Deficiency of CXCR2, but not other chemokine receptors, attenuates autoantibody-mediated arthritis in a murine model

Programmed Death Ligand 1-Expressing Macrophages and Their Protective Role in the Joint During Arthritis

OBJECTIVE

Arthritis associated with immune checkpoint inhibitor therapies highlights the importance of immune checkpoint expression for joint homeostasis. We investigated the role of programmed death ligand (PD-L) 1 in the synovium using a collagen-induced arthritis (CIA) mouse model.

METHODS

We blocked PD-L1 using blocking antibodies during CIA and assessed the arthritis severity by clinical and histologic scoring. PD-L1 expression and the origin of synovial macrophages were investigated using flow cytometry and parabiosis. We used Cre-Lox mice to ascertain the protective role of PD-L1-expressing macrophages in arthritis. The immune profile of human and murine synovial PD-L1+ macrophages was determined by reverse transcriptase-polymerase chain reaction, flow cytometry, and single-cell RNA sequencing.

RESULTS

Anti-PD-L1 antibody treatment during CIA worsened arthritis with increased immune cell infiltration compared with isotype control, supporting the regulatory role of PD-L1 in the joint. The main cells expressing PD-L1 in the synovium were macrophages. Using parabiosis, we showed that synovial PD-L1+ macrophages were both locally proliferating and partially replaced by the circulation. PD-L1+ macrophages had increased levels of MER proto-oncogene tyrosine kinase (MerTK) and interleukin (IL)-10 expression during acute CIA. Genetic depletion of PD-L1 on macrophages in LyzcrePD-L1fl/fl mice resulted in worsened CIA compared with controls. We found that human PD-L1+ macrophages in the synovium of healthy individuals and patients with rheumatoid arthritis express MerTK and IL-10.

CONCLUSION

PD-L1+ macrophages with efferocytotic and anti-inflammatory characteristics protect the synovium from severe arthritis in the CIA mouse model. Tissue-protective, PD-L1-expressing macrophages are also present in the human synovium at homeostasis and during rheumatoid arthritis.

Yoga maintains Th17/Treg cell homeostasis and reduces the rate of T cell aging in rheumatoid arthritis: a randomized controlled trial

The pathogenesis of rheumatoid arthritis (RA) is characterized by a Th17/Treg cell imbalance. A pro-inflammatory cytokine milieu that promotes the continued proliferation of Th17 cells is related to the development of autoinflammation. In RA, T cells have several hallmarks of cellular aging, and they accumulate DNA damage, predisposing to the occurrence of mutations and epigenetic alterations. Since the onset, progression, and treatment response are influenced by a variety of external stressors and environmental factors, this study aimed to evaluate the impact of 8-week yoga practice on disease severity, T cell subsets, markers of T cell ageing and inflammation, epigenetic alterations and gene expression patterns in active RA patients on standard disease-modifying anti-rheumatic drugs (DMARDs). A total of 64 participants with active RA were randomized into 2 groups, yoga group (n = 32) or non-yoga group (n = 32); that were assessed for disease severity, at baseline and after 8 week duration, for Disease Activity Score (DAS28-ESR), T cell subsets [Th17 (CD3+ CD4+ IL17+ RORγt+) cells and Treg (CD3+ CD4+ CD25+ CD127-Foxp3+) cells], markers of T cell aging [aged Th17 cells (CD3+ CD4+ IL17+ RORγt+ CD28-) and aged Treg cells (CD3+ CD4+ CD25+ CD127-Foxp3+ CD28-)], pro-inflammatory markers [IL-6, and IL-17], anti-inflammatory markers [TGF-β, and IL-10], epigenetic alterations [5-methyl cytosine, 5-hydroxymethyl cytosine, and HDAC1] and gene expression patterns [RORγt, FoxP3, IL-17, IL-6, TGF-β, CXCL2, CXCR2, and JUN]. In yoga group, there was a significant improvement in DAS28-ESR scores at the end of 8-weeks of yoga program. The Th17 cells and aged T cell subsets showed a significant decline whereas Treg cell population showed a significant elevation in yoga group. There were significant improvements observed in epigenetic markers as well as inflammatory markers post 8-weeks of yoga practice. The yoga group showed downregulation of RORγt, IL-17, IL-6, CXCL2, CXCR2, and upregulation of FoxP3 and TGF-β transcripts. Yoga enables the maintenance of immune-homeostasis as evident by increased Treg cell population and reduced Th17 cell population. Yoga reduces the rate of immunological aging in T cells, as seen by the reduction in population of aged Th17 cells and aged Treg cells. Yoga positively modifies transcriptome and epigenome by normalization of various inflammatory markers, gene expression patterns and epigenetic alterations. Taken together, yoga reduces RA severity, and aids in immune-modulation and hence can be beneficial as an adjunct therapy.

A review of the pleiotropic actions of the IFN-inducible CXC chemokine receptor 3 ligands in the synovial microenvironment

Chemokines are pivotal players in instigation and perpetuation of synovitis through leukocytes egress from the blood circulation into the inflamed articulation. Multitudinous literature addressing the involvement of the dual-function interferon (IFN)-inducible chemokines CXCL9, CXCL10 and CXCL11 in diseases characterized by chronic inflammatory arthritis emphasizes the need for detangling their etiopathological relevance. Through interaction with their mutual receptor CXC chemokine receptor 3 (CXCR3), the chemokines CXCL9, CXCL10 and CXCL11 exert their hallmark function of coordinating directional trafficking of CD4+ TH1 cells, CD8+ T cells, NK cells and NKT cells towards inflammatory niches. Among other (patho)physiological processes including infection, cancer, and angiostasis, IFN-inducible CXCR3 ligands have been implicated in autoinflammatory and autoimmune diseases. This review presents a comprehensive overview of the abundant presence of IFN-induced CXCR3 ligands in bodily fluids of patients with inflammatory arthritis, the outcomes of their selective depletion in rodent models, and the attempts at developing candidate drugs targeting the CXCR3 chemokine system. We further propose that the involvement of the CXCR3 binding chemokines in synovitis and joint remodeling encompasses more than solely the directional ingress of CXCR3-expressing leukocytes. The pleotropic actions of the IFN-inducible CXCR3 ligands in the synovial niche reiteratively illustrate the extensive complexity of the CXCR3 chemokine network, which is based on the intercommunion of IFN-inducible CXCR3 ligands with distinct CXCR3 isoforms, enzymes, cytokines, and infiltrated and resident cells present in the inflamed joints.

Modulation of Neutrophil Function by Recombinant Human IgG1 Fc Hexamer in the Endogenous K/BxN Mouse Model of Rheumatoid Arthritis

INTRODUCTION

Neutrophils are a pivotal cell type in the K/BxN mouse model of rheumatoid arthritis and play an essential role in the progression of the arthritis. They are readily activated by immune complexes (ICs) via their FcγRs to release IL-1β in addition to other cytokines, which are inducing cartilage destruction. Neutrophils also release neutrophil-active chemokines to recruit themselves in an autocrine manner to perpetuate tissue destruction. FcγR-expression on neutrophils is of crucial importance for the recognition of ICs.

METHODS

In this study, due to its high avidity for binding to FcγRs, we investigated the potential anti-inflammatory effect of a recombinant IgG1 Fc hexamer (rFc-µTP-L309C) on neutrophils in the K/BxN mouse model of endogenously generated chronic arthritis. 200 mg/kg rFc-µTP-L309C and human serum albumin (HSA), used as controls, were administered subcutaneously every other day. Mouse ankle joints were monitored daily to generate a clinical score. Immunohistology was used to evaluate neutrophil infiltration and TUNEL to assess apoptosis. ELISA was used to measure IL-1β.

RESULTS

Treatment with rFc-µTP-L309C, but not HSA, was able to significantly ameliorate the arthritis in the K/BxN mice. Significant neutrophil infiltration into the ankle joint was found, but treatment with rFc-µTP-L309C resulted in significantly less neutrophil infiltration. There was no significant influence of rFc-µTP-L309C on neutrophil death or apoptosis. Less neutrophil infiltration could not be correlated to chemokine-mediated migration. Significantly less IL-1β was measured in mice treated with rFc-µTP-L309C.

CONCLUSION

In the endogenous K/BxN mouse model of rheumatoid arthritis, amelioration can be explained in part by inhibition of neutrophil infiltration into the joints as well as inhibition of IL-1β production. Given the observed inhibitory properties on neutrophils, rFc-µTP-L309C may be a potential therapeutic candidate to treat autoimmune and inflammatory conditions in which neutrophils are the predominant cell type involved in pathogenesis.

Epigallocatechin-3-gallate inhibits osteoclastic differentiation by modulating mitophagy and mitochondrial functions

A natural plant product, epigallocatechin-3-gallate (EGCG), was evaluated for its effectiveness in the regulation of osteoclastogenesis. We found that EGCG inhibited the osteoclast (OC) differentiation in vitro, and in primary bone marrow cells in a dose-dependent manner. Quantitative RT-PCR studies showed that the EGCG reduced the expression of OC differentiation markers. DCFDA, MitoSOX, and JC-1 staining revealed that the EGCG attenuated the reactive oxygen species (ROS), and mitochondrial membrane potential; and flux analysis corroborated the effect of EGCG. We further found that the EGCG inhibited mRNA and protein expressions of mitophagy-related molecules. We confirmed that the OC differentiation was inhibited by EGCG by modulating mitophagy through AKT and p38MAPK pathways. Furthermore, in silico analysis revealed that the binding of RANK and RANKL was blocked by EGCG. Overall, we defined the mechanisms of osteoclastogenesis during arthritis for developing a new therapy using a natural compound besides the existing therapeutics.

Nonhematopoietic IRAK1 drives arthritis via neutrophil chemoattractants

IL-1 receptor-activated kinase 1 (IRAK1) is involved in signal transduction downstream of many TLRs and the IL-1R. Its potential as a drug target for chronic inflammatory diseases is underappreciated. To study its functional role in joint inflammation, we generated a mouse model expressing a functionally inactive IRAK1 (IRAK1 kinase deficient, IRAK1KD), which also displayed reduced IRAK1 protein expression and cell type–specific deficiencies of TLR signaling. The serum transfer model of arthritis revealed a potentially novel role of IRAK1 for disease development and neutrophil chemoattraction exclusively via its activity in nonhematopoietic cells. Consistently, IRAK1KD synovial fibroblasts showed reduced secretion of neutrophil chemoattractant chemokines following stimulation with IL-1β or human synovial fluids from patients with rheumatoid arthritis (RA) and gout. Together with patients with RA showing prominent IRAK1 expression in fibroblasts of the synovial lining, these data suggest that targeting IRAK1 may be therapeutically beneficial. As pharmacological inhibition of IRAK1 kinase activity had only mild effects on synovial fibroblasts from mice and patients with RA, targeted degradation of IRAK1 may be the preferred pharmacologic modality. Collectively, these data position IRAK1 as a central regulator of the IL-1β–dependent local inflammatory milieu of the joints and a potential therapeutic target for inflammatory arthritis.

Role of chemokine systems in cancer and inflammatory diseases

Chemokines are a large family of small secreted proteins that have fundamental roles in organ development, normal physiology, and immune responses upon binding to their corresponding receptors. The primary functions of chemokines are to coordinate and recruit immune cells to and from tissues and to participate in regulating interactions between immune cells. In addition to the generally recognized antimicrobial immunity, the chemokine/chemokine receptor axis also exerts a tumorigenic function in many different cancer models and is involved in the formation of immunosuppressive and protective tumor microenvironment (TME), making them potential prognostic markers for various hematologic and solid tumors. In fact, apart from its vital role in tumors, almost all inflammatory diseases involve chemokines and their receptors in one way or another. Modulating the expression of chemokines and/or their corresponding receptors on tumor cells or immune cells provides the basis for the exploitation of new drugs for clinical evaluation in the treatment of related diseases. Here, we summarize recent advances of chemokine systems in protumor and antitumor immune responses and discuss the prevailing understanding of how the chemokine system operates in inflammatory diseases. In this review, we also emphatically highlight the complexity of the chemokine system and explore its potential to guide the treatment of cancer and inflammatory diseases.

Machine learning to identify immune-related biomarkers of rheumatoid arthritis based on WGCNA network

OBJECTIVES

This study was designed to identify the potential diagnostic biomarkers of rheumatoid arthritis (RA) and to explore the potential pathological relevance of immune cell infiltration in this disease.

METHODS

Three previously published datasets containing gene expression data from 35 RA patients and 29 controls (GSE55235, GSE55457, and GSE12021) were downloaded from the GEO database, after which a weighted correlation network analysis (WGCNA) approach was utilized to clarify differentially abundant genes. Candidate biomarkers of RA were then identified via the use of a LASSO regression model and support vector machine recursive feature elimination (SVM-RFE) analyses. Data were validated based upon the area under the receiver operating characteristic curve (AUC) values, with hub genes being identified as those with an AUC > 85% and a P value < 0.05. Lastly, the CIBERSORT algorithm was used to assess immune cell infiltration of RA tissues, and correlations between immune cell infiltration and disease-related diagnostic biomarkers were assessed.

RESULTS

The green-yellow module containing 87 genes was found to be highly correlated with RA positivity. FADD, CXCL2, and CXCL8 were identified as potential RA diagnostic biomarkers (AUC > 0.85), and these results were validated using the GSE77298 dataset. Immune cell infiltration analyses revealed the expression of hub genes to be correlated with mast cells, monocytes, activated NK cells, CD8 T cells, resting dendritic cells, and plasma cells.

CONCLUSION

These data indicate that FADD, CXCL2, and CXCL8 are valuable diagnostic biomarkers of RA, offering new insight that can guide future studies of RA incidence and progression.

SETD2-mediated epigenetic regulation of noncanonical Wnt5A during osteoclastogenesis

To define the role of SETD2 in the WNT5a signaling in the context of osteoclastogenesis, we exploited two different models: in vitro osteoclast differentiation, and K/BxN serum-induced arthritis model. We found that SETD2 and WNT5a were upregulated during osteoclast differentiation and after induction of arthritis. Using gain- and loss-of-function approaches in the myeloid cell, we confirmed that SETD2 regulated the osteoclast markers, and WNT5a via modulating active histone marks by enriching H3K36me3, and by reducing repressive H3K27me3 mark. Additionally, during osteoclastic differentiation, the transcription of Wnt5a was also associated with the active histone H3K9 and H4K8 acetylations. Mechanistically, SETD2 directed induction of NF-κβ expression facilitated the recruitment of H3K9Ac and H4K8Ac around the TSS region of the Wnt5a gene, thereby, assisting osteoclast differentiation. Together these findings for the first time revealed that SETD2 mediated epigenetic regulation of Wnt5a plays a critical role in osteoclastogenesis and induced arthritis. Model for the Role of SETD2 dependent regulation of osteoclastic differentiation. A In monocyte cells SETD2-dependent H3K36 trimethylation help to create open chromatin region along with active enhancer mark, H3K27Ac. This chromatin state facilitated the loss of a suppressive H3K27me3 mark. B Additionally, SETD2 mediated induction of NF-κβ expression leads to the recruitment of histone acetyl transferases, P300/PCAF, to the Wnt5a gene and establish H3K9Ac and H4K8Ac marks. Along with other activation marks, these acetylation marks help in Wnt5a transcription which leads to osteoclastogenesis.

Chemokines as the critical factors during bladder cancer progression: an overview

Bladder cancer (BCa) is one of the most frequent urogenital malignancies which is mainly observed among men. There are various genetic and environmental risk factors associated with BCa progression. Transurethral endoscopic resection and open ablative surgery are the main treatment options for muscle invasive BCa. BCG therapy is also employed following the endoscopic resection to prevent tumor relapse. The tumor microenvironment is the main interaction site of tumor cells and immune system in which the immune cells are recruited via chemokines and chemokine receptors. In present review we summarized the main chemokines and chemokine receptors which have been associated with histopathological features of BCa patients in the world. This review highlights the chemokines and chemokine receptors as critical markers in early detection and therapeutic purposes among BCa patients and clarifies their molecular functions during BCa progression and metastasis.

NK cell-derived GM-CSF potentiates inflammatory arthritis and is negatively regulated by CIS

Despite increasing recognition of the importance of GM-CSF in autoimmune disease, it remains unclear how GM-CSF is regulated at sites of tissue inflammation. Using GM-CSF fate reporter mice, we show that synovial NK cells produce GM-CSF in autoantibody-mediated inflammatory arthritis. Synovial NK cells promote a neutrophilic inflammatory cell infiltrate, and persistent arthritis, via GM-CSF production, as deletion of NK cells, or specific ablation of GM-CSF production in NK cells, abrogated disease. Synovial NK cell production of GM-CSF is IL-18–dependent. Furthermore, we show that cytokine-inducible SH2-containing protein (CIS) is crucial in limiting GM-CSF signaling not only during inflammatory arthritis but also in experimental allergic encephalomyelitis (EAE), a murine model of multiple sclerosis. Thus, a cellular cascade of synovial macrophages, NK cells, and neutrophils mediates persistent joint inflammation via production of IL-18 and GM-CSF. Endogenous CIS provides a key brake on signaling through the GM-CSF receptor. These findings shed new light on GM-CSF biology in sterile tissue inflammation and identify several potential therapeutic targets.

Therapeutic blockade of CXCR2 rapidly clears inflammation in arthritis and atopic dermatitis models: demonstration with surrogate and humanized antibodies

Neutrophils are the most abundant effector cells of the innate immune system and represent the first line of defense against infection. However, in many common pathologies, including autoimmune diseases, excessive recruitment and activation of neutrophils can drive a chronic inflammatory response leading to unwanted tissue destruction. Several strategies have been investigated to tackle pathologic neutrophil biology, and thus provide a novel therapy for chronic inflammatory diseases. The chemokine receptor CXCR2 plays a crucial role in regulating neutrophil homeostasis and is a promising pharmaceutical target. In this study, we report the discovery and validation of a humanized anti-human CXCR2 monoclonal antibody. To enable in vivo studies, we developed a surrogate anti-mouse CXCR2 antibody, as well as a human knock-in CXCR2 mouse. When administered in models of atopic dermatitis (AD) and rheumatoid arthritis (RA), the antibodies rapidly clear inflammation. Our findings support further developments of anti-CXCR2 mAb approaches not only for RA and AD, but also for other neutrophil-mediated inflammatory conditions where neutrophils are pathogenic and medical needs are unmet.

Increased expression of CXCL2 in ACPA-positive rheumatoid arthritis and its role in osteoclastogenesis

Anti-citrullinated protein/peptide antibodies (ACPA) play important roles in the pathogenesis of rheumatoid arthritis (RA). ACPA-positive (ACPA⁺ ) and ACPA-negative (ACPA^- ) RA were suggested to be different disease subsets, with distinct differences in genetic variation and clinical outcomes. The aims of the present study were to compare gene expression profiles in ACPA⁺ and ACPA^- RA, and to identify novel candidate gene signatures that might serve as therapeutic targets. Comprehensive transcriptome analysis of peripheral blood mononuclear cells (PBMCs) from ACPA⁺ and ACPA^- RA patients and healthy controls was performed via RNA sequencing. A validation cohort was used to further investigate differentially expressed genes via polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Spearman's correlation test was used to evaluate the correlation of differentially expressed genes and the clinical and laboratory data of the patients. The role of differentially expressed genes in osteoclastogenesis was further investigated. Expression of C-X-C motif chemokine ligand 2 (CXCL2) was significantly increased in ACPA⁺ RA than in ACPA^- RA, which was validated in PBMCs and serum. CXCL2 promoted the migration of CD14⁺ monocytes and increased osteoclastogenesis in RA patients. RAW264.7 macrophages were used to investigate specific mechanisms, and the results suggested that CXCL2 stimulated osteoclastogenesis via extracellular receptor kinase (ERK) mitogen-activated protein kinase (MAPK) and nuclear factor kappa B pathways. In conclusion, CXCL2 was highly expressed in ACPA⁺ RA than in ACPA^- RA. CXCL2 promoted osteoclastogenesis and was related to bone erosion in RA, which suggests that the blockade of CXCL2 might be a novel strategy for the treatment of RA.

Targeting the Chemokine System in Rheumatoid Arthritis and Vasculitis

Arrest of circulating leukocytes and subsequent diapedesis is a fundamental component of inflammation. In general, the leukocyte migration cascade is tightly regulated by chemoattractants, such as chemokines. Chemokines, small secreted chemotactic cytokines, as well as their G-protein-coupled seven transmembrane spanning receptors, control the migratory patterns, positioning and cellular interactions of immune cells. Increased levels of chemokines and their receptors are found in the blood and within inflamed tissue in patients with rheumatoid arthritis (RA) and vasculitis. Chemokine ligand-receptor interactions regulate the recruitment of leukocytes into tissue, thus contributing in important ways to the pathogenesis of RA and vasculitis. Despite the fact that blockade of chemokines and chemokine receptors in animal models have yielded promising results, human clinical trials in RA using inhibitors of chemokines and their receptors have generally failed to show clinical benefits. However, recent early phase clinical trials suggest that strategies blocking specific chemokines may have clinical benefits in RA, demonstrating that the chemokine system remains a promising therapeutic target for rheumatic diseases, such as RA and vasuculitis and requires further study.

IL-4 controls activated neutrophil FcγR2b expression and migration into inflamed joints

Neutrophils are the most abundant immune cells found in actively inflamed joints of patients with rheumatoid arthritis (RA), and most animal models for RA depend on neutrophils for the induction of joint inflammation. Exogenous IL-4 and IL-13 protect mice from antibody-mediated joint inflammation, although the mechanism is not understood. Neutrophils display a very strong basal expression of STAT6, which is responsible for signaling following exposure to IL-4 and IL-13. Still, the role of IL-4 and IL-13 in neutrophil biology has not been well studied. This can be explained by the low neutrophil surface expression of the IL-4 receptor α-chain (IL-4Rα), essential for IL-4- and IL-13-induced STAT6 signaling. Here we identify that colony stimulating factor 3 (CSF3), released during acute inflammation, mediates potent STAT3-dependent neutrophil IL-4Rα up-regulation during sterile inflammatory conditions. We further demonstrate that IL-4 limits neutrophil migration to inflamed joints, and that CSF3 combined with IL-4 or IL-13 results in a prominent neutrophil up-regulation of the inhibitory Fcγ receptor (FcγR2b). Taking these data together, we demonstrate that the IL-4 and CSF3 pathways are linked and play important roles in regulating proinflammatory neutrophil behavior.

Mouse Models and Tools for the in vivo Study of Neutrophils

Neutrophils are the most abundant leukocytes in human blood and critical actors of the immune system. Many neutrophil functions and facets of their activity in vivo were revealed by studying genetically modified mice or by tracking fluorescent neutrophils in animals using imaging approaches. Assessing the roles of neutrophils can be challenging, especially when exact molecular pathways are questioned or disease states are interrogated that alter normal neutrophil homeostasis. This review discusses the main in vivo models for the study of neutrophils, their advantages and limitations. The side-by-side comparison underlines the necessity to carefully choose the right model(s) to answer a given scientific question, and exhibit caveats that need to be taken into account when designing experimental procedures. Collectively, this review suggests that at least two models should be employed to legitimately conclude on neutrophil functions.

Myeloid Krüppel-Like Factor 2 Critically Regulates K/BxN Serum-Induced Arthritis

Rheumatoid arthritis (RA) is an immune-mediated inflammatory disease, and Krüppel-like factor 2 (KLF2) regulates immune cell activation and function. Herein, we show that in our experiments 50% global deficiency of KLF2 significantly elevated arthritic inflammation and pathogenesis, osteoclastic differentiation, matrix metalloproteinases (MMPs), and inflammatory cytokines in K/BxN serum-induced mice. The severities of RA pathogenesis, as well as the causative and resultant cellular and molecular factors, were further confirmed in monocyte-specific KLF2 deficient mice. In addition, induction of RA resulted in a decreased level of KLF2 in monocytes isolated from both mice and humans along with higher migration of activated monocytes to the RA sites in humans. Mechanistically, overexpression of KLF2 decreased the level of MMP9; conversely, knockdown of KLF2 increased MMP9 in monocytes along with enrichment of active histone marks and histone acetyltransferases on the MMP9 promoter region. These findings define the critical regulatory role of myeloid KLF2 in RA pathogenesis.

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

KLF2 (kruppel-like factor 2 [lung]) regulates osteoclastogenesis by modulating autophagy

Macroautophagy/autophagy is involved in myeloid cellular repair, destruction, and osteoclast differentiation; conversely, KLF2 (kruppel-like factor 2 [lung]) regulates myeloid cell activation and differentiation. To investigate the specific role of KLF2 in autophagy, osteoclastic differentiation was induced in monocytes in presence or absence of the autophagy inhibitor 3-methyladenine (3-MA), KLF2 inducer geranylgeranyl transferase inhibitor (GGTI298), and adenoviral overexpression of KLF2. We found that the number of autophagic cells and multinucleated osteoclasts were significantly decreased in presence of 3-MA, GGTI298, and KLF2 overexpressed cells indicating involvement of KLF2 in these processes. In addition, autophagy-related protein molecules were significantly decreased after induction of KLF2 during the course of osteoclastic differentiation. Furthermore, induction of arthritis in mice reduced the level of Klf2 in monocytes, and enhanced autophagy during osteoclastic differentiation. Mechanistically, knocking down of KLF2 increased the level of Beclin1 (BECN1) expression, and conversely, KLF2 over-expression reduced the level of BECN1 in monocytes. Moreover, 3-MA and GGTI298 both reduced myeloid cell proliferation concomitantly upregulating senescence-related molecules (CDKN1A/p21 and CDKN1B/p27^kip1). We further confirmed epigenetic regulation of Becn1 by modulating Klf2; knocking down of Klf2 increased the levels of histone activation marks H3K9 and H4K8 acetylation in the promoter region of Becn1; and overexpression of Klf2 decreased the levels of H4K8 and H3K9 acetylation. In addition, osteoclastic differentiation also increased levels of H3K9 and H4K8 acetylation in the promoter region of Becn1. Together these findings for the first time revealed that Klf2 critically regulates Becn1-mediated autophagy process during osteoclastogenesis.Abbreviations: ACP5/TRAP: acid phosphatase 5, tartrate resistant; Ad-KLF2: adenoviral construct of KLF2; ATG3: autophagy related 3; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG12: autophagy related 12; BECN1: beclin 1, autophagy related; C57BL/6: inbred mouse strain C57 black 6; ChIP: chromatin immunoprecipitation; CSF1/MCSF: colony stimulating factor 1 (macrophage); CTSK: cathepsin K; EV: empty vector; GGTI298: geranylgeranyl transferase inhibitor; H3K9Ac: histone H3 lysine 9 acetylation; H4K8Ac: histone H4 lysine 8 acetylation; K/BxN mice: T cell receptor (TCR) transgene KRN and the MHC class II molecule A(g7) generates K/BxN mice; KLF2: kruppel-like factor 2 (lung); 3MA: 3-methyladenine; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MDC: monodansylcadaverine; NFATc1: nuclear factor of activated T cells 1; NFKB: nuclear factor of kappa light polypeptide gene enhancer in B cells; p21/CDKN1A: cyclin dependent kinase inhibitor 1A; p27^kip1/CDKN1B: cyclin-dependent kinase inhibitor 1B; PCR: polymerase chain reaction; PtdIns3K: phosphoinositide 3-kinase; RA: rheumatoid arthritis; siKlf2: small interfering KLF2 ribonucleic acid; NS: non-specific; RAW 264.7: abelson murine leukemia virus transformed macrophage cell line; TNFSF11/RANKL: tumor necrosis factor (ligand) superfamily, member 11; TSS: transcriptional start site; UCSC: University of California, Santa Cruz.

CXCR2: A Novel Mediator of Mammary Tumor Bone Metastasis

Most breast cancer patients die due to bone metastasis. Although metastasis accounts for 5% of the breast cancer cases, it is responsible for most of the deaths. Sometimes even before the detection of a primary tumor, most of the patients have bone and lymph node metastasis. Moreover, at the time of death, breast cancer patients have the bulk of the tumor burden in their bones. Therapy options are available for the treatment of primary tumors, but there are minimal options for treating breast cancer patients who have bone metastasis. C-X-C motif chemokine receptor type 2 (CXCR2) receptor-mediated signaling has been shown to play a critical role during bone-related inflammations and its ligands C-X-C motif chemokine ligand 6 (CXCL6) and 8 (CXCL8) aid in the resorption of bone during bone metastasis. In this study, we tested the hypothesis that CXCR2 contributes to mammary tumor-induced osteolysis and bone metastasis. In the present study, we examined the role of both tumor cell-derived and host-derived CXCR2 in influencing mammary tumor cell bone metastasis. For understanding the role of tumor cell-derived CXCR2, we utilized Cl66 CXCR2 knockdown (Cl66-shCXCR2) and Cl66-Control cells (Cl66-Control) and observed a significant decrease in tumor growth and tumor-induced osteolysis in Cl66-shCXCR2 cells in comparison with the Cl66-Control cells. Next, for understanding the role of host-derived CXCR2, we utilized mice with genomic knockdown of CXCR2 (Cxcr2^-/-) and injected Cl66-Luciferase (Cl66-Luc) or 4T1-Luciferase (4T1-Luc) cells. We observed decreased bone destruction and metastasis in the bone of Cxcr2^-/- mice. Our data suggest the importance of both tumor cell- and host-derived CXCR2 signaling in the bone metastasis of breast cancer cells.

Multi-omic analysis of signalling factors in inflammatory comorbidities

BACKGROUND

Inflammation is a core element of many different, systemic and chronic diseases that usually involve an important autoimmune component. The clinical phase of inflammatory diseases is often the culmination of a long series of pathologic events that started years before. The systemic characteristics and related mechanisms could be investigated through the multi-omic comparative analysis of many inflammatory diseases. Therefore, it is important to use molecular data to study the genesis of the diseases. Here we propose a new methodology to study the relationships between inflammatory diseases and signalling molecules whose dysregulation at molecular levels could lead to systemic pathological events observed in inflammatory diseases.

RESULTS

We first perform an exploratory analysis of gene expression data of a number of diseases that involve a strong inflammatory component. The comparison of gene expression between disease and healthy samples reveals the importance of members of gene families coding for signalling factors. Next, we focus on interested signalling gene families and a subset of inflammation related diseases with multi-omic features including both gene expression and DNA methylation. We introduce a phylogenetic-based multi-omic method to study the relationships between multi-omic features of inflammation related diseases by integrating gene expression, DNA methylation through sequence based phylogeny of the signalling gene families. The models of adaptations between gene expression and DNA methylation can be inferred from pre-estimated evolutionary relationship of a gene family. Members of the gene family whose expression or methylation levels significantly deviate from the model are considered as the potential disease associated genes.

CONCLUSIONS

Applying the methodology to four gene families (the chemokine receptor family, the TNF receptor family, the TGF- β gene family, the IL-17 gene family) in nine inflammation related diseases, we identify disease associated genes which exhibit significant dysregulation in gene expression or DNA methylation in the inflammation related diseases, which provides clues for functional associations between the diseases.

A bivalent compound targeting CCR5 and the mu opioid receptor treats inflammatory arthritis pain in mice without inducing pharmacologic tolerance

Background

Pain accompanies rheumatoid arthritis and other chronic inflammatory conditions and is difficult to manage. Although opioids provide potent analgesia, chronic opioid use can cause tolerance and addiction. Recent studies have demonstrated functional interactions between chemokine and opioid receptor signaling pathways. Reported heterodimerization of chemokine and opioid receptors led our group to develop bivalent compounds that bind both types of receptors, with the goal of targeting opioids to sites of inflammation. MCC22 is a novel bivalent compound containing a CCR5 antagonist and mu opioid receptor (MOR) agonist pharmacophores linked through a 22-atom spacer. We evaluated the efficacy of MCC22 in the K/B.g7 T-cell receptor transgenic mouse model of spontaneous inflammatory arthritis.

Methods

MCC22 or morphine was administered intraperitoneally at varying doses to arthritic K/B.g7 mice or nonarthritic control mice. Mechanical pain hypersensitivity was measured each day before and after drug administration, using the electronic von Frey test. The potency of MCC22 relative to that of morphine was calculated. Functional readouts of pain included grip strength and nesting behavior. A separate dosing regimen was used to determine whether the drugs induced pharmacologic tolerance.

Results

MCC22 provided ~ 3000-fold more potent analgesia than morphine in this model. Daily treatment with MCC22 also led to a cumulative analgesic effect, reducing the daily baseline pain level. MCC22 produced no observable analgesic effect in nonarthritic control mice. Importantly, repeated administration of MCC22 did not induce pharmacologic tolerance, whereas a similar regimen of morphine did. Both grip strength and nesting behaviors improved among arthritic mice treated with MCC22. Ankle thickness and arthritis scores were not affected by MCC22. The analgesic effect of MCC22 was abolished in K/B.g7 mice genetically lacking CCR5, demonstrating the receptor specificity of the antagonist pharmacophore.

Conclusions

MCC22 is a novel bivalent ligand that targets CCR5 and MOR. Our findings demonstrate that MCC22 provides highly potent analgesia and improved functional outcomes in a model of inflammatory arthritis, without inducing typical opioid tolerance. These findings suggest that MCC22 or similar compounds could be used to treat the pain associated with inflammatory arthritis and related conditions, while minimizing the risks typically associated with chronic opioid use.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1661-5) contains supplementary material, which is available to authorized users.

Uncovering Cellular retinoic acid-binding protein 2 as a potential target for rheumatoid arthritis synovial hyperplasia

Rheumatoid arthritis (RA) is a systemic autoimmune disease including synovitis and synovial hyperplasia that contribute to joint destruction. Pivotal pathogenic mechanisms in this process are the dysregulated proliferation and apoptosis of fibroblast-like synoviocytes (FLS). Unfortunately, the mechanisms of FLS dysregulation are not completely elucidated. Here, we explored a new hypothesis based in the potent anti-proliferative and pro-apoptotic activity of retinoids in some types of cancer. Specifically, we investigated the role of retinoids and of the retinoic acid binding proteins, CRABP2 and FABP5, on the proliferation and apoptosis of FLS from RA by adding all-trans retinoic acid (ATRA) or silencing CRABP2 and FABP5. We showed an unconventional behaviour of RA FLS, which were relatively insensitive to ATRA. In effect, ATRA increased the resistance to apoptosis despite the high CRABP2/FABP5 ratio of RA FLS; and CRABP2 suppression sensitized RA FLS to Fas-induced apoptosis. This latter effect was associated with changes in expression of kinases, ASK1 up-regulation and ERK down-regulation, and increased phosphorylation of JNK. In addition, the potentiation of FLS apoptosis by CRABP2 silencing persisted in the presence of pro-inflammatory mediators, TNF e IL1β. Therefore, the results point to CRABP2 as a potential target to decrease synovial hyperplasia in RA.

Directed evolution of broadly crossreactive chemokine-blocking antibodies efficacious in arthritis

Chemokine receptors typically have multiple ligands. Consequently, treatment with a blocking antibody against a single chemokine is expected to be insufficient for efficacy. Here we show single-chain antibodies can be engineered for broad crossreactivity toward multiple human and mouse proinflammatory ELR⁺ CXC chemokines. The engineered molecules recognize functional epitopes of ELR⁺ CXC chemokines and inhibit neutrophil activation ex vivo. Furthermore, an albumin fusion of the most crossreactive single-chain antibody prevents and reverses inflammation in the K/BxN mouse model of arthritis. Thus, we report an approach for the molecular evolution and selection of broadly crossreactive antibodies towards a family of structurally related, yet sequence-diverse protein targets, with general implications for the development of novel therapeutics.

CXCR2 antagonism has been shown to be anti-arthritic, but anti-chemokine therapies usually fail in the clinic owing to redundancy in chemokine-receptor interactions. Here the authors develop single-chain antibodies with multiple chemokine specificities to achieve high affinity and broad specificity to mouse and human CXC chemokines with efficacy in a K/BxN serum transfer model of arthritis.

Neutrophils: Beneficial and Harmful Cells in Septic Arthritis

Septic arthritis is an inflammatory joint disease that is induced by pathogens such as Staphylococcus aureus. Infection of the joint triggers an acute inflammatory response directed by inflammatory mediators including microbial danger signals and cytokines and is accompanied by an influx of leukocytes. The recruitment of these inflammatory cells depends on gradients of chemoattractants including formylated peptides from the infectious agent or dying cells, host-derived leukotrienes, complement proteins and chemokines. Neutrophils are of major importance and play a dual role in the pathogenesis of septic arthritis. On the one hand, these leukocytes are indispensable in the first-line defense to kill invading pathogens in the early stage of disease. However, on the other hand, neutrophils act as mediators of tissue destruction. Since the elimination of inflammatory neutrophils from the site of inflammation is a prerequisite for resolution of the acute inflammatory response, the prolonged stay of these leukocytes at the inflammatory site can lead to irreversible damage to the infected joint, which is known as an important complication in septic arthritis patients. Thus, timely reduction of the recruitment of inflammatory neutrophils to infected joints may be an efficient therapy to reduce tissue damage in septic arthritis.

CXCR2 is critical for bacterial control and development of joint damage and pain in Staphylococcus aureus-induced septic arthritis in mouse

Staphylococcus aureus is the main pathogen associated with septic arthritis. Upon infection, neutrophils are quickly recruited to the joint by different chemoattractants, especially CXCR1/2 binding chemokines. Although their excessive accumulation is associated with intense pain and permanent articular damage, neutrophils have an important function in controlling bacterial burden. This work aimed to study the role of CXCR2 in the control of infection, hypernociception and tissue damage in S. aureus-induced septic arthritis in mice. The kinetics of neutrophil recruitment correlated with the bacterial load recovered from inflamed joint after intra-articular injection of S. aureus. Treatment of mice from the start of infection with the non-competitive antagonist of CXCR1/2, DF2156A, reduced neutrophil accumulation, cytokine production in the tissue, joint hypernociception and articular damage. However, early DF2156A treatment increased the bacterial load locally. CXCR2 was important for neutrophil activation and clearance of bacteria in vitro and in vivo. Start of treatment with DF2156A 3 days after infection prevented increase in bacterial load and reduced the hypernociception in the following days, but did not improve tissue damage. In conclusion, treatment with DF2156A seems be effective in controlling tissue inflammation and dysfunction but its effects are highly dependent on the timing of the treatment start.

A time-course microarray data analysis reveals consistent dysregulated genes and upstream microRNAs in autoantibody-mediated arthritis

Background

The purpose of this study is to identify key genes and microRNAs (miRNAs) involved in autoantibody-mediated arthritis (AMA).

Methods

A time-course microarray data (ID: GSE27492) of peripheral blood leukocytes, ankle tissue, and synovial fluid from K/BxN mouse serum-transferred mice were downloaded from Gene Expression Omnibus. Those samples were collected at days 0, 1, 3, 7, 12, and 18 after serum injection. Limma of R was employed to identify differentially expressed genes (DEGs) in samples collected at days 1–18 compared with those collected at day 0. Consistent DEGs were obtained by taking the interaction of DEGs from different time points, followed by functional enrichment analysis. MiRNAs were screened out and constructed into regulatory network with DEGs using Cytoscape.

Results

In total, 17 consistent DEGs were obtained, including downregulated Ephx1 and upregulated AF251705, Adam8, Arg1, Basp1, Ccl2, Ccl7, Ccl9, Ccr2, Clec4a2, Clec4d, Cxcl1, Fabp5, Fcgr1, Gp49a, Il1rn, and Saa3. Those DEGs were associated with biological processes of immune response, inflammatory response, and defense response; chemokine signaling pathway; cytokine-cytokine receptor interaction; and NOD-like receptor signaling pathway. Additionally, 202 miRNAs were identified to have a regulatory effect on 9 of the 17 DEGs. Notably, miR-944, miR-374a, and miR374b were found to regulate the expression of Cxcl1, Ccl7, and Ccl2. Clec4d was targeted by 78 miRNAs.

Conclusions

Our study reveals that 17 DEGs and 202 miRNAs may be associated with autoimmune disorder in the progression of AMA, which could guide future researches.

Inflammation-a Critical Appreciation of the Role of Myeloid Cells

What is inflammation's big idea? In this brief overview of the role of myeloid cells in inflammation, we will critically discuss what drives the initiation, amplification, and resolution of inflammation in different anatomical sites in response to different pathological stimuli. It can be argued that we have a good understanding of the basic principles that underlie myeloid cell activation and the mobilization of innate immune cells to sites of injury and infection in acute inflammation. The challenge now for inflammation biologists is to understand how resolution of this normal physiological response goes wrong in hyperacute and chronic inflammation. A better understanding of how inflammation is regulated will allow us to develop new anti-inflammatory drugs that will reduce the burden of inflammatory disease without compromising the patient's immune defenses against infectious disease. Ideally such drugs should encourage a return to homeostasis and enhance tissue repair processes.

Altered activation state of circulating neutrophils in patients with neovascular age-related macular degeneration

Background

Neutrophil dysfunction plays a key role in the development of diseases characterized by inflammation and angiogenesis. Here, we studied the systemic expression of neutrophil markers reflecting activation, adhesion, and resolution of inflammation in patients with neovascular age-related macular degeneration (AMD).

Results

This was a prospective case-control study of patients with neovascular AMD and age-matched healthy control individuals. Patients were recruited from an outpatient program, and control individuals were recruited amongst patients’ relatives. Current smokers and individuals with either active immune-disease or ongoing cancer were not included, as these factors are known to affect neutrophil function. Fresh-drawn venous blood was processed for flow cytometric analysis of neutrophil markers. We determined percentages of positive cells and compared expression levels using fluorescence intensity measures. We found conditional differences on marker expression between patients with neovascular AMD (n = 29) and controls (n = 28): no differences were found when looking broadly, but several differences emerged when focusing on non-smokers. Here, patients with neovascular AMD had increased expression of the activity marker cluster of differentiation (CD) 66b (P = 0.003; Mann-Whitney U test), decreased expression of adhesion marker CD162 (P = 0.044; Mann-Whitney U test), and lower expression of the resolution of inflammation marker C-X-C chemokine receptor 2 (P = 0.044; Mann-Whitney U test).

Conclusions

We present novel evidence suggesting that the activity of circulating neutrophils, sensitive to smoking, may differ in patients with neovascular AMD.

Inflammatory Cell Migration in Rheumatoid Arthritis: A Comprehensive Review

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that primarily affects the joints. Self-reactive B and T lymphocytes cooperate to promote antibody responses against self proteins and are major drivers of disease. T lymphocytes also promote RA independently of B lymphocytes mainly through the production of key inflammatory cytokines, such as IL-17, that promote pathology. While the innate signals that initiate self-reactive adaptive immune responses are poorly understood, the disease is predominantly caused by inflammatory cellular infiltration and accumulation in articular tissues, and by bone erosions driven by bone-resorbing osteoclasts. Osteoclasts are giant multinucleated cells formed by the fusion of multiple myeloid cells that require short-range signals, such as the cytokines MCSF and RANKL, for undergoing differentiation. The recruitment and positioning of osteoclast precursors to sites of osteoclast differentiation by chemoattractants is an important point of control for osteoclastogenesis and bone resorption. Recently, the GPCR EBI2 and its oxysterol ligand 7a, 25 dihydroxycholesterol, were identified as important regulators of osteoclast precursor positioning in proximity to bone surfaces and of osteoclast differentiation under homeostasis. In chronic inflammatory diseases like RA, osteoclast differentiation is also driven by inflammatory cytokines such as TNFa and IL-1, and can occur independently of RANKL. Finally, there is growing evidence that the chemotactic signals guiding osteoclast precursors to inflamed articular sites contribute to disease and are of great interest. Furthering our understanding of the complex osteoimmune cell interactions should provide new avenues of therapeutic intervention for RA.

Reduction of GPSM3 expression akin to the arthritis-protective SNP rs204989 differentially affects migration in a neutrophil model

G Protein Signaling Modulator-3 (GPSM3) is a leukocyte-specific regulator of G protein-coupled receptors (GPCRs), which binds inactivated Gα_i·GDP subunits and precludes their reassociation with Gβγ subunits. GPSM3 deficiency protects mice from inflammatory arthritis and, in humans, GPSM3 single nucleotide polymorphisms (SNPs) are inversely associated with the risk of rheumatoid arthritis development; recently, these polymorphisms were linked to one particular SNP (rs204989) that decreases GPSM3 transcript abundance. However, the precise role of GPSM3 in leukocyte biology is unknown. Here we show that GPSM3 is induced in the human promyelocytic leukemia NB4 cell line following retinoic acid treatment, which differentiates this cell line into a model of neutrophil physiology (NB4*). Reducing GPSM3 expression in NB4* cells, akin to the effect ascribed to the rs204989 C>T transition, disrupts cellular migration toward leukotriene B4 (LTB4) and (to a lesser extent) interleukin-8 (a.k.a. IL-8 or CXCL8), but not migration toward formylated peptides (fMLP). As the chemoattractants LTB4 and CXCL8 are involved in recruitment of neutrophils to the arthritic joint, our results suggest that the arthritis-protective GPSM3 SNP rs204989 may act to decrease neutrophil chemoattractant responsiveness.

K/BxN Serum-Transfer Arthritis as a Model for Human Inflammatory Arthritis

The K/BxN serum-transfer arthritis (STA) model is a murine model in which the immunological mechanisms occurring in rheumatoid arthritis (RA) and other arthritides can be studied. To induce K/BxN STA, serum from arthritic transgenic K/BxN mice is transferred to naive mice and manifestations of arthritis occur a few days later. The inflammatory response in the model is driven by autoantibodies against the ubiquitously expressed self-antigen, glucose-6-phosphate isomerase (G6PI), leading to the formation of immune complexes that drive the activation of different innate immune cells such as neutrophils, macrophages, and possibly mast cells. The pathogenesis further involves a range of immune mediators including cytokines, chemokines, complement factors, Toll-like receptors, Fc receptors, and integrins, as well as factors involved in pain and bone erosion. Hence, even though the K/BxN STA model mimics only the effector phase of RA, it still involves a wide range of relevant disease mediators. Additionally, as a murine model for arthritis, the K/BxN STA model has some obvious advantages. First, it has a rapid and robust onset of arthritis with 100% incidence in genetically identical animals. Second, it can be induced in a wide range of strain backgrounds and can therefore also be induced in gene-deficient strains to study the specific importance of disease mediators. Even though G6PI might not be an essential autoantigen, for example, in RA, the K/BxN STA model is a useful tool to understand how autoantibodies, in general, drive the progression of arthritis by interacting with downstream components of the innate immune system. Finally, the model has also proven useful as a model wherein arthritic pain can be studied. Taken together, these features make the K/BxN STA model a relevant one for RA, and it is a potentially valuable tool, especially for the preclinical screening of new therapeutic targets for RA and perhaps other forms of inflammatory arthritis. Here, we describe the molecular and cellular pathways in the development of K/BxN STA focusing on the recent advances in the understanding of the important mechanisms. Additionally, this review provides a comparison of the K/BxN STA model to some other arthritis models.

Promotion of Inflammatory Arthritis by Interferon Regulatory Factor 5 in a Mouse Model

OBJECTIVE

Polymorphisms in the transcription factor interferon regulatory factor 5 (IRF5) are associated with an increased risk of developing rheumatoid arthritis (RA). This study was undertaken to determine the role of IRF5 in a mouse model of arthritis development.

METHODS

K/BxN serum-transfer arthritis was induced in mice deficient in IRF5, or lacking IRF5 only in myeloid cells, and arthritis severity was evaluated. K/BxN arthritis was also induced in mice deficient in TRIF, Toll-like receptor 2 (TLR2), TLR3, TLR4, and TLR7 to determine the pathways through which IRF5 might promote arthritis. In vitro studies were performed to determine the role of IRF5 in interleukin-1 (IL-1) receptor and TLR signaling.

RESULTS

Arthritis severity was reduced in IRF5-deficient, TRIF-deficient, TLR3-deficient, and TLR7-deficient mice. The expression of multiple genes regulating neutrophil recruitment or function and bioactive IL-1β formation was reduced in the joints during active arthritis in IRF5-deficient mice. In vitro studies showed that TLR7 and the TRIF-dependent TLR3 pathway induce proinflammatory cytokine production in disease-relevant cell types in an IRF5-dependent manner.

CONCLUSION

Our findings indicate that IRF5 contributes to disease pathogenesis in inflammatory arthritis. This is likely due at least in part to the role of IRF5 in mediating proinflammatory cytokine production downstream of TLR7 and TLR3. Since TLR7 and TLR3 are both RNA-sensing TLRs, this suggests that endogenous RNA ligands present in the inflamed joint promote arthritis development. These findings may be relevant to human RA, since RNA capable of activating TLR7 and TLR3 is present in synovial fluid and TLR7 and TLR3 are up-regulated in the joints of RA patients.

CXCR2 Mediates Brucella-Induced Arthritis in Interferon γ-Deficient Mice

BACKGROUND

Brucella species are facultative intracellular gram-negative bacteria that cause brucellosis, a common global zoonosis. Infection of the joints is the most common focal complication of brucellosis in humans. The purpose of this study was to identify mediators of focal inflammation during brucellosis.

METHODS

Wild-type (WT) mice are naturally resistant to Brucella infection; therefore, we infected anti-interferon γ (IFN-γ)-treated, or IFN-γ(-/-) mice with Brucella to induce osteoarticular and musculoskeletal inflammation, as we previously described. Mice were infected intraperitoneally with Brucella melitensis, and the clinical course of disease, histopathologic changes, and cytokine levels were compared among groups.

RESULTS

Rag1(-/-) mice (B- and T-cell deficient) and µMT(-/-) mice (B-cell deficient) developed paw inflammation at a similar rate and severity as WT mice following infection with B. melitensis and treatment with anti-IFN-γ. Joints from B. melitensis-infected IFN-γ(-/-) mice had markedly increased levels of CCR2 and CXCR2 ligands. While anti-IFN-γ-treated CCR2(-/-) and WT mice behaved similarly, anti-IFN-γ-treated CXCR2(-/-) or IFN-γ(-/-)/CXCR2(-/-) mice had strikingly reduced focal swelling relative to anti-IFN-γ-treated WT or IFN-γ(-/-) mice, respectively. Additionally, neutrophil recruitment was dependent on CXCR2.

CONCLUSIONS

Adaptive immune cells and CCR2 are dispensable, while CXCR2 is necessary for Brucella-induced focal neutrophil recruitment and inflammation.

RNA-seq analysis of the gonadal transcriptome during Alligator mississippiensis temperature-dependent sex determination and differentiation

Background

The American alligator (Alligator mississippiensis) displays temperature-dependent sex determination (TSD), in which incubation temperature during embryonic development determines the sexual fate of the individual. However, the molecular mechanisms governing this process remain a mystery, including the influence of initial environmental temperature on the comprehensive gonadal gene expression patterns occurring during TSD.

Results

Our characterization of transcriptomes during alligator TSD allowed us to identify novel candidate genes involved in TSD initiation. High-throughput RNA sequencing (RNA-seq) was performed on gonads collected from A. mississippiensis embryos incubated at both a male and a female producing temperature (33.5 °C and 30 °C, respectively) in a time series during sexual development. RNA-seq yielded 375.2 million paired-end reads, which were mapped and assembled, and used to characterize differential gene expression. Changes in the transcriptome occurring as a function of both development and sexual differentiation were extensively profiled. Forty-one differentially expressed genes were detected in response to incubation at male producing temperature, and included genes such as Wnt signaling factor WNT11, histone demethylase KDM6B, and transcription factor C/EBPA. Furthermore, comparative analysis of development- and sex-dependent differential gene expression revealed 230 candidate genes involved in alligator sex determination and differentiation, and early details of the suspected male-fate commitment were profiled. We also discovered sexually dimorphic expression of uncharacterized ncRNAs and other novel elements, such as unique expression patterns of HEMGN and ARX. Twenty-five of the differentially expressed genes identified in our analysis were putative transcriptional regulators, among which were MYBL2, MYCL, and HOXC10, in addition to conventional sex differentiation genes such as SOX9, and FOXL2. Inferred gene regulatory network was constructed, and the gene-gene and temperature-gene interactions were predicted.

Conclusions

Gonadal global gene expression kinetics during sex determination has been extensively profiled for the first time in a TSD species. These findings provide insights into the genetic framework underlying TSD, and expand our current understanding of the developmental fate pathways during vertebrate sex determination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2396-9) contains supplementary material, which is available to authorized users.

A homeostatic function of CXCR2 signalling in articular cartilage

OBJECTIVE

ELR+ CXC chemokines are heparin-binding cytokines signalling through the CXCR1 and CXCR2 receptors. ELR+ CXC chemokines have been associated with inflammatory arthritis due to their capacity to attract inflammatory cells. Here, we describe an unsuspected physiological function of these molecules in articular cartilage homeostasis.

METHODS

Chemokine receptors and ligands were detected by immunohistochemistry, western blotting and RT-PCR. Osteoarthritis was induced in wild-type and CXCR2(-/-) mice by destabilisation of the medial meniscus (DMM). CXCR1/2 signalling was inhibited in vitro using blocking antibodies or siRNA. Chondrocyte phenotype was analysed using Alcian blue staining, RT-PCR and western blotting. AKT phosphorylation and SOX9 expression were upregulated using constitutively active AKT or SOX9 plasmids. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay.

RESULTS

CXCL6 was expressed in healthy cartilage and was retained through binding to heparan sulfate proteoglycans. CXCR2(-/-) mice developed more severe osteoarthritis than wild types following DMM, with increased chondrocyte apoptosis. Disruption of CXCR1/2 in human and CXCR2 signalling in mouse chondrocytes led to a decrease in extracellular matrix production, reduced expression of chondrocyte differentiation markers and increased chondrocyte apoptosis. CXCR2-dependent chondrocyte homeostasis was mediated by AKT signalling since forced expression of constitutively active AKT rescued the expression of phenotypic markers and the apoptosis induced by CXCR2 blockade.

CONCLUSIONS

Our study demonstrates an important physiological role for CXCR1/2 signalling in maintaining cartilage homeostasis and suggests that the loss of ELR+ CXC chemokines during cartilage breakdown in osteoarthritis contributes to the characteristic loss of chondrocyte phenotypic stability.

Type 1 Diabetes Prone NOD Mice Have Diminished Cxcr1 mRNA Expression in Polymorphonuclear Neutrophils and CD4+ T Lymphocytes

In humans, CXCR1 and CXCR2 are two homologous proteins that bind ELR+ chemokines. Both receptors play fundamental roles in neutrophil functions such as migration and reactive oxygen species production. Mouse Cxcr1 and Cxcr2 genes are located in an insulin-dependent diabetes genetic susceptibility locus. The non obese diabetic (NOD) mouse is a spontaneous well-described animal model for insulin-dependent type 1 diabetes. In this disease, insulin deficiency results from the destruction of insulin-producing beta cells by autoreactive T lymphocytes. This slow-progressing disease is dependent on both environmental and genetic factors. Here, we report descriptive data about the Cxcr1 gene in NOD mice. We demonstrate decreased expression of mRNA for Cxcr1 in neutrophils and CD4+ lymphocytes isolated from NOD mice compared to other strains, related to reduced NOD Cxcr1 gene promoter activity. Looking for Cxcr1 protein, we next analyze the membrane proteome of murine neutrophils by mass spectrometry. Although Cxcr2 protein is clearly found in murine neutrophils, we did not find evidence of Cxcr1 peptides using this method. Nevertheless, in view of recently-published experimental data obtained in NOD mice, we argue for possible Cxcr1 involvement in type 1 diabetes pathogenesis.

A novel phenylcyclohex-1-enecarbothioamide derivative inhibits CXCL8-mediated chemotaxis through selective regulation of CXCR2-mediated signalling

BACKGROUND AND PURPOSE

Since the CXC chemokine receptor CXCR2 and its cognate ligand CXCL8 (IL-8) critically regulate neutrophil trafficking during inflammation, they have been implicated in a number of inflammatory lung diseases. Several CXCR2 antagonists have been described and the blockade of CXCR2 has shown promise in pre-clinical disease models and early clinical trials. However, given its potential, there are fewer distinct classes of antagonists of CXCR2 than of other clinically relevant molecular targets. Thus, we sought to identify additional classes of compounds that alter CXCR2 function.

EXPERIMENTAL APPROACH

We used the CXCR2 Tango(TM) assay to screen an in-house library of highly diverse chemical compounds. CX4338 [2-(benzylamino)-4,4-dimethyl-6-oxo-N-phenylcyclohex-1-enecarbothioamide] was identified from our screen and additional studies to characterize the compound were performed. Receptor internalization and second-messenger assays were used to assess the effects of CX4338 on CXCR2-mediated signalling. Wound healing, transwell cell migration and LPS-induced lung inflammation in mice were used to determine the in vitro and in vivo effects of CX4338.

KEY RESULTS

CX4338 selectively inhibited CXCR2-mediated recruitment of β-arrestin-2 and receptor internalization, while enhancing CXCR2-mediated MAPK activation. Additionally, CX4338 inhibited CXCL8-induced chemotaxis in CXCR2-overexpressing cells and human neutrophils. In vivo, CX4338 significantly reduced neutrophils in bronchoalveolar lavage induced by LPS in mice.

CONCLUSIONS AND IMPLICATIONS

A novel compound CX4338 inhibited CXCR2-mediated cell migration with a mechanism of action not previously reported. Also, selective inhibition of CXCR2-mediated β-arrestin-2 activation is sufficient to inhibit CXCL8-mediated chemotaxis.

Nonclassical Ly6C(-) monocytes drive the development of inflammatory arthritis in mice

Different subsets and/or polarized phenotypes of monocytes and macrophages may play distinct roles during the development and resolution of inflammation. Here, we demonstrate in a murine model of rheumatoid arthritis that nonclassical Ly6C(-) monocytes are required for the initiation and progression of sterile joint inflammation. Moreover, nonclassical Ly6C(-) monocytes differentiate into inflammatory macrophages (M1), which drive disease pathogenesis and display plasticity during the resolution phase. During the development of arthritis, these cells polarize toward an alternatively activated phenotype (M2), promoting the resolution of joint inflammation. The influx of Ly6C(-) monocytes and their subsequent classical and then alternative activation occurs without changes in synovial tissue-resident macrophages, which express markers of M2 polarization throughout the course of the arthritis and attenuate joint inflammation during the initiation phase. These data suggest that circulating Ly6C(-) monocytes recruited to the joint upon injury orchestrate the development and resolution of autoimmune joint inflammation.

The Src family kinases Hck, Fgr, and Lyn are critical for the generation of the in vivo inflammatory environment without a direct role in leukocyte recruitment

Kovács et al. examine the role of the Src family kinases Hck, Fgr, and Lyn in immune cell–mediated inflammation. Using arthritis and skin inflammation models, the authors show that mice lacking hematopoietic Hck, Fgr, and Lyn are protected from these inflammatory diseases, showing loss of myeloid cell recruitment and lack of inflammatory mediator production. Unexpectedly, the three kinases are dispensable for the intrinsic migratory ability of myeloid cells. These finding may have clinical implications in rheumatic and skin diseases.

Although Src family kinases participate in leukocyte function in vitro, such as integrin signal transduction, their role in inflammation in vivo is poorly understood. We show that Src family kinases play a critical role in myeloid cell–mediated in vivo inflammatory reactions. Mice lacking the Src family kinases Hck, Fgr, and Lyn in the hematopoietic compartment were completely protected from autoantibody-induced arthritis and skin blistering disease, as well as from the reverse passive Arthus reaction, with functional overlap between the three kinases. Though the overall phenotype resembled the leukocyte recruitment defect observed in β₂ integrin–deficient (CD18^−/−) mice, Hck^−/−Fgr^−/−Lyn^−/− neutrophils and monocytes/macrophages had no cell-autonomous in vivo or in vitro migration defect. Instead, Src family kinases were required for the generation of the inflammatory environment in vivo and for the release of proinflammatory mediators from neutrophils and macrophages in vitro, likely due to their role in Fcγ receptor signal transduction. Our results suggest that infiltrating myeloid cells release proinflammatory chemokine, cytokine, and lipid mediators that attract further neutrophils and monocytes from the circulation in a CD18-dependent manner. Src family kinases are required for the generation of the inflammatory environment but not for the intrinsic migratory ability of myeloid cells.

CCR1 plays a critical role in modulating pain through hematopoietic and non-hematopoietic cells

Inflammation is associated with immune cells infiltrating into the inflammatory site and pain. CC chemokine receptor 1 (CCR1) mediates trafficking of leukocytes to sites of inflammation. However, the contribution of CCR1 to pain is incompletely understood. Here we report an unexpected discovery that CCR1-mediated trafficking of neutrophils and CCR1 activity on non-hematopoietic cells both modulate pain. Using a genetic approach (CCR1^−/− animals) and pharmacological inhibition of CCR1 with selective inhibitors, we show significant reductions in pain responses using the acetic acid-induced writhing and complete Freund's adjuvant-induced mechanical hyperalgesia models. Reductions in writhing correlated with reduced trafficking of myeloid cells into the peritoneal cavity. We show that CCR1 is highly expressed on circulating neutrophils and their depletion decreases acetic acid-induced writhing. However, administration of neutrophils into the peritoneal cavity did not enhance acetic acid-induced writhing in wild-type (WT) or CCR1^−/− mice. Additionally, selective knockout of CCR1 in either the hematopoietic or non-hematopoietic compartments also reduced writhing. Together these data suggest that CCR1 functions to significantly modulate pain by controlling neutrophil trafficking to the inflammatory site and having an unexpected role on non-hematopoietic cells. As inflammatory diseases are often accompanied with infiltrating immune cells at the inflammatory site and pain, CCR1 antagonism may provide a dual benefit by restricting leukocyte trafficking and reducing pain.

Denervation protects limbs from inflammatory arthritis via an impact on the microvasculature

Two-way communication between the mammalian nervous and immune systems is increasingly recognized and appreciated. An intriguing example of such crosstalk comes from clinical observations dating from the 1930s: Patients who suffer a stroke and then develop rheumatoid arthritis atypically present with arthritis on only one side, the one not afflicted with paralysis. Here we successfully modeled hemiplegia-induced protection from arthritis using the K/BxN serum-transfer system, focused on the effector phase of inflammatory arthritis. Experiments entailing pharmacological inhibitors, genetically deficient mouse strains, and global transcriptome analyses failed to associate the protective effect with a single nerve quality (i.e., with the sympathetic, parasympathetic, or sensory nerves). Instead, there was clear evidence that denervation had a long-term effect on the limb microvasculature: The rapid and joint-localized vascular leak that typically accompanies and promotes serum-transferred arthritis was compromised in denervated limbs. This defect was reflected in the transcriptome of endothelial cells, the expression of several genes impacting vascular leakage or transendothelial cell transmigration being altered in denervated limbs. These findings highlight a previously unappreciated pathway to dissect and eventually target in inflammatory arthritis.

Fas signaling in macrophages promotes chronicity in K/BxN serum-induced arthritis

OBJECTIVE

A nonapoptotic role of Fas signaling has been implicated in the regulation of inflammation and innate immunity. This study was undertaken to elucidate the contribution of Fas signaling in macrophages to the development of arthritis.

METHODS

K/BxN serum-transfer arthritis was induced in a mouse line in which Fas was conditionally deleted in the myeloid lineage (Cre(LysM) Fas(flox/flox) mice). The arthritis was assessed clinically and histologically. Expression of interleukin-1β (IL-1β), CXCL5, IL-10, IL-6, and gp96 was determined by enzyme-linked immunosorbent assay. Bone marrow-derived macrophages were activated with IL-1β and gp96. Cell phenotype and apoptosis were analyzed by flow cytometry.

RESULTS

Arthritis onset in Cre(LysM) Fas(flox/flox) mice was comparable with that observed in control mice; however, resolution was accelerated during the chronic phase. The attenuated arthritis was associated with reduced articular expression of the endogenous Toll-like receptor 2 (TLR-2) ligand gp96 and the neutrophil chemotactic chemokine CXCL5, and enhanced expression of IL-10. Activation with IL-1β or gp96 induced increased IL-10 expression in Fas-deficient murine macrophages compared with control macrophages. IL-10 suppressed IL-6 and CXCL5 expression induced by IL-1β plus gp96. IL-1β-mediated activation of ERK, which regulates IL-10 expression, was increased in Fas-deficient mouse macrophages.

CONCLUSION

Taken together, our findings indicate that impaired Fas signaling results in enhanced expression of antiinflammatory IL-10 and reduced expression of gp96, and these effects are associated with accelerated resolution of inflammation during the chronic phase of arthritis. These observations suggest that strategies to reduce endogenous TLR ligands and increase IL-10 may be beneficial in the treatment of rheumatoid arthritis.

Development of a versatile enrichment analysis tool reveals associations between the maternal brain and mental health disorders, including autism

Background

A recent study of lateral septum (LS) suggested a large number of autism-related genes with altered expression in the postpartum state. However, formally testing the findings for enrichment of autism-associated genes proved to be problematic with existing software. Many gene-disease association databases have been curated which are not currently incorporated in popular, full-featured enrichment tools, and the use of custom gene lists in these programs can be difficult to perform and interpret. As a simple alternative, we have developed the Modular Single-set Enrichment Test (MSET), a minimal tool that enables one to easily evaluate expression data for enrichment of any conceivable gene list of interest.

Results

The MSET approach was validated by testing several publicly available expression data sets for expected enrichment in areas of autism, attention deficit hyperactivity disorder (ADHD), and arthritis. Using nine independent, unique autism gene lists extracted from association databases and two recent publications, a striking consensus of enrichment was detected within gene expression changes in LS of postpartum mice. A network of 160 autism-related genes was identified, representing developmental processes such as synaptic plasticity, neuronal morphogenesis, and differentiation. Additionally, maternal LS displayed enrichment for genes associated with bipolar disorder, schizophrenia, ADHD, and depression.

Conclusions

The transition to motherhood includes the most fundamental social bonding event in mammals and features naturally occurring changes in sociability. Some individuals with autism, schizophrenia, or other mental health disorders exhibit impaired social traits. Genes involved in these deficits may also contribute to elevated sociability in the maternal brain. To date, this is the first study to show a significant, quantitative link between the maternal brain and mental health disorders using large scale gene expression data. Thus, the postpartum brain may provide a novel and promising platform for understanding the complex genetics of improved sociability that may have direct relevance for multiple psychiatric illnesses. This study also provides an important new tool that fills a critical analysis gap and makes evaluation of enrichment using any database of interest possible with an emphasis on ease of use and methodological transparency.

Toll-like receptor-mediated IRE1α activation as a therapeutic target for inflammatory arthritis

In rheumatoid arthritis (RA), macrophage is one of the major sources of inflammatory mediators. Macrophages produce inflammatory cytokines through toll-like receptor (TLR)-mediated signalling during RA. Herein, we studied macrophages from the synovial fluid of RA patients and observed a significant increase in activation of inositol-requiring enzyme 1α (IRE1α), a primary unfolded protein response (UPR) transducer. Myeloid-specific deletion of the IRE1α gene protected mice from inflammatory arthritis, and treatment with the IRE1α-specific inhibitor 4U8C attenuated joint inflammation in mice. IRE1α was required for optimal production of pro-inflammatory cytokines as evidenced by impaired TLR-induced cytokine production in IRE1α-null macrophages and neutrophils. Further analyses demonstrated that tumour necrosis factor (TNF) receptor-associated factor 6 (TRAF6) plays a key role in TLR-mediated IRE1α activation by catalysing IRE1α ubiquitination and blocking the recruitment of protein phosphatase 2A (PP2A), a phosphatase that inhibits IRE1α phosphorylation. In summary, we discovered a novel regulatory axis through TRAF6-mediated IRE1α ubiquitination in regulating TLR-induced IRE1α activation in pro-inflammatory cytokine production, and demonstrated that IRE1α is a potential therapeutic target for inflammatory arthritis.

A systems analysis identifies a feedforward inflammatory circuit leading to lethal influenza infection

For acutely lethal influenza infections, the relative pathogenic contributions of direct viral damage to lung epithelium versus dysregulated immunity remain unresolved. Here, we take a top-down systems approach to this question. Multigene transcriptional signatures from infected lungs suggested that elevated activation of inflammatory signaling networks distinguished lethal from sublethal infections. Flow cytometry and gene expression analysis involving isolated cell subpopulations from infected lungs showed that neutrophil influx largely accounted for the predictive transcriptional signature. Automated imaging analysis, together with these gene expression and flow data, identified a chemokine-driven feedforward circuit involving proinflammatory neutrophils potently driven by poorly contained lethal viruses. Consistent with these data, attenuation, but not ablation, of the neutrophil-driven response increased survival without changing viral spread. These findings establish the primacy of damaging innate inflammation in at least some forms of influenza-induced lethality and provide a roadmap for the systematic dissection of infection-associated pathology.

Heme oxygenase-1 regulates the progression of K/BxN serum transfer arthritis

Background

Heme oxygenase-1 (HO-1) is induced in many cell types as a defense mechanism against stress. We have investigated the possible role of endogenous HO-1 in the effector phase of arthritis using the K/BxN serum transfer model of arthritis in HO-1 heterozygous and homozygous knock-out mice.

Methodology/Principal Findings

Arthritis was induced in C57/Black-6 xFVB (HO-1^+/+, HO-1^+/− and HO-1^−/−) mice by intraperitoneal injection of 150 µl serum from arthritic K/BxN mice at days 0 and 2. Blood was collected and animals were sacrificed at day 10. Histological analysis was performed in ankle sections. The levels of inflammatory mediators were measured in serum and paw homogenates by enzyme-linked immunosorbent assay or Multiplex technology. The incidence of arthritis was higher in HO-1^+/− and HO-1^−/− groups compared with HO-1^+/+. The inflammatory response was aggravated in HO-1^+/− mice as shown by arthritic score and the migration of inflammatory cells that could be related to the enhancement of CXCL-1 production. In addition, the HO-1^+/− group showed proteoglycan depletion significantly higher than HO-1^+/+ mice. Serum levels of matrix metalloproteinase-3, monocyte chemotactic protein-1, plasminogen activator inhibitor-1, E-selectin and intercellular adhesion molecule-1 were increased in arthritic HO-1^−/− mice, whereas vascular endothelial growth factor and some cytokines such as interferon-γ showed a reduction compared to HO-1^+/+ or HO-1^+/− mice. In addition, down-regulated gene expression of ferritin, glutathione S-reductase A1 and superoxide dismutase-2 was observed in the livers of arthritic HO-1^+/− animals.

Conclusion/Significance

Endogenous HO-1 regulates the production of systemic and local inflammatory mediators and plays a protective role in K/BxN serum transfer arthritis.

Interleukin-33 primes mast cells for activation by IgG immune complexes

Mast cells (MCs) are heterogeneous cells whose phenotype is modulated by signals received from the local microenvironment. Recent studies have identified the mesenchymal-derived cytokine IL-33 as a potent direct activator of MCs, as well as regulator of their effector phenotype, and have implicated this activity in the ability of mast cells to contribute to murine experimental arthritis. We explored the hypothesis that IL-33 enables participation of synovial MCs in murine K/BxN arthritis by promoting their activation by IgG immune complexes. Compared to wild-type (WT) control mice, transgenic animals lacking the IL-33 receptor ST2 exhibited impaired MC-dependent immune complex-induced vascular permeability (flare) and attenuated K/BxN arthritis. Whereas participation of MCs in this model is mediated by the activating IgG receptor FcγRIII, we pre-incubated bone marrow-derived MCs with IL-33 and found not only direct induction of cytokine release but also a marked increase in FcγRIII-driven production of critical arthritogenic mediators including IL-1β and CXCL2. This "priming" effect was associated with mRNA accumulation rather than altered expression of Fcγ receptors, could be mimicked by co-culture of WT but not ST2(-/-) MCs with synovial fibroblasts, and was blocked by antibodies against IL-33. In turn, WT but not ST2(-/-) MCs augmented fibroblast expression of IL-33, forming a positive feedback circuit. Together, these findings confirm a novel role for IL-33 as an amplifier of IgG immune complex-mediated inflammation and identify a potential MC-fibroblast amplification loop dependent on IL-33 and ST2.

A potential role of the GRO-α/CXCR2 system in Sjögren's syndrome: regulatory effects of pro-inflammatory cytokines

Chemokines, small pro-inflammatory cytokines, are involved in migration of inflammatory cells in inflamed tissues and recent studies established their role in angiogenesis, hematopoiesis, cancer and autoimmune conditions. Growth related oncogene-alpha (GRO-α), a member of the CXC chemokine family, and its receptor CXCR2 are involved in the inflammatory processes. Since there is no previous report that supports a possible role of GRO-α/CXCR2 receptor complex during inflammation and neovascularization existing in the autoimmune disease Sjögren's syndrome (SS), in this study, we examined CXCR2 and its ligand GRO-α expression in SS tissues. Immunohistochemistry revealed that GRO-α and its receptor CXCR2 were expressed at high levels in diseased tissues compared to healthy controls. In addition, human salivary gland epithelial cells (SGEC) cultures were submitted to a pro-inflammatory microenvironment using cytokines IL-6 and TNF-α in order to demonstrate that CXCR2 may change its initial expression pattern to another under inflammatory condition. The data show an increased expression of CXCR2 depending on the inflammatory cytokine used in culture in a time-dependent manner. Furthermore, silencing of the pro-angiogenic chemokine GRO-α is proportionally correlated with decreased expression of CXCR2 in pro-inflammatory cytokine-stimulated SGEC indicating the GRO-α/CXCR2 complex as a novel therapeutic target for the chronic inflammatory disease Sjögren's syndrome.

In vivo imaging implicates CCR2(+) monocytes as regulators of neutrophil recruitment during arthritis

The infiltration of neutrophils and monocytes is a prominent feature of inflammatory diseases including human rheumatoid arthritis. Understanding how neutrophil recruitment is regulated during pathogenesis is crucial for developing anti-inflammatory therapies. We optimized the K/B×N serum-induced mouse arthritis model to study neutrophil trafficking dynamics in vivo using two-photon microscopy. Arthritogenic serum was injected subcutaneously into one hind footpad to induce a local arthritis with robust neutrophil recruitment. Using this approach, we showed that the depletion of monocytes with clodronate liposomes impaired neutrophil recruitment specifically at the transendothelial migration step. The depletion of CCR2(+) monocytes with the monoclonal antibody MC-21 reproduced these effects, implicating CCR2(+) monocytes as key regulators of neutrophil extravasation during arthritis initiation. However, monocyte depletion did not prevent neutrophil extravasation in response to bacterial challenge. These findings suggest that anti-inflammatory therapies targeting monocytes may act in part through antagonizing neutrophil extravasation at sites of aseptic inflammation.