肠道屏障在机体健康中发挥重要作用，是抵御肠道感染的第一道防线，同时，肠道屏障功能失调也与肥胖、2型糖尿病、炎症性肠炎及自闭症等重大疾病的发生发展密切相关。肠黏膜潘氏细胞位于小肠隐窝底部，向肠道内分泌大量抗菌物质，在调控肠道菌群、维持肠道屏障功能中起关键作用。申请人的研究揭示了炎症性肠炎易感基因的作用及机制（Nat. Immunol. 2011, 12: 1063等）。申请人2012年回国后，研究潘氏细胞分泌机制及其在肠道稳态中的作用，发现肠炎易感基因LRRK2特异性调控潘氏细胞溶菌酶分泌而在控制肠道感染中发挥重要作用（未发表）。本项目拟在前期工作基础上，就潘氏细胞独特的分泌活动与其在肠黏膜中的作用展开研究，深入探讨肠道黏膜与肠道微生态的互作关系，以期发现维持肠道屏障功能的关键因子，并为预防肠道感染提出新思路。

The complex interaction between intestinal microbiota and underlying mucosal immunity plays a key role in human health. Microbial dysbiosis and impaired intestinal barrier function have been linked to the development of multiple diseases, including obesity, type 2 diabetes, inflammatory bowel disease (IBD), and autism spectrum disorders. Paneth cells located in the small intestinal crypts secrete large amounts of bactericidal peptides into intestinal lumen. Dysfunction of Paneth cells is a prime cause for IBD. Currently, it is largely unclear how dysfunctioning Paneth cells lead to dysbiosis and IBD occurrence. Our preliminary results have shown that lysozyme secretion in Paneth cells is specifically regulated by LRRK2, an IBD susceptibility gene. We found that Lrrk2 deficiency in mice led to a specific failure of lysozyme secretion, and such failure rendered the mice more susceptible to GI tract infection. We observed more commensal bacteria breached the intestinal barrier and located to lamina propria in LRRK2 deficient mice even at the steady state. Our data suggest that the lysozyme secreted from Paneth cells plays an important role in maintaining intestinal barrier, however the exact mechanism remains to be further determined. Furthermore, we found that Paneth cells produce high level of IL-17A at the steady state, whose function remains unknown. Thus, we propose to systematically investigate the role of Paneth cells in maintaining intestinal homeostasis. We will focus on the biological functions of the secreted contents from Paneth cells, including lysozyme and cytokines. We will investigate their roles in modulating microbiota, regulating intestinal barrier function, and controlling GI infection. We aim to illustrate 1) the mechanisms by which secretory activities of Paneth cells regulate microbiota and control infection, 2) the mechanism how secretory activities of Paneth cells are regulated. We believe that our proposed research will shed light on the mechanisms by which Paneth cells contribute to intestinal barrier maintenance. Furthermore, our proposed research will yield important insights in finding new approaches to promote the intestinal barrier function, which may have implications in preventing GI track infection.

肠道屏障在机体健康中发挥重要作用，是抵御肠道感染的第一道屏障，同时，肠道屏障功能失调也与肥胖、2型糖尿病、炎症性肠炎及自闭症等重大疾病的发生发展密切相关。肠黏膜潘氏细胞位于小肠隐窝底部，向肠道内分泌大量抗菌物质，在调控肠道菌群、维持肠道屏障功能中起关键作用。而目前对肠道共生菌如何调控潘氏细胞的生理活动还所知甚少。在本项目“肠道微生态与感染及代谢的研究”的支持下就肠道上皮屏障在肠道稳态中的作用深入研究，阐明了共生菌调控潘氏细胞货物分选的分子机制，发现了全新的分子通路，取得了重要进展。他们发现来自细菌细胞壁的肽聚糖可以直接调控溶菌酶在致密核心囊泡中的分拣以促进共生。潘氏细胞内Nod2由肽聚糖激活后，定位于致密核心囊泡表面，招募LRRK2，进而招募Rip2、Rab2a调控溶菌酶的转运。本课题绘制了一个遗传学通路Nod2–LRRK2–Rip2–Rab2a，该通路不同于经典Nod2分子响应病原菌通路（Nod2–Rip2–TAK1-NFKB），这条非经典通路响应肠道共生菌，对于潘氏细胞中溶菌酶分拣是必需的。本项工作从货物分拣的角度揭示了潘氏细胞异常在炎症性肠炎发生中的作用；也揭示了共生菌通过调控特殊物质的分拣来促进 “共生•互益”的初步机制。