NPC2 regulates biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport.
NPC2 regulates biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport.
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DOI：
10.1053/j.gastro.2011.01.050
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发表时间：
2011-05
期刊：
影响因子：
29.4
通讯作者：
Yoshihide Yamanashi;T. Takada;Takashi Yoshikado;Junnichi Shoda;H. Suzuki
中科院分区：
文献类型：
--
作者：
Yoshihide Yamanashi;T. Takada;Takashi Yoshikado;Junnichi Shoda;H. Suzuki
背景与目的胆汁胆固醇的分泌有助于维持胆固醇的动态平衡；胆汁胆固醇的分泌受胆固醇出口商三磷酸腺苷结合盒G5和G8(ABCG5/G8)和胆固醇进口商Niemann-Pick C1-like 1(NPC1L1)的调节。我们研究了另一种可能的胆固醇分泌到胆汁的调节因子，Niemann-Pick C2(NPC2)--一种由胆道系统分泌的胆固醇结合蛋白--并确定了它对转运蛋白介导的胆汁胆固醇分泌的影响。方法用腺病毒介导的基因转染法建立NPC2基因敲除小鼠和NPC2高表达小鼠模型，观察胆汁脂质的变化。使用过表达ABCG5/G8或NPC1L1的细胞，在体外检测分泌的NPC2对胆固醇转运体活性的影响。结果肝脏NPC2表达改变的小鼠的研究表明，NPC2的表达正向调节胆汁中胆固醇的分泌，并得到NPC2蛋白水平与人胆汁胆固醇之间的相关性的支持。体外分析表明，分泌的NPC2可促进ABCG5/G8介导的胆固醇外流，但不能刺激NPC1L1介导的胆固醇摄取。与这些观察结果一致的是，在ABCG5/G8基因缺失的小鼠中，肝脏过表达NPC2并未观察到胆汁胆固醇分泌的显著变化，表明NPC2需要ABCG5/G8来刺激胆固醇的分泌。对NPC2突变体的分析表明，胆汁NPC2的刺激作用不依赖于溶酶体NPC2作为细胞内胆固醇转运调节因子的功能。结论NPC2通过刺激ABCG5/G8介导的胆固醇转运，对胆汁胆固醇分泌起正向调节作用。
BACKGROUND & AIMS Biliary cholesterol secretion helps maintain cholesterol homeostasis; it is regulated by the cholesterol exporter adenosine triphosphate-binding cassettes G5 and G8 (ABCG5/G8) and the cholesterol importer Niemann-Pick C1-like 1 (NPC1L1). We studied another putative regulator of cholesterol secretion into bile, Niemann-Pick C2 (NPC2)--a cholesterol-binding protein secreted by the biliary system--and determined its effects on transporter-mediated biliary secretion of cholesterol. METHODS Mice with hepatic knockdown of Npc2 or that overexpressed NPC2 were created using adenovirus-mediated gene transfer; biliary lipids were characterized. The effects of secreted NPC2 on cholesterol transporter activity were examined in vitro using cells that overexpressed ABCG5/G8 or NPC1L1. RESULTS Studies of mice with altered hepatic expression of NPC2 revealed that this expression positively regulates the biliary secretion of cholesterol, supported by the correlation between levels of NPC2 protein and cholesterol in human bile. In vitro analysis showed that secreted NPC2 stimulated ABCG5/G8-mediated cholesterol efflux but not NPC1L1-mediated cholesterol uptake. Consistent with these observations, no significant changes in biliary cholesterol secretion were observed on hepatic overexpression of NPC2 in ABCG5/G8-null mice, indicating that NPC2 requires ABCG5/G8 to stimulate cholesterol secretion. Analyses of NPC2 mutants showed that the stimulatory effect of biliary NPC2 was independent of the function of lysosomal NPC2 as a regulator of intracellular cholesterol trafficking. CONCLUSIONS NPC2 is a positive regulator of biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport.