Cholesteryl Ester Transfer Protein mRNA Research Articles

Effects of lysine deficiency or excess on growth and the expression of lipid metabolism genes in slow-growing broilers

This experiment was conducted to evaluate the effects of lysine deficiency or excess on growth and the expression of lipid metabolism genes in slow-growing birds. A total of 360 one-day-old chicks were randomly divided into 3 groups, with 6 replicates of 20 birds each. The birds fed the basal diet with a total lysine 0.60% (LL), 1.00% (ML), or 1.40% (HL). The amount of lysine (ML) as the control group, LL and HL as the experimental group, the trial period last 3 wk. The results showed that compared with ML, LL significantly decreased average daily gain and average daily feed intake and remarkably increased feed conversion ratio of birds at 21 day old (P < 0.01), while the above indices in HL had no significant effects (P > 0.05). Besides, LL reduced the pectoral muscle rate (P < 0.01) and decreased the percentage of abdominal fat significantly (P < 0.05). In addition, compared with ML, the expression of fatty acid binding protein 1 (FABP1), acetyl-CoA carboxylase (ACC), malic enzyme (ME), and sterol regulatory element binding protein 1 (SREBP1c) mRNA of liver in LL was significantly decreased (P < 0.05), and the expression of cholesteryl ester transfer protein (CETP) mRNA was significantly increased (P < 0.01), whereas LL had no significant effects on the expression of peroxisome proliferator activated receptor alpha (PPARα) mRNA (P > 0.05). Moreover, compared with ML, HL significantly reduced the expression of FABP1, ACC, ME, SREBP-1c, and PPARα mRNA in the liver (P < 0.05), and had no significant effects on the expression of CETP mRNA (P > 0.05). The results of current research suggest that dietary lysine deficiency could reduce the growth and fat deposition of slow-growing broilers mainly by downregulating the expression of lipid synthesis genes.

Forhidrol, a bioactive fraction of Phaleria macrocarpa (Scheff.) Boerl., increases reverse cholesterol transport pathway by down-regulation of cholesteryl ester transfer protein activity

Phaleria macrocarpa (Scheff.) Boerl. is one of the most popular medicinal plants in Indonesia. This plant has traditionally been used to lower cholesterol and control hypertension. This study was performed to examine the effect of Forhidrol, a bioactive fraction of P. macrocarpa (Scheff.) Boerl., to increase reverse cholesterol transport through the down-regulation of cholesteryl ester transfer protein (CETP) activity in hepatocellular carcinoma cell lines. Measurement of target genes including liver X receptor (LXR), sterol regulatory element-binding protein 1 (SREBP1), scavenger receptor class B type 1, low-density lipoprotein (LDL) receptor, apolipoprotein B, CYP11B1, CYP11B2, peroxisome proliferatoractivated receptor α (PPARα), peroxisome proliferator-activated receptor δ (PPARδ) and peroxisome proliferator-activated receptor γ (PPARγ) were done using realtime polymerase chain reaction assay. Secreted CETP and apolipoprotein A-1 were analyzed using western blot. CETP activity in vitro was measured using CETP inhibitor drug screening kit and triglyceride synthesis was measured using enzyme-linked immunosorbent assay. Forhidrol was found to significantly down-regulate CETP mRNA expression, as well as total CETP and cholesteryl esters transfer activity (P&lt;0.05). It specifically reduced transcriptional level of regulatory genes of CETP promoter including SREBP-1 and LXR. Forhidrol also significantly increased PPARδ and PPARα expression (P&lt;0.05) and slightly repressed triglycerides synthesis. In vivo study showed elevated high-density lipoprotein (HDL) levels in rabbits after 4-week treatment of Forhidrol at a dose of 37.5 mg/1.5 kg body weight compared to placebo. Conversely, LDL, triglyceride and CETP activity were decreased. Forhidrol increased HDL levels by reducing CETP-dependent transfer of cholesterol from HDL to LDL particles. Looking at possible side effects, Forhidrol apparently acted as a safe agent without negative effect towards blood pressure. These findings suggested that Forhidrol may be further developed as a potential anti-atherogenic drug.

Downregulation of cholesteryl ester transfer protein by glucocorticoids: a randomised study on HDL.

High density lipoprotein (HDL) cholesterol is not decreased in hypercortisolism despite high triglycerides, which may be ascribed to effects on the cholesteryl ester transfer protein (CETP) pathway. We explored if CETP mRNA expression is modulated by glucocorticoid treatment in vitro. Effects of doubling the hydrocortisone (HCT) replacement dose on plasma CETP activity, and HDL characteristics were tested in patients with secondary adrenal insufficiency. Human THP-1 macrophages were incubated with corticosterone in vitro in the presence or absence of a liver X receptor (LXR) agonist, followed by determination of CETP mRNA levels by quantitative real-time PCR. In addition, a randomised double-blind cross-over study was performed in 47 patients with secondary adrenal insufficiency (university medical setting; 10 weeks exposure to a higher HCT dose (0·4-0·6 mg/kg body weight) vs. 10 weeks of a lower HCT dose (0·2-0·3 mg/kg body weight). Corticosterone dose dependently decreased CETP mRNA in THP-1 macrophages. Corticosterone also decreased CETP mRNA expression after LXR pretreatment. In patients, CETP activity decreased with doubling of the HCT dose (P = 0·049), coinciding with an increase in HDL cholesterol, apolipoprotein A-I and the HDL cholesterol/apolipoprotein A-I ratio (reflecting HDL size; P < 0·01 for each). The increase in the HDL cholesterol/apolipoprotein A-I ratio was correlated with the decrease in plasma CETP activity (r = -0·442, P = 0·002). Glucocorticoids downregulate CETP gene expression in a human macrophage cell system. In line, a higher glucocorticoid replacement dose decreases plasma CETP activity in patients, thereby contributing to higher HDL cholesterol and an increase in estimated HDL size.

Functional and association studies of the cholesteryl ester transfer protein (CETP) gene in a Wannan Black pig model.

Some polymorphisms of the human CETP gene are causally and significantly associated with serum lipids levels; however, the information regarding this gene in pigs is sparse. To evaluate the effects of CETP on blood lipid traits and fat deposition in pig, porcine CETP tissue expression patterns were observed by quantitative real-time polymerase chain reaction (qPCR) first. High expression was detected in liver, spleen, gluteus medius (GM) muscle and backfat. A de novo polymorphism (AF333037:g.795C>T) in the intron 1 region of porcine CETP was identified. This polymorphism was further genotyped by direct sequencing of the PCR products of 390 Wannan Black pigs, a Chinese native breed population. Association analyses at 45 and 300days of age revealed highly significant associations between CETP genotypes and serum lipid traits. Furthermore, this polymorphism was proved to be associated with differences in liver CETP mRNA levels: pigs at 300days of age with the TT genotype had higher levels than did those with other genotypes (P=0.021). Additionally, analysis at 300days of age showed that GM CETP mRNA expression correlated positively with serum lipids levels as well as with carcass backfat thickness and intramuscular fat content in GM. These results indicate that CETP is involved in serum, adipose and muscle lipid metabolism in pigs. The mechanisms underlying such relationships and their functional implications are worthy of further research.

A novel microdeletion affecting the CETP gene raises HDL-associated cholesterol levels.

We describe a novel, inherited 16q13 microdeletion that removes cholesteryl ester transfer protein (CETP) and several nearby genes. The proband was originally referred for severe childhood-onset obesity and moderate developmental delay, but his fasting lipid profile revealed relatively high levels of high density lipoprotein cholesterol (HDL-C) and relatively low levels of low density lipoprotein cholesterol (LDL-C) for age, despite his obesity. Testing of first-degree relatives identified two other microdeletion carriers. Functional assays in affected individuals showed decreased CETP mRNA expression and enzymatic activity. This microdeletion may or may not be pathogenic for obesity and developmental delay, but based on the lipid profile, the functional studies, and the phenotype of other patients with loss-of-function mutations of CETP, we believe this microdeletion to be antipathogenic for cardiovascular 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.

DNA topoisomerase II inhibitors induce human cholesteryl ester transfer protein expression via an LXR‐dependent pathway (605.17)

DNA topoisomerase II inhibitors induce human cholesteryl ester transfer protein expression via an LXR‐dependent pathway Mengyang Liu, Yuanli Chen, Yajun Duan, Jihong Han State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin 300071, China The human cholesteryl ester transfer protein (CETP) transfers cholesteryl esters from high‐density lipoproteins (HDL) to the triglyceride‐rich lipoproteins. CETP is mainly expressed and secreted from the liver. It is transcriptionally regulated by liver X receptor (LXR). Etoposide and teniposide are DNA topoisomerase II (Topo II) inhibitors and used as chemotherapeutic medications to treat patients with various cancers. We previously reported that etoposide and teniposide activated macrophage ABCA1 expression, a LXR‐targeted gene. Herein we show that treatment of HepG2 cells with etoposide and teniposide was also able to increase CETP protein expression and secretion which was associated with increased CETP mRNA expression and promoter activity in an LXR‐dependent manner. Knockdown of LXRα/β expression by siRNA reduced the inductive effect of etoposide and teniposide on CETP expression. Moreover, etoposide and teniposide increased the nuclear translocation of LXR while down‐regulated LXR co‐repressor gene expression, thereby resulting in activation of LXR. Taken together, our study demonstrates that etoposide and teniposide induce hepatic CETP expression in an LXR‐dependent mechanism. Our study also reveals another role of Topo II inhibitors in regulation of cholesterol homeostasis gene expression other than their anti‐tumorigenesis function.

Fibrates and fish oil, but not corn oil, up-regulate the expression of the cholesteryl ester transfer protein (CETP) gene

Cholesteryl ester transfer protein (CETP) is a plasma protein that reduces high density lipoprotein (HDL)-cholesterol (chol) levels and may increase atherosclerosis risk. n-3 and n-6 polyunsaturated fatty acids (PUFAs) are natural ligands, and fibrates are synthetic ligands for peroxisome proliferator activated receptor-alpha (PPARα), a transcription factor that modulates lipid metabolism. In this study, we investigated the effects of PUFA oils and fibrates on CETP expression. Hypertriglyceridemic CETP transgenic mice were treated with gemfibrozil, fenofibrate, bezafibrate or vehicle (control), and normolipidemic CETP transgenic mice were treated with fenofibrate or with fish oil (FO; n-3 PUFA rich), corn oil (CO, n-6 PUFA rich) or saline. Compared with the control treatment, only fenofibrate significantly diminished triglyceridemia (50%), whereas all fibrates decreased the HDL-chol level. Elevation of the CETP liver mRNA levels and plasma activity was observed in the fenofibrate (53%) and gemfibrozil (75%) groups. Compared with saline, FO reduced the plasma levels of nonesterified fatty acid (26%), total chol (15%) and HDL-chol (20%). Neither of the oil treatments affected the plasma triglyceride levels. Compared with saline, FO increased the plasma adiponectin level and reduced plasma leptin levels, whereas CO increased the leptin levels. FO, but not CO, significantly increased the plasma CETP mass (90%) and activity (23%) as well as increased the liver level of CETP mRNA (28%). In conclusion, fibrates and FO, but not CO, up-regulated CETP expression at both the mRNA and protein levels. We propose that these effects are mediated by the activation of PPARα, which acts on a putative PPAR response element in the CETP gene.

Antisense oligonucleotide inhibition of cholesteryl ester transfer protein enhances RCT in hyperlipidemic, CETP transgenic, LDLr-/- mice

Due to their ability to promote positive effects across all of the lipoprotein classes, cholesteryl ester transfer protein (CETP) inhibitors are currently being developed as therapeutic agents for cardiovascular disease. In these studies, we compared an antisense oligonucleotide (ASO) inhibitor of CETP to the CETP small molecule inhibitor anacetrapib. In hyperlipidemic CETP transgenic (tg) mice, both drugs provided comparable reductions in total plasma cholesterol, decreases in CETP activity, and increases in HDL cholesterol. However, only mice treated with the antisense inhibitor showed an enhanced effect on macrophage reverse cholesterol transport, presumably due to differences in HDL apolipoprotein composition and decreases in plasma triglyceride. Additionally, the ASO-mediated reductions in CETP mRNA were associated with less accumulation of aortic cholesterol. These preliminary findings suggest that CETP ASOs may represent an alternative means to inhibit that target and to support their continued development as a treatment for cardiovascular disease in man.

Farnesoid X receptor activation increases cholesteryl ester transfer protein expression in humans and transgenic mice

Cholesteryl ester transfer protein (CETP) activity results in a proatherogenic lipoprotein profile. In cholestatic conditions, farnesoid X receptor (FXR) signaling by bile acids (BA) is activated and plasma HDL cholesterol (HDL-C) levels are low. This study tested the hypothesis that FXR-mediated induction of CETP contributes to this phenotype. Patients with cholestasis and high plasma BA had lower HDL-C levels and higher plasma CETP activity and mass compared with matched controls with low plasma BA (each P < 0.01). BA feeding in APOE3*Leiden transgenic mice expressing the human CETP transgene controlled by its endogenous promoter increased cholesterol within apoB-containing lipoproteins and decreased HDL-C (each P < 0.01), while hepatic CETP mRNA expression and plasma CETP activity and mass increased (each P < 0.01). In vitro studies confirmed that FXR agonists substantially augmented CETP mRNA expression in hepatocytes and macrophages dependent on functional FXR expression (each P < 0.001). These transcriptional effects are likely mediated by an ER8 FXR response element (FXRE) in the first intron. In conclusion, using a translational approach, this study identifies CETP as novel FXR target gene. By increasing CETP expression, FXR activation leads to a proatherogenic lipoprotein profile. These results have clinical relevance, especially when considering FXR agonists as emerging treatment strategy for metabolic disease and atherosclerosis.

Cholesteryl Ester Transfer Protein (CETP) Polymorphisms Affect mRNA Splicing, HDL Levels, and Sex-Dependent Cardiovascular Risk

Polymorphisms in and around the Cholesteryl Ester Transfer Protein (CETP) gene have been associated with HDL levels, risk for coronary artery disease (CAD), and response to therapy. The mechanism of action of these polymorphisms has yet to be defined. We used mRNA allelic expression and splice isoform measurements in human liver tissues to identify the genetic variants affecting CETP levels. Allelic CETP mRNA expression ratios in 56 human livers were strongly associated with several variants 2.5–7 kb upstream of the transcription start site (e.g., rs247616 p = 6.4×10−5, allele frequency 33%). In addition, a common alternatively spliced CETP isoform lacking exon 9 (Δ9), has been shown to prevent CETP secretion in a dominant-negative manner. The Δ 9 expression ranged from 10 to 48% of total CETP mRNA in 94 livers. Increased formation of this isoform was exclusively associated with an exon 9 polymorphism rs5883-C>T (p = 6.8×10−10) and intron 8 polymorphism rs9930761-T>C (5.6×10−8) (in high linkage disequilibrium with allele frequencies 6–7%). rs9930761 changes a key splicing branch point nucleotide in intron 8, while rs5883 alters an exonic splicing enhancer sequence in exon 9.The effect of these polymorphisms was evaluated in two clinical studies. In the Whitehall II study of 4745 subjects, both rs247616 and rs5883T/rs9930761C were independently associated with increased HDL-C levels in males with similar effect size (rs247616 p = 9.6×10−28 and rs5883 p = 8.6×10−10, adjusted for rs247616). In an independent multiethnic US cohort of hypertensive subjects with CAD (INVEST-GENE), rs5883T/rs9930761C alone were significantly associated with increased incidence of MI, stroke, and all-cause mortality in males (rs5883: OR 2.36 (CI 1.29–4.30), p = 0.005, n = 866). These variants did not reach significance in females in either study. Similar to earlier results linking low CETP activity with poor outcomes in males, our results suggest genetic, sex-dependent CETP splicing effects on cardiovascular risk by a mechanism independent of circulating HDL-C levels.

Structure and Function of Cholesteryl Ester Transfer Protein in the Tree Shrew

Cholesteryl ester transfer protein (CETP) plays an important role in reverse cholesterol transport (RCT). To study on the structure and function of CETP in the tree shrew, a kind of animal resistant to atherosclerosis, we completed the cloning of the full-length tree-shrew CETP cDNA sequence based on the reported partial sequence. The full-length cDNA of tree shrew CETP was 1,704bp and the deduced protein of the cDNA showed a sequence identity of 81, 80 and 74%, respectively, with the human, monkey and rabbit CETP. The level of CETP mRNA in the liver was much more abundant than that in the other tissues. A mutant protein with a substitution of Asn at position 110 by Gln was found to possess an impaired secretion property compared with the wild-type tree shrew CETP. The mutant proteins, respectively, with a substitution of Pro at position 344 by Ser and a substitution of Gln at position 452 by Arg displayed similar secretion ability, but a decreased cholesteryl ester transfer capability compared with the wild type (48 and 26% lower, respectively). These findings demonstrate that liver is the main tissue synthesizing CETP in the tree shrew. Asn at position 110 plays an important role in the secretion of tree shrew CETP. The residues at position 344 and 452 play essential roles in cholesteryl ester transferring process.

Cholesteryl ester transfer protein and hepatic lipase gene polymorphisms: Effects on hepatic mRNA levels, plasma lipids and carotid atherosclerosis

ObjectiveHDL modifying effects of cholesteryl ester transfer protein (CETP) and hepatic lipase (LIPC) depend in part on each other. We studied associations of CETP-Taq1B and -514C>T-LIPC polymorphisms with hepatic mRNA levels, and their combined effects on plasma lipids and carotid atherosclerosis. MethodsWe genotyped the CETP-Taq1B and the -514C>T-LIPC polymorphisms in 67 obese women in whom hepatic CETP and LIPC transcript levels were determined as well as in 1549 participants of the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR). Carotid atherosclerosis was assessed by intima-media thickness and extent of plaques (B-score) of the carotid arteries. ResultsIn obese women, CETP-Taq1B and -514C>T-LIPC variant alleles were associated with reduced hepatic levels of CETP and LIPC mRNA, respectively. The CETP and LIPC polymorphisms accounted for 12.9 and 14.4% of the variability in respective transcripts. In the SAPHIR population, CETP-Taq1B showed independent effects on LDL diameter, HDL and LDL cholesterol, apolipoproteins AI and B and cholesterol/HDL cholesterol, while -514C>T-LIPC revealed independent effects on HDL cholesterol and apolipoprotein AI. The two polymorphisms displayed interactions at the level of HDL cholesterol. Compared to subjects carrying wild-type alleles at both loci, subjects homozygous for the CETP wild-type allele, but heterozygous for the LIPC polymorphism and subjects heterozygous for the CETP polymorphism, but homozygous for the LIPC wild-type allele showed an increased risk of carotid atherosclerosis (both P<0.05). ConclusionsCETP and LIPC polymorphisms influence the respective hepatic transcript levels, demonstrate interactions on HDL cholesterol and suggest that imbalances between CETP and LIPC activities may modulate the risk of carotid atherosclerosis.

Liver X Receptor–Mediated Induction of Cholesteryl Ester Transfer Protein Expression Is Selectively Impaired in Inflammatory Macrophages

Cholesteryl ester transfer protein (CETP) is a target gene for the liver X receptor (LXR). The aim of this study was to further explore this regulation in the monocyte-macrophage lineage and its modulation by lipid loading and inflammation, which are key steps in the process of atherogenesis. Exposure of bone marrow-derived macrophages from human CETP transgenic mice to the T0901317 LXR agonist increased CETP, PLTP, and ABCA1 mRNA levels. T0901317 also markedly increased CETP mRNA levels and CETP production in human differentiated macrophages, whereas it had no effect on CETP expression in human peripheral blood monocytes. In inflammatory mouse and human macrophages, LXR-mediated CETP gene upregulation was inhibited, even though ABCA1, ABCG1, and SREBP1c inductions were maintained. The inhibition of CETP gene response to LXR agonists in inflammatory cells was independent of lipid loading (ie, oxidized LDL increased CETP production in noninflammatory macrophages with a synergistic effect of synthetic LXR agonists). LXR-mediated induction of human CETP expression is switched on during monocyte-to-macrophage differentiation, is magnified by lipid loading, and is selectively lost in inflammatory macrophages, which suggests that inflammatory cells may not increase the circulating CETP pool on LXR agonist treatment.

Molecular cloning of hamster lipid transfer inhibitor protein (apolipoprotein F) and regulation of its expression by hyperlipidemia

Lipid transfer inhibitor protein (LTIP) is a regulator of cholesteryl ester transfer protein (CETP) function. Factors affecting plasma LTIP levels are poorly understood. In humans, plasma LTIP is elevated in hypercholesterolemia. To define possible mechanisms by which hyperlipidemia modifies LTIP, we investigated the effects of hypercholesterolemic diets on plasma LTIP and mRNA levels in experimental animals. The hamster, which naturally expresses CETP, was shown to express LTIP. Hamster LTIP mRNA, exclusively detected in the liver, defined a predicted LTIP protein that is 69% homologous to human, with an isoelectric point of 4.15 and Mr = approximately 16.4 kDa. Hyperlipidemia induced by feeding hydrogenated coconut oil, cholesterol, or both lipids increased plasma LTIP mass up to 2.5-fold, with LTIP mass correlating strongly with plasma cholesterol levels. CETP mass was similarly affected by these diets. In contrast, these diets reduced LTIP hepatic mRNA levels by >50%, whereas CETP mRNA was increased. Similar results for both CETP and LTIP were also observed in cholesterol-fed rabbits. In conclusion, we report in hamster and rabbit that dietary lipids regulate LTIP. Diet-induced hypercholesterolemia markedly increased plasma LTIP mass while concomitantly depressing LTIP gene expression. CETP and LTIP have distinct responses to dietary lipids.

Novel mutations of CETP gene in Italian subjects with hyeralphalipoproteinemia

Cholesteryl ester transfer protein (CETP) is a plasma glycoprotein that catalyses the transfer of cholesteryl esters from HDL to the other plasma lipoproteins. Genetic deficiency of CETP is one of the known causes of elevation of plasma HDL-C (primary hyperalphalipoproteinemia, HALP). We sequenced CETP gene in a group of 24 Italian subjects with primary HALP (HDL-C > 80 mg/dl) suspected to have CETP deficiency. Two unrelated subjects both coming from the same geographical district, were found to be heterozygous for a nucleotide substitution in exon 6 (c.544C > T) and another subject was found to be heterozygous for a C > T transition in exon 9 (c.802C > T). Both mutations introduce a premature stop codon and are predicted to cause the production of truncated proteins (Q165X and R268X, respectively) devoid of function. The fourth proband was found to carry a T > C substitution in intron 15 (c.1407 + 2T > C) predicted to abolish the function of the donor splice site. To define the effect of this mutation on CETP pre-mRNA splicing we analysed CETP mRNA in COS-1 cells expressing a CETP minigene harbouring the mutation. The analysis of minigene transcript in COS-1 cells showed that IVS15 + 2T > C mutation caused the formation of an abnormal mRNA in which exon 14 joins directly to exon 16, predicted to encode a truncated peptide of 435 amino acids. In mutation carriers plasma CETP activity was found to be reduced by 38–60%. These are the first mutations in the CETP gene found in Italian subjects with HALP.

Atorvastatin increases HDL cholesterol by reducing CETP expression in cholesterol-fed APOE*3-Leiden.CETP mice

Objective In addition to lowering low-density lipoprotein (LDL)-cholesterol, statins modestly increase high-density lipoprotein (HDL)-cholesterol in humans and decrease cholesteryl ester transfer protein (CETP) mass and activity. Our aim was to determine whether the increase in HDL depends on CETP expression. Methods and results APOE*3-Leiden ( E3L) mice, with a human-like lipoprotein profile and a human-like responsiveness to statin treatment, were crossbred with mice expressing human CETP under control of its natural flanking regions resulting in E3L.CETP mice. E3L and E3L.CETP mice were fed a Western-type diet with or without atorvastatin. Atorvastatin (0.01% in the diet) reduced plasma cholesterol in both E3L and E3L.CETP mice (−26 and −33%, P < 0.05), mainly in VLDL, but increased HDL-cholesterol only in E3L.CETP mice (+52%). Hepatic mRNA expression levels of genes involved in HDL metabolism, such as phospholipid transfer protein ( Pltp), ATP-binding cassette transporter A1 ( Abca1), scavenger receptor class B type I ( Sr-b1), and apolipoprotein AI ( Apoa1), were not differently affected by atorvastatin in E3L.CETP mice as compared to E3L mice. However, in E3L.CETP mice, atorvastatin down-regulated the hepatic CETP mRNA expression (−57%; P < 0.01) as well as the total CETP level (−29%) and cholesteryl esters (CE) transfer activity (−36%; P < 0.0 5) in plasma. Conclusions Atorvastatin increases HDL-cholesterol in E3L.CETP mice by reducing the CETP-dependent transfer of cholesterol from HDL to (V)LDL, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool.

Fenofibrate increases HDL-cholesterol by reducing cholesteryl ester transfer protein expression

In addition to efficiently decreasing VLDL-triglycerides (TGs), fenofibrate increases HDL-cholesterol levels in humans. We investigated whether the fenofibrate-induced increase in HDL-cholesterol is dependent on the expression of the cholesteryl ester transfer protein (CETP). To this end, APOE*3-Leiden (E3L) transgenic mice without and with the human CETP transgene, under the control of its natural regulatory flanking regions, were fed a Western-type diet with or without fenofibrate. Fenofibrate (0.04% in the diet) decreased plasma TG in E3L and E3L.CETP mice (-59% and -60%; P < 0.001), caused by a strong reduction in VLDL. Whereas fenofibrate did not affect HDL-cholesterol in E3L mice, fenofibrate dose-dependently increased HDL-cholesterol in E3L.CETP mice (up to +91%). Fenofibrate did not affect the turnover of HDL-cholesteryl ester (CE), indicating that fenofibrate causes a higher steady-state HDL-cholesterol level without altering the HDL-cholesterol flux through plasma. Analysis of the hepatic gene expression profile showed that fenofibrate did not differentially affect the main players in HDL metabolism in E3L.CETP mice compared with E3L mice. However, in E3L.CETP mice, fenofibrate reduced hepatic CETP mRNA (-72%; P < 0.01) as well as the CE transfer activity in plasma (-73%; P < 0.01). We conclude that fenofibrate increases HDL-cholesterol by reducing the CETP-dependent transfer of cholesterol from HDL to (V)LDL, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool.

Molecular characterization and expression of the cholesteryl ester transfer protein gene in chickens

The cDNA for cholesteryl ester transfer protein (CETP), a protein that catalyzes cholesteryl ester transfer between very low density and high density lipoproteins in plasma, was isolated from chicken liver. When the recombinant protein was overexpressed in HEK293 cells, cholesteryl ester transfer activity was observed in media and cell lysates. By Northern blot analysis, chicken CETP mRNA expression was detected in liver, brain, heart, and spleen. Changes in chicken CETP mRNA expression and plasma CETP activity with nutritional state were examined and found to increase following dietary supplementation with cholesterol in a similar way as in humans. Both the hepatic CETP mRNA levels and plasma CETP activity were significantly lower in mature (i.e egg-laying) hens than in immature female chickens, but were unaffected by age in male animals. Similar changes to those observed in female chickens were observed upon estradiol administration of males. The present study is the first to report the molecular characterization of an avian CETP, and the impairments of CETP gene and activity, which might be regulated by estrogen, play an important role in egg production in laying hens, demonstrating species-specific differences in the lipid metabolism of avian and mammalian species.

REGULATION OF HEPATIC CHOLESTEROL METABOLISM IN CETP+/–/LDLr+/– MICE BY CHOLESTEROL FEEDING AND BY DRUGS (CHOLESTYRAMINE AND LOVASTATIN) THAT LOWER PLASMA CHOLESTEROL

1. The hepatic mechanisms involved in the simultaneous regulation of plasma cholesterol concentration and cholesteryl ester transfer protein (CETP) activity were investigated by sharply modifying the hepatic rates of cholesterol synthesis. This was accomplished by cholestyramine, lovastatin and cholesterol feeding in human CETP transgenic mice cross-bred with low-density lipoprotein receptor (LDLr)-knockout mice, generating CETP(+/-)/LDLr(+/-) mice, which present a plasma lipoprotein profile resembling that of humans. 2. Analyses of pooled data showed that the plasma CETP activity correlated positively with plasma total cholesterol concentration, hepatic CETP mRNA and the liver microsomal cholesterol content; a negative correlation was found between plasma CETP activity and the liver 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and LDLr mRNA levels. These coordinated events represent an efficient control system that stabilizes the cell cholesterol content. 3. Nonetheless, not all cholesterol metabolism regulatory systems seem to fit into a coherent pattern of responses, suggesting that other unknown cellular mechanisms play roles depending on the type of pharmacological intervention. 4. For example, microsomal cholesterol content was not affected by cholestyramine, but was increased on cholesterol feeding (as predicted), and, surprisingly, on lovastatin treatment. Furthermore, although both plasma cholesterol-lowering drugs increased CYP7A1 mRNA and had no effect on CYP27 mRNA, other metabolic components were differentially modified. Cholestyramine and lovastatin, respectively, did not modify and increased both HMG-CoA and sterol responsive element binding protein 1c mRNA, did not modify and lowered liver X receptor alpha mRNA, lowered and increased ATP binding cassette A1 mRNA and lowered and did not modify scavenger receptor B1 mRNA. 5. That is, different to unabsorbed cholestyramine, lovastatin, as an absorbed plasma cholesterol-lowering drug, may have modified the activity of other unknown genes that play roles in the interaction of CETP with the metabolism of hepatic cholesterol.