Abstract
Trimethylamine-N-oxide (TMAO) gained considerable attention because of its role as a cardiovascular risk biomarker. Organic cation transporter 2 (OCT2) mediates TMAO uptake into renal proximal tubular cells. Here we investigated the potential role of multidrug and toxin extrusion protein 1 (MATE1) for translocation of TMAO across the luminal membrane of proximal tubular cells. HEK293 cells stably expressing OCT2 (HEK-OCT2) or MATE1 (HEK-MATE1) were used for uptake studies. Transcellular transport of TMAO was investigated using monolayers of MDCK control cells (MDCK-Co) as well as single- (MDCK-OCT2, MDCK-MATE1) and double-transfected cells (MDCK-OCT2-MATE1). In line with previous studies, HEK-OCT2 cells revealed a 2.4-fold uptake of TMAO compared to control cells (p < 0.001), whereas no significant uptake was observed in HEK-MATE1. In monolayers of MDCK cells, polarised TMAO transcellular transport was not significantly different between MDCK-Co and MDCK-OCT2 cells, but significantly increased in MDCK-MATE1 (p < 0.05) and MDCK-OCT2-MATE1 cells (p < 0.001). The OCT/MATE inhibitor trimethoprim abolished TMAO translocation in MDCK-OCT2-MATE1 cells (p < 0.05). The present data suggest that MATE1 contributes to renal elimination of TMAO. For selected MATE substrates, such as TMAO, uptake studies using non-polarised MATE-expressing cells can reveal false negative results compared to studies using polarised monolayers.
Highlights
Cardiovascular disease (CVD) and chronic kidney disease (CKD) are major burdens for public health
Organic cation transporter 2 (OCT2) typically works in conjunction with multidrug and toxin extrusion protein 1 (MATE1, SLC47A1), which is localised in the apical membrane of renal proximal tubular cells and functions as a proton-coupled antiporter[17,21,22]
Transcellular TMAO transport from the basal to the apical compartment was consistently higher in double-transfected Madin-Darby canine kidney II (MDCK)-OCT2-MATE1 and single-transfected MDCK-MATE1 cells compared to MDCK control cells (MDCK-Co) or single-transfected MDCK-OCT2 cells (Fig. 2)
Summary
Cardiovascular disease (CVD) and chronic kidney disease (CKD) are major burdens for public health. Renal secretion is frequently achieved by transporter-mediated uptake of substrates from blood into renal proximal tubular cells, followed by transporter-mediated export across the apical membrane into urine[16,17]. Recent studies identified organic cation transporter 2 (OCT2, SLC22A2) as a transporter mediating uptake of TMAO9,18 This transport protein is localised in the basolateral membrane of renal proximal tubular cells and mediates the uptake of organic cations and zwitterions from the blood into cells[19,20]. OCT2 typically works in conjunction with multidrug and toxin extrusion protein 1 (MATE1, SLC47A1), which is localised in the apical membrane of renal proximal tubular cells and functions as a proton-coupled antiporter[17,21,22]. The aim of this study was to investigate the role of MATE1 in conjunction with OCT2 in the transcellular transport of TMAO using a polarised cell system stably expressing OCT2 and MATE1 simultaneously, which reflects the anticipated role of both transporter proteins in the kidney
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