Activated T lymphocytes suppress osteoclastogenesis by diverting early monocyte/macrophage progenitor lineage commitment towards dendritic cell differentiation through down-regulation of receptor activator of nuclear factor-kappaB and c-Fos

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

Impact of Ravulizumab on Patient Outcomes and Quality of Life in Generalized Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune ion channel disorder in which antibodies to different end-plate antigens impair neuromuscular transmission, ultimately leading to muscle weakness and fatigability. In about 85% of patients with MG, autoantibodies against the acetylcholine receptor (AChR) activate the complement cascade, causing damage to the neuromuscular junction. MG is a chronic disorder for which standard therapies with corticosteroids, immunosuppressive drugs, and immunomodulation with plasma exchange or intravenous immunoglobulins modify the course of the disease, but the residual burden of physical, psychological, and social disability highlights several unmet needs, among these the need for specific, targeted, and well tolerated therapies able to improve the patients' quality of life. Complement inhibition paved the way to precision medicine in MG since, for the first time, a specific therapy targeting a crucial pathogenetic step has been designed, tested, and proven to be effective in a controlled fashion. Ravulizumab represents the first long-acting complement inhibitor approved for treatment of patients with generalized MG, able to provide rapid, complete, and sustained complement inhibition. Ravulizumab improved the MG Activity of Daily Living scale and other clinical parameters up to 26 weeks as shown by the CHAMPION MG trial, and by its open label extension, with the added value of being administered every 8 weeks. The schedule of administration is likely to improve patients' adherence and hence their quality of life. The introduction of complement inhibition will considerably change the traditional therapeutic strategy for MG.

Interspecies Single-Cell RNA-Seq Analysis Reveals the Novel Trajectory of Osteoclast Differentiation and Therapeutic Targets

Bone turnover is finely tuned by cells in the bone milieu, including osteoblasts, osteoclasts, and osteocytes. Osteoclasts are multinucleated giant cells with a bone-resorbing function that play a critical role in regulating skeletal homeostasis. Osteoclast differentiation is characterized by dramatic changes in morphology and gene expression following receptor activator of nuclear factor-kappa-Β ligand (RANKL) stimulation. We performed single-cell RNA-sequencing analyses of human and murine osteoclast-lineage cells (OLCs) and found that OLCs in the mitotic phase do not differentiate into mature osteoclasts. We also identified a guanosine triphosphatase (GTPase) family member, RAB38, as a highly expressed molecule in both human and murine osteoclast clusters; RAB38 gene expression is associated with dynamic changes in histone modification and transcriptional regulation. Silencing Rab38 expression by using short hairpin RNA (shRNA) inhibited osteoclast differentiation and maturation. In summary, we established an integrated fate map of human and murine osteoclastogenesis; this will help identify therapeutic targets in bone diseases. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Roles of the RANKL-RANK Axis in Immunity-Implications for Pathogenesis and Treatment of Bone Metastasis

A substantial amount patients with cancer will develop bone metastases, with 70% of metastatic prostate and breast cancer patients harboring bone metastasis. Despite advancements in systemic therapies for advanced cancer, survival remains poor for those with bone metastases. The interaction between bone cells and the immune system contributes to a better understanding of the role that the immune system plays in the bone metastasis of cancer. The immune and bone systems share various molecules, including transcription factors, signaling molecules, and membrane receptors, which can stimulate the differentiation and activation of bone-resorbing osteoclasts. The process of cancer metastasis to bone, which deregulates bone turnover and results in bone loss and skeletal-related events (SREs), is also controlled by primary cancer-related factors that modulate the intratumoral microenvironment as well as cellular immune process. The nuclear factor kappa B ligand (RANKL) and the receptor activator of nuclear factor kappa B (RANK) are key regulators of osteoclast development, bone metabolism, lymph node development, and T-cell/dendritic cell communication. RANKL is an osteoclastogenic cytokine that links the bone and the immune system. In this review, we highlight the role of RANKL and RANK in the immune microenvironment and bone metastases and review data on the role of the regulatory mechanism of immunity in bone metastases, which could be verified through clinical efficacy of RANKL inhibitors for cancer patients with bone metastases. With the discovery of the specific role of RANK signaling in osteoclastogenesis, the humanized monoclonal antibody against RANKL, such as denosumab, was available to prevent bone loss, SREs, and bone metastases, providing a unique opportunity to target RANKL/RANK as a future strategy to prevent bone metastases.

Murine osteoclastogenesis suppression using conditioned media produced by melanoma or activated and non-activated Jurkat-E6 cells

Conditioned medium (CM) (cell secretome) is a cocktail of growth factors, cytokines, and other soluble mediators secreted by cells into a culture medium. These growth factors are fundamental in many cellular processes such as cell growth, differentiation, and others and the composition of these factors is individual for each cell type. Osteoclasts are large multinucleated cells that are responsible for bone resorption. Immune and cancer cells are known to produce different growth factors, which are able to induce or inhibit osteoclast differentiation. Herein, we evaluated the effect of CM obtained from the supernatant of activated and non-activated Jukart-E6 cells, as well as from one murine (B16-F10) and one human melanoma cell line (SK-MEL-28). To induce osteoclast differentiation, murine bone marrow mononuclear cells were cultured in the presence and absence of differentiation factors (DF), such as macrophage colony-stimulating factor, prostaglandin E2, receptor activator of nuclear factor-κB ligand, and CM. We measured the concentration of interleukin 6, tumor necrosis factor-α and interferon γ (IFN-γ) in CM that can inhibit or induce osteoclastogenesis. Our study demonstrated that CM obtained from each cell line suppresses or inhibits osteoclasts formation at early and intermediate stages of differentiation in the absence or presence of DF. CM obtained from activated Jurkat-E6 cells demonstrates a stronger effect when compared with CM from naïve Jurkat-E6 cells or human and murine melanoma cells. Moreover, CM obtained from activated Jurkat-E6 cells shows higher secretion of IFN-γ, which is an inhibitor of osteoclastogenesis, in comparison with CM obtained from the three other cell lines. On the other hand, CM derived from B16-F10 cells showed a smaller inhibitory effect when compared with CM derived from the other cells.

Vγ9Vδ2 T cells inhibit immature dendritic cell transdifferentiation into osteoclasts through downregulation of RANK, c‑Fos and ATP6V0D2

Osteoimmunological studies have revealed that T cells exert a powerful impact on the formation and activity of osteoclasts and bone remodeling. Evidence demonstrates that immature dendritic cells (iDCs) are more efficient transdifferentiating into osteoclasts (OCs) than monocytes. However, whether Vγ9Vδ2 T (γδ T) cells stimulate or inhibit iDC transdifferentiation into OCs has never been reported. The aim of the present study was to investigate the effects of γδ T cells on this transdifferentiation process. γδ T cells and iDCs were isolated from the peripheral blood of healthy volunteers separately and were co-cultured with Transwelll inserts, with γδ T cells in the upper chamber and iDCs in the lower chamber. IDCs were treated with macrophage-colony stimulating factor and receptor activator of nuclear factor-κB (RANK) ligand. Tartrate resistant acid phosphatase (TRAP) assay and dentine resorption assay were performed to detect OC formation and their resorption capacity, respectively. The mRNA expression of OCs was examined using a micro-array and real time-quantitative polymerase chain reaction to trace the changes during iDC transdifferentiation into OCs. The results demonstrated that γδ T cells significantly inhibited the generation of the TRAP-positive OCs from iDCs and their resorption capacity. The microarray analysis identified decreased expression level of Fos proto-oncogene AP-1 transcription factor subunit (c-Fos), ATPase H⁺ transporting V0 subunit d (ATP6V0D2) and cathepsin K when iDCs were co-cultured with γδ T cells. These genes are associated with OC differentiation, indicating that γδ T cells suppressed iDCs osteoclastogenesis by downregulation of the RANK/c-Fos/ATP6V0D2 signaling pathway. The present findings provide novel insights into the interactions between human γδ T cells and iDCs, and demonstrate that γδ T cells are capable of inhibiting OC formation and their activity via downregulation of genes associated with OC differentiation.

Interferon-γ Released by Activated CD8+ T Lymphocytes Impairs the Calcium Resorption Potential of Osteoclasts in Calcified Human Aortic Valves

In calcific aortic valve disease (CAVD), activated T lymphocytes localize with osteoclast regions; however, the functional consequences of this association remain unknown. We hypothesized that CD8+ T cells modulate calcification in CAVD. CAVD valves (n = 52) dissected into noncalcified and calcified portions were subjected to mRNA extraction, real-time quantitative PCR, enzyme-linked immunosorbent assay, and immunohistochemical analyses. Compared with noncalcified portions, calcified regions exhibited elevated transcripts for CD8, interferon (IFN)-γ, CXCL9, Perforin 1, Granzyme B, and heat shock protein 60. Osteoclast-associated receptor activator of NK-κB ligand (RANKL), tartrate-resistant acid phosphatase (TRAP), and osteoclast-associated receptor increased significantly. The stimulation of tissue with phorbol-12-myristate-13-acetate and ionomycin, recapitulating CAVD microenvironment, resulted in IFN-γ release. Real-time quantitative PCR detected mRNAs for CD8+ T-cell activation (Perforin 1, Granzyme B). In stimulated versus unstimulated organoid cultures, elevated IFN-γ reduced the mRNAs encoding for RANKL, TRAP, and Cathepsin K. Molecular imaging showed increased calcium signal intensity in stimulated versus unstimulated parts. CD14+ monocytes treated either with recombinant human IFN-γ or with conditioned media-derived IFN-γ exhibited low levels of Cathepsin K, TRAP, RANK, and tumor necrosis factor receptor-associated factor 6 mRNAs, whereas concentrations of the T-cell co-activators CD80 and CD86 increased in parallel with reduced osteoclast resorptive function, effects abrogated by neutralizing anti-IFN-γ antibodies. CD8+ cell-derived IFN-γ suppresses osteoclast function and may thus favor calcification in CAVD.

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.

Cells of the immune system orchestrate changes in bone cell function

There is a complex interplay between the cells of the immune system and bone. Immune cells, such as T and NK cells, are able to enhance osteoclast formation via the production of RANKL. Yet there is increasing evidence to show that during the resolution of inflammation or as a consequence of increased osteoclastogenesis there is an anabolic response via the formation of more osteoblasts. Furthermore, osteoblasts themselves are involved in the control of immune cell function, thus promoting the resolution of inflammation. Hence, the concept of "coupling"-how bone formation is linked to resorption-needs to be more inclusive rather than restricting our focus to osteoblast-osteoclast interactions as in a whole organism these cells are never in isolation. This review will investigate the role of immune cells in normal bone homeostasis and in inflammatory diseases where the balance between resorption and formation is lost.

TGF-β in dentin matrix extract induces osteoclastogenesis in vitro

Previously, we have demonstrated that the extracellular matrix from dentin affects osteoclastic activity in co-culture between osteoclast and osteoblast-rich fraction from mouse marrow cells. In the present study, we aimed to investigate the mechanisms of dentin matrix extract-induced osteoclastogenesis in mouse bone marrow macrophages (BMMs). Dentin proteins were extracted from bovine incisor root dentin using 0.6 M HCl. BMMs were cultured in α-MEM containing macrophage colony-stimulating factor/receptor activator of nuclear factor kappa-B ligand in the presence or absence of dentin matrix extract. Tartrate-resistant acid phosphatase (TRAP)-positive cell number, total TRAP activity, and the mRNA levels of osteoclast-related genes, assayed by real-time RT-PCR, were determined as markers of osteoclastogenesis. A neutralizing antibody against transforming growth factor-β1 (TGF-β1), SB431542, a TGF-β receptor inhibitor, and ELISA were used to determine the role of TGF-β1. We observed increases in TRAP-positive cell number, TRAP activity, and the mRNA levels of osteoclast-related genes of BMMs cultured with dentin extract. The use of a neutralizing antibody against TGF-β1 or SB431542 inhibited the inductive effect of dentin extract, suggesting TGF-β1 involvement. The addition of exogenous TGF-β1, but not bone morphogenic protein-2, also increased osteoclastogenesis, corresponding to the ELISA determination of TGF-β1 in the dentin extract. In conclusion, our results indicate that proteins from dentin matrix have an inductive effect in osteoclastogenesis, which is mediated, in part, by TGF-β1.

Activated γδ T cells inhibit osteoclast differentiation and resorptive activity in vitro

Extensive evidence suggests that the immune system exerts powerful effects on bone cells, particularly in chronic disease pathologies such as rheumatoid arthritis (RA). The chronic inflammatory state in RA, particularly the excessive production of T cell-derived proinflammatory cytokines such as tumour necrosis factor (TNF)-α and interleukin (IL)-17, triggers bone erosions through the increased stimulation of osteoclast formation and activity. While evidence supports a role for IL-17 and TNF-α secreted by conventional CD4⁺ T cells in RA, recent evidence in animal models of RA have implicated γδ T cells as a major producer of pathogenic IL-17. However, the capacity of γδ T cells to influence osteoclast formation and activity in humans has not yet been investigated widely. To address this issue we investigated the effects of γδ T cells on osteoclast differentiation and resorptive activity. We have demonstrated that anti-CD3/CD28-stimulated γδ T cells or CD4⁺ T cells inhibit human osteoclast formation and resorptive activity in vitro. Furthermore, we assessed cytokine production by CD3/CD28-stimulated γδ T cells and observed a lack of IL-17 production, with activated γδ T cells producing abundant interferon (IFN)-γ. The neutralization of IFN-γ markedly restored the formation of osteoclasts from precursor cells and the resorptive activity of mature osteoclasts, suggesting that IFN-γ is the major factor responsible for the inhibitory role of activated γδ T cells on osteoclastogenesis and resorptive activity of mature osteoclasts. Our work therefore provides new insights on the interactions between γδ T cells and osteoclasts in humans.

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.

Suppressive effects on the immune response and protective immunity to a JEV DNA vaccine by co-administration of a GM-CSF-expressing plasmid in mice

As a potential cytokine adjuvant of DNA vaccines, granulocyte-macrophage colony–stimulating factor (GM-CSF) has received considerable attention due to its essential role in the recruitment of antigen-presenting cells, differentiation and maturation of dendritic cells. However, in our recent study of a Japanese encephalitis virus (JEV) DNA vaccine, co-inoculation of a GM-CSF plasmid dramatically suppressed the specific IgG response and resulted in decreased protection against JEV challenge. It is known that GM-CSF has been used in clinic to treat neutropenia for repopulating myeloid cells, and as an adjuvant in vaccine studies; it has shown various effects on the immune response. Therefore, in this study, we characterized the suppressive effects on the immune response to a JEV DNA vaccine by the co-administration of the GM-CSF-expressing plasmid and clarified the underlying mechanisms of the suppression in mice. Our results demonstrated that co-immunization with GM-CSF caused a substantial dampening of the vaccine-induced antibody responses. The suppressive effect was dose- and timing-dependent and likely related to the immunogenicity of the antigen. The suppression was associated with the induction of immature dendritic cells and the expansion of regulatory T cells but not myeloid-derived suppressor cells. Collectively, our findings not only provide valuable information for the application of GM-CSF in clinic and using as a vaccine adjuvant but also offer further insight into the understanding of the complex roles of GM-CSF.

The multiple faces of autoimmune-mediated bone loss

Inflammation perturbs normal bone homeostasis and is known to induce bone loss, as it promotes both local cartilage degradation and local and systemic bone destruction by osteoclasts, as well as inhibits bone formation by osteoblasts. Thus, not surprisingly, inflammatory autoimmune diseases often lead to local and/or general bone loss. However, the mechanisms that target the bone in autoimmune disease are complex and diverse, as they range from a direct attack on the bone and cartilage by the immune cells to indirect consequences of disturbances of the systemic control of bone remodeling. This Review discusses current understanding of the mechanisms of autoimmune-mediated bone loss in view of new insight from two new fields of research: osteoimmunology, which analyzes the direct effect of immune cells on bone, and the integrative metabolism approach, which established the existence of neuroendocrine loops that regulate bone remodeling.

Targeting Fas in osteoresorptive disorders

IMPORTANCE OF THE FIELD

Fas receptor is a mediator of the external apoptotic pathway in many cells and tissues. It is proposed that Fas receptor mediates osteoresorptive effects of estrogen deficiency and local/systemic inflammation.

AREAS COVERED IN THIS REVIEW

This review covers the past two decades of research on the expression and function of the Fas-Fas ligand system on bone cells, involvement in the pathogenesis of osteoresorption and potential therapeutic modulation.

WHAT THE READER WILL GAIN

We review the structure, biological function and intracellular signaling pathways of the Fas-Fas ligand system emphasizing the role of the non-apoptotic signaling pathways in bone cells, particularly osteoblast differentiation. We also present data on the in vitro expression and function of the Fas-Fas ligand system on osteoblast/osteoclast lineage cells, animal and human studies confirming its involvement in osteoresorptive disorders and potential therapeutic approaches to modulate its function.

TAKE HOME MESSAGE

Tissue specific therapeutic approaches need to be established to modify the Fas-Fas ligand system in osteoresorptive disorders as systemic targeting has many side effects. The most promising approach would be to target Fas signaling molecules coupled with osteoblast/osteoclast differentiation pathways, but a precise definition of these targets is still needed.

Natural killer cells trigger osteoclastogenesis and bone destruction in arthritis

Osteoclasts are bone-eroding cells that develop from monocytic precursor cells in the presence of receptor activator of NF-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Osteoclasts are essential for physiological bone remodeling, but localized excessive osteoclast activity is responsible for the periarticular bone destruction that characteristically occurs in patients with rheumatoid arthritis (RA). The origin of osteoclasts at sites of bone erosion in RA is unknown. Natural killer (NK) cells, as well as monocytes, are abundant in the inflamed joints of patients with RA. We show here that such NK cells express both RANKL and M-CSF and are frequently associated with CD14(+) monocytes in the RA synovium. Moreover, when synovial NK cells are cocultured with monocytes in vitro, they trigger their differentiation into osteoclasts, a process dependent on RANKL and M-CSF. As in RA, NK cells in the joints of mice with collagen-induced arthritis (CIA) express RANKL. Depletion of NK cells from mice before the induction of CIA reduces the severity of subsequent arthritis and almost completely prevents bone erosion. These results suggest that NK cells may play an important role in the destruction of bone associated with inflammatory arthritis.

The immune system and bone

T cells and B cells produce large amounts of cytokines which regulate bone resorption and bone formation. These factors play a critical role in the regulation of bone turnover in health and disease. In addition, immune cells of the bone marrow regulate bone homeostasis by cross-talking with bone marrow stromal cells and osteoblastic cells via cell surface molecules. These regulatory mechanisms are particularly relevant for postmenopausal osteoporosis and hyperparathyroidism, two common forms of bone loss caused primarily by an expansion of the osteoclastic pool only partially compensated by a stimulation of bone formation. This article describes the cytokines and immune factors that regulate bone cells, the immune cells relevant to bone, examines the connection between T cells and bone in health and disease, and reviews the evidence in favor of a link between T cells and the mechanism of action of estrogen and PTH in bone.

Reversal of chemotherapy-induced leukopenia using granulocyte macrophage colony-stimulating factor promotes bone metastasis that can be blocked with osteoclast inhibitors

Hematopoietic growth factors are used to reverse chemotherapy-induced leukopenia. However, some factors such as granulocyte macrophage colony-stimulating factor (GM-CSF) induce osteoclast-mediated bone resorption that can promote cancer growth in the bone. Accordingly, we evaluated the ability of GM-CSF to promote bone metastases of breast cancer or prostate cancer in a mouse model of chemotherapy-induced leukopenia. In this model, GM-CSF reversed cyclophosphamide-induced leukopenia but also promoted breast cancer and prostate cancer growth in the bone but not in soft tissue sites. Bone growth was associated with the induction of osteoclastogenesis, yet in the absence of tumor GM-CSF, it did not affect osteoclastogenesis. Two osteoclast inhibitors, the bisphosphonate zoledronic acid and the RANKL inhibitor osteoprotegerin, each blocked GM-CSF-induced tumor growth in the bone but did not reverse the ability of GM-CSF to reverse chemotherapy-induced leukopenia. Our findings indicate that it is possible to dissociate the bone-resorptive effects of GM-CSF, to reduce metastatic risk, from the benefits of this growth factor in reversing leukopenia caused by treatment with chemotherapy.

Peripheral blood expression profiles of bone morphogenetic proteins, tumor necrosis factor-superfamily molecules, and transcription factor Runx2 could be used as markers of the form of arthritis, disease activity, and therapeutic responsiveness

OBJECTIVE

To assess whether different forms of arthritis and disease activity could be distinguished by peripheral blood expression profiles of bone-regulatory factors including tumor necrosis factor (TNF)-superfamily [TNF-related apoptosis-inducing ligand (TRAIL), the Fas ligand (FasL), and the ligand for herpesvirus entry mediator (LIGHT)] and bone morphogenetic protein (BMP)-family members (BMP-2, BMP-4, BMP-6) as well as osteoblast differentiation gene Runx2.

METHODS

Blood cells from healthy controls (n = 25) and patients at different disease stages with rheumatoid arthritis (RA; n = 49), osteoarthritis (OA; n = 17), or spondyloarthritis, including ankylosing spondylitis (AS; n = 27) or psoriatic arthritis (PsA; n = 23), were processed for quantitative polymerase chain reaction. Gene expression was assessed in comparison with control samples, correlated with clinical data of different forms of arthritis, and analyzed for discriminative efficacy between groups by receiver-operation characteristic (ROC) curves. Results were confirmed on diagnostic RA (n = 5) and AS (n = 8) samples.

RESULTS

BMP-4, BMP-6, and Runx2 expressions were significantly decreased in patients with RA and OA versus controls. Patients with RA also had decreased FasL and LIGHT expression, while patients with AS had increased Runx2 expression. Negative correlation with disease activity was found for BMP-4, FasL, and Runx2 in RA and for Runx2 in PsA, while positive correlation was found for BMP-4 in PsA. Gene expression was higher in the therapy-resistant form of AS (for BMP-4, LIGHT, and Runx2) and in methotrexate-treated patients in RA (for BMP-2 and LIGHT). ROC curve analysis confirmed discrimination between groups, particularly decreased LIGHT and Runx2 for RA and increased Runx2 for AS.

CONCLUSION

Our study identified BMP and Runx2 as possible biomarkers of bone metabolism in several forms of arthritis, while lower FasL and LIGHT were associated with RA. Correlation between gene expression and disease activity may be clinically useful in assessing therapeutic effectiveness and disease monitoring.

Bone morphogenetic proteins and receptors are over-expressed in bone-marrow cells of multiple myeloma patients and support myeloma cells by inducing ID genes

We assessed the expression pattern and clinical relevance of BMPs and related molecules in multiple myeloma (MM). MM bone-marrow samples (n=32) had increased BMP4, BMP6, ACVR1 and ACVR2A, and decreased NOG expression compared with controls (n=15), with BMP6 having the highest sensitivity/specificity. Within MM bone-marrow, the source of BMPs was mainly CD138(+) plasma-cell population, and BMP6 and ACVR1 expression correlated with plasma-cell percentage. Using myeloma cell lines NCI H929 and Thiel we showed that BMPs induced ID1, ID2 and IL6, and suppressed CDKN1A and BAX gene expression, and BAX protein expression. Finally, BMPs partially protected myeloma cells from bortezomib- and TRAIL-induced apoptosis. We concluded that BMPs may be involved in MM pathophysiology and serve as myeloma cell biomarkers.

In vitro effects of erythromycin on RANKL and nuclear factor-kappa B by human TNF-alpha stimulated Jurkat cells

The receptor activator of NF-kappaB ligand (RANKL) and its signal downstream nuclear factor-kappaB (NF-kappaB) are critical regulators for immune responses as well as bone remodeling. The present study aimed to examine the effects of erythromycin (EM) on the activation of RANKL, correlation with NF-kappaB expression, proliferation and apoptosis of human Jurkat T cells. Jurkat T cells were pretreated with 100 pmol/l tumor necrosis factor-alpha (TNF-alpha) for 1 h followed by various concentrations of EM for 24 h. The mRNA expressions of RANKL and NF-kappaB were examined by RT-PCR. The protein expression of NF-kappaB was analyzed by Western blot. The protein level of RANKL was examined by flow cytometry, immunofluorescence microscopy and Western blot analyses. We also examined proliferation of Jurkat T cells by MTT assay, apoptosis by flow cytometry analysis after staining with PI and morphological observation after AO/EB staining. The results showed that EM inhibited TNF-alpha-induced expressions of RANKL and NF-kappaB at both mRNA and protein levels in a concentration-dependent manner. The expression of RANKL was correlated with the expression of NF-kappaB. Moreover, EM influenced the proliferation and apoptosis of human Jurkat T cells. These data suggest that EM acts as an anti-inflammatory agent not only to interact with the expression of NF-kappaB and the proliferation of human Jurkat T cells, but also to reduce the level of RANKL.

Association between apoptotis and CD4(+)/CD8(+) T-lymphocyte ratio in aseptic loosening after total hip replacement

Particle-induced osteolysis is a major cause of aseptic loosening after total joint replacement. While the osteolytic cascade initiated by cytokine release from macrophages has been studied extensively, the involvement of T-lymphocytes in this context is controversial and has been addressed by only a few authors. In a former study we detected that the quantity of T-lymphocytes may be influenced by apoptosis in patients with aseptic loosening. In this study we intended to find out more details about the apoptosis-induced shifting of the T-cell number. We focused our interest on the CD4⁺ and CD8⁺ T-cells and their relative ratio. Caspase-3 cleaved was evaluated immunohistochemically to detect apoptotic T-cells in capsules and interface membranes from patients with aseptic hip implant loosening and a varying degree of caspase-3 cleaved expression in CD4⁺ and CD8⁺ T-lymphocytes was detected. Moreover, a relationship between the intensity of the apoptotic reactions and the radiological extent of osteolysis was observed. The number of CD4⁺ cells was decreased in the presence of strong apoptotic reactions, respectively extensive osteolysis, while CD8⁺ cells were affected to a much lower degree. Thus, the CD4⁺/CD8⁺ ratio changed from 1.0 in cases with only small areas of periprosthetic osteolysis and minimally intense apoptosis to 0.33 in cases with large areas of osteolysis. This may suggest a causal relationship between the apoptosis-induced shift in the CD4⁺/CD8⁺ ratio and the osteolysis respectively aseptic loosening. It is possible that these findings may lead to a new understanding of particle-induced osteolysis.

Increased bone resorption and osteopenia are a part of the lymphoproliferative phenotype of mice with systemic over-expression of interleukin-7 gene driven by MHC class II promoter

Mice with interleukin (IL)-7 transgene under the control of E(alpha) promoter over-express IL-7 in MHC class II-positive cells and develop specific immune phenotype, marked by an increase in CD45R(+) cells in both the bone marrow and peripheral blood. We show that IL-7 transgenic mice have a bone phenotype characterized by an age-related loss of trabecular bone in both axial and long bones. Osteopenia was the result of increased number of active osteoclasts on the surface of trabecular bone. Furthermore, IL-7 transgenic mice showed increased osteoclastic but unchanged osteoblastic potential of the bone marrow in vitro. IL-7 over-expression also created osteoclastogenic microenvironment within the bone marrow which promoted the commitment of precursors towards the osteoclast lineage. These findings are important for immunological disturbances where IL-7 is involved and where alterations in the immune system are accompanied by changes in bone metabolism, such as multiple myeloma, rheumatoid arthritis and postmenopausal osteoporosis.

Estrogen deficiency increases osteoclastogenesis up-regulating T cells activity: a key mechanism in osteoporosis

Compelling evidences suggest that increased production of osteoclastogenic cytokines by activated T cells plays a relevant role in the bone loss induced by estrogen deficiency in the mouse. However, little information is available on the role of T cells in post-menopausal bone loss in humans. To investigate this issue we have assessed the production of cytokines involved in osteoclastogenesis (RANKL, TNFalpha and OPG), in vitro osteoclast (OC) formation in pre and post-menopausal women, the latter with or without osteoporosis. We evaluated also OC precursors in peripheral blood and the ability of peripheral blood mononuclear cells to produce TNFalpha in both basal and stimulated condition by flow cytometry in these subjects. Our data demonstrate that estrogen deficiency enhances the production of the pro-osteoclastogenetic cytokines TNFalpha and RANKL and increases the number of circulating OC precursors. Furthermore, we show that T cells and monocytes from women with osteoporosis exhibit a higher production of TNFalpha than those from the other two groups. Our findings suggest that estrogen deficiency stimulates OC formation both by increasing the production of TNFalpha and RANKL and increasing the number of OC precursors. Women with post-menopausal osteoporosis have a higher T cell activity than healthy post-menopausal subjects; T cells thus contribute to the bone loss induced by estrogen deficiency in humans as they do in the mouse.

CD137L- and RANKL-mediated reverse signals inhibit osteoclastogenesis and T lymphocyte proliferation

Members of the tumor necrosis factor-related family of ligands and receptors appear to be critical regulators of osteoclastogenesis and various cellular responses in T cells. In the present study, we have investigated CD137L and RANKL (receptor activator of nuclear factor (NF)-kappaB ligand)-induced biological responses in osteoclasts and T cells, respectively. Osteoclast-like cells were generated from murine bone marrow in the presence of RANKL and monocyte-macrophage colony-stimulating factor (M-CSF). RAW264.7 cells (murine monocytic cell line) constitutively express CD137L. Ligation of CD137L with anti-CD137L mAb (TKS-1) inhibits RANKL-induced osteoclast formation in a dose-dependent manner. Bone marrow cells expressed CD137L only when induced by treatment with M-CSF. In bone marrow cells, cross-linking of CD137L with anti-CD137L mAb (TKS-1) inhibits M-CSF/RANKL-evoked formation of multi-nucleated osteoclasts. Further we examined RANKL-mediated regulation of T cell proliferation. Both mouse CD4(+) and CD8(+) T cells expressed RANKL following their activation by anti-CD3 Ab and anti-CD137 Ab. Ligation of RANKL with OPG-Fc, the decoy receptor for RANKL, inhibited both mouse CD4(+) and CD8(+) T cell proliferation. From the above results, we suggest that the cellular responses in cell-to-cell interactions between T cells and osteoclasts are regulated through reciprocal regulations of CD137/CD137L and RANK/RANKL interactions.