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The dysregulation of cholesterol metabolism is a high-risk factor for non-alcoholic fatty liver disease (NAFLD), dyslipidemia, and atherosclerosis (AS). Cholesterol transport maintains whole-body cholesterol homeostasis. Low-density apolipoprotein receptor (LDLR) mediates cholesterol uptake in cells and plays an important role in the primary route of circulatory cholesterol clearance in liver cells. Caveolins 1 is an integral membrane protein and shuttle between the cytoplasm and cell membrane. Caveolins 1 not only plays a role in promoting cholesterol absorption in cells but also in the transport of cellular cholesterol efflux by interacting with the ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI). These proteins, which are associated with reverse cholesterol transport (RCT), are potential therapeutic targets for NAFLD and AS. Many studies have indicated that natural products have lipid-lowering effects. Moreover, natural molecules, derived from natural products, have the potential to be developed into novel drugs. However, the mechanisms underlying the regulation of cholesterol transport by natural molecules have not yet been adequately investigated. In this review, we briefly describe the process of cholesterol transport and summarize the mechanisms by which molecules regulate cholesterol transport. This article provides an overview of recent studies and focuses on the potential therapeutic effects of natural molecules; however, further high-quality studies are needed to firmly establish the clinical efficacies of natural molecules.

Accumulation of cholesterol‐laden macrophage foam cells characteristic of early stage atherosclerotic lesions. Phenethyl isothiocyanate (PEITC) is a naturally occurring isothiocyanate found in cruciferous vegetables that has reported a variety of activities including antioxidant and anti‐inflammatory properties. However, the protective effect of PEITC on foam cell formation and its precise mechanism is not yet clear. Therefore, we investigated whether PEITC suppresses foam cell formation and regulates the expression of genes related to lipid accumulation, cholesterol efflux, and inflammation in THP‐1 derived‐macrophages. We exposed THP‐1 derived‐macrophages to oxidized low‐density lipoprotein (ox‐LDL) (20 μg/mL) and lipopolysaccharide (LPS) (500 ng/ml) to mimic foam cell formation. Here, PEITC downregulated the expression of lectin‐like oxidized low‐density lipoprotein receptor‐1 (LOX‐1), cluster of differentiation 36 (CD36), scavenger receptor A1 (SR‐A1), and nuclear factor‐κB (NF‐κB), while upregulated ATP binding cassette subfamily A member 1 (ABCA1)/liver‐X‐receptor α (LXR‐α)/peroxisome proliferator‐activated receptor gamma (PPARγ) and sirtuin 1 (SIRT1) expression compared to co‐treated with ox‐LDL and LPS. Taken together, PEITC, at least in part, inhibits foam cell formation and reduces lipid accumulation in foam cells. Therefore, we suggest that PEITC may be a potential candidate for the treatment and prevention of vascular inflammation and atherosclerosis., PEITC control foam cell formation by promoting cholesterol efflux, reducing lipid accumulation, and modulating the SIRT1‐NF‐κB signaling pathway.

Background Sulfoxaflor is a new insecticide for controlling against Aphis gossypii in the field. ATP-binding cassette (ABC) transporters belong to a large superfamily of proteins and play an important role in the detoxification process. However, the potential role of ABC transporters in sulfoxaflor resistance in A. gossypii is unknown. Results In this study, an ABC transporter inhibitor, verapamil, dramatically increased the toxicity of sulfoxaflor in the resistant population with a synergistic ratio of 8.55. However, verapamil did not synergize sulfoxaflor toxicity in the susceptible population. The contents of ABC transporters were significantly increased in the Sul-R population. Based on RT-qPCR analysis, 10 of 23 ABC transcripts, ABCA1, ABCA2, ABCB1, ABCB5, ABCD1, ABCG7, ABCG16, ABCG26, ABCG27, and MRP7, were up-regulated in the Sul-R population compared to the Sus population. Meanwhile, inductive effects of ABCA1, ABCD1, ABCG7 and ABCG26 by sulfoxaflor were found in A. gossypii. Furthermore, knockdown of ABCA1 and ABCD1 using RNAi significantly increased the sulfoxaflor sensitivity in Sul-R aphids. Conclusion These results suggested that ABC transporters, especially the ABCA1 and ABCD1 genes, might be related with sulfoxaflor resistance in A. gossypii. This study will promote further work to validate the functional roles of these ABCs in sulfoxaflor resistance and might be helpful for the management of sulfoxaflor-resistant A. gossypii.

MicroRNA-328 (miR-328) was reported to protect against atherosclerosis, but its role in foam cell formation remains unknown. The aim of this study was to investigate the effect of miR-328-5p on macrophage lipid accumulation and the underlying mechanisms. The results showed that miR-328-5p expression was robustly decreased in oxidized low-density lipoprotein (ox-LDL)-treated macrophages. Treatment of human acute monocytic leukemia cel (THP-1) macrophage-derived foam cells with a miR-328-5p mimic markedly increased [3 H]-cholesterol efflux, inhibited lipid droplet accumulation, and decreased intracellular total cholesterol (TC), free cholesterol (FC) and cholesteryl ester (CE) contents. Upregulation of miR-328-5p also reduced the expression of histone deacetylase 3 (HDAC3) but increased the levels of ATP-binding cassette transporter A1 (ABCA1) in THP-1 macrophage-derived foam cells. Mechanistically, miR-328-5p inhibited HDAC3 expression by directly targeting its 3'UTR, thereby promoting ABCA1 expression and the subsequent cholesterol efflux. Furthermore, miR-328-5p mimic treatment did not affect the uptake of Dil-ox-LDL or the expression of scavenger receptor-A (SR-A), thrombospondin receptor (CD36) and ABCG1. Taken together, these findings suggest that miR-328-5p alleviates macrophage lipid accumulation through the HDAC3/ABCA1 pathway.

Atherosclerosis is a chronic inflammatory disease with high mortality worldwide. The reverse cholesterol transport pathway in macrophage plays an important role in the pathogenesis of coronary artery disease (CAD) and is strongly controlled by regulatory factors. The microRNAs can promote or prevent the formation of atherosclerotic lesions by post-transcriptional regulation of vital genes in this pathway. Therefore, this study was conducted to investigate the relationship between the expression levels of miR-27a, miR-329, ABCA1, and ABCG1 genes and serum levels of hs-CRP, ox-LDL, and indices of oxidative stress in the patients with established CAD and controls. A total of 84 subjects (42 patients with CAD and 42 controls) were included in this study. Expression levels of miR-27a-3p, miR-329-3p, ABCA1, and ABCG1 genes in the peripheral blood mononuclear cells (PBMCs) and serum concentration of hs-CRP and ox-LDL were measured by real time-PCR and ELISA, respectively. Also, oxidative stress parameters in the serum were evaluated by ferric-reducing antioxidant power (FRAP) and malondialdehyde (MDA) assays. ABCA1 and ABCG1 gene expression in PBMC and serum concentration of FRAP were significantly lower in the CAD group compared to the control group. Expression levels of miR-27a and miR-329 and serum levels of hs-CRP, ox-LDL, and MDA were significantly higher in the CAD group compared to the control group. Serum levels of hs-CRP, ox-LDL, and expression level of miR-27a have inversely related to ABCA1 and ABCG1 gene expression in all the subjects. An increase in the expression levels of miR-27a and miR-329 may lead to the progression of atherosclerosis plaque by downregulating the expression of ABCA1 and ABCG1 genes.

Apolipoprotein (apo) A-I, the major structural protein of high-density lipoprotein (HDL), is present in human and mouse cerebrospinal fluid (CSF) despite its lack of expression in brain cells. To identify the origin of apoA-I in CSF, we generated intestine-specific and liver-specific Apoa1 knockout mice (Apoa1(ΔInt) and Apoa1(Δliv) mice, respectively). Lipoprotein profiles of Apoa1(ΔInt) and Apoa1(ΔLiv) mice resembled those of control littermates, whereas knockout of Apoa1 in both intestine and liver (Apoa1(ΔIntΔLiv)) resulted in a 60-percent decrease in HDL-cholesterol levels, thus strongly mimicking the Apoa1(−/−) mice. Immunoassays revealed that mouse apoA-I was not present in the CSF of the Apoa1(ΔIntΔLiv) mice. Furthermore, apoA-I levels in CSF were highly correlated with plasma spherical HDL levels, which were regulated by ABCA1 and LCAT. Collectively, these results suggest that apoA-I protein in CSF originates in liver and small intestine and is taken up from the plasma.

Evidences indicate that the decline of female fertility is becoming a common problem over the past few decades. Environmental exposure of Bisphenol A (BPA) has been considered as an endocrine-disrupting chemical deleteriously affecting human reproductions. To better understand the effect of BPA exposure on human ovarian granulosa cells, we treated human ovarian granulosa cell line (KGN) with increasing concentrations (0.1, 1, 10, and 100 μM) of BPA for 24 hr. About 0.1, 1, and 10 μM BPA did not significantly affect the viability of KGN while 100 μM of BPA caused a statistically significant decrease in the viability of KGN. Treatment KGN with 10 μM BPA resulted in a significant decrease in progesterone biosynthesis. The treatment also significantly increased the expression of ATP binding cassette subfamily A member 1 (ABCA1) and steroidogenic acute regulatory protein (STAR). In the current study, exposure to BPA could lead to decreased progesterone production probably through the upregulation of ABCA1 in human granulosa cells.

Malaria in pregnancy (MiP) induces intrauterine growth restriction (IUGR) and preterm labour (PTL). However, its effects on yolk sac morphology and function are largely unexplored. We hypothesized that MiP modifies yolk sac morphology and efflux transport potential by modulating ABC efflux transporters. C57BL/6 mice injected with Plasmodium berghei ANKA (5 × 105 infected erythrocytes) at gestational day (GD) 13.5 were subjected to yolk sac membrane harvesting at GD 18.5 for histology, qPCR and immunohistochemistry. MiP did not alter the volumetric proportion of the yolk sac's histological components. However, it increased levels of Abcb1a mRNA (encoding P‐glycoprotein) and macrophage migration inhibitory factor (Mif chemokine), while decreasing Abcg1 (P

Remyelination is a regenerative process that is essential to recover saltatory conduction and to prevent neurodegeneration upon demyelination. The formation of new myelin involves the differentiation of oligodendrocyte progenitor cells (OPCs) toward oligodendrocytes and requires high amounts of cholesterol. Astrocytes (ASTRs) modulate remyelination by supplying lipids to oligodendrocytes. Remarkably, remyelination is more efficient in grey matter (GM) than in white matter (WM), which may relate to regional differences in ASTR subtype. Here, we show that a feeding layer of gmASTRs was more supportive to in vitro myelination than a feeding layer of wmASTRs. While conditioned medium from both gmASTRs and wmASTRs accelerated gmOPC differentiation, wmOPC differentiation is enhanced by secreted factors from gmASTRs, but not wmASTRs. In vitro analyses revealed that gmASTRs secreted more cholesterol than wmASTRs. Cholesterol efflux from both ASTR types was reduced upon exposure to pro‐inflammatory cytokines, which was mediated via cholesterol transporter ABCA1, but not ABCG1, and correlated with a minor reduction of myelin membrane formation by oligodendrocytes. Surprisingly, a wmASTR knockdown of Fdft1 encoding for squalene synthase (SQS), an enzyme essential for the first committed step in cholesterol biosynthesis, enhanced in vitro myelination. Reduced secretion of interleukin‐1β likely by enhanced isoprenylation, and increased unsaturated fatty acid synthesis, both pathways upstream of SQS, likely masked the effect of reduced levels of ASTR‐derived cholesterol. Hence, our findings indicate that gmASTRs export more cholesterol and are more supportive to myelination than wmASTRs, but specific inhibition of cholesterol biosynthesis in ASTRs is beneficial for wmASTR‐mediated modulation of myelination., Our findings revealed that regional differences in astrocytes (ASTRs) may contribute to the more efficient remyelination in grey matter (GM) than in white matter (WM). GmASTRs secrete more cholesterol (1) and are more supportive for in vitro myelination than wmASTRs. Surprisingly, impairing committed cholesterol biosynthesis in wmASTRs but not in gmASTRs increases in vitro myelination (2). The effect of decreased cholesterol levels is likely masked by enhanced synthesis of unsaturated fatty acid (3) and non‐sterol isoprenoids, the latter resulting in reduced secretion of ASTR‐derived cytokines, such as interleukin‐1β, that affect oligodendrocyte maturation (4). This may open new ASTR‐based therapeutic strategies aimed at promoting remyelination in multiple sclerosis lesions.

ATP-binding cassette transporter A1 (ABCA1) has a crucial role in removing intracellular cholesterol and plays a protective role against atherosclerosis. Therefore, genetic polymorphisms in this gene may alter the susceptibility to coronary artery disease (CAD). This study was aimed to examine the association of rs2230806 (c.1051 G > A; p.R219K) variation in the ABCA1 gene with CAD in a case-control design which was followed by a meta-analysis and in silico approach. In the case-control study, 300 subjects including 150 individuals with CAD and 150 healthy controls were recruited. The c.1051 G > A genotyping was done by polymerase chain reaction-restriction fragment length polymorphism method. In the meta-analysis, eligible studies were collected from PubMed, Google Scholar, and ScienceDirect databases and pooled odds ratio, heterogeneity, publication bias, and sensitivity analyses were carried. Finally, some bioinformatics tools were employed to assess the impacts of p.R219K variation on ABCA1 protein structure. Our case-control examination showed a statistically significant association between c.1051 G > A genetic polymorphism and CAD risk. In addition, the meta-analysis showed reliable significant associations between c.1051 G > A transition and risk of CAD in the Caucasian population. In silico analysis showed that the p.R219K substitution could alter the secondary structure, hydrophobicity pattern, and Ramachandran plot of ABCA1. These findings elucidate that the c.1051 G > A variation could be a genetic risk factor for CAD and it could be considered as a prognostic and predictive biomarker for susceptible individuals.

Huntington's disease is an autosomal-dominant, neurodegenerative disorder caused by a CAG repeat expansion in exon-1 of the huntingtin gene. Alterations in cholesterol metabolism and distribution have been reported in Huntington's disease, including abnormal interactions between mutant huntingtin and sterol regulatory element-binding proteins, decreased levels of apolipoprotein E/cholesterol/low-density lipoprotein receptor complexes, and alterations in the synthesis of ATP-binding cassette transporter A1. Plasma levels of 24S-hydroxycholestrol, a key intermediary in cholesterol metabolism and a possible marker in neurodegenerative diseases, decreased proportionally to the degree of caudate nucleus atrophy. The interaction of mutant huntingtin with sterol regulatory element-binding proteins is of particular interest given that sterol regulatory element-binding proteins play a dual role: They take part in lipid and cholesterol metabolism, but also in the inflammatory response that induces immune cell migration as well as toxic effects, particularly in astrocytes. This work summarizes current evidence on the metabolic and immune implications of sterol regulatory element-binding protein dysregulation in Huntington's disease, highlighting the potential use of drugs that modulate these alterations. © 2020 International Parkinson and Movement Disorder Society.

Cholesterol efflux from macrophages is the initial step of reverse cholesterol transport, an important process for high-density lipoprotein-mediated atheroprotection. G protein-coupled receptor (GPR) 120, which functions as long-chain fatty acid receptor, is well known for its anti-inflammatory and insulin-sensitizing function in macrophages. However, the role of GPR120 on macrophage foam cell formation, the hallmark of atherosclerotic plaques, has not been verified. In this study, we found for the first time that stimulation of GPR120 by its agonist GW9508 elevated the expression of ATP-binding cassette transporters (ABC) A1 and ABCG1 in THP-1 macrophage-derived foam cells and Raw264.7 macrophages, and promoted ABCA1- and ABCG1-mediated cholesterol efflux and reduced cellular cholesteryl ester (CE) content as well. In addition, GPR120 activation was accompanied with the stimulation of AMPK pathway in macrophages; however, the effect of GPR120 on macrophage cholesterol efflux was largely abolished by AMPK inhibition. Moreover, the AMPK activity and the expression of ABCA1 and ABCG1 were markedly abrogated by knockdown of GPR120, or application of phospholipase C (PLC) inhibitor, calcium chelator, or CaMKK inhibitor. Because only free cholesterol can be effluxed from macrophages, we found that activation of AMPK could lead to increase both neutral CEs hydrolysis by upregulation of neutral cholesterol ester hydrolase expression and acid CEs hydrolysis by activation of ULK1. In conclusion, these results demonstrated that GPR120 facilitated ABCA1- and ABCG1-mediated cholesterol efflux through activation of PLC/Ca2+ /CaMKK/AMPK signaling pathway, which induced CE hydrolysis and elevated the expression of ABCA1 and ABCG1 in macrophages.

During adhesion, cells develop filopodia to facilitate the attachment to the extracellular matrix. The small guanosine triphosphate (GTP)-binding protein, Cdc42, plays a central role in the formation of filopodia. It has been reported that Cdc42 activity is regulated by cholesterol (Chol). We examined Chol distribution in filopodia using Chol-binding domain 4 (D4) fragment of bacterial toxin, perfringolysin O that senses high membrane concentration of Chol. Our results indicate that fluorescent D4 was enriched at the tip of the outer leaflet of filopodia in the initiation phase of cell adhesion. This enrichment was accompanied by a defect of D4 labeling in the inner leaflet. Steady phase adhered cell experiment indicated that both Cdc42 and ATP-binding cassette transporter, ABCA1, were involved in the binding of D4 to the cell surface. Depletion of Chol activated Cdc42. Our results suggest that asymmetric distribution of Chol at the tip of filopodia induces activation of Cdc42, and thus, facilitates filopodia formation.

Background Silkworm pupa oil polyunsaturated fatty acid (SPO PUFA) has been confirmed to have a cholesterol-lowering function. Methods and results The effect of SPO PUFA and its main component, α-linolenic acid (ALA), on the metabolism of cholesterol and its regulation was investigated. The model of lipid denatured cells were constructed to carry out lipid accumulation, cholesterol metabolism and transformation. Real-time PCR and western blots were also used to analyze the expression levels of related genes and proteins to investigate the cholesterol efflux regulation mechanism. The data indicated that SPO PUFA and ALA dose-dependently decreased intracellular total cholesterol (TC) and enhanced total bile acid (TBA). They could also promote cholesterol removal by enhancing bile acid secretion and by upregulating genes LXRα, PPARγ, ABCA1, ABCG1, and CYP7A1, which were regulated by LXRα/PPARγ-ABCA1/ABCG1-CYP7A1 nuclear receptor signal pathways. Conclusions This study is of great significance in maintaining the balance of cholesterol and lipid metabolism, and in reducing the risk of steatohepatitis. © 2019 Society of Chemical Industry.

Niemann‐Pick disease type C (NPC) and Tangier disease are genetically and clinically distinct rare inborn errors of metabolism. NPC is caused by defects in either NPC1 or NPC2; whereas Tangier disease is caused by a defect in ABCA1. Tangier disease is currently without therapy, whereas NPC can be treated with miglustat, a small molecule inhibitor of glycosphingolipid biosynthesis that slows the neurological course of the disease. When a Tangier disease patient was misdiagnosed with NPC and treated with miglustat, her symptoms improved. This prompted us to consider whether there is mechanistic convergence between these two apparently unrelated rare inherited metabolic diseases. In this study, we found that when ABCA1 is defective (Tangier disease) there is secondary inhibition of the NPC disease pathway, linking these two diseases at the level of cellular pathophysiology. In addition, this study further supports the hypothesis that miglustat, as well as other substrate reduction therapies, may be potential therapeutic agents for treating Tangier disease as fibroblasts from multiple Tangier patients were corrected by miglustat treatment.

The contribution of soluble epoxide hydrolase (sEH) to atherosclerosis has been well defined. However, less is understood about the role of sEH and its underlying mechanism in the cholesterol metabolism of macrophages. The expression of sEH protein was increased in atherosclerotic aortas of apolipoprotein E‐deficient mice, primarily in macrophage foam cells. Oxidized low‐density lipoprotein (oxLDL) increased sEH expression in macrophages. Genetic deletion of sEH (sEH −/−) in macrophages markedly exacerbated oxLDL‐induced lipid accumulation and decreased the expression of ATP‐binding cassette transporters‐A1 (ABCA1) and apolipoprotein AI‐dependent cholesterol efflux following oxLDL treatment. The down‐regulation of ABCA1 in sEH −/− macrophages was due to an increase in the turnover rate of ABCA1 protein but not in mRNA transcription. Inhibition of phosphatase activity, but not hydrolase activity, of sEH decreased ABCA1 expression and cholesterol efflux following oxLDL challenge, which resulted in increased cholesterol accumulation. Additionally, oxLDL increased the phosphatase activity, promoted the sEH‐ABCA1 complex formation and decreased the phosphorylated level of ABCA1 at threonine residues. Overexpression of phosphatase domain of sEH abrogated the oxLDL‐induced ABCA1 phosphorylation and further increased ABCA1 expression and cholesterol efflux, leading to the attenuation of oxLDL‐induced cholesterol accumulation. Our findings suggest that the phosphatase domain of sEH plays a crucial role in the cholesterol metabolism of macrophages.

It has been reported that genistein could improve metabolic syndromes. Our study aimed to investigate the effects and potential mechanisms of genistein on improving cholesterol metabolism in HepG2 cell. HepG2 cells were cultured with 0, 0.01, 1.00, 10.00, and 50.00 µM genistein for 24 hr. The current results showed a dose-dependent manner between genistein and intracellular contents of total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), and cellular apolipoprotein A1 (Apo-A1) secretion. TC was increased by 25.69%, meanwhile HDL-C and Apo-A1 were decreased by 56.00% and 25.93%, respectively, when the dosage of genistein was 1.00 µM. Genistein dose-dependently upregulated the protein and mRNA levels of sterol regulatory element binding proteins-2 (SREBP-2), as well as the mRNA levels of low-density lipoprotein receptor (LDLR) and 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGCR), by 145.91%, 72.29%, 310.23%, and 123.08%, respectively, when we gave 1.00 µM genistein, indicating that intracellular cholesterol synthesis and absorption of exogenous cholesterol were increased. In addition, the mRNA levels of peroxisome proliferator-activated receptor-γ (PPARγ) and liver X receptor (LXRα), lowered by 58.23% and 34.86% at 0.01 µM genistein, were reduced in a dose-dependent manner. LXRα and ATP-binding cassette transporter A1 (ABCA1) protein levels were significantly (P < 0.05) decreased by 50.35% and 11.60% at 1.00 µM genistein, which indicated that cellular cholesterol efflux was inhibited. Taken together, our results suggested that genistein at dosage of more than 1.00 µM was able to increase the intracellular cholesterol levels by up regulating SREBP-2/LDLR/HMGCR pathway and suppressing PPARγ/LXRα/ABCA1 pathway. PRACTICAL APPLICATION: In this study, genistein appeared to be effective in reducing plasma cholesterol levels due to increase the intracellular cholesterol levels by upregulating cholesterol absorption through SREBP-2/LDLR/HMGCR pathway, and also downregulating cholesterol efflux via PPARγ/LXRα/ABCA1 pathway in vitro. In addition, plasma cholesterol is regarded as the key indicator of atherosclerosis; therefore, we believe that our findings could be used for further exploration on a possible therapeutic application of genistein for atherosclerosis.

Foam cells are specialized types of cells which predominate the necrotic core of atherosclerotic plaque. Recently, autophagy-mediated cholesterol efflux from foam cells has been proposed as a beneficial therapy for atherosclerosis. The purpose of this study was to delineate the underlying molecular mechanism of oligomeric proanthocyanidins (OPC) and epigallocatechin gallate (EGCG) induced autophagy of foam cells and associated cholesterol efflux. The oxidized low-density lipoprotein induced foam cells demonstrated impaired autophagy flux through the downregulated expressions of LC3BII/LC3BI, autophagy related gene-5, Class III phosphoinositide 3 kinase (Class III PI3K), Beclin1, ABCA1, and ABCG1 with concomitant increase in the expressions of protein 62, Class I phosphoinositide 3 kinase, Akt, and mammalian target of rapamycin. However, these effects were significantly abolished by treatment with OPC and EGCG through activation of autophagy flux via Class III PI3K/Beclin1 and with upregulated expression of transporter proteins ABCA1 and ABCG1. Furthermore, the cholesterol efflux process in the foam cells was activated by lysosomal acid lipase and cathepsin D facilitated lipolysis of lipid droplets. Taken together, our data demonstrate that OPC and EGCG treatment stimulated the coordinated activation of autophagy and cholesterol efflux through Class III PI3K/Beclin1 pathway in foam cells, suggesting a promising therapeutic strategy against atherosclerosis.

Podocyte injury is a critical factor for the initiation and progression of diabetic kidney disease (DKD). However, the underlying mechanisms of podocyte injury in DKD have not been completely elucidated. Studies suggested that intracellular cholesterol accumulation was correlated with podocyte injury, but the cause of podocyte cholesterol disorders in DKD are still unknown. ADP-ribosylation factor 6 (Arf6) is a small GTPase with pleiotropic effects and has previously been shown to regulate ATP-binding cassette transporter 1 (ABCA1) recycling, and thus, cholesterol homeostasis. However, Arf6 involvement in cholesterol metabolism in podocytes is scarce. To investigate the role of Arf6 in cholesterol modulation in podocytes, the effect of Arf6 on the regulation of the cholesterol transporter ABCA1 was studied in podocytes in vivo and in vitro. Intracellular cholesterol accumulation was significantly increased in podocytes from streptozotocin-induced diabetic rats and that hyperglycemia downregulated the expression of Arf6. Arf6 knockdown could cause ABCA1 recycling disorders, and thus, further aggravate cholesterol accumulation in podocytes under high-glucose (HG) conditions. Our results demonstrate that HG-induced cholesterol accumulation and cellular injury in podocytes may be related to the recycling disorder of ABCA1 caused by the downexpression of Arf6 in DKD.

The nuclear factor of activated T-cells 5 (NFAT5) is a transcriptional regulator of macrophage activation and T-cell development, which controls stabilizing responses of cells to hypertonic and biomechanical stress. In this study, we detected NFAT5 in the media layer of arteries adjacent to human arteriosclerotic plaques and analyzed its role in vascular smooth muscle cells (VSMCs) known to contribute to arteriosclerosis through the uptake of lipids and transformation into foam cells. Exposure of both human and mouse VSMCs to cholesterol stimulated the nuclear translocation of NFAT5 and increased the expression of the ATP-binding cassette transporter Abca1, required to regulate cholesterol efflux from cells. Loss of Nfat5 promoted cholesterol accumulation in these cells and inhibited the expression of genes involved in the management of oxidative stress or lipid handling, such as Sod1, Plin2, Fabp3, and Ppard. The functional relevance of these observations was subsequently investigated in mice fed a high-fat diet upon induction of a smooth muscle cell-specific genetic ablation of Nfat5 (Nfat5(SMC)-/- ). Under these conditions, Nfat5(SMC)-/- but not Nfat5fl/fl mice developed small, focal lipid-rich lesions in the aorta after 14 and 25 weeks, which were formed by intracellular lipid droplets deposited in the sub-intimal VSMCs layer. While known for being activated by external stimuli, NFAT5 was found to mediate the expression of VSMC genes associated with the handling of lipids in response to a cholesterol-rich environment. Failure of this protective function may promote the formation of lipid-laden arterial VSMCs and pro-atherogenic vascular responses.

Globally, COPD remains a major cause of disability and death. In the United States alone, it is estimated that approximately 14 million people suffer from the disease. Given the high disease burden and requirement for chronic, long-term medical care associated with COPD, it is essential that new disease modifying agents are developed to complement the symptomatic therapeutics currently available. In the present report, we have identified a potentially novel therapeutic agent through the use of a high throughput screen based on the knowledge that cigarette smoke induces the proteolytic enzyme MMP1 leading to destruction of the lung in COPD. A construct utilizing the cigarette responsive promoter element of MMP-1 was conjugated to a luciferase reporter and utilized in an in vitro assay to screen the NIH Molecular Libraries Small Molecule Repository to identify putative targets that suppressed luciferase expression in response to cigarette smoke extract (CSE). Selective serotonin reuptake inhibitors potently inhibited luciferase expression and were further validated. SSRI treatment suppressed MMP-1 production in small airway epithelial cells exposed to (CSE) in vitro as well as in smoke exposed rabbits. In addition, SSRI treatment inhibited inflammatory cytokine production while rescuing cigarette smoke induced downregulation in vivo of the anti-inflammatory lipid transporter ABCA1, previously shown by our laboratory to be lung protective. Importantly, SSRI treatment prevented lung destruction in smoke exposed rabbits as measured by morphometry. These studies support further investigation into SSRIs as a novel therapeutic for COPD may be warranted.

Introduction Tangier disease (TD) is an autosomal recessive disorder characterized by severe reduction in high-density lipoprotein and accumulation of cholesterol esters in peripheral nerves and other tissues. The aim of this study was to evaluate whether nerve high-resolution ultrasonography (HRUS) can detect morphological nerve changes in TD. Methods Three related patients of a previously reported Italian family with Tangier disease, carrying the Y1698X mutation in ABCA1, underwent clinical, neurophysiological, and quantitative nerve HRUS evaluation. Nerve HRUS data were compared with normal controls. Results Despite neurophysiological abnormalities, no quantitative HRUS abnormality was detected in peripheral nerves. Discussion Normalcy of HRUS in neurophysiologically abnormal nerves suggests possible subtle abnormalities that escape quantitative HRUS detection. Systematic studies in larger TD cohorts with different mutations are needed to confirm our findings. Muscle Nerve 59:587-587, 2019.

Obeticholic acid (OCA) activates the farnesoid X receptor (FXR) to lower circulating total cholesterol (TC) and high density lipoprotein‐cholesterol (HDL‐C) concentrations and to stimulate fecal cholesterol excretion in mice by increasing hepatic SR‐B1 expression. Here we show that hepatic SR‐B1 depletion by an adenovirus expressing Sr‐b1 shRNA (Ad‐shSR‐B1) attenuated these beneficial effects of OCA in mice on a chow diet. The mRNA levels of ABC cholesterol transporter genes (Abca1, Abcg1, Abcg5, and Abcg8) were unchanged in the liver of hepatic SR‐B1‐depleted mice regardless of OCA treatment; however, a modest increase in Abca1, Abcg5, and Abcg8 mRNA levels was observed in the ileum of vehicle‐treated control mice and Abca1 and Abcg8 mRNA levels were increased more by OCA administration. OCA treatment of Sr‐b1 knock out (KO) mice (Sr‐b1‐/‐) fed a normal chow diet (NCD) displayed a similar lack of transhepatic cholesterol movement, as well as a modest increase in the levels of ileum cholesterol transporter expression. However, OCA treatment of Sr‐b1 KO mice fed a cholesterol‐enriched diet reduced circulating cholesterol and increased fecal cholesterol output to comparable degrees to that of wild‐type (WT) mice, and these effects were accompanied by substantial elevations of mRNA levels of Abca1, Abcg1, Abcg5, and Abcg8 in the ileum of Sr‐b1 KO mice. Our studies suggest that FXR activation stimulates intestinal cholesterol excretion and reduces diet‐induced hyperlipidemia through increased expression of ileal cholesterol transporters when hepatic SR‐B1‐mediated cholesterol movement is absent., FXR activation in Srb1 KO mice fed a cholesterol‐enriched diet increased liver LDL receptor expression and stimulated the gene expression of cholesterol transporter in ileum, which let to the substantial reduction of serum cholesterol and the increased fecal cholesterol output.

Vitamin E is an essential molecule for our development and health. It has long been thought that it was absorbed and transported through cellular membranes by a passive diffusion process. However, data obtained during the past 15 years showed that its absorption is actually mediated, at least in part, by cholesterol membrane transporters including the scavenger receptor class B type I (SR-BI), CD36 molecule (CD36), NPC1-like transporter 1 (NPC1L1), and ATP-binding cassettes A1 and G1 (ABCA1 and ABCG1). This review focuses on the absorption process of vitamin E across the enterocyte. A special attention is given to the regulation of this process, including the possible competition with other fat-soluble micronutrients, and the modulation of transporter expressions. Overall, recent results noticeably increased the comprehension of vitamin E intestinal transport, but additional investigations are still required to fully appreciate the mechanisms governing vitamin E bioavailability. © 2018 IUBMB Life, 71(4):416-423, 2019.

At the time of diagnosis, 20% of patients with colorectal cancer present metastasis. Among individuals with primary lesions, 50% of them will develop distant tumours with time. Therefore, early diagnosis and prediction of aggressiveness is crucial for therapy design and disease prognosis. Tumoral cells must undergo significant changes in energy metabolism to meet increased structural and energetic demands for cell proliferation, and metabolic alterations are considered to be a hallmark of cancer. Here, we present the ATP-binding cassette transporter (ABCA1), a regulator of cholesterol transport, as a new marker for invasion and colorectal cancer survival. ABCA1 is significantly overexpressed in patients at advanced stages of colorectal cancer, and its overexpression confers proliferative advantages together with caveolin-1 dependent-increased migratory and invasive capacities. Thus, intracellular cholesterol imbalances mediated by ABCA1 overexpression may contribute to primary tumour growth and dissemination to distant locations. Furthermore, we demonstrate here that increased levels of apolipoprotein A1 (APOA1), a protein involved in cholesterol efflux and high-density lipoprotein constitution, in the extracellular compartment modulates expression of ABCA1 by regulating COX-2, and compensate for ABCA1-dependent excessive export of cholesterol. APOA1 emerges as a new therapeutic option to inhibit the promotion of colorectal cancer to metastasis by modulating intracellular cholesterol metabolism. Furthermore, we propose apabetalone, an orally available small molecule that is currently being evaluated in clinical trials for the treatment of atherosclerosis, as a new putative therapeutic option to prevent colorectal cancer progression by increasing APOA1 expression and regulating reverse transport of cholesterol, This work has been supported by Ministerio de Economía y Competitividad del Gobierno de España (MINECO, Plan Nacional I+D+i AGL2016-76736-C3), Gobierno regional de la Comunidad de Madrid (P2013/ABI-2728, ALIBIRD-CM), EU Structural Funds and AMAROUT-Marie Curie actions (COFUND2014-51539-04)

Macrophage infiltration is common to both emphysema and atherosclerosis, and cigarette smoke down-regulates the macrophage cholesterol efflux transporter ATP binding cassette (ABC)A1. This decreased cholesterol efflux results in lipid-laden macrophages. We hypothesize that cigarette smoke adversely affects cholesterol transport via an ABCA1-dependent mechanism in macrophages, enhancing TLR4/myeloid differentiation primary response gene 88 (Myd88) signaling and resulting in matrix metalloproteinase (MMP) up-regulation and exacerbation of pulmonary inflammation. ABCA1 is significantly down-regulated in the lung upon smoke exposure conditions. Macrophages exposed to cigarette smoke in vivo and in vitro exhibit impaired cholesterol efflux correlating with significantly decreased ABCA1 expression, up-regulation of the TLR4/Myd88 pathway, and downstream MMP-9 and MMP-13 expression. Treatment with liver X receptor (LXR) agonist restores ABCA1 expression after short-term smoke exposure and attenuates the inflammatory response; after long-term smoke exposure, there is also attenuated physiologic and morphologic changes of emphysema. In vitro, treatment with LXR agonist decreases macrophage inflammatory activation in wild-type but not ABCA1 knockout mice, suggesting an ABCA1-dependent mechanism of action. These studies demonstrate an important association between cigarette smoke exposure and cholesterol-mediated pathways in the macrophage inflammatory response. Modulation of these pathways through manipulation of ABCA1 activity effectively blocks cigarette smoke–induced inflammation and provides a potential novel therapeutic approach for the treatment of chronic obstructive pulmonary disease.—Sonett, J., Goldklang, M., Sklepkiewicz, P., Gerber, A., Trischler, J., Zelonina, T., Westerterp, M., Lemaître, V., Okada, V., D’Armiento, J. A critical role for ABC transporters in persistent lung inflammation in the development of emphysema after smoke exposure.

Agonists for the liver X receptor (LXR) are considered promising therapeutic moieties in cholesterol-driven diseases by promoting cellular cholesterol efflux pathways. However, current clinical application of these agents is hampered by concomitant LXR-induced activation of a lipogenic transcriptional network, leading to hepatic steatosis. Recent studies have suggested that protein arginine methyltransferase 3 (PRMT3) may act as a selective co-activator of LXR activity. Here, we verified the hypothesis that PRMT3 inhibition selectively disrupts the ability of LXR to stimulate lipogenesis while maintaining its capacity to modulate macrophage cholesterol homeostasis. A combination of the LXR agonist T0901317 and palm oil was administered to C57BL/6 mice to maximally stimulate LXR and PRMT3 activity. PRMT3 activity was inhibited using the allosteric inhibitor SGC707. Treatment with SGC707 did not negatively influence the T0901317/palm oil-induced up-regulation of the cholesterol efflux ATP-binding cassette transporter genes, ABCA1 and ABCG1, in peritoneal cells. In contrast, SGC707 treatment was associated with a significant decrease in the hepatic expression of the lipogenic gene fatty acid synthase (-64%). A similar trend was observed for stearoyl-coenzyme A desaturase and acetyl CoA carboxylase expression (-43%; -56%). This obstruction of lipogenic gene transcription coincided with a significant 2.3-fold decrease in liver triglyceride content as compared with the T0901317 and palm oil-treated control group. We showed that inhibition of PRMT3 activity by SGC707 treatment selectively impairs LXR-driven transcription of hepatic lipogenic genes, while the positive effect of LXR stimulation on macrophage cholesterol efflux pathways is maintained.

Airway remodeling is a key feature of asthma, characterized by abnormal proliferation and migration of airway smooth muscle cells (ASMCs). ABCA1, a member of the ATP-binding cassette family of active transporters, plays an essential role in the progression of lung diseases. However, the contributions of ABCA1 in ASMCs remain to be explored. The purpose of the present study was to investigate the functional role and potential molecular mechanism of ABCA1 in platelet derived growth factor (PDGF)-induced primary rat ASMC proliferation and migration. We observed that PDGF- led to a significant decrease in the expression of ABCA1. Overexpression of ABCA1 strikingly suppressed PDGF-induced ASMC proliferation accompanied by a decrease in the expression of PCAN stimulated by PDGF. Additionally, augmentation of ABCA1 dramatically restrained PDGF-induced migration concomitant with attenuate the accumulation of MMP-2 and MMP-9 in response to PDGF. Furthermore, forced expression of ABCA1 enhanced contractile phenotype markers proteins including α-SMA along with sm-MHC, sm-α-actin, and calponin reduced by PDGF. Meanwhile, introduction of ABCA1 depressed ECM over-deposition induced by PDGF as reflected by a decrease in the expression of ECM protein collagen I and fibronectin. More importantly, addition of ABCA1 effectively suppressed the activity of TLR2/NF-κB signaling as well as diminished the expression of NFATc1 in rat ASMCs after PDGF stimulation. Interestingly, blockage of TLR2/NF-κB signaling effectively inhibited PDGF-induced proliferation and migration, these effects were similar to ABCA1. Taken together, these data implicated that ABCA1 suppressed PDGF-induced proliferation, migration, and contraction in rat ASMCs at least partly through TLR2/NF-κB/NFATc1 signaling, which might offer hope for the future treatment of airway remodeling in asthma.

Background and purpose To further the development of new agents for the treatment of adrenocortical carcinoma (ACC), we characterized the molecular and cellular mechanisms of cytotoxicity by the adrenalytic compound ATR-101 (PD132301-02). Experimental approach We compared the effects of ATR-101, PD129337, and ABC transporter inhibitors on cholesterol accumulation and efflux, on cortisol secretion, on ATP levels, and on caspase activation in ACC-derived cell lines. We examined the effects of these compounds in combination with methyl-β-cyclodextrin or exogenous cholesterol to determine the roles of altered cholesterol levels in the effects of these compounds. Key results ATR-101 caused cholesterol accumulation, ATP depletion, and caspase activation within 30 minutes after addition to ACC-derived cells, whereas PD129337 did not. Suppression of cholesterol accumulation by methyl-β-cyclodextrin or exogenous cholesterol, prevented ATP depletion and caspase activation by ATR-101. ATR-101 blocked cholesterol efflux and cortisol secretion, suggesting that it inhibited ABCA1, ABCG1, and MDR1 transporters. Combinations of ABCA1, ABCG1, and MDR1 inhibitors were also cytotoxic. Combinations of ATR-101 with inhibitors of ABCG1, MDR1, or mitochondrial functions had increased cytotoxicity. Inhibitors of steroidogenesis reduced ATP depletion by ATR-101, whereas U18666A enhanced cholesterol accumulation and ATP depletion together with ATR-101. ATR-101 repressed ABCA1, ABCG1, and IDOL transcription by mechanisms that were distinct from the mechanisms that caused cholesterol accumulation. Conclusions and implications Inhibition of multiple ABC transporters and the consequent accumulation of cholesterol mediated the cytotoxicity of ATR-101. Compounds that replicate these effects in tumours are likely to be useful in the treatment of ACC.

Background To investigate the association between three single nucleotide polymorphisms (SNPs) of ABCA1 gene and susceptibility to coronary heart disease (CHD) in Chinese Han population. Methods A total of 484 CHD patients and 488 controls were included in the study. Three SNPs rs2230806 (R219K), rs4149313 (M8831I), and rs9282541 (R230C) in ABCA1 gene were genotyped by SNaPshot. Results Single nucleotide polymorphism rs1800977 was associated with susceptibility to CHD (AA vs GG, P = 0.013; A vs G, P = 0.029; recessive model, P = 0.020). Rs4149313 (AA vs GG, P = 0.010; recessive model, P = 0.011) and rs9282541 (T vs C, P = 0.029; dominant model, P = 0.039) were also risk factor for CHD. Conclusion This study suggests that three SNPs rs2230806, rs4149313, and rs9282541 in ABCA1 gene are significantly associated with susceptibility to CHD; further mechanism should be performed to be applied to drug research and development.

RORα is a member of nuclear receptor superfamily of transcription factors, which has a vital role in the regulation of various physiological processes. Cholesterol is a known ligand of RORα and is one of the key components that take part in cardiovascular diseases such as atherosclerosis. Therefore, it is possible that RORα might have a role in the development of atherosclerosis. To test this hypothesis, we investigated the presence of novel RORα response elements (ROREs) located in the promoter of CYP19A1, MIF and ABCA1 genes. Briefly, the occupancy of RORα in the promoter regions of these genes was demonstrated in THP-1 and HUVEC cell lines by ChIP analysis. In order to modulate RORα activity, THP-1 and HUVEC cells were treated with specific RORα ligands (CPG 52608 and SR1001) and then the expression levels of target genes were analysed. In the next step, we tested whether RORα activity in THP-1 macrophages was influenced by the presence of simvastatin, a cholesterol lowering drug. We found that in the presence of simvastatin the expression of the investigated target genes were down regulated and that this regulation was partially prevented by CPG 52608 and SR1001. Results of this study suggest that CYP19A1, MIF and ABCA1 are the direct target genes of RORα. In conclusion, it is important to demonstrate that certain genes involved in the development of atherosclerosis could be modulated by an inducible transcription factor. Therefore, these results offer a potential therapeutic approach for the treatment of atherosclerosis.

Clinical trials suggest that fenofibrate reduces the progression of retinopathies in patients with type 2 diabetes. Furthermore, patients with retinopathies have elevated levels of inflammatory chemokines and dysfunctional retinal angiogenesis. Therefore, we investigated the effects of fenofibrate on the production of inflammatory chemokines and genes associated with angiogenesis. Retinal pigment epithelial cells (RPECs) were cultured with IL-1β and fenofibrate ranging from 1-50 μM. ENA-78, IL-8, and RANTES were measured in cell culture by ELISA. ENA-78, ABCA1, and ABCG1 gene expression were tested by RT-PCR. IL-1β significantly induced the production of ENA-78, IL-8, and RANTES. Fenofibrate at concentrations of 25-50 uM blunted the IL-1β induced production of ENA-78 (p < 0.05) with no significant effects on RANTES and IL-8. Fenofibrate also reduced the expression of the ENA-78 gene as well as ABCA1 and ABCG1, which are genes involved in angiogenesis. Fenofibrate decreases ENA-78 production and ABCA1/ABCG1 gene expression in RPECs.

Liver X receptor (LXR) agonists are candidates for the treatment of atherosclerosis via induction of ABCA1 (ATP-binding cassette A1) gene expression, which contributes to reverse cholesterol transport (RCT) and to cholesterol efflux from the liver and intestine. However, LXR agonists also induce genes involved in lipogenesis, such as SREBP-1c (sterol regulatory binding element protein 1c) and FAS (fatty acid synthase), thereby causing an undesirable increase in plasma and hepatic triglyceride (TG) levels. Recent studies indicate that LXRα contributes to lipogenesis in liver, and selective LXRβ activation improves RCT in mice. Therefore, LXRβ-selective agonists are promising candidates to improve atherosclerosis without increasing plasma or hepatic TG levels. However, the ligand-binding domains in the two LXR isoforms α/β share high sequence identity, and few LXR ligands show subtype selectivity. In this study we identified a tetrachlorophthalimide analogue as an LXRβ-selective agonist. Structural development led to (E)-4,5,6,7-tetrachloro-2-(2-styrylphenyl)isoindoline-1,3-dione (24 a), which shows potent and selective LXRβ agonistic activity in reporter gene assays. In binding assays, compound 24 a bound to LXRβ preferentially over LXRα. It also induced the expression of ABCA1 mRNA but not SREBP-1c mRNA in cells. Compound 24 a appears to be a promising lead compound for therapeutic agents to treat atherosclerosis without the side effects induced by LXRα/β dual agonists.

Apolipoprotein A-I (apoA-I) is the major component of HDL and central to the ability of HDL to stimulate ATP-binding cassette transporter A1 (ABCA1)-dependent, antiatherogenic export of cholesterol from macrophage foam cells, a key player in the pathology of atherosclerosis. Cell-mediated modifications of apoA-I, such as chlorination, nitration, oxidation, and proteolysis, can impair its antiatherogenic function, although it is unknown whether macrophages themselves contribute to such modifications. To investigate this, human monocyte-derived macrophages (HMDMs) were incubated with human apoA-I under conditions used to induce cholesterol export. Two-dimensional gel electrophoresis and Western blot analysis identified that apoA-I is cleaved (∼20-80%) by HMDMs in a time-dependent manner, generating apoA-I of lower MW and isoelectric point. Mass spectrometry analysis identified a novel C-terminal cleavage site of apoA-I between Ser228-Phe229 Recombinant apoA-I truncated at Ser228 demonstrated profound loss of capacity to solubilize lipid and to promote ABCA1-dependent cholesterol efflux. Protease inhibitors, small interfering RNA knockdown in HMDMs, mass spectrometry analysis, and cathepsin B activity assays identified secreted cathepsin B as responsible for apoA-I cleavage at Ser228 Importantly, C-terminal cleavage of apoA-I was also detected in human carotid plaque. Cleavage at Ser228 is a novel, functionally important post-translational modification of apoA-I mediated by HMDMs that limits the antiatherogenic properties of apoA-I.-Dinnes, D. L. M., White, M. Y., Kockx, M., Traini, M., Hsieh, V., Kim, M.-J., Hou, L., Jessup, W., Rye, K.-A., Thaysen-Andersen, M., Cordwell, S. J., Kritharides, L. Human macrophage cathepsin B-mediated C-terminal cleavage of apolipoprotein A-I at Ser228 severely impairs antiatherogenic capacity.

Contemporary research suggests that macrophage foam cell and cholesterol efflux defect play pivotal role in atherogenesis. We reported on the heretofore unknown therapeutic effect of Danshensu (DSS) in reducing intracellular cholesterol level and unraveled the mechanism of DSS promotes cholesterol efflux. Oxidized low-density lipoprotein stimulation of Raw264.7 cells into foam cells, which were treated with DSS and co-treated with Simvastatin and Rosiglitazone. PPARγ, ABCA1, ABCG1, SR-BI, CD36, and LXR-α mRNA were quantified by Real-Time PCR. Western blotting was used to determine protein expression of PPARγ, ABCA1 and CD36. Cellular cholesterol handling was studied by measurement of intracellular lipid droplets concentration and cholesterol efflux. DSS significantly reduced scavenger receptor CD36 and its orthologue SR-BI. In addition, DSS stimulated the upregulation of cellular cholesterol exporters ABCA1 and ABCG1 to reduce intracellular lipid accumulation. DSS can reduce lipid deposition in Raw264.7 foam cells by balancing CD36 and ABCA1 protein expression.

Reactive oxygen species (ROS) generation during purine metabolism is associated with xanthine oxidase and uric acid. However, the direct effect of hypoxanthine on ROS generation and atherosclerosis has not been evaluated. Smoking and heavy drinking are associated with elevated levels of hypoxanthine. In this study, we investigated the role of hypoxanthine on cholesterol synthesis and atherosclerosis development, particularly in apolipoprotein E (APOE)‐deficient mice. The effect of hypoxanthine on the regulation of cholesterol synthesis and atherosclerosis were evaluated in Apoe knockout (KO) mice and cultured HepG2 cells. Hypoxanthine markedly increased serum cholesterol levels and the atherosclerotic plaque area in Apoe KO mice. In HepG2 cells, hypoxanthine increased intracellular ROS production. Hypoxanthine increased cholesterol accumulation and decreased APOE and ATP‐binding cassette transporter A1 (ABCA1) mRNA and protein expression in HepG2 cells. Furthermore, H2O2 also increased cholesterol accumulation and decreased APOE and ABCA1 expression. This effect was partially reversible by treatment with the antioxidant N‐acetyl cysteine and allopurinol. Hypoxanthine and APOE knockdown using APOE‐siRNA synergistically induced cholesterol accumulation and reduced APOE and ABCA1 expression. Hypoxanthine induces cholesterol accumulation in hepatic cells through alterations in enzymes that control lipid transport and induces atherosclerosis in APOE‐deficient cells and mice. These effects are partially mediated through ROS produced in response to hypoxanthine.

Interleukin-1 receptor-associated kinase-1 (IRAK1) is linked to the pathogenesis of atherosclerosis; however, its role in macrophage foam cell formation is not known. Therefore, the present study investigated the role of IRAK1 in lipid uptake, biosynthesis, and efflux in THP-1 derived macrophages and human monocyte-derived macrophages (HMDMs). Ox-LDL (40 μg/mL, 15 minutes-48 hours) treatment induced time-dependent increase in IRAK1, IRAK4, and Stat1 activation in THP-1 derived macrophages. IRAK1/4 inhibitor (INH) or IRAK1 siRNA significantly attenuated cholesterol accumulation, DiI-Ox-LDL binding, and uptake while cholesterol efflux to apoAI and HDL was enhanced in THP-1 derived macrophages and HMDMs. Ox-LDL treatment significantly increased the mRNA expression of CD36, LOX-1, SR-A, ABCA1, ABCG1, Caveolin-1, CYP27A1 while that of SR-BI was decreased. IRAK1/4 inhibition or IRAK1 knockdown, however, attenuated Ox-LDL-induced CD36 expression; augmented ABCA1 and ABCG1 expression while expression of others was unaffected in THP-1 derived macrophages and HMDMs. Moreover, IRAK1/4 inhibition had no significant effect on genes involved in lipid biosynthesis. In IRAK1/4 INH pre-treated THP-1 derived macrophages Ox-LDL-induced Stat1 phosphorylation and its binding to CD36 promoter was significantly attenuated while LXRα expression and its binding to the ABCA1/ABCG1 locus, NFATc2 activation and its binding to ABCA1 locus was enhanced. The present study thus demonstrates that IRAK regulates lipid accumulation by modulating CD36-mediated uptake and ABCA1-, ABCG1-dependent cholesterol efflux. Therefore, IRAK1 can be a potential target for preventing macrophage foam cell formation.

Many reports suggested that some statins are almost ineffective in reducing triglycerides or enhancing HDL-C plasma levels, although statin treatment was still efficacious in reducing LDL-C. In diabetic dyslipidemic patients, it may therefore be necessary to use a combination therapy with other drugs to achieve either LDL-C- and triglyceride-lowering or HDL-C-enhancing goals. Such ineffectiveness of statins can be attributed to their effect on the liver X receptor (LXR) which regulates the expression of the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. A decrease in the expression of these transporters eventually leads to decreased cholesterol efflux from peripheral tissues leading to low levels of HDL-C. Although manipulating the LXR pathway may complement the effects of statins, LXR synthetic ligands as T091317 have shown significant hypertriglyceridemic action which limits their use. We recently found that the antidiabetic drug vildagliptin stimulates LXR expression leading to increased ABCB1/ABCG1 expression which improves cholesterol efflux from adipocytes. Therefore, a combination of vildagliptin and statin may provide a solution without the hypertriglyceridemic action observed with LXR agonist. We hypothesize that a combination of vildagliptin and pravastatin will improve cholesterol efflux in adipocytes. Statin-treated 3T3-L1 adipocytes were treated with vildagliptin, and the expression of LXR-ABCA1/ABCG1 cascade and the cholesterol efflux were then determined. Our data indicate that a combination of vildagliptin and pravastatin significantly induces the expression of LXR-ABCA1/ABCG1 cascade and improves cholesterol efflux (P > 0.05) in adipocytes. Our data may explain, at least in part, the improvement in HDL-C levels observed in patients receiving both medications. © 2016 IUBMB Life, 68(7):535-543, 2016.

Here, we investigate the mechanism through which paraoxonase 1 (PON1) may regulate cholesterol efflux. Pretreatment of oxLDL with PON1 (oxLDL-PON1) contributed to the formation of LysoPC. In J774 macrophages, oxLDL-PON1 increased cholesterol efflux by more than 47% compared to oxLDL alone. oxLDL-PON1 significantly increased mRNA and protein expression of ABCA1 and ABCG1, as well as of PPARγ and LXRα compared to oxLDL alone. Intraperitoneal injection of oxLDL-PON1- or LysoPC-treated J774 macrophages significantly increased the fecal elimination of macrophage-derived cholesterol in these mice. Our results suggest that PON1 stimulates cholesterol efflux via a mechanism that involves oxidized phospholipid hydrolysis.

Previously, we found that Celastrus orbiculatus Thunb. (COT) decreases athero-susceptibility in lipoproteins and the aorta of guinea pigs fed a high-fat diet, and increases high-density lipoprotein (HDL). In the present study, we investigated the effect of COT in reducing lipid accumulation and promoting reverse cholesterol transport (RCT) in vivo and vitro. Healthy male mice were treated with high-fat diet alone, high-fat diet with COT (10.0 g/kg/d), or general fodder for 6 weeks. Serum levels of total cholesterol (TC), triglyceride (TG), HDL-C, non-HDL-C, and (3)H-cholesterol in plasma, liver, bile, and feces were determined. Pathological changes and the levels of TC and TG in liver were examined. The expression of hepatic genes and protein associated with RCT were analyzed. COT administration reduced lipid accumulation in the liver, ameliorated the pathological changes, and lessened liver injury, the levels of TG, TC, and non-HDL-C in plasma were decreased significantly, and COT led to a significant increase in plasma HDL-C and apolipoprotein A (apoA1). (3)H-cholesterol in plasma, liver, bile, and feces was also significantly increased in COT-treated mice compared to controls. Both mRNA and protein expression of SRB1, CYP7A1, LDLR, ATP-binding cassette transporters ABCA1, ABCG5, and LXRα were improved in COT-treated mice. An in vitro isotope tracing experiment showed that COT and its bioactive ingredients, such as celastrol, ursolic acid, oleanolic acid, and quercetin, significantly increased the efflux of (3)H-cholesterol. They also increased the expression of SRB1, ABCA1, and ABCG1 significantly in macrophages. Our findings provided a positive role of COT in reducing lipid accumulation by promoting RCT. These effects may be achieved by activating the SRB1 and ABC transporter pathway and promoting cholesterol metabolism via the CYP7A1 pathway in vivo. The effective ingredients in vitro are celastrol, ursolic acid, oleanolic acid, and quercetin.

Background and aim Abnormal cholesterol metabolism may contribute to the pathogenesis of non-alcoholic steatohepatitis (NASH) and fibrosis. miR-33 and miR-144 regulate adenosine triphosphate binding cassette transporter (ABCA1) and other target genes involved in cholesterol efflux, fatty acid oxidation and inflammation. We explored relationships between non-alcoholic fatty liver disease (NAFLD) and the hepatic expression of ABCA1/ABCG1, as well as other target genes regulated by miR-33 (carnitine O-octanoyltransferase, CROT and hydroxyacyl-CoA-dehydrogenase β-subunit, HADHB) and miR-144 (toll-like receptor-2, TLR2). Moreover, we evaluated whether the expression of these genes is correlated with miR-33a/b and miR-144 expression in Mexican individuals with morbid obesity. Methods Eighty-four morbidly obese subjects undergoing bariatric surgery were included in this study. Liver biopsies were obtained to measure hepatic triglyceride and free cholesterol contents, as well as ABCA1, ABCG1, CROT, HADHB, TLR2, miR-33a/b and miR-144 expression. Results Hepatic free cholesterol content was significantly increased in NASH as compared to non-NASH subjects, while ABCA1 and ABCG1 protein levels significantly decreased with NASH and fibrosis progression. The relative expression of miR-33a and miR-144 correlated inversely with ABCA1 but not with ABCG1 protein levels. Moreover, both miRNAs increased significantly in NASH individuals. miR-33 target genes CROT and HADHB correlated inversely with miR-33a. However, the expression of these genes was not associated with NASH. Conclusions miR-33a/144 and their target gene ABCA1 may contribute to the pathogenesis of NASH in morbidly obese subjects.