Functional osteoclastogenesis: the baseline variability in blood donor precursors is not associated with age and gender

Mononuclear osteoclast precursors circulate in the monocyte fraction of peripheral blood and form multinuclear cells with all osteoclastic phenotypic characteristics when cultured in the presence of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kB ligand (RANKL). The method to obtain osteoclast precursors from peripheral blood is simple but the number of recovered osteoclasts is often largely insufficient for functional analyses. The original aim of this study was to develop a rapid and efficient method that could overcome the donor variability and enrich the osteoclast precursors from a small volume of peripheral blood as a basis for future clinical studies to correlate the differentiation potential of circulating osteoclast precursors with bone lesions in cancer patients. We improved the efficiency of osteoclastogenesis by reducing isolation and purification times and overcame the use of flow cytometry and immunomagnetic purification procedures. In our culture system the osteoclast number was increased several-fold and the precursors were able to reach a full differentiation within seven days of culture. Both age as well as gender differences in osteoclastogenesis efficiency were no longer evident by processing limited volume blood samples with this simple and rapid method.

Interaction of Tumor Necrosis Factor Receptor-associated Factor 6 (TRAF6) and Vav3 in the Receptor Activator of Nuclear Factor κB (RANK) Signaling Complex Enhances Osteoclastogenesis

The signaling pathway downstream of stimulation of receptor activator of nuclear factor κB (RANK) by RANK ligand is crucial for osteoclastogenesis. RANK recruits TNF receptor-associated factor 6 (TRAF6) to TRAF6-binding sites (T6BSs) in the RANK cytoplasmic tail (RANKcyto) to trigger downstream osteoclastogenic signaling cascades. RANKcyto harbors an additional highly conserved domain (HCR) that also activates crucial signaling during RANK-mediated osteoclastogenesis. However, the functional cross-talk between T6BSs and the HCR in the RANK signaling complex remains unclear. To characterize the cross-talk between T6BSs and the HCR, we screened TRAF6-interacting proteins using a proteomics approach. We identified Vav3 as a novel TRAF6 binding partner and evaluated the functional importance of the TRAF6-Vav3 interaction in the RANK signaling complex. We demonstrated that the coiled-coil domain of TRAF6 interacts directly with the Dbl homology domain of Vav3 to form the RANK signaling complex independent of the TRAF6 ubiquitination pathway. TRAF6 is recruited to the RANKcyto mutant, which lacks T6BSs, via the Vav3 interaction; conversely, Vav3 is recruited to the RANKcyto mutant, which lacks the IVVY motif, via the TRAF6 interaction. Finally, we determined that the TRAF6-Vav3 interaction resulting from cross-talk between T6BSs and the IVVY motif in RANKcyto enhances downstream NF-κB, MAPK, and NFATc1 activation by further strengthening TRAF6 signaling, thereby inducing RANK-mediated osteoclastogenesis. Thus, Vav3 is a novel TRAF6 interaction partner that functions in the activation of cooperative signaling between T6BSs and the IVVY motif in the RANK signaling complex.

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.

Calcium in Gluten-Free Life: Health-Related and Nutritional Implications

Calcium deficiency and metabolic bone diseases are a frequent co-morbidity of coeliac disease (CD). Gluten-free diet (GFD) is the only effective treatment of CD. However, CD patients on the strict GFD consume less than the recommended amounts of calcium. In this review, the main etiological factors responsible for calcium deficiency in CD were presented. Additionally, the research on the application of calcium supplements in the gluten-free breadmaking was reviewed, and its effect on the technological and sensory properties of baked products was indicated. Calcium-fortified gluten-free products could increase the calcium content in the diet of CD patients, supplying the amount of calcium they need for prophylactic or therapeutic use. Apart from this, the consumption of the naturally GF products as well as functional ingredients beneficially affecting calcium absorption need to be encouraged.

Double-edged-sword effect of IL-1β on the osteogenesis of periodontal ligament stem cells via crosstalk between the NF-κB, MAPK and BMP/Smad signaling pathways

Microenvironmental conditions can interfere with the functional role and differentiation of mesenchymal stem cells (MSCs). Recent studies suggest that an inflammatory microenvironment can significantly impact the osteogenic potential of periodontal ligament stem cells (PDLSCs), but the precise effects and mechanisms involved remain unclear. Here, we show for the first time that interleukin-1β (IL-1β) has dual roles in the osteogenesis of PDLSCs at concentrations ranging from physiologically healthy levels to those found in chronic periodontitis. Low doses of IL-1β activate the BMP/Smad signaling pathway to promote the osteogenesis of PDLSCs, but higher doses of IL-1β inhibit BMP/Smad signaling through the activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling, inhibiting osteogenesis. These results demonstrate that crosstalk between NF-κB, MAPK and BMP/Smad signaling mediates this dual effect of IL-1β on PDLSCs. We also show that the impaired osteogenesis of PDLSCs results in more inflammatory cytokines and chemokines being released, inducing the chemotaxis of macrophages, which further clarifies the role of PDLSCs in the pathogenesis of periodontitis.

A review of UHMWPE wear-induced osteolysis: the role for early detection of the immune response

In a world where increasing joint arthroplasties are being performed on increasingly younger patients, osteolysis as the leading cause of failure after total joint arthroplasty (TJA) has gained considerable attention. Ultra-high molecular weight polyethylene wear-induced osteolysis is the process by which prosthetic debris mechanically released from the surface of prosthetic joints induces an immune response that favors bone catabolism, resulting in loosening of prostheses with eventual failure or fracture. The immune response initiated is innate in that it is nonspecific and self-propagating, with monocytic cells and osteoclasts being the main effectors. To date, detecting disease early enough to implement effective intervention without unwanted systemic side effects has been a major barrier. These barriers can be overcome using newer in vivo imaging techniques and modules linked with fluorescence and/or chemotherapies. We discuss the pathogenesis of osteolysis, and provide discussion of the challenges with imaging and therapeutics. We describe a positron emission tomography imaging cinnamoyl-Phe-(D)-Leu-Phe-(D)-Leu-Phe-Lys module, specific to macrophages, which holds promise in early detection of disease and localization of treatment. Further research and increased collaboration among therapeutic and three-dimensional imaging researchers are essential in realizing a solution to clinical osteolysis in TJA.

Vaccination with recombinant RgpA peptide protects against Porphyromonas gingivalis-induced bone loss

OBJECTIVE

Following Porphyromonas gingivalis infection in mice, the efficacy of vaccination by recombinant and native RgpA in modulating the early local anti-inflammatory and immune responses and periodontal bone loss were examined.

MATERIAL AND METHODS

Using the subcutaneous chamber model, exudates were analyzed for cytokines after treatment with native RgpA and adjuvant (test), or adjuvant and saline alone (controls). Mice were also immunized with recombinant RgpA after being orally infected with P. gingivalis. After 6 wk, serum was examined for anti-P. gingivalis IgG1 and IgG2a titers and for alveolar bone resorption.

RESULTS

Immunization with native RgpA shifted the immune response toward an anti-inflammatory response as demonstrated by decreased proinflammatory cytokine IL-1β production and greater anti-inflammatory cytokine IL-4 in chamber exudates. Systemically, immunization with recombinant RgpA peptide prevented alveolar bone loss by 50%, similar to immunization with heat-killed whole bacteria. Furthermore, recombinant RgpA shifted the humoral response toward high IgG1 and low IgG2a titers, representing an in vivo anti-inflammatory response.

CONCLUSIONS

The present study demonstrates the potential of RgpA to shift the early local immune response toward an anti-inflammatory response while vaccination with recRgpA protected against P. gingivalis-induced periodontitis.

Osteoclasts-Key Players in Skeletal Health and Disease

The differentiation of osteoclasts (OCs) from early myeloid progenitors is a tightly regulated process that is modulated by a variety of mediators present in the bone microenvironment. Once generated, the function of mature OCs depends on cytoskeletal features controlled by an αvβ3-containing complex at the bone-apposed membrane and the secretion of protons and acid-protease cathepsin K. OCs also have important interactions with other cells in the bone microenvironment, including osteoblasts and immune cells. Dysregulation of OC differentiation and/or function can cause bone pathology. In fact, many components of OC differentiation and activation have been targeted therapeutically with great success. However, questions remain about the identity and plasticity of OC precursors and the interplay between essential networks that control OC fate. In this review, we summarize the key principles of OC biology and highlight recently uncovered mechanisms regulating OC development and function in homeostatic and disease states.

Short-Term Effects of TNF Inhibitors on Bone Turnover Markers and Bone Mineral Density in Rheumatoid Arthritis

TNFα inhibitors (TNFαI) exert positive effects on disease activity in rheumatoid arthritis (RA). Bone involvement is a major determinant of functional impairment in this disease. Here we investigated the short-term effects of TNFαI therapy on bone metabolism and density. We studied 54 patients with RA starting a TNFαI biologic drug, in whom any factor known to interfere with bone metabolism was excluded or rigorously accounted for. We measured at baseline and after 6-month therapy bone turnover markers: N-propeptide of type I collagen (P1NP), and bone alkaline phosphates for bone formation and serum C-terminal telopeptide of type I collagen (CTX) for bone resorption. We also evaluated bone mineral density (BMD) at hip and lumbar by dual-energy X-ray absorptiometry. All bone markers rose significantly and these changes were not dependent on steroid dosage. A significant decrease in femoral neck BMD was also observed. These results indicate that TNFαI therapy in RA over 6 months is associated with an early increase in bone turnover and a decline in hip BMD.

Brucella abortus-infected B cells induce osteoclastogenesis

Brucella abortus is an intracellular bacterium that establishes lifelong infections in livestock and humans although the mechanisms of its chronicity are poorly understood. Activated B cells have long lifespan and B. abortus infection activates B cells. Our results indicate that the direct infection of B cells with B. abortus induced matrix metalloproteinase-9 (MMP-9), receptor activator for NF κB ligand (RANKL), tumor necrosis factor (TNF)-α and interleukin (IL)-6 secretion. In addition, supernatants from B. abortus-infected B cells induced bone marrow-derived monocytes to undergo osteoclastogenesis. Using osteoprotegerin, RANKL's decoy receptor, we determined that RANKL is involved in osteoclastogenesis induced by supernatants from B. abortus-infected B cells. The results presented here shed light on how the interactions of B. abortus with B cells may have a role in the pathogenesis of brucellar osteoarticular disease.

CCAAT/Enhancer-binding Protein α (C/EBPα) Is Important for Osteoclast Differentiation and Activity

CCAAT/enhancer-binding protein (C/EBPα) can appoint mouse bone marrow (MBM) cells to the osteoclast (OC) lineage for osteoclastogenesis. However, whether C/EBPα is also involved in OC differentiation and activity is unknown. Here we demonstrated that C/EBPα overexpression in MBM cells can promote OC differentiation and strongly induce the expression of the OC genes encoding the nuclear factor of activated T-cells, c1 (NFATc1), cathepsin K (Cstk), and tartrate-resistant acid phosphatase 5 (TRAP) with receptor activator of NF-κB ligand-evoked OC lineage priming. Furthermore, while investigating the specific stage of OC differentiation that is regulated by C/EBPα, our gene overexpression studies revealed that, although C/EBPα plays a stronger role in the early stage of OC differentiation, it is also involved in the later stage. Accordingly, C/EBPα knockdown drastically inhibits osteoclastogenesis and markedly abrogates the expression of NFATc1, Cstk, and TRAP during OC differentiation. Consistently, C/EBPα silencing revealed that, although lack of C/EBPα affects all stages of OC differentiation, it has more impact on the early stage. Importantly, we showed that ectopic expression of rat C/EBPα restores osteoclastogenesis in C/EBPα-depleted MBM cells. Furthermore, our subsequent functional assays showed that C/EBPα exhibits a dispensable role on actin ring formation by mature OCs but is critically involved in bone resorption by stimulating extracellular acidification and regulating cell survival. We revealed that C/EBPα is important for receptor activator of NF-κB ligand-induced Akt activation, which is crucial for OC survival. Collectively, these results indicate that C/EBPα functions throughout osteoclastogenesis as well as in OC function. This study provides additional understanding of the roles of C/EBPα in OC biology.

Subchondral and epiphyseal bone remodeling following surgical transection and noninvasive rupture of the anterior cruciate ligament as models of post-traumatic osteoarthritis

OBJECTIVE

Animal models are frequently used to study post-traumatic osteoarthritis (PTOA). A common anterior cruciate ligament (ACL) injury model is surgical transection, which may introduce confounding factors from surgery. Noninvasive models could model human injury more closely. The purpose of this study was to compare subchondral and epiphyseal trabecular bone remodeling after surgical transection and noninvasive rupture of the ACL.

METHODS

Thirty-six rats were randomized to an uninjured control, surgical transection (Transection), or noninvasive rupture (Rupture). Animals were randomized to 4 or 10 week time points (n = 6 per group). Micro computed tomography (μCT) imaging was performed with an isotropic voxel size of 12 μm. Subchondral and epiphyseal bone was segmented semi-automatically, and morphometric analysis was performed.

RESULTS

Transection caused a greater decrease in subchondral bone volume fraction (BV/TV) than Rupture in the femur and tibia. Rupture had greater subchondral bone tissue mineral density (TMD) at 4 and 10 weeks in the femur and tibia. Subchondral bone thickness (SCB.Th) was decreased in the femur in Transection only. Epiphyseal BV/TV was decreased in Transection only, and Rupture exhibited increased femoral epiphyseal TMD compared to both Control and Transection. Rupture exhibited greater femoral epiphyseal trabecular thickness (Tb.Th.) compared to Control and Transection at 4 weeks, and both Rupture and Transection had increased femoral epiphyseal Tb.Th. at 10 weeks. Epiphyseal trabecular number (Tb.N) was decreased in both injury groups at both time points. Femoral and tibial epiphyseal structure model index (SMI) increased in both groups.

CONCLUSIONS

The two injury models cause differences in post-injury bone morphometry, and surgical transection may be introducing confounding factors that affect downstream bony remodeling.

Alteration of Homeostasis in Pre-osteoclasts Induced by Aggregatibacter actinomycetemcomitans CDT

The dysbiotic microbiota associated with aggressive periodontitis includes Aggregatibacter actinomycetemcomitans, the only oral species known to produce a cytolethal distending toxin (AaCDT). Give that CDT alters the cytokine profile in monocytic cells, we aimed to test the hypothesis that CDT plays a role in bone homeostasis by affecting the differentiation of precursor cells into osteoclasts. Recombinant AaCDT was added to murine bone marrow monocytes (BMMC) in the presence or absence of RANKL and the cell viability and cytokine profile of osteoclast precursor cells were determined. Multinucleated TRAP(+) cell numbers, and relative transcription of genes related to osteoclastogenesis were also evaluated. The addition of AaCDT did not lead to loss in cell viability but promoted an increase in the average number of TRAP(+) cells with 1-2 nuclei in the absence or presence of RANKL (Tukey, p < 0.05). This increase was also observed for TRAP(+) cells with ≥3nuclei, although this difference was not significant. Levels of TGF-β, TNF-α, and IL-6, in the supernatant fraction of cells, were higher when in AaCDT exposed cells, whereas levels of IL-1β and IL-10 were lower than controls under the same conditions. After interaction with AaCDT, transcription of the rank (encoding the receptor RANK), nfatc1 (transcription factor), and ctpK (encoding cathepsin K) genes was downregulated in pre-osteoclastic cells. The data indicated that despite the presence of RANKL and M-CSF, AaCDT may inhibit osteoclast differentiation by altering cytokine profiles and repressing transcription of genes involved in osteoclastogenesis. Therefore, the CDT may impair host defense mechanisms in periodontitis.

TNF-α-induced NF-κB activation upregulates microRNA-150-3p and inhibits osteogenesis of mesenchymal stem cells by targeting β-catenin

Although systemic or local inflammation, commonly featured by cytokine activation, is implicated in patients with bone loss, the underlying mechanisms are still elusive. As microRNAs (miR), a class of small non-coding RNAs involved in essential physiological processes, have been found in bone cells, we aimed to investigate the role of miR for modulating osteogenesis in inflammatory milieu using human bone marrow mesenchymal stem cells (hBM-MSCs). Induced by proinflammatory cytokine TNF-α, miR-150-3p was identified as a key player in suppressing osteogenic differentiation through downregulating β-catenin, a transcriptional co-activator promoting bone formation. TNF-α treatment increased the levels of miR-150-3p, which directly targeted the 3'-UTR of β-catenin mRNA and in turn repressed its expression. In addition, we observed that miR-150-3p expression was increased by TNF-α via IKK-dependent NF-κB signalling. There are three putative NF-κB binding sites in the promoter region of miR-150, and we identified -686 region as the major NF-κB binding site for stimulation of miR-150 expression by TNF-α. Finally, the osteogenic differentiation of hBM-MSCs was inhibited by either miR-150-3p overexpression or TNF-α treatment, which was prevented by anti-miR-150-3p oligonucleotides. Taken together, our data suggested that miR-150-3p integrated inflammation signalling and osteogenic differentiation and may contribute to the inhibition effects of inflammation on bone formation, thus expanding the pathophysiological functions of microRNAs in bone diseases.

ARTD1 regulates osteoclastogenesis and bone homeostasis by dampening NF-κB-dependent transcription of IL-1β

While ADP-ribosyltransferase diphtheria toxin-like 1 (ARTD1, formerly PARP1) and its enzymatic activity have been shown to be important for reprogramming and differentiation of cells, such as during adipogenesis, their role and mechanism in regulating osteoclastogenesis and bone homeostasis are largely unknown. Here, in cell culture-based RANKL-induced osteoclastogenesis models, we show that silencing of ARTD1 or inhibition of its enzymatic activity enhances osteoclast differentiation and function. As a consequence of ARTD1 silencing or inhibition, the recruitment of p65/RelA to the IL-1β promoter, which is associated with transcriptionally active histone marks, IL-1β expression and inflammasome-dependent secretion of IL-1β are enhanced. This subsequently promotes sustained induction of the transcription factor Nfatc1/A and osteoclastogenesis in an autocrine manner via the IL-1 receptor. In vivo, Artd1-deficient mice display significantly decreased bone mass as a consequence of increased osteoclast differentiation. Accordingly, the expression of osteoclast markers is enhanced in mutant compared to wild-type mice. Together, these results indicate that ARTD1 controls osteoclast development and bone remodelling via its enzymatic activity by modulating the epigenetic marks surrounding the IL-1β promoter and expression of IL-1β and subsequently also Nfatc1/A.

Management of bone mineral density in HIV-infected patients

INTRODUCTION

Loss of bone mineral density is an emerging problem in persons living with HIV infection. Earlier and more rapid bone demineralization has been attributed not only to the high prevalence of traditional risk factors, but also to specific HIV-related factors. The aim of this guidance is to stimulate an appropriate management of osteoporosis in this population, to identify patients at risk and to better manage them.

AREAS COVERED

Appropriate screening of HIV-infected subjects to identify those at risk for bone fractures is described, as well as the recommended interventions. American and European recommendations in HIV-infected and non-infected populations were considered. As the etiology of bone loss is multifactorial, many factors have to be addressed. Overall, recommendations on traditional risk factors are the same for HIV-infected and non-HIV-infected subjects. However, we should consider some specific factors in the HIV-infected population, including an appropriate antiretroviral therapy in patients with low bone mineral density, and probably novel strategies that could provide an additional benefit, such as anti-inflammatory drugs, although data supporting this approach are scant.

EXPERT OPINION

Some personal opinions are highlighted on the management of bone health in HIV-infected subjects, mainly on the use of FRAX(®) score and DXA scans. In addition, the need to implement new strategies to delay demineralization is remarked upon.

Surgical Debridement Is Superior to Sole Antibiotic Therapy in a Novel Murine Posttraumatic Osteomyelitis Model

Introduction

Bone infections after trauma, i.e. posttraumatic osteomyelitis, pose one of the biggest problems of orthopedic surgery. Even after sufficient clinical therapy including vast debridement of infected bone and antibiotic treatment, regeneration of postinfectious bone seems to be restricted. One explanation includes the large sized defects resulting from sufficient debridement. Furthermore, it remains unclear if inflammatory processes after bone infection do affect bone regeneration. For continuing studies in this field, an animal model is needed where bone regeneration after sufficient treatment can be studied in detail.

Methods

For this purpose we created a stable infection in murine tibiae by Staphylococcus aureus inoculation. Thereafter, osteomyelitic bones were debrided thoroughly and animals were subsequently treated with antibiotics. Controls included debrided, non-infected, as well as infected animals exclusively treated with antibiotics. To verify sufficient treatment of infected bone, different assessments detecting S. aureus were utilized: agar plates, histology and RT-qPCR.

Results

All three detection methods revealed massive reduction or eradication of S. aureus within debrided bones 1 and 2 weeks postoperatively, whereas sole antibiotic therapy could not provide sufficient treatment of osteomyelitic bones. Debrided, previously infected bones showed significantly decreased bone formation, compared to debrided, non-infected controls.

Discussion

Thus, the animal model presented herein provides a reliable and fascinating tool to study posttraumatic osteomyelitis for clinical therapies.

Interferon-γ enhances the efficacy of autogenous bone grafts by inhibiting postoperative bone resorption in rat calvarial defects

PURPOSE

Interferon (IFN)-γ is a major cytokine produced by immune cells that plays diverse roles in modulating both the immune system and bone metabolism, but its role in autogenous bone grafting remains unknown. Here, we present that local IFN-γ administration improved the efficacy of autogenous bone graft treatment in an experimental rat model.

METHODS

An autogenous bone graft model was prepared with critically sized rat calvariae defects. Four weeks (w) after bone graft implantation, rats were treated locally with IFN-γ or were not treated. The effect of IFN-γ on bone formation was evaluated for up to 8w with micro-computed tomography, quantitative histomorphometry, and Von Kossa staining. Osteoclastogenesis was assessed by tartrate-resistant acid phosphatase staining. Immunohistochemistry staining or quantitative polymerase chain reactions were used to estimate the expression of osteoclast differentiation factor and inflammatory cytokines including tumor necrosis factor (TNF)-α, a well-known stimulant of osteoclastogenesis and an inhibitor of osteoblast activity, in defects.

RESULTS

Newly formed bone gradually replaced the autogenous bone grafts within 4w, although severe bone resorption with osteoclastogenesis and TNF-α expression occurred after 6w in the absence of IFN-γ administration. IFN-γ administration markedly attenuated bone loss, osteoclastogenesis, and TNF-α expression, while it enhanced bone formation at 8w.

CONCLUSION

Local IFN-γ administration promoted bone formation in autogenous bone grafts possibly via regulating osteoclastogenesis and TNF-α expression. The data provide insights into the potential roles of IFN-γ in autogenous bone grafting.

Dietary zinc deficiency induces oxidative stress and promotes tumor necrosis factor-α- and interleukin-1β-induced RANKL expression in rat bone

We investigated the effects of dietary zinc deficiency on oxidative stress and bone metabolism. Four-week-old male Wistar rats were randomly assigned to one of three groups for 4 weeks: a zinc-adequate group (30 ppm); a zinc-deficient group (1 ppm); and a pair-fed group (30 ppm) that was pair-fed to the zinc-deficient group. The iron content and the thiobarbituric acid reactive substance level in bone were higher in the zinc-deficient group than in the zinc-adequate and pair-fed groups. The mRNA expression level of osteoblastogenesis-related genes such as bone morphogenetic protein 2 and runt-related transcription factor 2 was lower in the zinc-deficient group than in the zinc-adequate and pair-fed groups. In contrast, the mRNA expression levels of tumor necrosis factor-α, interleukin-1β and osteoclastogenesis-related genes such as receptor activator of nuclear factor-κB ligand and nuclear factor of activated T cells cytoplasmic 1 were higher in the zinc-deficient group than in the zinc-adequate and pair-fed groups.

These findings suggested that dietary zinc deficiency reduced osteoblastogenesis via a decrease in the expression of bone morphogenetic protein 2 and increased osteoclastogenesis via enhancement of the expression of receptor for activator of nuclear factor-κB ligand induced by oxidative stress-stimulated tumor necrosis factor-α and interleukin-1β.

Decursin from Angelica gigas suppresses RANKL-induced osteoclast formation and bone loss

Osteoclasts are the only cells capable of breaking down bone matrix, and excessive activation of osteoclasts is responsible for bone-destructive diseases. In this study, we investigated the effects of decursin from extract of Angelica gigas root on receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast formation using mouse bone marrow-derived macrophages (BMMs). Decursin inhibited RANKL-induced osteoclast formation without cytotoxicity. In particular, decursin maintains the characteristics of macrophages by blocking osteoclast differentiation by RANKL. Furthermore, the RANKL-stimulated bone resorption was diminished by decursin. Mechanistically, decursin blocked the RANKL-triggered ERK mitogen-activated protein kinases (MAPK) phosphorylation, which results in suppression of c-Fos and the nuclear factor of activated T cells (NFATc1) expression. In accordance with the in vitro study, decursin reduced lipopolysaccharide (LPS)- or ovariectomy (OVX)-induced bone loss in vivo. Therefore, decursin exerted an inhibitory effect on osteoclast formation and bone loss in vitro and in vivo. Decursin could be useful for the treatment of bone diseases associated with excessive bone resorption.

Dry Extract of Matricaria recutita L. (Chamomile) Prevents Ligature-Induced Alveolar Bone Resorption in Rats via Inhibition of Tumor Necrosis Factor-α and Interleukin-1β

BACKGROUND

Matricaria recutita L. (chamomile) has demonstrated anti-inflammatory activity. Accordingly, the ability of the Matricaria recutita extract (MRE) to inhibit proinflammatory cytokines and its influence on alveolar bone resorption (ABR) in rats.

METHODS

Wistar rats were subjected to ABR by ligature with nylon thread in the second upper-left molar, with contralateral hemiarcade as control. Rats received polysorbate TW80 (vehicle) or MRE (10, 30, and 90 mg/kg) 1 hour before ligature and daily until day 11. The periodontium was analyzed by macroscopy, histometry, histopathology, and immunohistochemistry for the receptor activator of nuclear factor-kappa B ligand (RANKL), osteoprotegerin (OPG), and tartrate-resistant acid phosphatase (TRAP). The gingival tissue was used to quantify the myeloperoxidase (MPO) activity and tumor necrosis factor (TNF)-α and interleukin (IL)-1β levels by enzyme-linked immunosorbent assay. Blood samples were collected to evaluate bone-specific alkaline phosphatase (BALP), leukogram, and dosages of aspartate and alanine transaminases, urea, and creatinine. Aspects of liver, kidneys, spleen, and body mass variations were also evaluated.

RESULTS

The 11 days of ligature induced bone resorption, low levels of BALP, leukocyte infiltration; increase of MPO, TNF-α, and IL-1β; immunostaining increase for RANKL and TRAP; reduction of OPG and leukocytosis, which were significantly prevented by MRE, except for the low levels of BALP and the leukocytosis. Additionally, MRE did not alter organs or body weights of rats.

CONCLUSION

MRE prevented the inflammation and ABR by reducing TNF-α and IL-1β, preventing the osteoclast activation via the RANKL-OPG axis, without interfering with bone anabolism.

Epigallocatechin-3-gallate protects against tumor necrosis factor alpha induced inhibition of osteogenesis of mesenchymal stem cells

Anabolic bone accruement through osteogenic differentiation is important for the maintenance of physiological bone mass and often disrupted in various inflammatory diseases. Epigallocatechin-3-gallate, as an antioxidant and anti-inflammatory agent, has been suggested for potential therapeutic use in this context, possibly by the inhibition of bone resorption as well as the enhancement of bone formation through directly activating osteoblast differentiation. However, the reported effects of epigallocatechin-3-gallate modulating osteoblast differentiation are mixed, and the underlying molecular mechanism is still elusive. Moreover, there is limited information regarding the effects of epigallocatechin-3-gallate on osteogenic potential of mesenchymal stem cell in inflammation. Here, we examined the in vitro osteogenic differentiation of human mesenchymal stem cells. We found that the cell viability and osteoblast differentiation of human bone marrow-derived mesenchymal stem cells are significantly inhibited by inflammatory cytokine TNFα treatment. Epigallocatechin-3-gallate is able to enhance the cell viability and osteoblast differentiation of mesenchymal stem cells and is capable of reversing the TNFα-induced inhibition. Notably, only low doses of epigallocatechin-3-gallate have such benefits, which potentially act through the inhibition of NF-κB signaling that is stimulated by TNFα. These data altogether clarify the controversy on epigallocatechin-3-gallate promoting osteoblast differentiation and further provide molecular basis for the putative clinical use of epigallocatechin-3-gallate in stem cell-based bone regeneration for inflammatory bone loss diseases, such as rheumatoid arthritis and prosthetic osteolysis.

Elevated levels of Interleukin (IL)-33 induce bone pathology but absence of IL-33 does not negatively impact normal bone homeostasis

Interleukin (IL)-33 is a member of the IL-1 family. IL-33 effects are mediated through its receptor, ST2 and IL-1RAcP, and its signaling induces the production of a number of pro-inflammatory mediators, including TNFα, IL-1β, IL-6, and IFN-γ. There are conflicting reports on the role of IL-33 in bone homeostasis, with some demonstrating a bone protective role for IL-33 whilst others show that IL-33 induces inflammatory arthritis with concurrent bone destruction. To better clarify the role IL-33 plays in bone biology in vivo, we studied IL-33 KO mice as well as mice in which the cytokine form of IL-33 was overexpressed. Mid-femur cortical bone mineral density (BMD) and bone strength were similar in the IL-33 KO mice compared to WT animals during the first 8months of life. However, in the absence of IL-33, we observed higher BMD in lumbar vertebrae and distal femur in female mice. In contrast, overexpression of IL-33 resulted in a marked and rapid reduction of bone volume, mineral density and strength. Moreover, this was associated with a robust increase in inflammatory cytokines (including IL-6 and IFN-γ), suggesting the bone pathology could be a direct effect of IL-33 or an indirect effect due to the induction of other mediators. Furthermore, the detrimental bone effects were accompanied by increases in osteoclast number and the bone resorption marker of C-terminal telopeptide collagen-I (CTX-I). Together, these results demonstrate that absence of IL-33 has no negative consequences in normal bone homeostasis while high levels of circulating IL-33 contributes to pathological bone loss.

The pathophysiological basis of bone tissue alterations associated with eating disorders

Anorexia nervosa (AN) and obesity are two major eating disorders present nowadays in Western countries. They are both characterized by striking body composition variations and hormonal alterations, which impact on skeletal metabolism, inducing bone tissue modifications and, thus, often cause an increased risk for fractures. AN and obesity are characterized by a severe reduction in fat mass and a high expression of it, respectively, and in both conditions hormones secreted or modulated by body fat content are important determinants of low bone density, impaired bone structure and reduced bone strength. In addition, in both AN and obesity, increased marrow adiposity, which correlates with low bone density, has been observed. This review will discuss the pathophysiological basis of bone alterations associated with AN and obesity, conditions of extreme energy deficiency and excess, respectively.

The obesity of bone

During the last decades, obesity and osteoporosis have become important global health problems, and the belief that obesity is protective against osteoporosis has recently come into question. In fact, some recent epidemiologic and clinical studies have shown that a high level of fat mass might be a risk factor for osteoporosis and fragility fractures. Several potential mechanisms have been proposed to explain the complex relationship between adipose tissue and bone. Indeed, adipose tissue secretes various molecules, named adipokines, which are thought to have effects on metabolic, skeletal and cardiovascular systems. Moreover, fat tissue is one of the major sources of aromatase, an enzyme that synthesizes estrogens from androgen precursors, hormones that play a pivotal role in the maintenance of skeletal homeostasis, protecting against osteoporosis. Moreover, bone cells express several specific hormone receptors and recent observations have shown that bone-derived factors, such as osteocalcin and osteopontin, affect body weight control and glucose homeostasis. Thus, the skeleton is considered an endocrine target organ and an endocrine organ itself, likely influencing other organs as well. Finally, adipocytes and osteoblasts originate from a common progenitor, a pluripotential mesenchymal stem cell, which has an equal propensity for differentiation into adipocytes or osteoblasts (or other lines) under the influence of several cell-derived transcription factors. This review will highlight recent insights into the relationship between fat and bone, evaluating both potential positive and negative influences between adipose and bone tissue. It will also focus on the hypothesis that osteoporosis might be considered the obesity of bone.

Circulating monocytes: an appropriate model for bone-related study

Peripheral blood monocytes (PBMs) are an important source of precursors of osteoclasts, the bone-resorbing cells and the cytokines produced by PBMs that have profound effects on osteoclast differentiation, activation, and apoptosis. So PBMs represent a highly valuable and unique working cell model for bone-related study. Finding an appropriate working cell model for clinical and (epi-)genomic studies of human skeletal disorders is a challenge. Peripheral blood monocytes (PBMs) can give rise to osteoclasts, the bone-resorbing cells. Particularly, PBMs provide the sole source of osteoclast precursors for adult peripheral skeleton where the bone marrow is normally hematopoietically inactive. PBMs can secrete potent pro- and anti-inflammatory cytokines, which are important for osteoclast differentiation, activation, and apoptosis. Reduced production of PBM cytokines represents a major mechanism for the inhibitory effects of sex hormones on osteoclastogenesis and bone resorption. Abnormalities in PBMs have been linked to various skeletal disorders/traits, strongly supporting for the biological relevance of PBMs with bone metabolism and disorders. Here, we briefly review the origin and further differentiation of PBMs. In particular, we discuss the close relationship between PBMs and osteoclasts, and highlight the utility of PBMs in study the pathophysiological mechanisms underlying various skeletal disorders.

Mediators of inflammation and bone remodeling in rheumatic disease

Remodeling of bone is a continuous process that occurs throughout life. Under normal physiologic conditions, bone-resorbing osteoclasts and bone-forming osteoblasts are tightly coupled and regulated to ensure proper balance, such that there is no net change in bone mass. However, inflammation perturbs normal bone homeostasis. The impact of inflammation on bone is dependent upon the anatomic site affected, cell types, factors and cytokines present in the local microenvironment, and local mechanical forces. Cytokines are central to the pathogenesis of inflammation-induced bone loss and contribute to the uncoupling of osteoclast-mediated bone resorption and osteoblast-mediated bone formation, thereby disrupting normal remodeling. In this review, we will discuss the effects of cytokines on bone in two settings, rheumatoid arthritis and spondyloarthritis, a disease category that includes ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease, and juvenile onset spondyloarthropathy. The outcome for bone in these disease settings is quite different, and an understanding of the pathogenic mechanisms leading to the net impact on bone has been essential in developing new therapeutic approaches to bone health in these diseases.

IL-1R/TLR2 through MyD88 Divergently Modulates Osteoclastogenesis through Regulation of Nuclear Factor of Activated T Cells c1 (NFATc1) and B Lymphocyte-induced Maturation Protein-1 (Blimp1)

Toll-like receptors (TLR) and the receptor for interleukin-1 (IL-1R) signaling play an important role in bacteria-mediated bone loss diseases including periodontitis, rheumatoid arthritis, and osteomyelitis. Recent studies have shown that TLR ligands inhibit the receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation from un-committed osteoclast precursors, whereas IL-1 potentiates RANKL-induced osteoclast formation. However, IL-1R and TLR belong to the same IL-1R/TLR superfamily, and activate similar intracellular signaling pathways. Here, we investigate the molecular mechanisms underlying the distinct effects of IL-1 and Porphyromonas gingivalis lipopolysaccharide (LPS-PG) on RANKL-induced osteoclast formation. Our results show that LPS-PG and IL-1 differentially regulate RANKL-induced activation of osteoclast genes encoding Car2, Ctsk, MMP9, and TRAP, as well as expression of NFATc1, a master transcription factor of osteoclastogenesis. Regulation of osteoclast genes and NFATc1 by LPS-PG and IL-1 is dependent on MyD88, an important signaling adaptor for both TLR and IL-1R family members. Furthermore, LPS-PG and IL-1 differentially regulate RANKL-costimulatory receptor OSCAR (osteoclast-associated receptor) expression and Ca(2+) oscillations induced by RANKL. Moreover, LPS-PG completely abrogates RANKL-induced gene expression of B lymphocyte-induced maturation protein-1 (Blimp1), a global transcriptional repressor of anti-osteoclastogenic genes encoding Bcl6, IRF8, and MafB. However, IL-1 enhances RANKL-induced blimp1 gene expression but suppresses the gene expression of bcl6, irf8, and mafb. Our study reveals the involvement of multiple signaling molecules in the differential regulation of RANKL-induced osteoclastogenesis by TLR2 and IL-1 signaling. Understanding the signaling cross-talk among TLR, IL-1R, and RANK is critical for identifying therapeutic strategies to control bacteria-mediated bone loss.

Brucella abortus Invasion of Osteocytes Modulates Connexin 43 and Integrin Expression and Induces Osteoclastogenesis via Receptor Activator of NF-κB Ligand and Tumor Necrosis Factor Alpha Secretion

Osteoarticular brucellosis is the most common localization of human active disease. Osteocytes are the most abundant cells of bone. They secrete factors that regulate the differentiation of both osteoblasts and osteoclasts during bone remodeling. The aim of this study is to determine if Brucella abortus infection modifies osteocyte function. Our results indicate that B. abortus infection induced matrix metalloproteinase 2 (MMP-2), receptor activator for NF-κB ligand (RANKL), proinflammatory cytokines, and keratinocyte chemoattractant (KC) secretion by osteocytes. In addition, supernatants from B. abortus-infected osteocytes induced bone marrow-derived monocytes (BMM) to undergo osteoclastogenesis. Using neutralizing antibodies against tumor necrosis factor alpha (TNF-α) or osteoprotegerin (OPG), RANKL's decoy receptor, we determined that TNF-α and RANKL are involved in osteoclastogenesis induced by supernatants from B. abortus-infected osteocytes. Connexin 43 (Cx43) and the integrins E11/gp38, integrin-α, integrin-β, and CD44 are involved in cell-cell interactions necessary for osteocyte survival. B. abortus infection inhibited the expression of Cx43 but did not modify the expression of integrins. Yet the expression of both Cx43 and integrins was inhibited by supernatants from B. abortus-infected macrophages. B. abortus infection was not capable of inducing osteocyte apoptosis. However, supernatants from B. abortus-infected macrophages induced osteocyte apoptosis in a dose-dependent manner. Taken together, our results indicate that B. abortus infection could alter osteocyte function, contributing to bone damage.

α₂-Antiplasmin is involved in bone loss induced by ovariectomy in mice

The mechanism of postmenopausal osteoporosis is not fully understood. α2-Antiplasmin (α2-AP) is the primary inhibitor of plasmin in the fibrinolytic system, but is known to have activities beyond fibrinolysis. However, its role in bone metabolism and the pathogenesis of osteoporosis remains unknown. In the current study, we therefore examined the effects of α2-AP deficiency on ovariectomy (OVX)-induced bone loss by using wild-type and α2-AP-deficient mice. Quantitative computed tomography analysis revealed that α2-AP deficiency blunted OVX-induced trabecular bone loss in mice. Moreover, α2-AP deficiency significantly blunted serum levels of bone-specific alkaline phosphatase, cross-linked C-telopeptide of type I collagen, and interleukin (IL)-1β elevated by OVX. α2-AP treatment elevated the levels of IL-1β and tumor necrosis factor (TNF)-α mRNA in RAW 264.7 cells, although it suppressed osteoclast formation induced by receptor activator of nuclear factor-κB ligand. α2-AP treatment activated ERK1/2 and p38 MAP kinase pathways in RAW 264.7 cells, and these MAP kinase inhibitors antagonized the levels of IL-1β mRNA elevated by α2-AP. The data demonstrate that α2-AP is linked to bone loss due to OVX, through a mechanism that depends in part on the production of IL-1β and TNF-α in monocytes.

Evaluation of MicroRNA-146a and Its Targets in Gingival Tissues of Patients With Chronic Periodontitis

BACKGROUND

MicroRNAs (miRNAs) are a group of small non-coding RNAs that play an important role in the regulation of gene expression. miRNA-146a (miR-146a), a member of the miR-146 family, is involved in the control of inflammation. Periodontitis is a set of chronic inflammatory disorders of the tissues surrounding the teeth that lead to the breakdown of alveolar bone and tooth loss. In this study, expression levels of miR-146a and its targets, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, are evaluated in human patients with chronic periodontitis (CP).

METHODS

The study population consisted of 10 healthy controls and 20 individuals with CP. For each participant, clinical parameters including probing depth and clinical attachment level were measured, and a gingival tissue sample was collected. Levels of miR-146a, TNF-α, IL-1β, and IL-6 were quantified using real-time polymerase chain reaction.

RESULTS

Levels of miR-146a were significantly higher in patients with CP (P <0.001). There was a positive correlation between levels of miR-146a and clinical parameters (P <0.05). Elevated miR-146a was accompanied by a significant reduction in TNF-α and IL-6 (P <0.001).

CONCLUSIONS

Patients with CP had higher levels of miR-146a than healthy individuals, accompanied by reduced levels of TNF-α and IL-6. A positive relationship between miR-146a levels and clinical parameters suggests a pathophysiologic role of miR-146a in CP.

TNF Induction of NF-κB RelB Enhances RANKL-Induced Osteoclastogenesis by Promoting Inflammatory Macrophage Differentiation but also Limits It through Suppression of NFATc1 Expression

TNF induces bone loss in common bone diseases by promoting osteoclast formation directly and indirectly, but it also limits osteoclast formation by inducing expression of NF-κB p100. Osteoclast precursors (OCPs) are derived from M1 (inflammatory) and M2 (resident) macrophages. However, it is not known if TNF stimulates or limits osteoclast formation through regulation of M1 or M2 differentiation or if RelB, a partner of p100, is involved. To investigate these questions, we treated bone marrow cells (BMCs) with M-CSF alone or in combination with TNF to enrich for OCPs, which we called M-OCPs and T-OCPs, respectively. We found that TNF switched CD11b⁺F4/80⁺ M-OCPs from Ly6C^-Gr1^- M2 to Ly6C⁺Gr1^-CD11c⁺ and Ly6C^-Gr1^-CD11c⁺ M1 cells. RANKL induced osteoclast formation from both Ly6C⁺Gr1^- and Ly6C^-Gr1^- T-OCPs, but only from Ly6C⁺Gr1^- M-OCPs, which formed significantly fewer osteoclasts than T-OCPs. Importantly, Ly6C⁺Gr1^- cells from both M- and T-OCPs have increased expression of the M1 marker genes, iNOS, TNF, IL-1β and TGFβ1, compared to Ly6C^-Gr1^- cells, and Ly6C^-Gr1^- cells from T-OCPs also have increased expression of iNOS and TGFβ1 compared to cells from M-OCPs. Both RANKL and TNF increased RelB mRNA expression. TNF significantly increased RelB protein levels, but RANKL did not because it also induced RelB proteasomal degradation. TNF inhibited RANKL-induced NFATc1 mRNA expression and osteoclast formation from M-OCPs, but not from T-OCPs, and it did not induce Ly6C⁺Gr1^-CD11c⁺ or Ly6C^-Gr1^-CD11c⁺ M1 macrophages from RelB-/- BMCs. Furthermore, overexpression of RelB in M-OCPs reduced RANKL-induced osteoclast formation and NFATc1 mRNA expression, but it increased TNF-induced OC formation without affecting NFATc1 levels. Thus, TNF induction of RelB directly mediates terminal osteoclast differentiation independent of NFATc1 and limits RANKL-induced osteoclastogenesis by inhibiting NFATc1 activation. However, the dominant role of TNF is to expand the OCP pool by switching the differentiation of M-CSF-induced M2 to M1 macrophages with enhanced osteoclast forming potential. Strategies to degrade RelB could prevent TNF-induced M2/M1 switching and reduce osteoclast formation.

The IVVY Motif and Tumor Necrosis Factor Receptor-associated Factor (TRAF) Sites in the Cytoplasmic Domain of the Receptor Activator of Nuclear Factor κB (RANK) Cooperate to Induce Osteoclastogenesis

Receptor activator of NF-κB (RANK) activation by RANK ligand (RANKL) mediates osteoclastogenesis by recruiting TNF receptor-associated factors (TRAFs) via three cytoplasmic motifs (motif 1, PFQEP(369-373); motif 2, PVQEET(559-564); and motif 3, PVQEQG(604-609)) to activate the NF-κB and MAPK signaling pathways. RANK also has a TRAF-independent motif (IVVY(535-538)), which is dispensable for the activation of TRAF-induced signaling pathways but essential for osteoclast lineage commitment by inducing the expression of nuclear factor of activated T-cells c1 (NFATc1) to regulate osteoclast gene expression. Notably, TNF/IL-1-mediated osteoclastogenesis requires RANK ligand assistance, and the IVVY motif is also critical for TNF/IL-1-mediated osteoclastogenesis by rendering osteoclast genes responsive to these two cytokines. Here we show that the two types of RANK cytoplasmic motifs have to be on the same RANK molecule to mediate osteoclastogenesis, suggesting a functional cooperation between them. Subsequent osteoclastogenesis assays with TNF or IL-1 revealed that, although all three TRAF motifs play roles in TNF/IL-1-mediated osteoclastogenesis, motifs 2 and 3 are more potent than motif 1. Accordingly, inactivation of motifs 2 and 3 blocksTNF/IL-1-mediated osteoclastogenesis. Mechanistically, double mutation of motifs 2 and 3, similar to inactivation of the IVVY motif, abrogates the expression of nuclear factor of activated T-cells c1 and osteoclast genes in assays reflecting RANK-initiated and TNF/IL-1-mediated osteoclastogenesis. In contrast, double inactivation of motifs 2 and 3 did not affect the ability of RANK to activate the NF-κB and MAPK signaling pathways. Collectively, these results indicate that the RANK IVVY motif cooperates with the TRAF-binding motifs to promote osteoclastogenesis, which provides novel insights into the molecular mechanism of RANK signaling in osteoclastogenesis.

Modeling effects of dexamethasone on disease progression of bone mineral density in collagen-induced arthritic rats

A mechanism-based model was developed to characterize the crosstalk between proinflammatory cytokines, bone remodeling biomarkers, and bone mineral density (BMD) in collagen-induced arthritic (CIA) rats. Male Lewis rats were divided into five groups: healthy control, CIA control, CIA receiving single 0.225 mg kg⁻¹ subcutaneous (SC) dexamethasone (DEX), CIA receiving single 2.25 mg kg⁻¹ SC DEX, and CIA receiving chronic 0.225 mg kg⁻¹ SC DEX. The CIA rats underwent collagen induction at day 0 and DEX was injected at day 21 post-induction. Disease activity was monitored throughout the study and rats were sacrificed at different time points for blood and paw collection. Protein concentrations of interleukin (IL)-1β, IL-6, receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), and tartrate-resistant acid phosphatase 5b (TRACP-5b) in paws were measured by enzyme-linked immunosorbent assays (ELISA). Disease progression and DEX pharmacodynamic profiles of IL-1β, IL-6, RANKL, and OPG were fitted simultaneously and parameters were sequentially applied to fit the TRACP-5b and BMD data. The model was built according to the mechanisms reported in the literature and modeling was performed using ADAPT 5 software with naïve pooling. Time profiles of IL-1β and IL-6 protein concentrations correlated with their mRNAs. The RANKL and OPG profiles matched previous findings in CIA rats. DEX inhibited the expressions of IL-1β, IL-6, and RANKL, but did not alter OPG. TRACP-5b was also inhibited by DEX. Model predictions suggested that anti-IL-1β therapy and anti-RANKL therapy would result in similar efficacy for prevention of bone loss among the cytokine antagonists.

NF-κB decoy oligodeoxynucleotide inhibits wear particle-induced inflammation in a murine calvarial model

Wear particles induce periprosthetic inflammation and osteolysis through activation of nuclear factor kappa B (NF-κB), which up-regulates the downstream target gene expression for proinflammatory cytokines in macrophages. It was hypothesized that direct suppression of NF-κB activity in the early phases of this disorder could be a therapeutic strategy for preventing the inflammatory response to wear particles, potentially mitigating osteolysis. NF-κB activity can be suppressed via competitive binding with double stranded NF-κB decoy oligodeoxynucleotides (ODNs) that blocks this transcription factor from binding to the promoter regions of targeted genes. In this murine calvarial study, clinically relevant polyethylene particles (PEs) with/without ODN were subcutaneously injected over the calvarial bone. In the presence of PE particles, macrophages migrated to the inflammatory site and induced tumor necrosis factor alpha (TNF-α) and receptor activator of nuclear factor kappa B ligand (RANKL) expression, resulting in an increase in the number of osteoclasts. Local injections of ODN mitigated the expression of TNF-α, RANKL, and induced the expression of two anti-inflammatory, antiresorptive cytokines: interleukin-1 receptor antagonist and osteoprotegerin. Local intervention with NF-κB decoy ODN in early cases of particle-induced inflammation in which the prosthesis is still salvageable may potentially preserve periprosthetic bone stock.

Inflammation and skeletal metastasis

On the road to metastasis a cancer cell has to overcome two major obstacles: the physical escape from the primary tumor to a distant tissue and the adaptation to the new microenvironment via colonization and the formation of a secondary tumor. Accumulated scientific findings support the hypothesis that inflammation is a critical component of the tumor microenvironment and develops as a result of tumor-induced recruitment of inflammatory cells and their reciprocal interaction with other cells from the tumor network. These interactions modulate immune responses to suppress antitumor immunity and activate feedback amplification signaling loops that link nearly all the cells in the cancer inflammatory milieu. The coordinated regulation of cytokines/chemokines, receptors and other inflammatory mediators enables the different steps of the metastatic cascade. As a target organ for colonization, the bone is rich in inflammatory mediators that are critical for successful cancer growth. In this review, we focus on the inflammatory cells, molecules and mechanisms that facilitate the expansion of cancer cells from the primary tumor to their new 'home' in the skeleton.

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

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

Sexual Dimorphism in MAPK-Activated Protein Kinase-2 (MK2) Regulation of RANKL-Induced Osteoclastogenesis in Osteoclast Progenitor Subpopulations

Osteoclasts (OCs) are bone-resorptive cells critical for maintaining skeletal integrity through coupled bone turnover. OC differentiation and activation requires receptor activator of NF-kB ligand (RANKL) signaling through the p38 MAPK pathway. However the role of the p38 MAPK substrate, MAPK-activated protein kinase 2 (MK2), is not clearly delineated. Within the bone marrow exists a specific subpopulation of defined osteoclast progenitor cells (dOCPs) with surface expression of B220^-Gr1^-CD11b^lo/-CD115⁺ (dOCP^lo/-). In this study, we isolated dOCPs from male and female mice to determine sex-specific effects of MK2 signaling in osteoclastogenesis (OCgen). Male Mk2^-/- mice display an increase in the dOCP^lo cell population when compared to Mk2^+/+ mice, while female Mk2^-/- and Mk2^+/+ mice exhibit no difference. Defined OCPs from male and female Mk2^+/+ and Mk2^-/- bone marrow were treated with macrophage colony stimulation factor (M-CSF) and RANKL cytokines to promote OCgen. RANKL treatment of dOCP^lo cells stimulated p38 and MK2 phosphorylation. Tartrate-resistant acid phosphatase (TRAP) assays were used to quantify OC number, size, and TRAP enzyme activity post-RANKL stimulation. MK2 signaling was critical for male dOCP^lo OCgen, yet MK2 signaling regulated OCgen from female dOCP^- and CD11b^hi subpopulations as well. The functional gene, Ctsk, was attenuated in both male and female Mk2^-/- dOCP^lo-derived OCs. Conversely, MK2 signaling was only critical for gene expression of pre-OC fusion genes, Oc-stamp andTm7sf4, in male OCgen. Therefore, these data suggest there is a sexual dimorphism in MK2 signaling of OCP subpopulations.

Bone Loss Triggered by the Cytokine Network in Inflammatory Autoimmune Diseases

Bone remodeling is a lifelong process in vertebrates that relies on the correct balance between bone resorption by osteoclasts and bone formation by osteoblasts. Bone loss and fracture risk are implicated in inflammatory autoimmune diseases such as rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease, and systemic lupus erythematosus. The network of inflammatory cytokines produced during chronic inflammation induces an uncoupling of bone formation and resorption, resulting in significant bone loss in patients with inflammatory autoimmune diseases. Here, we review and discuss the involvement of the inflammatory cytokine network in the pathophysiological aspects and the therapeutic advances in inflammatory autoimmune diseases.

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.

Compression and hypoxia play independent roles while having combinative effects in the osteoclastogenesis induced by periodontal ligament cells

OBJECTIVE

To investigate the isolated and combined effects of compression and hypoxia on the osteoclastogenesis induced by periodontal ligament cells (PDLCs).

MATERIALS AND METHODS

A periodontal ligament tissue model (PDLtm) was established by 3-D culturing human PDLCs on a thin sheet of poly lactic-co-glycolic acid scaffold. The PDLtm was treated with hypoxia and/or compression for 6, 24, or 72 hours. After that, a real-time polymerase chain reaction was used for gene expression analysis. The conditioned media were used for the coculture of osteoblast and osteoclast (OC) precursors; tartrate-resistant acid phosphatase staining was done to examine OC formation.

RESULTS

Either compression or hypoxia alone significantly up-regulated the gene expression of pro-osteoclastogenic cytokines in the PDLtm and enhanced osteoclastogenesis in the cocultures, and the combination of the two had significantly stronger effects than either stimulation alone. In addition, comparing the two stimulants, we found that the osteoclastogenic property of the PDLCs peaked earlier (at 6 hours) in the compression group than in the hypoxia group (at 24 hours).

CONCLUSIONS

Both compressive force and hypoxia may take part in initiating osteoclastogenesis in orthodontic tooth movement and may have combinatory effects, which could update our concepts of the mechanisms involved in the initiation of bone resorption on the pressure side of the tooth in question.

MicroRNA-20a regulates autophagy related protein-ATG16L1 in hypoxia-induced osteoclast differentiation

Autophagy and autophagy-related proteins (ATGs) play decisive roles in osteoclast differentiation. Emerging lines of evidence show the deregulation of miRNA in autophagic responses. However, the role of hypoxia and involvement of miRNA in osteoclast differentiation are unclear. In the present study, we demonstrate that hypoxia caused induction of autophagy and osteoclast differentiation markers in RAW264.7 cells stimulated with M-CSF and RANKL. In addition, miR-20a was significantly repressed during hypoxia and identified as the prime candidate involved in hypoxia-induced osteoclast differentiation. The results from dual luciferase reporter assay revealed that miR-20a directly targets Atg16l1 by binding to its 3'UTR end. Further, miR-20a transfection studies showed significant down regulation of autophagic proteins (LC3-II and ATG16L1) and osteoclast differentiation markers (Nfatc1, Traf6, and Trap) thus confirming the functional role of miR-20a under hypoxic conditions. Results of chromatin immunoprecipitation assay showed that HIF-1α binds to miRNA-20a. From miRNA Q-PCR results, we confirmed that shRNA HIF-1α knockdown significantly downregulated both autophagy (LC3, p62, Atg5, Atg12, Atg16l1, Atg7, Becn1, Atg9a) and osteoclast markers (Traf6, Nfatc1, Ctsk, cFos, Mmp9, Trap) in RAW264.7 cells. Thus, our findings suggest that the regulatory axis of HIF-1α-miRNA-20a-Atg16l1 might be a critical mechanism for hypoxia-induced osteoclast differentiation.

The antidepressant bupropion exerts alleviating properties in an ovariectomized osteoporotic rat model

AIM

Depression is a risk factor for impaired bone mass and micro-architecture, but several antidepressants were found to increase the incidence of osteoporotic fractures. In the present study we used ovariectomized (OVX) rats as a model of osteoporosis to investigate the effects of the antidepressant bupropion on the femoral bones.

METHODS

OVX animals were treated with bupropion (30, 60 mg·kg(-1)·d(-1)) for six weeks. Bone turnover biomarkers (urinary DPD/Cr ratio, serum BALP, OC, TRAcP 5b, CTX and sRANKL levels) and inflammatory cytokines (TNF-α, IL-1β and IL-6) were determined using ELISA. Inductively coupled plasma mass spectroscopy (ICP-MS) was used to determine the femoral bone mineral concentrations. The cortical and trabecular morphometric parameters of femoral bones were determined using micro-CT scan and histopathology.

RESULTS

In OVX rats, the levels of bone turnover biomarkers and inflammatory cytokines were significantly elevated and femoral bone Ca(2+) and PO4(3-) concentrations were significantly reduced. Moreover, cortical and trabecular morphometric parameters and histopathology of femoral bones were severely altered by ovariectomy. Bupropion dose-dependently inhibited the increases in bone turnover biomarkers and inflammatory cytokines. OVX rats treated with the high dose of bupropion showed normal mineral concentrations in femoral bones. The altered morphometric parameters and histopathology of femoral bones were markedly attenuated by the treatment.

CONCLUSION

Bupropion exerts osteo-protective action in OVX rats through suppressing osteoclastogenesis-inducing factors and inflammation, which stabilize the osteoclasts and decrease bone matrix degradation or resorption.

Enterococcus faecalis attenuates the differentiation of macrophages into osteoclasts

INTRODUCTION

Enterococcus faecalis is closely associated with refractory apical periodontitis, manifesting periapical lesions and alveolar bone loss. Macrophages playing an important role in the induction of inflammation can differentiate into bone-resorbing osteoclasts. In the present study, we investigated the effect of E. faecalis on the differentiation and function of macrophages as osteoclast precursors.

METHODS

Bone marrow-derived macrophages (BMMs) were differentiated into osteoclasts with macrophage colony-stimulating factor and receptor activator of nuclear factor kappa B ligand in the presence or absence of heat-killed E. faecalis (HKEF). Tartrate-resistant acid phosphatase-positive multinucleated giant cells were analyzed to determine osteoclast differentiation. Western blotting was performed to examine the expression of c-Fos and NFATc1 transcription factors. Phagocytic capacity was analyzed by measuring uptake of carboxyfluorescein succinimidyl ester-labeled E. faecalis. Secretion of tumor necrosis factor-α, interleukin-6, keratinocyte-derived chemokine, and monocyte chemotactic protein-1 was determined by enzyme-linked immunosorbent assay.

RESULTS

Differentiation of BMMs into osteoclasts was attenuated in the presence of HKEF, and expression of c-Fos and NFATc1 was inhibited. HKEF exposure also prevented a reduction in the phagocytic capacity of BMMs after differentiation into osteoclasts. Concomitantly, HKEF induced the expression of chemokines monocyte chemotactic protein-1 and keratinocyte-derived chemokine and proinflammatory cytokines tumor necrosis factor-α and interleukin-6.

CONCLUSIONS

E. faecalis attenuated macrophages from differentiating into osteoclasts, allowing them to keep their ability to phagocytose and kill pathogens and to induce proinflammatory cytokine and chemokine secretion.