Fas/FasL在系统感染中的效应及机制研究

In this proposal we focus on the role of apoptotic molecules in innate immune response to bacterial and fungal infections. The pathogenesis of systemic infection or sepsis is a result of an uncontrolled hyperinflammatory, predominantly cytokine-mediated, response of the host. We focus on the Fas/FasL system that was originally studied within the context of cell death. Interestingly, in addition to its pro-death function, the Fas/FasL system also transduces non-apoptotic signals into the Fas/FasL-expressing cells. Importantly, our previous work has demonstrated that Fas ligation induced secretion of IL-1 beta by dendritic cells (DCs), instead of apoptosis. Also, FasL ligation could promote secretion of TNF- α and IL-6, indicating that FasL can transduce reverse signal in DCs. All these results indicate that Fas/FasL might involve in systemic infection induced cytokines secretion. Further experiment showed that Fas-mutant lpr mice are less susceptible to Gram-negative bacteria and fungi and displayed lower mortality and lower level of inflammatory cytokines, including IL-1β and TNF-α. Based on this preliminary data, we anticipate to elucidate the role of Fas or FasL in the inflammatory responses of infection. Then, we propose to study the transduction of Fas signal and FasL reverse signal, and also, their crosstalk with the major pathogen-sensing system Toll-like receptors and C-type lectin receptors. We hope to have a deeper understanding on the non-apoptotic effect of the classical apoptotic molecules and its underlying mechanisms, so that to provide a novel theoretical basis for the sepsis treatment.

败血症的发病与大量炎性细胞因子，包括IL-1β, TNFα和IL-6的分泌密切相关。我们之前的研究表明，凋亡诱导分子Fas可以促进树突状细胞分泌IL-1β, 而FasL可以传递反向信号，诱导DC分泌TNFα和IL-6。进一步实验发现：与对照小鼠相比，Fas突变的lpr小鼠接受绿脓杆菌或白色念珠菌静脉感染后，生存期明显延长，血清中IL-1β 和 TNF-α水平明显降低。该结果提示，Fas/FasL系统可能参与调节炎性因子的分泌，而且，作为识别细菌和真菌的重要的模式识别受体，Toll样受体（TLR）和C型凝集素型受体（CLR）与Fas/FasL系统可能在此过程中存在相互作用。因此，我们希望： 1 明确Fas/FasL在系统性感染中的作用; 2. 深入研究Fas/FasL与 TLR和CLR在胞内信号传导的相互作用。以期深入了解凋亡分子在感染中的非凋亡效应及机制，为败血症的治疗提供新的理论基础。

Fas/FasL系统作为经典的凋亡诱导信号，其在炎症中的效应一直未得到深入的研究。我们基于以往的研究基础发现Fas信号的非凋亡效应及感染后Fas/FasL系统缺失时造成的影响，希望通过该课题的研究，初步 明确Fas/FasL在系统性感染中的作用， 并深入研究Fas/FasL与 TLR和CLR在胞内信号传导的相互作用。 研究结果提示, FasL在巨噬细胞和树突状细胞中可以传递反向信号， 诱导TNFα和IL-6的分泌；该信号的缺失也会造成炎症水平的降低，并使系统性感染的小鼠的生存期延长。 虽然CLR的激动剂对Fas信号或者FasL缺失的DC的活化较野生型无明显变化，但Fas-Fc刺激Dectin-1和Dectin-2缺陷小鼠后，其分泌IL-6和TNFα的量明显降低，证明Dectin-1 和Dectin-2通路与FasL反向信号通路有一定交互作用， 具体机制在进一步深入研究中。同时我们的研究也发现， Fas/FasL通路也参与了慢性系统性炎症导致的纤维化的作用， DC表面的Fas 和FasL可以促进DC MMP9的表达增加，从而影响日本血吸虫导致的纤维化。通过以上研究，我们对 Fas/FasL通路的非凋亡效应有了更深入了解， 希望可以成为治疗系统性感染的新靶点。