Hepatic LDL Receptor Expression Research Articles

Unraveling Estrogen and PCSK9's Roles in Lipid Metabolism Disorders among Ovariectomized Mice.

We explore the interaction between estrogen and PCSK9 and their collective impact on lipid metabolism, especially concerning the regulation of low-density lipoprotein receptor levels. Utilizing both animal and cellular models, including ovariectomized mice and HepG2 cell lines, we demonstrate that estrogen deficiency leads to a disruption in lipid metabolism, characterized by elevated levels of total cholesterol and LDL-C. The study commences with mice undergoing ovariectomy, followed by a diet regimen comprising either high-fat diet or normal feed for a four-week duration. Key assessments include analyzing lipid metabolism, measuring PCSK9 levels in the bloodstream, and evaluating hepatic low-density lipoprotein receptor expression. We will also conduct correlation analyses to understand the relationship between PCSK9 and various lipid profiles. Further, a subset of ovariectomized mice on high-fat diet will undergo treatment with either estrogen or PCSK9 inhibitor for two weeks, with a subsequent re-evaluation of the earlier mentioned parameters. Our findings reveal that estrogen inhibits PCSK9-mediated degradation of low-density lipoprotein receptor, a process crucial for maintaining lipid homeostasis. Through a series of experiments, including immunohistochemistry and western blot analysis, we establish that PCSK9 is involved in lipid metabolism disorders caused by estrogen deficiency and that estrogen regulates PCSK9 and low-density lipoprotein receptor at post-transcriptional level. The study provides a mechanism for the involvement of PCSK9 in elucidating the disorders of lipid metabolism caused by estrogen deficiency due to perimenopause and ovarian decline.

Tetrahydroberberine alleviates high-fat diet-induced hyperlipidemia in mice via augmenting lipoprotein assembly-induced clearance of low-density lipoprotein and intermediate-density lipoprotein

The promotion of excess low-density lipoprotein (LDL) clearance stands as an effective clinical approach for treating hyperlipidemia. Tetrahydroberberine, a metabolite of berberine, exhibits superior bioavailability compared to berberine and demonstrates a pronounced hypolipidemic effect. Despite these characteristics, the impact of tetrahydroberberine on improving excessive LDL clearance in hyperlipidemia has remained unexplored. Thus, this study investigates the potential effects of tetrahydroberberine on high-fat diet-induced hyperlipidemia in mice. The findings reveal that tetrahydroberberine exerts a more potent lipid-lowering effect than berberine, particularly concerning LDL-cholesterol in hyperlipidemic mice. Notably, tetrahydroberberine significantly reduces serum levels of upstream lipoproteins, including intermediate-density lipoprotein (IDL) and very low-density lipoprotein, by promoting their conversion to LDL. This reduction is further facilitated by the upregulation of hepatic LDL receptor expression induced by tetrahydroberberine. Intriguingly, tetrahydroberberine enhances the apolipoprotein E (ApoE)/apolipoprotein B100 (ApoB100) ratio, influencing lipoprotein assembly in the serum. This effect is achieved through the activation of the efflux of ApoE-containing cholesterol in the liver. The ApoE/ApoB100 ratio exhibits a robust negative correlation with serum levels of LDL and IDL, indicating its potential as a diagnostic indicator for hyperlipidemia. Moreover, tetrahydroberberine enhances hepatic lipid clearance without inducing lipid accumulation in the liver and alleviates existing liver lipid content. Importantly, no apparent hepatorenal toxicity is observed following tetrahydroberberine treatment for hyperlipidemia. In summary, tetrahydroberberine demonstrates a positive impact against hyperlipidemia by modulating lipoprotein assembly-induced clearance of LDL and IDL. The ApoE/ApoB100 ratio emerges as a promising diagnostic indicator for hyperlipidemia, showcasing the potential clinical significance of tetrahydroberberine in lipid management.

Chrysin 7-O-β-d-glucopyranoside increases hepatic low-density lipoprotein receptor expression through AMP-activated protein kinase activation.

Elevated plasma low-density lipoprotein (LDL) cholesterol level is a risk factor for developing atherosclerosis. Increased LDL receptor (LDLR) expression is expected to reduce the risk of atherosclerotic disease since hepatic LDLR is essential for clearing plasma LDL cholesterol. Here, we screened human LDLR promoter effectors and observed that extracts from peduncles of sweet cherry (Prunus avium) 'Sato-Nishiki' induce LDLR gene promoter activity. We used several analytical and chemical methods to show that chrysin 7-O-β-d-glucopyranoside (chrysin-7G) is one of the compounds that stimulate LDLR gene promoter activity in cherry peduncle extracts. Furthermore, synthetic chrysin-7G increased the expression and activity of LDLR. The chrysin-7G-mediated increase in LDLR expression and activity was completely abolished by treatment with an AMP-activated protein kinase (AMPK) inhibitor, compound C. These results indicate that chrysin-7G increases LDLR expression through AMPK activation and may be a useful compound that can be recycled from waste parts of agricultural products.

Effects of statins on the inducible degrader of low-density lipoprotein receptor in familial hypercholesterolemia.

The inducible degrader of low-density lipoprotein receptor (IDOL) is an E3 ubiquitin ligase involved in the post-transcriptional regulation of LDL receptor (LDLR). Statins lower plasma LDL by activating transcription of hepatic LDLR expression, and we have determined whether statins modulate IDOL expression and influence LDLR protein abundance. IDOL expression in monocytes and serum IDOL level was determined in statin-treated familial hypercholesterolemia (FH) patients and compared with control subjects. Serum IDOL level was also evaluated in a group of untreated FH patients before and after the initiation of statin. The mechanism underlying the inhibitory effect of statin on IDOL expression was investigated in vitro. In statin-treated FH patients, serum IDOL level and its expression in monocytes was reduced compared with control (P < 0.05). In contrast, untreated FH patients had higher serum levels of IDOL and proprotein convertase subtilisin/kexintype 9 (PCSK9) than control (P < 0.05), and serum IDOL level decreased after statin therapy (P < 0.05) whereas an increase was observed in PCSK9 level (P < 0.01). In vitro, atorvastatin significantly decreased IDOL abundance in a dose-dependent manner in cultured macrophages and hepatocytes with a concomitant increase in LDLR expression. The transcription of IDOL was restored by adding either an LXR agonist T0901317 or oxysterol 22(R)-hydroxycholesterol, indicating that statin inhibited IDOL expression by reducing LXR activation. The LXR-IDOL-LDLR axis can be modulated by statins in vitro and in vivo. Statins inhibit IDOL expression by reducing LXR activation and upregulate LDLR, and statins exert the opposite effect on IDOL and PCSK9.

Caffeine blocks SREBP2-induced hepatic PCSK9 expression to enhance LDLR-mediated cholesterol clearance

Evidence suggests that caffeine (CF) reduces cardiovascular disease (CVD) risk. However, the mechanism by which this occurs has not yet been uncovered. Here, we investigated the effect of CF on the expression of two bona fide regulators of circulating low-density lipoprotein cholesterol (LDLc) levels; the proprotein convertase subtilisin/kexin type 9 (PCSK9) and the low-density lipoprotein receptor (LDLR). Following the observation that CF reduced circulating PCSK9 levels and increased hepatic LDLR expression, additional CF-derived analogs with increased potency for PCSK9 inhibition compared to CF itself were developed. The PCSK9-lowering effect of CF was subsequently confirmed in a cohort of healthy volunteers. Mechanistically, we demonstrate that CF increases hepatic endoplasmic reticulum (ER) Ca2+ levels to block transcriptional activation of the sterol regulatory element-binding protein 2 (SREBP2) responsible for the regulation of PCSK9, thereby increasing the expression of the LDLR and clearance of LDLc. Our findings highlight ER Ca2+ as a master regulator of cholesterol metabolism and identify a mechanism by which CF may protect against CVD.

Lactobacillus johnsonii BFE6154 Ameliorates Diet-Induced Hypercholesterolemia.

The functional characteristics of Lactobacillus johnsonii BFE6154, first isolated from Maasai traditional fermented milk, were previously identified in vitro, but its cholesterol-lowering properties have not been verified yet. In this study, we investigated the effect of L. johnsonii BFE6154 on cholesterol regulation and the mode of action. Stimulation of Caco-2 intestinal epithelial cells with L. johnsonii BFE6154 downregulated the gene expression of Niemann-Pick C1-like 1 (NPC1L1) through the activation of liver X receptor (LXR). Also, stimulation of HepG2 cells with the metabolites produced by L. johnsonii BFE6154 revealed an increase in the gene expression of low-density lipoprotein receptor (LDLR). Oral administration of L. johnsonii BFE6154 in mice receiving a high-fat and high-cholesterol diet (HFHCD), reduced total cholesterol and low-density lipoprotein-cholesterol (LDL) and increased high-density lipoprotein-cholesterol (HDL) in the blood, compared to the control. Diet-induced hypercholesterolemic mice receiving L. johnsonii BFE6154 showed a suppression of cholesterol absorption under the control of NPC1L1 in the intestine. Furthermore, L. johnsonii BFE6154 consumption ameliorated the hepatic cholesterol level and LDLR expression, which was reduced by HFHCD. These molecular modulations led to the increase of cholesterol excretion and the decrease of cholesterol levels in the feces and liver, respectively. Taken together, these results suggest that L. johnsonii BFE6154 may protect against diet-induced hypercholesterolemia through the regulation of cholesterol metabolism in the intestine and liver.

High-Throughput Screening Identifies MicroRNAs Regulating Human PCSK9 and Hepatic Low-Density Lipoprotein Receptor Expression.

Investigations into the regulatory mechanisms controlling cholesterol homeostasis have proven fruitful in identifying low-density lipoprotein (LDL)-lowering therapies to reduce the risk of atherosclerotic cardiovascular disease. A major advance was the discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9), a secreted protein that binds the LDL receptor (LDLR) on the cell surface and internalizes it for degradation, thereby blunting its ability to take up circulating LDL. The discovery that loss-of-function mutations in PCSK9 lead to lower plasma levels of LDL cholesterol and protection from cardiovascular disease led to the therapeutic development of PCSK9 inhibitors at an unprecedented pace. However, there remain many gaps in our understanding of PCSK9 regulation and biology, including its posttranscriptional control by microRNAs. Using a high-throughput region(3′-UTR) of human microRNA library screen, we identified microRNAs targeting the 3′ untranslated region of human PCSK9. The top 35 hits were confirmed by large-format PCSK9 3′-UTR luciferase assays, and 10 microRNAs were then selected for further validation in hepatic cells, including effects on PCSK9 secretion and LDLR cell surface expression. These studies identified seven novel microRNAs that reduce PCSK9 expression, including miR-221-5p, miR-342-5p, miR-363-5p, miR-609, miR-765, and miR-3165. Interestingly, several of these microRNAs were also found to target other genes involved in LDLR regulation and potently upregulate LDLR cell surface expression in hepatic cells. Together, these data enhance our understanding of post-transcriptional regulators of PCSK9 and their potential for therapeutic manipulation of hepatic LDLR expression.

Polysaccharide-rich red algae (Gelidium amansii) hot-water extracts ameliorate the altered plasma cholesterol and hepatic lipid homeostasis in high-fat diet-fed rats.

We have demonstrated that red algae Gelidium amansii (GA) hot-water extract (GHE) is a polysaccharide-rich fraction, containing 68.54% water-soluble indigestible carbohydrate polymers; the molecular weight of major polysaccharide is 892. Here, we investigated the mechanisms of GHE on plasma and hepatic lipid metabolisms in high-fat (HF) diet-fed rats. Rats were divided into: normal diet group, HF-diet group, HF-diet+5% GHE group, and HF-diet+1% cholestyramine group. GHE supplementation for 8 weeks significantly decreased plasma cholesterol, LDL-C, and VLDL-C levels and increased the fecal triglyceride and bile acid excretion in HF diet-fed rats. GHE group has lower lipid contents in the liver and adipose tissues. GHE supplementation decreased the activities of acetyl-CoA carboxylase, fatty acid synthase, and HMG-CoA reductase in the livers. The levels of increased phosphorylated AMP-activated protein kinase (AMPK), peroxisome proliferator activated receptor (PPAR)-α, farnesoid-X receptor (FXR), low density lipoprotein receptor (LDLR), and cytochrome P450-7A1 (CYP7A1) protein expression, and the decreased PPAR-γ protein expression in the livers were observed in GHE group. These results suggest that GHE supplementation is capable of interfering in cholesterol metabolism and increasing hepatic LDLR and CYP7A1 expression to decrease blood cholesterol, and activating FXR and AMPK to inhibit lipogenic enzyme activities and reduce the hepatic lipid accumulation.

Deficiency of Nardilysin in the Liver Reduces Serum Cholesterol Levels.

Nardilysin (NRDC) has been shown to be involved in post-translational histone modifications, in addition to enhancement in ectodomain shedding of membrane-anchored protein, which play significant roles in various pathophysiology, including glucose homeostasis, inflammatory diseases and cancer. The present study sought to determine roles of NRDC in the liver on lipid and lipoprotein metabolism. We established liver-specific NRDC deficient mice by use of NRD1 floxed mice and albumin promoter-Cre recombinase (Cre) transgenic mice, and found that their serum low-density lipoprotein (LDL) cholesterol levels were significantly lower than those in control littermate mice. In the liver, LDL receptor (LDLR) mRNA expression was significantly upregulated, while inducible degrader of LDLR (IDOL) and microsomal triglyceride transfer protein (MTP) mRNA expression was significantly downregulated, in liver-specific NRDC deficient mice. Hepatic cell-surface LDLR expression levels were significantly elevated and serum pro-protein convertase subtilisin-kexin type 9 (PCSK9) levels were significantly reduced in mice with hepatic NRDC deficiency. In cultured hepatocytes, NRDC deficiency significantly reduced secreted PCSK9 and increased cell-surface LDLR expression. On the other hand, NRDC overexpression in cultured hepatocytes significantly increased secreted PCSK9 and lowered cell-surface LDLR expression. Thus, NRDC in murine hepatocytes appears to play key roles in cholesterol homeostasis, although the precise molecular mechanisms remain to be determined.

Aqueous extracts of lingonberry and blackberry leaves identified by high-content screening beneficially act on cholesterol metabolism.

Decreasing circulating low-density lipoprotein (LDL) cholesterol levels leads to decreased risk of cardiovascular diseases. Natural compounds are capable of lowering LDL-cholesterol even on top of lifestyle modification or medication. To identify novel plant-derived compounds to lower plasma LDL cholesterol levels, we performed high-content screening based on the transcriptional activation of the promoter of the LDL receptor (LDLR). The identified hits were thoroughly validated in human hepatic cell lines in terms of increasing LDLR mRNA and protein levels, lowering cellular cholesterol levels and increasing cellular LDL uptake. By means of this incremental validation process in vitro, aqueous extracts prepared from leaves of lingonberries (Vaccinium vitis-idaea) as well as blackberries (Rubus fruticosus) were found to have effects comparable to lovastatin, a prototypic cholesterol-lowering drug. When applied in vivo in mice, both extracts induced subtle increases in hepatic LDLR expression. In addition, a significant increase in high-density lipoprotein (HDL) cholesterol was observed. Taken together, aqueous extracts from lingonberry or blackberry leaves were identified and characterized as strong candidates to provide cardiovascular protection.

Recent insights into low-density lipoprotein metabolism and therapy.

Elevated levels of low-density lipoprotein cholesterol (LDL-C) are causal to atherosclerosis and, thus, the reduction of LDL-C represents a major objective for the prevention of cardiovascular disease. Aim of this review is to provide an overview on novel strategies to lower LDL-C. Although inhibiting liver cholesterol biosynthesis by statins is used as the main therapeutic approach to increase hepatic LDL-receptor expression and lower plasma cholesterol levels, novel insights into lipid and lipoprotein biology have led to the development of additional lipid-lowering therapies that can be used in combination with or as an alternative to statins in patients with statin-intolerance. New approaches include bempedoic acid, proprotein convertase subtilisin/kexin type 9 inhibitors, and angiopoietin-like protein 3 inhibitors. In the last decade, several novel therapeutic approaches have been tested and some of them have been approved as lipid-lowering agents. Some drugs are already available in clinical practice, whereas others are at late stages of development.

Regulation of Lipoprotein Homeostasis by Self-Assembling Peptides.

High levels of serum low-density lipoprotein (LDL) cholesterol contribute to atherosclerosis, a key risk factor of cardiovascular diseases. PCSK9 is a circulatory enzyme that downregulates expression of hepatic LDL receptors, concomitantly increasing serum LDL-C. This work investigates a small, self-assembling peptide, EPep2-8, as a peptide inhibitor of PCSK9. EPep2-8 is a multidomain peptide comprising a self-assembling domain, E2, conjugated to a bioactive domain, Pep2-8, previously shown to inhibit PCSK9. The E2 domain facilitates self-assembly of EPep2-8 into long, nanofibrous polymers with an underlying supramolecular β-sheet secondary structure. Intermolecular interactions between nanofibers drive EPep2-8 to form a thixotropic and cytocompatible hydrogel in aqueous and charge-neutral solutions. These properties enable EPep2-8 to be delivered as an in situ depot for regulation of lipoprotein homeostasis. In surface plasmon resonance studies, EPep2-8 bound specifically to PCSK9 with an apparent, noncovalent, and irreversible dissociation, significantly improving the binding affinity of Pep2-8 alone (KD = 667 ± 48 nM). Increased binding affinity of EPep2-8 is primarily due to the superstoichiometric interaction of the peptide with PCSK9. Promisingly, EPep2-8 retains bioactivity in vitro, engendering dose-dependent uptake of LDL-C in hepatocytes. This mechanism of self-assembly on a target site may be a simple method to improve the affinity of peptide inhibitors.

Zygophyllum album saponins prevent atherogenic effect induced by deltamethrin via attenuating arterial accumulation of native and oxidized LDL in rats.

The current study aimed to examine, for the first time, the relationship between exposure to deltamethrin (DLM) and atherogenic lipid profile disorders in adult Wistar rats, as well as, to verify the mechanism of the beneficial role of Zygophyllum album leaves extracts (ZALE). The experimental study was assessed using DLM (4mg/kg b.w) either alone or co administered with ZALE (400mg/kg b.w) orally for 90 days in rats. RP-HPLC-DAD-ESI-QTOF-MS was used to identify the bioactive metabolites present in ZALE. Plasmatic and aortic total cholesterol (TC), LDL-cholesterol (LDL-C), native LDL (LDL-apo B-100) and oxidized LDL (ox-LDL) were evaluated using auto-analyzer and a sandwich ELISA, respectively. The protein expressions of LDLR (native LDL receptor) and CD36 (Scavenger receptor class B) were evaluated in aorta or liver with a Western blot. The pathology has been confirmed with lipid stain (Oil Red O). Phytochemicals analysis revealed the presence of fifteen saponins in ZALE. Rats intoxicated with DLM revealed a significant increase in plasmatic and aortic lipid profile (TC, LDL-C, LDL-apo B-100 and ox-LDL), as well as, the concentration of the plasmatic cytokines include TNF-α, IL-2 and IL-6, compared to control. Hepatic native LDL and aortic CD36 receptor expression were increased in DLM treated group, however aortic LDL-R does not present any modification, when compared to control. The detected disturbances in lipid parameters were supported by Oil Red O applied. Due to their antioxidant activity, the bioactive compounds in ZALE as powerful agents able to prevent the pro-atherogenic effect observed in DLM-treated animals. These metabolites modulated most of inflammatory markers, prevented accumulation of lipid and lipoprotein biomarkers, regulated the major receptor regulators of hepatic cholesterol metabolism, as well as normalize lipid distribution in liver and aorta tissue.

A small-molecule inhibitor of PCSK9 transcription ameliorates atherosclerosis through the modulation of FoxO1/3 and HNF1α.

BackgroundProprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that down-regulates hepatic low-density lipoprotein receptor (LDLR) by binding and shuttling LDLR to lysosomes for degradation. The development of therapy that inhibits PCSK9 has attracted considerable attention for the management of cardiovascular disease risk. However, only monoclonal antibodies of PCSK9 have reached the clinic use. Oral administration of small-molecule transcriptional inhibitors has the potential to become a therapeutic option.MethodsHere, we developed a cell-based small molecule screening platform to identify transcriptional inhibitors of PCSK9. Through high-throughput screening and a series of evaluation, we found several active compounds. After detailed investigation on the pharmacological effect and molecular mechanistic characterization, 7030B-C5 was identified as a potential small-molecule PCSK9 inhibitor.FindingsOur data showed that 7030B-C5 down-regulated PCSK9 expression and increased the total cellular LDLR protein and its mediated LDL-C uptake by HepG2 cells. In both C57BL/6 J and ApoE KO mice, oral administration of 7030B-C5 reduced hepatic and plasma PCSK9 level and increased hepatic LDLR expression. Most importantly, 7030B-C5 inhibited lesions in en face aortas and aortic root in ApoE KO mice with a slight amelioration of lipid profiles. We further provide evidences suggesting that transcriptional regulation of PCSK9 by 7030B-C5 mostly depend on the transcriptional factor HNF1α and FoxO3. Furthermore, FoxO1 was found to play an important role in 7030B-C5 mediated integration of hepatic glucose and lipid metabolism.Interpretation7030B-C5 with potential suppressive effect of PCSK9 expression may serve as a promising lead compound for drug development of cholesterol/glucose homeostasis and cardiovascular disease therapy.FundThis work was supported by grants from the National Natural Science Foundation of China (81473214, 81402929, and 81621064), the Drug Innovation Major Project of China (2018ZX09711001-003-006, 2018ZX09711001-007 and 2018ZX09735001-002), CAMS Innovation Fund for Medical Sciences (2016-I2M-2-002, 2016-I2M-1-011 and 2017-I2M-1-008), Beijing Natural Science Foundation (7162129).

Conjugated linoleic acid regulates lipid metabolism through the expression of selected hepatic genes in laying hens

The effect of dietary conjugated linoleic acid (CLA) supplementation on lipid metabolism in laying hens was investigated. A total of 360 eighteen-wk-old Hy-Line Brown layers were randomly divided into 4 groups that consisted of 6 replicates with 15 birds each. Birds were fed basal diets with 0, 1%, 2%, and 4% CLA addition. The experiment lasted for 56 D after a 7-D adaptation period. Results showed that dietary CLA addition linearly reduced (P < 0.05) abdominal fat percentage but linearly increased (P < 0.05) relative liver weight of layers on day 56. A linear reduction (P < 0.05) in serum low-density lipoprotein cholesterol (LDL-C) level and a linear elevation (P < 0.05) in the ratio of serum high-density lipoprotein cholesterol level to LDL-C level of layers on both days 28 and 56 were observed with dietary CLA addition, which also linearly decreased (P < 0.05) cholesterol content in the liver of layers on day 56 as well as in eggs on both days 28 and 56. Besides, there were linear reductions (P < 0.05) in the gene expression and contents of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and cholesterol 7 alpha hydroxylase 1 (CYP7A1), along with a linear increase (P < 0.05) in the gene expression and content of hepatic low-density lipoprotein receptor (LDLR) in layers responded to dietary CLA addition. In conclusion, dietary CLA supplementation decreased the accumulation of lipids including abdominal fat and cholesterol in the liver and egg of laying hens, probably by upregulating hepatic LDLR expression and downregulating hepatic HMGR and CYP7A1 expression.

Design, synthesis, and biological evaluation of novel tetrahydroprotoberberine derivatives (THPBs) as proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators for the treatment of hyperlipidemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators may attenuate PCSK9-induced low-density lipoprotein receptor (LDLR) degradation in lysosome and promote the clearance of circulating low-density lipoprotein cholesterol (LDL-C). A novel series of tetrahydroprotoberberine derivatives (THPBs) were designed, synthesized, and evaluated as PCSK9 modulators for the treatment of hyperlipidemia. Among them, eight compounds exhibited excellent activities in downregulating hepatic PCSK9 expression better than berberine in HepG2 cells. In addition, five compounds 15, 18, 22, (R)-22, and (S)-22 showed better performance in the low-density lipoprotein, labeled with 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanine perchlorate (DiI-LDL) uptake assay, compared with berberine at the same concentration. Compound 22, selected for in vivo evaluation, demonstrated significant reductions of total cholesterol (TC) and LDL-C in hyperlipidemic hamsters with a good pharmacokinetic profile. Further exploring of the lipid-lowering mechanism showed that compound 22 promoted hepatic LDLR expression in a dose-dependent manner in HepG2 cells. Additional results of human ether-à-go-go related gene (hERG) inhibition assay indicated the potential druggability for compound 22, which is a promising lead compound for the development of PCSK9 modulator for the treatment of hyperlipidemia.

Diet-induced hepatic steatosis abrogates cell-surface LDLR by inducing de novo PCSK9 expression in mice

The worldwide prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing rapidly. Although this condition is generally benign, accumulating evidence now suggests that patients with NAFLD are also at increased risk of cardiovascular disease (CVD); the leading cause of death in developed nations. Despite the well-established role of the liver as a central regulator of circulating low-density lipoprotein (LDL) cholesterol levels, a known driver of CVD, the mechanism(s) by which hepatic steatosis contributes to CVD remains elusive. Interestingly, a recent study has shown that circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels correlate positively with liver steatosis grade. Given that PCSK9 degrades the LDL receptor (LDLR) and prevents the removal of LDL from the blood into the liver, in the present study we examined the effect of hepatic steatosis on LDLR expression and circulating LDL cholesterol levels. We now report that in a manner consistent with findings in patients, diet-induced steatosis increases circulating PCSK9 levels as a result of de novo expression in mice. We also report the finding that steatosis abrogates hepatic LDLR expression and increases circulating LDL levels in a PCSK9-dependent manner. These findings provide important mechanistic insights as to how hepatic steatosis modulates lipid regulatory genes, including PCSK9 and the LDLR, and also highlights a novel mechanism by which liver disease may contribute to CVD.

Berberrubine and its analog, hydroxypropyl-berberrubine, regulate LDLR and PCSK9 expression via the ERK signal pathway to exert cholesterol-lowering effects in human hepatoma HepG2 cells.

Berberine (BBR), the major isoquinoline alkaloid in Chinese herb Rhizoma coptidis, has significant lipid-lowering effect by upregulating hepatic low-density lipoprotein receptor (LDLR) expression. In a previous study, we have indicated that berberrubine (M3), a major metabolite of BBR in vivo, displays the most potential hypolipidemic effects via upregulating LDLR expression in human hepatoma (HepG2) cells compared with BBR and 3 other metabolites. Accordingly,9 M3 analogs (A1-A9) were modified at the C9 position. We aimed to find a new promising agent by evaluating the cholesterol-lowering effect and clarifying the related molecular mechanism. In the current study, the cellular cholesterol content was assayed with a commercial cholesterol assay kit. Real-time polymerase chain reaction and Western blot assay were used to explore the molecular mechanism of M3 and its analogs on the hypolipidemic effect. Among M3 and its analogs, hydroxypropyl-berberrubine (A8) exhibited the highest potential effects on the upregulation of LDLR expression, which was accompanied by a steady decline of proprotein convertase subtilisin/kexin type 9 (PCSK9) messenger RNA and protein levels. Furthermore, inhibition of extracellular signal-regulated kinase (ERK) activity with PD98059 prevented the upregulation of LDLR and downregulation of PCSK9 induced by A8. The current study revealed that M3 and its structurally modified analog, A8, could regulate hepatic LDLR and PCSK9 expression to exert lipid-lowering effects via the ERK signal pathway, while A8 showed a stronger effect and might be a promising drug candidate against hyperlipidemia.

Liraglutide downregulates hepatic LDL receptor and PCSK9 expression in HepG2 cells and db/db mice through a HNF-1a dependent mechanism

BackgroundProprotein convertase subtilisin/kexin type 9 (PCSK9), a major regulator of cholesterol homeostasis, is associated with glucose metabolism. Liraglutide, a glucagon-like peptide-1 receptor agonist, can increase insulin secretion in a glucose-dependent manner and lower blood glucose. We aimed to investigate the relationship between liraglutide and PCSK9.MethodsAt the cellular level, the expressions of PCSK9 and hepatocyte nuclear factor 1 alpha (HNF1α) protein in HepG2 cells stimulated by liraglutide was examined using Western blot. Seven-week old db/db mice and wild type (WT) mice were administered either liraglutide (200 μg/kg) or equivoluminal saline subcutaneously, twice daily for 7 weeks. Fasting glucose level, food intake and body weight were measured every week. After the 7-week treatment, the blood was collected for lipid and PCSK9 levels detection and the liver was removed from the mice for oil red O staining, immunohistochemical analysis, immunofluorescence test and Western bolt.ResultsFirstly, liraglutide suppressed both PCSK9 and HNF1α expression in HepG2 cells in a time and concentration dependent manner. Secondly, liraglutide induced weight loss in WT and db/db mice, decreased serum PCSK9, glucose and lipid levels and improved hepatic accumulation in db/db but not WT mice. Thirdly, liraglutide reduced both hepatic PCSK9 and low-density lipoprotein receptor (LDLR) expression with a decrease in HNF1α in db/db mice but not in WT mice.ConclusionsLiraglutide suppressed PCSK9 expression through HNF1α-dependent mechanism in HepG2 cells and db/db mice, and decreased LDLR possibly via PCSK9-independent pathways in db/db mice.

Novel Reversible Model of Atherosclerosis and Regression Using Oligonucleotide Regulation of the LDL Receptor.

Animal models have been used to explore factors that regulate atherosclerosis. More recently, they have been used to study the factors that promote loss of macrophages and reduction in lesion size after lowering of plasma cholesterol levels. However, current animal models of atherosclerosis regression require challenging surgeries, time-consuming breeding strategies, and methods that block liver lipoprotein secretion. We sought to develop a more direct or time-effective method to create and then reverse hypercholesterolemia and atherosclerosis via transient knockdown of the hepatic LDLR (low-density lipoprotein receptor) followed by its rapid restoration. We used antisense oligonucleotides directed to LDLR mRNA to create hypercholesterolemia in wild-type C57BL/6 mice fed an atherogenic diet. This led to the development of lesions in the aortic root, aortic arch, and brachiocephalic artery. Use of a sense oligonucleotide replicating the targeted sequence region of the LDLR mRNA rapidly reduced circulating cholesterol levels because of recovery of hepatic LDLR expression. This led to a decrease in macrophages within the aortic root plaques and brachiocephalic artery, that is, regression of inflammatory cell content, after a period of 2 to 3 weeks. We have developed an inducible and reversible hepatic LDLR knockdown mouse model of atherosclerosis regression. Although cholesterol reduction decreased early en face lesions in the aortic arches, macrophage area was reduced in both early and late lesions within the aortic sinus after reversal of hypercholesterolemia. Our model circumvents many of the challenges associated with current mouse models of regression. The use of this technology will potentially expedite studies of atherosclerosis and regression without use of mice with genetic defects in lipid metabolism.