Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Sci Signal. 2012 Apr 3;5(218):ra27. doi: 10.1126/scisignal.2002498.
Metabotropic glutamate receptor (mGluR)-dependent calcium ion (Ca²+) signaling in astrocytic processes regulates synaptic transmission and local blood flow essential for brain function. However, because of difficulties in imaging astrocytic processes, the subcellular spatial organization of mGluR-dependent Ca²+ signaling is not well characterized and its regulatory mechanism remains unclear. Using genetically encoded Ca²+ indicators, we showed that despite global stimulation by an mGluR agonist, astrocyte processes intrinsically exhibited a marked enrichment of Ca²+ responses. Immunocytochemistry indicated that these polarized Ca²+ responses could be attributed to increased density of surface mGluR5 on processes relative to the soma. Single-particle tracking of surface mGluR5 dynamics revealed a membrane barrier that blocked the movement of mGluR5 between the processes and the soma. Overexpression of mGluR or expression of its carboxyl terminus enabled diffusion of mGluR5 between the soma and the processes, disrupting the polarization of mGluR5 and of mGluR-dependent Ca²+ signaling. Together, our results demonstrate an mGluR5-selective diffusion barrier between processes and soma that compartmentalized mGluR Ca²+ signaling in astrocytes and may allow control of synaptic and vascular activity in specific subcellular domains.
代谢型谷氨酸受体 (mGluR)-依赖性钙离子 (Ca²+) 信号在星形胶质细胞突起中调节突触传递和局部血流，对大脑功能至关重要。然而，由于难以对星形胶质细胞突起进行成像，mGluR 依赖性 Ca²+ 信号的亚细胞空间组织尚未得到很好的描述，其调节机制仍不清楚。使用基因编码的 Ca²+ 指示剂，我们发现，尽管被 mGluR 激动剂整体刺激，星形胶质细胞突起中仍表现出 Ca²+ 反应的明显富集。免疫细胞化学表明，这些极化的 Ca²+ 反应可归因于突起表面 mGluR5 的密度相对于胞体增加。表面 mGluR5 动力学的单颗粒追踪显示存在一个膜屏障，阻止 mGluR5 在突起和胞体之间移动。mGluR 的过表达或其羧基末端的表达使 mGluR5 能够在胞体和突起之间扩散，破坏 mGluR5 和 mGluR 依赖性 Ca²+ 信号的极化。总之，我们的结果表明，突起和胞体之间存在 mGluR5 选择性扩散屏障，使星形胶质细胞中的 mGluR Ca²+ 信号分隔，并可能允许在特定亚细胞域中控制突触和血管活动。
