Role of Bai1 and Elmo Proteins in Apoptotic Cell Clearance

描述（由申请人提供）：作为正常稳态的一部分，我们每天在体内周转数十亿个细胞，并且这些细胞中的许多细胞通过凋亡过程死亡。凋亡细胞在体内以“免疫沉默”的方式被吞噬细胞迅速清除。迅速清除的缺陷导致继发性坏死，细胞内内容物从垂死细胞中释放，促进慢性组织炎症，这与自身免疫性疾病如SLE、气道炎症和动脉粥样硬化有关。因此，更好地了解凋亡细胞识别和清除的机制对于对抗这些疾病是必要的。目前的竞争性续期申请是基于前两个为期4年的资助期所取得的进展。我们首先鉴定了一种新的细胞质吞噬衔接蛋白ELMO 1，并将埃尔莫/Dock 180/Rac信号通路定义为促进凋亡细胞吞噬的进化保守模块。然后，我们确定了膜蛋白BAI 1作为ELMO 1上游的吞噬受体;独立地，我们产生了Elmo 1的敲除小鼠，以确定其在睾丸中的凋亡生殖细胞清除中的需求，以及在大脑中的神经发生过程中。这些工作还提出了一些令人兴奋的下一组问题，即通过体内BAI 1/ELMO 1模块进行信号传导，以及该途径如何抑制组织中的炎症。在本提案的目标1中，使用我们实验室最近产生的小鼠，其中Bai 1基因座已被靶向删除（floxed以及直敲除），我们将测试BAI 1在两种不同组织（胸腺和睾丸）中体内凋亡细胞清除中发挥作用的假设。此外，使用过表达野生型或突变形式的BAI 1的诱导型转基因小鼠，我们将测试BAI 1是否在体内促进吞噬中提供独特的相对于冗余的信号。目的2关注凋亡细胞识别如何转化为抗炎细胞因子的产生，这是凋亡细胞清除的关键特征，尚未完全了解。我们将测试的假设，BAI 1-ELMO 1介导的信号有助于抗炎反应的吞噬细胞。具体来说，我们将测试ELMO 1和转录机制组件（我们在初步研究中发现）之间的意外相互作用如何有助于吞噬过程中的抗炎基因转录。我们将在组织炎症的小鼠模型中使用Elmo 2缺陷的小鼠（我们最近产生的）来扩展这些体内研究。总的来说，我们希望这些研究提供令人兴奋的新信息信号通过BAI 1/Elmo 1信号通路在体内细胞清除。由于ELMO 1和BAI 1的表达改变与人类炎症性疾病有遗传联系，因此拟议研究的结果可能与炎症性疾病的治疗干预有关。

DESCRIPTION (provided by applicant): We turnover billions of cells in the body each day as part of normal homeostasis, and many of these cells die by the process of apoptosis. The apoptotic cells are quickly cleared by phagocytes in vivo, in an 'immunologically silent' fashion. Defects in prompt removal leads to secondary necrosis, with the release of intracellular contents from the dying cells promoting chronic tissue inflammation, which has been linked to autoimmune disorders such as SLE, airway inflammation, and atherosclerosis. Thus, a better knowledge of the mechanisms of apoptotic cell recognition and clearance becomes necessary for countering these disorders. This current competitive renewal application is based on the progress made during the two previous funding periods of 4 years each. We first identified a novel cytoplasmic engulfment adapter protein ELMO1, and defined the ELMO/Dock180/Rac signaling pathway as an evolutionarily conserved module for promoting apoptotic cell engulfment. We then identified the membrane protein BAI1 as the engulfment receptor upstream of ELMO1; independently, we generated knockout mice for Elmo1 to identify its requirement in apoptotic germ cell clearance in the testes, and during neurogenesis in the brain. These works have also raised a number of exciting next set of questions on signaling via the BAI1/ELMO1 module in vivo, and how this pathway may dampen inflammation in tissues. In Aim1 of this proposal, using mice recently generated in our laboratory where the Bai1 locus has been targeted for deletion (floxed as well as straight knockout), we will test the hypothesis that BAI1 plays a role in apoptotic cell clearance in vivo in two different tissues, the thymus and the testes. Moreover, using inducible transgenic mice that overexpress wild type or a mutant form of BAI1, we will test whether BAI1 provides unique versus redundant signals in promoting engulfment in vivo. Aim 2 focuses on how apoptotic cell recognition translates to anti-inflammatory cytokine production, key feature of apoptotic cell clearance that is not fully understood. We will test the hypothesis that the BAI1-ELMO1-mediated signaling contributes to anti-inflammatory responses of phagocytes. Specifically, we will test how an unexpected interaction between ELMO1 and components of the transcriptional machinery (which we have discovered in our preliminary studies), contribute to the anti-inflammatory gene transcription during engulfment. We will extend these in vivo using mice deficient in Elmo2 (that we have recently generated) in a mouse model of tissue inflammation. Collectively, we expect these studies to provide exciting new information on signaling via the BAI1/Elmo1 signaling pathway in cell clearance in vivo. Since altered expression of ELMO1 and BAI1 are genetically linked to inflammatory disorders in humans, the results from the proposed studies could be relevant for therapeutic intervention in inflammatory disorders.