The role of cytoskeletal mechanotransduction and its regulation by Filamin C in pathological cardiac hypertrophy

项目摘要 心脏病仍然是一个全球性的医学挑战和死亡的主要原因。多种形式的心脏 疾病伴随着心肌肥厚和重塑，增加了突发性心脏病的风险。 心源性死亡，使心室肥大成为收缩功能障碍和心脏进展的主要预测因素 失败遗传性心肌病是肥厚性心脏病的一个重要亚型， 肥厚型和扩张型心肌病（分别为HCM和DCM）。HCM的特点是 心肌细胞（CM）和心室壁的向心性肥大（增厚）导致舒张 扩张型心肌病的特征是离心性CM肥大（延长）和室扩张， 收缩功能障碍同心HCM重塑通常与肌节突变有关， 获得机械功能，而扩张型DCM重塑更典型地与功能丧失相关 肌节突变或编码细胞骨架蛋白的基因突变， 在CM中的机械传递或机械转导。我们的总体假设是， 响应由机械力传递的各向异性和外部载荷相对于 肌原纤维轴，使得机械改变重新分配CM应力的轴向与径向分量 和应变（即，改变CM力学的各向异性）被转换成区分各向异性的信号 通过不同的机械传感器和机械换能器的CM生长。膜中的分子复合物， CM的皮质细胞骨架被认为是外周机械传感器或换能器， 介导不同的肥大反应。一种这样的结构是肋节，其将肌节连接到 细胞膜上含有黏着斑蛋白和细丝蛋白C（FLNC）。发现小鼠心脏中纽蛋白的丢失 导致DCM，之前皮质膜刚度降低，导致径向增加， 收缩期应变，而非轴向收缩期应变。目前尚不清楚心脏FLNC的缺失是否也会导致 CM中皮质僵硬和收缩应变的各向异性，但研究表明成纤维细胞中细丝蛋白的丢失 降低了细胞内力分布对所施加的外部机械载荷的响应的各向异性。我 本项目的目标是采用一种新的心脏特异性和可诱导FLNC缺失的小鼠模型 并整合细胞骨架力学，costameric加载分布， 和机械敏感性基因表达来检验FLNC调节这种关系的假设。 皮质细胞结构、肌细胞内应变的各向异性和转导之间的关系 机械刺激到差异生长，支撑DCM。使用FLNC空CM，我将阐明 皮质细胞骨架中各向异性力对CM中肥大信号的依赖性和信息 用于治疗或预防肥大性心脏病的新的机械生物学靶点。

Project Summary Heart disease continues to be a global medical challenge and a major cause of mortality. Many forms of heart disease are accompanied by hypertrophy and remodeling of the myocardium that increases the risk of sudden cardiac death, making ventricular hypertrophy a leading predictor of contractile dysfunction and progressive heart failure. Inherited cardiomyopathies represent a significant subset of hypertrophic heart disease, the two primary forms being hypertrophic and dilated cardiomyopathy (HCM & DCM, respectively). HCM is characterized by a concentric hypertrophy (thickening) of cardiomyocytes (CMs) and ventricular walls leading to diastolic dysfunction, while DCM is characterized by eccentric CM hypertrophy (lengthening) and chamber dilation with systolic dysfunction. Concentric HCM remodeling is often associated with sarcomeric mutations that confer a gain of mechanical function, whereas dilated DCM remodeling is more typically associated with loss-of-function sarcomeric mutations or mutations in genes encoding cytoskeletal proteins that may mediate mechanotransmission or mechanotransduction in CMs. Our overall hypothesis is that differential hypertrophic responses are regulated by the anisotropy of mechanical force transmission and external loading relative to the myofibrillar axis such that mechanical alterations redistribute the axial versus radial components of CM stress and strain (i.e., change the anisotropy of CM mechanics) are converted into signals that differentiate anisotropic CM growth via distinct mechanosensors and mechanotransducers. Molecular complexes in the membrane and cortical cytoskeleton of CMs are thought to serve as peripheral mechanosensors or transducers that likely mediate differential hypertrophic responses. One such structure is the costamere, which links the sarcomere to the cell membrane and contains vinculin and filamin C (FLNC). A loss of vinculin in mouse hearts was found to cause DCM which was preceded by a reduction of cortical membrane stiffness that led to an increase in radial systolic strain but not axial systolic strain in CMs. It is unknown if a loss of FLNC in the heart also dysregulates cortical stiffness and anisotropy of systolic strain in CMs, but it has been shown that a loss of filamin in fibroblasts reduces the anisotropy of intracellular force distributions in response to applied external mechanical loading. My goal in this project is to employ a new mouse model with cardiac-specific and inducible FLNC deletion and integrate nanoscale measurements of cytoskeletal mechanics, costameric loading distributions, and mechanosensitive gene expression to test the hypothesis that FLNC regulates the relationship between cortical cytoarchitecture, the anisotropy of intra-myocyte strain, and the transduction mechanical stimuli into differential growth that underpins DCM. Using FLNC-null CMs, I will elucidate the dependence of the anisotropy of forces in the cortical cytoskeleton on hypertrophic signaling in CMs and inform novel mechanobiological targets for the treatment or prevention hypertrophic heart disease.