Effect of phospholipase A2 inhibitory peptide on inflammatory arthritis in a TNF transgenic mouse model: a time-course ultrastructural study

Single-cell multimodal analysis identifies common regulatory programs in synovial fibroblasts of rheumatoid arthritis patients and modeled TNF-driven arthritis

BACKGROUND

Synovial fibroblasts (SFs) are specialized cells of the synovium that provide nutrients and lubricants for the proper function of diarthrodial joints. Recent evidence appreciates the contribution of SF heterogeneity in arthritic pathologies. However, the normal SF profiles and the molecular networks that govern the transition from homeostatic to arthritic SF heterogeneity remain poorly defined.

METHODS

We applied a combined analysis of single-cell (sc) transcriptomes and epigenomes (scRNA-seq and scATAC-seq) to SFs derived from naïve and hTNFtg mice (mice that overexpress human TNF, a murine model for rheumatoid arthritis), by employing the Seurat and ArchR packages. To identify the cellular differentiation lineages, we conducted velocity and trajectory analysis by combining state-of-the-art algorithms including scVelo, Slingshot, and PAGA. We integrated the transcriptomic and epigenomic data to infer gene regulatory networks using ArchR and custom-implemented algorithms. We performed a canonical correlation analysis-based integration of murine data with publicly available datasets from SFs of rheumatoid arthritis patients and sought to identify conserved gene regulatory networks by utilizing the SCENIC algorithm in the human arthritic scRNA-seq atlas.

RESULTS

By comparing SFs from healthy and hTNFtg mice, we revealed seven homeostatic and two disease-specific subsets of SFs. In healthy synovium, SFs function towards chondro- and osteogenesis, tissue repair, and immune surveillance. The development of arthritis leads to shrinkage of homeostatic SFs and favors the emergence of SF profiles marked by Dkk3 and Lrrc15 expression, functioning towards enhanced inflammatory responses and matrix catabolic processes. Lineage inference analysis indicated that specific Thy1+ SFs at the root of trajectories lead to the intermediate Thy1+/Dkk3+/Lrrc15+ SF states and culminate in a destructive and inflammatory Thy1- SF identity. We further uncovered epigenetically primed gene programs driving the expansion of these arthritic SFs, regulated by NFkB and new candidates, such as Runx1. Cross-species analysis of human/mouse arthritic SF data determined conserved regulatory and transcriptional networks.

CONCLUSIONS

We revealed a dynamic SF landscape from health to arthritis providing a functional genomic blueprint to understand the joint pathophysiology and highlight the fibroblast-oriented therapeutic targets for combating chronic inflammatory and destructive arthritic disease.

Low-Intensity Pulsed Ultrasound Alleviates Osteoarthritis Condition Through Focal Adhesion Kinase-Mediated Chondrocyte Proliferation and Differentiation

OBJECTIVE

Osteoarthritis (OA) is a prevalent chronic multifactorial degenerative disease characterized by joint tissue inflammation, osteophyte formation, subchondral bone sclerosis, and articular cartilage degradation. Low-intensity pulsed ultrasound (LIPUS), a noninvasive ultrasound technique, is widely used to attenuate diseases. The aim of this study was to investigate whether LIPUS can ameliorate OA, and to explore its underlying molecular mechanism.

DESIGN

The OA model was established in a C57BL/6 mouse by the anterior cruciate ligament transaction method. OA was assessed using arthritis scoring and weightbearing parameters. Chondrocyte proliferation was detected by a CCK-8 assay. The levels of interleukin-6 (IL-6), IL-8 and tumor necrosis factor-α (TNF-α) in synovial fluid of the mice were measured by enzyme-linked immunosorbent assay.

RESULTS

In OA mice, the arthritis score and weightbearing abilities were dramatically improved by LIPUS treatment. LIPUS also remarkably declined the levels of inflammatory cytokines IL-6, IL-8, and TNF-α in synovial fluid of OA mice. Moreover, LIPUS promoted chondrocyte proliferation and differentiation by activating focal adhesion kinase (FAK) signaling. Inhibition of FAK significantly blocked LIPUS-mediated cell proliferation and differentiation in vitro, as well as inflammation condition in OA mice.

CONCLUSION

LIPUS alleviates OA through promoting chondrocytes proliferation and differentiation by activating FAK, which could act as an intervening target for OA treatment.

Preparation and characterization of a fully human monoclonal antibody specific for human tumor necrosis factor alpha

Tumor necrosis factor alpha (TNFα) is an important inflammatory factor. It plays a cardinal role in inflammatory synovitis and articular matrix degradation, and is, therefore, a prime target for directed immunotherapy in autoimmune diseases. In this study, we screened and isolated the B cells secreting anti-TNFα antibody from patients with rheumatoid arthritis. The heavy-chain and light-chain sequences of the antibody were cloned and used to generate a stable Chinese hamster ovary (CHO) cell line producing the antibody, which was named Haidalimumab. Haidalimumab showed a TNFα binding affinity comparable to that of the antibody Humira, which is the best TNF inhibitor on the market. Furthermore, Haidalimumab could effectively neutralize recombinant human tumor necrosis factor alpha (rhTNFα) toxicity in a C57BL/6 mouse model and showed significant therapeutic effect in a tumor necrosis factor transgenic (TNF-Tg) mouse arthritis model. In conclusion, we developed a high-affinity, fully human anti-TNFα antibody with low immunogenicity that could potentially have significant therapeutic applications in rheumatoid arthritis or other autoimmune diseases.Abbreviations: ELISAenzyme linked immunosorbent assayRArheumatoid arthritisSDS-PAGEsodium dodecyl sulfate polyacrylamide gel electrophoresisrhTNFαrecombinant human tumor necrosis factor-alphaEC50concentration for 50% of maximal effectTNF-Tg micetumor necrosis factor transgenic miceAMDactinomycin DMTTmethylthiazolyldiphenyl-tetrazolium bromidePBSphosphate-buffered saline.

Imperatorin and β-sitosterol have synergistic activities in alleviating collagen-induced arthritis

Rheumatoid arthritis (RA) is a chronic disease with complex molecular network of pathophysiology, single drug is usually not full satisfactory because it is almost impossible to target the whole molecular network of the disease. Drug combinations that act synergistically with each another is an effective strategy in RA therapy. In this study, we aimed to establish a new strategy to search effective synergized compounds from Chinese herbal medicine (CHM) used in RA. Based on multi‐information integrative approaches, imperatorin (IMP) and β‐sitosterol (STO) were predicted as the most effective pair for RA therapy. Further animal experiments demonstrated that IMP+STO treatment ameliorated arthritis severity of collagen‐induced arthritis (CIA) rats in a synergistic manner, whereas IMP or STO administration separately had no such effect. RNA sequencing and IPA analysis revealed that the synergistic mechanism of IMP+STO treatment was related to its regulatory effect on 5 canonical signaling pathways, which were not found when IMP or STO used alone. Moreover, LTA, CD83, and SREBF1 were 3 important targets for synergistic mechanism of IMP+STO treatment. The levels of these 3 genes were significantly up‐regulated in IMP+STO group compared to model group, whereas IMP or STO administration separately had no effect on them. In conclusion, this study found that IMP and STO were 2 synergistic compounds from the CHM in RA therapy, whose synergistic mechanism was closely related to regulate the levels of LTA, CD83, and SREBF1.

The Adipokine Network in Rheumatic Joint Diseases

Rheumatic diseases encompass a diverse group of chronic disorders that commonly affect musculoskeletal structures. Osteoarthritis (OA) and rheumatoid arthritis (RA) are the two most common, leading to considerable functional limitations and irreversible disability when patients are unsuccessfully treated. Although the specific causes of many rheumatic conditions remain unknown, it is generally accepted that immune mechanisms and/or uncontrolled inflammatory responses are involved in their etiology and symptomatology. In this regard, the bidirectional communication between neuroendocrine and immune system has been demonstrated to provide a homeostatic network that is involved in several pathological conditions. Adipokines represent a wide variety of bioactive, immune and inflammatory mediators mainly released by adipocytes that act as signal molecules in the neuroendocrine-immune interactions. Adipokines can also be synthesized by synoviocytes, osteoclasts, osteoblasts, chondrocytes and inflammatory cells in the joint microenvironment, showing potent modulatory properties on different effector cells in OA and RA pathogenesis. Effects of adiponectin, leptin, resistin and visfatin on local and systemic inflammation are broadly described. However, more recently, other adipokines, such as progranulin, chemerin, lipocalin-2, vaspin, omentin-1 and nesfatin, have been recognized to display immunomodulatory actions in rheumatic diseases. This review highlights the latest relevant findings on the role of the adipokine network in the pathophysiology of OA and RA.

An Anti-hTNF-α Variable New Antigen Receptor Format Demonstrates Superior in vivo Preclinical Efficacy to Humira® in a Transgenic Mouse Autoimmune Polyarthritis Disease Model

Tumor necrosis factor-alpha (TNF-α), an established pro-inflammatory cytokine plays a central role in the induction and progression of several chronic inflammatory and autoimmune diseases. Targeting TNF-α as a treatment modality has shown tremendous success, however there are several limitations associated with the current anti-TNF-α biologic drugs including: immunogenicity, life-threatening infections, resistance to treatment, complexity of manufacture and cost of treatment. Here, we report the in vivo efficacy of novel anti-TNF-α formats generated from molecular engineering of variable new antigen receptors (VNARs), originally derived from the immune system of an immunized nurse shark. Two anti-TNF-α VNAR formats, a tandem multivalent trimer, D1-BA11-C4 and an Fc-fused quadrivalent D1-Fc-C4 (Quad-X™) construct were tested in a clinically relevant, preclinical mouse efficacy model of polyarthritis (Tg197) and compared to the commercial anti-TNF-α "best in class" therapy, Adalimumab (Humira®). Both VNAR formats bind and neutralize TNF-α through an epitope that appears to be different from those recognized by other anti-TNF biologics used clinically. All doses of Quad-X™, from 0.5 to 30 mg/kg, significantly blocked the development of polyarthritis. At 0.5 mg/kg Quad-X™, the arthritis score was improved by 76% and the histopathology score by 63%. At 3 mg/kg Quad-X™, control of disease was almost complete at 90% (arthritis) and 88% (histopathology). In marked contrast, 1 mg/kg Humira® saw profound disease breakthrough with scores of 39 and 16% respectively, increasing to a respectable 82 and 86% inhibition at 10 mg/kg Humira®. We have previously reported the superior potency of anti-TNF-α VNARs in vitro and in these studies translate this superiority into an in vivo setting and demonstrate the potential of VNAR formats to meet the requirements of next-generation anti-TNF-α therapies.

Sustained secretion of anti-tumor necrosis factor α monoclonal antibody from ex vivo genetically engineered dermal tissue demonstrates therapeutic activity in mouse model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a symmetric inflammatory polyarthritis associated with high concentrations of pro-inflammatory, cytokines including tumor necrosis factor (TNF)-α. Adalimumab is a monoclonal antibody (mAb) that binds TNF-α, and is widely used to treat RA. Despite its proven clinical efficacy, adalimumab and other therapeutic mAbs have disadvantages, including the requirement for repeated bolus injections and the appearance of treatment limiting anti-drug antibodies. To address these issues, we have developed an innovative ex vivo gene therapy approach, termed transduced autologous restorative gene therapy (TARGT), to produce and secrete adalimumab for the treatment of RA.

METHODS

Helper-dependent (HD) adenovirus vector containing adalimumab light and heavy chain coding sequences was used to transduce microdermal tissues and cells of human and mouse origin ex vivo, rendering sustained secretion of active adalimumab. The genetically engineered tissues were subsequently implanted in a mouse model of RA.

RESULTS

Transduced human microdermal tissues implanted in SCID mice demonstrated 49 days of secretion of active adalimumab in the blood, at levels of tens of microgram per milliliter. In addition, transduced autologous dermal cells were implanted in the RA mouse model and demonstrated statistically significant amelioration in RA symptoms compared to naïve cell implantation and were similar to recombinant adalimumab bolus injections.

CONCLUSIONS

The results of the present study report microdermal tissues engineered to secrete active adalimumab as a proof of concept for sustained secretion of antibody from the novel ex vivo gene therapy TARGT platform. This technology may now be applied to a range of antibodies for the therapy of other diseases.

Bivalent Llama Single-Domain Antibody Fragments against Tumor Necrosis Factor Have Picomolar Potencies due to Intramolecular Interactions

The activity of tumor necrosis factor (TNF), a cytokine involved in inflammatory pathologies, can be inhibited by antibodies or trap molecules. Herein, llama-derived variable heavy-chain domains of heavy-chain antibody (VHH, also called Nanobodies™) were generated for the engineering of bivalent constructs, which antagonize the binding of TNF to its receptors with picomolar potencies. Three monomeric VHHs (VHH#1, VHH#2, and VHH#3) were characterized in detail and found to bind TNF with sub-nanomolar affinities. The crystal structures of the TNF-VHH complexes demonstrate that VHH#1 and VHH#2 share the same epitope, at the center of the interaction area of TNF with its TNFRs, while VHH#3 binds to a different, but partially overlapping epitope. These structures rationalize our results obtained with bivalent constructs in which two VHHs were coupled via linkers of different lengths. Contrary to conventional antibodies, these bivalent Nanobody™ constructs can bind to a single trimeric TNF, thus binding with avidity and blocking two of the three receptor binding sites in the cytokine. The different mode of binding to antigen and the engineering into bivalent constructs supports the design of highly potent VHH-based therapeutic entities.

Endogenous phospholipase A2 inhibitors in snakes: a brief overview

The blood plasma of numerous snake species naturally comprises endogenous phospholipase A₂ inhibitors, which primarily neutralize toxic phospholipases A₂ that may eventually reach their circulation. This inhibitor type is generally known as snake blood phospholipase A₂ inhibitors (sbPLIs). Most, if not all sbPLIs are oligomeric glycosylated proteins, although the carbohydrate moiety may not be essential for PLA₂ inhibition in every case. The presently known sbPLIs belong to one of three structural classes – namely sbαPLI, sbβPLI or sbγPLI – depending on the presence of characteristic C-type lectin-like domains, leucine-rich repeats or three-finger motifs, respectively. Currently, the most numerous inhibitors described in the literature are sbαPLIs and sbγPLIs, whereas sbβPLIs are rare. When the target PLA₂ is a Lys49 homolog or an Asp49 myotoxin, the sbPLI is denominated a myotoxin inhibitor protein (MIP). In this brief overview, the most relevant data on sbPLIs will be presented. Representative examples of sbαPLIs and sbγPLIs from two Old World – Gloydius brevicaudus and Malayopython reticulatus – and two New World – Bothrops alternatus and Crotalus durissus terrificus – snake species will be emphasized.

Progranulin: A key player in autoimmune diseases

Autoimmune disease encompasses an array of conditions with a variety of presentations and the involvement of multiple organs. Though the etiologies of many autoimmune conditions are unclear, uncontrolled inflammatory immune response is believed to be a major cause of disease development and progression. Progranulin (PGRN), an anti-inflammatory molecule with therapeutic effect in inflammatory arthritis, was identified as an endogenous antagonist of TNFα by competitively binding to TNFR. PGRN exerts its anti-inflammatory activity through multiple pathways, including induction of T_reg differentiation and IL-10 expression and inhibition of chemokine release from macrophages. In addition, the protective role of PGRN has also been demonstrated in osteoarthritis, inflammatory bowel disease, and psoriasis. Intriguingly, PGRN was reported to contribute to development of insulin resistance in high-fat diet induced diabetes. Emerging evidences indicate that PGRN may also be associated with various autoimmune diseases, including systemic lupus erythematous, systemic sclerosis, multiple sclerosis and Sjogren's syndrome. This review summarizes recent studies of PGRN as a novel target molecule in the field of autoimmune disease, and provides updated information to inspire future studies.

Novel phospholipase A2 inhibitors from python serum are potent peptide antibiotics

Antimicrobial peptides (AMPs) play a vital role in defense against resistant bacteria. In this study, eight different AMPs synthesized from Python reticulatus serum protein were tested for bactericidal activity against various Gram-positive and Gram-negative bacteria (Staphylococcus aureus, Burkholderia pseudomallei (KHW and TES strains), and Proteus vulgaris) using a disc-diffusion method (20 μg/disc). Among the tested peptides, phospholipase A2 inhibitory peptide (PIP)-18[59-76], β-Asp65-PIP[59-67], D-Ala66-PNT.II, and D60,65E-PIP[59-67] displayed the most potent bactericidal activity against all tested pathogens in a dose-dependent manner (100-6.8 μg/ml), with a remarkable activity noted against S. aureus at 6.8 μg/ml dose within 6 h of incubation. Determination of minimum inhibitory concentrations (MICs) by a micro-broth dilution method at 100-3.125 μg/ml revealed that PIP-18[59-76], β-Asp65-PIP[59-67] and D-Ala66-PNT.II peptides exerted a potent inhibitory effect against S. aureus and B. pseudomallei (KHW) (MICs 3.125 μg/ml), while a much less inhibitory potency (MICs 12.5 μg/ml) was noted for β-Asp65-PIP[59-67] and D-Ala66-PNT.II peptides against B. pseudomallei (TES). Higher doses of peptides had no effect on the other two strains (i.e., Klebsiella pneumoniae and Streptococcus pneumoniae). Overall, PIP-18[59-76] possessed higher antimicrobial activity than that of chloramphenicol (CHL), ceftazidime (CF) and streptomycin (ST) (30 μg/disc). When the two most active peptides, PIP-18[59-76] and β-Asp65-PIP[59-67], were applied topically at a 150 mg/kg dose for testing wound healing activity in a mouse model of S. aureus infection, the former accelerates faster wound healing than the latter peptide at 14 days post-treatment. The western blot data suggest that the topical application of peptides (PIP-18[59-67] and β-Asp65-PIP[59-67]) modulates NF-kB mediated wound repair in mice with relatively little haemolytic (100-1.56 μg/ml) and cytotoxic (1000-3.125 μg/ml) effects evident on human cells in vitro.

Wnt4 signaling prevents skeletal aging and inflammation by inhibiting nuclear factor-κB

Aging-related bone loss and osteoporosis affect millions of patients worldwide. Chronic inflammation associated with aging and arthritis promotes bone resorption and impairs bone formation. Here we show that Wnt4 attenuated bone loss in osteoporosis and skeletal aging by inhibiting nuclear factor-kappa B (NF-κB) via non-canonical Wnt signaling. Transgenic mice expressing Wnt4 from osteoblasts were significantly protected from bone loss and chronic inflammation induced by ovariectomy, tumor necrosis factor or natural aging. In addition to promoting bone formation, Wnt4 could inhibit osteoclast formation and bone resorption. Mechanistically, Wnt4 inhibited transforming growth factor beta-activated kinase 1-mediated NF-κB activation in macrophages and osteoclast precursors independent of β-catenin. Moreover, recombinant Wnt4 proteins were able to alleviate osteoporotic bone loss and inflammation by inhibiting NF-κB in vivo. Taken together, our results suggest that Wnt4 might be used as a therapeutic agent for treating osteoporosis by attenuating NF-κB.

Secreted phospholipase A2 type II is present in Paget's disease of bone and modulates osteoclastogenesis, apoptosis and bone resorption of human osteoclasts independently of its catalytic activity in vitro

OBJECTIVES

To study the role of secreted phospholipase A2 (sPLA2) in the pathophysiology of human osteoclasts (OCs).

METHODS

Immunohistochemistry and sPLA2 inhibitors were to determine the localization of sPLA2 and its role in OCs biology.

RESULTS

sPLA2 is expressed by OCs from healthy fetal bone and OCs from Paget's disease but not in normal bone. Inhibition of sPLA2 greatly reduces in vitro osteoclastogenesis.

DISCUSSION

The decrease in OCs formed could be attributed to a decline in the viability of CD14(+) OC precursors as well as a reduced viability of mature OCs. Inhibition of sPLA2 strongly decreases bone resorption by OCs independently of actin cytoskeleton remodeling, probably also by reducing OCs viability.

CONCLUSION

High amounts of this enzyme are present in fetal and Pagetic bone samples. Inhibition of sPLA2in vitro decreases osteoclastogenesis and OC activity and might constitute an interesting pharmacologic target for diseases with high bone turnover.

Secreted phospholipases A2 of snake venoms: effects on the peripheral neuromuscular system with comments on the role of phospholipases A2 in disorders of the CNS and their uses in industry

Neuro- and myotoxicological signs and symptoms are significant clinical features of envenoming snakebites in many parts of the world. The toxins primarily responsible for the neuro and myotoxicity fall into one of two categories--those that bind to and block the post-synaptic acetylcholine receptors (AChR) at the neuromuscular junction and neurotoxic phospholipases A2 (PLAs) that bind to and hydrolyse membrane phospholipids of the motor nerve terminal (and, in most cases, the plasma membrane of skeletal muscle) to cause degeneration of the nerve terminal and skeletal muscle. This review provides an introduction to the biochemical properties of secreted sPLA2s in the venoms of many dangerous snakes and a detailed discussion of their role in the initiation of the neurologically important consequences of snakebite. The rationale behind the experimental studies on the pharmacology and toxicology of the venoms and isolated PLAs in the venoms is discussed, with particular reference to the way these studies allow one to understand the biological basis of the clinical syndrome. The review also introduces the involvement of PLAs in inflammatory and degenerative disorders of the central nervous system (CNS) and their commercial use in the food industry. It concludes with an introduction to the problems associated with the use of antivenoms in the treatment of neuro-myotoxic snakebite and the search for alternative treatments.

Enhanced COMP catabolism detected in serum of patients with arthritis and animal disease models through a novel capture ELISA

OBJECTIVE

The study aimed determining whether assessment of cartilage oligomeric matrix protein (COMP) degradation products could serve as a serological disease course and therapeutic response predictor in arthritis.

METHODS

We generated a panel of monoclonal antibodies against COMP fragments and developed a novel capture enzyme-linked immunosorbent assay (ELISA) for detecting COMP fragments in patients with osteoarthritis (OA) and rheumatoid arthritis (RA). This test was also used to monitor COMP fragments in surgically-induced OA, collagen-induced arthritis (CIA), and tumor necrosis factor (TNF) transgenic animal models.

RESULTS

Compared with a commercial COMP ELISA kit that detected no significant difference in COMP levels between OA and control groups, a significant increase of the COMP fragments were noted in the serum of OA patients assayed by this newly established ELISA. In addition, serum COMP fragment levels were well correlated with severity in OA patients and the progression of surgically-induced OA in murine models. Furthermore, the serum levels of COMP fragments in RA patients, mice with CIA, and TNF transgenic mice were significantly higher when compared with their controls. Interestingly, treatment with TNFα inhibitors and methotrexate led to a significant decrease of serum COMP fragments in RA patients. Additionally, administration of Atsttrin [Tang, et al., Science 2011;332(6028):478] also resulted in a significant reduction in COMP fragments in arthritis mice models.

CONCLUSION

A novel sandwich ELISA is capable of reproducibly measuring serum COMP fragments in both arthritic patients and rodent arthritis models. This test also provides a valuable means to utilize serum COMP fragments for monitoring the effects of interventions in arthritis.

Selective targeted delivery of the TNF-alpha receptor p75 and uteroglobin to the vasculature of inflamed tissues: a preliminary report

Background

Ligand-targeted approaches have proven successful in improving the therapeutic index of a number of drugs. We hypothesized that the specific targeting of TNF-alpha antagonists to inflamed tissues could increase drug efficacy and reduce side effects.

Results

Using uteroglobin (UG), a potent anti-inflammatory protein, as a scaffold, we prepared a bispecific tetravalent molecule consisting of the extracellular ligand-binding portion of the human TNF-alpha receptor P75 (TNFRII) and the scFv L19. L19 binds to the ED-B containing fibronectin isoform (B-FN), which is expressed only during angiogenesis processes and during tissue remodeling. B-FN has also been demonstrated in the pannus in rheumatoid arthritis. L19-UG-TNFRII is a stable, soluble homodimeric protein that maintains the activities of both moieties: the immuno-reactivity of L19 and the capability of TNFRII to inhibit TNF-alpha. In vivo bio-distribution studies demonstrated that the molecule selectively accumulated on B-FN containing tissues, showing a very fast clearance from the blood but a very long residence time on B-FN containing tissues. Despite the very fast clearance from the blood, this fusion protein was able to significantly improve the severe symptomatology of arthritis in collagen antibody-induced arthritis (CAIA) mouse model.

Conclusions

The recombinant protein described here, able to selectively deliver the TNF-alpha antagonist TNFRII to inflamed tissues, could yield important contributions for the therapy of degenerative inflammatory diseases.

Progranulin: a growth factor, a novel TNFR ligand and a drug target

Progranulin (PGRN) is abundantly expressed in epithelial cells, immune cells, neurons, and chondrocytes, and reportedly contributes to tumorigenesis. PGRN is a crucial mediator of wound healing and tissue repair. PGRN also functions as a neurotrophic factor and mutations in the PGRN gene resulting in partial loss of the PGRN protein cause frontotemporal dementia. PGRN has been found to be a novel chondrogenic growth factor and to play an important role in cartilage development and inflammatory arthritis. Although research has shown that PGRN exhibits anti-inflammatory properties, the details about the exact molecular pathway of such effects, and, in particular, the PGRN binding receptor, have not been identified so far. Recently, researchers have shown that PGRN binds to tumor necrosis factor (TNF)-receptors (TNFR), interfering with the interaction between TNFα and TNFR. They further demonstrated that mice deficient in PGRN are susceptible to collagen-induced arthritis, an experimental model of rheumatoid arthritis, and that administration of PGRN reversed the arthritic process. An engineered protein made of three PGRN fragments (Atsttrin), displayed selective TNFR binding and was more active than natural PGRN. Both PGRN and Atsttrin prevented inflammation in various arthritis mouse models and inhibited TNFα-induced intracellular signaling pathways. Thus, PGRN is a key regulator of inflammation and it may mediate its anti-inflammatory effects, at least in part, by blocking TNF binding to its receptors. As we discuss here, TNFR-based interventions may both stimulate and suppress the growth of cancer cells, and the same may be true in analogy for Atsttrin as a new player.

Progranulin: a promising therapeutic target for rheumatoid arthritis

Progranulin (PGRN) is an autocrine growth factor with multiple functions. This review provides updates about the interplays of PGRN with extracellular matrix proteins, proteolytic enzymes, inflammatory cytokines, and cell surface receptors in cartilage and arthritis, with a special focus on the interaction between PGRN and TNF receptors (TNFR) and its implications in inflammatory arthritis. The paper also highlights Atsttrin, an engineered protein composed of three PGRN fragments that prevents inflammation in several inflammatory arthritis models. Identification of PGRN as a ligand of TNFR and an antagonist of TNFα signaling, together with the discovery of Atsttrin, not only betters our understanding of the pathogenesis of arthritis, but also provides new therapeutic interventions for various TNFα-mediated pathologies and conditions, including rheumatoid arthritis.

The growth factor progranulin binds to TNF receptors and is therapeutic against inflammatory arthritis in mice

The growth factor progranulin (PGRN) has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation, but its receptors remain unidentified. We report that PGRN bound directly to tumor necrosis factor receptors (TNFRs) and disturbed the TNFα-TNFR interaction. PGRN-deficient mice were susceptible to collagen-induced arthritis, and administration of PGRN reversed inflammatory arthritis. Atsttrin, an engineered protein composed of three PGRN fragments, exhibited selective TNFR binding. PGRN and Atsttrin prevented inflammation in multiple arthritis mouse models and inhibited TNFα-activated intracellular signaling. Collectively, these findings demonstrate that PGRN is a ligand of TNFR, an antagonist of TNFα signaling, and plays a critical role in the pathogenesis of inflammatory arthritis in mice. They also suggest new potential therapeutic interventions for various TNFα-mediated pathologies and conditions, including rheumatoid arthritis.

Interplay between TNF and regulatory T cells in a TNF-driven murine model of arthritis

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) are involved in several autoimmune diseases, including rheumatoid arthritis. TNF-α blockers induce therapeutic benefits in rheumatoid arthritis via a variety of mechanisms. We aimed to characterize the impact on Treg of TNF-α overexpression in vivo and of TNF-α inhibiting treatments. We used human TNF-α transgenic mice as a model of strictly TNF-α-dependent arthritis. Our study showed that initial Treg frequency was lower in TNF-α transgenic mice than in wild-type mice. However, the course of arthritis was marked by elevation of Treg frequency and a dramatic increase in expression of TNFR2. Antagonizing TNF-α with either the anti-human TNF-α Ab (infliximab) or active immunotherapy (TNF-kinoid) increased the Treg frequency and upregulated CTLA-4, leading to enhancement of suppressor activity. Moreover, both anti-TNF-α strategies promoted the differentiation of a CD62L(-) Treg population. In conclusion, in an in vivo model of TNF-α-driven arthritis, Treg frequency increased with inflammation but failed to control the inflammatory process. Both passive and active TNF-α-inhibiting strategies restored the suppressor activity of Treg and induced the differentiation of a CD62L(-) Treg population.

Suppressive effect of secretory phospholipase A2 inhibitory peptide on interleukin-1beta-induced matrix metalloproteinase production in rheumatoid synovial fibroblasts, and its antiarthritic activity in hTNFtg mice

INTRODUCTION

Secretory phospholipase A2 (sPLA2) and matrix metalloproteinase (MMP) inhibitors are potent modulators of inflammation with therapeutic potential, but have limited efficacy in rheumatoid arthritis (RA). The objective of this study was to understand the inhibitory mechanism of phospholipase inhibitor from python (PIP)-18 peptide in cultured synovial fibroblasts (SF), and to evaluate its therapeutic potential in a human tumor necrosis factor (hTNF)-driven transgenic mouse (Tg197) model of arthritis.

METHODS

Gene and protein expression of sPLA2-IIA, MMP-1, MMP-2, MMP-3, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1, and TIMP-2 were analyzed by real time PCR and ELISA respectively, in interleukin (IL)-1beta stimulated rheumatoid arthritis (RA) and osteoarthritis (OA) synovial fibroblasts cells treated with or without inhibitors of sPLA2 (PIP-18, LY315920) or MMPs (MMP Inhibitor II). Phosphorylation status of mitogen-activated protein kinase (MAPK) proteins was examined by cell-based ELISA. The effect of PIP-18 was compared with that of celecoxib, methotrexate, infliximab and antiflamin-2 in Tg197 mice after ip administration (thrice weekly for 5 weeks) at two doses (10, 30 mg/kg), and histologic analysis of ankle joints. Serum sPLA2 and cytokines (tumor necrosis factor (TNF)alpha, IL-6) were measured by Escherichia coli (E coli) assay and ELISA, respectively.

RESULTS

PIP-18 inhibited sPLA2-IIA production and enzymatic activity, and suppressed production of MMPs in IL-1beta-induced RA and OA SF cells. Treatment with PIP-18 blocked IL-1beta-induced p38 MAPK phosphorylation and resulted in attenuation of sPLA2-IIA and MMP mRNA transcription in RA SF cells. The disease modifying effect of PIP-18 was evidenced by significant abrogation of synovitis, cartilage degradation and bone erosion in hTNF Tg197 mice.

CONCLUSIONS

Our results demonstrate the benefit that can be gained from using sPLA2 inhibitory peptide for RA treatment, and validate PIP-18 as a potential therapeutic in a clinically relevant animal model of human arthritis.

TNFalpha kinoid vaccination-induced neutralizing antibodies to TNFalpha protect mice from autologous TNFalpha-driven chronic and acute inflammation

The proinflammatory cytokine TNFalpha is a potent mediator of septic shock and a therapeutic target for chronic inflammatory pathologies including rheumatoid arthritis and Crohn's disease. As an alternative to anti-human TNFalpha (hTNFalpha) mAbs and other hTNFalpha blocker approved drugs, we developed an active anti-hTNFalpha immunotherapy, based on a vaccine comprised of a keyhole limpet hemocyanin-hTNFalpha heterocomplex immunogen (hTNFalpha kinoid) adjuvanted in incomplete Freund's adjuvant. In mice transgenic for hTNFalpha (TTg mice), hTNFalpha kinoid vaccination elicited high titers of Abs that neutralized hTNFalpha bioactivities but did not result in a cellular response to hTNFalpha. The vaccine was safe and effective in two experimental models. Kinoid-immunized but not control TTg mice resisted hTNFalpha-driven shock in one model and were prevented from spontaneous arthritis, inflammatory synovitis, and articular destruction in a second model. These data demonstrate an anti-cytokine induction of autoimmune protection against both acute and chronic hTNFalpha exposure. They show that active vaccination against a human cytokine can be achieved, and that the immune response can be effective and safe.

Rheumatic diseases: the effects of inflammation on bone

Rheumatoid arthritis, juvenile idiopathic arthritis, the seronegative spondyloarthropathies including psoriatic arthritis, and systemic lupus erythematosus are all examples of rheumatic diseases in which inflammation is associated with skeletal pathology. Although some of the mechanisms of skeletal remodeling are shared among these diseases, each disease has a unique impact on articular bone or on the axial or appendicular skeleton. Studies in human disease and in animal models of arthritis have identified the osteoclast as the predominant cell type mediating bone loss in arthritis. Many of the cytokines and growth factors implicated in the inflammatory processes in rheumatic diseases have also been demonstrated to impact osteoclast differentiation and function either directly, by acting on cells of the osteoclast-lineage, or indirectly, by acting on other cell types to modulate expression of the key osteoclastogenic factor receptor activator of nuclear factor (NF) kappaB ligand (RANKL) and/or its inhibitor osteoprotegerin (OPG). Further elucidation of the mechanisms responsible for inflammation-induced bone loss will potentially lead to the identification of novel therapeutic strategies for the prevention of bone loss in these diseases. In this review, we provide an overview of the cell types, inflammatory mediators, and mechanisms that are implicated in bone loss and new bone formation in inflammatory joint diseases.