A Two-Step Mechanism for Free Cholesterol and Phospholipid Efflux from Human Vascular Cells to Apolipoprotein A-1

Fielding, Phoebe E.; Nagao, Koji; Hakamata, Hideki; Chimini, Giovanna; Fielding, Christopher J.

doi:10.1021/bi0004192

Cited by 193 publications

(197 citation statements)

References 48 publications

(74 reference statements)

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“…Transfer of cellular cholesterol to apoA-I from peripheral tissues is a two-step process, with the initially bound phospholipids facilitating subsequent efflux of FC (4). Conformational transitions in apoA-I occur in a complex cellular environment that is seldom accessible for direct physical studies.…”

Section: Resultsmentioning

confidence: 99%

“…More than 30 years of sustained research (2) has gone into understanding the mechanism(s) of protection that apoA-I provides against heart disease. The protective action of apoA-I and HDL is attributed to their central role in reverse cholesterol transport (RCT); a process in which apoA-I acts as an acceptor for sequential transfers of phospholipids and free cholesterol (FC) from peripheral tissues and transports cholesterol to the liver and other tissues for excretion and steroidogenesis (3,4). Modulation of the RCT pathway presents significant potential for treatment of heart disease (5).…”

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confidence: 99%

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RETRACTED: Crystal structure of human apolipoprotein A-I: Insights into its protective effect against cardiovascular diseases

Ajees

Anantharamaiah

Mishra

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

201

200

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Despite three decades of extensive studies on human apolipoprotein A-I (apoA-I), the major protein component in high-density lipoproteins, the molecular basis for its antiatherogenic function is elusive, in part because of lack of a structure of the full-length protein. We describe here the crystal structure of lipid-free apoA-I at 2.4 Å. The structure shows that apoA-I is comprised of an N-terminal four-helix bundle and two C-terminal helices. The N-terminal domain plays a prominent role in maintaining its lipid-free conformation, indicating that mutants with truncations in this region form inadequate models for explaining functional properties of apoA-I. A model for transformation of the lipid-free conformation to the high-density lipoprotein-bound form follows from an analysis of solvent-accessible hydrophobic patches on the surface of the structure and their proximity to the hydrophobic core of the four-helix bundle. The crystal structure of human apoA-I displays a hitherto-unobserved array of positively and negatively charged areas on the surface. Positioning of the charged surface patches relative to hydrophobic regions near the C terminus of the protein offers insights into its interaction with cell-surface components of the reverse cholesterol transport pathway and antiatherogenic properties of this protein. This structure provides a much-needed structural template for exploration of molecular mechanisms by which human apoA-I ameliorates atherosclerosis and inflammatory diseases.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

RETRACTED: Crystal structure of human apolipoprotein A-I: Insights into its protective effect against cardiovascular diseases

Ajees

Anantharamaiah

Mishra

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

201

200

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“…5). LY-A and LY-A/CERT cells showed similar sensitivity to amphotericin B, which kills cells by binding to cholesterol in the plasma mem- brane, 3 suggesting that they contain similar number of cholesterol molecules in the plasma membrane. These results suggested that the plasma membrane was reorganized and more cholesterol existed in non-raft domains in LY-A cells when SM content was reduced.…”

Section: Cholesterol Available To Cold M␤cd Extraction Ismentioning

confidence: 98%

Enhanced ApoA-I-dependent Cholesterol Efflux by ABCA1 from Sphingomyelin-deficient Chinese Hamster Ovary Cells

Nagao

Takahashi

Hanada

et al. 2007

Journal of Biological Chemistry

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ATP binding cassette protein A1 (ABCA1) plays a major role in cholesterol homeostasis and high density lipoprotein (HDL) metabolism. It is proposed that ABCA1 reorganizes the plasma membrane and generates more loosely packed domains that facilitate apoA-I-dependent cholesterol efflux. In this study, we examined the effects of the cellular sphingomyelin level on HDL formation by ABCA1 by using a Chinese hamster ovary-K1 mutant cell line, LY-A, which has a missense mutation in the ceramide transfer protein CERT. When LY-A cells were cultured in Nutridoma-BO medium and sphingomyelin content was reduced, apoA-I-dependent cholesterol efflux by ABCA1 from LY-A cells increased 1.65-fold compared with that from LY-A/CERT cells stably transfected with human CERT cDNA. Exogenously added sphingomyelin significantly reduced the apoA-I-dependent efflux of cholesterol from LY-A cells, confirming that the decrease in sphingomyelin content in the plasma membrane stimulates cholesterol efflux by ABCA1. The amount of cholesterol available to cold methyl-␤-cyclodextrin (M␤CD) extraction from LY-A cells was increased by 40% by the expression of ABCA1 and was 1.6-fold higher than that from LY-A/CERT cells. This step in ABCA1 function, making cholesterol available to cold M␤CD, was independent of apoA-I. These results suggest that the function of ABCA1 could be divided into two steps: (i) a flopping step to move phosphatidylcholine and cholesterol from the inner to outer leaflet of the plasma membrane, where cholesterol becomes available to cold M␤CD extraction, and (ii) a loading step to load phosphatidylcholine and cholesterol onto apoA-I to generate HDL. ATP binding cassette protein A1 (ABCA1)2 plays a major role in cholesterol homeostasis and high density lipoprotein (HDL) metabolism (1). It has been reported that apolipoprotein A-I (apoA-I) binds to ABCA1 and cellular-free cholesterol (FC) and phospholipids (PL) are loaded onto apoA-I to form pre-␤ HDL. It is clear that ABCA1 is involved in PL-rich HDL generation in plasma, because plasma PL concentration of Abca1 Ϫ/Ϫ mice was decreased by more than 75%, mostly due to a reduction of HDL (2); however, the molecular mechanism behind ABCA1-mediated pre-␤HDL formation is still poorly understood.Several models have been proposed for the mechanism of ABCA1-mediated pre-␤ HDL formation: (a) A two-step process model proposed by Fielding et al. (3) and Wang et al. (4) that ABCA1 first mediates PL efflux to apoA-I and this apolipoprotein-PL complex accepts FC in an ABCA1-independent manner; (b) a concurrent process model that FC and PL efflux by ABCA1 to apoA-I are tightly coupled to each other (5); and (c) a phosphatidylserine flopping model that ABCA1 mediates the translocation of phosphatidylserine to the outer leaflet and extracellular exposure of phosphatidylserine promotes apoA-I binding to the cell surface and subsequent translocation of phosphatidylcholine (PC) and cholesterol to apoA-I (6). To explore the mechanism of ABCA1-mediated pre-␤ HDL formation, we purified human ABCA1 a...

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“…2, G and H). To further confirm that the cholesterol efflux function mediates apoE-induced A␤ degradation, we blocked the ABCA1 activity with glyburide (46,47). ABCA1 mediates cholesterol efflux onto apolipoproteins to form HDL particles, and blocking the FIGURE 2.…”

Section: Facilitation Of A␤ Degradation Is a Common Feature Of Hdlmentioning

confidence: 99%

Apolipoprotein E Promotes β-Amyloid Trafficking and Degradation by Modulating Microglial Cholesterol Levels

Lee

Tse

Smith

et al. 2012

Journal of Biological Chemistry

143

125

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Background: Intracellular A␤ degradation is enhanced in the presence of apoE. Results: Lowering cellular cholesterol levels facilitates intracellular trafficking of A␤ to lysosomes and enhances its degradation. Conversely, increasing cholesterol levels retards the delivery and inhibits degradation of A␤. Conclusion:The cholesterol efflux function of apoE mediates its ability to promote A␤ degradation. Significance: We demonstrate a direct role for cholesterol in AD.

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A Two-Step Mechanism for Free Cholesterol and Phospholipid Efflux from Human Vascular Cells to Apolipoprotein A-1

Cited by 193 publications

References 48 publications

RETRACTED: Crystal structure of human apolipoprotein A-I: Insights into its protective effect against cardiovascular diseases

RETRACTED: Crystal structure of human apolipoprotein A-I: Insights into its protective effect against cardiovascular diseases

Enhanced ApoA-I-dependent Cholesterol Efflux by ABCA1 from Sphingomyelin-deficient Chinese Hamster Ovary Cells

Apolipoprotein E Promotes β-Amyloid Trafficking and Degradation by Modulating Microglial Cholesterol Levels

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