Innate Immune Sensing of Bacterial Sugars

描述（由申请人提供）：先天免疫系统使用种系编码的受体识别微生物病原体，该受体识别微生物产生的保守结构。例如，“模式识别受体”TLR 4识别作为革兰氏阴性细菌细胞壁的一部分产生的脂多糖。当专职吞噬细胞如巨噬细胞和树突状细胞内化并降解微生物时，结构可以被释放。例如，细菌细胞壁肽聚糖可以被切割以释放胞壁酰二肽，胞质模式识别受体Nod 2的配体。在这个项目中，我们将延伸模式识别受体的定义，包括宿主酶己糖激酶，细胞葡萄糖代谢的中心酶。我们已经表明，在吞噬体中肽聚糖降解后，一种组分糖N-乙酰葡糖胺被释放并转运到细胞溶质中，在那里它与己糖激酶相互作用，导致酶从线粒体表面释放。从线粒体释放己糖激酶启动信号传导过程，最终激活“炎性体”复合物中的半胱天冬酶-1，其负责加工和释放关键的促炎细胞因子IL-1和IL-18（以及其他作用）。因此，己糖激酶是检测这种微生物来源的糖的存在的“受体”。内源性产生的N-乙酰葡糖胺在胞质溶胶中通常不游离，因此不参与己糖激酶。在这个项目中，我们将进一步描述这种先天免疫机制的三个目标。在目标一中，我们将描述巨噬细胞和树突状细胞中己糖激酶信号传导的细胞生物学特征，并确定该过程是如何调节的，从而不会对细胞产生毒性。在目标二中，我们将通过表征宿主酶N-乙酰葡糖胺激酶在体外和敲除小鼠体内作为负调节剂的功能来定义该途径在宿主防御中的作用。在目标三，以及将探索如何革兰氏阳性肽聚糖循环系统可以被操纵，以影响信号通过这一途径在免疫细胞和改变微生物的发病机制。

DESCRIPTION (provided by applicant): The innate immune system recognizes microbial pathogens using germ line encoded receptors which recognize conserved structures made by microbes. For example, the "pattern recognition receptor" TLR4 recognizes lipopolysaccharides produced as part of the cell walls of Gram-negative bacteria. When professional phagocytic cells such as macrophages and dendritic cells internalize and degrade microbes, structures may be released. For example, bacterial cell wall peptidoglycan may be cleaved to release muramyl dipeptide, a ligand for the cytosolic pattern recognition receptor Nod2. In this project, we will stretch the definition of a pattern recognition receptor to include the host enzyme hexokinase, a central enzyme in cellular glucose metabolism. We have shown that upon degradation of peptidoglycan in phagosomes a component sugar, N-acetylglucosamine, is freed up and transported into the cytosol where it interacts with hexokinase causing release of the enzyme from the mitochondrial surface. Hexokinase release from mitochondria initiates a signaling process culminating in activation of caspase-1 in an "inflammasome" complex which is responsible for processing and release of the key pro-inflammatory cytokines IL-1¿ and IL-18 (among other effects). Thus hexokinase is the "receptor" that detects the presence of this microbe-derived sugar. Endogenously produced N-acetylglucosamine is not normally found free in the cytosol and thus does not engage hexokinase. In this project we will characterize this innate immune mechanism further in three aims. In aim one we will characterize the cell biology of hexokinase signaling in macrophages and dendritic cells and determine how the process is regulated so as not to be toxic to the cells. In aim two we will define the role of the pathway in host defense through characterizing the function of the host enzyme N-acetylglucosamine kinase as a negative regulator in vitro and in vivo in knockout mice. In aim three well will explor how the Gram-positive peptidoglycan recycling system can be manipulated to influence signaling by this pathway in immune cells and alter microbial pathogenesis.