Strong induction of PCSK9 gene expression through HNF1alpha and SREBP2: mechanism for the resistance to LDL-cholesterol lowering effect of statins in dyslipidemic hamsters

Actinidia chinensis Planch root extract inhibits cholesterol metabolism in hepatocellular carcinoma through upregulation of PCSK9

Actinidia chinensis Planch root extract (acRoots) is a traditional Chinese medicine with anti-tumor efficacy. To investigate the mechanisms responsible for this activity, we examined the effects of acRoots on cholesterol metabolism in hepatocellular carcinoma (HCC). mRNA chip analysis was used to identify the metabolic genes regulated by acRoots. The effects of acRoots on cholesterol synthesis and uptake were evaluated by measuring intracellular cholesterol levels and 3,3′-dioctadecylindocarbocyanine-labeled low-density lipoprotein (Dil-LDL) uptake. Expression of metabolic genes was analyzed using quantitative reverse transcription PCR, western blotting, and flow cytometry. acRoots reduced the viability of LM3 and HepG2 cells at 5 mg/mL and HL-7702 cells at 30 mg/mL. Gene expression profiling revealed that treatment with acRoots altered expression of genes involved in immune responses, inflammation, proliferation, cell cycle control, and metabolism. We also confirmed that acRoots enhances expression of PCSK9, which is important for cholesterol metabolism. This resulted in decreased LDL receptor expression, inhibition of LDL uptake by LM3 cells, decreased total intracellular cholesterol, and reduced proliferation. These effects were promoted by PCSK9 overexpression and rescued by PCSK9 knockdown. Our data demonstrate that acRoots is a novel anti-tumor agent that inhibits cholesterol metabolism though a PCSK9-mediated signaling pathway.

JF, Lichtenstein AH. The Ossabaw Pig Is a Suitable Translational Model to Evaluate Dietary Patterns and Coronary Artery Disease Risk

Background

Animal models that mimic diet-induced human pathogenesis of chronic diseases are of increasing importance in preclinical studies. The Ossabaw pig is an established model for obesity-related metabolic disorders when fed extreme diets in caloric excess.

Objective

To increase the translational nature of this model, we evaluated the effect of diets resembling 2 human dietary patterns, the Western diet (WD) and the Heart Healthy Diet (HHD), without or with atorvastatin (-S or +S) therapy, on cardiometabolic risk factors and atherosclerosis development.

Methods

Ossabaw pigs (n = 32; 16 boars and 16 gilts, aged 5-8 wk) were randomized according to a 2 × 2 factorial design into 4 groups (WD-S, WD+S, HHD-S, and HHD+S) and were fed the respective diets for 6 mo. The WD (high in saturated fat, cholesterol, and refined grain) and the HHD (high in unsaturated fat, whole grain, and fruit and vegetables) were isocaloric [38% of energy (%E) from fat, 47%E from carbohydrate, and 15%E from protein]. Body composition was determined by using dual-energy X-ray absorptiometry, serum fatty acid (FA) profiles by gas chromatography, cardiometabolic risk profile by standard procedures, and degree of atherosclerosis by histopathology.

Results

Serum FA profiles reflected the predominant dietary FA. Pigs fed the WD had 1- to 4-fold higher concentrations of LDL cholesterol, non-HDL cholesterol, HDL cholesterol, high-sensitivity C-reactive protein (hs-CRP), tumor necrosis factor α (TNF-α), alkaline phosphatase (ALP), and alanine aminotransferase (ALT) compared with HHD-fed pigs (all P-diet < 0.05). Statin therapy significantly lowered concentrations of LDL cholesterol (-39%), non-HDL cholesterol (-38%), and triglycerides (-6%) (P-statin < 0.02). A greater degree of atheromatous changes (macrophage infiltration, foam cells, fatty streaks) and lesion incidence was documented in the coronary arteries (P-diet < 0.05), as well as 2- to 3-fold higher lipid deposition in the aortic arch or thoracic aorta of WD- compared with HHD-fed pigs (P-diet < 0.001).

Conclusions

Ossabaw pigs manifested a dyslipidemic and inflammatory profile accompanied by early-stage atherosclerosis when fed a WD compared with an HHD, which was moderately reduced by atorvastatin therapy. This phenotype presents a translational model to examine mechanistic pathways of whole food-based dietary patterns on atherosclerosis development.

Rosuvastatin Reduces Aortic Sinus and Coronary Artery Atherosclerosis in SR-B1 (Scavenger Receptor Class B Type 1)/ApoE (Apolipoprotein E) Double Knockout Mice Independently of Plasma Cholesterol Lowering

Supplemental Digital Content is available in the text.

Objective—

Rosuvastatin has been widely used in the primary and secondary prevention of coronary heart disease. However, its antiatherosclerotic properties have not been tested in a mouse model that could mimic human coronary heart disease. The present study was designed to test the effects of rosuvastatin on coronary artery atherosclerosis and myocardial fibrosis in SR-B1 (scavenger receptor class B type 1) and apoE (apolipoprotein E) double knockout mice.

Approach and Results—

Three-week-old SR-B1^−/−/apoE^−/− mice were injected daily with 10 mg/kg of rosuvastatin for 2 weeks. Compared with saline-treated mice, rosuvastatin-treated mice showed increased levels of hepatic PCSK9 (proprotein convertase subtilisin/kexin type-9) and LDLR (low-density lipoprotein receptor) message, increased plasma PCSK9 protein but decreased levels of hepatic LDLR protein and increased plasma total cholesterol associated with apoB (apolipoprotein B) 48-containing lipoproteins. In spite of this, rosuvastatin treatment was associated with decreased atherosclerosis in both the aortic sinus and coronary arteries and reduced platelet accumulation in atherosclerotic coronary arteries. Cardiac fibrosis and cardiomegaly were also attenuated in rosuvastatin-treated SR-B1^−/−/apoE^−/− mice. Two-week treatment with rosuvastatin resulted in significant decreases in markers of oxidized phospholipids in atherosclerotic plaques. In vitro analysis showed that incubation of bone marrow-derived macrophages with rosuvastatin substantially downregulated cluster of differentiation (CD)36 and inhibited oxidized LDL-induced foam cell formation.

Conclusions—

Rosuvastatin protected SR-B1^−/−/apoE^−/− mice against atherosclerosis and platelet accumulation in coronary arteries and attenuated myocardial fibrosis and cardiomegaly, despite increased plasma total cholesterol. The ability of rosuvastatin to reduce oxidized phospholipids in atherosclerotic plaques and inhibit macrophage foam cell formation may have contributed to this protection.

Thyroid stimulating hormone exhibits the impact on LDLR/LDL-c via up-regulating hepatic PCSK9 expression

CONTEXT

Thyroid stimulating hormone (TSH) has received increasing attention as being closely associated with increased low-density lipoprotein cholesterol (LDL-c) level and higher atherosclerotic risks. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is known for increasing circulating LDL-c level by inducing LDL receptor degradation. However, whether TSH influences hepatic PCSK9 expression and LDL-c metabolism remains unclear.

METHODS

First, the correlation between TSH and lipid profiles were investigated in euthyroid population and in subclinical hypothyroidism patients. Then, an in vitro study was conducted to validate the effects of TSH on hepatic PCSK9 expression in HepG2 cells.

RESULTS

Serum TSH concentrations positively correlated with LDL-c levels in euthyroid subjects. Subclinical hypothyroidism patients with higher serum TSH levels showed significantly increased serum PCSK9 levels than the matched euthyroid participants (151.29 (89.51-293.03) vs. 84.70 (34.98-141.72) ng/ml, P<0.001), along with increased LDL-c concentrations. In HepG2 cells, LDLR expression on the plasma membrane was decreased, and PCSK9 mRNA and protein levels were synchronously upregulated after recombinant human TSH (rhTSH) treatment, while the effects could be blocked by TSH receptor blocking antibody K1-70. Sterol regulatory element binding protein (SREBP) 1c and SREBP2 mRNA expressions were enhanced after rhTSH treatment, and specific siRNAs significantly inhibited the effects of rhTSH. Furthermore, there was a noticeable induction of PCSK9 expression by rhTSH even though HMGCR gene expression was silenced.

CONCLUSION

We conclude a regulating role of TSH on hepatic PCSK9 expression, which further contributing to a higher LDL-c level.

A Therapeutic Peptide Vaccine Against PCSK9

Vaccination provides a promising approach for treatment of hypercholesterolemia and improvement in compliance. In this study, the appropriate virus-like particle (VLP)-peptide vaccines targeting proprotein convertase subtilisin/kexin type 9 (PCSK9) were screened. The screening criteria of target peptides were as follows: (1) located in catalytic domain of PCSK9, or regulating the binding of PCSK9 and LDL receptors (LDLR); (2) having low/no-similarity when matched with the host proteome; (3) possessing ideal antigenicity and hydrophilicity; (4) including the functional mutation site of PCSK9. It was found that mice vaccinated with VLP -PCSK9 peptide vaccines, especially PCSK9Qβ-003 vaccine, developed high titer IgG antibodies against PCSK9. PCSK9Qβ-003 vaccine obviously decreased plasma total cholesterol in both Balb/c mice and LDLR^+/- mice. Also, PCSK9Qβ-003 vaccine decreased plasma PCSK9 level and up-regulated LDLR expression in liver. Additionally, PCSK9Qβ-003 vaccine injection was associated with significant up-regulation of sterol-regulatory element-binding protein-2 (SREBP-2), hepatocyte nuclear factor 1α (HNF-1α), and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in LDLR^+/- mice. No obvious immune injury was detected in vaccinated animals. The PCSK9Qβ-003 vaccine, therefore, may be an attractive treatment approach for hypercholesterolemia through decreasing cholesterol and regulating lipid homeostasis.

Lipid Lowering Therapy and Circulating PCSK9 Concentration

Hypercholesterolemia, particularly an increase in low-density lipoprotein cholesterol (LDL-C) levels, contributes substantially to the development of coronary artery disease and the risk for cardiovascular events. As the first-line pharmacotherapy, statins have been shown to reduce both LDL-C levels and cardiovascular events. However, despite intensive statin therapy, a sizable proportion of statin-treated patients are unable to achieve the recommended target LDL-C levels, and not all patients can avoid future cardiovascular events. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a key role in cholesterol homeostasis by enhancing the degradation of hepatic low-density lipoprotein receptor (LDLR). Owing to its importance in lipid metabolism, PCSK9 has emerged as a novel pharmacological target for lowering LDL-C levels. In this review, the potential role of circulating PCSK9 as a new biomarker of lipid metabolism is described. Next, previous studies evaluating the effects of lipid-modifying pharmacological agents, particularly statins, on circulating PCSK9 concentrations are summarized. Statins decrease hepatic intracellular cholesterol, resulting in increased LDLRs as well as increased PCSK9 protein. There is a clear dose-response effect of statin treatment on PCSK9 level, as increasing doses of statins also increase the level of circulating PCSK9. Finally, the available therapeutic strategies to inhibit PCSK9 are present. Monoclonal antibodies against PCSK9, in combination with statins, are one of the most promising and novel approaches to achieve further reduction of LDL-C levels and reduce the risk of cardiovascular events.

PCSK9 signaling pathways and their potential importance in clinical practice

In the following review, authors described the structure and biochemical pathways of PCSK9, its involvement in LDL metabolism, as well as significances of proprotein convertase subtilisin/kexin type 9 targeted treatment. PCSK9 is a proprotein convertase, which plays a crucial role in LDL receptor metabolism. Transcription and translation of PCSK9 is controlled by different nuclear factors, such as, SREBP and HNF1α. This review focuses on interactions between PCSK9 and LDL receptor, VLDLR, ApoER2, CD36, CD81, and others. The role of PCSK9 in the inflammatory process is presented and its influence on cytokine profile (IL-1, IL-6, IL-10, TNF) in atherosclerotic plaque. Cholesterol metabolism converges also with diabetes by mTORC1 pathways. PCSK9 can be altered by oncologic pathways with utilization of kinases, such as Akt, JNK, and JAK/STAT. Finally, the article shows that blocking PCSK9 has proapoptotic capabilities. Administration of monoclonal antibodies against PCSK9 reduced mortality rate and cardiovascular events in randomized trials. On the other hand, immunogenicity of new drugs may play a crucial role in their efficiency. Bococizumab ended its career following SPIRE-1,2 outcome. PCSK9 inhibitors have enormous potential, which had been reflected by introducing them (as a new class of drugs reducing LDL concentration cholesterol) into New Lipid Guidelines from Rome 2016. Discoveries in drugs development are focused on blocking PCSK9 on different levels. For example, silencing messenger RNA (mRNA of PCSK9) is a new alternative against hypercholesterolemia. Peptides mimicking EGF-A domain of the LDL receptor are gaining significance and hopefully they will soon join others. The significance of PCSK9 has just been uncovered and further data is still required to understand their activity.

Regulation of PCSK9 by nutraceuticals

PCSK9 (proprotein convertase subtilisin kexin type 9) is a liver secretory enzyme that regulates plasma low-density lipoprotein (LDL) cholesterol (LDL-C) levels through modulation of LDL receptor (LDLR) density on the surface of hepatocytes. Inhibition of PCSK9 using monoclonal antibodies can efficiently lower plasma LDL-C, non-high-density lipoprotein cholesterol and lipoprotein (a). PCSK9 inhibition is also an effective adjunct to statin therapy; however, the cost-effectiveness of currently available PCSK9 inhibitors is under question. Nutraceuticals offer a safe and cost-effective option for PCSK9 inhibition. Several nutraceuticals have been reported to modulate PCSK9 levels and exert LDL-lowering activity. Mechanistically, those nutraceuticals that inhibit PCSK9 through a SREBP (sterol-responsive element binding protein)-independent pathway can be more effective in lowering plasma LDL-C levels compared with those inhibiting PCSK9 through the SREBP pathway. The present review aims to collect available data on the nutraceuticals with PCSK9-inhibitory effect and the underlying mechanisms.

PCSK9 inhibitors - from discovery of a single mutation to a groundbreaking therapy of lipid disorders in one decade

Hypercholesterolemia is one of the main risk factors for coronary heart disease and significantly contributes to the high mortality associated with cardiovascular diseases. Statin therapy represents the gold standard in the reduction of low-density lipoprotein cholesterol concentration. Nevertheless, many patients still cannot achieve the recommended target levels, due to either inadequate effectiveness or intolerance of these drugs. Monoclonal antibodies that inhibit proprotein convertase subtilisin/kexin type 9 (PCSK9) have emerged as a promising option in lipid-lowering treatment. After confirmation of their efficacy and safety in clinical trials, evolocumab and alirocumab received approval from the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) for introduction into clinical practice. In this review, we present a history of the development and mechanisms of action, as well as the results of the most important studies concerning PCSK9 inhibitors.

Physiological and therapeutic regulation of PCSK9 activity in cardiovascular disease

Ischemic heart disease is the main cause of death worldwide and is accelerated by increased levels of low-density lipoprotein cholesterol (LDL-C). Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a potent circulating regulator of LDL-C through its ability to induce degradation of the LDL receptor (LDLR) in the lysosome of hepatocytes. Only in the last few years, a number of breakthroughs in the understanding of PCSK9 biology have been reported illustrating how PCSK9 activity is tightly regulated at several levels by factors influencing its transcription, secretion, or by extracellular inactivation and clearance. Two humanized antibodies directed against the LDLR-binding site in PCSK9 received approval by the European and US authorities and additional PCSK9 directed therapeutics are climbing up the phases of clinical trials. The first outcome data of the PCSK9 inhibitor evolocumab reported a significant reduction in the composite endpoint (cardiovascular death, myocardial infarction, or stroke) and further outcome data are awaited. Meanwhile, it became evident that PCSK9 has (patho)physiological roles in several cardiovascular cells. In this review, we summarize and discuss the recent biological and clinical data on PCSK9, the regulation of PCSK9, its extra-hepatic activities focusing on cardiovascular cells, molecular concepts to target PCSK9, and finally briefly summarize the data of recent clinical studies.

PCSK9 targets important for lipid metabolism

Ischemic heart disease is the main cause of death worldwide and it is accelerated by increased low-density lipoprotein (LDL) cholesterol (LDL-C) and/or lipoprotein (a) (Lp(a)) concentrations. Proprotein convertase subtilisin/kexin type 9 (PCSK9) alters both LDL-C and in part Lp(a) concentrations through its ability to induce degradation of the LDL receptor (LDLR). PCSK9, however, has additional targets which are potentially involved in lipid metabolism regulation such as the very low density lipoprotein receptor (VLDL), CD36 (cluster of differentiation 36) and the epithelial cholesterol transporter (NPC1L1) and it affects expression of apolipoprotein B48. The PCSK9 activity is tightly regulated at several levels by factors influencing its transcription, secretion, or by extracellular inactivation and clearance. Many comorbidities (kidney insufficiency, hypothyreoidism, hyperinsulinemia, inflammation) modify PCSK9 expression and release. Two humanized antibodies directed against extracellular PCSK9 received approval by the European and US authorities and additional PCSK9 directed therapeutics (such as silencing RNA) are already in clinical trials. Their results demonstrate a significant reduction in both LDL-C and Lp(a) concentrations – independent of the concomitant medication – and one of them reduced plaque size in high risk cardiovascular patients; results of two ongoing large clinical endpoints studies are awaited. In this review, we summarize and discuss the recent biological data on PCSK9, the regulation of PCSK9, and finally briefly summarize the data of recent clinical studies in the context of lipid metabolism.

PCSK9 Monoclonal Antibodies in 2016: Current Status and Future Challenges

Cardiovascular disease remains the leading cause of morbidity and mortality in developed nations, with elevated low-density lipoprotein-cholesterol (LDL-C) levels being a major modifiable risk factor for coronary atherosclerosis. While lipid-lowering therapies such as statins are effective in lowering LDL-C, a proportion of patients do not achieve target LDL-C goals with statins or are intolerant to statins necessitating other treatment options. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors are a new class of agents that reduce LDL-C beyond the maximum achievable LDL-C reductions with statins, and have been well studied in different patient groups. However, there are concerns regarding their potential adverse effects and cost, given that morbidity and mortality benefits have not yet been demonstrated. This state-of-the art review provides an overview of the development of PCSK9 inhibitors, the evidence regarding their clinical efficacy in specific target populations, and highlights future trials and challenges that need to be addressed before PCSK9 inhibitors are widely adopted into contemporary clinical practice.

PCSK9 inhibitors: A new era of lipid lowering therapy

Hyperlipidemia is a well-established risk factor for developing cardiovascular disease (CVD). The recent American College of Cardiology and American Heart Association guidelines on lipid management emphasize treatment of individuals at increased risk for developing CVD events with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) at doses proven to reduce CVD events. However, there are limited options for patients who are either intolerant to statin therapy, develop CVD despite being on maximally tolerated statin therapy, or have severe hypercholesterolemia. Recently the Food and Drug Administration approved two novel medications for low-density lipoprotein (LDL)-cholesterol reduction: Evolocumab and Alirocumab. These agents target and inactivate proprotein convertase subtilsin-kexin type 9 (PCSK9), a hepatic protease that attaches and internalizes LDL receptors into lysosomes hence promoting their destruction. By preventing LDL receptor destruction, LDL-C levels can be lowered 50%-60% above that achieved by statin therapy alone. This review explores PCSK-9 biology and the mechanisms available to alter it; clinical trials targeting PCSK9 activity, and the current state of clinically available inhibitors of PCSK9.

Hepatic HNF1 transcription factors control the induction of PCSK9 mediated by rosuvastatin in normolipidemic hamsters

Proprotein convertase subtilisin/kexin type 9 (PCSK9) impedes low‑density lipoprotein (LDL) receptor (LDLR)-mediated LDL-cholesterol uptake and has hence emerged as a critical regulator of serum cholesterol levels and a new therapeutic target for the treatment of hypercholesterolemia. Statins have been shown to elevate circulating PCSK9 levels by stimulating PCSK9 gene transcription, which reduces the clinical efficacy of statin in LDL‑cholesterol reduction. The transcription of PCSK9 is partially controlled by the hepatocyte nuclear factor 1 (HNF1) binding site embedded in the proximal region of its promoter. In this study, we utilized adenoviral shRNA delivery vectors to generate liver-specific knockdown of HNF1α (Ad‑shHNF1α) or HNF1β (Ad‑shHNF1β) in hamsters to examine the impact of reduced hepatic expression of HNF1 transcription factors on statin‑induced elevation of PCSK9 expression and serum cholesterol levels. We showed that the administration of rosuvastatin (RSV) to normolipidemic hamsters significantly augmented hepatic PCSK9 expression and serum PCSK9 levels. In addition, RSV treatment increased hepatic HNF1α protein levels without a clear effect on HNF1α mRNA expression. Injection of Ad-shHNF1α or Ad‑shHNF1β into hamsters both blunted RSV‑induced elevation of PCSK9 serum concentration and hepatic mRNA and protein levels, which led to significant increases in liver LDLR protein abundance. Furthermore, hepatic depletion of HNF1 factors lowered circulating total cholesterol and non‑high density lipoprotein cholesterol levels in RSV‑treated hamsters. Our study demonstrates that both HNF1α and HNF1β are positive regulators of hepatic PCSK9 transcription in hamster species and that transient, liver-specific knockdown of either HNF1α or HNF1β could antagonize the RSV‑induced elevation of serum PCSK9 and reduce circulating cholesterol levels.

The Proprotein Convertases in Hypercholesterolemia and Cardiovascular Diseases: Emphasis on Proprotein Convertase Subtilisin/Kexin 9

The secretory proprotein convertase (PC) family comprises nine members, as follows: PC1/3, PC2, furin, PC4, PC5/6, paired basic amino acid cleaving enzyme 4, PC7, subtilisin kexin isozyme 1/site 1 protease (SKI-1/S1P), and PC subtilisin/kexin type 9 (PCSK9). The first seven PCs cleave their substrates at single/paired basic residues and exhibit specific and often essential functions during development and/or in adulthood. The essential SKI-1/S1P cleaves membrane-bound transcription factors at nonbasic residues. In contrast, PCSK9 cleaves itself once, and the secreted inactive protease drags the low-density lipoprotein receptors (LDLR) and very LDLR (VLDLR) to endosomal/lysosomal degradation. Inhibitory PCSK9 monoclonal antibodies are now prescribed to treat hypercholesterolemia. This review focuses on the implication of PCs in cardiovascular functions and diseases, with a major emphasis on PCSK9. We present a phylogeny of the PCs and the analysis of PCSK9 haplotypes in modern and archaic human species. The absence of PCSK9 in mice led to the discovery of a sex- and tissue-specific subcellular distribution of the LDLR and VLDLR. PCSK9 inhibition may have other applications because it reduces inflammation and sepsis in a LDLR-dependent manner. Our present understanding of the cellular mechanism(s) that enables PCSK9 to induce the degradation of receptors is reviewed, as well as the consequences of its key natural mutations. The PCSK9 ongoing clinical trials are reviewed. Finally, how the other PCs may impact cardiovascular disease and the metabolic syndrome, and become relevant targets, is discussed.

Comparing expression and activity of PCSK9 in SPRET/EiJ and C57BL/6J mouse strains shows lack of correlation with plasma cholesterol

Objective

Low-density lipoprotein receptor (LDLR) and proprotein convertase subtilisin/kexin type 9 (PCSK9) are opposing regulators of plasma LDL-cholesterol levels. The PCSK9 gene exhibits many single or compound polymorphisms within or among mammalian species. This is case between the SPRET/EiJ (SPRET) and C57BL/6J (B6) mouse strains. We examined whether these polymorphisms could be associated with differential expression and activity of their respective PCSK9 molecules.

Methods

Liver expression of LDLR and PCSK9 transcripts were assessed by RT-PCR, and that of their corresponding proteins by immunoblotting. Purified recombinant PCSK9 proteins were assayed for their ability to degrade LDLR. Pcsk9 gene proximal promoters were tested for activation of a luciferase reporter gene.

Results

SPRET and B6 mice carried comparable levels of plasma cholesterol in spite of the fact that SPRET mice expressed less PCSK9 and more LDLR in liver. There were indels and single-base differences between their Pcsk9 cDNA and promoter sequences. Ex vivo, SPRET PCSK9 protein was less secreted but was more active at degrading LDLR. Its gene promoter was more active at driving expression of the luciferase reporter.

Conclusions

Collectively, these results suggest that, compared to the B6 mouse, the SPRET mouse may represent an example of absence of direct correlation between PCSK9 and cholesterol levels in plasma, due to genetic variations leading to reduced secretion of PCSK9 associated with greater LDLR-degrading activity.

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.

LDL-Cholesterol: Standards of Treatment 2016: A German Perspective

Decreasing low-density lipoprotein cholesterol (LDL-C) is one of the few established and proven principles for the prevention and treatment of atherosclerosis. The higher the individual cardiovascular risk, the higher the benefit of lipid-lowering pharmacotherapy. Therefore, treatment options are chosen based on a patient's total cardiovascular risk. The latter depends not only on the levels of LDL-C but also on the presence of cardiovascular disease (CVD) and on the number and severity of other risk factors. Current guidelines recommend the lowering of LDL-C to 115 mg/dl (3 mmol/l) in patients with low and moderate risk. The LDL-C treatment target is <100 mg/dl (2.6 mmol/l) for patients at high risk and <70 mg/dl (1.8 mmol/l) for patients at very high risk. Although lifestyle measures remain a fundamental part of treatment, many patients require drug therapy to achieve their LDL-C targets. Statins are the drugs of choice, with other options including ezetimibe and the newly available monoclonal antibodies against PCSK9 (proprotein convertase subtilisin/kexin type 9). In some cases, bile acid-binding sequestrants and fibrates can also be considered. Nicotinic acid is no longer available in Germany. PCSK9 antibodies decrease LDL-C about 50-60 % and are well tolerated. Their effects on clinical endpoints are being investigated in large randomized trials. The aim of the present review is to summarize the current guidelines and treatment options for hypercholesterolemia. Moreover, we provide an appraisal of PCSK9 antibodies and propose their use in selected patient populations, particularly in those at very high cardiovascular risk whose LDL-C levels under maximally tolerated lipid-lowering therapy are significantly over their treatment target.

Tanshinone IIA Modulates Low Density Lipoprotein Uptake via Down-Regulation of PCSK9 Gene Expression in HepG2 Cells

Tanshinone IIA, one of the most pharmacologically bioactive phytochemicals isolated from Salvia miltiorrhiza Bunge, possesses several biological activities such as anti-inflammation, anti-cancer, neuroprotection and hypolipidemic activities. In this study, we aim to investigate the hypocholesterolemic effect of tanshinone IIA in hepatic cells. We demonstrated that tanshinone IIA significantly increased the amount of low-density lipoprotein receptor (LDLR) and LDL uptake activity in HepG2 cells at the post-transcriptional regulation. We further demonstrated that tanshinone IIA inhibited the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA and mature protein, which may lead to an increase the cell-surface LDLR in hepatic cells. We further identified a regulatory DNA element involved in the tanshinone IIA-mediated PCSK9 down-regulation, which is located between the -411 and -336 positions of the PCSK9 promoter. Moreover, we found that tanshinone IIA markedly increased the nuclear forkhead box O3a (FoxO3a) level, enhanced FoxO3a/PCSK9 promoter complexes formation and decreased the PCSK9 promoter binding capacity of hepatocyte nuclear factor 1α (HNF-1α), resulting in suppression of PCSK9 gene expression. Finally, we found that the statin-induced PCSK9 overexpression was attenuated and the LDLR activity was elevated in a synergic manner by combination of tanshinone IIA treatment in HepG2 cells. Overall, our results reveal that the tanshinone IIA modulates LDLR level and activity via down-regulation of PCSK9 expression in hepatic cells. Our current findings provide a molecular basis of tanshinone IIA to develop PCSK9 inhibitors for cholesterol management.

Combined Effects of Rosuvastatin and Exercise on Gene Expression of Key Molecules Involved in Cholesterol Metabolism in Ovariectomized Rats

The purpose of this study was to investigate the effects of three weeks of rosuvastatin (Ros) treatment alone and in combination with voluntary training (Tr) on expression of genes involved in cholesterol metabolism (LDLR, PCSK9, LRP-1, SREBP-2, IDOL, ACAT-2 and HMGCR) in the liver of eight week-old ovariectomized (Ovx) rats. Sprague Dawley rats were Ovx or sham-operated (Sham) and kept sedentary for 8 weeks under a standard diet. Thereafter, rats were transferred for three weeks in running wheel cages for Tr or kept sedentary (Sed) with or without Ros treatment (5mg/kg/day). Six groups were formed: Sham-Sed treated with saline (Sal) or Ros (Sham-Sed-Sal; Sham-Sed-Ros), Ovx-Sed treated with Sal or Ros (Ovx-Sed-Sal; Ovx-Sed-Ros), Ovx trained treated with Sal or Ros (Ovx-Tr-Sal; Ovx-Tr-Ros). Ovx-Sed-Sal rats depicted higher (P < 0.05) body weight, plasma total cholesterol (TC) and LDL-C, and liver TC content compared to Sham-Sed-Sal rats. In contrast, mRNA levels of liver PCSK9, LDLR, LRP-1 as well as plasma PCSK9 concentrations and protein levels of LRP-1 were reduced (P < 0.01) in Ovx-Sed-Sal compared to Sham-Sed-Sal rats. However, protein levels of LDLR increased (P < 0.05) in Ovx-Sed-Sal compared to Sham-Sed-Sal rats. Treatment of Ovx rats with Ros increased (P < 0.05) mRNA and protein levels of LRP-1 and PCSK9 but not mRNA levels of LDLR, while its protein abundance was reduced at the level of Sham rats. As a result, plasma LDL-C was not reduced. Exercise alone did not affect the expression of any of these markers in Ovx rats. Overall, Ros treatment corrected Ovx-induced decrease in gene expression of markers of cholesterol metabolism in liver of Ovx rats, but without reducing plasma LDL-C concentrations. Increased plasma PCSK9 levels could be responsible for the reduction of liver LDLR protein abundance and the absence of reduction of plasma LDL-C after Ros treatment.

Genistein upregulates LDLR levels via JNK-mediated activation of SREBP-2

Background

Genistein has been proved in vitro and in vivo to lower LDLR level. It is also widely consumed and implicated for its anti-atherogenic effects. However, the molecular mechanism by which genistein lowers the LDL level is still unknown.

Objective

To understand the anti-atherogenic molecular mechanism of action, genistein was investigated for its impact on the expression of LDLR, the receptor for LDL cholesterol, and related signaling pathways in a human hepatoma cell line.

Design

HepG2 cell was used for the experiments. Genistein with different concentrations was diluted in media and was incubated for 24 h or more as indicated. Protein levels were measured by western blotting, and mRNA expression was detected by RT-qPCR. Chromatin immunoprecipitation assay (CHIP) assay was used to determine protein binding levels, and luciferase assay was used to measure promoter activity.

Result

Genistein increased the mRNA and protein levels of LDLR in a time-dependent manner. Genistein increased the transcriptional activity of the LDLR promoter containing the reporter gene (pLDLR-luc, −805 to +50). But the sterol regulatory element deletion mutant construct failed to be activated by genistein. Genistein increased the nuclear fraction of SREBP-2 and the DNA-binding activity of SREBP-2 to LDLR promoter, as assessed by CHIP. The genistein-phosphorylated JNK inhibitor (SP600126) abolished the genistein-stimulated levels of LDLR and the nuclear SREBP-2. The addition of cholesterol up to 5 µg/mL for 24 h did not affect the effect of genistein on LDLR protein expression. Even the addition of 40 µM genistein increased the cholesterol uptake by more than 10% in the human hepatoma cell line.

Conclusion

Our data support the idea that genistein may have anti-atherogenic effects by activating JNK signals and SREBP-2 processing, which is followed by the upregulation of LDLR.

Effects of Tanshinone IIA on the modulation of miR‑33a and the SREBP‑2/Pcsk9 signaling pathway in hyperlipidemic rats

Tanshinone IIA is the active compound isolated from Salvia miltiorrhiza bunge, which is a traditional Chinese medicine known as Danshen. The aim of the present study was to assess the effect of Tanshinone IIA on the regulation of lipid metabolism in the livers of hyperlipidemic rats and the underlying molecular events. An in vivo model of hyperlipidemia was established in rats, with the animals receiving a daily dose of Tanshinone IIA. The serum lipid profiles were analyzed using an automatic biochemical analyzer, and the histopathological alterations and lipid deposition in liver tissue were assessed using hematoxylin and eosin staining, and oil red O staining, respectively. The mRNA expression levels of microRNA (miR)‑33a, ATP‑binding cassette transporter (ABC)A1, ABCG1, sterol regulatory element‑binding protein 2 (SREBP‑2), proprotein convertase subtilisin/kexin type 9 (Pcsk9) and low‑density lipoprotein receptor (LDL‑R) in liver tissues were measured using reverse transcription‑quantitative polymerase chain reaction, and the protein expression levels of ABCA1, ABCG1, SREBP‑2, Pcsk9, and LDL‑R were analyzed using western blotting. Tanshinone IIA reduced lipid deposition and improved histopathology in the rat liver tissue, however, did not alter the lipid profile in rat serum. In addition, Tanshinone IIA treatment suppressed the expression of miR‑33a, whereas the protein expression levels of ABCA1, SREBP‑2, Pcsk9 in addition to LDL‑R mRNA and protein were upregulated. In conclusion, the present study indicated that Tanshinone IIA attenuated lipid deposition in the livers of hyperlipidemic rats and modulated the expression of miR‑33a and SREBP‑2/Pcsk9 signaling pathway proteins.

PCSK9 inhibition as an emerging lipid lowering therapy: Unanswered questions

Although statins have been used for the treatment of hypercholesterolemia for more than two decades, cardiovascular disease (CVD), which is related at least in part to high levels of low-density lipoprotein cholesterol (LDL-C), is the number one cause of death in Europe and the USA. Several studies have shown that the reduction in cardiovascular (CV) events is proportional to the absolute LDL-C lowering achieved with statins. In the quest for further reduction in LDL-C and CV events, new drugs that mainly support statin action have emerged. Since 2003, with the discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9), which is a key factor in the LDL clearance pathway, new modalities, mainly in the form of monoclonal antibodies that block this protein (PCSK9 inhibitors), have reached phase III of clinical development with very promising efficacy and safety data. With a mean further reduction of LDL-C levels of ∼60% beyond that achieved with statins, the PCSK9 inhibitors set the bar even lower in terms of LDL-C levels. This review manuscript addresses important questions about the efficacy, safety and clinical use of PCSK9 inhibitors to evaluate the role of these agents in reducing CV risk.

Increase of circulating cholesterol in vitamin D deficiency is linked to reduced vitamin D receptor activity via the Insig-2/SREBP-2 pathway

SCOPE

Individuals deficient in vitamin D are more likely to have higher circulating cholesterol levels and cardiovascular diseases. However, the underlying mechanisms are still unclear.

METHODS AND RESULTS

A cross-sectional survey, animal study, and in vitro experiments were conducted to investigate the effect and mechanisms of vitamin D deficiency on endogenous cholesterol metabolism. We demonstrated that vitamin D deficiency was positively associated with an increase of total serum cholesterol and low-density lipoprotein cholesterol levels in northern Chinese individuals. The vitamin D deficiency-induced increase of cholesterol concentration was mainly due to enhanced cholesterol biosynthesis rather than reduced catabolism. Under vitamin D deficiency, the transcriptional activity of vitamin D receptor (VDR) was decreased, leading to the downregulation of insulin-induced gene-2 (Insig-2) expression and thus its inhibitory role on sterol regulatory element-binding protein 2 activation; 3-hydroxy-3-methylglutaryl-coenzyme A reductase expression was accordingly increased. Vitamin D3 was protective against vitamin D deficiency-induced cholesterol increase by maintaining the transcriptional activity of VDR and Insig-2 expression.

CONCLUSION

Vitamin D deficiency is associated with the increase of circulating cholesterol in the people of northern China by enhancing hepatic cholesterol biosynthesis, which was linked to the reduction of transcriptional activity of VDR.

Effect of Leptin Replacement on PCSK9 in ob/ob Mice and Female Lipodystrophic Patients

Leptin treatment has beneficial effects on plasma lipids in patients with lipodystrophy, but the underlying mechanism is unknown. Proprotein convertase subtilisin/kexin type 9 (PCSK9) decreases low-density lipoprotein (LDL) clearance, promotes hypercholesterolemia, and has recently emerged as a novel therapeutic target. To determine the effect of leptin on PCSK9, we treated male and female ob/ob mice with leptin for 4 days via sc osmotic pumps (∼24 μg/d). Leptin reduced body weight and food intake in all mice, but the effects of leptin on plasma PCSK9 and lipids differed markedly between the sexes. In male mice, leptin suppressed PCSK9 but had no effect on plasma triglycerides or cholesterol. In female mice, leptin suppressed plasma triglycerides and cholesterol but had no effect on plasma PCSK9. In parallel, we treated female lipodystrophic patients (8 females, ages 5-23 y) with sc metreleptin injections (∼4.4 mg/d) for 4-6 months. In this case, leptin reduced plasma PCSK9 by 26% (298 ± 109 vs 221 ± 102 ng/mL; n = 8; P = .008), and the change in PCSK9 was correlated with a decrease in LDL cholesterol (r(2) = 0.564, P = .03). In summary, in leptin-deficient ob/ob mice, the effects of leptin on PCSK9 and plasma lipids appeared to be independent of one another and strongly modified by sex. On the other hand, in lipodystrophic females, leptin treatment reduced plasma PCSK9 in parallel with LDL cholesterol.

SREBP2 Activation Induces Hepatic Long-chain Acyl-CoA Synthetase 1 (ACSL1) Expression in Vivo and in Vitro through a Sterol Regulatory Element (SRE) Motif of the ACSL1 C-promoter

Long-chain acyl-CoA synthetase 1 (ACSL1) plays a key role in fatty acid metabolism. To identify novel transcriptional modulators of ACSL1, we examined ACSL1 expression in liver tissues of hamsters fed a normal diet, a high fat diet, or a high cholesterol and high fat diet (HCHFD). Feeding hamsters HCHFD markedly reduced hepatic Acsl1 mRNA and protein levels as well as acyl-CoA synthetase activity. Decreases in Acsl1 expression strongly correlated with reductions in hepatic Srebp2 mRNA level and mature Srebp2 protein abundance. Conversely, administration of rosuvastatin (RSV) to hamsters increased hepatic Acsl1 expression. These new findings were reproduced in mice treated with RSV or fed the HCHFD. Furthermore, the RSV induction of acyl-CoA activity in mouse liver resulted in increases in plasma and hepatic cholesterol ester concentrations and reductions in free cholesterol amounts. Investigations on different ACSL1 transcript variants in HepG2 cells revealed that the mRNA expression of C-ACSL1 was specifically regulated by the sterol regulatory element (SRE)-binding protein (SREBP) pathway, and RSV treatment increased the C-ACSL1 abundance from a minor mRNA species to an abundant transcript. We analyzed 5'-flanking sequence of exon 1C of the human ACSL1 gene and identified one putative SRE site. By performing a promoter activity assay and DNA binding assays, we firmly demonstrated the key role of this SRE motif in SREBP2-mediated activation of C-ACSL1 gene transcription. Finally, we demonstrated that knockdown of endogenous SREBP2 in HepG2 cells lowered ACSL1 mRNA and protein levels. Altogether, this work discovered an unprecedented link between ACSL1 and SREBP2 via the specific regulation of the C-ACSL1 transcript.

Antilipidemic Drug Therapy Today and in the Future

The armamentarium for the treatment of dyslipidemia today comprises six different modes of action with overall around 24 different drugs. The treatment of lipid disorders was revolutionized with the introduction of statins which have become the most important therapeutic option available today to reduce and prevent atherosclerosis and its detrimental consequences like cardiovascular diseases and stroke. With and optimized reduction of elevated LDL levels with statins, the risk for cardiovascular diseases (CVD) can be reduced by 30%, indicating a residual remaining risk of 70% for the development and progression of CVD notifying still a high medical need for more effective antilipidemic drugs. Consequently, the search for novel lipid-modifying drugs is still one of the most active areas in research and development in the pharmaceutical industry. Major focus lies on approaches to LDL-lowering drugs superior to statins with regard to efficacy, safety, and patient compliance and on approaches modifying plasma levels and functionality of HDL particles based on the clinically validated inverse relationship between high-plasma HDL levels and the risk for CVD. The available drugs today for the treatment of dyslipidemia are small organic molecules or nonabsorbable polymers for binding of bile acids to be applied orally. Besides small molecules for novel targets, biological drugs such as monoclonal antibodies, antisense or gene-silencing oligonucleotides, peptidomimetics, reconstituted synthetic HDL particles and therapeutic proteins are novel approaches in clinical development are which have to be applied by injection or infusion. The promising clinical results of several novel drug candidates, particularly for LDL cholesterol lowering with monoclonal antibodies raised against PCSK9, may indicate more than a decade after the statins, the entrance of new breakthrough therapies to treat lipid disorders.

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

Background

Site-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.

Methods

A hepatic-specific knockdown (KD) of S1P was achieved using floxed S1P mouse models (S1P^f/f and LDLR^-/-S1P^f/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.

Results

A 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 S1P^f/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.

Conclusion

Hepatic 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.

Recent developments in modulating atherogenic lipoproteins

PURPOSE OF REVIEW

Randomized clinical trials have assessed the effects of several classes of drugs on plasma cholesterol levels in patients with coronary artery disease. Agents including niacin, fibrates and statins significantly lower LDL-cholesterol, but tolerance issues and undesirable side-effects are common. Residual risk may also be present in patients with persistently low HDL-cholesterol despite a reduction in LDL-cholesterol. Recent trials of drugs that increase circulating HDL-cholesterol have also been disappointing.

RECENT FINDINGS

Ongoing efforts target the development of new pharmacotherapies to reduce circulating levels of atherogenic lipoproteins. The goal of this review is to discuss recent advances in the treatment of coronary artery disease and other vascular diseases characterized by an increase in circulating atherogenic lipoproteins. These include the development of inhibitors of ATP citrate lyase and proprotein convertase subtilisin/kexin type 9. We also discuss recent developments in HDL therapy, including the clinical assessment of cholesteryl ester transfer protein inhibitors and apolipoprotein E mimetic peptides.

SUMMARY

Several new classes of drug are undergoing clinical evaluation that show promise for atherogenic lipoprotein reduction in patients who are statin intolerant.

Endogenous Sterol Metabolites Regulate Growth of EGFR/KRAS-Dependent Tumors via LXR

Meiosis-activating sterols (MAS) are substrates of SC4MOL and NSDHL in the cholesterol pathway and are important for normal organismal development. Oncogenic transformation by epidermal growth factor receptor (EGFR) or RAS increases the demand for cholesterol, suggesting a possibility for metabolic interference. To test this idea in vivo, we ablated Nsdhl in adult keratinocytes expressing KRAS(G12D). Strikingly, Nsdhl inactivation antagonized the growth of skin tumors while having little effect on normal skin. Loss of Nsdhl induced the expression of ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, reduced the expression of low-density lipoprotein receptor (LDLR), decreased intracellular cholesterol, and was dependent on the liver X receptor (LXR) α. Importantly, EGFR signaling opposed LXRα effects on cholesterol homeostasis, whereas an EGFR inhibitor synergized with LXRα agonists in killing cancer cells. Inhibition of SC4MOL or NSDHL, or activation of LXRα by sterol metabolites, can be an effective strategy against carcinomas with activated EGFR-KRAS signaling.

MicroRNA-27a decreases the level and efficiency of the LDL receptor and contributes to the dysregulation of cholesterol homeostasis

RATIONALE

A strong risk factor for atherosclerosis- the leading cause of heart attacks and strokes- is the elevation of low-density lipoprotein cholesterol (LDL-C) in blood. The LDL receptor (LDLR) is the primary pathway for LDL-C removal from circulation, and their levels are increased by statins -the main treatment for high blood LDL-C. However, statins have low efficiency because they also increase PCSK9 which targets LDLR for degradation. Since microRNAs have recently emerged as key regulators of cholesterol homeostasis, our aim was to identify potential microRNA-based therapeutics to decrease blood LDL-C and prevent atherosclerosis.

METHODS AND RESULTS

We over expressed and knocked down miR-27a in HepG2 cells to assess its effect on the expression of key players in the LDLR pathway using PCR Arrays, Elisas, and Western blots. We found that miR-27a decreases LDLR levels by 40% not only through a direct binding to its 3' untranslated region but also indirectly by inducing a 3-fold increase in PCSK9, which enhances LDLR degradation. Interestingly, miR-27a also directly decreases LRP6 and LDLRAP1, two other key players in the LDLR pathway that are required for efficient endocytosis of the LDLR-LDL-C complex in the liver. The inhibition of miR-27a using lock nucleic acids induced a 70% increase in LDLR levels and, therefore, it would be a more efficient treatment for hypercholesterolemia because of its desirable effects not only on LDLR but also on PCSK9.

CONCLUSION

The results presented here provide evidence supporting the potential of miR-27a as a novel therapeutic target for the prevention of atherosclerosis.

Reduction of circulating PCSK9 and LDL-C levels by liver-specific knockdown of HNF1α in normolipidemic mice

The transcription factors hepatic nuclear factor (HNF)1α and HNF1β can bind to the HNF1 site on the proprotein convertase subtilisin/kexin type 9 (PCSK9) promoter to activate transcription in HepG2 cells. However, it is unknown whether one or both HNF1 factors are obligatory for transactivating hepatic PCSK9 gene expression in vivo. We developed shRNA adenoviral constructs (Ad-shHNF1α and Ad-shHNF1β) to examine the effects of knockdown of HNF1α or HNF1β on PCSK9 expression and its consequent impact on LDL receptor (LDLR) protein levels in cultured hepatic cells and liver tissue. We demonstrated that infection with Ad-shHNF1α, but not Ad-shHNF1β, markedly reduced PCSK9 mRNA expression in HepG2 cells with a concomitant increase in LDLR protein abundance. Injecting Ad-shHNF1α in mice fed a normal diet significantly (∼ 50%) reduced liver mRNA expression and serum concentration of PCSK9 with a concomitant increase (∼ 1.9-fold) in hepatic LDLR protein abundance. Furthermore, we observed a modest but significant reduction in circulating LDL cholesterol after knockdown of HNF1α in these normolipidemic mice. Consistent with the observation that knockdown of HNF1β did not affect PCSK9 mRNA or protein expression in cultured hepatic cells, Ad-shHNF1β infection in mice resulted in no change in the hepatic mRNA expression or serum content of PCSK9. Altogether, our study demonstrates that HNF1α, but not HNF1β, is the primary positive regulator of PCSK9 transcription in mouse liver.

PPARδ activation induces hepatic long-chain acyl-CoA synthetase 4 expression in vivo and in vitro

The arachidonic acid preferred long-chain acyl-CoA synthetase 4 (ACSL4) is a key enzyme for fatty acid metabolism in various metabolic tissues. In this study, we utilized hamsters fed a normal chow diet, a high-fat diet or a high cholesterol and high fat diet (HCHFD) as animal models to explore novel transcriptional regulatory mechanisms for ACSL4 expression under hyperlipidemic conditions. Through cloning hamster ACSL4 homolog and tissue profiling ACSL4 mRNA and protein expressions we observed a selective upregulation of ACSL4 in testis and liver of HCHFD fed animals. Examination of transcriptional activators of the ACSL family revealed an increased hepatic expression of PPARδ but not PPARα in HCHFD fed hamsters. To explore a role of PPARδ in dietary cholesterol-mediated upregulation of ACSL4, we administered a PPARδ specific agonist L165041 to normolipidemic and dyslipidemic hamsters. We observed significant increases of hepatic ACSL4 mRNA and protein levels in all L165041-treated hamsters as compared to control animals. The induction of ACSL4 expression by L165041 in liver tissue in vivo was recapitulated in human primary hepatocytes and hepatocytes isolated from hamster and mouse. Moreover, employing the approach of adenovirus-mediated gene knockdown, we showed that depletion of PPARδ in hamster hepatocytes specifically reduced ACSL4 expression. Finally, utilizing HepG2 as a model system, we demonstrate that PPARδ activation leads to increased ACSL4 promoter activity, mRNA and protein expression, and consequently higher arachidonoyl-CoA synthetase activity. Taken together, we have discovered a novel PPARδ-mediated regulatory mechanism for ACSL4 expression in liver tissue and cultured hepatic cells.

Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9)

The proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising treatment target to lower serum cholesterol, a major risk factor of cardiovascular diseases. Gain-of-function mutations of PCSK9 are associated with hypercholesterolemia and increased risk of cardiovascular events. Conversely, loss-of-function mutations cause low-plasma LDL-C levels and a reduction of cardiovascular risk without known unwanted effects on individual health. Experimental studies have revealed that PCSK9 reduces the hepatic uptake of LDL-C by increasing the endosomal and lysosomal degradation of LDL receptors (LDLR). A number of clinical studies have demonstrated that inhibition of PCSK9 alone and in addition to statins potently reduces serum LDL-C concentrations. This review summarizes the current data on the regulation of PCSK9, its molecular function in lipid homeostasis and the emerging evidence on the extra-hepatic effects of PCSK9.

Removal of plasma mature and furin-cleaved proprotein convertase subtilisin/kexin 9 by low-density lipoprotein-apheresis in familial hypercholesterolemia: development and application of a new assay for PCSK9

CONTEXT

Proprotein convertase subtilisin/kexin 9 (PCSK9) is known to be a good target to decrease LDL cholesterol (LDL-C) and two forms of PCSK9, mature and furin-cleaved PCSK9, circulate in blood. However, it has not been clarified whether and how the levels of each PCSK9 are affected by LDL-apheresis (LDL-A) treatment, a standard therapy in patients with severe forms of familial hypercholesterolemia (FH).

OBJECTIVE

Our objective was to investigate the differences in LDL-A-induced reduction of mature and furin-cleaved PCSK9 between homozygous and heterozygous FH, and between dextran sulfate (DS) cellulose adsorption and double membrane (DM) columns and to clarify the mechanism of their removal.

DESIGN

A sandwich ELISA to measure two forms of PCSK9s using monoclonal antibodies was developed. Using the ELISA, PCSK9 levels were quantified before and after LDL-A with DS columns in 7 homozygous and 11 heterozygous FH patients. A crossover study between the two column types was performed. The profiles of PCSK9s were analyzed after fractionation by gel filtration chromatography. Immunoprecipitation of apolipoprotein B (apoB) in FH plasma was performed.

RESULTS

Both mature and furin-cleaved PCSK9s were significantly decreased by 55-56% in FH homozygotes after a single LDL-A treatment with DS columns, and by 46-48% or 48-56% in FH heterozygotes after treatment with DS or DM columns. The reduction ratios of LDL-C were strongly correlated with that of PCSK9 in both FH homozygotes and heterozygotes. In addition, more than 80% of plasma PCSK9s were in the apoB-deficient fraction and a significant portion of mature PCSK9 was bound to apoB, as shown by immunoprecipitation.

CONCLUSIONS

Both mature and furin-cleaved PCSK9s were removed by LDL-A in homozygous and heterozygous FH either by binding to apoB or by other mechanisms. The ELISA method to measure both forms of plasma PCSK9 would be useful for investigating physiological or pathological roles of PCSK9.

Inhibition of PCSK9 transcription by berberine involves down-regulation of hepatic HNF1α protein expression through the ubiquitin-proteasome degradation pathway

Our previous in vitro studies have identified hepatocyte nuclear factor 1α (HNF1α) as an obligated trans-activator for PCSK9 gene expression and demonstrated its functional involvement in the suppression of PCSK9 expression by berberine (BBR), a natural cholesterol-lowering compound. In this study, we investigated the mechanism underlying the inhibitory effect of BBR on HNF1α-mediated PCSK9 transcription. Administration of BBR to hyperlipidemic mice and hamsters lowered circulating PCSK9 concentrations and hepatic PCSK9 mRNA levels without affecting the gene expression of HNF1α. However, hepatic HNF1α protein levels were markedly reduced in BBR-treated animals as compared with the control. Using HepG2 cells as a model system, we obtained evidence that BBR treatment let to accelerated degradation of HNF1α protein. By applying inhibitors to selectively block the ubiquitin proteasome system (UPS) and autophagy-lysosomal pathway, we show that HNF1α protein content in HepG2 cells was not affected by bafilomycin A1 treatment, but it was dose-dependently increased by UPS inhibitors bortezomib and MG132. Bortezomib treatment elevated HNF1α and PCSK9 cellular levels with concomitant reductions of LDL receptor protein. Moreover, HNF1α protein displayed a multiubiquitination ladder pattern in cells treated with BBR or overexpressing ubiquitin. By expressing GFP-HNF1α fusion protein in cells, we observed that blocking UPS resulted in accumulation of GFP-HNF1α in cytoplasm. Importantly, we show that the BBR reducing effects on HNF1α protein and PCSK9 gene transcription can be eradicated by proteasome inhibitors. Altogether, our studies using BBR as a probe uncovered a new aspect of PCSK9 regulation by ubiquitin-induced proteasomal degradation of HNF1α.

PCSK9: A key factor modulating atherosclerosis

Coronary artery disease (CAD) due to obstructive atherosclerosis is a leading cause of death and has been recognized as a worldwide health threat. Measures to decrease low-density lipoprotein cholesterol (LDL-C) levels are the cornerstone in the management of patients with atherosclerotic cardiovascular disease, particularly those with CAD, for over two decades. Proprotein convertase subtilisin/kexin type 9 (PCSK9), a newly recognized protein, plays a key role in cholesterol homeostasis by enhancing degradation of hepatic LDL receptor (LDLR). Interestingly, PCSK9 is also involved in the inflammatory process. Plasma PCSK9 and lipid or nonlipid cardiovascular risk factors are correlated, and the associations between PCSK9 with cardiovascular health and disease make this protein worthy of attention for the treatment of hyperlipidemia and atherosclerosis. Here, we provide an overview of the physiological role of PCSK9, which contributes to atherosclerosis, and provide data on PCSK9 as a novel pharmacological target. Clinical evidence shows that PCSK9 inhibition is as promising as statins as a target to treat CAD. The efficacy of these drugs may potentially enable effective CAD prophylaxis for more patients.

Policosanol attenuates statin-induced increases in serum proprotein convertase subtilisin/kexin type 9 when combined with atorvastatin

Objective. Statin treatment alone has been demonstrated to significantly increase plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) levels. The effect of policosanol combined with statin on PCSK9 is unknown. Methods. Protocol I: 26 patients with atherosclerosis were randomly assigned to receive either atorvastatin 20 mg/d or policosanol 20 mg/d + atorvastatin 20 mg/d for 8 weeks. Protocol II: 15 healthy volunteers were randomly assigned to either policosanol 20 mg/d or a control group for 12 weeks. Serum levels of PCSK9 were determined at day 0 and the end of each protocol. Results. Protocol I: atorvastatin 20 mg/d significantly increased serum PCSK9 level by 39.4% (256 ± 84 ng/mL versus 357 ± 101 ng/mL, P = 0.002). However, policosanol 20 mg/d + atorvastatin 20 mg/d increased serum PCSK9 level by only 17.4% without statistical significance (264 ± 60 ng/mL versus 310 ± 86 ng/mL, P = 0.184). Protocol II: there was a trend toward decreasing serum PCSK9 levels in the policosanol group (289 ± 71 ng/mL versus 235 ± 46 ng/mL, P = 0.069). Conclusion. Policosanol combined with statin attenuated the statin-induced increase in serum PCSK9 levels. This finding indicates that policosanol might have a modest effect of lowering serum PCSK9 levels.

PCSK9 and lipid lowering drugs

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a novel circulating protein, which plays an important role in the regulation of cholesterol metabolism. Over the past decade, experimental and clinical studies have established that over- or poor expression of PCSK9 had a key impact not only on circulating PCSK9 and low density lipoprotein cholesterol (LDL-C) levels but also on cardiovascular risk and atherosclerotic process. Since the first discovery of PCSK9-related gene in 2003, factors that can influence circulating PCSK9 concentration are of great interest in a variety of medical fields, especially in pharmacology. In this review we focus on the impact of lipid-lowering drugs on circulating PCSK9 concentration and its clinical implications in order to optimal consideration for the current strategies with regard to cholesterol control.