NPC2 Regulates Biliary Cholesterol Secretion via Stimulation of ABCG5/G8-Mediated Cholesterol Transport

• Published in: Gastroenterology (New York, N.Y. 1943) Vol. 140; no. 5; pp. 1664 - 1674
• Main Authors: Yamanashi, Yoshihide, Takada, Tappei, Yoshikado, Takashi, Shoda, Jun–Ichi, Suzuki, Hiroshi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2011
• Subjects: ABC Transporter; Animals; ATP Binding Cassette Transporter, Sub-Family G, Member 5; ATP Binding Cassette Transporter, Sub-Family G, Member 8; ATP-Binding Cassette Transporters - metabolism; Bile - chemistry; Bile Acids; Biological Transport; Cholesterol - secretion; Disease Models, Animal; Gastroenterology and Hepatology; Gene Expression Regulation; Humans; Lipoproteins - metabolism; Liver; Mice; Mice, Knockout; Phospholipids; Polymerase Chain Reaction; RNA, Messenger; Vesicular Transport Proteins - biosynthesis; Vesicular Transport Proteins - genetics; tetracycline-responsive transcriptional activator-expressing adenovirus; ABCG8; ABCG5; Niemann–Pick C1; Niemann–Pick C2; Bile Acids; Liver; Ad-GFP; MOI; plaque forming unit; Phospholipids; green fluorescent protein–expressing adenovirus; adenosine triphosphate–binding cassette G8; multiplicity of infection; NPC1; Ad-tTA; NPC1L1; NPC2; ABC Transporter; Niemann–Pick C1-like 1; adenosine triphosphate–binding cassette G5; pfu
• ISSN: 0016-5085; 1528-0012
• DOI: 10.1053/j.gastro.2011.01.050

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.