Basic fibroblast growth factor stimulates expression of interstitial collagenase and inhibitors of metalloproteinases in rat bone cells

Fibroblast Growth Factor 2 as an Antifibrotic: Antagonism of Myofibroblast Differentiation and Suppression of Pro-Fibrotic Gene Expression

Fibrosis is a pathological condition that is characterized by the replacement of dead or damaged tissue with a nonfunctional, mechanically aberrant scar, and fibrotic pathologies account for nearly half of all deaths worldwide. The causes of fibrosis differ somewhat from tissue to tissue and pathology to pathology, but in general some of the cellular and molecular mechanisms remain constant regardless of the specific pathology in question. One of the common mechanisms underlying fibroses is the paradigm of the activated fibroblast, termed the "myofibroblast," a differentiated mesenchymal cell with demonstrated contractile activity and a high rate of collagen deposition. Fibroblast growth factor 2 (FGF2), one of the members of the mammalian fibroblast growth factor family, is a cytokine with demonstrated antifibrotic activity in non-human animal, human, and in vitro models. FGF2 is highly pleiotropic and its receptors are present on many different cell types throughout the body, lending a great deal of variety to the potential mechanisms of FGF2 effects on fibrosis. However, recent reports demonstrate that a substantial contribution to the antifibrotic effects of FGF2 comes from the inhibitory effects of FGF2 on connective tissue fibroblasts, activated myofibroblasts, and myofibroblast progenitors. FGF2 demonstrates effects antagonistic towards fibroblast activation and towards mesenchymal transition of potential myofibroblast-forming cells, as well as promotes a gene expression paradigm more reminiscent of regenerative healing, such as that which occurs in the fetal wound healing response, than fibrotic resolution. With a better understanding of the mechanisms by which FGF2 alters the wound healing cascade and results in a shift away from scar formation and towards functional tissue regeneration, we may be able to further address the critical need of therapy for varied fibrotic pathologies across myriad tissue types.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

Early reversal cells in adult human bone remodeling: osteoblastic nature, catabolic functions and interactions with osteoclasts

The mechanism coupling bone resorption and formation is a burning question that remains incompletely answered through the current investigations on osteoclasts and osteoblasts. An attractive hypothesis is that the reversal cells are likely mediators of this coupling. Their nature is a big matter of debate. The present study performed on human cancellous bone is the first one combining in situ hybridization and immunohistochemistry to demonstrate their osteoblastic nature. It shows that the Runx2 and CD56 immunoreactive reversal cells appear to take up TRAcP released by neighboring osteoclasts. Earlier preclinical studies indicate that reversal cells degrade the organic matrix left behind by the osteoclasts and that this degradation is crucial for the initiation of the subsequent bone formation. To our knowledge, this study is the first addressing these catabolic activities in adult human bone through electron microscopy and analysis of molecular markers. Periosteoclastic reversal cells show direct contacts with the osteoclasts and with the demineralized resorption debris. These early reversal cells show (1) ¾-collagen fragments typically generated by extracellular collagenases of the MMP family, (2) MMP-13 (collagenase-3) and (3) the endocytic collagen receptor uPARAP/Endo180. The prevalence of these markers was lower in the later reversal cells, which are located near the osteoid surfaces and morphologically resemble mature bone-forming osteoblasts. In conclusion, this study demonstrates that reversal cells colonizing bone surfaces right after resorption are osteoblast-lineage cells, and extends to adult human bone remodeling their role in rendering eroded surfaces osteogenic.

Basic fibroblastic growth factor affects the osteogenic differentiation of dental pulp stem cells in a treatment-dependent manner

AIM

To determine how basic fibroblastic growth factor (bFGF) affected the osteogenic differentiation of human dental pulp stem cells (DPSCs) in vitro and in vivo.

METHODOLOGY

Basic fibroblastic growth factor stimulation of DPSCs was divided into a pre-treatment period and an osteogenic differentiation period. Alizarin red quantification experiments and alkaline phosphatase activity quantification assay were performed to examine the osteogenic differentiation of DPSCs after different bFGF stimulation. Quantification reverse transcription polymerase chain reaction was used to analyze the osteogenic gene expression of DPSCs after different bFGF stimulation. In addition, DPSCs that received the 1 and 2 weeks bFGF pre-treatments as in the in vitro experiments were mineralized for 1 week and seeded into hydroxyapatite/tricalcium phosphate (HA/TCP) pills and subcutaneously transplanted into naked mice for 2 or 3 months. The transplants were removed, sliced and stained using Modified Ponceau Trichrome Stain to observe the formation of mineralized tissue.

RESULTS

Basic fibroblastic growth factor stimulation in the osteogenic differentiation period decreased the in vitro osteogenic differentiation ability of DPSCs. One week pre-treatment with bFGF increased the in vitro osteogenic differentiation ability of DPSCs, whereas 2 weeks pre-treatment with bFGF decreased the in vitro osteogenic differentiation ability of DPSCs. The pre-treatment period was vital for the osteogenic differentiation of DPSCs in vitro. The in vivo results were similar to the in vitro results.

CONCLUSIONS

Basic fibroblastic growth factor affected the osteogenic differentiation of DPSCs in a treatment-dependent manner both in vitro and in vivo.

Therapeutic potential of fibroblast growth factor-2 for hypertrophic scars: upregulation of MMP-1 and HGF expression

Although hypertrophic scars (HTSs) and keloids are challenging problems, their pathogenesis is not well understood, making therapy difficult. We showed that matrix metalloproteinase (MMP)-1 expression was downregulated in HTS compared with normal skin from the same patients, whereas type 1 and 3 collagen and transforming growth factor-β (TGF-β) were upregulated. These differences, however, were not seen in cultured fibroblasts, suggesting the involvement of microenvironmental factors in the pathogenesis of HTS. Fibroblast growth factor-2 (FGF-2) highly upregulated the expression of MMP-1 and hepatocyte growth factor (HGF) in both HTS-derived and control fibroblasts; the upregulation was reversed by extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) inhibitors. An animal study using human HTS tissue implanted into nude mice indicated that controlled-release FGF-2 resulted in significantly less weight and decreased hydroxyproline content in HTS. Degradation of collagen fibers in FGF-2-treated HTS was also confirmed histologically. Western blotting showed that FGF-2-treated HTS expressed significantly higher MMP-1 protein than control. Decreased MMP-1 expression may be an important transcriptional change in HTS, and its reversal as well as upregulation of HGF by FGF-2 could be a new therapeutic approach for HTS.

Activation of the FGF signaling pathway and subsequent induction of mesenchymal stem cell differentiation by inorganic polyphosphate

Inorganic polyphosphate [poly(P)] is a biopolymer existing in almost all cells and tissues, although its biological functions in higher eukaryotes have not been completely elucidated. We previously demonstrated that poly(P) enhances the function of fibroblast growth factors (FGFs) by stabilizing them and strengthening the affinity between FGFs and their cell surface receptors. Since FGFs play crucial roles in bone regeneration, we further investigated the effect of poly(P) on the cell differentiation of human stem cells via FGF signaling systems. Human dental pulp cells (HDPCs) isolated from human dental pulp show the characteristics of multipotent mesenchymal stem cells (MSCs). HDPCs secreted FGFs and the proliferation of HDPCs was shown to be enhanced by treatment with poly(P). Cell surface receptor-bound FGF-2 was stably maintained for more than 40 hours in the presence of poly(P). The phosphorylation of ERK1/2 was also enhanced by poly(P). The effect of poly(P) on the osteogenic differentiation of HDPCs and human MSCs (hMSCs) were also investigated. After 5 days of treatment with poly(P), type-I collagen expression of both cell types was enhanced. The C-terminal peptide of type-I collagen was also released at higher levels in poly(P)-treated HDPCs. Microarray analysis showed that expression of matrix metalloproteinase-1 (MMP1), osteopontin (OPN), osteocalcin (OC) and osteoprotegerin was induced in both cell types by poly(P). Furthermore, induced expression of MMP1, OPN and OC genes in both cells was confirmed by real-time PCR. Calcification of both cell types was clearly observed by alizarin red staining following treatment with poly(P). The results suggest that the activation of the FGF signaling pathway by poly(P) induces both proliferation and mineralization of stem cells.

Molecular Basis for the Regenerative Properties of a Secretion of the Mollusk Cryptomphalus aspersa

A screen for natural products bearing pharmacological properties has yielded a secretion of the mollusk Cryptomphalus aspersa (SCA), which possesses skin-regenerative properties. In this report, we outline some of the cellular and molecular effects underlying this observation. First, we found that SCA contained antioxidant SOD and GST activities. In addition, SCA stimulated fibroblast proliferation and rearrangement of the actin cytoskeleton. Additional mechanisms involved in the regenerative effect of SCA included the stimulation of extracellular matrix assembly and the regulation of metalloproteinase activities. Together, these effects provide an array of molecular mechanisms underlying SCA-induced cellular regeneration and postulate its use in regeneration of wounded tissue.

Role of matrix metalloproteinase 13 in both endochondral and intramembranous ossification during skeletal regeneration

Extracellular matrix (ECM) remodeling is important during bone development and repair. Because matrix metalloproteinase 13 (MMP13, collagenase-3) plays a role in long bone development, we have examined its role during adult skeletal repair. In this study we find that MMP13 is expressed by hypertrophic chondrocytes and osteoblasts in the fracture callus. We demonstrate that MMP13 is required for proper resorption of hypertrophic cartilage and for normal bone remodeling during non-stabilized fracture healing, which occurs via endochondral ossification. However, no difference in callus strength was detected in the absence of MMP13. Transplant of wild-type bone marrow, which reconstitutes cells only of the hematopoietic lineage, did not rescue the endochondral repair defect, indicating that impaired healing in Mmp13^−/− mice is intrinsic to cartilage and bone. Mmp13^−/− mice also exhibited altered bone remodeling during healing of stabilized fractures and cortical defects via intramembranous ossification. This indicates that the bone phenotype occurs independently from the cartilage phenotype. Taken together, our findings demonstrate that MMP13 is involved in normal remodeling of bone and cartilage during adult skeletal repair, and that MMP13 may act directly in the initial stages of ECM degradation in these tissues prior to invasion of blood vessels and osteoclasts.

Overexpression of Runx2 directed by the matrix metalloproteinase-13 promoter containing the AP-1 and Runx/RD/Cbfa sites alters bone remodeling in vivo

The activator protein-1 (AP-1) and runt domain binding (Runx/RD/Cbfa) sites and their respective binding proteins, c-Fos/c-Jun and Runx2 (Cbfa1), regulate the rat matrix metalloproteinase-13 (MMP-13) promoter in both parathyroid hormone (PTH)-treated and differentiating osteoblastic cells in culture. To determine the importance of these regulatory sites in the expression of MMP-13 in vivo, transgenic mice containing either wild-type (-456 or -148) or AP-1 and Runx/RD/Cbfa sites mutated (-148A3R3) MMP-13 promoters fused with the E. coli lacZ reporter were generated. The wild-type transgenic lines expressed higher levels of bacterial beta-galactosidase in bone, teeth, and skin compared to the mutant and non-transgenic lines. Next, we investigated if overexpression of Runx2 directed by the MMP-13 promoter regulated expression of bone specific genes in vivo, and whether this causes morphological changes in these animals. Real time RT-PCR experiments identified increased mRNA expression of bone forming genes and decreased MMP-13 in the tibiae of transgenic mice (14 days and 6 weeks old). Histomorphometric analyses of the proximal tibiae showed increased bone mineralization surface, mineral apposition rate, and bone formation rate in the transgenic mice which appears to be due to decreased osteoclast number. Since MMP-13 is likely to play a role in recruiting osteoclasts to the bone surface, decreased expression of MMP-13 may cause reduced osteoclast-mediated bone resorption, resulting in greater bone formation in transgenic mice. In summary, we show here that the 148 bp upstream of the MMP-13 transcriptional start site is sufficient and necessary for gene expression in bone, teeth, and skin in vivo and the AP-1 and Runx/RD/Cbfa sites are likely to regulate this. Overexpression of Runx2 by these regulatory elements appears to alter the balance between the bone formation-bone resorption processes in vivo.

Insuffizienzfrakturen in der Rheumatologie

Stress fractures occur as insufficiency fractures, with a prevalence of 0.8% in patients with rheumatological illness. The main sites of insufficiency fractures are the pelvis and sacrum, parts of the tibia and fibula that are close to the joints, and the calcaneus and hip. Since the painful symptoms overlap with the clinical picture of the painful joint diseases and because of the low sensitivity of conventional diagnostic X-ray, insufficiency fractures are not diagnosed directly or their diagnosis is delayed. The high sensitivity of computer tomography, skeletal scintigraphy and nuclear magnetic resonance imaging should be exploited in the diagnosis of insufficiency fractures. The case report presented describes insufficiency fractures of the distal right tibia and fibula in an elderly female patient with rheumatoid arthritis being treated with long-term glucocorticoids. In addition to advanced age, female gender, immobility and rheumatoid arthritis requiring long-term cortisone, there are further risk factors for insufficiency fractures: fluoride treatment over many years in the past, hypovitaminosis D3, renal failure. The DXA bone density values of the neck of the femur and the lumbar vertebrae do not show any osteoporosis, and the calcium concentration in the serum is low; phosphate is raised and parathormone is normal; osteocalcin, beta crosslaps and alkaline phosphatase are raised. Bone biopsy specimens taken from the iliac crest and the proximal femur and investigated for the purpose of differential diagnosis revealed renal osteopathy with secondary hyperparathyroidism and osteomalacia. In elderly patients with kidney failure, the possibility of renal osteopathy must be considered as the possible cause of reduced bone quality with a raised risk of insufficiency fractures, even when the parathormone levels are normal. In view of the frequency of osteopathies in rheumatological patients, osteology is of enormous significance in rheumatology.

Functions and regulations of fibroblast growth factor signaling during embryonic development

Fibroblast growth factors (FGF) are secreted molecules which function through the activation of specific tyrosine kinases receptors, the FGF receptors that transduce the signal by activating different pathways including the Ras/MAP kinase and the phospholipase-C gamma pathways. FGFs are involved in the regulation of many developmental processes including patterning, morphogenesis, differentiation, cell proliferation or migration. Such a diverse set of activities requires a tight control of the transduction signal which is achieved through the induction of different feedback inhibitors such as the Sproutys, Sef and MAP kinase phosphatase 3 which are responsible for the attenuation of FGF signals, limiting FGF activities in time and space.

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.

Matrix metalloproteinases and their clinical applications in orthopaedics

Imbalance in the expression of matrix metalloproteinases and their inhibitors contribute considerably to abnormal connective tissue degradation prevalent in various orthopaedic joint diseases such as rheumatoid arthritis and osteoarthritis. Matrix metalloproteinase expression has been detected in ligament, tendon, and cartilage tissues in the joint. They are known to contribute to the development, remodeling, and maintenance of healthy tissue through their ability to cleave a wide range of extracellular matrix substrates. Their role has been extended to cell growth, migration, differentiation, and apoptosis. In orthopaedics, their clinical applications constantly are being explored. The multiple steps in matrix metalloproteinase regulation offer potential targets for inhibition, useful in drug therapy. The correlation between matrix metalloproteinases and progression in joint erosion presents potential prognostic and diagnostic tools in rheumatoid arthritis. Matrix metalloproteinases also can be incorporated into scaffold design to control the degradation rate of engineered tissue constructs. This current review aims to summarize and emphasize the importance of matrix metalloproteinases and their natural inhibitors in the maturation of musculoskeletal tissue through matrix remodeling and, therefore, in the generation of a new clinical potential in orthopaedics.

Transforming growth factor-beta 1 regulation of collagenase-3 expression in osteoblastic cells by cross-talk between the Smad and MAPK signaling pathways and their components, Smad2 and Runx2

Transforming growth factor-beta (TGF-beta) plays a key role in osteoblast differentiation and bone development and remodeling. Collagenase-3 (matrix metalloproteinase-13) is expressed by osteoblasts and seems to be involved in osteoclastic bone resorption. Here, we show that TGF-beta 1 stimulates collagenase-3 expression in the rat osteoblastic cell line UMR 106-01 and requires de novo protein synthesis. Dominant-negative Smad2/3 constructs indicated that Smad signaling is essential for TGF-beta 1-stimulated collagenase-3 promoter activity. Inhibitors of the ERK1/2 and p38 MAPK pathways, but not the JNK pathway, reduced TGF-beta 1-stimulated collagenase-3 expression, indicating that the p38 MAPK and ERK1/2 pathways are also required for TGF-beta 1-stimulated collagenase-3 expression in UMR 106-01 cells. These inhibitors did not prevent nuclear localization of Smad proteins, but they inhibited Smad-mediated transcriptional activation. We have shown for the first time that Runx2 (a bone transcription factor and a potential substrate for the MAPK pathway) is phosphorylated in response to TGF-beta 1 treatment in osteoblastic cells. Cotransfection of Smad2 and Runx2 constructs had a cooperative effect on TGF-beta 1-stimulated collagenase-3 promoter activity in these cells. We further identified ligand-independent physical interaction between Smad2 and Runx2. Taken together, our results provide an important role for cross-talk between the Smad and MAPK pathways and their components in expression of collagenase-3 following TGF-beta 1 treatment in UMR 106-01 cells.

Transcriptional regulation of collagenase-3 by interleukin-1 alpha in osteoblasts

Interleukin-1 (IL-1)alpha is an autocrine/paracrine agent of the skeletal tissue and it regulates bone remodeling. Collagenase-3 or matrix metalloproteinase (MMP)-13 is expressed in osteoblasts and its expression is modulated by several cytokines including IL-1alpha. Because the molecular mechanism of increased synthesis of collagenase-3 in bone cells by IL-1alpha is not known, we investigated if collagenase-3 expression by IL-1alpha in osteoblasts is mediated by transcriptional or post-transcriptional mechanisms. Exposure of rat osteoblastic cultures (Ob cells) to IL-1alpha at concentrations higher than 0.5 nM increased the synthesis of collagenase-3 mRNA up to eightfold and the secretion of immunoreactive protein up to 21-fold. The effects of IL-1alpha on collagenase-3 were time- and dose-dependent. Although prostaglandins stimulate collagenase-3 expression, stimulation of collagenase-3 in Ob cells by IL-1alpha was not mediated through increased biosynthesis of prostaglandins. The half-life of collagenase-3 mRNA from control and IL-1alpha-treated Ob cells was similar suggesting that the stabilization of collagenase-3 mRNA did not contribute to the increase in collagenase-3. However, IL-1alpha stimulated the rate of transcription of the collagenase-3 gene by twofold to fourfold indicating regulation of collagenase-3 expression in Ob cells at the transcriptional level. Stimulation of collagenase-3 by IL-1alpha in osteoblasts may in part mediate the effects of IL-1alpha in bone metabolism.

Involvement of FGF-2 in the action of Emdogain on normal human osteoblastic activity

OBJECTIVE

The present study was designed to evaluate the pharmacological characteristics of Emdogain (EMD) on cell growth and cell activity in human osteoblasts.

METHODS

Cell proliferation as well as several gene and protein expressions were examined using reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) procedures in human osteoblastic cells (SaM-1) treated with EMD (30 microg ml(-1)).

RESULTS

Treatment of osteoblasts with EMD significantly stimulated cell proliferation and fibroblast growth factor (FGF)-2 expression but decreased alkaline phosphatase expression. In addition, increases in cyclooxygenase (COX)-2 expression and decreases in matrix metalloproteinases (MMP)-1 expression were observed in osteoblasts treated with EMD. The effects of EMD on FGF-2 and MMP-1 expressions were not observed in osteoblasts treated with NS-398, an inhibitor of COX-2. The decrease in MMP-1 mRNA by EMD was prevented by treatment with antisense oligodeoxynucleotide (AS-ODN) for FGF-2.

CONCLUSION

Emdogain showing both stimulation of cell proliferation and inhibition of cell differentiation has been shown to increase FGF-2 expression in the mediation of prostaglandin E2 and to decrease MMP-1 mRNA expression through the activation of FGF-2. FGF-2 may underlie in the action of EMD on osteoblasts during periodontal regeneration.

Basic fibroblast growth factor induces the expression of matrix metalloproteinase-3 in human periodontal ligament cells through the MEK2 mitogen-activated protein kinase pathway

Basic fibroblast growth factor (bFGF, FGF-2) is one of the potent mitogens for periodontal ligament (PDL) cells. However, the role of bFGF on the matrix metalloproteinase-3 (MMP-3) expression in PDL cells is unknown. In this study, the effect of bFGF on MMP-3 expression in PDL cells and the mechanism of this process were examined. Human PDL cells were exposed to bFGF at various concentrations (0.01-10 ng/ml) in monolayer cultures. bFGF increased [3H]thymidine incorporation and suppressed proteoglycan synthesis concentration-dependently. However, similar concentration ranges of bFGF increased the release of the cell-associated proteoglycans into the medium. Furthermore, bFGF increased MMP-3 mRNA levels concentration-dependently as examined by reverse transcription-polymerase chain reaction (RT-PCR). Induction of MMP-3 after the stimulation with bFGF was observed as early as 12 h with maximal at 24 h. Thereafter, the MMP-3 mRNA level gradually decreased until 72 h. Cycloheximide blocked the induction of MMP-3 by bFGF, indicating the requirement of de novo protein synthesis for this stimulation. Furthermore, MMP-3 expression induced by bFGF was abrogated by U0126, a specific inhibitor of MEK1/2 and ERK1/2 in mitogen-activated protein (MAP) kinase pathway, not by PD98059, a specific inhibitor of MEK1. In addition, bFGF up-regulated the phosphorylated ERK1/2 in 5 min with the maximal at 20 min as examined by Western blotting, and U0126 inhibited the ERK1/2 phosphorylation induced by bFGF. These findings suggest that bFGF induces MMP-3 expression in PDL cells through the activation of the MEK2 in MAP kinase pathway. bFGF stimulation on MMP-3 synthesis may be involved in the control of the cell-associated proteoglycans in PDL cells during periodontal regeneration and degradation.

IL-1beta, TNF-alpha, TGF-beta, and bFGF expression in bone biopsies before and after parathyroidectomy

BACKGROUND

There is growing evidence pointing to an involvement of cytokines and growth factors in renal osteodystrophy. In this study, the expression of interleukin-l beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (bFGF) in bone biopsies taken from uremic patients before and 1 year after parathyroidectomy (PTX) was evaluated. Biochemical features and histomorphometric outcome were also studied.

METHODS

Iliac bone biopsies were taken before and 1 year after PTX in nine uremic patients with severe hyperparathyroidism (HPT). Immunohistochemical techniques were used to identify the expression of IL-1 beta, TNF-alpha, TGF-beta, and bFGF in these bone samples.

RESULTS

At the time of the second bone biopsy, the mean serum total alkaline phosphatase activity was normal, whereas mean serum intact parathyroid hormone (iPTH) level was slightly above the upper limit of normal values. Histomorphometric analysis showed a decrease in resorption parameters and static bone formation parameters after PTX. Dynamically, mineral apposition rate (MAR) and mineralization surface (MS/BS) decreased significantly. There was a marked local expression of IL-1beta, TNF-alpha, TGF-beta, and bFGF in bone biopsies before PTX, particularly in fibrous tissue and resorption areas. One year after PTX, IL-1beta decreased from 23.6 +/- 7.5% to 9.9 +/- 3.1%, TNF-alpha from 4.5 +/- 1.5% to 0.7 +/- 0.8%, TGF-beta from 49.6 +/- 9.8% to 15.2 +/- 4.6%, and bFGF from 50.9 +/- 12.7% to 12.9 +/- 7.9% (P < 0.001). A significant correlation was documented between cytokines and growth factors expression in bone with iPTH levels before and after PTX (P < 0.05).

CONCLUSIONS

Based on these results, we suggest that IL-1beta, TNF-alpha, TGF-beta, and bFGF are involved in bone remodeling regulation, acting as local effectors, possibly under the control of PTH.

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.

Tissue inhibitor of metalloproteinases 1 and 2 directly stimulate the bone-resorbing activity of isolated mature osteoclasts

Tissue inhibitor metalloproteinases 1 (TIMP-1) and 2 have been reported to inhibit bone resorption. However, here, we report the direct action of both TIMP-1 and TIMP-2 on isolated rabbit mature osteoclasts to stimulate their bone-resorbing activity at significantly lower concentrations (approximately ng/ml) than those (approximately microg/ml) required for the inhibition of bone resorption. The cell population used in this study consisted of a mature osteoclast population with >95% purity. TIMP-1 (approximately 50 ng/ml) and TIMP-2 (approximately 8-10 ng/ml) increased the pit area excavated by the isolated mature osteoclasts. The stimulatory effects of TIMPs were abolished by simultaneous addition of anti-TIMP antibodies. At higher concentrations, the stimulation of bone resorption decreased reversely to the control level. The magnitude of the stimulatory effect of TIMP-2 was more than that of TIMP-1. Metalloproteinase inhibitors such as BE16627B and R94138 could not replace TIMPs with respect to the bone-resorbing activity, suggesting that the osteoclast-stimulating activity of TIMPs was independent of the inhibitory activity on matrix metalloproteinases (MMPs). TIMPs stimulated tyrosine phosphorylation of cellular proteins in the isolated mature osteoclasts. Both herbimycin A, an inhibitor of tyrosine kinases, and PD98059 and U0126, inhibitors of mitogen-activated protein kinase (MAPK), completely blocked the TIMP-induced stimulation of osteoclastic bone-resorbing activity. On the plasma membrane of osteoclasts, some TIMP-2-binding proteins were detected by a cross-linking experiment. These findings show that TIMPs directly stimulate the bone-resorbing activity of isolated mature osteoclasts at their physiological concentrations and that the stimulatory action of TIMPs is likely to be independent of their activities as inhibitors of MMPs.

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.

Basic fibroblast growth factor stimulates collagenase-3 promoter activity in osteoblasts through an activator protein-1-binding site

Basic fibroblast growth factor (bFGF) stimulates collagenase-3 synthesis in fetal rat osteoblast-enriched (Ob) cells. In this study we examined the mechanism of collagenase-3 regulation in Ob cells. bFGF at 0.6 nM or more increased the transcriptional rate of collagenase-3 by 3- to 7-fold. bFGF at 0.6 nM increased the activity of collagenase-3 promoter-luciferase reporter deletion constructs from -721 to -53 nucleotides transiently transfected into Ob cells by 3- to 5-fold. The minimal bFGF response was retained within the -53 to +28 sequence. Mutational analysis revealed that the bFGF effect was mediated through an activator protein-1 (AP-1)-binding site located at -48 to -42 nucleotides in the promoter. bFGF stimulated the binding of nuclear factors to the collagenase AP-1 site by 3- to 4-fold, as determined by electrophoretic mobility shift assays. Supershift analysis of nuclear extracts revealed that bFGF stimulates the occupancy of AP-1 site by c-Jun, JunB, JunD, c-Fos, FosB, and Fra2. In conclusion, bFGF increases collagenase-3 gene transcription, an effect mediated through an AP-1 site, due to the induction or activation of Jun and Fos family transcription factors. The stimulation of collagenase-3 synthesis by bFGF may be critical in mediating the actions of this growth factor in bone remodeling.

Triiodothyronine induces collagenase-3 and gelatinase B expression in murine osteoblasts

Triiodothyronine (T3) increases bone resorption, but its effects on matrix metalloprotease (MMP) expression in bone are unknown. We tested the effects of T3 on collagenase-3 and gelatinase A and B expression in MC3T3 osteoblastic cells. T3 at 1 nM to 1 microM for 24-72 h increased collagenase-3 and gelatinase B mRNA levels, but it did not increase gelatinase A transcripts. In addition, T3 increased immunoreactive collagenase and gelatinase activity. Cycloheximide prevented the stimulatory effect of T3 on collagenase-3 but not on gelatinase B transcripts. Indomethacin did not prevent the effect of T3 on either MMP. T3 did not alter the decay of collagenase-3 or gelatinase B mRNA in transcriptionally arrested MC3T3 cells, and it increased the rate of collagenase-3 and gelatinase B gene transcription. Although T3 enhanced the expression of the tissue inhibitor of metalloproteinase-1 in MC3T3 cells, it increased collagen degradation in cultured intact rat calvariae. In conclusion, T3 increases collagenase-3 and gelatinase B synthesis in osteoblasts by transcriptional mechanisms. This effect may contribute to the actions of T3 on bone matrix remodeling.

Parathyroid hormone regulates the expression of fibroblast growth factor-2 mRNA and fibroblast growth factor receptor mRNA in osteoblastic cells

We examined the effect of parathyroid hormone (PTH) on basic fibroblast growth factor-2 (FGF-2) and FGF receptor (FGFR) expression in osteoblastic MC3T3-E1 cells and in neonatal mouse calvariae. Treatment of MC3T3-E1 cells with PTH(1-34) (10-8M) or forskolin (FSK; 10-5M) transiently increased a 7 kb FGF-2 transcript with a peak at 2 h. The PTH increase in FGF-2 mRNA was maintained in the presence of cycloheximide. PTH also increased FGFR-1 mRNA at 2 h and transiently increased FGFR-2 mRNA at 1 h. FGFR-3 and FGFR-4 mRNA transcripts were not detected in MC3T3-E1 cells. In cells transiently transfected with an 1800-bp FGF-2 promoter-luciferase reporter, PTH and FSK increased luciferase activity at 2 h and 4 h. Immunohistochemistry showed that PTH and FSK increased FGF-2 protein labeling in the nuclei of MC3T3-E1 cells. PTH also increased FGF-2 mRNA, and FGFR-1 and FGFR-2 mRNA levels within 30 minutes in neonatal mouse calvarial organ cultures. We conclude that PTH and cAMP stimulate FGF-2 mRNA abundance in part through a transcriptional mechanism. PTH also regulated FGFR gene expression. We hypothesize that some effects of PTH on bone remodeling may be mediated by regulation of FGF-2 and FGFR expression in osteoblastic cells.

Skeletal bone morphogenetic proteins suppress the expression of collagenase-3 by rat osteoblasts

Bone morphogenetic proteins (BMPs) are secreted by skeletal cells, induce the differentiation of mesenchymal cells into cells of the osteoblastic lineage, and increase their differentiated function. BMPs also decrease collagenase-3 expression by the osteoblast. We tested the autocrine role of BMPs on collagenase-3 expression in osteoblast-enriched cells from fetal rat calvariae (Ob cells) by examining the effects of noggin, a specific inhibitor of BMP binding and function. Although collagenase-3 transcript expression declined in untreated Ob cells in culture over a 24-h period, BMP-2, -4, and -6 decreased collagenase-3 messenger RNA levels in cells treated for 2-24 h. The addition of noggin prevented the decrease of collagenase-3 transcripts in control cultures, opposed the inhibitory actions of BMP-2, and increased the levels of the protease in the culture medium. Noggin did not alter the decay of collagenase-3 messenger RNA in transcriptionally arrested cells, and it increased the levels of collagenase-3 heterogeneous nuclear RNA in Ob cells. In conclusion, noggin enhances the synthesis of collagenase-3 in osteoblasts, supporting the notion that BMPs act as autocrine suppressors of collagenase-3 in skeletal cells, an effect that may contribute to the maintenance of the bone matrix.

Recombinant human bone morphogenetic protein-2 stimulates osteoblast differentiation and suppresses matrix metalloproteinase-1 production in human bone cells isolated from mandibulae

Bone morphogenetic protein (BMP), a member of the transforming growth factor superfamily, is one of the most potent growth factors that stimulate osteoblast differentiation and bone formation. We investigated the effects of recombinant human BMP-2 (rhBMP-2) on osteoblast differentiation and matrix metalloproteinase-1 (MMP-1) production in human bone cells (HBC) isolated from mandibulae of 3 adult patients. rhBMP-2 at concentrations over 50 ng/ml significantly stimulated alkaline phosphatase activity and parathyroid hormone (PTH)-dependent 3', 5'-cyclic adenosine monophosphate accumulation, which are early markers of osteoblast differentiation, in HBCs. rhBMP-2 (500 ng/ml) also enhanced the level of PTH/PTH related-peptide receptor mRNA expression in HBCs. Although neither HBCs untreated nor treated with rhBMP-2 produced measurable amounts of osteocalcin, which is a marker of more mature osteoblasts, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] induced ostocalcin mRNA expression and its protein synthesis in these cells. rhBMP-2 inhibited 1,25(OH)2D3-induced osteocalcin synthesis in HBCs at both the mRNA and protein level. rhBMP-2 also significantly suppressed MMP-1 production and MMP-1 mRNA expression at concentrations over 500 ng/ml. These results suggest that rhBMP-2 exerts anabolic effects on human osteoblastic cells derived from mandibulae by stimulation of osteoblast differentiation and down-regulation of MMP-1 synthesis.

Collagenase-3 (MMP-13) expression in chondrosarcoma cells and its regulation by basic fibroblast growth factor

Human collagenase-3 (MMP-13) is a member of the matrix metalloproteinase family of enzymes that was originally identified in breast carcinomas and subsequently detected during fetal ossification and in arthritic processes. In this work, we have found that collagenase-3 is produced by HCS-2/8 human chondrosarcoma cells. An analysis of the ability of different cytokines and growth factors to induce the expression of collagenase-3 in these cells revealed that basic fibroblast growth factor (bFGF or FGF-2) strongly up-regulated the expression of this gene. By contrast, other factors, including interleukin-1beta and transforming growth factor-beta, previously found to induce collagenase-3 expression in other cell types, did not exhibit any effect on the expression of this gene in chondrosarcoma cells. Further analysis of the bFGF-induced expression of collagenase-3 in human chondrosarcoma cells revealed that its effect was time and dose dependent, but independent of the de novo synthesis of proteins. Western blot analysis revealed that the up-regulatory effect of bFGF on collagenase-3 was also reflected at the protein level as demonstrated by the increase of immunoreactive protein in the conditioned medium of HCS-2/8 cells treated with bFGF. Immunohistochemical analysis of the presence of collagenase-3 in a series of 8 benign and 16 malignant cartilage-forming neoplasms revealed that all analyzed malignant chondrosarcomas stained positively for collagenase-3, whereas only 2 of 8 benign lesions produced this protease. In addition, the finding that bFGF was detected in all analyzed chondrosarcomas, together with the above in vitro studies on HCS-2/8 cells, suggest that this growth factor may be an in vivo modulator of collagenase-3 expression in these malignant tumors. These results extend the pattern of tumor types with ability to produce this matrix metalloproteinase and suggest that collagenase-3 upregulation may contribute to the progression of human chondrosarcomas.

Dual regulation of stromelysin-3 by fibroblast growth factor-2 in murine osteoblasts

Osteoblasts express stromelysin-3, a matrix metalloproteinase associated with normal remodeling processes and with stromal fibroblasts surrounding many invasive carcinomas. Fibroblast growth factors (FGFs) play an important role in skeletal development, fracture repair, and osteoblast function. The osteoblastic cell line MC3T3 was used to study the regulation of stromelysin-3 by FGF-2. Acutely, FGF-2 decreased stromelysin-3 mRNA levels, whereas prolonged treatment caused an induction of stromelysin-3 mRNA. RNA stability studies and nuclear run-off assays indicated that acute treatment with FGF-2 decreased stromelysin-3 mRNA stability but did not alter gene transcription. However, the induction of stromelysin-3 after prolonged treatment with FGF-2 resulted from increased gene transcription, with no effect on RNA stability. The stimulatory effect was protein synthesis-dependent, whereas the inhibitory effect was not. This study demonstrates dual regulation of stromelysin-3 by FGF-2: acute destabilization of stromelysin-3 mRNA, followed by induction of gene transcription. This complex regulation may be important in the function of stromelysin-3 in bone and in remodeling processes, such as wound and fracture repair.

Non-coordinate control of bone formation displayed by growth factor combinations with IGF-I

Polypeptide growth factors (GFs) promote osteogenesis by enhancing the mitogenesis, migration, and matrix synthesis of osteoblasts. Most previous investigators have evaluated only the effects of single GFs on these parameters. Studies on single GFs might overlook large biological responses comparable with those documented in the cell cycle literature when GFs are used in combinations that interact synergistically. In this study, we screened for synergistic interactions between IGF-I and three additional GFs (PDGF-BB, TGF-beta 1, and bFGF) on the regulation of bone growth and differentiation. Fetal bovine osteoblasts were assessed for osteoblast mitogenesis, collagenous and non-collagenous protein synthesis, and alkaline phosphatase activity (ALP). Our results show synergistic interactions between IGF-I and the other GFs on osteoblast mitogenic activity and protein synthesis. In contrast to synergistic mitogenic and protein synthesis. In contrast to synergistic mitogenic and protein synthesis effects, IGF-I failed to increase ALP activity when combined with TGF-beta 1, PDGF-BB, and bFGF in bovine osteoblast-like cells.

Cell type-specific inhibition of keratinocyte collagenase-1 expression by basic fibroblast growth factor and keratinocyte growth factor. A common receptor pathway

Collagenase-1 is invariantly expressed by migrating basal keratinocytes in all forms of human skin wounds, and its expression is induced by contact with native type I collagen. However, net differences in enzyme production between acute and chronic wounds may be modulated by soluble factors present within the tissue environment. Basic fibroblast growth factor (bFGF, FGF-2) and keratinocyte growth factor (KGF, FGF-9), which are produced during wound healing, inhibited collagenase-1 expression by keratinocytes in a dose-dependent manner. However, KGF was >100-fold more effective than bFGF at inhibiting collagenase-1 expression, suggesting that this differential signaling is transduced via an FGF receptor that binds these ligands with different affinities. Reverse transcriptase-polymerase chain reaction analysis of human keratinocyte mRNA for fibroblast growth factor receptors (FGFRs) revealed expression of only FGFR-2 IIIb, the KGF-specific receptor, which also binds bFGF with low affinity, and FGFR-3 IIIb, which does not bind bFGF or KGF. FGFRs that bind bFGF with high affinity were not detected. Our results suggest that bFGF and KGF inhibit collagenase-1 expression through the KGF cell-surface receptor (FGFR-2 IIIb). Because bFGF induces collagenase-1 in most cell types, cell-specific expression of FGFR family members may dictate the regulation of matrix metalloproteinases in a tissue-specific manner.

Growth factor regulation of insulin-like growth factor binding protein-6 expression in osteoblasts

Previously we have shown that transforming growth factor beta (TGF beta) 1, basic fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF) BB inhibit the synthesis of insulin-like growth factor (IGF) II, but their effects on IGF binding protein (IGFBP)-6 in osteoblast cultures are not known. IGFBP-6 binds IGF II with high affinity and prevents IGF II-mediated effects, so that a possible mode of regulating the IGF II available to bone cells would be by changing the levels of IGFBP-6. To enhance our understanding of the actions of growth factors on the IGF II axis in bone, we tested the effects of TGF beta 1, basic FGF, PDGF BB, IGF I, and IGF II on the expression of IGFBP-6 in cultures of osteoblast-enriched cells from 22 day fetal rat calvariae (Ob cells). Treatment of Ob cells with TGF beta 1 caused a time- and dose-dependent decrease in IGFBP-6 mRNA levels, as determined by Northern blot analysis. The effect was maximal after 48 h and observed with TGF beta 1 concentrations of 0.04 nM and higher. TGF beta 1 also decreased IGFBP-6 polypeptide levels in the medium, as determined by Western immunoblot analysis. Cycloheximide at 3.6 microM decreased IGFBP-6 transcripts and prevented the effect of TGF beta 1. The decay of IGFBP-6 mRNA in transcriptionally arrested Ob cells was not modified by TGF beta 1. In addition, TGF beta 1 decreased the rates of IGFBP-6 transcription as determined by a nuclear run-on assay. In contrast, basic FGF, PDGF BB, IGF I, and IGF II did not change IGFBP-6 mRNA levels in Ob cells. In conclusion, TGF beta 1 inhibits IGFBP-6 expression in Ob cells by transcriptional mechanisms. Since IGFBP-6 binds IGF II and prevents its effects on bone cells, decreased synthesis of IGFBP-6 induced by TGF beta 1 could be a local feedback mechanism to increase the amount of IGF II available in the bone microenvironment.

Fibroblast growth factor receptor signaling activates the human interstitial collagenase promoter via the bipartite Ets-AP1 element

Interstitial collagenases participate in the remodeling of skeletal matrix and are regulated by fibroblast growth factor (FGF). A 0.2-kb fragment of the proximal human interstitial collagenase [matrix metalloproteinase (MMP1)] promoter conveys 4- to 8-fold induction of a luciferase reporter in response to FGF2 in MC3T3-E1 osteoblasts. By 5'-deletion, this response maps to nucleotides -100 to -50 relative to the transcription initiation site. The 63- bp MMP1 promoter fragment -123 to -61 confers this FGF2 response on the rous sarcoma virus minimal promoter. Intact Ets and AP1 cognates in this element are both required for responsiveness. The AP1 site supports basal and FGF-inducible promoter activity. The intact Ets cognate represses basal transcriptional activity in both heterologous and native promoter contexts and is also required for FGF activation. FGF2 up-regulates a DNA-binding activity that recognizes the MMP1 AP1 cognate and contains immunoreactive Fra1 and c-Jun. Both constitutive and FGF-inducible DNA-binding activities are present in MC3T3-E1 cells that recognize the MMP1 Ets cognate; prototypic Ets transcriptional activators are not present in these complexes. Inhibitors of protein kinase C, phosphatidyl inositol 3-OH kinase, and calmodulin-dependent protein kinase do not attenuate MMP1 promoter activation. FGF2 activates ERK1/ERK2 signaling in osteoblasts; however, 25 microM MAPK-ERK kinase (MEK) inhibitor PD98059 (inhibits by > 85% the phosphorylation of ERK1/ERK2) has no effect on MMP1 promoter activation by FGF2. Ligand-activated and constitutively active FGF receptors initiate MMP1 induction. Dominant negative Ras abrogates MMP1 induction by constitutively active FGFR2-ROS, but dominant negative Rho and Rac do not inhibit induction. The mitogen-activated protein kinase (MAPK) phosphatase MKP2 [inactivates extracellular regulated kinase (ERK) = Jun N-terminal kinase (JNK) > p38 MAPK] completely abrogates MMP1 activation, whereas PAC1 (inactivates ERK = p38 > JNK) attenuates but does not completely prevent induction. Thus, a Ras- and MKP2-regulated MAPK pathway, independent of ERK1/ERK2 MAPK activity, mediates FGF2 transcriptional activation of MMP1 in MC3T3-E1 osteoblasts, converging upon the bipartite Ets-AP1 element. The DNA-protein interactions and signal cascades mediating FGF induction of the MMP1 promoter are distinct from two other recently described FGF response elements: the MMP1 promoter (-123 to -61) represents a third FGF-activated transcriptional unit.

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

Interleukin-6 (IL-6), a cytokine produced by skeletal cells, increases bone resorption, but its effects on collagenase expression are unknown. We tested the effects of IL-6 and its soluble receptor on collagenase 3 expression in osteoblast-enriched cells from fetal rat calvariae (Ob cells). IL-6 caused a small increase in collagenase mRNA levels, but in the presence of IL-6-soluble receptor (IL-6sR), IL-6 caused a marked increase in collagenase transcripts after 2-24 h. In addition, IL-6sR increased collagenase mRNA when tested alone. IL-6 and IL-6sR increased immunoreactive collagenase levels. Cycloheximide and indomethacin did not prevent the effect of IL-6 and IL-6sR on collagenase mRNA levels. IL-6 and IL-6sR did not alter the decay of collagenase mRNA in transcriptionally arrested Ob cells and increased the levels of collagenase heterogeneous nuclear RNA and the rate of collagenase gene transcription in Ob cells. IL-6 and IL-6sR increased collagenase 3 mRNA in MC3T3 cells but only modestly in skin fibroblasts. IL-6 and IL-6sR enhanced the expression of tissue inhibitor of metalloproteinases 1. In conclusion, IL-6, in the presence of IL-6sR, increases collagenase 3 synthesis in osteoblasts by transcriptional mechanisms. This effect may contribute to the action of IL-6 on bone matrix degradation and bone resorption.

Matrix metalloproteinase activities in avian tibial dyschondroplasia

Tibial dyschondroplasia (TD) in poultry is a disorder of growth plate cartilage that fails to resorb and consequently prevents bone formation. Matrix metalloproteinases (MMP) contribute to the process of resorption through the degradation of extracellular matrices and facilitating vascularization, growth plate remodeling, and maturation. In order to understand the cause of the failure of cartilage degradation in TD, the gelatinase and collagenase activities, and the levels of collagen and glycosaminoglycans of conditioned media derived from cartilage-explant cultures of normal and TD growth plates were measured. Substrate zymography exhibited two prominent gelatinolytic and collagenolytic bands corresponding to MW 63, 59, and a broad but fuzzy band of activity between 100 and 200 kDa. On treatment with 4-aminophenylmercuric acetate, a compound that converts proenzyme forms of MMP, the 63 kDa MW gelatinolytic band migrated as a approximately 60 kDa band and contributed to the broadening of the 59 kDa band. The TD-growth plate-conditioned media had significantly lower collagenolytic-gelatinolytic activities. The sulfated glycosaminoglycans, but not the collagen contents of the conditioned media from TD-explant cultures, were also reduced significantly. It is likely that the decreased matrix metalloproteinase activities of growth plate chondrocyte may contribute to a reduced turnover of extracellular matrices (ECM), leading to the retention of cartilage and its lack of vascularity in TD-affected growth plates.

Regulation of collagenase-3 by bone morphogenetic protein-2 in bone cell cultures

Bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor superfamily of peptides, induces ectopic bone formation in vivo. The actions of BMP-2 on osteoblastic cells include stimulation of collagen synthesis, but the role of BMP-2 on collagen degradation is not known. We examined whether BMP-2 affects the expression of collagenase-3, an enzyme that degrades type I collagen at neutral pH, and that of tissue inhibitors of matrix metalloproteinases (TIMPs) in primary osteoblast-enriched cells from 22-day-old fetal rat calvariae. BMP-2 suppressed collagenase messenger RNA (mRNA) and immunoreactive protein levels. BMP-2 did not affect collagenase mRNA stability, but it reduced collagenase heterogeneous nuclear RNA levels and decreased the rate of transcription of the collagenase gene. BMP-2 also stimulated TIMP 1 and TIMP 3 mRNA levels, but failed to alter TIMP 2 expression. In conclusion, our studies indicate that BMP-2 suppresses collagenase-3 gene transcription and stimulates TIMP 1 and TIMP 3 expression in osteoblasts. The regulation of collagenase and TIMPs by BMP-2 in osteoblasts may play a role in osteoinduction.

Transforming growth factor beta1 inhibits collagenase 3 expression by transcriptional and post-transcriptional mechanisms in osteoblast cultures

Transforming growth factor (TGF) beta1 is an autocrine regulator of bone cell function. We demonstrated that TGF beta1 enhances bone collagen synthesis, but its effects on collagen degradation are not well characterized. We tested the effects of TGF beta1 on rat collagenase 3 expression in cultures of osteoblast-enriched cells from fetal rat calvariae (Ob cells). Treatment with TGF beta1 at 0.4 nM decreased steady state collagenase mRNA levels after 2 to 24 h. This dose-dependent effect was observed at TGF beta1 concentrations of 4 pM to 1.2 nM, and was accompanied by decreased levels of immunoreactive procollagenase. The protein synthesis inhibitor cycloheximide increased collagenase transcripts, but did not prevent the effect of TGF beta1 on collagenase mRNA levels. TGF beta1 accelerated the decay of collagenase mRNA in transcriptionally arrested Ob cells. In addition, TGF beta1 decreased the levels of collagenase heterogeneous nuclear RNA and the rate of collagenase gene transcription in Ob cells. TGF beta1 enhanced the expression of tissue inhibitors of metalloproteinases (TIMP) 1 and 3 and caused a modest decrease of TIMP 2 mRNA levels. In conclusion, TGF beta1 decreases interstitial collagenase transcripts and protease levels in Ob cells by transcriptional and post-transcriptional mechanisms, and this effect may contribute to its actions on bone matrix.

Acidic fibroblast growth factor inhibits osteoblast differentiation in vitro: altered expression of collagenase, cell growth-related, and mineralization-associated genes

Fibroblast growth factors (FGF) are osteoblast mitogens, but their effects on bone formation are not clearly understood. Most in vitro studies examining the effects of FGFs on osteoblasts have been performed only during the initial proliferative stage of osteoblast culture. In these studies, we examined the consequential effect of acidic FGF in cultures of rat fetal diploid osteoblasts that undergo a developmental differentiation program producing a mineralized bone-like matrix. During the initial growth period (days 1-10), addition of acidic FGF (100 micrograms/ml) to actively proliferating cells increased (P < 0.05) 3H-thymidine uptake (2,515 +/- 137, mean +/- SEM vs. 5,884 +/- 818 cpm/10(4) cells). During the second stage of maturation (days 10-15), osteoblasts form multilayered nodules of cells and accumulate matrix, followed by mineralization (stage 3, days 16-29). Addition of acidic FGF to the osteoblast cultures from days 7 to 15 completely blocked nodule formation. Furthermore, addition of acidic FGF after nodule formation (days 14-29) inhibited matrix mineralization, which was associated with a marked increase in collagenase gene expression, and resulted in a progressive change in the morphology of the nodules, with only a few remnants of nonmineralized nodules present by day 29. Histochemical and biochemical analyses revealed a decrease in alkaline phosphatase and mineral content, confirming the acidic FGF-induced inhibition of nodule and matrix formation. To identify mechanisms contributing to these changes, we examined expression of cell growth and bone phenotypic markers. Addition of acidic FGF during the proliferative phase (days 7-8) enhanced histone H4, osteopontin, type I collagen, and TGF-beta mRNA levels, which are coupled to proliferating osteoblasts, and blocked the normal developmental increase in alkaline phosphatase and osteocalcin gene expression and calcium accumulation. Addition of acidic FGF to the cultures during matrix maturation (days 14-15) reactivated H4, osteopontin, type I collagen, and TGF-beta gene expression, and decreased alkaline phosphatase and osteocalcin gene expression. In an in vivo experiment, rats were treated with up to 60 micrograms/kg/day acidic FGF intravenously for 30 days. Proliferation of osteoblasts and deposition of bone occurred in the marrow space of the diaphysis of the femur in a dose-related fashion. The metaphyseal areas were unaffected by treatment. In conclusion, our data suggest that acidic FGF is a potent mitogen for early stage osteoblasts which leads to modifications in the formation of the extracellular matrix; increases in TGF-beta and collagenase are functionally implicated in abrogating competency for nodule formation. Persistence of proliferation prevented expression of alkaline phosphatase and osteocalcin, also contributing to the block in the progression of the osteoblast developmental sequence.

Expression of mRNA for matrix metalloproteinases and tissue inhibitors of metalloproteinases in periodontitis-affected human gingival tissue

It is known that the host responds to an increased concentration of collagenase [or matrix metalloproteinase (MMP)-1] by preferentially expressing mRNA for the tissue inhibitor of metalloproteinase-1 (TIMP-1) in order to overcome tissue destruction due to periodontitis. To further elucidate the relation between MMPs and TIMPs in periodontitis-affected tissues, the expression of mRNA for MMP-1, -3 and -8, and TIMP-1 and -2, in 10 gingival samples from patients and five from healthy individuals was assessed by reverse transcription-polymerase chain reaction. The diseased group showed significantly higher levels of MMP-1, -3, -8 and TIMP-1 mRNA relative to beta-actin than the control group (mean +/- SE: diseased vs healthy (%): 0.26 +/- 0.05 vs 0.018 +/- 0.0040 for MMP-1; 0.09 +/- 0.16 vs 0.063 +/- 0.016 for MMP-3; 0.068 +/- 0.017 vs 0.006 +/- 0.0010 for MMP-8; 12.66 +/- 2.90 vs 2.71 +/- 0.54 for TIMP-1; p < 0.01). TIMP-2 did not significantly differ between the two groups (1.79 +/- 0.33 vs 1.42 +/- 0.53; p > 0.05). The preferential increase in the level of MMP-3 mRNA relative to that of MMP-1 and -8 in inflamed gingiva would be relevant to tissue destruction because MMP-3 is a broad-spectrum MMP and a pivotal activator of latent MMP-1 and -8. Therefore, the overall increase in MMP-1, -3 and -8 mRNA in periodontitis-affected gingiva might account for a concerted action of MMPs during connective tissue destruction in periodontitis.