摘要
Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in m>MYBPC3m> encoding cardiac myosin-binding protein C (cMyBP-C). The mechanisms leading from gene mutations to the HCM phenotype remain incompletely understood, partially because current mouse models of HCM do not faithfully reflect the human situation and early hypertrophy confounds the interpretation of functional alterations. The goal of this study was to evaluate whether myofilament Cap>2+p> sensitization and diastolic dysfunction are associated or precede the development of left ventricular hypertrophy (LVH) in HCM. We evaluated the function of skinned and intact cardiac myocytes, as well as the intact heart in a recently developed m>Mybpc3m>-targeted knock-in mouse model carrying a point mutation frequently associated with HCM. Compared to wild-type, 10-week old homozygous knock-in mice exhibited i) higher myofilament Cap>2+p> sensitivity in skinned ventricular trabeculae, ii) lower diastolic sarcomere length, and faster Cap>2+p> transient decay in intact myocytes, and iii) LVH, reduced fractional shortening, lower E/A and E鈥?A鈥? and higher E/E鈥?ratios by echocardiography and Doppler analysis, suggesting systolic and diastolic dysfunction. In contrast, heterozygous knock-in mice, which mimic the human HCM situation, did not exhibit LVH or systolic dysfunction, but exhibited higher myofilament Cap>2+p> sensitivity, faster Cap>2+p> transient decay, and diastolic dysfunction. These data demonstrate that myofilament Cap>2+p> sensitization and diastolic dysfunction are early phenotypic consequences of m>Mybpc3m> mutations independent of LVH. The accelerated Cap>2+p> transients point to compensatory mechanisms directed towards normalization of relaxation. We propose that HCM is a model for diastolic heart failure and this mouse model could be valuable in studying mechanisms and treatment modalities.