Regulation of Apoptotic Envelope Formation by MTB in the Host Macrophage

结核分枝杆菌(Mtb)生长在人类巨噬细胞中，巨噬细胞是主要的宿主细胞，在那里它占据了一个利基，使其能够在不被宿主识别的情况下进行复制。减毒的结核分枝杆菌可诱导宿主巨噬细胞的凋亡，从而抑制细菌并被吞噬细胞清除。毒力结核分枝杆菌和毒力因子的一个基本特性是诱导坏死，其特征是质膜溶解并将细菌释放到细胞间隙，从而导致感染的传播。相反，减毒的结核分枝杆菌主要诱导宿主巨噬细胞的凋亡。细胞凋亡的一个特征是存在一个15 nm厚的细胞表面被膜支架，由包括(Annexin-1和蛋白酶抑制物蛇毒纤溶酶原激活剂2(PAI-2)在内的交叉连接的蛋白质组成，如从 角质形成细胞的角化包膜。Annexin-1是一种带有磷脂酰丝氨酸结合区和多聚谷氨酸区的37 kDa蛋白质，在细胞凋亡过程中被转运到巨噬细胞表面，并与凋亡单核细胞表面的PS晶格结合。我们发现，膜联蛋白-1不仅是感染减毒结核分枝杆菌感染的巨噬细胞凋亡包膜的共同成分，而且是转谷氨酰胺酶使包膜交联所必需的一种组织原理。在PAI-2等蛋白酶抑制剂的存在下，Annexin-1的蛋白降解导致缺少L1的非活性产物，多聚谷氨酰胺区域被阻断，并能够形成凋亡包膜。在这一应用中，我们建议研究毒力Mtb通过调节Annexin-1的蛋白水解性降解及其向细胞表面的运输来干扰宿主巨噬细胞凋亡膜的形成。我们将进一步研究膜修复机制在Mtb感染巨噬细胞在形成凋亡包膜中的作用。这些研究将增强我们对结核病中关键宿主-病原体相互作用的知识，这可能会促进新的治疗和预防方法的发展。

Mycobacterium tuberculosis (Mtb) grows in human macrophages, the principal host cell, where it occupies a niche allowing it to replicate without being recognized by the host. Attenuated Mtb induce apoptosis of the host macrophages resulting in containment of the bacilli and their elimination by phagocytes. An essential property of virulent Mtb and a virulence factor is the induction of necrosis characterized by plasma membrane lysis and release of the bacilli into the intercellular space that leads to spread of the infection. In contrast, attenuated Mtb induce predominantly apoptosis in the host macrophage. A hallmark of apoptosis is the presence of a 15 nm thick cell surface envelope scaffold consisting of cross-linked proteins including (annexin-1 and the protease inhibitor serpin plasminogen activator type 2 (PAI-2) as first described from the lkornified envelope of keratinocytes. Annexin-1, a 37 kDa protein with a phosphatidyl serine (PS) binding domain and a poly-gln region required for cross-linking is transported to the macrophage surface during apoptosis and binds to the PS lattice on the surface of the apoptotic Mcp. We found that annexin-1 is not only a common constituent of the apoptotic envelope of the macrophage infected with attenuated Mtb, but also an lorganizing principle required for cross-linking of the envelope by transglutaminases. In the presence of [protease inhibitors such as PAI-2 proteolytic degradation of annexin-1 resulting in an inactive product lacking lthe poly-gln region is blocked and formation of the apoptotic envelope is enabled. In this application we lpropose to investigate the capacity of virulent Mtb to interfere with the formation of the apoptotic envelope on host macrophages by modulating proteolytic degradation of annexin-1 and its transport to the cell surface. We will further study the role of membrane repair mechanisms in Mtb infection of the macrophage in the formation of the apoptotic envelope. These studies will enhance our knowledge about critical host-pathogen interactions in tuberculosis that could foster development of novel approaches to treatment and prevention.