INNATE IMMUNITY AND MYOCARDIAL INJURY

在没有感染证据的情况下，患有心力衰竭的人和实验动物在心脏中表现出炎症细胞因子的表达增加，包括TNF， il -1 β和IL-6，以及iNOS。虽然适应性不良的心脏重塑归因于这些蛋白，但触发和维持其表达的近端事件尚不清楚。然而，现在已知这些介质中的每一种都与先天免疫有关，先天免疫是免疫系统的一个进化上古老的分支，由模式识别受体（PRRs）触发，例如无脊椎动物和脊椎动物表达的toll样受体（TLRs），它们识别病原体上基本不变的结构基元。现在认识到，先天免疫PRRs也可能在真核生物中进化，通过识别在受损细胞或程序性死亡细胞上发现的相对不变的基序，识别和修复或清除受伤或死亡细胞。基于这些观察结果和我们自己的初步数据，我们假设由心肌细胞表达的脊椎动物TLR4在心脏损伤反应中起关键作用。具体而言，我们将研究：1)体外心肌细胞TLR4表达在紫外光、蒽环类抗生素和环双轴应变耦合电场起搏诱导下的损伤反应，以及实验性心肌梗死后心室肌重构中心肌细胞的原位表达；2)心肌细胞中活化的TLR4激活NFkappaB和MAP激酶的信号转导途径及其可能定位于空泡微域；3) TLR4在体外和体内肌细胞损伤应答中的功能作用；具体来说，我们将验证以下假设：i)组成型激活的TLR4构建体在体外传递存活信号；ii) TLR4参与凋亡细胞的识别和清除；iii)靶向破坏TLR4或其直接下游信号靶标MyD88的动物在心肌梗死时表现出心室重构率的改变。

Both humans and experimental animals with heart failure exhibit increased expression in the heart of inflammatory cytokines, including TNF, IL-1beta and IL-6, as well as iNOS, in the absence of evidence of infection. While maladaptive cardiac remodeling has been attributed to these proteins, the proximal events that trigger and sustain their expression are not well understood. Each of these mediators, however, are now known to be related to innate immunity, an evolutionarily ancient arm of the immune system that is triggered by pattern recognition receptors (PRRs), such as the toll-like receptors (TLRs) expressed by invertebrates and vertebrates, that recognize largely invariant structural motifs on pathogens. It is now recognized that innate immune PRRs also may have evolved in eukaryotes to recognize and repair or remove injured or dying cells, again by recognizing relatively invariant motifs found on injured cells or on cells programmed to die. Based on these observations and our own preliminary data, we hypothesize that vertebrate TLR4, which is expressed by cardiac myocytes, plays a pivotal role in the response to injury in the heart. Specifically, we will examine: 1) the regulation of TLR4 expression in cardiac myocytes in vitro in response to injury induced by UV light, by anthracycline antibiotics and by cyclic biaxial strain coupled with electric field pacing, as well as in cardiac myocytes in situ in remodeling murine ventricular muscle following experimental myocardial infarction; 2) the signal transduction pathways leading to NFkappaB and MAP kinase activation by activated TLR4 in cardiac myocytes and their possible localization to caveolar microdomains; and 3) the functional role(s) of TLR4 in the response to myocyte injury in vitro and in vivo; specifically, we will test the hypothesis that: i) a constitutively activated TLR4 construct conveys a survival signal in vitro; ii) that TLR4 participates in the recognition and removal of apoptotic cells; and iii) that animals with targeted disruption of TLR4, or of its immediate downstream signaling target MyD88, exhibit altered rates of ventricular remodeling in response to myocardial infarction.