Retamal Mauricio A, Froger Nicolas, Palacios-Prado Nicolas, Ezan Pascal, Sáez Pablo J, Sáez Juan C, Giaume Christian
Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Santiago 6513492, Chile.
J Neurosci. 2007 Dec 12;27(50):13781-92. doi: 10.1523/JNEUROSCI.2042-07.2007.
Astrocytes have a role in maintaining normal neuronal functions, some of which depend on connexins, protein subunits of gap junction channels and hemichannels. Under inflammatory conditions, microglia release cytokines, including interleukin-1beta and tumor necrosis factor-alpha, that reduce intercellular communication via gap junctions. Now, we demonstrate that either conditioned medium harvested from activated microglia or a mixture of these two cytokines enhances the cellular exchange with the extracellular milieu via Cx43 hemichannels. These changes in membrane permeability were not detected in astrocytes cultured from Cx43 knock-out mice and were abrogated by connexin hemichannel blockers, including La3+, mimetic peptides, and niflumic acid. Both the reduction in gap junctional communication and the increase in membrane permeability were mediated by a p38 mitogen-activated protein kinase-dependent pathway. However, the increase in membrane permeability, but not the gap junction inhibition, was rapidly reversed by the sulfhydryl reducing agent dithiothreitol, indicating that final regulatory mechanisms are different. Treatment with proinflammatory cytokines reduced the total and cell surface Cx43 levels, suggesting that the increase in membrane permeability was attributable to an increase in hemichannels activity. Indeed, unitary events of approximately 220 pS corresponding to Cx43 hemichannels were much more frequent in astrocytes treated with microglia conditioned medium than under control conditions. Finally, the effect of cytokines enhanced the uptake and reduced the intercellular diffusion of glucose, which might explain changes in the metabolic status of astrocytes under inflammatory conditions. Accordingly, this opposite regulation may affect glucose trafficking and certainly will modify the metabolic status of astrocytes involved in brain inflammation.
星形胶质细胞在维持正常神经元功能中发挥作用，其中一些功能依赖于连接蛋白，即缝隙连接通道和半通道的蛋白质亚基。在炎症条件下，小胶质细胞释放细胞因子，包括白细胞介素 -1β和肿瘤坏死因子 -α，这些细胞因子会减少通过缝隙连接的细胞间通讯。现在，我们证明，从活化的小胶质细胞收集的条件培养基或这两种细胞因子的混合物会通过Cx43半通道增强细胞与细胞外环境的交换。在从Cx43基因敲除小鼠培养的星形胶质细胞中未检测到这些膜通透性的变化，并且连接蛋白半通道阻滞剂，包括La3 +、模拟肽和尼氟灭酸，可消除这些变化。缝隙连接通讯的减少和膜通透性的增加均由p38丝裂原活化蛋白激酶依赖性途径介导。然而，巯基还原剂二硫苏糖醇可迅速逆转膜通透性的增加，但不能逆转缝隙连接的抑制，这表明最终的调节机制不同。促炎细胞因子处理降低了总Cx43水平和细胞表面Cx43水平，这表明膜通透性的增加归因于半通道活性的增加。事实上，在用小胶质细胞条件培养基处理的星形胶质细胞中，对应于Cx43半通道的约220 pS的单通道事件比对照条件下更为频繁。最后，细胞因子的作用增强了葡萄糖的摄取并减少了葡萄糖的细胞间扩散，这可能解释了炎症条件下星形胶质细胞代谢状态的变化。因此，这种相反的调节可能会影响葡萄糖转运，并且肯定会改变参与脑部炎症的星形胶质细胞的代谢状态。
