水通道蛋白4表达减少与新生大鼠缺氧缺血脑水肿的关系

Relationship between the decrease in aquaporin-4 expression and hypoxic-ischemic cerebral edema in neonatal rats

摘要:

目的：目前,有关水在细胞内外或跨过血脑屏障的转运机制尚不清楚。水通道蛋白4(AQP4)是水通道蛋白家族中在脑表达最丰富的一个亚型,该文旨在探讨新生大鼠脑缺氧缺血后AQP4表达的改变及其与磁共振(MR)显示的脑水肿的关系。方法：7日龄新生大鼠24只,在缺氧前,缺氧后0h,1h和24h行MR扫描获得T2加权成像和表面弥散系数(ADC),应用免疫组化染色观察脑内AQP4表达和血脑屏障通透性的改变,并用蛋白质印迹行AQP4半定量分析。结果：缺氧后0h,整个缺血半球ADC值明显下降,缺氧后1h时ADC部分恢复,缺氧后24h时ADC改变与1h时类似。缺氧后缺血半球T2值增高,其动态变化类似ADC变化。缺氧后0h时可见IgG渗出脑血管外,随着缺氧后时间延长,IgG渗出逐渐加重。缺氧后缺血半球AQP4免疫染色减弱,其变化在缺氧后各时间点与ADC和T2改变相对应。蛋白质印迹分析显示仅缺氧后24h时AQP4减少。结论：新生大鼠脑缺氧缺血后AQP4表达减少,其减少可能参与了急性缺氧缺血性脑水肿的形成。缺氧后AQP4表达的快速减少可能与AQP4蛋白质构像改变或分布异位有关。

Abstract:

OBJECTIVE: Aquaporin- 4 (AQP4) is a member of a family of water-selective channel proteins that is highly expressed in the brain. This study investigated the alterations of AQP4 expression and its relationship with cerebral edema monitored by magnetic resonance(MR) imaging in neonatal rats following hypoxia-ischemia (HI). METHODS: Seven-day-old neonatal rats were subjected to right carotid artery occlusion plus hypoxia in 8% oxygen. T2 values and apparent diffuse coeffcient (ADC) were acquired by MR imaging before HI, and 0, 1 and 24 hrs after HI. AQP4 expression in the brain and permeability of blood brain barrier were examined by immunohistological staining. Semiquantitive analysis of AQP4 protein was done by Western blotting. RESULTS: ADC significantly decreased in almost entire cerebral hemisphere ipsilateral to the occlusion at 0 hr after HI, recovered partially at 1 hr after HI, and at 24 hrs after HI the changes remained similar to that at 1 hr after HI. T2 values increased in the ipsilateral hemisphere at 0 hr after HI, recovered partially at 1 hr after HI, and then remained unchanged until 24 hrs after HI. IgG extravasation was observed at o hr after HI, and gradually increased after HI. AQP4 immunoreactive expression in the ipsilateral hemisphere to the occlusion decreased at 0 hr, 1 hr or 24 hrs after HI. The areas of AQP4 immunoreactive expression decrease coincided well with the regions of ADC and T2 changes after HI. Western blotting analysis demonstrated that AQP4 protein was not significantly reduced until 24 hrs after HI. CONCLUSIONS: AQP4 expression in the brain decreased in the neonatal rats following HI and the decrease of AQP4 expression may be involved in the development of acute HI cerebral edema. The rapid decrease in AQP4 immunoreactive expression following HI is likely due to conformational changes or translocation of AQP4 protein.