Impaired skeletal development in interleukin-6-transgenic mice: a model for the impact of chronic inflammation on the growing skeletal system

The role of interleukin 6 in the pathophysiology of rheumatoid arthritis

Interleukin 6 (IL-6) is a pleiotropic cytokine with a pivotal role in the pathophysiology of rheumatoid arthritis (RA). It is found in abundance in the synovial fluid and serum of patients with RA and the level correlates with the disease activity and joint destruction. IL-6 can promote synovitis and joint destruction by stimulating neutrophil migration, osteoclast maturation and vascular endothelial growth factor (VEGF)-stimulated pannus proliferation. IL-6 may also be mediating many of the systematic manifestations of RA including inducing the acute-phase reaction [including C-reactive protein (CRP)], anaemia through hecipidin production, fatigue via the hypothalamic-pituitary-adrenal (HPA) axis) and osteoporosis from its effect on osteoclasts. In addition, IL-6 may contribute to the induction and maintenance of the autoimmune process through B-cell maturation and TH-17 differentiation. All of the above makes IL-6 blockade a desirable therapeutic option in the treatment of RA. Following successful animal studies, a humanized anti-interleukin-6 receptor (anti-IL-6R) monoclonal antibody, tocilizumab (TCZ), entered into clinical trials and it has been shown to be an effective treatment in several large phase III clinical trials in RA with rapid and sustained improvement in disease activity, reducing radiographic joint damage and improving physical function.

Interleukin-6: from identification of the cytokine to development of targeted treatments

Interleukin-6 (IL-6) was identified based on extensive research conducted simultaneously on a variety of topics ranging from hepatocyte production of acute-phase proteins to plasmacytoma growth. IL-6 is a cytokine produced by a broad array of cell types and can exert its effects on virtually all cells. IL-6 can induce cell signaling not only via the classic pathway involving the transmembrane receptor IL-6Rα (restricted cellular expression) associated with gp130 (ubiquitous and responsible for signal transmission), but also via the soluble receptor IL-6Rα, which binds to IL-6 and induces a signal mediated by the ubiquitous gp130 molecule (transsignaling). IL-6 is deregulated in many inflammatory and autoimmune diseases, including rheumatoid arthritis (RA). By virtue of its multiple effects, IL-6 is involved in the various phases of RA development, including the acute phase, immuno-inflammatory phase, and destructive phase. IL-6 has an impact on the many pathogenic factors identified in RA and, consequently, holds promise for targeted treatments. However, anti-IL-6 monoclonal antibodies evaluated as IL-6 antagonists, instead, increased the half-life of the cytokine. In contrast, monoclonal antibody (tocilizumab) to transmembrane and soluble IL-6Rα has been found effective in patients with RA. Tocilizumab is now indicated for the treatment of adults with RA who have failed at least one synthetic disease-modifying antirheumatic drug or TNFα antagonist.

The role of interleukin-6 in rheumatoid arthritis-associated osteoporosis

INTRODUCTION

Osteoporosis is highly prevalent in patients with rheumatoid arthritis (RA) and is a frequent cause of fractures, disability, reduced quality of life and increased use of healthcare resources.

DISCUSSION

Factors associated with the development of osteoporosis and fractures in patients with RA include disease activity, inflammation, gender, age, low body mass and glucocorticoid exposure. Several processes contribute towards the pathology of RA-associated osteoporosis, and increased osteoclast activation and subsequent bone resorption mediated by pro-inflammatory cytokines are thought to play major roles. Given the key effects of interleukin-6 (IL-6) in both RA and osteoporosis, and its ability to modulate other inflammatory mediators, IL-6 may be an important factor specifically associated with osteoporosis in patients with RA.

CONCLUSION

The development of agents that modulate the actions of IL-6 and those of other pro-inflammatory mediators of bone loss may provide alternative osteoporosis management strategies for patients with RA than existing general osteoporosis therapies.

Role for interleukin-6 in structural joint damage and systemic bone loss in rheumatoid arthritis

Interleukin-6 (IL-6) plays a key role in the local and systemic manifestations of rheumatoid arthritis (RA). IL-6 is not only a proinflammatory cytokine, but also interacts in complex ways with the cells involved in bone remodeling. In RA, IL-6 may indirectly promote osteoclastogenesis by increasing the release of RANK-L by osteoblasts and synovial cells. However, IL-6 inhibits osteoclastogenesis in vitro, via a direct mechanism. The effects of IL-6 on osteoblasts may vary with the cell differentiation stage: thus, IL-6 may promote the differentiation of pre-osteoblasts to mature osteoblasts while also diminishing the proliferation of osteoblasts at late differentiation stages. Thus, the effects of IL-6 on bone remodeling are complex and may occur in opposite directions depending on the model or experimental conditions. Nevertheless, results from studies in animal models and humans support a negative effect of IL-6 on bone. Thus, in patients with RA, blocking IL-6 may be effective both in diminishing the inflammatory manifestations and in preventing the bone complications of the disease.

Targeting interleukin-6 in pediatric rheumatic diseases

PURPOSE OF REVIEW

To describe the most recent data regarding the role of interleukin-6 (IL-6) in immune and inflammatory responses, the mode of action and safety information on tocilizumab, the only available IL-6 inhibitor, and discuss recent results on the therapeutic inhibition of IL-6 in pediatric rheumatic diseases.

RECENT FINDINGS

New data on the effects of IL-6 on T and B cells have been published. Clinical trials with tocilizumab in adults, particularly with rheumatoid arthritis, provide new data on mechanism of action and a reasonably wide safety database. A withdrawal design trial showed marked efficacy in systemic juvenile idiopathic arthritis (s-JIA). Open label studies or anecdotal reports suggest possible efficacy also in other JIA subtypes, as well as other rheumatic diseases.

SUMMARY

Targeting IL-6 activities is an effective approach in the treatment of chronic inflammatory diseases. The long-term benefit and safety of tocilizumab have to be defined in long-term extension studies. The risk/benefit ratio appears to be particularly favorable in s-JIA. With the increasing number of biologics becoming available, future efforts should be directed to the definition of biomarkers that will identify responders to each novel biologic, allowing a personalized approach.

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.

Therapeutic targets in rheumatoid arthritis: the interleukin-6 receptor

RA is a chronic, debilitating disease in which articular inflammation and joint destruction are accompanied by systemic manifestations including anaemia, fatigue and osteoporosis. IL-6 is expressed abundantly in the SF of RA patients and is thought to mediate many of the local and systemic effects of this disease. Unlike a number of other cytokines, IL-6 can activate cells through both membrane-bound (IL-6R) and soluble receptors (sIL-6R), thus widening the number of cell types responsive to this cytokine. Indeed, trans-signalling, where IL-6 binds to the sIL-6R, homodimerizes with glycoprotein 130 subunits and induces signal transduction, has been found to play a key role in acute and chronic inflammation. Elevated levels of IL-6 and sIL-6R in the SF of RA patients can increase the risk of joint destruction and, at the joint level, IL-6/sIL-6R can stimulate pannus development through increased VEGF expression and increase bone resorption as a result of osteoclastogenesis. Systemic effects of IL-6, albeit through conventional or trans-signalling, include regulation of acute-phase protein synthesis, as well as hepcidin production and stimulation of the hypothalamo-pituitary-adrenal axis, the latter two actions potentially leading to anaemia and fatigue, respectively. This review aims to provide an insight into the biological effects of IL-6 in RA, examining how IL-6 can induce the articular and systemic effects of this disease.

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.

Osteoporosis in children: pediatric and pediatric rheumatology perspective: a review

It is increasingly recognized that osteoporosis affects children as well as adults both as a primary problem and as secondary to various diseases, medications, and lifestyle issues. In this review, we emphasize the correct diagnosis of osteoporosis in children as opposed to adults, etiology, and pharmaceutical and non-pharmaceutical treatments. We especially focus on rheumatologic conditions associated with osteoporosis and management issues.

Mechanisms of growth impairment in pediatric Crohn's disease

Crohn's disease manifests during childhood or adolescence in up to 25% of patients. The potential for linear growth impairment as a complication of chronic intestinal inflammation is unique to pediatric patient populations. Insulin-like growth factor I (IGF-I), produced by the liver in response to growth hormone (GH) stimulation, is the key mediator of GH effects at the growth plate of bones. An association between impaired growth in children with Crohn's disease and low IGF-I levels is well recognized. Early studies emphasized the role of malnutrition in suppression of IGF-I production. However, a simple nutritional hypothesis fails to explain all the observations related to growth in children with Crohn's disease. The direct, growth-inhibitory effects of proinflammatory cytokines are increasingly recognized and explored. The potential role of noncytokine factors, such as lipopolysaccharides, and their potential to negatively influence the growth axis have recently been investigated with intriguing results. There is now reason for optimism that the modern anticytokine therapeutic agents available for treating children and adolescents with Crohn's disease will reduce the prevalence of this otherwise common complication. As our understanding of the mechanisms that underlie growth impairment advance, so too should the opportunity for developing further novel and targeted therapies.

Misexpression of CCAAT/enhancer binding protein beta causes osteopenia

CCAAT/enhancer binding proteins (C/EBPs) are expressed by osteoblasts and adipocytes during differentiation. C/EBP beta is critical for adipogenesis; however, its role in osteoblastogenesis is unclear, and its function in the postnatal skeleton is not known. To study C/EBP beta in osteoblasts in vivo, we created transgenic mice expressing full length C/EBP beta under the control of a 3.8 kb fragment of the human osteocalcin promoter. Two transgenic lines were established in a friend leukemia virus strain B genetic background, and compared with wild type littermate controls. Both C/EBP beta transgenic lines exhibited osteopenia, with a 30% decrease in bone volume, due to a decrease in trabecular number. The number of osteoblasts and osteoclasts per bone perimeter was not changed. Bone marrow stromal cells from C/EBP beta transgenics showed reduced mineralization, and reduced alkaline phosphatase mRNA levels. Calvarial osteoblasts from C/EBP beta transgenics displayed reduced alkaline phosphatase activity. To determine the consequences of the Cebpb deletion in vivo, the phenotype of Cebpb null mice was compared with that of wild type controls of identical genetic composition. Cebpb null mice exhibited reduced weight, body fat, and bone mineral density, and decreased bone volume, due to a decrease in trabecular number. The number of osteoblasts and osteoclasts per bone perimeter was not changed. C/EBP beta downregulation by RNA interference in calvarial osteoblasts had no effect on osteoblast differentiation/function. The phenotype of the Cebpb inactivation may be secondary to systemic indirect effects, and to direct effects of C/EBP beta in osteoblasts. In conclusion, C/EBP beta plays a role in mesenchymal cell differentiation and its misexpression in vivo causes osteopenia.

Mechanical loading highly increases IL-6 production and decreases OPG expression by osteoblasts

OBJECTIVES

In osteoarthritis (OA), mechanical factors play a key role, not only in cartilage degradation, but also in subchondral bone sclerosis. The aim of this study was to develop on original compression model for studying the effect of mechanical stress on osteoblasts.

MATERIALS AND METHODS

We investigate the effects of compression on primary calvaria osteoblasts isolated from newborn mice and cultured for 28 days in monolayer. At the end of this period, osteoblasts were embedded in a newly synthesized extracellular matrix which formed a three-dimensional membrane. This membrane was then submitted to compression in Biopress Flexercell plates (1-1.7 MPa compressions at 1 Hz frequency) during 1-8h. The expression of 20 genes was investigated by real time reverse transcriptase polymerase chain reaction. Interleukin (IL)-6, matrix metalloproteinase (MMP)-3 and prostaglandin (PG)E(2) were assayed in the culture medium by specific immunoassays.

RESULTS

The compression highly increased IL-6 and cyclooxygenase (COX)-2 mRNA levels in osteoblasts. In parallel, increased amount of IL-6 and PGE(2) was found in the supernatant of loaded osteoblasts. This stimulation reached a maximum after 4h of 10% compression. MMP-2, MMP-3, and MMP-13 mRNA levels were also increased by compressive stress, while 15-hydroxyprostaglandin-dehydrogenase and osteoprotegerin (OPG) start to decrease at hour 4. COX-1, microsomial PG E synthase-1 (mPGES1), mPGES2 and cytosolic PGES and receptor activator of nuclear factor ligand (RANKL) were unmodified. Finally, we observed that alpha 5 beta 1 integrin, intracellular Ca(++), nuclear factor-kappaB and extracellular signal-regulated kinase 1/2 pathways were involved in the compression-induced IL-6 and PGE(2) production. IL-6 neutralizing antibodies and piroxicam inhibited the decrease OPG expression, but did not modify RANKL mRNA level, indicating that IL-6 and PGE(2) induce a decrease of the OPG/RANKL ratio.

CONCLUSION

This work demonstrates that IL-6 is mechano-sensitive cytokine and probably a key factor in the biomechanical control of bone remodeling in OA.

Bone tissue content of TGF-beta2 changes with time in human heterotopic ossification after total hip arthroplasty

Transforming growth factor beta isoforms (TGF-beta(1), TGF-beta(2), and TGF-beta(3)) most likely play a role in bone physiology, but little is known about their relative importance in normal as well as in heterotopic bone. This study focused on possible differences in the localization and relative content of different TGF beta isoforms in heterotopic ossifications (HO) by comparing HOs, which have developed less than 17 months (immature HOs) with those developed 3-9 years (mature HOs). The HOs were harvested after total hip arthroplasty (THA) during revision surgery. The HO samples were decalcified, embedded in paraffin and sectioned. Azan staining was used to evaluate histological structure of the ossifications and immunohistochemical analysis was performed to estimate the localization of three TGF beta isoforms in the HOs. Comparison of different TGF beta isoforms in the immature and the mature ossifications showed that the content of TGF-beta(2) was decreased by almost three times in the mature HO as compared to the immature HO (p = 0.0064). The proportions of other isoforms in HOs did not differ significantly. This study shows that the relative importance of TGF betas change with HO development.

Bone mass and microarchitecture of irradiated and bone marrow-transplanted mice: influences of the donor strain

Total body irradiation and bone marrow transplantation induced dramatic trabecular bone loss and cortical thickening in mice. Transplanted cells were engrafted in bone marrow, along trabeculae, and in periosteal and endosteal envelopes. None of the osteocytes were of donor origin. Bone microarchitecture of transplanted mice changed to tend toward the donor phenotype.

INTRODUCTION

Osteopenia and osteoporosis are complications of bone marrow transplants (BMT) attributed to related chemotherapy. However, the specific influence of total body irradiation (TBI) is unknown.

METHODS

We investigated the effects of TBI and BMT on bone mass and microarchitecture by micro-CT. Eighteen C57Bl/6 (B6) mice receiving lethal TBI had a BMT with marrow cells from green fluorescent protein--transgenic-C57Bl/6 (GFP) mice. Transplanted (T(GFP)B6), B6, and GFP mice were euthanized 1, 3, and 6 months after BMT or at a related age.

RESULTS

T(GFP)B6 presented a dramatic bone loss compared with B6 and did not restore their trabecular bone mass over time, despite a cortical thickening 6 months after BMT. Serum testosterone levels were not significantly reduced after BMT. During aging, GFP mice have less trabeculae, thicker cortices, but a narrower femoral shaft than B6 mice. From 3 months after BMT, cortical characteristics of T(GFP)B6 mice differed statistically from B6 mice and were identical to those of GFP mice. GFP(+) cells were located along trabecular surfaces and in periosteal and endosteal envelopes, but none of the osteocytes expressed GFP.

CONCLUSION

Our findings suggest that engrafted cells did not restore the irradiation-induced trabecular bone loss, but reconstituted a marrow microenvironment and bone remodeling similar to those of the donor. The effects of irradiation and graft on bone remodeling differed between cortical and trabecular bone.

Inhibiting interleukin-6 in rheumatoid arthritis

Interleukin (IL)-6 is the most abundant proinflammatory cytokine in the circulation and synovial joints of patients with active rheumatoid arthritis. It has pivotal roles in the immune response and inflammation. In rheumatoid arthritis, it causes synovitis, joint destruction, and many systemic manifestations. Clinical trials of tocilizumab, a humanized anti-IL-6 receptor monoclonal antibody that blocks IL-6 signaling, have demonstrated therapeutic benefit. It heralds a new era of anticytokine therapy in rheumatoid arthritis.

Bone density, structure, and strength in juvenile idiopathic arthritis: importance of disease severity and muscle deficits

OBJECTIVE

To identify determinants of musculoskeletal deficits (muscle cross-sectional area [mCSA], trabecular volumetric bone mineral density [vBMD], and cortical bone strength [section modulus]) in patients with juvenile idiopathic arthritis (JIA) and to determine if cortical bone strength is appropriately adapted to muscle forces.

METHODS

Peripheral quantitative computed tomography (pQCT) of the tibia was performed in 101 patients with JIA (79% female; 24 with oligoarticular JIA, 40 with polyarticular JIA, 18 with systemic JIA, and 19 with spondylarthritis [SpA]) and 830 healthy control subjects; all were ages 5-22 years. Outcomes of pQCT were expressed as sex- and race-specific Z scores. Multivariable linear regression models assessed mCSA and bone status in JIA patients compared with controls and identified factors associated with musculoskeletal deficits in JIA.

RESULTS

The median duration of JIA was 40 months; 29% of the JIA patients had active arthritis, and 28% had received glucocorticoid therapy during the previous year. Compared with the controls, the mCSA and section modulus Z scores were significantly lower in patients with polyarticular JIA and those with SpA. Trabecular vBMD Z scores were significantly lower in patients with polyarticular JIA, those with systemic JIA, and those with SpA. Significant predictors of musculoskeletal deficits included active arthritis in the previous 6 months (mCSA), temporomandibular joint disease (mCSA and section modulus), functional disability (mCSA and vBMD), short stature (vBMD), infliximab exposure (vBMD), and JIA duration (section modulus). The section modulus was significantly reduced relative to mCSA in patients with JIA after adjustment for age and limb length.

CONCLUSION

Marked deficits in vBMD and bone strength occur in JIA in association with severe and longstanding disease. Contrary to the findings of previous studies, bone deficits were greater than expected relative to the mCSA, which illustrates the importance of adjusting for age and bone length.

Interleukin-6 inhibits receptor activator of nuclear factor kappaB ligand-induced osteoclastogenesis by diverting cells into the macrophage lineage: key role of Serine727 phosphorylation of signal transducer and activator of transcription 3

Osteoclasts are bone-resorptive cells that differentiate from hematopoietic precursors upon receptor activator of nuclear factor kappaB ligand (RANKL) activation. Previous studies demonstrated that IL-6 indirectly stimulates osteoclastogenesis through the production of RANKL by osteoblasts. However, few data described the direct effect of IL-6 on osteoclasts. To investigate this effect, we used several models: murine RAW264.7 cells, mouse bone marrow, and human blood monocytes. In the three models used, the addition of IL-6 inhibited RANKL-induced osteoclastogenesis. Furthermore, IL-6 decreased the expression of osteoclast markers and up-modulated macrophage markers. To elucidate this inhibition, signal transducer and activator of transcription (STAT) 3, the main signaling molecule activated by IL-6, was analyzed. Addition of two STAT3 inhibitors completely abolished RANKL-induced osteoclastogenesis, revealing a key role of STAT3. We demonstrated that a basal level of phosphorylated-STAT3 on Serine(727) associated with an absence of phosphorylation on Tyrosine(705) is essential for osteoclastogenesis. Furthermore, a decrease of Serine(727) phosphorylation led to an inhibition of osteoclast differentiation, whereas an increase of Tyrosine(705) phosphorylation upon IL-6 stimulation led to the formation of macrophages instead of osteoclasts. In conclusion, we showed for the first time that IL-6 inhibits RANKL-induced osteoclastogenesis by diverting cells into the macrophage lineage, and demonstrated the functional role of activated-STAT3 and its form of phosphorylation in the control of osteoclastogenesis.

IL-6 receptor expression and IL-6 effects change during osteoblast differentiation

Studies of the effects of interleukin-6 on osteoblasts have yielded conflicting results. In several earlier in vitro studies it has been stated that IL-6 has no effects on osteoblasts unless soluble IL-6 receptor is added. These results are contradictory to the fact that IL-6 receptors are expressed in osteoblasts in vivo. In this study, MC3T3 preosteoblast cells and rat bone marrow stromal cells were cultured in bone inducing medium containing ascorbic acid, beta-glycerophosphate or dexamethasone. We found that IL-6 receptor expression increased in both types of cells during in vitro differentiation. Furthermore in MC3T3 cells IL-6 decreased proliferation and enhanced expression of two osteoblast-specific differentiation markers, Runx2 and osteocalcin, in proper sequential order. Interestingly, in both cell types IL-6-induced apoptosis only in later culture stages. We also found in MC3T3 cells that IL-6 induced STAT3 activation was significantly higher in later culture stages, i.e. when IL-6 receptor expression was high. The present study shows that IL-6 receptor expression increases during in vitro osteoblast differentiation and that IL-6 functions as a differentiation regulator of preosteoblast cells and an apoptosis initiator in more mature cells.

Cytokine mRNA expression is decreased in the subplantar muscle of rat paw subjected to carrageenan-induced inflammation after low-level laser therapy

OBJECTIVE

The objective of this work was to investigate the anti-inflammatory effects of low-level laser therapy, applied at different wavelengths (660 and 684 nm), on cytokine mRNA expression after carrageenan-induced acute inflammation in rat paw.

BACKGROUND DATA

Low-level laser therapy (LLLT) has been observed to reduce pain in inflammatory disorders. However, little is known about the mechanisms behind this effect or whether it is wavelength-specific.

MATERIALS AND METHODS

The test sample consisted of 32 rats divided into four groups: A(1) (control-saline), A(2) (carrageenan-only), A(3) (carrageenan + 660 nm laser therapy), and A(4) (carrageenan + 684 nm laser therapy). The animals from groups A(3) and A(4) were irradiated 1 h after induction of inflammation by carrageenan injection. Continuous-wave red lasers with wavelengths of 660 and 684 nm and dose of 7.5 J/cm(2) were used.

RESULTS

Both the 660 nm and 684 nm laser groups had 30%-40% lower mRNA expression for cytokines TNF-alpha, IL-1beta, and IL-6 in the paw muscle tissue than the carrageenan-only control group. Cytokine measurements were made 3 h after laser irradiation of the paw muscle, and all cytokine differences between the carrageenan-only control group and the LLLT groups were statistically significant (p < 0.001).

CONCLUSIONS

LLLT at the 660-nm and 684-nm wavelengths administered to inflamed rat paw tissue at a dose of 7.5 J/cm(2) reduce cytokine mRNA expression levels within 3 h in the laser-irradiated tissue.

Osteoclast receptors and signaling

Osteoclasts are bone-resorbing cells derived from hematopoietic precursors of the monocyte-macrophage lineage. Besides the well known Receptor Activator of Nuclear factor-kappaB (RANK), RANK ligand and osteoprotegerin axis, a variety of factors tightly regulate osteoclast formation, adhesion, polarization, motility, resorbing activity and life span, maintaining bone resorption within physiological ranges. Receptor-mediated osteoclast regulation is rather complex. Nuclear receptors, cell surface receptors, integrin receptors and cell death receptors work together to control osteoclast activity and prevent both reduced or increased bone resorption. Here we will discuss the signal transduction pathways activated by the main osteoclast receptors, integrating their function and mechanisms of action.

A case of Castleman's disease associated with diffuse idiopathic skeletal hyperostosis and ossification of the posterior longitudinal ligament of the spine

Castleman's disease (CD), diffuse idiopathic skeletal hyperostosis (DISH), and ossification of the posterior longitudinal ligament of the spine (OPLL) are three different entities. Castleman's disease displaying a variety of calcifications in the abdomen and/or pelvis has been reported in some papers. However, there were no reports suggesting an association between CD and ossification/calcification in spine and joints. So far, there has been no case report regarding the coexistence of these diseases in the literature. Herein, we detail a 75-year-old man suffering from CD who demonstrated the features of DISH with coexisting features of OPLL. The cardinal symptoms such as fatigue, high fever, and swollen glands in this case were reduced by corticosteroid therapy. However, it is possible to produce actual symptoms of ossifying/calcified diathesis of entheses and ligaments as a consequence, like the pathology of calcification found in the region of the spleen. In this paper, we describe this patient in order to discuss the association of these diseases.

Osteopenia, decreased bone formation and impaired osteoblast development in Sox4 heterozygous mice

The transcription factor Sox4 is vital for fetal development, as Sox4–/– homozygotes die in utero. Sox4 mRNA is expressed in the early embryonic growth plate and is regulated by parathyroid hormone, but its function in bone modeling/remodeling is unknown. We report that Sox4+/– mice exhibit significantly lower bone mass (by dual-energy X-ray absorptiometry) from an early age, and fail to obtain the peak bone mass of wild-type (WT) animals. Microcomputed tomography (μCT), histomorphometry and biomechanical testing of Sox4+/– bones show reduced trabecular and cortical thickness, growth plate width, ultimate force and stiffness compared with WT. Bone formation rate (BFR) in 3-month-old Sox4+/– mice is 64% lower than in WT. Primary calvarial osteoblasts from Sox4+/– mice demonstrate markedly inhibited proliferation, differentiation and mineralization. In these cultures, osterix (Osx) and osteocalcin (OCN) mRNA expression was reduced, whereas Runx2 mRNA was unaffected. No functional defects were found in osteoclasts. Silencing of Sox4 by siRNA in WT osteoblasts replicated the defects observed in Sox4+/– cells. We demonstrate inhibited formation and altered microarchitecture of bone in Sox4+/– mice versus WT, without apparent defects in bone resorption. Our results implicate the transcription factor Sox4 in regulation of bone formation, by acting upstream of Osx and independent of Runx2.

Expression profiling of Dexamethasone-treated primary chondrocytes identifies targets of glucocorticoid signalling in endochondral bone development

Background

Glucocorticoids (GCs) are widely used anti-inflammatory drugs. While useful in clinical practice, patients taking GCs often suffer from skeletal side effects including growth retardation in children and adolescents, and decreased bone quality in adults. On a physiological level, GCs have been implicated in the regulation of chondrogenesis and osteoblast differentiation, as well as maintaining homeostasis in cartilage and bone. We identified the glucocorticoid receptor (GR) as a potential regulator of chondrocyte hypertrophy in a microarray screen of primary limb bud mesenchyme micromass cultures. Some targets of GC regulation in chondrogenesis are known, but the global effects of pharmacological GC doses on chondrocyte gene expression have not been comprehensively evaluated.

Results

This study systematically identifies a spectrum of GC target genes in embryonic growth plate chondrocytes treated with a synthetic GR agonist, dexamethasone (DEX), at 6 and 24 hrs. Conventional analysis of this data set and gene set enrichment analysis (GSEA) was performed. Transcripts associated with metabolism were enriched in the DEX condition along with extracellular matrix genes. In contrast, a subset of growth factors and cytokines were negatively correlated with DEX treatment. Comparing DEX-induced gene expression data to developmental changes in gene expression in micromass cultures revealed an additional layer of complexity in which DEX maintains the expression of certain chondrocyte marker genes while inhibiting factors that promote vascularization and ultimately ossification of the cartilaginous template.

Conclusion

Together, these results provide insight into the mechanisms and major molecular classes functioning downstream of DEX in primary chondrocytes. In addition, comparison of our data with microarray studies of DEX treatment in other cell types demonstrated that the majority of DEX effects are tissue-specific. This study provides novel insights into the effects of pharmacological GC on chondrocyte gene transcription and establishes the foundation for subsequent functional studies.