Scavenger receptor class B, type I is expressed in porcine brain capillary endothelial cells and contributes to selective uptake of HDL-associated vitamin E.
It is clearly established that an efficient supply to the brain of alpha-tocopherol (alphaTocH), the most biologically active member of the vitamin E family, is of the utmost importance for proper neurological functioning. Although the mechanism of uptake of alphaTocH into cells constituting the blood-brain barrier (BBB) is obscure, we previously demonstrated that high-density lipoprotein (HDL) plays a major role in the supply of alphaTocH to porcine brain capillary endothelial cells (pBCECs). Here we studied whether a porcine analogue of human and rodent scavenger receptor class B, type I mediates selective (without concomitant lipoprotein particle internalization) uptake of HDL-associated alphaTocH in a similar manner to that described for HDL-associated cholesteryl esters (CEs). In agreement with this hypothesis we observed that a major proportion of alphaTocH uptake by pBCECs occurred by selective uptake, exceeding HDL3 holoparticle uptake by up to 13-fold. The observation that selective uptake of HDL-associated CE exceeded HDL3 holoparticle up to fourfold suggested that a porcine analogue of SR-BI (pSR-BI) may be involved in lipid uptake at the BBB. In line with the observation of selective lipid uptake, RT-PCR and northern and western blot analyses revealed the presence of pSR-BI in cells constituting the BBB. Adenovirus-mediated overexpression of the human analogue of SR-BI (hSR-BI) in pBCECs resulted in a fourfold increase in selective HDL-associated alphaTocH uptake. In accordance with the proposed function of SR-BI, selective HDL-CE uptake was increased sixfold in Chinese hamster ovary cells stably transfected with murine SR-BI (mSR-BI). Most importantly stable mSR-BI overexpression mediated a twofold increase in HDL-associated [14C]alphaTocH selective uptake in comparison with control cells. In line with tracer experiments, mass transfer studies with unlabelled lipoproteins revealed that mSR-BI overexpression resulted in a twofold increase in endogenous HDL3-associated alphaTocH uptake. The results of this study indicate that SR-BI promotes the uptake of HDL-associated alphaTocH into cells constituting the BBB and plays an important role during the supply of the CNS with this indispensable micronutrient.
Goti
D
D
Institute of Medical Biochemistry and Molecular Biology, Karl Franzens University Graz, Austria.
Hrzenjak
A
A
Levak-Frank
S
S
Frank
S
S
van der Westhuyzen
D R
DR
Malle
E
E
Sattler
W
W
D000818:Animals; D001812:Blood-Brain Barrier / Q000502:physiology; D001921:Brain / Q000098:blood supply; D018955:CD36 Antigens / Q000096:biosynthesis* / Q000235:genetics; D016466:CHO Cells; D002196:Capillaries / Q000166:cytology / Q000378:metabolism*; D002478:Cells, Cultured; D006224:Cricetinae; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism*; D053440:Lipoproteins, HDL3; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013552:Swine; D014162:Transfection; D014810:Vitamin E / Q000378:metabolism / Q000493:pharmacokinetics*
D018955:CD36 Antigens; D008075:Lipoproteins, HDL; D053440:Lipoproteins, HDL3; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D014810:Vitamin E