We investigated the impact of the phosphomimetic (Ser15 → Asp15) myosin regulatory light chain (S15D‐RLC) on the Super‐Relaxed (SRX) state of myosin using previously characterized transgenic (Tg) S15D‐D166V rescue mice, comparing them to the Hypertrophic Cardiomyopathy (HCM) Tg‐D166V model and wild‐type (WT) RLC mice. In the Tg‐D166V model, we observed a disruption of the SRX state, resulting in a transition from SRX to DRX (Disordered Relaxed) state, which explains the hypercontractility of D166V‐mutated myosin motors. The presence of the S15D moiety in Tg‐S15D‐D166V mice restored the SRX/DRX balance to levels comparable to Tg‐WT, thus mitigating the hypercontractile behavior associated with the HCM‐D166V mutation. Additionally, we investigated the impact of delivering the S15D‐RLC molecule to the hearts of Tg‐D166V mice via adeno‐associated virus (AAV9) and compared their condition to AAV9‐empty vector‐injected or non‐injected Tg‐D166V animals. Tg‐D166V mice injected with AAV9 S15D‐RLC exhibited a significantly higher proportion of myosin heads in the SRX state compared to those injected with AAV9 empty vector or left non‐injected. No significant effect was observed in Tg‐WT hearts treated similarly. These findings suggest that AAV9‐delivered phosphomimetic S15D‐RLC modality mitigates the abnormal Tg‐D166V phenotype without impacting the normal function of Tg‐WT hearts. Global longitudinal strain analysis supported these observations, indicating that the S15D moiety can alleviate the HCM‐D166V phenotype by restoring SRX stability and the SRX ↔ DRX equilibrium.

中文翻译：

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肌球蛋白调节轻链磷酸化拯救肥厚型心肌病的机制基础

我们使用先前表征的转基因 (Tg) S15D-D166V 救援小鼠研究了磷模拟 (Ser15 → Asp15) 肌球蛋白调节轻链 (S15D-RLC) 对肌球蛋白超级放松 (SRX) 状态的影响，并将其与肥大小鼠进行比较心肌病 (HCM) Tg-D166V 模型和野生型 (WT) RLC 小鼠。在 Tg-D166V 模型中，我们观察到 SRX 状态的破坏，导致从 SRX 到 DRX（无序松弛）状态的转变，这解释了 D166V 突变肌球蛋白运动的超收缩性。 Tg-S15D-D166V 小鼠中 S15D 部分的存在将 SRX/DRX 平衡恢复到与 Tg-WT 相当的水平，从而减轻与 HCM-D166V 突变相关的过度收缩行为。此外，我们研究了通过腺相关病毒（AAV9）将 S15D-RLC 分子递送至 Tg-D166V 小鼠心脏的影响，并将其状况与注射 AAV9 空载体或未注射的 Tg-D166V 动物进行比较。与注射 AAV9 空载体或未注射的小鼠相比，注射 AAV9 S15D-RLC 的 Tg-D166V 小鼠表现出处于 SRX 状态的肌球蛋白头比例显着更高。在类似处理的 Tg-WT 心脏中没有观察到显着效果。这些发现表明，AAV9 递送的拟磷 S15D-RLC 方式减轻了异常的 Tg-D166V 表型，而不影响 Tg-WT 心脏的正常功能。全局纵向应变分析支持了这些观察结果，表明 S15D 部分可以通过恢复 SRX 稳定性和 SRX ↔ DRX 平衡来减轻 HCM-D166V 表型。