LDL Receptor mRNA Expression Research Articles

Low Very low-Density Lipoprotein Cholesterol but High Very low-Density Lipoprotein Receptor mRNA Expression in Peripheral White Blood Cells: An Atherogenic Phenotype for Atherosclerosis in a Community-Based Population

Very low-density lipoprotein cholesterol (VLDL-C), via binding very low-density lipoprotein receptor (VLDLR), can induce the development of atherosclerosis. Besides monocytes, VLDLR expression is detected in various peripheral white blood cells (WBCs), yet its underlying role remains unclear. We thereby aimed to test the hypothesis that VLDLR in all types of peripheral WBCs may be involved in the association between VLDL-C and atherosclerosis. VLDLR mRNA expression in peripheral WBC and plasma VLDL-C levels were measured in 747 participants from a community-based study. Plaque prevalence and total plaque area (TPA) were used to evaluate the burden of carotid atherosclerosis. VLDL-C was positively associated with atherosclerosis risk, whereas this association was modified by VLDLR mRNA level. In participants with the lowest VLDL-C but the highest VLDLR mRNA expression, the risk for plaque prevalence unexpectedly was the highest. This association was also observed for TPA. Moreover, this association remained unchanged after adjusting for WBC or monocytes. Our findings described an atherogenic phenotype characterized by low VLDL-C but high VLDLR mRNA expression in peripheral WBCs, which suggested that VLDLR in all types of peripheral WBCs may be involved in lipid deposition, and VLDL-C and VLDLR may co-determine the development of atherosclerosis.

Deep sea water improves hypercholesterolemia and hepatic lipid accumulation through the regulation of hepatic lipid metabolic gene expression

A high‑fat diet or high‑cholesterol diet (HCD) is a major cause of metabolic diseases, including obesity and diabetes; vascular diseases, including hypertension, stroke and arteriosclerosis; and liver diseases, including hepatic steatosis and cirrhosis. The present study aimed to evaluate the effects of deep sea water (DSW) on rats fed a HCD. DSW decreased HCD‑induced increases in total cholesterol and low‑density lipoprotein (LDL) cholesterol in the blood, and recovered high‑density lipoprotein cholesterol. In addition, DSW decreased levels of liver injury markers, which were increased in response to HCD, including glutamate‑oxaloacetate transaminase, glutamate‑pyruvate transferase and alkaline phosphatase. Lower lipid droplet levels were observed in the livers of rats fed a HCD and treated with DSW at a hardness of 1,500, as compared with those in the HCD only group. Semi‑quantitative reverse transcription‑polymerase chain reaction (RT‑PCR) revealed that mRNA expression levels of fatty acid synthase and sterol regulatory element binding protein‑1c (SREBP‑1c) in rats fed a HCD with DSW were lower compared with the HCD only group. Furthermore, quantitative RT‑PCR revealed that DSW enhanced LDL receptor (LDLR) mRNA expression in a hardness‑dependent manner. Combined, the results of the present study indicated that DSW may reduce HCD‑induced increases in blood and liver lipid levels, indicating that DSW may protect against hypercholesterolemia and non‑alcoholic hepatic steatosis. In addition, the present study demonstrated that DSW‑induced downregulation of lipids in the blood and hepatic lipid accumulation was mediated by enhancement of LDLR expression and suppression of fatty acid synthase and SREBP‑1c.

Enhanced pro-protein convertase subtilisin/kexin type 9 expression by C-reactive protein through p38MAPK-HNF1α pathway in HepG2 cells.

Plasma C‐reactive protein (CRP) concentration is associated positively with cardiovascular risk, including dyslipidemia. We suggested a regulating role of CRP on pro‐protein convertase subtilisin/kexin type 9 (PCSK9), a key regulator of low‐density lipoprotein (LDL) metabolism, and demonstrated the PCSK9 as a pathway linking CRP and LDL regulation. Firstly, experiments were carried out in the presence of human CRP on the protein and mRNA expression of PCSK9 and LDL receptor (LDLR) in human hepatoma cell line HepG2 cells. Treatment with CRP (10 μg/ml) enhanced significantly the mRNA and protein expression of PCSK9 and suppressed the expression of LDLR. Of note, a late return of LDLR mRNA levels occurred at 12 hrs, while the LDLR protein continued to decrease at 24 hrs, suggesting that the late decrease in LDLR protein levels was unlikely to be accounted for the decrease in LDL mRNA. Secondly, the role of PCSK9 in CRP‐induced LDLR decrease and the underlying pathways were investigated. As a result, the inhibition of PCSK9 expression by small interfering RNA (siRNA) returned partly the level of LDLR protein and LDL uptake during CRP treatment; CRP‐induced PCSK9 increase was inhibited by the p38MAPK inhibitor, SB203580, resulting in a significant rescue of LDLR protein expression and LDL uptake; the pathway was involved in hepatocyte nuclear factor 1α (HNF1α) but not sterol responsive element‐binding proteins (SREBPs) preceded by the phosphorylation of p38MAPK. These findings indicated that CRP increased PCSK9 expression by activating p38MAPK‐HNF1α pathway, with a certain downstream impairment in LDL metabolism in HepG2 cells.

Expressions of lipoprotein receptors and cholesterol efflux regulatory proteins during luteolysis in bovine corpus luteum.

The corpus luteum (CL) synthesises and secretes progesterone (P4), which is essential for the establishment and maintenance of pregnancy in mammals. P4 is synthesised from cholesterol. Cholesterol is internalised by low-density lipoprotein receptor (LDLR) and/or scavenger receptor B1 (SR-BI), and is effluxed by ATP-binding cassette (ABC) transporter A1 (ABCA1) and G1 (ABCG1). To test the hypothesis that lipoprotein receptors and ABC transporters are involved in functional luteolysis, we examined the expression of LDLR, SR-BI, ABCA1 and ABCG1 in bovine CL during the luteal stages and after injection of prostaglandin (PG) F2α on Day 10 after ovulation. Expression of LDLR and SR-BI mRNA and protein was lower in the regressed luteal than late luteal stage. Injection of cows with a PGF2α did not affect LDLR mRNA and protein levels in the CL. Although expression of SR-BI mRNA did not change, SR-BI protein expression decreased 12 and 24h after PGF2α injection. The overall findings of the present study suggest that the decreased expression of SR-BI induced by PGF2α is one of the factors responsible for the continuous decrease in P4 production during functional luteolysis.

Fucoidan improves serum lipid levels and atherosclerosis through hepatic SREBP-2-mediated regulation

Hyperlipidemia is associated with increased risk of the development of cardiovascular diseases. Although a great deal of attention has been paid to the hypolipidemic activity of fucoidan, complex polysaccharides from brown seaweeds, the underlying mechanism is still unclear. This study was performed to investigate whether and how fucoidan has lipid-lowering potential in poloxamer-407 (P407)-induced hyperlipidemic mice. Fucoidan treatment 2 h after acute administration of P407 in these mice significantly reduced serum total cholesterol, triglycerides, and LDL cholesterol levels, but increased the levels of HDL cholesterol. In HepG2 hepatocytes and the liver, fucoidan decreased the expression of FAS and ACC mRNA with no or only a moderate inhibitory effect on SREBP-1c mRNA expression. Furthermore, fucoidan attenuated the hepatic expression of mature SREBP-2 protein with a subsequent decrease in hepatic HMG-CoA reductase mRNA expression and an increase in hepatic LDL receptor mRNA expression. In addition, atherosclerotic lesions in the aorta of chronically P407-treated mice were also reduced by fucoidan. These findings indicate that fucoidan improves serum lipid levels by regulating the expression of key enzymes of cholesterol and triglyceride syntheses in the liver through modulation of SREBP-2.

Synthetic High-Density Lipoprotein-Like Nanocarrier Improved Cellular Transport of Lysosomal Cholesterol in Human Sterol Carrier Protein-Deficient Fibroblasts.

Sterol carrier protein-2 (SCP-2), which is not found in tissues of people with Zellweger syndrome, facilitates the movement of cholesterol within cells, resulting in abnormal accumulation of cholesterol in SCP-2-deficient cells. This study investigated whether synthetic high-density lipoprotein-like nanocarrier (sHDL-NC) improves the cellular transport of lysosomal cholesterol to plasma membrane in SCP-2-deficient fibroblasts. Human SCP-2-deficient fibroblasts were incubated with [(3)H-cholesterol]LDL as a source of cholesterol and sHDL-NC. The cells were fractionated by centrifugation permit tracking of [(3)H]-cholesterol from lysosome into plasma membrane. Furthermore, cellular content of cholesteryl ester as a storage form and mRNA expression of low-density lipoprotein (LDL) receptor were measured to support the cholesterol transport to plasma membrane. Incubation with sHDL-NC for 8 h significantly increased uptake of [(3)H]-cholesterol to lysosome by 53% and further enhanced the transport of [(3)H]-cholesterol to plasma membrane by 32%. Treatment with sHDL-NC significantly reduced cellular content of cholesteryl ester and increased mRNA expression of LDL receptor (LDL-R). In conclusion, sHDL-NC enables increased transport of lysosomal cholesterol to plasma membrane. In addition, these data were indirectly supported by decreased cellular content of cholesteryl ester and increased gene expression of LDL-R. Therefore, sHDL-NC may be a useful vehicle for transporting cholesterol, which may help to prevent accumulation of cholesterol in SCP-2-deficient fibroblasts.

Hepatic S1P deficiency lowers plasma cholesterol levels in apoB-containing lipoproteins when LDLR function is compromised.

BackgroundSite-1 protease (S1P) is the key enzyme required for activation of the sterol regulatory element binding proteins (SREBPs) that govern lipid synthesis. While S1P has been speculated to influence plasma apoB-containing lipoprotein (Blp) metabolism, there has been little investigative work. LDL receptor (LDLR) is the major receptor for clearing plasma LDL cholesterol (LDL-c). Proprotein convertase subtilisin kexin type 9 (PCSK9) modulates LDL-c through post-translational degradation of the LDLR.MethodsA hepatic-specific knockdown (KD) of S1P was achieved using floxed S1P mouse models (S1Pf/f and LDLR-/-S1Pf/f) and hepatic expression of Cre recombinase. Lipids were measured in total plasma and size fractionated plasma using colorimetric assays. Realtime polymerase chain reaction, western blotting and ELISA were used to determine hepatic expression of key genes/protein. Plasmid mediated overexpression and siRNA mediated knockdown of genes were performed in mouse primary hepatocytes to determine the mechanistic basis of PCSK9 gene regulation.ResultsA hepatic-specific KD of S1P resulted in a 45 % and 38 % reduction in plasma total cholesterol and triglyceride levels, respectively. Hepatic S1P KD had a minimal effect on plasma Blp cholesterol (Blp-c) in S1Pf/f mice, despite significantly reducing VLDL secretion. Notably, hepatic S1P KD decreased the LDL receptor (LDLR) mRNA expression by 50 %. However, the reduction in LDLR protein levels was less than that of mRNA expression, especially under fed conditions. Further assessment of hepatic S1P deficiency revealed that it increased LDLR protein stability in vivo. Mechanistically, hepatic S1P KD was shown to decrease the liver and plasma levels of the protein proprotein convertase subtilisin/kexin type 9 (PCSK9), which degrades LDLR protein. This effect was more prominent in the fed condition and sufficient to account for the discordance in LDLR mRNA and protein levels. Furthermore, hepatic S1P was shown to regulate PCSK9 expression through activation of the SREBPs. In the LDLR-/- background, hepatic S1P KD significantly reduced Blp-c levels.ConclusionHepatic S1P is a physiological modulator of plasma Blp metabolism through its regulation of LDLR and PCSK9. Hepatic S1P is a valid target for lowering plasma Blp-c levels in the situation where LDLR function is compromised.

Abstract 544: A Novel Peroxisome Proliferator Response Element Modulates LDL-receptor Transcription in Response to PPAR Agonists.

Hepatic LDL receptor (LDLR) binds to and internalizes circulating LDL-cholesterol thereby facilitating its clearance from the serum. LDLR is regulated primarily at the transcriptional level by a sterol-regulatory element (SRE) in its proximal promoter region which is the site of action of SRE-binding protein (SREBP1/2). Additionally, SRE-dependent modulation of LDLR by peroxisome proliferator-activated receptor gamma (PPARγ) has also been previously described. However whether additional promoter elements directly regulate LDLR transcription is not very well understood. We observed that treatment with the PPARδ agonist L165041 elevated luciferase-reported activity of human LDLR promoter as well as the mRNA and protein expression of LDLR in both, human and mouse cell lines. The induction of LDLR mRNA in HepG2 cells was dose-dependent with maximal expression observed at 20uM. We also observed that the half-life of LDLR mRNA was similar in control and L165041 treated samples, suggesting that the induction was a result of transactivation of mRNA synthesis. Combinatorial treatment of HepG2 cells with L165041 and rosuvastain (RSV) demonstrated additive effects of the two compounds on LDLR mRNA as well as protein expression. Transcription factor prediction programs indicated presence of a single PPAR-response element (PPRE)-like sequence motif in the human LDLR promoter, located at -768 to -752 bases upstream of the translation start site. Luciferase reporter analyses indicated that mutation or deletion of this PPRE-like element resulted in attenuation of L165041 mediated upregulation of LDLR promoter luciferase activity. Electrophoretic mobility shift assays further confirmed the binding of PPARδ/RXR heterodimers to the LDLR-PPRE site. Taken together, our studies identify a novel PPRE in the proximal promoter of LDLR and suggest that combinatorial treatment of statin with PPAR agonist may have advantageous effects on LDLR expression.

Hypolipidemic Effect and Mechanism of Palmatine from Coptis chinensis in Hamsters Fed High-Fat diet.

Palmatine (PAL) is one of the main alkaloids in Coptis chinensis. The present aim was to investigate the hypolipidemic effect and mechanism of palmatine in hamsters fed with high-fat diet (HFD). PAL treatment decreased serum total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) levels, as well as increased fecal excretion of TC and total bile acids (TBA) in hyperlipidemic hamsters. Furthermore, PAL treatment up-regulated low-density lipoprotein receptor (LDLR) and cholesterol 7α-hydroxylase (CYP7A1) mRNA and protein expression and down-regulated apical sodium-dependent bile salt transporter (ASBT) mRNA and protein expression. These results demonstrated that PAL as a potential natural cholesterol lowering agent works by up-regulating LDLR and CYP7A1 mRNA and protein expression, down-regulating ASBT mRNA and protein expression, as well as enhancing fecal excretion of TC and TBA. The findings in our study suggest that palmatine could be a potential natural agent for treating hyperlipidemia.

Energy replacement using glucose does not increase postprandial lipemia after moderate intensity exercise.

BackgroundAerobic exercise can decrease postprandial triglyceride (TG) concentrations but the relationship between exercise-induced energy deficits and postprandial lipemia is still unclear. The aim of the present study was to examine the effect of a single bout of aerobic exercise, with and without energy replacement, on postprandial lipemia and on peripheral blood mononuclear cell (PBMC) mRNA expression of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) receptors and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR).MethodsNine healthy male humans completed three two-day trials in a random order. On day 1, volunteers rested (CON), completed 60 minutes of treadmill walking at 50% of VO2peak (EX) or completed the same bout of walking but with the energy replaced afterwards with a glucose solution (EXG). On day 2, volunteers rested and consumed a high fat test meal in the morning.ResultsTotal and incremental TG AUC were significantly lower on the EXG (P < 0.05) and EX (P < 0.05) trials than the CON trial with no difference between the two exercise trials. No significant difference was observed in VLDL or LDL receptor mRNA expression among the trials (P > 0.05).ConclusionsIn conclusion, energy replacement by glucose did not affect the decrease in postprandial TG concentrations observed after moderate intensity exercise and exercise does not affect changes in PBMC HMGCR, VLDL and LDL receptor mRNA expression.

Negative feedback loop of cholesterol regulation is impaired in the livers of patients with Alagille syndrome

AimTo characterize cholesterol regulation in the liver of patients with Alagille syndrome (AGS). MethodsSerum total cholesterol (TC) and total bile acid (TBA) levels were measured in 23 AGS patients. The expressions of genes involved in cholesterol regulation, including low-density lipoprotein receptor (LDLR), scavenger receptor class B type I (SR-BI), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), cholesterol 7α-hydroxylase (CYP7A1), ATP-binding cassette transporter (ABC) A1, and ABCG1/5/8, were measured in liver tissues from five of these patients. Expression of regulators for these genes, including farnesoid X receptor/small heterodimer partner (SHP), liver X receptor α (LXRα) and mature Sterol regulatory element-binding protein 2 (SREBP2) was measured. The expression of mature SREBP2 protein was also examined. ResultsSerum TC and TBA levels were correlated in the AGS patients. Liver cholesterol was also increased compared with controls, and correlated with bile acid contents. LDLR, SR-BI, HMGCR, and ABCGs mRNA expression were upregulated, while CYP7A1 mRNA expression was downregulated in AGS livers. SHP and LXRα mRNA expression was also increased, but maturation of SREBP2 was not suppressed in the patients. ConclusionsThe major upregulators of liver cholesterol might be increased in AGS patients, indicating an impaired negative feedback mechanism and accelerated liver cholesterol accumulation.

고콜레스테롤 식이 투여 마우스에서 복분자 미숙과 추출물과 홍삼농축액 복합 투여의 콜레스테롤 개선 효과

본 연구는 복분자 미숙과 물 추출물과 홍삼농축액으로 C57BL/6J 수컷 마우스를 이용하여 콜레스테롤 억제 효과 및 지질대사에 미치는 영향을 살펴보고, 기능성 식품으로의 가능성을 알아보았다. 실험동물은 C57BL/6J 수컷 마우스를 사용하였으며, 12주 동안 고콜레스테롤 식이를 급여하면서 복분자 미숙과 물 추출물과 홍삼농축액을 경구투여 하였다. 그 결과로 고콜레스테롤 식이군과 비교하였을 때 복분자 미숙과 추출물과 홍삼농축액 식이군에서 체중증가량, 식이섭취량에는 변화가 없었다. 콜레스테롤 합성의 가장 중요한 기작인 LDL receptor와 SREBP2 발현에서는 복분자 미숙과 추출물 투여군과 복분자와 홍삼 복합 투여군 모두 유의적으로 증가하여 세포 안으로의 LDL 흡수를 촉진시킴으로써 체내 콜레스테롤을 낮추는 것으로 판단된다. HDL 관련 유전자 발현에서도 복분자 미숙과 추출물 투여군과 복분자와 홍삼 복합 투여군에서 HDL uptake 유전자인 SR-B1의 발현을 증가시켜 콜레스테롤 개선 효과를 보였다. 또한 간의 형태학적 변화에서는 고콜레스테롤 식이군과 비교하였을 때 복분자 미숙과 물 추출물과 홍삼농축액 복합 투여군에서 지방 형성이 현저히 줄어들었고, leptin과 FAS의 농도를 측정한 결과 유의적으로 감소하였다. 결과적으로 복분자 미숙과 물 추출물과 홍삼농축액 복합 투여가 콜레스테롤과 고지혈증 예방에 긍정적인 효과를 보일 것으로 사료된다.

LDL Cholesterol in the Adenoma-Carcinoma Sequence of Colorectal Cancer: More Answers and New Questions

Introduction: Malignant colon tumors are thought to be involved in cholesterol catabolism since increased expression of LDL receptor mRNA has been described in colon cancer tissue. We previously showed that LDL cholesterol levels are higher in colorectal cancer (CRC) subjects compared to subjects with colon adenomatous polyps, and that total cholesterol level inversely correlates with polyp size. We compared the serum lipids in colon cancer patients before and after surgical resection with those in controls without known history of colon polyps or CRC. Methods: We performed a retrospective study in adult subjects who underwent curative or noncurative surgery for CRC. Controls included patients coming to the ambulatory clinic during the same period for routine visits, without a known history of colon polyps, CRC, or other malignancy. We collected demographic data, serum lipid levels before and after surgery, histology of the tumor, statin use, and metastases. Data were analyzed using SPSS; results are shown as median (range). Results: Two hundred thirty-four patients with CRC and 130 controls were included in the study. The gender distribution was similar in the 2 groups (females 58% vs 55%, respectively). The median age was 66 years (range 25-97 years). Twenty percent of CRC subjects had metastatic disease at the time of surgery. Most of the tumors (57%) were located in the left colon, and 94% were adenocarcinomas. Significantly lower levels of LDL cholesterol (median 97 mg/dL vs. 111 mg/dL; p<0.006) and HDL cholesterol (41 mg/dL vs. 45 mg/dL; p<0.016) were found in CRC subjects compared to controls. After surgery, the LDL cholesterol and HDL cholesterol levels were still lower in CRC patients than in controls (80 mg/dL vs. 111 mg/dL; p<0.001, and 40 mg/dL vs. 45 mg/dL; p<0.003, respectively). The difference after surgery was found to be due to the CRC subjects without metastatic disease who had a further decrease in LDL level (99 mg/dL to 78 mg/dL; p=0.020) following curative surgery; the difference was true when controlling for statin use. No significant changes in the serum lipid levels before and after surgery were noted in CRC subjects with metastatic disease; their lipid levels after sugery were not significantly different from those of controls. Conclusion: Low cholesterol levels are present in CRC subjects compared to controls without known history of colon polyps, and they decrease further after curative surgery. No significant changes occur in subjects with metastatic disease undergoing surgery. Serum cholesterol seems to be more than a bystander in the adenoma-carcinoma sequence of CRC; elucidating this complex relationship may offer further opportunities for diagnosis and treatment.

Gene therapy for rhesus monkeys heterozygous for LDL receptor deficiency by balloon catheter hepatic delivery of helper-dependent adenoviral vector.

Autosomal dominant familial hypercholesterolemia (FH) is a monogenic life-threatening disease. We tested the efficacy of low-density lipoprotein receptor (LDLR) gene therapy using helper-dependent adenoviral vector (HDAd) in a nonhuman primate model of FH, comparing intravenous injection versus intrahepatic arterial injection in the presence of balloon catheter-based hepatic venous occlusion. Rhesus monkeys heterozygous for mutant LDLR gene (LDLR+/−) developed hypercholesterolemia while on a high cholesterol diet. We treated them with HDAd-LDLR either by intravenous delivery, or by catheter-based intra-hepatic artery injection. Intravenous injection of ≤1.1×1012 viral particles (vp)/kg failed to have any effect on plasma cholesterol. Increasing the dose to 5×1012 vp/kg led to a 59% lowering of the plasma cholesterol that lasted for 30 days before it returned to pretreatment levels by day 40. A further increase in dose to 8.4×1012 vp/kg resulted in severe lethal toxicity. In contrast, direct hepatic artery injection following catheter-based hepatic venous occlusion enabled the use of a reduced HDAd-LDLR dose of 1×1012 vp/kg that lowered plasma cholesterol within a week, and reached a nadir of 59% pretreatment level on days 20 to 48 after injection. Serum alanine aminotransaminase (ALT) remained normal until day 48 when it went up slightly and stayed mildly elevated on day 72 before it returned to normal on day 90. In this monkey, the HDAd-LDLR-induced trough of hypocholesterolemia started trending upwards on day 72 and returned to pretreatment levels on day 120. We measured the LDL apolipoprotein B turnover rate at 10 days before, and again 79 days after, HDAd-LDLR treatment in two monkeys that exhibited a cholesterol lowering response. HDAd-LDLR therapy increased the LDL fractional catabolic rate by 78% and 50%, respectively, in the two monkeys, coincident with an increase in hepatic LDLR mRNA expression. In conclusion, HDAd-mediated LDLR gene delivery to the liver using a balloon catheter occlusion procedure is effective in reversing hypercholesterolemia in a nonhuman primate FH model; however, the unsustainability of the hypocholesterolemic response during 3–4 months of follow up and heterogeneous response to the treatment remains a challenge.

Effects of alkaloids from Coptidis Rhizoma on blood lipid metabolism and low-denstity lipoprotein receptor mRNA in golden hamsters

To study the effects of alkaloids from Coptidis Rhizoma on low-density lipoprotein receptor (LDLR) mRNA expression and antihyperlipedemic levels. The LDLR mRNA expression were detected by real time fluorescence quantitative PCR, and the levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein (LDL-c) and high-density lipoprotein cholesterol (HDL-c) in serum were measured at the first and last examination. The results show that, after the drug treatment, compared with the model group, each drug group showed a lipid-lowering effect. Especially, coptisine, palmatine, jatrorrhinze were significantly reduced TC, TG, LDL-c (P < 0.05, P < 0.01), and increased HDL-c (P < 0.01). In addition, they also increased mRNA expression of the LDLR in liver and HepG2 cells. The results showed that alkaloids from Coptidis Rhizoma can regulate lipid metabolism disorder, and coptisine have the best lipid-lowering effect.

The Sirt1 activator SRT3025 provides atheroprotection in Apoe−/− mice by reducing hepatic Pcsk9 secretion and enhancing Ldlr expression

AimsThe deacetylase sirtuin 1 (Sirt1) exerts beneficial effects on lipid metabolism, but its roles in plasma LDL-cholesterol regulation and atherosclerosis are controversial. Thus, we applied the pharmacological Sirt1 activator SRT3025 in a mouse model of atherosclerosis and in hepatocyte culture.Methods and resultsApolipoprotein E-deficient (Apoe−/−) mice were fed a high-cholesterol diet (1.25% w/w) supplemented with SRT3025 (3.18 g kg−1 diet) for 12 weeks. In vitro, the drug activated wild-type Sirt1 protein, but not the activation-resistant Sirt1 mutant; in vivo, it increased deacetylation of hepatic p65 and skeletal muscle Foxo1. SRT3025 treatment decreased plasma levels of LDL-cholesterol and total cholesterol and reduced atherosclerosis. Drug treatment did not change mRNA expression of hepatic LDL receptor (Ldlr) and proprotein convertase subtilisin/kexin type 9 (Pcsk9), but increased their protein expression indicating post-translational effects. Consistent with hepatocyte Ldlr and Pcsk9 accumulation, we found reduced plasma levels of Pcsk9 after pharmacological Sirt1 activation. In vitro administration of SRT3025 to cultured AML12 hepatocytes attenuated Pcsk9 secretion and its binding to Ldlr, thereby reducing Pcsk9-mediated Ldlr degradation and increasing Ldlr expression and LDL uptake. Co-administration of exogenous Pcsk9 with SRT3025 blunted these effects. Sirt1 activation with SRT3025 in Ldlr−/− mice reduced neither plasma Pcsk9, nor LDL-cholesterol levels, nor atherosclerosis.ConclusionWe identify reduction in Pcsk9 secretion as a novel effect of Sirt1 activity and uncover Ldlr as a prerequisite for Sirt1-mediated atheroprotection in mice. Pharmacological activation of Sirt1 appears promising to be tested in patients for its effects on plasma Pcsk9, LDL-cholesterol, and atherosclerosis.

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.

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.

Cross-talk between TLR4-MyD88-NF-κB and SCAP-SREBP2 pathways mediates macrophage foam cell formation

Myeloid differentiation factor 88 (MyD88) and NF-κB play central roles in mediating signal transduction of the Toll-like receptor (TLR) superfamily in human macrophages. The feedback regulation of LDL receptor (LDLR) and 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoAR) are mediated by the sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP)-SREBP2 pathway and are key regulatory elements for cholesterol homeostasis in human cells. This study was designed to investigate cross-talk between TLR4-MyD88-NF-κB and SCAP-SREBP2 pathways in macrophage foam cell formation. phorbol 12-myristate 13-acetate-activated THP-1 macrophages were transfected with negative control or MyD88 small interfering (si)RNA. Transfected cells were incubated with LPS in the absence or presence of LDL or IκB kinase (IKK) inhibitor (BMS-345541). Intracellular cholesterol content was assessed. mRNA and protein expression of LDLR, HMG-CoAR, SCAP, and SREBP2 were examined by real-time RT-PCR and Western blot analysis. Intracellular translocation of SCAP in the organelles was detected by immunofluorecence and confocal microscopy. We demonstrated that LPS-induced cholesterol accumulation was attenuated by applying siRNA against MyD88 in the absence or presence of LDL. LPS increased both gene and protein expression of LDLR and HMG-CoAR by increasing expression and abnormal translocation of SCAP from the endoplasmic reticulum to the Golgi. These effects were blocked by knockdown of MyD88 or blockade of IKK or by knockdown of SCAP, suggesting that the cross-talk between NF-κB and SCAP plays an important role in macrophage foam cell formation and that interfering with the cross-talk might be a potential approach in preventing LPS-induced macrophage foam cell formation.