Organic Anion Transporting Polypeptide (OATP) 1B3 is a Significant Transporter for Hepatic Uptake of Conjugated Bile Acids in Humans

BACKGROUND & AIMS: OATP1B3/SLCO1B3 is a human liver-specific transporter for the clearance of endogenous compounds (eg, bile acid [BA]) and xenobiotics. The functional role of OATP1B3 in humans has not been characterized, as SLCO1B3 is poorly conserved among species without mouse orthologs. METHODS: Slc10a1-knockout (Slc10a1(-/-)), Slc10a1(hSLCO1B3) (endogenous mouse Slc10a1 promoter-driven human-SLCO1B3 expression in Slc10a1(-/-) mice), and human SLCO1B3 liver-specific transgenic (hSLCO1B3-LTG) mice were generated and challenged with 0.1% ursodeoxycholic-acid (UDCA), 1% cholic-acid (CA) diet, or bile duct ligation (BDL) for functional studies. Primary hepatocytes and hepatoma-PLC/RPF/5 cells were used for mechanistic studies. RESULTS: Serum BA levels in Slc10a1(-/-) mice were substantially increased with or without 0.1% UDCA feeding compared with wild-type (WT) mice. This increase was attenuated in Slc10a1(hSLCO1B3)-mice, indicating that OATP1B3 functions as a significant hepatic BA uptake transporter. In vitro assay using primary hepatocytes from WT, Slc10a1(-/-), and Slc10a1(hSLCO1B3)-mice indicated that OATP1B3 has a similar capacity in taking up taurocholate/TCA as Ntcp. Furthermore, TCA-induced bile flow was significantly impaired in Slc10a1(-/-) mice but partially recovered in Slc10a1(hSLC01B3)-mice, indicating that OATP1B3 can partially compensate the NTCP function in vivo. Liver-specific overexpression of OATP1B3 markedly increased the level of hepatic conjugated BA and cholestatic liver injury in 1% CA-fed and BDL mice. Mechanistic studies revealed that conjugated BAs stimulated Ccl2 and Cxcl2 in hepatocytes to increase hepatic neutrophil infiltration and proinflammatory cytokine production (eg, IL-6), which activated STAT3 to repress OATP1B3 expression by binding to its promoter. CONCLUSIONS: Human OATP1B3 is a significant BA uptake transporter and can partially compensate Ntcp for conjugated BA uptake in mice. Its downregulation in cholestasis is an adaptive protective response.