How are necrotic neurons recognized by their phagocytes

在动物的一生中，为了支持发育，大量的细胞经历了凋亡--细胞自杀 并保持身体的动态平衡。此外，在中风、癌症和其他创伤情况下， 损伤后细胞发生坏死的数量。这些细胞通过以下途径迅速被其他细胞内化 吞噬(吞噬)并在吞噬细胞内降解。死亡细胞的快速清除可以防止 组织损伤、炎症反应和自身免疫反应，清除受伤区域，促进 组织修复。坏死也与神经元变性密切相关。坏死物的吞噬作用 神经元和轴突碎片有助于神经元功能的修复和恢复。吞噬细胞的活性 小胶质细胞也是阿尔茨海默病突触丢失的原因之一。我的长期目标是理解 死亡细胞是如何通过吞噬细胞来识别、内化和降解的，利用线虫 秀丽线虫是一种模式生物。因为许多生理机制是高度保守的 在整个进化过程中，我们从线虫身上学到的东西可以转化为人类。这份提案调查了 促进磷脂酰丝氨酸(PS)暴露在表面的机制，磷脂酰丝氨酸(PS)是一个“吃我”的信号 坏死和凋亡的细胞吸引吞噬细胞。在线虫中，六个机械感受器的坏死 神经元(也称为触觉神经元)是由一组特定的质膜离子突变引起的 通道蛋白，包括MEC-4的显性突变，MEC-4是机械感受性Na+通道的一个亚单位。 我们发现了两种蛋白质，ABC转运蛋白CED-7和哺乳动物的蠕虫同源物Anoh-1 磷脂加扰酶TMEM16F，平行作用促进PS在坏死细胞表面的暴露。 最近，我们发现PS在坏死细胞上的暴露是由胞浆内钙离子介导的。 此外，我们还发现了两种提高细胞质中钙离子水平的替代机制，一种是 依赖于内质网(ER)的钙离子释放，另一种不依赖于内质网。在……里面 此外，我们还发现了多个调节PS暴露的基因。为了进一步调查 PS暴露的分子机制(S)，我建议确定一个转甲状腺素样蛋白的新功能 蛋白和PS Flppase促进PS在小鼠坏死细胞表面的暴露 响应Ca~(2+)信号(目标1和2)，并从缺陷突变体中鉴定新的PS暴露基因 在暴露在死亡细胞上的PS中，我们在正向遗传筛查中分离出(目标3)。团结在一起， 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 还将揭示调控该过程每一步的新分子机制，其中一些是 预计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.