The β-Chain of Cell Surface F ₀ F ₁ ATPase Modulates ApoA-I and HDL Transcytosis Through Aortic Endothelial Cells

Abstract

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 ␤-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 ␤-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 ␤-ATPase and ABCA1 had no additive effects on the cell association and transport of apoA-I. Reduced cell association of HDL by ␤-ATPase inhibition was not further decreased by additional knock-down of ABCG1 or SR-BI. Conclusion-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. Key Words: apolipoproteins Ⅲ endothelium Ⅲ lipoproteins Ⅲ F0F1 ATPase Ⅲ transcytosis P lasma levels of HDL cholesterol as well as apolipoprotein A-I (apoA-I) are inversely correlated with the risk of atherosclerosis. In addition, both apoA-I and HDL exert several atheroprotective properties within the arterial wall rather than in the blood stream, including cholesterol efflux from macrophage foam cells. 1 HDLs are indeed the most abundant lipoproteins in the extravascular space. 2-5 Recently, we provided evidence that endothelial cells bind, internalize, and transcytose apoA-I and HDL in a saturable and temperature-dependent manner. 6 By siRNA interference we also showed that the ATP-binding cassette transporter (ABC) A1 modulates endothelial transport of apoA-I, 7 whereas ABCG1 and the scavenger receptor BI (SR-BI) modulate the transport of HDL. 8 In addition, we showed that the transendothelial apoA-I transport is a 2-step process in which apoA-I is initially lipidated by ABCA1 and then further processed by mechanisms that are independent of ABCA1 but involve Previously, the ectopically expressed ␤-chain of F 0 F 1 ATPase (␤-ATPase) has been identified as a hepatic receptor for apoA-I. 10 F 0 F 1 ATPase is an enzymatic complex responsible for the synthesis of ATP in mitochondria, prokaryote membranes, and chloroplasts. The mitochondrial F 0 F 1 ATPase (about 600 kDa) is composed of 2 ...

HDL and Atherothrombotic Vascular Disease

“…Conversely, siRNA-mediated gene silencing experiments revealed that the cell surface binding and transport of HDLs through aortic endothelial cells are highly dependent on SR-BI and ABCG1, but not on ABCA1 (Rohrer et al 2009). Subsequent research has demonstrated expression of the ectopic β-chain of F0F1 ATPase (β-ATPase) on the endothelial cell surface (Cavelier et al 2012). The results of this study further suggest that the binding of lipid-free apoA-I to endothelial cell surface β-ATPase facilitates the uptake and transport of lipidated apoA-I and mature HDLs by enhancing β-ATPase-mediated hydrolysis of extracellular ATP into ADP and inducing consecutive activation of the purinergic P2Y12 receptor (Cavelier et al 2012).…”

“…Subsequent research has demonstrated expression of the ectopic β-chain of F0F1 ATPase (β-ATPase) on the endothelial cell surface (Cavelier et al 2012). The results of this study further suggest that the binding of lipid-free apoA-I to endothelial cell surface β-ATPase facilitates the uptake and transport of lipidated apoA-I and mature HDLs by enhancing β-ATPase-mediated hydrolysis of extracellular ATP into ADP and inducing consecutive activation of the purinergic P2Y12 receptor (Cavelier et al 2012). More recently, transendothelial transport of HDL particles was found to be modulated by endothelial lipase both through its enzymatic lipolytic activity and its ability to bridge the binding of lipoproteins to the endothelial surface (Robert et al 2013).…”

Beyond the Genetics of HDL: Why Is HDL Cholesterol Inversely Related to Cardiovascular Disease?

“…A subsequent study demonstrated a major role of cytoskeleton reorganization in F(1)-ATPase/P2Y(13)-dependent HDL endocytosis under the control of the small GTPase RhoA and its effector ROCK I (Malaval et al 2009). Others showed that binding of HDL to this receptor triggers the generation of ADP, which via the activation of the purinergic receptor P2Y13 stimulates the uptake and transport of HDL and initially lipid-free apoA-I by endothelial cells (Cavelier et al 2012). So far, there is no genetic support for the involvement of beta-chain of ATP synthase and/or P2Y(13), but even mild mutations could have in the case of ATPB5 lethal consequences.…”

High-Density Lipoprotein

“…In this as-yet-poorlyunderstood pathway, a high-affinity interaction of apoA-I with ectopic F0F1-ATPase leads to the formation of ADP, which activates purinergic receptors to induce the uptake of HDL by an as-yet-unidentified low-affinity HDL receptor. [34][35][36] The 2 better-characterized pathways mediate the removal of lipids from HDL independently of its protein moiety: CETP exchanges triglycerides of apoB-containing lipoproteins for cholesteryl esters of HDL, which are ultimately eliminated via the LDL receptor pathway, and SR-BI mediates the selective uptake of HDL lipids into the liver and steroidogenic organs. 11,33 The removal of cholesteryl esters by CETP and SR-BI, as well as the lipolysis of triglycerides and phospholipids by hepatic lipase and endothelial lipase, respectively, leads to the conversion of HDL 2 into HDL 3 as well as the generation of pre-β 1 -HDL.…”