结核分枝杆菌调控PPAR-γ诱导泡沫巨噬细胞形成的机制及其在结核病免疫中的作用

As the main parasitic cells of Mycobacterium tuberculosis (Mtb), macrophages (MΦ) play a central role in the immunity against tuberculosis (TB), by acting as the main effector cells in this immune course. Meanwhile, as one of the successful human pathogens, MTB can manipulate the function of macrophage through a series of strategies. Inducing the formation of foamy macrophage (FM) is one of such strategies. Our preliminary studies found that PPAR-γ plays a key role in the process of FM formation upon the infection of MTB, which suggest that MTB can manipulates the function of MΦ and the immunity against TB by inducing the PPAR-γ-dependent FM formation. However, upon the infection of MTB, the pathways of PPAR-γ activation and mechanisms of FM formation after the activation of PPAR-γ are still unclear. The direct evidence of the impacts of the FM formation on the TB-related immunity and the progress of TB are still absent. In this program, the in vitro infection model of MΦ, the in vitro model of tuberculous granuloma and mouse model of tuberculosis are planed to be constructed and analyzed on the molecular, cellular and animal test levels. This program aims to investigate the signal transduction pathways through which MTB activate the PPAR-γ, illuminate the mechanisms of PPAR-γ-dependent FM formation, and demonstrate the significance of FM formation in the course of tuberculous granuloma development and the immunity against TB. This research may deepen our understanding on the mechanisms of TB-related immunity; discover potential new molecular targets for TB therapy.

巨噬细胞(MΦ)是结核病(TB)免疫的主要效应细胞，但也是结核菌在体内的主要寄生细胞。研究发现，结核菌能通过一系列策略调控MΦ的功能，诱导泡沫巨噬细胞(FM)形成就是其中之一。课题组前期研究发现，结核菌诱导FM形成的过程是PPAR-γ依赖性的，提示结核菌可通过调控PPAR-γ诱导FM形成参与对MΦ功能和TB免疫的调控。但结核菌通过何种途径活化PPAR-γ、PPAR-γ活化后又是通过何种机制诱导FM形成等目前还不清楚，这一过程对TB免疫及TB的发生发展有何影响等也未见报道。本项目拟在前期研究基础上，通过建立MΦ体外感染模型、体外结核性肉芽肿模型和小鼠TB模型，分别在分子、细胞和动物水平探讨结核菌活化MΦ PPAR-γ的途径，明确PPAR-γ活化后诱导FM形成的相关机制，探讨FM形成在TB免疫中的相关作用及其对TB进展的影响，以期深化我们对TB相关免疫的理解，发现新的TB治疗的潜在分子靶点。

诱导巨噬细胞发生泡沫样改变进而形成泡沫巨噬细胞是结核分枝杆菌抑制巨噬细胞功能，实现其在人体内存活的重要机制之一，也是结核病潜伏感染者向活动性结核病转变的重要机制，但相关的分子机制并不清楚。在本研究中，通过建立巨噬细胞的体外感染模型，课题组筛查和鉴定了结核分枝杆菌活化巨噬细胞PPAR-γ的途径，以及PPAR-γ活化后诱导泡沫巨噬细胞形成的分子机制；通过建立体外结核性肉芽肿模型，探讨了泡沫巨噬细胞形成对结核性肉芽肿形成和发展的影响。我们的研究发现:（1）结核分枝杆菌感染巨噬细胞后，可通过促进细胞内活性氧的生成下调巨噬细胞PPAR-γ的表达，通过调节ROS的水平可调控巨噬细胞PPAR-γ的表达；（2）PPAR-γ表达下调可上调CD36和SR-A1等脂质摄入分子的表达，同时抑制巨噬细胞表面脂质外排分子ABCG1的表达，导致巨噬细胞脂质摄入增加同时外排脂质的能力下降，从而诱导泡沫巨噬细胞的生成；（3）调控PPAR-γ的表达对结核性肉芽肿的生成没有显著影响。本研究在国内外首次发现ROS参与了巨噬细胞PPAR-γ的表达调控，并明确了ROS-PPAR-γ-ABCG1通路在巨噬细胞脂质代谢和泡沫巨噬细胞形成中的作用。本研究奠定了PPAR-γ作为泡沫巨噬细胞形成调控靶点分子的理论基础，同时进一步深化了人们对结核分枝杆菌调控巨噬细胞功能的机制的认识。