5-脂氧酶代谢物对哮喘神经免疫内分泌的调节机制

Hormones secretived by hypothalamic-pituitary-adrenal axis plays a critical role in in asthma. Despite intensive studies focused on the pathophysiology of asthmatic inflammation, little is known about how cross-talk between neuroendocrine and immune systems regulates the inflammatory response during an asthmatic attack. We recently showed corresponding changes of cytokines and leukotriene B4 (LTB4) in brain and lung tissues of antigen-challenged asthmatic rats. This study expands our concept of the regulatory role of intracranial inflammatory mediators in inflammatory diseases including asthma, and suggests a link between intracranial LTB4 and neuroendocrine networks. This study also suggests that increases in LTB4 levels are involved in the pathophysiology of allergy, regardless of the target organ affected, and appear to be part of a negative feedback regulation system associated with corticosterone production resulting from activation of the HPA axis. To further investigate the regulate effect of LTB in central nervous system (CNS) on neuro-endocrine-immune (NEI) in asthma, gene knockout mice, receptor specific tools such as inhibitors and molecular meth od will be employed in the program. First, LTB4 in brain induced glucocorticoid receptor (GR) and its subtypes such as GRα and GRβ expression as well as signaling pathway will be investigated; Second,the changes of GR expression how to effect hypothalamic pituitary adrenal (HPA) axis secreting glucocorticoid and tolerance of glucocorticoid will be studied; Finally, glucocorticoid secreting of HPA axis and tolerance of glucocorticoid are associated with pathophysiology of asthma will be studied.

HPA轴分泌的激素在调控哮喘发病中起着关键性的作用。本项目组的研究证明：致敏动物在抗原攻击后中枢和肺组织的5-脂氧酶代谢物白三烯B4(LTB4)水平升高与肺功能下降相关，而脑室注射LTB4通过增加HPA轴分泌激素可抑制哮喘肺功能下降和肺组织炎性浸润变化，这一作用可被U75302所抑制所阻断，提示中枢LTB4增加在哮喘中可能涉及到神经-内分泌-免疫调节机制。为了进一步确定中枢LTB4在哮喘中的神经-内分泌-免疫中调节作用，本项目将采用基因敲除的小鼠、受体特异性抑制剂等工具和分子学方法，首先研究脑内LTB4诱导糖皮质激素受体(GR)和亚型GRα和GRβ表达的影响以及上调表达的信号通路；其次研究GR表达变化对HPA轴分泌激素有何影响，对激素耐受有何意义；最后研究前脑局部GR敲除后对HPA轴分泌激素和激素耐受与哮喘病理生理关系。通过神经-免疫-内分泌学研究"炎症双向学说"，为哮喘防治提供新理论。

我们先前的研究表明，在大鼠的哮喘发作期间，脑内白三烯B4（LTB4）水平增加会通过调高的系统性糖皮质激素对哮喘的发作产生反馈调节作用。然而，正常情况下或神经炎症过程中的LTB4诱导的这种糖皮质激素受体(GR)表达及其功能作用在仍不清楚。本研究进一步探讨了LTB4诱导下丘脑-垂体-肾上腺(HPA)轴GR表达在调节致敏大鼠抗原诱导哮喘反应中作用及其机制。在整体试验中。用卵白蛋白(OVA)-致敏大鼠后抗原攻击诱导哮喘，LTB4和U75302(一种选择性LTB4 BLT1受体抑制剂)或LY255283(一种选择性LTB4 BLT2受体抑制剂)在抗原攻击前30分钟通过下丘脑注射预处理。在离体试验中应用一种下丘脑的器官培养系统和下丘脑细胞系mHypoE-N37 (N37)细胞建立模型。结果显示：在整体试验中，抗原攻击增加了对致敏大鼠GR的表达。而致敏大鼠在抗原攻击后，通过下丘脑注射的LTB4进一步显著增加了HPA轴上GR基因和蛋白的水平。在离体试验中，正常或致敏大鼠的离体培养下丘脑组织，用LTB4 (30 ng/mL)刺激上调GR基因和蛋白的表达。在N37细胞中，LTB4剂量依赖诱导GR基因和蛋白表达，主要是诱导GR亚型GRα的表达，这些反应均可被U75302和LY255283预处理所抑制。U75302和LY255283通过抑制TB4诱导的Erk1/2和p38 MAPK信号产生调节作用。综上所述，结果表明，在HPA轴上LTB4通过BLT受体结合激活MAPK信号途径，上调GR基因和蛋白表达。我们的研究结果阐明了在哮喘发作过程中，LTB4水平的升高可以上调HPA轴GR的表达，从而增加机体其自身对炎症介质的下调，使得哮喘发作中机体自身炎症和抗炎产生平衡，从而导致哮喘的自身缓解。