et al. (2007) studied Hypertrophic and dilated cardiomyopathy. HCM and DCM mutant myosins vs. Wild type myosin was evaluated on Maximal force-generating capacity (F(max)). HCM-causing mutations increased maximal force-generating capacity by 50% and 80% compared to wild type, whereas DCM-causing mutations led to depressed function.
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