Liebner S, Kniesel U, Kalbacher H, Wolburg H
Institute of Pathology, University of Tübingen, Germany.
Eur J Cell Biol. 2000 Oct;79(10):707-17. doi: 10.1078/0171-9335-00101.
Endothelial cells of the blood-brain barrier form complex tight junctions, which are more frequently associated with the protoplasmic (P-face) than with the exocytoplasmic (E-face) membrane leaflet. The association of tight junctional particles with either membrane leaflet is a result of the expression of various claudins, which are transmembrane constituents of tight junction strands. Mammalian brain endothelial tight junctions exhibit an almost balanced distribution of particles and lose this morphology and barrier function in vitro. Since it was shown that the brain endothelial tight junctions of submammalian species form P-face-associated tight junctions of the epithelial type, the question of which molecular composition underlies the morphological differences and how do these brain endothelial cells behave in vitro arose. Therefore, rat and chicken brain endothelial cells were investigated for the expression of junctional proteins in vivo and in vitro and for the morphology of the tight junctions. In order to visualize morphological differences, the complexity and the P-face association of tight junctions were quantified. Rat and chicken brain endothelial cells form tight junctions which are positive for claudin-1, claudin-5, occludin and ZO-1. In agreement with the higher P-face association of tight junctions in vivo, chicken brain endothelia exhibited a slightly stronger labeling for claudin-1 at membrane contacts. Brain endothelial cells of both species showed a significant alteration of tight junctions in vitro, indicating a loss of barrier function. Rat endothelial cells showed a characteristic switch of tight junction particles from the P-face to the E-face, accompanied by the loss of claudin-1 in immunofluorescence labeling. In contrast, chicken brain endothelial cells did not show such a switch of particles, although they also lost claudin-1 in culture. These results demonstrate that the maintenance of rat and chicken endothelial barrier function depends on the brain microenvironment. Interestingly, the alteration of tight junctions is different in rat and chicken. This implies that the rat and chicken brain endothelial tight junctions are regulated differently.
血脑屏障的内皮细胞形成复杂的紧密连接，这些紧密连接与原生质（P面）的关联比与外吐细胞质（E面）的膜小叶更为频繁。紧密连接颗粒与任一膜小叶的关联是各种紧密连接蛋白表达的结果，这些紧密连接蛋白是紧密连接链的跨膜成分。哺乳动物脑内皮紧密连接呈现出颗粒几乎平衡的分布，并且在体外会丧失这种形态和屏障功能。由于已表明非哺乳动物物种的脑内皮紧密连接形成上皮类型的与P面相关的紧密连接，因此出现了以下问题：何种分子组成是形态差异的基础，以及这些脑内皮细胞在体外的行为如何。因此，对大鼠和鸡的脑内皮细胞进行了体内和体外连接蛋白表达以及紧密连接形态的研究。为了可视化形态差异，对紧密连接的复杂性和与P面的关联进行了量化。大鼠和鸡的脑内皮细胞形成对紧密连接蛋白-1、紧密连接蛋白-5、闭合蛋白和ZO-1呈阳性的紧密连接。与体内紧密连接与P面的较高关联一致，鸡脑内皮在膜接触处对紧密连接蛋白-1的标记略强。两种物种的脑内皮细胞在体外均显示紧密连接有显著改变，表明屏障功能丧失。大鼠内皮细胞显示紧密连接颗粒从P面到E面的特征性转变，同时免疫荧光标记中紧密连接蛋白-1缺失。相比之下，鸡脑内皮细胞虽然在培养中也丧失了紧密连接蛋白-1，但未显示出颗粒的这种转变。这些结果表明，大鼠和鸡内皮屏障功能的维持取决于脑微环境。有趣的是，大鼠和鸡的紧密连接改变有所不同。这意味着大鼠和鸡的脑内皮紧密连接受到不同的调节。
