MRI of Myocardial Function in Post-Infarct Knockout Mice

描述(由申请人提供)：使用转基因和基因敲除小鼠的研究为每一种主要心血管疾病背后的遗传、分子和细胞机制提供了巨大的见解。绝大多数此类研究都采用了体外或体内侵入性的方法来评估基因操作的结果。我们开发和应用了新的MRI方法来研究遗传操作小鼠的心脏左心室(LV)结构和功能的非侵入性表型。这些方法对单个基因在心脏病中的体内功能作用提供了新的见解。我们正在研究的特定疾病是从急性心肌梗死(MI)到心力衰竭的进展，通过MI后左室重构。我们开发的特殊MRI技术是2D电影位移编码和刺激回声(Cine Density)，它在多个2D切片上量化局部2D心肌应变，但体积覆盖有限，不能量化3D应变。除了即刻收缩功能障碍外，急性心肌梗死还会引发炎症反应，包括巨噬细胞渗入心脏。炎症之后是疤痕的形成。这一系列事件设定了驱动长期LV重塑的条件。磁共振成像方法评估小鼠的细胞炎症将使研究单个基因在左心室结构和功能变化的细胞病理生理学中的作用成为可能。最近的研究表明，血栓反应蛋白-1(TSP-1)在心肌梗死后在梗死灶边缘区域表达，并且(2)在限制巨噬细胞在梗死灶的初始区域的渗透中起重要作用。TSP-1被认为是梗死区边缘的分子屏障，将炎症反应和组织纤维化的范围限制在非梗死区。到目前为止，还没有关于心肌梗死后TSP-1-/-小鼠的左心功能的研究，也没有研究过急性心肌梗死后的TSP-1-/-小鼠，也没有研究过TSP-1过度表达的小鼠对MI的反应。该建议的具体目的是(1)开发3D电影高密度磁共振成像，以量化整个小鼠心脏的局部3D应变，具有高空间和时间分辨率；(2)开发并验证MRI细胞跟踪方法，用于成像小鼠心肌梗死后巨噬细胞浸润的时空分布；(3)使用MRI验证TSP-1促进心肌梗死后愈合受限并导致长期左室重构减少的假说。该项目的成功完成将导致改进小鼠心脏MRI的方法，并将为TSP-1在心肌梗死后左室重构中的作用，包括其作为新的治疗靶点的潜力提供新的线索。 公共卫生回顾：在美国，心肌梗死和随后的心力衰竭仍然是发病率和死亡率的主要原因。这项拨款建议开发和应用转基因和基因敲除小鼠的非侵入性磁共振成像，以研究单个基因在从急性心肌梗死到心力衰竭的疾病进展中的体内作用。

DESCRIPTION (provided by applicant): Research using transgenic and knockout mice has provided tremendous insights into the genetic, molecular, and cellular mechanisms underlying every major cardiovascular disease. The vast majority of such research has employed in vitro or invasive in vivo methods for assessing the results of gene manipulation. We have developed and applied novel MRI methods to noninvasively phenotype cardiac left ventricular (LV) structure and function in genetically-manipulated mice. These methods provide new insights into the in vivo functional roles of individual genes in heart disease. The specific disease that we are investigating is the progression from acute myocardial infarction (MI) toward heart failure via post-MI LV remodeling. The specific MRI technique that we developed is 2D cine displacement-encoding with stimulated echoes (cine DENSE), which quantifies regional 2D myocardial strain throughout multiple 2D slices, but has limited volumetric coverage and does not quantify 3D strain. In addition to immediate contractile dysfunction, acute MI triggers an inflammatory response involving the infiltration of macrophages into the heart. Inflammation is followed by scar formation. This sequence of events sets the conditions that drive long-term LV remodeling. MRI methods to assess cellular inflammation in mice would enable studies of the roles of individual genes in the cellular pathophysiology underlying changes in LV structure and function. Thrombospondin-1 (TSP-1) has recently been shown (1) to be expressed after MI at the infarct border zone, and (2) to play an important role in confining the infiltration of macrophages to the initial region of infarction. TSP-1 has been described as a molecular barrier at the infarct border, limiting extension of the inflammatory response and tissue fibrosis to the noninfarcted areas. To date, LV function has not been studied in post-MI TSP-1-/- mice, TSP-1-/- mice have not been studied beyond the acute post-MI period, nor has the response to MI in mice overexpressing TSP-1 been studied. The specific aims of this proposal are (1) To develop 3D cine DENSE MRI for quantifying regional 3D strain throughout the mouse heart with high spatial and temporal resolution; (2) To develop and validate MRI cell tracking methods for imaging the spatiotemporal distribution of post-MI macrophage infiltration in mice; and (3) To use MRI to test the hypothesis that TSP-1 facilitates confinement of post-MI infarct healing and leads to reduced long-term LV remodeling. The successful completion of this project will lead to improved methods for cardiac MRI in mice, and will shed new light on the role of TSP-1 in post-MI LV remodeling, including its potential as a new therapeutic target. PUBLIC HEALTH REVELANCE: Myocardial infarction and subsequent heart failure continues to be a major cause of morbidity and mortality in the United States. This grant proposes to develop and apply noninvasive magnetic resonance imaging of transgenic and knockout mice to study the in vivo roles of individual genes in the progression of disease from acute myocardial infarction toward heart failure.