Adipose Modulation of High-Density Lipoprotein Cholesterol (original) (raw)
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Common ABCA1 variants, HDL levels, and cellular cholesterol efflux in subjects with familial low HDL
The Journal of Lipid Research, 2007
HDL promotes cholesterol efflux from peripheral cells via ABCA1 in the first step of reverse cholesterol transport (RCT). We investigated whether the early steps of RCT were disturbed in subjects with familial low HDL and an increased risk for early atherosclerosis. Cholesterol efflux from monocyte-derived macrophages to lipid-free apolipoprotein A-I (apoA-I; %) was measured in 22 patients with familial low HDL without Tangier disease mutations and in 21 healthy controls. In addition, we defined the different alleles of ABCA1 using single-nucleotide polymorphism haplotypes and measured ABCA1 and ABCG1 mRNA transcript levels in cholesterol-loaded macrophages. Similar ABCA1-mediated cholesterol efflux levels were observed for macrophages derived from control subjects and from low-HDL subjects. However, when efflux of cholesterol was estimated as cholesterol efflux to apoA-I (%)/relative ABCA1 mRNA expression level, cholesterol removal was significantly (P 5 0.001) lower in the low-HDL group. Cholesterol-loaded macrophages from low-HDL subjects showed significantly increased levels of ABCA1 mRNA but not of ABCG1 mRNA and were more often carriers of the rare ABCA1 alleles L158 and R219K.
Cardiogenetics, 2013
Cholesterol deposition plays a central role in atherogenesis. The accumulation of lipid material is the result of an imbalance between the influx and efflux of cholesterol within the arterial wall. High levels of plasma low-density lipoprotein-cholesterol are considered the major mechanism responsible for the influx and accumulation of cholesterol in the arterial wall, while high-density lipoprotein (HDL)cholesterol seems responsible for its efflux. The mechanism by which cholesterol is removed from extra-hepatic organs and delivered to the liver for its catabolism and excretion is called reverse cholesterol transport (RCT). Epidemiological evidence has associated high levels of HDL-cholesterol/ApoA-I with protection against atherosclerotic disease, but the ultimate mechanism(s) responsible for the beneficial effect is not well established. HDLs are synthesized by the liver and small intestine and released to the circulation as a lipid-poor HDL (nascent HDL), mostly formed by ApoA-I and phospholipids. Through their metabolic maturation, HDLs interact with the ABCA1 receptor in the macrophage surface increasing their lipid content by taking phospholipids and cholesterol from macrophages becoming mature HDL. The cholesterol of the HDLs is transported to the liver, via the scavenger receptor class B, type I, for further metabolization and excretion to the intestines in the form of bile acids and cholesterol, completing the process of RCT. It is clear that an inherited mutation or acquired abnormality in any of the key players in RCT mat affect the atherosclerotic process
Dysfunctional HDL and atherosclerotic cardiovascular disease
Nature Reviews Cardiology, 2015
High-density lipoproteins (HDLs) protect against atherosclerosis by removing excess cholesterol from macrophages through the ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G1 (ABCG1) pathways involved in reverse cholesterol transport. Factors that impair the availability of functional apolipoproteins or the activities of ABCA1 and ABCG1 could, therefore, strongly influence atherogenesis. HDL also inhibits lipid oxidation, restores endothelial function, exerts anti-inflammatory and antiapoptotic actions, and exerts anti-inflammatory actions in animal models. Such properties could contribute considerably to the capacity of HDL to inhibit atherosclerosis. Systemic and vascular inflammation has been proposed to convert HDL to a dysfunctional form that has impaired antiatherogenic effects. A loss of anti-inflammatory and antioxidative proteins, perhaps in combination with a gain of proinflammatory proteins, might be another important component in rendering HDL dysfunctional. The proinflammatory enzyme myeloperoxidase induces both oxidative modification and nitrosylation of specific residues on plasma and arterial apolipoprotein A-I to render HDL dysfunctional, which results in impaired ABCA1 macrophage transport, the activation of inflammatory pathways, and an increased risk of coronary artery disease. Understanding the features of dysfunctional HDL or apolipoprotein A-I in clinical practice might lead to new diagnostic and therapeutic approaches to atherosclerosis.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2006
Objective-Mutations in ATP-binding cassette transporter A1 (ABCA1), the cellular lipid transport molecule mutated in Tangier disease, result in the rapid turnover of high-density lipoprotein (HDL)-associated apolipoproteins that presumably are cleared by the kidneys. However, the role of ABCA1 in the liver for HDL apolipoprotein and cholesteryl ester (CE) catabolism in vivo is unknown. Methods and Results-Murine HDL was radiolabeled with 125 I in its apolipoprotein and with [ 3 H]cholesteryl oleyl ether in its CE moiety. HDL protein and lipid metabolism in plasma and HDL uptake by tissues were investigated in ABCA1-overexpressing bacterial artificial chromosome (BAC)-transgenic (BAC ϩ ) mice and in mice harboring deletions of total (ABCA1 Ϫ/Ϫ ) and liver-specific ABCA1 (ABCA1 ϪL/ϪL ). In BAC ϩ mice with elevated ABCA1 expression, fractional catabolic rates (FCRs) of both the protein and the lipid tracer were significantly decreased in plasma and in the liver, yielding a diminished hepatic selective CE uptake from HDL. In contrast, ABCA1 Ϫ/Ϫ or ABCA1 ϪL/ϪL mice had significantly increased plasma and liver FCRs for both HDL tracers. An ABCA1 deficiency was associated with increased selective HDL CE uptake by the liver under all experimental conditions. Conclusions-Hepatic ABCA1 has a critical role for HDL catabolism in plasma and for HDL selective CE uptake by the liver. (Arterioscler Thromb Vasc Biol. 2006;26:1821-1827.)
Cardiovascular Research, 2007
Objective: Elevated levels of high-density lipoprotein (HDL) cholesterol are inversely related to the risk of cardiovascular disease. The antiatherosclerotic function of HDL is mainly ascribed to its role in reverse cholesterol transport, and requires the integrity of HDL structure. Experimental evidence suggests that the ability of HDL to promote removal of excess cholesterol from peripheral cells is impaired upon oxidation. On the other hand, tyrosylation of HDL enhances its protective function, suggesting that not all forms of modified lipoprotein may be atherogenic. In the present study we investigated the effect of a mild oxidation of HDL 3 on its function as cholesterol acceptor. Methods and results: A mild oxidative stress (induced by 15 min exposure of HDL 3 to 1 μM Cu ++ or to 15-lipoxygenase) caused the formation of pre-β-migrating particles. Compared to native lipoprotein, mildly modified HDL 3 induced a significant ATP-binding cassette transporter 1 (ABCA1)-mediated increase of cholesterol and phospholipids efflux from J774 macrophages. This effect was abolished by an inhibitor of ABCA1-mediated lipid efflux (glyburide) and was absent in Tangier fibroblasts. Conclusions: A mild oxidative modification of HDL 3 may improve its function as cholesterol acceptor, increasing ABCA1-mediated lipid efflux from macrophages, a process that may reduce foam cell formation.
Atherosclerosis, 2001
HDL cholesterol (HDL-C) deficiency is the most common lipid abnormality observed in patients with premature coronary heart disease (CHD). Recently, our laboratory and others demonstrated that mutations in the ATP-binding cassette transporter 1 (ABCA1) gene are responsible for Tangier disease, a rare genetic disorder characterized by severely diminished plasma HDL-C concentrations and a predisposition for CHD. To address the question of whether common variants within the coding sequence of ABCA1 may affect plasma HDL-C levels and CHD risk in the general population, we determined the frequencies of three common ABCA1 variants (G596A, A2589G and G3456C) in men participating in the Veterans Affairs Cooperative HDL Cholesterol Intervention Trial (VA-HIT), a study designed to examine the benefits of HDL raising in men having low HDL-C (540 mg/dl) and established CHD, as well as in CHD-free men from the Framingham Offspring Study (FOS). Allele frequencies (%) in VA-HIT were 31, 16, and 4 for the G596A, A2589G, and G3456C variants, respectively, versus 27, 12, and 2 in FOS (PB 0.03). None of the variants were significantly associated with plasma HDL-C concentrations in either population; however, in VA-HIT, the G3456C variant was associated with a significantly increased risk for CHD end points, suggesting a role for this variant in the premature CHD observed in this population.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2013
A TP-binding cassette transporter A1 (ABCA1) is a key protein determining high-density lipoprotein (HDL) function. In 1999, it was discovered by 3 independent groups that mutations in the gene for ABCA1 underlie the molecular defect in the HDL deficiency syndrome Tangier disease. Subsequent studies with genetically engineered mice lacking or overexpressing ABCA1 provided evidence that ABCA1 modulates atherosclerosis susceptibility on either end of the reverse cholesterol transport pathway. In the liver (and to a lesser extent in intestine), it determines the biogenesis of nascent HDL particles, whereas in macrophages it is essential for the prevention of the excess cholesterol accumulation by facilitating the transport of cellular cholesterol and phospholipid onto lipid-poor apo AI, the major apoprotein of HDL.