Xenobiotic-dependent induction of the tricarboxylate carrier Slc13a5 in primary cultures of rat hepatocytes

• Published in: Zeitschrift für Gastroenterologie
• Main Authors: Neuschäfer-Rube, F, Lieske, S, Birkenfeld, AL, Püschel, GP
• Format: Conference Proceeding
• Language: English; German
• Published: 16.01.2015
• ISSN: 0044-2771; 1439-7803
• DOI: 10.1055/s-0034-1397151

Background: The tricarboxylate carrier Slc13a5 (mINDY) is an active transporter that mediates concentrative uptake of citrate in symport with sodium ions across the plasma membrane of cells. In mammals, it is expressed predominantly in hepatocytes and appears to contribute to the cytosolic citrate homeostasis. Citrate is an important intermediate and regulator of fatty acid synthesis. Accordingly, knock down of the Slc13a5 gene in mice was associated with reduced liver fat content and consequently improved insulin sensitivity under a high fat diet. Exposure to xenobiotics often results in hepatic lipid accumulation. The study thus aimed at elucidating the impact of xenobiotics on Slc13a5 expression. Methods: Primary cultures of rat hepatocytes were exposed to two xenobiotics, the constitutive androstane receptor (CAR)-activator phenobarbital (PB) and the aryl-hydrocarbon receptor (AhR) activator beno[a]pyrene (BaP) alone or in combination for 48h. AhR, CAR and Slc13a5 gene expression, activity and activity were determined by qPCR, reporter gene assay and radioactive citrate uptake assay, respectively. Results: Exposure of hepatocytes to PB, BaP or a combination of both induced Slc13a5 mRNA 2-fold, 5-fold and 32-fold, respectively. The more than additive induction by the combination of both xenobiotics resulted from a mutual induction of the respective nuclear receptors: CAR was induced 10-fold by BaP while the AhR was induced 6-fold by PB. A combination of PB and BaP induced the expression of a reporter gene under the control of a 1,8 kb Slc13a5 promoter fragment about 3-fold. This induction was abrogated by elimination of a putative AhR binding site at -770. Induction of Slc13a5 by a combination of PB and BaP resulted in an about 50% increase in citrate uptake. Conclusion: Xenobiotic exposure, in particular simultaneous activation of the two nuclear receptors CAR and AhR may increase Slc13a5 expression and thereby might contribute to xenobitoic-induced citrate uptake and hence lipid accumulation in hepatocytes. Corresponding author: Püschel, Gerhard P. E-Mail: gpuesche@uni-potsdam.de