Role of TLR-cfB Signaling in Sepsis

描述(由申请人提供)：败血症的发病率为75万例，每年夺走20多万人的生命。心脏抑制和严重的血管扩张导致的心血管衰竭是感染性休克的主要特征，也是导致其高死亡率的原因之一。虽然目前的重症监护治疗提供了生存益处，但因心功能不全而导致的败血症死亡率仍然很高。因此，需要更好地了解感染性休克时导致心功能障碍的分子机制，以进一步改善严重脓毒症患者的护理。天然免疫信号，如通过Toll样受体(TLRs)及其信号分子MyD88和Trif的信号，是抵御微生物感染的第一道防线，并在脓毒症中发挥作用，但它们在心功能障碍中的作用及其在脓毒症中的潜在机制仍不清楚。我们最近证实，TLR2信号的激活抑制了心肌细胞(CM)的功能，并且TLR2缺乏的动物显著改善了多菌腹膜炎脓毒症的心功能和存活率。在多菌败血症引起的心功能障碍和死亡率中，MyD88是必需的，但不是TRIF。补体系统也是先天免疫的一部分，但它在脓毒症时与TLRs的相互作用尚不清楚。我们的初步数据清楚地表明，体外TLR刺激或体内多菌败血症特异性地诱导心脏中强大的补体因子B(CFB)表达，这是替代途径的关键组成部分。此外，在脓毒症期间，与野生型(WT)小鼠相比，CFB缺陷小鼠的心功能和存活率显著提高。该提议基于以下三个假设：1)TLR2/4-MyD88信号是脓毒症所致心功能障碍的重要决定因素，介导了脓毒症时心肌CFB的特异性表达；2)CFB通过不同的细胞内机制参与脓毒症所致的心功能障碍，包括钙调节功能受损、线粒体功能障碍和氧化应激；以及3)CFB的基因缺失或药物抑制可以在多菌败血症时改善心功能和提高存活率。在特定的目标1中，我们将确定TLR2和TLR4在介导脓毒症心脏CFB表达中的作用。在特定的目标2中，我们将描述MyD88信号在脓毒症中CFB表达和心功能不全中的作用。在具体目标3中，我们将明确CFB在多菌败血症心功能不全发病机制中的作用。在具体目标4中，我们将确定药物抑制CFB对脓毒症所致心功能不全的保护作用。这些目标将进一步加深我们对1)脓毒症时心脏中TLR信号和补体系统之间的复杂相互作用，2)MyD88信号在败血症心脏功能障碍中的作用，3)CFB和替代途径在多菌败血症中的关键作用，以及4)抗CFB抗体在临床相关的多菌败血症模型中的治疗效果的理解。我们相信，这些洞察力将为未来开发新的治疗方法来治疗严重脓毒症奠定基础。

DESCRIPTION (provided by applicant): Sepsis has a prevalence of 750,000 cases and claims more than 200,000 lives each year. Cardiovascular collapse induced by cardiac depression and profound vasodilatation represents a main feature of septic shock and contributes to its high mortality. While the current critical care therapy offers survival benefit, the septic mortality due to cardiac dysfunction remains high. Therefore, a better understanding of the molecular mechanisms that lead to cardiac dysfunction during septic shock is needed to further improve the care of patients with severe sepsis. Innate immune signaling such as those via Toll-like receptors (TLRs) and their signaling molecules MyD88 and Trif represents the first line of defense against microbial infection and play a role in sepsis, but their role in cardiac dysfunction and the underlying mechanisms during sepsis remain poorly defined. We have recently demonstrated that activation of TLR2 signaling inhibits cardiomyocyte (CM) function and that animals deficient in TLR2 have markedly improved cardiac function and survival in polymicrobial peritonitis sepsis. MyD88, but not Trif, is essential in polymicrobial sepsis-induced cardiac dysfunction and mortality. The complement system is also a part of innate immunity but its interaction with TLRs during sepsis is poorly understood. Our preliminary data have clearly demonstrated that TLR stimulation in vitro or polymicrobial sepsis in vivo specifically induces a robust complement factor B (cfB) expression in the heart, a key component of alternative pathway. Moreover, mice deficient in cfB have a significantly improved cardiac function and survival compared with wild-type (WT) mice during sepsis. The proposal is based on the following three hypotheses: 1) TLR2/4-MyD88 signaling, an important determinant in sepsis-induced cardiac dysfunction, mediates the specific myocardial cfB expression in sepsis, 2) cfB contributes to the sepsis-induced cardiac dysfunction via distinct intracellular mechanisms including impaired Ca2+ handling, mitochondrial dysfunction, and oxidative stress, and 3) genetic deletion or pharmacological inhibition of cfB can lead to improved cardiac function and better survival during polymicrobial sepsis. In Specific Aim 1, we will determine the role of TLR2 and TLR4 in mediating cardiac cfB expression in sepsis. In Specific Aim 2, we will delineate the role of MyD88 signaling in cfB expression and cardiac dysfunction in sepsis. In Specific Aim 3, we will define the role of cfB in the pathogenesis of cardiac dysfunction in polymicrobial sepsis. In Specific Aim 4, we will determine the efficacy of pharmacological cfB inhibition to protect against sepsis-induced cardiac dysfunction. Together these aims will further our understanding of 1) the complex interaction between TLR signaling and the complement system in the heart during sepsis, 2) the role of MyD88 signaling in septic cardiac dysfunction, 3) the critical role of cfB and alternative pathway in polymicrobial sepsis, and 4) the therapeutic efficacy of an anti-cfB antibody in a clinically relevant model of polymicrobial sepsis. We believe that such insights will serve as a foundation for the future development of novel therapeutic approaches to the clinical management of severe sepsis.