Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom.
J Immunol. 2011 Apr 15;186(8):4973-83. doi: 10.4049/jimmunol.1003600. Epub 2011 Mar 14.
It is well-known that dead and dying neurons are quickly removed through phagocytosis by the brain's macrophages, the microglia. Therefore, neuronal loss during brain inflammation has always been assumed to be due to phagocytosis of neurons subsequent to their apoptotic or necrotic death. However, we report in this article that under inflammatory conditions in primary rat cultures of neurons and glia, phagocytosis actively induces neuronal death. Specifically, two inflammatory bacterial ligands, lipoteichoic acid or LPS (agonists of glial TLR2 and TLR4, respectively), stimulated microglial proliferation, phagocytic activity, and engulfment of ∼30% of neurons within 3 d. Phagocytosis of neurons was dependent on the microglial release of soluble mediators (and peroxynitrite in particular), which induced neuronal exposure of the eat-me signal phosphatidylserine (PS). Surprisingly, however, eat-me signaling was reversible, so that blocking any step in a phagocytic pathway consisting of PS exposure, the PS-binding protein milk fat globule epidermal growth factor-8, and its microglial vitronectin receptor was sufficient to rescue up to 90% of neurons without reducing inflammation. Hence, our data indicate a novel form of inflammatory neurodegeneration, where inflammation can cause eat-me signal exposure by otherwise viable neurons, leading to their death through phagocytosis. Thus, blocking phagocytosis may prevent some forms of inflammatory neurodegeneration, and therefore might be beneficial during brain infection, trauma, ischemia, neurodegeneration, and aging.
众所周知,大脑中的巨噬细胞(小胶质细胞)通过吞噬作用迅速清除死亡和垂死的神经元。因此,人们一直认为,在大脑炎症期间神经元的丢失是由于神经元凋亡或坏死后的吞噬作用所致。然而,我们在本文中报告称,在原代大鼠神经元和神经胶质细胞培养物的炎症条件下,吞噬作用会主动诱导神经元死亡。具体而言,两种炎症性细菌配体,脂磷壁酸或 LPS(分别为小胶质细胞 TLR2 和 TLR4 的激动剂)刺激小胶质细胞增殖、吞噬活性,并在 3 天内吞噬了约 30%的神经元。神经元的吞噬作用依赖于小胶质细胞释放可溶性介质(特别是过氧亚硝酸盐),这诱导神经元暴露了“吃我”信号磷脂酰丝氨酸(PS)。然而,令人惊讶的是,“吃我”信号是可逆的,因此,阻断吞噬作用途径中的任何一步,包括 PS 暴露、PS 结合蛋白乳脂肪球表皮生长因子 8 及其小胶质细胞 vitronectin 受体,就足以挽救多达 90%的神经元,而不会减少炎症。因此,我们的数据表明了一种新形式的炎症性神经退行性变,其中炎症可以导致原本存活的神经元暴露“吃我”信号,从而通过吞噬作用导致其死亡。因此,阻断吞噬作用可能预防某些形式的炎症性神经退行性变,因此在大脑感染、创伤、缺血、神经退行性变和衰老期间可能有益。