Genetic variants in PCSK9 in the Japanese population: Rare genetic variants in PCSK9 might collectively contribute to plasma LDL cholesterol levels in the general population

The role of PCSK9 in heart failure and other cardiovascular diseases-mechanisms of action beyond its effect on LDL cholesterol

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a protein that regulates low-density lipoprotein (LDL) cholesterol metabolism by binding to the hepatic LDL receptor (LDLR), ultimately leading to its lysosomal degradation and an increase in LDL cholesterol (LDLc) levels. Treatment strategies have been developed based on blocking PCSK9 with specific antibodies (alirocumab, evolocumab) and on blocking its production with small regulatory RNA (siRNA) (inclisiran). Clinical trials evaluating these drugs have confirmed their high efficacy in reducing serum LDLc levels and improving the prognosis in patients with atherosclerotic cardiovascular diseases. Most studies have focused on the action of PCSK9 on LDLRs and the subsequent increase in LDLc concentrations. Increasing evidence suggests that the adverse cardiovascular effects of PCSK9, particularly its atherosclerotic effects on the vascular wall, may also result from mechanisms independent of its effects on lipid metabolism. PCSK9 induces the expression of pro-inflammatory cytokines contributing to inflammation within the vascular wall and promotes apoptosis, pyroptosis, and ferroptosis of cardiomyocytes and is thus involved in the development and progression of heart failure. The elimination of PCSK9 may, therefore, not only be a treatment for hypercholesterolaemia but also for atherosclerosis and other cardiovascular diseases. The mechanisms of action of PCSK9 in the cardiovascular system are not yet fully understood. This article reviews the current understanding of the mechanisms of PCSK9 action in the cardiovascular system and its contribution to cardiovascular diseases. Knowledge of these mechanisms may contribute to the wider use of PCSK9 inhibitors in the treatment of cardiovascular diseases.

Familial hypercholesterolemia with special focus on Japan

Familial hypercholesterolemia (FH) is an inherited disorder characterized by increased low-density lipoprotein LDL) cholesterol and atherosclerotic cardiovascular disease. Although initial genetic analysis linked FH to LDL receptor mutations, subsequent work demonstrated that a gain-of-function mutation in the proprotein convertase subtilisin/kexin type 9 (PCSK9), which causes LDL-R degradation, was shown to be the cause of FH. In this review, we describe the history of research on FH, its clinical phenotyping and genotyping and advances in treatment with special focus on Japan.

Meta-GWAS on PCSK9 concentrations reveals associations of novel loci outside the PCSK9 locus in White populations

BACKGROUND AND AIMS

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key regulator of lipid homeostasis. A few earlier genome-wide association studies (GWAS) investigated genetic variants associated with circulating PCSK9 concentrations. However, uncertainty remains about some of the genetic loci discovered beyond the PCSK9 locus. By conducting the largest PCSK9 meta-analysis of GWAS (meta-GWAS) so far, we aimed to identify novel loci and validate the previously reported loci that regulate PCSK9 concentrations.

METHODS

We performed GWAS for PCSK9 concentrations in two large cohorts (GCKD (n = 4,963) and KORA F3 (n = 2,895)). These were meta-analyzed with previously published data encompassing together 20,579 individuals. We further conducted a second meta-analysis in statin-naïve individuals (n = 15,390). A genetic risk score (GRS) was constructed on PCSK9-increasing SNPs and assessed its impact on the risk for coronary artery disease (CAD) in 394,943 statin-naïve participants (17,077 with events) of the UK Biobank by performing CAD-free survival analysis.

RESULTS

Nine loci were genome-wide significantly associated with PCSK9 concentrations. These included the previously described PCSK9, APOB, KCNA1/KCNA5, and TM6SF2/SUGP1 loci. All imputed SNPs in the PCSK9 locus account for ∼15% of variance of PCSK9 concentrations. We further identified FADS2 as a novel locus that was also found in statin-naïve participants. All imputed SNPs within the FADS2 locus explain ∼1.2% of variance of PCSK9 concentrations. Additionally, four further loci (a region on chromosome 5, SDK1, SPATA16 and HPR) were genome-wide significant in either the main model or the statin-naïve subset. The linear increase in a PCSK9 genetic risk score was associated with 1.41-fold (95%CI 1.16-1.72, p < 0.001) higher risk for incident CAD.

CONCLUSIONS

We identified five novel loci (FADS2, SPATA16, SDK1, HPR and a region on chromosome 5) for PCSK9 concentrations that would require further research. Additionally, we confirm the genome-wide significant loci that were previously detected.

Targeting PCSK9 to tackle cardiovascular disease

Lowering blood cholesterol levels efficiently reduces the risk of developing atherosclerotic cardiovascular disease (ASCVD), including coronary artery disease (CAD), which is the main cause of death worldwide. CAD is caused by plaque formation, comprising cholesterol deposits in the coronary arteries. Proprotein convertase subtilisin kexin/type 9 (PCSK9) was discovered in the early 2000s and later identified as a key regulator of cholesterol metabolism. PCSK9 induces lysosomal degradation of the low-density lipoprotein (LDL) receptor in the liver, which is responsible for clearing LDL-cholesterol (LDL-C) from the circulation. Accordingly, gain-of-function PCSK9 mutations are causative of familial hypercholesterolemia, a severe condition with extremely high plasma cholesterol levels and increased ASCVD risk, whereas loss-of-function PCSK9 mutations are associated with very low LDL-C levels and protection against CAD. Since the discovery of PCSK9, extensive investigations in developing PCSK9 targeting therapies have been performed. The combined delineation of clear biology, genetic risk variants, and PCSK9 crystal structures have been major drivers in developing antagonistic molecules. Today, two antibody-based PCSK9 inhibitors have successfully progressed to clinical application and shown to be effective in reducing cholesterol levels and mitigating the risk of ASCVD events, including myocardial infarction, stroke, and death, without any major adverse effects. A third siRNA-based inhibitor has been FDA-approved but awaits cardiovascular outcome data. In this review, we outline the PCSK9 biology, focusing on the structure and nonsynonymous mutations reported in the PCSK9 gene and elaborate on PCSK9-lowering strategies under development. Finally, we discuss future perspectives with PCSK9 inhibition in other severe disorders beyond cardiovascular disease.

Advanced progress of the relationship between PCSK9 monoclonal antibodies and hyperglycemic adverse events

Purpose of Review

Long-term use of statins had been confirmed to cause an increase in hyperglycemic adverse events (HAEs), whose mechanism has been well understood. Proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibodies (PCSK9-mAbs), a kind of new lipid-lowering drug, can effectively reduce plasma low-density lipoprotein cholesterol levels in patients with CHD and have been widely used. However, animal experiments, Mendelian randomization studies, clinical researches and Meta-analyses which focused on the relationship between PCSK9-mAbs and HAEs had reached different conclusions, which has attracted great attention from clinicians.

Recent Findings

The newest FOURIER-OLE randomized controlled trial followed PCSK9-mAbs users for over 8 years, whose results suggested that long-term use of PCSK9-mAbs did not increase the incidence of HAEs. Newest Meta-analyses also indicated that there was no relationship between PCSK9-mAbs and NOD. Meanwhile, genetic polymorphisms and variants related to PCSK9 might have effects on HAEs.

Conclusion

According to the results of current studies, there is no significant relationship between PCSK9-mAbs and HAEs. However, longer-term follow-up studies are still needed to confirm it. Although PCSK9 genetic polymorphisms and variants may affect the possible occurrence of HAEs, there is no need to perform relevant genetic testing before applying PCSK9-mAbs.

Proprotein convertase subtilisin/kexin type 9 genetic screening using the vervet (Chlorocebus aethiops) model

BACKGROUND

The proprotein convertase subtilisin/kexin type 9 (PCSK9) gene has come to prominence due to its reported function in the clearance of low-density lipoprotein cholesterol. The vervet monkey (Chlorocebus aethiops) was utilized to study the genetics of PCSK9 gene.

METHOD

Sixteen vervet monkeys were selected to screen for possible PCSK9 polymorphisms and to determine gene expression.

RESULTS

Four PCSK9 sequence variants (T112T, R148S, H177N and G635G) were identified and three of these variants (H177N, R148S, and G635G) were categorized as loss of function mutations. A decline in gene expression levels was also observed in animals harboring these three variants. Although the selected variants might have affected the level of gene expression in the selected animals, individual variation was also noticed in some of these individuals with the G635G variant.

CONCLUSION

Based on the findings obtained from this study, it is suggestive that the activity of PCSK9 was hindered.

Association study of PCSK9 SNPs (rs505151 & rs562556) and their haplotypes with CVDs in Indian population

BACKGROUND

Cardiovascular disease (CVD) has emerged as the most prevalent cause of death in India. Pro-protein Convertase Subtilisin/Kexin Type 9 (PCSK9) gene has been found to be associated with lipid levels and a biomarker for susceptibility of CVD.

AIM

To study the association of PCSK9 SNPs rs505151 & rs562556 and their haplotypes with CVDs in the Indian population.

SUBJECTS & METHODS

The present study comprised of 102 angiographically proven CVD patients & 100 healthy subjects. To study polymorphism, Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP) method was used. Biochemical parameters were analysed by enzymatic methods or automated analysers. Haplotype analysis was done using SHEsis software.

RESULTS

The dominant genetic model with an odds ratio (confidence interval) of 4.71 (2.59 - 8.5), (p value = .0001), shows the risk of CVDs. However, rs562556 (I474V) variant was not found to be associated with clinical parameters and risk of CVDs (p value >.05). Out of four haplotypes, H3 (G-A) was found to be associated with the CVDs (OR- 3.137, p value = .0001).

CONCLUSION

This study concludes that G allele of rs505151 SNP (PCSK9) and the H3 (G-A) haplotype of rs505151 & rs562556 were found to be risk factors for CVDs in the Indian population.

The R93C Variant of PCSK9 Reduces the Risk of Premature MI in a Chinese Han Population

Background: Dyslipidemia is a common risk factor for premature myocardial infarction (PMI). Our previous work has shown that single-nucleotide polymorphisms (SNPs) of LDLR, APOB, and PCSK9 are associated with dyslipidemia, but how these SNPs correlate with risk for PMI is unknown.

Objective: This study aims to evaluate the association between SNPs of LDLR, APOB, and PCSK9 and risk of PMI in Chinese Han population.

Methods: Two cohorts were established. In Cohort 1 (413 in the PMI group and 1,239 in the control group), SNPs of APOB, LDLR, and PCSK9 with minor allele frequency (MAF) > 1%, which has been shown to impact the risk of PMI in a Chinese Han population, were thoroughly examined, and gene–environment interactions were analyzed. A model for PMI risk prediction was developed in Cohort 1 and externally validated in Cohort 2 (577 in the PMI group and 270 in the control group).

Results: The distribution of the T allele at the PCSK9 R93C variant (rs151193009, C > T) was lower in the PMI group than that in the control group (PMI vs. Control in Cohort 1, 0.8% vs. 2.3%, P_adjust < 0.05; in Cohort 2, 1.0% vs. 2.4%, P_adjust < 0.05). The T allele at PCSK9 R93C variant (rs151193009, C > T) reduced the risk of PMI by ∼60% regardless of adjusting for confounding factors (in Cohort 1, adjusted odds ratio (OR) 0.354, 95% confidence interval (CI) 0.139–0.900, p = 0.029; in Cohort 2, adjusted OR 0.394, 95% CI 0.157–0.987, p = 0.047). No gene–environment interactions were observed between the R93C variant and diabetes/hypertension/smoking in PMI occurrence in this Chinese Han population. Our model showed good performance in predicting the risk of PMI in Cohort 1 (AUC 0.839, 95% CI 0.815–0.862, p < 0.001) and in an external cohort (AUC 0.840, 95% CI 0.810–0.871, p < 0.001).

Conclusions: The PCSK9 R93C variant was associated with significantly reduced risk of PMI in the Chinese Han population, and the model we developed performed well in predicting PMI risk in this Chinese Han population.

A Resuscitated Case of Acute Myocardial Infarction with both Familial Hypercholesterolemia Phenotype Caused by Possibly Oligogenic Variants of the PCSK9 and ABCG5 Genes and Type I CD36 Deficiency

A 56-year-old postmenopausal woman with out-of-hospital cardiac arrest caused by acute myocardial infraction was successfully resuscitated by intensive treatments and recovered without any neurological disability. She was diagnosed as having familial hypercholesterolemia (FH) based on a markedly elevated low-density lipoprotein cholesterol (LDL-C) level and family history of premature coronary artery disease. Genetic testing in her family members showed that a variant of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene (c.2004C＞A, p.S668R), which had been previously reported as having uncertain significance, was associated with FH, indicating that the variant is a potential candidate for the FH phenotype. Next-generation sequencing analysis for the proband also showed that there was a heterozygous mutation of the ATP-binding cassette sub-family G member 5 ( ABCG5) gene (c.1166G＞A, R389H), which has been reported to increase LDL-C level and the risk of cardiovascular disease. She was also diagnosed as having type 1 CD36 deficiency based on a lack of myocardial uptake of 123I-labeled 15-(p-iodophenyl)-3-R,S-methyl-pentadecanoic acid in scintigraphy and the absence of CD36 antigen in both monocytes and platelets in flow cytometry. She had a homozygous mutation of the CD36 gene (c.1126-5_1127delTTTAGAT), which occurs in a canonical splice site (acceptor) and is predicted to disrupt or distort the normal gene product. To our knowledge, this is the first report of a heterozygous FH phenotype caused by possibly oligogenic variants of the PCSK9 and ABCG5 genes complicated with type I CD36 deficiency caused by a novel homozygous mutation. Both FH phenotype and CD36 deficiency might have caused extensive atherosclerosis, leading to acute myocardial infarction in the present case.

Association Between Circulating Proprotein Convertase Subtilisin/Kexin Type 9 Concentrations and Cardiovascular Events in Cardiovascular Disease: A Systemic Review and Meta-Analysis

Background: A large amount of evidence suggests that proprotein convertase subtilisin/Kexin type 9 (PCSK9) inhibitors have clinical benefits in patients with cardiovascular disease (CVD). However, whether PCSK9 concentrations predict future cardiovascular (CV) events remains unclear.

Methods: We conducted a meta-analysis to investigate the ability of PCSK9 concentrations to predict future CV events in patients with established CVD. A comprehensive search of electronic databases was conducted in June 2021. We included relative risk (RR) estimates with 95% CI or events of interest.

Results: Eleven cohort studies including 8,471 patients with CVD were enrolled. The pooled RR of CV events for the increase in the circulating baseline PCSK9 concentrations by 1 SD showed a positive association in a random-effect model (RR 1.226, 95% CI: 1.055–1.423, P = 0.008). Similarly, the risk of the total CV events increased by 52% in the patients in the highest tertile compared with those in the lowest tertile of circulating PCSK9 concentrations (RR 1.523, 95% CI: 1.098–2.112, P = 0.012). The association between PCSK9 and CV events was stronger in stable patients with CVD, patients treated with statins, and Asian patients.

Conclusions: High PCSK9 concentrations are significantly related to the increased risk of future CV events. These results enrich the knowledge of PCSK9 function and suggest the further possible clinical role of PCSK9 inhibitors.

PCSK9 Gene Participates in the Development of Primary Dyslipidemias

Dyslipidemias are a group of diseases, which are characterized by abnormal blood concentrations of cholesterol, triglycerides and/or low-density lipoprotein-cholesterol (LDL-c). Dyslipidemia is a determinant condition for the progress of an atherosclerotic plaque formation. The resulting atherogenicity is due to at least two mechanisms: first, to the accumulation in the plasma of lipid particles that have the capacity to alter the function of the endothelium and deposit at the atheromatous plaque, and second, at an insufficient concentration of multifactorial type of high density lipoprotein-cholesterol (HDL-c), whose function is to protect against the development of atherosclerosis. Its highest prevalence is encountered among individuals with diabetes, hypertension or overweight. Hyperlipidemia is one of the main predisposing factors for the development of cardiovascular disease. Hyperlipidemia can be the result of a genetic condition, the secondary expression of a primary process or the consequence of exogenous factors (food, cultural, socio-economic, etc.), all of which lead to the elevation of plasma lipid levels. The objective of this study was to carry out an analysis of the genes involved in the development of dyslipidemias that lead to cardiovascular disease with special emphasis on the proprotein convertase subtilin/kexin type 9 (PCSK9) gene. The PCSK9 gene participates in the development of primary dyslipidemias, mainly familial hypercholesterolemia, currently the pharmacological treatment of choice to reduce LDL-c are statins, however, it has been observed that these have been insufficient to eliminate cardiovascular risk, especially in subjects with primary forms of hypercholesterolemia related to genetic mutations, or statin intolerance.

Normal plasma apoB48 despite the virtual absence of apoB100 in a compound heterozygote with novel mutations in the MTTP gene

"Normotriglyceridemic abetalipoproteinemia (ABL)" was originally described as a clinical entity distinct from either ABL or hypobetalipoproteinemia. Subsequent studies identified mutations in APOB gene which encoded truncated apoB longer than apoB48. Therefore, "Normotriglyceridemic ABL" can be a subtype of homozygous familial hypobetalipoproteinemia 1. Here, we report an atypical female case of ABL who was initially diagnosed with "normotriglyceridemic ABL", because she had normal plasma apoB48 despite the virtual absence of apoB100 and low plasma TG level. Next generation sequencing revealed that she was a compound heterozygote of two novel MTTP mutations: nonsense (p.Q272X) and missense (p.G709R). We speculate that p.G709R might confer residual triglyceride transfer activity of MTTP preferentially in the intestinal epithelium to the hepatocytes, allowing production of apoB48. Together, "normotriglyceridemic ABL" may be a heterogenous disorder which is caused by specific mutations in either APOB or MTTP gene.

Familial hypercholesterolemia in Southeast and East Asia

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Even though at least a quarter of the world's FH population lives in Southeast and East Asia, there are substantial gaps in knowledge regarding the epidemiology of FH due to low awareness, the absence of national screening programs, and limited availability of genetic testing.

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We discuss the most recent and relevant information available related to diagnostic criteria, prevalence, awareness, clinical characteristics, genetic epidemiology, and treatment in the FH population of Southeast and East Asia.

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Increasing awareness and improving the diagnosis and management of FH will reduce the burden of premature CHD in these regions of the world.

Familial hypercholesterolemia (FH) is a relatively common autosomal dominant disorder associated with a significantly increased risk of coronary heart disease (CHD). Most (~85–90%) cases are due to pathogenic variants in the LDL-receptor gene (LDLR), while the remaining are due to pathogenic variants in the apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes, though the proportion may vary depending on geographic location. Even though at least a quarter of the world's FH population lives in Southeast and East Asia, there are substantial gaps in knowledge regarding the epidemiology of FH due to low awareness, the absence of national screening programs, and limited availability of genetic testing. In this review, we discuss the most recent and relevant information available related to diagnostic criteria, prevalence, awareness, clinical characteristics, genetic epidemiology, and treatment in the FH population of Southeast and East Asia. Increasing awareness and improving the diagnosis and management of FH will reduce the burden of premature CHD in these regions of the world.

Molecular diagnosis methods in familial hypercholesterolemia

Familial hypercholesterolemia (FH) is considered the genetic cause of coronary heart disease and ischemic stroke. FH is mainly an autosomal codominant pattern-based disorder and is primarily determined by point mutations within the low-density lipoprotein receptor, apolipoprotein B, and proprotein convertase subtilisin/kexin type 9 genes, causing increased low-density lipoprotein cholesterol levels in the serum of untreated individuals. The accumulation will eventually lead to atherosclerotic cardiovascular disease. Although clinical criteria comprising several prognosis scores, such as the Simon Broome, Dutch Lipid Clinic Network, Make Early Diagnosis to Prevent Early Death, and the recently proposed Montreal-FH-SCORE, are the conventional basis of diagnosing FH, the genetic diagnosis made by single nucleotide polymorphism genotyping, multiplex ligation-dependent probe amplification analysis, and sequencing (both Sanger and Next-Generation sequencing) offers unequivocal diagnosis. Given the heterogeneity of known mutations, the genetic diagnosis of FH is often difficult to establish, despite the growing evidence of the causative mutations, as well as the polygenic aspect of this pathology and the importance of cascade screening of the FH patient’s healthy family members. This review article details different genetic techniques that can be used in FH identification when there is a clinical FH suspicion based on criteria comprised in prognosis scores, knowing that none of these are exhaustive in the diagnosis, yet they efficaciously overlap and complement each other for confirming the disease at the molecular level.

Novel PCSK9 (Proprotein Convertase Subtilisin Kexin Type 9) Variants in Patients With Familial Hypercholesterolemia From Cape Town

OBJECTIVE

Familial hypercholesterolemia (FH) is characterized by elevated low-density lipoprotein-cholesterol and markedly increased cardiovascular risk. In patients with a genetic diagnosis, low-density lipoprotein receptor (LDLR) mutations account for >90% of cases, apolipoprotein B (APOB) mutations for ≈5% of cases, while proprotein convertase subtilisin kexin type 9 (PCSK9) gain of function mutations are rare (<1% of cases). We aimed to evaluate the functional impact of several novel PCSK9 variants in a cohort of patients with FH by genetic cascade screening and in vitro functionality assays. Approach and Results: Patients with clinically diagnosed FH underwent genetic analysis of LDLR, and if negative, sequential testing of APOB and PCSK9. We analyzed cosegregation of hypercholesterolemia with novel PCSK9 variants. Gain of function status was determined by in silico analyses and validated by in vitro functionality assays. Among 1055 persons with clinical FH, we identified nonsynonymous PCSK9 variants in 27 (2.6%) patients and 7 of these carried one of the 4 previously reported gain of function variants. In the remaining 20 patients with FH, we identified 7 novel PCSK9 variants. The G516V variant (c.1547G>T) was found in 5 index patients and cascade screening identified 15 additional carriers. Low-density lipoprotein-cholesterol levels were higher in these 15 carriers compared with the 27 noncarriers (236±73 versus 124±35 mg/dL; P<0.001). In vitro studies demonstrated the pathogenicity of the G516V variant.

CONCLUSIONS

In our study, 1.14% of cases with clinical FH were clearly attributable to pathogenic variants in PCSK9. Pathogenicity is established beyond doubt for the G516V variant.

PCSK9 Variants in Familial Hypercholesterolemia: A Comprehensive Synopsis

Autosomal dominant familial hypercholesterolemia (FH) affects approximately 1/250, individuals and potentially leads to elevated blood cholesterol and a significantly increased risk of atherosclerosis. Along with improvements in detection and the increased early diagnosis and treatment, the serious burden of FH on families and society has become increasingly apparent. Since FH is strongly associated with proprotein convertase subtilisin/kexin type 9 (PCSK9), increasing numbers of studies have focused on finding effective diagnostic and therapeutic methods based on PCSK9. At present, as PCSK9 is one of the main pathogenic FH genes, its contribution to FH deserves more explorative research.

Physiology and role of PCSK9 in vascular disease: Potential impact of localized PCSK9 in vascular wall

Proprotein convertase subtilisin/kexin type-9 (PCSK9), a member of the proprotein convertase family, is an important drug target because of its crucial role in lipid metabolism. Emerging evidence suggests a direct role of localized PCSK9 in the pathogenesis of vascular diseases. With this in our consideration, we reviewed PCSK9 physiology with respect to recent development and major studies (clinical and experimental) on PCSK9 functionality in vascular disease. PCSK9 upregulates low-density lipoprotein (LDL)-cholesterol levels by binding to the LDL-receptor (LDLR) and facilitating its lysosomal degradation. PCSK9 gain-of-function mutations have been confirmed as a novel genetic mechanism for familial hypercholesterolemia. Elevated serum PCSK9 levels in patients with vascular diseases may contribute to coronary artery disease, atherosclerosis, cerebrovascular diseases, vasculitis, aortic diseases, and arterial aging pathogenesis. Experimental models of atherosclerosis, arterial aneurysm, and coronary or carotid artery ligation also support PCSK9 contribution to inflammatory response and disease progression, through LDLR-dependent or -independent mechanisms. More recently, several clinical trials have confirmed that anti-PCSK9 monoclonal antibodies can reduce systemic LDL levels, total nonfatal cardiovascular events, and all-cause mortality. Interaction of PCSK9 with other receptor proteins (LDLR-related proteins, cluster of differentiation family members, epithelial Na⁺ channels, and sortilin) may underlie its roles in vascular disease. Improved understanding of PCSK9 roles and molecular mechanisms in various vascular diseases will facilitate advances in lipid-lowering therapy and disease prevention.

Regions of conformational flexibility in the proprotein convertase PCSK9 and design of antagonists for LDL cholesterol lowering

The proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates plasma LDL cholesterol levels by binding to the liver LDL receptor (LDLR) and promoting its degradation. Therefore, PCSK9 has become a compelling new therapeutic target for lipid lowering and the prevention of cardiovascular disease. PCSK9 contains two regions of conformational flexibility, the N-terminal regions of the prodomain and of the catalytic domain. The recognition that the latter region, the so-called P′ helix, is able to transition from an α-helical to a disordered state gave rise to new strategies to develop small molecule inhibitors of PCSK9 for lipid lowering. In the ordered state the P′ helix is buried in a groove of the PCSK9 catalytic domain located next to the main LDLR binding site. The transition to a disordered state leaves the groove site vacated and accessible for compounds to antagonize LDLR binding. By use of a groove-directed phage display strategy we were able to identify several groove-binding peptides. Based on structural information of PCSK9-peptide complexes, a minimized groove-binding peptide was generated and utilized as an anchor to extend towards the adjacent main LDLR binding site, either by use of a phage-displayed peptide extension library, or by appending organic moieties to yield organo-peptides. Both strategies led to antagonists with pharmacologic activities in cell-based assays. The intricate bipartite mechanism of the potent organo-peptide inhibitors was revealed by structural studies, showing that the core peptide occupies the N-terminal groove, while the organic moiety interacts with the LDLR binding site to create antagonism. These findings validate the PCSK9 groove as an attractive target site and should inspire the development of a new class of small molecule antagonists of PCSK9.

New Pharmacological Approaches to Target PCSK9

PURPOSE OF REVIEW

Proprotein convertase subtilisin kexin 9 (PCSK9) plays a crucial role in regulating circulating levels of LDL-C as a consequence of its ability to inhibit LDL receptor recycling in the liver. Loss of function variants in the PCSK9 gene result in low LDL-C levels and associate with reduced cardiovascular risk, whereas gain of-function variants associate with hypercholesterolemia and increased risk of early cardiovascular events. Thus, PCSK9 inhibition has been established as an additional approach for the treatment of hypercholesterolemia. The aim of this review is to provide a brief overview of current strategies targeting PCSK9 and discuss clinical results of the emerging approaches.

RECENT FINDINGS

Two monoclonal antibodies targeting circulating PCSK9 (evolocumab and alirocumab) have been approved for the treatment of hypercholesterolemia and cardiovascular disease. Later, a gene silencing approach (inclisiran), which inhibits hepatic PCSK9 synthesis, was shown to be as effective as monoclonal antibodies but with a twice a year injection and is currently under evaluation for approval. Due to the elevated costs of such therapies, several other approaches have been explored, including peptide-based anti PCSK9 vaccination, and small oral PCSK9 inhibitors, which are still in preclinical phase. In the coming years, we will assist to a progressive introduction of novel anti-PCSK9 approaches in the clinical practice for the treatment of patients with hypercholesterolemia as well as patients at high cardiovascular risk.

Fragment-based design of small molecule PCSK9 inhibitors using simulated annealing of chemical potential simulations

PCSK9 is a protein secreted by the liver that binds to the low-density lipoprotein receptor (LDLR), causing LDLR internalization, decreasing the clearance of circulating LDL particles. Mutations in PCSK9 that strengthen its interactions with LDLR result in familial hypercholesterolemia (FH) and early onset atherosclerosis, while nonsense mutations of PCSK9 result in cardio-protective hypocholesterolemia. These observations led to PCSK9 inhibition for cholesterol lowering becoming a high-interest therapeutic target, with antibody drugs reaching the market. An orally-available small molecule drug is highly desirable, but inhibiting the PCSK9/LDLR protein-protein interaction (PPI) has proven challenging. Alternate approaches to finding good lead candidates are needed. Motivated by the FH mutation data on PCSK9, we found that modeling the PCSK9/LDLR interface revealed extensive electron delocalization between and within the protein partners. Based on this, we hypothesized that compounds assembled from chemical fragments could achieve the affinity required to inhibit the PCSK9/LDLR PPI if they were selected to interact with PCSK9 in a way that, like LDLR, also involves significant fractional charge transfer to form partially covalent bonds. To identify such fragments, Simulated Annealing of Chemical Potential (SACP) fragment simulations were run on multiple PCSK9 structures, using optimized partial charges for the protein. We designed a small molecule, composed of several fragments, predicted to interact at two sites on the PCSK9. This compound inhibits the PPI with 1 μM affinity. Further, we designed two similar small molecules where one allows charge delocalization though a linker and the other doesn’t. The first inhibitor with charge delocalization enhances LDLR surface expression by 60% at 10 nM, two orders of magnitude more potent than the EGF domain of LDLR. The other enhances LDLR expression by only 50% at 1 μM. This supports our conjecture that fragments can have surprisingly outsized efficacy in breaking PPI’s by achieving fractional charge transfer leading to partially covalent bonding.

Genotyping and Frequency of PCSK9 Variations Among Hypercholesterolemic and Diabetic Subjects

Non-synonymous single-nucleotide polymorphism (SNPs) in the gene for proprotein convertase subtilisin/kexin type 9 (PCSK9) can influence cholesterol and glucose metabolism, leading to increased risk of cardiovascular disease and diabetes. To determine the frequency of four common PCSK9 SNPs, L10Ins, A56V, I474V, and E670G, in a population sample (n = 98) of the Hail region of Kingdom of Saudi Arabia. Blood was collected from participants; serum cholesterol, blood glucose and glycated hemoglobin were determined; genomic DNA was extracted and PCR amplicons from SNP-containing PCSK9 exons were subjected to Sanger sequencing. Out of 98 participants. 10 (10.20%) carried none of the SNPs, 2 (2.04%) the L10ins/A56V linked SNPs, 35 (35.71%) the I474V SNP, 22 (22.45%) both the I474V and E670G SNPs, and 29 (29.59%) the E670G SNP. Of the 30 eucholesterolemic diabetics patients, 11 (36.66%) carried the I474V SNP, 10 (33.33%) the E679G SNP and 6 (20%) the I474V/E679G. SNPs. Of 63 diabetic patients, 26 (41.26%) carry I474V SNP and 22 (34.92%) carry E670G SNP. Our data demonstrated that the I474V and E670G PCSK9 variants are very frequent in the Hail region of Saudi Arabia and are found at even higher frequency among diabetics. Further investigations are needed to determine whether these variations or another variant segregating with them can explain its apparent association with diabetes in this population.

Ser-Phosphorylation of PCSK9 (Proprotein Convertase Subtilisin-Kexin 9) by Fam20C (Family With Sequence Similarity 20, Member C) Kinase Enhances Its Ability to Degrade the LDLR (Low-Density Lipoprotein Receptor)

OBJECTIVE

PCSK9 (proprotein convertase subtilisin-kexin 9) enhances the degradation of the LDLR (low-density lipoprotein receptor) in endosomes/lysosomes. This study aimed to determine the sites of PCSK9 phosphorylation at Ser-residues and the consequences of such posttranslational modification on the secretion and activity of PCSK9 on the LDLR. Approach and Results: Fam20C (family with sequence similarity 20, member C) phosphorylates serines in secretory proteins containing the motif S-X-E/phospho-Ser, including the cholesterol-regulating PCSK9. In situ hybridization of Fam20C mRNA during development and in adult mice revealed a wide tissue distribution, including liver, but not small intestine. Here, we show that Fam20C phosphorylates PCSK9 at Serines 47, 666, 668, and 688. In hepatocytes, phosphorylation enhances PCSK9 secretion and maximizes its induced degradation of the LDLR via the extracellular and intracellular pathways. Replacing any of the 4 Ser by the phosphomimetic Glu or Asp enhanced PCSK9 activity only when the other sites are phosphorylated, whereas Ala substitutions reduced it, as evidenced by Western blotting, Elisa, and LDLR-immunolabeling. This newly uncovered PCSK9/LDLR regulation mechanism refines our understanding of the implication of global PCSK9 phosphorylation in the modulation of LDL-cholesterol and rationalizes the consequence of natural mutations, for example, S668R and E670G. Finally, the relationship of Ser-phosphorylation to the implication of PCSK9 in regulating LDL-cholesterol in the neurological Fragile X-syndrome disorder was investigated.

CONCLUSIONS

Ser-phosphorylation of PCSK9 maximizes both its secretion and activity on the LDLR. Mass spectrometric approaches to measure such modifications were developed and applied to quantify the levels of bioactive PCSK9 in human plasma under normal and pathological conditions.

Structure and Function of Proprotein Convertase Subtilisin/kexin Type 9 (PCSK9) in Hyperlipidemia and Atherosclerosis

Background:

One of the important factors in Low-Density Lipoprotein (LDL) metabolism is the LDL receptor (LDLR) by its capacity to bind and subsequently clear cholesterol derived from LDL (LDL-C) in the circulation. Proprotein Convertase Subtilisin-like Kexin type 9 (PCSK9) is a newly discovered serine protease that destroys LDLR in the liver and thereby controls the levels of LDL in plasma. Inhibition of PCSK9-mediated degradation of LDLR has, therefore, become a novel target for lipid-lowering therapy.

Methods:

We review the current understanding of the structure and function of PCSK9 as well as its implications for the treatment of hyperlipidemia and atherosclerosis.

Results:

New treatments such as monoclonal antibodies against PCSK9 may be useful agents to lower plasma levels of LDL and hence prevent atherosclerosis.

Conclusion:

PCSK9's mechanism of action is not yet fully clarified. However, treatments that target PCSK9 have shown striking early efficacy and promise to improve the lives of countless patients with hyperlipidemia and atherosclerosis.

Effects of familial hypercholesterolemia-associated genes on the phenotype of premature myocardial infarction

Background

The incidence of premature myocardial infarction (PMI) has gradually increased in recent years. Genetics plays a central role in the development of PMI. Familial hypercholesterolemia (FH) is one of the most common genetic disorders of cholesterol metabolism leading to PMI.

Objective

This study investigated the relationship between FH-associated genes and the phenotype of PMI to clarify the genetic spectrum of PMI diseases.

Method

This study enrolled PMI patients (n = 225) and detected the mutations in their FH-associated genes (LDLR, APOB, PCSK9, LDLRAP1) by Sanger sequencing. At the same time, patients free of PMI (non-FH patients, n = 56) were enrolled as control, and a logistic regression analysis was used to identify risk factors associated with PMI. The diagnosis of FH was confirmed using “2018 Chinese expert consensus of FH screening and diagnosis” before the prevalence and clinical features of FH were analyzed.

Results

Pathogenic mutations in LDLR, APOB, PCSK9 and LDLRAP1 genes were found in 17 of 225 subjects (7.6%), and all mutations were loss of function (LOF) and heterozygous. The genotype-phenotype relationship of patients carrying FH-associated mutations showed high heterogeneity. The logistic regression analysis showed that the smoking history, obesity and the family history of premature CHD were independent risk factors of PMI. In this study, a total of 19 patients (8.4%) were diagnosed as FH, and the proportion of smoking subjects in FH patients was higher than that in non-FH patients.

Conclusions

FH-associated gene mutations were present in about 7.6% of Chinese patients with PMI. In addition to genetic factors, smoking history, lifestyle and other environmental factors may play a synergistic role in determining the phenotype of PMI.

Trial registration

Essential gene mutation of cholesterol metabolism in patients with premature myocardial infarction. ChiCTR-OCH-12002349.Registered 26 December 2014, http://www.chictr.org.cn/showproj.aspx?proj=7201.

Identification of a Helical Segment within the Intrinsically Disordered Region of the PCSK9 Prodomain

Proprotein convertase subtilisin/kexin 9 (PCSK9) is a key regulator of lipid metabolism by degrading liver LDL receptors. Structural studies have provided molecular details of PCSK9 function. However, the N-terminal acidic stretch of the PCSK9 prodomain (Q31-T60) has eluded structural investigation, since it is in a disordered state. The interest in this region is intensified by the presence of human missense mutations associated with low and high LDL-c levels (E32K, D35Y, and R46L, respectively), as well as two posttranslationally modified sites, sulfated Y38 and phosphorylated S47. Herein we show that a segment within this region undergoes disorder-to-order transition. Experiments with acidic stretch-derived peptides demonstrated that the folding is centered at the segment Y38-L45, which adopts an α-helix as determined by NMR analysis of free peptides and by X-ray crystallography of peptides in complex with antibody 6E2 (Ab6E2). In the Fab6E2-peptide complexes, the structured region features a central 2 1/4-turn α-helix and encompasses up to 2/3 of the length of the acidic stretch, including the missense mutations and posttranslationally modified sites. Experiments with helix-breaking proline substitutions in peptides and in PCSK9 protein indicated that Ab6E2 specifically recognizes the helical conformation of the acidic stretch. Therefore, the observed quantitative binding of Ab6E2 to native PCSK9 from various cell lines suggests that the disorder-to-order transition is a true feature of PCSK9 and not limited to peptides. Because the helix provides a constrained spatial orientation of the missense mutations and the posttranslationally modified residues, it is probable that their biological functions take place in the context of an ordered conformational state.

Blood lipid-related low-frequency variants in LDLR and PCSK9 are associated with onset age and risk of myocardial infarction in Japanese

Recent studies have revealed the importance of rare variants in myocardial infarction (MI) susceptibility in European populations. Because genetic architectures vary in different populations, we investigated how they contribute to MI susceptibility in Japanese subjects. We performed targeted sequencing of 36 coronary artery disease risk genes, identified by genome-wide association studies, in 9,956 cases and 8,373 controls. Gene-based association tests identified significant enrichment of rare variants in LDLR and PCSK9 in MI cases. We identified 52 (novel 22) LDLR variants predicted to be damaging. Carriers of these variants showed a higher risk of MI (carriers/non-carriers 89/9867 in cases, 17/8356 controls, OR = 4.4, P = 7.2 × 10⁻¹⁰), higher LDL-cholesterol levels and younger age of onset for MI. With respect to PCSK9, E32K carriers showed higher LDL-cholesterol levels and younger age of onset for MI, whereas R93C carriers had lower LDL-cholesterol levels. A significant correlation between LDL-cholesterol levels and onset age of MI was observed in these variant carriers. In good agreement with previous studies in patients with familial hypercholesterolaemia, our study in the Japanese general population showed that rare variants in LDLR and PCSK9 were associated with the onset age of MI by altering LDL-cholesterol levels.

Malaria severity: Possible influence of the E670G PCSK9 polymorphism: A preliminary case-control study in Malian children

Aim

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is a hepatic secretory protein which promotes the degradation of low-density lipoprotein receptors leading to reduced hepatic uptake of plasma cholesterol. Non-synonymous single-nucleotide polymorphisms in its gene have been linked to hypo- or hyper- cholesterolemia, depending on whether they decrease or increase PCSK9 activity, respectively. Since the proliferation and the infectivity of Plasmodium spp. partially depend on cholesterol from the host, we hypothesize that these PCSK9 genetic polymorphisms could influence the course of malaria infection in individuals who carry them. Here we examined the frequency distribution of one dominant (C679X) and two recessive (A443T, I474V) hypocholesterolemic polymorphisms as well as that of one recessive hypercholesterolemic polymorphism (E670G) among healthy and malaria-infected Malian children.

Methods

Dried blood spots were collected in Bandiagara, Mali, from 752 age, residence and ethnicity-matched children: 253 healthy controls, 246 uncomplicated malaria patients and 253 severe malaria patients. Their genomic DNA was extracted and genotyped for the above PCSK9 polymorphisms using Taqman assays. Associations of genotype distributions and allele frequencies with malaria were evaluated.

Results

The minor allele frequency of the A443T, I474V, E670G, and C679X polymorphisms in the study population sample was 0.12, 0.20, 0.26, and 0.02, respectively. For each polymorphism, the genotype distribution among the three health conditions was statistically insignificant, but for the hypercholesterolemic E670G polymorphism, a trend towards association of the minor allele with malaria severity was observed (P = 0.035). The association proved to be stronger when allele frequencies between healthy controls and severe malaria cases were compared (Odd Ratio: 1.34; 95% Confidence Intervals: 1.04–1.83); P = 0.031).

Conclusions

Carriers of the minor allele of the E670G PCSK9 polymorphism might be more susceptible to severe malaria. Further investigation of the cholesterol regulating function of PCSK9 in the pathophysiology of malaria is needed.

Stepwise processing analyses of the single-turnover PCSK9 protease reveal its substrate sequence specificity and link clinical genotype to lipid phenotype

Proprotein convertase subtilisin/kexin type 9 (PCSK9) down-regulates the low-density lipoprotein (LDL) receptor, elevating LDL cholesterol and accelerating atherosclerotic heart disease, making it a promising cardiovascular drug target. To achieve its maximal effect on the LDL receptor, PCSK9 requires autoproteolysis. After cleavage, PCSK9 retains its prodomain in the active site as a self-inhibitor. Unlike other proprotein convertases, however, this retention is permanent, inhibiting any further protease activity for the remainder of its life cycle. Such inhibition has proven a major challenge toward a complete biochemical characterization of PCSK9's proteolytic function, which could inform therapeutic approaches against its hypercholesterolemic effects. To address this challenge, we employed a cell-based, high-throughput method using a luciferase readout to evaluate the single-turnover PCSK9 proteolytic event. We combined this method with saturation mutagenesis libraries to interrogate the sequence specificities of PCSK9 cleavage and proteolysis-independent secretion. Our results highlight several key differences in sequence identity between these two steps, complement known structural data, and suggest that PCSK9 self-proteolysis is the rate-limiting step of secretion. Additionally, we found that for missense SNPs within PCSK9, alterations in both proteolysis and secretion are common. Last, we show that some SNPs allosterically modulate PCSK9's substrate sequence specificity. Our findings indicate that PCSK9 proteolysis acts as a commonly perturbed but critical switch in controlling lipid homeostasis and provide a new hope for the development of small-molecule PCSK9 inhibitors.

Rare and common variants of APOB and PCSK9 in Korean patients with extremely low low-density lipoprotein-cholesterol levels

Background

Screening of variants, related to lipid metabolism in patients with extreme cholesterol levels, is a tool used to identify targets affecting cardiovascular outcomes. The aim of this study was to examine the prevalence and characteristics of rare and common variants of APOB and PCSK9 in Korean patients with extremely low low-density lipoprotein-cholesterol (LDL-C) levels.

Methods

Among 13,545 participants enrolled in a cardiovascular genome cohort, 22 subjects, whose LDL-C levels without lipid-lowering agents were ≤1 percentile (48 mg/dL) of Korean population, were analyzed. Two target genes, APOB and PCSK9, were sequenced by targeted next-generation sequencing. Prediction of functional effects was conducted using SIFT, PolyPhen-2, and Mutation Taster, and matched against a public database of variants.

Results

Eight rare variants of the two candidate genes (five in APOB and three in PCSK9) were found in nine subjects. Two subjects had more than two different rare variants of either gene (one subject in APOB and another subject in APOB/PCSK9). Conversely, 12 common variants (nine in APOB and three in PCSK9) were discovered in 21 subjects. Among all variants, six in APOB and three in PCSK9 were novel. Several variants previously reported functional, including c.C277T (p.R93C) and c.G2009A (p.G670E) of PCSK9, were found in our population.

Conclusions

Rare variants of APOB or PCSK9 were identified in nine of the 22 study patients with extremely low LDL-C levels, whereas most of them had common variants of the two genes. The common novelty of variants suggested polymorphism of the two genes among them. Our results provide rare genetic information associated with this lipid phenotype in East Asian people.

Heparan sulfate proteoglycans present PCSK9 to the LDL receptor

Coronary artery disease is the main cause of death worldwide and accelerated by increased plasma levels of cholesterol-rich low-density lipoprotein particles (LDL). Circulating PCSK9 contributes to coronary artery disease by inducing lysosomal degradation of the LDL receptor (LDLR) in the liver and thereby reducing LDL clearance. Here, we show that liver heparan sulfate proteoglycans are PCSK9 receptors and essential for PCSK9-induced LDLR degradation. The heparan sulfate-binding site is located in the PCSK9 prodomain and formed by surface-exposed basic residues interacting with trisulfated heparan sulfate disaccharide repeats. Accordingly, heparan sulfate mimetics and monoclonal antibodies directed against the heparan sulfate-binding site are potent PCSK9 inhibitors. We propose that heparan sulfate proteoglycans lining the hepatocyte surface capture PCSK9 and facilitates subsequent PCSK9:LDLR complex formation. Our findings provide new insights into LDL biology and show that targeting PCSK9 using heparan sulfate mimetics is a potential therapeutic strategy in coronary artery disease.PCSK9 interacts with LDL receptor, causing its degradation, and consequently reduces the clearance of LDL. Here, Gustafsen et al. show that PCSK9 interacts with heparan sulfate proteoglycans and this binding favors LDLR degradation. Pharmacological inhibition of this binding can be exploited as therapeutic intervention to lower LDL levels.

PCSK9 inhibition in the management of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a frequent hereditary metabolic disease characterized by high serum low-density lipoprotein (LDL) cholesterol concentration and premature atherosclerotic cardiovascular disease (ASCVD). The discovery of the LDL receptor as one of the causative genes of FH enabled us to understand the pathophysiology of FH and paved the way for developing statins. Similar to LDL receptor, discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) also created an opportunity for developing its inhibitors. Since PCSK9 degrades LDL receptor protein, inhibiting PCSK9 will be an effective strategy. Evolocumab and alirocumab, anti-PCSK9 antibodies that inhibit binding between PCSK9 and LDL receptors, are now available in Japan. Adding an anti-PCSK9 antibody to standard therapy with statin alone or statin combined with ezetimibe further reduced serum LDL cholesterol levels by around 60% and they significantly decrease cardiovascular event incidence as compared with placebo. Additionally, the strong LDL cholesterol lowering effect of anti-PCSK9 antibody therapies has reportedly enabled the frequency of lipoprotein apheresis to be reduced or to be discontinued. As alternative strategies against PCSK9, antisense oligonucleotide agents that inhibit PCSK9 protein synthesis as well as a small interfering (or short interference) RNA (siRNA) for PCSK9 are also being developed. While relatively high cost can be given as a problem, PCSK9 inhibitors are able to reduce LDL cholesterol dramatically even in FH patients who could not achieve targets until now. To ensure that these drugs are given to the patients who really need them, it is necessary to raise the diagnosis rate and family screening has to be more actively conducted. Finally, it has been reported that PCSK9 is expressed not only in hepatocytes but also in other cells such as epithelial cells in small intestine and vascular smooth muscle cells in atherosclerotic plaque. Further research regarding extra-hepatic pathophysiology of PCSK9 is expected.

Impact of rare variants in autosomal dominant hypercholesterolemia causing genes

PURPOSE OF REVIEW

The systematic analysis of the major candidate genes in autosomal dominant hypercholesterolemia (ADH) and the use of next-generation sequencing (NGS) technology have made possible the discovery of several rare gene variants whose pathogenic effect in most cases remains poorly defined.

RECENT FINDINGS

One major advance in the field has been the adoption of a set of international guidelines for the assignment of pathogenicity to low-density lipoprotein receptor (LDLR) gene variants based on the use of softwares, complemented with data available from literature and public databases. The clinical impact of several novel rare variants in LDLR, APOB, PCSK9, APOE genes have been reported in large studies describing patients with ADH found to be homozygotes/compound heterozygotes, double heterozygotes, or simple heterozygotes. In-vitro functional studies have been conducted to clarify the effect of some rare ApoB variants on LDL binding to LDLR and the impact of a rare ApoE variant on the uptake of VLDL and LDL by hepatocytes.

SUMMARY

The update of the ADH gene variants database and the classification of variants in categories of pathogenicity is a major advance in the understanding the pathophysiology of ADH and in the management of this disorder. The studies of molecularly characterized patients with ADH have emphasized the impact of a specific variant and the variable clinical expression of different genotypes. The functional studies of some variants have increased our understanding of the molecular bases of some forms of ADH.

Association and differences in genetic polymorphisms in PCSK9 gene in subjects with lacunar infarction in the Han and Uygur populations of Xinjiang Uygur Autonomous Region of China

Polymorphisms in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene are associated with severe hypercholesterolemia and stroke. Here, we investigated the relationship between single nucleotide polymorphisms in PCSK9 and stroke in 237 patients with lacunar infarction in the Uygur and Han populations in Xinjiang Uygur Autonomous Region of China. Using the SNaPshot single-base terminal extension method, four PCSK9 gene polymorphisms were analyzed. We found a significantly strong relationship between the PCSK9 rs17111503 (G > A) polymorphism and increased susceptibility to lacunar infarction by variant homozygote comparison, and using the dominant and recessive models in the Han population but not in the Uygur population. Low triglyceride levels were found in AA carriers (rs17111503, G > A) in the Han population but not in the Uygur population. Association analysis revealed that the rs17111503 (G > A) polymorphism was not significantly associated with smoking, alcohol drinking, history of hypertension or diabetes in the Han or Uygur lacunar infarction patients. rs11583680, rs483462 and rs505151 were not associated with risk of lacunar infarction in the Han or Uygur populations. Our findings suggest that the PCSK9 rs17111503 (G > A) polymorphism is associated with susceptibility to lacunar infarction in the Han population but not in the Uygur population.

Proprotein convertase subtilisin/kexin type 9 inhibition: a new therapeutic mechanism for reducing cardiovascular disease risk

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in the regulation of cholesterol homeostasis. By binding to hepatic low-density lipoprotein (LDL) receptors and promoting their lysosomal degradation, PCSK9 reduces LDL uptake, leading to an increase in LDL cholesterol concentrations. Gain-of-function mutations in PCSK9 associated with high LDL cholesterol and premature cardiovascular disease have been causally implicated in the pathophysiology of autosomal-dominant familial hypercholesterolemia. In contrast, the more commonly expressed loss-of-function mutations in PCSK9 are associated with reduced LDL cholesterol and cardiovascular disease risk. The development of therapeutic approaches that inhibit PCSK9 function has therefore attracted considerable attention from clinicians and the pharmaceutical industry for the management of hypercholesterolemia and its associated cardiovascular disease risk. This review summarizes the effects of PCSK9 on hepatic and intestinal lipid metabolism and the more recently explored functions of PCSK9 in extrahepatic tissues. Therapeutic approaches that prevent interaction of PCSK9 with hepatic LDL receptors (monoclonal antibodies, mimetic peptides), inhibit PCSK9 synthesis in the endoplasmic reticulum (antisense oligonucleotides, siRNAs), and interfere with PCSK9 function (small molecules) are also described. Finally, clinical trials testing the safety and efficacy of monoclonal antibodies to PCSK9 are reviewed. These have shown dose-dependent decreases in LDL cholesterol (44%-65%), apolipoprotein B (48%-59%), and lipoprotein(a) (27%-50%) without major adverse effects in various high-risk patient categories, including those with statin intolerance. Initial reports from 2 of these trials have indicated the expected reduction in cardiovascular events. Hence, inhibition of PCSK9 holds considerable promise as a therapeutic option for decreasing cardiovascular disease risk.

Proprotein convertase subtilisin/kexin 9 V4I variant with LDLR mutations modifies the phenotype of familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is caused by mutations in the genes encoding low-density lipoprotein receptor (LDLR), apolipoprotein B, or proprotein convertase subtilisin/kexin 9 (PCSK9). However, FH shows variability of the clinical phenotype modified by other genetic variants or environmental factors.

OBJECTIVE

Our objective was to determine the distribution of PCSK9 variants in Japanese FH heterozygotes and to clarify whether those variants and the combination of those variants and LDLR mutations modify the clinical phenotypes.

METHODS

A direct sequence analysis was performed for all 18 exons of LDLR gene and 12 exons of PCSK9 gene in 269 clinically diagnosed FH heterozygotes. The serum lipid levels of the carriers of each variant were compared to those of noncarriers. We also assessed Achilles tendon xanthoma and the prevalence of coronary artery disease (CAD) in the patients aged ≥30 years.

RESULTS

Eleven PCSK9 variants were detected. There were 4 frequent PCSK9 variants: L21_22insL, A53 V, V4I, and E32 K. The PCSK9 L21_22insL and A53 V were in linkage disequilibrium with each other. There were no significant differences in serum lipids levels and the prevalence of CAD at the age of ≥ 30 years between PCSK9 V4I, L21_22insL/A53 V, or E32 K variant carriers and noncarriers without LDLR mutations. In the patients carrying LDLR mutations and aged ≥ 30 years, the additional PCSK9 V4I variant was linked to a significantly increased prevalence of CAD in accord with the elevation of the LDL-cholesterol level.

CONCLUSIONS

The addition of the PCSK9 V4I was suggested to modify the phenotype of patients carrying LDLR mutations by affecting their LDLR metabolism.

Characterization of Autosomal Dominant Hypercholesterolemia Caused by PCSK9 Gain of Function Mutations and Its Specific Treatment With Alirocumab, a PCSK9 Monoclonal Antibody

BACKGROUND

Patients with PCSK9 gene gain of function (GOF) mutations have a rare form of autosomal dominant hypercholesterolemia. However, data examining their clinical characteristics and geographic distribution are lacking. Furthermore, no randomized treatment study in this population has been reported.

METHODS AND RESULTS

We compiled clinical characteristics of PCSK9 GOF mutation carriers in a multinational retrospective, cross-sectional, observational study. We then performed a randomized placebo-phase, double-blind study of alirocumab 150 mg administered subcutaneously every 2 weeks to 13 patients representing 4 different PCSK9 GOF mutations with low-density lipoprotein cholesterol (LDL-C) ≥70 mg/dL on their current lipid-lowering therapies at baseline. Observational study: among 164 patients, 16 different PCSK9 GOF mutations distributed throughout the gene were associated with varying severity of untreated LDL-C levels. Coronary artery disease was common (33%; average age of onset, 49.4 years), and untreated LDL-C concentrations were higher compared with matched carriers of mutations in the LDLR (n=2126) or apolipoprotein B (n=470) genes. Intervention study: in PCSK9 GOF mutation patients randomly assigned to receive alirocumab, mean percent reduction in LDL-C at 2 weeks was 62.5% (P<0.0001) from baseline, 53.7% compared with placebo-treated PCSK9 GOF mutation patients (P=0.0009; primary end point). After all subjects received 8 weeks of alirocumab treatment, LDL-C was reduced by 73% from baseline (P<0.0001).

CONCLUSIONS

PCSK9 GOF mutation carriers have elevated LDL-C levels and are at high risk of premature cardiovascular disease. Alirocumab, a PCSK9 antibody, markedly lowers LDL-C levels and seems to be well tolerated in these patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01604824.

Plasma Membrane Tetraspanin CD81 Complexes with Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) and Low Density Lipoprotein Receptor (LDLR), and Its Levels Are Reduced by PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an important factor in plasma cholesterol regulation through modulation of low density lipoprotein receptor (LDLR) levels. Naturally occurring mutations can lead to hyper- or hypocholesterolemia in human. Recently, we reported that PCSK9 was also able to modulate CD81 in Huh7 cells. In the present study, several gain-of-function and loss-of-function mutants as well as engineered mutants of PCSK9 were compared for their ability to modulate the cell surface expression of LDLR and CD81. Although PCSK9 gain-of-function D374Y enhanced the degradation both receptors, D374H and D129N seemed to only reduce LDLR levels. In contrast, mutations in the C-terminal hinge-cysteine-histidine-rich domain segment primarily affected the PCSK9-induced CD81 degradation. Furthermore, when C-terminally fused to an ACE2 transmembrane anchor, the secretory N-terminal catalytic or hinge-cysteine-histidine-rich domain domains of PCSK9 were able to reduce CD81 and LDLR levels. These data confirm that PCSK9 reduces CD81 levels via an intracellular pathway as reported for LDLR. Using immunocytochemistry, a proximity ligation assay, and co-immunoprecipitation, we found that the cell surface level of PCSK9 was enhanced upon overexpression of CD81 and that both PCSK9 and LDLR interact with this tetraspanin protein. Interestingly, using CHO-A7 cells lacking LDLR expression, we revealed that LDLR was not required for the degradation of CD81 by PCSK9, but its presence strengthened the PCSK9 effect.

Living the PCSK9 adventure: from the identification of a new gene in familial hypercholesterolemia towards a potential new class of anticholesterol drugs

A decade after our discovery of the involvement of proprotein convertase subtilisin/kexin type 9 (PCSK9) in cholesterol metabolism through the identification of the first mutations leading to hypercholesterolemia, PCSK9 has become one of the most promising targets in cholesterol and cardiovascular diseases. This challenging work in the genetics of hypercholesterolemia paved the way for a plethora of studies around the world allowing the characterization of PCSK9, its expression, its impact on reducing the abundance of LDL receptor, and the identification of loss-of-function mutations in hypocholesterolemia. We highlight the different steps of this adventure and review the published clinical trials especially those with the anti-PCSK9 antibodies evolocumab (AMG 145) and alirocumab (SAR236553/REGN727), which are in phase III trials. The promising results in lowering LDL cholesterol levels raise hope that the PCSK9 adventure will lead, after the large and long-term ongoing phase III studies evaluating efficacy and safety, to a new anticholesterol pharmacological class.

Characterisation of de novo mutations in the C-terminal domain of proprotein convertase subtilisin/kexin type 9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of the hepatic low-density lipoprotein receptor (LDL-R) and is therefore a prominent therapeutic target for reducing LDL-cholesterol. The C-terminal domain of PCSK9 is unlikely to be involved in a direct extracellular interaction with the LDL-R. We probed the importance of the C-terminus for the degradation of the LDL-R by designing seven de novo mutants of PCSK9 that fill potential druggable cavities. The mutants were tested for their ability to diminish LDL uptake in human HepG2 cells and for affinity towards a calcium independent mutant of the EGF(A) domain of the human LDL-R. The later was done by a newly developed surface plasmon resonance-based assay format. We identified three mutant proteins (G517R, V610R and V644R) with decreased ability to block LDL uptake into HepG2 cells. These mutations define areas outside the direct interaction area between PCSK9 and the LDL-R that could be targeted to inhibit the PCSK9 triggered degradation of the LDL-R. We also describe the mechanistic rationalisation of the affinity changes seen with the natural occurring human D374Y (gain of function) mutation causing severe hypercholesterolaemia. The action of this mutant is due to a significantly decreased dissociation rate constant, whereas the mutation does not affect the association rate constant.

Clinical and genetic analysis of a family diagnosed with familial hypobetalipoproteinemia in which the proband was diagnosed with diabetes mellitus

OBJECTIVE

To perform clinical and genetic analysis of a family with familial hypobetalipoproteinemia in which the proband had been diagnosed with diabetes mellitus.

METHODS

Direct sequencing was performed on candidate genes such as APOB, PCSK9, and ANGPTL3. The effect of the mutant gene on lipid profile was investigated using biochemical methods.

RESULTS

A novel mutation Y344S in ANGPTL3 was identified but no variants were found in PCSK9 or APOB. Lipid profiles showed the levels of TG, TC, and LDL-C to be significantly lower in Y344S carriers than in non-carriers in this family. The levels of HDL-C and plasma concentrations of ANGPTL3 showed no significant differences. Western blot analysis revealed that the mutant ANGPTL3 proteins could not be secreted into the medium.

CONCLUSION

A novel mutation Y344S was found in ANGPTL3 gene in two diabetic patients with familial hypobetalipoproteinemia. The family study and genetic analysis suggest that this set of gene mutation may be a genetic basis for the lipid phenotypes, and may become a vascular protective factor in the probands with high risk of atherosclerosis.

Correlation of PCSK9 gene polymorphism with cerebral ischemic stroke in Xinjiang Han and Uygur populations

Background

Cerebral ischemic stroke (CIS) is a major cause of morbidity and mortality. Its main pathological basis is atherosclerosis (AS); in turn, the main risk factor in AS is dyslipidemia. Human proprotein convertase subtilisin/kexin9 (PCSK9) plays a key role in regulating plasma low-density lipoprotein (LDL) cholesterol levels. We sought to assess the association between PCSK9 and CIS in Chinese Han and Uygur populations.

Material/Methods

We selected 408 CIS patients and 348 control subjects and used a single-base terminal extension (SNaPshot) method to detect the genotypes of the 20 single-nucleotide polymorphisms (SNPs) in PCSK9.

Results

Distribution of SNP8 (rs529787) genotypes showed a significant difference between CIS and control participants (P=0.049). However, when analyzing Han and Uygur populations separately, we found that only Han subjects showed distribution of SNP1 (rs1711503), SNP2 (rs2479408), and SNP8 (rs529787) alleles that was significantly different between CIS and control participants (P=0.028, P=0.013, P=0.006, respectively), and distribution of SNP2 (rs2479408) in the dominant model (CC vs. CG + GG) was significantly different between CIS and control participants (P=0.013), even after adjustment for covariates (OR: 75.262, 95% confidence interval [CI]: 7.232–783.278, P<0.001). Distribution of the 2 haplotypes (A-C and G-C) (rs1711503 and rs2479408) was significantly different between CIS and control participants (both, P=0.011).

Conclusions

Both rs1711503 and rs2479408 of PCSK9 genes were associated with CIS in the Han population of China. A-C haplotype may be a genetic marker of CIS risk in this population.

Proprotein convertases subtilisin/kexin type 9, an enzyme turned escort protein: hepatic and extra hepatic functions

Proprotein Convertases Subtilisin/Kexin Type 9 (PCSK9) is a serine endoproteinase. Biosynthesized as a zymogen, it cleaves itself once, and then turns into an escort protein for transmembrane proteins, leading them into lysosomes for degradation. It is primarily produced and secreted by the liver. It attaches to the low-density lipoprotein receptor (LDLR) at the surface of hepatocytes and, after co-endocytosis, directs it into lysosomes where it is degraded. By downregulating LDLR, PCSK9 reduces hepatic clearance of LDL-cholesterol. Inborn or induced increase of this function causes hypercholesterolemia; its decrease causes hypocholesterolemia. This has been experimentally demonstrated ex vivo and in vivo, and corroborated by epidemiological studies associating PCSK9 genetic variations with plasma cholesterol levels. PCSK9 is now a proven target for inactivation in the treatment of hypercholesterolemia and associated atherosclerosis. However, it is still uncertain whether its severe or complete inactivation, combined with other predispositions, will be without undesirable side-effects. Some experimental data suggest that PCSK9 could contribute positively to the physiology of non-hepatic cells such as pancreatic islets β cells, adipocytes and macrophages, protecting them from excessive lipid uptake, in an endocrine, autocrine, or paracrine manner. Genetic variations that attenuate PCSK9 anti-LDLR activity are common in human populations. Their evolutionary significance still needs to be evaluated on the background of environmental pressures, such as infectious diseases, cold weather and famine, which have threatened survival and reproduction in the course of human prehistory and history.