Background-Patients with type 2 diabetes mellitus are at increased risk for the development of atherosclerosis. A pivotal event in the development of atherosclerosis is macrophage foam cell formation. The ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 regulate macrophage cholesterol efflux and hence play a vital role in macrophage foam cell formation. We have previously found that chronic elevated glucose reduces ABCG1 expression. In the present study, we examined whether patients with type 2 diabetes mellitus had decreased ABCG1 and/or ABCA1, impaired cholesterol efflux, and increased macrophage foam cell formation. Methods and Results-Blood was collected from patients with and without type 2 diabetes mellitus. Peripheral blood monocytes were differentiated into macrophages, and cholesterol efflux assays, immunoblots, histological analysis, and intracellular cholesteryl ester measurements were performed. Macrophages from patients with type 2 diabetes mellitus had a 30% reduction in cholesterol efflux with a corresponding 60% increase in cholesterol accumulation relative to control subjects. ABCG1 was present in macrophages from control subjects but was undetectable in macrophages from patients with type 2 diabetes mellitus. In contrast, ABCA1 expression in macrophages was similar in both control subjects and patients with type 2 diabetes mellitus. Macrophage expression of ABCG1 in both patients and control subjects was induced by treatment with the liver X receptor agonist TO-901317. Upregulation of liver X receptor dramatically reduced foam cell formation in macrophages from patients with type 2 diabetes mellitus. Conclusions-ABCG1

Objective-Activated endothelium and increased monocyte-endothelial interactions in the vessel wall are key early events in atherogenesis. ATP binding cassette (ABC) transporters play important roles in regulating sterol homeostasis in many cell types. Endothelial cells (EC) have a high capacity to efflux sterols and express the ABC transporter, ABCG1. Here, we define the role of ABCG1 in the regulation of lipid homeostasis and inflammation in aortic EC. Methods and Results-Using EC isolated from ABCG1-deficient mice (ABCG1 KO), we observed reduced cholesterol efflux to high-density lipoprotein compared to C57BL/6 (B6) EC. However, total cholesteryl ester levels were not changed in ABCG1 KO EC. Secretions of KC, MCP-1, and IL-6 by ABCG1 KO EC were significantly increased, and surface expressions of intercellular adhesion molecule-1 and E-selectin were increased several-fold on ABCG1 KO EC. Concomitant with these findings, we observed a 4-fold increase in monocyte adhesion to the intact aortic endothelium of ABCG1 KO mice ex vivo and to isolated aortic EC from these mice in vitro. In a gain-of-function study in vitro, restoration of ABCG1 expression in ABCG1 KO EC reduced monocyte-endothelial interactions. Utilizing pharmacological inhibitors for STAT3 and the IL-6 receptor, we found that blockade of STAT3 and IL-6 receptor signaling in ABCG1 KO EC completely abrogated monocyte adhesion to ABCG1 KO endothelium. Key Words: ABC transporters Ⅲ endothelial Ⅲ monocyte adhesion A key early event in atherosclerosis is the increased interaction of monocytes with endothelial cells (EC) in the vessel wall. 1 In early atherogenesis, EC in the artery wall become activated, in many cases by oxidized lipids. Activated EC secrete proinflammatory chemokines that recruit monocytes to the activated endothelium. Interaction of monocytes with adhesion molecules and integrins on the endothelial surface causes the monocytes to tether and firmly adhere to the endothelium, where they can subsequently transmigrate into the subendothelial space. [2][3][4] ABCG1 is an ATP-binding cassette transporter that has been well-studied in macrophages. ABCG1 has been shown to promote cholesterol efflux to high-density lipoprotein (HDL) particles in reverse cholesterol transport. 5,6 Deficiency of ABCG1 in macrophages leads to reduced cholesterol efflux and increased macrophage cholesteryl ester accumulation. 5,6 Rader et al 7 have elegantly shown that ABCG1 promotes reverse cholesterol transport in mice in vivo. We previously reported that ABCG1 expression and function are significantly reduced in patients with type 2 diabetes, potentially contributing to the formation of lipid-laden macrophages and accelerated atherosclerosis in these patients. 8 Aortic EC also express the ABC transporters ABCA1 and ABCG1 and efflux cholesterol to HDL. 9 EC have a dramatic ability to efflux cholesterol, most likely to aid in homeostasis to prevent endothelial activation in the vessel wall. 9,10 There is tight regulation of sterol content and ABC transporter expressi...

12/15-Lipoxygenase (12/15LO) plays a role in the pathogenesis of atherosclerosis and diabetes and has been implicated in low density lipoprotein oxidation. Murine macrophages express high levels of 12/15LO and are key cells involved in the accumulation and efflux of oxidized low density lipoprotein in the arterial wall. During this process, macrophages up-regulate scavenger receptors that regulate lipid uptake, and ATP-binding cassette (ABC) transporters, that regulate lipid efflux. We have previously demonstrated that 12/15LO enhances the turnover and serine phosphorylation of ABCG1. In the current study, we further elucidate the mechanisms by which 12/15LO regulates ABCG1. Proteasomal inhibitors blocked the down-regulation of ABCG1 expression and resulted in accumulation of phosphorylated ABCG1. Macrophages that lack 12/15LO have enhanced transporter expression, reduced ABCG1 phosphorylation, and increased cholesterol efflux. Conversely, macrophages that overexpress 12/15LO have reduced ABCG1 expression, increased transporter phosphorylation, and reduced cholesterol efflux. 12/15LO plays a key role in activating the MAPK pathway. Inhibition of the p38 or JNK pathways with pharmacological inhibitors or dominant negative constructs blocked 12S-hydroxyeicosatetranoic acid-mediated degradation of ABCG1. Moreover, we isolated macrophages from JNK1-, JNK2-, and MKK3-deficient mice to analyze the involvement of specific MAPK pathways. JNK2-and MKK3-, but not JNK1-deficient macrophages were resistant to the down-regulation of ABCG1 protein, reduction in efflux, and increase in serine phosphorylation by 12S-hydroxyeicosatetranoic acid. These findings provide evidence that 12/15LO regulates ABCG1 expression and function through p38-and JNK2-dependent mechanisms, and that targeting these pathways may provide novel approaches for regulating cholesterol homeostasis.Lipoxygenases comprise a family of enzymes capable of mediating selective lipid oxidation. 12/15-lipoxygenase (12/ 15LO) 2 catalyzes the conversion of arachidonic or linoleic acid to produce 12S-and 15S-hydroxyeicosatetranoic acids (12SHETE and 15SHETE) and 13S-hydroxyoctadecadienoic acid, respectively, and oxidizes esterified fatty acids within cholesteryl esters and phospholipids (1, 2). Mouse leukocyte 12/15LO is highly related to the 15LO enzyme in that they are ϳ74% identical in primary structure, and both are dual-specificity lipoxygenases (1). Mouse 12/15LO likely represents the orthologue of human 15LO (2-4). Murine macrophages express high levels of 12/15LO. Human or mouse peripheral blood monocytes do not express 12/15LO in circulation, but 12/15LO expression in these cells can be elicited by IL-4 or IL-13 (5-7).The role of 12/15LO in atherogenesis has been controversial, with studies attributing both pro-atherogenic (8 -10) and antiatherogenic properties to the enzyme (11). We and others have shown that mice overexpressing 12/15LO are more susceptible to developing spontaneous aortic fatty streak lesions on a rodent chow diet (9), whereas mice deficie...