Anti-ABCG4 (aa 635-646) polyclonal antibody

Here, we describe the initial characterization of Abcg4(-/-) mice and identify overlapping functions of ABCG4 and ABCG1 in the brain. Histological examination of tissues from Abcg4(+/-)/nlsLacZ and Abcg1(+/-)/nlsLacZ mice demonstrates that coexpression of Abcg4 and Abcg1 is restricted to neurons and astrocytes of the central nervous system (CNS). Interestingly, Abcg4 mRNA is undetectable outside the CNS, in contrast with the broad tissue and cellular expression of Abcg1. We also used primary astrocytes, microglia, neurons, and macrophages to demonstrate that the expression of Abcg1, but not Abcg4, is induced after the activation of liver X receptor. Cellular localization studies demonstrated that both proteins reside in RhoB-positive endocytic vesicle membranes. Furthermore, overexpression of either ABCG1 or ABCG4 increased the processing of sterol-regulatory element binding protein 2 (SREBP-2) to the transcriptionally active protein, thus accounting for the observed increase in the expression of SREBP-2 target genes and cholesterol synthesis. Consistent with these latter results, we show that the expression levels of the same SREBP-2 target genes are repressed in the brains of Abcg1(-/-) and, to a lesser extent, Abcg4(-/-) mice.

The accumulation of amyloid-beta peptide (A beta) in the brain is a critical hallmark of Alzheimer's disease. This high cerebral A beta concentration may be partly caused by impaired clearance of A beta across the blood-brain barrier (BBB). The low-density lipoprotein receptor-related protein-1 (LRP-1) and the ATP-binding cassette (ABC) protein ABCB1 (P-glycoprotein) are involved in the efflux of A beta across the BBB. We hypothesized that other ABC proteins, such as members of the G subfamily, are also involved in the BBB clearance of A beta. We therefore investigated the roles of ABCG2 (BCRP) and ABCG4 in the efflux of [H-3]A beta(1-40) from HEK293 cells stably transfected with human ABCG2 or mouse abcg4. We showed that ABCG2 and Abcg4 mediate the cellular efflux of [H-3]A beta(1-40). In addition, probucol fully inhibited the efflux of [H-3]A beta(1-40) from HEK293-abcg4 cells. Using the in situ brain perfusion technique, we showed that GF120918 (dual inhibitor of Abcb1 and Abcg2) strongly enhanced the uptake (Cl-up, mu l/g/s) of [H-3]A beta(1-40) by the brains of Abcb1-deficient mice, but not by the brains of Abcb1/Abcg2-deficient mice, suggesting that Abcg2 is involved in the transport of A beta at the mouse BBB. Perfusing the brains of Abcb1/Abcg2- and Abca1-deficient mice with [H-3]A beta(1-40) plus probucol significantly increased the Cl-up of A beta. This suggests that a probucol-sensitive transporter that is different from Abca1, Abcb1, and Abcg2 is involved in the brain efflux of A beta. We suggest that this probucol-sensitive transporter is Abcg4. We conclude that Abcg4 acts in concert with Abcg2 to efflux A beta from the brain across the BBB.