Objective: Both HDLs and their major protein constituent apolipoprotein A-I (apoA-I) are transported through aortic endothelial cells. The knock-down of the ATP-binding cassette transporters A1 (ABCA1), G1 (ABCG1), and of the scavenger receptor-BI (SR-BI) diminishes but does not completely block the transport of apoA-I or HDL, so that other receptors appear to be involved. The ectopic β-chain of F(0)F(1) ATPase has been previously characterized as an apoA-I receptor, triggering HDL internalization in hepatocytes.
Methods and results: The ectopic presence of the β-chain of F(0)F(1) ATPase on the surface of endothelial cells was confirmed by cell surface biotinylation. RNA-interference and the F(0)F(1) ATPase inhibitory peptide IF(1) reduced cell binding of apoA-I but not HDL, as well as association and transendothelial transport of both apoA-I and HDL. Furthermore, apoA-I stimulated F(0)F(1) ATPase catalyzed ATP hydrolysis. The generated ADP as well as apoA-I stimulated the binding, cell association, and internalization of HDL. Both in the presence and absence of ADP inhibition of the purinergic receptor P2Y(12) but not P2Y(1) decreased the cell association of apoA-I and HDL. Coinhibition of β-ATPase and ABCA1 had no additive effects on the cell association and transport of apoA-I. Reduced cell association of HDL by β-ATPase inhibition was not further decreased by additional knock-down of ABCG1 or SR-BI.
Conclusions: Binding of apoA-I to ectopic F(0)F(1) ATPase triggers the generation of ADP, which via activation of the purinergic receptor P2Y(12) stimulates the uptake and transport of HDL and initially lipid-free apoA-I by endothelial cells.