Is CYP2C70 the key to new mouse models to understand bile acids in humans?
Guo Grace L; Chiang John Y L
Journal of lipid research
2020
2020-03
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Journal Article
<a href="http://doi.org/10.1194/jlr.C120000621" target="_blank" rel="noreferrer noopener">10.1194/jlr.C120000621</a>
Fluorocholesterols, In Contrast To Hydroxycholesterols, Exhibit Interfacial Properties Similar To Cholesterol
a; bile-acids; Biochemistry & Molecular Biology; condensation; enzyme-catalyzed oxidation; isotherm; monolayers; orientation; orphan nuclear receptor; phosphatidylcholine; phosphatidylcholines; reductase-activity; side-chain; spectroscopic imaging; sterol synthesis; surface balance; surface potential
We used an automated Langmuir-Pockels surface balance to characterize the air-water interfacial properties of cholesterol (CH) and its derivatives with hydrophilic OH and F substitutions at isologous sites on the sterol body or side chain. We studied 6-fluorocholesterol, 25-fluorocholesterol, 25,26,26,26,27,27,27-heptafluorocholesterol, 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol, alone and in mixtures with 1-palmitoyl-2-oleoyl-sn-3-glycero-phosphocholine (POPC). Pressure-area isotherms of the fluorocholesterols were essentially indistinguishable from CH and all condensed POPC monomolecular layers (monolayers) to variable degrees. Both nucleus-substituted hydroxycholesterols formed expanded monolayers, with lift-offs from baseline 22-26 Angstrom(2)/molecule larger than CH, suggesting interfacial tilting; furthermore, in binary mixtures, they condensed POPC monolayers less than CH, In contrast, the side chain hydroxylated CHs were oriented horizontally in the interface at large molecular areas, and became vertical below 140 Angstrom(2)/molecule with the side chain-OH rather than 3-OH group anchored in the subphase, as evidenced by low collapse pressures and smaller molecular areas than CH. Both side chain hydrocholesterols expanded POPC monolayers at molar ratios <30%, but induced condensation with higher ratios, suggesting that OH-acyl chain (POPC) repulsion is superceded at higher mole fractions by lateral phase separation and intersteroidal H-bonding. These studies predict that fluorocholesterols should exhibit intramembrane spatial occupancy nearly identical to CH, whereas nucleus and especially side chain hydroxycholesterols will perturb membrane lipid packing notably.
Kauffman J M; Westerman P W; Carey M C
Journal of Lipid Research
2000
2000-06
Journal Article or Conference Abstract Publication
n/a
Cholesterol 7-alpha-hydroxylase - Evidence For Transcriptional Regulation By Cholesterol Or Metabolic Products Of Cholesterol In The Rat
bile-acid synthesis; bile fistula; bile-acid synthesis; Biochemistry & Molecular Biology; biosynthesis; cloning; enterohepatic circulation; enzyme; hepatic cholesterol; hepatocytes; hmg-coa reductase; liver microsomes; lovastatin; messenger-rna; mevalonate; stimulation
Cholesterol 7alpha-hydroxylase, the rate-determining enzyme in the bile acid biosynthesis pathway, is regulated in a negative feedback manner by hydrophobic bile salts returning to the liver via the portal circulation. The role of cholesterol in the regulation of cholesterol 7alpha-hydroxylase and the interrelationship between the cholesterol and bile acid biosynthesis pathways remain controversial. The objective of the present study was to define the role of cholesterol in the regulation of cholesterol 7alpha-hydroxylase and determine the molecular level of its control. In order to avoid intestinal or intravenous administration of cholesterol, we manipulated the flow of cholesterol within the hepatocytes by decreasing cholesterol synthesis with lovastatin in bile fistula rats (bile acid synthesis is up-regulated), or by increasing cholesterol supply by administering mevalonate, a precursor of cholesterol, to rats with intact enterohepatic circulation (bile acid synthesis is normal). In the first series of studies, lovastatin was administered as a single intravenous bolus (10 mg/kg) to rats with chronic bile fistula and to rats with intact enterohepatic circulation (cholesterol and bile acid synthesis is normal). Three hours after lovastatin administration, cholesterol 7alpha-hydroxylase specific activity, enzyme mass, mRNA, and gene transcriptional activity were decreased by 35%, 32%, 56%, and 34%, respectively, in rats with chronic bile fistula. In rats with intact enterohepatic circulation, lovastatin administration resulted in a similar decrease (34%) of cholesterol 7alpha-hydroxylase specific activity. In the second group of experiments, rats with intact enterohepatic circulation were administered a 180 mum bolus of mevalonate followed by a continuous infusion of 180 mumol/h for 1.5, 3, 4.5, and 24 h prior to being killed. Continuous infusion of mevalonate increased cholesterol 7-alpha-hydroxylase specific activity, mRNA levels, and transcriptional activity by an average of 2- to 3-fold at all time intervals. We conclude that under circumstances in which cholesterol is present in excess, cholesterol 7alpha-hydroxylase transcriptional activity is up-regulated and removal of cholesterol from the hepatocytes is facilitated by an increase of bile acid synthesis. When cholesterol availability is decreased, cholesterol 7alpha-hydroxylase transcriptional activity is down-regulated leading to a decreased elimination of cholesterol via bile acid synthesis. In both instances, hepatic cholesterol homeostasis is effectively maintained.
Jones M P; Pandak W M; Heuman D M; Chiang J Y L; Hylemon P B; Vlahcevic Z R
Journal of Lipid Research
1993
1993-06
Journal Article or Conference Abstract Publication
n/a
Saturated Fatty Acids Activate Erk Signaling To Downregulate Hepatic Sortilin 1 In Obese And Diabetic Mice
apolipoprotein-b secretion; Biochemistry & Molecular Biology; cells; diabetes; extracellular signal-regulated kinase; fatty liver; function; induced insulin-resistance; ldl; lipid metabolism; liver; mitogen-activated protein kinase; obesity; overproduction; oxidative stress; ubiquitination; vascular; vldl production
Hepatic VLDL overproduction is a characteristic feature of diabetes and an important contributor to diabetic dyslipidemia. Hepatic sortilin 1 (Sort1), a cellular trafficking receptor, is a novel regulator of plasma lipid metabolism and reduces plasma cholesterol and triglycerides by inhibiting hepatic apolipoprotein B production. Elevated circulating free fatty acids play key roles in hepatic VLDL overproduction and the development of dyslipidemia. This study investigated the regulation of hepatic Sort1 in obesity and diabetes and the potential implications in diabetic dyslipidemia. Results showed that hepatic Sort1 protein was markedly decreased in mouse models of type I and type II diabetes and in human individuals with obesity and liver steatosis, whereas increasing hepatic Sort1 expression reduced plasma cholesterol and triglycerides in mice. Mechanistic studies showed that the saturated fatty acid palmitate activated extracellular signal-regulated kinase (ERK) and inhibited Sort1 protein by mechanisms involving Sort1 protein ubiquitination and degradation. Consistently, hepatic ERK signaling was activated in diabetic mice, whereas blocking ERK signaling by an ERK inhibitor increased hepatic Sort1 protein in mice. These results suggest that increased saturated fatty acids downregulate liver Sort1 protein, which may contribute to the development of dyslipidemia in obesity and diabetes.
Bi L P; Chiang J Y L; Ding W X; Dunn W; Roberts B; Li T G
Journal of Lipid Research
2013
2013-10
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1194/jlr.M039347" target="_blank" rel="noreferrer noopener">10.1194/jlr.M039347</a>
Peroxisome Proliferator-activated Receptor Alpha (ppar Alpha) And Agonist Inhibit Cholesterol 7 Alpha-hydroxylase Gene (cyp7a1) Transcription
bezafibrate; bile acid synthesis; Biochemistry & Molecular Biology; cytochrome P450; drugs; elements; expression; fatty-acids; gallstones; HNF-4; hypolipidemic; hypolipidemic drugs; isoform; lipoprotein metabolism; nuclear receptors; peroxisome proliferators; rat; suppression
Marrapodi M; Chiang J Y L
Journal of Lipid Research
2000
2000-04
Journal Article or Conference Abstract Publication
n/a
Saturated Fatty Acids Activate Erk Signaling To Downregulate Hepatic Sortilin 1 In Obese And Diabetic Mice
apolipoprotein-b secretion; Biochemistry & Molecular Biology; cells; diabetes; extracellular signal-regulated kinase; fatty liver; function; induced insulin-resistance; ldl; lipid metabolism; liver; mitogen-activated protein kinase; Obesity; overproduction; oxidative stress; ubiquitination; vascular; vldl production
Bi L P; Chiang J Y L; Ding W X; Dunn W; Roberts B; Li T G
Journal of Lipid Research
2013
2013-10
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1194/jlr.M039347" target="_blank" rel="noreferrer noopener">10.1194/jlr.M039347</a>
Transcriptional activation of the cholesterol 7 alpha-hydroxylase gene (CYP7A) by nuclear hormone receptors
rat; liver; bile acid synthesis; Biochemistry & Molecular Biology; expression; messenger-rna; elements; metabolism; promoter; nuclear; mutations; cytochrome P450; cholesterol 7; alpha-hydroxylase; bile acid response element; factor coup-tf; gene transcription and regulation; hormone receptor; retinoic acid receptors
The gene encoding cholesterol 7 alpha-hydroxylase (CYP7A), the rate-limiting enzyme in bile acid synthesis, is transcriptionally regulated by bile acids and hormones. Previously, we have identified two bile acid response elements (BARE) in the promoter of the CYP7A gene, The BARE II is located in nt -149/-118 region and contains three hormone response element (HRE)-like sequences that form two overlapping nuclear receptor binding sites. One is a direct repeat separated by one nucleotide DR1 (-146-TGGACTtAGTTCA-134) and the other is a direct repeat separated by five nucleotides DR5 (-139-AGTTCAaggccGGG TAA-123). Mutagenesis of these HRE sequences resulted in lower transcriptional activity of the CYP7A promoter/reporter genes in transient transfection assay in HepG2 cells. The orphan nuclear receptor, hepatocyte nuclear factor 4 (HNF-4)(1), binds to the DR1 sequence as assessed by electrophoretic mobility shift assay, and activates the CYP7A promoter/reporter activity by about 9-fold. Cotransfection of HNF-4 plasmid with another orphan nuclear receptor, chicken ovalbumin upstream promoter-transcription factor LI (COUP-TRI), synergistically activated the CYP7A transcription by 80-fold. The DR5 binds the RXR/RAR heterodimer, A hepatocyte nuclear factor-3 (HNF-3) binding site (-175-TGTTTGTTCT-166) was identified. HNF-3 was required for both basal transcriptional activity and stimulation of the rat CYP7A promoter activity by retinoic acid, Combinatorial interactions and binding of these transcription factors to BAREs may modulate the promoter activity and also mediate bile acid repression of CYP7A gene transcription.
Crestani M; Sadeghpour A; Stroup D; Galli G; Chiang J Y L
Journal of Lipid Research
1998
1998-11
Journal Article or Conference Abstract Publication
n/a
Intestinal CYP3A4 protects against lithocholic acid-induced hepatotoxicity in intestine-specific VDR-deficient mice
metabolomics; 1; Biochemistry & Molecular Biology; disease; expression; absorption; permeability; Bile acids; bile-acid; cytochrome-p450 3a4; vitamin D receptor; vitamin D receptor; 25-dihydroxyvitamin d-3
Vitamin D receptor (VDR) mediates vitamin D signaling involved in bone metabolism, cellular growth and differentiation, cardiovascular function, and bile acid regulation. Mice with an intestine-specific disruption of VDR (Vdr(Delta IEpC)) have abnormal body size, colon structure, and imbalance of bile acid metabolism. Lithocholic acid (LCA), a secondary bile acid that activates VDR, is among the most toxic of the bile acids that when overaccumulated in the liver causes hepatotoxicity. Because cytochrome P450 3A4 (CYP3A4) is a target gene of VDR-involved bile acid metabolism, the role of CYP3A4 in VDR biology and bile acid metabolism was investigated. The CYP3A4 gene was inserted into Vdr(Delta IEpC) mice to produce the Vdr(Delta IEpC)/3A4 line. LCA was administered to control, transgenic-CYP3A4, Vdr(Delta IEpC), and Vdr(Delta IEpC)/3A4 mice, and hepatic toxicity and bile acid levels in the liver, intestine, bile, and urine were measured. VDR deficiency in the intestine of the Vdr(Delta IEpC) mice exacerbates LCA-induced hepatotoxicity manifested by increased necrosis and inflammation, due in part to over-accumulation of hepatic bile acids including taurocholic acid and taurodeoxycholic acid. Intestinal expression of CYP3A4 in the Vdr(Delta IEpC)/3A4 mouse line reduces LCA-induced hepatotoxicity through elevation of LCA metabolism and detoxification, and suppression of bile acid transporter expression in the small intestine.(jlr) This study reveals that intestinal CYP3A4 protects against LCA hepatotoxicity.
Cheng J; Fang Z Z; Kim J H; Krausz K W; Tanaka N; Chiang J Y L; Gonzalez F J
Journal of Lipid Research
2014
2014-03
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1194/jlr.M044420" target="_blank" rel="noreferrer noopener">10.1194/jlr.M044420</a>
Nuclear receptor-mediated repression of human cholesterol 7 alpha-hydroxylase gene transcription by bile acids
liver; bile acid synthesis; Biochemistry & Molecular Biology; expression; messenger-rna; activation; identification; promoter; cytochrome P450; shp; cyp7a; hepg2 cells; mechanism of gene regulation; orphan receptor
Hydrophobic bile acids strongly repressed transcription of the human cholesterol 7 alpha -hydroxylase gene (CYP7A1) in the bile acid biosynthetic pathway in the Ever. Farnesoid X receptor (FXR) repressed CYP7A1/Luc reporter activity in a transfection assay in human liver-derived HepG2 cells, but not in human embryonic kidney (HEK) 293 cells. FXR-binding activity was required for bile acid repression of CYP7A1 transcription despite the fact that FXR did not bind to the CYP7A1 promoter. FXR-induced liver-specific factors must be required for mediating bile acid repression. Bile acids and FXR repressed endogenous CYP7A1 but stimulated a-fetoprotein transcription factor (FTF) and small heterodimer partner (SHP) mRNA expression in HepG2 cells. Feeding of rats with chenodeoxycholic acid repressed CYP7A1, induced FIT, but had no effect on SHP mRNA expression in the liver. FIT strongly repressed CYP7A1 transcription in a dose-dependent manner, and SHP further inhibited CYP7A1 in HepG2 cells, but not in HEK 293 cells. FXR only moderately stimulated SHP transcription, whereas FIT strongly inhibited SHP transcription in HepG2 cells. Results revealed that FTF was a dominant negative factor that was induced by bile acid-activated FXR to inhibit both CYP7A1 and SHP transcription. Differential regulation of FTF and SHP expression by bile acids may explain the wide variation in CYP7A1 expression and the rate of bile acid synthesis and regulation in different species.
Chen W L; Owsley E; Yang Y Z; Stroup D; Chiang J Y L
Journal of Lipid Research
2001
2001-09
Journal Article or Conference Abstract Publication
n/a
CLOFIBRATE-INDUCIBLE RAT HEPATIC P450S IVA1 AND IVA3 CATALYZE THE OMEGA-HYDROXYLATION AND (OMEGA-1)-HYDROXYLATION OF FATTY-ACIDS AND THE OMEGA-HYDROXYLATION OF PROSTAGLANDINS-E1 AND F2-ALPHA
Biochemistry & Molecular Biology
Aoyama T; Hardwick J P; Imaoka S; Funae Y; Gelboin H V; Gonzalez F J
Journal of Lipid Research
1990
1990-08
Journal Article or Conference Abstract Publication
n/a
Structure and functions of human oxysterol 7 alpha-hydroxylase cDNAs and gene CYP7B1
27-hydroxycholesterol; 7-alpha-hydroxylase; bile-acid synthesis; bile-acid synthesis; Biochemistry & Molecular Biology; brain; cholesterol; cholesterol 7 alpha-hydroxylase; cytochrome P450; cytochrome P450; dehydroepiandrosterone (DHEA); dehydroepiandrosterone (DHEA); human liver-microsomes; identification; neurosteroids; transcription
Oxysterol 7 alpha-hydroxylase has broad substrate specificity for sterol metabolites and may be involved in many metabolic processes including bile acid synthesis and neurosteroid metabolism, The cloned human oxysterol 7 alpha-hydroxylase (CYP7B1) cDNA encodes a polypeptide of 506 amino acid residues that shares 40% sequence identity to human cholesterol 7 alpha-hydroxylase (CW7A1), the rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver. In contrast to the liver-specific expression of CYP7A1, CYP7B1 mRNA transcripts were detected in human tissues involved in steroid genesis (brain, testes, ovary, and prostate) and in bile acid synthesis (liver) and reabsorption (colon, kidney, and small intestine). The human oxysterol 7 alpha-hydroxylase transiently expressed in 293/T cells was able to catalyze 7 alpha-hydroxylation of 27-hydroxycholesterol and dehydroepiandrosterone (DHEA), The human CYP7A1 and CYP7B1 both contain six exons and five introns. However, CPP7B1 spans at least 65 kb of the genome and is about 6-fold longer than CYP7A1. The transcription start site (+1) was localized 204 bp upstream of the initiation codon, No TATA box-like sequence was found near the transcription start site. Transient transfection assays of CYP7B1 promoter/luciferase reporter constructs in HepG2 cells revealed that the promoter was highly active. The 5' upstream region from nt -83 to +189 is the core promoter of the gene.
Wu Z L; Martin K O; Javitt N B; Chiang J Y L
Journal of Lipid Research
1999
1999-12
Journal Article
n/a
Physicochemical characterization of a model digestive mixture by H-2 NMR
adult human-beings; bile salts; bile-salt; biliary lipid systems; Biochemistry & Molecular Biology; c-13 nmr; cholesterol; contents; digestion; fat; H-2-labeled lipids; human intestinal; intestinal lipids; liquid-crystalline phases; nuclear magnetic-resonance; phosphatidylcholine mixed micelles; physical-chemical behavior
H-2 nuclear magnetic resonance (NMR) spectra were obtained at 30.87 MHz for 8% (w/v) aqueous dispersions of mixtures of bile salts (MBS), mixed intestinal lipids (MIL; myristic acid, monomyristoylglycerol dimyristoylphos-phatidylcholine = 5:1:1), and cholesterol, in which a single lipid component is selectively H-2-labeled. Using the observation that the time averaged quadrupole splitting of a (CH3)-H-2 group varies according to whether it exists in a micellar, multilamellar or solid phase, one-, two-, and three-phase regions in the equilibrium phase diagram have been identified. From the intensities of the singlets and powder patterns in the wide-line H-2 NMR spectra, the relative amounts of these organized molecular assemblies were determined. With different (CH3)-H-2-labeled components in samples of identical total composition, the chemical composition of each phase was calculated for one point (20 mol % cholesterol; 50 mol % MIL, and 30 mol % MBS) in a two-phase region of the phase diagram where the H-2 NMR spectrum displayed both a sharp spectral component and a broad uniaxial powder pattern. X-ray diffraction measurements on this sample confirmed that the uniaxial powder pattern in the NMR spectra can be assigned to multilamellar vesicles. At this same point in the phase diagram with the H-2 label on the a-methylene site of myristic acid, both narrow and broad (Delta v = 37 kHz) spectral components were again observed. Relaxation time (T-1 and T?) measurements of the sharp spectral component indicate that this peak arises from rapidly tumbling aggregates which, at a total lipid concentration of 8% (w/v), are micellar particles and not unilamellar vesicles. These experiments demonstrate the feasibility of structural investigations of model digestive mixtures by H-2 NMR.
Westerman P W
Journal of Lipid Research
1995
1995-12
Journal Article
n/a
HNF4 and COUP-TFII interact to modulate transcription of the cholesterol 7 alpha-hydroxylase gene (CYP7A1)
bile-acid synthesis; bile acids; Biochemistry & Molecular Biology; chicken ovalbumin; cholesterol metabolism; dna-binding; hepatocyte nuclear factor 4; hepatocyte nuclear factor 4; hormone-receptor superfamily; messenger-rna; orphan receptors; promoter; receptors; response elements; retinoic acid; thyroid-hormone; transcriptional regulation; upstream promoter transcription factor II
The gene for cholesterol 7 alpha-hydroxylase (CYP7A1) contains a sequence at nt -149 to -118 that was found to play a large role in determining the overall transcriptional activity and regulation of the promoter. Hepatocyte nuclear factor 4 (HNF4) and chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) synergistically activate transcription of the CYP7A1 promoter, Transactivation of CYP7A1 by HNF4 in the human hepatoma cell line, HepG2, was enhanced by cotransfection with COUP-TFII or the basal transcription element binding protein (BTEB), HNF4 prepared from rat liver nuclear extracts bound to oligomers homologous to the nt -146 to -134 sequences in electrophoretic mobility shift assays (EMSA), which corresponded to a conserved region containing a direct repeat of hormone response elements spaced by one nucleotide (DR1), The sequences surrounding this DR1 were found to be essential for the HNF4 transactivation. In vitro-translated COUP-TFII was found to bind the adjacent sequences from nt -139 to -128 (DRO), but COUP-TFII interacted with this region at a much lower affinity than to the COUP-TFII-site at nt -72 to -57 (DR4), Mutations at nt -139 to -128 or nt -72 to -57 reduced the COUP-TFII and HNF4 synergy; however, these COUP-TFII-binding sequences were not absolutely required for the cooperative effect of HNF4 and COUP-TFII on transactivation. These results indicated that the observed transactivation was the result of protein/protein interactions facilitated by the juxtaposition of the binding elements.
Stroup D; Chiang J Y L
Journal of Lipid Research
2000
2000-01
Journal Article
n/a
Hormonal regulation of cholesterol 7 alpha-hydroxylase specific activity, mRNA levels, and transcriptional activity in vivo in the rat
bile-acid biosynthesis; Biochemistry & Molecular Biology; cholesterol; cholesterol 7 alpha-hydroxylase; cultures; gene; gene cyp7; glucocorticoid; hepatic cholesterol; hepatocyte cultures; liver; messenger-rna levels; monolayer-cultures; primary; protein-kinase-c; regulation; sterol 27-hydroxylase; thyroid; thyroid-hormone
In primary cultures of rat hepatocytes, transcription of the cholesterol 7 alpha-hydroxylase gene is induced synergistically by glucocorticoid and thyroid hormones. The objective of the present study was to evaluate the role of glucocorticoid and thyroid hormones in the maintenance of cholesterol 7 alpha-hydroxylase gene expression in vivo. Male Sprague-Dawley rats underwent adrenalectomy (A), thyroidectomy (T), adrenalectomy + thyroidectomy (A + T), hypophysectomy (H), or sham surgery (paired controls). Ten days post surgery, livers were harvested and cholesterol 7 alpha-hydroxylase specific activity, steady-state mRNA levels, and transcriptional activity were determined. Serum corticosterone levels were <2% of paired controls in A, A + T and H rats. Free thyroxine index was <32% of paired controls in rats with T and H. When compared to sham-operated controls, A + T and H led to decreases in cholesterol 7 alpha-hydroxylase specific activities of 44 +/- 8% and 57 +/- 3%, respectively (P < 0.03 and < 0.05). Similar changes were observed in cholesterol 7 alpha-hyroxylase steady-state mRNA levels, which decreased by 43 +/- 10% (P < 0.001) and 56 +/- 19% (P < 0.05), respectively. Cholesterol 7 alpha-hydroxylase transcriptional activity in A + T and H rats decreased by 34 +/- 11% (P < 0.01) and 61 +/- 4% (P < 0.001), respectively. The observed decreases were greater after H than after A + T, suggesting the possibility that another pituitary hormone plays a role in regulation of cholesterol 7 alpha-hydroxylase. Thyroidectomy alone led to a decrease in cholesterol 7 alpha-hydroxylase specific activity of 37 +/- 7% (P < 0.05) and a trend toward decreased steady-state mRNA levels (21 +/- 12%; P = ns). Adrenalectomy did not significantly decrease cholesterol 7 alpha-hydroxylase specific activity or mRNA levels. Neither thyroidectomy nor adrenalectomy alone affected transcriptional activity. We conclude that under physiologic circumstances, full expression of the cholesterol 7 alpha-hydroxylase gene requires synergistic action of glucocorticoids and thyroid hormone.
Pandak W M; Heuman D M; Redford K; Stravitz R T; Chiang J Y L; Hylemon P B; Vlahcevic Z R
Journal of Lipid Research
1997
1997-12
Journal Article
n/a
BILE-ACID SYNTHESIS .6. REGULATION OF CHOLESTEROL 7-ALPHA-HYDROXYLASE BY TAUROCHOLATE AND MEVALONATE
3-hydroxy-3-methylglutaryl; 7-alpha-hydroxylase; bile acids; Biochemistry & Molecular Biology; biosynthesis; circadian-rhythm; cloning; coenzyme; enzyme; hepatocytes; hmg-coa reductase; liver; messenger-rna; rat-liver microsomes; reductase; substrate
Taurocholate, a relatively hydrophobic bile salt, is a potent down-regulator of HMG-CoA reductase and cholesterol 7-alpha-hydroxylase (C7-alpha-H), the rate-determining enzymes of the cholesterol and bile acid biosynthetic pathways, respectively. Inhibition of cholesterol synthesis with a bolus dose of mevinolin (lovastatin) a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, profoundly decreases the specific activity of cholesterol 7-alpha-hydroxylase and rate of bile acid synthesis in rats with complete biliary diversion. It is therefore conceivable that taurocholate may suppress cholesterol 7-alpha-hydroxylase primarily by down-regulating the activity of HMG-CoA reductase. To test this hypothesis, taurocholate was coinfused simultaneously to rats with chronic bile fistula with mevalonate (administered as mevalonolactone), an intermediate in the cholesterol biosynthetic pathway. Mevalonolactone was administered to provide a constant supply of newly synthesized cholesterol to cholesterol 7-alpha-hydroxylase, in order to overcome any inhibitory effect of taurocholate on HMG-Coa reductase. Infusions were started 72 h after biliary diversion, and carried out for an additional 48 h. Complete biliary diversion resulted in an increase in C7-alpha-H specific activity (510%), protein mass (550%), steady-state mRNA levels (1430%), and transcriptional activities (330%) as compared to control rats with intact enterohepatic circulations. When rats with biliary diversion were infused intraduodenally with taurocholate, the specific activities of HMG-CoA reductase and cholesterol 7-alpha-hydroxylase activities decreased by 75% (P < 0.001) and 73% (P < 0.001), respectively. Cholesterol 7-alpha-hydroxylase mass, mRNA, and transcriptional activity decreased after intraduodenal infusion of taurocholate to levels similar to those of rats with an intact enterohepatic circulation. The combination of constant infusion of mevalonate and taurocholate failed to reverse the inhibitory effects of taurocholate on cholesterol 7-alpha-hydroxylase activity, mRNA levels, and in vitro transcriptional rates. These data provide evidence that taurocholate represses cholesterol 7-alpha-hydroxylase at the level of gene transcription, and not via down-regulation of HMG-CoA reductase. Infusion of mevalonate alone to biliary diverted rats did not alter cholesterol 7-alpha-hydroxylase activity or mRNA levels, while leading to a 57% decrease in C7-alpha-H gene transcription. This latter finding suggests that mevalonate or its metabolites may be capable of stabilizing C7-alpha-H mRNA levels while down-regulating transcriptional activity.
Pandak W M; Vlahcevic Z R; Chiang J Y L; Heuman D M; Hylemon P B
Journal of Lipid Research
1992
1992-05
Journal Article
n/a
The stimulatory effect of LXR alpha is blocked by SHP despite the presence of a LXR alpha binding site in the rabbit CYP7A1 promoter
alpha-fetoprotein transcription; bile-acid biosynthesis; Biochemistry & Molecular Biology; cholesterol 7 alpha-hydroxylase; cholesterol 7-alpha-hydroxylase gene; dietary-cholesterol; dietary-cholesterol; factor; farnesoid X receptor; farnesoid X receptor; inhibition; liver X receptor; messenger-rna levels; nuclear receptor; orphan; rat; SHP; taurocholate; transcription
The transcription of the cholesterol 7 alpha-hydroxylase gene (CYP7A1) is greatly decreased in cholesterol-fed rabbits. To determine whether the molecular structure of the promoter is responsible for this downregulation, we cloned the rabbit CYP7A1 promoter, identified the binding sites for a-fetoprotein transcription factor (FTF) and liver X receptor (LXR alpha), and studied the effects of FTF, LXR alpha, and SHP on its transcription. Adding LXR alpha/retinoid X receptor together with their ligands (L/R) to the promoter/reporter construct transfected into HepG2 cells greatly increased its activity. FTF did not increase promoter activity, nor did it enhance the stimulatory effect of L/R. Mutating the FTF binding site abolished the promoter baseline activity. Increasing amounts of SHP abolished the effect of L/R, and FTF enhanced the ability of SHP to decrease promoter activity below baseline levels. Thus, downregulation of CYP7A1 in cholesterol-fed rabbits is attributable secondarily to the activation of farnesoid X receptor, which increases SHP expression to override the positive effects of LXR alpha. Although FFF is a competent factor for maintaining baseline activity, it does not further enhance and may suppress CYP7A1 transcription.
Shang Q; Pan L X; Saumoy M; Chiang J Y L; Tint G S; Salen G; Xu G R
Journal of Lipid Research
2006
2006-05
Journal Article
<a href="http://doi.org/10.1194/jlr.M500449-JLR200" target="_blank" rel="noreferrer noopener">10.1194/jlr.M500449-JLR200</a>
Dissociation of diabetes and obesity in mice lacking orphan nuclear receptor small heterodimer partner
beta-oxidation; Biochemistry & Molecular Biology; birth-weight; diet-induced obesity; fatty-acid oxidation; hepatic steatosis; induced; insulin sensitivity; insulin-resistance; lipid-metabolism; liver; negative feedback-regulation; oxygen consumption; quotient; respiratory; retinoic acid; signaling pathways; skeletal-muscle
Mixed background SHP(-/-) mice are resistant to diet-induced obesity due to increased energy expenditure caused by enhanced PGC-1 alpha expression in brown adipocytes. However, congenic SHP(-/-) mice on the C57BL/6 background showed normal expression of PGC-1 alpha and other genes involved in brown adipose tissue thermogenesis. Thus, we reinvestigated the impact of small heterodimer partner (SHP) deletion on diet-induced obesity and insulin resistance using congenic SHP(-/-) mice. Compared with their C57BL/6 wild-type counterparts, SHP(-/-) mice subjected to a 6 month challenge with a Western diet (WestD) were leaner but more glucose intolerant, showed hepatic insulin resistance despite decreased triglyceride accumulation and increased beta-oxidation, exhibited alterations in peripheral tissue uptake of dietary lipids, maintained a higher respiratory quotient, which did not decrease even after WestD feeding, and displayed islet dysfunction. Hepatic mRNA expression analysis revealed that many genes expressed higher in SHP(-/-) mice fed WestD were direct peroxisome proliferator-activated receptor alpha (PPAR alpha) targets. Indeed, transient transfection and chromatin immunoprecipitation verified that SHP strongly repressed PPAR alpha-mediated transactivation. SHP is a pivotal metabolic sensor controlling lipid homeostasis in response to an energy-laden diet through regulating PPAR alpha-mediated transactivation. The resultant hepatic fatty acid oxidation enhancement and dietary fat redistribution protect the mice from diet-induced obesity and hepatic steatosis but accelerate development of type 2 diabetes.-Park, Y. J., S. C. Kim, J. Kim, S. Anakk, J. M. Lee, H-T. Tseng, V. Yechoor, J. Park, J-S. Choi, H. C. Jang, K-U. Lee, C. M. Novak, D. D. Moore, and Y. K. Lee. Dissociation of diabetes and obesity in mice lacking orphan nuclear receptor small heterodimer partner. J. Lipid Res. 2011. 52: 2234-2244.
Park Y J; Kim S C; Kim J; Anakk S; Lee J M; Tseng H T; Yechoor V; Park J; Choi J S; Jang H C; Lee K U; Novak C M; Moore D D; Lee Y K
Journal of Lipid Research
2011
2011-12
Journal Article
<a href="http://doi.org/10.1194/jlr.M016048" target="_blank" rel="noreferrer noopener">10.1194/jlr.M016048</a>
Structure and functions of human oxysterol 7alpha-hydroxylase cDNAs and gene CYP7B1.
Humans; Animals; Mice; Cell Line; Transfection; Base Sequence; Molecular Sequence Data; Chromosome Mapping; Cytochrome P450 Family 7; DNA; Luciferases/genetics; Cytochrome P-450 Enzyme System/*genetics/metabolism; Steroid Hydroxylases/*genetics/metabolism; Hydroxycholesterols/metabolism; Codon; Northern; Blotting; Transcription; Genetic; Cloning; Molecular; Genetic/genetics; Promoter Regions; Nucleic Acid; Complementary/biosynthesis/*isolation & purification; Initiator; Regulatory Sequences
Oxysterol 7alpha-hydroxylase has broad substrate specificity for sterol metabolites and may be involved in many metabolic processes including bile acid synthesis and neurosteroid metabolism. The cloned human oxysterol 7alpha-hydroxylase (CYP7B1) cDNA encodes a polypeptide of 506 amino acid residues that shares 40% sequence identity to human cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver. In contrast to the liver-specific expression of CYP7A1, CYP7B1 mRNA transcripts were detected in human tissues involved in steroid genesis (brain, testes, ovary, and prostate) and in bile acid synthesis (liver) and reabsorption (colon, kidney, and small intestine). The human oxysterol 7alpha-hydroxylase transiently expressed in 293/T cells was able to catalyze 7alpha-hydroxylation of
Wu Z; Martin K O; Javitt N B; Chiang J Y
Journal of lipid research
1999
1999-12
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Physicochemical characterization of a model digestive mixture by 2H NMR.
Deuterium; Lipids/*chemistry; Magnetic Resonance Spectroscopy; Radiation; Scattering
2H nuclear magnetic resonance (NMR) spectra were obtained at 30.87 MHz for 8% (w/v) aqueous dispersions of mixtures of bile salts (MBS), mixed intestinal lipids (MIL; myristic acid, monomyristoylglycerol, dimyristoylphosphatidylcholine = 5:1:1), and cholesterol, in which a single lipid component is selectively
Westerman P W
Journal of lipid research
1995
1995-12
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Transcriptional regulation of the human cholesterol 7 alpha-hydroxylase gene (CYP7A) in HepG2 cells.
Humans; Binding Sites; Gene Expression Regulation; Cell Line; Transfection; Base Sequence; Molecular Sequence Data; Phorbol Esters/pharmacology; DNA-Binding Proteins/genetics/metabolism; *Transcription Factors; Enzyme Repression; Cholesterol 7-alpha-Hydroxylase/biosynthesis/*genetics; Consensus Sequence; Glucocorticoids/pharmacology; Hepatocyte Nuclear Factor 3-alpha; Insulin/pharmacology; Nuclear Proteins/genetics/metabolism; Recombinant Fusion Proteins/biosynthesis; Thyroid Hormones/pharmacology; Genes; Receptors; Enzymologic/*drug effects; Genetic; *Promoter Regions; Reporter; *Transcription; Glucocorticoid/genetics/metabolism
A stable HepG2 cell line harboring a human cholesterol 7 alpha-hydroxylase (CYP7A) minigene/luciferase reporter gene construct was selected for studying transcriptional regulation of CYP7A gene promoter. Insulin and phorbol
Wang D P; Stroup D; Marrapodi M; Crestani M; Galli G; Chiang J Y
Journal of lipid research
1996
1996-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
HNF4 and COUP-TFII interact to modulate transcription of the cholesterol 7alpha-hydroxylase gene (CYP7A1).
Humans; Animals; Rats; Liver/metabolism; Recombinant Proteins/metabolism; Base Sequence; Mutation; DNA Primers; Cholesterol 7-alpha-Hydroxylase/*genetics; Transcription Factors/*metabolism; Hepatocyte Nuclear Factor 4; DNA-Binding Proteins/*metabolism; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Luciferases/genetics; COUP Transcription Factor II; COUP Transcription Factors; Phosphoproteins/*metabolism; Genes; Sprague-Dawley; Cultured; Genetic; Tumor Cells; Reporter; Promoter Regions; *Transcription; *Receptors; Steroid
The gene for cholesterol 7alpha-hydroxylase (CYP7A1) contains a sequence at nt -149 to -118 that was found to play a large role in determining the overall transcriptional activity and regulation of the promoter. Hepatocyte nuclear factor 4 (HNF4) and chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) synergistically activate transcription of the CYP7A1 promoter. Transactivation of CYP7A1 by HNF4 in the human hepatoma cell line, HepG2, was enhanced by cotransfection with COUP-TFII or the basal transcription element binding protein (BTEB). HNF4 prepared from rat liver nuclear extracts bound to oligomers homologous to the nt -146 to -134 sequences in electrophoretic mobility shift assays (EMSA), which corresponded to a conserved region containing a direct repeat of hormone response elements spaced by one nucleotide (DR1). The sequences surrounding this DR1 were found to be essential for the HNF4 transactivation. In vitro-translated COUP-TFII was found to bind the adjacent sequences from nt -139 to -128 (DR0), but COUP-TFII interacted with this region at a much lower affinity than to the COUP-TFII-site at nt -72 to -57 (DR4). Mutations at nt -139 to -128 or nt -72 to -57 reduced the COUP-TFII and HNF4 synergy; however, these
Stroup D; Chiang J Y
Journal of lipid research
2000
2000-01
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Peroxisome proliferator-activated receptor alpha (PPARalpha) and agonist inhibit cholesterol 7alpha-hydroxylase gene (CYP7A1) transcription.
Humans; Animals; Binding Sites; Protein Binding; Rats; Gene Expression Regulation; Species Specificity; Liver/metabolism; Transcriptional Activation; Hepatocyte Nuclear Factor 4; Response Elements; *DNA-Binding Proteins; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Retinoid X Receptors; Anticholesteremic Agents/pharmacology; Cholesterol 7-alpha-Hydroxylase/biosynthesis/*genetics; Clofibric Acid/pharmacology; Peroxisome Proliferators/pharmacology; Phosphoproteins/metabolism; Pyrimidines/pharmacology; Transcription Factors/*agonists/metabolism; Genes; Receptors; Models; Transcription; Genetic; Enzymologic; Reporter; Retinoic Acid/metabolism; Promoter Regions; Nucleic Acid; Cytoplasmic and Nuclear/*agonists; *Regulatory Sequences
Fibrates are widely used hypolipidemic drugs that regulate the expression of many genes involved in lipid metabolism by activating the peroxisome proliferator-activated receptor alpha (PPARalpha). The objective of this study was to investigate the mechanism of action of peroxisome proliferators and PPARalpha on the transcription of cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver. When cotransfected with the expression vectors for PPARalpha and RXRalpha, Wy14,643 reduced human and rat cholesterol 7alpha-hydroxylase gene (CYP7A1)/luciferase reporter activities by 88% and 43%, respectively, in HepG2 cells, but not in CV-1 or CHO cells. We have mapped the peroxisome proliferator response element (PPRE) to a conserved sequence containing the canonical AGGTCA direct repeats separated by one nucleotide (DR1). This DR1 sequence was mapped previously as a binding site for the hepatocyte nuclear factor 4 (HNF-4) which stimulates CYP7A1 transcription. Electrophoretic mobility shift assay (EMSA) showed no direct binding of in vitro synthesized PPARalpha/RXRalpha heterodimer to the DR1 sequence. PPARalpha and Wy14,643 did not affect HNF-4 binding to the DR1. However, Wy14,643 and PPARalpha/RXRalpha significantly reduced HNF-4 expression in HepG2 cells. These results suggest that PPARalpha and agonist repress cholesterol 7alpha-hydroxylase activity by reducing the availability of
Marrapodi M; Chiang J Y
Journal of lipid research
2000
2000-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Expression and purification of human cholesterol 7 alpha-hydroxylase in Escherichia coli.
Humans; Animals; Rats; Kinetics; Base Sequence; Catalysis; Molecular Sequence Data; Escherichia coli; Solubility; Cholesterol 7-alpha-Hydroxylase/biosynthesis/genetics/*isolation & purification; Cytochrome P-450 Enzyme System/biosynthesis/isolation & purification; Immunochemistry; Recombinant Proteins/biosynthesis; Subcellular Fractions/enzymology
Cholesterol 7 alpha-hydroxylase (P450c7) is the first and rate-limiting enzyme in bile acid biosynthesis and is the product of a cytochrome P450 gene, CYP7. We have previously reported the cloning of a full-length human cholesterol 7 alpha-hydroxylase cDNA (Karam, W. G., and J. Y. L. Chiang. 1992. Biochem. Biophys. Res. Commun. 185: 588-595). Using this clone in a polymerase chain reaction, we have generated a cDNA (H7 alpha 1.5) in which the codons for the
Karam W G; Chiang J Y
Journal of lipid research
1994
1994-07
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Transcriptional activation of the cholesterol 7alpha-hydroxylase gene (CYP7A) by nuclear hormone receptors.
Animals; Rats; Transcription Factors/metabolism; Base Sequence; Molecular Sequence Data; DNA/metabolism; Cholesterol 7-alpha-Hydroxylase/*genetics; Hepatocyte Nuclear Factor 4; Mutagenesis; Luciferases/genetics; Retinoid X Receptors; Phosphoproteins/metabolism; COUP Transcription Factor II; COUP Transcription Factors; *Transcriptional Activation; Bile Acids and Salts/biosynthesis; DNA-Binding Proteins/metabolism; Hormones/*physiology; Oligonucleotide Probes/metabolism; Genes; Cultured; Receptors; Genetic; Cytoplasmic and Nuclear/*physiology; Tumor Cells; Reporter; Retinoic Acid/metabolism; Promoter Regions; Nucleic Acid; Site-Directed; *Receptors; Repetitive Sequences; Steroid
The gene encoding cholesterol 7alpha-hydroxylase (CYP7A), the rate-limiting enzyme in bile acid synthesis, is transcriptionally regulated by bile acids and hormones. Previously, we have identified two bile acid response elements (BARE) in the promoter of the CYP7A gene. The BARE II is located in nt -149/-118 region and contains three hormone response element (HRE)-like sequences that form two overlapping nuclear receptor binding sites. One is a direct repeat separated by one nucleotide DR1 (-146- TGGACTtAGTTCA-134) and the other is a direct repeat separated by five nucleotides DR5 (-139-AGTTCAaggccGGG TAA-123). Mutagenesis of these HRE sequences resulted in lower transcriptional activity of the CYP7A promoter/reporter genes in transient transfection assay in HepG2 cells. The orphan nuclear receptor, hepatocyte nuclear factor 4 (HNF-4)1, binds to the DR1 sequence as assessed by electrophoretic mobility shift assay, and activates the CYP7A promoter/reporter activity by about 9-fold. Cotransfection of HNF-4 plasmid with another orphan nuclear receptor, chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), synergistically activated the CYP7A transcription by 80-fold. The DR5 binds the RXR/RAR heterodimer. A hepatocyte nuclear factor-3 (HNF-3) binding site (-175-TGTTTGTTCT-166) was identified. HNF-3 was required for both basal transcriptional activity and stimulation of the rat CYP7A promoter activity by retinoic acid. Combinatorial interactions and binding of these transcription factors to BAREs may modulate the promoter activity and also mediate bile acid repression of CYP7A gene transcription.
Crestani M; Sadeghpour A; Stroup D; Galli G; Chiang J Y
Journal of lipid research
1998
1998-11
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Hormonal regulation of the cholesterol 7 alpha-hydroxylase gene (CYP7).
Animals; Rats; Gene Expression Regulation; Cell Count; Transfection; Base Sequence; Molecular Sequence Data; Phorbol Esters/pharmacology; Cholesterol 7-alpha-Hydroxylase/*genetics; Luciferases/genetics; Cyclic AMP/pharmacology; Hormones/*pharmacology; Second Messenger Systems/physiology; Cultured; Genetic; Tumor Cells; Cloning; Molecular; *Promoter Regions; *Transcription; Enzymologic/*physiology
The transcriptional regulation of the rat cholesterol 7 alpha-hydroxylase gene (CYP7) by hormones and signal transduction pathways was studied by transient transfection assay of the promoter activity. HepG2 cells were transfected with deletion mutants of the CYP7 upstream region linked to the luciferase reporter gene. The transcription of CYP7/luciferase chimeric genes was higher in confluent than in subconfluent cultures of HepG2 cells. Glucocorticoid receptors, in the presence of dexamethasone, up-regulated the CYP7 gene through two regions located between -3262 and -2803, and between -344 and -222, respectively. Thyroid hormones did not have any effect on the promoter activity. Insulin inhibited the promoter activity through sequences located between -344 and -222, and abolished the stimulation by dexamethasone. Hence, the insulin effect was dominant over that of glucocorticoids. Treatment of transfected HepG2 cells with phorbol
Crestani M; Stroup D; Chiang J Y
Journal of lipid research
1995
1995-11
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Nuclear receptor-mediated repression of human cholesterol 7alpha-hydroxylase gene transcription by bile acids.
Humans; Animals; Rats; Cell Line; Transfection; Liver/metabolism; Reverse Transcriptase Polymerase Chain Reaction; DNA/metabolism; CHO Cells; Cricetinae; Cholesterol 7-alpha-Hydroxylase/*genetics; Bile Acids and Salts/*pharmacology; *Membrane Glycoproteins; *Hydroxysteroid Dehydrogenases; Caco-2 Cells; Carrier Proteins/genetics/physiology; DNA-Binding Proteins/drug effects/genetics/physiology; Gene Expression/*drug effects; Kidney; Luciferases/genetics; Recombinant Fusion Proteins/metabolism; Retinoid X Receptors; Taurocholic Acid/pharmacology; Transcription Factors/drug effects/genetics/physiology; Cultured; Receptors; RNA; Genetic/drug effects; Messenger/analysis; Transcription; Genetic; Tumor Cells; Promoter Regions; Embryo; Cytoplasmic and Nuclear/genetics/*physiology; Mammalian; Retinoic Acid/genetics/physiology
Hydrophobic bile acids strongly repressed transcription of the human cholesterol 7alpha-hydroxylase gene (CYP7A1) in the bile acid biosynthetic pathway in the liver. Farnesoid X receptor (FXR) repressed CYP7A1/Luc reporter activity in a transfection assay in human liver-derived HepG2 cells, but not in human embryonic kidney (HEK) 293 cells. FXR-binding activity was required for bile acid repression of CYP7A1 transcription despite the fact that FXR did not bind to the CYP7A1 promoter. FXR-induced liver-specific factors must be required for mediating bile acid repression. Bile acids and FXR repressed endogenous CYP7A1 but stimulated alpha-fetoprotein transcription factor (FTF) and small heterodimer partner (SHP) mRNA expression in HepG2 cells. Feeding of rats with chenodeoxycholic acid repressed CYP7A1, induced FTF, but had no effect on SHP mRNA expression in the liver. FTF strongly repressed CYP7A1 transcription in a dose-dependent manner, and SHP further inhibited CYP7A1 in HepG2 cells, but not in HEK 293 cells. FXR only moderately stimulated SHP transcription, whereas FTF strongly inhibited SHP transcription in HepG2 cells. Results revealed that FTF was a dominant negative factor that was induced by bile acid-activated FXR to inhibit both CYP7A1 and SHP transcription. Differential regulation of FTF and SHP expression by bile acids may explain the wide variation in CYP7A1 expression and the rate of bile acid synthesis and regulation in different species.
Chen W; Owsley E; Yang Y; Stroup D; Chiang J Y
Journal of lipid research
2001
2001-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Bile acids: regulation of synthesis.
Animals; Bile Acids and Salts/*metabolism; Biological; Cholesterol 7-alpha-Hydroxylase/metabolism; Cytoplasmic and Nuclear/metabolism; Humans; Models; Receptors; Signal Transduction/physiology
Bile acids are physiological detergents that generate bile flow and facilitate intestinal absorption and transport of lipids, nutrients, and vitamins. Bile acids also are signaling molecules and inflammatory agents that rapidly activate nuclear receptors and cell signaling pathways that regulate lipid, glucose, and energy metabolism. The enterohepatic circulation of bile acids exerts important physiological functions not only in feedback inhibition of bile acid synthesis but also in control of whole-body lipid homeostasis. In the liver, bile acids activate a nuclear receptor, farnesoid X receptor (FXR), that induces an atypical nuclear receptor small heterodimer partner, which subsequently inhibits nuclear receptors, liver-related homolog-1, and hepatocyte nuclear factor 4alpha and results in inhibiting transcription of the critical regulatory gene in bile acid synthesis, cholesterol 7alpha-hydroxylase (CYP7A1). In the intestine, FXR induces an intestinal hormone, fibroblast growth factor 15 (FGF15; or FGF19 in human), which activates hepatic FGF receptor 4 (FGFR4) signaling to inhibit bile acid synthesis. However, the mechanism by which FXR/FGF19/FGFR4 signaling inhibits CYP7A1 remains unknown. Bile acids are able to induce FGF19 in human hepatocytes, and the FGF19 autocrine pathway may exist in the human livers. Bile acids and bile acid receptors are therapeutic targets for development of drugs for treatment of cholestatic liver diseases, fatty liver diseases, diabetes, obesity, and metabolic syndrome.
Chiang John Y L
Journal of lipid research
2009
2009-10
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.R900010-JLR200" target="_blank" rel="noreferrer noopener">10.1194/jlr.R900010-JLR200</a>
TGFbeta1, TNFalpha, and insulin signaling crosstalk in regulation of the rat cholesterol 7alpha-hydroxylase gene expression.
*Gene Expression Regulation; Animals; Cell Line; Cholesterol 7-alpha-Hydroxylase/*genetics; Enzymologic; Forkhead Transcription Factors/physiology; Humans; Insulin/*physiology; Male; Nerve Tissue Proteins/physiology; Rats; Signal Transduction; Smad3 Protein/antagonists & inhibitors/pharmacology; Sprague-Dawley; Transforming Growth Factor beta1/*physiology; Tumor; Tumor Necrosis Factor-alpha/*physiology
The TGFbeta1/Smad pathway plays a critical role in cholestasis and liver fibrosis. Previous studies show that TGFbeta1, TNFalpha, and insulin inhibit cholesterol 7alpha-hydroxylase (CYP7A1) gene transcription and bile acid synthesis in human hepatocytes. In this study, we investigated insulin, TGFbeta1, and TNFalpha regulation of rat Cyp7a1 gene transcription. In contrast to inhibition of human CYP7A1 gene transcription, TGFbeta1 stimulates rat Cyp7a1 reporter activity. Smad3, FoxO1, and HNF4alpha synergistically stimulated rat Cyp7a1 gene transcription. Mutations of the Smad3, FoxO1, or HNF4alpha binding site attenuated the rat Cyp7a1 promoter activity. Furthermore, TNFalpha and cJun attenuated TGFbeta1 stimulation of rat Cyp7a1. Insulin or adenovirus-mediated expression of constitutively active AKT1 inhibited FoxO1 and Smad3 synergy. In streptozotocin-induced diabetic rats, Cyp7a1 mRNA expression levels were induced and insulin attenuated CYP7A1 mRNA levels. Chromatin immunoprecipitation assay showed that FoxO1 binding to Cyp7a1 chromatin was increased in diabetic rat livers and insulin reduced FoxO1 binding. These results suggest a mechanistic basis for induction of Cyp7a1 activity and bile acid synthesis in cholestatic rats and in diabetic rats. The crosstalk of insulin, TGFbeta and TNFalpha signaling pathways may regulate bile acid synthesis and lipid homeostasis in diabetes, fatty liver disease, and liver fibrosis.
Li Tiangang; Ma Huiyan; Chiang John Y L
Journal of lipid research
2008
2008-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M800140-JLR200" target="_blank" rel="noreferrer noopener">10.1194/jlr.M800140-JLR200</a>
PXR induces CYP27A1 and regulates cholesterol metabolism in the intestine.
*Lipid Metabolism; ATP Binding Cassette Transporter; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters/genetics; Base Sequence; Cell Line; Cholestanetriol 26-Monooxygenase/*metabolism; Cholesterol; Cholesterol/*metabolism; Fluorinated; Genes; Genetic/drug effects; Genetic/genetics; HDL/metabolism; Hepatocytes/drug effects/enzymology/metabolism; Humans; Hydrocarbons; Hydroxycholesterols/metabolism/pharmacology; Intestinal Mucosa/metabolism; Intestines/cytology/drug effects/enzymology; Member 1; Messenger/genetics/metabolism; Molecular Sequence Data; Pregnane X Receptor; Promoter Regions; Receptors; Reporter; Response Elements/genetics; Rifampin/pharmacology; RNA; Steroid/*metabolism; Subfamily G; Sulfonamides/pharmacology; Transcription; Up-Regulation/drug effects
Mitochondrial sterol 27-hydroxylase (CYP27A1) catalyzes oxidative cleavage of the sterol side chain in the bile acid biosynthetic pathway in the liver and
Li Tiangang; Chen Wenling; Chiang John Y L
Journal of lipid research
2007
2007-02
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M600282-JLR200" target="_blank" rel="noreferrer noopener">10.1194/jlr.M600282-JLR200</a>
Cholesterol 7alpha-hydroxylase protects the liver from inflammation and fibrosis by maintaining cholesterol homeostasis.
*bile acid; *Cholesterol 7-alpha-Hydroxylase/genetics/metabolism; *farnesoid X receptor; *Homeostasis; *Liver Cirrhosis/chemically induced/enzymology/genetics/prevention & control; *Liver/enzymology/pathology; *nuclear receptor; *Takeda G protein-coupled receptor 5; Animals; Cholesterol/genetics/*metabolism; G-Protein-Coupled/genetics/metabolism; Hep G2 Cells; Humans; Knockout; Mice; NF-kappa B/genetics/metabolism; Oxidative Stress; Receptors; Tumor Necrosis Factor-alpha/genetics/metabolism
Cholesterol 7alpha-hydroxylase (CYP7A1) plays a critical role in control of bile acid and cholesterol homeostasis. Bile acids activate farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) to regulate lipid, glucose, and energy metabolism. However, the role of bile acids in hepatic inflammation and fibrosis remains unclear. In this study, we showed that adenovirus-mediated overexpression of Cyp7a1 ameliorated lipopolysaccharide (LPS)-induced inflammatory cell infiltration and pro-inflammatory cytokine production in WT and
Liu Hailiang; Pathak Preeti; Boehme Shannon; Chiang John Y L
Journal of lipid research
2016
2016-10
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M069807" target="_blank" rel="noreferrer noopener">10.1194/jlr.M069807</a>
Cholesteryl ester transfer protein alters liver and plasma triglyceride metabolism through two liver networks in female mice.
*estrogen; *estrogen receptor alpha; *lipid and lipoprotein metabolism; *small heterodimer partner; *triglycerides; *very low density lipoprotein; Animals; Cholesterol Ester Transfer Proteins/*physiology; Estrogen Receptor alpha/metabolism; Estrogens/physiology; Female; Inbred C57BL; Lipid Metabolism; Liver/*metabolism; Metabolic Networks and Pathways; Mice; Oxidation-Reduction; Transgenic; Triglycerides/biosynthesis/*blood
Elevated plasma TGs increase risk of cardiovascular disease in women. Estrogen treatment raises plasma TGs in women, but molecular mechanisms remain poorly understood. Here we explore the role of cholesteryl ester transfer protein (CETP) in the regulation of TG metabolism in female mice, which naturally lack CETP. In transgenic CETP females, acute estrogen treatment raised plasma TGs 50%, increased TG production, and increased expression of genes involved in VLDL synthesis, but not in nontransgenic littermate females. In CETP females, estrogen enhanced expression of small heterodimer partner (SHP), a nuclear receptor regulating VLDL production. Deletion of liver SHP prevented increases in TG production and expression of genes involved in VLDL synthesis in CETP mice with estrogen treatment. We also examined whether CETP expression had effects on TG metabolism independent of estrogen treatment. CETP increased liver beta-oxidation and reduced liver TG content by 60%. Liver estrogen receptor alpha (ERalpha) was required for CETP expression to enhance beta-oxidation and reduce liver TG content. Thus, CETP alters at least two networks governing TG metabolism, one involving SHP to increase VLDL-TG production in response to estrogen, and another involving ERalpha to enhance beta-oxidation and lower liver TG content. These findings demonstrate a novel role for CETP in estrogen-mediated increases in TG production and a broader role for CETP in TG metabolism.
Palmisano Brian T; Le Thao D; Zhu Lin; Lee Yoon-Kwang; Stafford John M
Journal of lipid research
2016
2016-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M069013" target="_blank" rel="noreferrer noopener">10.1194/jlr.M069013</a>
Cholesterol 7alpha-hydroxylase-deficient mice are protected from high-fat/high-cholesterol diet-induced metabolic disorders.
*bile acids and salt/metabolism; *cholesterol/diet; *lipids; *liver; Animal; Animals; Bile Acids and Salts/genetics/metabolism; Cholesterol 7-alpha-Hydroxylase/*genetics/metabolism; Cholesterol/*metabolism; Diet; Disease Models; Exhalation/genetics; Glucose/metabolism; High-Fat; Homeostasis; Humans; Lipid Metabolism/genetics; Liver/enzymology/pathology; Metabolic Diseases/*genetics/metabolism; Mice
Cholesterol 7alpha-hydroxylase (CYP7A1) is the first and rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver. In addition to absorption and digestion of nutrients, bile acids play a critical role in the regulation of lipid, glucose, and energy homeostasis. We have backcrossed Cyp7a1(-/-) mice in a mixed B6/129Sv genetic background to C57BL/6J mice to generate Cyp7a1(-/-) mice in a near-pure C57BL/6J background. These mice survive well and have normal growth and a bile acid pool size approximately 60% of WT mice. The expression of the genes in the alternative bile acid synthesis pathway are upregulated, resulting in a more hydrophilic bile acid composition with reduced cholic acid (CA). Surprisingly, Cyp7a1(-/-) mice have improved glucose sensitivity with reduced liver triglycerides and fecal bile acid excretion, but increased fecal fatty acid excretion and respiratory exchange ratio (RER) when fed a high-fat/high-cholesterol diet. Supplementing chow and Western diets with CA restored bile acid composition, reversed the glucose tolerant phenotype, and reduced the RER. Our current study points to a critical role of bile acid composition, rather than bile acid pool size, in regulation of glucose, lipid, and energy metabolism to improve glucose and insulin tolerance, maintain metabolic homeostasis, and prevent high-fat diet-induced metabolic disorders.
Ferrell Jessica M; Boehme Shannon; Li Feng; Chiang John Y L
Journal of lipid research
2016
2016-07
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M064709" target="_blank" rel="noreferrer noopener">10.1194/jlr.M064709</a>
Aldo-keto reductase 1B7 is a target gene of FXR and regulates lipid and glucose homeostasis.
*Aldehyde Reductase/genetics/metabolism; Adenoviridae; Animal; Animals; Blood Glucose/*metabolism; Cholesterol/analysis; Cytoplasmic and Nuclear/genetics/*metabolism; Diabetes Mellitus/genetics/*metabolism/physiopathology; Disease Models; Fatty Liver/genetics/*metabolism/physiopathology; Gene Expression; Genetic Vectors; Gluconeogenesis/genetics; Homeostasis; Humans; Liver/*metabolism/physiopathology; Malondialdehyde/blood; Mice; Polymerase Chain Reaction; Receptors; Transfection; Transgenic; Triglycerides/analysis
Aldo-keto reductase 1B7 (AKR1B7) is proposed to play a role in detoxification of by-products of lipid peroxidation. In this article, we show that activation of the nuclear receptor farnesoid X receptor (FXR) induces AKR1B7 expression in the liver and intestine, and reduces the levels of malondialdehyde (MDA), the end product of lipid peroxidation, in the intestine but not in the liver. To determine whether AKR1B7 regulates MDA levels in vivo, we overexpressed AKR1B7 in the liver. Overexpression of AKR1B7 in the liver had no effect on hepatic or plasma MDA levels. Interestingly, hepatic expression of AKR1B7 significantly lowered plasma glucose levels in both wild-type and diabetic db/db mice, which was associated with reduced hepatic gluconeogenesis. Hepatic expression of AKR1B7 also significantly lowered hepatic triglyceride and cholesterol levels in db/db mice. These data reveal a novel function for AKR1B7 in lipid and glucose metabolism and suggest that AKR1B7 may not play a role in detoxification of lipid peroxides in the liver. AKR1B7 may be a therapeutic target for treatment of fatty liver disease associated with diabetes mellitus.
Ge Xuemei; Yin Liya; Ma Huiyan; Li Tiangang; Chiang John Y L; Zhang Yanqiao
Journal of lipid research
2011
2011-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M015859" target="_blank" rel="noreferrer noopener">10.1194/jlr.M015859</a>
A putative role of micro RNA in regulation of cholesterol 7alpha-hydroxylase expression in human hepatocytes.
3' Untranslated Regions/genetics; Base Sequence; Chenodeoxycholic Acid/pharmacology; Cholesterol 7-alpha-Hydroxylase/*genetics; Enzymologic/drug effects/*genetics; Fibroblast Growth Factors/pharmacology; Gene Expression Regulation; Genetic/drug effects/genetics; Hep G2 Cells; Hepatocytes/drug effects/enzymology/*metabolism; Humans; Isoxazoles/pharmacology; MicroRNAs/*genetics/*metabolism; Oligonucleotide Array Sequence Analysis; Post-Transcriptional/drug effects/genetics; RNA Processing; Transcription
Cholesterol 7alpha-hydroxylase (CYP7A1) plays a critical role in regulation of bile acid synthesis in the liver. CYP7A1 mRNAs have very short half-lives, and bile acids destabilize CYP7A1 mRNA via the 3'-untranslated region (3'-UTR). However, the underlying mechanism of translational regulation of CYP7A1 mRNA remains unknown. Screening of a human micro RNA (miRNA) microarray has identified five differentially expressed miRNAs in human primary hepatocytes treated with chenodeoxycholic acid, GW4064, or fibroblast growth factor (FGF)19. These compounds also significantly induced the expression of miR-122a, a liver-specific and the predominant miRNA in human hepatocytes. The putative recognition sequences for miR-122a and miR-422a were localized in the 3'-UTR of human CYP7A1 mRNA. The miR-122a and miR-422a mimics inhibited, whereas their inhibitors stimulated CYP7A1 mRNA expression. These miRNAs specifically inhibited the activity of the CYP7A1-3'-UTR reporter plasmids, and mutations of miRNA binding sites in 3'-UTR abrogated miRNA inhibition of reporter activity. These results suggest that miR-122a and miR-422a may destabilize CYP7A1 mRNA to inhibit CYP7A1 expression. However, these miRNAs did not play a role in mediating FGF19 inhibition of CYP7A1 transcription. Under certain conditions, miRNA may reduce CYP7A1 mRNA stability to inhibit bile acid synthesis, and the miR-122a antagomirs may stimulate bile acid synthesis to reduce serum cholesterol and triglycerides.
Song Kwang-Hoon; Li Tiangang; Owsley Erika; Chiang John Y L
Journal of lipid research
2010
2010-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M004531" target="_blank" rel="noreferrer noopener">10.1194/jlr.M004531</a>
Glucose stimulates cholesterol 7alpha-hydroxylase gene transcription in human hepatocytes.
*Gene Expression Regulation; Acetylation; AMP-Activated Protein Kinases/metabolism; ATP Citrate (pro-S)-Lyase/genetics/metabolism; Bile Acids and Salts/metabolism; Cells; Cholesterol 7-alpha-Hydroxylase/genetics/*metabolism; Cultured; DNA-Binding Proteins/metabolism; Enzymologic; Epigenesis; Genes; Genetic; Glucose/*administration & dosage; Hep G2 Cells; Hepatocyte Nuclear Factor 4/metabolism; Hepatocytes/*enzymology/metabolism; Histones/metabolism; Humans; Hyperglycemia/enzymology/*metabolism; Messenger/metabolism; Methylation; Reporter; RNA; RNA Interference
Bile acids play important roles in the regulation of lipid, glucose, and energy homeostasis. Recent studies suggest that glucose regulates gene transcription in the liver. The aim of this study was to investigate the potential role of glucose in regulation of bile acid synthesis in human hepatocytes. High glucose stimulated bile acid synthesis and induced mRNA expression of cholesterol 7alpha-hydroxylase (CYP7A1), the key regulatory gene in bile acid synthesis. Activation of an AMP-activated protein kinase (AMPK) decreased CYP7A1 mRNA, hepatocyte nuclear factor 4alpha (HNF4alpha) protein, and binding to CYP7A1 chromatin. Glucose increased ATP levels to inhibit AMPK and induce HNF4alpha to stimulate CYP7A1 gene transcription. Furthermore, glucose increased histone acetylation and decreased H3K9 di- and tri-methylation in the CYP7A1 chromatin. Knockdown of ATP-citrate lyase, which converts citrate to acetyl-CoA, decreased histone acetylation and attenuated glucose induction of CYP7A1 mRNA expression. These results suggest that glucose signaling also induces CYP7A1 gene transcription by epigenetic regulation of the histone acetylation status. This study uncovers a novel link between hepatic glucose metabolism and bile acid synthesis. Glucose induction of bile acid synthesis may have an important implication in metabolic control of glucose, lipid, and energy homeostasis under normal and diabetic conditions.
Li Tiangang; Chanda Dipanjan; Zhang Yanqiao; Choi Hueng-Sik; Chiang John Y L
Journal of lipid research
2010
2010-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1194/jlr.M002782" target="_blank" rel="noreferrer noopener">10.1194/jlr.M002782</a>