大鼠脑外伤诱导水通道蛋白4表达增强加重脑水肿

Enhanced Expression of Aquaporin-4 Aggravates Brain Edema after Traumatic Brain Injury in Rat

目的探讨大鼠外伤性脑水肿组织水通道蛋白4(aquaporin 4,AQP4)的表达变化及其与血-脑脊液屏障(blood-brain barrier,BBB)通透性的关系。方法SD大鼠94只,用随机数字表法分为脑外伤组(包括脑外伤后1、6、24、48和168 h)、假手术对照组及空白组。复制大鼠自由落体脑损伤模型,用干质量湿质量法测定脑组织水含量,用IgG免疫组化染色法检测血-脑脊液屏障通透性的变化,用免疫组化染色法及Western blotting法检测神经胶质纤维酸性蛋白(glial fibrillary acidic protein,GFAP)和AQP4蛋白的表达并进行图像分析。结果大鼠脑外伤后,损伤侧脑组织水含量较假手术组增加,6 h时差异有统计学意义,24 h达高峰。与假手术组比较损伤侧脑组织IgG漏出在外伤后1 h差异有统计学意义,6 h达高峰。免疫组化染色显示损伤周围处星形胶质细胞上AQP4的分布极性发生改变,不仅毛细血管周围的星形胶质细胞足突上AQP4表达增加,而且星形胶质细胞胞体亦出现AQP4表达。AQP4表达变化的时间与脑组织水含量变化一致,晚于IgG漏出的变化。损伤周围处GFAP在损伤后1 h～7d表达持续增强。结论大鼠脑损伤后先出现BBB通透性增加,并引起AQP4表达增加,二者均促进了脑水肿的发生。

Objective To investigate the expression changes in aquaporin-4 （AQP4） during brain traumatic edema in rat, and evaluate its relationship with the disruption of blood-brain barrier （BBB） permeability. Methods Ninety-four SD rats were randomly allocated into control group, sham operation group and brain injury group, with the last group further divided into groups of 1, 6, 24, 48 and 168 h after rat brain injury. In a rat impact-acceleration head injury model, brain water contents were measured by wet-dry weight method, BBB permeability was evaluated by immunohistochemical staining of IgG, and the expressions of AQP4 and GFAP in brain were determined by immunohistochemical stain and Western blotting. Results After rat brain trauma, cerebral water content of injured brain increased significantly at 6 h, and reached maximum at 24 h. The extravasation of IgG in injured brain occurred at 1 h, and peaked at 6h. Western blotting study detected enhancement AQP4 expression adjacent to injury site after brain trauma, and immunostaining revealed the changes in AQP4 polar distribution in the reactive astrocyte, with increased AQP4 expressions both in the peri-vascular astrocyte end-feet and cell body. The time course of enhanced AQP4 expressions was accompanied with the increase of brain water content and delayed after the maximum extravasation of IgG. Conclusion Enhanced expressions of AQP4 followed the disruption of BBB permeability, which means it may contribute to the development of brain edema after rat traumatic brain injury.