Fu Xuemei, Li Qiuping, Feng Zhichun, Mu Dezhi
Department of Pediatrics, Zhujiang Hospital, Nanfang University of Medical Sciences, Guangzhou, Guangdong 510282, China.
Glia. 2007 Jul;55(9):935-41. doi: 10.1002/glia.20515.
Aquaporin-4 (AQP4), a water channel protein, is abundantly expressed in astrocytes and plays a key role in the development of brain edema. However, it is not clear whether AQP4 contributes to astrocytic swelling in hypoxia-ischemia (HI). To investigate the roles of AQP4 in astrocytic swelling during HI and reoxygenation, we measured AQP4 expression and astrocytic cellular volume in cultured rat astrocytes following HI and reoxygenation. RNA interference was used to knockdown AQP4 expression (AQP4(-/-)). Real-time polymerase chain reaction and Western blot analysis were used to detect the inhibitory efficiency of AQP4. We found that the maximal inhibition of AQP4 mRNA and protein in astrocytes after AQP4 siRNA transfection (AQP4(-/-)) was approximately 77 and 85%, respectively, compared to wild-type AQP4 (AQP4(+/+)) expression. Cellular volume in both AQP4(-/-) and AQP4(+/+) astrocytes was significantly increased during HI compared to cells cultured in normoxia (P<0.05). However, cellular volume during HI in AQP4(-/-) astrocytes was significantly less than that in AQP4(+/+) astrocytes (P<0.05). After reoxygenation, the cellular volume gradually decreased to control levels at 7 days in AQP4(-/-) but at 5 days in AQP4(+/+) astrocytes. The different roles of AQP4 during HI and reoxygenation suggest that AQP4 knockdown may protect against water influx in the formation of astrocyte swelling during HI, and may also delay water clearance in the resolution of astrocyte swelling during reoxygenation. In conclusion, AQP4 mediates bidirectional transport of water across astrocytes during HI and reoxygenation. AQP4 manipulation may serve as a novel therapeutic strategy during different periods of hypoxic-ischemic brain edema in neonates.
水通道蛋白4（AQP4）是一种水通道蛋白，在星形胶质细胞中大量表达，在脑水肿的发展中起关键作用。然而，尚不清楚AQP4是否在缺氧缺血（HI）过程中导致星形胶质细胞肿胀。为了研究AQP4在HI和复氧过程中对星形胶质细胞肿胀的作用，我们在HI和复氧后的培养大鼠星形胶质细胞中测量了AQP4表达和星形胶质细胞体积。采用RNA干扰技术敲低AQP4表达（AQP4（-/-））。使用实时聚合酶链反应和蛋白质印迹分析来检测AQP4的抑制效率。我们发现，与野生型AQP4（AQP4（+/+））表达相比，AQP4 siRNA转染后星形胶质细胞中AQP4 mRNA和蛋白质的最大抑制率分别约为77%和85%。与在常氧条件下培养的细胞相比，HI期间AQP4（-/-）和AQP4（+/+）星形胶质细胞的细胞体积均显著增加（P<0.05）。然而，HI期间AQP4（-/-）星形胶质细胞的细胞体积显著小于AQP4（+/+）星形胶质细胞（P<0.05）。复氧后，AQP4（-/-）星形胶质细胞的细胞体积在7天时逐渐降至对照水平，而AQP4（+/+）星形胶质细胞在5天时降至对照水平。AQP4在HI和复氧过程中的不同作用表明，敲低AQP4可能在HI期间星形胶质细胞肿胀形成过程中防止水流入，并且在复氧期间星形胶质细胞肿胀消退过程中也可能延迟水清除。总之，AQP4在HI和复氧过程中介导水在星形胶质细胞中的双向转运。操纵AQP4可能作为新生儿缺氧缺血性脑水肿不同时期的一种新的治疗策略。
