Cardiac myosin missense mutations cause dilated cardiomyopathy in mouse models and depress molecular motor function

Area of Science:

• Cardiology
• Molecular Biology
• Genetics

Background:

• Dilated cardiomyopathy (DCM) is a significant cause of heart failure, with genetic factors accounting for about 30% of cases.
• Point mutations in cardiac myosin, the heart's molecular motor, are implicated in some genetic forms of DCM.
• The precise molecular mechanics underlying these myosin mutations and their contribution to DCM remain largely undetermined.

Purpose of the Study:

• To investigate the physiological, cellular, and molecular consequences of specific DCM-causing missense mutations (S532P and F764L) in the alpha-cardiac myosin heavy chain.
• To compare the effects of these mutations in engineered murine models against wild-type (WT) mice.
• To elucidate how these myosin mutations impact cardiac function at the molecular level.

Main Methods:

• Engineered murine models expressing DCM-associated alpha-cardiac myosin heavy chain mutations (S532P, F764L).
• Physiological assessments of cardiac morphology and function, including myocyte contractility and left ventricular function.
• In vitro motility assays and actin-activated ATPase activity measurements to assess myosin motor function.
• Single-molecule laser trap experiments to analyze myosin's chemomechanical cycle kinetics.

Main Results:

• Mutant mice exhibited DCM characteristics, including depressed myocyte contractile function preceding ventricular dilation.
• In vitro assays showed reduced actin translocation (V(actin)) and ATPase activity for mutant cardiac myosins, while force generation remained similar.
• Single-molecule studies indicated that the S532P mutation's reduced V(actin) stems from impaired step displacement and altered chemomechanical cycle kinetics.

Conclusions:

• DCM-causing mutations in cardiac myosin lead to depressed molecular motor function.
• This impaired myosin function, characterized by reduced actin translocation and altered kinetics, may be an initiating event in the pathogenesis of pathological cardiac remodeling and dilation.
• Understanding these molecular mechanisms provides insight into the development of heart failure due to genetic cardiomyopathies.