Zollner Gernot, Fickert Peter, Silbert Dagmar, Fuchsbichler Andrea, Marschall Hanns Ulrich, Zatloukal Kurt, Denk Helmut, Trauner Michael
Division of Gastroenterology and Hepatology, Department of Medicine, Karl-Franzens University, Auenbruggerplatz 15, A-8036, Graz, Austria.
J Hepatol. 2003 Jun;38(6):717-27. doi: 10.1016/s0168-8278(03)00096-5.
BACKGROUND/AIMS: Information about alterations of hepatobiliary transporter expression in primary biliary cirrhosis (PBC) could provide important insights into the pathogenesis of cholestasis. This study aimed to determine the expression of hepatobiliary transport systems for bile salts (Na(+)/taurocholate cotransporter, NTCP; bile salt export pump, BSEP), organic anions (organic anion transporting protein, OATP2; canalicular conjugate export pump, MRP2; basolateral MRP homologue, MRP3), organic cations (canalicular multidrug export pump, MDR1), and phospholipids (canalicular phospholipid flippase MDR3) in livers from patients with advanced stages of PBC.
Transporter mRNA and protein levels were assessed by reverse transcription polymerase chain reaction and Western blot analysis. Tissue distribution of transporters was investigated by immunohistochemistry and immunofluorescence microscopy. Hepatic bile acids were measured by gas chromatography-mass spectrometry.
Compared to controls, basolateral uptake systems (NTCP, OATP2) were reduced, canalicular export pumps for bile salts and bilirubin (BSEP, MRP2) were preserved, while canalicular MDR P-glycoproteins (MDR1, MDR3) and the basolateral efflux pump MRP3 were increased in PBC. Double immunofluorescence labeling with a canalicular marker (dipeptidyl peptidase IV) demonstrated proper canalicular localization of BSEP and MRP2 in PBC. OATP2 and MRP2 expression correlated inversely with hepatic levels of hydrophobic bile acids, while positively correlating with hepatic enrichment with ursodeoxycholic acid.
Down-regulation of basolateral uptake systems and maintenance/up-regulation of canalicular and basolateral efflux pumps may represent adaptive mechanisms limiting the accumulation of toxic biliary constituents.
背景/目的：原发性胆汁性肝硬化（PBC）中肝胆转运体表达改变的相关信息可为胆汁淤积的发病机制提供重要见解。本研究旨在确定晚期PBC患者肝脏中胆盐（钠离子/牛磺胆酸盐共转运体，NTCP；胆盐输出泵，BSEP）、有机阴离子（有机阴离子转运蛋白，OATP2；胆小管共轭输出泵，MRP2；基底外侧MRP同源物，MRP3）、有机阳离子（胆小管多药输出泵，MDR1）和磷脂（胆小管磷脂翻转酶MDR3）的肝胆转运系统的表达情况。
通过逆转录聚合酶链反应和蛋白质免疫印迹分析评估转运体的mRNA和蛋白水平。通过免疫组织化学和免疫荧光显微镜研究转运体的组织分布。采用气相色谱-质谱法测定肝脏胆汁酸。
与对照组相比，基底外侧摄取系统（NTCP、OATP2）减少，胆盐和胆红素的胆小管输出泵（BSEP、MRP2）保持不变，而PBC中胆小管MDR P-糖蛋白（MDR1、MDR3）和基底外侧外排泵MRP3增加。用胆小管标记物（二肽基肽酶IV）进行双重免疫荧光标记显示PBC中BSEP和MRP2在胆小管定位正常。OATP2和MRP2的表达与肝脏中疏水胆汁酸水平呈负相关，而与肝脏中熊去氧胆酸的富集呈正相关。
基底外侧摄取系统的下调以及胆小管和基底外侧外排泵的维持/上调可能代表了限制有毒胆汁成分蓄积的适应性机制。
