Sudo S, Tanaka J, Toku K, Desaki J, Matsuda S, Arai T, Sakanaka M, Maeda N
Department of Anesthesiology and Resuscitology, School of Medicine, Ehime University, Shigenobu, Ehime, 791-0295, Japan.
Exp Neurol. 1998 Dec;154(2):499-510. doi: 10.1006/exnr.1998.6911.
Although microglial cells are well known to become activated in the pathological brain, mechanisms underlying the microglial activation are not fully understood. In the present study, with an aim to elucidate whether neurons are involved in the microglial activation, we compared the morphology and the superoxide anion (O2-)-generating activity of rat microglial cells in pure culture with those of cells cocultured with rat primary cortical neurons. Microglial cells in pure culture in serum-free Eagle's minimum essential medium on poly-L-lysine-coated coverslips displayed ramified morphology and suppressed activity of O2- generation. In contrast, microglial cells in neuron-microglia coculture under the same conditions as those for the pure culture displayed ameboid shape and upregulated activity of O2- generation. Electron microscopic observation revealed that microglial cells in coculture were more abundant in Golgi apparatus and secretory granules than those in pure culture and that some of microglial cells in the vicinity of neurites exhibited membrane specialization reminiscent of a junctional apparatus with high electron density between a microglial soma and a neurite. Microglial cells in coculture tended to tie neurites in bundles by extending processes. Medium conditioned by neurons significantly enhanced O2- generation by microglia, but microglial cells in contact with or in close apposition to cocultured neurons were much more intensely activated than those remote from the neurons. Furthermore, the membrane fraction of cortical neurons activated microglial cells, and this effect was abolished by treating the neuronal membrane with trypsin or neuraminidase. In conclusion, neuronal-microglial contact may be necessary to mediate microglial activation. The present findings suggest that the contact of microglia with damaged neurons in the brain is a plausible cause to activate microglia in the neuropathological processes.
虽然小胶质细胞在病理性脑内被激活是众所周知的，但小胶质细胞激活的潜在机制尚未完全明确。在本研究中，为了阐明神经元是否参与小胶质细胞的激活，我们比较了纯培养的大鼠小胶质细胞与与大鼠原代皮质神经元共培养的细胞的形态以及超氧阴离子（O2-）生成活性。在聚-L-赖氨酸包被的盖玻片上，于无血清的伊格尔最低必需培养基中进行纯培养的小胶质细胞呈现出分支状形态，且O2-生成活性受到抑制。相比之下，在与纯培养相同条件下进行神经元-小胶质细胞共培养的小胶质细胞呈现出阿米巴样形态，且O2-生成活性上调。电子显微镜观察显示，共培养中的小胶质细胞比纯培养中的小胶质细胞含有更丰富的高尔基体和分泌颗粒，并且在神经突附近的一些小胶质细胞表现出膜特化，类似于小胶质细胞胞体与神经突之间具有高电子密度的连接装置。共培养中的小胶质细胞倾向于通过伸出突起将神经突捆绑成束。神经元条件培养基显著增强了小胶质细胞的O2-生成，但与共培养神经元接触或紧密相邻的小胶质细胞比远离神经元的小胶质细胞激活程度更强。此外，皮质神经元的膜组分激活了小胶质细胞，而用胰蛋白酶或神经氨酸酶处理神经元膜可消除这种效应。总之，神经元-小胶质细胞接触可能是介导小胶质细胞激活所必需的。本研究结果表明，在神经病理过程中，小胶质细胞与受损神经元的接触是激活小胶质细胞的一个合理原因。
