Leveraging Mechanical Control of Relaxation to Improve Diastolic Function

7.项目摘要/摘要 几乎所有患者都存在舒张期松弛受损，这是舒张期功能障碍的重要组成部分。 心力衰竭患者--射血分数减少和保留--在近25%的患者中 没有症状的个体。不幸的是，目前还没有治疗松弛受损的方法。最近，我的实验室 确定和定义松弛的机械控制为响应于 拉长的菌株。换句话说，松弛速率对心肌的应变率很敏感。我们的 数据表明，这种对松弛的机械调节可以将松弛速率提高两倍以上 限制肌球蛋白脱离肌动蛋白的生化过程，包括钙的去除和细丝的去除 停用。因此，舒张期功能障碍可能由两个因素引起：i)松弛对 应变率和ii)应变的衰减，限制应变率。潜在的分子机制 应变率敏感性尚不清楚，但我们的初步研究表明，肌球蛋白脱离动力学 都是关键。应变敏感型肌球蛋白脱离是一种特征性很差的生物物理特性，特别是在完全性肌球蛋白脱离中。 心脏组织。我们的初步数据进一步表明，体内血流动力学可以改变心肌 紧张。这一提议的总体假设是，肌球蛋白脱离动力学在生物物理上调节 放松的机械控制。该项目的目标是确认这一机制并确定 调节机械控制松弛的分子和血流动力学因素。目标一号将决定 肌球蛋白脱落率是否影响松弛速率对应变率的敏感性。我们 假设肌球蛋白亚型和肌球蛋白激活药物都将改变应变敏感的脱离 肌球蛋白的比率。使用肌球蛋白异构体改变疗法和肌球蛋白特异性激活药物，我们将 使用完整的心脏小梁评估机械控制松弛。重要的是，我们将评估肌球蛋白 使用x射线衍射技术的头部位置。目标2将根据刚性确定Titin的作用 放松的机械控制。我们的初步研究表明，高度的肌钙蛋白依从性可以消除 肌球蛋白脱离的长度(预负荷)依赖的变化。我们假设Titin介导的粗丝 延伸性是松弛的中介，并将在表达改变的小梁上验证这一假说 使用与目标1相同的技术。目标3将确定应变率和/或敏感性 应变速率的松弛速率在体内使用i)在AIMS 1中研究的分子修饰 以及2和ii)临床相关的果糖+高盐模型，复制了几个心力衰竭的标记物 保存的射血分数。提出的方法独特地考虑了心肌如何运动(应变)。 在整个心脏周期中，比标准方法(分离的肌原纤维、小梁)更先进 等轴测。这些研究将推动发现新的靶点，以改进治疗和诊断 通过隔离机械控制松弛的机制来削弱松弛。

7. PROJECT SUMMARY/ABSTRACT Impaired diastolic relaxation, an important component of diastolic dysfunction, is present in nearly all patients with heart failure-both with reduced and with preserved ejection fraction- and is present in nearly 25% of asymptomatic individuals. Unfortunately, no treatments for impaired relaxation exist. Recently, my lab identified and defined Mechanical Control of Relaxation as a faster relaxation rate in response to the rate of a lengthening strain. In other words, the relaxation rate is sensitive to the strain rate of the myocardium. Our data demonstrate that this mechanical regulation of relaxation can increase the relaxation rate two-fold beyond the biochemical processes that limit myosin detachment from actin, including calcium removal and thin filament deactivation. Thus, diastolic dysfunction might result from two factors: i) a loss of the sensitivity of relaxation to strain rate and ii) an attenuation in strain, restricting the strain rate. The molecular mechanism underlying strain-rate sensitivity remains unknown, but our preliminary studies indicate that myosin detachment kinetics are key. Strain-sensitive myosin detachment is a poorly characterized biophysical property, especially in intact cardiac tissues. Our preliminary data further demonstrates that in vivo hemodynamics can alter myocardial strain. The global hypothesis of this proposal is that myosin-detachment kinetics biophysically regulates Mechanical Control of Relaxation. The goals of this project are to confirm this mechanism and to identify molecular and hemodynamic factors that regulate Mechanical Control of Relaxation. Aim 1 will determine whether myosin detachment rate modifies the sensitivity of the relaxation rate to the strain rate. We hypothesize that both myosin isoforms and myosin activating drugs will modify the strain-sensitive detachment rate of myosin. Using myosin isoform altering treatments and myosin-specific activating drugs, we will evaluate Mechanical Control of Relaxation using intact cardiac trabeculae. Importantly, we will assess myosin head position using x-ray diffraction techniques. Aim 2 will determine the role of titin based stiffness on Mechanical Control of Relaxation. Our preliminary studies suggest that high titin compliance eliminates a length (preload)-dependent change in myosin detachment. We hypothesize that titin-mediated thick filament extensibility is a mediator of relaxation and will test this hypothesis in trabeculae expressing altered titin isoforms using the same techniques as in Aim 1. Aim 3 will determine how strain rate and/or the sensitivity of the relaxation rate to the strain rate is modified in vivo using i) the molecular modifications studied in Aims 1 and 2 and ii) a clinically relevant Fructose+High Salt model that replicates several markers of heart failure with preserved ejection fraction. The proposed methods uniquely consider how the myocardium moves (strains) throughout the cardiac cycle, an advance beyond standard methods (isolated myofibril, trabeculae) that are isometric. These studies will drive the discovery of novel targets to improve the treatment and diagnosis of impaired relaxation by isolating mechanisms underlying Mechanical Control of Relaxation.