Role of Toll-like Receptor 4 (TLR4) in Ischemic Myocardial Injury

描述(申请人提供)：围手术期心肌缺血和梗死是大量接受心脏移植、冠状动脉旁路移植和血运重建等手术的外科患者的主要致病和死亡原因。最近的研究表明，心肌细胞凋亡或程序性细胞死亡在缺血性心肌损伤中起着重要作用。 Toll样受体4(TLR4)等先天免疫系统是抵御感染的第一道防线。除了在宿主免疫中的关键作用外，最近的研究表明，TLR4在非感染性损伤中对组织炎症和细胞生存具有重要的功能贡献。我们的初步数据表明，TLR4信号在心脏和分离的心肌细胞对缺血损伤的心肌保护中起着关键作用。本研究的目的是明确心脏TLR4在缺血再灌注损伤(IRI)模型中保护心肌运动的作用，并确定介导这些作用的下游机制。我们预计，从拟议的研究中获得的见解将成为未来开发治疗缺血性心肌损伤的新方法的基础。 这一建议基于以下三个假设：1)通过其信号蛋白IRAK-1激活TLR4是心脏中一种重要的生存机制，2)一氧化氮合酶2(NOS2)介导了TLR4诱导的生存益处，3)心脏TLR4信号的增强将减少心肌损伤，在IRI中产生有意义的功能挽救。为了验证这些假设，我们将使用转基因动物和腺病毒基因转移来操纵TLR4和IRAK-1的心脏表达。具体目标1：我们将探讨TLR4在体外心肌细胞凋亡模型中保护心肌细胞的机制。在特定的目标2：我们将确定NOS2和NO如何在TLR4介导的心肌细胞抗凋亡效应中发挥作用。具体目标3：我们将确定心脏(与心脏外)TLR4在保护心脏免受IRI中的作用。具体目标4：我们将评估在IRI小鼠模型中操纵IRAK-1的解剖和功能后果。我们将测试IRAK-1缺失或心脏IRAK-1表达(通过基因转移)对IRI的影响。 明确控制心肌细胞存活的信号通路，并学会在心脏中操纵这些通路，可能为治疗某些心脏疾病，如缺血性损伤和心肌病提供新的途径。

DESCRIPTION (provided by applicant): Perioperative myocardial ischemia and infarction represent the major cause of morbidity and mortality for the large number of surgical patients who undergoes a variety of operations such as heart transplantation, coronary artery bypass grafting, and revascularization. Recent studies have demonstrated that cardiomyocyte apoptosis, or programmed cell death, plays an important role in ischemic myocardial injury. Innate immune system such as Toll-like receptor 4 (TLR4) represents the first line of defense against infection. In addition to its pivotal role in host immunity, recent studies have demonstrated that TLR4 is an important functional contributor to tissue inflammation and cell survival in response to non-infectious injury. Our preliminary data suggest that TLR4 signaling plays a critical role in cardioprotection against ischemic injury in the heart and in isolated cardiomyocytes. The goals of this proposal are to define the role of cardiac TLR4 in protecting cardiomvocvtes in models of ischemia-reperfusion injury (IRI) and to identify the downstream mechanisms that mediate these effects. We anticipate that insights gained from the proposed studies will serve as a foundation for the future development of novel therapeutic approaches for the management of ischemic myocardial injury. This proposal is based on the following three hypotheses: 1) that TLR4 activation via its signaling protein IRAK-1 represents an important survival mechanism in the heart, 2) that nitric oxide synthase 2 (NOS2) mediates the TLR4-induced survival benefits, and 3) that augmentation of cardiac TLR4 signaling will reduce myocardial damage and produce a meaningful functional rescue in IRI. To test these hypotheses, we will manipulate cardiac expression of TLR4 and IRAK-1 using genetically modified animals as well as adenoviral gene transfer. In Specific Aim 1: we will explore the mechanisms by which TLR4 protects cardiomyocytes in in vitro models of apoptosis. In Specific Aim 2: we will determine how NOS2 and NO contribute to the TLR4-mediated anti-apoptotic effects in isolated cardiomyocytes. In Specific Aim 3: we will ascertain the role of cardiac (vs. extra-cardiac) TLR4 in protecting the heart against IRI. In Specific Aim 4: we will evaluate the anatomic and functional consequences of manipulating IRAK-1 in mouse models of IRI. We will test the impact of IRAK-1 deletion or cardiac IRAK-1 expression (via gene transfer) on IRI. Defining the signaling pathways that control cardiomyocyte survival and learning to manipulate these pathways in the heart may provide novel approach for the treatment of some cardiac conditions such as ischemia injury and cardiomyopathy.