Background: Diastolic dysfunction is a prevalent and therapeutically intractable feature of heart failure (HF). Increasing ventricular compliance can improve diastolic performance, but the viscoelastic forces that resist diastolic filling and become elevated in human HF are poorly defined. Having recently identified post-translationally detyrosinated microtubules as a source of viscoelasticity in cardiomyocytes, we sought to test whether microtubules contribute meaningful viscoelastic resistance to diastolic stretch in human myocardium. Methods: Experiments were conducted in isolated human cardiomyocytes and trabeculae. First, slow and rapid (diastolic) stretch was applied to intact cardiomyocytes from non-failing and HF hearts, and viscoelasticity was characterized following interventions targeting microtubules. Next, intact left-ventricular trabeculae from HF patient hearts were incubated with colchicine or vehicle and subject to pre- and post-treatment mechanical testing, which consisted of a staircase protocol and rapid stretches from slack length to increasing strains. Results: Viscoelasticity was increased during diastolic stretch of HF cardiomyocytes compared to non-failing counterparts. Reducing either microtubule density or detyrosination reduced myocyte stiffness, particularly at diastolic strain rates, indicating reduced viscous forces. In myocardial tissue, we found microtubule depolymerization reduced myocardial viscoelasticity, with an effect that decreased with increasing strain. Colchicine reduced viscoelasticity at strains below, but not above, 15%, with a two-fold reduction in energy dissipation upon microtubule depolymerization. Post-hoc sub-group analysis revealed that myocardium from patients with HF with reduced ejection fraction (HFrEF) were more fibrotic and elastic than myocardium from patients with HF with preserved ejection fraction (HFpEF), which were relatively more viscous. Colchicine reduced viscoelasticity in both HFpEF and HFrEF myocardium. Conclusions: Failing cardiomyocytes exhibit elevated viscosity, and reducing microtubule density or detyrosination lowers viscoelastic resistance to diastolic stretch in human myocytes and myocardium. In failing myocardium, microtubules elevate stiffness over the typical working range of strains and strain rates, but exhibited diminishing effects with increasing length, consistent with an increasing contribution of the extracellular matrix and/or myofilament proteins at larger excursions. These studies indicate that a stabilized microtubule network provides a viscous impediment to diastolic stretch, particularly in HF.

中文翻译：

---

微管增加衰竭的人类心肌细胞和心肌的舒张硬度。

背景：舒张功能障碍是心力衰竭（HF）的一个普遍且难以治疗的特征。增加心室顺应性可以改善舒张功能，但抵抗舒张期充盈并在人类心力衰竭中升高的粘弹性力尚不清楚。最近确定翻译后去酪氨酸化微管是心肌细胞粘弹性的来源，我们试图测试微管是否对人类心肌的舒张期拉伸产生有意义的粘弹性阻力。方法：在分离的人心肌细胞和小梁中进行实验。首先，对来自非衰竭心脏和心力衰竭心脏的完整心肌细胞应用慢速和快速（舒张期）拉伸，并在针对微管的干预措施后表征粘弹性。接下来，将心力衰竭患者心脏的完整左心室小梁与秋水仙碱或载体一起孵育，并进行治疗前和治疗后机械测试，其中包括阶梯方案和从松弛长度到增加应变的快速拉伸。结果：与未衰竭心肌细胞相比，心力衰竭心肌细胞在舒张期拉伸时粘弹性增加。降低微管密度或去酪氨酸化可降低心肌细胞硬度，特别是在舒张应变率下，表明粘性力降低。在心肌组织中，我们发现微管解聚降低了心肌粘弹性，其效果随着应变的增加而减弱。秋水仙碱在应变下降低粘弹性低于但不高于 15%，微管解聚时能量耗散减少两倍。事后亚组分析显示，射血分数降低的心力衰竭 (HFrEF) 患者的心肌比射血分数保留的心力衰竭 (HFpEF) 患者的心肌纤维化程度更高、更有弹性，而射血分数保留的心力衰竭 (HFpEF) 患者的心肌相对更粘稠。秋水仙碱降低 HFpEF 和 HFrEF 心肌的粘弹性。结论：衰竭心肌细胞表现出粘度升高，并且降低微管密度或去酪氨酸降低了人类心肌细胞和心肌对舒张期拉伸的粘弹性阻力。在衰竭的心肌中，微管在应变和应变率的典型工作范围内提高了刚度，但随着长度的增加，其效果逐渐减弱，这与细胞外基质和/或肌丝蛋白在较大偏移时的贡献增加一致。这些研究表明，稳定的微管网络为舒张期拉伸提供了粘性障碍，特别是在心力衰竭中。