DNA topoisomerase II inhibitors induce macrophage ABCA1 expression and cholesterol efflux—An LXR-dependent mechanism

Targeting TOP2B as a vulnerability in aging and aging-related diseases

The ongoing trend of rapid aging of the global population has unavoidably resulted in an increase in aging-related diseases. There is an immense amount of interest in the scientific community for the identification of molecular targets that may effectively mitigate the process of aging and aging-related diseases. The enzyme Topoisomerase IIβ (TOP2B) plays a crucial role in resolving the topological challenges that occur during DNA-related processes. It is believed that the disruption of TOP2B function contributes to the aging of cells and tissues, as well as the development of age-related diseases. Consequently, targeting TOP2B appears to be a promising approach for interventions aimed at mitigating the effects of aging. This review focuses on recent advancements in the understanding of the role of TOP2B in the processing of aging and aging-related disorders, thus providing a novel avenue for the development of anti-aging strategies.

Danlou Recipe promotes cholesterol efflux in macrophages RAW264.7 and reverses cholesterol transport in mice with hyperlipidemia induced by P407

INTRODUCTION

Liver X Receptor (LXR) agonists could attenuate the development of atherosclerosis but bring excess lipid accumulation in the liver. Danlou Recipe was believed to be a benefit for improving the lipid profile. Thus, it is unclear whether Danlou Recipe could attenuate hyperlipidemia without excess lipid accumulated in the liver of mice. This study aimed to clarify if Danlou Recipe could alleviate the progression of hyperlipidemia in mice without extra lipids accumulated in the liver.

METHODS

Male murine macrophage RAW264.7 cells and murine peritoneal macrophages were used for the in vitro experiments. Cellular cholesterol efflux was determined using the fluorescent cholesterol labeling method. Those genes involved in lipid metabolism were evaluated by qRT-PCR and western blotting respectively. In vivo, a mouse model of hyperlipidemia induced by P407 was used to figure out the effect of Danlou Recipe on reverse cholesterol transport (RCT) and hyperlipidemia. Ethanol extract of Danlou tablet (EEDL) was prepared by extracting the whole powder of Danlou Prescription from ethanol, and the chemical composition was analyzed by ultra-performance liquid chromatography (UPLC).

RESULTS

EEDL inhibits the formation of RAW264.7 macrophage-derived foam cells, and promotes ABCA1/apoA1 conducted cholesterol efflux in RAW264.7 macrophages and mouse peritoneal macrophages. In the P407-induced hyperlipidemia mouse model, oral administration of EEDL can promote RCT in vivo and improve fatty liver induced by a high-fat diet. Consistent with the findings in vitro, EEDL promotes RCT by upregulating the LXR activities.

CONCLUSION

Our results demonstrate that EEDL has the potential for targeting RCT/LXR in the treatment of lipid metabolism disorders to be developed as a safe and effective therapy.

Osteopontin Promotes Macrophage M1 Polarization by Activation of the JAK1/STAT1/HMGB1 Signaling Pathway in Nonalcoholic Fatty Liver Disease

Background and Aims

Osteopontin (OPN) is reported to be associated with the pathogenesis of nonalcoholic fatty liver disease (NAFLD). However, the function of OPN in NAFLD is still inconclusive. Therefore, our aim in this study was to evaluate the role of OPN in NAFLD and clarify the involved mechanisms.

Methods

We analyzed the expression change of OPN in NAFLD by bioinformatic analysis, qRT-PCR, western blotting and immunofluorescence staining. To clarify the role of OPN in NAFLD, the effect of OPN from HepG2 cells on macrophage polarization and the involved mechanisms were examined by FACS and western blotting.

Results

OPN was significantly upregulated in NAFLD patients compared with normal volunteers by microarray data, and the high expression of OPN was related with disease stage and progression. OPN level was also significantly increased in liver tissue samples of NAFLD from human and mouse, and in HepG2 cells treated with oleic acid (OA). Furthermore, the supernatants of OPN-treated HepG2 cells promoted the macrophage M1 polarization. Mechanistically, OPN activated the janus kinase 1(JAK1)/signal transducers and activators of transcription 1 (STAT1) signaling pathway in HepG2 cells, and consequently HepG2 cells secreted more high-mobility group box 1 (HMGB1), thereby promoting macrophage M1 polarization.

Conclusions

OPN promoted macrophage M1 polarization by increasing JAK1/STAT1-induced HMGB1 secretion in hepatocytes.

Encapsulation of LXR ligand by D-Nap-GFFY hydrogel enhances anti-tumorigenic actions of LXR and removes LXR-induced lipogenesis

Background and purpose: Activation of liver X receptor (LXR) by its ligand T0901317 (T317) enhances interferon-γ (IFNγ) production to inhibit tumor growth. However, induction of severe hypertriglyceridemia and fatty liver by T317 limits its application. The naphthylacetic acid modified D-enantiomeric-glycine-phenylalanine-phenylalanine-tyrosine (D-Nap-GFFY) can form a nanofiber hydrogel which is selectively taken up by antigen-presenting cells (APCs). In this study, we determined if D-Nap-GFFY-encapsulated T317 (D-Nap-GFFY-T317) can potently inhibit tumor growth while having no adverse lipogenic effects on the liver. Methods: We prepared D-Nap-GFFY-T317 nanofiber hydrogel and subcutaneously injected it into IFNγ deficient (IFNγ^-/-) and wild-type (WT) mice with lung carcinoma, either inoculated LLC1 cells or urethane-induced carcinoma. Mice received oral T317 administration were used for comparison. Effects of treatment on tumor growth, lipogenesis and involved mechanisms were investigated. Results: Compared with T317 oral administration, injection of D-Nap-GFFY-T317 more potently inhibited LLC1 tumor growth in mice. The inhibition was dependent on LXR-activated IFNγ expression in APCs. D-Nap-GFFY-T317 increased M1 while reducing M2 type macrophages in tumors. Associated with activation of IFNγ expression, D-Nap-GFFY-T317 enhanced dendritic cell maturation and infiltration into tumors, increased CD3⁺/CD8⁺ cells in tumors, and inhibited tumor angiogenesis. Similarly, D-Nap-GFFY-T317 more potently inhibited growth of urethane-induced lung carcinomas than T317 oral administration. In these two tumor models, T317 oral administration, but not D-Nap-GFFY-T317 injection, activated hepatic lipogenesis and induced fatty liver. Conclusion: Our study demonstrates that D-Nap-GFFY-T317 inhibits lung tumor growth without adverse effects on the liver, indicating the hydrogel-encapsulated LXR ligand might be a novel therapy for tumor treatment.

Analysis of Low Molecular Weight Substances and Related Processes Influencing Cellular Cholesterol Efflux

Cholesterol efflux is the key process protecting the vascular system from the development of atherosclerotic lesions. Various extracellular and intracellular events affect the ability of the cell to efflux excess cholesterol. To explore the possible pathways and processes that promote or inhibit cholesterol efflux, we applied a combined cheminformatic and bioinformatic approach. We performed a comprehensive analysis of published data on the various substances influencing cholesterol efflux and found 153 low molecular weight substances that are included in the Chemical Entities of Biological Interest (ChEBI) database. Pathway enrichment was performed for substances identified within the Reactome database, and 45 substances were selected in 93 significant pathways. The most common pathways included the energy-dependent processes related to active cholesterol transport from the cell, lipoprotein metabolism and lipid transport, and signaling pathways. The activators and inhibitors of cholesterol efflux were non-uniformly distributed among the different pathways: the substances influencing ‘biological oxidations’ activate cholesterol efflux and the substances influencing ‘Signaling by GPCR and PTK6’ inhibit efflux. This analysis may be used in the search and design of efflux effectors for therapies targeting structural and functional high-density lipoprotein deficiency.

Brothers in Arms: ABCA1- and ABCG1-Mediated Cholesterol Efflux as Promising Targets in Cardiovascular Disease Treatment

Atherosclerosis is a leading cause of cardiovascular disease worldwide, and hypercholesterolemia is a major risk factor. Preventive treatments mainly focus on the effective reduction of low-density lipoprotein cholesterol, but their therapeutic value is limited by the inability to completely normalize atherosclerotic risk, probably due to the disease complexity and multifactorial pathogenesis. Consequently, high-density lipoprotein cholesterol gained much interest, as it appeared to be cardioprotective due to its major role in reverse cholesterol transport (RCT). RCT facilitates removal of cholesterol from peripheral tissues, including atherosclerotic plaques, and its subsequent hepatic clearance into bile. Therefore, RCT is expected to limit plaque formation and progression. Cellular cholesterol efflux is initiated and propagated by the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. Their expression and function are expected to be rate-limiting for cholesterol efflux, which makes them interesting targets to stimulate RCT and lower atherosclerotic risk. This systematic review discusses the molecular mechanisms relevant for RCT and ABCA1 and ABCG1 function, followed by a critical overview of potential pharmacological strategies with small molecules to enhance cellular cholesterol efflux and RCT. These strategies include regulation of ABCA1 and ABCG1 expression, degradation, and mRNA stability. Various small molecules have been demonstrated to increase RCT, but the underlying mechanisms are often not completely understood and are rather unspecific, potentially causing adverse effects. Better understanding of these mechanisms could enable the development of safer drugs to increase RCT and provide more insight into its relation with atherosclerotic risk. SIGNIFICANCE STATEMENT: Hypercholesterolemia is an important risk factor of atherosclerosis, which is a leading pathological mechanism underlying cardiovascular disease. Cholesterol is removed from atherosclerotic plaques and subsequently cleared by the liver into bile. This transport is mediated by high-density lipoprotein particles, to which cholesterol is transferred via ATP-binding cassette transporters ABCA1 and ABCG1. Small-molecule pharmacological strategies stimulating these transporters may provide promising options for cardiovascular disease treatment.

TRIM59 expression is regulated by Sp1 and Nrf1 in LPS-activated macrophages through JNK signaling pathway

Activated macrophages play an important role in many inflammatory diseases including septic shock and atherosclerosis. TRIM59 has been showed to participate in many pathological processes, such as inflammation, cytotoxicity and tumorigenesis. However, the molecular mechanisms controlling its expression in activated macrophages are not fully understood. Here we report that TRIM59 expression is regulated by Sp1 and Nrf1 in LPS-activated macrophages. TRIM59 is highly expressed in macrophages, and markedly decreased by LPS stimuli in vivo and in vitro. TRIM59 promoter activity is also significantly suppressed by LPS and further analysis demonstrated that Sp1 and Nrf1 directly bound to the proximal promoter of TRIM59 gene. LPS treatment significantly decreased Sp1 expression, nuclear translocation and reduced its binding to the promoter, whereas increased Nrf1 expression, nuclear translocation and enhanced its binding to the promoter. Moreover, LPS-decreased TRIM59 expression was reversed by JNK inhibitor. Finally, TRIM59 level is significantly decreased during atherosclerosis progression. Taken together, our results demonstrated that TRIM59 expression was precisely regulated by Sp1 and Nrf1 in LPS-activated macrophages, which may be dependent on the activation of JNK signaling pathway and TRIM59 may be a potential therapeutic target for inflammatory diseases such as atherosclerosis.

Inhibition of Vascular Calcification

Objective- Vascular calcification is a major risk factor for rupture of atherosclerotic plaques. High expression of BMP2 (bone morphogenetic protein 2) in lesions suggests its importance in vascular calcification during atherosclerosis. Teniposide is a Topo II (DNA topoisomerase II) inhibitor and is used for cancer treatment. Previously, we reported that teniposide activated macrophage ABCA1 (ATP-binding cassette transporter A1) expression and free cholesterol efflux indicating Topo II inhibitors may demonstrate antiatherogenic properties. Herein, we investigated the effects of teniposide on the development of atherosclerosis and vascular calcification in apoE^-/- (apoE deficient) mice. Approach and Results- apoE^-/- mice were fed high-fat diet containing teniposide for 16 weeks, or prefed high-fat diet for 12 weeks followed by high-fat diet containing teniposide for 4 weeks. Atherosclerosis and vascular calcification were determined. Human aortic smooth muscle cells were used to determine the mechanisms for teniposide-inhibited vascular calcification. Teniposide reduced atherosclerotic lesions. It also substantially reduced vascular calcification without affecting bone structure. Mechanistically, teniposide reduced vascular calcification by inactivating BMP2/(pi-Smad1/5/8 [mothers against decapentaplegic homolog 1, 5, and 8])/RUNX2 (runt-related transcription factor 2) axis in a p53-dependent manner. Furthermore, activated miR-203-3p by teniposide functioned as a link between activated p53 expression and inhibited BMP2 expression in inhibition of calcification. Conclusions- Our study demonstrates that teniposide reduces vascular calcification by regulating p53-(miR-203-3p)-BMP2 signaling pathway, which contributes to the antiatherogenic properties of Topo II inhibitors.

Thioredoxin-1 promotes macrophage reverse cholesterol transport and protects liver from steatosis

Atherosclerosis is characterized by the accumulation of excess cholesterol in plaques. Reverse cholesterol transport (RCT) plays a key role in the removal of cholesterol. In the present study, we examined the effect of thioredoxin-1 (Trx-1) on RCT and explored the underlying mechanism. We found that Trx-1 promoted RCT in vivo, as did T0901317, a known liver X receptor (LXR) ligand. T0901317 also inhibited the development of atherosclerotic plaques but promoted liver steatosis. Furthermore, Trx-1 promoted macrophage cholesterol efflux to apoAI in vitro. Mechanistically, Trx-1 promoted nuclear translocation of LXRα and induced the expression of ATP-binding cassette transporter A1 (ABCA1). Apolipoprotein E knockout (apoE-/-) mice fed an atherogenic diet were daily injected intraperitoneally with saline or Trx-1 (0.33 mg/kg). Trx-1 treatment significantly inhibited the development of atherosclerosis and induced the expression of ABCA1 in macrophages retrieved from apoE-/- mice. Moreover, the liver steatosis was attenuated by Trx-1. Overall, we demonstrated that Trx-1 promotes RCT by upregulating ABCA1 expression through induction of nuclear translocation of LXRα, and protects liver from steatosis.

High-Density Lipoprotein Components and Functionality in Cancer: State-of-the-Art

Cancer is the second leading cause of death in western countries, and thus represents a major global public health issue. Whilst it is well-recognized that diet, obesity, and smoking are risk factors for cancer, the role of low levels of high-density lipoprotein cholesterol (HDL-C) in cancer is less well appreciated. Conflicting evidence suggests that serum HDL-C levels may be either positively or negatively associated with cancer incidence and mortality. Such disparate associations are supported in part by the multitude of high-density lipoprotein (HDL) functions that can all have an impact on cancer cell biology. The aim of this review is to provide a comprehensive overview of the crosstalk between HDLs and cancer, focusing on the molecular mechanisms underlying this association.

Teniposide regulates the phenotype switching of vascular smooth muscle cells in a miR-21-dependent manner

The switch of vascular smooth muscle cells (SMCs) from the contractile phenotype to proliferative one can make contributions to atherosclerosis and neointima formation. MiR-21 can prevent the rupture of advanced lesion plaques. We previously reported the protection of DNA topoisomerase II (Topo II) inhibitors against atherosclerosis and vascular calcification. However, it remains unknown if Topo II inhibitors can change SMC phenotypes. Herein, we show that teniposide protected SMC phenotype switching during atherosclerosis by enhancing expression of smooth muscle α-actin (SMA) while reducing osteopontin (OPN) expression in aortic lesion plaques. In vitro, teniposide induced expression of smooth muscle protein 22-α and calponin 1, but inhibited expression of OPN and epiregulin in human aortic SMCs (HASMCs). Moreover, teniposide attenuated platelet derived growth factor-BB-induced HASMC proliferation and migration. Mechanistically, the effect of teniposide on SMC phenotypes was completed, at least in part, by activating miR-21 expression. In addition, teniposide ameliorated ligation-induced carotid artery remodeling in C57BL/6J mice by regulating SMA and OPN expression. Taken together, our study demonstrates that teniposide regulates SMC phenotype switching by upregulating expression of contractile genes in a miR-21-dependent manner, and this function is an important anti-atherogenic mechanism of teniposide.

Cholesterol negatively regulates IL-9-producing CD8+ T cell differentiation and antitumor activity

CD8⁺ T cells can be polarized into IL-9-secreting (Tc9) cells. We previously showed that adoptive therapy using tumor-specific Tc9 cells generated stronger antitumor responses in mouse melanoma than classical Tc1 cells. To understand why Tc9 cells exert stronger antitumor responses, we used gene profiling to compare Tc9 and Tc1 cells. Tc9 cells expressed different levels of cholesterol synthesis and efflux genes and possessed significantly lower cholesterol content than Tc1 cells. Unique to Tc9, but not other CD8⁺ or CD4⁺ T cell subsets, manipulating cholesterol content in polarizing Tc9 cells significantly affected IL-9 expression and Tc9 differentiation and antitumor response in vivo. Mechanistic studies showed that IL-9 was indispensable for Tc9 cell persistence and antitumor effects, and cholesterol or its derivatives inhibited IL-9 expression by activating liver X receptors (LXRs), leading to LXR Sumoylation and reduced p65 binding to Il9 promoter. Our study identifies cholesterol as a critical regulator of Tc9 cell differentiation and function.

Andrographolide Inhibits Oxidized LDL-Induced Cholesterol Accumulation and Foam Cell Formation in Macrophages

oxLDL is involved in the pathogenesis of atherosclerotic lesions through cholesterol accumulation in macrophage foam cells. Andrographolide, the bioactive component of Andrographis paniculata, possesses several biological activities such as anti-inflammatory, anti-oxidant, and anticancer functions. Scavenger receptors (SRs), including class A SR (SR-A) and CD36, are responsible for the internalization of oxLDL. In contrast, receptors for reverse cholesterol transport, including ABCA1 and ABCG1, mediate the efflux of cholesterol from macrophage foam cells. Transcription factor liver X receptor [Formula: see text] (LXR[Formula: see text] plays a key role in lipid metabolism and inflammation as well as in the regulation of ABCA1 and ABCG1 expression. Because of the contribution of inflammation to macrophage foam cell formation and the potent anti-inflammatory activity of andrographolide, we hypothesized that andrographolide might inhibit oxLDL-induced macrophage foam cell formation. The results showed that andrographolide reduced oxLDL-induced lipid accumulation in macrophage foam cells. Andrographolide decreased the mRNA and protein expression of CD36 by inducing the degradation of CD36 mRNA; however, andrographolide had no effect on SR-A expression. In contrast, andrographolide increased the mRNA and protein expression of ABCA1 and ABCG1, which were dependent on LXR[Formula: see text]. Andrographolide enhanced LXR[Formula: see text] nuclear translocation and DNA binding activity. Treatment with the LXR[Formula: see text] antagonist GGPP and transfection with LXR[Formula: see text] siRNA reversed the ability of andrographolide to stimulate ABCA1 and ABCG1 protein expression. In conclusion, inhibition of CD36-mediated oxLDL uptake and induction of ABCA1- and ABCG1-dependent cholesterol efflux are two working mechanisms by which andrographolide inhibits macrophage foam cell formation, which suggests that andrographolide could be a potential candidate to prevent atherosclerosis.

β3-Adrenoceptor activation upregulates apolipoprotein A-I expression in HepG2 cells, which might further promote cholesterol efflux from macrophage foam cells

Objective

The aim of this study was to explore the effects of β₃-adrenoceptor (β₃-AR) activation on HepG2 cells and its influence on cholesterol efflux from macrophage foam cells.

Materials and methods

HepG2 cells were cultured and treated with the β₃-AR agonist, BRL37344, and antagonist, SR52390A, and the expression of apolipoprotein (Apo) A-I, ApoA-II, ApoB, and β₃-AR in the supernatants and cells was determined. The expression of peroxisome proliferator-activated receptor (PPAR) γ and PPARα in the HepG2 cells was also assessed. Next, using the RAW264.7 macrophage foam cell model, we also assessed the influence of the HepG2 cell supernatants on lipid efflux. The cholesterol content of the foam cells was also measured, and the cholesterol efflux from the macrophages was examined by determining ³H-labeled cholesterol levels. Expression of ATP-binding cassette transporter (ABC) A1 and ABCG1 of the macrophage foam cells was also assessed.

Results

β₃-AR activation increased ApoA-I expression in both the HepG2 cells and the supernatants; PPARγ expression was upregulated, but PPARα expression was not. Treatment with GW9662 abolished the increased expression of ApoA-I induced by the β₃-AR agonist. The HepG2 cell supernatants decreased the lipid accumulation and increased the cholesterol efflux from the macrophage foam cells. ABCA1 expression, but not ABCG1 expression, increased in the macrophage foam cells treated with BRL37344-treated HepG2 cell supernatants.

Conclusion

Activation of β₃-AR in HepG2 cells upregulates ApoA-I expression, which might further promote cholesterol efflux from macrophage foam cells. PPARγ might be required for the induction of ApoA-I expression.

Expression profiling of TRIM protein family in THP1-derived macrophages following TLR stimulation

Activated macrophages play an important role in many inflammatory diseases including septic shock and atherosclerosis. However, the molecular mechanisms limiting macrophage activation are not completely understood. Members of the tripartite motif (TRIM) family have recently emerged as important players in innate immunity and antivirus. Here, we systematically analyzed mRNA expressions of representative TRIM molecules in human THP1-derived macrophages activated by different toll-like receptor (TLR) ligands. Twenty-nine TRIM members were highly induced (>3 fold) by one or more TLR ligands, among which 19 of them belong to TRIM C-IV subgroup. Besides TRIM21, TRIM22 and TRIM38 were shown to be upregulated by TLR3 and TLR4 ligands as previous reported, we identified a novel group of TRIM genes (TRIM14, 15, 31, 34, 43, 48, 49, 51 and 61) that were significantly up-regulated by TLR3 and TLR4 ligands. In contrast, the expression of TRIM59 was down-regulated by TLR3 and TLR4 ligands in both human and mouse macrophages. The alternations of the TRIM proteins were confirmed by Western blot. Finally, overexpression of TRIM59 significantly suppressed LPS-induced macrophage activation, whereas siRNA-mediated knockdown of TRIM59 enhanced LPS-induced macrophage activation. Taken together, the study provided an insight into the TLR ligands-induced expressions of TRIM family in macrophages.

Liver X receptors agonists suppress NLRP3 inflammasome activation

Inflammasomes are multiprotein complexes that control the production of IL-1β and IL-18. NLRP3 inflammasome, the most characterized inflammasome, plays prominent roles in defense against infection, however aberrant activation is deleterious and leads to diseases. Therefore, its tight control offers therapeutic promise. Liver X receptors (LXRs) have significant anti-inflammatory properties. Whether LXRs regulate inflammasome remains unresolved. We thus tested the hypothesis that LXR's anti-inflammatory properties may result from its ability to suppress inflammasome activation. In this study, LXRs agonists inhibited the induction of IL-1β production, caspase-1 cleavage and ASC oligomerization by NLRP3 inflammasome. The agonists also inhibited inflammasome-associated mtROS production. Importantly, the agonists inhibited the priming of inflammasome activation. In vivo data also showed that LXRs agonist prevented NLRP3-dependent peritonitis. In conclusion, LXRs agonists are identified to potently suppress NLRP3 inflammasome and the regulation of LXRs signaling is a potential therapeutic for inflammasome-driven diseases.

Multi-Layer Identification of Highly-Potent ABCA1 Up-Regulators Targeting LXRβ Using Multiple QSAR Modeling, Structural Similarity Analysis, and Molecular Docking

In this study, in silico approaches, including multiple QSAR modeling, structural similarity analysis, and molecular docking, were applied to develop QSAR classification models as a fast screening tool for identifying highly-potent ABCA1 up-regulators targeting LXRβ based on a series of new flavonoids. Initially, four modeling approaches, including linear discriminant analysis, support vector machine, radial basis function neural network, and classification and regression trees, were applied to construct different QSAR classification models. The statistics results indicated that these four kinds of QSAR models were powerful tools for screening highly potent ABCA1 up-regulators. Then, a consensus QSAR model was developed by combining the predictions from these four models. To discover new ABCA1 up-regulators at maximum accuracy, the compounds in the ZINC database that fulfilled the requirement of structural similarity of 0.7 compared to known potent ABCA1 up-regulator were subjected to the consensus QSAR model, which led to the discovery of 50 compounds. Finally, they were docked into the LXRβ binding site to understand their role in up-regulating ABCA1 expression. The excellent binding modes and docking scores of 10 hit compounds suggested they were highly-potent ABCA1 up-regulators targeting LXRβ. Overall, this study provided an effective strategy to discover highly potent ABCA1 up-regulators.

Intracellular cholesterol transport proteins: roles in health and disease

Effective cholesterol homoeostasis is essential in maintaining cellular function, and this is achieved by a network of lipid-responsive nuclear transcription factors, and enzymes, receptors and transporters subject to post-transcriptional and post-translational regulation, whereas loss of these elegant, tightly regulated homoeostatic responses is integral to disease pathologies. Recent data suggest that sterol-binding sensors, exchangers and transporters contribute to regulation of cellular cholesterol homoeostasis and that genetic overexpression or deletion, or mutations, in a number of these proteins are linked with diseases, including atherosclerosis, dyslipidaemia, diabetes, congenital lipoid adrenal hyperplasia, cancer, autosomal dominant hearing loss and male infertility. This review focuses on current evidence exploring the function of members of the ‘START’ (steroidogenic acute regulatory protein-related lipid transfer) and ‘ORP’ (oxysterol-binding protein-related proteins) families of sterol-binding proteins in sterol homoeostasis in eukaryotic cells, and the evidence that they represent valid therapeutic targets to alleviate human disease.

Regulation of Hepatic Cholesteryl Ester Transfer Protein Expression and Reverse Cholesterol Transport by Inhibition of DNA Topoisomerase II

Cholesteryl ester transfer protein (CETP) transfers cholesteryl esters from high density lipoprotein to triglyceride-rich lipoproteins. CETP expression can be transcriptionally activated by liver X receptor (LXR). Etoposide and teniposide are DNA topoisomerase II (Topo II) inhibitors. Etoposide has been reported to inhibit atherosclerosis in rabbits with un-fully elucidated mechanisms. In this study we determined if Topo II activity can influence cholesterol metabolism by regulating hepatic CETP expression. Inhibition of Topo II by etoposide, teniposide, or Topo II siRNA increased CETP expression in human hepatic cell line, HepG2 cells, which was associated with increased CETP secretion and mRNA expression. Meanwhile, inhibition of LXR expression by LXR siRNA attenuated induction of CETP expression by etoposide and teniposide. Etoposide and teniposide induced LXRα expression and LXRα/β nuclear translocation while inhibiting expression of receptor interacting protein 140 (RIP140), an LXR co-repressor. In vivo, administration of teniposide moderately reduced serum lipid profiles, induced CETP expression in the liver, and activated reverse cholesterol transport in CETP transgenic mice. Our study demonstrates a novel function of Topo II inhibitors in cholesterol metabolism by activating hepatic CETP expression and reverse cholesterol transport.