Inhibition of stimulated bone resorption in vitro by TIMP-1 and TIMP-2

Tissue inhibitor of metalloproteinase 1 suppresses growth and differentiation of osteoblasts and differentiation of osteoclasts by targeting the AKT pathway

Tissue inhibitor of metalloproteinase 1 (TIMP1) has various biological activities including the regulation of cell growth and differentiation. However, its role in bone homeostasis and remodeling remains poorly understood. In this study, we investigate the effects of TIMP1 on osteoblast and osteoclast activity at both cellular and molecular level using siRNA-mediated knockdown technique. Our results show that knockdown of TIMP1 stimulates proliferation and survival, but decreases apoptosis in osteoblastic MC3T3-E1 cells, suggesting that TIMP1 inhibits cell growth. TIMP1 also dampens differentiation of committed osteoblasts, as well as osteoblastogenesis of bone marrow-derived mesenchymal stem cells (BMSCs). We further show that the modulation of TIMP1 on osteoblast activity is independent of its MMP inhibition. Importantly, we uncover that TIMP1 suppresses osteoblast growth and differentiation by targeting the AKT pathway, and this is associated with TIMP1-mediated induction of PTEN via its binding to the cell surface receptor CD44. Therefore, our results highlight a novel TIMP1/CD44/PTEN/AKT signaling nexus that functions as a suppressor of osteoblast activity. Moreover, we show that TIMP1 also inhibits osteoclast differentiation in osteoclast precursor RAW 264.7 cells by targeting the AKT. In conclusion, our results demonstrate that TIMP1 can act as a suppressor of growth and differentiation of osteoblasts and differentiation of osteoclasts through the negative regulation of the AKT pathway. We propose that TIMP1 may serve as a potential target for low bone mass-related skeletal diseases, such as osteoporosis.

Tissue inhibitor of metalloproteinase gene from pearl oyster Pinctada martensii participates in nacre formation

Tissue inhibitors of metalloproteinases (TIMPs) are nature inhibitors of matrix metalloproteinases and play a vital role in the regulation of extracellular matrix turnover, tissue remodeling and bone formation. In this study, the molecular characterization of TIMP and its potential function in nacre formation was described in pearl oyster Pinctada martensii. The cDNA of TIMP gene in P. martensii (Pm-TIMP) was 901 bp long, containing a 5' untranslated region (UTR) of 51 bp, a 3' UTR of 169 bp, and an open reading fragment (ORF) of 681 bp encoding 226 amino acids with an estimated molecular mass of 23.37 kDa and a theoretical isoelectric point of 5.42; The predicted amino acid sequence had a signal peptide, 13 cysteine residues, a N-terminal domain and a C-terminal domain, similar to that from other species. Amino acid multiple alignment showed Pm-TIMP had the highest (41%) identity to that from Crassostrea gigas. Tissue expression analysis indicated Pm-TIMP was highly expressed in nacre formation related-tissues, including mantle and pearl sac. After decreasing Pm-TIMP gene expression by RNA interference (RNAi) technology in the mantle pallium, the inner nacreous layer of the shells showed a disordered growth. These results indicated that the obtained Pm-TIMP in this study participated in nacre formation.

Sc65 is a novel endoplasmic reticulum protein that regulates bone mass homeostasis

Members of the Leprecan family of proteins include enzymes, prolyl 3-hydroxylase 1 (P3h1), P3h2, and P3h3, and nonenzymatic proteins, Crtap and Sc65. Mutations in CRTAP and LEPRE1 (encoding P3H1) have been associated with human disease such as recessive osteogenesis imperfecta; however, the function of Sc65, which is closely related and highly homologous to Crtap, is unknown. Sc65 has been described as a synaptonemal complex protein, a nucleolar protein, and a cytoplasmic adapter protein. In light of its high sequence similarity with Crtap, an endoplasmic reticulum (ER)-associated protein, and the importance of post-translational modifications such as collagen prolyl 3-hydroxylation in bone metabolism, we hypothesized that Sc65 was an ER-resident protein that would have an important role in bone homeostasis. In this study, we demonstrate that Sc65 is a previously unrecognized ER protein and that it does not localize in the nucleus of somatic cells. Moreover, Sc65 is expressed and functional during skeletal development because loss of Sc65 results in a progressive osteopenia that affects both trabecular and cortical bone. Bone loss is the result of increased bone resorption mediated by a non-cell-autonomous effect on osteoclasts. Therefore, Sc65, like its related family member Crtap, is an important modulator of bone homeostasis, acting as a negative regulator of osteoclastogenesis.

Preclinical evaluation of zoledronate using an in vitro mimetic cellular model for breast cancer metastatic bone disease

BACKGROUND

The interactions between metastatic breast cancer cells and host cells of osteoclastic lineage in bone microenvironment are essential for osteolysis. In vitro studies to evaluate pharmacological agents are mainly limited to their direct effects on cell lines. To mimic the communication between breast cancer cells and human osteoclasts, a simple and reproducible cellular model was established to evaluate the effects of zoledronate (zoledronic acid, ZOL), a bisphosphonate which exerts antiresorptive properties.

METHODS

Human precursor osteoclasts were cultured on bone-like surfaces in the presence of stimuli (sRANKL, M-CSF) to ensure their activation. Furthermore, immature as well as activated osteoclasts were co-cultured with MDA-MB-231 breast cancer cells. TRAP5b and type I collagen N-terminal telopeptide (NTx) were used as markers. Osteoclasts' adhesion to bone surface and subsequent bone breakdown were evaluated by studying the expression of cell surface receptors and certain functional matrix macromolecules in the presence of ZOL.

RESULTS

ZOL significantly suppresses the precursor osteoclast maturation, even when the activation stimuli (sRANKL and M-SCF) are present. Moreover, it significantly decreases bone osteolysis and activity of MMPs as well as precursor osteoclast maturation by breast cancer cells. Additionally, ZOL inhibits the osteolytic activity of mature osteoclasts and the expression of integrin β3, matrix metalloproteinases and cathepsin K, all implicated in adhesion and bone resorption.

CONCLUSIONS

ZOL exhibits a beneficial inhibitory effect by restricting activation of osteoclasts, bone particle decomposition and the MMP-related breast cancer osteolysis.

GENERAL SIGNIFICANCE

The proposed cellular model can be reliably used for enhancing preclinical evaluation of pharmacological agents in metastatic bone disease.

An immunolocalization study of tissue inhibitors of metalloproteinase-1 of bone graft healing on parietal bone

This immunolocalization study was performed to investigate the temporal and spatial expression of tissue inhibitors of metalloproteinase (TIMP) 1 within endochondral and intramembranous bone grafts during the early stages of healing, in the hope of gaining a better understanding of the mechanisms of bone graft healing, which could influence the choice of bone graft used. Twenty-seven adult New Zealand White rabbits were used as the experimental model. Autogenous bone grafts taken from the cranial bone (intramembranous in origin) and the femur (endochondral in origin) were grafted into skull defects created on either side of the parietal suture. Rabbits were killed on days 1 to 9 postgrafting, and the bone graft alone was harvested for immunolocalization of TIMP-1. In endochondral bone grafts, TIMP-1 was expressed on days 1 to 3, followed by a period of absence until days 8 and 9. Intramembranous bone grafts did not express TIMP-1 until days 6 to 9. The timing and location of TIMP-1 expression coincided with osteogenesis, which indicates a role for TIMP-1 in preserving newly formed bone during the initial stages of graft healing. The differential temporal expression of TIMP-1 in endochondral and intramembranous bone grafts suggests that bone graft type plays an important role in influencing the healing process mediated by the host tissues. The earlier expression of TIMP-1 in endochondral bone grafts could be the reason for delayed vascularization of defects containing these grafts, whereas the delayed expression of TIMP-1 in intramembranous bone grafts could allow earlier vascularization of the intramembranous bone grafts.

In vitro effects of non-steroidal anti-inflammatory drugs on cytokine, prostanoid and matrix metalloproteinase production by interface membranes from loose hip or knee endoprostheses

OBJECTIVE

To study the effects of the non-steroidal anti-inflammatory drugs (NSAIDs) aceclofenac, piroxicam, tenoxicam and indomethacin on cytokine, matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and prostaglandin E2 (PGE2) production, by interface membranes (IFT), obtained at revision surgery for aseptic loosening of total joint arthroplasty. Involvement of these soluble factors is well documented and probably, a pharmaceutically induced inhibition of them might retard loosening.

METHODS

IFTs from 10 patients with a loose hip or knee endoprosthesis were collected. The possibility of septic loosening was thoroughly excluded by histopathologic and microbiologic evaluation. IFTs were cultured in the absence or presence of the tested drugs and the levels of the soluble mediators were determined, using electrophoretic and enzyme-linked immunosorbent assay techniques. Paracetamol was used as neutral drug.

RESULTS

All NSAIDs exhibited a pronounced inhibitory effect upon the production of interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha). This specific effect on IL-6 is reported in the literature for the first time. The majority of NSAIDs also induced the production of IL-1beta in an adequate portion of samples. These drugs did not have a clear effect on MMP synthesis, but they had a stimulatory tendency on TIMP-1 production. Paracetamol, significantly decreased the synthesis of TNF-alpha and that of the gelatinases.

CONCLUSION

Our in vitro results are encouraging, since it appears that the action of NSAIDs, globally considered, may be beneficial upon the loosening process. The inhibitory effect of paracetamol upon TNF-alpha and gelatinases is intriguing. Our data, if supported by similar observations, probably justify performance of long-term clinical trials.

Effect of recombinant human tissue inhibitor of matrix metalloproteinase-1 in rabbit mandibular distraction osteogenesis: A histological and immunohistochemical study

BACKGROUND

Bone matrix metalloproteinases are capable of degrading bone matrix during the remodelling, and their degradation activities can be down regulated by the tissue inhibitors of matrix metalloproteinases. This study evaluated the influence of exogenous tissue inhibitor of matrix metalloproteinase-1 on the expression of matrix metalloproteinases and endogenous tissue inhibitor of matrix metalloproteinases in mandibular distraction osteogenesis.

MATERIAL AND METHODS

Fifteen New Zealand white rabbits were assigned to three groups: a negative control; a sham control group implanted with a collagen sheet; and an experimental group implanted with recombinant human tissue inhibitor of matrix metalloproteinase-1 impregnated in a collagen sheet. Rabbits were sacrificed at 6 weeks, 12 weeks and 24 weeks of consolidation.

RESULTS

Major expression of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases was observed at the early stage of consolidation, only positive signals of tissue inhibitors of matrix metalloproteinases were observed at 24 weeks. The addition of recombinant human tissue inhibitor of matrix metalloproteinases-1 did not affect bone maturation and remodelling.

CONCLUSIONS

An equilibrium of bone formation and resorption was reached at 24 weeks of consolidation in the rabbit mandible. No obvious influence of recombinant human tissue inhibitor of matrix metalloproteinase-1 on bone remodelling of mandibular distraction osteogenesis was noted.

In vivo inhibition of osteoblastic metalloproteinases leads to increased trabecular bone mass

Mice specifically overexpressing TIMP-1 in osteoblasts have been generated to investigate the role of MMPs in bone in vivo. These mice displayed increased trabecular bone volume and decreased bone turnover. This model provides evidence of the role played by the MMPs in bone remodeling and balance.

INTRODUCTION

Although it has been suggested that the matrix metalloproteinases (MMPs) may play a role in initiating the bone resorption process in vitro, there is no evidence that they play any role in in vivo bone maintenance.

MATERIALS AND METHODS

We used an artificial promoter specifically driving cells of the osteoblastic lineage to overexpress the tissue inhibitor of MMPs (TIMP-1) cDNA in mice. Densitometric analysis, using DXA and pQCT, and static and dynamic histomorphometry were used to evaluate the bone phenotype both in male and female transgenic mice. We evaluated osteoblastic differentiation using a primary osteoblast culture and osteoclast activity using an ex vivo organ culture.

RESULTS AND CONCLUSION

We showed that at 1 and 2.5 months of age, only the female mice exhibited a bone phenotype. These mice displayed specific increases in the BMD and bone volume of trabecular bone. This increase was accompanied by decreased trabecular separation, suggesting a decrease in bone resorption. Using an ex vivo resorption assay, we demonstrated that parathyroid hormone (PTH)-stimulated bone resorption was reduced in these mice. Evaluation of the bone histomorphometric dynamic parameters showed that the mineralizing surfaces and bone formation rate were both reduced. There was no change in the mineralization lag time or number of osteocyte lacunae. Using primary osteoblast culture and molecular analysis, we showed that the differentiation and function of osteoblasts from transgenic mice were normal, but that the ex vivo formation of mineralized nodules was delayed. This model is the first to show that in vivo MMPs play a role in bone remodeling and bone balance. Moreover, our data suggest that MMP activity could be involved in the hormonal regulation of bone resorption by osteoblasts.

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.

Role of RANKL-induced osteoclast formation and MMP-dependent matrix degradation in bone destruction by breast cancer metastasis

Bone metastasis of breast cancer induces severe osteolysis with increased bone resorption. Osteoclast differentiation regulated by the receptor activator of NF-kappaB ligand (RANKL) in osteoblasts and matrix degradation induced by matrix metalloproteinases (MMPs) are thought to be involved in the process of bone resorption. When nude mice were inoculated with human breast cancer cells, MDA-MB-231(MDA-231), numerous osteoclasts resorbed bone and the degradation of the bone matrix markedly progressed in the femur and tibia with metastasis of the MDA-231 tumour. The expression of RANKL, MMP-13 and membrane-type 1-MMP mRNA was markedly elevated in bone with metastasis. When MDA-231 cells were cocultured with mouse calvaria, MDA-231 markedly induced bone resorption measured by calcium release from the calvaria, and the expression of RANKL, MMP-2 and MMP-13 was elevated in the calvaria after the coculture. The separation of MDA-231 from the calvaria using filter insert showed decreased bone resorption, suggesting that cell-to-cell interaction is essential for cancer-induced bone resorption. Adding MDA-231 cells to bone marrow cultures markedly induced osteoclast formation, and the expression of RANKL in osteoblasts was enhanced by contact with the cell surface of MDA-231 cells. These results indicate that RANKL-induced osteoclast formation and MMP-dependent matrix degradation are associated with osteolysis because of bone metastasis of breast cancer.

Regulation of tissue inhibitors of metalloproteinase-1 gene expression by cytokines in human gingival fibroblasts

Tissue inhibitors of metalloproteinase (TIMP) are important participants in various physiological processes that involve tissues remodeling. They help maintain a delicate balance between physiological degradation and synthesis of the extracellular matrix. A better understanding of TIMP activity will be helpful in understanding the etiology of periapical lesions and their means of treatment. The fibroblast is a prominent cellular component of the periapical tissues. The potential implications of cytokine-mediated tissue destruction still remain to be elucidated. The purpose of this study was to determine the effects of interleukin (IL)-1alpha and transforming growth factor (TGF)-beta on the expressing of TIMP-1 by primary gingival fibroblast cultures. After exposure to cytokines for 8 h, total RNA in gingival fibroblasts was isolated and evaluated by reverse-transcriptase polymerase chain reaction. Densitometric analysis of the TIMP-1 mRNA gene expression, after normalization by beta-actin, demonstrated that exposure to IL-1alpha resulted in a decreased level of TIMP-1 mRNA compared with the control groups. However, the TIMP-1 mRNA was up-regulated by TGF-beta. In addition, when the cells were cultured in combination with TGF-beta (1 ng/ml) and IL-1alpha for 8 h, the level of TIMP-1 mRNA was dramatically reduced. These results demonstrated that in human periapical tissue cytokines differentially and specifically regulate expression of TIMP-1 mRNA. An understanding of the actions of cytokines on gingival fibroblasts may result in new therapies to augment current treatment of periapical lesions.

Osteoprotegerin differentially regulates protease expression in osteoclast cultures

Cysteine proteases and matrix metalloproteinases (MMPs) are important factors in the degradation of organic matrix components of bone. Osteoprotegerin (OPG) is an osteoblast-secreted decoy receptor that inhibits osteoclast differentiation and activation. This study investigated the direct effects of human OPG on cathepsin K, MMP-9, MMP-2, and tissue inhibitors of metalloproteinases (TIMP1 and TIMP2) expressed by purified rabbit osteoclasts. The expression of two osteoclast markers, namely tartrate-resistant acid phosphatase (TRAP) and cathepsin K, was inhibited by 100 ng/mL hOPG, whereas MMP-9 expression was enhanced. Gelatinase activities were measured using a zymographic assay, and hOPG was shown to enhance both pro-MMP-9 and MMP-2 activities. Concomitantly, TIMP1 expression was greatly stimulated by hOPG, whereas TIMP2 mRNA levels were not modulated. Overall, these results show that hOPG regulates the proteases produced by purified osteoclasts differentially, producing a marked inhibitory effect on the expression of cathepsin K, the main enzyme involved in bone resorption.

Modulation of the host response in periodontal therapy

This paper was prepared by the Research, Science, and Therapy Committee of the American Academy of Periodontology to provide the dental profession an overview of current and potential methods to modulate the host response in the treatment of periodontal diseases. Specifically, it discusses components of periodontal disease pathogenesis (i.e., immune and inflammatory responses, excessive production of matrix metalloproteinases and arachidonic acid metabolites, and regulation of bone metabolism) and their modulation.

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.

Immunolocalization of matrix metalloproteinases and their inhibitors in clinical specimens of bone metastasis from breast carcinoma

Matrix metalloproteinases (MMPs) are essential in several stages of the metastatic process, and in normal bone development and remodeling. We explored whether the interaction between tumor cells and bone leads to changes in MMP and tissue inhibitor of MMP (TIMP) expression thus affecting osteolysis in metastatic bone disease. Using immunohistochemistry we have investigated the MMP/TIMP expression in tumor cells, fibroblasts, osteoblasts and osteoclasts. Thirty one specimens of bone metastasis from breast carcinoma were stained for MMP-1, -2, -9, MT1-MMP and TIMP-1, and -2 and compared with staining in normal breast tissue, primary breast carcinoma and normal bone. Specimens came from patients in three clinical scenarios: from open biopsies without or with pathological fracture, or bone marrow biopsies containing tumor from patients with pancytopenia but without clinical evidence of osteolysis. By bone histomorphometry the latter group showed a heavy tumor load not different from the open biopsy groups but displayed little active bone resorption and low numbers of osteoclasts. Cell type-specific MMP/TIMP expression was observed and the staining patterns were comparable between the three groups of patients. Though no major differences in the MMP/TIMP staining of tumor cells and fibroblasts were observed between bone metastasis and primary tumor, we showed that tumor cells do express MMPs capable of degrading bone matrix collagen. The number and activity of osteoclasts and osteoblasts was increased dramatically in bone metastases, their MMP/TIMP profiles, however, were not different from normal bone, suggesting that the mechanism of bone degradation by osteoclasts is not different from normal bone remodelling.

Tissue inhibitor of metalloproteinase-3 is a basement membrane-associated protein that is significantly decreased in human colorectal cancer

PURPOSE

The balance between local levels of matrix metalloproteinases and tissue inhibitor of metalloproteinases is believed to play a key role in tumor invasion and metastases. Because tissue inhibitor of metalloproteinase-3 suppresses tumorigenicity and tumor invasion in vitro, the aim of this study was to determine its expression in human colorectal cancer.

METHODS

Thirty-nine human colorectal cancer specimens, three adenomas, and matched normal adjacent mucosa from 39 colorectal cancer patients were analyzed. Tissue inhibitor of metalloproteinase-3 ribonucleic acid and protein expression were analyzed by Northern blot hybridization and Western blot analysis, respectively. The cellular localizations of tissue inhibitor of metalloproteinase-3 ribonucleic acid and protein were determined by in situ hybridization and immunolocalization.

RESULTS

Tissue inhibitor of metalloproteinase-3 ribonucleic acid expression was increased in colorectal cancer compared with paired normal mucosa. In contrast, tissue inhibitor of metalloproteinase-3 protein level was higher in normal mucosa than in the corresponding colorectal cancer. In addition, tissue inhibitor of metalloproteinase-3 protein levels progressively decreased with advancing colorectal cancer stages. Tissue inhibitor of metalloproteinase-3 protein tumor to normal mucosa ratio was 0.74 +/- 0.12, 0.51 +/- 0.18, 0.48 +/- 0.12, and 0.45 +/- 0.2 for Dukes A (n = 8), B (n = 9), C (n = 9), and D (n = 13) stages, respectively. Both tissue inhibitor of metalloproteinase-3 messenger ribonucleic acid and protein were located predominantly within spindle-shaped and round stromal cells. Furthermore, in colonic epithelium, tissue inhibitor of metalloproteinase-3 and type IV collagen protein were similarly concentrated in the basal region.

CONCLUSIONS

These data provide the first detailed description of the cellular expression of tissue inhibitor of metalloproteinase-3 in colorectal cancer and identify it as a basement membrane-associated protein. This is an important observation, because the presence of tissue inhibitor of metalloproteinase-3 protein near the basement membrane supports its role in preventing proteolytic degradation, angiogenesis, and apoptosis.

Cyclosporin A affects extracellular matrix synthesis and degradation by mouse MC3T3-E1 osteoblasts in vitro

BACKGROUND

Immunosuppressant therapy is thought to be a major contributor to post-transplant bone disease. Histological data and serum parameters suggest that Cyclosporin A (CsA) treatment causes osteopenia as a result of an altered bone turnover, but the pathogenic mechanisms of this process remain unclear. We investigate if CsA affects cell turnover and extracellular matrix (ECM) synthesis and degradation in MC3T3-E1 osteoblasts, as a surrogate model for in vivo events.

METHODS

Cells were exposed to increasing doses of CsA (0, 0.5, 1 and 5 microg/ml). Proliferation was evaluated by bromodeoxyuridine (BrdU) incorporation, viability by Trypan Blue exclusion and apoptosis by ELISA. Type I collagen was measured by ELISA and reverse transcription-polymerase chain reaction (RT-PCR), matrix metalloproteinases (MMP) by zymography and RT-PCR, and tissue inhibitors of MMP (TIMP) by reverse zymography.

RESULTS

CsA exposure for 48 h decreased osteoblast number in a dose-dependent manner in the absence of apoptosis or cytotoxicity. CsA at a dose of 5 microg/ml for 72 h caused decreased collagen type I mRNA expression and protein accumulation. While MMP-2 remained unaffected, MMP-9 activity increased. TIMP-1 activity was unaffected, while a dose-dependent increase of TIMP-2 was observed.

CONCLUSIONS

These data suggest that CsA alters ECM synthesis and degradation in MC3T3-E1 osteoblasts by decreasing type I collagen production and increasing MMP-9 activity. The combination of increased MMP-9 with unchanged TIMP-1 activity could reduce the osteoid matrix available for mineralization. In addition, decreased proliferation could further reduce the number of cells synthesizing new osteoid matrix and thus contribute to the process of bone loss.

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.

Further evidence for secretion of matrix metalloproteinase-1 by Meckel's chondrocytes during degradation of the extracellular matrix

We examined the possibility that chondrocytes in Meckel's cartilage might secrete matrix metalloproteinase-1 (MMP-1) during degradation of the extracellular matrix. Evidence for the secretion of MMP-1 was obtained by immunohistochemical staining and immunoelectron microscopy, in addition to general histochemical staining for proteoglycans. Not only staining with toluidine blue and alcian blue but also immunostaining for chondroitin sulfate proteoglycan (CSPG) revealed that levels of glycoproteins are rapidly reduced at the late stage of degradation. MMP-1 was detected continuously in cells from chondrocytes at the early stage to hypertrophic chondrocytes at the late stage. Immunoelectron microscopy revealed that the deposition of colloidal golds shifted from an intracellular localization in chondrocytes at the early stage to pericellular spaces at the late stage. The localization of tissue inhibitor of the metalloproteinase-1 (TIMP-1) at the early stage was similar to that of MMP-1, but the level of TIMP-1 decreased significantly in hypertrophic cartilage. These findings suggest that MMP-1 is present continuously in Meckel's chondrocytes but that the active form, which degrades the extracellular matrix, is the MMP-1 that accumulates in the pericellular spaces around hypertrophic chondrocytes.

Stromelysin (MMP-3) synthesis is up-regulated in estrogen-deficient mouse osteoblasts in vivo and in vitro

Sex steroids are important regulators of bone cell function and osteoblast-derived matrix metalloproteinases (MMPs) are key mediators of bone resorption during the initial stage of osteoid removal prior to osteoclast attachment. To investigate the mechanism of bone loss following estrogen deficiency, we examined the effects of estrogen on osteoblast synthesis of MMPs and tissue inhibitor of metalloproteinases (TIMPs). Immunolocalization in mouse bone samples ex vivo and primary mouse osteoblast (MOB) cultures was used to document the synthesis of mouse interstitial collagenase (MMP-13), stromelysin-1 (MMP-3), gelatinase-A (MMP-2), and gelatinase-B (MMP-9). Endosteal bone lining cells from distal femoral head and lumbar vertebral body showed an increase in the pattern of synthesis of stromelysin-1 following ovariectomy, compared with sham-operated controls; the synthesis of other MMPs was unaffected. The expression of all classes of MMPs and TIMP-1 and TIMP-2 by MOB in culture was demonstrated by reverse transcriptase-polymerase chain reaction. Following the withdrawal of 17beta-estradiol, MOB cultures showed a significant increase in the number of cells synthesizing stromelysin-1; this effect was enhanced by stimulation with either interleukin-1 or interleukin-6. Northern blot analysis showed only a slight increase in stromelysin-1 mRNA message following the withdrawal of 17beta-estradiol. Our data show an unexpected up-regulation of stromelysin-1 synthesis by osteoblasts both in vivo and in vitro following estrogen withdrawal. Although this effect was not reflected in a significant change in stromelysin-1 mRNA expression in vitro, there is evidence to suggest a role for this enzyme in the early stages of bone loss during the pathogenesis of osteoporosis.

Regulation of osteoclast activity

Osteoclasts are the primary cell type responsible for bone resorption. This paper reviews many of the known regulators of osteoclast activity, including hormones, cytokines, ions, and arachidonic acid metabolites. Most of the hormones and cytokines that inhibit osteoclast activity act directly on the osteoclasts. In contrast, most of the hormones and cytokines that stimulate osteoclast activity act indirectly through osteoblasts. Particularly interesting in this regard are agents that directly inhibit activity of highly purified osteoclasts yet stimulate activity of osteoclasts that are co-cultured with osteoblasts. Recent studies have demonstrated that the primary mechanism by which bone resorptive agents stimulate osteoclast activity indirectly is likely to be up-regulation of production of osteoclast differentiation factor/osteoprotegerin ligand (ODF/OPGL) by the osteoblasts. In addition to discussing regulators of osteoclast activity per se, this paper also reviews the role of osteoclast apoptosis to limit the extent of bone resorption.

Physiological roles of matrix metalloproteinases: implications for tumor growth and metastasis

Physiological processes involving remodelling of the extracellular matrix, such as wound healing, embryogenesis, angiogenesis, and the female reproductive cycle, require the activity of matrix metalloproteinases (MMPs). This group of proteases degrades basal membranes and connective tissues and plays an essential role in the homeostasis of the extracellular matrix. An imbalance in the expression or activity of MMPs can have important consequences in diseases such as multiple sclerosis, Alzheimer's disease, or the development of cancers. Because of the pathophysiological importance of MMPs, their activity is highly controlled in order to confine them to specific areas. An activation cascade, initiated by the proteolysis of plasminogen, cleaves proMMPs, and every step is controlled by specific activators or inhibitors. MMPs destabilize the organization of the extracellular matrix and influence the development of cancer by contributing to cell migration, tumor cell proliferation, and angiogenesis. Accordingly, these proteases possess an important role in cell-matrix interactions by affecting fundamental processes such as cell differentiation and proliferation. Therefore, the characterization of MMPs involved in specific types and stages of tumors will significantly improve the diagnosis and treatment of these cancers in humans.Key words: matrix metalloproteinases, physiology, cancer, cell invasion, extracellular matrix.

An odyssey from breast to bone: multi-step control of mammary metastases and osteolysis by matrix metalloproteinases

Development of metastases distant to the primary site of solid tumors marks late stages of tumor progression. Almost all malignant mammary tumors are carcinomas arising from the breast epithelium, but the morphological and molecular alterations in the mammary stroma surrounding the premalignant and the growing tumor contribute to its conversion into neoplastic tissue. Two parameters are critical for initiation of the metastatic process and access of tumor cells to the circulation. These are the ability of tumor cells to invade the basement membrane and the stroma, and the neovascularization of breast tumor tissue. A major site for development of distant metastases is the skeleton. After colonizing the bone, tumor cells promote a cascade of events leading to recruitment of osteoclasts and subsequent osteolytic bone destruction. A ubiquitous theme of neoplastic progression of breast tumors is the overproduction of matrix metalloproteinases. In this review, we summarize the recent insights into the functional consequences of matrix metalloproteinase expression and activation during malignant conversion in the breast, and after bone colonization. The current literature supports the hypothesis that matrix metalloproteinases play a key role in the metastatic expansion of most, if not all, mammary tumors and in the ensuing bone loss.

Immunolocalization of the cleavage of the aggrecan core protein at the Asn341-Phe342 bond, as an indicator of the location of the metalloproteinases active in the lysis of the rat growth plate

In view of the extensive lysis of hyaline cartilage known to take place during endochondral bone formation, the current study was designed to test the hypothesis that metalloproteinases are the agents that mediate this lysis. Since these enzymes have been shown in vitro to cleave the core protein of the major proteoglycan of cartilage, aggrecan, at the Asn341-Phe342 bond, an immunohistochemical method has been developed to find out whether or not there are sites in the growth plate of the rat tibia where cleavage of this bond takes place. The cleavage of aggrecan by metalloproteinases is followed by the retention of the fragment known as G1, for it includes the G1 domain. Since the G1 fragment terminates in the amino acid residues ...FVDIPEN, we prepared an antiserum against FVDIPEN, confirmed its specificity, then applied it to the growth plate of 21-day-old rat tibia in the hope of localizing the G1 fragments. The antiserum specificity was shown by its recognition of the ...FVDIPEN sequence at the C-terminus of peptides and of G1 fragments produced by aggrecan cleavage. When the antiserum was applied to Western blots of guanidinium chloride extracts prepared from epiphyseal growth plate, it recognized two species (56 and 52 kDa), which differed only in the degree of glycosylation. These fragments were comparable in size to the G1 fragments generated by the action of recombinant metalloproteinase in vitro, thus confirming antiserum specificity for these fragments. Applying the antiserum to cryosections of 21-day-old rat tibiae revealed immunostaining at two intensities within the growth plate matrix: a strong staining was observed in a 1-5 microm-wide layer designated "peripheral" matrix, which borders the epiphyseal and metaphyseal marrow spaces as well as the perichondrium, while a weak staining was found in the rest of the plate, designated "central" matrix. The abundance of G1 fragments terminating in ...FVDIPEN in the peripheral matrix indicates that this is where the growth plate is lysed to achieve longitudinal and latitudinal bone growth. The site where metalloproteinases exert their main lytic activity is a thin layer of matrix separating central from peripheral matrix.

Large scale isolation of osteoclast-specific genes by an improved method involving the preparation of a subtracted cDNA library

BACKGROUND

Osteoclasts play crucial roles in bone resorption, which triggers bone remodeling. Molecular mechanisms underlying these osteoclast-specific biological functions remain elusive because only a limited number of osteoclast-specific genes have been identified. To circumvent this, we isolated a large number of osteoclast-specific genes by preparing a subtracted cDNA library of high quality.

RESULTS

We first constructed a plasmid expression vector (pAP3neo) that allowed an efficient subtraction. Then, we improved the standard protocols for preparation of the cDNA library and the subsequent subtraction procedure. Using our protocol, we prepared a rabbit osteoclast cDNA library of high complexity. Subsequently, we prepared an osteoclast-specific cDNA library of high complexity by subtracting it with biotin-labelled mRNA, derived from rabbit spleen through the biotin-avidin method. The resulting library included a high proportion of full-length cDNA inserts. Using DNA dot blot analysis, we found that the osteoclast-specific cDNA clones were highly enriched in this subtracted cDNA library, i.e. nearly 70% of the analysed clones were primarily detected in osteoclasts but not in spleen. Multiple-tissue Northern analysis also showed that many of these clones were expressed almost exclusively in osteoclasts. DNA sequencing of randomly selected clones showed that 424 cDNA species out of 1136 analysed were novel. DNA sequencing also showed that our subtracted cDNA library was almost equalized, suggesting that the library may contain almost all of the osteoclast-specific genes.

CONCLUSION

From these data, we conclude that our subtraction protocols, and the subsequent procedure for the analysis of the isolated clones developed here, are useful for the comprehensive isolation and identification of transcriptionally up- or down-regulated genes in general.

EGF and IL-1 alpha modulate the release of collagenase, gelatinase and TIMP-1 as well as the release of calcium by rabbit calvarial bone explants

Matrix metalloproteinases (MMPs), among which is collagenase (MMP-1), are likely to be involved in various steps of the bone resorption process. As both production of these enzymes and bone resorption appear to be mediated by cytokines, we investigated the effects of two cytokines, IL-1 alpha and EGF, on the release of collagenase, gelatinase A (MMP-2), gelatinase B (MMP-9), TIMP-1 and calcium by rabbit calvariae. It was found that all these parameters increased under the influence of these cytokines. The release of calcium--used as a parameter of bone resorption--was highest in the combined presence of the cytokines. Although the absolute and relative enhancement by a combination of IL-1 alpha and EGF was most pronounced for collagenase (7-fold), both gelatinase A (5-fold) and gelatinase B (1.5-fold) had increased simultaneously. Calvariae produced a high level of MMP inhibitor (TIMP-1), especially under the influence of the cytokines; periosteum released little inhibitor. It is concluded that IL-1 alpha and EGF are likely to play a modulating role in the process of bone resorption.

Inhibition of osteolytic bone metastasis of breast cancer by combined treatment with the bisphosphonate ibandronate and tissue inhibitor of the matrix metalloproteinase-2

Multiple steps are involved in the metastasis of cancer cells from primary sites to distant organs. These steps should be considered in the design of pharmacologic approaches to prevent or inhibit the metastatic process. In the present study, we have compared the effects of inhibiting several steps involved in the bone metastatic process individually with inhibition of both together. The steps we chose were matrix metalloproteinase (MMP) secretion, likely involved in tumor cell invasion, and osteoclastic bone resorption, the final step in the process. We used an experimental model in which inoculation of human estrogen-independent breast cancer MDA-231 cells into the left cardiac ventricle of female nude mice causes osteolytic lesions in bone. To inhibit cancer invasiveness, the tissue inhibitor of the MMP-2 (TIMP-2), which is a natural inhibitor of MMPs, was overexpressed in MDA-231 cells. To inhibit bone resorption, a potent bisphosphonate, ibandronate (4 microg/mouse) was daily administered subcutaneously. Nude mice received either; (a) nontransfected MDA-231 cells; (b) nontransfected MDA231 cells and ibandronate; (c) TIMP-2-transfected MDA-231 cells; or (d) TIMP-2-transfected MDA-231 cells and ibandronate. In mice from group a, radiographs revealed multiple osteolytic lesions. However, in mice from group b or group c, osteolytic lesions were markedly decreased. Of particular note, in animals from group d receiving both ibandronate and TIMP-2-transfected MDA-231 cells, there were no radiologically detectable osteolytic lesions. Survival rate was increased in mice of groups c and d. There was no difference in local enlargement in the mammary fat pad between nontransfected and TIMP-2-transfected MDA-231 cells. These results suggest that inhibition of both MMPs and osteoclastic bone resorption are more efficacious treatment for prevention of osteolytic lesions than either alone, and suggest that when therapies are designed based on the uniqueness of the bone microenvironment and combined with several common steps in the metastatic process, osteolytic bone metastases can be more efficiently and selectively inhibited.

Calcitonin inhibits phospholipase A2 and collagenase activity of human osteoarthritic chondrocytes

Calcitonin (CT) is a known potent inhibitor of bone resorption but its effect on cartilage enzymatic degradation has been incompletely studied. Salmon CT, at a concentration of 0, 0.1, 0.25, 0.5, 2.5 and 50 ng/ml, was added at 24 or 72 h to the culture medium of chondrocytes from human osteoarthritic hips and knees. The spontaneous collagenolytic activity, measured using a radiolabeled type II collagen, was inhibited by CT in a dose-dependent manner. However, CT had no effect on the total collagenolytic activity assayed after APMA activation. Stromelysin and plasmin activity, measured by degradation of casein and a synthetic substrate, were also unaffected by CT. Chondrocyte phospholipase A2 activity, assayed using a labeled specific substrate, was decreased by CT. Chondrocyte pre-incubation with CT significantly decreased the cell binding of labeled TNF alpha, but did not affect IL-1 beta cell binding. Attachment of chondrocytes on fibronectin was markedly stimulated by CT, while attachment to type II collagen was not. Significant effects were obtained using at least 2 or 5 ng/ml of CT. CT appears to decrease collagenolytic activity by decreasing its activation and/or increasing its inhibition by tissue inhibitors of metalloproteinases (TIMP). CT might act on osteoarthritic chondrocyte activation via mechanisms such as phospholipase A2 activity, human necrosis factor-alpha or fibronectin receptor expression.

Regulation of tissue inhibitor of metalloproteinases-3 gene expression by transforming growth factor-beta and dexamethasone in bovine and human articular chondrocytes

Physiological and pathological degradation of cartilage extracellular matrix (ECM) is regulated by the balance between tissue inhibitors of metalloproteinases (TIMPs) and matrix metalloproteinases (MMPs). We examined the potential of chondrocytes from normal bovine or human osteoarthritic (OA) cartilage to express RNA for the new inhibitor TIMP-3 and studied its regulation by an inducer of matrix synthesis, transforming growth factor-beta (TGF-beta). Freshly released chondrocytes constitutively expressed three transcripts of TIMP-3 that are induced by serum factors. In primary cultures of chondrocytes, one of these factors, TGF-beta, increased TIMP-3 mRNA in a dose-dependent fashion that required de novo protein synthesis and transcription. TGF-beta did not alter stability of the TIMP-3 transcripts in RNA decay time-courses, suggesting a transcriptional control. Nuclear run-on assays confirmed increased rate of TIMP-3 gene transcription by TGF-beta. An antiinflammatory glucocorticoid, dexamethasone, inhibited the basal, and suppressed partially the TGF-beta-inducible, TIMP-3 expression in primary bovine and human chondrocytes. DNA sequencing of bovine TIMP-3 cDNA revealed an open reading frame of a 211-amino-acid protein containing signal peptide and 12 conserved cysteines. The encoded protein differed from human TIMP-3 at four positions. The constitutive expression and evolutionary conservation of TIMP-3 imply its important function. TIMP-3 induction by TGF-beta suggests the role of this factor and TIMP-3 in cartilage remodeling with important implications for arthritis.

Parathyroid hormone-induced resorption in fetal rat limb bones is associated with production of the metalloproteinases collagenase and gelatinase B

The role of matrix metalloproteinases in parathyroid hormone (PTH)-induced bone resorption was assayed using a fetal rat limb bone culture system. Cotreatment of bones with PTH and recombinant inhibitor of metalloproteinases, TIMP-1, in vitro, inhibited the PTH-stimulated 45Ca release from the limb bones without affecting beta-glucuronidase release. TIMP-1 was fully effective when added during only the final 24 h of a 72 h culture with PTH but was ineffective when added for only the first 24 h of the 72 h culture. In contrast, calcitonin (CT) was effective when added for either the first 24 or the final 24 h of the culture. Using in situ hybridization, the mRNA for collagenase was detected in mononuclear cells of cultured bone. Treatment of the bones with PTH resulted in an increase in the number of cells producing collagenase mRNA, some of which had osteoclastic morphology, PTH also caused a dramatic induction of the mRNA for the 92-kD gelatinase B metalloproteinase in both mononuclear and osteoclastic cells. There was no detectable mRNA for the metalloproteinases stromelysin-1, stromelysin-2, or matrilysin in PTH-treated or control cultures. These results suggest that PTH-induced bone resorption is mediated, at least in part, by the induction of collagenase and gelatinase B mRNA in bone cells.

Endogenous bone-resorbing factors in estrogen deficiency: cooperative effects of IL-1 and IL-6

Estrogen deficiency causes a marked bone loss by stimulating osteoclastic bone resorption. To explore the endogenous bone-resorbing factors involved in estrogen deficiency, we examined the bone-resorbing activity present in the supernatant fraction of mouse bone marrow collected from ovariectomized (OVX) mice. Adding bone marrow supernatants at 20-80% to organ cultures of mouse long bones dose-dependently stimulated bone resorption. The endogenous bone-resorbing activity present in bone marrow supernatants from OVX mice was much higher than that from sham-operated mice 2-4 weeks after surgery, and it was significantly diminished by indomethacin in vitro. Anti-IL-1 alpha antibody completely neutralized the bone-resorbing activity present in bone marrow supernatants from OVX mice. Antibodies against IL-1 beta, IL-6, and IL-6 receptors also neutralized it, but partially. The concentration of IL-1 alpha measured by ELISA was much higher in bone marrow supernatants than in sera, but it was not appreciably changed before or after OVX. The concentration of IL-1 beta in bone marrow supernatants from OVX mice was less than the detection limit. OVX stimulated IL-1 activity in bone marrow supernatants measured by means of the proliferation of thymocytes. However, the level of IL-1 alpha present in bone marrow supernatants from OVX mice was insufficient to stimulate bone resorption. Compared with the serum concentration, bone marrow supernatants contained a much higher level of IL-6 as well, and it was further increased by OVX. However, IL-6 alone present in bone marrow supernatants from OVX mice again did not stimulate bone resorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation of human osteoblastic cells in culture: modulation of proteases by extracellular matrix and tumor necrosis factor-alpha

We have followed the synthesis and secretion of urokinase-type plasminogen activator (u-PA) and its inhibitor, PAI-1, and matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMP-1) during differentiation of a human osteoblastic cell line, HOS TE85, and the effect of TNF-alpha on this process. Our results show that the ratio of u-PA/PAI-1 associated with the cell-matrix components increases during differentiation of these cells over a 14-day period. Although TNF-alpha suppresses the induced increase in steady-state mRNA levels of u-PA and PAI-1 during maturation of extracellular matrix (ECM), the u-PA/PAI-1 ratio is altered in such a way that PA activity associated with the ECM is higher than control cells. The expression of MMP-1 is low and remains essentially invariant over a culture period of 14 days. TNF-alpha enhances MMP-1 transcription nearly 12-fold initially, after which mRNA levels drop off but remain significantly higher than the controls. Activities and steady-state mRNA levels of MMP-2 and MMP-9 increase nearly 15-fold during maturation of the ECM, but the level of TIMP-1 mRNA is not appreciably altered. The presence of TNF-alpha suppresses maturation-induced transcription of MMP-2, enhances TIMP-1 transcription, but has little effect on MMP-9 mRNA levels. The data show that chronic exposure to TNF-alpha alters the balance between u-PA/PAI-1 and MMPs/TIMP-1, which favors higher activity of proteinases. Accordingly, the presence of TNF-alpha in chronic inflammatory episodes would be expected to alter bone remodeling by inhibiting maturation of ECM and formation of bone.

Matrix metalloproteinases and TIMP-1 localization at sites of osteogenesis in the craniofacial region of the rabbit embryo

BACKGROUND

The matrix metalloproteinases (MMPs) are a family of closely related enzymes, the principal members being the collagenases, gelatinases, and stromelysins. They are synthesized and secreted by connective tissue cells and are capable of degrading all the components of connective tissue matrices at physiological pH.

METHODS

Patterns of synthesis and distribution of MMPs and their inhibitor, tissue inhibitor of metalloproteinases-1 (TIMP-1), are documented in the craniofacial region at sites of bone formation during both intramembranous (e.g., calvaria, maxilla, and mandible) and endochondral ossification (e.g., cartilaginous cranial base and synchondroses) using indirect immunolocalization.

RESULTS

MMPs and TIMP-1 were detected both as bright intracellular accumulations, indicating active synthesis, and as diffuse matrix-bound extracellular deposits. Gelatinase-A had an extensive distribution in osteogenic tissues and was detected both in cells of the periosteum and spongiosum and as extracellular deposits in the osteoid layer of newly formed bone. In addition, gelatinase-AB synthesis was detected in osteoclasts. All regions of the early cartilaginous cranial base produced MMPs and TIMP-1, and synthesis continued in the established synchondrosis. MMPs and TIMP-1 were also documented in early tooth germs and in Meckel's cartilage.

CONCLUSIONS

These data document a prominent role for MMPs, and in particular gelatinase-A, in mediating matrix degradation during osteogenesis. Their detection in tooth germs and Meckel's cartilage further indicates a role for MMPs and TIMP-1 in matrix turnover during morphogenesis.

Inhibition of bone resorption in vitro by selective inhibitors of gelatinase and collagenase

Two low-molecular-mass inhibitors of matrix metalloproteinases (MMPs), CT1166, a concentration-dependent selective inhibitor of gelatinases A and B, and Ro 31-7467, a concentration-dependent selective inhibitor of collagenase, were examined for their effects on bone resorption and type-I collagenolysis. The test systems consisted of measuring (1) the release of [3H]proline from prelabelled mouse calvarial explants; (2) the release of 14C from prelabelled type-I collagen films by mouse calvarial osteoblasts; and (3) lacunar resorption by isolated rat osteoclasts cultured on ivory slices. In 24 h cultures, CT1166 and Ro 31-7467 inhibited both interleukin-1 alpha- (IL-1 alpha; 10(-10) M) and 1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated bone resorption in cultured neonatal mouse calvariae at concentration selective for the inhibition of gelatinase (10(-9) M for CT1166) and collagenase (10(-8) M for Ro 31-7467) respectively. For each compound the inhibition was dose-dependent, reversible, and complete at a 10(-7) M concentration. However, CT1166 (10(-9) M) and Ro 31-7467 (10(-8) M) in combination were required to completely abolish IL-1 alpha-stimulated bone resorption in mouse calvariae throughout a 96 h culture period. Neither of the inhibitors affected protein synthesis, DNA synthesis nor the IL-1 alpha-stimulated secretion of the lysosomal enzyme, beta-glucuronidase. Both CT1166 and Ro 31-7467 partially inhibited IL-1 alpha-stimulated lacunar resorption by isolated osteoclasts, but were without effect on unstimulated lacunar resorption. Rodent osteoclasts produced collagenase and gelatinases-A and -B activity. In contrast the substrate used to assess osteoclast lacunar resorption contained no detectable collagenase or gelatinase activity. Both compounds dose-dependently inhibited 1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated degradation of type-I collagen by mouse calvarial osteoblasts; however, complete inhibition of collagenolysis was only achieved at concentrations at which CT1166 and Ro 31-7467 act as general MMP inhibitors. This study demonstrates that collagenase and gelatinases A and/or B participate in bone resorption. While these MMPs may be primarily involved in osteoid removal, we conclude that they may also be released by osteoclasts, where they participate in bone collagen degradation within the resorption lacunae.

Tissue inhibitor of metalloproteinases-2 (TIMP-2) in rat liver cells is increased by lipopolysaccharide and prostaglandin E2

To explore the functional role of TIMP-2 in liver, we determined TIMP-2 mRNA levels in primary rat hepatocytes and in total rat liver. Rat hepatocytes constitutively express TIMP-2 mRNA at a low level. Incubation with dexamethasone, prostaglandin E2 and a combination of inflammatory cytokines leads to an up-regulation of TIMP-2 mRNA. In rats in vivo we found a dramatic increase of TIMP-2 expression after intraperitoneal injection of lipopolysaccharide. Compared to our previous findings on TIMP-1 we conclude that TIMP-2 mRNA expression is regulated in a distinct and partially opposite manner. Over-production of TIMP-2 could inhibit the activity of metalloproteinases and thus lead to matrix accumulation. Dysregulation of TIMP-2 synthesis might be involved in the development of liver fibrosis.

The effects of selective inhibitors of matrix metalloproteinases (MMPs) on bone resorption and the identification of MMPs and TIMP-1 in isolated osteoclasts

We have compared the effects of a general matrix metalloproteinase (MMP) inhibitor (CT435) with those of a concentration-dependent specific gelatinase inhibitor (CT543; Ki < 20 nM) on bone resorption in vitro. The test systems consisted of measuring: (i) the release of 45Ca2+ from prelabelled mouse calvarial explants; (ii) the release of 45Ca2+ from prelabelled osteoid-free calvarial explants co-cultured with purified chicken osteoclasts; and (iii) lacunar resorption by isolated rat osteoclasts cultured on ivory slices. Both CT435 and CT543 dose-dependently inhibited the release of 45Ca2+ from neonatal calvarial bones stimulated by either parathyroid hormone or 1,25-dihydroxyvitamin D3. Moreover, CT543 produced a 40% inhibition at a concentration (10(−8) M) selective for the inhibition of human gelatinases A and B. CT435 (10(−5) M) and CT543 (10(−5) M) partially inhibited the release of 45Ca2+ from osteoid-free calvarial explants by chicken osteoclasts with a maximum of approximately 25% for unstimulated cultures, and approximately 36% for cultures stimulated by interleukin-1 alpha (IL-1 alpha; 10(−10) M). Neither inhibitor prevented lacunar resorption on ivory by unstimulated rat osteoclasts, but the compounds produced a partial reduction in both the number and total surface area of lacunae in IL-1 alpha-stimulated cultures, with maximal action at 10(−5) M. Neither of the inhibitors affected protein or DNA synthesis, nor the IL-1 alpha-stimulated secretion of the lysosomal enzyme beta-glucuronidase. Immunocytochemistry demonstrated that isolated rabbit osteoclasts constitutively expressed gelatinase A and synthesized gelatinase B, collagenase and stromelysin, as well as the tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) following IL-1 alpha stimulation. These experiments have shown that in addition to collagenase, gelatinases A and B are likely to play a significant role in bone resorption. They further suggest that MMPs produced by osteoclasts are released into the sub-osteoclastic resorption zone where they participate in bone collagen degradation.

Rabbit calvarial osteoblasts in culture constitutively synthesize progelatinase-A, and TIMP-1 and TIMP-2

Defining the TIMPs (tissue inhibitors of metalloproteinases) produced by non-human bone cells is important because animal models and cells are used extensively for research on bone resorption, and because TIMP-2 can bind to and prevent activation of progelatinase-A. By zymography we show that rabbit calvarial osteoblasts in culture constitutively synthesize TIMP-2 in addition to TIMP-1 and progelatinase-A. Previously we found that human osteoblasts produced only low levels of TIMP-2 under any conditions. We also show that stimulated rabbit osteoblasts can degrade a type I collagen film even though both TIMPs are being synthesized.

Inhibition of bone resorption by selective inactivators of cysteine proteinases

Inactivators of cysteine proteinases (CPs) were tested as inhibitors of bone resorption in vitro and in vivo. The following four CP inactivators were tested: Ep475, a compound with low membrane permeability which inhibits cathepsins B, L, S, H, and calpain; Ep453, the membrane-permeant prodrug of Ep475; CA074, a compound with low membrane permeability which selectively inactivates cathepsin B; and CA074Me, the membrane-permeant prodrug of CA074. The test systems consisted of 1) monitoring the release of radioisotope from prelabelled mouse calvarial explants and 2) assessing the extent of bone resorption in an isolated osteoclast assay using confocal laser microscopy. Ep453, Ep475, and CA074Me inhibited both stimulated and basal bone resorption in vitro while CA074 was without effect; the inhibition was reversible and dose dependent. None of the inhibitors affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase, and N-acetyl-beta-glucosaminidase, or the spontaneous release of lactate dehydrogenase. Ep453, Ep475, and CA074Me dose-dependently inhibited the resorptive activity of isolated rat osteoclasts cultured on bone slices with a maximal effect at 50 microM. The number of resorption pits and their mean volume was reduced, whilst the mean surface area remained unaffected. Again, CA074 was without effect. Ep453, Ep475, and CA074Me, but not CA074, when administered subcutaneously at a dose of 60 micrograms/g body weight inhibited bone resorption in vivo as measured by an in vivo/in vitro assay, by about 20%. This study demonstrates that cathepsins B, L, and/or S are involved in bone resorption in vitro and in vivo. Whilst cathepsin L and/or S act extracellularly, and possibly intracellularly, cathepsin B mediates its effects intracellularly perhaps through the activation of other proteinases involved in subosteoclastic collagen degradation.

Gene encoding a novel murine tissue inhibitor of metalloproteinases (TIMP), TIMP-3, is expressed in developing mouse epithelia, cartilage, and muscle, and is located on mouse chromosome 10

Remodeling of the extracellular matrix (ECM) is an essential component of normal development and is also involved in the pathogenesis of arthritis and the spread of cancer. The matrix metalloproteinases and their natural inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), play an important role in this context. We have isolated mouse cDNA clones encoding a novel member of the TIMP family, designated TIMP-3. We have assigned the Timp-3 locus to the [C1-D1] region of mouse chromosome 10 using both genetic and cytogenetic methods. The conceptual translation product of the Timp-3 cDNA shows a high degree of similarity with ChIMP-3, a recently cloned chicken metalloproteinase inhibitor, as well as significant structural similarity with the amino acid sequences of the previously isolated members of this family, TIMP-1 and TIMP-2. The pattern of expression of Timp-3 in the developing mouse embryo is distinct from that previously reported for Timp-1. Timp-3 is expressed in cartilage and skeletal muscle, in myocardium, in the skin, oral and nasal epithelium, in the newborn mouse liver, in the epithelium of some tubular structures such as the developing bronchial tree, oesophagus, colon, urogenital sinus, bile duct, in the kidney, salivary glands, and in the choroid plexus of the brain. The patterns of Timp-3 expression in surface epithelia and in the epithelial lining of many tubular organs suggests that TIMP-3 may be involved in regulating ECM remodeling during the folding of epithelia and during the formation, branching, and expansion of epithelial tubes. In the mouse placenta, expression is seen in the trophoblast, raising the possibility that TIMP-3 may be involved in regulating trophoblastic invasion of the uterus. We propose a role for TIMP-3 in musculoskeletal and cardiac development, in the morphogenesis of certain epithelial structures, and placental implantation.

Tumor invasion, proteolysis, and angiogenesis

In this review, some of the current literature on the regulation of proteolysis and angiogenesis during tumor invasion is discussed. Due to the critical location of brain tumors, an understanding of tumor cell interactions with the local environment is particularly relevant. Tissue breakdown during tumor invasion is associated with proteolytic activity, mediated by tumor cells, and surrounding host cells. This review covers two classes of proteinases and inhibitors that have commonly been associated with tumor invasion i.e., plasminogen activator (PA)/plasmin and matrix metalloproteinases (MMP) with special emphasis on the MMP inhibitors, TIMP-1 and TIMP-2. At different steps of the metastatic process, tumor cells interact with endothelial cells. Tumor cells also stimulate the formation of new vessels through the expression of specific angiogenic molecules. At least eight angiogenic molecules have been purified, sequenced and cloned, four of which are discussed here. Regulation of angiogenic activity has been the focus of intense studies recently, and a wide range of synthetic and natural angiogenesis inhibitors have been discovered. Targeting of angiogenic molecules and tumor vasculature may prove useful in future cancer therapeutic strategies.