内毒素降解酶AOAH促进肺区域免疫防御的机制研究

Alveolar macrophages (AM) are professional phagocytes in the alveoli and they are essential for rapid and effective innate responses during lung infections. Endotoxin (Lipopolysaccharide, LPS) is a characteristic molecule of Gram-negative bacteria. After macrophages respond to LPS stimulation, they enter a tolerant state. Tolerance diminishes innate immune responses to a secondary stimulation and makes the host more susceptible to subsequent infection. Acyloxyacyl hydrolase (AOAH) is the only host endogenous enzyme that known to be able to degrade and inactivate LPS in tissues. We have shown that AOAH promotes the recovery from i.p. injected LPS-induced macrophage tolerance. So far, it is not clear whether AOAH may inactivate commensal LPS and therefore regulates the innate responses of macrophages. Our preliminary data show that Aoah-/- AM and alveolar epithelial cells were refractory to LPS stimulation and Aoah-/- mice were more susceptible to bacterial pneumonia. Aoah-/- feces and plasma had higher TLR4 stimulatory activities than did Aoah+/+ counterparts. Aoah-/- mice treated with antibiotic which depleted their commensal gram-negative bacteria had decreased TLR4 stimulatory activities in their feces and their AM regained responsiveness. These results strongly suggest that AOAH deactivates intestinal commensal LPS, and therefore maintains AM innate responses and promotes the lung immune defense. We propose to use Aoah-/- mice, mouse pneumonia models, immunological methods and microarray to study the role that AOAH plays in promoting AM functions and the lung immune homeostasis as well as the mechanisms. This study will shed light on how AOAH works through gut-lung axis to regulate the lung regional defense and may open new avenue toward clinical intervention of pneumonia.

肺泡巨噬细胞（AM）对肺区域免疫防御至关重要。内毒素(LPS)为革兰氏阴性菌特征性分子，能够刺激巨噬细胞继而诱导其耐受，削弱对再刺激的免疫应答。酰基羧酸水解酶(AOAH)为目前发现的唯一能在组织中降解灭活内毒素的宿主内源性酶，我们发现AOAH促进外源性LPS诱导巨噬细胞耐受的消退。迄今，AOAH能否通过降解体内来源如肠道共生菌LPS而调控巨噬细胞应答尚不明确。预实验结果表明Aoah-/-小鼠AM和肺泡上皮细胞均耐受，抗呼吸道感染能力减弱；Aoah-/-粪便和血液TLR4刺激活性增高，如用抗生素去除肠道革兰氏阴性菌后，AM免疫应答恢复，强烈提示AOAH通过调节肠道LPS活性维持AM免疫反应性进而保障肺区域免疫防御。我们拟运用Aoah-/-小鼠、感染性肺炎模型、免疫、转录组学等多项技术，从肠-肺轴这个新视角研究AOAH对AM功能和肺免疫稳态的调控及其机制，为感染性肺炎的干预开拓新途径。

肺泡巨噬细胞（AM）直接暴露于吸入的空气中，处于肺区域免疫防御的第一线。革兰氏阴性菌内毒素（脂多糖，LPS）是生物活性很强的PAMP分子。巨噬细胞被LPS刺激产生固有免疫应答后，进入低应答的内毒素耐受状态。AOAH是高度保守的能够降解LPS的宿主酯酶，我们前期发现AOAH促进LPS诱导的内毒素耐受的消退。在本项目中，我们研究了AOAH能否通过降解内源性如肠道共生菌LPS而调控肺泡巨噬细胞及肺泡上皮细胞应答。我们发现和对照Aoah+/+小鼠相比，Aoah-/-小鼠肺部免疫防御能力下降，Aoah-/-小鼠肺泡巨噬细胞和肺泡上皮细胞的固有免疫应答和吞噬细菌能力减弱，其糖酵解和线粒体质量减少。血液中活性LPS增加能够诱导肺固有免疫耐受，而用抗生素减少肠道菌后，Aoah-/-肺固有免疫应答恢复。因而AOAH通过降解肠道菌来源的LPS以保持肺免疫反应性，此外，我们还发现Aoah-/-小鼠对呼吸道过敏原的固有应答也减弱，因而不易发生过敏性哮喘。此项研究为感染性肺炎及过敏性哮喘的干预提供了新思路。