Immunohistochemical localization of subtilisin/kexin-like proprotein convertases in human atherosclerosis

Furin knockdown inhibited EndMT and abnormal proliferation and migration of endothelial cells

BACKGROUND

In the pathogenesis of atherosclerotic cardiovascular disorders, vascular endothelium is crucial. A critical step in the development of atherosclerosis is endothelial dysfunction. Furin may play a factor in vascular remodeling, inflammatory cell infiltration, regulation of plaque stability, and atherosclerosis by affecting the adhesion and migration of endothelial cells. It is yet unknown, though, how furin contributes to endothelial dysfunction.

METHODS

We stimulated endothelial cells with oxidized modified lipoprotein (ox-LDL). Endothelial-to-mesenchymal transition (EndMT) was found using immunofluorescence (IF) and western blot (WB). Furin expression level and Hippo/YAP signal activation were found using reverse transcription-quantitative PCR (RT-qPCR) and WB, respectively. To achieve the goal of furin knockdown, we transfected siRNA using the RNA transmate reagent. Following furin knockdown, cell proliferation, and migration were assessed by the CCK-8, scratch assay, and transwell gold assay, respectively. WB and IF both picked up on EndMT. WB and RT-qPCR, respectively, were used to find furin's expression level. We chose the important micrornas that can regulate furin and we then confirmed them using RT-qPCR.

RESULTS

EndMT was created by ox-LDL, evidenced by the up-regulation of mesenchymal cell markers and the down-regulation of endothelial cell markers. Furin expression levels in both protein and mRNA were increased, and the Hippo/YAP signaling pathway was turned on. Furin knockdown dramatically reduced the aberrant migration and proliferation of endothelial cells by ox-LDL stimulation. Furin knockdown can also suppress ox-LDL-induced EndMT, up-regulate indicators of endothelial cells, and down-regulate markers of mesenchymal cells. After ox-LDL stimulation and siRNA transfection, furin's expression level was up-regulated and down-regulated.

CONCLUSION

Our study demonstrated that furin knockdown could affect ox-LDL-induced abnormal endothelial cell proliferation, migration, and EndMT. This implies that furin plays an important role in endothelial dysfunction.

Functional and Multi-Omics Effects of an Optimized CRISPR-Mediated FURIN Depletion in U937 Monocytes

The pro-protein convertase FURIN (PCSK3) is implicated in a wide range of normal and pathological biological processes such as infectious diseases, cancer and cardiovascular diseases. Previously, we performed a systemic inhibition of FURIN in a mouse model of atherosclerosis and demonstrated significant plaque reduction and alterations in macrophage function. To understand the cellular mechanisms affected by FURIN inhibition in myeloid cells, we optimized a CRISPR-mediated gene deletion protocol for successfully deriving hemizygous (HZ) and nullizygous (NZ) FURIN knockout clones in U937 monocytic cells using lipotransfection-based procedures and a dual guide RNA delivery strategy. We observed differences in monocyte and macrophage functions involving phagocytosis, lipid accumulation, cell migration, inflammatory gene expression, cytokine release patterns, secreted proteomics (cytokines) and whole-genome transcriptomics between wild-type, HZ and NZ FURIN clones. These studies provide a mechanistic basis on the possible roles of myeloid cell FURIN in cardiovascular disorders.

Allele-Specific Epigenetic Regulation of FURIN Expression at a Coronary Artery Disease Susceptibility Locus

Genome-wide association studies have revealed an association between the genetic variant rs17514846 in the FURIN gene and coronary artery disease. We investigated the mechanism through which rs17514846 modulates FURIN expression. An analysis of isogenic monocytic cell lines showed that the cells of the rs17514846 A/A genotype expressed higher levels of FURIN than cells of the C/C genotype. Pyrosequencing showed that the cytosine (in a CpG motif) at the rs17514846 position on the C allele was methylated. Treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine increased FURIN expression. An electrophoretic mobility super-shift assay with a probe corresponding to the DNA sequence at and around the rs17514846 position of the C allele detected DNA-protein complex bands that were altered by an anti-MeCP2 antibody. A chromatin immunoprecipitation assay with the anti-MeCP2 antibody showed an enrichment of the DNA sequence containing the rs17514846 site. siRNA-mediated knockdown of MeCP2 caused an increase in FURIN expression. Furthermore, MeCP2 knockdown increased monocyte migration and proliferation, and this effect was diminished by a FURIN inhibitor. The results of our study suggest that DNA methylation inhibits FURIN expression and that the coronary artery disease-predisposing variant rs17514846 modulates FURIN expression and monocyte migration via an allele-specific effect on DNA methylation.

Therapeutic potential of the Proprotein Convertase Subtilisin/Kexin family in vascular disease

Proprotein convertase subtilisin/kexins (PCSKs) constitute a family of nine related proteases: PCSK1-7, MBTPS1, and PCSK9. Apart from PCSK9, little is known about PCSKs in cardiovascular disease. Here, we aimed to investigate the expression landscape and druggability potential of the entire PCSK family for CVD. We applied an integrative approach, combining genetic, transcriptomic and proteomic data from three vascular biobanks comprising carotid atherosclerosis, thoracic and abdominal aneurysms, with patient clinical parameters and immunohistochemistry of vascular biopsies. Apart from PCSK4, all PCSK family members lie in genetic regions containing variants associated with human cardiovascular traits. Transcriptomic analyses revealed that FURIN, PCSK5, MBTPS1 were downregulated, while PCSK6/7 were upregulated in plaques vs. control arteries. In abdominal aneurysms, FURIN, PCSK5, PCSK7, MBTPS1 were downregulated, while PCSK6 was enriched in diseased media. In thoracic aneurysms, only FURIN was significantly upregulated. Network analyses of the upstream and downstream pathways related to PCSKs were performed on the omics data from vascular biopsies, revealing mechanistic relationships between this protein family and disease. Cell type correlation analyses and immunohistochemistry showed that PCSK transcripts and protein levels parallel each other, except for PCSK9 where transcript was not detected, while protein was abundant in vascular biopsies. Correlations to clinical parameters revealed a positive association between FURIN plaque levels and serum LDL, while PCSK6 was negatively associated with Hb. PCSK5/6/7 were all positively associated with adverse cardiovascular events. Our results show that PCSK6 is abundant in plaques and abdominal aneurysms, while FURIN upregulation is characteristic for thoracic aneurysms. PCSK9 protein, but not the transcript, was present in vascular lesions, suggesting its accumulation from circulation. Integrating our results lead to the development of a novel ‘molecular’ 5D framework. Here, we conducted the first integrative study of the proprotein convertase family in this context. Our results using this translational pipeline, revealed primarily PCSK6, followed by PCSK5, PCSK7 and FURIN, as proprotein convertases with the highest novel therapeutic potential.

Proprotein convertase furin is a driver and potential therapeutic target in proliferative diabetic retinopathy

BACKGROUND

Furin converts inactive proproteins into bioactive forms. By activating proinflammatory and proangiogenic factors, furin might play a role in pathophysiology of proliferative diabetic retinopathy (PDR).

METHODS

We studied vitreous samples from PDR and nondiabetic patients, epiretinal membranes from PDR patients, retinal microvascular endothelial cells (HRMECs), retinal Müller cells and rat retinas by ELISA, Western blot analysis, immunohistochemistry and immunofluorescence microscopy. We performed in vitro angiogenesis assays and assessed adherence of monocytes to HRMECs.

RESULTS

Furin levels were significantly increased in PDR vitreous samples. In epiretinal membranes, immunohistochemistry analysis revealed furin expression in monocytes/macrophages, vascular endothelial cells and myofibroblasts. Furin was significantly upregulated in diabetic rat retinas. Hypoxia and TNF-α induced significant upregulation of furin in Müller cells and HRMECs. Furin induced upregulation of phospho-ERK1/2, p65 subunit of NF-κB, ADAM17 and MCP-1 in cultured Müller cells and phospho-ERK1/2 in cultured HRMECs and induced HRMECs migration. Treatment of monocytes with furin significantly increased their adhesion to HRMECs. Intravitreal administration of furin in normal rats induced significant upregulation of p65 subunit of NF-κB, phospho-ERK1/2 and ICAM-1 in the retina. Inhibition of furin with dec-CMK significantly decreased levels of MCP-1 in culture medium of Müller cells and HRMECs and significantly attenuated TNF-α-induced upregulation of p65 subunit of NF-κB, ICAM-1 and VCAM-1 in HRMECs. Dec-CMK significantly decreased adherence of monocytes to HRMECs and TNF-α-induced upregulation of adherence of monocytes to HRMECs. Treatment of HRMECs with dec-CMK significantly attenuated migration of HRMECs.

CONCLUSIONS

Furin is a potential driver molecule of PDR-associated inflammation and angiogenesis.

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.

Effect of FURIN SNP rs17514846 on coronary atherosclerosis in human cardiac specimens: An autopsy study of 106 cases

BACKGROUND

Coronary artery disease (CAD), including coronary atherosclerosis (CAS), is one of the most common causes of death. The FURIN SNP rs17514846 is assumed to be a risk factor for CAD. We evaluated this relationship using autopsy specimens and autopsy data, such as the histopathological degree of CAS.

MATERIALS AND METHODS

A total of 106 samples were genotyped from obtained blood samples. Myocardial and coronary arterial FURIN levels were quantified by ELISA. The degree of CAS was classified histopathologically according to the Stary classification, and the localization of FURIN was examined by immunostaining. The obtained data were analyzed statistically.

RESULTS

FURIN expression was widely observed in the myocardium, vascular smooth muscle cells, endothelial cells, adipocytes, and macrophages. FURIN level in the myocardium of cases with the AA genotype at the FURIN SNP rs17514846 was higher than that in CC cases. Additionally, FURIN levels in both coronary arteries and myocardium were higher at the early stage of CAS than at the late stage microscopically.

CONCLUSION

Our study suggested that the A allele of rs17514846 is associated with higher FURIN level in the heart and that FURIN exhibits a higher level in the early stage of CAS. These findings deepen our understanding of the mechanism of CAS.

In silico genome-wide gene-based association analysis reveals new genes predisposing to coronary artery disease

Genome-wide association study (GWAS) have identified more than 300 single nucleotide polymorphisms at 163 independent loci associated with coronary artery disease (CAD). However, there is no full understanding about the causal genes for CAD and the mechanisms of their action. We aimed to perform a post GWAS analysis to identify genes whose polymorphism may influence the risk of CAD. Using the UK Biobank GWAS summary statistics, we performed a gene-based association analysis. We found 63 genes significantly associated with CAD due to their within-gene polymorphisms. Many of these genes are well known. Some known CAD genes such as FURIN and SORT1 did not show the gene-based association because their variants had low GWAS signals or gene-based association was inflated by the strong GWAS signal outside the gene. For several known CAD genes, we demonstrated that their effects could be explained not only or not at all by their own variants but by the variants within the neighboring genes controlling their expression. Using several bioinformatics techniques, we suggested potential mechanisms underlying gene-CAD associations. Three genes, CDK19, NCALD, and ARHGEF12 were not previously associated with CAD. The role of these genes should be clarified in further studies.

Platelet Activation and Plasma Levels of Furin Are Associated With Prognosis of Patients With Coronary Artery Disease and COVID-19

[Figure: see text].

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.

Up-regulation of PCSK6 by lipid oxidation products: A possible role in atherosclerosis

Atherosclerosis is a degenerative disease characterized by lesions that develop in the wall of large- and medium-sized arteries due to the accumulation of low-density lipoproteins (LDLs) in the intima. A growing bulk of evidence suggests that cholesterol oxidation products, known as oxysterols, and the aldehyde 4-hydroxy-2-nonenal (HNE), the major pro-atherogenic components of oxidized LDLs, significantly contribute to atherosclerotic plaque progression and destabilization, with eventual plaque rupture. The involvement of certain members of the protein convertase subtilisin/kexin proteases (PCSKs) in atherosclerosis has been recently hypothesized. Among them, PCSK6 has been associated with plaque instability, mainly thanks to its ability to stimulate the activity of matrix metalloproteinases (MMPs) involved in extracellular matrix remodeling and to enhance inflammation. In U937 promonocytic cells and in human umbilical vein endothelial cells, an oxysterol mixture and HNE were able to up-regulate the level and activity of PCSK6, resulting in MMP-9 activation as demonstrated by PCSK6 silencing. Inflammation, enhanced by these lipid oxidation products, plays a key role in the up-regulation of PCSK6 activity as demonstrated by cell pretreatment with NS-398, with epigallocatechin gallate or with acetylsalicylic acid, all with anti-inflammatory effects. For the first time, we demonstrated that both oxysterols and HNE, which substantially accumulate in the atherosclerotic plaque, up-regulate the activity of PCSK6. Of note, we also suggest a potential association between PCSK6 activity and MMP-9 activation, pointing out that PCSK6 could contribute to atherosclerotic plaque development.

Analysis of Melanoma Secretome for Factors That Directly Disrupt the Barrier Integrity of Brain Endothelial Cells

We have recently demonstrated that invasive melanoma cells are capable of disrupting the brain endothelial barrier integrity. This was shown using ECIS biosensor technology, which revealed rapid disruption via the paracellular junctions. In this paper, we demonstrate that melanoma cells secrete factors (e.g., cytokines) that weaken the endothelial barrier integrity. Through proteome profiling, we attempt to identify the barrier-disrupting cytokines. Melanoma conditioned media were collected from three New Zealand melanoma lines. ECIS technology was used to assess if the conditioned media disrupted the endothelial barrier independent of the melanoma cells. The melanoma cell secretome was assessed using cytometric bead array (CBA), Luminex immunoassay and multiplex Proteome Profilers, to detect the expression of secretory proteins, which may facilitate metastasis. Finally, ECIS technology was used to assess the direct effects of secreted proteins identified as candidates from the proteome screens. We show that melanoma-conditioned media significantly disrupted the brain endothelial barrier, however, to a much lesser extent than the cells from which they were collected. Cytokine and proteome profiling of the conditioned media showed evidence of high concentrations of approximately 15 secreted proteins (including osteopontin, IL-8, GDF-15, MIF and VEGF). These 15 secreted proteins were expressed variably across the melanoma lines. Surprisingly, the addition of these individually to the brain endothelial cells did not substantially affect the barrier integrity. ANGPTL-4 and TGFβ were also produced by the melanoma cells. Whilst TGFβ-1 had a pronounced effect on the barrier integrity, surprisingly ANGPTL-4 did not. However, its C-terminal fragment did and within a very similar period to the conditioned media, albeit not to the same extent. Herein we show that melanoma cells produce a wide-range of soluble factors at high concentrations, which most likely favour support or survival of the cancer cells. Most of these, except for TGFβ-1 and the C-terminal fragment of ANGPTL-4, did not have an impact on the integrity of the brain endothelial cells.

COVID-19 outpatients: early risk-stratified treatment with zinc plus low-dose hydroxychloroquine and azithromycin: a retrospective case series study

The aim of this study was to describe the outcomes of patients with coronavirus disease 2019 (COVID-19) in the outpatient setting after early treatment with zinc, low-dose hydroxychloroquine and azithromycin (triple therapy) dependent on risk stratification. This was a retrospective case series study in the general practice setting. A total of 141 COVID-19 patients with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the year 2020 were included. The main outcome measures were risk-stratified treatment decision and rates of hospitalisation and all-cause death. A median of 4 days [interquartile range (IQR) 3–6 days; available for n = 66/141 patients] after the onset of symptoms, 141 patients (median age 58 years, IQR 40–67 years; 73.0% male) received a prescription for triple therapy for 5 days. Independent public reference data from 377 confirmed COVID-19 patients in the same community were used as untreated controls. Of 141 treated patients, 4 (2.8%) were hospitalised, which was significantly fewer (P < 0.001) compared with 58 (15.4%) of 377 untreated patients [odds ratio (OR) = 0.16, 95% confidence interval (CI) 0.06–0.5]. One patient (0.7%) in the treatment group died versus 13 patients (3.4%) in the untreated group (OR = 0.2, 95% CI 0.03–1.5; P = 0.12). No cardiac side effects were observed. Risk stratification-based treatment of COVID-19 outpatients as early as possible after symptom onset using triple therapy, including the combination of zinc with low-dose hydroxychloroquine, was associated with significantly fewer hospitalisations.

Elevated FURIN levels in predicting mortality and cardiovascular events in patients with acute myocardial infarction

OBJECTIVES

Proprotein convertase subtilisin/kexin (PCSK) family member 3 (FURIN) has been suggested to be involved in the development of atherosclerosis. The aim of this study was to investigate the prognostic implication of FURIN in patients after acute myocardial infarction (AMI).

METHODS

This prospective study analyzed data from a total of 1312 consecutive patients hospitalized with ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction from August 2013 to June 2016. FURIN levels were analyzed in plasma obtained from AMI patients.

RESULTS

The study included 1312 AMI patients. The patient population was predominantly male (63%) with a median age of 66 years (IQR: 19 years), and 59% were STEMI patients. During a follow-up of 2 years, 117 patients died, and 377 patients reached the combined endpoints of major adverse cardiac events (MACE). Patients with elevated FURIN levels had increased risk of MACE, all-cause mortality, recurrent MI and hospitalization for HF (log-rank test, p < 0.0001). After adjusting for clinical risk factors and established markers, the association of FURIN concentrations with the risk of MACE and its individual components and cardiovascular death was statistically significant in the higher tertile of FURIN concentrations. After the addition of FURIN to the models, FURIN showed additive prognostic significance for 2-year clinical outcomes. Variable importance plots of the models showed that FURIN was of high importance to predict both occurrence of MACE and all-cause mortality.

CONCLUSIONS

We found that FURIN was associated with all-cause mortality and recurrent cardiovascular events in AMI patients independent of conventional risk factors and established markers.

Obesity and COVID-19: Molecular Mechanisms Linking Both Pandemics

The coronavirus disease 2019 COVID-19 pandemic is rapidly spreading worldwide and is becoming a major public health crisis. Increasing evidence demonstrates a strong correlation between obesity and the COVID-19 disease. We have summarized recent studies and addressed the impact of obesity on COVID-19 in terms of hospitalization, severity, mortality, and patient outcome. We discuss the potential molecular mechanisms whereby obesity contributes to the pathogenesis of COVID-19. In addition to obesity-related deregulated immune response, chronic inflammation, endothelium imbalance, metabolic dysfunction, and its associated comorbidities, dysfunctional mesenchymal stem cells/adipose-derived mesenchymal stem cells may also play crucial roles in fueling systemic inflammation contributing to the cytokine storm and promoting pulmonary fibrosis causing lung functional failure, characteristic of severe COVID-19. Moreover, obesity may also compromise motile cilia on airway epithelial cells and impair functioning of the mucociliary escalators, reducing the clearance of severe acute respiratory syndrome coronavirus (SARS-CoV-2). Obese diseased adipose tissues overexpress the receptors and proteases for the SARS-CoV-2 entry, implicating its possible roles as virus reservoir and accelerator reinforcing violent systemic inflammation and immune response. Finally, anti-inflammatory cytokines like anti-interleukin 6 and administration of mesenchymal stromal/stem cells may serve as potential immune modulatory therapies for supportively combating COVID-19. Obesity is conversely related to the development of COVID-19 through numerous molecular mechanisms and individuals with obesity belong to the COVID-19-susceptible population requiring more protective measures.

FURIN Expression in Vascular Endothelial Cells Is Modulated by a Coronary Artery Disease-Associated Genetic Variant and Influences Monocyte Transendothelial Migration

Background Genome-wide association studies have shown an association between the single-nucleotide polymorphism rs17514846 on chromosome 15q26.1 and coronary artery disease susceptibility. The underlying biological mechanism is, however, not fully understood. rs17514846 is located in the FES Upstream Region (FURIN) gene, which is expressed in vascular endothelial cells (ECs). We investigated whether rs17514846 has an influence on FURIN expression in ECs and whether FURIN affects EC behavior. Methods and Results Quantitative reverse transcription-polymerase chain reaction analysis showed that cultured vascular ECs from individuals carrying the coronary artery disease risk allele of rs17514846 had higher FURIN expression than cells from noncarriers. In support, luciferase reporter analyses in ECs indicated that the risk allele had higher transcriptional activity than the nonrisk allele. Electrophoretic mobility shift assays using EC nuclear protein extracts detected a DNA-protein complex with allele-specific differential binding of a nuclear protein. Knockdown of FURIN in ECs reduced endothelin-1 secretion, nuclear factor-κB activity, vascular cell adhesion molecule-1, and MCP1 (monocyte chemotactic protein-1) expression and monocyte-endothelial adhesion and transmigration. A population-based study showed an association of the rs17514846 risk allele with higher circulating MCP1 levels and greater carotid intima-media thickness. Conclusions The coronary artery disease risk variant at the 15q26.1 locus modulates FURIN expression in vascular ECs. FURIN levels in ECs affect monocyte-endothelial adhesion and migration.

FURIN Inhibition Reduces Vascular Remodeling and Atherosclerotic Lesion Progression in Mice

Objective- Atherosclerotic coronary artery disease is the leading cause of death worldwide, and current treatment options are insufficient. Using systems-level network cluster analyses on a large coronary artery disease case-control cohort, we previously identified PCSK3 (proprotein convertase subtilisin/kexin family member 3; FURIN) as a member of several coronary artery disease-associated pathways. Thus, our objective is to determine the role of FURIN in atherosclerosis. Approach and Results- In vitro, FURIN inhibitor treatment resulted in reduced monocyte migration and reduced macrophage and vascular endothelial cell inflammatory and cytokine gene expression. In vivo, administration of an irreversible inhibitor of FURIN, α-1-PDX (α1-antitrypsin Portland), to hyperlipidemic Ldlr^-/- mice resulted in lower atherosclerotic lesion area and a specific reduction in severe lesions. Significantly lower lesional macrophage and collagen area, as well as systemic inflammatory markers, were observed. MMP2 (matrix metallopeptidase 2), an effector of endothelial function and atherosclerotic lesion progression, and a FURIN substrate was significantly reduced in the aorta of inhibitor-treated mice. To determine FURIN's role in vascular endothelial function, we administered α-1-PDX to Apoe^-/- mice harboring a wire injury in the common carotid artery. We observed significantly decreased carotid intimal thickness and lower plaque cellularity, smooth muscle cell, macrophage, and inflammatory marker content, suggesting protection against vascular remodeling. Overexpression of FURIN in this model resulted in a significant 67% increase in intimal plaque thickness, confirming that FURIN levels directly correlate with atherosclerosis. Conclusions- We show that systemic inhibition of FURIN in mice decreases vascular remodeling and atherosclerosis. FURIN-mediated modulation of MMP2 activity may contribute to the atheroprotection observed in these mice.

Influence of a Coronary Artery Disease-Associated Genetic Variant on FURIN Expression and Effect of Furin on Macrophage Behavior

Objective- Genome-wide association studies have revealed a robust association between genetic variation on chromosome 15q26.1 and coronary artery disease (CAD) susceptibility; however, the underlying biological mechanism is still unknown. The lead CAD-associated genetic variant (rs17514846) at this locus resides in the FURIN gene. In advanced atherosclerotic plaques, furin is expressed primarily in macrophages. We investigated whether this CAD-associated variant alters FURIN expression and whether furin affects monocyte/macrophage behavior. Approach and Results- A quantitative reverse transcription polymerase chain reaction analysis showed that leukocytes from individuals carrying the CAD risk allele (A) of rs17514846 had increased FURIN expression. A chromatin immunoprecipitation assay revealed higher RNA polymerase II occupancy in the FURIN gene in mononuclear cells of individuals carrying this allele. A reporter gene assay in transiently transfected monocytes/macrophages indicated that the CAD risk allele had higher transcriptional activity than the nonrisk allele (C). An analysis of isogenic monocyte cell lines created by CRISPR (clustered regularly interspaced short palindromic repeats)-mediated genome editing showed that isogenic cells with the A/A genotype for rs17514846 had higher FURIN expression levels than the isogenic cells with the C/C genotype. An electrophoretic mobility shift assay exhibited preferential binding of a nuclear protein to the risk allele. Studies of monocytes/macrophages with lentivirus-mediated furin overexpression or shRNA (short hairpin RNA)-induced furin knockdown showed that furin overexpression promoted monocyte/macrophage migration, increased proliferation, and reduced apoptosis whereas furin knockdown had the opposite effects. Conclusions- Our study shows that the CAD-associated genetic variant increases FURIN expression and that furin promotes monocyte/macrophage migration and proliferation while inhibiting apoptosis, providing a biological mechanism for the association between variation at the chromosome 15q26.1 locus and CAD risk.

Hepatic overexpression of the prodomain of furin lessens progression of atherosclerosis and reduces vascular remodeling in response to injury

OBJECTIVE

Atherosclerosis is a complex disease, involving elevated LDL-c, lipid accumulation in the blood vessel wall, foam cell formation and vascular dysfunction. Lowering plasma LDL-c is the cornerstone of current management of cardiovascular disease. However, new approaches which reduce plasma LDL-c and lessen the pathological vascular remodeling occurring in the disease should also have therapeutic value. Previously, we found that overexpression of profurin, the 83-amino acid prodomain of the proprotein convertase furin, lowered plasma HDL levels in wild-type mice. The question that remained was whether it had effects on apolipoprotein B (ApoB)-containing lipoproteins.

METHODS

Adenovirus mediated overexpression of hepatic profurin in Ldlr(-/-)mice and wild-type mice were used to evaluate effects of profurin on ApoB-containing lipoproteins, atherosclerosis and vascular remodeling.

RESULTS

Hepatic profurin overexpression resulted in a significant reduction in atherosclerotic lesion development in Ldlr(-/-)mice and a robust reduction in plasma LDL-c. Metabolic studies revealed lower secretion of ApoB and triglycerides in VLDL particles. Mechanistic studies showed that in the presence of profurin, hepatic ApoB, mainly ApoB100, was degraded by proteasomes. There was no effect on ApoB mRNA expression. Importantly, short-term hepatic profurin overexpression did not result in hepatic lipid accumulation. Blood vessel wall thickening caused by either wire-induced femoral artery injury or common carotid artery ligation was reduced. Profurin expression inhibited proliferation and migration in vascular smooth muscle cells in vitro.

CONCLUSION

These results indicate that a profurin-based therapy has the potential to treat atherosclerosis by improving metabolic lipid profiles and reducing both atherosclerotic lesion development and pathological vascular remodeling.

Proprotein convertases play an important role in regulating PKGI endoproteolytic cleavage and nuclear transport

Nitric oxide and cGMP modulate vascular smooth muscle cell (SMC) phenotype by regulating cell differentiation and proliferation. Recent studies suggest that cGMP-dependent protein kinase I (PKGI) cleavage and the nuclear translocation of a constitutively active kinase fragment, PKGIγ, are required for nuclear cGMP signaling in SMC. However, the mechanisms that control PKGI proteolysis are unknown. Inspection of the amino acid sequence of a PKGI cleavage site that yields PKGIγ and a protease database revealed a putative minimum consensus sequence for proprotein convertases (PCs). Therefore we investigated the role of PCs in regulating PKGI proteolysis. We observed that overexpression of PCs, furin and PC5, but not PC7, which are all expressed in SMC, increase PKGI cleavage in a dose-dependent manner in human embryonic kidney (HEK) 293 cells. Moreover, furin-induced proteolysis of mutant PKGI, in which alanines were substituted into the putative PC consensus sequence, was decreased in these cells. In addition, overexpression of furin increased PKGI proteolysis in LoVo cells, which is an adenocarcinoma cell line expressing defective furin without PC activity. Also, expression of α1-PDX, an engineered serpin-like PC inhibitor, reduced PC activity and decreased PKGI proteolysis in HEK293 cells. Last, treatment of low-passage rat aortic SMC with membrane-permeable PC inhibitor peptides decreased cGMP-stimulated nuclear PKGIγ translocation. These data indicate for the first time that PCs have a role in regulating PKGI proteolysis and the nuclear localization of its active cleavage product, which are important for cGMP-mediated SMC phenotype.

Proprotein convertases in human atherosclerotic plaques: the overexpression of FURIN and its substrate cytokines BAFF and APRIL

BACKGROUND

Proprotein convertase subtilisin/kexin (PCSK) enzymes cleave proproteins into mature end products. Previously, MBTPS1 and PCSK9 have been shown to regulate cholesterol metabolism and LDL receptor recycling, whereas FURIN and PCSK5 have been suggested to inactivate lipases and regulate inflammation in atherosclerosis. Here, we systematically analyzed the expression of PCSKs and their targets in advanced atherosclerotic plaques.

METHODS AND RESULTS

Microarray and quantitative real-time PCR experiments showed that FURIN (42.86 median fold, p = 2.1e-8), but no other PCSK, is universally overexpressed in the plaques of different vascular regions. The mRNA expression screen of PCSK target proteins in plaques identified many known factors, but it also identified the significant upregulation of the previously overlooked furin-processed B cell activating cytokines APRIL (TNFSF13, 2.52 median fold, p = 3.0e-5) and BAFF (TNFSF13B, 2.97 median fold, p = 7.6e-6). The dysregulation of FURIN did not associate with its htSNPs or the previously reported regulatory SNP (-229, rs4932178) in the promoter. Immunohistochemistry experiments showed the upregulation of FURIN in the plaque lymphocytes and macrophages where it was co-expressed with BAFF/TNFSF13B and APRIL/TNFSF13.

CONCLUSIONS

Our data unequivocally show that FURIN is the primary PCSK that is dysregulated in the immune cells of advanced human atherosclerotic plaques, which implies a role for this enzyme in plaque pathology. Therefore, drugs that inhibit FURIN in arteries may modulate the course of this disease.

The molecular biology of furin-like proprotein convertases in vascular remodelling

Vascular smooth muscle cell (VSMC) proliferation and migration represent key features in atherosclerosis and restenosis. The proprotein convertases (PCs) furin and PC5 are highly expressed in human atheroma and are putatively involved in vascular lesion formation via the activation of precursor proteins, essential for cell proliferation and migration. In vitro assays have identified these PCs to govern cell functions via endoproteolytic cleavage of key substrates, including pro-integrins and pro-matrix metalloproteinases. In vivo gene expression studies of furin/PC5 and their substrates demonstrate their coordinated regulation in animal models of vascular remodelling and in human atherosclerotic lesions. Here we describe in vitro and in vivo models to investigate the function of furin/PC5 in VSMCs and in vascular lesion formation. In conjunction with the development of novel PC inhibitors, this should facilitate the development of new strategies targeting PCs in cardiovascular disease.

Both PA63 and PA83 are endocytosed within an anthrax protective antigen mixed heptamer: A putative mechanism to overcome a furin deficiency

Anthrax toxin consists of protective antigen (PA), and lethal (LF) and edema (EF) factors. A 83 kDa PA monomer (PA83) precursor binds to the cell receptor. Furin-like proprotein convertases (PCs) cleave PA83 to generate cell-bound 63 kDa protein (PA63). PA63 oligomerizes to form a ring-shaped heptamer that binds LF-EF and facilitates their entry into the cells. Several additional PCs, as opposed to furin alone, are capable of processing PA83. Following the incomplete processing of the available pool of PA83, the functional heptamer includes both PA83 and PA63. The available structures of the receptor-PA complex imply that the presence of either one or two molecules of PA83 will not impose structural limitations on the formation of the heptamer and the association of either the (PA83)(1)(PA63)(6) or (PA83)(2)(PA63)(5) heteroheptamer with LF-EF. Our data point to the intriguing mechanism of anthrax that appears to facilitate entry of the toxin into the cells which express limiting amounts of PCs and an incompletely processed PA83 pool.

Proprotein convertases furin and PC5: targeting atherosclerosis and restenosis at multiple levels

Several growth factors, chemokines, adhesion molecules, and proteolytic enzymes important for cell-cell/cell-matrix interactions in atherosclerosis and restenosis are initially synthesized as inactive precursor proteins. Activation of proproteins to biologically active molecules is regulated by limited endoproteolytic cleavage at dibasic amino acid residues. This type of activation typically requires the presence of suitable proprotein convertases (PCs). The PC-isozymes furin and PC5 are expressed in human atherosclerotic lesions and have been found to be up-regulated, following vascular injury in animal models in vivo. In vitro, these PCs can regulate vascular smooth muscle cell and macrophage functions and signaling events, through activation of pro-alpha-integrins and/or pro-membrane-type matrix metalloproteinases. Integrins link the cytoskeleton with the extracellular matrix and mediate bidirectional signaling and mechanotransduction, whereas matrix metalloproteinases are the major matrix-degrading enzymes. Both activities are required for cell recruitment to the intima. Furthermore, cleavage of extracellular matrix molecules by matrix metalloproteinases potentially contributes to weakening of the fibrous cap, promoting plaque rupture. Based on these recent in vitro and in vivo data, furin and PC5 are potential contributors to the initiation, progression, and complications of atherosclerosis and restenosis. Targeting these PCs may provide future anti-atherosclerotic therapies.