结核分枝杆菌PE_PGRS家族抗原PE_PGRS41调控宿主免疫应答的分子机制研究

PE_PGRS抗原是结核分枝杆菌基因组一个独特的多基因家族，与分枝杆菌毒力相关。PE_PGRS41蛋白，又称酸性和吞噬体调控蛋白aprC，调控吞噬体酸化，具体的作用机制未知。我们的前期研究发现PE_PGRS41蛋白定位于分枝杆菌细胞壁，能够抑制巨噬细胞凋亡并调控宿主免疫应答反应，促进非致病性耻垢分枝杆菌在胞内存活。Ca2+作为重要的第二信使参与多个细胞信号的调控，包括吞噬体成熟及内质网应激介导的细胞凋亡。PE_PGRS41蛋白氨基酸序列中含有16个Ca2+结合基序，暗示PE_PGRS41可能调节巨噬细胞内Ca2+水平，阻碍吞噬体活化以及扰乱内质网应激介导的细胞凋亡，最终促进分枝杆菌在巨噬细胞内持留。本项目进一步研究PE_PGRS41蛋白在调控宿主免疫应答反应的分子机制，并在细胞和动物两个层次验证PE_PGRS41蛋白在分枝杆菌毒力中的重要性。

Tuberculosis (TB), caused by Mycobacterium tuberculosis, remains a global burden of morbidity and mortality. M. tuberculosis survives and persists in the host by modulating host immune responses. M. tuberculosis genome has a unique multigenic PE_PGRS family with highly conserved N-terminal Pro-Glu (PE) domain and a variable polymorphic GC-rich repetitive sequence (PGRS) domain. PE_PGRS proteins, with functions largely unknown, the distribution of PE_PGRS and its characteristic cell surface associated proteins implicated a role in virulence and pathogen-host interaction. PE_PGRS41, also known as acid and phagosome regulated protein C (aprC), which can modulate pH-driven adaptation to the macrophage phagosome. We showed that PE_PGRS41 is a cell wall associated protein, implicating in mycobacteria-host interaction. Functional studies revealed that PE_PGRS41 significantly suppressed pro-inflammatory cytokines TNF-α, IL-1β and IL-6 expression, while increased anti-inflammatory IL-10 production. Expression of PE_PGRS41 in nonpathogenic Mycobacterium smegmantis significantly increased intracellular survival of M. smegmantis within macrophage. M. tuberculosis blocks phagosome-lysosome fusion via inhibiting intracellular Ca2+, resulting in persistance within macrophage. Ca2+ is a ubiquitous and versatile intracellular second messenger involved in many signaling processes. Disruption of intracellular homeostasis of Ca2+ signaling will alter the ER stress-mediated apoptosis in response to various pathological conditions. PE_PGRS41 with 16 typical Ca2+ binding motifs can suppress cell apoptosis of macrophages, yet its role in Ca2+ signaling regulation and ER stress-mediated apoptosis remains unknown. The central theme of this proposal is thus to elucidate the molecular basis of PE_PGRS41 in regulating host immune response. We will also use the cell and animal model to evaluate if silencing of PE_PGRS41 will mitigate intracellular persistence. Our proposed studies therefore hold value in providing a better understanding on the role of PE_PGRS41 in the pathogenesis of M. tuberculosis.