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Objective- Atherosclerotic coronary artery disease is the leading cause of death worldwide, and current treatment options are insufficient. Using systems-level network cluster analyses on a large coronary artery disease case-control cohort, we previously identified PCSK3 (proprotein convertase subtilisin/kexin family member 3; FURIN) as a member of several coronary artery disease-associated pathways. Thus, our objective is to determine the role of FURIN in atherosclerosis. Approach and Results- In vitro, FURIN inhibitor treatment resulted in reduced monocyte migration and reduced macrophage and vascular endothelial cell inflammatory and cytokine gene expression. In vivo, administration of an irreversible inhibitor of FURIN, α-1-PDX (α1-antitrypsin Portland), to hyperlipidemic Ldlr -/- mice resulted in lower atherosclerotic lesion area and a specific reduction in severe lesions. Significantly lower lesional macrophage and collagen area, as well as systemic inflammatory markers, were observed. MMP2 (matrix metallopeptidase 2), an effector of endothelial function and atherosclerotic lesion progression, and a FURIN substrate was significantly reduced in the aorta of inhibitor-treated mice. To determine FURIN's role in vascular endothelial function, we administered α-1-PDX to Apoe -/- mice harboring a wire injury in the common carotid artery. We observed significantly decreased carotid intimal thickness and lower plaque cellularity, smooth muscle cell, macrophage, and inflammatory marker content, suggesting protection against vascular remodeling. Overexpression of FURIN in this model resulted in a significant 67% increase in intimal plaque thickness, confirming that FURIN levels directly correlate with atherosclerosis. Conclusions- We show that systemic inhibition of FURIN in mice decreases vascular remodeling and atherosclerosis. FURIN-mediated modulation of MMP2 activity may contribute to the atheroprotection observed in these mice.

Atherosclerosis is a progressive disease in which macrophages play an essential role. Macrophage infiltration into the arterial wall induces the development of an early atherosclerotic lesion. However, the dynamics of macrophage infiltration into the arterial wall during lesion progression remain poorly understood. In this study, low-density lipoprotein receptor knockout mice were fed a Western-type diet for 3, 6, 9, and 12 weeks to induce the formation of atherosclerotic lesions with different degrees of complexity. Subsequently, these mice underwent transplantation with bone marrow-overexpressing enhanced green fluorescent protein to track donor-derived cells, including macrophages. After 8 weeks of Western-type diet feeding after transplantation, macrophage infiltration was evaluated by immunohistochemical staining of donor-derived macrophages (enhanced green fluorescent protein-positive F4/80(+)) in the aortic roots. We found that the growth of pre-existing initial lesions was mainly caused by continued recruitment of donor-derived macrophages into the arterial wall. Interestingly, macrophage infiltration into pre-existing more advanced lesions was largely impaired, likely because of the formation of fibrous caps. In addition, interference with the expression of macrophage ATP-binding cassette transporter 1, an ATP-binding cassette transporter involved in cellular cholesterol efflux and macrophage recruitment into tissues, affects the infiltration of macrophages into pre-existing early lesions but not into advanced lesions. In conclusion, our data suggest that the dynamics of macrophage infiltration into the arterial wall vary greatly during atherogenesis and, thus, may affect the efficiency of pharmaceutical interventions aimed at targeting macrophage infiltration into the arterial wall., (Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Objective: The ATP-binding cassette transporter, subfamily A, member 1 (ABCA1) plays a key role in HDL cholesterol metabolism. However, the role of ABCA1 in modulating susceptibility to atherosclerosis is controversial., Methods and Results: We investigated the role of ABCA1 in atherosclerosis using a combination of overexpression and selective deletion models. First, we examined the effect of transgenic overexpression of a full-length human ABCA1-containing bacterial artificial chromosome (BAC) in the presence or absence of the endogenous mouse Abca1 gene. ABCA1 overexpression in the atherosclerosis-susceptible Ldlr(-/-) background significantly reduced the development of atherosclerosis in both the presence and absence of mouse Abca1. Next, we used mice with tissue-specific inactivation of Abca1 to dissect the discrete roles of Abca1 in different tissues on susceptibility to atherosclerosis. On the Apoe(-/-) background, mice lacking hepatic Abca1 had significantly reduced HDL cholesterol and accelerated atherosclerosis, indicating that the liver is an important site at which Abca1 plays an antiatherogenic role. In contrast, mice with macrophage-specific inactivation of Abca1 on the Ldlr(-/-) background displayed no change in atherosclerotic lesion area., Conclusions: These data indicate that physiological expression of Abca1 modulates the susceptibility to atherosclerosis and establish hepatic Abca1 expression as an important site of atheroprotection. In contrast, we show that selective deletion of macrophage Abca1 does not significantly modulate atherogenesis.

Background: ATP-binding cassette transporter A1 (ABCA1) is a key regulator of cellular cholesterol and phospholipid transport. Previously, we have shown that inactivation of macrophage ABCA1 induces atherosclerosis in low-density lipoprotein receptor knockout (LDLr-/-) mice. However, the possibly beneficial effects of specific upregulation of macrophage ABCA1 on atherogenesis are still unknown., Methods and Results: Chimeras that specifically overexpress ABCA1 in macrophages were generated by transplantation of bone marrow from human ABCA1 bacterial artificial chromosome (BAC) transgenic mice into LDLr-/- mice. Peritoneal macrophages isolated from the ABCA1 BAC --> LDLr-/- chimeras exhibited a 60% (P=0.0006) increase in cholesterol efflux to apolipoprotein AI. To induce atherosclerosis, the mice were fed a Western-type diet containing 0.25% cholesterol and 15% fat for 9, 12, and 15 weeks, allowing analysis of effects on initial lesion development as well as advanced lesions. No significant effect of macrophage ABCA1 overexpression was observed on atherosclerotic lesion size after 9 weeks on the Western-type diet (245+/-36x10(3) microm2 in ABCA1 BAC --> LDLr-/- mice versus 210+/-20x10(3) microm2 in controls). However, after 12 weeks, the mean atherosclerotic lesion area in ABCA1 BAC --> LDLr-/- mice remained only 164+/-15x10(3) microm2 (P=0.0008) compared with 513+/-56x10(3) microm2 in controls (3.1-fold lower). Also, after 15 weeks on the diet, lesions in mice transplanted with ABCA1 overexpressing bone marrow were still 1.6-fold smaller (393+/-27x10(3) microm2 compared with 640+/-59x10(3) microm2 in control transplanted mice; P=0.0015)., Conclusions: ABCA1 upregulation in macrophages inhibits the progression of atherosclerotic lesions.

Cholesterol and its metabolites play a variety of essential roles in living systems. Virtually all animal cells require cholesterol, which they acquire through synthesis or uptake, but only the liver can degrade cholesterol. The ABCA1 gene product regulates the rate-controlling step in the removal of cellular cholesterol: the efflux of cellular cholesterol and phospholipids to an apolipoprotein acceptor. Mutations in ABCA1, as seen in Tangier disease, result in accumulation of cellular cholesterol, reduced plasma high-density lipoprotein cholesterol, and increased risk for coronary artery disease. To date, more than 100 coding variants have been identified in ABCA1, and these variants result in a broad spectrum of biochemical and clinical phenotypes. Here we review genetic variation in ABCA1 and its critical role in cholesterol metabolism and atherosclerosis in the general population.

The ABC transporter ABCA1 plays a key role in the first steps of the reverse cholesterol transport pathway by mediating lipid efflux from macrophages. Previously, it was demonstrated that human ABCA1 overexpression in vivo in transgenic mice results in a mild elevation of plasma HDL levels and increased efflux of cholesterol from macrophages. In this study, we determined the effect of overexpression of ABCA1 on atherosclerosis development. Human ABCA1 transgenic mice (BAC(+)) were crossed with ApoE(-/-) mice, a strain that spontaneously develop atherosclerotic lesions. BAC(+)ApoE(-/-) mice developed dramatically smaller, less-complex lesions as compared with their ApoE(-/-) counterparts. In addition, there was increased efflux of cholesterol from macrophages isolated from the BAC(+)ApoE(-/-) mice. Although the increase in plasma HDL cholesterol levels was small, HDL particles from BAC(+)ApoE(-/-) mice were significantly better acceptors of cholesterol. Lipid analysis of HDL particles from BAC(+)ApoE(-/-) mice revealed an increase in phospholipid levels, which was correlated significantly with their ability to enhance cholesterol efflux. [ABSTRACT FROM AUTHOR]

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process. Unlabelled Image [ABSTRACT FROM AUTHOR]