Sub-lethal mitochondrial outer membrane permeabilization: mechanisms and regulation in bacterial infection

线粒体调节能量水平和代谢，并可通过释放膜间间隙蛋白细胞色素c和Smac，触发caspase激活和细胞凋亡。一个有趣的、目前正在发展的领域是线粒体凋亡装置中‘亚致死’信号的产生和作用。除了在细胞凋亡过程中细胞色素c/Smac的完全和快速释放外，线粒体也只能释放少量的这些蛋白，激活少量的凋亡caspase。目前的证据表明，这些亚致命信号是促炎信号，可能是先天免疫反应的一部分；迄今为止，在所有测试的细胞感染中都观察到了亚致命信号。亚致死信号使用主要的细胞凋亡机制，包括Bcl2家族蛋白，它们似乎与线粒体网络结构有关。该项目的目标是了解亚致死信号过程中线粒体的关键事件和参与者，并绘制非专业免疫细胞细菌感染期间的这些事件图。在细胞凋亡过程中，BH3活性蛋白如Bim、Noxa和Bad激活膜间隙蛋白释放的效应物Bax和Bak。就目前所知，在亚致命信号期间，玩家看起来是一样的，但实际情况尚不清楚。我们将评估在实验性诱导Bim时线粒体的事件，重点是Bax，Bak的激活，线粒体网络的局部激活和广泛激活的问题，以及亚致死信号和线粒体网络的裂变-融合活性的相互作用。我们将测试一种假设，即仅有BH3的蛋白质Noxa和Bad在诱导细胞凋亡方面的活性远低于Bim，实际上可能与亚致死信号的诱导更相关。这些实验将确定线粒体亚致死信号的一些细胞生物学事件。在项目的第二部分，我们将使用这些结果并测试在感染幽门螺杆菌(HP)和沙眼衣原体(CTR)这两种病原体感染人类上皮细胞期间的线粒体事件。这两种病原体都通过Bax/Bak产生亚致死信号和炎症活动；Ctr被描述为抑制线粒体分裂，而Hp可以促进分裂。通过对这两种病原体感染的研究，我们希望能够了解感染过程中线粒体的一些亚致死事件，并更好地理解线粒体网络中的凋亡系统和裂变-融合事件之间的联系。在我们看来，线粒体上的亚致死信号是感染过程中的重要事件，它们可能决定感染过程中炎症和免疫反应的启动。这个项目中的实验将有助于阐明这一角色。

Mitochondria regulate energy levels and metabolism and can, through the release of the intermembrane space proteins cytochrome c and Smac, trigger caspase-activation and apoptosis. An intriguing, currently evolving field is the generation and role of ‘sub-lethal’ signals in the mitochondrial apoptosis apparatus. In addition to the established complete and quick release of cytochrome c/Smac during apoptosis, mitochondria can also release only small amounts of these proteins, activating small amounts of apoptotic caspases. Current evidence suggests that these sub-lethal signals are pro-inflammatory and may be part of an innate immune response; sub-lethal signals have been observed in all cellular infections tested to date. Sub-lethal signals use the main apoptosis machinery, including Bcl-2-family proteins, and they appear to be linked to the structure of the mitochondrial network. The goals of this project are to understand key events and players at mitochondria during sub-lethal signaling, and to map these events during bacterial infection of non-professional immune cells. During apoptosis, active BH3-only proteins, such as Bim, Noxa and Bad, activate the effectors of intermembrane space protein release, Bax and Bak. During sub-lethal signaling, as far as is known, the players appear to be the same but the actual events are unclear. We will assess the events at mitochondria upon experimental induction of Bim, focusing on the activation of Bax, Bak, the question of localized vs. widespread activation of the mitochondrial network and the reciprocal interaction of sub-lethal signals and fission-fusion activity of the mitochondrial network. We will test the hypothesis that the BH3-only proteins Noxa and Bad, known to be far less active in the induction of apoptosis than Bim, may in fact be more relevant to the induction of sub-lethal signals. These experiments will identify some of the cell biological events of sub-lethal signaling at mitochondria. In the second part of the project, we will use these results and test for mitochondrial events during infection of human epithelial cells with the two pathogens, Helicobacter pylori (Hp) and Chlamydia trachomatis (Ctr). Both pathogens generate sub-lethal signals and inflammatory activity through Bax/Bak; while Ctr has been described to inhibit mitochondrial fission, Hp can increase fission. Through studying the infection with these two pathogens, we expect to be able to understand some of the sub-lethal events at mitochondria during infection, and better to appreciate the link between apoptosis-system and fission-fusion events at the mitochondrial network. In our view, sub-lethal signals at mitochondria are important events during infection, and they may determine the initiation of inflammation and an immune response during infection. The experiments in this project will help clarify this role.