Familial hypertrophic cardiomyopathy: functional effects of myosin mutation R723G in cardiomyocytes

J Mol Cell Cardiol. 2013 Apr;57:13-22. doi: 10.1016/j.yjmcc.2013.01.001. Epub 2013 Jan 11.

Abstract

Familial Hypertrophic Cardiomyopathy (FHC) is frequently caused by mutations in the β-cardiac myosin heavy chain (β-MyHC). To identify changes in sarcomeric function triggered by such mutations, distinguishing mutation effects from other functional alterations of the myocardium is essential. We previously identified a direct effect of mutation R723G (MyHC723) on myosin function in slow Musculus soleus fibers. Here we investigate contractile features of left ventricular cardiomyocytes of FHC-patients with the same MyHC723-mutation and compare these to the soleus data. In mechanically isolated, triton-permeabilized MyHC723-cardiomyocytes, maximum force was significantly lower but calcium-sensitivity was unchanged compared to donor. Conversely, MyHC723-soleus fibers showed significantly higher maximum force and reduced calcium-sensitivity compared to controls. Protein phosphorylation, a potential myocardium specific modifying mechanism, might account for differences compared to soleus fibers. Analysis revealed reduced phosphorylation of troponin I and T, myosin-binding-protein C, and myosin-light-chain 2 in MyHC723-myocardium compared to donor. Saturation of protein-kinaseA phospho-sites led to comparable, i.e., reduced MyHC723-calcium-sensitivity in cardiomyocytes as in M. soleus fibers, while maximum force remained reduced. Myofibrillar disarray and lower density of myofibrils, however, largely account for reduced maximum force in MyHC723-cardiomyocytes. The changes seen when phosphorylation of sarcomeric proteins in myocardium of affected patients is matched to control tissue suggest that the R723G mutation causes reduced Ca(++)-sensitivity in both cardiomyocytes and M. soleus fibers. In MyHC723-myocardium, however, hypophosphorylation can compensate for the reduced calcium-sensitivity, while maximum force generation, lowered by myofibrillar deficiency and disarray, remains impaired, and may only be compensated by hypertrophy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Calcium / physiology
  • Cardiac Myosins / genetics*
  • Cardiac Myosins / metabolism
  • Cardiomyopathy, Hypertrophic, Familial / genetics*
  • Cardiomyopathy, Hypertrophic, Familial / pathology
  • Cardiomyopathy, Hypertrophic, Familial / physiopathology
  • Female
  • Gene Expression
  • Heart Ventricles / pathology
  • Humans
  • Isometric Contraction
  • Male
  • Middle Aged
  • Muscle Proteins / metabolism
  • Mutation, Missense*
  • Myocardial Contraction
  • Myocardium / metabolism
  • Myocytes, Cardiac / metabolism*
  • Myocytes, Cardiac / physiology
  • Myosin Heavy Chains / genetics*
  • Myosin Heavy Chains / metabolism
  • Phosphorylation
  • Protein Processing, Post-Translational
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Sarcomeres / metabolism
  • Troponin / metabolism
  • Young Adult

Substances

  • MYH7 protein, human
  • Muscle Proteins
  • RNA, Messenger
  • Troponin
  • Cardiac Myosins
  • Myosin Heavy Chains
  • Calcium