(03378)Effect of Apolipoprotein A-I on ATP Binding Cassette Transporter A1 Degradation and Cholesterol Efflux in THP-1 Macrophage-derived Foam Cells

Chao-Ke TANG^1,2,
Guo-Hua TANG¹, Guang-Hui YI¹, Zuo WANG¹, Lu-Shan
LIU¹, Shuang WAN¹,
Zhong-Hua YUAN¹, Xiu-Sheng HE¹, Jun-Hao YANG¹,
Chang-Geng RUAN¹, and Yong-Zong YANG^1*
(1Institute of Cardiovascular Disease of Nanhua University, Hengyang 421001,
China;
2Xiangya Medical School, Central Southern University, Changsha 410078, China)

Abstract Cholesterol-loaded
macrophage foam cells are a central component of atherosclerotic lesions. ATP
binding cassette transporter A1 (ABCA1), the defective molecule in Tangier disease,
mediates the efflux of phospholipid and cholesterol from cells to apolipoprotein
A-I (apoA-I), reversing foam cell formation. This study investigated the effect
of apoA-I on ABCA1 degradation and cholesterol efflux in THP-1 macrophage-derived
foam cells. After exposure of the cultured THP-1 macrophage-derived foam cells
to apoA-I for different time, cholesterol efflux, ABCA1 mRNA and protein levels
were determined by FJ-2107P type liquid scintillator, RT-PCR and Western blot,
respectively. The mean ABCA1 fluorescence intensity on THP-1 macrophage-derived
foam cells was detected by flow cytometry. Results showed that apoA-I markedly
increased ABCA1-mediated cholesterol efflux from THP-1 macrophage-derived foam
cells. This was accompanied by an increase in the content of ABCA1. ApoA-I did
not alter ABCA1 mRNA abundance. Significantly, thiol protease inhibitors increased
the level of ABCA1 protein and slowed its decay in THP-1 macrophage-derived
foam cells, whereas none of the proteosome-specific inhibitor lactacystin, other
protease inhibitors, or the lysosomal inhibitor NH₄Cl showed such effects. The
apoA-I-mediated cellular cholesterol efflux was enhanced by thiol protease inhibitors.
Our results suggested that thiol protease inhibitors might provide an alternative
way to upregulate ABCA1 protein. This strategy is especially appealing since
it may mimic the stabilizing effect of the natural ligands apoA-I.

Key words ATP binding cassette
transporter A1; apoA-I; flow cytometry; cholesterol; lipoproteins

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Received: September 8, 2003 Accepted:
December 10, 2003
This work was supported by the grants from the Major State Basic Research Development
Program of China (No. G2000056905) and the Special Funds for Department of Science
and Technology of Hunan Province (No. 01SSY1003)
*Corresponding author: Tel, 86-734-8281288; Fax, 86-734-8281288; E-mail, [email protected]