Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH.
J Gen Physiol. 2021 Jul 5;153(7). doi: 10.1085/jgp.202012816.
Omecamtiv mecarbil (OM), a direct myosin motor activator, is currently being tested as a therapeutic replacement for conventional inotropes in heart failure (HF) patients. It is known that HF patients exhibit dysregulated β-adrenergic signaling and decreased cardiac myosin-binding protein C (cMyBPC) phosphorylation, a critical modulator of myocardial force generation. However, the functional effects of OM in conditions of altered cMyBPC phosphorylation have not been established. Here, we tested the effects of OM on force generation and cross-bridge (XB) kinetics using murine myocardial preparations isolated from wild-type (WT) hearts and from hearts expressing S273A, S282A, and S302A substitutions (SA) in the M domain, between the C1 and C2 domains of cMyBPC, which cannot be phosphorylated. At submaximal Ca2+ activations, OM-mediated force enhancements were less pronounced in SA than in WT myocardial preparations. Additionally, SA myocardial preparations lacked the dose-dependent increases in force that were observed in WT myocardial preparations. Following OM incubation, the basal differences in the rate of XB detachment (krel) between WT and SA myocardial preparations were abolished, suggesting that OM differentially affects the XB behavior when cMyBPC phosphorylation is reduced. Similarly, in myocardial preparations pretreated with protein kinase A to phosphorylate cMyBPC, incubation with OM significantly slowed krel in both the WT and SA myocardial preparations. Collectively, our data suggest there is a strong interplay between the effects of OM and XB behavior, such that it effectively uncouples the sarcomere from cMyBPC phosphorylation levels. Our findings imply that OM may significantly alter the in vivo cardiac response to β-adrenergic stimulation.
肌球蛋白马达激活剂奥马环素（OM）目前正在作为心力衰竭（HF）患者传统正性肌力药物的替代疗法进行测试。已知 HF 患者表现出β-肾上腺素能信号的失调和心肌肌球蛋白结合蛋白 C（cMyBPC）磷酸化减少，这是心肌力产生的关键调节剂。然而，OM 在 cMyBPC 磷酸化改变的情况下的功能影响尚未确定。在这里，我们使用来自野生型（WT）心脏和在 cMyBPC 的 C1 和 C2 结构域之间的 M 结构域中表达 S273A、S282A 和 S302A 取代（SA）的心脏的鼠心肌制剂测试了 OM 对力产生和交联（XB）动力学的影响，这些取代物不能被磷酸化。在亚最大 Ca2+激活下，SA 心肌制剂中的 OM 介导的力增强作用不如 WT 心肌制剂明显。此外，SA 心肌制剂缺乏在 WT 心肌制剂中观察到的力的剂量依赖性增加。OM 孵育后，WT 和 SA 心肌制剂之间 XB 脱离速率（krel）的基础差异消失，这表明当 cMyBPC 磷酸化减少时，OM 对 XB 行为产生不同的影响。类似地，在用蛋白激酶 A 预处理以磷酸化 cMyBPC 的心肌制剂中，在 WT 和 SA 心肌制剂中，OM 孵育均显著减慢了 krel。总的来说，我们的数据表明 OM 的作用和 XB 行为之间存在强烈的相互作用，使得它有效地将肌节与 cMyBPC 磷酸化水平解耦。我们的发现表明，OM 可能会显著改变体内对β-肾上腺素能刺激的心脏反应。
