ABCA1 and scavenger receptor class B, type I, are modulators of reverse sterol transport at an in vitro blood-brain barrier constituted of porcine brain capillary endothelial cells.
The objective of the present study was to investigate the involvement of key players in reverse cholesterol/24(S)OH-cholesterol transport in primary porcine brain capillary endothelial cells (pBCEC) that constitute the BBB. We identified that, in addition to scavenger receptor class B, type I (SR-BI), pBCEC express ABCA1 and apolipoprotein A-I (apoA-I) mRNA and protein. Studies on the regulation of ABCA1 by the liver X receptor agonist 24(S)OH-cholesterol revealed increased ABCA1 expression and apoA-I-dependent [3H]cholesterol efflux from pBCEC. In unpolarized pBCEC, high density lipoprotein, subclass 3 (HDL3)-dependent [3H]cholesterol efflux, was unaffected by 24(S)OH-cholesterol treatment but was enhanced 5-fold in SR-BI overexpressing pBCEC. Efflux of cellular 24(S)-[3H]OH-cholesterol was highly efficient, independent of ABCA1, and correlated with SR-BI expression. Polarized pBCEC were cultured on porous membrane filters that allow separate access to the apical and the basolateral compartment. Addition of cholesterol acceptors to the apical compartment resulted in preferential [3H]cholesterol efflux to the basolateral compartment. HDL3 was a better promoter of basolateral [3H]cholesterol efflux than lipid-free apoA-I. Basolateral pretreatment with 24(S)OH-cholesterol enhanced apoA-I-dependent basolateral cholesterol efflux up to 2-fold along with the induction of ABCA1 at the basolateral membrane. Secretion of apoA-I also occurred preferentially to the basolateral compartment, where the majority of apoA-I was recovered in an HDL-like density range. In contrast, 24(S)-[3H]OH-cholesterol was mobilized efficiently to the apical compartment of the in vitro BBB by HDL3, low density lipoprotein, and serum. These results suggest the existence of an autoregulatory mechanism for removal of potentially neurotoxic 24(S)OH-cholesterol. In conclusion, the apoA-I/ABCA1- and HDL/SR-BI-dependent pathways modulate polarized sterol mobilization at the BBB.
Institute of Medical Biochemistry and Medical Molecular Biology, University Graz, Harrachgasse 21, A-8010 Graz, Austria.
Ute
U
Panzenboeck
Zoltan
Z
Balazs
Andrea
A
Sovic
Andelko
A
Hrzenjak
Sanja
S
Levak-Frank
Andrea
A
Wintersperger
Ernst
E
Malle
Wolfgang
W
Sattler
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D018955:CD36 Antigens / Q000502:physiology*; D002196:Capillaries / Q000502:physiology*; D016764:Cell Polarity; D002478:Cells, Cultured; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002784:Cholesterol / Q000378:metabolism*; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein / Q000502:physiology; D051116:Receptors, Scavenger; D011994:Recombinant Proteins / Q000378:metabolism; D051122:Scavenger Receptors, Class B; D013261:Sterols / Q000378:metabolism*; D013552:Swine
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D018955:CD36 Antigens; D017931:DNA Primers; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011994:Recombinant Proteins; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D013261:Sterols; D002784:Cholesterol