Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis
Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis
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DOI：
10.1053/jhep.2003.50170
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发表时间：
2003-05-01
期刊：
影响因子：
13.5
通讯作者：
Marinelli, RA
中科院分区：
文献类型：
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作者：
Carreras, FI;Gradilone, SA;Marinelli, RA
肝细胞表达水通道水通道蛋白-8 (aquaporin-8, AQP8)，主要定位于细胞内囊泡，其腺苷3′，5′-环单磷酸腺苷（cAMP）诱导的向质膜的易位促进了小管胆汁分泌过程中的渗透水运动。因此，AQP8表达缺陷可能与肝外胆汁淤积引起的肝细胞分泌功能障碍有关。我们研究了胆管结扎1、3和7天对AQP8蛋白表达、亚细胞定位和信使RNA （mRNA）水平的影响；通过亚细胞膜免疫印迹、大量免疫组织化学、免疫金电镜和Northern印迹，在大鼠肝脏中测定。1天BDL不影响AQP8的表达和亚细胞定位。BDL治疗3天后，细胞内AQP8表达减少75% (P < 0.001)，但不影响其质膜表达。BDL后7 d，细胞内膜AQP8 （67%, P < 0.05）和血浆膜AQP8 （56%, P < 0.05）明显降低。二丁基cAMP不能增加肝片质膜AQP8，提示7天BDL大鼠AQP8易位缺陷。肝切片免疫组织化学和免疫电镜证实，bdl诱导肝细胞内囊泡和小管膜AQP8表达降低。AQP8 mRNA表达不受1天BDL影响，但在3天和7天BDL大鼠中显著增加约200%，表明蛋白水平降低的转录后机制。由此可见，bdl诱导的肝外胆汁淤积可引起肝细胞AQP8蛋白表达的转录后下调。aqp8水通道表达缺陷可能导致胆汁淤积肝细胞胆汁分泌功能障碍。
Hepatocytes express the water channel aquaporin-8 (AQP8), which is mainly localized in intracellular vesicles, and its adenosine 3',5'-cyclic monophosphate (cAMP)-induced translocation to the plasma membrane facilitates osmotic water movement during canalicular bile secretion. Thus, defective expression of AQP8 may be associated with secretory dysfunction of hepatocytes caused by extrahepatic cholestasis. We studied the effect of 1, 3, and 7 days of bile duct ligation (BDL) on protein expression, subcellular localization, and messenger RNA (mRNA) levels of AQP8; this was determined in rat livers by immunoblotting in subcellular membranes, lot immunohistochemistry, immunogold electron microscopy, and Northern blotting. One day of BDL did not affect expression or subcellular localization of AQP8. Three days of BDL reduced the amount of intracellular AQP8 (75%; P < .001) without affecting its plasma membrane expression. Seven days after BDL, AQP8 was markedly decreased in intracellular (67%; P < .05) and plasma (56%; P < .05) membranes. Dibutyryl cAMP failed to increase AQP8 in plasma membranes from liver slices, suggesting a defective translocation of AQP8 in 7-day BDL rats. Immunohistochemistry and immunoelectron microscopy in liver sections confirmed the BDL-induced decreased expression of hepatocyte AQP8 in intracellular vesicles and canalicular mem branes. AQP8 mRNA expression was unaffected by 1-day BDL but was significantly increased by about 200% in 3- and 7-day BDL rats, indicating a postmanscriptional mechanism for protein level reduction. In conclusion, BDL-induced extrahepatic cholestasis caused posttranscriptional downregulation of hepatocyte AQP8 protein expression. Defective expression ofAQP8 water channels may contribute to bile secretory dysfunction of cholestatic hepatocytes.