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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Aquaporin-4 square array assembly: Opposing actions of M1 and M23 isoforms
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Aquaporin-4 square array assembly: Opposing actions of M1 and M23 isoforms

机译：Aquaporin-4方阵组件：M1和M23亚型的相反作用

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摘要

Osmotic homeostasis in the brain involves movement of water through aquaporin-4 (AQP4) membrane channels. Perivascular astrocyte end-feet contain distinctive orthogonal lattices (square arrays) assembled from 4- to 6-nm intramembrane particles (IMPs) corresponding to individual AQP4 tetramers. Two isoforms of AQP4 result from translation initiation at methionine residues M1 and M23, but no functional differences are known. In this study, Chinese hamster ovary cells were transfected with M1, M23, or M1+M23 isoforms, and AQP4 expression was confirmed by immu-noblotting, immunocytochemistry, and immunogold labeling. Square array organization was examined by freeze-fracture electron microscopy. In astrocyte end-feet, >90% of 4- to 6-nm IMPs were found in square arrays, with 65% in arrays of 13-30 IMPs. In cells transfected with M23, 95% of 4- to 6-nm IMPs were in large assemblies (rafts), 85% of which contained >100 IMPs. However, in M1 cells, >95% of 4- to 6-nm IMPs were present as singlets, with <5% in incipient arrays of 2-12 IMPs. In M1+M23 cells, 4- to 6-nm IMPs were in arrays of intermediate sizes, resembling square arrays in astrocytes. Structural cross-bridges of 1 x 2 nm linked >90% of IMPs in M23 arrays (≈1,000 cross-bridges per μm~2) but were rarely seen in M1 cells. These studies show that M23 and M1 isoforms have opposing effects on intramembrane organization of AQP4: M23 forms large square arrays with abundant cross-bridges; M1 restricts square array assembly.
机译：大脑中的渗透稳态涉及水通过Aquaporin-4（AQP4）膜通道的运动。血管周围星形胶质细胞的末端含有从4到6 nm的膜内颗粒（IMP）组装而成的独特的正交格子（正方形阵列），对应于单个AQP4四聚体。 AQP4的两个同工型由蛋氨酸M1和M23的翻译起始产生，但没有功能差异。在这项研究中，中国仓鼠卵巢细胞被M1，M23或M1 + M23亚型转染，并且通过免疫印迹，免疫细胞化学和免疫金标记证实了AQP4的表达。通过冷冻断裂电子显微镜检查方阵组织。在星形胶质细胞末端，在正方形阵列中发现> 90％的4至6 nm IMPs，在13-30个IMPs中发现65％。在转染了M23的细胞中，95％的4至6 nm IMPs位于大型装配（筏）中，其中85％包含> 100个IMPs。但是，在M1细胞中，> 95％的4-nm至6-nm IMPs以单重态存在，而在2-12个IMPs的初始阵列中<5％。在M1 + M23细胞中，4至6纳米的IMP位于中等大小的阵列中，类似于星形胶质细胞中的方形阵列。 1 x 2 nm的结构性跨桥连接了M23阵列中大于90％的IMP（≈1,000跨桥/μm〜2），但在M1细胞中很少见。这些研究表明，M23和M1亚型对AQP4的膜内组织具有相反的影响：M23形成具有丰富跨桥的大正方形阵列； M1限制方阵装配。

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