Binding Immunoglobulin Protein (BIP) Inhibits TNF-α-Induced Osteoclast Differentiation and Systemic Bone Loss in an Erosive Arthritis Model.

OBJECTIVE: The association between inflammation and dysregulated bone remodeling is apparent in rheumatoid arthritis and is recapitulated in the human tumor necrosis factor transgenic (hTNFtg) mouse model. We investigated whether extracellular binding immunoglobulin protein (BiP) would protect the hTNFtg mouse from both inflammatory arthritis as well as extensive systemic bone loss and whether BiP had direct antiosteoclast properties in vitro. METHODS: hTNFtg mice received a single intraperitoneal administration of BiP at onset of arthritis. Clinical disease parameters were measured weekly. Bone analysis was performed by microcomputed tomography and histomorphometry. Mouse bone marrow macrophage and human peripheral blood monocyte precursors were used to study the direct effect of BiP on osteoclast differentiation and function in vitro. Monocyte and osteoclast signaling was analyzed by Western blotting, flow cytometry, and imaging flow cytometry. RESULTS: BiP-treated mice showed reduced inflammation and cartilage destruction, and histomorphometric analysis revealed a decrease in osteoclast number with protection from systemic bone loss. Abrogation of osteoclast function was also observed in an ex vivo murine calvarial model. BiP inhibited differentiation of osteoclast precursors and prevented bone resorption by mature osteoclasts in vitro. BiP also induced downregulation of CD115/c-Fms and Receptor Activator of NF-κB (RANK) messenger RNA and protein, causing reduced phosphorylation of the p38 mitogen-activated protein kinases, extracellular signal-regulated kinases 1/2 and p38, with suppression of essential osteoclast transcription factors, c-Fos and NFATc1. BiP directly inhibited TNF-α- or Receptor Activator of NF-κB Ligand (RANKL)-induced NF-κB nuclear translocation in THP-1 monocytic cells and preosteoclasts by the canonical and noncanonical pathways. CONCLUSION: BiP combines an anti-inflammatory function with antiosteoclast activity, which establishes it as a potential novel therapeutic for inflammatory disorders associated with bone loss.

Inhibition of HDAC activity by ITF2357 ameliorates joint inflammation and prevents cartilage and bone destruction in experimental arthritis.

Inhibition of histone deacetylases (HDAC) has been shown to modulate gene expression and cytokine production after stimulation with several stimuli. In the present study, the antiinflammatory effect of a potent HDACi, ITF2357, was explored in different experimental models of arthritis. In addition, the bone protective effect of ITF2357 was investigated in vitro. Treatment of acute arthritis (Streptococcus pyogenes cell wall [SCW] arthritis) with ITF2357 showed that joint swelling and cell influx into the joint cavity were reduced. Furthermore, the chondrocyte metabolic function was improved by treatment of ITF2357. The production of proinflammatory cytokines by synovial tissue was reduced after ITF2357 treatment. To examine the effect of HDAC inhibition on joint destruction, ITF2357 was applied to both rat adjuvant arthritis and mouse collagen type II arthritis. ITF2357 treatment both ameliorates the severity scores in arthritis models and prevents bone destruction. In an in vitro bone destruction assay, ITF2357 was highly effective at a dose of 100 nmol/L. In conclusion, inhibition of HDAC prevents joint inflammation and cartilage and bone destruction in experimental arthritis.

The effect of ultrasound on angiogenesis: an in vivo study using the chick chorioallantoic membrane.

PURPOSE: Ultrasound therapy induces clinical healing of irradiated avascular mandibular bone and fractures. In vitro ultrasound in tissue culture has been shown to stimulate bone formation synthesis and bone remodeling factors and to stimulate osteoblast proliferation. Therefore, the aim of the present study was to investigate the effect of short-wave (1-MHz) and long-wave (45-kHz) ultrasound on the vascularity of the chorioallantoic membrane (CAM) of a fertilized egg. MATERIALS AND METHODS: The nature of the angiogenic effect was investigated using the CAM of a fertilized egg by: (1) application of sonicated fibroblast media incorporated into methylcellulose disks onto the CAM and (2) direct application of the ultrasound, using both long-wave (45-kHz) and short-wave (1-MHz) frequencies at a range of intensities, to the surface of the egg. Angiogenesis was assessed quantitatively by three independent observers. RESULTS: Both ultrasound methods showed evidence of an angiogenic effect compared to controls. The most effective results were seen with direct application of a 45-kHz wave at an intensity of 15 mW/cm(2) and indirect application of the media of fibroblasts ultrasonicated at 1 MHz with an intensity of 0.4 W/cm(2). CONCLUSION: This model confirms that ultrasound can induce neoangiogenesis in vivo.

The two homologous chaperonin 60 proteins of Mycobacterium tuberculosis have distinct effects on monocyte differentiation into osteoclasts.

Mycobacterium tuberculosis produces two homologous chaperonin (Cpn)60 proteins, Cpn60.1 and Cpn60.2 (Hsp65). Both proteins stimulate human and murine monocyte cytokine synthesis but, unlike Cpn60 proteins from other microbial species, fail to stimulate the breakdown of cultured murine bone. Here, we have examined the mechanism of action of these proteins on bone remodelling and osteoclastogenesis, induced in vitro in murine calvarial explants and the murine monocyte cell line RAW264.7. Additionally, we have determined their effect on bone remodelling in vivo in an animal model of arthritis. Recombinant Cpn60.1 but not Cpn60.2 inhibited bone breakdown both in vitro, in murine calvaria and in vivo, in experimental arthritis. Analysis of the mechanism of action of Cpn60.1 suggests that this protein works by directly blocking the synthesis of the key osteoclast transcription factor, nuclear factor of activated T cells c1. The detection of circulating immunoreactive intact Cpn60.1 in a small number of patients with tuberculosis but not in healthy controls further suggests that the skeleton may be affected in patients with tuberculosis. Taken together, these findings reveal that M. tuberculosis Cpn60.1 is a potent and novel inhibitor of osteoclastogenesis both in vitro and in vivo and a potential cure for bone-resorptive diseases like osteoporosis.

Invasion of bone cells by Staphylococcus epidermidis.

Bone implants infected with Staphylococcus epidermidis often require surgical intervention because of the failure of antibiotic treatment. The reasons why such infections are resistant to therapy are poorly understood. We have previously reported that another bacterium, Staphylococcus aureus, can invade bone cells and thereby evade antimicrobial therapy. In this study we have investigated the hypothesis that S. epidermidis can also invade bone cells and may therefore explain the difficulties of treating infections with this organism. We found that S. epidermidis was capable of invading bone cells but that there were significant strain dependent differences in this capacity. A recombinant protein encompassing the D1-D4 repeat region of S. aureus fibronectin-binding protein B completely inhibited internalization of S. aureus but failed to block internalization of S. epidermidis. Similarly a blocking antibody to alpha5beta1 integrin inhibited internalization of S. aureus by bone cells but had no effect on the uptake of S. epidermidis. Therefore unlike S. aureus, S. epidermidis does not gain entrance into bone cells through a fibronectin bridge between the alpha5beta1 integrin and a bacterial adhesin.

Long wave ultrasound may enhance bone regeneration by altering OPG/RANKL ratio in human osteoblast-like cells.

Human osteoblast cell line (MG63) cells were treated with long wave (45 kHz, intensity 30 mW/cm(2)) continuous ultrasound (US) for 5 min and incubated for various time periods following the treatment. The reverse transcriptase polymerase chain reaction (RT-PCR) technique was used for observing the genetic expression and real-time PCR for quantitative analysis of receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) along with alkaline phosphatase (ALP), an early bone marker, and osteocalcin (OCN) a late marker. ELISA was performed to estimate the amount of the cytokine released into the culture media. The osteoblasts responded to US by significantly upregulating both the OPG mRNA and protein levels. There was no RANKL mRNA expression observed in both the US and control groups and the protein levels were also very low in both groups. There was also no TNF-alpha expression and the TNF-alpha protein levels were insignificant. ALP and OCN mRNA were significantly upregulated in the US group. To our knowledge, this is the first study that shows the effect of US on OPG, RANKL and TNF-alpha expression. US appears to upregulate OPG and may downregulate RANKL production. From these findings, we conclude that therapeutic ultrasound may increase bone regeneration by altering the OPG/RANKL ratio in the bone microenvironment.

Hypoxia is a major stimulator of osteoclast formation and bone resorption.

Hypoxia is known to act as a general stimulator of cells derived from marrow precursors. We investigated the effect of oxygen tension on the formation and function of osteoclasts, the cells responsible for bore resorption, which are of promonocytic origin. Using 7- and 13-day cultures of mouse marrow cells on ivory discs, we found that reducing oxygen tension from the ambient atmospheric level of 20% by increasing the proportion of nitrogen caused progressive increases in the formation of multinucleated osteoclasts and resorption pits. Peak effects occurred in 2% oxygen, where stimulations of resorption up to 21-fold were measured. Significant stimulations of osteoclast formation and resorption were observed even in severely hypoxic cultures gassed with 0.2% oxygen. Short-term cultures of cells disaggregated from rat bones indicated that hypoxia did not alter the resorptive activity of mature osteoclasts, but reduced their survival or adherence. In 3-day organ cultures of mouse calvarial bones, exposure to 2% oxygen resulted in maximal, fivefold stimulation of osteoclast-mediated calcium release, an effect equivalent to that of prostaglandin E(2) (PGE(2)), a reference osteolytic agent. Hypoxia also caused a moderate acidosis in calvarial cultures, presumably as a result of increased anaerobic metabolism; this observation is significant because osteoclast activation is dependent on extracellular acidification. Our experiments reveal a previously-overlooked mechanism of considerable potential importance for the regulation of bone destruction. These findings may help explain the bone loss associated with a wide range of pathological states involving local or systemic hypoxia, and emphasize the importance of the vasculature in bone.