In vivo evidence that furin from hepatocytes inactivates PCSK9

PCSK9 in metabolism and diseases

PCSK9 is a serine protease that regulates plasma levels of low-density lipoprotein (LDL) and cholesterol by mediating the endolysosomal degradation of LDL receptor (LDLR) in the liver. When PCSK9 functions unchecked, it leads to increased degradation of LDLR, resulting in elevated circulatory levels of LDL and cholesterol. This dysregulation contributes to lipid and cholesterol metabolism abnormalities, foam cell formation, and the development of various diseases, including cardiovascular disease (CVD), viral infections, cancer, and sepsis. Emerging clinical and experimental evidence highlights an imperative role for PCSK9 in metabolic anomalies such as hypercholesterolemia and hyperlipidemia, as well as inflammation, and disturbances in mitochondrial homeostasis. Moreover, metabolic hormones - including insulin, glucagon, adipokines, natriuretic peptides, and sex steroids - regulate the expression and circulatory levels of PCSK9, thus influencing cardiovascular and metabolic functions. In this comprehensive review, we aim to elucidate the regulatory role of PCSK9 in lipid and cholesterol metabolism, pathophysiology of diseases such as CVD, infections, cancer, and sepsis, as well as its pharmaceutical and non-pharmaceutical targeting for therapeutic management of these conditions.

Serum mature and furin-cleaved proprotein convertase subtilisin/kexin type 9 levels and their association with cardiovascular events in statin-treated patients with cardiovascular disease

BACKGROUND AND AIMS

Previous studies have not found a consistent association between circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels and the risk of cardiovascular events partly due to measurement methods that cannot distinguish between uncleaved and furin-cleaved forms of PCSK9.

METHODS

This is a prespecified sub-study of the REAL-CAD study which is a prospective, multicenter, randomized trial to compare high- versus low-dose statin in patients with stable coronary artery disease (CAD). The primary endpoint was major adverse cerebrovascular and cardiovascular events (MACCE) defined as a composite of cardiovascular death, nonfatal myocardial infarction, nonfatal ischemic stroke, or unstable angina requiring emergency hospitalization. In this case-cohort study, serum mature (uncleaved) and furin-cleaved PCSK9 levels obtained at 6 months after randomization were measured among 426 participants who developed MACCE (cases) and 1,478 randomly selected participants (sub-cohort).

RESULTS

From 1,478 patients in the sub-cohort, the Cox proportional hazards models with a pseudolikelihood method for case-cohort design revealed that the risk of the primary endpoint in patients with the highest quartile of mature PCSK9 levels was similar to that in the lowest quartile (hazard ratio [HR] 0.809; 95% confidence intervals [CI], 0.541-1.209). Similarly, the HR for the highest to lowest quartiles of furin-cleaved PCSK9 was 0.948 (95% CI, 0.645-1.392) (P = 0.784). Compared to the lowest quartile, neither serum mature nor furin-cleaved PCSK9 levels predicted MACCE.

CONCLUSIONS

In a large-scale secondary prevention cohort, serum mature and furin-cleaved PCSK9 levels did not provide useful information for predicting future cardiovascular events in statin-treated patients with stable CAD.

PCSK9 inhibitors as safer therapeutics for atherosclerotic cardiovascular disease (ASCVD): Pharmacophore design and molecular dynamics analysis

Cardiovascular disorders are still challenging and are among the deadly diseases. As a major risk factor for atherosclerotic cardiovascular disease, dyslipidemia, and high low-density lipoprotein cholesterol in particular, can be prevented primary and secondary by lipid-lowering medications. Therefore, insights are still needed into designing new drugs with minimal side effects. Proprotein convertase subtilisin/kexin 9 (PCSK9) enzyme catalyses protein-protein interactions with low-density lipoprotein, making it a critical target for designing promising inhibitors compared to statins. Therefore, we screened for potential compounds using a redesigned PCSK9 conformational behaviour to search for a significantly extensive chemical library and investigated the inhibitory mechanisms of the final compounds using integrated computational methods, from ligand essential functional group screening to all-atoms MD simulations and MMGBSA-based binding free energy. The inhibitory mechanisms of the screened compounds compared with the standard inhibitor. K31 and K34 molecules showed stronger interactions for PCSK9, having binding energy (kcal/mol) of -33.39 and -63.51, respectively, against -27.97 of control. The final molecules showed suitable drug-likeness, non-mutagenesis, permeability, and high solubility values. The C-α atoms root mean square deviation and root mean square fluctuation of the bound-PCSK9 complexes showed stable and lower fluctuations compared to apo PCSK9. The findings present a model that unravels the mechanism by which the final molecules proposedly inhibit the PCSK9 function and could further improve the design of novel drugs against cardiovascular diseases.

PCSK9 and Lipid Metabolism: Genetic Variants, Current Therapies, and Cardiovascular Outcomes

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a crucial role in the modulation of lipid metabolism as a critical negative regulator of hepatic low-density lipoprotein receptor (LDLR) levels and circulating low-density lipoprotein (LDL) clearance. Numerous gain-of-function (GOF) mutations in PCSK9 have been identified as causing familial hypercholesterolemia (FH) by reducing LDLR levels, and loss-of-function (LOF) mutations associated with a hypercholesterolemia phenotype protective against atherosclerosis. PCSK9 represents an example of successful translational research resulting in the identification of PCSK9 as a major drug target for a lipid-lowering therapy. To explore the genetic constitution of PCSK9 and its biologic role, in this review, we summarize the current evidence of clinically significant PCSK9 genetic variants involved in lipid metabolism as well as emphasize the importance of PCSK9 inhibition for the improvement of cardiovascular outcomes by conducting a meta-analysis of the available data on the incidence of cardiovascular disease events.

Functional Roles of Furin in Cardio-Cerebrovascular Diseases

Furin plays a major role in post-translational modification of several biomolecules, including endogenous hormones, growth factors, and cytokines. Recent reports have demonstrated the association of furin and cardio-cerebrovascular diseases (CVDs) in humans. This review describes the possible pathogenic contribution of furin and its substrates in CVDs. Early-stage hypertension and diabetes mellitus show a negative correlation with furin. A reduction in furin might promote hypertension by decreasing maturation of B-type natriuretic peptide (BNP) or by decreasing shedding of membrane (pro)renin receptor (PRR), which facilitates activation of the renin-angiotensin-aldosterone system (RAAS). In diabetes, furin downregulation potentially leads to insulin resistance by reducing maturation of the insulin receptor. In contrast, the progression of other CVDs is associated with an increase in furin, including dyslipidemia, atherosclerosis, ischemic stroke, myocardial infarction (MI), and heart failure. Upregulation of furin might promote maturation of membrane type 1-matrix metalloproteinase (MT1-MMP), which cleaves low-density lipoprotein receptor (LDLR), contributing to dyslipidemia. In atherosclerosis, elevated levels of furin possibly enhance maturation of several substrates related to inflammation, cell proliferation, and extracellular matrix (ECM) deposition and degradation. Neuronal cell death following ischemic stroke has also been shown to involve furin substrates (e.g., MT1-MMP, hepcidin, and hemojuvelin). Moreover, furin and its substrates, including tumor necrosis factor-α (TNF-α), endothelin-1 (ET-1), and transforming growth factor-β1 (TGF-β1), are capable of mediating inflammation, hypertrophy, and fibrosis in MI and heart failure. Taken together, this evidence provides functional significance of furin in CVDs and might suggest a potential novel therapeutic modality for the management of CVDs.

Unveiling Familial Hypercholesterolemia-Review, Cardiovascular Complications, Lipid-Lowering Treatment and Its Efficacy

Familial hypercholesterolemia (FH) is a genetic disorder primarily transmitted in an autosomal-dominant manner. We distinguish two main forms of FH, which differ in the severity of the disease, namely homozygous familial hypercholesterolemia (HoFH) and heterozygous familial hypercholesterolemia (HeFH). The characteristic feature of this disease is a high concentration of low-density lipoprotein cholesterol (LDL-C) in the blood. However, the level may significantly vary between the two mentioned types of FH, and it is decidedly higher in HoFH. A chronically elevated concentration of LDL-C in the plasma leads to the occurrence of certain abnormalities, such as xanthomas in the tendons and skin, as well as corneal arcus. Nevertheless, a significantly more severe phenomenon is leading to the premature onset of cardiovascular disease (CVD) and its clinical implications, such as cardiac events, stroke or vascular dementia, even at a relatively young age. Due to the danger posed by this medical condition, we have investigated how both non-pharmacological and selected pharmacological treatment impact the course of FH, thereby reducing or postponing the risk of clinical manifestations of CVD. The primary objective of this review is to provide a comprehensive summary of the current understanding of FH, the effectiveness of lipid-lowering therapy in FH and to explain the anatomopathological correlation between FH and premature CVD development, with its complications.

Targeting proprotein convertase subtilisin/kexin type 9 (PCSK9): from bench to bedside

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has evolved as a pivotal enzyme in lipid metabolism and a revolutionary therapeutic target for hypercholesterolemia and its related cardiovascular diseases (CVD). This comprehensive review delineates the intricate roles and wide-ranging implications of PCSK9, extending beyond CVD to emphasize its significance in diverse physiological and pathological states, including liver diseases, infectious diseases, autoimmune disorders, and notably, cancer. Our exploration offers insights into the interaction between PCSK9 and low-density lipoprotein receptors (LDLRs), elucidating its substantial impact on cholesterol homeostasis and cardiovascular health. It also details the evolution of PCSK9-targeted therapies, translating foundational bench discoveries into bedside applications for optimized patient care. The advent and clinical approval of innovative PCSK9 inhibitory therapies (PCSK9-iTs), including three monoclonal antibodies (Evolocumab, Alirocumab, and Tafolecimab) and one small interfering RNA (siRNA, Inclisiran), have marked a significant breakthrough in cardiovascular medicine. These therapies have demonstrated unparalleled efficacy in mitigating hypercholesterolemia, reducing cardiovascular risks, and have showcased profound value in clinical applications, offering novel therapeutic avenues and a promising future in personalized medicine for cardiovascular disorders. Furthermore, emerging research, inclusive of our findings, unveils PCSK9's potential role as a pivotal indicator for cancer prognosis and its prospective application as a transformative target for cancer treatment. This review also highlights PCSK9's aberrant expression in various cancer forms, its association with cancer prognosis, and its crucial roles in carcinogenesis and cancer immunity. In conclusion, this synthesized review integrates existing knowledge and novel insights on PCSK9, providing a holistic perspective on its transformative impact in reshaping therapeutic paradigms across various disorders. It emphasizes the clinical value and effect of PCSK9-iT, underscoring its potential in advancing the landscape of biomedical research and its capabilities in heralding new eras in personalized medicine.

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.

Relationship between Serum Proprotein Convertase Subtilisin/Kexin Type 9 Concentration and Prevalence of Coronary Artery Calcium in a Community-Based Sample of Japanese Men

AIMS

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a promising new target for reducing low-density lipoprotein cholesterol (LDL-C) and cardiovascular events in high-risk patients. However, the influence of circulating PCSK9 concentration on atherosclerotic plaque formation in the general population remains unknown. We assessed the relationship between serum PCSK9 concentration and coronary artery calcium (CAC) prevalence in the general population.

METHODS

Community-dwelling Japanese men (n=622) aged 46-82 years without a history of cardiovascular disease and lipid-lowering medications were included. Serum PCSK9 concentration and CAC score were measured using the Agatston method, and the multivariable analysis was used to assess their association. CAC was defined as an Agatston score of ＞10. We conducted further analysis stratified by age (＜60, 60-69, and ≥ 70 years).

RESULTS

The average age, LDL-C, and median serum PCSK9 concentration were 68 years, 122 mg/dL, and 240 ng/mL, respectively. After multivariable adjustment for traditional cardiovascular risk factors, no significant association was observed between serum PCSK9 concentration and CAC prevalence (adjusted relative risk [aRR] 1.05, 95% confidence interval [CI] 0.97-1.13). With age stratification, serum PCSK9 concentration was significantly associated with CAC prevalence in men aged ＜60 years (aRR 1.38, 95% CI 1.01-1.88) but not in men aged 60-69 years (aRR 0.96, 95% CI 0.85-1.10) or ≥ 70 years (aRR 1.08, 95% CI 0.99-1.19).

CONCLUSIONS

A higher serum PCSK9 concentration was associated with a higher CAC prevalence in men aged ＜60 years, which was independent of traditional cardiovascular risk factors.

Genetic and molecular architecture of familial hypercholesterolemia

Atherosclerotic cardiovascular disease is the leading cause of death globally. Despite its important risk of premature atherosclerosis and cardiovascular disease, familial hypercholesterolemia (FH) is still largely underdiagnosed worldwide. It is one of the most frequently inherited diseases due to mutations, for autosomal dominant forms, in either of the LDLR, APOB, and PCSK9 genes or possibly a few mutations in the APOE gene and, for the rare autosomal forms, in the LDLRAP1 gene. The discovery of the genes implicated in the disease has largely helped to improve the diagnosis and treatment of FH from the LDLR by Brown and Goldstein, as well as the introduction of statins, to PCSK9 discovery in FH by Abifadel et al., and the very rapid availability of PCSK9 inhibitors. In the last two decades, major progress has been made in clinical and genetic diagnostic tools and the therapeutic arsenal against FH. Improving prevention, diagnosis, and treatment and making them more accessible to all patients will help reduce the lifelong burden of the disease.

Heparin Does Not Regulate Circulating Human PCSK9 (Proprotein Convertase Subtilisin-Kexin Type 9) in a General Population-Brief Report

BACKGROUND

PCSK9 (proprotein convertase subtilisin-kexin type 9) chaperones the hepatic LDLR (low-density lipoprotein receptor) for lysosomal degradation, elevating serum LDL (low-density lipoprotein) cholesterol and promoting atherosclerotic heart disease. Though the major effect on the hepatic LDLR comes from secreted PCSK9, the details of PCSK9 reuptake into the hepatocyte remain unclear. In both tissue culture and animal models, HSPGs (heparan sulfate proteoglycans) on hepatocytes act as co-receptors to promote PCSK9 reuptake. We hypothesized that if this PCSK9:HSPG interaction is important in humans, disrupting it with unfractionated heparin (UFH) would acutely displace PCSK9 from the liver and increase plasma PCSK9.

METHODS

We obtained remnant plasma samples from 160 subjects undergoing cardiac catheterization before and after administration of intravenous UFH. PCSK9 levels were determined using a commercial enzyme-linked immunosorbent assay.

RESULTS

Median plasma PCSK9 was 113 ng/mL prior to UFH and 119 ng/mL afterward. This difference was not significant (P=0.83 [95% CI, -6.23 to 6.31 ng/mL]). Equivalence testing provided 95% confidence that UFH would not raise plasma PCSK9 by > 4.7%. Among all subgroups, only subjects with the lowest baseline PCSK9 concentrations exhibited a response to UFH (8.8% increase, adj. P=0.044). A modest correlation was observed between baseline plasma PCSK9 and the change in plasma PCSK9 due to UFH (RS=-0.3634; P<0.0001).

CONCLUSIONS

Administration of UFH does not result in a clinically meaningful effect on circulating PCSK9 among an unselected population of humans. The results cast doubt on the clinical utility of disrupting the PCSK9:HSPG interaction as a general therapeutic strategy for PCSK9 inhibition. However, the observations suggest that in selected populations, disrupting the PCSK9:HSPG interaction could still affect PCSK9 reuptake and offer a therapeutic benefit.

A cVLP-Based Vaccine Displaying Full-Length PCSK9 Elicits a Higher Reduction in Plasma PCSK9 Than Similar Peptide-Based cVLP Vaccines

Administration of PCSK9-specific monoclonal antibodies, as well as peptide-based PCSK9 vaccines, can lower plasma LDL cholesterol by blocking PCSK9. However, these treatments also cause an increase in plasma PCSK9 levels, presumably due to the formation of immune complexes. Here, we utilize a versatile capsid virus-like particle (cVLP)-based vaccine platform to deliver both full-length (FL) PCSK9 and PCSK9-derived peptide antigens, to investigate whether induction of a broader polyclonal anti-PCSK9 antibody response would mediate more efficient clearance of plasma PCSK9. This head-to-head immunization study reveals a significantly increased capacity of the FL PCSK9 cVLP vaccine to opsonize and clear plasma PCSK9. These findings may have implications for the design of PCSK9 and other vaccines that should effectively mediate opsonization and immune clearance of target antigens.

PCSK9 in Liver Cancers at the Crossroads between Lipid Metabolism and Immunity

Metabolic rewiring and defective immune responses are considered to be the main driving forces sustaining cell growth and oncogenesis in many cancers. The atypical enzyme, proprotein convertase subtilisin/kexin type 9 (PCSK9), is produced by the liver in large amounts and plays a major role in lipid metabolism via the control of the low density lipoprotein receptor (LDLR) and other cell surface receptors. In this context, many clinical studies have clearly demonstrated the high efficacy of PCSK9 inhibitors in treating hyperlipidemia and cardiovascular diseases. Recent data implicated PCSK9 in the degradation of major histocompatibility complex I (MHC-I) receptors and the immune system as well as in other physiological activities. This review highlights the complex crosstalk between PCSK9, lipid metabolism and immunosuppression and underlines the latest advances in understanding the involvement of this convertase in other critical functions. We present a comprehensive assessment of the different strategies targeting PCSK9 and show how these approaches could be extended to future therapeutic options to treat cancers with a main focus on the liver.

A missense mutation in the proprotein convertase gene furinb causes hepatic cystogenesis during liver development in zebrafish

Hepatic cysts are fluid-filled lesions in the liver that are estimated to occur in 5% of the population. They may cause hepatomegaly and abdominal pain. Progression to secondary fibrosis, cirrhosis, or cholangiocarcinoma can lead to morbidity and mortality. Previous studies of patients and rodent models have associated hepatic cyst formation with increased proliferation and fluid secretion in cholangiocytes, which are partially due to impaired primary cilia. Congenital hepatic cysts are thought to originate from faulty bile duct development, but the underlying mechanisms are not fully understood. In a forward genetic screen, we identified a zebrafish mutant that developed hepatic cysts during larval stages. The cyst formation was not due to changes in biliary cell proliferation, bile secretion, or impairment of primary cilia. Instead, time-lapse live imaging data showed that the mutant biliary cells failed to form interconnecting bile ducts because of defects in motility and protrusive activity. Accordingly, immunostaining revealed a disorganized actin and microtubule cytoskeleton in the mutant biliary cells. By whole-genome sequencing, we determined that the cystic phenotype in the mutant was caused by a missense mutation in the furinb gene, which encodes a proprotein convertase. The mutation altered Furinb localization and caused endoplasmic reticulum (ER) stress. The cystic phenotype could be suppressed by treatment with the ER stress inhibitor 4-phenylbutyric acid and exacerbated by treatment with the ER stress inducer tunicamycin. The mutant liver also exhibited increased mammalian target of rapamycin (mTOR) signaling. Treatment with mTOR inhibitors halted cyst formation at least partially through reducing ER stress. Conclusion: Our study has established a vertebrate model for studying hepatic cystogenesis and illustrated the contribution of ER stress in the disease pathogenesis.

The circulating furin-cleaved/mature PCSK9 ratio has a potential prognostic significance in statin-naïve patients with acute ST elevation myocardial infarction

Background and aims

Proprotein convertase subtilisin/kexin type 9 (PCSK9) circulates as mature and furin-cleaved forms, but their biological functions are uncertain. We investigated whether their levels associate with prognosis in patients with acute ST elevation myocardial infarction (STEMI).

Methods

We enrolled 160 statin-naïve patients with acute STEMI and followed for 3 years. PCSK9 subtype levels were determined by an enzyme-linked immunosorbent assay before and at five timepoints up to 48 h after emergent coronary intervention. The occurrence of coronary and cardiac events was compared between subjects stratified by the PCSK9 level.

Results

One hundred and twenty-six patients completed 3 years of follow-up. In the acute phase, both PCSK9 subtype levels decreased, and thereafter increased from 6 to 48 h (mature: from 198 ± 67 to 334 ± 116 ng/mL, furin-cleaved: from 20 ± 7 to 39 ± 16 ng/mL, both p < 0.01). Major cardiac events occurred in 46 patients. The furin-cleaved/mature PCSK9 ratio at 48 h after coronary intervention predicted the likelihood of experiencing of events; patients in the third tertile had lower event-free survival than those in the first and second tetiles in Kaplan-Meier analysis (p = 0.004). Multivariate Cox regression analysis revealed that this ratio had a greater impact (HR: 1.92; 95% CI: 1.06-3.45, p = 0.03) on events than other known atherosclerosis risk factors.

Conclusions

The furin-cleaved/mature PCSK9 ratio was associated with 3-year cardiovascular events in statin-naïve patients with acute STEMI, suggesting a potential link between furin cleavage process of PCSK9 and its effect on prognosis. (249 words).

PCSK9 is minimally associated with HDL but impairs the anti-atherosclerotic HDL effects on endothelial cell activation

Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) regulates the cell-surface localization of LDL receptors in hepatocytes and is associated with LDL and lipoprotein(a) [Lp(a)] uptake, reducing blood concentrations. However, the connection between PCSK9 and HDL is unclear. Here, we investigated the association of plasma PCSK9 with HDL subpopulations and examined the effects of PCSK9 on the atheroprotective function of HDL. We examined the association of PCSK9 with HDL in apoB-depleted plasma by ELISA, native PAGE, and immunoblotting. Our analyses showed that upon apoB-depletion, total circulating PCSK9 levels were 32% of those observed in normolipidemic plasma, and only 6% of PCSK9 in the apoB-depleted plasma, including both the mature and furin-cleaved forms, was associated with HDL. We also show human recombinant PCSK9 abolished the capacity of reconstituted HDL to reduce the formation of ROS in endothelial cells, while a PCSK9-blocking antibody enhanced the capacity of human HDL (in apoB-depleted plasma) to reduce ROS formation in endothelial cells and promote endothelial cell migration. Overall, our findings suggest that PCSK9 is only minimally associated with HDL particles, but PCSK9 in apoB-depleted plasma can affect the atheroprotective properties of HDL related to preservation of endothelial function. This study contributes to the elucidation of the pathophysiological role of plasma PCSK9 and highlights further the anti-atherosclerotic effect of PCSK9 inhibition.

Proprotein Convertases and the Complement System

Proteins destined for secretion - after removal of the signal sequence - often undergo further proteolytic processing by proprotein convertases (PCs). Prohormones are typically processed in the regulated secretory pathway, while most plasma proteins travel though the constitutive pathway. The complement system is a major proteolytic cascade in the blood, serving as a first line of defense against microbes and also contributing to the immune homeostasis. Several complement components, namely C3, C4, C5 and factor I (FI), are multi-chain proteins that are apparently processed by PCs intracellularly. Cleavage occurs at consecutive basic residues and probably also involves the action of carboxypeptidases. The most likely candidate for the intracellular processing of complement proteins is furin, however, because of the overlapping specificities of basic amino acid residue-specific proprotein convertases, other PCs might be involved. To our surprise, we have recently discovered that processing of another complement protein, mannan-binding lectin-associated serine protease-3 (MASP-3) occurs in the blood by PCSK6 (PACE4). A similar mechanism had been described for the membrane protease corin, which is also activated extracellularly by PCSK6. In this review we intend to point out that the proper functioning of the complement system intimately depends on the action of proprotein convertases. In addition to the non-enzymatic components (C3, C4, C5), two constitutively active complement proteases are directly activated by PCs either intracellularly (FI), or extracellularly (MASP-3), moreover indirectly, through the constitutive activation of pro-factor D by MASP-3, the activity of the alternative pathway also depends on a PC present in the blood.

Molecular and cellular biology of PCSK9: impact on glucose homeostasis

Proprotein convertase substilisin/kexin 9 (PCSK9) inhibitors (PCSK9i) revolutionised the lipid-lowering therapy. However, a risk of type 2 diabetes mellitus (T2DM) is evoked under PCSK9i therapy. In this review, we summarise the current knowledge on the link of PCSK9 with T2DM. A significant correlation was found between PCSK9 and insulin, homeostasis model assessment (HOMA) of insulin resistance and glycated haemoglobin. PCSK9 is also involved in inflammation. PCSK9 loss-of-function variants increased T2DM risk by altering insulin secretion. Local pancreatic low PCSK9 regulates β-cell LDLR expression which in turn promotes intracellular cholesterol accumulation and hampers insulin secretion. Nevertheless, the association of PCSK9 loss-of-function variants and T2DM is inconsistent. InsLeu and R46L polymorphisms were associated with T2DM, low HOMA for β-cell function and impaired fasting glucose, while the C679X polymorphism was associated with low fasting glucose in Black South African people. Hence, we assume that the impact of these variants on glucose homeostasis may vary depending on the genetic background of the studied populations and the type of effect caused by those genetic variants on the PCSK9 protein. Accordingly, these factors should be considered when choosing a genetic variant of PCSK9 to assess the impact of long-term use of PCSK9i on glucose homeostasis.

How Can We Identify Very High-Risk Heterozygous Familial Hypercholesterolemia?

Heterozygous familial hypercholesterolemia (HeFH) is a genetic disorder that elevates low-density lipoprotein cholesterol and increases the risk of premature atherosclerotic cardiovascular disease (ASCVD). However, despite their atherogenic lipid profiles, the cardiovascular risk of HeFH varies in each individual. Their variety of phenotypic features suggests the need for better risk stratification to optimize their therapeutic management. The current review summarizes three potential approaches, including (1) definition of familial hypercholesterolemia (FH)-related risk scores, (2) genetic analysis, and (3) biomarkers. The International Atherosclerosis Society has recently proposed a definition of severe FH to identify very high-risk HeFH subjects according to their clinical characteristics. Furthermore, published studies have shown the association of FH-related genetic phenotypes with ASCVD, which indicates the genetic analysis's potential to evaluate individual cardiovascular risks. Biomarkers reflecting disease activity have been considered to predict the formation of atherosclerosis and the occurrence of ASCVD in HeFH subjects. Incorporating these risk stratifications will be expected to allocate adequate intensity of lipid-lowering therapies in HeFH subjects, which ultimately improves cardiovascular outcomes.

The Multifaceted Biology of PCSK9

This article reviews the discovery of PCSK9, its structure-function characteristics, and its presently known and proposed novel biological functions. The major critical function of PCSK9 deduced from human and mouse studies, as well as cellular and structural analyses, is its role in increasing the levels of circulating low-density lipoprotein (LDL)-cholesterol (LDLc), via its ability to enhance the sorting and escort of the cell surface LDL receptor (LDLR) to lysosomes. This implicates the binding of the catalytic domain of PCSK9 to the EGF-A domain of the LDLR. This also requires the presence of the C-terminal Cys/His-rich domain, its binding to the secreted cytosolic cyclase associated protein 1, and possibly another membrane-bound "protein X". Curiously, in PCSK9-deficient mice, an alternative to the downregulation of the surface levels of the LDLR by PCSK9 is taking place in the liver of female mice in a 17β-estradiol-dependent manner by still an unknown mechanism. Recent studies have extended our understanding of the biological functions of PCSK9, namely its implication in septic shock, vascular inflammation, viral infections (Dengue; SARS-CoV-2) or immune checkpoint modulation in cancer via the regulation of the cell surface levels of the T-cell receptor and MHC-I, which govern the antitumoral activity of CD8+ T cells. Because PCSK9 inhibition may be advantageous in these processes, the availability of injectable safe PCSK9 inhibitors that reduces by 50% to 60% LDLc above the effect of statins is highly valuable. Indeed, injectable PCSK9 monoclonal antibody or small interfering RNA could be added to current immunotherapies in cancer/metastasis.

FURIN gene variants (rs6224/rs4702) as potential markers of deat hand cardiovascular traits in severe COVID-19

Furin is a protease that plays a key role in the infection cycle of SARS‐CoV‐2 by cleaving the viral proteins during the virus particle assembly. In addition, Furin regulates several physiological processes related to cardio‐metabolic traits. DNA variants in the FURIN gene are candidates to regulate the risk of developing these traits as well as the susceptibility to severe COVID‐19. We genotyped two functional FURIN variants (rs6224/rs4702) in 428 COVID‐19 patients in the intensive care unit. The association with death (N = 106) and hypertension, diabetes, and hyperlipidaemia was statistically evaluated. The risk of death was associated with age, hypertension, and hypercholesterolemia. The two FURIN alleles linked to higher expression (rs6224 T and rs4702 A) were significantly increased in the death cases (odds ratio= 1.40 and 1.43). Homozygosis for the two high expression genotypes (rs6224 TT and rs4702 AA) and for the T‐A haplotype was associated with an increased risk of hypercholesterolemia. In the multiple logistic regression both, hypercholesterolemia and the TT + AA genotype were significantly associated with death. In conclusion, besides its association with hypercholesterolemia, FURIN variants might be independent risk factors for the risk of death among COVID‐19 patients.

Furin plays an important role in the life‐cycle of SARS‐CoV‐2

Furin activity might regulate the risk for cardiovascular traits, such as hypertension and hypercholesterolemia.

Two functional FURIN variants were associated with the risk of death among critical COVID‐19 patients.

The observed association with mortality was independent of higher cholesterol levels.

FURIN gene variants might be predictors of COVID‐19 severity and mortaility.

The proprotein convertase furin in cancer: more than an oncogene

Furin is the first discovered proprotein convertase member and is present in almost all mammalian cells. Therefore, by regulating the maturation of a wide range of proproteins, Furin expression and/or activity is involved in various physiological and pathophysiological processes ranging from embryonic development to carcinogenesis. Since many of these protein precursors are involved in initiating and maintaining the hallmarks of cancer, Furin has been proposed as a potential target for treating several human cancers. In contrast, other studies have revealed that some types of cancer do not benefit from Furin inhibition. Therefore, understanding the heterogeneous functions of Furin in cancer will provide important insights into the design of effective strategies targeting Furin in cancer treatment. Here, we present recent advances in understanding how Furin expression and activity are regulated in cancer cells and their influences on the activity of Furin substrates in carcinogenesis. Furthermore, we discuss how Furin represses tumorigenic properties of several cancer cells and why Furin inhibition leads to aggressive phenotypes in other tumors. Finally, we summarize the clinical applications of Furin inhibition in treating human cancers.

Emerging Insights on the Diverse Roles of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in Chronic Liver Diseases: Cholesterol Metabolism and Beyond

Chronic liver diseases are commonly associated with dysregulated cholesterol metabolism. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease of the proprotein convertase family that is mainly synthetized and secreted by the liver, and represents one of the key regulators of circulating low-density lipoprotein (LDL) cholesterol levels. Its ability to bind and induce LDL-receptor degradation, in particular in the liver, increases circulating LDL-cholesterol levels in the blood. Hence, inhibition of PCSK9 has become a very potent tool for the treatment of hypercholesterolemia. Besides PCSK9 limiting entry of LDL-derived cholesterol, affecting multiple cholesterol-related functions in cells, more recent studies have associated PCSK9 with various other cellular processes, including inflammation, fatty acid metabolism, cancerogenesis and visceral adiposity. It is increasingly becoming evident that additional roles for PCSK9 beyond cholesterol homeostasis are crucial for liver physiology in health and disease, often contributing to pathophysiology. This review will summarize studies analyzing circulating and hepatic PCSK9 levels in patients with chronic liver diseases. The factors affecting PCSK9 levels in the circulation and in hepatocytes, clinically relevant studies and the pathophysiological role of PCSK9 in chronic liver injury are discussed.

PCSK9 as a Target for Development of a New Generation of Hypolipidemic Drugs

PCSK9 has now become an important target to create new classes of lipid-lowering drugs. The prevention of its interaction with LDL receptors allows an increase in the number of these receptors on the surface of the cell membrane of hepatocytes, which leads to an increase in the uptake of cholesterol-rich atherogenic LDL from the bloodstream. The PCSK9 antagonists described in this review belong to different classes of compounds, may have a low molecular weight or belong to macromolecular structures, and also demonstrate different mechanisms of action. The mechanisms of action include preventing the effective binding of PCSK9 to LDLR, stimulating the degradation of PCSK9, and even blocking its transcription or transport to the plasma membrane/cell surface. Although several types of antihyperlipidemic drugs have been introduced on the market and are actively used in clinical practice, they are not without disadvantages, such as well-known side effects (statins) or high costs (monoclonal antibodies). Thus, there is still a need for effective cholesterol-lowering drugs with minimal side effects, preferably orally bioavailable. Low-molecular-weight PCSK9 inhibitors could be a worthy alternative for this purpose.

Circulating Furin-Cleaved Proprotein Convertase Subtilisin/Kexin Type 9 Concentration Predicts Future Coronary Events in Japanese Subjects

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) circulates as mature and furin-cleaved forms, which differ in their properties to degrade low-density lipoprotein (LDL) receptors.

Objectives

In this study, we sought to investigate whether PCSK9 subtypes associate with atherosclerotic cardiovascular events.

Methods

We investigated 1,436 statin-naive Japanese subjects without any cardiovascular disease in the Suita Study, an epidemiologic Japanese cohort study. Total, mature, and furin-cleaved PCSK9 levels were measured by means of enzyme-linked immunosorbent assay. The occurrence of coronary and stroke events were compared in subjects stratified by PCSK9 level tertile.

Results

Total, mature, and furin-cleaved PCSK9 levels were associated with non–high-density lipoprotein cholesterol (all P < 0.001) and systolic blood pressure (P = 0.001, P = 0.004, and P < 0.001, respectively). Furthermore, only furin-cleaved PCSK9 level was correlated to high-sensitivity C-reactive protein (hs-CRP) (P < 0.001). During the 13.6-year observational period, furin-cleaved PCSK9 level predicted a greater likelihood of experiencing coronary events (tertile 2: hazard ratio [HR]: 2.84 [95% confidence interval [CI]: 1.21-6.65; P = 0.01]; tertile 3: HR: 2.81 [95% CI: 1.17-6.74; P = 0.02]), but not stroke (tertile 2: HR: 1.31 [95% CI: 0.72-2.40; P = 0.36]; tertile 3: HR: 1.27 [95% CI: 0.68-2.38; P = 0.44]). Total and mature PCSK9 levels were not associated with coronary events (total PCSK9: tertile 2: HR: 1.35 [95% CI: 0.68-2.68; P = 0.39]; tertile 3: HR: 1.13 [95% CI: 0.54-2.34; P = 0.73]; mature PCSK9: tertile 2: HR: 1.02 [95% CI: 0.52-2.02; P = 0.93]; tertile 3: HR: 0.96 [95% CI: 0.47-1.95; P = 0.92]) and stroke events (total PCSK9: tertile 2: HR: 0.90 [95% CI: 0.50-1.61; P = 0.72]; tertile 3: HR: 0.99 [95% CI:0.54-1.80; P = 0.97]; mature PCSK9: tertile 2: HR: 0.86 [95% CI: 0.47-1.57; P = 0.63]; tertile 3: HR: 1.11 [95% CI: 0.61-1.99; P = 0.72]), respectively.

Conclusions

Furin-cleaved but not total and mature PCSK9 was associated with both LDL cholesterol and hs-CRP and predicted future coronary events in the primary prevention settings. Our findings provide pathophysiological insights into the properties of PCSK9 subtypes in association with coronary events.

The PCSK9 discovery, an inactive protease with varied functions in hypercholesterolemia, viral infections, and cancer

In 2003, the sequences of mammalian proprotein convertase subtilisin/kexin type 9 (PCSK9) were reported. Radiolabeling pulse-chase analyses demonstrated that PCSK9 was synthesized as a precursor (proPCSK9) that undergoes autocatalytic cleavage in the endoplasmic reticulum into PCSK9, which is then secreted as an inactive enzyme in complex with its inhibitory prodomain. Its high mRNA expression in liver hepatocytes and its gene localization on chromosome 1p32, a third locus associated with familial hypercholesterolemia, other than LDLR or APOB, led us to identify three patient families expressing the PCSK9 variants S127R or F216L. Although Pcsk9 and Ldlr were downregulated in mice that were fed a cholesterol-rich diet, PCSK9 overexpression led to the degradation of the LDLR. This led to the demonstration that gain-of-function and loss-of-function variations in PCSK9 modulate its bioactivity, whereby PCSK9 binds the LDLR in a nonenzymatic fashion to induce its degradation in endosomes/lysosomes. PCSK9 was also shown to play major roles in targeting other receptors for degradation, thereby regulating various processes, including hypercholesterolemia and associated atherosclerosis, vascular inflammation, viral infections, and immune checkpoint regulation in cancer. Injectable PCSK9 monoclonal antibody or siRNA is currently used in clinics worldwide to treat hypercholesterolemia and could be combined with current therapies in cancer/metastasis. In this review, we present the critical information that led to the discovery of PCSK9 and its implication in LDL-C metabolism. We further analyze the underlying functional mechanism(s) in the regulation of LDL-C, as well as the evolving novel roles of PCSK9 in both health and disease states.

The association between plasma furin and cardiovascular events after acute myocardial infarction

Background

Furin is the key enzyme involved in the cleavage of pro-BNP and plays a critical role in the cardiovascular system through its involvement in lipid metabolism, blood pressure regulation and the formation of atheromatous plaques. NT-proBNP and recently, corin, also a key enzyme in the cleavage of pro-BNP, have been accepted as predictors of prognosis after acute myocardial infarction (AMI). This cohort study was conducted to investigate the relationship between plasma furin and the prognostic outcomes of AMI patients.

Methods

In total, 1100 AMI patients were enrolled in the study and their plasma furin concentrations were measured. The primary endpoint was major adverse cardiac events (MACE), a composite of cardiovascular (CV) death, non-fatal myocardial infarction (MI) and non-fatal stroke. The associations between plasma furin concentration and AMI outcomes were explored using Kaplan–Meier curves and multivariate Cox regression analysis.

Results

The results showed a slight increase in mean cTNT in patients with higher furin concentrations (P = 0.016). Over a median follow-up of 31 months, multivariate Cox regression analysis indicated that plasma furin was not significantly associated with MACE (HR 1.01; 95% CI 0.93–1.06; P = 0.807) after adjustment for potential conventional risk factors. However, plasma furin was associated with non-fatal MI (HR 1.09; 95% CI 1.01–1.17; P = 0.022) in the fully adjusted model. Subgroup analyses indicated no relationship between plasma furin and MACE in different subgroups.

Conclusions

This study found no association between plasma furin and risk of MACE. Thus, plasma furin may not be a useful predictor of poor prognosis after AMI. However, higher levels of plasma furin may be associated with a higher risk of recurrent non-fatal MI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-021-02029-y.

Asialoglycoprotein receptor 1 is a novel PCSK9-independent ligand of liver LDLR cleaved by furin

The hepatic carbohydrate-recognizing asialoglycoprotein receptor (ASGR1) mediates the endocytosis/lysosomal degradation of desialylated glycoproteins following binding to terminal galactose/N-acetylgalactosamine. Human heterozygote carriers of ASGR1 deletions exhibit ∼34% lower risk of coronary artery disease and ∼10% to 14% reduction of non-HDL cholesterol. Since the proprotein convertase PCSK9 is a major degrader of the low-density lipoprotein receptor (LDLR), we investigated the degradation and functionality of LDLR and/or PCSK9 by endogenous/overexpressed ASGR1 using Western blot and immunofluorescence in HepG2-naïve and HepG2-PCSK9-knockout cells. ASGR1, like PCSK9, targets LDLR, and both independently interact with/enhance the degradation of the receptor. This lack of cooperativity between PCSK9 and ASGR1 was confirmed in livers of wildtype (WT) and Pcsk9^−/− mice. ASGR1 knockdown in HepG2-naïve cells significantly increased total (∼1.2-fold) and cell-surface (∼4-fold) LDLR protein. In HepG2-PCSK9-knockout cells, ASGR1 silencing led to ∼2-fold higher levels of LDLR protein and DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate)-LDL uptake associated with ∼9-fold increased cell-surface LDLR. Overexpression of WT-ASGR1/2 primarily reduced levels of immature non-O-glycosylated LDLR (∼110 kDa), whereas the triple Ala-mutant of Gln240/Trp244/Glu253 (characterized by loss of carbohydrate binding) reduced expression of the mature form of LDLR (∼150 kDa), suggesting that ASGR1 binds the LDLR in both a sugar-dependent and -independent fashion. The protease furin cleaves ASGR1 at the RKMK¹⁰³↓ motif into a secreted form, likely resulting in a loss of function on LDLR. Altogether, we demonstrate that LDLR is the first example of a liver-receptor ligand of ASGR1. We conclude that silencing of ASGR1 and PCSK9 may lead to higher LDL uptake by hepatocytes, thereby providing a novel approach to further reduce LDL cholesterol levels.

Substantial PCSK9 inactivation in β-cells does not modify glucose homeostasis or insulin secretion in mice

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in cholesterol homeostasis by promoting the degradation of the LDL receptor (LDLR). PCSK9 loss-of-function mutations are associated with increased fasting plasma glucose levels and slightly elevated risk of type 2-diabetes. Considering the known detrimental effects of cholesterol accumulation in β-cell, and the widespread use of PCSK9 inhibitors to treat hypercholesterolemia, it is important to gain insight into the role of pancreatic PCSK9 in glucose homeostasis and β-cell function. We generated the first β-cell-specific KO of PCSK9 (βKO). PCSK9 mRNA and protein expression were reduced by 48% and 78% in βKO islets, respectively, indicating that β-cells constitute a major site of PCSK9 expression. In islets, loss of β-cell PCSK9 resulted in unchanged LDLR protein levels, but reduced LDLR mRNA, indicating that cholesterol internalization is enhanced and that β-cell PCSK9 promotes LDLR degradation. In contrast, whole body PCSK9 KO mice exhibited 2-fold higher LDLR protein levels in islets and a stable expression of cholesterogenic genes. Whole body KO and βKO mice presented normal glucose tolerance, insulin release in response to glucose load and insulin sensitivity. Ex vivo glucose-stimulated insulin secretion in presence or absence of fatty acids was similar in WT and KO islets. Like KO mice, individuals carrying loss-of-function PCSK9 variants may be protected from cholesterol-induced toxicity due to reduced circulating cholesterol levels. Using both whole body KO or βKO models, our data demonstrate that PCSK9 deletion in mouse does not have any toxic effect on β-cell function and glucose homeostasis.

Circulating Mature PCSK9 Level Predicts Diminished Response to Statin Therapy

Background Statin-mediated efficacy of lowering low-density lipoprotein (LDL) cholesterol varies in each individual, and its diminished response is associated with worse outcomes. However, there is no established approach to predict hyporesponse to statins. PCSK9 (proprotein convertase subxilisin/kexin type 9) is a serine-protease associated with LDL metabolism, which circulates as mature and furin-cleaved PCSK9. Since mature PCSK9 more potently degrades the LDL receptor, its evaluation may enable the identification of statin hyporesponders. Methods and Results We analyzed 101 statin-naive patients with coronary artery disease who commenced a statin. PCSK9 subtypes at baseline and 1 month after statin use were measured by ELISA. Hyporesponse to statins was defined as a percent reduction in LDL cholesterol <15%. The relationship between each PCSK9 subtype level and hyporesponse to statins was investigated. Statins significantly lowered LDL cholesterol level (percent reduction, 40%±21%), whereas 11% of study participants exhibited a hyporeseponse to statins. Multivariable logistic regression analysis demonstrated that baseline mature PCSK9 level was an independent predictor for hyporesponse to statins even after adjusting clinical characteristics (mature PCSK9 per 10-ng/mL increase: odds ratio [OR], 1.12; 95% CI, 1.01-1.24 [P=0.03]), whereas furin-cleaved level was not (per 10-ng/mL increase: OR, 1.37; 95% CI, 0.73-2.58 [P=0.33]). Receiver operating characteristic curve analysis identified mature PCSK9 level of 228 ng/mL as an optimal cutoff to predict hyporesponse to statins (area under the curve, 0.73 [sensitivity, 0.91; specificity, 0.56]). Conclusions Baseline mature PCSK9 level >228 ng/mL is associated with hyporesponse to statins. This finding suggests that mature PCSK9 might be a potential determinant of hyporesponse to statins.

Interfering with Host Proteases in SARS-CoV-2 Entry as a Promising Therapeutic Strategy

Due to its fast international spread and substantial mortality, the coronavirus disease COVID-19 evolved to a global threat. Since currently, there is no causative drug against this viral infection available, science is striving for new drugs and approaches to treat the new disease. Studies have shown that the cell entry of coronaviruses into host cells takes place through the binding of the viral spike (S) protein to cell receptors. Priming of the S protein occurs via hydrolysis by different host proteases. The inhibition of these proteases could impair the processing of the S protein, thereby affecting the interaction with the host-cell receptors and preventing virus cell entry. Hence, inhibition of these proteases could be a promising strategy for treatment against SARS-CoV-2. In this review, we discuss the current state of the art of developing inhibitors against the entry proteases furin, the transmembrane serine protease type-II (TMPRSS2), trypsin, and cathepsin L.

Mouse Models of Human Proprotein Convertase Insufficiency

The kexin-like proprotein convertases perform the initial proteolytic cleavages that ultimately generate a variety of different mature peptide and proteins, ranging from brain neuropeptides to endocrine peptide hormones, to structural proteins, among others. In this review, we present a general introduction to proprotein convertase structure and biochemistry, followed by a comprehensive discussion of each member of the kexin-like subfamily of proprotein convertases. We summarize current knowledge of human proprotein convertase insufficiency syndromes, including genome-wide analyses of convertase polymorphisms, and compare these to convertase null and mutant mouse models. These mouse models have illuminated our understanding of the roles specific convertases play in human disease and have led to the identification of convertase-specific substrates; for example, the identification of procorin as a specific PACE4 substrate in the heart. We also discuss the limitations of mouse null models in interpreting human disease, such as differential precursor cleavage due to species-specific sequence differences, and the challenges presented by functional redundancy among convertases in attempting to assign specific cleavages and/or physiological roles. However, in most cases, knockout mouse models have added substantively both to our knowledge of diseases caused by human proprotein convertase insufficiency and to our appreciation of their normal physiological roles, as clearly seen in the case of the furin, proprotein convertase 1/3, and proprotein convertase 5/6 mouse models. The creation of more sophisticated mouse models with tissue- or temporally-restricted expression of specific convertases will improve our understanding of human proprotein convertase insufficiency and potentially provide support for the emerging concept of therapeutic inhibition of convertases.

Association Between Circulating Proprotein Convertase Subtilisin/Kexin Type 9 and Major Adverse Cardiovascular Events, Stroke, and All-Cause Mortality: Systemic Review and Meta-Analysis

Background: Proprotein convertase subtilisin/kexin type 9 (PCSK9), a pivotal protein in low-density lipoprotein cholesterol metabolism, has been validated to be an established target for cardiovascular (CV) risk reduction. Nevertheless, prospective studies concerning the associations between circulating PCSK9 and the risk of CV events and mortality have yielded, so far, inconsistent results. Herein, we conducted a meta-analysis to evaluate the association systemically. Methods: Pertinent studies were identified from PubMed, EMBASE, and Cochrane Library database through July 2020. Longitudinal studies investigating the value of circulating PCSK9 for predicting major adverse cardiovascular events (MACEs) or stroke or all-cause mortally with risk estimates and 95% confidence intervals (CI) were included in the analyses. Dose-response meta-analysis was also applied to evaluate circulating PCSK9 and risk of MACEs in this study. Results: A total of 22 eligible cohorts comprising 28,319 participants from 20 eligible articles were finally included in the study. The pooled relative risk (RR) of MACEs for one standard deviation increase in baseline PCSK9 was 1.120 (95% CI, 1.056-1.189). When categorizing subjects into tertiles, the pooled RR for the highest tertile of baseline PCSK9 was 1.252 (95% CI, 1.104-1.420) compared with the lowest category. This positive association between PCSK9 level and risk of MACEs persisted in sensitivity and most of the subgroup analyses. Twelve studies were included in dose-response meta-analysis, and a linear association between PCSK9 concentration and risk of MACEs was observed (x2 test for non-linearity = 0.31, P non-linearity = 0.575). No significant correlation was found either on stroke or all-cause mortality. Conclusion: This meta-analysis added further evidence that high circulating PCSK9 concentration significantly associated with increased risk of MACEs, and a linear dose-response association was observed. However, available data did not suggest significant association either on stroke or all-cause mortality. Additional well-designed studies are warranted to further investigate the correlations between PCSK9 concentration and stroke and mortality.

Nuclear magnetic resonance reveals postprandial low-density lipoprotein cholesterol determined by enzymatic method could be a misleading indicator

BACKGROUND

Serum concentration of low-density lipoprotein cholesterol (LDL-C) is markedly reduced after a meal. Does postprandial cholesterol in LDL truly decline via clearance of LDL particles or is there simply a redistribution of cholesterol in LDL subclasses? Thus, we sought to evaluate whether postprandial decline of LDL-C reflects a reduction of LDL particle and to assess the correlation between proprotein convertase subtilisin/kexin type 9 (PCSK9) concentration and postprandial atherogenic lipoproteins profile.

METHODS

Eighty-seven persons were enrolled in this study. We measured lipid profiles by enzymatic and nuclear magnetic resonance (NMR)-based methods and serum PCSK9 concentration by enzyme-linked immunosorbent assays before and after a meal. Plasma samples were collected after a 10-h fasting and 2 and 4 h post-meal.

RESULTS

Compared to the fasting status, there was significant postprandial decline of LDL-C measured enzymatically (LDL-Ce) at 2nd and 4th h [99.38 (80.43, 120.65) vs 95.51 (74.25, 117.17) vs 87.01 (69.99, 108.28) mg/dl, p < 0.000]. But there was no significant reduction in LDL particle and its cholesterol content (LDL-Cn) determined by NMR. Just the postprandial large LDL particle [186.45 (151.36, 229.42) vs 176.92 (147.43, 220.91) vs 181.77 (149.05, 224.17), p < 0.000] and its cholesterol content [19.10 (15.09, 22.37) vs 18.28 (14.59, 21.84) vs 17.79 (14.62, 22.14), p < 0.000] were greatly decreased at 2nd and 4th h compared to the fasting one. Interestingly, postprandial serum PCSK9 was decreased at 2nd and 4th h compared with fasting concentration [298.75 (233.25, 396.92) vs 257.34 (207.52, 342.36) vs 250.57 (215.02, 339.66) ng/ml, p < 0.000]. The postprandial percent decrease in serum PCSK9 at 4th h was positively correlated to the percent decline in postprandial LDL-Ce (r = 0.252, p = 0.019) but was independently associated with the percent increase in remnant cholesterol (r = 0.262, p = 0.016).

CONCLUSIONS

Postprandial decline of LDL-C determined enzymatically was not confirmed by NMR-based methods. Indeed, there exists cholesterol redistribution in LDL subclasses following a meal. The decrease of postprandial PCSK9 may be secondary to the increase in intrahepatic lipids following food intake.

SARS-CoV-2, Early Entry Events

Viruses are obligate intracellular parasites, and host cell entry is the first step in the viral life cycle. The SARS-CoV-2 (COVID-19) entry process into susceptible host tissue cells is complex requiring (1) attachment of the virus via the conserved spike (S) protein receptor-binding motif (RBM) to the host cell angiotensin-converting-enzyme 2 (ACE2) receptor, (2) S protein proteolytic processing, and (3) membrane fusion. Spike protein processing occurs at two cleavage sites, i.e., S1/S2 and S2'. Cleavage at the S1/S2 and S2' sites ultimately gives rise to generation of competent fusion elements important in the merging of the host cell and viral membranes. Following cleavage, shedding of the S1 crown results in significant conformational changes and fusion peptide repositioning for target membrane insertion and fusion. Identification of specific protease involvement has been difficult due to the many cell types used and studied. However, it appears that S protein proteolytic cleavage is dependent on (1) furin and (2) serine protease transmembrane protease serine 2 proteases acting in tandem. Although at present not clear, increased SARS-CoV-2 S receptor-binding motif binding affinity and replication efficiency may in part account for observed differences in infectivity. Cleavage of the ACE2 receptor appears to be yet another layer of complexity in addition to forfeiture and/or alteration of ACE2 function which plays an important role in cardiovascular and immune function.

Insights into the kinetics and dynamics of the furin-cleaved form of PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates cholesterol metabolism by inducing the degradation of hepatic low density lipoprotein receptors (LDLRs). Plasma PCSK9 has 2 main molecular forms: a 62 kDa mature form (PCSK9_62) and a 55 kDa, furin-cleaved form (PCSK9_55). PCSK9_55 is considered less active than PCSK9_62 in degrading LDLRs. We aimed to identify the site of PCSK9_55 formation (intracellular vs. extracellular) and to further characterize the LDLR-degradative function of PCSK9_55 relative to PCSK9_62. Coexpressing PCSK9_62 with furin in cell culture induced formation of PCSK9_55, most of which was found in the extracellular space. Under the same conditions, we found that i) adding a cell-permeable furin inhibitor preferentially decreased the formation of PCSK9_55 extracellularly; ii) using pulse-chase analysis, we observed the formation of PCSK9_55 exclusively extracellularly in a time-dependent manner. A recombinant form of PCSK9_55 was efficiently produced but displayed impaired secretion that resulted in its intracellular trapping. However, the nonsecreted PCSK9_55 was able to induce degradation of LDLR, though with 50% lower efficiency than PCSK9_62. Collectively, our data show that 1) PCSK9_55 is formed extracellularly; 2) PCSK9_55 has a shorter half-life; 3) there is a small intracellular pool of PCSK9_55 that is not secreted; and 4) PCSK9_55 retained within the cell maintains a reduced efficiency to cause LDLR degradation.

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.

Secretion of the epithelial sodium channel chaperone PCSK9 from the cortical collecting duct links sodium retention with hypercholesterolemia in nephrotic syndrome

The proprotein PCSK9 functions as a chaperone for the epithelial sodium channel in the cortical collecting duct (CCD), is highly expressed in the liver, and plays a significant role in the pathogenesis of hypercholesterolemia. Lower levels of PCSK9 expression also occur in the normal kidney and intestine. Here, we found increased PCSK9 expression in the CCD of biopsies of patients with primary glomerular disease and explored a possible relationship with hypercholesterolemia of nephrotic syndrome. Significantly elevated serum PCSK9 and cholesterol levels were noted in two models of focal and segmental glomerulosclerosis, the Rrm2b-/- mouse and the Buffalo/Mna rat. Increased expression of PCSK9 in the kidney occurred when liver expression was reduced in both models. The impact of reduced or increased PCSK9 in the CCD on hypercholesterolemia in nephrotic syndrome was next studied. Mice with selective deficiency of PCSK9 expression in the collecting duct failed to develop hypercholesterolemia after injection of nephrotoxic serum. Blocking epithelial sodium channel activity with Amiloride in Rrm2b-/- mice resulted in increased expression of its chaperone PCSK9 in the CCD, followed by elevated plasma levels and worsening hypercholesterolemia. Thus, our data suggest that PCSK9 in the kidney plays a role in the initiation of hypercholesterolemia in nephrotic syndrome and make a case for depletion of PCSK9 early in patients with nephrotic syndrome to prevent the development of hypercholesterolemia.

Progress and prospects of biological approaches targeting PCSK9 for cholesterol-lowering, from molecular mechanism to clinical efficacy

INTRODUCTION

Cardiovascular disorders are one of the leading causes of mortality and morbidity worldwide. Recent advances showed a promising role of proprotein convertase subtilisin/kexin type 9 (PCSK9) as a critical player in regulating plasma LDL levels and lipid metabolism.

AREAS COVERED

This review addresses the molecular functions of PCSK9 with a vision on the clinical progress of utilizing monoclonal antibodies and other biological approaches to block PCSK9 activity. The successful clinical trials with monoclonal antibodies are reviewed. Recent advances in (pre)clinical trials of other biological approaches, such as small interfering RNAs, are also discussed.

EXPERT OPINION

Discovery of PCSK9 and clinical use of its inhibitors to manage lipid metabolism is a step forward in hypolipidaemic therapy. A better understanding of the molecular activity of PCSK9 can help to identify new approaches in the inhibition of PCSK9 expression/activity. Whether if PCSK9 plays a role in other cardiometabolic conditions may provide grounds for further development of therapies.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection: let the virus be its own demise

There has been a collaborative global effort to construct novel therapeutic and prophylactic approaches to SARS-CoV-2 management. Although vaccine development is crucial, acute management of newly infected patients, especially those with severe acute respiratory distress syndrome, is a priority. Herein we describe the rationale and potential of repurposing a dual plasmid, Vigil (pbi-shRNA^furin-GM-CSF), now in Phase III cancer trials, for the treatment of and, in certain circumstances, enhancement of the immune response to SARS-CoV-2.

Plasma kinetics of mature PCSK9, furin-cleaved PCSK9, and Lp(a) with or without administration of PCSK9 inhibitors in acute myocardial infarction

BACKGROUND

There are two types of circulating proprotein convertase subtilisin/kexin type 9 (PCSK9), mature and furin-cleaved. Most types of lipoprotein(a) [Lp(a)], an independent risk factor of cardiovascular events, bind to mature PCSK9.

OBJECTIVE

This study examined the effects of monoclonal anti-PCSK9 antibody on plasma PCSK9 and Lp(a) levels in acute myocardial infarction (MI).

METHODS

Acute MI patients (n=36) were randomly divided into evolocumab (140mg; n=17) and non-evolocumab (n=19) groups. Changes in plasma PCSK9 and Lp(a) levels were monitored before and 1, 3, 5, 10, and 20 days after evolocumab administration.

RESULTS

In the non-evolocumab group, plasma levels of mature PCSK9, furin-cleaved PCSK9, and Lp(a) (236.4±57.3ng/mL, 22.4±5.8ng/mL, and 19.2.±16.5mg/dL, respectively) significantly increased by day 3 (408.8±77.1ng/mL, p<0.001; 47.2±15.7ng/mL, p<0.001; and 39.7±21.3mg/dL, p<0.005, respectively) and returned to the baseline by day 10 or 20. In the evolocumab group, mature PCSK9 significantly increased by >1000ng/mL with a simultaneous decline of furin-cleaved PCSK9 below the measurement sensitivity level after day 3. The incremental area under the curve for plasma Lp(a) levels was significantly smaller in the evolocumab group compared with the non-evolocumab group (p=0.038).

CONCLUSION

Mature and furin-cleaved PCSK9 are transiently upregulated after MI onset. Evolocumab significantly increases mature PCSK9 and decreases furin-cleaved PCSK9 and might inhibit transient increase of plasma Lp(a) in acute MI.

Angiopoietin1 Deficiency in Hepatocytes Affects the Growth of Colorectal Cancer Liver Metastases (CRCLM)

Colorectal cancer liver metastases (CRCLM) that receive their blood supply via vessel co-option are associated with a poor response to anti-angiogenic therapy. Angiopoietins (Ang1 and Ang2) with their Tyrosine-protein kinase receptor (Tie2) have been shown to support vessel co-option. We demonstrate significantly higher expression of Ang1 in hepatocytes adjacent to the tumor region of human chemonaïve and treated co-opting (replacement histopathological growth patterns: RHGP) tumors. To investigate the role of the host Ang1 expression, Ang1 knockout (KO) mice were injected intra-splenically with metastatic MC-38 colon cancer cells that develop co-opting liver metastases. We observed a reduction in the number of liver metastases and interestingly, for the first time, the development of angiogenic driven desmoplastic (DHGP) liver metastases. In addition, in-vitro, knockout of Ang1 in primary hepatocytes inhibited viability, migration and invasion ability of MC-38 cells. We also demonstrate that Ang 1 alone promotes the migration and growth of both human and mouse colon cancer cell lines These results provide evidence that high expression of Ang1 in the host liver is important to support vessel co-option (RHGP lesions) and when inhibited, favours the formation of angiogenic driven liver metastases (DHGP lesions).

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.

Furin-mediated protein processing in infectious diseases and cancer

Proteolytic cleavage regulates numerous processes in health and disease. One key player is the ubiquitously expressed serine protease furin, which cleaves a plethora of proteins at polybasic recognition motifs. Mammalian substrates of furin include cytokines, hormones, growth factors and receptors. Thus, it is not surprising that aberrant furin activity is associated with a variety of disorders including cancer. Furthermore, the enzymatic activity of furin is exploited by numerous viral and bacterial pathogens, thereby enhancing their virulence and spread. In this review, we describe the physiological and pathophysiological substrates of furin and discuss how dysregulation of a simple proteolytic cleavage event may promote infectious diseases and cancer. One major focus is the role of furin in viral glycoprotein maturation and pathogenicity. We also outline cellular mechanisms regulating the expression and activation of furin and summarise current approaches that target this protease for therapeutic intervention.

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Inhibitors, Reality or Dream in Managing Patients with Cardiovascular Disease

BACKGROUND

Statins have been a major keystone in the management of patients with atherosclerotic cardiovascular disease. The benefits of inhibiting HMG CoA reductase, via statins, were translated into reduction in LDL-c with proportionate decrease in cardiovascular events in response to the magnitude of LDL-c reduction. Despite major advances in pharmacological treatments, including the use of high-dose statins, there are urgent need to further reduce future cardiovascular risk. This is in particularly important since 1 out of 5 high-risk atherosclerotic patients who achieve low LDL-c return with a second cardiovascular event within five years. Although this residual risk post-statin is largely heterogeneous, lowering LDL-c beyond 'normal' or guidelines-recommended level using novel therapies has resulted in further reduction in cardiovascular events.

OBJECTIVE

The current review will discuss the use of PCSK9 inhibitors in patients with atherosclerotic disease. PCSK9 inhibitors are a new class of lipid-lowering drugs that are either fully human monoclonal antibodies (evolocumab and alirocumab) or humanised monoclonal antibodies (bococizumab) that effectively reduce LDL-c to unprecedented level. By blocking circulating PCSK9, these drugs would preserve LDL receptors and prevent them from cellular degradation. This process promotes recycling of LDL receptors back to hepatocytes surface, leading into further reduction of LDL-c. Combining PCSK9 inhibitors with statin have led into lower LDL-c, reduction in plaque volume and more importantly reduction in future cardiovascular events.

CONCLUSION

These drugs are very promising, nonetheless, the unselective approach of applying these monoclonal antibodies may not prove to be cost-effective and potentially exposing some patients to unnecessary side effects.

A single domain antibody against the Cys- and His-rich domain of PCSK9 and evolocumab exhibit different inhibition mechanisms in humanized PCSK9 mice

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that binds and escorts the low density lipoprotein receptor (LDLR) into the lysosomal degradation pathway. Prescribed monoclonal antibodies (mAbs) against PCSK9 prevent its binding to the LDLR, and result in ~60% lower LDL cholesterol (LDLc) levels. Although efficient, mAbs are expensive. Hence other PCSK9 inhibitors are needed. For screening purpose, we developed C57BL/6J mice expressing the human PCSK9 gene under the control of its own promoter, but lacking endogenous mouse PCSK9. All lines recapitulate the endogenous PCSK9 expression pattern. The Tg2 line that expresses physiological levels of human PCSK9 (hPCSK9) was selected to characterize the inhibitory properties of a previously reported single domain antibody (sdAb), PKF8-mFc, which binds the C-terminal domain of PCSK9. Upon intraveinous injection of 10 mg/kg, PKF8-mFc and the mAb evolocumab neutralized ~50% and 100% of the hPCSK9 impact on total cholesterol (TC) levels, respectively, but PKF8-mFc had a more sustained effect. PKF8-mFc barely affected hPCSK9 levels, whereas evolocumab promoted a 4-fold increase 3 days post-injection, suggesting very different inhibitory mechanisms. The present study also shows that the new transgenic mice are well suited to screen a variety of hPCSK9 inhibitors.

Changes in circulating pro-protein convertase subtilisin/kexin type 9 levels - experimental and clinical approaches with lipid-lowering agents

Regulation of pro-protein convertase subtilisin/kexin type 9 (PCSK9) by drugs has led to the development of a still small number of agents with powerful activity on low-density lipoprotein cholesterol levels, associated with a significant reduction of cardiovascular events in patients in secondary prevention. The Further Cardiovascular Outcomes Research with PCSK9 Inhibition in Subjects with Elevated Risk (FOURIER) and Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab (ODYSSEY OUTCOMES) studies, with the two available PCSK9 antagonists, i.e. evolocumab and alirocumab, both reported a 15% reduction in major adverse cardiovascular events. Regulation of PCSK9 expression is dependent upon a number of factors, partly genetic and partly associated to a complex transcriptional system, mainly controlled by sterol regulatory element binding proteins. PCSK9 is further regulated by concomitant drug treatments, particularly by statins, enhancing PCSK9 secretion but decreasing its stimulatory phosphorylated form (S688). These complex transcriptional mechanisms lead to variable circulating levels making clinical measurements of plasma PCSK9 for cardiovascular risk assessment a debated matter. Determination of total PCSK9 levels may provide a diagnostic tool for explaining an apparent resistance to PCSK9 inhibitors, thus indicating the need for other approaches. Newer agents targeting PCSK9 are in clinical development with a major interest in those with a longer duration of action, e.g. RNA silencing, allowing optimal patient compliance. Interest has been expanded to areas not only limited to low-density lipoprotein cholesterol reduction but also investigating other non-lipid pathways raising cardiovascular risk, in particular inflammation associated to raised high-sensitivity C-reactive protein levels, not significantly affected by the present PCSK9 antagonists.

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.

Plasma levels of the proprotein convertase furin and incidence of diabetes and mortality

BACKGROUND

Diabetes mellitus is linked to premature mortality of virtually all causes. Furin is a proprotein convertase broadly involved in the maintenance of cellular homeostasis; however, little is known about its role in the development of diabetes mellitus and risk of premature mortality.

OBJECTIVES

To test if fasting plasma concentration of furin is associated with the development of diabetes mellitus and mortality.

METHODS

Overnight fasted plasma furin levels were measured at baseline examination in 4678 individuals from the population-based prospective Malmö Diet and Cancer Study. We studied the relation of plasma furin levels with metabolic and hemodynamic traits. We used multivariable Cox proportional hazards models to investigate the association between baseline plasma furin levels and incidence of diabetes mellitus and mortality during 21.3-21.7 years follow-up.

RESULTS

An association was observed between quartiles of furin concentration at baseline and body mass index, blood pressure and plasma concentration of glucose, insulin, LDL and HDL cholesterol (|0.11| ≤ β ≤ |0.31|, P < 0.001). Plasma furin (hazard ratio [HR] per one standard deviation increment of furin) was predictive of future diabetes mellitus (727 events; HR = 1.24, CI = 1.14-1.36, P < 0.001) after adjustment for age, sex, body mass index, systolic and diastolic blood pressure, use of antihypertensive treatment, alcohol intake and fasting plasma level of glucose, insulin and lipoproteins cholesterol. Furin was also independently related to the risk of all-cause mortality (1229 events; HR = 1.12, CI = 1.05-1.19, P = 0.001) after full multivariable adjustment.

CONCLUSION

Individuals with high plasma furin concentration have a pronounced dysmetabolic phenotype and elevated risk of diabetes mellitus and premature mortality.