Expression of reverse cholesterol transport proteins ATP-binding cassette A1 (ABCA1) and scavenger receptor BI (SR-BI) in the retina and retinal pigment epithelium.
OBJECTIVE
Excessive lipid accumulation in Bruch's membrane (BrM) is a hallmark of ageing, the major risk factor for age-related macular degeneration (AMD). Retinal pigment epithelial (RPE) cells may utilise reverse cholesterol transport (RCT) activity to move lipid into BrM, mediated through ATP-binding cassette A1 (ABCA1) and scavenger receptor BI (SR-BI).


METHODS
ABCA1 expression was assessed by reverse transcription polymerase chain reaction (RT-PCR) and western blotting of human RPE cell extracts. Lipid transport assays were performed using radiolabelled photoreceptor outer segments (POS). ABCA1 and SR-BI expression was examined in normal mouse eyes by immunofluorescence staining. BrMs of ABCA1 and SR-BI heterozygous mice were examined microscopically.


RESULTS
Human RPE cells expressed ABCA1 mRNA and protein. The ABCA1 and SR-BI inhibitor glyburide (also known as glibenclamide) abolished basal transport of POS-derived lipids in RPE cells in the presence of high-density lipoprotein. Mouse retina and RPE expressed ABCA1 and SR-BI. SR-BI was highly expressed in RPE. BrMs were significantly thickened in SR-BI heterozygous mice, but not in ABCA1 heterozygous mice.


CONCLUSIONS
RPE cells express ABCA1 and SR-BI. This implies a significant role for SR-BI and ABCA1 in lipid transport and RCT in the retina and RPE.
Duncan
K G
KG
Department of Ophthalmology, University of California, San Francisco, California 94143, USA.
Hosseini
K
K
Bailey
K R
KR
Yang
H
H
Lowe
R J
RJ
Matthes
M T
MT
Kane
J P
JP
LaVail
M M
MM
Schwartz
D M
DM
Duncan
J L
JL
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D000818:Animals; D016570:Bruch Membrane / Q000648:ultrastructure; D002478:Cells, Cultured; D004596:Electroretinography; D005136:Eye Proteins / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D050356:Lipid Metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008854:Microscopy, Electron; D012333:RNA, Messenger / Q000235:genetics; D012160:Retina / Q000378:metabolism* / Q000502:physiology; D055213:Retinal Pigment Epithelium / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D051122:Scavenger Receptors, Class B / Q000378:metabolism*
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D005136:Eye Proteins; D012333:RNA, Messenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B