P-Glycoprotein, Breast Cancer Resistance Protein, Organic Anion Transporter 3, and Transporting Peptide 1a4 during Blood–Brain Barrier Maturation: Involvement of Wnt/β-Catenin and Endothelin-1 Signaling

Abstract

Our current knowledge about drug transporters in the maturational brain is very limited. In this study, we provide a comprehensive overview of the expression and activity profile of P-glycoprotein (P-gp), Breast Cancer Resistance Protein (bcrp), Organic Anion Transporter 3 (oat3), and Transporting Peptide 1a4 (oatp1a4) transporters during blood-brain barrier (BBB) maturation. Gene and protein expressions of the analyzed transporters increase as the brain matures, with no variation in their activity for P-gp and bcrp, while the transport activity of oat3 and oatp1a4 increases during brain maturation from preterm up to adulthood. For the first time, we illustrate a downregulation of nuclear β-catenin expression in brain capillaries when bcrp, P-gp, oat3, and oatp1a4 transporters are at their highest expression levels. In vivo activation of β-catenin in rat brains, by intracerebroventricular (ICV) injection of a GSK-3 inhibitor, enhances the activity of P-gp, bcrp, oat3, and oatp1a4. Interestingly, in an in vitro BBB model consisting of a coculture of primary endothelial brain cells with astrocytes or in vivo, activation of β-catenin enhances the mRNA expression of ET-1. Interestingly, blocking the ETA receptor for endothelin-1 in vivo by ICV injection of a ETA antagonist decreases transporter activity mediated by the activation of β-catenin. These findings shed light on the role of an interaction between β-catenin and endothelin-1 signaling in the regulation of these transporters at the BBB.

Ontogeny of ABC and SLC transporters in the microvessels of developing rat brain

“…Little information has been published concerning the ontogeny of Mrps and Bcrp genes in the BBB. Bcrp expression in rat brain microvessels was shown to increase after P2 . The presented BCRP efflux activity results did not show maturation in BCRP activity at the BBB level, although Abcg2 gene expression significantly increased between P14 and P56.…”

“…Our results show, therefore, a maturational increase in BBB P-gP activity during brain development. Previous studies had reported no difference in P-gP efflux activity between immature and adult rats [9]. Nonetheless, in mice embryos, rhodamine-123 efflux coincides with the increased Figure 2 Expression levels Ontogeny of selected SLC transporters in isolated rat brain microvessels at post-natal days 14, 21, and 56 (P14, P21, and P56, respectively).…”

The effect of organic anion transporter 3 inhibitor probenecid on bumetanide levels in the brain: an integrated in vivo microdialysis study in the rat

“…Bumetanide is a reported substrate of oat3, which is present at the BBB. [27,28] Even though probenecid can inhibit other oat transporters, oat3 is the only member of the family of transporters that has been detected in rat BCEC. [29,30,54] Thus, any increase in brain bumetanide that was independent of changes in plasma bumetanide could be attributed to the inhibition of efflux by oat3 at the rat BBB.…”

“…[10,22,23] In addition, bumetanide has been reported to be a substrate of organic anion transporter 3, both human (OAT3) and rodent (oat3). [24][25][26][27][28] OAT3/oat3 is predominantly expressed in two sites within the body, the basolateral membrane of proximal renal tubule cells, and the basolateral side of the BBB. [29,30] OAT3 is an efflux transporter involved in effluxing anions, such as bumetanide, from the blood into renal tubule cells, and from the brain via the BBB.…”

“…[29,30] OAT3 is an efflux transporter involved in effluxing anions, such as bumetanide, from the blood into renal tubule cells, and from the brain via the BBB. [24,27,28,[30][31][32][33] Oat3 is the only member of the Oat family to be found in BCEC or the brain to a quantifiable extent. [27,29,30] It has been reported that substrate specificity does not differ much between human and rat forms of oat3.…”