Bile duct ligation causes opposite impacts on the expression and function of BCRP and P-gp in rat brain partly via affecting membrane expression of ezrin/radixin/moesin proteins.

Abstract

Breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) are co-located at blood-brain barrier (BBB) cells, preventing their substrates from entering brain. Accumulating evidence demonstrates that liver failure impairs P-gp and BCRP expression and function in the brain. In the current study, we investigated how liver failure influenced the expression and function of brain BCRP and P-gp in rats subjected to bile duct ligation (BDL). The function of BCRP, P-gp and BBB integrity was assessed using distribution of prazosin, rhodamine 123 and fluorescein, respectively. We showed that BDL significantly decreased BCRP function, but increased P-gp function without affecting BBB integrity. Furthermore, we found that BDL significantly downregulated the expression of membrane BCRP and upregulated the expression of membrane P-gp protein in the cortex and hippocampus. In human cerebral microvascular endothelial cells, NH4Cl plus unconjugated bilirubin significantly decreased BCRP function and expression of membrane BCRP protein, but upregulated P-gp function and expression of membrane P-gp protein. The decreased expression of membrane BCRP protein was linked to the decreased expression of membrane radixin protein, while the increased expression of membrane P-gp protein was related to the increased location of membrane ezrin protein. Silencing ezrin impaired membrane location of P-gp, whereas silencing radixin impaired membrane location of BCRP protein. BDL rats showed the increased expression of membrane ezrin protein and decreased expression of membrane radixin protein in the brain. We conclude that BDL causes opposite effects on the expression and function of brain BCRP and P-gp, attributing to the altered expression of membrane radixin and ezrin protein, respectively, due to hyperbilirubinemia and hyperammonemia.