Centre for Molecular Biology and Neuroscience, Institute of Basic Medical Sciences, University of Oslo, Norway.
Glia. 2012 Dec;60(12):2018-26. doi: 10.1002/glia.22416. Epub 2012 Sep 17.
Key roles of macroglia are inextricably coupled to specialized membrane domains. The perivascular endfoot membrane has drawn particular attention, as this domain contains a unique complement of aquaporin-4 (AQP4) and other channel proteins that distinguishes it from perisynaptic membranes. Recent studies indicate that the polarization of macroglia is lost in a number of diseases, including temporal lobe epilepsy and Alzheimer's disease. A better understanding is required of the molecular underpinning of astroglial polarization, particularly when it comes to the significance of the dystrophin associated protein complex (DAPC). Here, we employ immunofluorescence and immunogold cytochemistry to analyze the molecular scaffolding in perivascular endfeet in macroglia of retina and three regions of brain (cortex, dentate gyrus, and cerebellum), using AQP4 as a marker. Compared with brain astrocytes, Müller cells (a class of retinal macroglia) exhibit lower densities of the scaffold proteins dystrophin and α-syntrophin (a DAPC protein), but higher levels of AQP4. In agreement, depletion of dystrophin or α-syntrophin--while causing a dramatic loss of AQP4 from endfoot membranes of brain astrocytes--had only modest or insignificant effect, respectively, on the AQP4 pool in endfoot membranes of Müller cells. In addition, while polarization of brain macroglia was less affected by dystrophin depletion than by targeted deletion of α-syntrophin, the reverse was true for retinal macroglia. These data indicate that the molecular scaffolding in perivascular endfeet is more complex than previously assumed and that macroglia are heterogeneous with respect to the mechanisms that dictate their polarization.
神经胶质细胞的主要功能与特化的膜结构域密不可分。血管周足膜特别受到关注，因为这个区域含有独特的水通道蛋白-4（AQP4）和其他通道蛋白，使其与突触周膜区分开来。最近的研究表明，在包括颞叶癫痫和阿尔茨海默病在内的许多疾病中，神经胶质细胞的极化丧失。需要更好地了解星形胶质细胞极化的分子基础，特别是当涉及到与肌营养不良蛋白相关的蛋白复合物（DAPC）的意义时。在这里，我们使用免疫荧光和免疫胶体金细胞化学方法，以 AQP4 作为标记，分析视网膜和大脑三个区域（皮质、齿状回和小脑）的血管周足神经胶质细胞中的分子支架。与大脑星形胶质细胞相比，Müller 细胞（一类视网膜神经胶质细胞）的支架蛋白肌营养不良蛋白和α- 连蛋白（DAPC 蛋白）密度较低，但 AQP4 水平较高。与之一致的是，尽管肌营养不良蛋白或 α-连蛋白的耗竭导致大脑星形胶质细胞血管周足膜上的 AQP4 大量丢失，但对 Müller 细胞血管周足膜上的 AQP4 池的影响分别是适度的或微不足道的。此外，尽管大脑神经胶质细胞的极化受肌营养不良蛋白耗竭的影响小于靶向α-连蛋白缺失，但对于视网膜神经胶质细胞来说则相反。这些数据表明，血管周足的分子支架比之前假设的更为复杂，并且神经胶质细胞在决定其极化的机制方面存在异质性。
