Cardiac myosin‐binding protein C as a candidate biomarker in heart failure: rational but not revolutionary

Rationale : A stable 40-kDa fragment is produced from cardiac myosin-binding protein C when the heart is stressed using a stimulus, such as ischemia-reperfusion injury. Elevated levels of the fragment can be detected in the diseased mouse and human heart, but its ability to interfere with normal cardiac function in the intact animal is unexplored. Objective : To understand the potential pathogenicity of the 40-kDa fragment in vivo and to investigate the molecular pathways that could be targeted for potential therapeutic intervention. Methods and Results : We generated cardiac myocyte–specific transgenic mice using a Tet-Off inducible system to permit controlled expression of the 40-kDa fragment in cardiomyocytes. When expression of the 40-kDa protein is induced by crossing the responder animals with tetracycline transactivator mice under conditions in which substantial quantities approximating those observed in diseased hearts are reached, the double-transgenic mice subsequently experience development of sarcomere dysgenesis and altered cardiac geometry, and the heart fails between 12 and 17 weeks of age. The induced double-transgenic mice had development of cardiac hypertrophy with myofibrillar disarray and fibrosis, in addition to activation of pathogenic MEK–ERK pathways. Inhibition of MEK–ERK signaling was achieved by injection of the mitogen-activated protein kinase (MAPK)/ERK inhibitor U0126. The drug effectively improved cardiac function, normalized heart size, and increased probability of survival. Conclusions : These results suggest that the 40-kDa cardiac myosin-binding protein C fragment, which is produced at elevated levels during human cardiac disease, is a pathogenic fragment that is sufficient to cause hypertrophic cardiomyopathy and heart failure.

Download Full-text

Phosphorylation of cardiac myosin–binding protein-C contributes to calcium homeostasis

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.013296 ◽

2020 ◽

Vol 295 (32) ◽

pp. 11275-11291 ◽

Cited By ~ 1

Author(s):

Mohit Kumar ◽

Kobra Haghighi ◽

Evangelia G. Kranias ◽

Sakthivel Sadayappan

Keyword(s):

Heart Failure ◽

Protein C ◽

Contractile Function ◽

Binding Protein ◽

Stress Conditions ◽

Calcium Handling ◽

Cardiac Myosin ◽

Myosin Binding Protein ◽

Myosin Binding Protein C ◽

Myosin Binding

Cardiac myosin–binding protein-C (cMyBP-C) is highly phosphorylated under basal conditions. However, its phosphorylation level is decreased in individuals with heart failure. The necessity of cMyBP-C phosphorylation for proper contractile function is well-established, but the physiological and pathological consequences of decreased cMyBP-C phosphorylation in the heart are not clear. Herein, using intact adult cardiomyocytes from mouse models expressing phospho-ablated (AAA) and phosphomimetic (DDD) cMyBP-C as well as controls, we found that cMyBP-C dephosphorylation is sufficient to reduce contractile parameters and calcium kinetics associated with prolonged decay time of the calcium transient and increased diastolic calcium levels. Isoproterenol stimulation reversed the depressive contractile and Ca2+-kinetic parameters. Moreover, caffeine-induced calcium release yielded no difference between AAA/DDD and controls in calcium content of the sarcoplasmic reticulum. On the other hand, sodium–calcium exchanger function and phosphorylation levels of calcium-handling proteins were significantly decreased in AAA hearts compared with controls. Stress conditions caused increases in both spontaneous aftercontractions in AAA cardiomyocytes and the incidence of arrhythmias in vivo compared with the controls. Treatment with omecamtiv mecarbil, a positive cardiac inotropic drug, rescued the contractile deficit in AAA cardiomyocytes, but not the calcium-handling abnormalities. These findings indicate a cascade effect whereby cMyBP-C dephosphorylation causes contractile defects, which then lead to calcium-cycling abnormalities, resulting in aftercontractions and increased incidence of cardiac arrhythmias under stress conditions. We conclude that improvement of contractile deficits alone without improving calcium handling may be insufficient for effective management of heart failure.

Download Full-text