Functional Expression of Organic Cation/carnitine Transporter 2 (OCTN2/SLC22A5) in Human Brain Capillary Endothelial Cell Line hCMEC/D3, a Human Blood-brain Barrier Model

Abstract

  The aim of this study was to examine whether organic cation/carnitine transporter 2 (OCTN2/SLC22A5) plays a role in the human blood-brain barrier (BBB) by evaluating its functional activity in human brain endothelial cells (hCMEC/D3), which are considered to be a model of the BBB. The uptake of [³H]L-carnitine by hCMEC/D3 cells was time-, extracellular sodium- and concentration-dependent, with a K_m value of 15.7 µM. These results are consistent with the properties of OCTN2-mediated L-carnitine transport. hCMEC/D3 cells showed relatively high expression of OCTN2 mRNA, and this expression was effectively decreased at 24–72 h after lipofection of cells with OCTN2 siRNA under optimized conditions. [³H]L-Carnitine uptake was dramatically suppressed by silencing of the OCTN2 gene. The inhibitory effect of OCTN2 gene silencing was similar to that of an excess amount of unlabeled L-carnitine. These results indicate that OCTN2 is involved in L-carnitine transport at the human BBB.