Human ABCA7 supports apolipoprotein-mediated release of cellular cholesterol and phospholipid to generate high density lipoprotein
JOURNAL OF BIOLOGICAL CHEMISTRY
Authors: Abe-Dohmae, S; Ikeda, Y; Matsuo, M; Hayashi, M; Okuhira, K; Ueda, K; Yokoyama, S
Apolipoprotein-mediated release of cellular cholesterol and phospholipids was induced in HEK293 cells by expressing human ATP-binding cassette transporter A7 (ABCA7) and ABC transporter A1 (ABCA1) proteins, whether transient or stable, to generate cholesterol-rich high density lipoprotein (HDL). Green fluorescent protein (GFP) attached at their C termini did not influence the lipid release reactions. Transfected ABCA7-GFP induced apolipoprotein-mediated assembly of cholesterol-containing HDL also in L929 cells, which otherwise generate only cholesterol-deficient HDL with their endogenous ABCA1. Time-dependent release of cholesterol and phospholipid by apolipoprotein A ( apoA)-I was parallel both with ABCA1 and with ABCA7 when highly expressed in HEK293 cells, but dose-dependent profiles of lipid release on apoA-I and apoA-II were somewhat different between ABCA1 and ABCA7. Analyses of the stable clones with ABCA1-GFP (293/2c) and ABCA7-GFP (293/6c) by using the same vector indicated some differences in regulation of their activities by protein kinase modulators. Dibutyryl cyclic AMP increased ABCA1-GFP and the release of cholesterol and phospholipid in 293/2c but increased neither ABCA7-GFP nor the lipid release in 293/6c. Expression of ABCA1-GFP- and apoA-I-mediated lipid release were enhanced in parallel by phorbol 12-myristate 13-acetate (PMA) in 293/2c cells. In contrast, the same treatment of 293/6c increased ABCA7-GFP, but apoA-I-mediated lipid release was significantly suppressed. Despite these different responses to PMA, all of the effects of PMA were reversed by a specific protein kinase C inhibitor Go6976, suggesting that the changes were in fact due to protein kinase C activation. A thiol protease inhibitor, N-acetyl-Leu-Leu-norleucinal, increased the protein levels of ABCA1-GFP in 293/2c and ABCA7-GFP in 293/6c, indicating their common degradation pathway. The data indicated that human ABCA7 would compensate the function of ABCA1 for release of cell cholesterol in a certain condition(s), but post-transcriptional regulation of their activity is different.
Markers of cholesterol transport are associated with amyloid deposition in the brain
NEUROBIOLOGY OF AGING
Authors: Hughes, Timothy M.; Lopez, Oscar L.; Evans, Rhobert W.; Kamboh, M. Ilyas; Williamson, Jeff D.; Klunk, William E.; Mathis, Chester A.; Price, Julie C.; Cohen, Ann D.; Snitz, Beth E.; DeKosky, Steven T.; Kuller, Lewis H.
Cholesterol is implicated in the development of late-onset Alzheimer's disease (AD). We sought to determine the associations between beta amyloid (Ab) plaque deposition in vivo using Pittsburgh compound B (PiB) and several indices of cholesterol homeostasis (i.e., total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, apolipoprotein E (ApoE), clusterin, oxysterol metabolites of cholesterol, and previously reported genes associated with late-onset AD) in 175 nondemented elderly subjects. High Ab deposition was associated significantly with a lower Mini-Mental State Examination score (<27 points, p = 0.04), high systolic blood pressure (p 0.04), carrying the apolipoprotein E epsilon 4 allele (p < 0.01), and lower plasma ApoE levels (p = 0.02), and variation in the ABCA7 (p = 0.02) and EPHA1 genes (p = 0.02). Cholesterol measures were not related to Ab deposition in this cohort of nondemented elderly adults. However, plasma and genetic factors relating to cholesterol transport were associated with Ab deposition in the brain. A better understanding of cholesterol transport mechanisms may lead to the design of potential targets for the prevention of Ab deposition in the brain. (C) 2014 Elsevier Inc. All rights reserved.