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，可使死亡率加倍，并增加心肌梗死 (MI) 后的心力衰竭。 IMR 的有效修复一直难以实现，这是由左心室 (LV) 重塑引起的，左心室重塑束缚二尖瓣 (MV) 小叶并限制其关闭 - 瓣膜和 LV 尺寸之间的不匹配。晚期瓣膜也僵硬且纤维化，进一步限制了有效闭合。标准疗法假设瓣膜尺寸是固定的，但瓣膜具有细胞激活的潜力，并且灵活扩大系留的 MV 可以降低 IMR。瓣膜适应性可能受到机械拉伸、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，使用 3D 回波独立改变这些因素，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，由乳头肌牵引引起的机械束缚在产生 MR 的情况下会在两个月内增加 MV 面积和厚度，并重新激活内皮间质转化 (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（有限心尖左室重塑）可显着增加 EMT，并伴有促纤维化转化生长因子 (TGF)-¿ 的表达、内皮激活 (VCAM-1)、胶原沉积和 CD45 细胞浸润。血源性伤口愈合 CD45 细胞通过分化为产生胶原蛋白的肌成纤维细胞而导致其他器官硬化。因此，我们将测试中心假设，即 IMR 设置中的早期代偿性 MV 生长机制后来变得失代偿，导致僵硬，从而增加 MR。目标 1 将在 MI 束缚模型和临床型情景（下质 MI）中将纤维化和硬度与 TGF-¿ 表达、内皮激活和 CD45 细胞浸润在 2、6 和 10 个月时相关联。目标2将分离MV CD45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 CD45 细胞与 MI 释放的细胞因子刺激的 MV 内皮细胞的粘附、分化为肌成纤维细胞，以及可能影响天然 MV 细胞经历类似的促纤维化变化。目标 3 基于初步研究，即 TGF-β 抑制剂洛沙坦可在束缚 MI 模型中减少两个月时的 EMT、CD45 细胞、内皮活化和 MV 增厚；相反，当左室机械约束相对减少左室重塑时，这些发现仍然存在。氯沙坦还在体外抑制 TGF-β 介导的 EMT。我们将测试洛沙坦是否与 LV 限制不同，在拴系 MI 模型中将长期促纤维化事件从 2 个月减少到 6 个月和 10 个月，并研究下游 TGF-¿ 信号传导，最近显示出具有治疗意义。该提案结合了生理建模和成像、MV 组织病理学、内皮细胞生物学和生物力学方面互补优势的研究人员。它解决了常见疾病中未满足的临床需求，旨在增加我们对 MV 适应的理解。它开始测试潜在的疗法，如果得到证实，可以迅速转化为降低患者的 IMR。 公众健康相关性：二尖瓣反流 (MR) 是心肌梗死 (MI) 的一种常见且难以修复的并发症，可导致心力衰竭和死亡率加倍；它是由于心壁受损和膨胀导致二尖瓣束缚（拉伸）而导致瓣膜无法闭合，并且后期瓣膜僵硬会加剧这种情况。直到最近，二尖瓣尺寸在这种情况下仍被认为是固定的，但如果能够保持瓣膜灵活性，适应栓系的瓣膜生长可以减少这种反流。在这个项目中，一个跨学科团队将通过增加我们对适应性瓣膜过程如何变得适应不良的理解，使用一种新模型来满足常见疾病中未满足的临床需求，并将开始测试新疗法以减少这种并发症，如果得到证实，可以迅速转化为造福患者。

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.