Blood-brain barrier transport proteins expression

Figure 17.2 Transport proteins expressed at the blood-brain barrier.

Isolated capillaries have been used for a long time to study transport and metabolic function of the blood-brain barrier [61, 72, 75, 76, 78, 87-91], In contrast to monolayer cell cultures, which are susceptible to induction or inhibition of carrier protein expression, experiments with freshly isolated capillaries directly reflect the situation at the luminal side of brain capillaries. 

Active efflux transporters also exist in the placenta, analogous to the gut and blood-brain barrier. These are Pgp, multidrug resistance-associated protein (MRP), and breast cancer resistance protein (BCRP). These transport proteins are located in many tissues but also appear to be expressed in the placenta. Though the substrate specificities of these proteins have not been completely described, they appear to function as efflux transporters, moving endogenous and exogenous chemicals from the placental cells back to the systemic circulation. In this way, they serve as a mechanism to protect the fetus from exposure to unintended chemicals. 

The best characterized multidrug transporter is P-gp which is a membrane protein encoded by the mdrl gene. The most intriguing feature of P-gp is its ability to interact with a large number of structurally and functionally different amphiphilic compounds. P-gp expression can be acquired during the course of treatment (e.g., in leukemias, lymphomas, ovarian carcinomas) or it is constitutive (e.g., in colorectal and renal cancers). In normal tissues of mammals P-gp is localized on the luminal surface of transporting epithelia in liver, kidney, small intestine, testes, and blood-brain barrier. 

Cisternino S, Mercier C, Bourasset F, Roux F, Scherrmann JM. Expression, up-regulation, and transport activity of the multidrug-resistance protein Abcg2 at the mouse blood-brain barrier. Cancer Res 2004 64 3296-301. 

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