Mechanical Stress-Dependent Remodeling of the Cardiac Microtubule Network

心力衰竭通常表现为心脏组织僵硬，损害心脏的放松能力。微管网络是心肌细胞骨架的一部分，它提供的内部僵硬会阻碍心肌细胞的收缩和松弛。我们最近发现，心肌细胞微管网络的刚性受到翻译后酪氨酸降解的严格调节，在心力衰竭时，微管、酪氨酸化和细胞骨架交联物持续升高，并伴随着心肌细胞刚性的增加。我们的研究发现，减少酪氨酸化可以减少晚期心力衰竭患者心肌细胞中的微管网络密度和收缩缺陷，支持将酪氨酸化作为治疗靶点。与此同时，这些发现提出了一些重要的问题，即心力衰竭时驱动微管网络重构的过程，以及随着时间的推移微管网络持续增加的后果。因此，这项拟议的研究将检验这样的假设，即心脏微管网络的重塑是对改变的机械应力的可逆适应，当机械应力持续时，会导致病理性肥大和收缩功能障碍。三个目标下的研究将解决这一假设的多个组成部分。目的1利用机械生物学工具箱分离三个主要机械应力源(前负荷、后负荷和基质硬度)对微管网络重构的影响，以确定机械应力是否足以驱动微管网络的细胞自主重构。目的2实验将我们的机械操作扩展到组织和器官水平，以表征体内相关环境下的微管网络重构。目的3研究将采用体外和体内的遗传操作，以确定在存在和不存在慢性压力超负荷的情况下，酪氨酸酶的持续增加是否有助于病理性心肌肥厚。我们的整体研究设计使用了新颖和互补的实验方法，既利用了模型系统的优点，又减少了它们的缺点。这包括来自人类心肌的原代心肌细胞，以补充动物模型和工程化组织结构的发现。这种跨物种、多尺度的方法平衡了简约主义严谨和综合相关性的双重目标，进一步促进了最终的临床翻译。总之，这项工作将提供对心力衰竭微管网络变化的原因的洞察，并有助于确定预防或逆转这些变化是否在治疗上有益。

Heart failure is often marked by stiffening of cardiac tissue that impairs the heart’s ability to relax. The microtubule network – a part of the cardiomyocyte cytoskeleton – provides an internal stiffness that can impede cardiomyocyte contraction and relaxation. We have recently found that cardiomyocyte microtubule network stiffness is tightly regulated by post-translational detyrosination and that microtubules, detyrosination, and cytoskeletal cross-linkers are consistently elevated in heart failure, with concomitant increases in cardiomyocyte stiffness. Our findings that reducing detyrosination lessens microtubule network density and contractile defects in cardiomyocytes from patients with advanced heart failure supports detyrosination as a therapeutic target. At the same time, these findings raise important questions about the processes driving remodeling of the microtubule network in heart failure and the consequences of sustained increases in the microtubule network over time. Accordingly, the proposed research will test the hypothesis that remodeling of the cardiac microtubule network is a reversible adaptation to altered mechanical stress, which when sustained, contributes to pathological hypertrophy and contractile dysfunction. Studies under three aims will address the multiple components of this hypothesis. Aim 1 experiments will determine if mechanical stress is sufficient to drive cell-autonomous remodeling of the microtubule network using a mechanobiology toolkit to isolate the contribution of three key mechanical stressors (pre-load, after-load, and matrix stiffness) on microtubule network remodeling. Aim 2 experiments will extend our mechanical manipulations to the tissue and organ level to characterize microtubule network remodeling under relevant in vivo contexts. Aim 3 studies will employ in vitro and in vivo genetic manipulations to determine whether sustained increases in detyrosination contribute to pathologic cardiac hypertrophy in the presence and absence of chronic pressure overload. Our overall study design uses novel and complementary experimental approaches to both exploit strengths of model systems and mitigate their shortcomings. This includes primary cardiomyocytes from human myocardium to complement findings from animal models and engineered tissue constructs. This cross-species, multi-scale approach balances the dual goals of reductionist rigor and integrative relevance that furthers ultimate clinical translation. Together this work will provide insight into the causes of microtubule network changes in heart failure and help determine if preventing or reversing these changes is therapeutically beneficial.