Mechanotransduction in myocardial adaptation to ischemia

描述（由申请人提供）：缺血性心脏病（IHD）是导致心力衰竭的心肌梗死、疤痕和肥大的主要潜在原因。心肌通过诱导瘢痕形成来适应这种缺血性损伤，瘢痕形成对于稳定缺血区域和防止破裂至关重要;然而，随着时间的推移，这些患者中经常发生心脏纤维化。因此，心肌梗死后心脏的适应性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个重大挑战。CF向肌成纤维细胞的分化是心肌梗死后关键的第一步，肌成纤维细胞的不成比例的产生和延长的存活可产生过量的ECM蛋白沉积，导致病理性纤维化。虽然TGF β 1和机械应力（由ECM硬度产生）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肌成纤维细胞分化为肌成纤维细胞的机械转导机制。我们的初步结果表明，机械敏感离子通道TRPV 4（瞬时受体电位香草酸4）是TGF-β 1诱导的CF分化为肌纤维所必需的。重要的是，我们发现TGF-β 1诱导的肌成纤维细胞分化需要高刚度基质，这是一种被TRPV 4阻断减弱的反应。TGF-β 1处理增强CFs中TRPV 4的表达、膜转位（通过p38 MAPK）和活性。此外，我们发现TRPV 4通过Rho依赖性机制激活机械敏感性转录因子MRTF-A（myocardin related transcription factor-A）。重要的是，我们发现，与野生型小鼠相比，TRPV 4KO小鼠在遭受MI时，心脏功能得到保留，纤维化减少。最后，将Rho激活剂CNF 1注射到TRPV 4KO小鼠的心脏中引起MI后心脏中的心脏纤维化，证实了该机械转导途径在心脏纤维化的介导中的作用。我们的工作假设是，机械敏感离子通道，TRPV 4，通过整合化学（TGF-β 1）和机械信号调节心肌成纤维细胞分化为肌成纤维细胞。我们将在以下具体目标中检验这一假设：1）确定TGF-β 1调节心脏成纤维细胞中TRPV 4表达、运输和活性的分子机制; 2）探究机械转导 TRPV 4介导心脏成纤维细胞分化的机制和3）确定TRPV 4在心肌梗死后心脏纤维化中的致病作用。TRPV 4通道尚未被研究为心肌梗死的潜在治疗靶点。我们提出的研究将建立TRPV 4作为心肌适应缺血所需的机械和化学信号的整合剂，并可能为心肌缺血和病理性心脏纤维化的开发治疗开辟全新的途径。

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.