title: Acceleration of crossbridge kinetics by protein kinase A phosphorylation of cardiac myosin binding protein C modulates cardiac function.
abstract: Normal cardiac function requires dynamic modulation of contraction. beta1-adrenergic-induced protein kinase (PK)A phosphorylation of cardiac myosin binding protein (cMyBP)-C may regulate crossbridge kinetics to modulate contraction. We tested this idea with mechanical measurements and echocardiography in a mouse model lacking 3 PKA sites on cMyBP-C, ie, cMyBP-C(t3SA). We developed the model by transgenic expression of mutant cMyBP-C with Ser-to-Ala mutations on the cMyBP-C knockout background. Western blots, immunofluorescence, and in vitro phosphorylation combined to show that non-PKA-phosphorylatable cMyBP-C expressed at 74% compared to normal wild-type (WT) and was correctly positioned in the sarcomeres. Similar expression of WT cMyBP-C at 72% served as control, ie, cMyBP-C(tWT). Skinned myocardium responded to stretch with an immediate increase in force, followed by a transient relaxation of force and finally a delayed development of force, ie, stretch activation. The rate constants of relaxation, k(rel) (s-1), and delayed force development, k(df) (s-1), in the stretch activation response are indicators of crossbridge cycling kinetics. cMyBP-C(t3SA) myocardium had baseline k(rel) and k(df) similar to WT myocardium, but, unlike WT, k(rel) and k(df) were not accelerated by PKA treatment. Reduced dobutamine augmentation of systolic function in cMyBP-C(t3SA) hearts during echocardiography corroborated the stretch activation findings. Furthermore, cMyBP-C(t3SA) hearts exhibited basal echocardiographic findings of systolic dysfunction, diastolic dysfunction, and hypertrophy. Conversely, cMyBP-C(tWT) hearts performed similar to WT. Thus, PKA phosphorylation of cMyBP-C accelerates crossbridge kinetics and loss of this regulation leads to cardiac dysfunction.
authors.affiliation: Department of Physiology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA.
authors.forename: Carl W
authors.initials: CW
authors.lastname: Tong
authors.forename: Julian E
authors.initials: JE
authors.lastname: Stelzer
authors.forename: Marion L
authors.initials: ML
authors.lastname: Greaser
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Powers
authors.forename: Richard L
authors.initials: RL
authors.lastname: Moss
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D006332:Cardiomegaly / Q000000981:diagnostic imaging / Q000201:enzymology* / Q000503:physiopathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004280:Dobutamine / Q000494:pharmacology; D015150:Echocardiography, Doppler; D006801:Humans; D007700:Kinetics; D040542:Mechanotransduction, Cellular; D051379:Mice; D008822:Mice, Transgenic; D053580:Muscle Strength; D009154:Mutation; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D009210:Myofibrils / Q000201:enzymology; D010766:Phosphorylation; D012518:Sarcomeres / Q000201:enzymology; D019210:Troponin I / Q000378:metabolism; D000099163:Myosin Binding Protein C
chemical_list: D000318:Adrenergic beta-Agonists; D002352:Carrier Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D004280:Dobutamine; D019210:Troponin I; D000099163:Myosin Binding Protein C
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