The contributions of cardiac myosin binding protein C and troponin I phosphorylation to β‐adrenergic enhancement of in vivo cardiac function

Abstract

Key pointsr β-adrenergic stimulation increases cardiac myosin binding protein C (MyBP-C) and troponin I phosphorylation to accelerate pressure development and relaxation in vivo, although their relative contributions remain unknown.r Using a novel mouse model lacking protein kinase A-phosphorylatable troponin I (TnI) and MyBP-C, we examined in vivo haemodynamic function before and after infusion of the β-agonist dobutamine.r Mice expressing phospho-ablated MyBP-C displayed cardiac hypertrophy and prevented full acceleration of pressure development and relaxation in response to dobutamine, whereas expression of phosphor-ablated TnI alone had little effect on the acceleration of contractile function in response to dobutamine.r Our data demonstrate that MyBP-C phosphorylation is the principal mediator of the contractile response to increased β-agonist stimulation in vivo.r These results help us understand why MyBP-C dephosphorylation in the failing heart contributes to contractile dysfunction and decreased adrenergic reserve in response to acute stress.Abstract β-adrenergic stimulation plays a critical role in accelerating ventricular contraction and speeding relaxation to match cardiac output to changing circulatory demands. Two key myofilaments proteins, troponin I (TnI) and myosin binding protein-C (MyBP-C), are phosphorylated following β-adrenergic stimulation; however, their relative contributions to the enhancement of in vivo cardiac contractility are unknown. To examine the roles of TnI and MyBP-C phosphorylation in β-adrenergic-mediated enhancement of cardiac function, transgenic (TG) mice expressing non-phosphorylatable TnI protein kinase A (PKA) residues (i.e. serine to alanine substitution at Ser23/24; TnI PKA− ) were bred with mice expressing non-phosphorylatable MyBP-C PKA residues (i.e. serine to alanine substitution at Ser273, Ser282 and Ser302; MyBPC PKA− ) to generate a novel mouse model expressing non-phosphorylatable PKA residues in TnI and MyBP-C (DBL PKA− ). MyBP-C dephosphorylation produced cardiac hypertrophy and increased wall thickness in MyBPC PKA− and DBL PKA− mice, and in vivo echocardiography and pressure-volume catheterization studies revealed impaired systolic function and prolonged diastolic relaxation compared to wild-type and TnI PKA-mice. Infusion of the β-agonist dobutamine resulted in accelerated rates of pressure development and relaxation in all mice; however, MyBPC PKA− and DBL PKA− mice displayed a blunted contractile response compared to wild-type and TnI PKA-mice. Furthermore, unanaesthesized MyBPC PKA− and DBL PKA− mice displayed depressed maximum systolic pressure in response to dobutamine as measured using implantable telemetry devices. Taken together, our data show that MyBP-C phosphorylation is a critical modulator of the in vivo acceleration of pressure development and relaxation as a result of enhanced β-adrenergic stimulation, and reduced MyBP-C phosphorylation may underlie depressed adrenergic reserve in heart failure. Abbreviations dp/dt, rate of LV pressure ...

Dose-Dependent Effects of the Myosin Activator Omecamtiv Mecarbil on Cross-Bridge Behavior and Force Generation in Failing Human Myocardium

“…41 Thus, slowed k rel at higher OM doses may act to prolong XB-mediated thin filament activation which is a net effect of all bound XBs, thereby prolonging the SET –potentially delaying ventricular pressure decay and reducing diastolic filling. 42 In contrast, incubations of skinned myocardium with 0.5μM OM produced relatively smaller enhancements in force generation, but did not slow k rel , suggesting that it is possible to optimize OM dose to elicit beneficial effects on systolic force generation without the potential adverse impact of excessive prolongation of SET that can infringe on the diastolic filling phase.…”

“…Slowed k rel likely plays a major role in determining the total systolic ejection time (SET) and the commencement of ventricular relaxation and diastolic filling. 42 In particular, in the late systolic ejection phase, during which a substantial amount of blood is pumped into the circulation, the Ca 2+ transient wanes off 43 and XBs begin to rapidly detach due to shortening-induced cooperative deactivation of the thin filaments. 41 Thus, slowed k rel at higher OM doses may act to prolong XB-mediated thin filament activation which is a net effect of all bound XBs, thereby prolonging the SET –potentially delaying ventricular pressure decay and reducing diastolic filling.…”

Genetically Encoded Biosensors Reveal PKA Hyperphosphorylation on the Myofilaments in Rabbit Heart Failure

“…Meanwhile, we observe a high tonic PKA activity on the myofilaments, which is consistent with a relatively high PKA phosphorylation of MyBP-C and TnI in healthy cardiac tissues. 28 …”

Thick Filament Protein Network, Functions, and Disease Association

“…The regulation of MyBP-C via PTM, and particularly phosphorylation, has been a major focus of several groups (199, 213, 347, 394, 451) (Fig. 9 and Table 8).…”