RANK signaling is not required for TNFalpha-mediated increase in CD11(hi) osteoclast precursors but is essential for mature osteoclast formation in TNFalpha-mediated inflammatory arthritis

Ferroptosis in Osteocytes as a Target for Protection Against Postmenopausal Osteoporosis

Ferroptosis is a necrotic form of iron-dependent regulatory cell death. Estrogen withdrawal can interfere with iron metabolism, which is responsible for the pathogenesis of postmenopausal osteoporosis (PMOP). Here, it is demonstrated that estrogen withdrawal induces iron accumulation in the skeleton and the ferroptosis of osteocytes, leading to reduced bone mineral density. Furthermore, the facilitatory effect of ferroptosis of osteocytes is verified in the occurrence and development of postmenopausal osteoporosis is associated with over activated osteoclastogenesis using a direct osteocyte/osteoclast coculture system and glutathione peroxidase 4 (GPX4) knockout ovariectomized mice. In addition, the nuclear factor erythroid derived 2-related factor-2 (Nrf2) signaling pathway is confirmed to be a crucial factor in the ferroptosis of osteocytic cells. Nrf2 regulates the expression of nuclear factor kappa-B ligand (RANKL) by regulating the DNA methylation level of the RANKL promoter mediated by DNA methyltransferase 3a (Dnmt3a), which is as an important mechanism in osteocytic ferroptosis-mediated osteoclastogenesis. Taken together, this data suggests that osteocytic ferroptosis is involved in PMOP and can be targeted to tune bone homeostasis.

Phytoconstituents-Based Nanotherapeutic Approach for the Effective Management of Joint Inflammatory Condition: Arthritis

Arthritis, a prevalent inflammatory joint condition, presents challenges for effective therapeutic interventions, with conventional treatments often limited in efficacy and associated with adverse effects. Recent years have witnessed a growing interest in exploring natural compounds, particularly phytoconstituents, renowned for their anti-inflammatory and joint-protective properties. This review aims to illuminate the potential of employing nanotherapeutic approaches with phytoconstituents for enhanced arthritis management. The integration of nanotechnology with phytoconstituents emerges as a promising strategy, addressing limitations in traditional arthritis treatments. Nanocarriers like liposomes and nanoparticles provide a platform for targeted drug delivery, improving the bioavailability of phytoconstituents. Furthermore, the combined effects of phytoconstituents can be leveraged to target multiple pathways in arthritis pathogenesis, including inflammation, oxidative stress, and cartilage degradation. Key phytoconstituents, such as curcumin, resveratrol, and quercetin, exhibit anti-inflammatory and immunomodulatory properties. Nevertheless, their therapeutic potential is often impeded by challenges like poor solubility, stability, and bioavailability. Nanocarriers offer solutions by enhancing pharmacokinetics and enabling sustained release, thereby boosting overall therapeutic efficacy. The review explores the mechanisms underlying the anti-arthritic effects of phytoconstituents and their nanoformulations, including the modulation of pro-inflammatory cytokines, inhibition of matrix metalloproteinases, and reduction of oxidative stress. In summary, the integration of phytoconstituents with nanotechnology presents a promising avenue for developing targeted and effective arthritis therapies. This comprehensive review serves as a valuable resource for researchers, clinicians, and pharmaceutical developers seeking innovative approaches to address the intricate challenges associated with arthritis management.

Carboxymethyl chitosan regulates oxidative stress and decreases the expression levels of tumor necrosis factor α in macrophages induced by wear particles

The aim of the present study was to determine the effects of carboxymethyl chitosan (CMC) on titanium particles-induced oxidative stress in mouse RAW264.7 macrophages. The mouse RAW264.7 macrophages were divided into four groups: (i) the control group; (ii) the CMC group received stimulation of CMC for 4 h; (iii) the titanium particles group received stimulation of titanium particles for 12 h; and (iv) the CMC group received pre-stimulation of CMC hydrogels for 4 h followed by treatment of titanium particles for 12 h. Afterwards, reactive oxygen species (ROS) level in the cells was measured by flow cytometry. A spectrophotometer was used to measure the activities of oxidases and antioxidant enzymes. Fluorescence quantitative PCR was performed to analyze mRNA levels of enzymes and tumor necrosis factor α (TNF-α). ELISA was used to detect the mass concentration of TNF-α after indicated treatment. CMC effectively suppressed titanium particles-induced oxidative stress in RAW264.7 cells, as evidenced by the decrease in intracellular ROS level, the transcription of oxidases, and TNF-α concentration as well as the increase in the transcription of antioxidant enzymes. CMC exerts a protective impact against wear particles-induced oxidative stress and reduces the release of TNF-α in RAW264.7 cells.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.

MicroRNAs-mediated regulation pathways in rheumatic diseases

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are two common rheumatic disorders marked by persistent inflammatory joint disease. Patients with RA have osteodestructive symptoms, but those with AS have osteoproliferative manifestations. Ligaments, joints, tendons, bones, and muscles are all affected by rheumatic disorders. In recent years, many epigenetic factors contributing to the pathogenesis of rheumatoid disorders have been studied. MicroRNAs (miRNAs) are small, non-coding RNA molecules implicated as potential therapeutic targets or biomarkers in rheumatic diseases. MiRNAs play a critical role in the modulation of bone homeostasis and joint remodeling by controlling fibroblast-like synoviocytes (FLSs), chondrocytes, and osteocytes. Several miRNAs have been shown to be dysregulated in rheumatic diseases, including miR-10a, 16, 17, 18a, 19, 20a, 21, 27a, 29a, 34a, 103a, 125b, 132, 137, 143, 145, 146a, 155, 192, 203, 221, 222, 301a, 346, and 548a.The major molecular pathways governed by miRNAs in these cells are Wnt, bone-morphogenic protein (BMP), nuclear factor (NF)-κB, receptor activator of NF-κB (RANK)-RANK ligand (RANKL), and macrophage colony-stimulating factor (M-CSF) receptor pathway. This review aimed to provide an overview of the most important signaling pathways controlled by miRNAs in rheumatic diseases.

Osteoclasts, Master Sculptors of Bone

Osteoclasts are multinucleated cells with the unique ability to resorb bone matrix. Excessive production or activation of osteoclasts leads to skeletal pathologies that affect a significant portion of the population. Although therapies that effectively target osteoclasts have been developed, they are associated with sometimes severe side effects, and a fuller understanding of osteoclast biology may lead to more specific treatments. Along those lines, a rich body of work has defined essential signaling pathways required for osteoclast formation, function, and survival. Nonetheless, recent studies have cast new light on long-held views regarding the origin of these cells during development and homeostasis, their life span, and the cellular sources of factors that drive their production and activity during homeostasis and disease. In this review, we discuss these new findings in the context of existing work and highlight areas of ongoing and future investigation.

Postmenopausal Osteoporosis: A Literature Review

A substantial proportion of the population of females in India falls in the perimenopausal and postmenopausal age groups. One of the complications associated with older age in women is the weakening of bones and the fall in bone mineral density (BMD). This has a severe debilitating consequence in a woman’s life and leads to reduced quality of life along with a greater incidence of fractures. If the fracture involves the hip or the vertebrae, it can cause immobility and be devastating. Postmenopausal osteoporosis is linked with the deficiency of estrogen that occurs with the cessation of the function of the ovaries as age progresses. The function of estrogen in the bone remodeling process is very well understood after years of research; estrogen plays a part in both the formation of bone as well as the prevention of the resorption of bone. A diagnosis can be made by dual-energy X-ray absorptiometry (DEXA). It is the gold standard and can spot low bone density at particular sites. The treatment options are selected according to the severity and rate of progression and factors pertaining to each patient. All postmenopausal women should be made aware of this disorder, and they should be encouraged to cultivate a healthy lifestyle through the implementation of a proper diet and inculcation of a regular exercise routine. Smoking and drinking alcohol should be limited, and calcium and vitamin D supplementation should be started in all women of the postmenopausal age group with or without osteoporosis. In patients who have been diagnosed with the disorder, pharmacological intervention is done. Drugs should be selected based on their side effects and contradictions. Follow-up is essential, and patient compliance should be carefully monitored. This article attempts to review the existing literature on this very prevalent disorder to spread awareness about it so that all postmenopausal women can take the necessary steps to prevent the weakening of their bones, and deal with its progression.

TGF-beta pathway inhibition as the therapeutic acceleration of diabetic bone regeneration

Bone regeneration and fracture healing are impaired in diabetic patients due to defective functions of associated cells. Thus, the search for molecular causes and new treatment strategies are of particular clinical relevance. We investigated the gene expression profile of bones from type 2 diabetic (db^- /db^- ) mice and wild-type (wt) mice by comparative microarray analyses before and after placing tibial defects and examined the expression of several osteogenesis- and osteoclastogenesis-related markers by quantitative real-time polymerase chain reaction. In regenerating wt bones, pathways related to, for example, inhibition of matrix metalloproteases were activated, whereas in db^- /db^- bones activation of pathways related to, for example, osteoarthritis, transforming growth factor-beta (Tgfb), or hypoxia-inducible factor 1a were detected during regeneration. We defined the Tgfb pathway as a potential therapeutic target and locally applied a single dose (0.5 µg) of the Tgfb 1, 2, and 3 neutralizing antibody 1D11 on tibial defects in db^- /db^- mice (n = 7). Seven days postoperation, histological and immunohistochemical stainings were performed. Decreased bone regeneration, osteogenic differentiation, osteoclast invasion, and angiogenesis in db^- /db^- mice were significantly restored by local 1D11 application in comparison to the phosphate-buffered saline controls. Thus, local treatment of db^- /db^- bony defects with Tgfb neutralizing antibody 1D11 might be considered a good candidate for the successful acceleration of bone regeneration.

Immunomodulatory role of T helper cells in rheumatoid arthritis : a comprehensive research review

Rheumatoid arthritis (RA) is an autoimmune disease that involves T and B cells and their reciprocal immune interactions with proinflammatory cytokines. T cells, an essential part of the immune system, play an important role in RA. T helper 1 (Th1) cells induce interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α), and interleukin (IL)-2, which are proinflammatory cytokines, leading to cartilage destruction and bone erosion. Th2 cells primarily secrete IL-4, IL-5, and IL-13, which exert anti-inflammatory and anti-osteoclastogenic effects in inflammatory arthritis models. IL-22 secreted by Th17 cells promotes the proliferation of synovial fibroblasts through induction of the chemokine C-C chemokine ligand 2 (CCL2). T follicular helper (Tfh) cells produce IL-21, which is key for B cell stimulation by the C-X-C chemokine receptor 5 (CXCR5) and coexpression with programmed cell death-1 (PD-1) and/or inducible T cell costimulator (ICOS). PD-1 inhibits T cell proliferation and cytokine production. In addition, there are many immunomodulatory agents that promote or inhibit the immunomodulatory role of T helper cells in RA to alleviate disease progression. These findings help to elucidate the aetiology and treatment of RA and point us toward the next steps.

Cite this article: Bone Joint Res 2022;11(7):426–438.

Effect of bisphosphonates on selected markers of bone turnover in patients after total knee arthroplasty

PURPOSE

Osteoporosis is a problem for many patients after total knee arthroplasty (TKA). The aseptic loosening of the prosthesis is also a significant problem. Therefore, in these patients, bisphosphonates (BPs) are used that, by influencing the level of bone turnover markers, reduce the risk of osteoporotic fractures and aseptic revisions in TKA. The purpose of the study was to assess whether the Pamifos® present in bone cement has any effect on the level of selected bone turnover markers and cytokines in patients after total knee arthroplasty.

METHODS

The study group consisted of 30 women with degenerative changes of the knee joint, whose total knee prosthesis was stabilized with cement enriched with Pamifos®. The control group consisted of 30 women treated for degenerative changes of the knee joint without the use of bisphosphonate-enriched cement for prosthetic stabilization.

RESULTS

In the study group, we found a decrease in tumour necrosis factor (TNF-α) levels 12 weeks after surgery, whereas the control group experienced an almost twofold increase in TNF-α level. The concentration of OPG, a natural RANKL antagonist, was highest in patients of the study group six weeks after surgery and was four times higher compared to the control group. Statistically significant differences were found in the RANKL level (P < 0.05). In the control group, there was a continuous increase in RANKL concentration from the first to the 12th week after surgery. The highest level of RANKL in patients of the study group was found six weeks after the surgery, and 12 weeks after knee arthroplasty, it was significantly lower. It was found that the concentration of osteocalcin (OC) in the study group was the lowest three weeks after the surgery, then it increased and remained at a similar level after 12 weeks. The concentrations of selected cytokines (IL-1β, IL-2, IL-6, IL-10, IL-17AF) also showed statistically significant differences.

CONCLUSIONS

The BP-stimulated increase in the level of OPG and the decrease in the level of RANKL, as well as the impact on the level of the analyzed interleukins in the bone microenvironment, may be an important element of the mechanisms limiting bone resorption. Therefore, the use of BP-enriched cement implants appears to be justified.

Connection between Mesenchymal Stem Cells Therapy and Osteoclasts in Osteoarthritis

The use of mesenchymal stem cells constitutes a promising therapeutic approach, as it has shown beneficial effects in different pathologies. Numerous in vitro, pre-clinical, and, to a lesser extent, clinical trials have been published for osteoarthritis. Osteoarthritis is a type of arthritis that affects diarthritic joints in which the most common and studied effect is cartilage degradation. Nowadays, it is known that osteoarthritis is a disease with a very powerful inflammatory component that affects the subchondral bone and the rest of the tissues that make up the joint. This inflammatory component may induce the differentiation of osteoclasts, the bone-resorbing cells. Subchondral bone degradation has been suggested as a key process in the pathogenesis of osteoarthritis. However, very few published studies directly focus on the activity of mesenchymal stem cells on osteoclasts, contrary to what happens with other cell types of the joint, such as chondrocytes, synoviocytes, and osteoblasts. In this review, we try to gather the published bibliography in relation to the effects of mesenchymal stem cells on osteoclastogenesis. Although we find promising results, we point out the need for further studies that can support mesenchymal stem cells as a therapeutic tool for osteoclasts and their consequences on the osteoarthritic joint.

Pharmacogenomics of Anti-TNF Treatment Response Marks a New Era of Tailored Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is the most commonly occurring chronic inflammatory arthritis, the exact mechanism of which is not fully understood. Tumor Necrosis Factor (TNF)-targeting drugs has been shown to exert high effectiveness for RA, which indicates the key importance of this cytokine in this disease. Nevertheless, the response to TNF inhibitors varies, and approximately one third of RA patients are non-responders, which is explained by the influence of genetic factors. Knowledge in the field of pharmacogenomics of anti-TNF drugs is growing, but has not been applied in the clinical practice so far. Different genome-wide association studies identified a few single nucleotide polymorphisms associated with anti-TNF treatment response, which largely map genes involved in T cell function. Studies of the gene expression profile of RA patients have also indicated specific gene signatures that may be useful to develop novel prognostic tools. In this article, we discuss the significance of TNF in RA and present the current knowledge in pharmacogenomics related to anti-TNF treatment response.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

The role of NK cells in rheumatoid arthritis

OBJECTIVE

Natural killer (NK) cells are part of the innate immune system which not only provides a primary response to pathogenic conditions but can also play an important regulatory role in immune responses. Furthermore, these cells can influence immune responses by affecting other involved cells. Human NK cells can be classified as CD56^dim and CD56^bright; the former demonstrates mostly cytotoxic effects, while the latter comprises mostly tolerant or regulatory NK cells. These cells participate in the immunopathogenesis of rheumatoid arthritis (RA) and their role remains still unclear.

METHODS

We searched PubMed/MEDLINE and Scopus databases to review and analyze relevant literature on the impact of NK cells in the pathogenesis of RA.

RESULTS

Although the percentage of NK cells increases in peripheral blood of RA patients compared to healthy individuals, the cytotoxic function of these cells is impaired. It is demonstrated by reduced "perforin⁺ NK cells" and decreased per-cell lytic function. These cytotoxic NK cells may control the pathogenic bone absorptive function of osteoclasts by directly targeting these cells.

CONCLUSION

Collectively, the evidence collected in the current review emphasizes the possible protective role of CD56^dim NK cells in the pathogenesis of RA.

Blockade of NF-κB Translocation and of RANKL/RANK Interaction Decreases the Frequency of Th2 and Th17 Cells Capable of IL-4 and IL-17 Production, Respectively, in a Mouse Model of Allergic Asthma

The main purpose of this study was to investigate whether the blockade of the interaction between the receptor activator of nuclear factor-κB (NF-ĸB) ligand (RANKL) and its receptor RANK as well as the blockade of NF-κB inhibitor kinase (IKK) and of NF-κB translocation have the potential to suppress the pathogenesis of allergic asthma by inhibition and/or enhancement of the production by CD4⁺ and CD8⁺ T cells of important cytokines promoting (i.e., IL-4 and IL-17) and/or inhibiting (i.e., IL-10 and TGF-β), respectively, the development of allergic asthma. Studies using ovalbumin(OVA)-immunized mice have demonstrated that all the tested therapeutic strategies prevented the OVA-induced increase in the absolute number of IL-4- and IL-17-producing CD4⁺ T cells (i.e., Th2 and Th17 cells, respectively) indirectly, i.e., through the inhibition of the clonal expansion of these cells in the mediastinal lymph nodes. Additionally, the blockade of NF-κB translocation and RANKL/RANK interaction, but not IKK, prevented the OVA-induced increase in the percentage of IL-4-, IL-10- and IL-17-producing CD4⁺ T cells. These latter results strongly suggest that both therapeutic strategies can directly decrease IL-4 and IL-17 production by Th2 and Th17 cells, respectively. This action may constitute an important mechanism underlying the anti-asthmatic effect induced by the blockade of NF-κB translocation and of RANKL/RANK interaction. Thus, in this context, both these therapeutic strategies seem to have an advantage over the blockade of IKK. None of the tested therapeutic strategies increased both the absolute number and frequency of IL-10- and TGF-β-producing Treg cells, and hence they lacked the potential to inhibit the development of the disease via this mechanism.

TNF-α modulation via Etanercept restores bone regeneration of atrophic non-unions

Treatment of atrophic non-unions, especially in long bones is a challenging problem in orthopedic surgery due to the high revision and failure rate after surgical intervention. Subsequently, there is a certain need for a supportive treatment option besides surgical treatment. In our previous study we gained first insights into the dynamic processes of atrophic non-union formation and observed a prolonged inflammatory reaction with upregulated TNF-α levels and bone resorption. In this study we aimed to improve bone regeneration of atrophic non-unions via TNF-α modulation in a previously established murine femoral segmental defect model. Animals that developed atrophic non-unions of the femur after 5 and 10 weeks were treated systemically for 10 and 5 weeks with Etanercept, a soluble TNF-α antibody. μCT scans and histology revealed bony bridging of the fracture gap in the treatment group, while bone formation in control animals without treatment was not evident. Moreover, osteoclasts were markedly decreased via modulation of the RANKL/OPG axis due to Etanercept treatment. Additionally, immunomodulatory effects via Etanercept could be observed as further inflammatory agents, such as TGF-β, IL6, MMP9 and 13 were decreased in both treatment groups. This study is the first showing beneficial effects of Etanercept treatment on bone regeneration of atrophic non-union formation. Moreover, the results of this study provide a new and promising therapeutic option which might reduce the failure rate of revision surgeries of atrophic non-unions.

Osteoclasts and their circulating precursors in rheumatoid arthritis: Relationships with disease activity and bone erosions

Patients with rheumatoid arthritis (RA) have very different outcomes, particularly with regard to bone erosions. Since osteoclasts are responsible for bone destruction adjacent to rheumatoid synovium, profiling osteoclasts from circulating precursors in RA could help identify patients at risk for bone destruction. In this study, we sought to determine whether the functional characteristics of osteoclasts generated from their blood precursors were modified by RA activity or were intrinsic to osteoclasts and associated with the RA phenotype (erosive or not).

Osteoclasts were generated in vitro from peripheral blood mononuclear cells (PBMCs) of subjects with RA (n = 140), as well as sex- and age-matched healthy controls (n = 101). Osteoclastic parameters were analyzed at baseline and during the follow-up for up to 4 years, with regular assessment of RA activity, bone erosions, and bone mineral density (BMD). As a validation cohort, we examined RA patients from the Early Undifferentiated PolyArthritis (EUPA) study (n = 163).

The proportion of CD14⁺ PBMC was higher in RA than in control subjects, but inversely correlated with the 28-joint disease activity score (DAS28). Also surprisingly, in osteoclast cultures from PBMCs, active RA was associated with lower osteoclastogenic capacity, while in vitro bone resorption per osteoclast and resistance to apoptosis were similar in both active and quiescent RA. In a small subgroup analysis, osteoclasts from subjects with recent RA that had progressed at four years to an erosive RA exhibited at baseline greater resistance to apoptosis than those from patients remaining non-erosive.

Our findings establish that when RA is active, circulating monocytes have a reduced potential to generate osteoclasts from PBMCs in vitro. In addition, osteoclasts associated with erosive disease had resistance to apoptosis from the start of RA.

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Osteoclasts are derived in vitro from circulating monocytes in rheumatoid arthritis.

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Blood CD14⁺ monocytes (%) are higher but inversely correlated with disease activity.

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Active rheumatoid arthritis is associated with reduced osteoclast formation in vitro.

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Inflammation alters the ability to generate osteoclasts from circulating monocytes.

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Osteoclast resistance to apoptosis is stable and associated with long-term erosions.

Bone mineral density and trabecular bone score in treatment-naïve patients with non-cirrhotic hepatitis C virus infection

We studied 112 treatment-naïve chronic HCV patients without cirrhosis, and we found that, especially HCV+ postmenopausal women, they had lower TBS and BMD values than healthy controls. This suggests that HCV infection is an independent risk factor for osteoporosis, and therefore, screening for osteoporosis in postmenopausal HCV+ women should be considered.

PURPOSE

To know whether patients in earlier stages of chronic HCV infection are at increased risk of developing low bone mass and bone microarchitectural changes and whether there is an association between bone metabolism and the severity of the liver disease.

METHODS

We studied 112 treatment-naïve chronic HCV outpatients and 233 healthy age- and sex-matched controls. Bone mineral density (BMD) and trabecular bone score (TBS) were assessed by DXA. Serum 25(OH)D, PTH, P1NP, and CTX were determined by electrochemiluminescence.

RESULTS

TBS values were significantly lower in HCV patients than in controls, both considering the population as a whole (1.337 ± 0.119 vs. 1.377 ± 0.122; p < 0.005) and after stratifying by sex (1.347 ± 0.12 vs. 1.381 ± 0.13 in men and 1.314 ± 0.10 vs. 1.369 ± 0.11 in women). The difference remained significant (p < 0.0001 in all cases) after adjusting for confounders. BMD was also lower in HCV patients (lumbar spine, 0.935 ± 0.151 vs. 0.991 ± 0.143 g/cm², p 0.001; femoral neck, 0.764 ± 0.123 vs. 0.818 ± 0.123 g/cm², p 0.0001; total hip, 0.926 ± 0.148 vs. 0.963 ± 0.132 g/cm², p 0.02), although, after adjustment, differences kept a clear trend towards statistical significance in women at the lumbar spine and femoral neck. However, in men and at the total hip in women, differences were no longer significant. We find no relationship between these parameters and the severity of the disease. No significant difference was observed in PTH and 25OHD status after adjustment. Finally, serum P1NP, but not CTX, was higher in HCV patients.

CONCLUSIONS

Our findings suggest that HCV infection is an independent risk factor for osteoporosis, especially among postmenopausal women. Therefore, the appropriateness of screening for osteoporosis in postmenopausal HCV-positive women should be considered.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.

Inflammatory processes and elevated osteoclast activity chaperon atrophic non-union establishment in a murine model

Background

Delayed bone healing, especially in long bones poses one of the biggest problems in orthopeadic and reconstructive surgery and causes tremendous costs every year. There is a need for exploring the causes in order to find an adequate therapy. Earlier investigations of human scaphoid non-union revealed an elevated osteoclast activity, accompanied by upregulated levels of TGF-beta and RANKL. Interestingly, scaphoid non-union seemed to be well vascularized.

Methods

In the current study, we used a murine femur-defect model to study atrophic non unions over a time-course of 10 weeks. Different time points were chosen, to gather insights into the dynamic processes of non-union establishment.

Results

Histological analyses as well as western blots and qRT-PCR indicated enhanced osteoclast activity throughout the observation period, paralleled by elevated levels of TGF-beta, TNF-alpha, MMP9, MMP13 and RANKL, especially during the early phases of non-union establishment. Interestingly, elevated levels of these mediators decreased markedly over a period of 10 weeks, as inflammatory reaction during non-union establishment seemed to wear out. To our surprise, osteoblastogenesis seemed to be unaffected during early stages of non-union establishment.

Conclusion

Taken together, we gained first insights into the establishment process of atrophic non unions, in which inflammatory processes accompanied by highly elevated osteoclast activity seem to play a leading role.

iNOS dependent and independent phases of lymph node expansion in mice with TNF-induced inflammatory-erosive arthritis

Introduction

A pivotal effect of lymphatic vessel (LV) function in joint homeostasis was identified in the tumor necrosis factor-transgenic (TNF-Tg) mouse model of rheumatoid arthritis (RA). Specifically, loss of LV contractions is associated with progressive synovitis and erosions. Furthermore, draining lymph node expansion is a biomarker of arthritic progression, and both macrophages and lymphatic endothelial cells express inducible nitric oxide synthase (iNOS), which disrupts LV contraction and transport of immune cells to the draining lymph nodes. Therefore, to directly assess these relationships, we tested the hypothesis that TNF-Tg mice with global genetic ablation of iNOS (iNOS^−/−) will show delayed draining lymph node expansion, maintained LV contractions, and decreased synovitis and erosions.

Method

iNOS^−/−× TNF-Tg female and male mice, and control littermates (iNOS^−/−, TNF-Tg, and WT), were examined with (1) ultrasound to determine popliteal lymph node (PLN) volume and (2) near-infrared imaging (NIR) to assess popliteal LV contraction frequency, and differences between genotypes were assessed at 3, 4, 5, and 6 months of age. Knees and PLN were harvested at 4 months in females and 6 months in males, to assess synovitis, bone erosions, and cellular accumulation in PLN sinuses via histology.

Results

Initially, an increase in PLN volume was observed for both female and male iNOS^−/−× TNF-Tg and TNF-Tg compared to their WT and iNOS^−/− counterparts at 2 and 3 months, respectively. Subsequently, TNF-Tg PLNs continue to increase in volume, while iNOS^−/−× TNF-Tg did not increase in volume from the initial timepoints. WT and iNOS^−/− PLN volume was unchanged throughout the experiment. LV contraction frequency was increased at 4 months in females and 5 months in males, in the iNOS^−/−× TNF-Tg mice compared to the TNF-Tg. Synovitis and erosions were moderately reduced in iNOS^−/−× TNF-Tg versus TNF-Tg knees in females, while no differences in knee pathology were observed in males.

Conclusions

Genetic iNOS ablation maintains draining lymph node volume and LV function during TNF-induced inflammatory arthritis and is associated with moderately decreased joint inflammation and damage.

Vitamin D Inhibition of TRPV5 Expression During Osteoclast Differentiation

BACKGROUND

Vitamin D is an important steroid that can regulate bone metabolism including osteoclast (OC) differentiation. Transient receptor potential cation channel subfamily V member 5 (TRPV5), is a calcium channel protein involved in OC differentiation. However, the impact of vitamin D on TRPV5 expression during OC differentiation is not clear.

OBJECTIVES

To determine if 1,25-dihydroxyvitamin D3 (1,25(OH)₂D₃) regulates the expression of TRPV5 during OC differentiation.

METHODS

Bone marrow mononuclear macrophage (BMMs) were induced to differentiate into OC with or without treatment with 10 nM 1,25(OH)₂D₃. The expression levels of vitamin D receptor (VDR) and TRPV5 were examined. The expression of several OC markers, including tartrate resistant acid phosphatase (TRAP), carbonic anhydrase II (Ca II), cathepsin K (CTSK), and vacuolar-type H⁺-ATPase (V-ATPase) were also detected.

RESULTS

We found that the VDR was expressed in murine bone marrow-derived macrophages at the early stage of OC differentiation. TRPV5 expression was increased during OC differentiation, which was down-regulated by 1,25(OH)₂D₃ after a prolonged exposure. The 1,25(OH)₂D₃ and TRPV5 inhibitors inhibited OC differentiation.

CONCLUSIONS

1,25(OH)₂D₃ can inhibit TRPV5 expression as well as TRPV5 inhibitors during OC differentiation. This suggests that 1,25(OH)₂D₃ may suppress OC differentiation by inhibiting TRPV5 expression.

TGFβ-induced degradation of TRAF3 in mesenchymal progenitor cells causes age-related osteoporosis

Inflammaging induces osteoporosis by promoting bone destruction and inhibiting bone formation. TRAF3 limits bone destruction by inhibiting RANKL-induced NF-κB signaling in osteoclast precursors. However, the role of TRAF3 in mesenchymal progenitor cells (MPCs) is unknown. Mice with TRAF3 deleted in MPCs develop early onset osteoporosis due to reduced bone formation and enhanced bone destruction. In young mice TRAF3 prevents β-catenin degradation in MPCs and maintains osteoblast formation. However, TRAF3 protein levels decrease in murine and human bone samples during aging when TGFβ1 is released from resorbing bone. TGFβ1 induces degradation of TRAF3 in murine MPCs and inhibits osteoblast formation through GSK-3β-mediated degradation of β-catenin. Thus, TRAF3 positively regulates MPC differentiation into osteoblasts. TRAF3 deletion in MPCs activated NF-κB RelA and RelB to promote RANKL expression and enhance bone destruction. We conclude that pharmacologic stabilization of TRAF3 during aging could treat/prevent age-related osteoporosis by inhibiting bone destruction and promoting bone formation.

Imaging the Bone-Immune Cell Interaction in Bone Destruction

Bone is a highly dynamic organ that is continuously being remodeled by the reciprocal interactions between bone and immune cells. We have originally established an advanced imaging system for visualizing the in vivo behavior of osteoclasts and their precursors in the bone marrow cavity using two-photon microscopy. Using this system, we found that the blood-enriched lipid mediator, sphingosine-1-phosphate, controlled the migratory behavior of osteoclast precursors. We also developed pH-sensing chemical fluorescent probes to detect localized acidification by bone-resorbing osteoclasts on the bone surface in vivo, and identified two distinct functional states of differentiated osteoclasts, "bone-resorptive" and "non-resorptive." Here, we summarize our studies on the dynamics and functions of bone and immune cells within the bone marrow. We further discuss how our intravital imaging techniques can be applied to evaluate the mechanisms of action of biological agents in inflammatory bone destruction. Our intravital imaging techniques would be beneficial for studying the cellular dynamics in arthritic inflammation and bone destruction in vivo and would also be useful for evaluating novel therapies in animal models of bone-destroying diseases.

Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli

Bone homeostasis is preserved by the balance of maintaining between the activity of osteogenesis and osteoclastogenesis. However, investigations for the osteoclastogenesis were hampered by considerable difficulties associated with isolating and culturing osteoclast in vivo. As the alternative, stimuli‐induced osteoclasts formation from RAW264.7 cells (RAW‐OCs) have gain its importance for extensively osteoclastogenic study of bone diseases, such as rheumatoid arthritis, osteoporosis, osteolysis and periodontitis. However, considering the RAW‐OCs have not yet been well‐characterized and RAW264.7 cells are polymorphic because of a diverse phenotype of the individual cells comprising this cell linage, and different fate associated with various stimuli contributions. Thus, in present study, we provide an overview for current knowledge of the phenotype of RAW264.7 cells, as well as the current understanding of the complicated interactions between various stimuli and RAW‐OCs in the light of the recent progress.

New Insights for RANKL as a Proinflammatory Modulator in Modeled Inflammatory Arthritis

Receptor activator of nuclear factor-κB ligand (RANKL), a member of the Tumor Necrosis Factor (TNF) superfamily, constitutes the master regulator of osteoclast formation and bone resorption, whereas its involvement in inflammatory diseases remains unclear. Here, we used the human TNF transgenic mouse model of erosive inflammatory arthritis to determine if the progression of inflammation is affected by either genetic inactivation or overexpression of RANKL in transgenic mouse models. TNF-mediated inflammatory arthritis was significantly attenuated in the absence of functional RANKL. Notably, TNF overexpression could not compensate for RANKL-mediated osteopetrosis, but promoted osteoclastogenesis between the pannus and bone interface, suggesting RANKL-independent mechanisms of osteoclastogenesis in inflamed joints. On the other hand, simultaneous overexpression of RANKL and TNF in double transgenic mice accelerated disease onset and led to severe arthritis characterized by significantly elevated clinical and histological scores as shown by aggressive pannus formation, extended bone resorption, and massive accumulation of inflammatory cells, mainly of myeloid origin. RANKL and TNF cooperated not only in local bone loss identified in the inflamed calcaneous bone, but also systemically in distal femurs as shown by microCT analysis. Proteomic analysis in inflamed ankles from double transgenic mice overexpressing human TNF and RANKL showed an abundance of proteins involved in osteoclastogenesis, pro-inflammatory processes, gene expression regulation, and cell proliferation, while proteins participating in basic metabolic processes were downregulated compared to TNF and RANKL single transgenic mice. Collectively, these results suggest that RANKL modulates modeled inflammatory arthritis not only as a mediator of osteoclastogenesis and bone resorption but also as a disease modifier affecting inflammation and immune activation.

C-X-C Motif Chemokine 12 Enhances Lipopolysaccharide-Induced Osteoclastogenesis and Bone Resorption In Vivo

C-X-C motif chemokine 12 (CXCL12) belongs to the family of CXC chemokines. Lipopolysaccharide (LPS) induces inflammation-induced osteoclastogenesis and bone resorption, and in recent years, stimulatory effects of CXCL12 on bone resorption have also been reported. In the present study, we investigated the effects of CXCL12 on LPS-induced osteoclastogenesis and bone resorption. LPS was administered with or without CXCL12 onto mouse calvariae by daily subcutaneous injection. Numbers of osteoclasts and bone resorption were significantly elevated in mice co-administered LPS and CXCL12 compared with mice administered LPS alone. Moreover, receptor activator of NF-kB ligand (RANKL) and tumor necrosis factor-α (TNF-α) mRNA levels were higher in mice co-administered LPS and CXCL12 compared with mice administered LPS alone. These in vitro results confirmed a direct stimulatory effect of CXCL12 on RANKL- and TNF-α-induced osteoclastogenesis. Furthermore, TNF-α and RANKL mRNA levels were elevated in macrophages and osteoblasts, respectively, co-treated in vitro with CXCL12 and LPS, in comparison with cells treated with LPS alone. Our results suggest that CXCL12 enhances LPS-induced osteoclastogenesis and bone resorption in vivo through a combination of increasing LPS-induced TNF-α production by macrophages, increasing RANKL production by osteoblasts, and direct enhancement of osteoclastogenesis.

In vivo visualisation of different modes of action of biological DMARDs inhibiting osteoclastic bone resorption

OBJECTIVES

Osteoclasts play critical roles in inflammatory bone destruction. Precursor cell migration, cell differentiation, and functional cell activation are all in play. Biological disease-modifying antirheumatic drugs (DMARDs) have been shown to significantly inhibit both bone erosion as well as synovitis, although how such agents reduce osteoclastic bone destructionin vivo has not been fully explained. Here, we used an intravital time-lapse imaging technique to directly visualise mature osteoclasts and their precursors, and explored how different biological DMARDs acted in vivo.

METHODS

Lipopolysaccharide (LPS) was injected into the calvarial periosteum of fluorescent reporter mice to induce inflammatory bone destruction. Time-lapse imaging was performed via intravital multiphoton microscopy 5 days after LPS injection. Biological DMARDs, including monoclonal antibodies (mAbs) against the interleukin (IL) 6 receptor (IL-6R) and tumour necrosis factor α (TNFα), or cytotoxic T-lymphocyte-associated protein 4 (CTLA4)-Ig, were intraperitoneally administered at the time of LPS injection. We determined CD80/86 expression levels in mature osteoclasts and their precursors by flow cytometry, quantitative PCR and immunohistochemistry.

RESULTS

Of the biologicals tested, anti-IL-6R and anti-TNFα mAbs affected mature osteoclasts and switched bone-resorbing osteoclasts to non-resorbing cells. CTLA4-Ig had no action on mature osteoclasts but mobilised osteoclast precursors, eliminating their firm attachment to bone surfaces. In agreement with these results, CD80/86 (the target molecules of CTLA4-Ig) were prominently expressed only in osteoclast precursor cells, being suppressed during osteoclast maturation.

CONCLUSIONS

Intravital imaging revealed that various biological DMARDs acted at specific therapeutic time points during osteoclastic bone destruction, with different efficacies. These results enable us to grasp the real modes of action of drugs, optimising the usage of drug regimens.

Identification of prolargin expression in articular cartilage and its significance in rheumatoid arthritis pathology

Qualitative 2D gel-electrophoresis (2DE) protein profiling for osteoarthritis (OA) and rheumatoid arthritis (RA) is challenging because of selective protein loss due to discrepancies in protein precipitation methodologies. Thus, we aimed at developing qualitative protein representation from OA/RA articular cartilage without protein precipitation towards identification of clinically relevant proteins. Chondroitinase digested human articular cartilages from RA patients were subjected to protein extraction using guanidinium hydrochloride (GuHCl) or 8 M urea with 10 or 2% ASB-14-4 or 0.45 M urea with 2% ASB-14-4 with cetylpyridinium chloride (CPC). The GuHCl extract is further protein precipitated with acetone or ammonium acetate-methanol or centricon-fractionated using 100 kDa cut filters and protein precipitated using ethanol. Processed extracts were subjected to 2DE to identify protein profiles. Poor proteins representations were observed in 2D gels with protein precipitated samples compared to qualitative protein representations seen in 2D gels of 0.45 M urea and 2%ASB-14-4 extraction procedure reproducibly. The strategy circumventing protein precipitation generated qualitative 2D gels. RA vs OA gel comparison showed elevated prolargin levels in RA with biglycan levels remaining unaltered. Up regulation of prolargin in RA suggests the likelihood of an adaptive mechanism to control the increased osteoclastogenesis in RA and may have therapeutic value in controlling the disease.

TNFα blockade mediates bone protection in antigen-induced arthritis by reducing osteoclast precursor supply

Bone protective effects of TNFα inhibition in rheumatoid arthritis are thought to be mediated by inhibiting synovial osteoclast differentiation and activity. However, it has not been addressed, if TNFα inhibitors alter the pool of peripheral osteoclast precursor cells (OPCs). Here, we blocked TNFα function in C57BL/6 mice with antigen induced arthritis (AIA) using the soluble TNFα receptor etanercept. Synovial bone lesions and osteoclasts were markedly reduced upon Etanercept in the early chronic phase of AIA. Unexpectedly this was not associated with a reduced recruitment of circulating OPCs to the arthritic joint nor to reduced synovial inflammation. In contrast we found that OPC numbers in bone marrow and blood were significantly reduced. Overall our study suggests that arrest of osteoclast mediated bone lesions upon inhibition of TNFα is, at least initially, based on reduced OPC availability in the periphery, and not on OPC recruitment or local anti-inflammatory effects in the arthritic joint.

Age-dependent alterations in osteoblast and osteoclast activity in human cancellous bone

It is assumed that the activity of osteoblasts and osteoclasts is decreased in bone tissue of aged individuals. However, detailed investigation of the molecular signature of human bone from young compared to aged individuals confirming this assumption is lacking. In this study, quantitative expression analysis of genes related to osteogenesis and osteoclastogenesis of human cancellous bone derived from the distal radius of young and aged individuals was performed. Furthermore, we additionally performed immunohistochemical stainings. The young group included 24 individuals with an average age of 23.2 years, which was compared to cancellous bone derived from 11 body donators with an average age of 81.0 years. In cancellous bone of young individuals, the osteogenesis-related genes RUNX-2, OSTERIX, OSTEOPONTIN and OSTEOCALCIN were significantly up-regulated compared to aged individuals. In addition, RANKL and NFATc1, both markers for osteoclastogenesis, were significantly induced in cancellous bone of young individuals, as well as the WNT gene family member WNT5a and the matrix metalloproteinases MMP-9. However, quantitative RT-PCR analysis of BMP-2, ALP, FGF-2, CYCLIN-D1, MMP-13, RANK, OSTEOPROTEGERIN and TGFb1 revealed no significant difference. Furthermore, Tartrate-resistant acid phosphatase (TRAP) staining was performed which indicated an increased osteoclast activity in cancellous bone of young individuals. In addition, pentachrome stainings revealed significantly less mineralized bone matrix, more osteoid and an increased bone density in young individuals. In summary, markers related to osteogenesis as well as osteoclastogenesis were significantly decreased in the aged individuals. Thus, the present data extends the knowledge about reduced bone regeneration and healing capacity observed in aged individuals.

Osteoimmunology: The Conceptual Framework Unifying the Immune and Skeletal Systems

The immune and skeletal systems share a variety of molecules, including cytokines, chemokines, hormones, receptors, and transcription factors. Bone cells interact with immune cells under physiological and pathological conditions. Osteoimmunology was created as a new interdisciplinary field in large part to highlight the shared molecules and reciprocal interactions between the two systems in both heath and disease. Receptor activator of NF-κB ligand (RANKL) plays an essential role not only in the development of immune organs and bones, but also in autoimmune diseases affecting bone, thus effectively comprising the molecule that links the two systems. Here we review the function, gene regulation, and signal transduction of osteoimmune molecules, including RANKL, in the context of osteoclastogenesis as well as multiple other regulatory functions. Osteoimmunology has become indispensable for understanding the pathogenesis of a number of diseases such as rheumatoid arthritis (RA). We review the various osteoimmune pathologies, including the bone destruction in RA, in which pathogenic helper T cell subsets [such as IL-17-expressing helper T (Th17) cells] induce bone erosion through aberrant RANKL expression. We also focus on cellular interactions and the identification of the communication factors in the bone marrow, discussing the contribution of bone cells to the maintenance and regulation of hematopoietic stem and progenitors cells. Thus the time has come for a basic reappraisal of the framework for understanding both the immune and bone systems. The concept of a unified osteoimmune system will be absolutely indispensable for basic and translational approaches to diseases related to bone and/or the immune system.

p-Coumaric acid, a dietary polyphenol ameliorates inflammation and curtails cartilage and bone erosion in the rheumatoid arthritis rat model

This study was designed to explore the underlying mechanism of p-coumaric acid (CA), a dietary polyphenol in adjuvant-induced arthritis (AIA) rat model with reference to synovitis and osteoclastogenesis. Celecoxib (COX-2 selective inhibitor) (5 mg/kg b.wt) was used as a reference drug. CA remarkably suppressed the paw edema, body weight loss and inflammatory cytokine and chemokine levels (TNF-α, IL-1β, IL-6, and MCP-1) in serum and ankle joint of arthritic rats. Consistently, CA reduced the expression of osteoclastogenic factors (RANKL and TRAP), pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-17), and inflammatory enzymes (iNOS and COX-2) in arthritic rats. However, OPG expression was found elevated. Besides, the abundance of transcription factors (NF-κB-p65, and p-NF-κB-p65, NFATc-1, and c-Fos) and MAP kinases (JNK, p-JNK, and ERK1/2) expression was alleviated in CA administered arthritic rats. In addition, CA truncated osteoclastogenesis by regulating the RANKL/OPG imbalance in arthritic rats and suppressing the RANKL-induced NFATc-1 and c-Fos expression in vitro. Radiological (CT and DEXA scan) and histological assessments authenticated that CA inhibited TRAP, bone destruction and cartilage degradation in association with enhanced bone mineral density. Taken together, our findings suggest that CA demonstrated promising anti-arthritic effect and could prove useful as an alternative drug in RA therapeutics. © 2017 BioFactors, 43(5):698-717, 2017.

RANK-Independent Osteoclast Formation and Bone Erosion in Inflammatory Arthritis

OBJECTIVE

Proinflammatory molecules promote osteoclast-mediated bone erosion by up-regulating local RANKL production. However, recent evidence suggests that combinations of cytokines, such as tumor necrosis factor (TNF) plus interleukin-6 (IL-6), induce RANKL-independent osteoclastogenesis. The purpose of this study was to better understand TNF/IL-6-induced osteoclast formation and to determine whether RANK is absolutely required for osteoclastogenesis and bone erosion in murine inflammatory arthritis.

METHODS

Myeloid precursors from wild-type (WT) mice or mice with either germline or conditional deletion of Rank, Nfatc1, Dap12, or Fcrg were treated with either RANKL or TNF plus IL-6. Osteoprotegerin, anti-IL-6 receptor (anti-IL-6R), and hydroxyurea were used to block RANKL, the IL-6R, and cell proliferation, respectively. Clinical scoring, histologic assessment, micro-computed tomography, and quantitative polymerase chain reaction (qPCR) were used to evaluate K/BxN serum-transfer arthritis in WT and RANK-deleted mice. Loss of Rank was verified by qPCR and by osteoclast cultures.

RESULTS

TNF/IL-6 generated osteoclasts in vitro that resorbed mineralized tissue through a pathway dependent on IL-6R, NFATc1, DNAX-activation protein 12, and cell proliferation, but independent of RANKL or RANK. Bone erosion and osteoclast formation were reduced, but not absent, in arthritic mice with inducible deficiency of RANK. TNF/IL-6, but not RANKL, induced osteoclast formation in bone marrow and synovial cultures from animals deficient in Rank. Multiple IL-6 family members (IL-6, leukemia inhibitory factor, oncostatin M) were up-regulated in the synovium of arthritic mice.

CONCLUSION

The persistence of bone erosion and synovial osteoclasts in Rank-deficient mice, and the ability of TNF/IL-6 to induce osteoclastogenesis, suggest that more than one cytokine pathway exists to generate these bone-resorbing cells in inflamed joints.

Targeting Notch-Activated M1 Macrophages Attenuates Joint Tissue Damage in a Mouse Model of Inflammatory Arthritis

Expression levels of Notch signaling molecules are increased in synovium from patients with rheumatoid arthritis (RA). However, it is not known which cell type(s) in RA synovium have Notch activation or if they play a pathogenetic role in RA. Here, we used Hes1-GFP/TNF-transgenic (TNF-Tg) mice to investigate the role of cells with active Notch signaling (GFP+) in RA. The number of GFP+ cells was significantly increased in synovium in Hes1-GFP/TNF-Tg mice and about 60% of them were F4/80+ macrophages expressing the inflammatory macrophage (M1) marker. TNF-Tg mice transplanted with Hes1-GFP/TNF-Tg bone marrow (BM) had significantly more GFP+ cells in their synovium than in BM. Intraarticular injection of Hes1-GFP/TNF-Tg or Hes1-GFP+ BM macrophages into WT and TNF-Tg mice showed the highest synovial GFP+ cells in the TNF-Tg mice that received Hes1-GFP/TNF-Tg cells. Thapsigargin (THAP), a Notch inhibitor, decreased TNF-induced M1 and increased M2 numbers and reduced joint lesion, synovial M1s, and GFP+ cells in Hes1-GFP/TNF-Tg mice. THAP did not affect M1s from mice carrying a constitutively active Notch1. Thus, the main cells with activated Notch signaling in the inflamed synovium of TNF-Tg mice are M1s derived from BM and targeting them may represent a new therapeutic approach for patients with inflammatory arthritis. © 2017 American Society for Bone and Mineral Research.

The role of stromal cells in inflammatory bone loss

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation, local and systemic bone loss and a lack of compensatory bone repair. Fibroblast-like synoviocytes (FLS) are the most abundant cells of the stroma and a key population in autoimmune diseases such as RA. An increasing body of evidence suggests that these cells play not only an important role in chronic inflammation and synovial hyperplasia, but also impact bone remodelling. Under inflammatory conditions FLS release inflammatory cytokines, regulate bone destruction and formation and communicate with immune cells to control bone homeostasis. Other stromal cells, such as osteoblasts and terminally differentiated osteoblasts, termed osteocytes, are also involved in the regulation of bone homeostasis and are dysregulated during inflammation. This review highlights our current understanding of how stromal cells influence the balance between bone formation and bone destruction. Increasing our understanding of these processes is critical to enable the development of novel therapeutic strategies with which to treat bone loss in RA.

TNF-α promotes osteoclastogenesis through JNK signaling-dependent induction of Semaphorin3D expression in estrogen-deficiency induced osteoporosis

Tumor necrosis factor α (TNF-α)-induced osteoclast formation have been demonstrated to play an important role in the pathogenesis of estrogen deficiency-mediated bone loss, but the exact mechanisms by which TNF-α enhanced osteoclast differentiation were not fully elucidated. The class III semaphorins members were critical to regulate bone homeostasis. Here, we identified a novel mechanism whereby TNF-α increasing Semaphorin3D expression contributes to estrogen deficiency-induced osteoporosis. In this study, we found that Semaphorin3D expression was upregulated by TNF-α during the process of RANKL-induced osteoclast differentiation. Inhibition of Semaphorin3D in pre-osteoclasts could attenuate the stimulatory effects of TNF-α on osteoclast proliferation and differentiation. Mechanistically, blocking of the Jun N-terminal kinase (JNK) signaling markedly rescued TNF-α-induced Semaphorin3D expression, suggesting that JNK signaling was involved in the regulation of Semaphorin3D expression by TNF-α. In addition, silencing of Semaphorin3D in vivo could alleviate estrogen deficiency-induced osteoporosis. Our results revealed a novel function for Semaphorin3D and suggested that increased Semaphorin3D may contribute to enhanced bone loss by increased TNF-α in estrogen deficiency-induced osteoporosis. Thus, Semaphorin3D may provide a potential therapeutic target for the treatment of estrogen-deficiency induced osteoporosis.

Inflammatory Cell Migration in Rheumatoid Arthritis: A Comprehensive Review

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

Soluble RANKL Cleaved from Activated Lymphocytes by TNF-α-Converting Enzyme Contributes to Osteoclastogenesis in Periodontitis

Host immune responses play a key role in promoting bone resorption in periodontitis via receptor activator of NF-κB ligand (RANKL)-dependent osteoclastogenesis. Both membrane-bound RANKL (mRANKL) expressed on lymphocytes and soluble RANKL (sRANKL) are found in periodontal lesions. However, the underlying mechanism and cellular source of sRANKL release and its biological role in periodontitis are unclear. TNF-α-converting enzyme (TACE) is reported to cleave the following: 1) precursor TNF-α with release of mature, soluble TNF-α and 2) mRANKL with release of sRANKL. Both soluble TNF-α and sRANKL are found in the periodontitis lesion, leading to the hypothesis that TACE expressed on lymphocytes is engaged in RANKL shedding and that the resulting sRANKL induces osteoclastogenesis. In the current study, upon stimulating PBLs with mitogens in vitro, RANKL expression, sRANKL secretion, and TACE expression were all upregulated. Among the four putative mRANKL sheddases examined in neutralization assays, TACE was the only functional sheddase able to cleave mRANKL expressed on PBL. Moreover, PBL culture supernatant stimulated with mitogens in the presence of anti-TACE Ab or anti-RANKL Ab showed a marked reduction of osteoclastogenesis from osteoclast precursors, indicating that TACE-mediated sRANKL may possess sufficient osteoclastogenic activity. According to double-color confocal microscopy, B cells expressed a more pronounced level of RANKL and TACE expression than T cells or monocytes in periodontally diseased gingiva. Conditioned medium of patients' gingival lymphocyte culture increased in vitro osteoclastogenic activity, which was suppressed by the addition of anti-TACE Ab and anti-RANKL Ab. Therefore, TACE-mediated cleavage of sRANKL from activated lymphocytes, especially B cells, can promote osteoclastogenesis in periodontitis.

Production of RANKL by Memory B Cells: A Link Between B Cells and Bone Erosion in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone-resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development.

METHODS

RANKL production by total B cells or sorted B cell subpopulations in the peripheral blood and synovial tissue from healthy donors or anti-cyclic citrullinated peptide-positive patients with RA was examined by flow cytometry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemical analysis. To define direct effects on osteoclastogenesis, B cells were cocultured with CD14+ monocytes, and OCs were enumerated by tartrate-resistant acid phosphatase staining.

RESULTS

Healthy donor peripheral blood B cells were capable of expressing RANKL upon stimulation, with switched memory B cells (CD27+IgD-) having the highest propensity for RANKL production. Notably, switched memory B cells in the peripheral blood from RA patients expressed significantly more RANKL compared to healthy controls. In RA synovial fluid and tissue, memory B cells were enriched and spontaneously expressed RANKL, with some of these cells visualized adjacent to RANK+ OC precursors. Critically, B cells supported OC differentiation in vitro in a RANKL-dependent manner, and the number of OCs was higher in cultures with RA B cells than in those derived from healthy controls.

CONCLUSION

These findings reveal the critical importance of B cells in bone homeostasis and their likely contribution to joint destruction in RA.

Animal Models of Bone Loss in Inflammatory Arthritis: from Cytokines in the Bench to Novel Treatments for Bone Loss in the Bedside-a Comprehensive Review

Throughout life, bone is continuously remodelled. Bone is formed by osteoblasts, from mesenchymal origin, while osteoclasts induce bone resorption. This process is tightly regulated. During inflammation, several growth factors and cytokines are increased inducing osteoclast differentiation and activation, and chronic inflammation is a condition that initiates systemic bone loss. Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that is characterised by active synovitis and is associated with early peri-articular bone loss. Peri-articular bone loss precedes focal bone erosions, which may progress to bone destruction and disability. The incidence of generalised osteoporosis is associated with the severity of arthritis in RA and increased osteoporotic vertebral and hip fracture risk. In this review, we will give an overview of different animal models of inflammatory arthritis related to RA with focus on bone erosion and involvement of pro-inflammatory cytokines. In addition, a humanised endochondral ossification model will be discussed, which can be used in a translational approach to answer osteoimmunological questions.

Molecular Actions of Glucocorticoids in Cartilage and Bone During Health, Disease, and Steroid Therapy

Cartilage and bone are severely affected by glucocorticoids (GCs), steroid hormones that are frequently used to treat inflammatory diseases. Major complications associated with long-term steroid therapy include impairment of cartilaginous bone growth and GC-induced osteoporosis. Particularly in arthritis, GC application can increase joint and bone damage. Contrarily, endogenous GC release supports cartilage and bone integrity. In the last decade, substantial progress in the understanding of the molecular mechanisms of GC action has been gained through genome-wide binding studies of the GC receptor. These genomic approaches have revolutionized our understanding of gene regulation by ligand-induced transcription factors in general. Furthermore, specific inactivation of GC signaling and the GC receptor in bone and cartilage cells of rodent models has enabled the cell-specific effects of GCs in normal tissue homeostasis, inflammatory bone diseases, and GC-induced osteoporosis to be dissected. In this review, we summarize the current view of GC action in cartilage and bone. We further discuss future research directions in the context of new concepts for optimized steroid therapies with less detrimental effects on bone.

The sphingosine-1-phosphate receptor 1 binding molecule FTY720 inhibits osteoclast formation in rats with ligature-induced periodontitis

BACKGROUND AND OBJECTIVE

Osteoclast precursors (OPs) re-migrate from the bone surface into blood vessels through sphingosine-1-phosphate receptor 1 (S1PR1) expression. T cells also express S1PR1, mediating their migration from the lymph nodes into blood vessels. OP and T-cell migration are one of the sequential steps related to osteoclast formation. To characterize the role of S1PR1 in osteoclast formation induced by periodontitis, we investigated the effect of S1PR1-binding molecule FTY720 (FTY) on the number of OPs and T cells in periodontal tissue and peripheral blood of rats with ligature-induced periodontitis.

MATERIAL AND METHODS

Rats were divided into four groups; control (Con), FTY, periodontitis (Peri), and periodontitis+FTY (Peri+FTY) groups. Ligatures were placed around the first molars in the left and right mandibles. The rats were intraperitoneally injected with vehicle or 3 mg/kg FTY daily until they were killed. The number of osteoclasts and cluster of differentiation (CD)11b, CD3 and receptor activator of NF-κB ligand (RANKL)-positive cells in first molar furcation were counted by tartrate-resistant acid phosphatase or immunohistochemistry staining. The number of CD11b- and CD3-positive cells in peripheral blood was estimated by flow cytometry.

RESULTS

The number of osteoclasts in the Peri group was higher than Con, Peri+FTY and FTY groups (p < 0.05) and CD11b, CD3 and RANKL-positive cells were also higher in the Peri group than other groups in furcation (p < 0.05). While CD11b-positive cells in furcation of the Peri+FTY group were lower than the Peri group (p < 0.05), they were higher in peripheral blood (p < 0.05). Dissimilar to CD11b-positive cells, CD3-positive cells in the Peri+FTY group were lower in peripheral blood as well as furcation than the Peri group (p < 0.05). RANKL-positive cells in furcation of the Peri+FTY group were also lower than Peri group (p < 0.05).

CONCLUSION

These results indicate that FTY may facilitate re-migration of OPs from the alveolar bone surface into blood vessels, blocking T-cell migration from the lymph nodes into blood vessels and subsequently reducing osteoclast formation induced by periodontitis. This suggests that S1PR1-S1P binding may play a role in osteoclast formation of periodontitis by modulating OP and T-cell migration.

The pathogenesis of chronic chikungunya: evolving concepts

Chikungunya virus (CHIKV) re-emerged and caused an outbreak in the Caribbean and the Americas. CHIKV can cause incapacitating arthralgia, which may be evolved in chronic arthritis that is similar to rheumatoid arthritis that lasts for months or years. This review provides an overview of known and hypothesized mechanisms that CHIKV uses to promote chronic arthritis. We hypothesized that the chronic inflammatory response that is stimulated by persisting CHIKV replication in the joints results in the arthritic symptoms seen in patients. Most hypotheses proposed in this review need to be tested or confirmed, which may help in the development of new specific treatments and vaccines against CHIKV that will not only combat viral persistence but also prevent tissue damage.

Inflammatory signaling induced bone loss

A broad spectrum of inflammatory disorders have the capacity to target the skeleton and to de-regulate the processes of physiological bone remodeling. This review will focus on the systemic inflammatory rheumatologic disorders, which target articular and peri-articular bone tissues. Many of these disorders also affect extra-articular tissues and organs, and in addition, have the capacity to produce systemic bone loss and increased risk of osteoporotic fractures. Attention will focus on rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and the seronegative spondyloarthropathies (SpAs), which include ankylosing spondylitis (AS), reactive arthritis (formerly designated as Reiter's syndrome), the arthritis of inflammatory bowel disease, juvenile onset spondyloarthropathy and psoriatic arthritis. The discussion will principally focus on RA, which is a prototypical model of an inflammatory disorder that de-regulates bone remodeling, but also will review the other forms of inflammatory joint disease to highlight the differential effects of inflammation on bone remodeling in these conditions. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Cytokines and MicroRNAs as Candidate Biomarkers for Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease, with varied course and symptoms. Its etiology is very complex and not clearly understood. There is growing evidence of the important role of cytokines in SLE pathogenesis, as well as their utility as biomarkers and targets in new therapies. Other potential new SLE biomarkers are microRNAs. Recently, over one hundred different microRNAs have been demonstrated to have a significant impact on the immune system. Various alterations in these microRNAs, associated with disease pathogenesis, have been described. They influence the signaling pathways and functions of immune response cells. Here, we aim to review the emerging new data on SLE etiology and pathogenesis.