Human Genetic Variation in Na+-Taurocholate Co-transporting Polypeptide (NTCP; SLC10A1) and Targeted Slc10a1 Disruption in Mice: Effects on Bile Acid and Rosuvastatin Transport
Abstract
Sodium-taurocholate co-transporting polypeptide (NTCP, SLC10A1) is the central bile acid uptake transporter on the basolateral membrane of hepatocytes. Pharmacological inhibition of NTCP is also being used to treat Hepatitis B and D, and NTCP transports a variety of drugs including cholesterol-lowering statins. Despite these crucial roles, limited knowledge exists regarding the effects of genetic variation in SLC10A1 on bile acid and rosuvastatin transport.
To address this, we characterized activity and protein expression of genetically variant SLC10A1 in vitro. Seven SLC10A1 genetic variants displayed robust reductions in NTCP-mediated transport of taurocholic acid and rosuvastatin and virtually absent NTCP protein expression at the plasma membrane. In silico tools were employed to assess their performance to predict deleterious function, however these did not generate robust enough predictions to replace in vitro studies.
To elucidate the in vivo effects of targeted Slc10a1 disruption, serum bile acid composition and hepatic, renal, and ileal gene expression were assessed in male Slc10a1-/- mice. Conjugated serum hypercholanemia and absence of Oatp1a1 (Slco1a1) mRNA were observed in a subset of Slc10a1-/- mice. Additional changes in gene mRNA expression and mouse necropsy studies suggest these mice were unable to thrive as a result of nutrient malabsorption and disrupted nuclear receptor signaling.
Sex-related differences were evaluated in serum bile acid composition and hepatic gene expression in Slc10a1-/-mice. No important sex-related differences were observed in serum bile acid composition. Oatp1a1 mRNA was nearly undetectable in both male and female hypercholanemic mice. Sex associated differences in hepatic gene expression in control and normocholanemic Slc10a1-/-mice were consistent with literature, however these sex-specific differences were reversed for certain bile acid genes in hypercholanemic mice.
These findings identify novel loss of function genetic variants in the SLC10A1 gene in vitro. Additionally, our studies in Slc10a1-/-mice provide evidence of altered nuclear receptor signaling that may have important implications on bile acid physiology and drug response.