Differentiation of monocytes into multinucleated giant bone-resorbing cells: two-step differentiation induced by nurse-like cells and cytokines

The effects of seeding density and osteoclastic supplement concentration on osteoclastic differentiation and resorption

The bone resorbing osteoclasts are a complex type of cell essential for in vivo bone remodeling. There is no consensus on medium composition and seeding density for in vitro osteoclastogenesis, despite the importance thereof on osteoclastic differentiation and activity. The aim of this study was to investigate the relative effect of monocyte or peripheral blood mononuclear cell (PBMC) seeding density, osteoclastic supplement concentration and priming on the in vitro generation of functional osteoclasts, and to explore and evaluate the usefulness of commonly used markers for osteoclast cultures. Morphology and osteoclast formation were analyzed with fluorescence imaging for tartrate resistant acid phosphatase (TRAP) and integrin β3 (Iβ3). TRAP release was analyzed from supernatant samples, and resorption was analyzed from culture on Corning® Osteo Assay plates. In this study, we have shown that common non-standardized culturing conditions of monocyte or PBMCs had a significant effect on the in vitro generation of functional osteoclasts. We showed how increased osteoclastic supplement concentrations supported osteoclastic differentiation and resorption but not TRAP release, while priming resulted in increased TRAP release as well. Increased monocyte seeding densities resulted in more and large TRAP positive bi-nuclear cells, but not directly in more multinucleated osteoclasts, resorption or TRAP release. Increasing PBMC seeding densities resulted in more and larger osteoclasts and more resorption, although resorption was disproportionally low compared to the monocyte seeding density experiment. Exploration of commonly used markers for osteoclast cultures demonstrated that Iβ3 staining was an excellent and specific osteoclast marker in addition to TRAP staining, while supernatant TRAP measurements could not accurately predict osteoclastic resorptive activity. With improved understanding of the effect of seeding density and osteoclastic supplement concentration on osteoclasts, experiments yielding higher numbers of functional osteoclasts can ultimately improve our knowledge of osteoclasts, osteoclastogenesis, bone remodeling and bone diseases.

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

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

Nucleotides modulate synoviocyte proliferation and osteoclast differentiation in macrophages with potential implications for rheumatoid arthritis

P2 receptors are nucleotide-activated receptors involved in inflammation, cell proliferation osteoblastogenesis, osteoclastogenesis and their function. They can be potential role players in the pathophysiology of rheumatoid arthritis (RA). Our analysis of gene expression datasets of synovial tissue biopsy from the GEO database shows changes in the expression levels of P2 receptors. HIG-82, a synovial fibroblast cell line and RAW 264.7, a macrophage cell line are good in vitro models to study RA. Nucleotide addition experiments showed UDP Glucose significantly increased the proliferation of synovial fibroblasts (HIG-82). Similarly, nucleotides such as Adenosine tri-phosphate (ATP), Adenosine di-phosphate (ADP), Uridine tri-phosphate (UTP), Uridine di-phosphate (UDP) and Uridine diphosphoglucose (UDPG) induced elevated reactive oxygen species (ROS) and tartrate Resistant Acid Phosphatase (TRAP) activity in RAW264.7 cells. The ADP-induced TRAP could be inhibited by clopidogrel a P2Y₁₂ inhibitor. ATP, ADP, UTP, UDP and UDPG also induced osteoclastogenesis as evident from fused multinucleate cells and expression of osteoclast markers (TRAP, Cathepsin K [CTSK]) as determined by Q-PCR. Apyrase (APY) a nucleotidase and an enzyme that is used to modulate extracellular nucleotide concentration is sufficient to induce osteoclastogenesis. Taken together our results show that nucleotides modulate synoviocyte proliferation and macrophage differentiation into osteoclast and play an important role in RA. Nucleotide receptors might be potential therapeutic targets in RA.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03052-8.

Comprehensive Analysis of Potential miRNA-Target mRNA-Immunocyte Subtype Network in Cerebral Infarction

INTRODUCTION

Cerebral infarction (CI) is one of the leading causes of serious long-term disability and mortality.

OBJECTIVE

We aimed to identify potential miRNAs and target mRNAs and assess the involvement of immunocyte infiltration in the process of CI.

METHODS

First, miRNA and mRNA data were downloaded from the Gene Expression Omnibus database, followed by differential expression analysis. Second, correlation analysis between differentially expressed mRNAs and differential immunocyte subtypes was performed through the CIBERSORT algorithm. Third, the regulatory network between miRNAs and immunocyte subtype-related mRNAs was constructed followed by the functional analysis of these target mRNAs. Fourth, correlation validation between differentially expressed mRNAs and differential immunocyte subtypes was performed in the GSE37587 dataset. Finally, the diagnostic ability of immunocyte subtype-related mRNAs was tested.

RESULTS

Up to 17 differentially expressed miRNAs and 3,267 differentially expressed mRNAs were identified, among which 310 differentially expressed mRNAs were significantly associated with immunocyte subtypes. Several miRNA-target mRNA-immunocyte subtype networks including hsa-miR-671-3p-ZC3HC1-neutrophils, hsa-miR-625-CD5-monocytes, hsa-miR-122-ACOX1/DUSP1/NEDD9-neutrophils, hsa-miR-455-5p-SLC24A4-monocytes, and hsa-miR-455-5p-SORL1-neutrophils were identified. LAT, ACOX1, DUSP1, NEDD9, ZC3HC1, BIN1, AKT1, DNMT1, SLC24A4, and SORL1 had a potential diagnostic value for CI.

CONCLUSIONS

The network including miRNA, target mRNA, and immunocyte subtype may be novel regulators and diagnostic and therapeutic targets in CI.

Zn-0.8Mg-0.2Sr (wt.%) Absorbable Screws-An In-Vivo Biocompatibility and Degradation Pilot Study on a Rabbit Model

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated.

Recombinant thrombomodulin lectin-like domain attenuates porphyromonas gingivalis lipopolysaccharide-induced osteoclastogenesis and periodontal bone resorption

BACKGROUND

Evidence demonstrates that the thrombomodulin (TM) lectin domain (TMD1) exerts anti-inflammatory functions. Lipopolysaccharides derived from Porphyromonas gingivalis (Pg-LPS) are considered a major pathogenic factor for chronic periodontitis, promoting inflammation, osteoclastogenesis and alveolar bone resorption. Herein, we aimed to evaluate the potential therapeutic effect of recombinant TMD1 (rTMD1) in suppression of Pg-LPS-induced osteoclastogenesis and periodontal bone loss.

METHODS

In vitro, the effects of Pg-LPS, tumor necrosis factor (TNF)-α and rTMD1 on osteoclast differentiation were investigated using receptor activator of nuclear factor-κB ligand (RANKL)-stimulated RAW 264.7 macrophages. In vivo, the effects of rTMD1 treatment were evaluated in a model of experimental periodontitis induced by direct injection of Pg-LPS into the vestibular gingiva.

RESULTS

Administration of Pg-LPS to RANKL-stimulated RAW 264.7 macrophages resulted in upregulation of CD86 and osteoclast marker (eg, Dc-stamp and Trap) gene expression and increase of pro-inflammatory cytokine production (e.g., TNF-α) during osteoclast differentiation, and rTMD1 can attenuate these effects. Also, rTMD1 inhibited Pg-LPS-enhanced in vitro bone resorption in a dose-dependent manner. Moreover, TNF-α promoted phosphorylation of p38 and ERK during osteoclast differentiation, and the signal activation can be inhibited by rTMD1. Finally, treatment with rTMD1 hindered Pg-LPS-induced alveolar bone loss in experimental periodontitis in mice.

CONCLUSION

Our study demonstrated that rTMD1 attenuates Pg-LPS-enhanced M1 macrophage polarization, osteoclastogenesis and periodontal bone resorption and thus holds therapeutic promise for periodontitis.

Organically modified hydroxyapatite (ormoHAP) nanospheres stimulate the differentiation of osteoblast and osteoclast precursors: a co-culture study

Isolated nanospheres consisting of organically modified hydroxyapatite (ormoHAP), prepared by an electric field-assisted ion double migration process, were embedded in foamed gelatin to form a composite scaffold. Degradation rates have been demonstrated to correlate with the crosslinking degree (40%, 80%) as well as with the mineral content of the scaffolds (0%, 20%, 40%). A human co-culture model of osteoblasts and osteoclasts, derived from bone marrow stromal cells and monocytes, respectively, without external addition of the factors RANKL and M-CSF, was run for up to 42 d in order to characterize the action of the ormoHAP-gelatin scaffolds on the co-culture. Examination was performed by quantitative biochemical methods (DNA, LDH, ALP, TRAP5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) and confocal laser scanning microscopy (cell nuclei, actin, CD68, TRAP). Results confirm that ormoHAP embedded in the gelatin matrix enhanced TRAP 5b activity. As a feedback, ALP activity and gene expression of BSP II of osteoblasts increased. Finally, a sequence of cell cross-talk actions is suggested, which can explain the behavior of the formed vital co-culture and moreover the influence of the presence and concentration of ormoHAP.

Nurse-like cells in rheumatoid arthritis: Formation of survival niches cooperating between the cell types

Nurse-like cells (NLCs) established from bone marrow and synovial tissue of rheumatoid arthritis (RA) patients were found to promote maturation and differentiation of B lineage cells as well as T cells. In co-culture of RA-NLCs and B cells, tight physical interactions (pseudoemperipolesis) developed, which resulted in activation of both cell types. RA-NLCs also supported myeloid cell maturation, promoting their differentiation into tartrate-resistant acid phosphatase-positive mononuclear cells, which are precursor cells of osteoclasts. In RA synovial tissue, the characteristic dendritic-shaped cells (the DCs) were electron microscopically found to form direct physical interactions with adjacent plasma cells (PCs) suspecting to be pseudoemperipolesis. The numbers of PCs accumulating in various areas tended to correlate with the numbers of the DCs, which appeared to have RA-NLC functions forming survival niches for PCs. Immunohistochemical staining analysis indicated that CD14+ cells including the DCs formed survival niches for CD138+ PCs by RA-NLC functions. Quantitative dual immunofluorescence staining studies of these areas indicated that the majority of CD14+ cells were of myeloid lineage. These survival niches promoted by RA-NLCs appear to play important roles in supporting immunological functions in RA bone marrow and synovial tissues.

Methyl Gallate Inhibits Osteoclast Formation and Function by Suppressing Akt and Btk-PLCγ2-Ca2+ Signaling and Prevents Lipopolysaccharide-Induced Bone Loss

In the field of bone research, various natural derivatives have emerged as candidates for osteoporosis treatment by targeting abnormally elevated osteoclastic activity. Methyl gallate, a plant-derived phenolic compound, is known to have numerous pharmacological effects against inflammation, oxidation, and cancer. Our purpose was to explore the relation between methyl gallate and bone metabolism. Herein, we performed screening using methyl gallate by tartrate resistant acid phosphatase (TRAP) staining and revealed intracellular mechanisms responsible for methyl gallate-mediated regulation of osteoclastogenesis by Western blotting and quantitative reverse transcription polymerase chain reaction (RT-PCR). Furthermore, we assessed the effects of methyl gallate on the characteristics of mature osteoclasts. We found that methyl gallate significantly suppressed osteoclast formation through Akt and Btk-PLCγ2-Ca²⁺ signaling. The blockade of these pathways was confirmed through transduction of cells with a CA-Akt retrovirus and evaluation of Ca²⁺ influx intensity (staining with Fluo-3/AM). Indeed, methyl gallate downregulated the formation of actin ring-positive osteoclasts and resorption pit areas. In agreement with in vitro results, we found that administration of methyl gallate restored osteoporotic phenotype stimulated by acute systemic injection of lipopolysaccharide in vivo according to micro-computed tomography and histological analysis. Our data strongly indicate that methyl gallate may be useful for the development of a plant-based antiosteoporotic agent.

Myeloid thrombomodulin lectin-like domain inhibits osteoclastogenesis and inflammatory bone loss

Osteoclastogenesis is an essential process during bone metabolism which can also be promoted by inflammatory signals. Thrombomodulin (TM), a transmembrane glycoprotein, exerts anti-inflammatory activities such as neutralization of proinflammatory high-mobility group box 1 (HMGB1) through TM lectin-like domain. This study aimed to identify the role of myeloid TM (i.e., endogenous TM expression on the myeloid lineage) in osteoclastogenesis and inflammatory bone loss. Using human peripheral blood mononuclear cells and mouse bone marrow-derived macrophages, we observed that the protein levels of TM were dramatically reduced as these cells differentiated into osteoclasts. In addition, osteoclastogenesis and extracellular HMGB1 accumulation were enhanced in primary cultured monocytes from myeloid-specific TM-deficient mice (LysMcre/TM^flox/flox) and from TM lectin-like domain deleted mice (TM^LeD/LeD) compared with their respective controls. Micro-computerized tomography scans showed that ovariectomy-induced bone loss was more pronounced in TM^LeD/LeD mice compared with controls. Finally, the inhibiting effects of recombinant TM lectin-like domain (rTMD1) on bone resorption in vitro, and bone loss in both the ovariectomized model and collagen antibody-induced arthritis model has been detected. These findings suggested that the myeloid TM lectin-like domain may inhibit osteoclastogenesis by reducing HMGB1 signaling, and rTMD1 may hold therapeutic potential for inflammatory bone loss.

Modulation of peripheral T-cell function by interleukin-7 in rheumatoid arthritis

Introduction

Interleukin-7 (IL-7) is a cytokine essential for T-cell lymphopoiesis, survival and polarization with an emerging role in autoimmunity. We previously demonstrated reduced levels of circulating IL-7 in rheumatoid arthritis (RA), although high amounts are expressed in joints, suggesting differences between systemic and synovial effects. We observed healthy levels of IL-7 in 48% of RA patients in clinical remission (CR) and aimed to investigate the consequences of IL-7 deficiency on T-cell responses.

Methods

We used RA patients with active disease and in CR presenting various levels of IL-7, to investigate its modulatory effects on T cells by analysing responses to phyto-haemagglutinin (PHA), expression of polarization or survival factors, or suppression by regulatory T cells (Tregs).

Results

IL-7 levels were normal (>10 pg/ml) in 48% of RA patients in CR. Amongst 63 CR patients followed up for 18 months, lack of IL-7 recovery was observed in 13 out of 15 (86%) patients experiencing relapse but only 11 out of 48 (23%) of those who did not (P = 0.0002). Binary regressions showed high significance for below normal IL-7 levels for self-reported maternal family history of arthritis (odds ratio (OR): 7.66, P = 0.006) and a trend for smoking (OR: 3.33, P = 0.068) with no further demographic or clinical associations. Serum IL-7 correlated with restored CD4⁺T-cell response to PHA (rho = 0.879); this was not related to an increase in T-cell proliferation capacity or expression of survival factors B-cell lymphoma 2 (BCL2) and BCL2-associated protein X (BAX). Expression of Th1 polarization factor (TBET) was also dependent on exposure to IL-7 in vivo (rho = 0.600). In contrast CD25^highTregs’ response to PHA was not affected by in vivo IL-7, but their suppression capabilities were related to circulating IL-7 (rho = 0.589). Co-stimulation with IL-7 (mimicking the joint environment) increased responsiveness of CD4⁺T-cells to PHA, lowering the ability of CD25^highTregs to suppress them.

Conclusions

Our data demonstrate that IL-7 has a critical role in modulating T-cell function in vivo, possibly explaining opposing effects observed systemically and in the joint. Lack of IL-7 recovery in CR by maintaining a suppressed immune system may be a determinant factor in the occurrence of relapse.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0511-3) contains supplementary material, which is available to authorized users.

MafB is a downstream target of the IL-10/STAT3 signaling pathway, involved in the regulation of macrophage de-activation

In spite of the numerous reports implicating MafB transcription factor in the molecular control of monocyte-macrophage differentiation, the precise genetic program underlying this activity has been, to date, poorly understood. To clarify this issue, we planned a number of experiments that were mainly conducted on human primary macrophages. In this regard, a preliminary gene function study, based on MafB inactivation and over-expression, indicated MMP9 and IL-7R genes as possible targets of the investigated transcription factor. Bioinformatics analysis of their promoter regions disclosed the presence of several putative MARE elements and a combined approach of EMSA and luciferase assay subsequently demonstrated that expression of both genes is indeed activated by MafB through a direct transcription mechanism. Additional investigation, performed with similar procedures to elucidate the biological relevance of our observation, revealed that MafB is a downstream target of the IL-10/STAT3 signaling pathway, normally inducing the macrophage de-activation process. Taken together our data support the existence of a signaling cascade by which stimulation of macrophages with the IL-10 cytokine determines a sequential activation of STAT3 and MafB transcription factors, in turn leading to an up-regulated expression of MMP9 and IL-7R genes.

The novel role of IL-7 ligation to IL-7 receptor in myeloid cells of rheumatoid arthritis and collagen-induced arthritis

Although the role of IL-7 and IL-7R has been implicated in the pathogenesis of rheumatoid arthritis (RA), the majority of the studies have focused on the effect of IL-7/IL-7R in T cell development and function. Our novel data, however, document that patients with RA and greater disease activity have higher levels of IL-7, IL-7R, and TNF-α in RA monocytes, suggesting a feedback regulation between IL-7/IL-7R and TNF-α cascades in myeloid cells that is linked to chronic disease progression. Investigations into the involved mechanism showed that IL-7 is a novel and potent chemoattractant that attracts IL-7R(+) monocytes through activation of the PI3K/AKT1 and ERK pathways at similar concentrations of IL-7 detected in RA synovial fluid. To determine whether ligation of IL-7 to IL-7R is a potential target for RA treatment and to identify their mechanism of action, collagen-induced arthritis (CIA) was therapeutically treated with anti-IL-7 Ab or IgG control. Anti-IL-7 Ab treatment significantly reduces CIA monocyte recruitment and osteoclast differentiation as well as potent joint monocyte chemoattractants and bone erosion markers, suggesting that both direct and indirect pathways might contribute to the observed effect. We also demonstrate that reduction in joint MIP-2 levels is responsible for suppressed vascularization detected in mice treated with anti-IL-7 Ab compared with the control group. To our knowledge, we show for the first time that expression of IL-7/IL-7R in myeloid cells is strongly correlated with RA disease activity and that ligation of IL-7 to IL-7R contributes to monocyte homing, differentiation of osteoclasts, and vascularization in the CIA effector phase.

Characterization of interleukin-7 and interleukin-7 receptor in the pathogenesis of rheumatoid arthritis

OBJECTIVE

To characterize the expression of interleukin-7 (IL-7) and IL-7 receptor (IL-7R) in rheumatoid arthritis (RA) synovial tissue and to examine their regulation and pathogenic role in macrophages, endothelial cells, and synovial tissue fibroblasts in RA.

METHODS

Expression of IL-7 and IL-7R in RA and normal synovial tissue was demonstrated by immunohistochemistry. Expression and regulation of IL-7 and IL-7R in RA peripheral blood in vitro-differentiated macrophages, RA synovial tissue fibroblasts, and human microvascular endothelial cells (HMVECs) were determined by real-time reverse transcription-polymerase chain reaction and/or flow cytometry. Enzyme-linked immunosorbent assay was used to examine production of proangiogenic factors by IL-7-activated macrophages, RA fibroblasts, and endothelial cells.

RESULTS

IL-7 and IL-7R were coexpressed on RA synovial tissue lining and sublining macrophages and endothelial cells. Expression of IL-7 and its receptor was significantly elevated in RA synovial fluid and peripheral blood macrophages as well as RA fibroblasts, compared to normal cells. Toll-like receptor 4 ligation (with lipopolysaccharide) and tumor necrosis factor α (TNFα) stimulation modulated expression of IL-7 and IL-7R on RA macrophages and HMVECs. However, in RA fibroblasts, lipopolysaccharide and TNFα activation increased expression of IL-7R only. IL-7 also mediated RA pathogenesis by inducing production of potent proangiogenic factors from macrophages and endothelial cells.

CONCLUSION

We have identified, for the first time, regulators of IL-7 and IL-7R expression in RA fibroblasts, RA peripheral blood in vitro-differentiated macrophages, and endothelial cells. Our results document a novel role of IL-7 in RA angiogenesis.

Immune and inflammatory pathways are involved in inherent bone marrow ossification

BACKGROUND

Bone marrow plays a key role in bone formation and healing. Although a subset of marrow explants ossifies in vitro without excipient osteoinductive factors, some explants do not undergo ossification. The disparity of outcome suggests a significant heterogeneity in marrow tissue in terms of its capacity to undergo osteogenesis.

QUESTIONS/PURPOSES

We sought to identify: (1) proteins and signaling pathways associated with osteogenesis by contrasting the proteomes of ossified and poorly ossified marrow explants; and (2) temporal changes in proteome and signaling pathways of marrow ossification in the early and late phases of bone formation.

METHODS

Explants of marrow were cultured. Media conditioned by ossified (n = 4) and poorly ossified (n = 4) subsets were collected and proteins unique to each group were identified by proteomic analysis. Proteomic data were processed to assess proteins specific to the early phase (Days 1-14) and late phase (Days 15-28) of the culture period. Pathways involved in bone marrow ossification were identified through bioinformatics.

RESULTS

Twenty-eight proteins were unique to ossified samples and eight were unique to poorly ossified ones. Twelve proteins were expressed during the early phase and 15 proteins were specific to the late phase. Several identified pathways corroborated those reported for bone formation in the literature. Immune and inflammatory pathways were specific to ossified samples.

CONCLUSIONS

The marrow explant model indicates the inflammatory and immune pathways to be an integral part of the osteogenesis process.

The interaction of monocytes with rheumatoid synovial cells is a key step in LIGHT-mediated inflammatory bone destruction

Formation of osteoclasts and consequent joint destruction are hallmarks of rheumatoid arthritis (RA). Here we show that LIGHT, a member of the tumour necrosis factor (TNF) superfamily, induced the differentiation into tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs) of CD14(+) monocytes cocultured with nurse-like cells isolated from RA synovium, but not of freshly isolated CD14(+) monocytes. Receptor activator of nuclear factor-kappaB ligand (RANKL) enhanced this LIGHT-induced generation of TRAP-positive MNCs. The MNCs showed the phenotypical and functional characteristics of osteoclasts; they showed the expression of osteoclast markers such as cathepsin K, actin-ring formation, and the ability to resorb bone. Moreover, the MNCs expressed both matrix metalloproteinase 9 (MMP-9) and MMP-12, but the latter was not expressed in osteoclasts induced from CD14(+) monocytes by RANKL. Immunohistochemical analysis showed that the MMP-12-producing MNCs were present in the erosive areas of joints in RA, but not in the affected joints of osteoarthritic patients. These findings suggested that LIGHT might be involved in the progression of inflammatory bone destruction in RA, and that osteoclast progenitors might become competent for LIGHT-mediated osteoclastogenesis via interactions with synoviocyte-like nurse-like cells.

Production of interleukin-6 and interleukin-8 by nurse-like cells from rheumatoid arthritis patients after stimulation with monocytes

It has been reported that nurse-like cells (NLCs) play a critical role in the pathogenesis of rheumatoid arthritis (RA). The interaction between NLCs established from RA patients (RA-NLCs), and freshly isolated blood monocytes was analyzed to further elucidate the pathogenesis of RA. RA-NLC lines were established from the synovium of RA patients. The RA-NLCs were cultured with monocytes freshly isolated from peripheral blood of healthy donors, and induction of interleukin (IL)-6 and IL-8 as well as the mRNA expression of these cytokines was examined. The levels of IL-6 were over 400 times higher in the supernatant from coculture of RA-NLCs and monocytes than in those from cultures of RA-NLCs alone. Anti-tumor necrosis factor (TNF)-alpha monoclonal antibody inhibited the induction of both cytokine in a dose-dependent fashion, although there was no detectable level of TNF-alpha in the supernatant from coculture. In addition, coculture of RA-NLCs and monocytes without direct cell contact did not induce cytokine production. To determine IL-6 producing cells, RA-NLCs and monocytes were separated into each fraction after coculture for 24 h. Cocultured RA-NLCs contained approximately 80 times higher IL-6 mRNA than the RA-NLCs cultured alone. The levels of IL-8 were also much higher (about 900 times) in the supernatant from coculture than in those from cultures of RA-NLCs alone. Cocultured RA-NLCs expressed IL-8 mRNA about 620 times higher than those cultured alone. These results indicate that NLCs produce high levels of IL-6 and IL-8 after cell-cell interaction with monocytes/macrophages via membrane-bound TNF-alpha, and that activation of NLCs by monocytes/macrophages may be involved in the pathogenesis of RA through maintenance of synovial inflammation.

Mesenchymal stromal cells. Nurse-like cells reside in the synovial tissue and bone marrow in rheumatoid arthritis

A major question concerning the immunopathology of rheumatoid arthritis is why the disease is localized to particular joints. A possible explanation could be the presence within the synovium of cells that foster inflammation or easy accessibility of the synovium to migratory disease enhancing cells. Within both the bone marrow and the synovium, fibroblastic stromal cells play an important role in supporting the differentiation and survival of normal cells, and also contribute to the pathologic processes. Among fibroblastic stromal cells in synovial tissue and bone marrow, nurse-like cells are a unique population having the specific capacity to promote pseudoemperipolesis (adhesion and holding beneath) of lymphocytes, and also the ability to promote the growth and function of some populations of lymphocytes and monocytes. Nurse-like cells could therefore contribute to the immunopathogenesis of rheumatoid arthritis, and may contribute to the localization of inflammation within specific joints. The present review considers the evidence that supports these possibilities.

Induction of osteoclast-like cells derived from the synovial lavage fluids of patients with temporomandibular joint disorders

OBJECTIVE

Although biochemical studies have examined the synovial fluid (SF) of patients with temporomandibular joint (TMJ) disorders (TMDs), the details of the molecular mechanism of bone destruction and remodeling remain unknown. In this study, we induced and characterized osteoclast-like cells from the SF of patients with TMD and investigated the participation of these cells in the pathogenesis of TMD.

METHODS

We collected SF cells from patients with TMD after a pumping procedure, cultured osteoclast-like cells, and examined their characteristics, including osteoclast markers and bone resorption activities. In addition, we obtained fibroblastic cells from the SF of TMD patients by continuous sub-culturing. Using these fibroblastic cells, we examined fibroblast markers using immunocytochemical staining and analyzed the receptor activator of nuclear-factor-kappaB ligand (RANKL) mRNA levels. Detection of soluble form of RANKL (sRANKL) in the SF was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Osteoclast-like cells were induced from the SF cells of patients with TMD by adding recombinant human (rh) macrophage colony stimulating factor (M-CSF) and either 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] or prostaglandin E2 (PGE2). These multinucleated giant cells were positive for tartrate-resistant acid phosphatase (TRAP) and had the ability to absorb bone. The fibroblastic cells from the SF of TMD patients were positive for fibroblast markers and RANKL mRNA was up-regulated. Detection of sRANKL in SF of patient group was significantly higher than control group.

CONCLUSION

The results suggest that the joint-infiltrating SF cells from TMD patients play important roles in the pathogenesis of these disorders, which is characterized by progressive bone destruction or remodeling.

RANKL-induced expression of tetraspanin CD9 in lipid raft membrane microdomain is essential for cell fusion during osteoclastogenesis

We showed that CD9, a member of tetraspanin superfamily proteins, is expressed in a specific membrane microdomain, called "lipid raft," and is crucial for cell fusion during osteoclastogenesis after activation of the RANK/RANKL system.

INTRODUCTION

Osteoclasts are bone-resorbing multinuclear polykaryons that are essential for bone remodeling and are formed through cell fusion of mononuclear macrophage/monocyte lineage precursors. Although osteoclastogenesis has been shown to be critically regulated by the RANK/RANKL system, the mechanism how precursor cells fuse with each other remains unclear. We examined the function of CD9, a member of tetraspanin superfamily, which has previously been shown to form macromolecular membrane microdomains and to regulate cell-cell fusion in various cell types.

MATERIALS AND METHODS

We used RAW264.7, a macrophage/monocyte lineage cell line, which can differentiate into osteoclast-like polykaryons on the application of RANKL. Expression and distribution of CD9 was assessed by Western blotting, fluorescence-assorted cell sorting (FACS) and immunohistochemistry with light and electron microscopy. A specific neutralizing antibody and RNA interference were used to inhibit the function of CD9, and green fluorescent protein (GFP)-CD9 was exogenously expressed to enhance the effect of CD9. The distribution of CD9 in lipid microdomain was examined by biochemical (sucrose density gradient) isolation and imaging technique.

RESULTS

CD9 is expressed on cell surfaces of RAW264.7, which is enhanced by RANKL. Targeted inhibition of CD9 decreases the number of osteoclast-like cells. On the other hand, overexpression of CD9 promotes spontaneous cell fusion even in the absence of RANKL. CD9 is localized in detergent-insoluble "lipid raft" microdomain in RANKL stimulation, and disruption of lipid rafts markedly reduces the formation of osteoclast-like polykaryons. Immunohistochemical studies of bone tissues revealed the expression of CD9 in osteoclasts in vivo.

CONCLUSIONS

These data suggest that function of tetraspanin CD9 and its expression in lipid rafts are crucial for cell fusion during osteoclastogenesis.

Nurse-like cells from patients with rheumatoid arthritis support the survival of osteoclast precursors via macrophage colony-stimulating factor production

OBJECTIVE

To elucidate the role of nurse-like cells (NLCs) obtained from rheumatoid arthritis (RA) patients in bone loss during progressive synovial expansion.

METHODS

CD14+ monocytes were cocultured with NLCs for 4 weeks and collected as NLC-supported CD14+ (NCD14+) monocytes. To determine their ability to differentiate into osteoclasts, NCD14+ monocytes were further cultured with macrophage colony-stimulating factor (M-CSF) together with RANKL or tumor necrosis factor alpha (TNFalpha). NCD14+ monocytes were also cocultured with SaOS-4/3 cells, which were shown to support osteoclastogenesis in response to parathyroid hormone (PTH). CD14+ monocytes were cocultured with SaOS-4/3 cells to elucidate how SaOS-4/3 cells and NLCs supported CD14+ monocytes for a long period. Synovial expansion adjacent to bone in RA patients was examined immunohistochemically to detect osteoclast precursors such as NCD14+ monocytes.

RESULTS

NLCs supported the survival of CD14+ monocytes for 4 weeks. NCD14+ as well as CD14+ monocytes differentiated into osteoclasts in the presence of M-CSF together with RANKL or TNFalpha. NCD14+ monocytes also differentiated into osteoclasts in PTH-treated cocultures with SaOS-4/3 cells. SaOS-4/3 cells supported the survival of CD14+ monocytes for 4 weeks in the presence, but not absence, of PTH. Treatment of SaOS-4/3 cells with PTH up-regulated the expression of M-CSF messenger RNA. Neutralizing antibodies against M-CSF inhibited the NLC-supported survival of CD14+ monocytes. CD68+ monocytes and M-CSF+ fibroblast-like synoviocytes were colocalized in regions adjacent to the destroyed bone of RA patients.

CONCLUSION

Our findings suggest that NLCs are involved in RA-induced bone destruction by maintaining osteoclast precursors via production of M-CSF.

AZT enhances osteoclastogenesis and bone loss

A variety of metabolic complications have been reported to be associated with highly active antiretroviral therapy (HAART), including osteopenia and osteoporosis. In this study, we determine the effects of zidovudine (AZT), a nucleoside reverse transcriptase inhibitor, on osteoclastogenesis in a cultured mouse macrophage preosteoclast cell line (RAW264.7), in mouse primary bone marrow macrophage-monocyte precursors, and on bone mineral density in mice. The results indicate that AZT induces an increase in osteoclastogenesis in the mouse preosteoclast cell line and in mouse bone marrow osteoclast precursors in the presence of RANKL. This increased osteoclastogenesis is dependent upon the concentration of AZT. AZT increases the promoter activity of tartrate-resistant acid phosphatase (TRAP) and the binding and function of the nuclear transcription protein, NF-kappaB, in RAW264.7 cells. Therefore, the effect of AZT is mediated, at least in part, by enhancing RANKL-mediated osteoclastogenesis. Bone mineral density (BMD) in AZT-treated mice is decreased and histopathology shows marked osteopenia. These results support an important role of AZT-stimulated osteoclastogenesis in HAART-induced osteopenia.

Osteoclastic potential of human CFU-GM: biphasic effect of GM-CSF

Human osteoclasts can be efficiently generated in vitro from cord blood mononuclear cells and derived CFU-GM colonies. However, CFU-M colonies are poorly osteoclastogenic. Short-term (2-48 h) treatment with GM-CSF stimulates osteoclast formation by proliferating precursors, whereas longer exposure favors dendritic cell formation.

INTRODUCTION

Osteoclasts (OC) differentiate from cells of the myelomonocytic lineage under the influence of macrophage-colony stimulating factor (M-CSF) and RANKL. However, cells of this lineage can also differentiate to macrophages and dendritic cells (DC) depending on the cytokine environment. The aims of this study were to develop an efficient human osteoclastogenesis model and to investigate the roles of granulocyte macrophage-colony stimulating factor (GM-CSF) and M-CSF in human OC differentiation.

MATERIALS AND METHODS

A human osteoclastogenesis model, using as precursors colony forming unit-granulocyte macrophage (CFU-GM) colonies generated from umbilical cord mononuclear cells cultured in methylcellulose with GM-CSF, interleukin (IL)-3 and stem cell factor (SCF), has been developed. CFU-GM, colony forming unit-macrophage (CFU-M), or mixed colonies were cultured on dentine with soluble RANKL (sRANKL) and human M-CSF with and without GM-CSF. Major endpoints were OC number, dentine resorption, and CD1a+ DC clusters.

RESULTS

Osteoclast generation from CFU-GM and mixed colonies treated with M-CSF and sRANKL for 7-14 days was highly efficient, but CFU-M colonies were poorly osteoclastogenic under these conditions. Pretreatment of precursors with M-CSF for 7 or 14 days maintained the precursor pool, but OCs were smaller and resorption was reduced. The effect of GM-CSF treatment was biphasic, depending on the timing and duration of exposure. Short-term treatment (2-48 h) at the beginning of the culture stimulated cell proliferation and enhanced OC formation up to 100%, independent of sRANKL. Longer-term GM-CSF treatment in the presence of sRANKL, however, inhibited OC generation with the formation of extensive CD1a+ DC clusters, accompanied by downregulation of c-Fos mRNA. Delaying the addition of GM-CSF resulted in progressively less inhibition of osteoclastogenesis.

CONCLUSIONS

Human CFU-GM, but not CFU-M, progenitors have high osteoclastogenic potential. GM-CSF plays an important role in osteoclastogenesis and has a biphasic effect: Short-term treatment potentiates OC differentiation by proliferating precursors, but persistent exposure favors DC formation.

Obesity is associated with macrophage accumulation in adipose tissue

Obesity alters adipose tissue metabolic and endocrine function and leads to an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications. To further characterize the changes that occur in adipose tissue with increasing adiposity, we profiled transcript expression in perigonadal adipose tissue from groups of mice in which adiposity varied due to sex, diet, and the obesity-related mutations agouti (Ay) and obese (Lepob). We found that the expression of 1,304 transcripts correlated significantly with body mass. Of the 100 most significantly correlated genes, 30% encoded proteins that are characteristic of macrophages and are positively correlated with body mass. Immunohistochemical analysis of perigonadal, perirenal, mesenteric, and subcutaneous adipose tissue revealed that the percentage of cells expressing the macrophage marker F4/80 (F4/80+) was significantly and positively correlated with both adipocyte size and body mass. Similar relationships were found in human subcutaneous adipose tissue stained for the macrophage antigen CD68. Bone marrow transplant studies and quantitation of macrophage number in adipose tissue from macrophage-deficient (Csf1op/op) mice suggest that these F4/80+ cells are CSF-1 dependent, bone marrow-derived adipose tissue macrophages. Expression analysis of macrophage and nonmacrophage cell populations isolated from adipose tissue demonstrates that adipose tissue macrophages are responsible for almost all adipose tissue TNF-alpha expression and significant amounts of iNOS and IL-6 expression. Adipose tissue macrophage numbers increase in obesity and participate in inflammatory pathways that are activated in adipose tissues of obese individuals.

Transforming growth factor-beta controls human osteoclastogenesis through the p38 MAPK and regulation of RANK expression

Although RANK-L is essential for osteoclast formation, factors such as transforming growth factor-beta (TGF-beta) are potent modulators of osteoclastogenic stimuli. To systematically investigate the role of TGF-beta in human osteoclastogenesis, monocytes were isolated from peripheral blood by three distinct approaches, resulting in either a lymphocyte-rich, a lymphocyte-poor, or a pure osteoclast precursor (CD14-positive) cell population. In each of these osteoclast precursor populations, the effect of TGF-beta on proliferation, TRAP activity, and bone resorption was investigated with respect to time and length of exposure. When using the highly pure CD14 osteoclast precursor cell population, the effect of TGF-beta was strongly dependent on the stage of osteoclast maturation. When monocytes were exposed to TGF-beta during the initial culture period (days 1-7), TRAP activity and bone resorption were increased by 40%, whereas the cell number was reduced by 25%. A similar decrease in cell number was observed when TGF-beta was present during the entire culture period (days 1-21), but in direct contrast, TRAP activity, cell fusion, cathepsin K, and matrix metalloproteinase (MMP)-9 expression as well as bone resorption were almost completely abrogated. Moreover, we found that latent TGF-beta was strongly activated by incubation with MMP-9 and suggest this to be a highly relevant mechanism for regulating osteoclast activity. To further investigate the molecular mechanism responsible for the divergent effects of continuous versus discontinuous exposure to TGF-beta, we examined RANK expression and p38 MAPK activation. We found the TGF-beta strongly induced p38 MAPK in monocytes, but not in mature osteoclasts, and that continuous exposure of TGF-beta to monocytes down-regulated RANK expression. The current results suggest that TGF-beta promotes human osteoclastogenesis in monocytes through stimulation of the p38 MAPK, whereas continuous exposure to TGF-beta abrogates osteoclastogenesis through down-regulation of RANK expression and therefore attenuation of RANK-RANK-L signaling.

Practical Modeling Concepts for Connective Tissue Stem Cell and Progenitor Compartment Kinetics

Stem cell activation and development is central to skeletal development, maintenance, and repair, as it is for all tissues. However, an integrated model of stem cell proliferation, differentiation, and transit between functional compartments has yet to evolve. In this paper, the authors review current concepts in stem cell biology and progenitor cell growth and differentiation kinetics in the context of bone formation. A cell-based modeling strategy is developed and offered as a tool for conceptual and quantitative exploration of the key kinetic variables and possible organizational hierarchies in bone tissue development and remodeling, as well as in tissue engineering strategies for bone repair.

Tartrate resistant acid phosphatase (TRAP) positive cells in rheumatoid synovium may induce the destruction of articular cartilage

OBJECTIVE

To examine the role of tartrate resistant acid phosphatase (TRAP) positive mononuclear and multinucleated cells in the destruction of articular cartilage in patients with rheumatoid arthritis (RA).

METHODS

The presence of TRAP positive cells in the synovial tissue of patients with RA was examined by enzyme histochemistry and immunohistochemistry. Expression of mRNAs for matrix metalloproteinases (MMPs) was assessed by the reverse transcriptase-polymerase chain reaction (RT-PCR) and northern blot analysis. Production of MMPs by mononuclear and multinucleated TRAP positive cells was examined by immunocytochemistry, enzyme linked immunosorbent assay (ELISA) of conditioned medium, and immunohistochemistry of human RA synovial tissue. In addition, a cartilage degradation assay was performed by incubation of (35)S prelabelled cartilage discs with TRAP positive cells.

RESULTS

TRAP positive mononuclear cells and multinucleated cells were found in proliferating synovial tissue adjacent to the bone-cartilage interface in patients with RA. Expression of MMP-2 (gelatinase A), MMP-9 (gelatinase B), MMP-12 (macrophage metalloelastase), and MMP-14 (MT1-MMP) mRNA was detected in TRAP positive mononuclear and multinucleated cells by both RT-PCR and northern blot analysis. Immunocytochemistry for these MMPs showed that MMP-2 and MMP-9 were produced by both TRAP positive mononuclear and multinucleated cells, whereas MMP-12 and MMP-14 were produced by TRAP positive multinucleated cells. MMP-2 and MMP-9 were detected in the conditioned medium of TRAP positive mononuclear cells. TRAP positive mononuclear cells also induced the release of (35)S from prelabelled cartilage discs.

CONCLUSION

This study suggests that TRAP positive mononuclear and multinucleated cells located in the synovium at the cartilage-synovial interface produce MMP-2 and MMP-9, and may have an important role in articular cartilage destruction in patients with RA.

The molecular mechanism of osteoclastogenesis in rheumatoid arthritis

Bone-resorbing osteoclasts are formed from hemopoietic cells of the monocyte-macrophage lineage under the control of bone-forming osteoblasts. We have cloned an osteoblast-derived factor essential for osteoclastogenesis, the receptor activator of NF-kappaB ligand (RANKL). Synovial fibroblasts and activated T lymphocytes from patients with rheumatoid arthritis also express RANKL, which appears to trigger bone destruction in rheumatoid arthritis as well. Recent studies have shown that T lymphocytes produce cytokines other than RANKL such as IL-17, granulocyte-macrophage colony-stimulating factor and IFN-gamma, which have powerful regulatory effects on osteoclastogenesis. The possible roles of RANKL and other cytokines produced by T lymphocytes in bone destruction are described.