Galectin-8通过识别结核菌胞壁糖组分arabinogalactan调控自噬的机制研究

Macrophage is critical for host defense against Mycobacteriu tuberculosis (Mtb) infection. Though it has long been proposed that Mtb persists in the phagosome of macrophage by blocking phagosome maturation and fusion with lysosome, Mtb still releases different molecules including extracellular DNA and cyclic di-AMP from the phagosome or directly escapes from phagosome into the cytosol, followed by activation of cytosolic survellance pathway. Mtb cell wall is rich of glycans including arabinoglacan. However, it unknown how these non-self constituents escaped into the cytosol are sensed by host cells. Galectins are a type of animal lectin which specifically bind to beta-galactoside and serve as important pattern recognition receptors. Previously, we observed that 1) galectin-8 was recruited to Mtb in infected macrophage; 2) knockdown of galectin-8 significantly inhibited NDP52- and p62-mediated selective autophagy and enhanced intracellular survival of Mtb in macrophage; 3) galectin-8 directly interacted with arabinogalactan from larch wood; 4) arabinogalactan recruites galectin-8 and induces selective autophagy. Therefore, in this study we will further study whether galectin-8 is a receptor of cytosolic Mtb by recognition of arabinogalactan and calarify the downstream events and underlying mechanisms. Hopefully, we will identify a novel receptor in the recognition of cytosolic Mtb and provide a novel concept for cytosolic sensing of intracellular bacteria. This will further our understanding the fundamental biology of Mtb infection and provide novel molecule target for the development of drugs and vaccines against TB.

宿主识别结核菌（MTB）是由一系列不同定位的模式识别受体参与的动态过程。MTB可损伤吞噬体并释放相关分子到胞浆或甚至直接逃逸到胞浆中。然而，一旦进入胞内，其细胞壁中富含的糖组分如阿拉伯半乳聚糖（Arabinogalactan，AG）作为“非我”（non-self）组分如何被宿主识别至今未知。Galectin-8是一种重要的模式识别受体，其在MTB感染过程中的作用未见报道。我们前期发现，galectin-8可直接结合AG，且在MTB感染过程中，galectin-8可被“招募”至菌体，并促进NDP52与p62介导的选择性自噬，进而抑制MTB胞内存活。为此，本项目拟进一步研究galectin-8对AG的识别作用及该识别过程对MTB感染的调控机制。研究结果有望确立一种宿主细胞识别MTB感染的新模式，既能加深对MTB感染过程中基本生物学问题的理解，又能为结核病的药物治疗和疫苗设计提供新的分子靶标。

宿主识别结核分枝杆菌（Mycobacterium tuberculosis， MTB）是由一系列不同定位的模式识别受体参与的动态过程。MTB细胞壁重要组分arabinogalactan（AG）的功能及其作为“非我”组分是否可以被宿主识别并激活免疫应答完全未知。本项目从分子、细胞、动物感染模型等不同层次研究 galectin-8对胞内MTB 的识别作用及机制，并明确其对 MTB 感染过程的调节作用。MTB细胞壁组分AG可以影响细胞内许多基因的表达，尤其是基质金属蛋白酶MMPs的产生，本研究实施过程中，我们首次发现结核菌细胞壁组分AG是结核菌重要的毒力因子，在结核分枝杆菌感染宿主过程中发挥重要作用。本研究首次确立了凝集素受体galectin-9作为一种重要的模式识别受体（Pattern Recognition Receptors，PRRs），阐明Galectin-9对结核菌细胞壁组分AG的识别作用，并提出了AG的胞内信号转导通路机制，阐明AG可通过Galectin-9-TAK1-ERK-MMPs信号轴诱导肺损伤，当用AG特异性适配子阻断结核菌AG，可以显著降低MTB的致病性。本研究加深了对结核病发病机制的认识，确立了一种宿主细胞识别MTB感染的崭新模式，是MTB识别领域的重要创新突破。同时，本研究为靶向AG-galectin-9相互作用界面，开发新型结核病干预和治疗手段提供重要基础。