Mechanotransduction in myocardial adaptation to ischemia

描述（由申请人提供）：缺血性心脏病（IHD）是心肌梗死、瘢痕形成和肥厚导致心力衰竭的主要潜在原因。心肌通过诱导瘢痕形成来适应这种缺血性损伤，这对稳定缺血区域和防止破裂至关重要；然而，随着时间的推移，这些患者往往会出现心脏纤维化。因此，心肌梗死后心脏的适应对其长期功能至关重要，心肌梗死后心脏纤维化的临床管理是一项重大挑战。CFs向肌成纤维细胞的分化是心肌梗死后至关重要的第一步，不成比例的肌成纤维细胞生成和长期存活可产生过多的ECM蛋白沉积，导致病理性纤维化。虽然TGFb1和机械应力（由ECM刚度产生）被认为是肌成纤维细胞分化的主要介质，但协调这些可溶性信号和机械信号的分子信号仍然难以捉摸。本研究的长期目标是了解心脏成纤维细胞向肌成纤维细胞分化的机械转导机制。我们的初步结果表明，机械敏感离子通道TRPV4（瞬时受体电位香草样蛋白4）是TGF-b1诱导的CF向肌纤维化分化所必需的。重要的是，我们发现tgf -b1诱导的肌成纤维细胞分化需要高硬度基质，这一反应被TRPV4阻断剂减弱。TGF-b1处理增强了TRPV4在CFs中的表达、膜易位（通过p38 MAPK）和活性。此外，我们发现TRPV4通过rho依赖机制激活一种机械敏感的转录因子MRTF-A（心肌素相关转录因子- a）。重要的是，我们发现，与野生型小鼠相比，当遭受心肌梗死时，TRPV4KO小鼠的心功能得到保留，纤维化减少。最后，向TRPV4KO小鼠心脏注射Rho激活剂CNF1引起心肌梗死后心脏纤维化，证实了这一机械转导途径在介导心肌纤维化中的作用。我们的工作假设是机械敏感离子通道TRPV4通过化学（TGF-b1）和机械信号的整合调节心脏成纤维细胞向肌成纤维细胞的分化。我们将在以下具体目标中验证这一假设1)确定TGF-b1调节心脏成纤维细胞中TRPV4表达、运输和活性的分子机制2)询问机械转导

DESCRIPTION (provided by applicant): Ischemic heart disease (IHD) is the major underlying cause of myocardial infarction, scarring, and hypertrophy leading to heart failure. The myocardium adapts to this ischemic injury by inducing scar formation which is crucial to stabilize the ischemic area and prevent rupture; however, cardiac fibrosis often develops in these patients over time. Therefore, post-MI adaptation of the heart is crucial for its long term functio and clinical management of cardiac fibrosis post-MI presents a major challenge. The differentiation of CFs to myofibroblasts is a critical first step following myocardial infarction ad disproportionate production and prolonged survival of myofibroblasts can generate excessive ECM protein deposition leading to pathological fibrosis. Although TGFb1 and mechanical stress (generated by ECM stiffness) are recognized as major mediators of myofibroblast differentiation, the molecular signals that coordinate these soluble and mechanical signals are still elusive. The long-term objective of this proposal is to understand the mechanotransduction mechanisms of cardiac fibroblast differentiation to myofibroblasts. Our preliminary results demonstrate that the mechanosensitve ion channel TRPV4 (Transient Receptor Potential Vanilloid 4) is required for TGF-b1- induced differentiation of CF into myoFibs. Importantly, we have found that TGF-b1-induced myofibroblast differentiation required a high stiffness matrix, a response that was attenuated by TRPV4 blockade. TGF-b1 treatment enhanced TRPV4 expression, membrane translocation (via p38 MAPK) and activity in CFs. Further, we found that TRPV4 activates a mechanosensitive transcription factor, MRTF-A (myocardin related transcription factor-A), via Rho-dependent mechanism. Importantly, we found that when subjected to MI, cardiac function was preserved and fibrosis was reduced in the TRPV4KO mice compared to wild type mice. Finally, injection of Rho activator, CNF1 in to the hearts of TRPV4KO mice caused cardiac fibrosis in post-MI hearts confirming the role of this mechanotransduction pathway in the mediation of cardiac fibrosis. Our working hypothesis is that the mechanosensitive ion channel, TRPV4, regulates cardiac fibroblast differentiation to myofibroblasts through the integration of chemical (TGF-b1) and mechanical signaling. We will test this hypothesis in the following specific aims 1) Define the molecular mechanisms by which TGF-b1 regulates TRPV4 expression, trafficking, and activity in cardiac fibroblasts 2) Interrogate the mechanotransduction mechanisms by which TRPV4 mediates cardiac fibroblast differentiation and 3) Determine a causative role of TRPV4 in cardiac fibrosis following myocardial infarction. TRPV4 channels have not been studied as potential therapeutic targets for myocardial infarction. Our proposed studies will establish TRPV4 as an integrator of mechanical and chemical signals required for myocardial adaptation to ischemia and may open entirely new avenues for development therapeutics for myocardial ischemia and pathological cardiac fibrosis.