Hypercontractile properties of cardiac muscle fibers in a knock-in mouse model of cardiac myosin-binding protein-C.
Myosin-binding protein-C (MyBP-C) is a component of all striated-muscle sarcomeres, with a well established structural role and a possible function for force regulation. Multiple mutations within the gene for cardiac MyBP-C, one of three known isoforms, have been linked to familial hypertrophic cardiomyopathy. Here we generated a knock-in mouse model that carries N-terminal-shortened cardiac MyBP-C. The mutant protein was designed to have a similar size as the skeletal MyBP-C isoforms, whereas known myosin and titin binding sites as well as the phosphorylatable MyBP-C motif were not altered. We have shown that mutant cardiac MyBP-C is readily incorporated into the sarcomeres of both heterozygous and homozygous animals and can still be phosphorylated by cAMP-dependent protein kinase. Although histological characterization of wild-type and mutant hearts did not reveal obvious differences in phenotype, left ventricular fibers from homozygous mutant mice exhibited an increased Ca(2+) sensitivity of force development, particularly at lower Ca(2+) concentrations, whereas maximal active force levels remained unchanged. The results allow us to propose a model of how cMyBP-C may affect myosin-head mobility and to rationalize why N-terminal mutations of the protein in some cases of familial hypertrophic cardiomyopathy could lead to a hypercontractile state.
Witt
C C
CC
Max-Delbrück-Center of Molecular Medicine, D-13122 Berlin, Germany.
Gerull
B
B
Davies
M J
MJ
Centner
T
T
Linke
W A
WA
Thierfelder
L
L
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018390:Gene Targeting; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D051379:Mice; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000096:biosynthesis; D017384:Sequence Deletion; D000099163:Myosin Binding Protein C
D002118:Calcium; D002352:Carrier Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D012333:RNA, Messenger; D000099163:Myosin Binding Protein C