Interleukin-6 and its soluble receptor cause a marked induction of collagenase 3 expression in rat osteoblast cultures

Making sense of IL-6 signalling cues in pathophysiology

Unravelling the molecular mechanisms that account for functional pleiotropy is a major challenge for researchers in cytokine biology. Cytokine-receptor cross-reactivity and shared signalling pathways are considered primary drivers of cytokine pleiotropy. However, reports epitomized by studies of Jak-STAT cytokine signalling identify interesting biochemical and epigenetic determinants of transcription factor regulation that affect the delivery of signal-dependent cytokine responses. Here, a regulatory interplay between STAT transcription factors and their convergence to specific genomic enhancers support the fine-tuning of cytokine responses controlling host immunity, functional identity, and tissue homeostasis and repair. In this review, we provide an overview of the signalling networks that shape the way cells sense and interpret cytokine cues. With an emphasis on the biology of interleukin-6, we highlight the importance of these mechanisms to both physiological processes and pathophysiological outcomes.

Ets-2 Propagates IL-6 Trans-Signaling Mediated Osteoclast-Like Changes in Human Rheumatoid Arthritis Synovial Fibroblast

Rheumatoid arthritis synovial fibroblasts (RASFs) contribute to synovial inflammation and bone destruction by producing a pleiotropic cytokine interleukin-6 (IL-6). However, the molecular mechanisms through which IL-6 propels RASFs to contribute to bone loss are not fully understood. In the present study, we investigated the effect of IL-6 and IL-6 receptor (IL-6/IL-6R)-induced trans-signaling in human RASFs. IL-6 trans-signaling caused a significant increase in tartrate-resistant acid phosphatase (TRAP)-positive staining in RASFs and enhanced pit formation by ~3-fold in the osteogenic surface in vitro. IL-6/IL-6R caused dose-dependent increase in expression and nuclear translocation of transcription factor Ets2, which correlated with the expression of osteoclast-specific signature proteins RANKL, cathepsin B (CTSB), and cathepsin K (CTSK) in RASFs. Chromatin immunoprecipitation (ChIP) analysis of CTSB and CTSK promoters showed direct Ets2 binding and transcriptional activation upon IL-6/IL-6R stimulation. Knockdown of Ets2 significantly inhibited IL-6/IL-6R-induced RANKL, CTSB, and CTSK expression and TRAP staining in RASFs and suppressed markers of RASF invasive phenotype such as Thy1 and podoplanin (PDPN). Mass spectrometry analysis of the secretome identified 113 proteins produced by RASFs uniquely in response to IL-6/IL-6R that bioinformatically predicted its impact on metabolic reprogramming towards an osteoclast-like phenotype. These findings identified the role of Ets2 in IL-6 trans-signaling induced molecular reprogramming of RASFs to osteoclast-like cells and may contribute to RASF heterogeneity.

Biomimetic Calcium Phosphate Coatings for Bioactivation of Titanium Implant Surfaces: Methodological Approach and In Vitro Evaluation of Biocompatibility

Ti6Al4V as a common implant material features good mechanical properties and corrosion resistance. However, untreated, it lacks bioactivity. In contrast, coatings with calcium phosphates (CaP) were shown to improve cell-material interactions in bone tissue engineering. Therefore, this work aimed to investigate how to tailor biomimetic CaP coatings on Ti6Al4V substrates using modified biomimetic calcium phosphate (BCP) coating solutions. Furthermore, the impact of substrate immersion in a 1 M alkaline CaCl2 solution (pH = 10) on subsequent CaP coating formation was examined. CaP coatings were characterized via scanning electron microscopy, x-ray diffraction, energy-dispersive x-ray spectroscopy, and laser-scanning microscope. Biocompatibility of coatings was carried out with primary human osteoblasts analyzing cell morphology, proliferation, collagen type 1, and interleukin 6 and 8 release. Results indicate a successful formation of low crystalline hydroxyapatite (HA) on top of every sample after immersion in each BCP coating solution after 14 days. Furthermore, HA coating promoted cell proliferation and reduced the concentration of interleukins compared to the uncoated surface, assuming increased biocompatibility.

Subchondral bone sclerosis in osteoarthritis: not just an innocent bystander

Abstract  Osteoarthritis (OA) is considered to be a complex illness in which the tissues of the joint play a significant role in the initiation and/or progression of the pathophysiology. We still do not completely understand what initiates the degradation and loss of cartilage. However, it has been suggested that increased catabolism due to elevated cytokines and growth factors in OA joints plays a significant role. Recent evidence suggests a key role for the subchondral bone tissue in the progression and/or initiation of OA. Indeed, the subchondral bone tissue produces a number of similar proinflammatory cytokines, and growth factors are involved in cartilage tissue remodeling. Interestingly, studies have shown the presence of clefts or channels in the tidemark that appears early in OA, indicating a possible way to traffic cytokines and growth factors from the subchondral compartment to the overlying cartilage. Therefore, it is possible that certain bone-derived products drive cartilage metabolism. Potential candidates include insulin-like growth factor-1 (IGF-1), transforming growth factor-β (TGF-β) interleukin 1β (IL-1β), and interleukin-6 (IL-6). Demonstrating that the subchondral bone plays a role in the initiation of OA would greatly contribute to furthering our knowledge of this pathology and provide new insights for therapeutic approaches.

Changes in serum runt-related transcription factor 2 levels after a 6-month treatment with recombinant human parathyroid hormone in patients with osteoporosis

BACKGROUND

The mechanisms regulating the anabolic response of the skeleton for recombinant human PTH (1- 34) [rhPTH (1-34)] administration has not been fully elucidated.

AIM

The aim of this study was to evaluate the effect of rhPTH (1-34) on serum levels of runt-related transcription factor 2 (Runx2) in women with osteoporosis.

METHODS

Sixty post-menopausal women with osteoporosis (EO group) and 45 control subjects (NC group) were enrolled in this study. The EO group received daily injection of 20 μg rhPTH (1-34) plus oral 500 mg elemental calcium and 400 IU vitamin D3 for 6 months. Runx2 and Matrix metalloproteinase 13 (MMP-13) were measured with commercially available enzyme-linked immunosorbent assay kits. Bone mineral density (BMD) was also measured before and 6 months after rhPTH (1-34) treatment.

RESULTS

Serum total Ca2+, phosphate, and bone-specific alkaline phosphatase were significantly increased (p<0.05 or p<0.01), and the lumbar spine BMD (LS-BMD) was also increased by 4% in patients with osteoporosis after treatment with rhPTH (1-34) (p<0.05). On the contrary, serum Runx2 and MMP-13 were significantly decreased at post treatment (13.1% and 36.6%, respectively, p<0.05 and p<0.01). At baseline, serum Runx2 positively correlated with MMP-13 (r=0.74, p<0.01), the correction remained after adjusting for age and body mass index.

CONCLUSION

The daily injection of rhPTH (1-34) was able to stimulate bone formation. The therapy of 20 μg rhPTH (1- 34) for 6 months resulted in decrease of serum Runx2 and MMP-13. These changes might reflect the increase of active osteoblasts and the better bone homeostasis.

Microarray and proteomic analysis of breast cancer cell and osteoblast co-cultures: role of osteoblast matrix metalloproteinase (MMP)-13 in bone metastasis

Dynamic reciprocal interactions between a tumor and its microenvironment impact both the establishment and progression of metastases. These interactions are mediated, in part, through proteolytic sculpting of the microenvironment, particularly by the matrix metalloproteinases, with both tumors and stroma contributing to the proteolytic milieu. Because bone is one of the predominant sites of breast cancer metastases, we used a co-culture system in which a subpopulation of the highly invasive human breast cancer cell line MDA-MB-231, with increased propensity to metastasize to bone, was overlaid onto a monolayer of differentiated osteoblast MC3T3-E1 cells in a mineralized osteoid matrix. CLIP-CHIP® microarrays identified changes in the complete protease and inhibitor expression profile of the breast cancer and osteoblast cells that were induced upon co-culture. A large increase in osteoblast-derived MMP-13 mRNA and protein was observed. Affymetrix analysis and validation showed induction of MMP-13 was initiated by soluble factors produced by the breast tumor cells, including oncostatin M and the acute response apolipoprotein SAA3. Significant changes in the osteoblast secretomes upon addition of MMP-13 were identified by degradomics from which six novel MMP-13 substrates with the potential to functionally impact breast cancer metastasis to bone were identified and validated. These included inactivation of the chemokines CCL2 and CCL7, activation of platelet-derived growth factor-C, and cleavage of SAA3, osteoprotegerin, CutA, and antithrombin III. Hence, the influence of breast cancer metastases on the bone microenvironment that is executed via the induction of osteoblast MMP-13 with the potential to enhance metastases growth by generating a microenvironmental amplifying feedback loop is revealed.

Expression of MMP-8 and MMP-13 in the development of periradicular lesions

AIM

To elucidate the expressions of MMP-8 and MMP-13 in experimentally induced rat periradicular lesions by means of the reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical staining.

METHODOLOGY

Thirty rats were used and periradicular lesions in mandibular first molar teeth were established following pulp exposure. The animals were sacrificed at 0 (no exposure control), 1, 2, 3, 4 and 6 weeks after pulp exposure. The right molars were used for RT-PCR analysis of MMP-8 and MMP-13. The left molars were subjected to immunohistochemical staining with both MMPs. The areas of these lesions were measured histometrically, and the numbers of both reactive cells in the periapical portion were counted per unit area. Significant differences were analysed by the Mann-Whitney U-test.

RESULTS

MMP-8 gene expression gradually increased from 2 to 4 weeks, but slightly decreased at 6 weeks. MMP-13 gene expression gradually increased from 1 to 3 weeks. At 4 and 6 weeks, the level of expression was as high as that at 3 weeks. Immunohistochemically, MMP-8 was first detected at 2 weeks and gradually increased until 4 weeks. MMP-13 gradually increased from 1 to 4 weeks. Both MMPs decreased at 6 weeks. The area of the periradicular lesions gradually increased from 1 to 4 weeks, showing a large increase in week 2 and 3 in particular, but then decreased in week 6. MMP-13-expressing cells were significantly greater than MMP-8-positive cells at week 1 and 2.

CONCLUSIONS

These findings indicate that MMP-8 and MMP-13 were related to the development of periradicular lesions. It is suggested that MMP-13 increased from an early stage during their development and that MMP-8 is involved in the progression of tissue destruction including bone resorption.

Although IL-6 trans-signaling is sufficient to drive local immune responses, classical IL-6 signaling is obligate for the induction of T cell-mediated autoimmunity

IL-6-mediated T cell-driven immune responses are associated with signaling occurring through the membrane-bound cognate receptor α-chain (mIL-6Rα). Once formed, IL-6-mIL-6Rα complexes induce the homodimerization and subsequent phosphorylation of the ubiquitously expressed signal-transducing protein, gp130. This signaling event is defined as classical IL-6 signaling. However, many inflammatory processes assigned to IL-6 may be mediated via binding a naturally occurring soluble IL-6Rα, which forms an agonistic complex (IL-6/soluble IL-6Rα) capable of evoking responses on a wide range of cell types that lack mIL-6Rα (IL-6 trans-signaling). To dissect the differential contribution of the two IL-6 signaling pathways in cell-mediated inflammatory processes, we pharmaceutically targeted each using two murine models of human arthritis. Whereas intra-articular neutralization of trans-signaling attenuated local inflammatory responses, the classical pathway was found to be obligate and sufficient to induce pathogenic T cells and humoral responses, leading to systemic disease. Our data illustrate that mechanisms occurring in the secondary lymphoid organs underlying arthropathies are mediated via the classical pathway of IL-6 signaling, whereas trans-signaling contributes only at the local site, that is, in the affected tissues.

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.

Osteoblasts derived from osteophytes produce interleukin-6, interleukin-8, and matrix metalloproteinase-13 in osteoarthritis

To clarify the significance of the osteophytes that appear during the progression of osteoarthritis (OA), we investigated the expression of inflammatory cytokines and proteases in osteoblasts from osteophytes. We also examined the influence of mechanical stress loading on osteoblasts on the expression of inflammatory cytokines and proteases. Osteoblasts were isolated from osteophytes in 19 patients diagnosed with knee OA and from subchondral bone in 4 patients diagnosed with femoral neck fracture. Messenger RNA expression and protein production of inflammatory cytokines and proteases were analyzed using real-time RT-PCR and ELISA, respectively. To examine the effects of mechanical loading, continuous hydrostatic pressure was applied to the osteoblasts. We determined the mRNA expression and protein production of IL-6, IL-8, and MMP-13, which are involved in the progression of OA, were increased in the osteophytes. Additionally, when OA pathological conditions were simulated by applying a nonphysiological mechanical stress load, the gene expression of IL-6 and IL-8 increased. Our results suggested that nonphysiological mechanical stress may induce the expression of biological factors in the osteophytes and is involved in OA progression. By controlling the expression of these genes in the osteophytes, the progression of cartilage degeneration in OA may be reduced, suggesting a new treatment strategy for OA.

Enhanced expression of interleukin-6, matrix metalloproteinase-13, and receptor activator of NF-kappaB ligand in cells derived from osteoarthritic subchondral bone

BACKGROUND

The aim of this study was to clarify the significance of subchondral bone in the pathology of osteoarthritis (OA) by investigating the expression of inflammatory cytokines, proteases, and receptor activator of NF-kappaB ligand (RANKL)/receptor activator of NF-kappaB (RANK)/osteoprotegerin (OPG) involved in cartilage degeneration.

METHODS

Subchondral bone was obtained from 19 patients diagnosed with knee OA and 4 patients diagnosed with femoral neck fracture. Subchondral bone osteoblasts (SBOs) were isolated, and total RNA was extracted. Messenger RNA expression of inflammatory cytokines, proteases, and RANKL/RANK/OPG were analyzed using a real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Real-time RT-PCR showed that mRNA expressions of interleukin-6 (IL-6), matrix metalloproteinase-13 (MMP-13), and RANKL were significantly enhanced in OA SBOs compared to SBOs without OA. The expressions of these genes was greater in patients with severe cartilage damage than in those with mild cartilage damage. A high correlation between mRNA expression of IL-6 and that of MMP-13 was found in OA SBOs.

CONCLUSION

The increases in IL-6, MMP-13, and RANKL expression in OA SBOs suggest that in subchondral bone OA progression involves abnormal osseous tissue remodeling, which induces mechanical property changes. Cartilage degeneration in OA may also be due, at least in part, to IL-6 and MMP-13 produced by SBOs. Comprehensive research on these pathological features may lead to the development of more effective therapies for OA by administration of molecules that affect bone remodeling and metabolism.

sIL-6R: more than an agonist?

On target cells, interleukin-6 (IL-6) interacts with its receptor complex consisting of the membrane-bound IL-6 receptor (IL-6R) and the signal transducing protein gp130. IL-6R can exist as a soluble protein (sIL-6R), which binds the ligand IL-6. This soluble complex can bind to gp130 on cells that lack the membrane-bound IL-6R and initiate signaling. This process is named transsignaling. The significance of transsignaling via sIL-6R is underlined by different publications and exceeds very probably the significance of the membrane-bound IL-6R. It is the general assumption that sIL-6R acts as an agonist in combination with IL-6 resulting in an enhancement of the IL-6 effects. In this article, we suppose 'non-agonistic' properties. There are several publications that give reasons to speculate that sIL-6R (a) has IL-6-antagonistic effects, (b) has orphan properties and (c) interacts with yet unknown binding partners different from IL-6. Knowledge about additional properties of sIL-6R will enlarge the biologic understanding of this molecule and might give an explanation for the sometimes contrasting effects of the cytokine IL-6.

Callus mineralization and maturation are delayed during fracture healing in interleukin-6 knockout mice

IL-6 is a pleiotropic cytokine involved in cell signaling in the musculoskeletal system, but its role in bone healing remains uncertain. The purpose of this study was to examine the role of IL-6 in fracture healing. Eight-week-old male C57BL/6 and IL-6 -/- mice were subjected to transverse, mid-diaphyseal osteotomies on the right femora. Sacrifice time points were 1, 2, 4, or 6 weeks post-fracture (N=14 per group). Callus tissue properties was analyzed by microcomputed tomography (micro-CT) and Fourier transform infrared imaging spectroscopy (FT-IRIS). Cartilage and collagen content, and osteoclast density were measured histologically. In intact unfractured bone, IL-6 -/- mice had reduced crystallinity, mineral/matrix ratio, tissue mineral density (TMD), and bone volume fraction (BVF) compared to wildtype mice. This suggests that there was an underlying deficit in baseline bone quality in IL-6 -/- mice. At 2 weeks post-fracture, the callus of IL-6 -/- mice had reduced crystallinity and mineral/matrix ratio. These changes were less evident at 4 weeks. At 2 weeks, the callus of the IL-6 -/- mice had an increased tissue mineral density (TMD), an increased cartilage and collagen content, and reduced osteoclast density compared to these parameters in wildtype mice. By 4 and 6 weeks, these parameters were no longer different between the two strains of mice. In conclusion, IL-6 -/- mice had delayed callus maturity, mineralization, and remodeling compared with the callus of the wildtype mice. These effects were transient indicating that the role of IL-6 appears to be most important in the early stages of fracture healing.

Quercetin accelerates TNF-alpha-induced apoptosis of MC3T3-E1 osteoblastic cells through caspase-dependent and JNK-mediated pathways

The bioflavonoid, quercetin, is believed to inhibit bone loss by regulating many systemic and local factors including hormones and cytokines. However, our previous findings revealed that quercetin did not inhibit but facilitate the tumor necrosis factor (TNF)-alpha-mediated apoptosis of MC3T3-E1 osteoblastic cells. Therefore, this study was carried out to examine the cellular mechanisms for how quercetin accelerates TNF-alpha-mediated apoptosis, and to determine whether the accelerating effect of quercetin is a general effect in osteoblastic cells. Quercetin promoted the TNF-alpha-induced apoptosis of MC3T3-E1 cells through both the mitochondrial-mediated and caspase-dependent mechanisms. Quercetin also augmented the TNF-alpha-mediated apoptosis by activating c-Jun N-terminal kinase (JNK) with the attendant activation of activator protein-1, where the nuclear translocation of c-Jun protein appeared to be a critical event responsible for the accelerating action of quercetin. However, TNF-alpha-mediated apoptosis and its acceleration by quercetin were not observed in primary osteoblasts. These results strongly suggest that quercetin accelerates TNF-alpha-mediated apoptosis of osteoblasts through caspase-dependent and JNK-mediated pathways, and that the cellular responses of osteoblasts to TNF-alpha and/or quercetin might differ according to their origins.

Expression of MMP-13 in osteoblast cells and rat tibia after exposure to gamma rays or accelerated carbon ions

In past research, we found that carbon ion irradiation increased bone volume in rats, and a significant amount of cartilage remained inside the carbon ion-irradiated trabeculae. The amounts of matrix metalloproteinase 13 (MMP-13) mRNA in osteoblast-like MC3T3-E1 cells tended to decrease after carbon ion irradiation. The level of MMP-13 mRNA in non-irradiated cells was stable during the experimental period, but in gamma ray-irradiated cells it tended to increase. When localization of MMP-13 in locally irradiated experimental rats was investigated, it was found in the marginal trabeculae in both non-irradiated and gamma ray-irradiated animals. MMP-13 was detected in osteoid and neogenetic bone in the trabeculae surface. The trabeculae in carbon ion-irradiated bone remained cartilaginous. Carbon ion-irradiated rats exhibited weak expression of MMP-13 around the cartilage inside the trabeculae. We conclude that carbon ion irradiation reduced expression of MMP-13, thus suppressing both chondrocyte maturation and cartilage resorption. Increases in hyperplasia of the bone trabeculae and of bone volume were caused by ongoing bone addition and calcification in the absence of sufficient cartilage resorption.

Interleukin-6: discovery of a pleiotropic cytokine

In the late 1960s, the essential role played by T cells in antibody production was reported. This led to our hypothesis that certain molecules would have to be released from T cells to effect the stimulation of B cells. This hypothesis was shown to be true. There were certain factors present in the culture supernatant of T cells that induced proliferation and differentiation of B cells. The factor that induced B cells to produce immunoglobulins was initially named B cell stimulatory factor-2. The cDNA encoding the human B cell stimulatory factor-2 was cloned in 1986. At the same time, IFN-β₂ and a 26 kDa protein in the fibroblasts were independently cloned and found to be identical to B cell stimulatory factor-2. Later, a hybridoma/plasmacytoma growth factor and a hepatocyte stimulating factor were also proven to be the same molecule as B cell stimulatory factor-2. Various names were used for this single molecule because of its multiple biological activities, but these have all been unified and the molecule is now known as IL-6. Since the discovery of IL-6, rapid progress has been made in our understanding of IL-6 activities, the IL-6 receptor system and the IL-6 signal transduction mechanism. More importantly, it has been shown to be involved in a number of diseases such as rheumatoid arthritis and Castleman's disease. When taking into account all the accumulated basic research on the various aspects of this molecule, it appeared that blocking the activity of IL-6 was a feasible, new therapeutic approach for chronic inflammatory diseases.

Antibody Array-Generated Cytokine Profiles of Tears of Patients with Vernal Keratoconjunctivitis or Giant Papillary Conjunctivitis

PURPOSE

To investigate differences in the cytokine and chemokine profiles of patients with vernal keratoconjunctivitis (VKC) or giant papillary conjunctivitis (GPC).

METHODS

The study included six patients (six eyes) with VKC, five patients (five eyes) with GPC, and five healthy volunteers (five eyes) as controls. None of the patients had received any anti-allergic treatment prior to this study. One patient with VKC was given a tear examination to evaluate the effect of anti-inflammatory treatment with a steroid on the tear cytokine profile about the treatment. Tear samples were collected with the Schirmer I method, using filter paper. Tear samples were eluted and analyzed by an antibody array system for inflammation-related factors, including cytokines and chemokines.

RESULTS

In the patients with VKC, four inflammation-related factors, eotaxin, interleukin (IL)-11, monocyte chemoattractant protein (MCP)-1, and macrophage-colony stimulating factor (M-CSF) increased to four times the values in the control group, and seven inflammation-related factors, eotaxin-2, IL-4, IL-6, interleukin-6 soluble receptor (IL-6sR), IL-7, macrophage inflammatory protein (MIP)-1delta, and tissue inhibitor of metalloproteinases (TIMP)-2, increased to eight times the control values. In the patients with GPC, three inflammation-related factors, IL-6, M-CSF, and monokine-induced gamma interferon (MIG), increased to four times those in the control group, and five inflammation-related factors, eotaxin-2, IL-6sR, IL-11, MIP-1delta, and TIMP-2, increased to eight times the control values. The increase in IL-6sR relative to the controls was statistically significant in both the VKC and GPC groups. The increase in eotaxin-2 was significant only in the VKC group, and that in TIMP-2 was significant only in the GPC group, compared with the controls.

CONCLUSIONS

The present study demonstrated the presence of crucial cytokines, soluble cytokine receptors, and chemokines in tears of patients with VKC and GPC. In particular, IL-6sR increased significantly in both the VKC and GPC groups, whereas eotaxin-2 increased significantly only in the VKC group. Thus, IL-6sR may play an important pathophysiological role in giant papillary proliferation in VKC and GPC, and eotaxin-2 may play an important role in eosinophilic inflammation in VKC.

Quercetin, a bioflavonoid, accelerates TNF-α-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells

The bioflavonoid quercetin is believed to play an important role in preventing bone loss by affecting osteoclastogenesis and regulating many systemic and local factors including hormones and cytokines. This study examined how quercetin acts on tumor necrosis factor-alpha (TNF-alpha)-mediated growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells. Tritium uptake assay showed that a quercetin treatment accelerated TNF-alpha-induced inhibition of DNA synthesis in the cells in a dose-dependent manner. Both the 3-(4,5-dimethylthiazol-2yl-)-2,5-diphenyl tetrazolium bromide and trypan blue staining assays also showed the quercetin-mediated facilitation of TNF-alpha-induced cytotoxicity in the cells. Apoptosis assays revealed an accelerating effect of quercetin on TNF-alpha-induced apoptosis in MC3T3-E1 cells. In addition, Fas activation and poly (ADP ribose) polymerase cleavage are thought to be closely associated with the TNF-alpha-induced apoptosis and its acceleration by the quercetin treatment in the cells. Collectively, this study showed that quercetin accelerates the TNF-alpha-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells.

Interleukin-6: An osteotropic factor influencing bone formation?

Interleukin (IL)-6 has long been considered as an osteoresorptive factor. However, recent data indicate that IL-6 could influence bone formation in conditions of increased bone turnover. In this paper, the effects of IL-6 and its soluble receptor on osteoblast proliferation, differentiation and apoptosis are readdressed. A brief summary of IL-6 signaling after binding to its receptor is provided and hypotheses concerning IL-6 and the central control of bone formation are also highlighted.

Osteoblasts from the sclerotic subchondral bone downregulate aggrecan but upregulate metalloproteinases expression by chondrocytes. This effect is mimicked by interleukin-6, -1beta and oncostatin M pre-treated non-sclerotic osteoblasts

OBJECTIVE

To determine the effects of osteoarthritic (OA) subchondral osteoblasts on the metabolism of human OA chondrocytes in alginate beads.

METHODS

Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 4 days in the absence or in the presence of osteoblasts isolated from non-sclerotic (N) or sclerotic (SC) zones of human OA subchondral bone in monolayer (co-culture system). Before co-culture, osteoblasts were incubated for 72 h with or without 1.7ng/ml interleukin (IL)-1beta, 100 ng/ml IL-6 with its soluble receptor (50 ng/ml) or 10 ng/ml oncostatin M (OSM). Aggrecan (AGG) and matrix metalloproteases (MMP)-3 and -13 mRNA levels in chondrocytes were quantified by real-time polymerase chain reaction. AGG production was assayed by a specific enzyme amplified sensitivity immunoassay.

RESULTS

SC, but not N, osteoblasts induced a significant inhibition of AGG production and AGG gene expression by human OA chondrocytes in alginate beads, and significantly increased MMP-3 and MMP-13 gene expression by chondrocytes. When they were pre-incubated with IL-1beta, IL-6 or OSM, N osteoblasts inhibited AGG synthesis and increased MMP-3 and -13 gene expression by chondrocytes in alginate beads in a same order of magnitude as SC osteoblasts.

CONCLUSIONS

These results demonstrate that SC OA subchondral osteoblasts could contribute to cartilage degradation by stimulating chondrocytes to produce more MMP and also by inhibiting AGG synthesis.

Subchondral bone osteoblasts induce phenotypic changes in human osteoarthritic chondrocytes

OBJECTIVE

To determine the influence of osteoarthritic (OA) phenotype of subchondral osteoblasts on the phenotype of human chondrocytes.

METHODS

Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 4 or 10 days in the absence or in the presence of osteoblasts in monolayer. The osteoblasts were either isolated from non-sclerotic (N) or sclerotic (SC) zones of human subchondral bone. Before co-culture, osteoblasts were incubated for 72 h with or without 1.7 ng/ml interleukin (IL)-1beta, 100 ng/ml IL-6 with its soluble receptor (50 ng/ml) or 10 ng/ml oncostatin M. SOX9, type I, II and X collagen (COL1, COL2, COL10), osteoblasts-stimulating factor (OSF)-1, bone alkaline phosphatase (ALP), parathyroid hormone related peptide (PTHrP) and its receptor (PTH-R) messenger RNA (mRNA) levels in chondrocytes were quantified by real-time polymerase chain reaction.

RESULTS

In comparison with chondrocytes cultured alone in alginate beads, chondrocytes after 4 days in co-culture with N or SC osteoblasts expressed significantly less SOX9 and COL2 mRNA. The decrease of SOX9 and COL2 gene expression was significantly more pronounced in the presence of SC than in the presence of N osteoblasts (P<0.001). OSF-1 mRNA level in chondrocyte was increased by both N and SC osteoblasts, but to a larger extent by SC osteoblasts (P<0.001). PTHrP expression in chondrocytes was 21-fold increased by N osteoblasts but four-fold inhibited by SC osteoblasts. PTHrP secretion was also increased by N but reduced by SC osteoblasts. SC, but not N osteoblasts, induced a significant decrease of PTH-R gene expression in chondrocyte. In our experimental conditions, chondrocytes did not express COL1, COL10 or ALP, even after 10 days of co-culture with osteoblasts.

CONCLUSIONS

In co-culture, SC subchondral osteoblasts decrease SOX9, COL2, PTHrP and PTH-R gene expression by chondrocytes but increase that of OSF-1. These findings suggest that SC osteoblasts could initiate chondrocyte phenotype shift towards hypertrophic differentiation and subsequently further matrix mineralization.

Bone morphogenetic protein-2 suppresses collagenase-3 promoter activity in osteoblasts through a runt domain factor 2 binding site

Transforming growth factor-beta (TGFbeta) superfamily of growth factors, which include bone morphogenetic proteins (BMPs), have multiple effects in osteoblasts. In this study, we examined the regulation of collagenase-3 promoter activity by BMP-2 in osteoblast-enriched (Ob) cells from fetal rat calvariae. BMP-2 suppressed the activity of a -2 kb collagenase-3 promoter/luciferase recombinant in a time- and dose-dependent manner. The BMP-2 effect on the collagenase-3 promoter was further tested in several collagenase-3 promoter deletion constructs and it was narrowed down to a -148 to -94 nucleotide segment of the promoter containing a runt domain factor 2 (Runx2) site at nucleotide -132 to -126. The effect of BMP-2 was obliterated in a collagenase-3 promoter/luciferase construct containing a mutated Runx2 (mRunx2) sequence indicating that the Runx2 site mediates the BMP-2 response. Electrophoretic mobility shift assays, using nuclear extracts from control and BMP-2-treated Ob cells, indicated that the Runx2 protein is a component of the specific DNA-protein complex formed on the Runx2 site and that the BMP-2 effect may be associated with minor protein modifications rather than major changes in the composition of specific proteins interacting with the Runx2 site. We confirmed that other members of the TGFbeta family can down-regulate the collagenase-3 promoter by showing that TGFbeta1 also suppresses the promoter activity in a time- and dose-dependent manner. In conclusion, this study demonstrates that BMP-2 and TGFbeta1 suppress collagenase-3 promoter activity in osteoblasts and establishes a link between BMP-2 action and collagenase-3 expression via Runx2, a major regulator of osteoblast formation and function.

Interleukin-6 receptor shedding is enhanced by interleukin-1? and tumor necrosis factor ? and is partially mediated by tumor necrosis factor ?-converting enzyme in osteoblast-like cells

OBJECTIVE

Interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R) activation of gp130 represents an alternative pathway for osteoclast development in inflammatory conditions. The goal of the present study was to investigate changes in sIL-6R levels in response to the inflammatory cytokines IL-1beta and tumor necrosis factor alpha (TNFalpha) and to determine the role of TNFalpha-converting enzyme (TACE) in this process.

METHODS

Levels of sIL-6R in the culture media of MG63 and SAOS-2 osteoblast-like cell lines after exposure to various agents were determined by immunoassay. TACE protein levels were measured by Western immunoblotting. Cells were transfected with small interfering RNA (siRNA) or with an expression plasmid for IL-6R and TACE to determine the potential involvement of TACE in IL-6R shedding.

RESULTS

IL-1beta and TNFalpha increased the levels of sIL-6R in the culture media of MG63 osteoblast-like cells. This effect was not influenced by cycloheximide or 5,6-dichlorobenzimidazole riboside but was markedly inhibited by the calcium chelator EGTA and by the TACE and matrix metalloproteinase inhibitor hydroxamate (Ru36156). IL-1beta and TNFalpha had no influence on the alternatively spliced form of IL-6R RNA. Levels of sIL-6R were reduced when MG63 cells were transiently transfected with TACE siRNA. Transfection of SAOS-2 cells with expression plasmids for IL-6R and TACE produced a dose-dependent increase in sIL-6R levels.

CONCLUSION

IL-1beta- and TNFalpha-mediated induction of IL-6R shedding in osteoblast-like cells is at least partly dependent on TACE activation.

Differential regulation of chondrocyte metabolism by oncostatin M and interleukin-6

OBJECTIVE

To determine the effects of interleukin (IL)-6 and oncostatin M (OSM) added separately or in combination with IL-1beta on human osteoarthritic (OA) chondrocytes in alginate beads.

DESIGN

Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 12 days, in the absence or in the presence of increasing amounts of IL-6 (20-500ng/ml) with its soluble receptor or OSM (0.1-10ng/ml) and with or without IL-1beta (1.7ng/ml). Aggrecan (AGG), transforming growth factor-beta1 (TGF-beta1), stromelysin-1 [matrix metalloprotease (MMP)-3], tissue inhibitor of metalloproteinases-1 (TIMP-1), macrophage inflammatory protein-1 beta (MIP-1beta), IL-6 and IL-8 productions were assayed by specific enzyme amplified sensitivity immunoassays. Prostaglandin (PG)E(2) was measured by a specific radioimmunoassay and nitrite (NO(2)(-)) by a spectrophotometric method based upon the Griess reaction.

RESULTS

OSM, but not IL-6, decreased basal AGG and TGF-beta1 synthesis. Although IL-6 stimulated basal TIMP-1 production, it did not significantly modify MMP-3/TIMP-1 ratio. In contrast, 10ng/ml OSM highly increased TIMP-1 production, and decreased by half the ratio MMP-3/TIMP-1. IL-1beta highly stimulated *NO, IL-8, IL-6, MIP-1beta and PGE(2) synthesis but decreased AGG and TGF-beta1 production. Neither IL-6 nor OSM modulated IL-1beta-inhibitory effect on AGG production. IL-6, but not OSM, reversed IL-1beta-induced TGF-beta1 inhibition. At 1-10ng/ml, OSM significantly decreased IL-1beta-stimulated IL-8, MIP-1beta, PGE(2) and *NO production but amplified IL-1beta stimulating effect on IL-6 production. IL-6 had no effect on these parameters.

CONCLUSIONS

OSM and IL-6, two glycoprotein 130 binding cytokines, show different activity profiles on OA chondrocytes, indicating that these cytokines could play different roles in the OA disease process.

Regulation of collagen deposition and lysyl oxidase by tumor necrosis factor-alpha in osteoblasts

Tumor necrosis factor-alpha (TNF-alpha) inhibits osteoblast function in vitro by inhibiting collagen deposition. Studies generally support that TNF-alpha does not inhibit collagen biosynthesis by osteoblasts but that collagen deposition is in some way diminished. The study investigated TNF-alpha regulation of biosynthetic enzymes and proteins crucial for posttranslational extracellular collagen maturation in osteoblasts including procollagen C-proteinases, procollagen C-proteinase enhancer, and lysyl oxidase. The working hypothesis is that such regulation could inhibit collagen deposition by osteoblasts. We report that in phenotypically normal MC3T3-E1 osteoblasts, TNF-alpha decreases collagen deposition without decreasing collagen mRNA levels or procollagen protein synthesis. Analyses of the cell layers revealed that TNF-alpha diminished the levels of mature collagen cross-links, pyridinoline and deoxypyridinoline. Further analyses revealed that the mRNA expression for lysyl oxidase, the determining enzyme required for collagen cross-linking, is down-regulated by TNF-alpha in a concentration- and time-dependent manner by up to 50%. The decrease was accompanied by a significant reduction of lysyl oxidase protein levels and enzyme activity. By contrast, Northern and Western blotting studies revealed that procollagen C-proteinases bone morphogenic protein-1 and mammalians Tolloid and procollagen C-proteinase enhancer were expressed in MC3T3-E1 cells and not down-regulated. The data together demonstrate that TNF-alpha does not inhibit collagen synthesis but does inhibit the expression and activity of lysyl oxidase in osteoblasts, thereby contributing to perturbed collagen cross-linking and accumulation. These studies identify a novel mechanism in which proinflammatory cytokine modulation of an extracellular biosynthetic enzyme plays a determining role in the control of collagen accumulation by osteoblasts.

Pathogenesis of pterygia: role of cytokines, growth factors, and matrix metalloproteinases

Pterygium is a common ocular surface disease apparently only observed in humans. Chronic UV exposure is a widely accepted aetiological factor in the pathogenesis of this disease and this concept is supported by epidemiological data, ray tracing models and histopathological changes that share common features with UV damaged skin. The mechanism(s) of pterygium formation is incompletely understood. Recent data have provided evidence implicating a genetic component, anti-apoptotic mechanisms, cytokines, growth factors, extracellular matrix remodelling (through the actions of matrix metalloproteinases), immunological mechanisms and viral infections in the pathogenesis of this disease. In this review, the current knowledge on pterygium pathogenesis is summarised, highlighting recent developments. In addition, we provide novel data further demonstrating the complexity of this intriguing disease.

Acute effect of drinking red and white wines on circulating levels of inflammation-sensitive molecules in men with coronary artery disease

There is evidence that moderate consumption of red wine with its high content of polyphenolic antioxidants may be more protective than white wine against development of coronary artery disease (CAD). The aim of this study was to compare the acute effects of ingestion of red wine and white wine on markers of inflammation in men with CAD. Thirteen men with angiographically-proven CAD were studied in a cross-over trial. The men consumed 4 mL/kg (2 to 3 glasses) red wine and white wine in random order during a light meal and with at least a week between interventions. Later, the men also consumed an isoenergetic nonalcoholic beverage (control) in the same study protocol. Venous blood was taken at baseline, 1 hour, and 6 hours after the drinks. Plasma interleukin-6 (IL-6), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), blood alcohol, plasma lipids, and plasma polyphenols were measured. Mean +/- SD blood alcohol was 6.5 +/- 2.2 mmol/L and 6.9 +/- 1.1 mmol/L at 1 hour and returned to baseline at 6 hours after intake of red wine and white wine, respectively. Plasma IL-6 concentration increased significantly (P =.01) during 6 hours after ingestion of red wine (56%) and white wine (63%). The increase in plasma IL-6 concentration after ingestion of wine was significantly higher (P =.045) compared with the corresponding increase (11%) following intake of the nonalcoholic beverage. Plasma IL-6 levels at 6 hours (r =.631, P =.02) were correlated significantly with plasma alcohol levels at 1 hour after ingestion of red wine. These data suggest that moderate wine intake may acutely increase plasma levels of IL-6 in men with CAD. It is possible that this increase in plasma IL-6 is a response to alcohol-induced oxidative stress in the liver.

Soluble IL-6 receptor governs IL-6 activity in experimental arthritis: blockade of arthritis severity by soluble glycoprotein 130

Studies in IL-6-deficient (IL-6(-/-)) mice highlight that IL-6 contributes to arthritis progression. However, the molecular mechanism controlling its activity in vivo remains unclear. Using an experimental arthritis model in IL-6(-/-) mice, we have established a critical role for the soluble IL-6R in joint inflammation. Although intra-articular administration of IL-6 itself was insufficient to reconstitute arthritis within these mice, a soluble IL-6R-IL-6 fusion protein (HYPER-IL-6) restored disease activity. Histopathological assessment of joint sections demonstrated that HYPER-IL-6 increased arthritis severity and controlled intrasynovial mononuclear leukocyte recruitment through the CC-chemokine CCL2. Activation of synovial fibroblasts by soluble IL-6R and IL-6 emphasized that these cells may represent the source of CCL2 in vivo. Specific blockade of soluble IL-6R signaling in wild-type mice using soluble gp130 ameliorated disease. Consequently, soluble IL-6R-mediated signaling represents a promising therapeutic target for the treatment of rheumatoid arthritis.

Subchondral bone in osteoarthritis: a biologic link with articular cartilage leading to abnormal remodeling

PURPOSE OF REVIEW

This review deals with new findings highlighting the concept of cross-talk between subchondral bone tissue and articular cartilage that may be crucial for the initiation and/or progression of osteoarthritis. In this review, new factors either produced by subchondral bone tissue or modifying osteoblast metabolism, yet implicated in osteoarthritis, are discussed.

RECENT FINDINGS

The development of cartilage degeneration is concomitant with subchondral bone thickness in osteoarthritis, whereas it is related to higher subchondral bone activity and dysregulation in the synthesis of bone proteins. As an immediate consequence, homotrimers of type 1 collagen are formed that could lead to undermineralization of this tissue. This dysregulation also leads to abnormal production of different factors by osteoblasts such as prostaglandins, leukotrienes, and growth factors. Because microcracks or neovascularization provide a link between the subchondral bone tissue and articular cartilage, these factors could contribute to the abnormal remodeling of osteoarthritic cartilage.

SUMMARY

These findings have an immediate implication for research because new tools need to be developed to study the subchondral bone-cartilage functional unit. Moreover, it could lead to a possible cure for osteoarthritis because this pathology should be considered both a bone and cartilage disease.

The role of soluble receptors in cytokine biology: the agonistic properties of the sIL-6R/IL-6 complex

Cytokines perform ever-increasing roles in both, the regulation of general homeostasis and in orchestrating the immune response during disease. To ensure that control of the cytokine network is tightly regulated, nature has developed a series of systems designed for this purpose. In this respect, researchers have placed considerable emphasis on identifying and characterising the regulatory properties of soluble cytokine receptors. These proteins bind their ligands with similar affinities to those of their cognate transmembrane receptors and are effective at prolonging the circulating half-life of cytokines they bind. However, it is the individual capacity of these soluble receptors to act as either antagonists or agonists which has been the principal focus of most research studies. This review provides an overview of the activities of soluble cytokine receptors, but primarily concentrates on those that possess agonistic properties.

Expression of MMP-8 and MMP-13 mRNAs in rat periodontium during tooth eruption

The present study was designed to investigate mRNA expression of matrix metalloproteinase-8 (MMP-8) and MMP-13 in forming periodontium during tooth eruption in the rat. RT-PCR for the decalcified paraffin sections indicated expression of MMP-8 and MMP-13 in the periodontal tissues. In situ hydridization demonstrated expression of MMP-8 in osteoblasts, osteocytes, periodontal ligament cells, cementoblasts, and cementocytes along with collagen types I and III. In contrast, transcripts of MMP-13 were confined to a small population of osteoblasts and osteocytes in alveolar bone. The results suggested that MMP-8 may be involved in remodeling the periodontium during tooth eruption, and its expression may be coordinated with that of collagen types I and III, whereas the participation of MMP-13 may be rather limited.

The role of soluble interleukin (IL)-6 receptor in mediating the effects of IL-6 on matrix metalloproteinase-1 and tissue inhibitor of metalloproteinase-1 expression by gingival fibroblasts

BACKGROUND

Interleukin-6 (IL-6) is a multifunctional cytokine thought to play a role in the tissue destruction that characterizes periodontal disease. IL-6 exerts its cellular effects through a cell-surface receptor which also exists in a soluble form (sIL-6r). This study investigated the effects of IL-6 on matrix metalloproteinase (MMP)-1 activity in gingival fibroblast cultures, specifically determining the role of the sIL-6r in mediating these actions.

METHODS

Fibroblasts were grown to confluence, washed in Hank's balanced saline solution (HBSS), and then cultured for 72 hours in serum-free medium supplemented with 0.2% bovine serum albumin, 1 microgram/ml Escherichia coli LPS and containing various combinations of IL-6 and its soluble receptor over the concentration range 0 to 1,000 ng/ml. MMP-1 and tissue inhibitor of MMP (TIMP)-1 protein levels in the conditioned medium were assessed by enzyme-linked immunosorbent assay (ELISA) and collagenolytic activity determined using a 3H-acetylated type I collagen degradation assay.

RESULTS

Results indicated that the addition of IL-6 alone to cultures, over the concentration range 0 to 1,000 ng/ml, had no significant effect on MMP-1 protein expression. However, addition of IL-6 in combination with its soluble receptor resulted in a statistically significant, dose-dependent upregulation in MMP-1 expression. The IL-6/sIL-6r combination also induced a significant increase in collagenolytic activity in cultures. IL-6 and sIL-6r, either alone or in combination, had no marked effect on TIMP expression or cell growth.

CONCLUSIONS

These data strongly suggest that future clinical studies investigating the role of IL-6 in periodontal disease must also determine the levels of sIL-6r within the periodontal tissues.

Effect of Crohn's disease on bone metabolism in vitro: a role for interleukin-6

Circulating proinflammatory cytokines may be involved in osteopenia associated with Crohn's disease (CD). Therefore, the effect of interleukin (IL)-6, IL-1beta, and tumor necrosis factor (TNF) a contained in Crohn's serum on bone formation was examined in a bone organ culture system. Initially, serum levels of IL-6, IL-1beta, and TNF-a were determined by ELISA in newly diagnosed, untreated children with CD and healthy age-matched controls. Serum IL-6 levels were significantly higher in patients with CD than in controls (23.9 +/- 2.8 pg/ml vs. 0.7 pg/ml +/- 0.2; p < 0.001), whereas IL-1beta and TNF-alpha serum levels were not. In the organ culture studies, 20-day-old fetal rat parietal bones were incubated for 96 h with CD or control serum, serum preincubated with a neutralizing antibody to each cytokine or a nonimmune immunoglobulin control, and with IL-6. Bone formation measured by assaying calcium content and dry weight was significantly decreased in bones exposed to Crohn's serum. Light microscopy of the bones treated with CD serum revealed a discontinuous, uneven mineralized bone matrix and disorganized osteoblasts with altered morphology. Incubation with an antibody that neutralized IL-6 activity prevented the change in osteoblast and bone morphology. TNF-a and IL-1beta antibodies had no apparent effects. Collagen synthesis and DNA content were not affected by CD serum. Also, addition of IL-6 to the culture medium decreased mineralization. These results suggest that IL-6 is a mediator of the effects of Crohn's serum on in vitro mineralization and may be a contributing factor to the osteopenia associated with CD.

Macrophage migration inhibitory factor up-regulates matrix metalloproteinase-9 and -13 in rat osteoblasts. Relevance to intracellular signaling pathways

Neutral matrix metalloproteinases (MMPs) play an important role in bone matrix degradation accompanied by bone remodeling. We herein show for the first time that macrophage migration inhibitory factor (MIF) up-regulates MMP-13 (collagenase-3) mRNA of rat calvaria-derived osteoblasts. The mRNA up-regulation was seen at 3 h in response to MIF (10 microg/ml), reached the maximum level at 6-12 h, and returned to the basal level at 36 h. MMP-13 mRNA up-regulation was preceded by up-regulation of c-jun and c-fos mRNA. Tissue inhibitor of metalloproteinase (TIMP)-1 and MMP-9 (92-kDa type IV collagenase) were also up-regulated, but to a lesser extent. The MMP-13 mRNA up-regulation was significantly suppressed by genistein, herbimycin A and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine. Similarly, a selective mitogen-activated protein kinase (MAPK) kinase (MEK)1/2 inhibitor (PD98059) and c-jun/activator protein (AP)-1 inhibitor (curcumin) suppressed MMP-13 mRNA up-regulation induced by MIF. The mRNA levels of c-jun and c-fos in response to MIF were also inhibited by PD98059. Consistent with these results, MIF stimulated phosphorylation of tyrosine, autophosphorylation of Src, activation of Ras, activation of extracellular signal-regulated kinases (ERK) 1/2, a MAPK, but not c-Jun N-terminal kinase or p38, and phosphorylation of c-Jun. Osteoblasts obtained from calvariae of newborn JunAA mice, defective in phosphorylation of c-Jun, or newborn c-Fos knockout (Fos -/- ) mice, showed much less induction of MMP-13 with the addition of MIF than osteoblasts obtained from wild-type or littermate control mice. Taken together, these results suggest that MIF increases the MMP-13 mRNA level of rat osteoblasts via the Src-related tyrosine kinase-, Ras-, ERK1/2-, and AP-1-dependent pathway.

Gene expression of MMP8 and MMP13 during embryonic development of bone and cartilage in the rat mandible and hind limb

Matrix metalloproteinases (MMPs) 8 and 13 comprise the collagenase subfamily in rats and mice, and only MMP13 has been implicated in degradation of the collagenous matrices during development of bone and cartilage. On the hypothesis that MMP8 is also involved in bone and cartilage development, the present study was designed to investigate gene expression of MMP8 in rat embryonic mandibles and hind limbs. Expression of MMP8 was examined with in situ hybridization and RT-PCR and was compared with that of MMP13. Osteoblastic and chondrocytic cells expressing collagenous matrix molecules were identified using in situ hybridization for collagen Types I and II. The results demonstrated that MMP8 is expressed by osteoblastic progenitors, differentiated osteoblasts, osteocytes, and chondrocytes in the growth plate for the first time. Furthermore, the expression of MMP8 is much broader than that of MMP13, for which expression is confined to differentiated phenotypes of osteoblastic and chondrocytic lineage.

Neuroprotective effect of interleukin-6 and IL6/IL6R chimera in the quinolinic acid rat model of Huntington's syndrome

Ciliary neurotrophic factor prevents behavioural deficits and striatal degeneration in rat and primate models of Huntington's disease. Interleukin-6, another member of the cytokine family, and the chimeric molecule (IL6/IL6R) in which interleukin-6 and its soluble receptor are fused, have been shown to exert trophic action on various neuronal populations in the central nervous system. Therefore, we investigated the neuroprotective effect of these two molecules in the quinolinic acid model of Huntington's disease. LacZ-, interleukin-6- and IL6/IL6R-expressing lentiviral vectors were stereotaxically injected into the striatum of Wistar rats. Three weeks later the animals were lesioned through the intrastriatal injection of 180 nmol of quinolinic acid. The extent of the striatal damage was significantly diminished in the rats that had been treated with interleukin-6 or IL6/IL6R. The neuroprotective effect was, however, more pronounced with the IL6/IL6R chimera than with interleukin-6 as indicated by the volume of the lesions (38.6 +/- 10% in the IL6/IL6R group, 63.3 +/- 3.6% in the IL-6 group and 84.3 +/-2.9% in the control group). Quantitative analysis of striatal interneurons further demonstrated that the IL6/IL6R chimera is more neuroprotective than IL-6 on ChAT- and NADPH-d-immunoreactive neurons. These results suggest that the IL6/IL6R chimera is a potential treatment for Huntington's disease.

A combination of a chemically modified doxycycline and a bisphosphonate synergistically inhibits endotoxin-induced periodontal breakdown in rats

BACKGROUND

Chemically modified non-antimicrobial tetracyclines (CMTs) have been shown to inhibit pathologically elevated collagenase (and other matrix metalloproteinase, MMP) activity and bone resorption in vivo and in vitro.

METHODS

In the current study, suboptimal doses of CMT-8 (a non-antimicrobial chemically modified doxycycline) and a bisphosphonate (clodronate, an anti-bone resorption compound) were administered daily, either as a single agent or as a combination therapy, to rats with experimental periodontitis induced by repeated injection of bacterial endotoxin (LPS) into the gingiva. At the end of the 1-week protocol, the gingival tissues were dissected, extracted, and the extracts analyzed for MMPs (collagenases and gelatinases) and for elastase, and the defleshed jaws were morphometrically analyzed for alveolar bone loss.

RESULTS

LPS injection significantly (P<0.001) increased alveolar bone loss and increased collagenase (MMP-8), gelatinase (MMP-9), and elastase activities. Treatment of the LPS-injected rats with suboptimal CMT-8 alone or suboptimal clodronate alone produced slight reductions in the tissue-destructive proteinases and no significant reductions in alveolar bone loss. However, a combination of suboptimal CMT-8 and clodronate "normalized" the pathologically elevated levels of MMPs, elastase, and alveolar bone loss, indicating synergistic inhibition of tissue breakdown in this animal model of periodontitis.

CONCLUSIONS

Combination of a CMT and a bisphosphonate may be a useful treatment to optimally suppress periodontal destruction and tooth loss and in other tissue-destructive inflammatory diseases such as arthritis.

Synergistic effects of glycoprotein 130 binding cytokines in combination with interleukin-1 on cartilage collagen breakdown

OBJECTIVE

To determine whether other glycoprotein 130 (gp130) binding cytokines can mimic the effects of oncostatin M (OSM) in acting synergistically with interleukin-1alpha (IL-1alpha) to induce cartilage collagen breakdown and collagenase expression, and to determine which receptors mediate these effects.

METHODS

The release of collagen and proteoglycan was assessed in bovine and human cartilage explant cultures. Messenger RNA (mRNA) and protein production from immortalized human chondrocytes (T/C28a4) was analyzed by Northern blotting and specific enzyme-linked immunosorbent assays. Collagenase activity was measured by bioassay. Cell surface receptors were detected by flow cytometry.

RESULTS

OSM in combination with IL-1alpha caused a rapid synergistic induction of matrix metalloproteinase 1 mRNA, which was sustained over a 72-hour period. Flow cytometric analyses detected both the OSM-specific receptor and the gp130 receptor at the chondrocyte cell surface, but failed to detect the leukemia inhibitory factor receptor (LIFR). Cartilage degradation assays revealed that, of the gp130 binding cytokines, only OSM and IL-6, in the presence of its soluble receptor (sIL-6R), were able to act synergistically with IL-1alpha to promote collagen release.

CONCLUSION

This study demonstrates that IL-6 can mimic OSM in synergizing with IL-1alpha to induce chondrocyte-mediated cartilage collagen breakdown and collagenase production. In order to have this effect, IL-6 requires the presence of its soluble receptor. The apparent absence of LIFR explains why other gp130 binding cytokines do not act in synergy with IL-1alpha. Since OSM, IL-6, and sIL-6R levels have all been shown to be elevated in the rheumatoid joint, our findings suggest that these cytokines may be key mediators of cartilage collagen catabolism in the inflammatory arthritides.

Catecholamines stimulate interleukin-6 synthesis in rat cardiac fibroblasts

Proinflammatory cytokines have been implicated in the pathophysiology of different heart diseases. Recent evidence suggests that interleukin-6 (IL--6) may play a role in mechanisms leading to cardiac hypertrophy. In addition, catecholamines are known to induce cardiac hypertrophy. In the present study, we examined whether cardiac fibroblasts may be a potential source of IL--6 production in the rat heart and whether catecholamines can modulate the IL--6 synthesis. Only a small amount of IL--6 mRNA was detected in unstimulated rat cardiac fibroblasts. However, a 50-fold increase of IL--6 mRNA was found after stimulation with norepinephrine (NE). Addition of carvedilol, a alpha- and beta-adrenergic receptor antagonist, prevented almost completely the NE-induced synthesis of IL--6 mRNA. Phenylephrine, an alpha-adrenergic agonist, and isoproterenol, a beta-adrenergic agonist, also induced an increase in IL--6. However, the stimulation via beta-receptors led to a more pronounced elevation. These data show that NE increases IL--6 expression in rat cardiac fibroblasts and that IL--6 may play an important autocrine/paracrine role in cardiac disease states associated with hypertrophy.

AP-1 and Cbfa/runt physically interact and regulate parathyroid hormone-dependent MMP13 expression in osteoblasts through a new osteoblast-specific element 2/AP-1 composite element

The expression of MMP13 (collagenase-3), a member of the matrix metalloproteinase family, is increased in vivo as well as in cultured osteosarcoma cell lines by parathyroid hormone (PTH), a major regulator of calcium homeostasis. Binding sites for AP-1 and Cbfa/Runt transcription factors in close proximity have been identified as cis-acting elements in the murine and rat mmp13 promoter required for PTH-induced expression. The cooperative function of these factors in response to PTH in osteoblastic cells suggests a direct interaction between AP-1 and Cbfa/Runt transcription factors. Here, we demonstrate interaction between c-Jun and c-Fos with Cbfa/Runt proteins. This interaction depends on the leucine zipper of c-Jun or c-Fos and the Runt domain of Cbfa/Runt proteins, respectively. Moreover, c-Fos interacts with the C-terminal part of Cbfa1 and Cbfa2, sharing a conserved transcriptional repression domain. In addition to the distal osteoblast-specific element 2 (OSE2) element in the murine and rat mmp13 promoter, we identified a new proximal OSE2 site overlapping with the TRE motif. Both interaction of Cbfa/Runt proteins with AP-1 and the presence of a functional proximal OSE2 site are required for enhanced transcriptional activity of the mmp13 promoter in transient transfected fibroblasts and in PTH-treated osteosarcoma cells.

IL-1- and TNF-induced bone resorption is mediated by p38 mitogen activated protein kinase

We have previously shown that p38 mitogen-activated protein kinase (MAPK) inhibitors, which block the production and action of inflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1), are effective in models of bone and cartilage degradation. To further investigate the role of p38 MAPK, we have studied its activation in osteoblasts and chondrocytes, following treatment with a panel of proinflammatory and osteotropic agents. In osteoblasts, significant activation of p38 MAPK was observed following treatment with IL-1 and TNF, but not parathyroid hormone, transforming growth factor-beta (TGF-beta), 1,25(OH)(2)D(3), insulin-like growth factor-1 (IGF-1), or IGF-II. Similar results were obtained using primary bovine chondrocytes and an SV40-immortalized human chondrocyte cell line, T/C28A4. SB 203580, a selective inhibitor of p38 MAPK, inhibited IL-1 and TNF-induced p38 MAPK activity and IL-6 production (IC(50)s 0.3--0.5 microM) in osteoblasts and chondrocytes. In addition, IL-1 and TNF also activated p38 MAPK in fetal rat long bones and p38 MAPK inhibitors inhibited IL-1- and TNF-stimulated bone resorption in vitro in a dose-dependent manner (IC(50)s 0.3--1 microM). These data support the contention that p38 MAPK plays a central role in regulating the production of, and responsiveness to, proinflammatory cytokines in bone and cartilage. Furthermore, the strong correlation between inhibition of kinase activity and IL-1 and TNF-stimulated biological responses indicates that selective inhibition of the p38 MAPK pathway may have therapeutic utility in joint diseases such as rheumatoid arthritis (RA).

Cultures of human osteoblastic cells from dialysis patients: influence of bone turnover rate on in vitro selection of interleukin-6 and osteoblastic cell makers

The factors contributing to renal osteodystrophy are still incompletely characterized. A variety of cytokines and growth factors appear to have ill-defined roles in this disease. Our aim is to compare osteoblastic cell growth and different osteoblastic markers in vitro with histomorphometric bone parameters and some serum bone-turnover markers in vivo in dialysis patients with either high- (HTBD) or low-turnover (LTBD) bone disease. Six patients were diagnosed to have LTBD, and another five patients, HTBD. Intact parathyroid hormone (PTH) and osteocalcin (OC) levels in serum were greater in patients with HTBD than in those with LTBD. Osteoblastic cells isolated from iliac crest biopsy specimens were grown in culture medium for different times up to 13 days. Osteoblastic cell growth (cell number and area under the cell growth curve) was greater in patients with HTBD than in those with LTBD. Static and dynamic bone formation parameters correlated with serum PTH levels. No correlation was found between PTH and osteoblastic cell proliferation. OC, C-terminal type I procollagen, and alkaline phosphatase osteoblastic secretion in vitro were similar in the HTBD and LTBD groups. However, interleukin-6 (IL-6) secretion was greater in cells isolated from patients with LTBD. Our results indicate that osteoblastic cell growth and osteoblastic IL-6 secretion are related to bone turnover in patients with osteodystrophy. Our findings support the hypothesis that factors other than PTH level might have an important role in affecting osteoblastic function in renal osteodystrophy.

The soluble interleukin 6 receptor: mechanisms of production and implications in disease

Interleukin 6 (IL-6) performs a prominent role during disease and has been described as both a pro- and anti-inflammatory cytokine. A key feature in the regulation of IL-6 responses has been the identification of a soluble interleukin 6 receptor (sIL-6R), which forms a ligand-receptor complex with IL-6 that is capable of stimulating a variety of cellular responses including proliferation, differentiation and activation of inflammatory processes. Elevated sIL-6R levels have been documented in numerous clinical conditions indicating that its production is coordinated as part of a disease response. Thus, sIL-6R has the potential to regulate both local and systemic IL-6-mediated events. This review will outline the central role of sIL-6R in the coordination of IL-6 responses. Details relating to the mechanisms of sIL-6R production will be provided, while the potential significance of sIL-6R during the development of clinical conditions will be emphasized. We want to convey, therefore, that when thinking about the inflammatory capability of IL-6, it is essential to consider not only the action of IL-6 itself, but also the effect sIL-6R may have on cellular processes.

Alendronate stimulates collagenase 3 expression in osteoblasts by posttranscriptional mechanisms

Bisphosphonates inhibit bone resorption by reducing osteoclastic cell number and activity. Alendronate is a nitrogen-containing bisphosphonate analog used in the treatment of postmenopausal osteoporosis. The effects of alendronate in osteoclasts are well documented; however, there is limited information on the actions of alendronate in osteoblasts (Ob's). In this study, we investigated the effects of alendronate at concentrations of 1-100 microM on the synthesis of collagenase 3 or matrix metalloproteinase 13 (MMP-13) and tissue inhibitors of MMPs (TIMPs) 1, 2, and 3 in primary Ob-enriched cells from 22-day-old fetal rat calvariae. Alendronate at concentrations higher than 10 microM markedly stimulated the synthesis of collagenase messenger RNA (mRNA) and immunoreactive protein in Ob's. Alendronate did not stimulate the transcriptional rate of the collagenase 3 gene. However, in transcriptionally arrested cells, alendronate prolonged the half-life of collagenase transcripts. Alendronate did not alter the expression of TIMP 1 and 2, but modestly stimulated the expression of TIMP 3. The actions of alendronate in Ob's suggest potential additional effects in bone remodeling.

The expression of metalloproteinase-2, -9, and -14 and of tissue inhibitors-1 and -2 is developmentally modulated during osteogenesis in vitro, the mature osteoblastic phenotype expressing metalloproteinase-14

During osteogenesis, in vitro, of tibial-derived rat osteoblasts (ROB) and derived clones, changes occur in the interactions of mature osteoblasts with the endogenous extracellular matrix (ECM) and these culminate in the formation of tridimensional nodules, which become sites of mineral deposition. We investigated if these changes might be mediated by remodeling of ECM, and we focused our study on the neutral metalloproteinases (MMPs), known agents of matrix remodeling, and on their tissue inhibitors (TIMPs). We report that during in vitro differentiation, osteoblasts express the secreted MMP-2 and -9 and the membrane gelatinase MMP-14. These, along with the tissue inhibitors TIMP-1 and -2, are developmentally regulated according to the maturation stage of osteoblasts. Their levels change in a similar association with osteoblast phenotypic maturation in different populations of ROB, which take different times to complete osteogenesis in vitro. MMP-14 expression coincides in both cell populations with the mature osteoblastic phenotype and is localized in the cells forming nodules. MMP-2 and -9 are expressed diffusely in the osteoblast population. Developmentally associated changes in the activation of MMP-2 are detected, associated in their timing with the expression of MMP-14 in both populations of ROB, and MMP-14 activates pro-MMP-2 in vitro. Expression of messenger RNAs (mRNAs) for the three MMPs increases up to the time of nodule formation. At this stage, TIMP-1 mRNA levels are lowest. TIMP-2 mRNA decreases throughout osteogenesis. In situ hybridization in 7-day-old rat tibias shows the strongest expression of MMP-14 among osteogenic cells, in lining osteoblasts on the newly formed trabeculae under the growth plate, and on the endosteal surface of cortical bone. Our data support the concept that the developmentally regulated expression of MMP-14 triggers localized proteolysis within the osteogenic population, concomitant in vitro to nodule formation.

Platelet-derived growth factor induces collagenase 3 transcription in osteoblasts through the activator protein 1 complex

Platelet-derived growth factor (PDGF) BB is a mitogen that stimulates bone resorption and increases collagenase 3 transcription in osteoblasts, although the mechanisms involved are as yet unknown. We examined the effect of PDGF BB on collagenase 3 transcription in cultures of osteoblasts from fetal rat calvariae (Ob cells). PDGF BB increased the activity of collagenase 3 promoter fragments transiently transfected into Ob cells. Deletion analysis of the collagenase promoter revealed three regions that impaired the induction of collagenase 3 by PDGF BB. A construct spanning base pair -53 to +28 collagenase 3 sequences, in relation to the start site of transcription +1, was fully responsive to PDGF BB and was studied in detail. Targeted mutations of an AP-1 site in this fragment decreased basal collagenase promoter activity and the responsiveness to PDGF BB, whereas mutations of Stat3 and Ets binding sites did not alter the response to PDGF. Electrophoretic mobility shift assay, using nuclear extracts from control and treated cells, revealed AP-1 nuclear protein complexes that were enhanced in extracts from PDGF BB-treated Ob cells. Supershift assays revealed that antibodies to c-Fos, Fos B, Fra-2, c-Jun, Jun B, and Jun D shifted the binding of nuclear extracts from cells treated with PDGF BB to AP-1 sequences. In conclusion, PDGF BB induces collagenase 3 transcription in osteoblasts by regulating nuclear proteins interacting with AP-1 sequences.