scholarly journals Regulation of Macrophage Cholesterol Efflux through Hydroxymethylglutaryl-CoA Reductase Inhibition

2005 ◽  
Vol 280 (23) ◽  
pp. 22212-22221 ◽  
Author(s):  
Carmen A. Argmann ◽  
Jane Y. Edwards ◽  
Cynthia G. Sawyez ◽  
Caroline H. O'Neil ◽  
Robert A. Hegele ◽  
...  
Keyword(s):  
Cholesterol Efflux ◽  
Foam Cell ◽  
Cell Formation ◽  
Dominant Negative ◽  
Foam Cell Formation ◽  
Peroxisome Proliferator ◽  
Very Low Density Lipoproteins ◽  
Peroxisome Proliferator Activated Receptor ◽  
Abca1 Expression ◽  
Coa Reductase

The cholesterol biosynthetic pathway produces numerous signaling molecules. Oxysterols through liver X receptor (LXR) activation regulate cholesterol efflux, whereas the non-sterol mevalonate metabolite, geranylgeranyl pyrophosphate (GGPP), was recently demonstrated to inhibit ABCA1 expression directly, through antagonism of LXR and indirectly through enhanced RhoA geranylgeranylation. We used HMG-CoA reductase inhibitors (statins) to test the hypothesis that reduced synthesis of mevalonate metabolites would enhance cholesterol efflux and attenuate foam cell formation. Preincubation of THP-1 macrophages with atorvastatin, dose dependently (1–10 μm) stimulated cholesterol efflux to apolipoprotein AI (apoAI, 10–60%, p < 0.05) and high density lipoprotein (HDL3) (2–50%, p < 0.05), despite a significant decrease in cholesterol synthesis (2–90%). Atorvastatin also increased ABCA1 and ABCG1 mRNA abundance (30 and 35%, p < 0.05). Addition of mevalonate, GGPP or farnesyl pyrophosphate completely blocked the statin-induced increase in ABCA1 expression and apoAI-mediated cholesterol efflux. A role for RhoA was established, because two inhibitors of Rho protein activity, a geranylgeranyl transferase inhibitor and C3 exoenzyme, increased cholesterol efflux to apoAI (20–35%, p < 0.05), and macrophage expression of dominant-negative RhoA enhanced cholesterol efflux to apoAI (20%, p < 0.05). In addition, atorvastatin increased the RhoA levels in the cytosol fraction and decreased the membrane localization of RhoA. Atorvastatin treatment activated peroxisome proliferator activated receptor γ and increased LXR-mediated gene expression suggesting that atorvastatin induces cholesterol efflux through a molecular cascade involving inhibition of RhoA signaling, leading to increased peroxisome proliferator activated receptor γ activity, enhanced LXR activation, increased ABCA1 expression, and cholesterol efflux. Finally, statin treatment inhibited cholesteryl ester accumulation in macrophages challenged with atherogenic hypertriglyceridemic very low density lipoproteins indicating that statins can regulate foam cell formation.

Abstract 168: The Acceleration of Foam Cell Formation by Chlamydia Pneumoniae Requires Nlrp3 Inflammasome Activation and Il-1 Signaling

2015 ◽  
Vol 35 (suppl_1) ◽  
Author(s):  
Gantsetseg Tumurkhuu ◽  
Jargalsaikhan Dagvadorj ◽  
Timothy R Crother ◽  
Kenichi Shimada ◽  
Moshe Arditi ◽  
...  
Keyword(s):  
Nlrp3 Inflammasome ◽  
Cholesterol Efflux ◽  
Molecular Mechanisms ◽  
Chlamydia Pneumoniae ◽  
Foam Cell ◽  
Cell Formation ◽  
Peritoneal Macrophages ◽  
Foam Cell Formation ◽  
Inflammasome Activation ◽  
Abca1 Expression

Background & Objective: Foam cell formation (FCF) due to excessive accumulation of cholesterol by macrophages is a pathological hallmark of atherosclerosis. Chlamydia pneumoniae (Cp) promotes FCF in the presence of oxLDL, but the exact molecular mechanisms are still not completely delineated. Recent data indicates that the Nlrp3 inflammasome plays an important role in the formation of atherosclerotic plaques. Here we investigated the role of the Nlrp3 inflammasome during the acceleration of FCF by Cp infection. Methods and Results: In order to determine if the NLRP3 inflammasome played a role in Cp infection induced acceleration of FCF, we treated resident peritoneal macrophages exposed to oxLDL and Cp with the IL-1R antagonist, Anakinra, to block IL-1 signaling. Treatment with Anakinra resulted in a significant reduction in FCF. Nlrp3-/-, Casp1-/-, and WT macrophages were also treated with live Cp in the presence or absence of oxLDL. We found that Nlrp3-/- and Casp1-/- macrophages had significantly less FCF compared with WT cells. Interestingly, both ABCA1 (cholesterol efflux transporter) and its transcription factor, liver X receptor (LXR-α), were increased in Nlrp3-/- and Casp1-/- macrophages compared with WT cells. Addition of rIL-1β to Nlrp3-/- macrophages led to a decrease in ABCA1 expression and greater FCF. Importantly, Il1r-/- macrophages also had greater ABCA1 expression and reduced FCF when exposed to oxLDL and Cp infection. Conclusion: These data suggest that Cp infection facilitates foam cell formation in the presence of oxLDL by producing NLRP3 dependent IL-1 cytokines, which then feed back on the macrophages and interferes with cholesterol efflux by negatively regulating ABCA1. In the absence of IL-1 signaling, the expression of ABCA1 is upregulated leading to greater cholesterol efflux and reduced FCF. Thus we have identified a novel regulatory loop controlling FCF. Understanding these interacting pathways will lead to new therapeutic strategies against atherosclerosis.

scholarly journals An Innate Immunity Signaling Process Suppresses Macrophage ABCA1 Expression through IRAK-1-Mediated Downregulation of Retinoic Acid Receptor α and NFATc2

2009 ◽  
Vol 29 (22) ◽  
pp. 5989-5997 ◽  
Author(s):  
Urmila Maitra ◽  
John S. Parks ◽  
Liwu Li
Keyword(s):  
Innate Immunity ◽  
Retinoic Acid ◽  
Cholesterol Efflux ◽  
Foam Cell ◽  
Cell Formation ◽  
Proximal Promoter ◽  
Foam Cell Formation ◽  
Wild Type ◽  
Increased Risk ◽  
Abca1 Expression

ABSTRACT ATP-binding cassette transporter A1 (ABCA1) plays a central role in promoting cholesterol efflux from macrophages, thereby reducing the risk of foam cell formation and atherosclerosis. The expression of ABCA1 is induced by members of the nuclear receptor family of transcription factors, including retinoic acid receptors (RARs). A key innate immunity signaling kinase, IRAK-1, has been associated with an increased risk of atherosclerosis in humans and mice. This prompted us to investigate the potential connection between IRAK-1 and the expression of ABCA1. Here, we demonstrate that nuclear RARα levels are dramatically elevated in IRAK-1−/− macrophages. Correspondingly, IRAK-1−/− macrophages exhibit increased expression of ABCA1 mRNA and protein, as well as elevated cholesterol efflux in response to the RAR ligand ATRA. Analysis of the ABCA1 proximal promoter revealed binding sites for both RAR and NFAT. Chromatin immunoprecipitation assays demonstrated increased binding of RARα and NFATc2 to the ABCA1 promoter in IRAK-1−/− macrophages compared to wild-type macrophages. Additionally, lipopolysaccharide pretreatment reduced the nuclear levels of RARα and decreased ABCA1 expression and cholesterol efflux in wild-type but not in IRAK-1−/− cells. In summary, this study reveals a novel connection between innate immunity signaling processes and the regulation of ABCA1 expression in macrophages and defines a potential therapeutic target for treating atherosclerosis.

Abstract 43: Cholesterol Efflux Pathways Suppress Inflammasome Activation in Mice and Humans

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
Marit Westerterp ◽  
Panagiotis Fotakis ◽  
Mireille Ouimet ◽  
Andrea E Bochem ◽  
Hanrui Zhang ◽  
...  
Keyword(s):  
Plasma Levels ◽  
Cholesterol Efflux ◽  
Foam Cell ◽  
Cell Formation ◽  
Density Lipoprotein ◽  
Foam Cell Formation ◽  
Inflammasome Activation ◽  
Loss Of Function ◽  
Caspase 1 ◽  
Macrophage Cholesterol Efflux

Plasma high-density-lipoprotein (HDL) has several anti-atherogenic properties, including its key role in functioning as acceptor for ATP-binding cassette A1 and G1 (ABCA1 and ABCG1) mediated cholesterol efflux. We have shown previously that macrophage Abca1/g1 deficiency accelerates atherosclerosis, by enhancing foam cell formation and inflammatory cytokine expression in atherosclerotic plaques. Macrophage cholesterol accumulation activates the inflammasome, leading to caspase-1 cleavage, required for IL-1β and IL-18 secretion. Several studies have suggested that inflammasome activation accelerates atherogenesis. We hypothesized that macrophage Abca1/g1 deficiency activates the inflammasome. In Ldlr -/- mice fed a Western type diet (WTD), macrophage Abca1/g1 deficiency increased IL-1β and IL-18 plasma levels (2-fold; P <0.001), and induced caspase-1 cleavage. Deficiency of the inflammasome components Nlrp3 or caspase-1 in macrophage Abca1/g1 knockouts reversed the increase in plasma IL-18 levels ( P <0.001), indicating these changes were inflammasome dependent. We found that macrophage Abca1/g1 deficiency induced caspase-1 cleavage in splenic CD115 + monocytes and CD11b + macrophages. While mitochondrial ROS production or lysosomal function were not affected, macrophage Abca1/g1 deficiency led to an increased splenic population of monocytes (2.5-fold; P <0.01). Monocytes secrete ATP, and as a result, ATP secretion from total splenic cells was increased (2.5-fold; P <0.01), likely contributing to inflammasome activation. Caspase-1 deficiency decreased atherosclerosis in macrophage Abca1/g1 deficient Ldlr -/- mice fed WTD for 8 weeks (225822 vs 138606 μm 2 ; P <0.05). Of therapeutic interest, one injection of reconstituted HDL (100 mg/kg) in macrophage Abca1/g1 knockouts decreased plasma IL-18 levels ( P <0.05). Tangier disease patients, with a homozygous loss-of-function for ABCA1, showed increased IL-1β and IL-18 plasma levels (3-fold; P <0.001), suggesting that cholesterol efflux pathways also suppress inflammasome activation in humans. These findings suggest that macrophage cholesterol efflux pathways suppress inflammasome activation, possibly contributing to the anti-atherogenic effects of HDL treatment.

scholarly journals Altered PPARγ Expression Promotes Myelin-Induced Foam Cell Formation in Macrophages in Multiple Sclerosis

2020 ◽  
Vol 21 (23) ◽  
pp. 9329
Author(s):  
Elien Wouters ◽  
Elien Grajchen ◽  
Winde Jorissen ◽  
Tess Dierckx ◽  
Suzan Wetzels ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Mononuclear Cells ◽  
Foam Cell ◽  
Cell Formation ◽  
Autoimmune Disorder ◽  
Foam Cell Formation ◽  
Peroxisome Proliferator ◽  
Peripheral Blood Mononuclear ◽  
Peroxisome Proliferator Activated Receptors ◽  
Pparγ Expression

Macrophages play a crucial role during the pathogenesis of multiple sclerosis (MS), a neuroinflammatory autoimmune disorder of the central nervous system. Important regulators of the metabolic and inflammatory phenotype of macrophages are liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs). Previously, it has been reported that PPARγ expression is decreased in peripheral blood mononuclear cells of MS patients. The goal of the present study was to determine to what extent PPARγ, as well as the closely related nuclear receptors PPARα and β and LXRα and β, are differentially expressed in monocytes from MS patients and how this change in expression affects the function of monocyte-derived macrophages. We demonstrate that monocytes of relapsing-remitting MS patients display a marked decrease in PPARγ expression, while the expression of PPARα and LXRα/β is not altered. Interestingly, exposure of monocyte-derived macrophages from healthy donors to MS-associated proinflammatory cytokines mimicked this reduction in PPARγ expression. While a reduced PPARγ expression did not affect the inflammatory and phagocytic properties of myelin-loaded macrophages, it did impact myelin processing by increasing the intracellular cholesterol load of myelin-phagocytosing macrophages. Collectively, our findings indicate that an inflammation-induced reduction in PPARγ expression promotes myelin-induced foam cell formation in macrophages in MS.

Pomegranate peel polyphenols inhibit lipid accumulation and enhance cholesterol efflux in raw264.7 macrophages

2016 ◽  
Vol 7 (7) ◽  
pp. 3201-3210 ◽  
Author(s):  
Shengjuan Zhao ◽  
Jianke Li ◽  
Lifang Wang ◽  
Xiaoxia Wu
Keyword(s):  
Lipid Accumulation ◽  
Cholesterol Efflux ◽  
Foam Cell ◽  
Cell Formation ◽  
Foam Cell Formation ◽  
Pomegranate Peel ◽  
Raw264.7 Macrophages

Pomegranate peel polyphenols hindered ox-LDL-induced raw264.7 foam cell formation, by decreasing CD36 and promoting ABCA1 and LXRα expression.

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