Effects of Sarcomere Activators and Inhibitors Targeting Myosin Cross-Bridges on Ca²⁺-Activation of Mature and Immature Mouse Cardiac Myofilaments

Abstract

We tested the hypothesis that isoform shifts in sarcomeres of the immature heart modify the effect of cardiac myosin-directed sarcomere inhibitors and activators. Omecamtiv mecarbil (OM) activates tension and is in clinical trials for the treatment of adult acute and chronic heart failure.Mavacamten (Mava) inhibits tension and is in clinical trials to relieve hyper-contractility and outflow obstruction in advanced genetic hypertrophic cardiomyopathy (HCM) linked commonly to mutations in sarcomeric proteins. To address the effect of these agents in developing sarcomeres we isolated heart fiber bundles, extracted membranes with Triton X-100, and measured tension developed over a range of Ca 2+ concentrations with and without OM or Mava treatment. We made measurements in fiber bundles from hearts of adult non-transgenic controls (NTG) expressing cardiac troponin I (cTnI), and from hearts of transgenic mice (TG-ssTnI) expressing the fetal/neonatal form, slow skeletal troponin I (ssTnI). We also compared fibers from 7+14-day-old NTG mice expressing ssTnI and cTnI. These studies were repeated with 7+14-day old transgenic mice (TG-cTnT-R92Q) expressing a mutant form of cardiac TnT (cTnT) linked to HCM. OM increased Ca 2+ -sensitivity and decreased cooperative activation in both ssTnI-and cTnI-regulated myofilaments with a similar effect reducing sub-maximal tension in immature and mature myofilaments. Although Mava decreased tension similarly in cTnI-and ssTnI-regulated myofilaments controlled either by cTnT or cTnT-R92Q, its effect involved a depressed Ca 2+ -sensitivity in the mature cTnT-R92-myofilaments. Our data demonstrate an influence of myosin and thin filament-associated proteins on the actions of myosin-directed agents such as OM and Mava. Significance StatementThe effects of myosin-targeted activators and inhibitors on Ca 2+ -activated tension in developing cardiac sarcomeres presented here provide novel, ex-vivo evidence as to their actions in earlystage cardiac disorders. These studies advance understanding of the molecular mechanisms of This article has not been copyedited and formatted. The final version may differ from this version.

Emerging Concepts of Mechanisms Controlling Cardiac Tension: Focus on Familial Dilated Cardiomyopathy (DCM) and Sarcomere-Directed Therapies

“…We reported in vitro studies that demonstrated that OM increased the Ca 2+ sensitivity of Tm-E54K myofilaments [109]. Although also reported by others, the effect of OM to increase sarcomere Ca 2+ sensitivity and modify cooperative activation is not generally discussed in considerations of its mechanism of action [110,111]. Kieu et al [112] reported that at physiological temperatures, there is a prominent effect of OM in increasing skinned fiber sub-maximal tensions in the force-Ca 2+ relation with no effect on maximum tension.…”

Emerging Concepts of Mechanisms Controlling Cardiac Tension: Focus on Familial Dilated Cardiomyopathy (DCM) and Sarcomere-Directed Therapies

“…We reported in vitro studies that demonstrated that OM increased the Ca-sensitivity of Tm-E54K myofilaments [105]. Although we and others had previously reported an effect of OM to increase sarcomere Ca-sensitivity [106,107], and modify cooperative activation, this effect is not generally discussed in considering the mechanism of action. Kieu et al [108] reported that at physiological temperatures there is a prominent effect of OM in increasing skinned fiber sub-maximal tensions in the force-Ca relation with no effect on maximum tension.…”

Danshensu exerts cardioprotective effects in rats with acute myocardial infarction via reduction of infiltration of inflammatory cells and mitigation of myocardial fibrosis

“…It is a serious disease often seen in cardiology clinics. When AMI occurs in heart failure, the main pathophysiological event is cardiac remodeling which leads to apoptosis and hypertrophy of cardiac cells, as well as myocardial fibrosis and inflammatory response [2]. The use of anti-inflammatory drugs results in significant inhibition of AMI, thereby protecting myocardial function, and preventing extracellular matrix accumulation.…”