Phytosterols differentially influence ABC transporter expression, cholesterol efflux and inflammatory cytokine secretion in macrophage foam cells

Phytosterol supplements lower low-density lipoprotein (LDL) cholesterol, but accumulate in vascular lesions of patients and limit the anti-atherosclerotic effects of LDL lowering in apolipoprotein E (Apo E)-deficient mice, suggesting that the cholesterol-lowering benefit of phytosterol supplementation may not be fully realized. Individual phytosterols have cell-type specific effects that may be either beneficial or deleterious with respect to atherosclerosis, but little is known concerning their effects on macrophage function. The effects of phytosterols on ABCA1 and ABCG1 abundance, cholesterol efflux and inflammatory cytokine secretion were determined in cultured macrophage foam cells. Among the commonly consumed phytosterols, stigmasterol increased expression of ABCA1 and ABCG1 and increased efflux of cholesterol to apolipoprotein (Apo) AI and high-density lipoprotein (HDL). Campesterol and sitosterol had no effect on ABCA1 or ABCG1 levels. Sitosterol had no effect on cholesterol efflux to Apo AI or HDL, whereas campesterol had a modest but significant reduction in cholesterol efflux to HDL in THP-1 macrophages. Whereas stigmasterol blunted aggregated LDL (agLDL) induced increases in tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β secretion, sitosterol exacerbated these effects. The presence of campesterol had no effect on agLDL-induced inflammatory cytokine secretion from THP-1 macrophages. In conclusion, the presence of stigmasterol in modified lipoproteins promoted cholesterol efflux and suppressed inflammatory cytokine secretion in response to lipid loading in macrophage foam cells. While campesterol was largely inert, the presence of sitosterol increased the proinflammatory cytokine secretion.     

PLK1 promotes cholesterol efflux and alleviates atherosclerosis by up-regulating ABCA1 and ABCG1 expression via the AMPK/PPARγ/LXRα pathway

Polo-like kinase 1 (PLK1) is a serine/threonine kinase involving lipid metabolism and cardiovascular disease. However, its role in atherogenesis has yet to be determined. The aim of this study was to observe the impact of PLK1 on macrophage lipid accumulation and atherosclerosis development and to explore the underlying mechanisms. We found a significant reduction of PLK1 expression in lipid-loaded macrophages and atherosclerosis model mice. Lentivirus-mediated overexpression of PLK1 promoted cholesterol efflux and inhibited lipid accumulation in THP-1 macrophage-derived foam cells. Mechanistic analysis revealed that PLK1 stimulated the phosphorylation of AMP-activated protein kinase (AMPK), leading to activation of the peroxisome proliferator-activated receptor γ (PPARγ)/liver X receptor α (LXRα) pathway and up-regulation of ATP binding cassette transporter A1 (ABCA1) and ABCG1 expression. Injection of lentiviral vector expressing PLK1 increased reverse cholesterol transport, improved plasma lipid profiles and decreased atherosclerotic lesion area in apoE-deficient mice fed a Western diet. PLK1 overexpression also facilitated AMPK and HSL phosphorylation and enhanced the expression of PPARγ, LXRα, ABCA1, ABCG1 and LPL in the aorta. In summary, these data suggest that PLK1 inhibits macrophage lipid accumulation and mitigates atherosclerosis by promoting ABCA1- and ABCG1-dependent cholesterol efflux via the AMPK/PPARγ/LXRα pathway.     

Arctigenin promotes cholesterol efflux from THP-1 macrophages through PPAR-γ/LXR-α signaling pathway

Cholesterol efflux from macrophages is a critical mechanism to prevent the development of atherosclerosis. Here, we sought to investigate the effects of arctigenin, a bioactive component of Arctium lappa, on the cholesterol efflux in oxidized low-density lipoprotein (oxLDL)-loaded THP-1 macrophages. Our data showed that arctigenin significantly accelerated apolipoprotein A-I- and high-density lipoprotein-induced cholesterol efflux in both dose- and time-dependent manners. Moreover, arctigenin treatment enhanced the expression of ATP binding cassette transporter A1 (ABCA1), ABCG1, and apoE, all of which are key molecules in the initial step of cholesterol efflux, at both mRNA and protein levels. Arctigenin also caused a concentration-dependent elevation in the expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ) and liver X receptor-alpha (LXR-α). The arctigenin-mediated induction of ABCA1, ABCG1, and apoE was abolished by specific inhibition of PPAR-γ or LXR-α using small interfering RNA technology. Our results collectively indicate that arctigenin promotes cholesterol efflux in oxLDL-loaded THP-1 macrophages through upregulation of ABCA1, ABCG1 and apoE, which is dependent on the enhanced expression of PPAR-γ and LXR-α.     

Genetic deletion of low density lipoprotein receptor impairs sterol-induced mouse macrophage ABCA1 expression. A new SREBP1-dependent mechanism

Low density lipoprotein receptor (LDLR) mutations cause familial hypercholesterolemia and early atherosclerosis. ABCA1 facilitates free cholesterol efflux from peripheral tissues. We investigated the effects of LDLR deletion (LDLR(-/-)) on ABCA1 expression. LDLR(-/-) macrophages had reduced basal levels of ABCA1, ABCG1, and cholesterol efflux. A high fat diet increased cholesterol in LDLR(-/-) macrophages but not wild type cells. A liver X receptor (LXR) agonist induced expression of ABCA1, ABCG1, and cholesterol efflux in both LDLR(-/-) and wild type macrophages, whereas expression of LXRalpha or LXRbeta was similar. Interestingly, oxidized LDL induced more ABCA1 in wild type macrophages than LDLR(-/-) cells. LDL induced ABCA1 expression in wild type cells but inhibited it in LDLR(-/-) macrophages in a concentration-dependent manner. However, lipoproteins regulated ABCG1 expression similarly in LDLR(-/-) and wild type macrophages. Cholesterol or oxysterols induced ABCA1 expression in wild type macrophages but had little or inhibitory effects on ABCA1 expression in LDLR(-/-) macrophages. Active sterol regulatory element-binding protein 1a (SREBP1a) inhibited ABCA1 promoter activity in an LXRE-dependent manner and decreased both macrophage ABCA1 expression and cholesterol efflux. Expression of ABCA1 in animal tissues was inversely correlated to active SREBP1. Oxysterols inactivated SREBP1 in wild type macrophages but not in LDLR(-/-) cells. Oxysterol synergized with nonsteroid LXR ligand induced ABCA1 expression in wild type macrophages but blocked induction in LDLR(-/-) cells. Taken together, our studies suggest that LDLR is critical in the regulation of cholesterol efflux and ABCA1 expression in macrophage. Lack of the LDLR impairs sterol-induced macrophage ABCA1 expression by a sterol regulatory element-binding protein 1-dependent mechanism that can result in reduced cholesterol efflux and lipid accumulation in macrophages under hypercholesterolemic conditions.     

Urotensin II increases foam cell formation by repressing ABCA1 expression through the ERK/NF-κB pathway in THP-1 macrophages

Objective

Foam cell formation in the arterial wall plays a key role in the development of atherosclerosis. Recent studies showed that Urotensin II (U II) is involved in the pathogenesis of atherosclerosis. Here we examined the effects of human U II on ATP-binding cassette transporter A1 (ABCA1) expression and the underlying mechanism in THP-1 macrophages.

Methods and results

Cultured THP-1 macrophages were treated with U II, followed by measuring the intracellular lipid contents, cholesterol efflux and ABCA1 levels. The results showed that U II dramatically decreased ABCA1 levels and impaired cholesterol efflux. However, the effects of U II on ABCA1 protein expression and cellular cholesterol efflux were partially reversed by inhibition of extracellular signal regulated kinase 1/2 (ERK1/2) and nuclear factor kappa B (NF-κB) activity, suggesting the potential roles of ERK1/2 and NF-κB in ABCA1 expression, respectively.

Conclusion

Our current data indicate that U II may have promoting effects on the progression of atherosclerosis, likely through suppressing ABCA1 expression via activation of the ERK/NF-κB pathway and reducing cholesterol efflux to promote macrophage foam cell formation.     

Effects of miR-33a-5P on ABCA1/G1-Mediated Cholesterol Efflux under Inflammatory Stress in THP-1 Macrophages

The present study is to investigate whether inflammatory cytokines inhibit ABCA1/ABCG1-mediated cholesterol efflux by regulating miR-33a-5P in THP-1 macrophages. We used interleukin-6 and tumor necrosis factor-alpha in the presence or absence of native low density lipoprotein (LDL) to stimulate THP-1 macrophages. THP-1 macrophages were infected by either control lentivirus vectors or lentivirus encoding miR-33a-5P or antisense miR-33a-5P. The effects of inflammatory cytokines, miR-33a-5P and antisense miR-33a-5P on intracellular lipids accumulation and intracellular cholesterol contents were assessed by oil red O staining and quantitative intracellular cholesterol assay. ApoA-I-mediated cholesterol efflux was examined using the fluorescent sterol (BODIPY-cholesterol). The gene and protein expressions of the molecules involved in cholesterol trafficking were examined using quantitative real-time polymerase chain reaction and Western blotting. Inflammatory cytokines or miR-33a-5P increased intracellular lipid accumulation and decreased apoA-I-mediated cholesterol efflux via decreasing the expression of ABCA1 and ABCG1 in the absence or presence of LDL in THP-1 macrophages. However, antisense miR-33a-5P reversed the effects of inflammatory cytokines on intracellular lipid accumulation, cholesterol efflux, and the expression of miR-33a-5P, ABCA1 and ABCG1 in the absence or presence of LDL in THP-1 macrophages. This study indicated that inflammatory cytokines inhibited ABCA1/ABCG1-mediated cholesterol efflux by up-regulating miR-33a-5P in THP-1 macrophages.     

Lysophosphatidylcholine promotes cholesterol efflux from mouse macrophage foam cells via PPARgamma-LXRalpha-ABCA1-dependent pathway associated with apoE

Formation of macrophage-derived foam cells is a hallmark in earlier stages of atherosclerosis (AS). Increased cholesterol efflux from macrophage foam cells promote atherosclerotic regression. In the present study, lysophosphatidylcholine (LPC) promoting cholesterol efflux from macrophage foam cells was observed, and the mechanism underlying the action was investigated. Macrophage foam cells from mice were incubated with different concentrations of LPC (10, 20, 40, 80 microM), and the free cholesterol in medium increased but total intracellular cholesterol decreased. At the same time, the expression of PPARgamma, LXRalpha, ABCA1 was enhanced in a dose-dependent manner. The treatment of macrophage foam cells with 40 microM LPC for 12, 24 and 48 h promoted cellular cholesterol efflux in a time-dependent manner, meanwhile expression of PPARgamma, LXRalpha, ABCA1 was also raised respectively. Addition of different specific inhibitors of PPARgamma (GW9662), LXRalpha (GGPP), ABCA1 (DIDS) to the foam cells significantly suppressed LPC-induced cholesterol efflux. Also treatment with specific inhibitors of PPARgamma or LXRalpha decreased ABCA1 mRNA and protein expressions. LPC (40 microM)-induced cholesterol efflux was significantly lower in macrophage foam cells from apoE deficient mice than from normal C57BL/6J mice. In contrast, 10 microg apoAI-induced cholesterol efflux from foam cells remained in apoE deficient mice. The present results indicate that LPC promotes cholesterol efflux from macrophage foam cells via a PPARgamma-LXRalpha-ABCA1-dependent pathway. Furthermore, apoE may be involved in this process.     

Regulation of macrophage cholesterol efflux through hydroxymethylglutaryl-CoA reductase inhibition: a role for RhoA in ABCA1-mediated cholesterol efflux

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 microm) stimulated cholesterol efflux to apolipoprotein AI (apoAI, 10-60%, p < 0.05) and high density lipoprotein (HDL(3)) (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 gamma 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 gamma 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.     

α-Lipoic acid ameliorates foam cell formation via liver X receptor α-dependent upregulation of ATP-binding cassette transporters A1 and G1

α-Lipoic acid (α-LA), a key cofactor in cellular energy metabolism, has protective activities in atherosclerosis, yet the detailed mechanisms are not fully understood. In this study, we examined whether α-LA affects foam cell formation and its underlying molecular mechanisms in murine macrophages. Treatment with α-LA markedly attenuated oxidized low-density lipoprotein (oxLDL)-mediated cholesterol accumulation in macrophages, which was due to increased cholesterol efflux. Additionally, α-LA treatment dose-dependently increased protein levels of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 but had no effect on the protein expression of SR-A, CD36, or SR-BI involved in cholesterol homeostasis. Furthermore, α-LA increased the mRNA expression of ABCA1 and ABCG1. The upregulation of ABCA1 and ABCG1 by α-LA depended on liver X receptor α (LXRα), as evidenced by an increase in the nuclear levels of LXRα and LXRE-mediated luciferase activity and its prevention of the expression of ABCA1 and ABCG1 after inhibition of LXRα activity by the pharmacological inhibitor geranylgeranyl pyrophosphate (GGPP) or knockdown of LXRα expression with small interfering RNA (siRNA). Consistently, α-LA-mediated suppression of oxLDL-induced lipid accumulation was abolished by GGPP or LXRα siRNA treatment. In conclusion, LXRα-dependent upregulation of ABCA1 and ABCG1 may mediate the beneficial effect of α-LA on foam cell formation.     

SR-BI inhibits ABCG1-stimulated net cholesterol efflux from cells to plasma HDL

This study compares the roles of ABCG1 and scavenger receptor class B type I (SR-BI) singly or together in promoting net cellular cholesterol efflux to plasma HDL containing active LCAT. In transfected cells, SR-BI promoted free cholesterol efflux to HDL, but this was offset by an increased uptake of HDL cholesteryl ester (CE) into cells, resulting in no net efflux. Coexpression of SR-BI with ABCG1 inhibited the ABCG1-mediated net cholesterol efflux to HDL, apparently by promoting the reuptake of CE from medium. However, ABCG1-mediated cholesterol efflux was not altered in cholesterol-loaded, SR-BI-deficient (SR-BI(-/-)) macrophages. Briefly cultured macrophages collected from SR-BI(-/-) mice loaded with acetylated LDL in the peritoneal cavity did exhibit reduced efflux to HDL. However, this was attributable to reduced expression of ABCG1 and ABCA1, likely reflecting increased macrophage cholesterol efflux to apolipoprotein E-enriched HDL during loading in SR-BI(-/-) mice. In conclusion, cellular SR-BI does not promote net cholesterol efflux from cells to plasma HDL containing active LCAT as a result of the reuptake of HDL-CE into cells. Previous findings of increased atherosclerosis in mice transplanted with SR-BI(-/-) bone marrow probably cannot be explained by a defect in macrophage cholesterol efflux.     

LXR-Mediated ABCA1 Expression and Function Are Modulated by High Glucose and PRMT2

High cholesterol and diabetes are major risk factors for atherosclerosis. Regression of atherosclerosis is mediated in part by the Liver X Receptor (LXR) through the induction of genes involved in cholesterol transport and efflux. In the context of diabetes, regression of atherosclerosis is impaired. We proposed that changes in glucose levels modulate LXR-dependent gene expression. Using a mouse macrophage cell line (RAW 264.7) and primary bone marrow derived macrophages (BMDMs) cultured in normal or diabetes relevant high glucose conditions we found that high glucose inhibits the LXR-dependent expression of ATP-binding cassette transporter A1 (ABCA1), but not ABCG1. To probe for this mechanism, we surveyed the expression of a host of chromatin-modifying enzymes and found that Protein Arginine Methyltransferase 2 (PRMT2) was reduced in high compared to normal glucose conditions. Importantly, ABCA1 expression and ABCA1-mediated cholesterol efflux were reduced in Prmt2 ^-/- compared to wild type BMDMs. Monocytes from diabetic mice also showed decreased expression of Prmt2 compared to non-diabetic counterparts. Thus, PRMT2 represents a glucose-sensitive factor that plays a role in LXR-mediated ABCA1-dependent cholesterol efflux and lends insight to the presence of increased atherosclerosis in diabetic patients.     

Effect of apolipoprotein A-I on ATP binding cassette transporter A1 degradation and cholesterol efflux in THP-1 macrophage-derived foam cells

The accumulation of lipoprotein cholesterol in theartery wall is thought to be an important factor in thedevelopment of atherosclerosis. After retentionand modi-fication in arteries, atherogenic lipoproteins are taken upby macrophages, bringing about macrophage-derived foamcells. High-density lipoprotein (HDL) plays a role in trans-porting cholesterol from peripheral tissues to the liver.The elevated level of HDL is associated with a decreasein atherosclerosis and the apolipoproteins to remo…     

Regulation of cholesterol homeostasis in macrophages and consequences for atherosclerotic lesion development

Foam cell formation due to excessive accumulation of cholesterol by macrophages is a pathological hallmark of atherosclerosis. Macrophages cannot limit the uptake of cholesterol and therefore depend on cholesterol efflux pathways for preventing their transformation into foam cells. Several ABC-transporters, including ABCA1 and ABCG1, facilitate the efflux of cholesterol from macrophages. These transporters, however, also affect membrane lipid asymmetry which may have important implications for cellular endocytotic pathways. We propose that in addition to the generally accepted role of these ABC-transporters in the prevention of foam cell formation by induction of cholesterol efflux from macrophages, they also influence the macrophage endocytotic uptake.     

Inhibition of ERK1/2 and Activation of Liver X Receptor Synergistically Induce Macrophage ABCA1 Expression and Cholesterol Efflux

ATP-binding cassette transporter A1 (ABCA1), a molecule mediating free cholesterol efflux from peripheral tissues to apoAI and high density lipoprotein (HDL), inhibits the formation of lipid-laden macrophage/foam cells and the development of atherosclerosis. ERK1/2 are important signaling molecules regulating cellular growth and differentiation. The ERK1/2 signaling pathway is implicated in cardiac development and hypertrophy. However, the role of ERK1/2 in the development of atherosclerosis, particularly in macrophage cholesterol homeostasis, is unknown. In this study, we investigated the effects of ERK1/2 activity on macrophage ABCA1 expression and cholesterol efflux. Compared with a minor effect by inhibition of other kinases, inhibition of ERK1/2 significantly increased macrophage cholesterol efflux to apoAI and HDL. In contrast, activation of ERK1/2 reduced macrophage cholesterol efflux and ABCA1 expression. The increased cholesterol efflux by ERK1/2 inhibitors was associated with the increased ABCA1 levels and the binding of apoAI to cells. The increased ABCA1 by ERK1/2 inhibitors was due to increased ABCA1 mRNA and protein stability. The induction of ABCA1 expression and cholesterol efflux by ERK1/2 inhibitors was concentration-dependent. The mechanism study indicated that activation of liver X receptor (LXR) had little effect on ERK1/2 expression and activation. ERK1/2 inhibitors had no effect on macrophage LXRα/β expression, whereas they did not influence the activation or the inhibition of the ABCA1 promoter by LXR or sterol regulatory element-binding protein (SREBP). However, inhibition of ERK1/2 and activation of LXR synergistically induced macrophage cholesterol efflux and ABCA1 expression. Our data suggest that ERK1/2 activity can play an important role in macrophage cholesterol trafficking.     

Robust passive and active efflux of cellular cholesterol to a designer functional mimic of high density lipoprotein

The ability of HDL to support macrophage cholesterol efflux is an integral part of its atheroprotective action. Augmenting this ability, especially when HDL cholesterol efflux capacity from macrophages is poor, represents a promising therapeutic strategy. One approach to enhancing macrophage cholesterol efflux is infusing blood with HDL mimics. Previously, we reported the synthesis of a functional mimic of HDL (fmHDL) that consists of a gold nanoparticle template, a phospholipid bilayer, and apo A-I. In this work, we characterize the ability of fmHDL to support the well-established pathways of cellular cholesterol efflux from model cell lines and primary macrophages. fmHDL received cell cholesterol by unmediated (aqueous) and ABCG1- and scavenger receptor class B type I (SR-BI)-mediated diffusion. Furthermore, the fmHDL holoparticle accepted cholesterol and phospholipid by the ABCA1 pathway. These results demonstrate that fmHDL supports all the cholesterol efflux pathways available to native HDL and thus, represents a promising infusible therapeutic for enhancing macrophage cholesterol efflux. fmHDL accepts cholesterol from cells by all known pathways of cholesterol efflux: unmediated, ABCG1- and SR-BI-mediated diffusion, and through ABCA1.     

Caveolin-1 interacts with ATP binding cassette transporter G1 (ABCG1) and regulates ABCG1-mediated cholesterol efflux

ATP-binding cassette transporter G1 (ABCG1) plays an important role in macrophage reverse cholesterol transport in vivo by promoting cholesterol efflux onto lipidated apoA-I. However, the underlying mechanism is unclear. Here, we found that ABCG1 co-immunoprecipitated with caveolin-1 (CAV1) but not with flotillin-1 and -2. Knockdown of CAV1 expression using siRNAs significantly reduced ABCG1-mediated cholesterol efflux without detectable effect on ABCA1-mediated cholesterol efflux. Disruption of the putative CAV1 binding site in ABCG1, through replacement of tyrosine residues at positions 487 and 489 or at positions 494 and 495 with alanine (Y487AY489A and Y494AY495A), impaired the interaction of ABCG1 with CAV1 and significantly decreased ABCG1-mediated cholesterol efflux. The substitution of Tyr494 and Tyr495 with Phe or Trp that resulted in an intact CAV1 binding site had no effect. Furthermore, Y494AY495A affected trafficking of ABCG1 to the cell surface. The mutant protein is mainly located intracellularly. Finally, we found that CAV1 co-immunoprecipitated with ABCG1 and regulated cholesterol efflux to reconstituted HDL in THP-1-derived macrophages upon the liver X receptor agonist treatment. These findings indicate that CAV1 interacts with ABCG1 and regulates ABCG1-mediated cholesterol efflux.     

Neopterin negatively regulates expression of ABCA1 and ABCG1 by the LXRα signaling pathway in THP-1 macrophage-derived foam cells

To investigate the effects of neopterin on ABCA1 expression and cholesterol efflux in human THP-1 macrophage-derived foam cells, and to explore the role of the liver X receptor alpha (LXRα) involved. In the present study, THP-1 cells were pre-incubated with ox-LDL to become foam cells. The protein and mRNA expression were examined by Western blot assays and real-time quantitative PCR, respectively. Liquid scintillation counting and high performance liquid chromatography assays were used to test cellular cholesterol efflux and cholesterol content. Neopterin decreased ABCA1 expression and cholesterol efflux in a time- and concentration-dependent manner in THP-1 macrophage-derived foam cells, and the LXRα siRNA can reverse the inhibitory effects induced by neopterin. Neoterin has a negative regulation on ABCA1 expression via the LXRα signaling pathway, which suggests the aggravated effects of neopterin on atherosclerosis.     

Inhibition of the NLRP3 inflammasome attenuates foam cell formation of THP-1 macrophages by suppressing ox-LDL uptake and promoting cholesterol efflux

The NOD-like receptor family, pyrin domain–containing protein 3 (NLRP3) inflammasome plays an important role in the development of atherosclerosis. The activated NLRP3 inflammasome has been reported to promote macrophage foam cell formation, but not all studies have obtained the same result, and how NLRP3 inflammasome is involved in the formation of foam cells remains elusive. We used selective NLRP3 inflammasome inhibitors and NLRP3-deficient THP-1 cells to assess the effect of NLRP3 inflammasome inhibition on macrophage foam cell formation, oxidized low-density lipoprotein (ox-LDL) uptake, esterification, and cholesterol efflux, as well as the expression of associated proteins. Inhibition of the NLRP3 inflammasome attenuated foam cell formation, diminished ox-LDL uptake, and promoted cholesterol efflux from THP-1 macrophages. Moreover, it downregulated CD36, acyl coenzyme A: cholesterol acyltransferase-1 and neutral cholesterol ester hydrolase expression; upregulated ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI) expression; but had no effect on the expression of scavenger receptor class A and ATP-binding cassette transporter G1. Collectively, our findings show that inhibition of the NLRP3 inflammasome decreases foam cell formation of THP-1 macrophages via suppression of ox-LDL uptake and enhancement of cholesterol efflux, which may be due to downregulation of CD36 expression and upregulation of ABCA1 and SR-BI expression, respectively.