Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL.
Department of Neurology, University of Miami Miller School of Medicine, Miami, FL.
J Gen Physiol. 2021 Jul 5;153(7). doi: 10.1085/jgp.202012801. Epub 2021 May 20.
In this study, we assessed the super relaxed (SRX) state of myosin and sarcomeric protein phosphorylation in two pathological models of cardiomyopathy and in a near-physiological model of cardiac hypertrophy. The cardiomyopathy models differ in disease progression and severity and express the hypertrophic (HCM-A57G) or restrictive (RCM-E143K) mutations in the human ventricular myosin essential light chain (ELC), which is encoded by the MYL3 gene. Their effects were compared with near-physiological heart remodeling, represented by the N-terminally truncated ELC (Δ43 ELC mice), and with nonmutated human ventricular WT-ELC mice. The HCM-A57G and RCM-E143K mutations had antagonistic effects on the ATP-dependent myosin energetic states, with HCM-A57G cross-bridges fostering the disordered relaxed (DRX) state and the RCM-E143K model favoring the energy-conserving SRX state. The HCM-A57G model promoted the switch from the SRX to DRX state and showed an ∼40% increase in myosin regulatory light chain (RLC) phosphorylation compared with the RLC of normal WT-ELC myocardium. On the contrary, the RCM-E143K-associated stabilization of the SRX state was accompanied by an approximately twofold lower level of myosin RLC phosphorylation compared with the RLC of WT-ELC. Upregulation of RLC phosphorylation was also observed in Δ43 versus WT-ELC hearts, and the Δ43 myosin favored the energy-saving SRX conformation. The two disease variants also differently affected the duration of force transients, with shorter (HCM-A57G) or longer (RCM-E143K) transients measured in electrically stimulated papillary muscles from these pathological models, while no changes were displayed by Δ43 fibers. We propose that the N terminus of ELC (N-ELC), which is missing in the hearts of Δ43 mice, works as an energetic switch promoting the SRX-to-DRX transition and contributing to the regulation of myosin RLC phosphorylation in full-length ELC mice by facilitating or sterically blocking RLC phosphorylation in HCM-A57G and RCM-E143K hearts, respectively.
在这项研究中，我们评估了两种心肌病病理模型和一种近乎生理的心脏肥大模型中心肌球蛋白和肌节蛋白磷酸化的超松弛（SRX）状态。这些心肌病模型在疾病进展和严重程度上有所不同，并表达了人类心室肌球蛋白必需轻链（ELC）的肥厚（HCM-A57G）或限制（RCM-E143K）突变，该基因由 MYL3 基因编码。我们将它们的作用与近生理心脏重构进行了比较，代表物是 N 端截断的 ELC（Δ43 ELC 小鼠），并与未突变的人类心室 WT-ELC 小鼠进行了比较。HCM-A57G 和 RCM-E143K 突变对 ATP 依赖性肌球蛋白能量状态有拮抗作用，其中 HCM-A57G 交联桥促进无序松弛（DRX）状态，而 RCM-E143K 模型有利于能量保存的 SRX 状态。HCM-A57G 模型促进了从 SRX 到 DRX 状态的转换，与正常 WT-ELC 心肌的肌球蛋白调节轻链（RLC）磷酸化相比，增加了约 40%。相反，与 WT-ELC 相比，RCM-E143K 相关的 SRX 状态的稳定伴随着肌球蛋白 RLC 磷酸化水平约降低两倍。与 WT-ELC 相比，在Δ43 与 WT-ELC 心脏中也观察到 RLC 磷酸化的上调，并且Δ43 肌球蛋白有利于节能的 SRX 构象。两种疾病变体还以不同的方式影响力瞬变的持续时间，在这些病理模型的电刺激乳头肌中测量到较短（HCM-A57G）或较长（RCM-E143K）的力瞬变，而Δ43 纤维则没有变化。我们提出，ELC 的 N 端（N-ELC）缺失了Δ43 心脏中的 N 端，作为一个能量开关，促进了 SRX 到 DRX 的转变，并通过促进或空间上阻止 HCM-A57G 和 RCM-E143K 心脏中的 RLC 磷酸化，有助于调节全长 ELC 小鼠中肌球蛋白 RLC 的磷酸化。
