Neuroscience Program, University of Miami School of Medicine, Miami, FL 33136, USA.
J Gen Physiol. 2010 Oct;136(4):425-42. doi: 10.1085/jgp.201010476.
Microglia, the immune cells of the central nervous system, are attracted to sites of injury. The injury releases adenosine triphosphate (ATP) into the extracellular space, activating the microglia, but the full mechanism of release is not known. In glial cells, a family of physiologically regulated unpaired gap junction channels called innexons (invertebrates) or pannexons (vertebrates) located in the cell membrane is permeable to ATP. Innexons, but not pannexons, also pair to make gap junctions. Glial calcium waves, triggered by injury or mechanical stimulation, open pannexon/innexon channels and cause the release of ATP. It has been hypothesized that a glial calcium wave that triggers the release of ATP causes rapid microglial migration to distant lesions. In the present study in the leech, in which a single giant glial cell ensheathes each connective, hydrolysis of ATP with 10 U/ml apyrase or block of innexons with 10 µM carbenoxolone (CBX), which decreased injury-induced ATP release, reduced both movement of microglia and their accumulation at lesions. Directed movement and accumulation were restored in CBX by adding ATP, consistent with separate actions of ATP and nitric oxide, which is required for directed movement but does not activate glia. Injection of glia with innexin2 (Hminx2) RNAi inhibited release of carboxyfluorescein dye and microglial migration, whereas injection of innexin1 (Hminx1) RNAi did not when measured 2 days after injection, indicating that glial cells' ATP release through innexons was required for microglial migration after nerve injury. Focal stimulation either mechanically or with ATP generated a calcium wave in the glial cell; injury caused a large, persistent intracellular calcium response. Neither the calcium wave nor the persistent response required ATP or its release. Thus, in the leech, innexin membrane channels releasing ATP from glia are required for migration and accumulation of microglia after nerve injury.
小胶质细胞是中枢神经系统的免疫细胞，它们被吸引到损伤部位。损伤会将三磷酸腺苷 (ATP) 释放到细胞外空间，从而激活小胶质细胞，但释放的完整机制尚不清楚。在神经胶质细胞中，一组被称为连接蛋白 (无脊椎动物) 或连接蛋白 (脊椎动物) 的生理调节的非配对间隙连接通道位于细胞膜上，对 ATP 具有通透性。连接蛋白不仅可以配对形成间隙连接，还可以配对形成间隙连接。由损伤或机械刺激引发的神经胶质钙波会打开连接蛋白/连接蛋白通道并导致 ATP 释放。有人假设，引发 ATP 释放的神经胶质钙波会导致快速的小胶质细胞迁移到远处的损伤部位。在本研究中，在水蛭中，每个连接体都被一个巨大的神经胶质细胞包裹，用 10 U/ml 的 apyrase 水解 ATP 或用 10 µM 的 carbenoxolone (CBX) 阻断连接蛋白，这会减少损伤引起的 ATP 释放，减少小胶质细胞的运动和它们在损伤处的聚集。在 CBX 中加入 ATP 可以恢复定向运动和聚集，这与 ATP 和一氧化氮的独立作用一致，一氧化氮是定向运动所必需的，但不会激活神经胶质细胞。向神经胶质细胞注射连接蛋白 2 (Hminx2) RNAi 会抑制羧基荧光素染料的释放和小胶质细胞的迁移，而在注射后 2 天测量时，注射连接蛋白 1 (Hminx1) RNAi 则不会，这表明神经胶质细胞通过连接蛋白释放 ATP 是神经损伤后小胶质细胞迁移所必需的。机械或用 ATP 进行的局部刺激会在神经胶质细胞中产生钙波；损伤会引起大的、持续的细胞内钙反应。钙波和持续反应都不需要 ATP 或其释放。因此，在水蛭中，神经胶质细胞释放的连接蛋白膜通道对于神经损伤后小胶质细胞的迁移和聚集是必需的。
