Unexpected roles for PCSK9 in lipid metabolism

PCSK9 deficiency alters brain lipid composition without affecting brain development and function

PCSK9 induces lysosomal degradation of the low-density lipoprotein (LDL) receptor (LDLR) in the liver, hereby preventing removal of LDL cholesterol from the circulation. Accordingly, PCSK9 inhibitory antibodies and siRNA potently reduce LDL cholesterol to unprecedented low levels and are approved for treatment of hypercholesterolemia. In addition, PCSK9 inactivation alters the levels of several other circulating lipid classes and species. Brain function is critically influenced by cholesterol and lipid composition. However, it remains unclear how the brain is affected long-term by the reduction in circulating lipids as achieved with potent lipid lowering therapeutics such as PCSK9 inhibitors. Furthermore, it is unknown if locally expressed PCSK9 affects neuronal circuits through regulation of receptor levels. We have studied the effect of lifelong low peripheral cholesterol levels on brain lipid composition and behavior in adult PCSK9 KO mice. In addition, we studied the effect of PCSK9 on neurons in culture and in vivo in the developing cerebral cortex. We found that PCSK9 reduced LDLR and neurite complexity in cultured neurons, but neither PCSK9 KO nor overexpression affected cortical development in vivo. Interestingly, PCSK9 deficiency resulted in changes of several lipid classes in the adult cortex and cerebellum. Despite the observed changes, PCSK9 KO mice had unchanged behavior compared to WT controls. In conclusion, our findings demonstrate that altered PCSK9 levels do not compromise brain development or function in mice, and are in line with clinical trials showing that PCSK9 inhibitors have no adverse effects on cognitive function.

PCSK9 Functions in Atherosclerosis Are Not Limited to Plasmatic LDL-Cholesterol Regulation

The relevance of PCSK9 in atherosclerosis progression is demonstrated by the benefits observed in patients that have followed PCSK9-targeted therapies. The impact of these therapies is attributed to the plasma lipid-lowering effect induced when LDLR hepatic expression levels are recovered after the suppression of soluble PCSK9. Different studies show that PCSK9 is involved in other mechanisms that take place at different stages during atherosclerosis development. Indeed, PCSK9 regulates the expression of key receptors expressed in macrophages that contribute to lipid-loading, foam cell formation and atherosclerotic plaque formation. PCSK9 is also a regulator of vascular inflammation and its expression correlates with pro-inflammatory cytokines release, inflammatory cell recruitment and plaque destabilization. Furthermore, anti-PCSK9 approaches have demonstrated that by inhibiting PCSK9 activity, the progression of atherosclerotic disease is diminished. PCSK9 also modulates thrombosis by modifying platelets steady-state, leukocyte recruitment and clot formation. In this review we evaluate recent findings on PCSK9 functions in cardiovascular diseases beyond LDL-cholesterol plasma levels regulation.

Inhibition of proprotein convertase subtilisin/kexin type 9 attenuates 2,4,6-trinitrobenzenesulfonic acid-induced colitis via repressing toll-like receptor 4/nuclear factor-kappa B

Inflammatory bowel disease (IBD) is characterized by recurring inflammatory disorders in digestive system, and devoid of effective treatment. Proprotein convertase subtilisin/kexin type 9 (PCSK9), stimulated via inflammation whose inhibition could decrease secretion of inflammatory factors. We then determined whether inhibition of PCSK9 could improve the inflammation. First, rats model of colitis was first established via administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS), and then verified via determination of body weight loss, myeloperoxidase (MPO) activity, and histopathological analysis of colonic damage. Results showed that treatment with TNBS induced a great body weight loss, MPO activity increase, and serious colonic damage, showing an obviously character of IBD. PCSK9 was elevated in TNBS-induced rats, and PCSK9 inhibition delivered by adenovirus vector increased the body weight, decreased MPO activity, and ameliorated histological change of colon. Second, the protective effect of PCSK9 inhibition against TNBS-induced colitis was accompanied by decrease of proinflammatory factors secretion, including tumor necrosis factor-α, interleukin-1β, interleukin-6, intercellular adhesion molecule 1, and monocyte chemoattractant protein-1. TNBS could activate toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signaling pathway, while PCSK9 inhibition suppressed activation of TLR4/NF-κB in TNBS-induced rats. In conclusion, PCSK9 inhibition attenuated TNBS-induced rat colitis through anti-inflammatory effect under inactivation of TLR4/NF-κB, suggesting potential therapeutic strategy in IBD.

Effect of Sleeve Gastrectomy on Proprotein Convertase Subtilisin/Kexin Type 9 (Pcsk9) Content and Lipid Metabolism in the Blood Plasma and Liver of Obese Wistar Rats

Nowadays, obesity and its complications are heavy burdens to western civilization. Surgical procedures remain one of the available therapies for obesity and obesity-associated diseases treatment. Among them, sleeve gastrectomy is the most common bariatric procedure. Despite the well-established fact that sleeve gastrectomy results in significant weight loss, some of its other divergent effects still need to be established. To fulfill this knowledge gap, we examined whether sleeve gastrectomy affects lipid metabolism in the plasma and liver of obese rats. We demonstrated that chronic high-fat diet feeding led to an increment in the level of Proprotein Convertase Subtilisin/Kexin (PCSK)-a regulator of plasma cholesterol concentration-in the liver, which was decreased after the gastrectomy. Moreover, we noticed significant increases in both plasma and liver contents of free fatty acids, diacylgycerides and triacylglycerides in the obese animals, with their reduction after the bariatric surgery. In conclusion, we revealed, presumably for the first time, that sleeve gastrectomy affects lipid metabolism in the liver of obese rats.

Effect of Quercetin on Atherosclerosis Based on Expressions of ABCA1, LXR-α and PCSK9 in ApoE-/- Mice

OBJECTIVE

To investigate the effect of quercetin on ATP binding cassette transporter A1 (ABCA1), liver X receptor (LXR), and proprotein convertase subtilisin/kexin type 9 (PCSK9) expressions in apoE-knockout (ApoE^-/-) mice.

METHODS

The high-fat diet-induced atherosclerosis (AS) in ApoE^-/- mice was established. Thirty-six mice were divided into 3 groups using random number table method: model group (n=12), quercetin group (n=12), and atorvastatin group (n=12), with C57BL/6J mice of the same strain and age as the control group (n=12). Quercetin group and atorvastatin group were administrated with quercetin and atorvastatin by oral gavage, with doses of 12.5 and 4 mg/(kg•d), respectively. Animals in the control and model groups were given an equal volume of distilled water by oral gavage once per day for a total of 12 weeks. Western blot and immunohistochemical methods were employed to determine the aortic ABCA1, LXR-α and PCSK9 protein expression. Enzyme linked immunosorbent assay method was used to detect the expression of serum total cholesterol (TC), triglyceride (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-10, combined with tissue pathological examination.

RESULTS

ApoE^-/- mice fed with a high-fat diet had notable atherosclerosis lesions, with reduced ABCA1, LXR-α and IL-10 levels (all P<0.01), elevated PCSK9, TNF-α and IL-6 expression, and increased TC and LDL-C contents (all P<0.01). After quercetin intervention, the areas of AS plaques and the expressions of PCSK9, TNF-α and IL-6 were significantly reduced (all P<0.01), while the expressions of ABCA1 and LXR-α were increased significantly (all P<0.01).

CONCLUSION

Quercetin effectively interfered with AS development by regulating the expressions of ABCA1, LXR- α and PCSK9 in ApoE^-/- mice.

PCSK9: A novel inflammation modulator in atherosclerosis?

Proprotein convertase subtilisin/kexin 9 (PCSK9) is the ninth member of the secretory serine protease family. It binds to low-density lipoprotein receptor (LDLR) for endocytosis and lysosome degradation in the liver, resulting in an increasing in circulating LDL-cholesterol (LDL-c) level. Since a PCSK9 induced increase in plasma LDL-c contributes to atherosclerosis, PCSK9 inhibition has become a new strategy in preventing and treating atherosclerosis. However, in addition to the effect of PCSK9 on elevating blood LDL-c levels, accumulating evidence shows that PCSK9 plays an important role in inflammation, likely representing another major mechanism for PCSK9 to promote atherosclerosis. In this review, we discuss the association of PCSK9 and inflammation, and highlight the specific effects of PCSK9 on different vascular cellular components involved in the atherosclerotic inflammation. We also discuss the clinical evidence for the association between PCSK9 and inflammation in atherosclerotic cardiovascular disease. A better understanding of the direct association of PCSK9 with atherosclerotic inflammation might help establish a new role for PCSK9 in vascular biology and identify a novel molecular mechanism for PCSK9 therapy.

Foam cell formation: A new target for fighting atherosclerosis and cardiovascular disease

During atherosclerosis, the gradual accumulation of lipids into the subendothelial space of damaged arteries results in several lipid modification processes followed by macrophage uptake in the arterial wall. The way in which these modified lipoproteins are dealt with determines the likelihood of cholesterol accumulation within the monocyte-derived macrophage and thus its transformation into the foam cell that makes up the characteristic fatty streak observed in the early stages of atherosclerosis. The unique expression of chemokine receptors and cellular adhesion molecules expressed on the cell surface of monocytes points to a particular extravasation route that they can take to gain entry into atherosclerotic site, in order to undergo differentiation into the phagocytic macrophage. Indeed several GWAS and animal studies have identified key genes and proteins required for monocyte recruitment as well cholesterol handling involving lipid uptake, cholesterol esterification and cholesterol efflux. A re-examination of the previously accepted paradigm of macrophage foam cell origin has been called into question by recent studies demonstrating shared expression of scavenger receptors, cholesterol transporters and pro-inflammatory cytokine release by alternative cell types present in the neointima, namely; endothelial cells, vascular smooth muscle cells and stem/progenitor cells. Thus, therapeutic targets aimed at a more heterogeneous foam cell population with shared functions, such as enhanced protease activity, and signalling pathways, mediated by non-coding RNA molecules, may provide greater therapeutic outcome in patients. Finally, studies targeting each aspect of foam cell formation and death using both genetic knock down and pharmacological inhibition have provided researchers with a clearer understanding of the cellular processes at play, as well as helped researchers to identify key molecular targets, which may hold significant therapeutic potential in the future.

Quercetin protects against ox‑LDL‑induced injury via regulation of ABCAl, LXR‑α and PCSK9 in RAW264.7 macrophages

Quercetin is a flavonoid that has anti‑inflammatory, anti‑oxidant and lipid metabolic effects. It has also been reported to reduce the risk of cardiovascular disease. The present study measured the effects of quercetin on the expression of ATP‑binding cassette transporter 1 (ABCAl), ATP‑binding cassette sub‑family G member 1 (ABCG1), liver X receptor‑α (LXR‑α), proprotein convertase subtilisin/kexin type 9 (PCSK9), p53, p21 and p16 induced by oxidized low density lipoprotein (ox‑LDL). RAW264.7 macrophages were exposed to ox‑LDL with or without 20 µmol/l quercetin and cell proliferation and senescence were quantified using β‑gal staining. Superoxide dismutase (SOD), malondialdehyde (MDA) and lipid droplets were measured in the cytoplasm using oil red staining, while intracellular and total cholesterol (TC) were measured using filipin staining and a TC kit. Immunofluorescent studies and western blot analysis were performed to quantify the expression of ABCAl, ABCG1, LXR‑α, PCSK9, p53, p21 and p16. Quercetin increased RAW264.7 cell viability and reduced lipid accumulation, senescence, lipid droplets, intracellular cholesterol and TC. It was concluded that quercetin inhibits ox‑LDL‑induced lipid droplets in RAW264.7 cells by upregulation of ABCAl, ABCG1, LXR‑α and downregulation of PCSK9, p53, p21 and p16.

Lipid Target in Very High-Risk Cardiovascular Patients: Lesson from PCSK9 Monoclonal Antibodies

The role of low-density lipoproteins (LDLs) as a major risk factor for cardiovascular disease has been demonstrated by several epidemiological studies. The molecular basis for LDLs in atherosclerotic plaque formation and progression is not completely unraveled yet. Pharmacological modulation of plasma LDL-C concentrations and randomized clinical trials addressing the impact of lipid-lowering interventions on cardiovascular outcome have clearly shown that reducing plasma LDL-C concentrations results in a significant decrease in major cardiovascular events. For many years, statins have represented the most powerful pharmacological agents available to lower plasma LDL-C concentrations. In clinical trials, it has been shown that the greater the reduction in plasma LDL-C concentrations, the lower the rate of major cardiovascular events, especially in high-risk patients, because of multiple risk factors and recurrent events. However, in a substantial number of patients, the recommended LDL target is difficult to achieve because of different factors: genetic background (familial hypercholesterolemia), side effects (statin intolerance), or high baseline plasma LDL-C concentrations. In the last decade, our understanding of the molecular mechanisms involved in LDL metabolism has progressed significantly and the key role of proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged. This protein is an enzyme able to bind the LDL receptors (LDL-R) on hepatocytes, favoring their degradation. Blocking PCSK9 represents an intriguing new therapeutic approach to decrease plasma LDL-C concentrations, which in recent studies has been demonstrated to also result in a significant reduction in major cardiovascular events.

Peripheral vascular atherosclerosis in a novel PCSK9 gain-of-function mutant Ossabaw miniature pig model

Hypercholesterolemia is a major risk factor for atherosclerosis. Remaining challenges in the management of atherosclerosis necessitate development of animal models that mimic human pathophysiology. We characterized a novel mutant pig model with DNA transposition of D374Y gain-of-function (GOF) cDNA of chimp proprotein convertase subtilisin/kexin type-9 (PCSK9), and tested the hypothesis that it would develop peripheral vascular remodeling and target organ injury in the kidney. Wild-type or PCSK9-GOF Ossabaw miniature pigs fed a standard or atherogenic diet (AD) (n = 7 each) were studied in vivo after 3 and 6 months of diet. Single-kidney hemodynamics and function were studied using multidetector computed tomography and kidney oxygenation by blood oxygen level-dependent magnetic resonance imaging. The renal artery was evaluated by intravascular ultrasound, aortic stiffness by multidetector computed tomography, and kidney stiffness by magnetic resonance elastography. Subsequent ex vivo studies included the renal artery endothelial function and morphology of abdominal aorta, renal, and femoral arteries by histology. Compared with wild type, PCSK9-GOF pigs had elevated cholesterol, triglyceride, and blood pressure levels at 3 and 6 months. Kidney stiffness increased in GOF groups, but aortic stiffness only in GOF-AD. Hypoxia, intrarenal fat deposition, oxidative stress, and fibrosis were observed in both GOF groups, whereas kidney function remained unchanged. Peripheral arteries in GOF groups showed medial thickening and development of atheromatous plaques. Renal endothelial function was impaired only in GOF-AD. Therefore, the PCSK9-GOF mutation induces rapid development of atherosclerosis in peripheral vessels of Ossabaw pigs, which is exacerbated by a high-cholesterol diet. This model may be useful for preclinical studies of atherosclerosis.

The Effect of PCSK9 Loss-of-Function Variants on the Postprandial Lipid and ApoB-Lipoprotein Response

CONTEXT

Proprotein convertase subtilisin kexin 9 (PCSK9) mediates degradation of the low-density lipoprotein receptor (LDLR), thereby increasing plasma low-density lipoprotein cholesterol (LDL-C). Variations in the PCSK9 gene associated with loss of function (LOF) of PCSK9 result in greater expression of hepatic LDLR, lower concentrations of LDL-C, and protection from cardiovascular disease (CVD). Apolipoprotein-B (apoB) remnants also contribute to CVD risk and are similarly cleared by the LDLR. We hypothesized that PCSK9-LOF carriers would have lower fasting and postprandial remnant lipoproteins on top of lower LDL-C.

OBJECTIVE

To compare fasting and postprandial concentrations of triglycerides (TGs), total apoB, and apoB48 as indicators of remnant lipoprotein metabolism in PCSK9-LOF carriers with those with no PCSK9 variants.

DESIGN

Case-control, metabolic study.

SETTING

Clinical Research Center of The Ottawa Hospital.

PARTICIPANTS

Persons with one or more copies of the L10ins/A53V and/or I474V and/or R46L PCSK9 variant and persons with no PCSK9 variants.

INTERVENTION

Oral fat tolerance test.

MAIN OUTCOMES MEASURES

Fasting and postprandial plasma TG, apoB48, total apoB, total cholesterol, and PCSK9 were measured at 0, 2, 4, and 6 hours after an oral fat load.

RESULTS

Participants with PCSK9-LOF variants (n = 22) had reduced fasting LDL-C (-14%) as well as lower fasting TG (-21%) compared with noncarrier controls (n = 23). LOF variants also had reduced postprandial total apoB (-17%), apoB48 (-23%), and TG (-18%). Postprandial PCSK9 declined in both groups (-24% vs -16%, respectively).

CONCLUSIONS

Participants carrying PCSK9-LOF variants had attenuated levels of fasting and postprandial TG, apoB48, and total apoB. This may confer protection from CVD and further validate the use of PCSK9 inhibitors to lower CVD risk.

Activation of Adiponectin Receptor Regulates Proprotein Convertase Subtilisin/Kexin Type 9 Expression and Inhibits Lesions in ApoE-Deficient Mice

Objective—

The reduced adiponectin levels are associated with atherosclerosis. Adiponectin exerts its functions by activating adiponectin receptor (AdipoR). Proprotein convertase subtilisin kexin type 9 (PCSK9) degrades LDLR protein (low-density lipoprotein receptor) to increase serum LDL-cholesterol levels. PCSK9 expression can be regulated by PPARγ (peroxisome proliferator–activated receptor γ) or SREBP2 (sterol regulatory element-binding protein 2). The effects of AdipoR agonists on PCSK9 and LDLR expression, serum lipid profiles, and atherosclerosis remain unknown.

Approach and Results—

At cellular levels, AdipoR agonists (ADP355 and AdipoRon) induced PCSK9 transcription/expression that solely depended on activation of PPAR-responsive element in the PCSK9 promoter. AdipoR agonists induced PPARγ expression; thus, the AdipoR agonist-activated PCSK9 expression/production was impaired in PPARγ deficient hepatocytes. Meanwhile, AdipoR agonists transcriptionally activated LDLR expression by activating SRE in the LDLR promoter. Moreover, AMP-activated protein kinase α (AMPKα) was involved in AdipoR agonist-activated PCSK9 expression. In wild-type mice, ADP355 increased PCSK9 and LDLR expression and serum PCSK9 levels, which was associated with activation of PPARγ, AMPKα and SREBP2 and reduction of LDL-cholesterol levels. In contrast, ADP355 reduced PCSK9 expression/secretion in apoE-deficient (apoE −/− ) mice, but it still activated hepatic LDLR, PPARγ, AMPKα, and SREBP2. More importantly, ADP355 inhibited lesions in en face aortas and sinus lesions in aortic root in apoE −/− mice with amelioration of lipid profiles.

Conclusions—

Our study demonstrates that AdipoR activation by agonists regulated PCSK9 expression differently in wild-type and apoE −/− mice. However, ADP355 activated hepatic LDLR expression and ameliorated lipid metabolism in both types of mice and inhibited atherosclerosis in apoE −/− mice.

Genetically modified pigs to model human diseases

Genetically modified mice are powerful tools to investigate the molecular basis of many human diseases. Mice are, however, of limited value for preclinical studies, because they differ significantly from humans in size, general physiology, anatomy and lifespan. Considerable efforts are, thus, being made to develop alternative animal models for a range of human diseases. These promise powerful new resources that will aid the development of new diagnostics, medicines and medical procedures. Here, we provide a comprehensive review of genetically modified porcine models described in the scientific literature: various cancers, cystic fibrosis, Duchenne muscular dystrophy, autosomal polycystic kidney disease, Huntington’s disease, spinal muscular atrophy, haemophilia A, X-linked severe combined immunodeficiency, retinitis pigmentosa, Stargardt disease, Alzheimer’s disease, various forms of diabetes mellitus and cardiovascular diseases.

The clinical significance and regulation mechanism of hypoxia-inducible factor-1 and miR-191 expression in pancreatic cancer

The aim of study was to discuss the correlation and regulatory mechanism of HIF-1 and miR-191 expression in pancreatic tumor. The association between the miR-191 and the clinicopathologic characteristics and the prognosis of pancreatic cancer was further explored. After hypoxic cultured for 6 and 12 h, qRT-PCR and Western blot were practiced to analyze the miR-191 and HIF-1 expression of MIA PaCa-2 and Aspac1 cells. We regulated the HIF-1 expression via plasmid and siRNA transfection to observe the alteration of HIF-1 and miR-191 expression. ChIP sequencing identified the binding sites of HIF-1 and miR-191. Dual luciferase assays were practiced to verify the binding sites. Immunohistochemical staining was practiced to analyze the expression of HIF-1, while qRT-PCR were done for investigating miR-191 in tumor tissues. Then, the association between the expression of them and the clinicopathologic characteristics and prognosis of pancreatic cancer were analyzed. After hypoxic cultured 12 h, the expression of HIF-1 protein, HIF-1mRNA and miR-191 of MIA PaCa-2 and AsPC-1 cells increased significantly (P < 0.05). After HIF-1 overexpressing plasmid transfected to the MIA PaCa-2 and AsPC-1 cells for 48 h, the expression of HIF-1 protein, HIF-1mRNA, and miR-191 upregulated significantly (P < 0.05). While after transfected the MIA PaCa-2 cells by HIF-1 siRNA, the significant decreasing of HIF-1 protein, HIF-1mRNA, and miR-191 expression were observed (P < 0.05). ChIP sequencing showed the protein synthesis of HIF-1 increased in hypoxia situation. Only the HRE5 (-1,169 bp, ChIP4) were significantly brighter in hypoxia in comparing with normoxic cells. In dual luciferase assays, after pGL3-miR-191 and HIF-1 overexpressing plasmid co-transfect the MIAPaCa-2 cells for 48 h, its relative expression of bioluminescence was higher than those co-transfected by mutant miR-191 vectors and HIF-1 overexpressing plasmid or by pGL3-miR-191 and HIF-1 empty plasmid. The expression of miR-191 closely associated with the tumor size, pTNM stage, lymph node metastasis, and perineural invasion (P < 0.05). Patients with higher expression of miR-191 were a risk factor for prognosis of pancreatic cancers. Expression of HIF-1 in pancreatic cancer cells increased under the condition of chronic hypoxia, which may bind to HRE2 in 5'flanking region of miR-191 and initiate transcription of miR-191. Expression of miR-191 was significantly higher in pancreatic tumor tissues. The expression of miR-191 closely associated with the tumor size, pTNM stage, lymph node metastasis and perineural invasion and poor prognosis of pancreatic cancer.

Genetic experimental preparations for studying atherosclerosis

Atherosclerosis is a pathological process with several inputs (biological, chemical, physiological, and others) interacting slowly over a lifetime leading to coronary artery disease, significant morbidity, and a limited lifespan. Over the past two decades, biologists have used experimental preparations from cells, animals, and man to understand the biology of atherosclerosis. Much has been discovered but our use of the standard gene-targeted experimental preparations is now nearing its limit. Better preparations to answer the remaining questions in the field of atherosclerosis biology are needed.

PCSK9 and resistin at the crossroads of the atherogenic dyslipidemia

The atherogenic dyslipidemia is a pathophysiological lipid triad, composed of high triglycerides and low-density lipoprotein and low high-density lipoprotein. The dyslipidemia is highly prevalent in individuals who are obese, insulin resistant and those with Type 2 diabetes and is the major contributing factor to the high atherosclerotic cardiovascular disease risk in these subjects. The primary initiating event in atherogenic dyslipidemia development is the hepatic overproduction of very-low-density lipoprotein (VLDL). The intracellular and extracellular protein triggers of hepatic VLDL production were not known until the recent identification of the causal roles of PCSK9 and resistin. Both PCSK9 and resistin act in large part by targeting and reducing the hepatic degradation of VLDL apoB through distinctly different mechanisms. In the current review, we discuss both the individual roles and the interaction of these proteins in driving atherogenic dyslipidemia, and thus, atherosclerotic cardiovascular disease progression in humans. We further explore the important therapeutic implications of these findings.

Familial hypercholesterolemia and atherosclerosis in cloned minipigs created by DNA transposition of a human PCSK9 gain-of-function mutant

Lack of animal models with human-like size and pathology hampers translational research in atherosclerosis. Mouse models are missing central features of human atherosclerosis and are too small for intravascular procedures and imaging. Modeling the disease in minipigs may overcome these limitations, but it has proven difficult to induce rapid atherosclerosis in normal pigs by high-fat feeding alone, and genetically modified models similar to those created in mice are not available. D374Y gain-of-function mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene cause severe autosomal dominant hypercholesterolemia and accelerates atherosclerosis in humans. Using Sleeping Beauty DNA transposition and cloning by somatic cell nuclear transfer, we created Yucatan minipigs with liver-specific expression of human D374Y-PCSK9. D374Y-PCSK9 transgenic pigs displayed reduced hepatic low-density lipoprotein (LDL) receptor levels, impaired LDL clearance, severe hypercholesterolemia, and spontaneous development of progressive atherosclerotic lesions that could be visualized by noninvasive imaging. This model should prove useful for several types of translational research in atherosclerosis.

Beyond LDL-C lowering: distinct molecular sphingolipids are good indicators of proprotein convertase subtilisin/kexin type 9 (PCSK9) deficiency

OBJECTIVES

Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) has been proposed to be a potential new therapeutic target for treatment of hypercholesterolaemia. However, little is known about the effects of PCSK9 inhibition on the lipidome.

METHODS

We performed molecular lipidomic analyses of plasma samples obtained from PCSK9-deficient mice, and serum of human carriers of a loss-of-function variant in the PCSK9 gene (R46L).

RESULTS

In both mouse and man, PCSK9 deficiency caused a decrease in several cholesteryl esters (CE) and short fatty acid chain containing sphingolipid species such as CE 16:0, glucosyl/galactosylceramide (Glc/GalCer) d18:1/16:0, and lactosylceramide (LacCer) d18:1/16:0. In mice, the changes in lipid concentrations were most prominent when animals were given regular chow diet. In man, a number of molecular lipid species was shown to decrease significantly even when LDL-cholesterol was non-significantly reduced by 10% only. Western diet attenuated the lipid lowering potency of PCSK9 deficiency in mice.

CONCLUSIONS

Plasma molecular lipid species may be utilized for characterizing novel compounds inhibiting PCSK9 and as sensitive efficacy markers of the PCSK9 inhibition.

PCSK9 siRNA suppresses the inflammatory response induced by oxLDL through inhibition of NF-κB activation in THP-1-derived macrophages

Proprotein convertase subtilisin/kexin 9 (PCSK9), a member of the protein-converting enzyme family, is highly expressed in adult hepatocytes and small intestinal enterocytes. To our knowledge, in this study, we demonstrate for the first time that PCSK9 is upregulated in a dose-dependent manner via oxidized low-density lipoprotein (oxLDL) stimulation in THP-1-derived macrophages. PCSK9 small interfering RNA (siRNA) suppresses the oxLDL-induced inflammatory cytokine expression in THP-1-derived macrophages. The exposure of macrophages to oxLDL markedly increased the expression of NF-κB protein in the nucleus. However, this effect was significantly attenuated by PCSK9 siRNA. These findings indicate that PCSK9 expression is induced by oxLDL, and that PCSK9 siRNA protects against inflammation via the inhibition of NF-κB activation in oxLDL-stimulated THP-1-derived macrophages. Our results suggest that PCSK9 may be used as a therapeutic target for the treatment of atherosclerosis since PCSK9 siRNA suppresses oxLDL-induced IκB-α degradation and NF-κB nuclear translocation into THP-1-derived macrophages.

Common and Low-Frequency Genetic Variants in the PCSK9 Locus Influence Circulating PCSK9 Levels

Objective —

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a circulating protein that influences plasma low-density lipoprotein concentration and susceptibility to coronary heart disease. Circulating PCSK9 levels show considerable interindividual differences, but the factors responsible for this variation are largely unknown.

Methods and Results—

We analyzed circulating PCSK9 levels in 4 cohorts of healthy, middle-aged Swedes (n=5722) and found that PCSK9 levels varied over ≈50-fold range, showed a positive relationship with plasma low-density lipoprotein–cholesterol concentration, and were associated with plasma triglyceride, fibrinogen, insulin, and glucose concentrations. A genome-wide association study conducted in 2 cohorts (n=1215) failed to uncover common genetic variants robustly associated with variation in circulating PCSK9 level. As expected, the minor allele of the PCSK9 R46L variant was in all cohorts associated with reduced PCSK9 levels and decreased plasma low-density lipoprotein–cholesterol concentrations, but no relationship was observed with the plasma triglyceride concentration. Further mapping of the PCSK9 locus revealed a common polymorphism (rs2479415, minor allele frequency 43.9%), located ≈6 kb upstream from PCSK9 , which is independently associated with increased circulating PCSK9 levels.

Conclusion—

Common and low-frequency genetic variants in the PCSK9 locus influence the pronounced interindividual variation in circulating PCSK9 levels in healthy, middle-aged white (predominantly Swedish) subjects.

Peroxisome Proliferator-activated receptor γ activation by ligands and dephosphorylation induces proprotein convertase subtilisin kexin type 9 and low density lipoprotein receptor expression

Proprotein convertase subtilisin kexin type 9 (PCSK9) plays an important role in cholesterol homeostasis by enhancing the degradation of LDL receptor (LDLR) protein. Peroxisome proliferator-activated receptor γ (PPARγ) has been shown to be atheroprotective. PPARγ can be activated by ligands and/or dephosphorylation with ERK1/2 inhibitors. The effect of PPARγ on PCSK9 and LDLR expression remains unknown. In this study, we investigated the effects of PPARγ on PCSK9 and LDLR expression. At the cellular levels, PPARγ ligands induced PCSK9 mRNA and protein expression in HepG2 cells. PCSK9 expression was induced by inhibition of ERK1/2 activity but inhibited by ERK1/2 activation. The mutagenic study and promoter activity assay suggested that the induction of PCSK9 expression by ERK1/2 inhibitors was tightly linked to PPARγ dephosphorylation. However, PPARγ activation by ligands or ERK1/2 inhibitors induced hepatic LDLR expression. The promoter assay indicated that the induction of LDLR expression by PPARγ was sterol regulatory element-dependent because PPARγ enhanced sterol regulatory element-binding protein 2 (SREBP2) processing. In vivo, administration of pioglitazone or U0126 alone increased PCSK9 expression in mouse liver but had little effect on PCSK9 secretion. However, the co-treatment of pioglitazone and U0126 enhanced both PCSK9 expression and secretion. Similar to in vitro, the increased PCSK9 expression by pioglitazone and/or U0126 did not result in decreased LDLR expression and function. In contrast, pioglitazone and/or U0126 increased LDLR protein expression and membrane translocation, SREBP2 processing, and CYP7A1 expression in the liver, which led to decreased total and LDL cholesterol levels in serum. Our results indicate that although PPARγ activation increased PCSK9 expression, PPARγ activation induced LDLR and CYP7A1 expression that enhanced LDL cholesterol metabolism.

Targeted In Situ Gene Correction of Dysfunctional APOE Alleles to Produce Atheroprotective Plasma ApoE3 Protein

Cardiovascular disease is the leading worldwide cause of death. Apolipoprotein E (ApoE) is a 34-kDa circulating glycoprotein, secreted by the liver and macrophages with pleiotropic antiatherogenic functions and hence a candidate to treat hypercholesterolaemia and atherosclerosis. Here, we describe atheroprotective properties of ApoE, though also potential proatherogenic actions, and the prevalence of dysfunctional isoforms, outline conventional gene transfer strategies, and then focus on gene correction therapeutics that can repair defective APOE alleles. In particular, we discuss the possibility and potential benefit of applying in combination two technical advances to repair aberrant APOE genes: (i) an engineered endonuclease to introduce a double-strand break (DSB) in exon 4, which contains the common, but dysfunctional, ε2 and ε4 alleles; (ii) an efficient and selectable template for homologous recombination (HR) repair, namely, an adeno-associated viral (AAV) vector, which harbours wild-type APOE sequence. This technology is applicable ex vivo, for example to target haematopoietic or induced pluripotent stem cells, and also for in vivo hepatic gene targeting. It is to be hoped that such emerging technology will eventually translate to patient therapy to reduce CVD risk.

Hypomethylation of the hsa-miR-191 locus causes high expression of hsa-mir-191 and promotes the epithelial-to-mesenchymal transition in hepatocellular carcinoma

hsa-miR-191 is highly expressed in hepatocellular carcinoma (HCC), but the factors regulating this elevated expression are unknown. This study aimed to investigate the epigenetic mechanisms of increased hsa-miR-191 expression by analyzing the relationship between the DNA methylation status of hsa-miR-191 and miR-191 expression. Methylation-specific polymerase chain reaction (PCR), bisulfite sequencing PCR, Northern blot, and quantitative real-time PCR were performed to examine hsa-miR-191 methylation and expression levels. Western blot, transwell, and scratch assays were performed to examine the function and molecular mechanisms of hsa-miR-191. Approximately 58.9% of hsa-miR-191 expression was higher in HCC tissues than in adjacent noncancerous tissues; this high expression was associated with poor prognosis. The hypomethylation observed in some HCC cell lines and HCC tissues was correlated with the hsa-miR-191 expression level. This correlation was validated by treatment with the 5-aza-DAC demethylation agent. The level of hypomethylation was 63.0% in 73 clinical HCC tissue samples and was associated with increased (2.1-fold) hsa-miR-191 expression. The elevated expression of hsa-miR-191 in the SMMC-771 HCC cell line induced the cells to transition into mesenchymal-like cells; they exhibited characteristics such as loss of adhesion, down-regulation of epithelial cell markers, up-regulation of mesenchymal cell markers, and increased cell migration and invasion. Inhibiting hsa-miR-191 expression in the SMMC-7721 cell line reversed this process (as assessed by cell morphology and cell markers). Furthermore, hsa-miR-191 probably exerted its function by directly targeting TIMP metallopeptidase inhibitor 3 and inhibiting TIMP3 protein expression. Our results suggest that hsa-miR-191 locus hypomethylation causes an increase in hsa-miR-191 expression in HCC clinical tissues and that this expression induces HCC cells to transition into mesenchymal-like cells.