Improving Mitral Compensation in Ischemic Regurgitation

描述（由申请人提供）：缺血性二尖瓣返流（IMR）是一种常见并发症，可使心肌梗死（MI）后死亡率加倍并增加心力衰竭。IMR的有效修复一直难以实现，IMR是由左心室（LV）重塑引起的，左心室重塑束缚二尖瓣（MV）瓣叶并限制其闭合-瓣膜和LV尺寸之间的不匹配。晚期瓣膜也是僵硬和纤维化的，进一步限制了有效闭合。标准治疗假设瓣膜尺寸是固定的，但瓣膜具有细胞激活的可能性，并且系留MV的灵活扩大可以减少IMR。瓣膜适应性可受到机械牵拉、缺血环境和MR湍流的影响。因此，我们开发了一种大型动物模型，使用3D回波独立地改变这些因素，以无创地跟踪MV区域，并与细胞和分子研究相关。在该模型中，由乳头肌牵拉引起的机械拴系在两个月内增加了MV面积和厚度，并重新激活了内皮-间充质转化（EMT），这是一个发育过程。在两个月的机械栓系中添加远端心尖MI（有限的心尖LV重塑）显著增加了EMT，伴促纤维化转化生长因子（TGF）-β表达、内皮活化（VCAM-1）、胶原沉积和CD 45+细胞浸润。血源性伤口愈合CD 45+细胞通过分化成产生胶原的肌成纤维细胞而产生其他器官的硬化。因此，我们将测试中心假设，即IMR环境中的早期代偿性MV生长机制后来变得失代偿，导致增加MR的僵硬。目的1将在MI+栓系模型和临床类型场景下，在2个月、6个月和10个月时将纤维化和僵硬与TGF-β表达、内皮活化和CD 45+细胞浸润相关。目的2将分离MV CD 45+细胞，并测试它们是否具有纤维细胞、循环肌成纤维细胞前体的特征;将测试MV和外周血CD 45+细胞与由MI释放的细胞因子刺激的MV内皮细胞的粘附、分化成肌成纤维细胞以及可能影响天然MV细胞经历类似的促纤维化变化。目的3是基于初步研究，即Losartan，一种TGF-β抑制剂，在栓系+MI模型中减少两个月时的EMT、CD 45+细胞、内皮活化和MV增厚;相反，当LV重塑通过机械LV约束而显著减少时，这些发现持续存在。Losartan还在体外抑制TGF-β介导的EMT。我们将测试氯沙坦是否与LV限制不同，在栓系+MI模型中减少2至6和10个月的长期促纤维化事件，并研究下游TGF-β信号传导，最近显示具有治疗意义。该提案将研究人员与生理建模和成像，MV组织病理学，内皮细胞生物学和生物力学的互补优势结合起来。它解决了一种常见疾病中未满足的临床需求，旨在增加我们对MV适应性的理解。它开始测试潜在的治疗方法，如果得到证实，可以迅速转化为减少患者的IMR。

DESCRIPTION (provided by applicant): Ischemic mitral regurgitation (IMR) is a common complication that doubles mortality and increases heart failure after myocardial infarction (MI). Effective repair has been elusive for IMR, which is caused by left ventricular (LV) remodeling that tethers the mitral valve (MV) leaflets and restricts their closure - a mismatch between valve and LV size. Late-stage valves are also stiff and fibrotic, further limiting effective closure. Standard therapies assume valve size is fixed, but valves have the potential for cellular activation, and flexible enlargement of the tethered MV could reduce IMR. Valve adaptation can be affected by mechanical stretch, the ischemic milieu, and MR turbulence. We therefore developed a large-animal model to vary these factors independently using 3D echo to follow MV area noninvasively, correlated with cellular and molecular studies. In that model, mechanical tethering induced by papillary muscle traction short of producing MR increases MV area and thickness over two months with reactivated endothelial-mesenchymal transformation (EMT), a developmental process. Adding a distal apical MI (limited apical LV remodeling) to mechanical tethering over two months markedly increases EMT, with expression of pro-fibrotic transforming growth factor (TGF)-¿, endothelial activation (VCAM-1), collagen deposition, and infiltration of CD45+ cells. Blood-borne wound- healing CD45+ cells create sclerosis of other organs by differentiating into collagen-producing myofibroblasts. We will therefore test the central hypothesis that early compensatory MV growth mechanisms in the IMR setting later become decompensatory, leading to stiffness that increases MR. Aim 1 will correlate fibrosis and stiffness with TGF-¿ expression, endothelial activation and CD45+ cell infiltration at 2, 6 and 10 months in models of MI+tethering and the clinical-type scenario, inferior MI. Aim 2 will isolate the MV CD45+ cells and test whether they have the characteristics of fibrocytes, circulating myofibroblast precursors; MV and peripheral blood CD45+ cells will be tested for adhesion to MV endothelial cells stimulated by MI-released cytokines, differentiation into myofibroblasts, and possibly influencing native MV cells to undergo similar pro-fibrotic change. Aim 3 is based on preliminary studies that Losartan, a TGF-¿ inhibitor, reduces EMT, CD45+ cells, endothelial activation and MV thickening at two months in the tethering+MI model; in contrast, those findings persist when LV remodeling is comparably reduced by mechanical LV constraint. Losartan also inhibits TGF- ¿-mediated EMT in vitro. We will test whether Losartan, unlike LV constraint, reduces long-term pro-fibrotic events from 2 to 6 and 10 months in the tethering+MI model, and study downstream TGF-¿ signaling, recently shown to have therapeutic implications. This proposal combines investigators with complementary strengths in physiologic modeling and imaging, MV histopathology, endothelial cell biology and biomechanics. It addresses unmet clinical needs in a common disease, aiming to increase our understanding of MV adaptation. It begins to test potential therapies that, if corroborated, could be rapidly translated to reduce IMR in patients.