Regulatory mechanisms of expression and localization of aquaporin water channels in brain microvessels

我们研究了水通道蛋白(AQP)作为调节血脑水通透性的分子在脑微血管中表达和定位的调控机制，并对其病理生理机制进行了初步探讨。糖皮质激素地塞米松以浓度和时间依赖的方式上调转录，上调了培养的脑微血管内皮细胞GP8细胞AQP1的表达。AQP1主要集中在脂质微域筏上，提示AQP1与脂质的相互作用对AQP1的细胞内转运具有重要作用，AQP1的诱导可能参与了糖皮质激素对脑水肿的改善作用。此外，我们还鉴定了细胞外基质蛋白agrin是调节AQP定位的关键分子。在脑微血管中表达的集聚蛋白的主要异构体是长N端(LN)集聚蛋白，其N端含有一簇疏水氨基酸，这是一个可能的分泌信号序列。融合了绿色荧光蛋白的LN集聚蛋白的N端被分泌到细胞外环境中。为了解水通道蛋白在中枢神经系统水肿形成中的作用，我们观察了内毒素性葡萄膜炎大鼠视网膜中水通道蛋白4的表达。AQP4在面对微血管的Muller细胞中的表达在内毒素处理后略有下降，然后恢复到对照水平。经内毒素处理后，Kir4.1钾通道的表达降至一半以下，并维持在较低水平。AQP4和Kir4.1在内毒素诱导的葡萄膜炎中的差异表达提示视网膜中水和钾的运输障碍，这可能是眼部炎症时视网膜水肿的原因之一。

We have studied the regulatory mechanisms of expression and localization of aquaporin (AQP) water channels in brain microvessels as molecules regulating water permeability between blood and brain, and have tried to their pathophysiologicalThe expression of AQP1 in cultured brain microvascular endothelial GP8 cells was increased by the treatment with dexamethasone, a glucocorticoid, by increasing transcription in a concentration-and time-dependent manner. AQP1 was concentrated in lipid microdomain rafts, suggesting that the interaction of AQP1 and lipid is important for intracellular transport of AQP1 and that the induction of AQP1 may be involved in the ameliorating effects of glucocorticoid in brain edema.In addition, we have characterized agrin, an extracellular matrix protein, as a key molecule regulating the localization of AQP. The major isoform of agrin expressed in the brain microvessels was long N-terminal (LN) agrin, and its N-terminal contained a cluster of hydrophobic amino, a putative signal sequence for secretion. The N-terminal of LN agrin fused with green fluorescence protein was secreted into extracellular milieu. It is suggested that LN agrin expressed by the brain microvessels may regulate the localization of AQPs at the interface between brain microvessels and astrocytes.To know role of AQP in the edema formation in the CNS, we have investigated the expression of AQP4 in the retina during endotoxin-induced uveitis in rats. The expression of AQP4 in the Muller cells facing the microvessels reduced slightly after endotoxin treatment, then returned to the control level. The expression of Kir4.1 potassium channel reduced to less than half by the endotoxin treatment, and remained at low level. The differential expression of AQP4 and Kir4.1 during endotoxin-induced uveitis implies a disturbance of water and potassium transport in the retina, which may contribute to the retinal edema during ocular inflammation.