Lymphocytes and synovial fluid fibroblasts support osteoclastogenesis through RANKL, TNFalpha, and IL-7 in an in vitro model derived from human psoriatic arthritis

Circulating Immune Landscape Profiling in Psoriasis Vulgaris and Psoriatic Arthritis by Mass Cytometry

Background

Psoriasis, a systemic disorder mediated by the immune system, can appear on the skin, joints, or both. Individuals with cutaneous psoriasis (PsC) have an elevated risk of developing psoriatic arthritis (PsA) during their lifetime. Despite this known association, the cellular and molecular mechanisms underlying this progression remain unclear.

Methods

We performed high-dimensional, in-depth immunophenotyping of peripheral blood mononuclear cells (PBMCs) in patients with PsA and psoriasis vulgaris (PsV) by mass cytometry. Blood samples were collected before and after therapy for a longitudinal study. Then three sets of comparisons were made here: active PsA vs. active PsV, untreated PsV vs. treated PsV, and untreated PsA vs. treated PsA.

Results

Marked differences were observed in multiple lymphocyte subsets of PsA related to PsV, with expansion of CD4+ T cells, CD16- NK cells, and B cells. Notably, two critical markers, CD28 and CD127, specifically differentiated PsA from PsV. The expression levels of CD28 and CD127 on both Naïve T cells (TN) and central memory CD4+ T cells (TCM) were considerably higher in PsA than PsV. Meanwhile, after treatment, patients with PsV had higher levels of CD28hi CD127hi CD4+ TCM cells, CD28hi CD127hi CD4+ TN cells, and CD16- NK cells.

Conclusion

In the circulation of PsA patients, the TN and CD4+ TCM are characterized with more abundant CD28 and CD127, which effectively distinguished PsA from PsV. This may indicate that individuals undergoing PsV could be stratified at high risk of developing PsA based on the circulating levels of CD28 and CD127 on specific cell subsets.

Psoriatic Arthritis Involving TMJ: A Review on Pathogenesis and Consideration on Eventual Gender Differences

Psoriatic arthritis is defined as chronic inflammatory arthritis associated with psoriasis. The current data regarding gender differences in clinical manifestation and therapeutic outcomes of psoriatic arthritis are limited. Generally, men show a peripheral disease manifestation, while women have an axial distribution of the lesions. If we look at temporomandibular joint (TMJ) involvement, epidemiological data on the involvement of the TMJ are hard to find. Few studies on therapeutic management and the related impact on the quality of life are reported in the literature. Given the morpho-functional peculiarities of the TMJ and the different pain burdens between male and female genders, when manifestation of psoriatic arthritis occurs, clinicians should face it using a multidisciplinary approach for a correct diagnosis and successful treatment. This review aims to examine the diagnostic signs of psoriatic arthritis in the TMJ, the eventual variations of this disease in male and female patients, and the therapeutical strategies. The coordination of different specialties is fundamental to the remission of clinical symptoms and lesion regression.

In vitro osteoclastogenesis in autoimmune diseases - Strengths and pitfalls of a tool for studying pathological bone resorption and other disease characteristics

Osteoclasts play a critical role in bone pathology frequently associated with autoimmune diseases. Studying the etiopathogenesis of these diseases and their clinical manifestations can involve in vitro osteoclastogenesis, an experimental technique that utilizes osteoclast precursors that are relatively easily accessible from peripheral blood or synovial fluid. However, the increasing number of methodical options to study osteoclastogenesis in vitro poses challenges in translating findings to clinical research and practice. This review compares and critically evaluates previous research work based on in vitro differentiation of human osteoclast precursors originating from patients, which aimed to explain autoimmune pathology in rheumatic and enteropathic diseases. The discussion focuses primarily on methodical differences between the studies, including the origin of osteoclast precursors, culture conditions, and methods for identifying osteoclasts and assessing their activity. Additionally, the review examines the clinical significance of the three most commonly used in vitro approaches: induced osteoclastogenesis, spontaneous osteoclastogenesis, and cell co-culture. By analyzing and integrating the gathered information, this review proposes general connections between different studies, even in cases where their results are seemingly contradictory. The derived conclusions and future directions aim to enhance our understanding of a potential and limitations of in vitro osteoclastogenesis and provide a foundation for discussing novel methods (such as osteoclastogenesis dynamic) and standardized approaches (such as spontaneous osteoclastogenesis) for future use in autoimmune disease research.

Investigational monoclonal antibodies in early development for psoriatic arthritis: beyond the biosimilars

INTRODUCTION

Psoriatic Arthritis (PsA) is an inflammatory arthritis that is present in approximately 25% of psoriasis patients. Currently, several targeted therapies are available to manage PsA; however, many patients fail these therapies. Several new therapeutic options, with differing mechanisms of action, are currently being evaluated.

AREAS COVERED

This article reviews available results from phase I to phase III trials of several investigational monoclonal antibodies that the FDA has not yet approved for PsA. The proposed mechanisms of the new therapeutic agents and their relevance to the pathogenesis of PsA will be discussed. The investigational agents' efficacy and safety will be summarized, and their potential clinical applications for managing PsA will be contemplated.

EXPERT OPINION

Due to recent advances in understanding psoriatic arthritis, therapeutic agents are increasingly focused on inhibiting interleukin-17 and interleukin-23 pathways. Various strategies have been used to inhibit these cytokines, demonstrating favorable efficacy and acceptable safety profile.

Phospholipase A1 Member A Deficiency Alleviates Mannan-Induced Psoriatic Arthritis in Mice Model

Synovial fluids from rheumatoid and psoriatic arthritis patients have high levels of PLA1A. The current study was to understand PLA1A functions in the pathophysiology of rheumatic diseases. We generated Pla1a−/− mice to assess their phenotype and the impact of PLA1A deficiency on the development of mannan-induced psoriatic arthritis (MIP). Mice were evaluated routinely for the induced symptoms. On the day of sacrifice, blood samples were collected for hematology analysis and prepared for plasma. Livers were collected. Lymph node immune cells were analyzed using flow cytometry. We performed μCT scans of hind paws from naïve and mannan-induced female mice. Cytokines/chemokines were quantified using Luminex in hind paw tissues and plasma of female mice. Pla1a−/− mice showed a slight increase in circulating and lymph node lymphocytes. CD4+ T cells contributed most to this increase in lymph nodes (p = 0.023). In the MIP model, the lymph node ratios of CD3+ to CD19+ and CD4+ to CD8+ were higher in Pla1a−/− mice. Pla1a−/− mice were less susceptible to MIP (p < 0.001) and showed reduced bone erosions. Pla1a−/− mice also showed reduced IL-17, KC, IP-10, MIP-1β, LIF, and VEGF in hind paw tissues as compared to WT mice (p < 0.05). These findings indicated that PLA1A deficiency protected from the development of the MIP disease. The data suggested that PLA1A could contribute to MIP through increased activation of lymphocytes, possibly those producing IL-17.

Significance of IL-7 and IL-7R in RA and autoimmunity

While physiological levels of IL-7 are essential for T cell proliferation, survival and co-stimulation, its escalated concentration has been associated with autoimmune diseases such as Rheumatoid arthritis (RA). Expression of IL-7 and IL-7R in RA monocytes is linked to disease activity score and TNF transcription. TNF stimulation can modulate IL-7 secretion and IL-7R frequency in myeloid cells, however, only IL-7R transcription levels are downregulated in anti-TNF responsive patients. Elevated levels of IL-7 in RA synovial tissue and fluid are involved in attracting RA monocytes into the inflammatory joints and remodeling them into proinflammatory macrophages and mature osteoclasts. Further, IL-7 amplification of RA Th1 cell differentiation and IFNγ secretion, can directly prime myeloid IL-7R expression and thereby exacerbate IL-7-mediated joint inflammatory and erosive imprints. In parallel, IL-7 accentuates joint angiogenesis by expanding the production of proangiogenic factors from RA macrophages and endothelial cells. In preclinical models, blockade of IL-7 or IL-7R can effectively impair joint inflammation, osteoclast formation, and neovascularization primarily by impeding monocyte and endothelial cell infiltration as well as inhibition of pro-inflammatory macrophage and Th1/Th17 cell differentiation. In conclusion, disruption of IL-7/IL-7R signaling can uniquely intercept the crosstalk between RA myeloid and lymphoid cells in their ability to trigger neovascularization.

The Programmed Death-1 Pathway Counter-Regulates Inflammation-Induced Osteoclast Activity in Clinical and Experimental Settings

Objective

The programmed death-1 (PD-1) pathway is essential for maintaining self-tolerance and plays an important role in autoimmunity, including rheumatoid arthritis (RA). Here, we investigated how membrane-bound and soluble (s)PD-1 influence bone homeostasis during chronic inflammation, exemplified in RA.

Methods

Bone mineral density and bone microstructure were examined in PD-1 and PD-L1 knockout (KO) mice and compared with wild-type (WT) mice. Receptor activator of nuclear factor kappa-B ligand (RANKL) was measured in serum, and the expression examined on activated bone marrow cells. Osteoclast formation was examined in cells from murine spleen and bone marrow and from human synovial fluid cells. sPD-1 was measured in chronic and early (e)RA patients and correlated to markers of disease activity and radiographic scores.

Results

PD-1 and PD-L1 KO mice showed signs of osteoporosis. This was supported by a significantly reduced trabecular bone volume fraction and deteriorated microstructure, as well as increased osteoclast formation and an increased RANKL/OPG ratio. The recombinant form of sPD-1 decreased osteoclast formation in vitro, but was closely associated with disease activity markers in eRA patients. Sustained elevated sPD-1 levels indicated ongoing inflammation and were associated with increased radiographic progression.

Conclusion

The PD-1 pathway is closely associated with bone homeostasis, and lacking members of this pathway causes a deteriorated bone structure. The immunological balance in the microenvironment determines how the PD-1 pathway regulates osteoclast formation. In eRA patients, sPD-1 may serve as a biomarker, reflecting residual but clinically silent disease activity and radiographic progression.

Importance of lymphocyte-stromal cell interactions in autoimmune and inflammatory rheumatic diseases

Interactions between lymphocytes and stromal cells have an important role in immune cell development and responses. During inflammation, stromal cells contribute to inflammation, from induction to chronicity or resolution, through direct cell interactions and through the secretion of pro-inflammatory and anti-inflammatory mediators. Stromal cells are imprinted with tissue-specific phenotypes and contribute to site-specific lymphocyte recruitment. During chronic inflammation, the modified pro-inflammatory microenvironment leads to changes in the stromal cells, which acquire a pathogenic phenotype. At the site of inflammation, infiltrating B cells and T cells interact with stromal cells. These interactions induce a plasma cell-like phenotype in B cells and T cells, associated with secretion of immunoglobulins and inflammatory cytokines, respectively. B cells and T cells also influence the stromal cells, inducing cell proliferation, molecular changes and cytokine production. This positive feedback loop contributes to disease chronicity. This Review describes the importance of these cell interactions in chronic inflammation, with a focus on human disease, using three selected autoimmune and inflammatory diseases: rheumatoid arthritis, psoriatic arthritis (and psoriasis) and systemic lupus erythematosus. Understanding the importance and disease specificity of these interactions could provide new therapeutic options.

Associations of plasma YKL-40 concentrations with heel ultrasound parameters and bone turnover markers in the general adult population

OBJECTIVE

YKL-40, also known as chitinase-3-like protein 1, is a new proinflammatory biomarker, that might play a role in tissue remodeling and bone resorption. Here we evaluated the associations of the YKL-40 plasma concentration with heel ultrasound parameters and bone turnover markers (BTMs) in adult men and women from the general population. We tested for a causal role of YKL-40 on bone metabolism using published single nucleotide polymorphisms (SNPs) with consequences for YKL-40 expression and function.

METHODS

Data were obtained from two population-based cohorts: the Study of Health in Pomerania (SHIP) and SHIP-Trend. Quantitative ultrasound (QUS) measurements at the heel were performed and bone turnover was assessed by measurement of intact amino-terminal propeptide of type I procollagen (PINP) and carboxy-terminal telopeptide of type I collagen (CTX). Associations between the YKL-40 plasma concentration and the QUS-based parameters, bone turnover marker (BTM) concentrations and 44 SNPs, including the lead SNP rs4950928, were evaluated in 382 subjects. Furthermore, we assessed the associations between the same SNPs and the QUS-based parameters (n = 5777) or the BTM concentrations (n = 7190).

RESULTS

Sex-specific linear regression models adjusted for a comprehensive panel of interfering covariantes revealed statistically significant inverse associations between YKL-40 and all QUS-based parameters as well as positive associations with CTX in women. The rs4950928 polymorphism was associated with YKL-40 in men and women but none of the tested SNPs was associated with the QUS-based parameters or the BTMs after correction for multiple testing.

CONCLUSIONS

Plasma YKL-40 concentrations are associated with QUS-based parameters as well as CTX concentrations in women but these associations are probably not causal.

Chronic lymphocytic leukemia cells impair osteoblastogenesis and promote osteoclastogenesis: role of TNFα, IL-6 and IL-11 cytokines

Bone skeletal alterations are no longer considered a rare event in Chronic Lymphocytic Leukemia (CLL), especially at more advanced stages of the disease. This study is aimed at elucidating the mechanisms underlying this phenomenon. Bone marrow stromal cells, induced to differentiate toward osteoblasts in osteogenic medium, appeared unable to complete their maturation upon co-culture with CLL cells, CLL cells-derived conditioned media (CLL-cm) or CLL-sera (CLL-sr). Inhibition of osteoblast differentiation was documented by decreased levels of RUNX2 and osteocalcin mRNA expression, by increased osteopontin and DKK-1 mRNA levels, and by a marked reduction of mineralized matrix deposition. The addition of neutralizing TNFα, IL-11 or anti-IL-6R monoclonal antibodies to these co-cultures resulted into restoration of bone mineralization, indicating the involvement of these cytokines: these findings were further supported by silencing TNFα, IL-11 and IL-6 in leukemic cells. We also demonstrated that the addition of CLL-cm to monocytes, previously stimulated with MCSF and RANKL, significantly amplified the formation of large mature osteoclasts as well as their bone resorption activity. Moreover enhanced osteoclastogenesis, induced by CLL-cm, was significantly reduced by treating cultures with the anti-TNFα moAb Infliximab; an analogous effect was observed by the use of the BTK inhibitor Ibrutinib. CLL cells, co-cultured with mature osteoclasts, were interestingly protected from apoptosis and upregulated Ki-67. These experimental results parallel the direct correlation between TNFα amounts in CLL sera and the degree of compact bone erosion we previously described, further strengthening the indication of a reciprocal influence between leukemic cells expansion and bone structure derangement.

Macrophages are the primary effector cells in IL-7-induced arthritis

Synovial macrophages are crucial in the development of joint inflammation and bone damage; however, the pathways that control macrophage remodeling in inflammatory M1 cells or bone-eroding osteoclasts are not fully understood. We determined that elevated IL-7R/CD127 expression is the hallmark of rheumatoid arthritis (RA) M1 macrophages and that these cells are highly responsive to interleukin-7 (IL-7)-driven osteoclastogenesis. We established that lipopolysaccharide (LPS), interferon-γ (IFNγ), and tumor necrosis factor-α (TNFα), the classic M1 macrophage mediators, enhance IL-7R expression in RA and murine macrophages. The local expression of IL-7 provokes arthritis, predominantly through escalating the number of F480+iNOS+ cells rather than CD3+ T cells. Ectopic LPS injection stabilizes IL-7-induced arthritis by increasing myeloid IL-7R expression, in part via IFNγ induction. Hence, in RAG-/- mice, IL-7-mediated arthritis is suppressed because of the reduction in myeloid IL-7R expression due to the lack of IFNγ. Moreover, the amelioration of IL-7-induced arthritis by anti-TNF therapy is due to a decrease in the number of cells in the unique F480+iNOS+IL-7R+CCL5+ subset, with no impact on the F480+Arginase+ cell or CD3+ T cell frequency. Consistent with the preclinical findings, the findings of a phase 4 study performed with RA patients following 6 months of anti-TNF therapy revealed that IL-7R expression was reduced without affecting the levels of IL-7. This study shifts the paradigm by discovering that IL-7-induced arthritis is dependent on F480+iNOS+IL-7R+CCL5+ cell function, which activates TH-1 cells to amplify myeloid IL-7R expression and disease severity.

Hydrogen Sulfide as Potential Regulatory Gasotransmitter in Arthritic Diseases

The social and economic impact of chronic inflammatory diseases, such as arthritis, explains the growing interest of the research in this field. The antioxidant and anti-inflammatory properties of the endogenous gasotransmitter hydrogen sulfide (H₂S) were recently demonstrated in the context of different inflammatory diseases. In particular, H₂S is able to suppress the production of pro-inflammatory mediations by lymphocytes and innate immunity cells. Considering these biological effects of H₂S, a potential role in the treatment of inflammatory arthritis, such as rheumatoid arthritis (RA), can be postulated. However, despite the growing interest in H₂S, more evidence is needed to understand the pathophysiology and the potential of H₂S as a therapeutic agent. Within this review, we provide an overview on H₂S biological effects, on its role in immune-mediated inflammatory diseases, on H₂S releasing drugs, and on systems of tissue repair and regeneration that are currently under investigation for potential therapeutic applications in arthritic diseases.

Zinc supplements and bone health: The role of the RANKL-RANK axis as a therapeutic target

BACKGROUND

To this day, empirical data suggests that zinc has important roles in matrix synthesis, bone turnover, and mineralization and its beneficial effects on bone could be mediated through different mechanisms. The influence of zinc on bone turnover could be facilitated via regulating RANKL/RANK/OPG pathway in bone tissue. Therefore, the aim of the study was to conduct a review to investigate the possible effect of the zinc mediated bone remodeling via RANKL/RANK/OPG pathway.

METHODS

A comprehensive systematic search was performed in MEDLINE/PubMed, Cochrane Library, SCOPUS, and Google Scholar to explore the studies investigating the effect of zinc as a bone remodeling factor via RANKL/RANK/OPG pathway regulation. Subsequently, the details of the pathway and the impact of zinc supplements on RANKL/RANK/OPG pathway regulation were discussed.

RESULTS

The pathway could play an important role in bone remodeling and any imbalance between RANKL/RANK/OPG components could lead to extreme bone resorption. Although the outcomes of some studies are equivocal, it is evident that zinc possesses protective properties against bone loss by regulating the RANKL/RANK/OPG pathway. There are several experiments where zinc supplementation resulted in upregulation of OPG expression or decreases RANKL level. However, the results of some studies oppose this.

CONCLUSION

It is likely that sufficient zinc intake will elicit positive effects on bone health by RANKL/RANK/OPG regulation. Although the outcomes of a few studies are equivocal, it seems that zinc can exert the protective properties against bone loss by suppressing osteoclastogenesis via downregulation of RANKL/RANK. Additionally, there are several experiments where zinc supplementation resulted in upregulation of OPG expression. However, the results of limited studies oppose this. Therefore, aside from the positive role zinc possesses in preserving bone mass, further effects of zinc in RANKL/RANK/OPG system requires further animal/human studies.

Programmed death ligand 2 - A link between inflammation and bone loss in rheumatoid arthritis

Objective

Active rheumatoid arthritis (RA) is accompanied by increased appendicular and axial bone loss, closely associated to the degree of inflammation. The programmed death-1 (PD-1) pathway is important for maintaining peripheral tolerance, and its ligand PD-L2 has recently been associated with bone morphogenetic protein activity. Here, we report that PD-L2 plays a central role in RA osteoimmunology.

Methods

Femoral bone mineral density (BMD) and trabecular bone microstructure were evaluated by micro-CT in wild type (WT) and PD-L2^−/− mice. Osteoclasts were generated from RA synovial fluid mononuclear cells and peripheral blood monocytes. The effects of recombinant PD-L2, was evaluated by tartrate-resistant acid phosphatase (TRAP) activity and the development of bone erosions in the presence of anti-citrullinated protein antibodies (ACPA). Plasma soluble (s)PD-L2 levels were measured in patients with early (e)RA (n ​= ​103) treated with methotrexate alone or in combination with the TNF inhibitor Adalimumab.

Results

PD-L2^−/− mice had a decreased BMD and deteriorated trabecular bone microstructure that was not related to the RANKL/OPG pathway. PD-L2 decreased TRAP activity in osteoclasts and decreased ACPA-induced erosions. In the RA synovial membrane PD-L2 was highly expressed especially in the lining layer and plasma sPD-L2 levels were increased in eRA patients and decreased with treatment. One-year sPD-L2 correlated inversely with erosive progression two years after treatment initiation with methotrexate and placebo.

Conclusion

PD-L2 regulates bone homeostasis in RA. Our findings provide new insight into the relationship between the immune system and bone homeostasis, and suggest a potential therapeutic target for limiting inflammatory bone loss in RA.

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PD-L2 is closely related to bone homeostasis in a mouse model.

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PD-L2 inhibits osteoclastogenesis and osteoclast activation in vitro.

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PD-L2 is highly expressed by cells in the synovial membrane of rheumatoid arthritis.

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PD-L2 is associated with less radiographic progression in patients with early rheumatoid arthritis.

From Crosstalk between Immune and Bone Cells to Bone Erosion in Infection

Bone infection and inflammation leads to the infiltration of immune cells at the site of infection, where they modulate the differentiation and function of osteoclasts and osteoblasts by the secretion of various cytokines and signal mediators. In recent years, there has been a tremendous effort to understand the cells involved in these interactions and the complex pathways of signal transduction and their ultimate effect on bone metabolism. These crosstalk mechanisms between the bone and immune system finally emerged, forming a new field of research called osteoimmunology. Diseases falling into the category of osteoimmunology, such as osteoporosis, periodontitis, and bone infections are considered to have a significant implication in mortality and morbidity of patients, along with affecting their quality of life. There is a much-needed research focus in this new field, as the reported data on the immunomodulation of immune cells and their signaling pathways seems to have promising therapeutic benefits for patients.

IL-7 is a Key Driver Cytokine in Spondyloarthritis?

The rationale for a type 17 signature in the pathogenesis of spondyloarthritis (SpA) has been increasing and being ratified in studies recently. IL-7 is a cytokine whose ability to stimulate IL-17 production in both innate and adaptive immunity cells has made it a promising target not only for a better understanding of the disease as well as an important potential therapeutic target in patients with SpA.

Experience in the Adaptive Immunity Impacts Bone Homeostasis, Remodeling, and Healing

Bone formation as well as bone healing capacity is known to be impaired in the elderly. Although bone formation is outpaced by bone resorption in aged individuals, we hereby present a novel path that considerably impacts bone formation and architecture: Bone formation is substantially reduced in aged individual owing to the experience of the adaptive immunity. Thus, immune-aging in addition to chronological aging is a potential risk factor, with an experienced immune system being recognized as more pro-inflammatory. The role of the aging immune system on bone homeostasis and on the bone healing cascade has so far not been considered. Within this study mice at different age and immunological experience were analyzed toward bone properties. Healing was assessed by introducing an osteotomy, immune cells were adoptively transferred to disclose the difference in biological vs. chronological aging. In vitro studies were employed to test the interaction of immune cell products (cytokines) on cells of the musculoskeletal system. In metaphyseal bone, immune-aging affects bone homeostasis by impacting bone formation capacity and thereby influencing mass and microstructure of bone trabeculae leading to an overall reduced mechanical competence as found in bone torsional testing. Furthermore, bone formation is also impacted during bone regeneration in terms of a diminished healing capacity observed in young animals who have an experienced human immune system. We show the impact of an experienced immune system compared to a naïve immune system, demonstrating the substantial differences in the healing capacity and bone homeostasis due to the immune composition. We further showed that in vivo mechanical stimulation changed the immune system phenotype in young mice toward a more naïve composition. While this rescue was found to be significant in young individuals, aged mice only showed a trend toward the reconstitution of a more naïve immune phenotype. Considering the immune system's experience level in an individual, will likely allow one to differentiate (stratify) and treat (immune-modulate) patients more effectively. This work illustrates the relevance of including immune diagnostics when discussing immunomodulatory therapeutic strategies for the progressively aging population of the industrial countries.

What Are the Peripheral Blood Determinants for Increased Osteoclast Formation in the Various Inflammatory Diseases Associated With Bone Loss?

Local priming of osteoclast precursors (OCp) has long been considered the main and obvious pathway that takes place in the human body, where local bone lining cells and RANKL-expressing osteocytes may facilitate the differentiation of OCp. However, priming of OCp away from bone, such as in inflammatory tissues, as revealed in peripheral blood, may represent a second pathway, particularly relevant in individuals who suffer from systemic bone loss such as prevalent in inflammatory diseases. In this review, we used a systematic approach to review the literature on osteoclast formation in peripheral blood in patients with inflammatory diseases associated with bone loss. Only studies that compared inflammatory (bone) disease with healthy controls in the same study were included. Using this core collection, it becomes clear that experimental osteoclastogenesis using peripheral blood from patients with bone loss diseases in prevalent diseases such as rheumatoid arthritis, osteoporosis, periodontitis, and cancer-related osteopenia unequivocally point toward an intrinsically increased osteoclast formation and activation. In particular, such increased osteoclastogenesis already takes place without the addition of the classical osteoclastogenesis cytokines M-CSF and RANKL in vitro. We show that T-cells and monocytes as OCp are the minimal demands for such unstimulated osteoclast formation. In search for common and disease-specific denominators of the diseases with inflammation-driven bone loss, we demonstrate that altered T-cell activity and a different composition—such as the CD14+CD16+ vs. CD14+CD16– monocytes—and priming of OCp with increased M-CSF, RANKL, and TNF- α levels in peripheral blood play a role in increased osteoclast formation and activity. Future research will likely uncover the barcodes of the OCp in the various inflammatory diseases associated with bone loss.

A potential peptide derived from cytokine receptors can bind proinflammatory cytokines as a therapeutic strategy for anti-inflammation

Chronic inflammation is a pivotal event in the pathogenesis of cardiovascular diseases, including atherosclerosis, restenosis, and coronary artery disease. The efficacy of current treatment or preventive strategies for such inflammation is still inadequate. Thus, new anti-inflammatory strategies are needed. In this study, based on molecular docking and structural analysis, a potential peptide KCF18 with amphiphilic properties (positively charged and hydrophobic residues) derived from the receptors of proinflammatory cytokines was designed to inhibit cytokine-induced inflammatory response. Simulations suggested that KCF18 could bind to cytokines simultaneously, and electrostatic interactions were dominant. Surface plasmon resonance detection showed that KCF18 bound to both tumor necrosis factor-α (TNF-α) and interleukin-6, which is consistent with MM/PBSA binding free energy calculations. The cell experiments showed that KCF18 significantly reduced the binding of proinflammatory cytokines to their cognate receptors, suppressed TNF-α mRNA expression and monocyte binding and transmigration, and alleviated the infiltration of white blood cells in a peritonitis mouse model. The designed peptide KCF18 could remarkably diminish the risk of vascular inflammation by decreasing plasma cytokines release and by directly acting on the vascular endothelium. This study demonstrated that a combination of structure-based in silico design calculations, together with experimental measurements can be used to develop potential anti-inflammatory agents.

Genetic variation at the glycosaminoglycan metabolism pathway contributes to the risk of psoriatic arthritis but not psoriasis

OBJECTIVE

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis affecting up to 30% of patients with psoriasis (Ps). To date, most of the known risk loci for PsA are shared with Ps, and identifying disease-specific variation has proven very challenging. The objective of the present study was to identify genetic variation specific for PsA.

METHODS

We performed a genome-wide association study in a cohort of 835 patients with PsA and 1558 controls from Spain. Genetic association was tested at the single marker level and at the pathway level. Meta-analysis was performed with a case-control cohort of 2847 individuals from North America. To confirm the specificity of the genetic associations with PsA, we tested the associated variation using a purely cutaneous psoriasis cohort (PsC, n=614) and a rheumatoid arthritis cohort (RA, n=1191). Using network and drug-repurposing analyses, we further investigated the potential of the PsA-specific associations to guide the development of new drugs in PsA.

RESULTS

We identified a new PsA risk single-nucleotide polymorphism at B3GNT2 locus (p=1.10e-08). At the pathway level, we found 14 genetic pathways significantly associated with PsA (p_FDR<0.05). From these, the glycosaminoglycan (GAG) metabolism pathway was confirmed to be disease-specific after comparing the PsA cohort with the cohorts of patients with PsC and RA. Finally, we identified candidate drug targets in the GAG metabolism pathway as well as new PsA indications for approved drugs.

CONCLUSION

These findings provide insights into the biological mechanisms that are specific for PsA and could contribute to develop more effective therapies.

Periodontal disease influences osteoclastogenic bone markers in subjects with and without rheumatoid arthritis

Background

Periodontal disease (PD) and rheumatoid arthritis (RA) are bone pathologies mediated through immuno-inflammatory mechanisms. The aim of this study was to investigate the serum markers osteopontin (OPN), tumor necrosis factor receptors 1 (TNFR1) and 2 (TNFR2) receptor activator of nuclear factor‐kappa B ligand (RANKL) and RANKL/ osteoprotegerin (OPG) ratio and compare them in PD and RA groups.

Materials & methods

RA (with PD = 19 and without PD = 19), PD (n = 38) and 14 healthy subjects underwent bleeding on probing (BOP) and probing pocket depth (PPD) measurement. PD was defined as PPD measuring ≥5mm registered in ≥3 sites. Marginal bone loss (MBL) for premolars and molars was measured on digital panoramic radiographs. Serum samples were collected from all subjects. OPN, TNFR1, TNFR2 and RANKL were measured by enzyme-linked immunosorbent assays (ELISAs). OPG was measured as part of a multiplex proximity extension assay (PEA).

Results

OPN, TNFR1, TNFR2 and RANKL serum levels were the highest in the RA group with PD, while the RA group without PD were comparable to PD subjects only. The RANKL/OPG ratios were comparable between PD group and both RA groups with (p = 0.051) and without PD (p = 0.37). Serum RANKL levels were associated with MBL (p = 0.008) and PPD ≥ 5mm (p = 0.01).

Conclusion

Peripheral osteoclastogenesis is a feature of periodontal disease with systemic levels of osteoclastogenic markers comparable to the effects observed in rheumatoid arthritis.

The pathogenesis of psoriatic arthritis

Psoriatic arthritis is a chronic, immune-mediated, inflammatory arthropathy that presents with inflammation of the joints and entheses, including those of the axial skeleton, and is associated with increased mortality from cardiovascular disease. Diagnosis is primarily based on clinical phenotype because of the diversity of the associated features, which can include skin and nail disease, dactylitis, uveitis, and osteitis. Improved understanding of the pathogenesis of psoriatic arthritis has led to the development of effective biologics and small-molecular drugs targeting specific cytokines and signalling pathways, which can prevent disease progression and improve quality of life. However, at least 40% of patients with psoriatic arthritis have only a partial response or fail to respond to such treatments. Cytokine inhibitors, mainly those specific for tumour necrosis factor and, more recently, the interleukin 23-T-helper-17 cell pathway, have been highly successful in the treatment of disease manifestations in several different tissues, although targeting the interleukin 23-T-helper-17 cell pathway might be more effective in psoriasis than in arthritis. However, the precise mechanisms underlying the pathogenesis of psoriatic arthritis-which include genetics, environmental factors, and immune-mediated inflammation-are complex, and the relationship between disease of the joint and that of other domains is poorly understood. Improving our understanding of psoriatic arthritis pathogenesis could help to establish validated biomarkers for diagnosis, predict therapeutic response and remission, develop precision medicines, and predict which patients will respond to which therapy. We discuss advances in pathogenetic translational research that could inform these issues.

Mechanical Stretching of Fibronectin Fibers Upregulates Binding of Interleukin-7

Since evidence is rising that extracellular matrix (ECM) fibers might serve as reservoirs for growth factors and cytokines, we investigated the interaction between fibronectin (FN) and interleukin-7 (IL-7), a cytokine of immunological significance and a target of several immunotherapies. By employing a FN fiber stretch assay and Förster resonance energy transfer (FRET) confocal microscopy, we found that stretching of FN fibers increased IL-7 binding. We localized the FN binding site on the CD loop of IL-7, since a synthetic CD loop peptide also bound stronger to stretched than to relaxed FN fibers. On the basis of a structural model, we propose that the CD loop can bind to FN, while IL-7 is bound to its cognate cell surface receptors. Sequence alignment with bacterial adhesins, which also bind the FN N-terminus, suggests that a conserved motif on the CD loop (₁₁₀TKSLEEN₁₁₆ and the truncated ₁₁₂SLEE₁₁₅ in human and mouse IL-7, respectively) might bind to the second FN type I module (FnI₂) and that additional epitopes enhance the stretch-upregulated binding. FN fiber stretching might thus serve as a mechano-regulated mechanism to locally concentrate IL-7 in an ECM-bound state, thereby upregulating the potency of IL-7 signaling. A feedback model mechanism is proposed that could explain the well-known, but poorly understood, function of IL-7 in ECM homeostasis. Understanding how local IL-7 availability and signaling might be modulated by the tensional state of the ECM niche, which is adjusted by residing stroma cells, is highly relevant for basic science but also for advancing IL-7 based immunotherapies.

Interleukin-7 Induces Osteoclast Formation via STAT5, Independent of Receptor Activator of NF-kappaB Ligand

Interleukin-7 (IL-7), which is required for the development and survival of T cells in the thymus and periphery, plays a role in joint destruction. However, it remains unclear how IL-7 affects osteoclast formation. Thus, we investigated the mechanism by which IL-7 induced osteoclast formation through IL-7 receptor α (IL-7Rα) in osteoclast precursors. We cultured peripheral blood mononuclear cells or synovial fluid mononuclear cells with IL-7 in the presence or absence of an appropriate inhibitor to analyze osteoclast formation. We also constructed IL-7Rα-expressing RAW264.7 cells to uncover the mechanism(s) by which IL-7 induced osteoclast formation differed from that of receptor activator of nuclear factor κB ligand (RANKL). We found that IL-7 induced osteoclast formation of human monocytes from peripheral blood or synovial fluid in a RANKL-independent and a signal transducer and activator of transcription 5 (STAT5)-dependent manner. IL-7-induced osteoclasts had unique characteristics, such as small, multinucleated tartrate-resistant acid phosphatase positive cells and no alterations even when RANKL was added after IL-7 pretreatment. RAW264.7 cells, if overexpressing IL-7Rα, also were able to differentiate into osteoclasts by IL-7 through a STAT5 signaling pathway. Furthermore, IL-7-induced osteoclast formation was repressed by inhibitors of the IL-7R signaling molecules Janus kinase and STAT5. Our findings demonstrate that IL-7 is a truly osteoclastogenic factor, which may induce osteoclast formation via activation of STAT5, independent of RANKL. We also suggest the possibility that an IL-7R pathway blocker could alleviate joint damage by inhibiting osteoclast formation, especially in inflammatory conditions.

Melittin inhibits osteoclast formation through the downregulation of the RANKL-RANK signaling pathway and the inhibition of interleukin-1β in murine macrophages

Melittin is a major toxic component of bee venom (Apis mellifera). It is not known whether melittin is involved in bone metabolism and osteoclastogenesis. The aim of this study was to determine the role of melittin in the regulation of osteoclastogenesis. In vitro osteoclastogenesis assays were performed using mouse RAW 264.7 cells and bone marrow-derived macrophages (BMMs) treated with receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Morphologic and functional analyses for osteoclast-like multinucleated cells (MNCs) were performed by tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining and pit formation methods. The gene expression of TRAP, cathepsin K, matrix metalloproteinase-9 (MMP-9) and carbonic anhydrase II was measured by reverse transcription-quantitative PCR. The protein expression levels of mitogen-activated protein kinases (MAPKs), the p65 subunit of nuclear factor-κB (NF-κB), c-Fos, c-Jun, nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), TNF receptor-associated factor-6 (TRAF6), and interleukin-1β (IL-1β) were assessed by western blot analysis. Melittin inhibited the mRNA expression of TRAP, cathepsin K, MMP-9 and carbonic anhydrase II in RANKL-stimulated RAW 264.7 cells. The increased protein expression of TRAF6, p-extracellular signal-regulated kinase (ERK), p-JNK, p-p65, p-c-Fos and NFATc1 induced by RANKL was significantly suppressed in the RAW 264.7 cells treated with melittin. A synergistic effect of IL-1β on the formation of RANKL-induced osteoclast-like MNCs was found in two experimental cells. The increased expression of IL-1β following the stimulation of RAW 264.7 cells with RANKL activated TRAF6, p-ERK, p-JNK, p-p65, p-c-Fos and NFATc1. These effects were attenuated by the downregulation of IL-1β using siRNA against IL-1β, and also by treatment with melittin. On the whole, the findings of this study demonstrate that melittin inhibits the formation of osteoclast-like MNCs by interfering with the RANKL-RANK signaling pathway.

Optimal management of dactylitis in patients with psoriatic arthritis

Psoriatic arthritis (PsA) is an inflammatory arthropathy associated with cutaneous psoriasis, which is currently classified as a seronegative spondyloarthropathy. The presence of cutaneous psoriasis is important for correct and early diagnosis of PsA, because the onset of cutaneous lesions usually precedes the appearance of joint manifestation. Thus, dermatologists are able to detect the condition at its inception. PsA has several unique characteristics such as enthesopathy, dactylitis, and abnormal bone remodeling. In particular, dactylitis occurs on the easily observed sites such as digits, and is thus a significant indicator of PsA. It is important to observe not only the fingers but also the toes, because dactylitis involves both digits of the hands and feet. Recently, new ideas regarding the involvement of the interleukin (IL)-23/Th17 axis have emerged, and the dramatic effects of targeting therapies have highlighted the physiological roles of key cytokines such as tumor necrosis factor-α, IL-17A, and IL-23 in psoriasis. As recent insights are shedding light on the pathogenesis of PsA, understanding of the pathogenesis of dactylitis and enthesitis are also progressing. In this article, current views on the optimal management of dactylitis are discussed.

Monosodium Urate in the Presence of RANKL Promotes Osteoclast Formation through Activation of c-Jun N-Terminal Kinase

The aim of this study was to clarify the role of monosodium urate (MSU) crystals in receptor activator of nuclear factor kB ligand- (RANKL-) RANK-induced osteoclast formation. RAW 264.7 murine macrophage cells were incubated with MSU crystals or RANKL and differentiated into osteoclast-like cells as confirmed by staining for tartrate-resistant acid phosphatase (TRAP) and actin ring, pit formation assay, and TRAP activity assay. MSU crystals in the presence of RANKL augmented osteoclast differentiation, with enhanced mRNA expression of NFATc1, cathepsin K, carbonic anhydrase II, and matrix metalloproteinase-9 (MMP-9), in comparison to RAW 264.7 macrophages incubated in the presence of RANKL alone. Treatment with both MSU crystals and RANKL induced osteoclast differentiation by activating downstream molecules in the RANKL-RANK pathway including tumor necrosis factor receptor-associated factor 6 (TRAF-6), JNK, c-Jun, and NFATc1. IL-1b produced in response to treatment with both MSU and RANKL is involved in osteoclast differentiation in part through the induction of TRAF-6 downstream of the IL-1b pathway. This study revealed that MSU crystals contribute to enhanced osteoclast formation through activation of RANKL-mediated pathways and recruitment of IL-1b. These findings suggest that MSU crystals might be a pathologic causative agent of bone destruction in gout.

Proinflammatory and proosteoclastogenic potential of peripheral blood mononuclear cells from Gaucher patients: Implication for bone pathology

Gaucher disease (GD) is caused by mutations in the GBA gene that confer a deficient level of activity of glucocerebrosidase (GCase). This deficiency leads to the accumulation of the glycolipid glucocerebroside in the lysosomes of cells of monocyte/macrophage system. Bone compromise in Gaucher disease patients is the most disabling aspect of the disease. However, pathophysiological aspects of skeletal alterations are still poorly understood. On the other hand it is well known that inflammation is a key player in GD pathology. In this work, we revealed increased levels of the proinflammatory CD14(+)CD16(+) monocyte subset and increased inflammatory cytokine production by monocytes and T cells in the circulation of GD patients. We showed increased levels of osteoclast precursors in PBMC from patients and a higher expression of RANKL in the surface of T cells. PBMC from patients presented higher osteoclast differentiation compared to healthy controls when cultured in the presence of M-CSF alone or in combination with RANKL. In vitro treatment with Velaglucerase reduced osteoclast levels to control levels. On the other hand THP-1 derived osteoclast precursors cultured in the presence of conditioned media from PBMC of GD patients presented higher differentiation to active osteoclasts. This induction involved TNF-α and RANKL.

Vitamin D3 levels and bone mineral density in patients with psoriasis and/or psoriatic arthritis

Limited data are available on the vitamin D3 status and bone mineral density (BMD) of patients with psoriasis or with psoriatic arthritis. Our study intended to explore possible correlations between vitamin D status and BMD, as well as among these parameters and the features of the underlying disorder. Seventy-two patients with psoriasis/or psoriatic arthritis (female : male ratio, 40:32; mean age, 58.5 ± 11.6 years; mean duration of follow up, 142.7 ± 147.7 months) participated in the study. We evaluated the characteristic clinical features of the underlying disease, performed bone densitometry of the lumbar spine and the hip region, measured the serum vitamin 25(OH)D3 levels of the patients, and undertook the statistical analysis of the relationships between the clinical and the laboratory parameters. The proportion of patients with a low BMD value did not exceed that seen in the general population. We found an inverse correlation between the serum level of vitamin 25(OH)D3 and body mass index, as well as between the former and the severity of skin involvement. Furthermore, the activity of psoriatic arthritis was significantly higher in patients with inadequate vitamin D3 status. In patients with psoriatic arthritis, BMD significantly exceeded the values measured in patients suffering from psoriatic skin lesions only. Our findings suggest the importance of evaluating the vitamin D3 status and screening for comorbid conditions in patients with psoriasis or psoriatic arthritis. This appears justified, in particular, due to the possible role of hypovitaminosis D3 in provoking the development of skin lesions and joint symptoms.

Bone-immune cell crosstalk: bone diseases

Bone diseases are associated with great morbidity; thus, the understanding of the mechanisms leading to their development represents a great challenge to improve bone health. Recent reports suggest that a large number of molecules produced by immune cells affect bone cell activity. However, the mechanisms are incompletely understood. This review aims to shed new lights into the mechanisms of bone diseases involving immune cells. In particular, we focused our attention on the major pathogenic mechanism underlying periodontal disease, psoriatic arthritis, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis, metastatic solid tumors, and multiple myeloma.

B Cell Production of Both OPG and RANKL is Significantly Increased in Aged Mice

Aging is a risk factor for osteoclastic bone loss and bone fracture. Receptor activator of NF-κB ligand (RANKL) is the key effector cytokine for osteoclastogenesis and bone resorption, and is moderated by its decoy receptor osteoprotegerin (OPG). The development of an inflammatory environment during aging leads to increased bone resorption and loss of bone mineral density (BMD). Interestingly, animal and clinical studies show that OPG is actually increased in aging but fails to fully compensate for endogenous RANKL. Osteoblast- and B-lineage cells are significant sources of physiological OPG, however osteoblast OPG production declines with age, suggesting that elevated OPG in aging may be a consequence of changes in B cell function. In this study we examined BMD and indices of trabecular bone structure during aging, and B cell production of both RANKL and OPG in young and aged mice. Our data reveal significant loss of BMD and trabecular structure with age commensurate with significantly elevated concentrations of both OPG and RANKL in aged mice, and a decline in B cell populations in aged animals. Taken together our data suggest that B cells may be responsible for the elevated concentrations of OPG during aging and are essential to counteract excessive age-associated bone resorption. Paradoxically, B cells themselves likely contribute RANKL in aging and the loss of B cells with age may further contribute to the imbalance in OPG relative to RANKL that predisposes age-associated bone loss.

Psoriatic inflammation facilitates the onset of arthritis in a mouse model

Psoriatic arthritis (PsA) is a seronegative, inflammatory joint disease associated with psoriasis. In most patients with PsA, skin lesions precede arthritis; however, the causality of skin inflammation for the development of arthritis remains unclear. Gp130F759/F759 knock-in (F759) mice develop autoimmune arthritis after 1 year of age through persistent signal transducer and activator of transcription 3 (Stat3) activation due to impairment in SOCS3-dependent negative regulation. Here, we crossed F759 mice with K5.Stat3C transgenic mice, in which keratinocytes express constitutive active Stat3 (Stat3C), leading to generation of psoriasis-like skin change. F759 mice harboring the K5.Stat3C transgene not only had aggravated skin lesions but also spontaneously developed arthritis with high penetrance in adjacent paws as early as 3 weeks of age. The joint lesions included swelling of the peripheral paws and nail deformities contiguous with the skin lesions, closely resembling PsA. Histopathologic study revealed enthesitis and bone erosions, with mononuclear cell infiltrates. Quantitative reverse transcriptase-PCR (RT-PCR), immunohistochemical analyses, and flow cytometry showed upregulation of the IL-23/T helper type 17 (Th17) pathway in affected joints. Furthermore, enforced generation of psoriasis-like skin inflammation by topical treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) in F759 mice induced swelling of the underlying joints. This animal model renders psoriatic inflammation as the driver of arthritis and helps to further understand the pathogenesis of PsA.

Bone metastases: When and how lung cancer interacts with bone

Bone metastasis is a common and debilitating consequence of lung cancer: 30%-40% of patients with non-small cell lung cancer develop bone metastases during the course of their disease. Lung cancer cells find a favorable soil in the bone microenvironment due to factors released by the bone matrix, the immune system cells, and the same cancer cells. Many aspects of the cross-talk among lung tumor cells, the immune system, and bone cells are not clear, but this review aims to summarize the recent findings in this field, with particular attention to studies conducted to identify biomarkers for early detection of lung cancer bone metastases.

The expanding role of IL-7 and thymic stromal lymphopoietin as therapeutic target for rheumatoid arthritis

INTRODUCTION

The discovery of IL-7 and thymic stromal lymphopoietin (TSLP) has been a major step in the understanding of arthritis. IL-7 amplifies the inflammation induced by other cytokines, primarily TNF. In animal models of arthritis, inhibition of IL-7 limits inflammation and joint erosion. TSLP is an IL-7-like cytokine that triggers dendritic cell-mediated Th2-type inflammatory responses and is considered as a master switch for allergic inflammation. TSLP is a downstream molecule of TNF-α and as such may be involved in the pathophysiology of inflammatory arthritis.

AREAS COVERED

This review summarizes current knowledge of the role of IL-7 and TSLP derived from both animal models and studies in patients with rheumatoid arthritis (RA). The emergence of IL-7 blockade as a future therapy in RA is highlighted, along with the potential goals and limitations of this therapeutic approach. The write-up also highlights the functional capacities of TSLP in arthritis.

EXPERT OPINION

Evidences suggest important roles for IL-7 and TSLP in the pathogenesis of RA and can be viewed as potential therapeutic targets. Regulation of these at genetic level is a promising investigational area. Given the difficulty in reconstituting T cells in patients with RA, therapeutic approaches that minimize the elimination of T cells are likely to be more desirable.

Osteoclastogenic potential of peripheral blood mononuclear cells in cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal dysplasia characterized by hypoplastic or aplastic clavicles, dental abnormalities, and delayed closure of the cranial sutures. In addition, mid-face hypoplasia, short stature, skeletal anomalies and osteoporosis are common. We aimed to evaluate osteoclastogenesis in a child (4 years old), who presented with clinical signs of CCD and who have been diagnosed as affected by deletion of RUNX2, master gene in osteoblast differentiation, but also affecting T cell development and indirectly osteoclastogenesis. The results of this study may help to understand whether in this disease is present an alteration in the bone-resorptive cells, the osteoclasts (OCs). Unfractionated and T cell-depleted Peripheral Blood Mononuclear Cells (PBMCs) from patient were cultured in presence/absence of recombinant human M-CSF and RANKL. At the end of the culture period, OCs only developed following the addition of M-CSF and RANKL. Moreover, real-time PCR experiment showed that freshly isolated T cells expressed the osteoclastogenic cytokines (RANKL and TNFα) at very low level, as in controls. This is in accordance with results arising from flow cytometry experiments demonstrating an high percentage of circulating CD4(+)CD28(+) and CD4(+)CD27(+) T cells, not able to produce osteoclastogenic cytokines. Also RANKL, OPG and CTX serum levels in CCD patient are similar to controls, whereas QUS measurements showed an osteoporotic status (BTT-Z score -3.09) in the patient. In conclusions, our findings suggest that the heterozygous deletion of RUNX2 in this CCD patient did not alter the osteoclastogenic potential of PBMCs in vitro.

Experimental model for studying the involvement of regulatory cytotoxic T cells in bone resorption

T cells may affect the activity of osteoclasts, the bone resorbing cells. In particular, recently authors focalize their attention on CD8(+) T cells, demonstrating that murine pre-osteoclasts can recruit naïve CD8(+) T cells and induce them to differentiate in regulatory cytotoxic T cells (TcREG), which in turn may suppress osteoclast formation and activity. Thus, here we describe the methodological approach needed to obtain TcREG and to evaluate TcREG effects on murine osteoclast activity and formation in an in vitro experimental model.

The role of TNF-α and TNF superfamily members in the pathogenesis of calcific aortic valvular disease

Calcific aortic valve disease (CAVD) represents a slowly progressive pathologic process associated with major morbidity and mortality. The process is characterized by multiple steps: inflammation, fibrosis, and calcification. Numerous studies focalized on its physiopathology highlighting different "actors" for the multiple "acts." This paper focuses on the role of the tumor necrosis factor superfamily (TNFSF) members in the pathogenesis of CAVD. In particular, we discuss the clinical and experimental studies providing evidence of the involvement of tumor necrosis factor-alpha (TNF-α), receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL), its membrane receptor RANK and its decoy receptor osteoprotegerin (OPG), and TNF-related apoptosis-inducing ligand (TRAIL) in valvular calcification.

Association of systemic and intra-articular osteoclastogenic potential, pro-inflammatory mediators and disease activity with the form of inflammatory arthritis

PURPOSE

We aimed to assess osteoclastogenic potential of peripheral blood mononuclear cells (PBMC) and synovial fluid-derived mononuclear cells (SFMC) in different forms of arthritis and to correlate it with inflammatory mediators within intra-articular and circulatory compartments.

METHODS

Paired PBMC and SFMC samples of patients with rheumatoid arthritis (RA; n = 10) and psoriatic arthritis (PsA; n = 10), and PBMC of healthy controls were cultured to assess osteoclastogenic potential by the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts (OCs) and expression of OC-related genes (receptor activator of nuclear factor-κΒ (RANK), cFMS, and TRAP). Osteoclastogenesis was correlated with the arthritis-related inflammatory indicators in serum and synovial fluid (SF).

RESULTS

Number of OCs differentiated from PBMC was significantly higher in RA and PsA compared with control, with RA having more OCs compared with PsA. There was no difference in SFMC OC number between arthritic patients, but RANK expression in OCs differentiated from SFMC was higher in PsA compared with RA. SF of PsA patients more potently induced OC differentiation from control CD3(-)CD19(-)CD56(-)CD11b(+)CD115(+) PBMC compared with RA, paralleled with higher RANK-ligand expression in PsA SFMC. Positive correlations of OC number with erythrocyte sedimentation rate, serum level of CCL2, and PBMC gene expression of interleukin-18 and Fas-ligand were observed.

CONCLUSION

Osteoclastogenic potential is systemically enhanced in patients with RA, paralleled by disordered systemic and local expression of proinflammatory mediators, whereas PsA involves specific deregulation in RANKL/RANK axis. Our study reveals arthritis-specific mediators associated with the form of arthritis, indicating clinical relevance for diagnosis and treatment.

The Interplay between the bone and the immune system

In the last two decades, numerous scientists have highlighted the interactions between bone and immune cells as well as their overlapping regulatory mechanisms. For example, osteoclasts, the bone-resorbing cells, are derived from the same myeloid precursor cells that give rise to macrophages and myeloid dendritic cells. On the other hand, osteoblasts, the bone-forming cells, regulate hematopoietic stem cell niches from which all blood and immune cells are derived. Furthermore, many of the soluble mediators of immune cells, including cytokines and growth factors, regulate the activities of osteoblasts and osteoclasts. This increased recognition of the complex interactions between the immune system and bone led to the development of the interdisciplinary osteoimmunology field. Research in this field has great potential to provide a better understanding of the pathogenesis of several diseases affecting both the bone and immune systems, thus providing the molecular basis for novel therapeutic strategies. In these review, we reported the latest findings about the reciprocal regulation of bone and immune cells.

Bone effects of biologic drugs in rheumatoid arthritis

Biologic agents used in the treatment of rheumatoid arthritis (RA) are able to reduce both disease activity and radiographic progression of joint disease. These drugs are directed against several proinflammatory cytokines (TNF α , IL-6, and IL-1) which are involved both in the pathogenesis of chronic inflammation and progression of joint structural damage and in systemic and local bone loss typically observed in RA. However, the role of biologic drugs in preventing bone loss in clinical practice has not yet clearly assessed. Many clinical studies showed a trend to a positive effect of biologic agents in preventing systemic bone loss observed in RA. Although the suppression of inflammation is the main goal in the treatment of RA and the anti-inflammatory effects of biologic drugs exert a positive effect on bone metabolism, the exact relationship between the prevention of bone loss and control of inflammation has not been clearly established, and if the available biologic drugs against TNF α , IL-1, and IL-6 can exert their effect on systemic and local bone loss also through a direct mechanism on bone cell metabolism is still to be clearly defined.

Postmenopausal osteoporosis: the role of immune system cells

In the last years, new evidences of the relationship between immune system and bone have been accumulated both in animal models and in humans affected by bone disease, such as rheumatoid arthritis, bone metastasis, periodontitis, and osteoporosis. Osteoporosis is characterized by low bone mass and microarchitectural deterioration of bone tissue with a subsequent increase in bone fragility and susceptibility to fractures. The combined effects of estrogen deprivation and raising of FSH production occurring in menopause cause a marked stimulation of bone resorption and a rapid bone loss which is central for the onset of postmenopausal osteoporosis. This review focuses on the role of immune system in postmenopausal osteoporosis and on therapeutic strategies targeting osteoimmunology pathways.

Osteoimmunology and the influence of pro-inflammatory cytokines on osteoclasts

Bone and immune system are functionally interconnected. Immune and bone cells derive from same progenitors in the bone marrow, they share a common microenvironment and are being influenced by similar mediators. The evidence on increased bone resorption associated with inappropriate activation of T cells such as during inflammation, is well established. However, the molecular mechanisms beyond this clinical observation have begun to be intensively studied with the advancement of osteoimmunology. Now days, we have firm evidence on the influence of numerous proinflammatory cytokines on bone cells, with the majority of data focused on osteoclasts, the bone resorbing cells. It has been shown that some proinflammatory cytokines could possess osteoclastogenic and/or anti-osteoclastogenic properties and can target osteoclasts directly or via receptor activator of nuclear factor κB (RANK)/RANK ligand(RANKL)/osteoprotegerin (OPG) system. Several studies have reported opposing data regarding (anti)osteoclastogenic properties of these cytokines.

Therefore, the first part of this review is summarizing current evidence on the influence of pro-inflammatory cytokines on osteoclasts and thus on bone resorption. In the second part, the evidence on the role of pro-inflammatory cytokines in osteoporosis and osteoarthritis is reviewed to show that unravelling the mechanisms beyond such complex bone diseases, is almost impossible without considering skeletal and immune systems as an indivisible integrated system.

Rib fractures and death from deletion of osteoblast βcatenin in adult mice is rescued by corticosteroids

Ribs are primarily made of cortical bone and are necessary for chest expansion and ventilation. Rib fractures represent the most common type of non-traumatic fractures in the elderly yet few studies have focused on the biology of rib fragility. Here, we show that deletion of βcatenin in Col1a2 expressing osteoblasts of adult mice leads to aggressive osteoclastogenesis with increased serum levels of the osteoclastogenic cytokine RANKL, extensive rib resorption, multiple spontaneous rib fractures and chest wall deformities. Within days of osteoblast specific βcatenin deletion, animals die from respiratory failure with a vanishing rib cage that is unable to sustain ventilation. Increased bone resorption is also observed in the vertebrae and femur. Treatment with the bisphosphonate pamidronate delayed but did not prevent death or associated rib fractures. In contrast, administration of the glucocorticoid dexamethasone decreased serum RANKL and slowed osteoclastogenesis. Dexamethasone preserved rib structure, prevented respiratory compromise and strikingly increased survival. Our findings provide a novel model of accelerated osteoclastogenesis, where deletion of osteoblast βcatenin in adults leads to rapid development of destructive rib fractures. We demonstrate the role of βcatenin dependent mechanisms in rib fractures and suggest that glucocorticoids, by suppressing RANKL, may have a role in treating bone loss due to aggressive osteoclastogenesis.

The Role of Inflammatory Cytokines, the RANKL/OPG Axis, and the Immunoskeletal Interface in Physiological Bone Turnover and Osteoporosis

Although it has long been recognized that inflammation, a consequence of immune-driven processes, significantly impacts bone turnover, the degree of centralization of skeletal and immune functions has begun to be dissected only recently. It is now recognized that formation of osteoclasts, the bone resorbing cells of the body, is centered on the key osteoclastogenic cytokine, receptor activator of NF- κ B ligand (RANKL). Although numerous inflammatory cytokines are now recognized to promote osteoclast formation and skeletal degradation, with just a few exceptions, RANKL is now considered to be the final downstream effector cytokine that drives osteoclastogenesis and regulates osteoclastic bone resorption. The biological activity of RANKL is moderated by its physiological decoy receptor, osteoprotegerin (OPG). New discoveries concerning the sources and regulation of RANKL and OPG in physiological bone turnover as well as under pathological (osteoporotic) conditions continue to be made, opening a window to the complex regulatory processes that control skeletal integrity and the depth of integration of the skeleton within the immune response. This paper will examine the interconnection between bone turnover and the immune system and the implications thereof for physiological and pathological bone turnover.