Role of TLR-cfB Signaling in Sepsis

描述（由申请人提供）：败血症的患病率为75万例，每年夺去20多万人的生命。由心脏抑制和血管深度扩张引起的心血管衰竭是感染性休克的主要特征，也是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优势，但由于心功能障碍导致的脓毒性死亡率仍然很高。因此，需要更好地了解脓毒症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。先天免疫信号，如toll样受体（TLRs）及其信号分子MyD88和Trif，是抵御微生物感染的第一道防线，在败血症中发挥作用，但它们在败血症期间心功能障碍中的作用和潜在机制仍不明确。我们最近证明，TLR2信号的激活抑制心肌细胞（CM）功能，TLR2缺陷的动物在多微生物腹膜炎败血症中显著改善心功能和生存率。MyD88，而不是Trif，在多微生物败血症引起的心功能障碍和死亡率中是必不可少的。补体系统也是先天免疫的一部分，但其与tlr在败血症中的相互作用尚不清楚。我们的初步数据清楚地表明，体外TLR刺激或体内多微生物脓毒症特异性诱导心脏中补体因子B （cfB）的强劲表达，这是替代途径的关键组成部分。此外，与野生型（WT）小鼠相比，缺乏cfB的小鼠在败血症期间心功能和存活率显著改善。该建议基于以下三个假设：1) TLR2/4-MyD88信号是脓毒症诱导心功能障碍的重要决定因素，介导脓毒症中心肌cfB的特异性表达；2)cfB通过Ca2+处理受损、线粒体功能障碍和氧化应激等不同的细胞内机制参与脓毒症诱导的心功能障碍；3)基因缺失或药理抑制cfB可改善多微生物脓毒症期间的心功能和生存率。在Specific Aim 1中，我们将确定TLR2和TLR4在脓毒症中介导心脏cfB表达的作用。在Specific Aim 2中，我们将描述MyD88信号在败血症中cfB表达和心功能障碍中的作用。在特异性目标3中，我们将定义cfB在多微生物脓毒症心功能障碍发病机制中的作用。在Specific Aim 4中，我们将确定cfB药物抑制对脓毒症引起的心功能障碍的保护作用。综上所述，这些目标将进一步加深我们对以下方面的理解：1)败血症期间TLR信号与心脏补体系统的复杂相互作用；2)MyD88信号在败血症心功能障碍中的作用；3)cfB及其替代途径在多微生物败血症中的关键作用；4)抗cfB抗体在多微生物败血症临床相关模型中的治疗效果。我们相信，这些见解将作为未来发展新的治疗方法的基础，以临床管理严重败血症。

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.