Interleukin (IL)-6 induction of osteoclast differentiation depends on IL-6 receptors expressed on osteoblastic cells but not on osteoclast progenitors

Cell-specific paracrine actions of IL-6 family cytokines from bone, marrow and muscle that control bone formation and resorption

Bone renews itself and changes shape throughout life to account for the changing needs of the body; this requires co-ordinated activities of bone resorbing cells (osteoclasts), bone forming cells (osteoblasts) and bone's internal cellular network (osteocytes). This review focuses on paracrine signaling by the IL-6 family of cytokines between bone cells, bone marrow, and skeletal muscle in normal physiology and in pathological states where their levels may be locally or systemically elevated. These functions include the support of osteoclast formation by osteoblast lineage cells in response to interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM) and cardiotrophin 1 (CT-1). In addition it will discuss how bone-resorbing osteoclasts promote osteoblast activity by secreting CT-1, which acts as a "coupling factor" on osteocytes, osteoblasts, and their precursors to promote bone formation. OSM, produced by osteoblast lineage cells and macrophages, stimulates bone formation via osteocytes. IL-6 family cytokines also mediate actions of other bone formation stimuli like parathyroid hormone (PTH) and mechanical loading. CT-1, OSM and LIF suppress marrow adipogenesis by shifting commitment of pluripotent precursors towards osteoblast differentiation. Ciliary neurotrophic factor (CNTF) is released as a myokine from skeletal muscle and suppresses osteoblast differentiation and bone formation on the periosteum (outer bone surface in apposition to muscle). Finally, IL-6 acts directly on marrow-derived osteoclasts to stimulate release of "osteotransmitters" that act through the cortical osteocyte network to stimulate bone formation on the periosteum. Each will be discussed as illustrations of how the extended family of IL-6 cytokines acts within the skeleton in physiology and may be altered in pathological conditions or by targeted therapies.

Generation of a transgenic mouse line for conditional expression of human IL-6

IL-6 is a cytokine that is involved in various physiological and pathological conditions, and approaches using gain-of-function transgenic animals have contributed in elucidating IL-6 function. However, studies of the multiple functions of IL-6 in vivo are very time consuming because they require the generation of transgenic mice that harbor the gene encoding IL-6 under the control of specific promoters to mimic different pathologies. Here, we report the establishment of a conditional human IL-6 transgenic mouse, LGL-IL6, which conditionally expresses human IL-6 by taking advantage of the well-characterized Cre recombinase drivers.

ABL kinases promote breast cancer osteolytic metastasis by modulating tumor-bone interactions through TAZ and STAT5 signaling

Bone metastases occur in up to 70% of advanced breast cancer. For most patients with breast cancer, bone metastases are predominantly osteolytic. Interactions between tumor cells and stromal cells in the bone microenvironment drive osteolytic bone metastasis, a process that requires the activation of osteoclasts, cells that break down bone. We report that ABL kinases promoted metastasis of breast cancer cells to bone by regulating the crosstalk between tumor cells and the bone microenvironment. ABL kinases protected tumor cells from apoptosis induced by TRAIL (TNF-related apoptosis-inducing ligand), activated the transcription factor STAT5, and promoted osteolysis through the STAT5-dependent expression of genes encoding the osteoclast-activating factors interleukin-6 (IL-6) and matrix metalloproteinase 1 (MMP1). Furthermore, in breast cancer cells, ABL kinases increased the abundance of the Hippo pathway mediator TAZ and the expression of TAZ-dependent target genes that promote bone metastasis. Knockdown of ABL kinases or treatment with ABL-specific allosteric inhibitor impaired osteolytic metastasis of breast cancer cells in mice. These findings revealed a role for ABL kinases in regulating tumor-bone interactions and provide a rationale for using ABL-specific inhibitors to limit breast cancer metastasis to bone.

WHI-131 Promotes Osteoblast Differentiation and Prevents Osteoclast Formation and Resorption in Mice

The small molecule WHI-131 is a potent therapeutic agent with anti-inflammatory, antiallergic, and antileukemic potential. However, the regulatory effects of WHI-131 on osteoblast and osteoclast activity are unclear. We examined the effects of WHI-131 on osteoblast and osteoclast differentiation with respect to bone remodeling. The production of receptor activator of nuclear factor kappa-B ligand (RANKL) by osteoblasts in response to interleukin (IL)-1 or IL-6 stimulation decreased by 56.8% or 50.58%, respectively, in the presence of WHI-131. WHI-131 also abrogated the formation of mature osteoclasts induced by IL-1 or IL-6 stimulation. Moreover, WHI-131 treatment decreased RANKL-induced osteoclast differentiation of bone marrow-derived macrophages, and reduced the resorbing activity of mature osteoclasts. WHI-131 further decreased the mRNA and protein expression levels of c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) by almost twofold, and significantly downregulated the mRNA expression of the following genes: tartrate-resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR), DC-STAMP, OC-STAMP, ATP6v0d2, and cathepsin K (CtsK) compared with the control group. WHI-131 further suppressed the phosphorylation of protein kinase B (Akt) and degradation of inhibitor of kappa B (IκB); Ca(2+) oscillation was also affected, and phosphorylation of the C-terminal Src kinase (c-Src)-Bruton agammaglobulinemia tyrosine kinase (Btk)-phospholipase C gamma 2 (PLCγ2) (c-Src-Btk-PLCg2 calcium signaling pathway) was inhibited following WHI-131 treatment. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway was activated by WHI-131, accompanied by phosphorylation of STAT3 Ser727 and dephosphorylation of STAT6. In osteoblasts, WHI-131 caused an approximately fourfold increase in alkaline phosphatase activity and Alizarin Red staining intensity. Treatment with WHI-131 increased the mRNA expression levels of genes related to osteoblast differentiation, and induced the phosphorylation of Akt, p38, and Smad1/5/8. Furthermore, 5-week-old ICR mice treated with WHI-131 exhibited antiresorbing effects in a lipopolysaccharide-induced calvaria bone loss model in vivo and increased bone-forming activity in a calvarial bone formation model. Therefore, the results of this study show that WHI-131 plays a dual role by inhibiting osteoclast differentiation and promoting osteoblast differentiation. Thus, WHI-131 could be a useful pharmacological agent to treat osteoporosis by promoting bone growth and inhibiting resorption.

Stromal-Initiated Changes in the Bone Promote Metastatic Niche Development

More than 85% of advanced breast cancer patients suffer from metastatic bone lesions, yet the mechanisms that facilitate these metastases remain poorly understood. Recent studies suggest that tumor-derived factors initiate changes within the tumor microenvironment to facilitate metastasis. However, whether stromal-initiated changes are sufficient to drive increased metastasis in the bone remains an open question. Thus, we developed a model to induce reactive senescent osteoblasts and found that they increased breast cancer colonization of the bone. Analysis of senescent osteoblasts revealed that they failed to mineralize bone matrix and increased local osteoclastogenesis, the latter process being driven by the senescence-associated secretory phenotype factor, IL-6. Neutralization of IL-6 was sufficient to limit senescence-induced osteoclastogenesis and tumor cell localization to bone, thereby reducing tumor burden. Together, these data suggest that a reactive stromal compartment can condition the niche, in the absence of tumor-derived signals, to facilitate metastatic tumor growth in the bone.

Activin-βC modulates cachexia by repressing the ubiquitin-proteasome and autophagic degradation pathways

BACKGROUND

Cancer-associated cachexia and muscle wasting are considered key determinants of cancer-related death and reduction in the quality of life of cancer patients. A crucial link has been established between activin signaling and skeletal muscle atrophy-hypertrophy. We previously showed that activin-βC, a novel activin-A antagonist, is a tumor modulator that abolishes the cancer-associated cachexia in a mouse genetic model of gonadal tumorigenesis, in which the normal balance of inhibin/activin signalling is disrupted by a targeted mutation in the Inha gene (inhibin α-KO mouse). This study aimed to identify the molecular mechanism by which activin-βC increases survival and abolishes cancer-associated cachexia in α-KO mice. We hypothesized that overexpression of activin-βC modulates the cachexia phenotype by antagonizing the activin signaling pathway and repressing muscle wasting via the ubiquitin-proteasome and the autophagic-lysosomal degradation pathways.

METHODS

Male and female ActC++, α-KO, and α-KO/ActC++ mice and WT littermate controls were studied. Western blot analysis for the specific E3 ubiquitin ligases, atrogin-1 and MuRF1, markers of the autophagic-lysosomal pathway, Beclin-1, p62, and LC3A/B, effectors Smad-2, Smad-3 and myostatin was performed in the gastrocnemius of age-matched mice. Histopathology of the gastrocnemius and survival analysis were also conducted in animals from the same breeding cohort. Serum levels of activin-A, inflammatory cytokines, hormonal profile, and bone density were also assessed.

RESULTS

Increased levels of atrogin-1, MuRF-1, Beclin-1, p62, LC3A/B-I, Smad-2 and serum levels of activin-A were noted in the α-KO mice. These mice developed gonadal cancers followed by severe weight loss, and reduced survival. Overexpression of activin- βC antagonized the activin signaling cascade, attenuating the ubiquitin-proteasome and the autophagic-lysosomal degradation pathways, and reduced serum levels of activin-A. α-KO/ActC++ mice displayed a less aggressive cachectic phenotype, reduced tumor weight, and prolonged survival.

CONCLUSION

Our findings show for the first time a specific effect of activin-βC on muscle wasting and transcription factors involved in muscle protein degradation. The study indicates that activin-βC may be a novel therapy to abrogate cancer-associated weight loss and prolong survival.

Ablation of p38α MAPK Signaling in Osteoblast Lineage Cells Protects Mice From Bone Loss Induced by Estrogen Deficiency

Estrogen deficiency causes bone loss by increasing the number of bone-resorbing osteoclasts. Selective p38α MAPK inhibitors prevent bone-wasting effects of estrogen withdrawal but implicated mechanisms remain to be identified. Here, we show that inactivation of the p38α-encoding gene in osteoblast lineage cells with the use of an osteocalcin-cre transgene protects mice from ovariectomy-induced bone loss (a murine model of postmenopausal osteoporosis). Ovariectomy fails to induce bone loss, increase bone resorption, and stimulate receptor activator of nuclear factor κB ligand and IL-6 expression in mice lacking p38α in osteoblasts and osteocytes. Finally, TNFα or IL-1, which are osteoclastogenic cytokines overproduced in the bone marrow under estrogen deficiency, can activate p38α signaling in osteoblasts, but those cytokines cannot enhance Rankl and Il6 expressions or increase osteoclast formation in p38a-deficient osteoblast cultures. These findings demonstrate that p38α MAPK signaling in osteoblast lineage cells mediates ovariectomy-induced bone loss by up-regulating receptor activator of nuclear factor κB ligand and IL-6 production.

Glycoprotein130 (Gp130)/interleukin-6 (IL-6) signalling in osteoclasts promotes bone formation in periosteal and trabecular bone

Interleukin-6 (IL-6) and interleukin-11 (IL-11) receptors (IL-6R and IL-11R, respectively) are both expressed in osteoclasts and transduce signal via the glycoprotein130 (gp130) co-receptor, but the physiological role of this pathway is unclear. To determine the critical roles of gp130 signalling in the osteoclast, we generated mice using cathepsin K Cre (CtskCre) to disrupt gp130 signalling in osteoclasts. Bone marrow macrophages from CtskCre.gp130(f/f) mice generated more osteoclasts in vitro than cells from CtskCre.gp130(w/w) mice; these osteoclasts were also larger and had more nuclei than controls. While no increase in osteoclast numbers was observed in vivo, osteoclasts on trabecular bone surfaces of CtskCre.gp130(f/f) mice were more spread out than in control mice, but had no functional defect detectable by serum CTX1 levels or trabecular bone cartilage remnants. However, trabecular osteoblast number and mineralising surfaces were significantly lower in male CtskCre.gp130(f/f) mice compared to controls, and this was associated with a significantly lower trabecular bone volume at 12 weeks of age. Furthermore, CtskCre.gp130(f/f) mice exhibited greatly suppressed periosteal bone formation at this age, indicated by significant reductions in both double-labelled surface and mineral apposition rate. By 26 weeks of age, CtskCre.gp130(f/f) mice exhibited narrower femora, with lower periosteal and endocortical perimeters than CtskCre.gp130(w/w) controls. Since IL-6 and IL-11R global knockout mice exhibited a similar reduction in femoral width, we also assessed periosteal bone formation in those strains, and found bone forming surfaces were also reduced in male IL-6 null mice. These data suggest that IL-6/gp130 signalling in the osteoclast is not essential for normal bone resorption in vivo, but maintains both trabecular and periosteal bone formation in male mice by promoting osteoblast activity through the stimulation of osteoclast-derived "coupling factors" and "osteotransmitters", respectively.

Secreted Frizzled-related protein 3 (sFRP3)-mediated suppression of interleukin-6 receptor release by A disintegrin and metalloprotease 17 (ADAM17) is abrogated in the osteoarthritis-associated rare double variant of sFRP3

A disintegrin and metalloprotease 17 (ADAM17) activity and secreted Frizzled-related protein 3 (sFRP3) down-regulation or expression of its rare double variant is associated with arthritis. sFRP3 interacts with interleukin-6 receptor (IL-6R) and ADAM17 and suppresses ADAM17 activity, whereas the rare variant does not; these findings provide explanation for their opposing pathogenic associations.

IL-6 and IGF-1 Signaling Within and Between Muscle and Bone: How Important is the mTOR Pathway for Bone Metabolism?

Insulin-like growth factor 1 (IGF-1) and interleukin 6 (IL-6) play an important role in the adaptation of both muscle and bone to mechanical stimuli. Here, we provide an overview of the functions of IL-6 and IGF-1 in bone and muscle metabolism, and the intracellular signaling pathways that are well known to mediate these functions. In particular, we discuss the Akt/mammalian target of rapamycin (mTOR) pathway which in skeletal muscle is known for its key role in regulating the rate of mRNA translation (protein synthesis). Since the role of the mTOR pathway in bone is explored to a much lesser extent, we discuss what is known about this pathway in bone and the potential role of this pathway in bone remodeling. We will also discuss the possible ways of influencing IGF-1 or IL-6 signaling by osteocytes and the clinical implications of pharmacological or nutritional modulation of the Akt/mTOR pathway.

Histological Evidence of Increased Osteoclast Cell Number and Asymmetric Bone Resorption Activity in the Tibiae of Interleukin-6-Deficient Mice

Interleukin-6 (IL-6) is a multifunctional cytokine considered to modulate bone homeostasis. Based on previous contradictory studies, we aimed to verify the influence of IL-6 deficiency on bone remodeling using an IL-6 knockout (IL-6-/-) murine model. Eight-month-old male mice, homozygous for the disrupted IL-6 gene, and their wild type (WT) littermates (control), were used. After transcardiac perfusion, tibiae were removed for histochemical analysis. Compared with the control group, IL-6 deficiency increased tartrate resistant acid phosphatase (TRAP)-positive osteoclast numbers and up-regulated the alkaline phosphatase (ALP) activity of osteoblasts in the metaphysis of the tibia. However, further analysis of serial histological sections from IL-6-/- mice found a significant discrepancy in osteoclast number, with the higher number of TRAP-positive osteoclasts conflicting with the lower number of cathepsin K-positive osteoclasts. Moreover, TUNEL staining identified a significantly higher rate of osteoclast apoptosis in IL-6-/- mice as compared with their WT controls. IL-6 deficiency induced abundant TRAP-positive osteoclasts but delayed bone remodeling by significantly inhibiting the bone resorption activity of osteoclasts and promoting osteoclast apoptosis.

IL-6 Alters Osteocyte Signaling toward Osteoblasts but Not Osteoclasts

Mechanosensitive osteocytes regulate bone mass in adults. Interleukin 6 (IL-6), such as present during orthodontic tooth movement, also strongly affects bone mass, but little is known about the effect of IL-6 on osteocyte function. Therefore we aimed to determine in vitro whether IL-6 affects osteocyte mechanosensitivity, and osteocyte regulation of osteoclastogenesis and osteoblast differentiation. MLO-Y4 osteocytes were incubated with/without IL-6 (1 or 10 pg/mL) for 24 hr. Subsequently, osteocytes were subjected to mechanical loading by pulsating fluid flow (PFF) for 1 hr. Mouse osteoclast precursors were cultured for 7 days on top of IL-6-treated osteocytes. Conditioned medium from osteocytes treated with/without IL-6 was added to MC3T3-E1 pre-osteoblasts for 14 days. Exogenous IL-6 (10 pg/mL) did not alter the osteocyte response to PFF. PFF significantly enhanced IL-6 production by osteocytes. IL-6 enhanced Rankl expression but reduced caspase 3/7 activity by osteocytes, and therefore did not affect osteocyte-stimulated osteoclastogenesis. Conditioned medium from IL-6-treated osteocytes reduced alkaline phosphatase (ALP) activity and Runx2 expression in osteoblasts, but increased expression of the proliferation marker Ki67 and osteocalcin. Our results suggest that IL-6 is produced by shear-loaded osteocytes and that IL-6 may affect bone mass by modulating osteocyte communication toward osteoblasts.

Impact of genetic variants of IL-6, IL6R, LRP5, ESR1 and SP7 genes on bone mineral density in postmenopausal Mexican-Mestizo women with obesity

BACKGROUND

Since obesity and osteoporosis present a high genetic predisposition and polymorphisms of IL-6, IL6R, LRP5, ESR1 and SP7 may influence the risk of both diseases, the aim of this study was to analyze the possible association of polymorphisms in these genes, as well as their haplotypes, with BMD variations in postmenopausal Mexican-Mestizo women with grade 2 or grade 3 obesity.

METHODS

One hundred eighty unrelated postmenopausal women with grade 2 or grade 3 obesity were included. BMD was measured in total hip and lumbar spine by dual-energy X-ray absorptiometry. DNA was obtained from blood leukocytes. Rs1800795 of IL-6, rs2228145 of IL6R, rs3736228 of LRP5, rs9340799 (XbaI) and rs2234693 (PvuII), of ESR1, rs10876432 and rs2016266, of SP7 (and their haplotypes), were studied by real-time PCR allelic discrimination. Deviations from Hardy-Weinberg equilibrium were tested. Pairwise linkage disequilibrium between single nucleotide polymorphisms was calculated by direct correlation r(2), and haplotype analysis was conducted.

RESULTS

Using WHO criteria, 54.5% had grade 2 obesity, and 45.5% had grade 3 obesity. Regarding DXA results, 11.1% women had osteoporosis, 41.7% had osteopenia, and 47.2% had normal BMD. Genotype and haplotype analysis showed no significant differences with BMD variations at the lumbar spine, total hip or femoral neck.

CONCLUSIONS

We did not find a significant association between the polymorphisms analyzed or their haplotypes and BMD variations in postmenopausal women with obesity. The higher BMD observed in women with obesity could be the result of an adaptive response to the higher loading of the skeleton.

A novel ex vivo culture model for inflammatory bone destruction

Pathological alterations in the balance of bone metabolism are central to the progression of inflammatory bone diseases such as periodontal disease. We have developed and characterized a novel ex vivo murine mandible model of inflammatory bone destruction. Slices of mandible were cultured for 14 days in the presence or absence of P. gingivalis lipopolysaccharide (LPS) or pro-inflammatory cytokines. Following culture, cell viability and tissue histomorphometry were assessed with quantification of matrix proteins, resident osteoclasts, ligament cells, monocytes, macrophages, and neutrophils. In the absence of inflammatory factors, culture viability, osteoclasts, and matrix components were maintained. LPS or TNFα stimulation demonstrated an increase in cellular proliferation, monocyte cells, osteoclast differentiation, and matrix degradation. Pathophysiological bone metabolism can be induced via exposure to LPS and direct influence of TNFα within the model despite the absence of systemic circulation, providing a model for inflammatory bone destruction and investigation of the effects of novel therapeutics.

Interleukin-17A stimulates granulocyte-macrophage colony-stimulating factor release by murine osteoblasts in the presence of 1,25-dihydroxyvitamin D(3) and inhibits murine osteoclast development in vitro

OBJECTIVE

To investigate the effects of interleukin-17A (IL-17A) on osteoclastogenesis in vitro.

METHODS

Bone marrow cells (BMCs) were isolated from the excised tibia and femora of wild-type C57BL/6J mice, and osteoblasts were obtained by sequential digestion of the calvariae of ddY, C57BL/6J, and granulocyte-macrophage colony-stimulating factor-knockout (GM-CSF(-/-)) mice. Monocultures of BMCs or cocultures of BMCs and osteoblasts were supplemented with or without 1,25-dihydroxyvitamin D(3)(1,25[OH](2)D(3)), recombinant human macrophage colony-stimulating factor (M-CSF), RANKL, and IL-17A. After 5-6 days, the cultures were fixed with 4% paraformaldehyde and subsequently stained for the osteoclast marker enzyme tartrate-resistant acid phosphatase (TRAP). Osteoprotegerin (OPG) and GM-CSF expression were measured by enzyme-linked immunosorbent assay, and transcripts for RANK and RANKL were detected by real-time polymerase chain reaction.

RESULTS

In both culture systems, IL-17A alone did not affect the development of osteoclasts. However, the addition of IL-17A plus 1,25(OH)(2)D(3) to cocultures inhibited early osteoclast development within the first 3 days of culture and induced release of GM-CSF into the culture supernatants. Furthermore, in cocultures of GM-CSF(-/-) mouse osteoblasts and wild-type mouse BMCs, IL-17A did not affect osteoclast development, corroborating the role of GM-CSF as the mediator of the observed inhibition of osteoclastogenesis by IL-17A.

CONCLUSION

These findings suggest that IL-17A interferes with the differentiation of osteoclast precursors by inducing the release of GM-CSF from osteoblasts.

Interleukin-6 receptor blockade induces limited repair of bone erosions in rheumatoid arthritis: a micro CT study

INTRODUCTION

Interleukin-6 receptor (IL-6R) blockade improves the signs and symptoms of rheumatoid arthritis (RA) and retards bone damage. Whether IL-6R blockade allows repair of existing bone erosions is so far unclear.

METHODS

This study examined bone erosions in the metacarpophalangeal joints of 20 patients receiving treatment with the IL-6R blocker tocilizumab using micro CT (µCT). The maximal width and depth of individual bone erosions was measured at baseline and after 1 year of treatment.

RESULTS

133 bone erosions were identified at baseline with a mean (±SD) size of 2.23±1.26 mm and depth of 2.16±1.50 mm. Distribution analysis showed predominant involvement of the second compared with the third and fourth metacarpophalangeal joints, the metacarpal heads compared with the phalangeal bases and the radial quadrants compared with all other surfaces. Repair of bone erosions during tocilizumab treatment was confined to those lesions showing sclerosis at baseline and/or at follow-up and those with a width larger than 1.6 mm. The mean decrease in width of sclerosed erosions was thus 0.14±0.05 mm (p=0.0086) and 0.20±0.08 mm (p=0.019) for sclerosing lesions after 1 year of treatment.

CONCLUSIONS

Blockade of IL-6R by tocilizumab can induce limited repair in a subset of erosions, particularly in large lesions with sclerosis. Repair of erosions during tocilizumab treatment reflects the favourable impact of IL-6R blockade on local bone remodelling in patients with RA.

The association of IL-6 and IL-6R gene polymorphisms with chronic periodontitis in a Chinese population

OBJECTIVE

The aim of our investigation is to reveal the association of interleukin-6 (IL-6) and interleukin-6 receptor (IL-6R) gene polymorphisms with chronic periodontitis in Northwestern Chinese Han Population.

MATERIAL AND METHODS

A case-control study of 199 cases of chronic periodontitis patients and 216 healthy controls was performed. Genomic DNA was isolated from whole venous blood, and four single nucleotide polymorphisms (IL-6 -572 G/C and -1363 G/T, IL-6R -183 G/A and +48892 A/C) were analysed using polymerase chain reaction, followed by restriction fragment length polymorphism analysis and sequencing methods.

RESULTS

Our SNP analyses showed that the distribution of the IL-6 -572 G/C and IL-6R -183 G/A polymorphisms did not differ between patients and controls. The frequency of the IL-6 -1363 G/T genotype GG was significantly increased chronic periodontitis cases (P = 0.023, odds ratio (OR) = 2.825 adjusted for gender and age.) The IL-6R +48892 A/C polymorphisms genotype CC was found to be protective against chronic periodontitis (P = 0.004, OR = 0.318 adjusted for gender and age.). In addition, compared with the other haplotypes, haplotype A(+48892) A(-183) was significantly associated with chronic periodontitis, with an odds ratio of 0.720 (P = 0.0235).

CONCLUSION

Our results suggest that the IL-6 -1363 G/T and IL-6R +48892 A/C polymorphisms may contribute to genetic susceptibility to chronic periodontitis in Northwestern Chinese Han population.

Novel genetically-humanized mouse model established to evaluate efficacy of therapeutic agents to human interleukin-6 receptor

For clinical trials of therapeutic monoclonal antibodies (mAbs) to be successful, their efficacy needs to be adequately evaluated in preclinical experiments. However, in many cases it is difficult to evaluate the candidate mAbs using animal disease models because of lower cross-reactivity to the orthologous target molecules. In this study we have established a novel humanized Castleman's disease mouse model, in which the endogenous interleukin-6 receptor gene is successfully replaced by human IL6R, and human IL6 is overexpressed. We have also demonstrated the therapeutic effects of an antibody that neutralizes human IL6R, tocilizumab, on the symptoms in this mouse model. Plasma levels of human soluble IL6R and human IL6 were elevated after 4-week treatment of tocilizumab in this mouse model similarly to the result previously reported in patients treated with tocilizumab. Our mouse model provides us with a novel means of evaluating the in vivo efficacy of human IL6R-specific therapeutic agents.

Peri-implant crestal bone loss: a putative mechanism

Purpose. The immunological mechanisms of peri-implant crestal bone loss have, hitherto, not been elucidated. We hypothesized that bacterial products from the microgap cause upregulation of cytokines in otherwise healthy peri-implant cells, which results in osteoclast formation and, ultimately, in bone resorption. Materials and Methods. We used RT-PCR and ELISA to assay mediators of osteoclastogenesis in rat and human macrophages (r-and hMO); bone marrow derived stromal cells (r-and hBMCs); and human gingival fibroblasts (hGF)—with or without stimulation by LPS. TRAP positive multinucleate cells were assessed for their resorptive ability. Results. We show that IL-1α, IL-1β, and IL-6 were expressed by all examined cell types, and TNF-α was upregulated in hGF. Secretion of IL-1α and IL-1β proteins was stimulated in hMO by LPS, and IL-6 protein secretion was highly stimulated in hBMCs and hGF. Both LPS and RANKL stimulated macrophages to form osteoclast-like TRAP positive cells, which resorbed calcium phosphate substrates. Conclusion. Taken together, the results of our study support the hypothesis that bacterial endotoxins upregulate enhanced mediators of osteoclastogenesis in resident cells found in the healthy peri-implant compartment and that the local synergistic action of cytokines secreted by such cells results in the genesis of resorptively active osteoclasts.

The role of osteoblast cells in the pathogenesis of unicameral bone cysts

PURPOSE

The pathogenesis of unicameral bone cysts (UBCs) remains largely unknown. Osteoclasts have been implicated, but the role of osteoblastic cells has, to date, not been explored. This study investigated the pathophysiology of UBCs by examining the interactions between the cyst fluid and human bone marrow stromal cells (hBMSCs) and the effect of the fluid on osteogenesis.

METHODS

Fluid was aspirated from two UBCs and analysed for protein, electrolyte and cytokine levels. Graded concentrations of the fluid were used as culture media for hBMSCs to determine the effects of the fluid on hBMSC proliferation and osteogenic differentiation. The fibrocellular lining was analysed histologically and by electron microscopy.

RESULTS

Alkaline phosphatase (ALP) staining of hBMSCs that were cultured in cyst fluid demonstrated increased cell proliferation and osteogenic differentiation compared to basal media controls. Biochemical analysis of these hBMSCs compared to basal controls confirmed a marked increase in DNA content (as a marker of proliferation) and ALP activity (as a marker of osteogenic differentiation) which was highly significant (p < 0.001). Osteoclasts were demonstrated in abundance in the cyst lining. The cyst fluid cytokine profile revealed levels of the pro-osteoclast cytokines IL-6, MIP-1α and MCP-1 that were 19×, 31× and 35× greater than those in reference serum.

CONCLUSIONS

Cyst fluid promoted osteoblastic growth and differentiation. Despite appearing paradoxical that the cyst fluid promoted osteogenesis, osteoblastic cells are required for osteoclastogenesis through RANKL signalling. Three key cytokines in this pathway (IL-6, MIP-1α, MCP-1) were highly elevated in cyst fluid. These findings may hold the key to the pathogenesis of UBCs, with implications for treatment methods.

IL-6 receptor inhibition positively modulates bone balance in rheumatoid arthritis patients with an inadequate response to anti-tumor necrosis factor therapy: biochemical marker analysis of bone metabolism in the tocilizumab RADIATE study (NCT00106522)

OBJECTIVE

To evaluate changes in biochemical markers of bone metabolism in response to tocilizumab in patients with anti-tumor necrosis factor-refractory rheumatoid arthritis (RA).

METHODS

RADIATE was a randomized, double-blind, placebo-controlled, parallel-group phase 3 trial. C-reactive protein, osteocalcin (OC), C-terminal telopeptides of type-I collagen (C-terminal telopeptides of type-1 collagen (CTX-I) and type-I collagen degradation product), and matrix metalloproteinase-3 (MMP-3) serum levels were analyzed from 299 RA patients. Patients were randomly assigned to either tocilizumab (4 or 8 mg/kg) or placebo intravenously every 4 weeks, along with concomitant stable methotrexate (10 to 25 mg weekly) in all treatment arms. The change in biochemical markers CTX-I and OC in combination was evaluated as a measure of net bone balance, a reflection of the change in equilibrium between resorption and formation.

RESULTS

Both tocilizumab doses decreased C-reactive protein levels and significantly inhibited cathepsin K-mediated bone resorption in RADIATE subjects, as measured by a decrease in CTX-I. There was a significant overall improvement in net bone balance at week 16 as measured by a decrease in the CTX-I:OC ratio (-25%, P < 0.01). Furthermore, a significant reduction in MMP-3 (43%, P < 0.001) and type-I collagen degradation product levels (18%, P < 0.001) were observed following treatment, both consistent with decreased MMP-mediated type-I collagen catabolism in joint tissue.

CONCLUSIONS

In anti-tumor necrosis factor-refractory patients, tocilizumab significantly reduced the levels of biochemical markers of cathepsin K-mediated bone resorption and MMP-mediated tissue degradation and remodeling. These observations suggest that tocilizumab has a positive effect on bone balance, which could in part explain the retardation of progressive structural damage observed with tocilizumab. Clinical trial registry number: NCT00106522.

R848, a toll-like receptor 7 agonist, inhibits osteoclast differentiation but not survival or bone-resorbing function of mature osteoclasts

R848, also known as resiquimod, acts as a ligand for toll-like receptor 7 (TLR7) and activates immune cells. In this study, we examined the effects of R848 on differentiation, survival, and bone-resorbing function of osteoclasts. R848 inhibited osteoclast differentiation of mouse bone marrow-derived macrophages (BMMs) and human peripheral blood-derived monocytes induced by receptor activator of NF-κB ligand in a dose-dependent manner. In addition, it inhibited mouse osteoclast differentiation induced in cocultures of bone marrow cells and osteoblasts in the presence of dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. However, R848 did not affect the survival or bone-resorbing activity of mouse mature osteoclasts. R848 also upregulated the mRNA expression levels of interleukin (IL)-6, IL-12, interferon (IFN)-γ, and inducible nitric oxide synthase in mouse BMMs expressing TLR7. IFN-β was consistently expressed in the BMMs and addition of neutralizing antibodies against IFN-β to the cultures partially recovered osteoclast differentiation inhibited by R848. These results suggest that R848 targets osteoclast precursors and inhibits their differentiation into osteoclasts via TLR7.

Global gene expression analysis of the interaction between cancer cells and osteoblasts to predict bone metastasis in breast cancer

BACKGROUND

Bone metastasis is a main cause of morbidity in breast cancer. Since breast cancer is a heterogeneous disease, the interactions of cancer cells with the skeletal host cells might also be diverse. We hypothesized that gene expression signatures induced by heterotypic interaction of breast cancer cells and osteoblasts might be of clinical relevance.

METHODOLOGY/PRINCIPAL FINDINGS

We established an ex vivo co-culture model using benign breast epithelial cells or a panel of 5 malignant breast epithelial cells in combination with primary human osteoblasts and determined associated gene expression changes with HEEBO microarrays. Pretreatment gene expression profiles of 295 early stage breast cancers published from the Netherlands Cancer Institute with a median follow up of 12.6 years allowed evaluating in vitro effects in the in vivo situation.The effects of the interaction between osteoblasts and breast cancer cell lines of different origin were very heterogeneous. Hs578T cells started to proliferate in co-culture with osteoblasts, SKBR-3 induced a TGF-β response and MDA-MB231 cells showed two distinct sets of up-regulated genes: A set of interferon response genes associated with an up-regulation of STAT1 was in vivo remarkably coherent providing a basis for segregation of tumors into two groups. In a uni-variate analysis, early stage tumors with high expression levels (n = 136) of this gene set had a significantly lower overall survival rate (p = 0.005) (63% at 10 years) than tumors with low expression levels (n = 159) (overall survival: 77% at 10 years). The second gene set was associated with IL-6 and did not significantly change the overall survival rate (p = 0.165), but was significantly associated with a shorter time to bone metastasis (p = 0.049; 74% vs. 83% at 10 years).

CONCLUSION/SIGNIFICANCE

An IL-6 gene expression pattern induced by heterotypic interaction of breast cancer cells with osteoblasts in vitro is associated with a higher rate of bone metastasis in vivo.

Immune regulation of osteoclast function in postmenopausal osteoporosis: a critical interdisciplinary perspective

Extensive studies on cross talk between immune and skeletal systems in autoimmune diseases give rise to a new discipline of 'osteoimmunology', which explores the molecular regulation of osteoclasts by immune system. Postmenopausal osteoporosis is recognized as a cytokine driven disease, but the mechanism that how estrogen deficiency interplaying with cytokines to stimulate bone loss remains to be elucidated. Although the effect of individual cytokines on osteoclast formation is well characterized, the major challenge is to fit a multitude of redundant pathways and cytokines into a systemic model of postmenopausal osteoporosis. This review presents current findings and hypothesis to explain estrogen deficiency-stimulated bone loss in a critical interdisciplinary perspective. To better understand the interaction between osteoclasts and immune system in postmenopausal osteoporosis, many of the lessons have been explored in animal models.

Effects of inflammatory and anti-inflammatory cytokines on the bone

BACKGROUND

Inflammatory diseases are linked to enhanced bone loss. The effect of inflammation on bone is mediated by proinflammatory cytokines, which regulate bone formation as well as bone resorption thereby altering bone homeostasis.

MATERIALS AND METHODS

In this article we summarize the key insights in cytokine regulation of bone. We describe the major pro- and anti-inflammatory mediators, which are involved in the regulation of bone and describe the mechanisms by which these cytokines alter bone balance.

RESULTS

We describe the effects of tumor necrosis factor (TNF), interleukin (IL)- 1 family members, IL-6, IL-17 and interferons (IFN) on bone and discuss the mechanisms by which these individual cytokines affect the bone resorbing and the bone forming cells.

CONCLUSIONS

Several proinflammatory cytokines (such as TNFa, IL-1 and IL-17) are major triggers for osteoclast activation explaining the enhanced bone loss during inflammation. Other such as IL-12, IL-18, IL-33 and IFN are strong suppressors of osteoclast differentiation and inhibit bone loss. Thus the cytokine composition of an inflammatory tissue is decisive whether inflammation triggers bone loss or not.

Actin and ERK1/2-CEBPβ signaling mediates phagocytosis-induced innate immune response of osteoprogenitor cells

Wear particles at the host bone-implant interface are a major challenge for successful bone implant arthoplasties. Current understanding of aseptic loosening consists of macrophage-mediated inflammatory responses and increasing osteoclastogenesis, which lead to an imbalance between bone formation and resorption. Despite its significant role in bone regeneration and implant osteointegration, the osteoprogenitor response to wear particles has been examined recent years. More specifically, the intracellular mechanism of osteoprogenitor mediated inflammation has not been fully elucidated. In this study, we examined the role of osteoprogenitors and the cellular mechanism by which metal wear particles elicit an inflammatory cascade. Through both in vivo and in vitro experiments, we have demonstrated that osteoprogenitor cells are capable of initiating inflammatory responses by phagocytosing wear particles, which lead to subsequent accumulation of macrophages and osteoclastogenesis, and the ERK_CEBP/β intracellular signaling is a key inflammatory pathway that links phagocytosis of wear particles to inflammatory gene expression in osteoprogenitors. AZD6244 treatment, a potent inhibitor of the ERK pathway, attenuated particle mediated inflammatory osteolysis both in vivo and in vitro. This study advances our understanding of the mechanisms of osteoprogenitor-mediated inflammation, and provides further evidence that the ERK_CEBP/β pathway may be a suitable therapeutic target in the treatment of inflammatory osteolysis.

GP130 cytokines and bone remodelling in health and disease

Cytokines that bind to and signal through the gp130 co-receptor subunit include interleukin (IL)-6, IL-11, oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and ciliary neutrophic factor (CNTF). Apart from contributing to inflammation, gp130 signalling cytokines also function in the maintenance of bone homeostasis. Expression of each of these cytokines and their ligand-specific receptors is observed in bone and joint cells, and bone-active hormones and inflammatory cytokines regulate their expression. gp130 signalling cytokines have been shown to regulate the differentiation and activity of osteoblasts, osteoclasts and chondrocytes. Furthermore, cytokine and receptor specific gene-knockout mouse models have identified distinct roles for each of these cytokines in regulating bone resorption, bone formation and bone growth. This review will discuss the current models of paracrine and endocrine actions of gp130-signalling cytokines in bone remodelling and growth, as well as their impact in pathologic bone remodelling evident in periodontal disease, rheumatoid arthritis, spondylarthropathies and osteoarthritis.

Bone density and hyperlipidemia: the T-lymphocyte connection

Osteoporosis, which contributes to morbidity and mortality, often coexists with cardiovascular disease, especially atherosclerosis. We have reported recently that in vitro exposure of human T-lymphocytes to oxidized lipids induced expression of a key osteoclastogenic cytokine, receptor activator of NF-κB ligand (RANKL). Our previous studies have shown that mice fed an atherogenic high-fat diet developed osteopenia and that bone marrow preosteoclasts from these hyperlipidemic mice have increased osteoclastic potential. To investigate the role of T-lymphocytes in the diet-induced bone loss, C57BL/6 mice were fed either chow or a high-fat diet, and bone parameters and T-lymphocyte activation were assessed at 6 and 11 months. Consistent with our previous findings, peripheral quantitative computed tomographic (pQCT) analysis showed that mice in the high-fat group had lower bone mineral content than mice in the chow group. Furthermore, histomorphometric analysis showed decreased structural parameters in the high-fat group. Coculture studies showed that bone marrow cells isolated from the high-fat group, which contained increased levels of activated memory T-lymphocytes compared with bone marrow cells from the chow mice, supported osteoclastic differentiation of RAW 264.7 cells. Additionally, RANKL expression was upregulated significantly in the T-lymphocytes isolated from the bone marrow of the high-fat group. Splenic T-lymphocytes isolated from the high-fat group also had increased expression of transcripts for the receptor for oxidized lipids (LOX-1) as well as for inflammatory and osteoclastogenic cytokines, including RANKL, interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), IL-1β, and interferon γ (IFN-γ). Together these findings suggest that T-lymphocytes play a key role in the osteoclastogenesis induced by a high-fat diet and may contribute to the bone loss associated with diet-induced osteopenia.

CCAAT/enhancer binding protein beta is up-regulated in giant cell tumor of bone and regulates RANKL expression

Giant cell tumor (GCT) of bone is an aggressive non-cancerous tumor, which consists of multi-nucleated osteoclast-like giant cells, stromal cells, and monocytes. It is believed that stromal cells are the neoplastic component of this tumor. Expression of the receptor activator of nuclear factor kappa B ligand (RANKL) in the stromal cells stimulates the monocytes to form giant multi-nucleated osteoclast-like cells, causing bone over-resorption at the tumor site. Previously, our group has reported the up-regulation of RANKL in GCT of bone stromal cells, but the mechanism is unknown. Using stromal cell culture of GCT obtained from patients, we demonstrated the up-regulation of the transcriptional activator CCAAT/enhancer binding protein beta (C/EBPbeta). RANKL promoter studies revealed that C/EBPbeta over-expression induced RANKL promoter activity in a dose-dependent manner and a CCAAT-box within the region nt -357/-1 contributed to the basal transcription activity, with a possible C/EBPbeta binding element in the region nt -460/-358 leading to further induction. Furthermore, we also showed that C/EBPbeta bound to the RANKL promoter in GCT stromal cells in vivo by chromatin immunoprecipitation. To conclude, our study has shown that C/EBPbeta is a RANKL promoter activator in stromal cells of GCT of bone and we have proposed a model in which C/EBPbeta plays an important role in the osteolytic characteristics and pathological causes of GCT of bone.

Characterisation of the osteoclastogenic potential of human osteoblastic and fibroblastic conditioned media

Although M-CSF and RANKL are sufficient to promote in vitro osteoclastogenesis, in vivo this is a complex process which requires the action of many signalling molecules and cellular crosstalks. In this work, isolated or combined conditioned media, obtained from human adult skin fibroblast and bone marrow cells, were tested for their osteoclastogenic potential, through an indirect co-culture system, in the absence of recombinant M-CSF and RANKL. Osteoclastogenesis was assessed on human peripheral blood mononuclear cells (PBMC) and CD14+ cell cultures by quantification of total protein content, tartrate-resistant acid phosphatase (TRAP) activity, presence of multinucleated cells positive for TRAP, RT-PCR of TRAP, CATK, CA2, c-myc and c-src and presence of multinucleated cells displaying actin rings, vitronectin and calcitonin receptors. Cultures supplemented with M-CSF and RANKL were used as positive controls. It was observed that the conditioned medium from dexamethasone osteogenic-induced bone marrow cell cultures displayed the highest osteoclastogenic potential, with similar behaviour to that observed in the presence of both M-CSF and RANKL. Comparatively, fibroblastic conditioned medium elicited a slightly lower osteoclastogenic response. Combination of both conditioned media resulted in a significant increase of TRAP activity. On the other hand, conditioned medium from non-osteogenic-induced bone marrow cell cultures presented the lowest osteoclastogenic potential. These results were observed for both PBMC and CD14+ cell cultures, suggesting that fibroblast and osteoblast cells are able to modulate osteoclastogenesis in the absence of physical cell-cell interactions. In addition, osteoclastogenic potential of bone marrow cells increases with their osteoblastic differentiation.

Ciliary neurotrophic factor inhibits bone formation and plays a sex-specific role in bone growth and remodeling

Ciliary neurotrophic factor (CNTF) receptor (CNTFR) expression has been described in osteoblast-like cells, suggesting a role for CNTF in bone metabolism. When bound to CNTF, neuropoietin (NP), or cardiotrophin-like-cytokine (CLC), CNTFR forms a signaling complex with gp130 and the leukemia inhibitory factor receptor, which both play critical roles in bone cell biology. This study aimed to determine the role of CNTFR-signaling cytokines in bone. Immunohistochemistry detected CNTF in osteoblasts, osteocytes, osteoclasts, and proliferating chondrocytes. CNTFR mRNA was detected in primary calvarial osteoblasts and was upregulated during osteoblast differentiation. Treatment of osteoblasts with CNTF or CLC, but not NP, significantly inhibited mineralization and osterix mRNA levels. Twelve-week-old male CNTF ( -/- ) mice demonstrated reduced femoral length, cortical thickness, and periosteal circumference; but femoral trabecular bone mineral density (Tb.BMD) and tibial trabecular bone volume (BV/TV) were not significantly different from wild-type, indicating a unique role for CNTF in bone growth in male mice. In contrast, female CNTF ( -/- ) femora were of normal width, but femoral Tb.BMD, tibial BV/TV, trabecular number, and trabecular thickness were all increased. Female CNTF ( -/- ) tibiae also demonstrated high osteoblast number and mineral apposition rate compared to wild-type littermates, and this was intrinsic to the osteoblast lineage. CNTF is expressed locally in bone and plays a unique role in female mice as an inhibitor of trabecular bone formation and in male mice as a stimulus of cortical growth.

Interaction of staphylococci with bone

Staphylococci, in particular Staphylococcus aureus, are the predominant cause of bone infections worldwide. These infections are painful, debilitating and with the rise in antibiotic-resistant forms, increasingly difficult to treat. The growth in the number of prosthetic joint replacement procedures also provides new opportunities for these infections to take hold. Comprehending the mechanisms by which staphylococci interact with and damage bone is critical to the development of new approaches to meet this challenge. This review summarises current understanding of the mechanisms by which staphylococci infect and damage bone. We address the role of the inflammatory response to staphylococcal infection in disrupting the homeostatic balance of bone matrix deposition and resorption and thereby mediating bone destruction. A number of virulence factors that have been shown to contribute to bone infection and pathology are discussed, however no single factor has been defined as being specific to bone infections. Although traditionally considered an extracellular pathogen, there is increasing evidence that staphylococci are able to invade host cells, and that an intracellular lifestyle may facilitate long-term persistence in bone tissue, enabling evasion of antimicrobials and host immune responses. ‘Small colony variant’ strains, with mutations disabling the electron transport pathway appear particularly adept at invading and persisting within host cells, and exhibit enhanced antimicrobial resistance, and may represent a further complication in the treatment and management of staphylococcal bone disease.

gp130 signaling in bone cell biology: multiple roles revealed by analysis of genetically altered mice

The receptor subunit gp130 is utilized by a wide range of cytokines, many of which have critical functions in regulating the actions of osteoclasts and osteoblasts. In vitro studies have revealed remarkably consistent effects of many of these family members, specifically, actions on receptors in the osteoblast lineage that stimulate osteoblast differentiation and stimulate production of RANKL, thereby increasing the formation of osteoclasts. In contrast to this simple model of gp130 action on bone, deletion of cytokines or receptors that interact with gp130 reveal a range of bone phenotypes implicating critical roles for gp130 signaling in longitudinal bone growth, bone resorption and bone formation. In most cases, deletion of gp130, ligands or ligand-specific receptors interacting with gp130 causes a low level of bone formation; a high level of bone formation was only observed in gp130(Y757F/Y757F) mice, gp130 signaling mutants, where it is caused by a cell-lineage autonomous increase in osteoclast formation and an IL-6-dependent coupling pathway. On the other hand, the range of gene knockouts may cause either a reduction or an increase in osteoclast formation, and in many cases alterations in osteoclast size and ability to resorb bone. Since some knockouts are neonatal lethal, interpretation of ex vivo analyses and the contribution of each component to bone remodeling are not clearly defined, and there is still much work to be done before these questions can be resolved. Taken together these results indicate multiple roles for gp130 cytokines in controlling osteoblasts and osteoclast function, including paracrine roles to mediate signaling between these two cell types.

A novel distal enhancer mediates cytokine induction of mouse RANKl gene expression

Chronic inflammatory states are associated with increased bone loss. This increase is often linked to an elevation in receptor activator of nuclear factor-kappaB ligand (RANKL), a TNFalpha-like factor essential to osteoclast formation. In this study, we document the ability of IL-6 in combination with IL-6 soluble receptor (IL-6/IL-6sR) and oncostatin M to induce Rankl expression in stromal cells via signal transducer and activator of transcription 3 (STAT3). We used chromatin immunoprecipitation-tiled DNA microarray analysis to determine sites of action of STAT3 at the Rankl locus and to assess the consequences of binding on histone H4 acetylation and RNA polymerase II recruitment. Both IL-6/IL-6 soluble receptor and oncostatin M stimulated STAT3 binding upstream of the Rankl transcriptional start site. Although previously identified enhancers bound STAT3, a more distal enhancer termed mRLD6 was a particular focus of STAT3 binding. When fused to a heterologous promoter, this enhancer was highly active, containing two functionally active STAT response elements. Importantly, small interfering RNA knockdown of Stat3 mRNA and protein, but not that of Stat1 or Stat5a, was effective in limiting Rankl mRNA up-regulation. Interestingly, although RNA polymerase II and histone H4 acetylation marked many of the enhancers under basal conditions, the levels of both were strongly increased after cytokine treatment, particularly at mRLD6. Finally, mRLD6 was also a target for forskolin-induced cellular response element-binding protein (CREB) recruitment, which potentiated cytokine activity. Our studies provide new insight into mechanisms by which glycoprotein 130 activating cytokines induce RANKL expression.

Inhibition of interleukin-6 receptor directly blocks osteoclast formation in vitro and in vivo

OBJECTIVE

To investigate the efficacy of a murine anti-interleukin-6 receptor (anti-IL-6R) antibody in directly blocking tumor necrosis factor (TNF)- and RANKL-mediated osteoclastogenesis in vitro and in vivo.

METHODS

The efficacy of a murine antibody against IL-6R in blocking osteoclast differentiation of mononuclear cells stimulated with RANKL was tested. In addition, arthritic human TNFalpha-transgenic mice were treated with anti-IL-6R antibody, and osteoclast formation and bone erosion were assessed in arthritic paws.

RESULTS

Blockade of IL-6R dose dependently reduced osteoclast differentiation and bone resorption in monocyte cultures stimulated with RANKL or RANKL plus TNF. In human TNFalpha-transgenic mice, IL-6R blockade did not inhibit joint inflammation, but it strongly reduced osteoclast formation in inflamed joints as well as bone erosion in vivo. Neither the cell influx into joints nor the synovial expression of IL-6 and RANKL changed with IL-6R blockade, while the synovial expression of IL-1 was significantly reduced. In contrast, TNF-mediated systemic bone loss was not inhibited by IL-6R blockade.

CONCLUSION

These data suggest that blockade of IL-6R directly affects osteoclast formation in vitro and in vivo, suggesting a direct and specific effect of anti-IL-6R therapy on osteoclasts independently of its antiinflammatory effects. This effect adds significantly to the structure-sparing potential of pharmacologic blockade of IL-6R in arthritis.

Co-Cr-Mo alloy particles induce tumor necrosis factor alpha production in MLO-Y4 osteocytes: a role for osteocytes in particle-induced inflammation

Wear debris-induced osteolysis is purportedly the limiting problem affecting the long term results of joint arthroplasty. Pathogenic effects of wear debris in peri-implant cells such as macrophages, osteoblasts and osteoclasts have been well studied. In contrast, the effects of wear debris on osteocytes, which make up over 90% of all bone cells, remain unknown. We hypothesized that metal implant debris can induce the pro-inflammatory response in osteocytes. This study demonstrated the effects of cobalt-chromium-molybdenum alloy (Co-Cr-Mo) particles on a well-characterized MLO-Y4 osteocyte cell line. Co-Cr-Mo alloy particle treatment significantly (p<0.05) up-regulated tumor necrosis factor alpha (TNFalpha) gene expression after 3 and 6 h and TNFalpha protein production after 24 h, but down-regulated interleukin-6 (IL-6) gene expression after 6 h. Co-Cr-Mo alloy particle treatment also induced osteocyte apoptosis after 24 h. This apoptotic effect was partially (40%) dependent on TNFalpha. Therefore, our results suggest that osteocytes play a role in particle-induced inflammation and bone resorption following total joint arthroplasty by inducing pro-inflammatory cytokines and inducing osteocyte apoptosis.

Cord blood--an alternative source for bone regeneration

Bone regeneration is one of the best investigated pathways in mesenchymal stromal cell (MSC) biology. Therefore strong efforts have been made to introduce tissue engineering and cell therapeutics as an alternative treatment option for patients with bone defects. This review of the literature gives an overview of MSC biology aiming for clinical application including advantages but also specific challenges and problems which are associated with cord blood derived stromal cell (CB-MSC) as a source for bone regeneration. The use of postnatal CB-MSC is ethically uncomplicated and requires no invasive harvesting procedure. Moreover, most data document a high osteogenic potential of CB-MCS and also low immunoreactivity compared with other MSC types. The expression profile of CB-MSC during osteogenic differentiation shows similarities to that of other MSC types. Within the umbilical cord different MSC types have been characterized which are potent to differentiate into osteoblasts. In contrast to a large number of in vitro investigations there are only few in vivo studies available so far.

Blockade of interleukin-6 signaling augments regulatory T-cell reconstitution and attenuates the severity of graft-versus-host disease

Graft-versus-host disease (GVHD) is the major complication after allogeneic bone marrow transplantation and is characterized by the overproduction of proinflammatory cytokines. In this study, we have identified interleukin-6 (IL-6) as a critical inflammatory cytokine that alters the balance between the effector and regulatory arms of the immune system and drives a proinflammatory phenotype that is a defining characteristic of GVHD. Our results demonstrate that inhibition of the IL-6 signaling pathway by way of antibody-mediated blockade of the IL-6 receptor (IL-6R) markedly reduces pathologic damage attributable to GVHD. This is accompanied by a significant increase in the absolute number of regulatory T cells (Tregs) that is due to augmentation of thymic-dependent and thymic-independent Treg production. Correspondingly, there is a significant reduction in the number of T helper 1 and T helper 17 cells in GVHD target organs, demonstrating that blockade of IL-6 signaling decreases the ratio of proinflammatory T cells to Tregs. These studies demonstrate that antibody blockade of the IL-6R serves to recalibrate the effector and regulatory arms of the immune system and represents a novel, potentially clinically translatable, strategy for the attenuation of GVHD.

Derivation of a novel undifferentiated human foetal phenotype in serum-free cultures with BMP-2

Skeletal stem and progenitor populations provide a platform for cell-based tissue regeneration strategies. Optimized conditions for ex vivo expansion will be critical and use of serum-free culture may allow enhanced modelling of differentiation potential. Maintenance of human foetal femur-derived cells in a chemically defined medium (CDM) with activin A and fibroblast growth factor-2 generated a unique undifferentiated cell population in comparison to basal cultures, with significantly reduced amino acid depletion, appearance and turnover, reduced alkaline phosphatase (ALP) activity and loss of type I and II collagen expression demonstrated by fluorescence immunocytochemistry. Microarray analysis demonstrated up-regulation of CLU, OSR2, POSTN and RABGAP1 and down-regulation of differentiation-associated genes CRYAB, CSRP1, EPAS1, GREM1, MT1X and SRGN as validated by quantitative real-time polymerase chain reaction. Application of osteogenic conditions to CDM cultures demonstrated partial rescue of ALP activity. In contrast, the addition of bone morphogenetic protein-2 (BMP-2) resulted in reduced ALP levels, increased amino acid metabolism and, strikingly, a marked shift to a cobblestone-like cellular morphology, with expression of SOX-2 and SOX-9 but not STRO-1 as shown by immunocytochemistry, and significantly altered expression of metabolic genes (GFPT2, SC4MOL and SQLE), genes involved in morphogenesis (SOX15 and WIF1) and differentiation potential (C1orf19, CHSY-2,DUSP6, HMGCS1 and PPL). These studies demonstrate the use of an intermediary foetal cellular model for differentiation studies in chemically defined conditions and indicate the in vitro reconstruction of the mesenchymal condensation phenotype in the presence of BMP-2, with implications therein for rescue studies, screening assays and skeletal regeneration research.