title: Familial hypertrophic cardiomyopathy: functional effects of myosin mutation R723G in cardiomyocytes.
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.
authors: Molecular and Cell Physiology, Hannover Medical School, D-30625 Hannover, Germany. Kraft.Theresia@mh-hannover.de
authors: Theresia
authors: T
authors: Kraft
authors: E Rosalie
authors: ER
authors: Witjas-Paalberends
authors: Nicky M
authors: NM
authors: Boontje
authors: Snigdha
authors: S
authors: Tripathi
authors: Almuth
authors: A
authors: Brandis
authors: Judith
authors: J
authors: Montag
authors: Julie L
authors: JL
authors: Hodgkinson
authors: Antonio
authors: A
authors: Francino
authors: Francisco
authors: F
authors: Navarro-Lopez
authors: Bernhard
authors: B
authors: Brenner
authors: Ger J M
authors: GJ
authors: Stienen
authors: Jolanda
authors: J
authors: van der Velden
mesh_terms: D000328:Adult; D002118:Calcium / Q000502:physiology; D024722:Cardiac Myosins / Q000235:genetics* / Q000378:metabolism; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D005260:Female; D015870:Gene Expression; D006352:Heart Ventricles / Q000473:pathology; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism; D020125:Mutation, Missense; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism; D014336:Troponin / Q000378:metabolism; D055815:Young Adult
chemical_list: C501641:MYH7 protein, human; D009124:Muscle Proteins; D012333:RNA, Messenger; D014336:Troponin; D024722:Cardiac Myosins; D018995:Myosin Heavy Chains; D002118:Calcium