Autoantibodies against unmodified and citrullinated human endogenous retrovirus K envelope protein in rheumatoid arthritis patients

Objective Autoantibodies against proteins encoded by human endogenous retrovirus K (HERV-K) have been reported in patients with rheumatoid arthritis (RA), but their relevance, if any, has remained unresolved. We revisited this question and tested if such autoantibodies may react with citrullinated epitopes on the envelope (Env) protein of HERV-K. Methods Immunoblotting and ELISAs were conducted with unmodified Env protein and with Env citrullinated by protein arginine deiminase (PAD) 4. Sera from 100 RA patients, plasma from 32 juvenile idiopathic arthritis (JIA) patients, and healthy adult and pediatric controls were included. Antibody reactivity was evaluated for correlations with clinical and laboratory parameters of the patients. Results We replicated and expanded upon published data that patients with RA or JIA have autoantibodies against HERV-K Env, some with high titers. Anti-HERV-K antibodies correlated with cigarette smoking and with circulating DNA-myeloperoxidase complexes indicative of nonapoptotic neutrophil cell death. Furthermore, most of the RA patients, but not JIA patients, had autoantibodies that reacted more strongly with Env that was citrullinated by PAD4. These anticitrullinated Env autoantibodies correlated with seropositivity and tended to be higher in patients with erosive disease. Conclusion Our data suggest that anti-HERV-K immunity is elevated in RA and JIA and may have a connection with pathogenic protein citrullination in RA.

Epitope-Based Chicken-Derived Novel Anti-PAD2 Monoclonal Antibodies Inhibit Citrullination

The aberrant upregulation of protein arginine deiminase 2- (PAD2-) catalyzed citrullination is reported in various autoimmune diseases (rheumatoid arthritis and multiple sclerosis) and several cancers. Currently, there are no anti-PAD2 monoclonal antibodies (mAbs) that can inhibit the citrullination reaction. Here, an epitope 341YLNRGDRWIQDEIEFGY357 was examined as an antigenic site of PAD2. Chickens were immunized with this epitope, and the generated mAbs were screened for its reactivity against the full-length PAD2. Enzyme-linked immunosorbent assay revealed that six mAbs, which were screened from the phage display library, crossreacted with mouse PAD2. Kinetic analysis revealed that mAbs are bound to PAD2 in the nanomolar range, which indicated a strong binding. Results of the in vitro citrullination inhibition assay revealed that the half-maximal effective concentration values of mAbs for the inhibition of histone or benzoyl-L-arginine ethyl ester citrullination were in the range of 6–75 nM which supports strong inhibition capabilities. Alanine scanning of epitope revealed that the peptide fragment 344RGDRWIQDEIEF355 was responsible for generating strong antibody responses that inhibit the PAD2-catalyzed citrullination reaction. These antibodies can aid in understanding the extracellular PAD2 function and treating diseases associated with aberrant citrullination.

Targeted delivery of protein arginine deiminase-4 inhibitors to limit arterial intimal NETosis and preserve endothelial integrity

Aims Recent evidence suggests that ‘vulnerable plaques’, which have received intense attention as underlying mechanism of acute coronary syndromes over the decades, actually rarely rupture and cause clinical events. Superficial plaque erosion has emerged as a growing cause of residual thrombotic complications of atherosclerosis in an era of increased preventive measures including lipid lowering, antihypertensive therapy, and smoking cessation. The mechanisms of plaque erosion remain poorly understood, and we currently lack validated effective diagnostics or therapeutics for superficial erosion. Eroded plaques have a rich extracellular matrix, an intact fibrous cap, sparse lipid, and few mononuclear cells, but do harbour neutrophil extracellular traps (NETs). We recently reported that NETs amplify and propagate the endothelial damage at the site of arterial lesions that recapitulate superficial erosion in mice. We showed that genetic loss of protein arginine deiminase (PAD)-4 function inhibited NETosis and preserved endothelial integrity. The current study used systemic administration of targeted nanoparticles to deliver an agent that limits NETs formation to probe mechanisms of and demonstrate a novel therapeutic approach to plaque erosion that limits endothelial damage. Methods and results We developed Collagen IV-targeted nanoparticles (Col IV NP) to deliver PAD4 inhibitors selectively to regions of endothelial cell sloughing and collagen IV-rich basement membrane exposure. We assessed the binding capability of the targeting ligand in vitro and evaluated Col IV NP targeting to areas of denuded endothelium in vivo in a mouse preparation that recapitulates features of superficial erosion. Delivery of the PAD4 inhibitor GSK484 reduced NET accumulation at sites of intimal injury and preserved endothelial continuity. Conclusions NPs directed to Col IV show selective uptake and delivery of their payload to experimentally eroded regions, illustrating their translational potential. Our results further support the role of PAD4 and NETs in superficial erosion.

Abstract 15700: Targeted Nanoparticle Delivery of a Protein Arginine Deiminase-4 Inhibitor Limits Arterial Intimal Netosis and Preserves Endothelial Integrity in Mouse Arterial Erosion-like Injury

Introduction: Superficial plaque erosion has emerged as a growing cause of residual thrombotic complications of atherosclerosis in an era of effective lipid lowering, anti-hypertensive therapy, and smoking cessation. The mechanisms of plaque erosion remain poorly understood, and we currently lack validated effective diagnostics or therapeutics for superficial erosion. Lesions complicated by erosion have a rich extracellular matrix, sparse lipid, and few mononuclear cells, but do harbor neutrophil extracellular traps (NETs). We recently reported that NETs amplify and propagate the endothelial damage at the site of arterial lesions that recapitulate in mice elements of superficial erosion. We previously showed that genetic loss of protein arginine deiminase (PAD)-4 function inhibited NETosis and preserved endothelial integrity. Hypothesis: We hypothesized that Col IV-targeted NPs (Col IV-NPs) can deliver PAD4 inhibitors selectively to regions of EC sloughing and collagen IV-rich basement membrane exposure, and attenuate the amplification, persistence, and propagation of superficial erosion and consequent thrombosis. Methods: We developed Col IV-NPs to deliver PAD4 inhibitors selectively to regions of endothelial cell sloughing and collagen IV-rich basement membrane exposure using our validated experimental preparation that reproduces in mice some of the conditions ascribed to lesions associated with superficial erosion. Results and Conclusions: We first demonstrated the binding of the targeting ligand in vitro and evaluated Col IV NP targeting towards areas of denuded endothelium in vivo in this mouse preparation. Delivery of the PAD4 inhibitor GSK484 as cargo in these nanoparticles reduced NETs release at sites of eroded areas. Compared to non-targeted NPs, Col IV NPs showed a 1.8-fold increased accumulation at regions of endothelial injury (p<0.0001). When loaded with the PAD4 inhibitor GSK484, Col IV NPs effectively reduced NET accumulation by 2.5 fold at sites of intimal lesions (p<0.01) and preserved endothelial continuity (a 4-fold increase in endothelial continuity percentage, p<0.001). These results indicate the feasibility of using nanotechnology to address the unmet need of specific therapy for superficial erosion.

Protein Arginine Deiminase 2 and 4 (PAD2 & PAD4) are independent predictors of good prognosis in colorectal cancer

Objective: Protein arginine deiminase (PADs) are a family of enzymes that catalyse the post translational modification (PTM) of proteins. In this study the prognostic significance of PAD2 and PAD4 in colorectal cancer (CRC) was assessed. Design: PAD2 and PAD4 expression was assessed immunohistochemically in a cohort of CRC patients. Association between PAD expression with clinicopathology, protein expression and outcome was determined. Results: CRC tissues expressed variable levels of PAD2 which was mainly localised in the cytoplasm and correlated with patient survival (p=0.005); high expression increased survival time from 43.5 to 67.6 months. Expression of cytoplasmic PAD2 correlated with expression of nuclear β catenin, PAD4 and alpha-enolase. In contrast expression of nuclear PAD2 correlated with a decrease in survival (p=0.010), with high expression decreasing survival from 76.4 to 42.9 months. CRC tissues expressed variable levels of PAD4 in both the nucleus and cytoplasm. Expression of cytoplasmic PAD4 correlated with survival (p=0.001) with high expression increasing survival time from 48.1 to 71.8 months. Expression of cytoplasmic PAD4 correlated with expression of, nuclear β catenin, alpha-enolase (p≤ 0.0001, p=0.002) and the apoptotic related protein, Bcl-2. Expression of nuclear PAD4 also correlated with survival (p=0.011) with high expression of nuclear PAD4 increasing survival time from 55.4 to 74 months. Expression of nuclear PAD4 correlated with p53, alpha-enolase and Bcl-2. Multivariate analysis showed that TNM stage and cytoplasmic PAD2 and PAD4 remained independent prognostic factors in CRC. Conclusion: Both PAD2 and PAD4 are good prognostic factors in CRC.

OP0118 DECIPHERING THE ANTI-PROTEIN-ARGININE DEIMINASE (PAD) RESPONSE IDENTIFIES PAD1 AND PAD6 AS NOVEL AUTOANTIGENS IN RHEUMATOID ARTHRITIS

Background:Protein-arginine deiminase (PAD) 4 enzymes play a central role in the pathogenesis of rheumatoid arthritis (RA) and represents an antigenic target. Among the five known family members (PAD1, PAD2, PAD3, PAD4 and PAD6), only PAD2, PAD3 and PAD4 have been described to have autoantigenic properties. Furtheremore, very little is known on the the isotype usage of these autoantibodies. Understanding the molecular basis of the anti-PAD antibody reponse has the potential to open novel approaches for precision medicine in RA.Objectives:The objectives of this study were to screen for the presence of antibodies to the five PAD family members and to evaluate the isotype usage of the anti-PAD4 response in RA.Methods:First, we developed a panel for the detection of anti-PAD IgG based on a particle-based multi-analyte technology (PMAT), that utilized paramagnetic particles coupled with the different human recombinant PAD proteins (PAD1, PAD2, PAD3, PAD4 and PAD6) and anti-human IgG conjugate. This panel was used to test sera from RA patients (n=33) and non-RA controls (n=36). The controls were comprised of apparently healthy individuals (n=10), and patients with infectious diseases (n=10), systemic lupus erythematosus (n=7), systemic sclerosis (n=9) and Sjogren’s syndrome (n=1). Next, the PAD4-coupled beads were tested with anti-human IgM, IgA and IgG conjugates on an extended cohort of RA patients (n=62) and the same non-RA controls.Results:All five anti-PAD IgG (Figure 1) demonstrated the ability to discriminate between RA patients and controls. At greater than 90% specificity, anti-PAD4 IgG, followed by anti-PAD3 IgG, showed the best diagnostic performance. Significantly higher levels of the five antibodies were observed in RAvs.controls (p-values of 0.0041, <0.0001, 0.0014, 0.0039, and 0.0140 for anti-PAD1, 2, 3, 4 and 6, respectively). Significant correlation was observed between all the antibodies, with the highest between anti-PAD1 and anti-PAD4 (Spearman´srho=0.87,p<0.0001) and the lowest between anti-PAD4 and anti-PAD2 (Spearman’srho=0.38,p=0.0015) and anti-PAD4 and anti-PAD6 (Spearman’srho=0.38,p=0.0011). While principal component analysis (PCA) (Figure 2) showed an association between all anti-PAD antibodies, there was further discrimination that displayed closer association between anti-PAD1, 3 and 4 on one hand, and between anti-PAD2 and 6. For the extended testing of anti-PAD4 with IgG, IgA and IgM, all three isotypes were identified in the sera of RA patients. Higher levels of the three isotypes were observed in RA patients with erosive disease when compared with the patients without erosion, but this association was only significant for anti-PAD4 IgA (p=0.0086).Figure 1.Receiver operating characteristics (ROC) analysis of the discrimination between rheumatoid arthritis (RA) and controls of IgG to protein-arginine deiminase (PAD) 1, PAD2, PAD3, PAD4 and PAD6. The area under the curve (AUC) values are shown in brackets for each biomarker.Abbreviations:TPF: true positive fraction; FPF: false positive fractionFigure 2.Two dimensional principal component analysis (PCA) plot of the anti-PAD levels in RA patients (n=33) and controls (n=36). Anti-PAD1, 3 and 4 have the main contribution to PC1, which explains 51.7% of the variance, and anti-PAD2 and 6 to PC2, that represents 20.8% of it.Abbreviations:PC: principal componentConclusion:Our study is the first to describe PAD1 and PAD6 as novel antigenic targets in RA and to demostrate that the anti-PAD4 B-cell immune response uses all three isotypes (IgG, IgA and IgM). The strong and significant association between anti-PAD4 IgA and joint erosion is of particular clinical relevance.Disclosure of Interests:Laura Martinez-Prat Employee of: I am an employee of Inova Diagnostics, an in vitro diagnostics company., Mary Ann Aure Employee of: I am an employee of Inova Diagnostics, an in vitro diagnostics company., Chelsea Bentow Employee of: I am an employee of Inova Diagnostics, an in vitro diagnostics company., David Lucia Employee of: I am an employee of Inova Diagnostics, an in vitro diagnostics company., Marcos Lopez-Hoyos Consultant of: Inova Diagnostics, an in vitro diagnostics company., Michael Mahler Employee of: I am an employee of Inova Diagnostics, an in vitro diagnostics company.