How are necrotic neurons recognized by their phagocytes

在动物的一生中，大量的细胞经历凋亡-细胞自杀，以支持发展 并维持身体内环境稳定。此外，在中风、癌症和其他创伤情况下， 损伤后坏死的细胞数量。这些细胞迅速被其他细胞内化， 吞噬作用（吞噬），并在吞噬细胞内降解。迅速清除垂死细胞 组织损伤，炎症反应和自身免疫反应，清除受伤区域，并促进 组织修复坏死也与神经元变性密切相关。吞噬坏死的 神经元和轴突碎片促进神经元功能的修复和恢复。吞噬活性 小胶质细胞也会导致阿尔茨海默病中突触的丧失。我的长期目标是了解 死亡细胞是如何被吞噬细胞特异性识别、内化和降解的， 秀丽隐杆线虫作为模式生物。由于许多生理机制高度保守， 在整个进化过程中，我们从C. elegans线虫can be translated翻译to humans人类.该提案调查了 促进磷脂酰丝氨酸（PS）暴露的机制，一个“吃我”的信号，在表面上， 坏死和凋亡细胞吸引吞噬细胞。In C. elegans，六个机械感觉的坏死 神经元（也称为触摸神经元）是由一组特定的质膜离子突变引起的。 通道蛋白，包括MEC-4中的显性突变，MEC-4是机械感觉Na+通道的亚基。 我们发现两种蛋白质，ABC转运蛋白CED-7和ANOH-1，哺乳动物的蠕虫同源物， 磷脂攀爬酶TMEM 16 F平行作用以促进坏死细胞表面上的PS暴露。 最近，我们已经确定，PS对坏死细胞的暴露是由胞浆Ca ~（2+）介导的。 此外，我们发现了两种增加细胞质中Ca 2+水平的替代机制， 一种依赖于内质网（ER）释放Ca ~（2+），另一种不依赖于ER。在 此外，我们已经确定了多个基因的作用，以调节PS曝光。进一步调查 PS暴露的分子机制，我建议确定甲状腺素运载蛋白样的新功能， 蛋白和一种建议的PS翻转酶在促进PS暴露在坏死细胞表面， 响应Ca 2+信号（目的1和2），并确定新的PS暴露基因的突变体缺陷 在暴露于PS的垂死细胞，我们分离在一个向前的遗传筛选（目的3）。统称 结果将使我们能够建立促进PS暴露的途径，以响应上游信号。他们 还将揭示调节该过程每个步骤的新分子机制，其中一些是 预期是坏死或凋亡细胞所特有的。

In an animal’s life, a large number of cells undergo apoptosis – cell suicide, to support development and maintain body homeostasis. In addition, during stroke, cancer, and other traumatic situations, a large number of cells undergo necrosis after injury. These cells are rapidly internalized by other cells via phagocytosis (engulfment) and degraded inside engulfing cells. The swift removal of dying cells prevents tissue injury, inflammatory responses, and auto-immune responses, clears the wounded area, and promotes tissue repair. Necrosis is also closely associated with neuron degeneration. The phagocytosis of necrotic neurons and axon debris facilitates the repair and recovery of neuron functions. Phagocytic activity by the microglia also contribute to the loss of synapses in Alzheimer’s disease. My long-term goal is to understand how dying cells are specifically recognized, internalized, and degraded by engulfing cells, using the nematode Caenorhabditis elegans as a model organism. As many physiological mechanisms are highly conserved throughout evolution, what we learn from C. elegans can be translated to humans. This proposal investigates the mechanisms that promote the exposure of phosphatidylserine (PS), an “eat me” signal, on the surfaces of necrotic and apoptotic cells to attract engulfing cells. In C. elegans, the necrosis of six mechanosensory neurons (also called touch neurons) is induced by mutations in a particular group of plasma membrane ion channel proteins, including the dominant mutations in MEC-4, a subunit of the mechanosensory Na+ channel. We found that two proteins, the ABC transporter CED-7, and ANOH-1, the worm homolog of the mammalian phospholipid scramblase TMEM16F, act in parallel to promote PS exposure on the surfaces of necrotic cells. Recently, we have identified that the exposure of PS on necrotic cells is mediated by cytoplasmic Ca2+. Furthermore, we discovered two alternative mechanisms that increase Ca2+ level in the cytoplasm, one dependent on the release of Ca2+ from the endoplasmic reticulum (ER), the other independent of the ER. In addition, we have identified multiple genes that act to regulate PS exposure. To further investigate the molecular mechanism(s) of PS exposure, I propose to determine the novel functions of a transthyretin-like protein and a proposed PS flippase in promoting the exposure of PS on the surfaces of necrotic cells in response to the Ca2+ signaling (Aims 1 and 2), and to identify new PS-exposure genes from mutants defective in the exposure of PS on dying cells that we isolated in a forward genetic screen (Aim 3). Together, the outcomes will allow us to establish pathways that promote PS exposure in response to upstream signals. They will also reveal novel molecular mechanisms regulating each step of the process, some of which are anticipated to be unique to necrotic or apoptotic cells.