PAK1信号调控树突状细胞归巢的机制及在哮喘中的意义

The homing of dentritic cells（DC）to lung-draining lymph nodes is an important step for DC activating Th2 immunoresponse, and blocking the homing of DC is a key strategy for asthma therpapy. Based on our premier findings that intratracheal injection of PAK1 inhibitor, IPA-3, significantly inhibited OVA migration to draining lymph nodes, and increased its detention in the lungs; IPA-3 decreased the OVA-induced increases of lymphocyte numbers in draining lymph nodes and OVA-induced inflammatory cells infiltration into lungs and airway hyperresponsiveness, we will further study the detailed effects of PAK1 on DC homing and its significance in experimental therapy of astham by using cell culture, conventional and knockout animal models, especially, we will focus on the roles of Bac1/CDC42 and MAPK1 which could be the potential upstream and downstream molecules involving PAK1 signaling in DC homing and development of asthma. By this study, we will provide with the new theory for pathogenesis of asthma and the new potential target for therapeutical intervention of asthma.

树突状细胞从气道组织归巢到灌流淋巴结是哮喘中触发Th2细胞免疫应答的关键步骤，阻断树突状细胞归巢是哮喘治疗的重要策略之一。然而，关于树突状细胞归巢的信号机制却知之甚少。我们前期的探索性研究表明，PAK1（P21-activated kinase 1）抑制剂IPA-3气道内给药能显著地减少树突状细胞纵隔淋巴结内迁移，增加其在肺内的滞留；同时，IPA-3 能显著减少纵隔淋巴结内淋巴细胞数,并减轻哮喘气道炎症和气道高反应性,提示PAK1可能通过影响树突状细胞的归巢而调控哮喘的病理。以此为基础，我们拟进一步利用体外培养的细胞模型、常规和基因敲除的小鼠模型研究PAK1调控树突状细胞归巢的具体效应和在哮喘实验性治疗中的意义，重点分析Rac1/CDC42、MAPKs等信号分子的作用。本项目研究，将为哮喘发病机制提供新的理论，也为哮喘药物治疗提供新的靶点。

当过敏体质患者接触变应原后，呼吸道组织内树突状细胞（dendritic cell，DC）携带捕获的变应原进入引流纵隔淋巴结，激活初始T细胞并进一步促进T细胞向2型辅助性T细胞(Th2)方向分化并增殖，引发变应性炎症反应，导致哮喘发作。DC细胞的纵隔引流淋巴结归巢决定于DC细胞的迁移信号，而P21活化激酶1（P21-activated kinase，PAK1）是一保守的丝氨酸／苏氨酸蛋白激酶作为Rho家族小G蛋白（Rho small GTPase）分子Rac1和CDC42下游重要的靶蛋白参与调控细胞迁移。本研究发现，全身性给予或者气道内局部给予PAK1抑制剂IPA-3均能显著地抑制哮喘动物模型中炎症细胞特别是嗜酸细胞的浸润，进一步抑制DC细胞内PAK活性后回输DC细胞入肺内对哮喘炎症也产生明显的减轻作用，从而证实了DC细胞的PAK1活性调控DC细胞的纵隔引流淋巴结归巢并在哮喘炎症发生中具有重要的角色。同时，我们进一步发现抑制PAK1活性并不影响DC细胞凋亡、DC细胞摄取抗原、DC细胞激活T细胞，但PAK1介导CCL19、Rac1、cofillin的活性而调控DC细胞的迁移，提示PAK1可能通过调控DC细胞的迁移信号而影响DC细胞的淋巴结内归巢以及哮喘炎症的发生和发展。这一研究不仅明确了PAK1在哮喘中的重要作用，进一步阐明了PAK调控哮喘发生发展的可能机制，为哮喘的发病以及防治提供了新的理论。