Role of Toll-Like Receptor Signaling in Cardiac Ischemia

描述(申请人提供)：先天免疫反应在心肌缺血/再灌注(I/R)损伤的病理生理学中起核心作用。然而，其机制尚不清楚。Toll样受体(Toll-like Receptor，TLR)介导的信号转导在先天免疫应答的诱导中起着关键作用。在上一次授予期间，我们证实了TLR4介导了I/R反应中的心肌损伤。我们发现PI3K/Akt信号可能是TLR4反应的负反馈调节因子。我们的数据表明，TLR和PI3K/Akt通路的不同调控决定了心肌对缺血损伤的反应的命运。在目前的方案中，我们将研究TLRs和PI3K/Akt信号在心肌I/R过程中的差异调节和相互作用。我们的长期目标是阐明心肌缺血损伤的机制，并开发有效的方法来预防心肌I/R损伤。我们的假设是：TLR和PI3K/Akt信号通路的不同调控决定了心肌对缺血/再灌注损伤的反应的命运。具体目的1将明确TLR4介导I/R后心肌细胞凋亡的机制。我们发现，I/R时TLR4的激活直接促进了心肌细胞的凋亡。我们将确定TLR4是否会刺激心肌I/R后的凋亡信号通路。具体目的2将阐明TLR4负调控心肌I/R期间PI3K/Akt活性的机制。TLR4在心脏I/R的病理过程中发挥重要作用。PI3K/Akt依赖的机制试图抑制TLR4信号在I/R中的有害影响。我们将确定TLR4如何在心脏I/R损伤中负向调节PI3K/Akt信号，从而限制其有益作用。特异靶3将研究TLR2激活PI3K/Akt，从而保护心肌的机制。我们发现，刺激TLR2通过依赖PI3K/Akt的机制来诱导心脏保护。具体机制尚不清楚。我们将确定TLR2的调节如何导致PI3K/Akt的激活，从而导致心脏保护。这项研究的结果将增加我们对心肌I/R的先天免疫反应以及先天免疫调节如何诱导心脏保护的基础科学知识。此外，我们的数据还可能具有实际意义，因为它可能导致开发新的和新的治疗缺血性心脏损伤的策略。公共卫生相关性据估计，每年有50万美国人死于心脏病发作，而缺血性心脏病(心脏血流减少)是心脏死亡的90%原因。免疫反应参与了心肌缺血/再灌注(血流再灌注，I/R)损伤和心力衰竭的发病机制。然而，与I/R中有害免疫反应相关的细胞和分子机制尚未阐明。Toll样受体(Toll-like Receptor，TLRs)是一类信号分子，在调节免疫和炎症反应中发挥重要作用。我们发现TLR4介导的信号转导介导了心肌I/R损伤。更重要的是，其他分子(称为PI3K/Akt)的激活诱导了对I/R损伤的心脏保护。因此，我们的研究结果表明，过度激活TLR4介导的信号通路将导致I/R后明显的心脏损伤，而PI3K/Akt信号通路的激活将保护心脏免受I/R损伤。在接下来的应用中，我们建议定义TLR4介导心脏损伤的细胞和分子机制，更重要的是，PI3K/Akt通路的调节如何介导I/R中的心脏保护。我们还将定义TLRs和PI3K/Akt在心肌I/R中的相互作用。本研究的结果将增加我们对心肌I/R的免疫反应以及免疫反应的调节如何诱导心脏保护的基础科学知识。因此，这项拟议的工作不仅意义重大，而且具有创新性，因为我们的数据可能还具有实际意义，因为它可能导致开发新的和新的心脏病发作治疗策略。

DESCRIPTION (provided by applicant): The innate immune response plays a central role in the pathophysiology of myocardial ischemia/reperfusion (I/R) injury. However, the mechanisms are unclear. Toll-like receptor (TLR) mediated signaling plays a critical role in the induction of the innate immune response. During the last grant period, we demonstrated that TLR4 mediates myocardial injury in response to I/R. We discovered that PI3K/Akt signaling may be a negative feedback regulator of the TLR4 response. Our data suggest that differential regulation of TLR and PI3K/Akt pathways determines the fate of the myocardium in response to ischemic insult. In the current proposal, we will investigate the differential regulation and interplay between TLRs and PI3K/Akt signaling during myocardial I/R. Our long term goals are to elucidate the mechanisms of cardiac ischemic injury and to develop effective approaches to prevent myocardial I/R injury. Our hypothesis is: Differential regulation of TLR and PI3K/Akt signaling pathways determines the fate of the myocardium in response to ischemia/reperfusion insult. Specific Aim 1 will define the mechanisms by which TLR4 mediates cardiomyocyte apoptosis following I/R. We found that TLR4 activation in I/R directly contributes to myocardial apoptosis. We will determine whether TLR4 will stimulate apoptotic signaling pathways following myocardial I/R. Specific aim 2 will elucidate the mechanisms of TLR4 negative regulation of PI3K/Akt activity during myocardial I/R. TLR4 plays a major role in the pathology of cardiac I/R. PI3K/Akt dependent mechanisms attempt to inhibit the deleterious effects of TLR4 signaling in I/R. We will define how TLR4 negatively regulates PI3K/Akt signaling in cardiac I/R injury, thereby limiting its beneficial effect. Specific aim 3 will examine the mechanism by which TLR2 activates PI3K/Akt, resulting in protection of the myocardium from I/R. We found that stimulation of TLR2 induces cardioprotection through PI3K/Akt dependent mechanisms. The specific mechanisms are unknown. We will determine how modulation of TLR2 results in activation of PI3K/Akt, leading to cardioprotection. The results of this research will increase our basic science knowledge of the innate immune response to myocardial I/R and how modulation of innate immunity induces cardioprotection. In addition, our data may also have practical significance in that it may lead to the development of new and novel treatment strategies for ischemic heart injury. PUBLIC HEALTH RELEVANCE It is estimated that 500,000 Americans die of heart attacks each year and ischemic heart disease (reduced blood flow in the heart) is responsible for 90% of cardiac mortalities. It is well established that immune responses are involved in the pathogenesis of myocardial ischemia/reperfusion (blood flow again, I/R) injury and heart failure. However, the cellular and molecular mechanisms associated with deleterious immune responses in I/R have not been elucidated. Toll-like receptors (TLRs) are signaling molecules which play a critical role in mediating immune and inflammatory responses. We discovered that TLR4-mediated signaling mediates myocardial I/R injury. Of greater significance, activation of the other molecules (called PI3K/Akt) induces the protection of heart from I/R injury. Thus, our findings indicate that excessive activation of the TLR4-mediated signaling pathway will result in significant heart damage following I/R, while activation of the PI3K/Akt signaling pathway will protect the heart from I/R injury. In this continuation application, we propose to define the cellular and molecular mechanisms by which TLR4 mediates cardiac injury and, more importantly, how modulation of the PI3K/Akt pathway mediates cardioprotection in I/R. We will also define the interplay between TLRs and PI3k/Akt in myocardial I/R. The results of this research will increase our basic science knowledge of the immune response to myocardial I/R and how modulation of immune response induces cardioprotection. Therefore, the work proposed is not only significant but also innovative because our data may also have practical significance in that it may lead to the development of new and novel treatment strategies for heart attack.