LDL Receptor mRNA Research Articles

L-Cysteine-induced up-regulation of the low-density lipoprotein receptor is mediated via a transforming growth factor-alpha signalling pathway

Sulphur-containing amino acids regulate plasma cholesterol levels in animals and humans. However, their mechanism of action remains unclear. Low-density lipoprotein receptor (LDLR) plays an important role in cholesterol metabolism. We therefore investigated the effects of sulphur-containing amino acids on the expression of LDLR in hepatocytes. HepG2 cells were cultured in Dulbecco’s Modified Eagle’s Medium with or without sulphur-containing amino acids and cysteine-containing compounds. We found that l-cysteine increased LDLR mRNA and enhanced LDLR gene promoter activity through the extracellular-signal-related kinase and p38 mitogen-activated protein kinase signalling pathways in HepG2 cells. Moreover, we observed that l-cysteine stimulated the release of transforming growth factor-alpha (TGF-α) and that TGF-α increased the LDLR mRNA levels. This study provides a report of the l-cysteine mediated up-regulation of the LDLR expression via TGF-α signalling pathway. Our findings provide insights into cholesterol homeostasis and amino acid signalling.

Ameliorative effect of Pracparatum mungo extract on high cholesterol diets in hamsters

This study was designed to test the lipid-lowering and antioxidative activities of Pracparatum mungo extract (PME), in comparison to its components berberine and glycyrrhizin in cholesterol-fed hamsters. The PME and berberine significantly lowered the atherogenic index compared to glycyrrhizin and the control (P < 0.05). The hepatic HMG-CoA reductase activity was significantly lower in the PME and berberine groups than in the glycyrrhizin group (P < 0.05), while the hepatic ACAT activity was significantly decreased by all treatments with respect to the high cholesterol fed group (P < 0.05). The overall potential of the antioxidant system was significantly enhanced by the PME, berberine and glycyrrhizin supplements as the plasma and hepatic TBARS levels were lowered while the hepatic superoxide dismutase activity and glutathione levels, HMG-CoA reductase, LDL receptor, PPAR, SREBP-2 and CYP7A1 mRNA expressions were increased by the treatments of PME and berberine in comparison with the high cholesterol fed hamsters (P < 0.05). Collectively, these results suggest that the supplementation of PME, berberine and glycyrrhizin increased antioxidant activity in hamsters. Furthermore, we observed that PME and berberine groups promoted the excretion of neutral and acidic sterols (P < 0.05), that could contribute to explain the lower plasma and hepatic cholesterol levels found in the treated animals.

Effects of lovastatin on hepatic expression of the low-density lipoprotein receptor in nephrotic rats

To investigate the effect of the HMG-CoA reductase inhibitor lovastatin on the expression of the receptor for hepatic low-density lipoprotein (LDL) in a rat model with kidney disease, and to identify the mechanisms in statin treatment of nephrotic syndrome with hyperlipidemia, a rat model with nephrotic syndrome was established. Thirty male Sprague-Dawley rats were treated with lovastatin for 2 weeks using gavage. The expression of protein and mRNA of the LDL receptor in the rat liver was detected with Western blot and RT-PCR, respectively, and blood-biochemical indices were also recorded for each group. Compared with the untreated control group, lovastatin treatment significantly decreased the levels of serum total cholesterol, LDL cholesterol, triglycerides, and urinary protein. In addition, lovastatin treatment significantly increased the levels of serum albumin and hepatic LDL receptor proteins, but had no effect on the expression of hepatic LDL receptor mRNA. Treatment with lovastatin markedly increased the expression of the hepatic LDL receptor in rats with nephrotic syndrome, which was accompanied by significantly improved hyperlipidemia.

Berberine metabolites could induce low density lipoprotein receptor up-regulation to exert lipid-lowering effects in human hepatoma cells

Berberine (BBR) is an isoquinoline alkaloid isolated from several Chinese herbal medicines, such as Coptis chinensis, Berberis aristata, and Coptis japonica. It exhibits a lipid-lowering effect by up-regulating the hepatic low density lipoprotein receptor (LDLR) expression. However, the plasma concentration of BBR is very low after oral administration for the reason that BBR is poorly absorbed and rapidly metabolized. Therefore, it is hard to explain the pharmacological effects of BBR in vivo. Here, RT-PCR, Western blotting and Oil Red O staining were used to investigate the effects of four BBR metabolites on LDLR expression and lipid accumulation in human hepatoma Hep G2 cells. Our results suggested that BBR increased the LDLR mRNA and protein levels in a time- and dose-dependent manner. Four metabolites of BBR, jatrorrhizine, columbamine, berberrubine and demethyleneberberine, were found to be able to up-regulate LDLR mRNA and protein expression. Moreover, almost all the metabolites had potent effects on inhibiting cellular lipid accumulation. These results suggest that both BBR and its metabolites exhibit lipid-lowering effects by up-regulating LDLR expression, and BBR and its metabolites might be the in vivo active forms of BBR produced after oral administration. This study provides information to help us understand the mechanisms underlying the hypolipidemic effects of BBR in vivo.

Difference in LDL Receptor Feedback Regulation in Macrophages and Vascular Smooth Muscle Cells: Foam Cell Transformation Under Inflammatory Stress

Macrophages and vascular smooth muscle cells (VSMCs) are the major cell types involved in foam cell formation associated with atherosclerosis. The aim of this experiment was to clarify cell-specific regulation of LDL receptor in THP-1 macrophages and human VSMCs under physiological and inflammatory conditions and its potential mechanisms. Inflammatory stress was induced by adding lipopolysaccharide (LPS) to human THP-1 macrophages and human VSMCs. Intracellular total cholesterol, free cholesterol, and cholesterol ester were measured by an enzymic assay. Oil Red O staining was used to visualize lipid droplet accumulation in cells. Total cellular RNA was isolated from cells for detecting LDL receptor, sterol regulatory element binding protein (SREBP)-2 and SREBP cleavage-activating protein (SCAP) mRNA levels using real-time quantitative polymerase chain reaction. LDL receptor, SREBP-2 and SCAP protein expression were examined by Western blotting. The translocation of SCAP from ER to Golgi was detected by confocal microscopy. LDL loading increased intracellular cholesterol level, reducing LDL receptor mRNA level in both THP-1 macrophages and VSMCs under physiological conditions. The IC50 in VSMCs was 11.25 μg/ml, which is much lower than 18.125 μg/ml in THP-1 macrophages. With the increase in concentration of LPS (0-400 ng/ml), the LDL receptor mRNA levels were upregulated in both cells, but the curve of LDL receptor mRNA in VSMCs exhibited a flatter profile than that of THP-1 macrophages. Under the treatment of 200 ng/ml of LPS, the upregulation fold of the LDL receptor mRNA in THP-1 macrophages was much higher than that of VSMCs (0.33 vs 0.04). LDL receptor blocking agent heparin decreased lipid droplets induced by LPS significantly in THP-1 macrophages and VSMCs. LDL loading reduced the SREBP2 and SCAP protein expression under physiological conditions. Exposure to LPS caused overexpression of SREBP2 and SCAP despite a high concentration of LDL in the culture medium, and increased translocation of SCAP from the ER to the Golgi in the presence of 25 μg/ml of LDL. Inflammatory stress disrupts LDL receptor negative feedback regulation induced by intracellular cholesterol in both cell types, to a greater degree in THP-1 macrophages, which could be one reason why THP-1 macrophages are more prone to become foam cells under inflammatory stress.

Role of PCSK9 and IDOL in the pathogenesis of acquired LDL receptor deficiency and hypercholesterolemia in nephrotic syndrome

Nephrotic syndrome (NS) leads to elevation of serum total and LDL cholesterol. This is largely due to impaired LDL clearance, which is caused by hepatic LDL receptor (LDLR) deficiency despite normal LDLR mRNA expression, pointing to a post-transcriptional process. The mechanism(s) by which NS causes LDLR deficiency is not known. By promoting degradation of LDLR, Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) and inducible degrader of the LDL receptor (IDOL) play a major role in post-translational regulation of LDLR. We, therefore, tested the hypothesis that LDLR deficiency despite its normal gene expression in NS may be due to upregulation of hepatic PCSK9 and IDOL. LDLR, IDOL and PCSK9 expressions and nuclear translocation of liver X receptor (LXR) that regulates IDOL expression were determined in the liver of rats with puromycin-induced NS and control (CTL) rats. Compared with the CTLs, the NS rats showed marked elevation of serum total and LDL cholesterol and a significant reduction in hepatic LDLR protein expression. This was accompanied by marked upregulation of hepatic PCSK9 and IDOL expressions and heightened LXR activation. LDLR deficiency, hypercholesterolemia and elevated plasma LDL in NS are associated with upregulation of PCSK9 and IDOL. Interventions targeting these pathways may be effective in the management of hypercholesterolemia and the associated cardiovascular and other complications of NS.

The Critical Role of mRNA Destabilizing Protein Heterogeneous Nuclear Ribonucleoprotein D in 3′ Untranslated Region–Mediated Decay of Low-Density Lipoprotein Receptor mRNA in Liver Tissue

Previous studies showed that low-density lipoprotein receptor (LDLR) mRNA 3' untranslated region (UTR) contains regulatory elements responsible for rapid mRNA turnover in hepatic cells and mediates the mRNA stabilization induced by berberine (BBR). Here, we elucidate the underlying mechanism of BBR's action by characterizing mRNA-binding proteins that modulate LDLR mRNA decay via 3'UTR in liver tissue in vivo. We generated a transgenic mouse model (Alb-Luc-UTR) that expresses Luc-LDLR3'UTR reporter gene driven by the albumin promoter to study 3'UTR function in mediating LDLR mRNA decay in liver tissue. We show that treating Alb-Luc-UTR mice with BBR led to significant increases in hepatic bioluminescence signals, Luc-UTR mRNA, and LDLR mRNA levels as compared with control mice. These effects were accompanied by specific reductions of mRNA decay-promoting factor heterogeneous nuclear ribonucleoprotein D (hnRNP D) in liver of BBR-treated mice. Knockdown and overexpression studies further demonstrated that hnRNP D p37 isoform plays a major role in promoting hepatic LDLR mRNA degradation. In addition, we examined LDLR mRNA half-life, Luc-UTR reporter activity, and hnRNP D expression levels in cell lines derived from extrahepatic tissues. We demonstrated that strengths of 3'UTR in promoting mRNA degradation correlate with hnRNP D cellular abundances in nonhepatic cell lines, thereby suggesting its involvement in LDLR mRNA degradation beyond liver tissue. hnRNP D is critically involved in LDLR mRNA degradation in liver tissue in vivo. The inverse relationship of hnRNP D abundance with LDLR mRNA levels after BBR treatment suggests the potential of hnRNP D of being a novel therapeutic target for LDL cholesterol lowering.

손바닥선인장 복합물이 Streptozotocin으로 유발된 당뇨 쥐의 지질대사에 미치는 효과

Abstract This study was conducted to examine the effects of Opuntia ficus-indica complex (OF) on the lipid metabolism, bile acid in feces, alanine aminotransferase (ALT) activity, aspatate aminotransferase (AST) activity, composition of urine and expression of cholesterol related mRNA in streptozotocin (STZ)-induced diabetic rats. Thirty two male Sprague-Dawley rats were randomly divided into non-diabetic control (NC), diabetic control (DC), diabetic OF of 2% (OF-2) and diabetic OF of 5% (OF-5), then each group was fed for 3 weeks. Plasma total cholesterol, non-esterified fatty acids (NEFA), total cholesterol, low density lipoprotein (LDL), very low density lipoprotein (VLDL) were decreased significantly (p<0.05) in OF-5 group compared to DC, but high density lipoprotein (HDL) was not changed. AST and ALT were also reduced and bile acid excretion was improved. Composition of urine in OF-5 was almost same in NC. The expression of cholesterol 7α-hydroxylase (CYP7A1), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA-R), Low density lipoprotein receptor (LDL-R) mRNA indicated that feeding OF have the effects of cholesterol decreation in plasma by synthesis of bile acid from cholesterol. These results provide experimental evidence about improved lipid metabolism of the OF feeding in the STZ-induced diabetic rats.Key words: Opuntia ficus-indica, streptozotocin, total cholesterol, NEFA, CYP7A1

노팔 복합물이 II형 당뇨생쥐에서 지질대사에 미치는 효과

This study investigated the effects of Opuntia ficus-indica and other natural resources (OF) in db/db and C57 mice. Plasma triglycerides, cholesterol, alanine aminotransferase (ALT) activity, aspartate aminotransferase (AST) activity, fecal bile acid excretion, the histopathological appearance of the liver, and cholesterol-related mRNA expression were determined. Mice (12 db/db mice and 12 C57 mice) were assigned to diabetic-control (db-C), diabetic-OF treatment (db-OF), normal-control (C57-C), and normal-OF treatment (C57-OF) groups. Animals in the control group were fed an AIN-76 recommended diet and animals in the OF group were fed an experimental diet containing 5% of OF for 4 weeks. Concentrations of total plasma cholesterol, triglyceride, low density lipoprotein (LDL)-cholesterol, and very low density lipoprotein (VLDL)-cholesterol decreased with the administration of OF. In contrast, high density lipoprotein (HDL)-cholesterol levels were minimally affected by the experimental diet. Plasma AST and ALT showed lower activities in the db-OF group, and the fecal excretion of bile acid was reduced in the db-OF group. Histopathological analysis of the liver showed that fatty liver conditions in the db-OF group were more improved than db-C. Low-density lipoprotein receptor (LDL-R) and cholesterol 7-hydroxylase (CYP7A1) mRNA expression were increased in the db-OF group as well. However, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA-R) mRNA expression was lower in the db-OF group. These results provide experimental evidence about improved lipid metabolism of the OF feeding in the db/db mice.

Effect of Licorice Flavonoid Oil on Cholesterol Metabolism in High Fat Diet Rats

Dietary licorice fravonoid oil (LFO) significantly decreased hepatic cholesterol and plasma lipoprotein cholesterol levels in high-fat diet rats. It significantly suppressed hydroxymethylglutaryl-CoA synthase activity and increased cholesterol 7α-hydroxylase activity. The low density lipoprotein receptor mRNA level was significantly increased by LFO. These results suggest that dietary LFO improves cholesterol metabolism in obese animals.

Changes in levels of gene expression in human aortal intima during atherogenesis

Changes in the contents of 36 mRNAs species related to lipid turnover, inflammation, metabolism and the action of sex hormones in samples of aortal intima along the "intact tissue - lesions of type I - lesions of type II - lesions of type Va" sequence were analyzed using quantitative PCR. The expression of several mRNAs coding for components of the vesicular transfer and lipid turnover machinery was found to be resistant to atherogenesis or even decline in the course of atherogenesis. Decrease in expression was also recorded for steroid sulfatase, androgen receptor, and low density lipoprotein receptor mRNAs. However, the contents of the majority of other mRNA species increased gradually during disease progression. The earliest changes found as early as in lesions of type I were characteristic for estrogen sulfotransferase, apolipoprotein E, scavenger receptor SR-BI, collagen COL1A2, as well as chemokine CCL18 mRNAs. The contents of several mRNAs in intact tissue and atherosclerotic injuries had gender differences. Additionally, responses of two mRNAs, for aromatase and sterol regulatory element binding protein 2, to atherosclerotic lesion were also sex-differentiated. The contents of the majority of analyzed mRNAs in peripheral blood monocyte-derived macrophages were higher than in intact aorta. The correlations found in atherosclerotic lesions between mRNA species that predominant in macrophages and those expressed at comparable levels in macrophages and intact aorta or mainly in aorta suggest that the observed rise in the content of the majority of mRNAs during atherogenesis is determined by increase in expression in resident cells. The data suggest that the revealed absence of homeostatic regulation of expression of a number of genes associated with vesicular transfer and lipid turnover can serve as one of the reasons for lysosomal function insufficiency that leads to foam cell formation in atheroma. The observed sex differences in expression of a number of mRNAs suggest that estrogens in women perform their atheroprotective effects starting with predisposition to the disease and finishing with advanced stages of the pathologic process.

HYPOCHOLESTEROLEMIC EFFECT OF DIETARY APPLE POLYPHENOL IS ASSOCIATED WITH ALTERATIONS IN HEPATIC GENE EXPRESSION RELATED TO CHOLESTEROL METABOLISM IN RATS

Apple polyphenol (AP) mainly consists of procyanidins and has been reported to improve blood cholesterol levels and promote excretion of cholesterol in rats fed high-cholesterol diets. To understand the molecular mechanisms underlying the effects of AP, we investigated whether dietary AP changed the hepatic expression of genes related to cholesterol metabolism and steroid transport. Four-week-old male Sprague-Dawley rats were pair-fed with diets containing 0.5% cholesterol together with 0% (control), 0.2%, and 0.5% AP, respectively, for 30 days. Administration of 0.5% AP was found to improve serum total cholesterol levels (0.69fold vs. control, p < 0.05), and increase hepatic LDL receptor (LDLR) mRNA (1.59-fold vs. control, p < 0.0001). There was a negative correlation between serum non-HDL cholesterol and LDLR mRNA (p < 0.001). Administration of 0.5% AP increased excretion of primary bile acids (2.96-fold vs. control, p < 0.0001) and up-regulated the expression of steroid catabolism genes such as sterol 12αhydroxylase (CYP8B1). However, improvements in cholesterol levels were not associated with the hepatic expression of cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid biosynthesis. Expression of farnesoid X receptor (FXR), which is involved in the regulation of bile acid biosynthesis, was up-regulated by 0.5% AP (1.56-fold vs. control, p < 0.01), and FXR mRNA levels correlated positively with bile acid excretion (p < 0.01). These results show that dietary AP improved blood cholesterol levels with adequate intake of LDL from blood by increasing hepatic LDLR expression and promoting production of bile acid with an upregulation of genes related to steroid catabolism. KeywordsApple Polyphenol; Procyanidin; Cholesterol Metabolism; LDL Receptor

A common polymorphism in the LDL receptor gene has multiple effects on LDL receptor function

A common synonymous single nucleotide polymorphism in exon 12 of the low-density lipoprotein receptor (LDLR) gene, rs688, has been associated with increased plasma total and LDL cholesterol in several populations. Using immortalized lymphoblastoid cell lines from a healthy study population, we confirmed an earlier report that the minor allele of rs688 is associated with increased exon 12 alternative splicing (P < 0.05) and showed that this triggered nonsense-mediated decay (NMD) of the alternatively spliced LDLR mRNA. However, since synonymous single nucleotide polymorphisms may influence structure and function of the encoded proteins by co-translational effects, we sought to test whether rs688 was also functional in the full-length mRNA. In HepG2 cells expressing LDLR cDNA constructs engineered to contain the major or minor allele of rs688, the latter was associated with a smaller amount of LDLR protein at the cell surface (-21.8 ± 0.6%, P = 0.012), a higher amount in the lysosome fraction (+25.7 ± 0.3%, P = 0.037) and reduced uptake of fluorescently labeled LDL (-24.3 ± 0.7%, P < 0.01). Moreover, in the presence of exogenous proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that reduces cellular LDL uptake by promoting lysosomal degradation of LDLR, the minor allele resulted in reduced capacity of a PCSK9 monoclonal antibody to increase LDL uptake. These findings are consistent with the hypothesis that rs688, which is located in the β-propeller region of LDLR, has effects on LDLR activity beyond its role in alternative splicing due to impairment of LDLR endosomal recycling and/or PCSK9 binding, processes in which the β-propeller is critically involved.

Effect of Dai-Saiko-To (Da-Chai-Hu-Tang) on LDL-Receptor Gene Expression in Human Hepatoma Cell Line (HepG2)

We previously reported that Dai-saiko-to (Da-Chai-Hu-Tang), a traditional Japanese kampo medicine, increased LDL receptor mRNA expression in the liver of the hypercholesterolemic rabbits. In this study, we focused on LDL receptor gene expression in a human hepatoma cell line (HepG2) treated with Dai-saiko-to extract and the extracts of eight herbs presented in Dai-saiko-to. Dai-saiko-to extract significantly increased LDL receptor gene and SREBP2 gene expression compared with the control. The extracts of four herbs, Bupleurum root, Pinellia tuber, Scutellaria root and Peony root significantly increased the LDL receptor gene expression. Whereas, Jujube, Immature orange, Ginger and Rhubarb extracts did not change the gene expression. These results suggest that Dai-saiko-to increased the expression of the cholesterol transport gene (LDL receptor) regulated by SREBP2 gene in the human hepatoma cell line. The pharmacological activity of Dai-saiko-to against hypercholesterolemia and atheromatous lesions related for these four herbal components.

Adrenal-Specific Scavenger Receptor BI Deficiency Induces Glucocorticoid Insufficiency and Lowers Plasma Very-Low-Density and Low-Density Lipoprotein Levels in Mice

We determined the physiological consequences of adrenocortical-specific deletion of scavenger receptor BI (SR-BI) function in C57BL/6 wild-type mice. One adrenal from 10-day-old SR-BI knockout (KO) mice or wild-type controls was transplanted under the renal capsule of adrenalectomized C57BL/6 recipient mice. The fasting plasma corticosterone level increased over time in transplanted mice. Corticosterone values in SR-BI KO transplanted mice remained ≈50% lower (P<0.001) as compared with wild-type transplanted mice, which coincided with adrenocortical lipid depletion. A 6.5-fold higher (P<0.01) plasma adrenocorticotropic hormone level was present in SR-BI KO transplanted mice reminiscent of primary glucocorticoid insufficiency. On feeding with cholic acid-containing high cholesterol/high fat diet, SR-BI KO transplanted mice exhibited a 26% (P<0.05) reduction in their liver triglyceride level. Hepatic myosin regulatory light chain interacting protein/inducible degrader of the low-density lipoprotein receptor mRNA expression was 48% (P<0.01) decreased in adrenal-specific SR-BI KO mice, which was paralleled by a marked decrease (-46%; P<0.01) in proatherogenic very-low-density and low-density lipoprotein levels. Adrenal-specific disruption of SR-BI function induces glucocorticoid insufficiency and lowers plasma very-low-density and low-density lipoprotein levels in atherogenic diet-fed C57BL/6 mice. These findings further highlight the interaction between adrenal high-density lipoprotein-cholesterol uptake by SR-BI, adrenal steroidogenesis, and the regulation of hepatic lipid metabolism.

Alleviative effects of resveratrol on nonalcoholic fatty liver disease are associated with up regulation of hepatic low density lipoprotein receptor and scavenger receptor class B type I gene expressions in rats

Lipid metabolic disorders are widely considered to be one of the most critical and basic link in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). The aim of this study was to illustrate the alleviation function of resveratrol (Res) on NAFLD and the roles of hepatic fatty acid synthase (FAS), low density lipoprotein receptor (LDLr), scavenger receptor class B type I (SR-BI), and thyroid hormone receptor β1 (TRβ1), which are the key molecules involved in lipid metabolism. Adult male Wistar rats were fed a normal diet or high fat/sucrose diet (HFS) with or without resveratrol for 13weeks. HFS induced NAFLD formation and increased the lipids concentrations in serum and livers of rats, while noticeable improvement has been reached by Res intervention. Moreover, Res protected against HFS-induced decrease in hepatic LDLr and SR-BI mRNA and protein expressions, whereas TRβ1 expressions were impervious with/without Res. Unexpectedly, hepatic FAS gene expressions were markedly diminished in NAFLD rats and were gradually increased by treatment with Res. These data indicate that the alleviative effects of Res on NAFLD are associated with up regulation of hepatic LDLr and SR-BI gene expressions, which provide new insights into the pharmacological targets of Res in the prevention of NAFLD.

Ablation of gp78 in Liver Improves Hyperlipidemia and Insulin Resistance by Inhibiting SREBP to Decrease Lipid Biosynthesis

gp78 is a membrane-anchored ubiquitin ligase mediating the degradation of HMG-CoA reductase (HMGCR) and Insig-1. As a rate-limiting enzyme in cholesterol biosynthesis, HMGCR undergoes rapid sterol-promoted degradation. In contrast, destruction of Insig-1 releases its inhibition on SREBP and stimulates the expression of lipogenic genes. Thus, gp78 has opposite effects on lipid biosynthesis. We here generated liver-specific gp78 knockout (L-gp78(-/-)) mice and showed that although the degradation of HMGCR was blunted, SREBP was suppressed due to the elevation of Insig-1/-2, and therefore the lipid biosynthesis was decreased. The L-gp78(-/-) mice were protected from diet-/age-induced obesity and glucose intolerance. The livers of L-gp78(-/-) mice produced more FGF21, which activated thermogenesis in brown adipocytes and enhanced energy expenditure. Together, the major function of gp78 in liver is regulating lipid biosynthesis through SREBP pathway. Ablation of gp78 decreases the lipid levels and increases FGF21, and is beneficial to patients with metabolic diseases.

The effects of berberine on hyperhomocysteinemia and hyperlipidemia in rats fed with a long-term high-fat diet

BackgroundThe study was undertaken to examine the effects of berberine (BBR) on serum homocysteine, lipids and the aortic lesion in Sprague–Dawley (SD) rats fed with a long-term high-fat diet (HFD).MethodsHealthy male SD rats weighing 190-210 g received randomly standard diet or a high-fat diet for 24 weeks. After 8 weeks of feeding, rats fed with HFD were randomized to receive berberine (200 mg · kg-1· day-1) or vehicle by gavage for 16 weeks. After overnight fasting, all rats were sacrificed and total blood samples were also collected for determinant of fasting serum homocysteine (Hcy), total cholesterol (TC) and low density lipoprotein cholesterol (LDL-c) levels. The aorta was stained with hematoxylin and eosin (HE) and Sudan Ш to evaluate aortic lesion. The livers were dissected out and snap-frozen in liquid nitrogen for hepatic TC content and molecular analysis. 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), Lipoprotein receptors and apolipoproteins gene expression in the liver were determined by real-time PCR.ResultsIntragastrical administration with berberine for 16 weeks lowered serum Hcy in rats fed with a high-fat diet. In parallel, it also decreased body weight and improved serum TC and LDL-c. Berberine also tended to decrease hepatic cholesterol. Consistently, berberine also upregulated LDL receptor (LDLR) mRNA level and suppressed HMGR gene expression. Meanwhile, upon berberine-treated rats, there was a significant increase in apolipoprotein E (apoE) mRNA, but no change in apoAI and scavenger receptor (SR) mRNA in the liver. Further, no atherosclerotic lesions were developed in berberine-treated rats for 16 weeks.ConclusionBerberine can counteract HFD-elicited hyperhomocysteinemia and hyperlipidemia partially via upregulating LDLR and apoE mRNA levels and suppressing HMGR gene expression.

Blockade of cholesterol absorption by ezetimibe reveals a complex homeostatic network in enterocytes

Enterocyte cholesterol homeostasis reflects aggregated rates of sterol synthesis, efflux, and uptake from plasma and gut lumen. Cholesterol synthesis and LDL uptake are coordinately regulated by sterol regulatory element-binding proteins (SREBP), whereas sterol efflux is regulated by liver X receptors (LXR). How these processes are coordinately regulated in enterocytes, the site of cholesterol absorption, is not well understood. Here, we treat mice with ezetimibe to investigate the effect of blocking cholesterol absorption on intestinal SREBPs, LXRs, and their effectors. Ezetimibe increased nuclear SREBP-2 8-fold. HMG-CoA reductase (HMGR) and LDL receptor (LDLR) mRNA levels increased less than 3-fold, whereas their protein levels increased 30- and 10-fold, respectively. Expression of inducible degrader of LDLR (IDOL), an LXR-regulated gene that degrades LDLRs, was reduced 50% by ezetimibe. Coadministration of ezetimibe with the LXR agonist T0901317 abolished the reduction in IDOL and prevented the increase in LDLR protein. Ezetimibe-stimulated LDLR expression was independent of proprotein convertase subtilisin/kexin type 9 (PSCK9), a protein that degrades LDLRs. To maintain cholesterol homeostasis in the face of ezetimibe, enterocytes boost LDL uptake by increasing LDLR number, and they boost sterol synthesis by increasing HMGR and other cholesterologenic genes. These studies reveal a hitherto undescribed homeostatic network in enterocytes triggered by blockade of cholesterol absorption.

Transcriptional Activation of Low-Density Lipoprotein Receptor Gene by DJ-1 and Effect of DJ-1 on Cholesterol Homeostasis

DJ-1 is a novel oncogene and also causative gene for familial Parkinson’s disease park7. DJ-1 has multiple functions that include transcriptional regulation, anti-oxidative reaction and chaperone and mitochondrial regulation. For transcriptional regulation, DJ-1 acts as a coactivator that binds to various transcription factors, resulting in stimulation or repression of the expression of their target genes. In this study, we found the low-density lipoprotein receptor (LDLR) gene is a transcriptional target gene for DJ-1. Reduced expression of LDLR mRNA and protein was observed in DJ-1-knockdown cells and DJ-1-knockout mice and this occurred at the transcription level. Reporter gene assays using various deletion and point mutations of the LDLR promoter showed that DJ-1 stimulated promoter activity by binding to the sterol regulatory element (SRE) with sterol regulatory element binding protein (SREBP) and that stimulating activity of DJ-1 toward LDLR promoter activity was enhanced by oxidation of DJ-1. Chromatin immunoprecipitation, gel-mobility shift and co-immunoprecipitation assays showed that DJ-1 made a complex with SREBP on the SRE. Furthermore, it was found that serum LDL cholesterol level was increased in DJ-1-knockout male, but not female, mice and that the increased serum LDL cholesterol level in DJ-1-knockout male mice was cancelled by administration with estrogen, suggesting that estrogen compensates the increased level of serum LDL cholesterol in DJ-1-knockout female mice. This is the first report that DJ-1 participates in metabolism of fatty acid synthesis through transcriptional regulation of the LDLR gene.