Mechanisms of apoptotic neuron clearance in the peripheral nervous system

描述（由申请人提供）：在哺乳动物神经系统的正常发育过程中，存在广泛的程序性细胞死亡，这是建立适当细胞数量和连接所必需的。许多病理，如神经损伤和阿尔茨海默氏症等疾病也会导致细胞凋亡。由此产生的神经元尸体必须被有效地移除，以防止免疫系统反应，这可能涉及炎症和自身免疫。事实上，许多自身免疫性疾病都与不能正确清除死细胞有关。不幸的是，这种吞噬过程的分子机制，特别是在神经系统中，人们对其了解甚少。在周围神经系统中，人们对死亡神经元是如何被移除的几乎一无所知。因此，本研究的总体目标是阐明周围神经系统中凋亡神经元吞噬的细胞和分子机制。在秀丽隐杆线虫中，两种参与凋亡细胞清除的途径已经被遗传定义；第一种包括CED-1、-6、-7和-10，第二种包括CED-2、-5、-10和-12。大多数这些基因的哺乳动物同源物已被确定；然而，对于CED-1，被认为是细胞尸体的受体，已经提出了几种可能的同源物，包括MEGF10， LRP-1和清扫剂受体SREC，但尚未达成共识。这些通路是否参与哺乳动物发育过程中凋亡神经元的清除尚不清楚。我们的初步数据表明，MEGF10和相关蛋白Jedi是背根神经节（DRG）神经元吞噬所必需的，并且神经节中的卫星细胞表达这些基因并负责清除死亡神经元。因此，我们假设卫星细胞在胚胎发生过程中吞噬死亡的DRG神经元涉及CED-1的同源物MEGF10和Jedi。为了解决这一假设，我们提出以下具体目标：(1)确定MEGF10和/或Jedi是否作为凋亡神经元被卫星细胞吞噬的受体；(2)明确MEGF10和Jedi在发育小鼠中的表达模式；(3)确定Jedi或MEGF10是否通过CED-1通路的同源物来调控Rac；(4)确定在发育过程中是否需要在体内进行神经元尸体吞噬。阐明凋亡神经元被吞噬的机制不仅将增强我们对哺乳动物神经系统发育的理解，而且可能为自身免疫性神经病的病因学提供重要的见解。公共卫生相关性：神经元细胞死亡是哺乳动物神经系统发育的正常部分，是建立适当的细胞数量和连接所必需的，但也可能发生在各种损伤和神经病变中；例如，中风、阿尔茨海默病和化学疗法。不能清除死细胞会导致炎症反应和自身免疫性疾病；然而，这些死亡的神经元是如何被清除的还不是很清楚，在周围神经系统中是完全未知的。该应用程序的目的是确定在发育中的周围神经系统中死亡神经元清除的细胞和分子机制。

DESCRIPTION (provided by applicant): During the normal development of the mammalian nervous system there is extensive programmed cell death, which is required for establishing proper cell numbers and connections. A number of pathologies, such as nerve injury and diseases such as Alzheimer's can lead to apoptosis as well. The resulting neuronal corpses must be efficiently removed in order to prevent an immune system response, which can involve inflammation and autoimmunity. Indeed, a number of autoimmune diseases have been associated with a failure to properly clear dead cells. Unfortunately, the molecular mechanisms underlying this phagocytic process are poorly understood, particularly in the nervous system. In the peripheral nervous system, there is virtually nothing known about how the dead neurons are removed. Hence, the overall goal of this study is to elucidate the cellular and molecular mechanisms underlying the phagocytosis of apoptotic neurons in the developing peripheral nervous system. In C. elegans, two pathways involved in apoptotic cell clearance have been genetically defined; the first includes CED-1, -6, -7 and -10 and the second CED-2, -5, -10 and -12. The mammalian homologs of most of these genes have been identified; however, for CED-1, which is thought to function as a receptor for cell corpses, there have been several possible homologs proposed, including MEGF10, LRP-1 and the scavenger receptor SREC, but no consensus has been reached. Whether these pathways participate in the removal of apoptotic neurons during mammalian development is not known. Our preliminary data suggest that MEGF10 and a related protein, Jedi, are required for dorsal root ganglia (DRG) neuron engulfment and that satellite cells in the ganglia express these genes and are responsible for the removal of the dead neurons. Therefore, we hypothesize that the phagocytosis of dead DRG neurons during embryogenesis by satellite cells involves the putative CED-1 homologs MEGF10 and Jedi. To address this hypothesis we propose the following specific aims: (1) Determine whether MEGF10 and/or Jedi functions as a receptor for apoptotic neuron engulfment by satellite cells; (2) Define the expression pattern of MEGF10 and Jedi in the developing mouse; (3) Determine whether Jedi or MEGF10 signal through homologs of the CED-1 pathway to regulate Rac; (4) Determine whether Jedi is required in vivo for neuronal corpse engulfment during development. Elucidating the mechanisms by which apoptotic neurons are phagocytosed will not only enhance our understanding of the development of the mammalian nervous system, but will likely provide important insights into the etiology of autoimmune neuropathies. PUBLIC HEALTH RELEVANCE: Neuronal cell death is a normal part of the development of the mammalian nervous system, required for establishing proper cell numbers and connections, but can also occur in various injuries and neuropathologies; for example, stroke, Alzheimer's disease and chemotherapeutic treatment. The failure to remove dead cells can lead to an inflammatory response and autoimmune diseases; however, how these dead neurons are cleared is not well understood and in the peripheral nervous system is completely unknown. The goal of this application is to determine the cellular and molecular mechanisms underlying the clearance of dead neurons in the developing peripheral nervous system.