Mast Cell Derived PGD2 and LTC4 in Lung Inflammation

肥大细胞(MC)对天然刺激或高亲和力IgE受体(FceRI)的激活做出反应，通过产生二十烷基类化合物，特别是半胱氨酰白三烯(CysLTs)和前列腺素(PG)D2，与哮喘的炎症过程直接相关。虽然CysLTs在哮喘中的作用是通过阻断它们的合成或在1型(CysLT-I)受体上的作用的治疗剂的疗效来确定的，但PGD2的类似证据正在等待人类使用的特定抑制剂的开发。我们的初步研究表明，PGD2意外地抑制小鼠骨髓来源的MCs(MBMMCs)产生LTC4合成酶(LTC4S)和LTC4，并且微生物信号Etidoglycan(PGN)诱导mBMMCs表达LTC4S(但不诱导造血的PGD2合成酶)。与IL-4不同，PGN通过信号转导转录激活因子(STAT)6独立的信号通路上调LTC4S，该信号通路可能涉及核因子KB(NF-ICB)和其他Toll样受体(TLR)依赖的信号。我们假设：(1)PGD2通过DP2受体介导的信号抑制LTC4S功能，该信号主要针对 翻译后机制，PGN通过上调LTC4S表达 (2)在肺部炎症的过敏原激发模型中，CysLT1在炎症反应中起更重要的作用，而CysLT2与肺重塑更相关，MC来源的PGD2和PGE2通过抑制LTC4S而对抗cysLTs的作用；(3)LTC4S是均三聚体，每个单体含有四个α螺旋，Arg-51和Tyr-93参与催化，而LLE-27、Val-35、Val-49、Arg-51、Ala-52、Asn-55、Tyr-59、Tyr-93、Tyr-97和Ala-112形成LTA4和GSH的结合部位。因此，我们提出以下具体目标：1)阐明PGN上调和 PGD2下调mBMMCs中LTC4S的表达；2)检测LTC4和PGD2在肥大细胞依赖的气道炎症模型和慢性气道重塑模型中的体内作用；3)通过X射线结晶学确定人LTC4S的三维结构。

Mast cells (MCs) to respond to activation by innate stimuli or cross linking of the high-affinity receptor for IgE (FceRI) by generating eicosanoids, particularly the cysteinyl leukotrienes (cysLTs) and prostaglandin (PG) D2, providing a direct link to the inflammatory processes in bronchial asthma. While the role of cysLTs in bronchial asthma is established by the efficacy of therapeutic agents that block their synthesis or their action at the type 1 (CysLT-i) receptor, comparable evidence for PGD2 awaits development of specific inhibitors for human use. Our Preliminary studies now reveal that PGD2 unexpectedly suppresses LTC4 synthase (LTC4S) and LTC4 generation by mouse bone marrow-derived MCs (mBMMCs), and that a microbial signal, eptidoglycan (PGN), induces the expression of LTC4S (but not hematopoietic PGD2 synthase) by mBMMCs. Unlike IL-4, PGN upregulates LTC4S by a signal transducer activator of transcription (STAT)6 independent signaling pathway that likely involves nuclear factor KB (NF-icB) and other Toll-like receptor (TLR)-dependent signals. We hypothesize that (1) that PGD2 inhibits LTC4S function by a DP2 receptor-mediated signal directed predominantly to a post translational mechanism, that PGN upregulates LTC4S expression through NF-KB-dependent transcription and that the PGD2 mediated down regulation of LTC4S action will be dominant over the enhancement action of PGN; (2) that in allergen challenge models of pulmonary inflammation, CysLT1 is more important in the inflammatory response and CysLT2 is more relavent to pulmonary remodeling, and that MC-derived PGD2 and PGE2, through suppression of LTC4S, will counter the effects of cysLTs; and (3) that LTC4S functions as homotrimer with each monomer containing four alpha helixes, and that Arg-51 and Tyr-93 are involved in catalysis while lle-27, Val-35, Val-49, Arg-51, Ala-52, Asn-55, Tyr-59, Tyr-93, Tyr-97, and Ala-112 form the binding sites for LTA4 and GSH. We therefore propose the following Specific Aims: 1) To elucidate the mechanism by which PGN upregulates and PGD2 downregulates the expression of LTC4S in mBMMCs; 2) To examine the in vivo role of LTC4 and PGD2 in mast cell dependent models of airway inflammation and in chronic models with remodeling of airways; and 3) To determine the three-dimensional structure of human LTC4S by X-ray crystallography.