TABLE 1.

Main functions of ABC transporters involved in Aβ efflux.

ABC transporter	Functions	Regulation	Expression in AD brain
ABCA1	Transfer of cholesterol, other lipids to apoE	LXRs	Decreased
ABCA7	Transfer of phospholipids to HDL; mediates macrophage, microglial phagocytosis	SREBP2 pathway	Increased; gene variants are risk factors for LOAD
ABCB1 (p-gp)	Efflux of xenobiotic substances from cells; works with LRP1 to promote Aβ efflux across BBB	Nuclear receptors (RXR, PXR, PPAR, others), inflammation, oxidative stress, receptor tyrosine kinases, growth factors	Decreased
ABCC1	Efflux of xenobiotics, organic anions, glutathione	Notch1, transcription factors (GC elements, E-box elements)	Unclear; increased in AD mouse models
ABCC5	Efflux of nucleoside/nucleotide analogs, glutamate analogs, cAMP, cGMP	Forkhead box M1, dexamethasone, human chorionic gonadotropin	Unknown; activity decreased in vitro after exposure of endothelial cells to Ab42
ABCG1	Transfers cholesterol to HDL, phospholipid vesicles, lipidated apoE	LXR, PPAR activators, RXR agonists	Unknown; ABCG1 SNPs reported to be AD risk factors
ABCG2	Transport of xenobiotics	Inflammatory cytokines, dexamethasone, hypoxia, hormones, growth factors, gene amplification, epigenetic regulation	Conflicting reports
ABCG4	Efflux of cholesterol and desmosterol to HDL	LXRs	Increased in AD plaque-associated microglia

AD, Alzheimer’s disease; ApoE, apolipoprotein E; BBB, blood brain barrier; cAMP, cyclic adenosine monophosphate; cGMP, cyclic guanosine monophosphate; HDL, high density lipoproteins; LOAD, late onset Alzheimer’s disease; LRP1, low density lipoprotein receptor-related protein 1; LXR, liver X receptor; PPAR, peroxisome proliferator–activated receptor; PXR, pregnane X receptor; RXR, retinoid X receptor; SNP, single nucleotide polymorphism; SREBP2, sterol regulatory element-binding protein 2.