In Vitro Study of the Functional Expression of Organic Anion Transporting Polypeptide 3 at Rat Choroid Plexus Epithelial Cells and Its Involvement in the Cerebrospinal Fluid-to-Blood Transport of Estrone-3-Sulfate

Abstract

The cerebrospinal fluid-to-blood efflux transport of estrone-3-sulfate (E 1 S) via the blood-cerebrospinal fluid barrier (BCSFB) may play an important role in regulating E 1 S levels in the brain. Here, we investigated the efflux transport of E 1 S at the BCSFB using conditionally immortalized rat choroid plexus epithelial cells (TR-CSFB) and identified the responsible transporter. The [ 3 H]E 1 S uptake by TR-CSFB cells was composed of saturable and nonsaturable components, and the K m and V max values of the saturable component were determined to be 16.8 Ϯ 5.1 M and 12.3 Ϯ 2.3 pmol/min/mg of protein, respectively. [ 3 H]E 1 S uptake was inhibited by probenecid, cholate, taurocholate, sulfobromophthalein, dehydroepiandrosterone sulfate, triiodothyronine, thyroxin, and digoxin but not by p-aminohippuric acid, ␥-aminobutyric acid, or methotrexate, suggesting the involvement of organic anion transporting polypeptide (oatp) in the uptake. Reverse transcription-polymerase chain reaction analysis revealed that oatp3 was expressed in TR-CSFB cells and isolated rat choroid plexus, although oatp1 was not detected in either. Xenopus laevis oocytes expressing oatp3 exhibited [ 3 H]E 1 S uptake activity with a K m of 8.09 Ϯ 2.83 M and V max of 8.02 Ϯ 0.87 pmol/h/oocyte. Moreover, oatp3 is localized at the brush-border membrane of choroid plexus epithelial cells. These results suggest that oatp3 is involved in the E 1 S efflux transport at the BCSFB.

Localization of organic anion transporting polypeptide 3 (oatp3) in mouse brain parenchymal and capillary endothelial cells

“…1). These results suggest that mouse oatp2 and 3 play roles at the BCSFB similar to those in the case of rat BCSFB (Gao et al 1999;Ohtsuki et al 2003).…”

“…Our recent report has shown that rat oatp3, but not oatp1, is localized at the brush-border membrane of rat choroid plexus epithelial cells (Ohtsuki et al 2003). In mouse, oatp3 mRNA was detected in choroid plexus, but oatp1 mRNA was not (Fig.…”

“…We have reported that oatp3 is localized at the rat choroid plexus (Ohtsuki et al 2003) and this finding raises the issue of whether oatp3 is expressed at the brain capillaries. Oatp3 accepts prostaglandin E 2 (PGE 2 ) as a substrate, whereas oatp2 and oatp14 do not (Cattori et al 2001;Sugiyama et al 2003).…”

“…Although it was believed that THs enter target cells by passive diffusion, the recent reports have demonstrated that their cellular uptake by cells, including neurons and astrocytes, is carrier-mediated (Francon et al 1989;Chantoux et al 1995;Hennemann et al 2001). Although roles of oatp family members in neural cells have not been considered yet, it is conceivable that oatps mediate TH uptake of the target cells in the brain.Expression of oatp3 mRNA in rat brain has been detected by means of RNase protection assay and RT-PCR analysis (Walters et al 2000;Ohtsuki et al 2003). Since oatp3 mediates transport of THs, such as triiodothyronine (T 3 ) and thyroxine (T 4 ) (Abe et al 1998), we hypothesize that oatp3 is expressed at the neural cells and mediates their TH uptake.…”

“…Expression of oatp3 mRNA in rat brain has been detected by means of RNase protection assay and RT-PCR analysis (Walters et al 2000;Ohtsuki et al 2003). Since oatp3 mediates transport of THs, such as triiodothyronine (T 3 ) and thyroxine (T 4 ) (Abe et al 1998), we hypothesize that oatp3 is expressed at the neural cells and mediates their TH uptake.…”