Peptidylarginine Deiminase 4 Promotes the Renal Infiltration of Neutrophils and Exacerbates the TLR7 Agonist-Induced Lupus Mice

Screening of peptidyl arginine deiminase 4 inhibitors in traditional herbal medicines

Peptidyl arginine deiminase 4 (PAD4) is a promising target for the treatment of metabolic diseases associated with autoimmune and central nervous system disease. By now there are limited numbers of PAD4 inhibitors, and no one is ready for clinical use. This study aims to find efficient and specific PAD4 inhibitors from traditional herbal medicines and to investigate their inhibitory mechanisms. The inhibitory effects of forty-eight extracts from sixteen traditional herbal medicines which are widely used in traditional herbal medicines were investigated. Salvia miltiorrhiza was found to have the most potent PAD4 inhibitory activity. After that, a practical bioactivity-guided fractionation coupling with a chemical profiling strategy was used to identify the fractions from Salvia miltiorrhiza with strong PAD4 inhibition activity, and the major constituents in these bioactive fractions were characterized by LC-MS/MS. Seven compounds were found to have inhibition on PAD4 with IC50 values ranging from 33.52 μM to 667 μM, in which salvianolic acid A showed the most potent inhibitory activity, with an IC50 value of 33.52 μM. Inhibition kinetic analyses indicated that salvianolic acid A effectively inhibited PAD4 in a mixed inhibitory manner, and computer simulation analyses demonstrated that salvianolic acid A binds to PAD4 mainly using hydrogen bonding. Overall, our results suggest that salvianolic acid A from Salvia miltiorrhiza is a potent inhibitor of PAD4, and that salvianolic acid A can be used as a promising lead compound for the development of more potent PAD4 inhibitors.

[Determination of the derivatization reactivity between α/β-dicarbonyl compounds and standard citrullinated peptides based on matrix-assisted laser desorption ionization-time-of-flight mass spectrometry]

Protein citrullination is an irreversible post-translational modification process regulated by peptidylarginine deiminases (PADs) in the presence of Ca2+. This process is closely related to the occurrence and development of autoimmune diseases, cancers, neurological disorders, cardiovascular and cerebrovascular diseases, and other major diseases. The analysis of protein citrullination by biomass spectrometry confronts great challenges owing to its low abundance, lack of affinity tags, small mass-to-charge ratio change, and susceptibility to isotopic and deamidation interferences. The methods commonly used to study the protein citrullination mainly involve the chemical derivatization of the urea group of the guanine side chain of the peptide to increase the mass-to-charge ratio difference of the citrullinated peptide. Affinity-enriched labels are then introduced to effectively improve the sensitivity and accuracy of protein citrullination by mass spectrometry. 2,3-Butanedione or phenylglyoxal compounds are often used as derivatization reagents to increase the mass-to-charge ratio difference of the citrullinated peptide, and the resulting derivatives have been observed to contain α-dicarbonyl structures. To date, however, no relevant studies on the reactivity of dicarbonyl compounds with citrullinated peptides have been reported. In this study, we determined whether six α-dicarbonyl and two β-dicarbonyl compounds undergo derivatization reactions with standard citrullinated peptides using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Among the α-dicarbonyl compounds, 2,3-butanedione and glyoxal reacted efficiently with several standard citrullinated peptides, but yielded a series of by-products. Phenylglyoxal, methylglyoxal, 1,2-cyclohexanedione, and 1,10-phenanthroline-5,6-dione also derivated efficiently with standard citrullinated peptides, generating a single derivative. Thus, a new derivatization method that could yield a single derivative was identified. Among the β-dicarbonyl compounds, 1,3-cyclohexanedione and 2,4-pentanedione successfully reacted with the standard citrullinated peptides, and generated a single derivative. However, their reaction efficiency was very low, indicating that the β-dicarbonyl compounds are unsuitable for the chemical derivatization of citrullinated peptides. The above results indicate that the α-dicarbonyl structure is necessary for realizing the efficient and specific chemical derivatization of citrullinated peptides. Moreover, the side chains of the α-dicarbonyl structure determine the structure of the derivatives, derivatization efficiency, and generation (or otherwise) of by-products. Therefore, the specific enrichment and precise identification of citrullinated peptides can be achieved by synthesizing α-dicarbonyl structured compounds containing affinity tags. The proposed method enables the identification of citrullinated proteins and their modified sites by MS, thereby providing a better understanding of the distribution of citrullinated proteins in different tissues. The findings will be beneficial for studies on the mechanism of action of citrullinated proteins in a variety of diseases.

Neutrophil attachment via Mac-1 (αMβ2; CD11b/CD18; CR3) integrins induces PAD4 deimination of profilin and histone H3

Neutrophil adhesion to endothelia, entry into tissues and chemotaxis constitute essential steps in the immune response to infections that drive inflammation. Neutrophils bind to other cells and migrate via adhesion receptors, notably the αMβ2 integrin dimer (also called Mac-1, CR3 or CD11b/CD18). Here, the response of neutrophils to integrin engagement was examined by monitoring the activity of peptidylarginine deiminase 4 (PAD4). Histone H3 deimination was strongly stimulated by manganese, an integrin-activating divalent cation, even in the absence of additional inflammatory stimuli. Manganese-induced cell attachment resulted in neutrophil swarm formation that paralleled histone deimination, whereas antibodies that impair integrin binding prevented both cell adhesion and histone deimination. Manganese treatment led to putative deimination of profilin, a protein that functions as an actin-organizing hub, as detected by two-dimensional gel electrophoresis and citrulline immunoblotting. Cl-amidine, a covalent inhibitor of PAD4, and GSK484, a specific PAD4 inhibitor, blocked profilin deimination. Neutrophil migration toward leukotriene B4 and toward synovial fluid from a rheumatoid arthritis patient were inhibited by chloramidine, thus supporting the contribution of deimination to chemotaxis. The data, based on a simplified system for integrin activation, imply a mechanism whereby integrin attachment coordinates neutrophil responses to inflammation and orchestrates deimination of nuclear and cytoskeletal proteins. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Phosphopeptides P140 cause oxidative burst responses of pulmonary macrophages in an imiquimod-induced lupus model

Recent studies challenge the dogma that a 21-mer phosphopeptide P140 protects against direct cell damage in the phase-III clinical trial (NCT02504645) for lupus, involving reactive oxygen species (ROS)-dependent release of citrullinated histone H3 (H3cit)-linked neutrophil extracellular traps. An open question is the cellular location of ROS production and H3cit formation in lupus. In this study, we examined the effects of P140 peptides on ROS production and H3cit location in lupus with in vivo and situ fluorescence imaging with subcellular resolution. We developed a mouse model of the B6 strain harbouring a bioluminescent reporter under the control of the Lysozyme M promoter. Based on the imiquimod-induced disease model of B6 mice, we used bioluminescent imaging, flow cytometry analysis, and immunohistology staining to study the effects of P140 peptides in lupus. We found a profound accumulation of CX3CR1-positive macrophages in the lungs of lupus mice after the application of P140, accompanied by lung fibrosis formation. The defined P140-mediated macrophage responses were associated with an increase of H3cit in the cytosol, interleukin-1 receptor type 1 on the extracellular membrane, and intracellular production of ROS. Of interest, the disease of imiquimod-induced lupus was prevented with an antioxidant drug apocynin. This study shows that P140 peptides play a role in aggravated murine lupus in a manner dependent on ROS production and H3cit upregulation through pulmonary macrophages.

The Role of Neutrophil Extracellular Traps (NETs) in the Pathogenesis of Systemic Lupus Erythematosus and Antiphospholipid Syndrome

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease of unknown aetiology [...].

Alleviation of arthritis through prevention of neutrophil extracellular traps by an orally available inhibitor of protein arginine deiminase 4

Protein arginine deiminases (PAD) 4 is an enzyme that catalyzes citrullination of protein and its role in autoimmune diseases has been established through clinical genetics and gene knock out studies in mice. Further, studies with PAD4 - deficient mice have shown that PAD4 deficiency does not lead to increased infection or immune suppression, which makes PAD4 an attractive therapeutic target for auto-immune and inflammatory diseases. PAD4 has critical enzymatic role of promoting chromatin decondensation and neutrophil extracellular traps (NETs) formation that is associated with a number of immune-mediated pathological conditions. Here, we present a non-covalent PAD4 inhibitor JBI-589 with high PAD4 isoform selectivity and delineated its binding mode at 2.88 Å resolution by X-ray crystallography. We confirmed its effectiveness in inhibiting NET formation in vitro. Additionally, by using two mouse arthritis models for human rheumatoid arthritis (RA), the well-known disease associated with PAD4 clinically, we established its efficacy in vivo. These results suggest that JBI-589 would be beneficial for both PAD4 and NET-associated pathological conditions.

Title: Bioinformatic Identification of Genes Involved in Diabetic Nephropathy Fibrosis and their Clinical Relevance

Tubulointerstitial fibrosis is an important pathological feature of diabetic nephropathy that is associated with impaired renal function. However, the mechanism by which fibrosis occurs in diabetic nephropathy is unclear. Differentially expressed genes were identified from transcriptome profiles of renal tissue from diabetic patients and unilateral ureteral obstruction mice and intersected to obtain genes that may be involved in diabetic fibrosis. Biological function analysis and protein-protein interaction network analysis were performed. ROC curve and Pearson correlation analysis between hub genes were performed and glomerular filtration rate estimated. Finally, the RNA levels of hub genes were measured using real-time PCR. A total of 283 genes were identified as potentially involved in diabetic nephropathy fibrosis. TYROBP, CTSS, LCP2, LUM and TLR7 were identified as aberrantly expressed hub genes. Immune cell infiltration analysis demonstrated higher numbers of cytotoxic lymphocytes, B lineage cells, monocyte lineage cells, myeloid dendritic cells, neutrophils, and fibroblasts in the diabetic nephropathy group. The areas under ROC curves for TYROBP, CTSS, LCP2, LUM and TLR7 were 0.9167, 0.9583, 0.9917, 0.93333, and 0.9583, respectively (P < 0.001), and their correlation coefficients with estimated glomerular filtration rate were - 0.8332, - 0.752, - 0.7875, - 0.7567, and - 0.7136, respectively (P < 0.001). The RNA levels of TYROBP, CTSS, LUM and TLR7 were upregulated in high-glucose-treated human renal tubular epithelial cells (P < 0.005). Our study identified TYROBP, CTSS, LCP2, LUM and TLR7 as potentially involved in diabetic nephropathy fibrosis. Furthermore, TYROBP, CTSS, LUM and TLR7 may be associated with epithelial-mesenchymal transition of tubular epithelial cells.

Role of the PADI family in inflammatory autoimmune diseases and cancers: A systematic review

The peptidyl arginine deiminase (PADI) family is a calcium ion-dependent group of isozymes with sequence similarity that catalyze the citrullination of proteins. Histones can serve as the target substrate of PADI family isozymes, and therefore, the PADI family is involved in NETosis and the secretion of inflammatory cytokines. Thus, the PADI family is associated with the development of inflammatory autoimmune diseases and cancer, reproductive development, and other related diseases. In this review, we systematically discuss the role of the PADI family in the pathogenesis of various diseases based on studies from the past decade to provide a reference for future research.

Serum extracellular traps associate with the activation of myeloid cells in SLE patients with the low level of anti-DNA antibodies

Neutrophil extracellular traps (NETs) are involved in systemic lupus erythematosus (SLE). We sought to cluster SLE patients based on serum NET levels. Serum NET levels were higher in SLE patients than healthy controls. Frequencies of pleuritis and myositis were increased in patients with high serum NET levels. Serum NET levels negatively correlated with anti-double stranded DNA (anti-dsDNA) antibody titers and C1q-binding immune complexes, but positively correlated with C-reactive protein (CRP) and monocyte counts. Neutrophil transcriptome analysis demonstrated no difference in NET-associated signatures, irrespective of serum NET levels, suggesting anti-dsDNA antibody-mediated clearance of NETs. In serum, NET levels were significantly correlated with myeloid cell-derived inflammatory molecules. Serum NET-based cluster analysis revealed 3 groups of patients based on serum NET and CRP levels, anti-dsDNA antibody titers, and monocyte count. Monocytes were consistently activated following NET-containing immune complex (NET-IC) stimulation. In conclusion, SLE patients with high serum NET levels had lower anti-dsDNA antibody titers and higher inflammatory responses. NET-IC-stimulated monocytes might associate with an inflammatory response characterized by elevated CRP levels. These findings can apply to precision medicine, as inflammatory processes, rather than antibody-dependent processes, can be targeted in specific subpopulations of SLE patients.

Neutrophil extracellular traps in systemic autoimmune and autoinflammatory diseases

Systemic autoimmune diseases are characterized by the failure of the immune system to differentiate self from non-self. These conditions are associated with significant morbidity and mortality, and they can affect many organs and systems, having significant clinical heterogeneity. Recent discoveries have highlighted that neutrophils, and in particular the neutrophil extracellular traps that they can release upon activation, can have central roles in the initiation and perpetuation of systemic autoimmune disorders and orchestrate complex inflammatory responses that lead to organ damage. Dysregulation of neutrophil cell death can lead to the modification of autoantigens and their presentation to the adaptive immune system. Furthermore, subsets of neutrophils that seem to be more prevalent in patients with systemic autoimmune disorders can promote vascular damage and increased oxidative stress. With the emergence of new technologies allowing for improved assessments of neutrophils, the complexity of neutrophil biology and its dysregulation is now starting to be understood. In this Review, we provide an overview of the roles of neutrophils in systemic autoimmune and autoinflammatory diseases and address putative therapeutic targets that may be explored based on this new knowledge.

Pathological mechanisms and crosstalk among different forms of cell death in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by a profound immune dysregulation and the presence of a variety of autoantibodies. Aberrant activation of programmed cell death (PCD) signaling and accelerated cell death is critical in the immunopathogenesis of SLE. Accumulating cellular components from the dead cells and ineffective clearance of the dead cell debris, in particular the nucleic acids and nucleic acids-protein complexes, provide a stable source of self-antigens, which potently activate auto-reactive B cells and promote IFN-I responses in SLE. Different cell types display distinct susceptibility and characteristics to a certain type of cell death, while different PCDs in various cells have mutual and intricate connections to promote immune dysregulation and contribute to the development of SLE. In this review, we discuss the role of various cell death pathways and their interactions in the pathogenesis of SLE. An in depth understanding of the interconnections among various forms cell death in SLE will lead to a better understanding of disease pathogenesis, shedding light on the development of novel therapeutic targets.

PAD4 controls chemoattractant production and neutrophil trafficking in malaria

Peptidylarginine deiminase 4 (PAD4) is a key regulator of inflammation but its function in infections remains incompletely understood. We investigate PAD4 in the context of malaria and demonstrate a role in regulation of immune cell trafficking and chemokine production. PAD4 regulates liver immunopathology by promoting neutrophil trafficking in a Plasmodium chabaudi mouse malaria model. In human macrophages, PAD4 regulates expression of CXCL chemokines in response to stimulation with TLR ligands and P. falciparum. Using patient samples, we show that CXCL1 may be a biomarker for severe malaria. PAD4 inhibition promotes disease tolerance and may represent a therapeutic avenue in malaria.

Bacterial-Driven Inflammation and Mutant BRAF Expression Combine to Promote Murine Colon Tumorigenesis That Is Sensitive to Immune Checkpoint Therapy

Colorectal cancer is multifaceted, with subtypes defined by genetic, histologic, and immunologic features that are potentially influenced by inflammation, mutagens, and/or microbiota. Colorectal cancers with activating mutations in BRAF are associated with distinct clinical characteristics, although the pathogenesis is not well understood. The Wnt-driven multiple intestinal neoplasia (MinApcΔ716/+) enterotoxigenic Bacteroides fragilis (ETBF) murine model is characterized by IL17-dependent, distal colon adenomas. Herein, we report that the addition of the BRAF V600E mutation to this model results in the emergence of a distinct locus of midcolon tumors. In ETBF-colonized BRAF V600E Lgr5 CreMin (BLM) mice, tumors have similarities to human BRAF V600E tumors, including histology, CpG island DNA hypermethylation, and immune signatures. In comparison to Min ETBF tumors, BLM ETBF tumors are infiltrated by CD8+ T cells, express IFNγ signatures, and are sensitive to anti-PD-L1 treatment. These results provide direct evidence for critical roles of host genetic and microbiota interactions in colorectal cancer pathogenesis and sensitivity to immunotherapy. SIGNIFICANCE: Colorectal cancers with BRAF mutations have distinct characteristics. We present evidence of specific colorectal cancer gene-microbial interactions in which colonization with toxigenic bacteria drives tumorigenesis in BRAF V600E Lgr5 CreMin mice, wherein tumors phenocopy aspects of human BRAF-mutated tumors and have a distinct IFNγ-dominant immune microenvironment uniquely responsive to immune checkpoint blockade.This article is highlighted in the In This Issue feature, p. 1601.

Neutrophil Dysregulation in the Pathogenesis of Systemic Lupus Erythematosus

The recent identifications of a subset of proinflammatory neutrophils, low-density granulocytes, and their ability to readily form neutrophil extracellular traps led to a resurgence of interest in neutrophil dysregulation in the pathogenesis of systemic lupus erythematosus (SLE). This article presents an overview on how neutrophil dysregulation modulates the innate and adaptive immune responses in SLE and their putative roles in disease pathogenesis. The therapeutic potential of targeting this pathogenic process in the treatment of SLE is also discussed.

Targeting citrullination in autoimmunity: insights learned from preclinical mouse models

INTRODUCTION

Aberrant citrullination and excessive peptidylarginine deiminase (PAD) activity are detected in numerous challenging autoimmune diseases such as rheumatoid arthritis, inflammatory bowel diseases, systemic lupus erythematosus, multiple sclerosis, and type 1 diabetes. Because excessive PAD activity is a common denominator in these diseases, PADs are interesting potential therapeutic targets for future therapies.

AREAS COVERED

This review summarizes the advances made in the design of PAD inhibitors, their utilization and therapeutic potential in preclinical mouse models of autoimmunity. Relevant literature encompasses studies from 1994 to 2021 that are available on PubMed.gov.

EXPERT OPINION

Pan-PAD inhibition is a promising therapeutic strategy for autoimmune diseases. Drugs achieving pan-PAD inhibition were capable of ameliorating, reversing, and preventing clinical symptoms in preclinical mouse models. However, the implications for PADs in key biological processes potentially present a high risk for clinical complications and could hamper the translation of PAD inhibitors to the clinic. We envisage that PAD isozyme-specific inhibitors will improve the understanding the role of PAD isozymes in disease pathology, reduce the risk of side-effects and enhance prospects for future clinical translation.