Improving Mitral Compensation in Ischemic Regurgitation

描述（由申请人提供）：缺血性二尖瓣反流（IMR）是一种常见的并发症，可使心肌梗死（MI）后的死亡率增加一倍，并增加心力衰竭。IMR的有效修复一直难以实现，这是由左室（LV）重塑引起的，它束缚了二尖瓣（MV）小叶并限制了它们的关闭——瓣膜和左室大小不匹配。晚期瓣膜也会硬化和纤维化，进一步限制了有效的关闭。标准治疗方法假设瓣膜大小是固定的，但瓣膜具有细胞活化的潜力，灵活扩大系留的MV可以减少IMR。阀的适应性会受到机械拉伸、缺血环境和MR湍流的影响。因此，我们开发了一个大型动物模型来独立改变这些因素，使用3D回声无创地跟踪MV区域，与细胞和分子研究相关。在该模型中，通过乳头肌牵拉诱导的机械栓系，在两个月的时间里，再激活内皮-间充质转化（EMT），一个发育过程，增加了MV面积和厚度。在机械栓系术中添加远端根尖心肌梗死（有限根尖左室重塑）两个月后，EMT明显增加，促纤维化转化生长因子(TGF)-¿的表达、内皮细胞活化（VCAM-1）、胶原沉积和CD45+细胞的浸润。血源性伤口愈合的CD45+细胞通过分化为产生胶原的肌成纤维细胞而使其他器官硬化。因此，我们将验证中心假设，即IMR环境下早期代偿性MV生长机制后来成为失代偿性，导致mr僵硬增加。Aim 1将在MI+系扣模型和临床类型场景下，在2、6和10个月时，将纤维化和僵硬与TGF-¿表达、内皮活化和CD45+细胞浸润联系起来。Aim 2将分离MV CD45+细胞，并测试它们是否具有纤维细胞的特征。循环肌成纤维细胞前体；将检测中压细胞和外周血CD45+细胞在mi释放的细胞因子刺激下与中压内皮细胞的粘附，分化为肌成纤维细胞，并可能影响天然中压细胞发生类似的促纤维化变化。Aim 3基于初步研究，TGF-¿抑制剂氯沙坦在栓系+心肌梗死模型中，可在2个月时降低EMT、CD45+细胞、内皮活化和MV增厚；相反，当机械性左室约束相对减少左室重构时，这些发现仍然存在。氯沙坦对TGF-介导的EMT也有抑制作用。在栓系+心肌梗死模型中，我们将测试氯沙坦是否与左室约束不同，能减少2至6个月和10个月的长期促纤维化事件，并研究下游TGF-¿信号，最近显示其具有治疗意义。该提案将研究人员在生理建模和成像，MV组织病理学，内皮细胞生物学和生物力学方面的互补优势结合起来。它解决了一种常见疾病未满足的临床需求，旨在增加我们对MV适应的理解。它开始测试潜在的治疗方法，如果得到证实，可以迅速转化为降低患者的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. PUBLIC HEALTH RELEVANCE: Mitral regurgitation (MR) is a frequent, difficult to repair complication of myocardial infarction (MI) that doubles heart failure and mortality; it is caused b tethering (stretch) of the mitral valve by damaged and bulging heart walls that prevents valve closure, and is compounded by late valve stiffening. Until recently, mitral valve size has been viewed as fixed in this setting, but valve growth in adaptation to tethering could reduce this regurgitation if valve flexibility can be maintained. In this project, an interdisciplinary team wil use a new model to fill this unmet clinical need in a common disease by increasing our understanding of how adaptive valve processes can become maladaptive, and will begin to test new therapies to reduce this complication that, if corroborated, can be rapidly translated to benefit patients.