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

线粒体调节能量水平和代谢，并可以通过释放膜间空间蛋白细胞色素c和Smac，触发caspase激活和凋亡。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。除了细胞色素c/Smac在细胞凋亡过程中完全快速释放外，线粒体也只能释放少量的这些蛋白，激活少量的凋亡半胱天冬酶。目前的证据表明，这些亚致死信号是促炎的，可能是先天免疫反应的一部分；迄今为止，在所有检测的细胞感染中都观察到亚致死信号。亚致死信号使用主要的凋亡机制，包括bcl -2家族蛋白，它们似乎与线粒体网络的结构有关。该项目的目标是了解亚致死信号传导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过程中的这些事件。在细胞凋亡过程中，活性BH3-only蛋白（如Bim、Noxa和Bad）激活膜间空间蛋白释放效应器Bax和Bak。就目前所知，在亚致死信号期间，参与者似乎是相同的，但实际事件尚不清楚。我们将通过实验诱导Bim来评估线粒体的事件，重点关注Bax、Bak的激活，线粒体网络的局部激活与广泛激活的问题，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BH3-only蛋白Noxa和Bad的假设，已知它们在诱导凋亡方面远不如Bim活跃，实际上可能与诱导亚致死信号更相关。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两种病原体幽门螺杆菌（Hp）和沙眼衣原体（Ctr）感染人类上皮细胞时的线粒体事件。这两种病原体都通过Bax/Bak产生亚致死信号和炎症活性；Ctr被描述为抑制线粒体分裂，而Hp可以增加线粒体分裂。通过研究这两种病原体的感染，我们希望能够了解感染过程中线粒体的一些亚致死事件，并更好地了解线粒体网络中凋亡系统和裂变融合事件之间的联系。在我们看来，线粒体的亚致死信号是感染期间的重要事件，它们可能决定感染期间炎症和免疫反应的启动。这个项目中的实验将有助于澄清这一角色。

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.