Slijepcevic Davor, Kaufman Christina, Wichers Catharina G K, Gilglioni Eduardo H, Lempp Florian A, Duijst Suzanne, de Waart Dirk R, Elferink Ronald P J Oude, Mier Walter, Stieger Bruno, Beuers Ulrich, Urban Stephan, van de Graaf Stan F J
Tytgat Institute for Liver and Intestinal Research and Department of Gastroenterology and Hepatology, AMC, Amsterdam, The Netherlands.
Department of Infectious Diseases and of Molecular Virology, University Hospital Heidelberg, Heidelberg, Germany.
Hepatology. 2015 Jul;62(1):207-19. doi: 10.1002/hep.27694. Epub 2015 May 8.
The Na(+) -taurocholate cotransporting polypeptide (NTCP) mediates uptake of conjugated bile acids (BAs) and is localized at the basolateral membrane of hepatocytes. It has recently been recognized as the receptor mediating hepatocyte-specific entry of hepatitis B virus and hepatitis delta virus. Myrcludex B, a peptide inhibitor of hepatitis B virus entry, is assumed to specifically target NTCP. Here, we investigated BA transport and Myrcludex B binding in the first Slc10a1-knockout mouse model (Slc10a1 encodes NTCP). Primary Slc10a1(-/-) hepatocytes showed absence of sodium-dependent taurocholic acid uptake, whereas sodium-independent taurocholic acid uptake was unchanged. In vivo, this was manifested as a decreased serum BA clearance in all knockout mice. In a subset of mice, NTCP deficiency resulted in markedly elevated total serum BA concentrations, mainly composed of conjugated BAs. The hypercholanemic phenotype was rapidly triggered by a diet supplemented with ursodeoxycholic acid. Biliary BA output remained intact, while fecal BA excretion was reduced in hypercholanemic Slc10a1(-/-) mice, explained by increased Asbt and Ostα/β expression. These mice further showed reduced Asbt expression in the kidney and increased renal BA excretion. Hepatic uptake of conjugated BAs was potentially affected by down-regulation of OATP1A1 and up-regulation of OATP1A4. Furthermore, sodium-dependent taurocholic acid uptake was inhibited by Myrcludex B in wild-type hepatocytes, while Slc10a1(-/-) hepatocytes were insensitive to Myrcludex B. Finally, positron emission tomography showed a complete abrogation of hepatic binding of labeled Myrcludex B in Slc10a1(-/-) mice.
The Slc10a1-knockout mouse model supports the central role of NTCP in hepatic uptake of conjugated BAs and hepatitis B virus preS1/Myrcludex B binding in vivo; the NTCP-independent hepatic BA uptake machinery maintains a (slower) enterohepatic circulation of BAs, although it is occasionally insufficient to clear BAs from the circulation.
钠-牛磺胆酸共转运多肽（NTCP）介导结合型胆汁酸（BAs）的摄取，定位于肝细胞的基底外侧膜。它最近被认为是介导乙型肝炎病毒和丁型肝炎病毒肝细胞特异性进入的受体。Myrcludex B是一种乙型肝炎病毒进入的肽抑制剂，被认为特异性靶向NTCP。在此，我们在首个Slc10a1基因敲除小鼠模型（Slc10a1编码NTCP）中研究了胆汁酸转运和Myrcludex B结合情况。原代Slc10a1(-/-)肝细胞显示钠依赖性牛磺胆酸摄取缺失，而钠非依赖性牛磺胆酸摄取未改变。在体内，这表现为所有基因敲除小鼠血清胆汁酸清除率降低。在一部分小鼠中，NTCP缺乏导致血清总胆汁酸浓度显著升高，主要由结合型胆汁酸组成。补充熊去氧胆酸的饮食迅速引发了高胆汁血症表型。胆汁酸的胆汁输出保持完整，而高胆汁血症的Slc10a1(-/-)小鼠粪便胆汁酸排泄减少，这可由Asbt和Ostα/β表达增加来解释。这些小鼠还显示肾脏中Asbt表达降低以及肾脏胆汁酸排泄增加。结合型胆汁酸的肝脏摄取可能受到OATP1A1下调和OATP1A4上调的影响。此外，在野生型肝细胞中，Myrcludex B抑制钠依赖性牛磺胆酸摄取，但Slc10a1(-/-)肝细胞对Myrcludex B不敏感。最后，正电子发射断层扫描显示Slc10a1(-/-)小鼠肝脏中标记的Myrcludex B结合完全消失。
Slc10a1基因敲除小鼠模型支持NTCP在体内肝脏摄取结合型胆汁酸以及乙型肝炎病毒前S1/Myrcludex B结合中的核心作用；尽管偶尔不足以从循环中清除胆汁酸，但不依赖NTCP的肝脏胆汁酸摄取机制维持了（较慢的）胆汁酸肠肝循环。
