Proprotein Convertase Subtilisin/kexin Type 9 Gene Research Articles

GENETIC RESEARCHES AMONG MALAYSIAN FAMILIAL HYPERCHOLESTEROLAEMIC POPULATION

ABSTRACT Background: Familial hypercholesterolaemia (FH) is one of the most frequent inherited metabolic disorders that can lead to a risk of premature cardiovascular disease. Publications on FH are mainly from western patients as there is little research on Asians, including Malaysians. The aim of this review is to provide an up-to- date information on Malaysian studies on FH genotyping and its relation to the phenotype of the affected patients. Method: A search was conducted for data from online databases on FH in Malaysia. Results: The mutation spectrum for FH among Malaysian patients was extremely broad. The gene variants were located mainly in the low-density lipoprotein receptor (LDLR) and apolipoprotein B-100 (APOB-100) genes rather than in the proprotein convertase subtilisin kexin type 9 (PCSK9) gene. The exon 9 and 14 were the hotspots in the LDLR gene. The most frequent mutation was p.Cys255Ser, at 12.5%, followed by p.Arg471Gly, at 11%, and the most common single nucleotide polymorphism (SNP) was c.1060+7 T>C at 11.7%. The LDLR gene variants were more common compared to the APOB-100 gene variants, while variants in the PCSK9 gene were very few. Phenotype-genotype associations were identified. Subjects with LDLR and APOB-100 genes mutations had a higher frequency of cardiovascular disease, a family history of hyperlipidaemia and tendon xanthoma and a higher low-density lipoprotein cholesterol (LDL-C) level than non-carriers. Conclusion: Research on Malaysian familial hypercholesterolaemic patients by individual groups is encouraging. However, more extensive molecular studies on FH on a national scale, with a screening of the disease-causing mutations together with a comprehensive genotype-phenotype association study, can lead to a better outcome for patients with the disease.

Molecular genetics of familial hypercholesterolemia in Israel–revisited

Background and aimsFamilial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the genes for LDL receptor (LDLR), apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type9 (PCSK9). The purpose of the current investigation was to define the current spectrum of mutations causing FH in Israel. MethodsNew families were collected through the MEDPED (Make Early Diagnosis Prevent Early Death) FH program. Molecular analysis of the LDLR, PCSK9 and APOB genes was done using High Resolution Melt and direct sequencing in 67 index cases. A 6-SNP LDL-C gene score calculation for polygenic hypercholesterolaemia was done using TaqMan genotyping. ResultsMean serum cholesterol was 7.48 ± 1.89 mmol/L and the mean serum LDL-C was 5.99 ± 1.89 mmol/L. Mutations in the LDLR and APOB gene were found in 24 cases (35.8%), with 16 in LDLR, none in PCSK9 and one, p.(R3527Q), in the APOB gene, which is the first APOB mutation carrier identified in the Israeli population. Of the LDLR mutations, two were novel; p.(E140A) and a promoter variant, c.-191C > A. The c.2479G > A p.(V827I) in exon 17 of the LDLR gene was found in 8 patients (33.3% of the mutations) with modestly elevated LDL-C, but also in a compound heterozygous patient with a clinical homozygous FH phenotype, consistent with this being a “mild” FH-causing variant. A significantly higher 6-SNP LDL-C score was found in mutation-negative cases compared with a normal Caucasian cohort (p = 0.03), confirming that polygenic inheritance of common LDL-C raising SNPs can produce an FH phenocopy. ConclusionsThe results indicate a different spectrum of genetic causes of FH from that found previously, in concordance with the heterogeneous and changing origins of the Israeli population, and confirm that a polygenic cause is also contributing to the FH phenotype in Israel.

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

ObjectiveLow-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. MethodsLiver 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. ResultsSPRET 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. ConclusionsCollectively, 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.

Integrative mutation, haplotype and G × G interaction evidence connects ABGL4, LRP8 and PCSK9 genes to cardiometabolic risk.

This study is expected to investigate the association of ATP/GTP binding protein-like 4 (AGBL4), LDL receptor related protein 8 (LRP8) and proprotein convertase subtilisin/kexin type 9 (PCSK9) gene single nucleotide variants (SNVs) with lipid metabolism in 2,552 individuals (Jing, 1,272 and Han, 1,280). We identified 12 mutations in this motif. The genotype and allele frequencies of these variants were different between the two populations. Multiple-locus linkage disequilibrium (LD) elucidated the detected sites are not statistically independent. Possible integrative haplotypes and gene-by-gene (G × G) interactions, comprising mutations of the AGBL4, LRP8 and PCSK9 associated with total cholesterol (TC, AGBL4 G-G-A, PCSK9 C-G-A-A and G-G-A-A-C-A-T-T-T-G-G-A), triglyceride (TG, AGBL4 G-G-A, LRP8 G-A-G-C-C, PCSK9 C-A-A-G, A-A-G-G-A-G-C-C-C-A-A-G and A-A-G-G-A-G-C-C-C-G-A-A), HDL cholesterol (HDL-C, AGBL4 A-A-G and A-A-G-A-A-G-T-C-C-A-A-G) and the apolipoprotein(Apo)A1/ApoB ratio (A1/B, PCSK9 C-A-A-G) in Jing minority. However, in the Hans, with TG (AGBL4 G-G-A, LRP8 G-A-G-C-C, PCSK9 C-A-A-G, A-A-G-G-A-G-C-C-C-A-A-G and A-A-G-G-A-G-C-C-C-G-A-A), HDL-C (LRP8 A-A-G-T-C), LDL-C (LRP8 A-A-G-T-C and A-A-G-A-A-G-T-C-C-A-A-G) and A1/B (LRP8 A-C-A-T-T and PCSK9 C-A-A-G). Association analysis based on haplotype clusters and G × G interactions probably increased power over single-locus tests especially for TG.

Abstract 12151: PCSK9 Mediates Atherogenesis

Background: Proprotein convertase subtilisin kexin type 9 (PCSK9) negatively regulates the low-density lipoprotein (LDL) receptor (LDLR), resulting in increased LDL cholesterol levels. We have suggested that PCSK9 regulates apolipoprotein B (apoB) metabolism via an autophagic process that is independent of the LDLR. Furthermore, whether PCSK9 plays a causal role in atherogenesis independent of LDLR has been controversial. Here, we investigated the molecular mechanisms by which PCSK9 modulates autophagy and the LDLR-independent effects of PCSK9 on atherogenesis. Methods and Results: Deletion of the PCSK9 gene from atherosclerosis prone LDb ( Ldlr-/-Apobec1-/-) mice resulted in substantially less atherosclerosis (> 4-fold), as well as a substantial reduction of plasma apoB, lipids, and triglyceride-rich lipoproteins, but increased HDL particles. The triple knockout mice had a decreased rate of apoB secretion resulting from increased autophagic flux. The deletion of PCSK9 also had profound influences on aortic endothelial cell response to exposure to LDL. LDL associated with PCSK9 increased the expression of TLR2, Lox-1, ICAM-1, CCL2, CCL7, IL-6, IL-1β, Beclin-1, p62, and TRAF6, compared to LDL without PCSK9. Conclusion: Deletion of PCSK9 markedly decreases apoB production by increasing autophagic flux. The absence of PCSK9 results in decreased lipid levels and marked reduction of atherosclerosis, independent of LDLR. The influence on atherogenesis is in part due to the direct effects of PCSK9 on endothelial cell receptors and on proinflammatory and autophagy molecules. These findings suggest that there may be clinical benefits of PCSK9 inhibition due to mechanisms unrelated to increased LDLR activity.

Role of lipoproteins and proprotein convertase subtilisin/kexin type 9 in endotoxin clearance in sepsis.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is a recent high-impact cardiovascular intervention aimed at reducing low-density lipoprotein (LDL) cholesterol levels. Notably, pathogen lipids are also carried in lipoprotein particles and are cleared by hepatocyte LDL receptors. Therefore, the role of PCSK9 in sepsis is reviewed. Endogenous PCSK9 decreases clearance of LDL cholesterol by decreasing the number of LDL receptors on hepatocytes. Similarly, PCSK9 decreases clearance of pathogen lipids, such as endotoxin, carried in LDL. Pathogen lipids, such as lipopolysaccharide (LPS) from gram-negative organisms or lipoteichoic acid from gram-positive organisms, are carried in high-density lipoprotein, LDL, and very low-density lipoprotein particles. Transfer proteins that handle pathogen lipids (e.g., LPS binding protein) are homologous to transfer proteins that handle cholesterol (e.g., phospholipid transfer protein, cholesterol ester transfer protein). Reduction in PCSK9 function results in increased LPS clearance, a decreased inflammatory response, and improved clinical outcomes in mice. PCSK9 inhibition improves survival in septic mice. Similarly, humans who carry loss-of-function variants of the PCSK9 gene have increased survival in sepsis. PCSK9 inhibition may be a useful strategy to increase pathogen lipid clearance in the treatment of patients with sepsis.

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.

Studying genetic resilience to improve human health.

In 2015, for the first time in three decades, novel lipid-lowering drugs for the treatment of hypercholesterolemia were approved by the FDA in the US and EMA in Europe (US Food and Drug Administration 2015a, US Food and Drug Administration 2015b, European Medicines Agency 2015a, European Medicines Agency 2015b). Proprotein convertase subtilisin/kexin type 9 (PCSK9), an enzyme encoded by the PCSK9 gene in humans, is the target of these novel therapeutics. In the early 2000s, PCSK9 was found to play a role in cholesterol homeostasis by promoting the degradation of the low-density lipoprotein (LDL) receptor in the liver, reducing its ability to remove LDL from circulation (Maxwell & Breslow, 2004, Park et al., 2004, Benjannet et al., 2004, Maxwell et al., 2005). At the same time, Dr. Helen H. Hobbs and Dr. Jonathan Cohen at UT-Southwestern had been studying people with very high and very low cholesterol. Based on its role in cholesterol metabolism, they sequenced the PCSK9 gene in people with very low cholesterol and found nonsense mutations that caused the PCSK9 enzyme to lose its function (Cohen et al., 2005). “Resilience” to hypercholesterolemia was conferred on individuals harboring loss-of-function mutations in the PCSK9 gene, opening the door for the development of drugs based on this novel mechanism of action. The pursuit of resilience through genome-wide analyses is now underway and will undoubtedly further our understanding of the biology of disease, provide promising therapeutic targets, and potentially improve human health and aging. This article is protected by copyright. All rights reserved.

PCSK9: Regulation and Target for Drug Development for Dyslipidemia.

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a secreted zymogen expressed primarily in the liver. PCSK9 circulates in plasma, binds to cell surface low-density lipoprotein (LDL) receptors, is internalized, and then targets the receptors to lysosomal degradation. Studies of naturally occurring PCSK9 gene variants that caused extreme plasma LDL cholesterol (LDL-C) deviations and altered atherosclerosis risk unleashed a torrent of biological and pharmacological research. Rapid progress in understanding the physiological regulation of PCSK9 was soon translated into commercially available biological inhibitors of PCSK9 that reduced LDL-C levels and likely also cardiovascular outcomes. Here we review the swift evolution of PCSK9 from novel gene to drug target, to animal and human testing, and finally to outcome trials and clinical applications. In addition, we explore how the genetics-guided path to PCSK9 inhibitor development exemplifies a new paradigm in pharmacology. Finally, we consider some potential challenges as PCSK9 inhibition becomes established in the clinic.

Disadvantages of Current LDL-cholesterol Lowering and the Role of PCSK9 Inhibitors.

LDL cholesterol (LDL-C) is a strong independent cardiovascular (CV) risk factor that can be easily influenced. Today, statins are the therapy of choice for the achievement of target LDL-C values. Although controlled clinical trials have demonstrated their effectiveness and safety, in practice we are often met with statin intolerance as well as a failure to achieve target LDL-C values in a significant portion of the patients despite maximal doses. In patients with high and very high CV risk, other antilipemic pharmacotherapy is often also insufficient. PCSK9 inhibitors (PCSK9-I) are new revolutionary drugs with a potent effect on LDL-C. The rapid development of PCSK9-I began in 2003 with the discovery of a PCSK9 gene mutation in patients with familial hypercholesterolemia. The product of this gene, proprotein convertase subtilisin/kexin type 9 (PCSK9), has an important role in the expression of LDL receptors and cholesterol metabolism. Animal models demonstrated that inactivation of the PCSK9 gene lowers LDL-C with regression of atherosclerotic changes in the aorta. Heterozygotes and homozygotes with the inactivation mutation of PCSK9 have lower LDL-C values and lower incidence of atherosclerosis. Among the various groups of PCSK9-I, monoclonal antibodies saw strong development (alirocumab, evolocumab, bococizumab). Phase 3 clinical trials on familial and primary hypercholesterolemia with statin intolerance or resistance have demonstrated a strong positive effect of alirocumab and evolocumab on LDL-C values (a reduction of 60%), with high safety and good tolerability. The OSLER study on evolocumab also demonstrated positive effects on CV outcomes. Multiple clinical trials on PCSK9-I are currently monitoring their effect on CV morbidity and mortality. Positive results from these studies would confirm the great potential of PCSK9-I for better prevention and treatment of CV diseases.

PCSK9: estructura y función. PCSK9 y receptor de lipoproteínas de baja densidad. Mutaciones y cambios derivados de estas

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein receptor (LDLr) and then targets it for lysosomal degradation in cells, thus preventing LDLr from recycling back to the hepatocyte surface, with a consequent decrease in LDLr density and clearance of LDL-cholesterol (LDLc). There have been reports of both gain-of-function mutations in the PCSK9 gene that cause a marked increase in LDLc conentrations and loss-of-function mutations, which lead to modest reductions in LDLc and low rates of coronary heart disease. The PCSK9 gene has become a promising therapeutic target to reduce blood cholesterol levels. This review discusses the most interesting recent data on PCSK9 regulation and its molecular function in cholesterol homeostasis.

Alirocumab

Alirocumab

E670G polymorphism of PCSK9 gene of patients with coronary heart disease among Han population in Hainan and three provinces in the northeast of China.

To investigate the correlation between E670G polymorphism of proprotein convertase subtilisin/kexin type 9 (PCSK9) gene and coronary heart disease (CHD), and contrastively study the regional differences of E670G polymorphism of PCSK9 gene between patients with CHD among the Han population in Hainan and three provinces in the northeast of China (TPNC), providing scientific basis for prevention and treatment of patients with CHD in different regions. A total of 233 cases of patients with CHD were selected from the Han population in Hainan and TPNC as the experimental group (118 cases from Hainan, 115 cases from TPNC), and 239 cases with non-CHD were selected among the Han population also in the two regions as control group (125 cases from Hainan, 114 cases from TPNC). The triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol and low density lipoprotein cholesterol (LDL-C) levels of plasma were tested and PCR-RFLP method was used to test the E670G polymorphism of PCSK9 gene. The statistical software package SPSS 21.0 was used for the statistical analysis and P<0.05 was considered as statistically significant. The levels of systolic pressure, diastolic blood pressure, fasting blood sugar, TC, TG, and LDL-C of patients in CHD group were significantly higher than those in non-CHD group, while the high density lipoprotein cholesterol level was lower than that in non-CHD group (P<0.05). In CHD group, the frequencies of AG, GG genotypes of PCSK9 gene and G allele were higher than those in non-CHD group (P<0.05), and in CHD group, the frequencies of AG, GG genotypes and G allele of patients both in Hainan and TPNC were higher than those in control group (P<0.05). Among the patients with CHD, the frequencies of GG genotype and G allele of patients in Hainan were lower than those in TPNC (P<0.05), and in CHD group, the levels of TG, TC and LDL-C of GG genotype were higher than those of AA genotype (P<0.05). While in non-CHD group, there were no significant differences between the frequencies of GG genotype and G allele of patients in Hainan and TPNC (P>0.05). There was a close correlation between the E670G polymorphism of PCSK9 gene and CHD with serum lipid level. Among Han population in Hainan and TPNC, the E670G polymorphism of PCSK9 gene of patients with CHD exhibited regional differences.

Association between the DOCK7, PCSK9 and GALNT2 Gene Polymorphisms and Serum Lipid levels.

This study was to determine the association between several single nucleotide polymorphisms (SNPs) in the dedicator of cytokinesis 7 (DOCK7), proprotein convertase subtilisin/kexin type 9 (PCSK9) and polypeptide N-acetylgalactosaminyltransferase 2 (GALNT2) and serum lipid levels. Genotyping of 9 SNPs was performed in 881 Jing subjects and 988 Han participants. Allele and genotype frequencies of the detected SNPs were different between the two populations. Several SNPs were associated with triglyceride (TG, rs10889332, rs615563, rs7552841, rs1997947, rs2760537, rs4846913 and rs11122316), high-density lipoprotein (HDL) cholesterol (rs1997947), low-density lipoprotein (LDL) cholesterol (rs1168013 and rs7552841), apolipoprotein (Apo) A1 (rs1997947), ApoB (rs10889332 and rs7552841), and ApoA1/ApoB ratio (rs7552841) in Jing minority; and with TG (rs10889332, rs615563, rs7552841, rs11206517, rs1997947, rs4846913 and rs11122316), HDL cholesterol (rs11206517 and rs4846913), LDL cholesterol (rs1168013), ApoA1 (rs11206517 and rs4846913), ApoB (rs7552841), and ApoA1/ApoB ratio (rs4846913) in Han nationality. Strong linkage disequilibria were noted among the SNPs. The commonest haplotype was G-C-G-C-T-G-C-C-G (>10%). The frequencies of C-C-G-C-T-G-T-C-G, G-C-A-C-T-G-C-C-G, G-C-G-C-T-A-C-C-A, G-C-G-C-T-G-C-C-A, G-C-G-C-T-G-T-C-A haplotypes were different between the two populations. Haplotypes could explain much more serum lipid variation than any single SNP alone especially for TG. Differences in lipid profiles between the two populations might partially attribute to these SNPs and their haplotypes.

Lower the Low-density Lipoprotein Cholesterol to the Level When You Born

Lower the Low-density Lipoprotein Cholesterol to the Level When You Born

Abstract 17990: Common PCSK9 Gain-of-function E32K Variant Carriers Reveal Milder LDL-C but Higher TG Elevation Compared With LDLR Mutations

Background: Proprotein convertase subtilisin kexin type 9 (PCSK9) gene is the third causal gene of familial hypercholesterolemia (FH), and is now an emerging therapeutic target. We have found Gain-of-function mutation E32K in PCSK9 gene is common in Japanese FH. We investigated clinical characteristics of gain-of-function PCSK9 variant carriers. Methods: A total of 940 Clinically diagnosed FH heterozygotes were investigated for LDLR, PCSK9, and APOB gene. High-resolution melting (HRM) method followed by Sanger sequence were used for point mutation, and multiplex ligation-dependent probe amplification methods were applied for large rearrangements in LDLR. Fasting lipid levels without lipid-lowering drugs were analyzed. Results: LDLR mutations were identified in 732 patients (78%) and 10% of them were large rearrangements. PCSK9 E32K mutation was identified in 56 patients (6%). No APOB mutations causing FH were identified, and 143 patients showed no known FH-gene mutations. LDLR mutation carriers showed significantly higher LDL-C (LDLR 268±73, PCSK9 198±82, No mutation 198±65 mg/dL, p &lt;0.001) and higher apoB (183±51, 130±49, 148±42 mg/dL, p &lt;0.001) compared with other two groups. On the other hand, PCSK9 and No mutation group had higher TG compared with LDLR mutations (126±94, 150±84, 145±74 mg/dL, p &lt;0.05 in log-transformed TG). Hypertriglyceridemia was common in PCSK9 mutation (25%, 41%, 36%, p &lt;0.01). HDL-C was higher in No mutation group (47±15, 51±51, 55±27 mg/dL, p &lt;0.01). Achilles tendon xanthoma was more frequent in LDLR mutations. Lp(a) levels did not significantly different with PCSK9 mutation. Results: PCSK9 gain-of-function mutation E32K showed mild LDL-C elevation, but with frequent hypertriglyceridemia. This result will support basic reports that PCSK9 regulates not only LDL-R degradation but also VLDL metabolism.

Abstract 9772: Antagonism of Rosuvastatin-induced Elevation of Circulating PCSK9 in Hamsters by Liver-specific Knockdown of HNF1α or HNF1β

Proprotein convertase subtilisin/kexin type 9 (PCSK9) induces hepatic LDL receptor (LDLR) degradation and lowers the removal of LDL-cholesterol from circulation. Thus, PCSK9 has become an important therapeutic target for the treatment of hypercholesterolemia. The transcription of PCSK9 is prominently controlled by the HNF1 binding motif embedded in its proximal promoter region that binds to HNF1α or HNF1β as homodimers or heterodimers. Our previous in vivo studies showed that only HNF1α but not HNF1β regulates PCSK9 transcription in mouse liver. Statin has been shown to elevate circulating PCSK9 levels through stimulating PCSK9 gene transcription, which reduces the clinical efficacy of statin in LDL-cholesterol reduction. In this study, we utilized adenoviral shRNA expression vectors (Ad-shHNF1α and Ad-shHNF1β) to generate liver specific knockdown of HNF1α or HNF1β in hamsters to examine the impact of reduced expression of HNF1 transcription factors on statin-induced elevation of PCSK9. Administration of rosuvastatin (RSV) at a daily dose of 15 mg/kg to hamsters infected with a control adenovirus significantly increased liver PCSK9 mRNA levels by 94% and serum PCSK9 levels by 37%. However, injection of Ad-shHNF1α into hamsters largely abolished the RSV-induced elevation of PCSK9 serum levels and hepatic mRNA levels, which was accompanied by a significant increase in liver LDLR protein abundance by 64% as compared to hamsters injected with control virus. Surprisingly, injection of Ad-shHNF1β produced similar inhibitory effects on the RSV-induced PCSK9 expression as that of Ad-shHNF1α. This was different from the negative results of HNF1β knockdown conducted in mice. In addition to changes in PCSK9 levels, we observed a modest but significant reduction in serum non-HDL cholesterol level after knockdown of HNF1α (27%) or HNF1β (32%) in hamsters treated with RSV. Altogether, our study demonstrates that unlike mice, 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 non-HDL cholesterol levels.

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

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

Evaluation of the Potential Role of Alirocumab in the Management of Hypercholesterolemia in Patients with High-Risk Cardiovascular Disease.

A high level of low-density lipoprotein cholesterol (LDL-C) has proved to have a positive correlation with mortality from cardiovascular disease, and it is the key modifiable risk factor for cardiovascular disease. Lowering levels of LDL-C with statins reduces both vascular morbidity and mortality; however, myalgias occur in 10% to 15% of patients, and many patients managed with statins achieve suboptimal levels of LDL-C. The injectable drug alirocumab-the first of a new class of drugs called proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors-is a monoclonal antibody to the PCSK9 gene, which regulates LDL receptor expression and circulating levels of LDL-C. In this review, we evaluated the efficacy and safety of alirocumab and its potential role in the management of patients with high-risk cardiovascular disease. Data were gathered from articles indexed in the PubMed database (2006-April 2015). All English-language, prospective, randomized, double-blinded trials evaluating the efficacy of alirocumab, as a monotherapy or in combination with statins, for treatment of hypercholesterolemia were identified. Five clinical trials were evaluated, and the results from these studies revealed that the use of alirocumab, both as monotherapy or in combination with statins, significantly reduced LDL-C levels. Patients treated with alirocumab, with or without statins, were more likely to achieve LDL-C goals of less than 100 or 70mg/dl compared with placebo. Despite its ability to lower LDL-C level, one study did not show any antiinflammatory activity (i.e., reduced C-reactive protein level) among patients who received alirocumab; however, more clinical trials will be needed to further assess this effect. Alirocumab also appears to cause regression of plaque. The most commonly reported adverse effect was mild injection-site reaction. With increased odds of statin discontinuation among patients taking high-intensity statins, alirocumab will contribute to atherosclerotic cardiovascular disease risk reduction. However, morbidity and mortality data, as well as long-term safety data, are pending. Therefore, we propose that alirocumab will better serve as an adjuvant therapy for the management of hypercholesterolemia in patients at high risk for cardiovascular events. As with all new promising injectable drugs, cost will also be a key consideration.

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.