鼠伤寒沙门氏菌的宿主特异性和致病性进化机制研究

Salmonella enterica serovar Typhimurium (S. Typhimurium) exhibits notable host-specific pathogenicity. It causes severe systemic infection in mice, but inducing only mild gastroenteritis in humans. The ability to replicate within host macrophages is the key step for developing systemic Salmonella infection. Our preliminary research showed that the major virulence factor of S. Typhimurium, Salmonella pathogenicity island -2 (SPI-2) genes express at much higher levels in murine macrophages than levels in human macrophages, leading to strongly enhanced replication of the pathogen in murine macrophages, consequently systemic infection to mice. As the known signal systems for SPI-2 induction are present both in murine and human macrophages, other unknown regulatory systems and/or host specific signaling systems are likely involved in the induction of SPI-2 genes in murine macrophages. This project aims to investigate regulatory systems and host signals underlying the higher SPI-2 expression of S. Typhimurium in murine macrophages. A high virulent S. Typhimurium isolates ST313 recently emerged in sub-Saharan Africa that has evolved to induce systemic human disease. Our preliminary research found that intracellular expression levels of SPI-2 genes in ST313 were not changed while the virulence strain showed increased replication in human macrophages, indicating that ST313 utilized other mechanisms to enhance its replication ability. This work will also investigate mechanisms for the evolving of ST313 as a more virulent human pathogen. The outcome of this project is expected to contribute largely to understand mechanisms for host specificity of S. Typhimurium pathogenicity and its adaptive evolution in humans.

鼠伤寒沙门氏菌的致病性有显著的宿主特异性：感染人引起肠炎，感染小鼠引起致死性的系统性疾病。巨噬细胞内复制是该菌引起系统性疾病的关键要素。我们前期发现鼠伤寒沙门氏菌的必需毒力因子致病岛2基因在鼠巨噬细胞内的表达水平显著高于在人巨噬细胞内的水平，从而使该菌在鼠细胞内高水平复制，引起鼠的系统性疾病。鼠巨噬细胞内已知的调控致病岛2表达的信号在人细胞内都存在，我们推测未知的调控体系和鼠巨噬细胞内特有的信号能诱导致病岛2的高表达。本研究将探究该菌在鼠巨噬细胞内致病岛2高表达相关的信号调控系统。非洲最近出现的ST313型鼠伤寒沙门氏菌有引起人系统性疾病的能力，我们发现该型在人巨噬细胞内的复制力有明显提高，但致病岛2的表达水平不变，表明ST313有其它提高复制力的机制。本研究将对ST313进化为人系统性致病菌的机理进行研究。项目成果对理解鼠伤寒沙门氏菌这一重要致病菌的宿主特异性和毒力进化机制具有重要意义。

沙门氏菌是一种重要的肠道病原菌，能引起肠炎或致死性的系统性疾病，严重威胁人类健康。沙门氏菌不同血清型具有明显的宿主范围和宿主特异性的差异，感染宿主后引起的疾病取决于不同的血清型/宿主组合。鼠伤寒沙门氏菌是最典型的致病性沙门氏菌血清型，感染人引起肠炎，感染小鼠引起致死性的系统性疾病，其对鼠特异性致系统性疾病的机制未知。在巨噬细胞内复制是该菌引起系统性疾病的关键要素，鼠伤寒沙门氏菌在小鼠巨噬细胞内的复制能力显著高于其在人巨噬细胞内的复制能力，与其对鼠和人的致病能力相对应。本项目结合多组学分析技术和多种先进的分子生物学技术，解析了与鼠伤寒沙门氏菌在小鼠巨噬细胞内高复制力相关的分子机理。结果发现，鼠伤寒沙门氏菌以鼠巨噬细胞内产生的一氧化氮（NO）作为一种信号分子，激活其沙门致病岛2（SPI-2）毒力基因的表达，进而提高鼠伤寒沙门氏菌的在小鼠巨噬细胞内的复制能力和对小鼠的致病能力。人巨噬细胞被感染后，只能产生低浓度的NO，该信号调节系统不启动，部分造成了鼠伤寒沙门氏菌在人巨噬细胞内的低复制力。另外，我们的研究结果揭示ST313型鼠伤寒沙门氏菌对人致病性提高的原因与其丢失了四个基因的功能相关，并且揭示了这四个基因在小鼠巨噬细胞内被下调的分子机制。此外，通过研究鼠伤寒沙门氏菌与巨噬细胞在代谢水平上的互作机制，我们发现鼠伤寒沙门氏菌能诱导巨噬细胞的代谢重编程，以细胞内积累的代谢物作为营养物或激活其毒力基因表达的信号分子，进而提高自身在细胞内的复制能力和致病能力；确定了鞭毛基因在巨噬细胞内被下调的分子机制。本项目研究结果对于深入理解鼠伤寒沙门氏菌的宿主特异性和毒力进化机制具有重要意义，为全面理解沙门氏菌的致病机理奠定了重要基础。

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