Deciphering the molecular mechanisms and physiological consequences of macrophage polarisation during Salmonella infection

巨噬细胞是一种关键的免疫细胞，它可以对抗致病微生物，如细菌。它们的作用方式是：1)形成杀死病原体的敌对环境，直接对抗感染；2)产生分子，提醒其他免疫细胞注意危险，最终产生炎症反应。巨噬细胞除了采取这种“杀死”状态外，还可以采取“修复”状态，在这种状态下，它们会发起活动以减少炎症、解决感染并修复在炎症反应中受损的组织。巨噬细胞采取任何一种状态的过程，称为巨噬细胞极化，需要细胞内的通信，这被称为细胞信号传递。蛋白质是在细胞中执行关键功能的大分子，从化学反应(酶)到转录调节。转录使RNA来自细胞内包含的遗传物质(DNA)，并可由称为转录因子的蛋白质控制。然后，RNA就是制造新蛋白质的密码。每一种蛋白质都是由一串称为氨基酸的较小构件组成的。氨基酸序列决定了蛋白质的三维结构和功能。在细胞信号传递过程中，小化学基团对蛋白质的修饰可以增加、减少或改变它们的功能。在磷酸化过程中，蛋白质的特定氨基酸中添加了一种称为磷酰基的物质。这一反应是由一种名为激酶的酶进行的。一些酶只修饰特定类型的氨基酸，称为丝氨酸和苏氨酸，而另一些酶也可以修饰氨基酸酪氨酸。像沙门氏菌这样的致病细菌使用自己的蛋白质来干扰宿主细胞的信号传递，从而干扰宿主免疫。我们最近发现，一种名为Stee的蛋白质从沙门氏菌输送到巨噬细胞，与宿主激酶结合，而宿主激酶通常只修饰丝氨酸和苏氨酸氨基酸。当与STEE一起时，该激酶现在在一个新的靶点上修饰一个酪氨酸氨基酸，这是一个转录因子。最终，这会促使巨噬细胞不适当地采取“修复”状态，而不是“杀死”状态。这促进了沙门氏菌在宿主体内的存活和长期存留。该项目将1)确定在沙门氏菌感染过程中STEE介导的巨噬细胞DNA转录的变化，并测试是否需要额外的宿主蛋白来指示巨噬细胞的“沙门氏菌友好”状态。2)研究沙门氏菌感染过程中宿主小分子(代谢物)的变化。3)研究Stee和宿主激酶的3D排列是如何改变的，以允许新的底物被修饰。总之，这些发现将揭示沙门氏菌蛋白Stee如何促进疾病的机制，并为宿主免疫过程提供有价值的见解。沙门氏菌是人类健康的主要挑战；它会导致人类的一系列疾病，从自限性腹泻疾病到伤寒，一种威胁生命的系统性疾病。我们的发现将使我们能够对一种全球性的致病细菌的发病机制有深刻的了解。最终，这可能会促进抗击细菌感染的新方法的发展，随着抗药性细菌菌株的崛起，这一点非常重要。

Macrophages are a key type of immune cell that fights disease-causing microorganisms, such as bacteria. They act by 1) directly fighting the infection by forming a hostile environment to kill the pathogen and 2) producing molecules to alert other immune cells to the danger and ultimately create an inflammatory response. As well as adopting this "killing" state, macrophages can also adopt a "repairing" state, in which they initiate events to reduce inflammation, resolve infection and repair tissues damaged during the inflammatory response. The process by which macrophages adopt either state, known as macrophage polarisation, requires communication within a cell, which is referred to as cell signalling. Proteins are large molecules that carry out critical functions in our cells, from chemical reactions (enzymes) to the regulation of transcription. Transcription makes RNA from the hereditary material (DNA) contained within the cell and can be controlled by proteins called transcription factors. RNA is then the code to make new proteins. Every protein is made up by a unique string of smaller building blocks called amino acids. The sequence of amino acids determines the 3-dimensional structure and function of a protein. During cell signalling, protein modification by small chemical groups can increase, decrease or change their function. During phosphorylation, something called a phosphoryl group is added to specific amino acids of the protein. This reaction is carried out by enzymes called kinases. Some kinases only modify specific types of amino acids called serine and threonine amino acids whereas others can also modify the amino acid tyrosine. Disease-causing bacteria, like Salmonella, use their own proteins to interfere with host cell signalling and thereby host immunity. We have recently found that a protein called SteE, delivered from Salmonella into macrophages, binds a host kinase that normally only modifies serine and threonine amino acids. When together with SteE the kinase now modifies a tyrosine amino acid on a new target, which is a transcription factor. Ultimately, this prompts macrophages to inappropriately adopt the "repair" state rather than the "killing" state. This promotes Salmonella survival and long-term persistence inside the host. This project will 1) define the changes in macrophage DNA transcription mediated by SteE during Salmonella-infection and test whether additional host proteins are required to instruct the "Salmonella-friendly" state of macrophages. 2) Investigate host changes in small molecules (metabolites) during Salmonella infection. 3) Study how the 3D arrangement of SteE and the host kinase are altered in order to allow novel substrates to be modified. Collectively, these findings will reveal the mechanism of how the Salmonella protein SteE promotes disease and provide valuable insight into host immune processes.Salmonella is a major human health challenge; causing a wide range of diseases in humans, from self-limiting diarrhoeal disease, to typhoid fever, a life-threatening systemic disease. Our findings will enable us to gain profound understanding on the pathogenesis of a global, disease-causing bacterium. Ultimately, this may promote the development of novel ways to combat bacterial infections, something which is of vast importance with the rise of antibiotic-resistant bacterial strains.