Prostanoid-induced expression of matrix metalloproteinase-1 messenger ribonucleic acid in rat osteosarcoma cells

Arachidonic acid increases matrix metalloproteinase 9 secretion and expression in human monocytic MonoMac 6 cells

Background

Dietary fatty acids may modulate inflammation in macrophages of the atherosclerotic plaque, affecting its stability. The n-6 polyunsaturated fatty acid (PUFA) arachidonic acid (AA) generally promotes inflammation, while the PUFAs of the n-3 series eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) are considered anti-inflammatory. We determined how these PUFAs influence MMP-9 expression and secretion by the human monocytic cell line (MonoMac 6) at baseline and after 24-hour exposure. MMP-9 protein was measured by zymography and relative levels of MMP-9 mRNA were determined using quantitative real time PCR.

Results

Supplementation with AA (but not the n-3 fatty acids) increased, in a dose-dependent manner, expression of MMP-9 protein. This stimulation was regulated at the mRNA level. MMP-9 secretion started after 1 h of incubation and could not be prevented by simultaneous presence of n-3 series fatty acids. Finally, the secretion could be attenuated by LY 294002, a specific phosphatidylinositol-3-kinase (PI3K) inhibitor and by SH-5, a selective Akt inhibitor, suggesting that activation of PI3K by AA leads to augmented and sustained MMP-9 production.

Conclusion

This study shows that of the PUFA studied, AA alone influences the expression of MMP-9, which might have implications in MMP-9 induced plaque rupture.

BCP crystals increase prostacyclin production and upregulate the prostacyclin receptor in OA synovial fibroblasts: potential effects on mPGES1 and MMP-13

OBJECTIVE

To investigate the potential involvement of prostacyclin in basic calcium phosphate (BCP) crystal-induced responses in osteoarthritic synovial fibroblasts (OASF).

METHODS

OASF grown in culture were stimulated with BCP crystals. Prostacyclin production was measured by enzyme immunoassay. Expression of messenger RNA (mRNA) transcripts was assessed by real-time polymerase chain reaction (PCR). Expression of prostacyclin synthase (PGIS) and the prostacyclin (IP) receptor was measured. The effects of iloprost, a prostacyclin analogue, on expression of genes implicated in osteoarthritis such as microsomal prostaglandin E2 synthase 1 (mPGES1) and matrix metalloproteinases (MMPs) were also studied. FPT inhibitor II, a farnesyl transferase inhibitor, was used to antagonize iloprost-induced responses.

RESULTS

BCP crystal stimulation led to a five-fold increase in prostacyclin production in OASF compared to untreated cells. This induction was attenuated by cyclooxygenase (COX)-2 and COX-1 inhibition at 4 and 32h, respectively. PGIS and IP receptor transcripts were constitutively expressed in OASF. BCP crystals upregulated IP receptor expression two-fold. While iloprost diminished BCP crystal-stimulated IP receptor upregulation, the inhibitory effect of iloprost was blocked by the farnesyl transferase inhibitor. In addition, iloprost upregulated mPGES1 and downregulated MMP-13 expression in BCP crystal-stimulated OASF, effects that were not influenced by the farnesyl transferase inhibitor.

CONCLUSIONS

These data showed for the first time that BCP crystals can increase prostacyclin production and upregulate expression of the IP receptor in OASF. The potential of prostacyclin to influence BCP crystal-stimulated responses was supported by the effects of iloprost on the expression of the IP receptor, mPGES1 and MMP-13. These data demonstrate the potential involvement of prostacyclin in BCP crystal-associated osteoarthritis (OA) and suggest that inhibition of PG synthesis with non-steroidal anti-inflammatory drugs may have both deleterious and beneficial effects in BCP crystal-associated OA.

Bradykinin stimulates MMP-2 production in guinea pig tracheal smooth muscle cells

The implication of bradykinin (BK) receptors in the release of the matrix metalloproteinase-2 (MMP-2; gelatinase A) was studied in guinea pig tracheal smooth muscle cells (GP-TSMC). Bradykinin (10(-8)-10(-4) M) induced a time- and concentration-dependent upregulation of MMP-2 production from cultured GP-TSMC. Pretreatment of the GP-TSMC with the bradykinin B2 receptor (BKB2-R) antagonist Hpp-HOE-140 (Hpp-D-Arg0-Hyp3-Thi5-D-Tic7-Oic8-BK; 10(-8)-10(-4) M) significantly inhibited the BK-stimulated upregulation of MMP-2 in GP-TSMC in a concentration-related manner. Conversely, GP-TSMC pretreated with the selective bradykinin B1 receptor (BKB1-R) antagonist R-954 (Ac-Om[Oic2, alpha-MePhe5, D-betaNal7, Ile8]desArg9BK; 10(-8)-10(-4) M) did not show any change in the response to BK. Moreover, the selective BKB2-R agonist Lys0BK (kallidin; 10(-8)-10(-4) M) stimulated whereas the selective BKB1-R agonist desArg9BK (DBK; 10(-8)-10(-4) M) had no effect on MMP-2 release from GP-TSMC. Further, the nonselective cyclooxygenase (COX) enzyme inhibitor indomethacin (IND; 10(-5) M), the glucocorticosteroid dexamethasone (DEX; 1 ng/mL) and the protein synthesis inhibitors, cycloheximide (CHX; 10(-6) M) and actinomycin D (ACT-D; 10(-8) M) also inhibited BK-induced MMP-2 release from GP-TSMC. These results provide the first evidence for the involvement of BK in the release of MMP-2 from airway smooth muscle cells through activation of the BKB2-R. Such response is mostly mediated by the induction of COX and the subsequent production of endogenous prostaglandins (PGs). It could therefore be suggested that MMP-2 might play a role in the process of airway remodeling.

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.

Sequential expressions of MMP-1, TIMP-1, IL-6, and COX-2 genes in induced periapical lesions in rats

To elucidate the pathogenesis of periapical lesion-associated bone resorption, a disease model of Wistar rat molar was employed. After lesion induction, the mRNAs encoding for matrix metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), interleukin-6 (IL-6), and cyclooxygenase-2 (COX-2) in the developing lesions were detected by in situ hybridization at day 5, 10, 15 and 20, respectively. At day 5, MMP-1, IL-6 and COX-2 mRNAs appeared predominantly in macrophages. During day 15 to day 20, increased expressions of these mediators were also found in osteoblasts but to a lesser extent compared with those in macrophages. MMP-1 mRNA was also detected in osteoclasts. In contrast, expression of the TIMP-1 gene was noted primarily in osteoblasts and was less pronounced compared with that of MMP-1. The mediator-expressing cells aggregated in the vicinity of bone resorption areas and their numbers increased with time. These data suggest that macrophages and osteoblasts are involved in the development of periapical lesions, and that they promote bone resorption by producing MMP-1, IL-6 and COX-2. In addition, administration of a specific COX-2 inhibitor, meloxicam, reduced the extent of periapical bone resorption by 43% and simultaneously diminished the numbers of cells synthesizing MMP-1 and IL-6 mRNAs. These results further elucidate the significance of COX-2 in disease progression of periapical lesions as it modulates indirectly the production of MMP-1 and IL-6.

Effects of TNFalpha and prostaglandin E2 on the expression of MMPs in human periodontal ligament fibroblasts

Accumulating evidence indicates that TNFalpha plays an important role in the pathogenesis of periodontitis, but the effect of TNFalpha on the degradation of the periodontal ligament is not well understood. This study used reverse transcriptase-PCR to investigate the effects of TNFalpha on matrix metalloproteinase (MMP) mRNA expression in human periodontal ligament fibroblasts. TNFalpha increased MMP-1, MMP-3 and MMP-13 mRNA levels in both a time-dependent (0-24 h) and a dose-dependent (0.1-10 ng/ml) manner. TNFalpha also increased COX-2 mRNA levels. Because elevation of COX-2 mRNA levels enhances the production of prostaglandins, we therefore investigated whether endogenous prostaglandins are involved in the MMP mRNA expression that is enhanced by TNFalpha. Pretreatment with the selective COX-2 inhibitor, NS-398, increased MMP-13 mRNA levels, while prostaglandin E2 and dibutyryl cyclic AMP decreased MMP-13 mRNA levels. Neither MMP-1 nor MMP-3 mRNA levels were affected by these chemicals. These findings indicate that prostaglandin E2 has a lowering effect on TNFalpha-enhanced MMP-13 mRNA levels, and that this effect is dependent on cAMP. Our results suggest that TNFalpha participates in periodontal ligament destruction by stimulating the production of MMPs (MMP-1, MMP-3 and MMP-13), while endogenous prostaglandin E2 has a negative feedback role in TNFalpha-enhanced MMP-13 production.

Effects of non-steroidal antiinflammatory drugs and dexamethasone on the activity and expression of matrix metalloproteinase-1, matrix metalloproteinase-3 and tissue inhibitor of metalloproteinases-1 by bovine articular chondrocytes

OBJECTIVE

To determine the in-vitro effects of several non-steroidal antiinflammatory drugs and the glucocorticoid dexamethasone on the IL-1 altered expression and activity of MMP-1, MMP-3 and TIMP-1 by bovine articular chondrocytes.

DESIGN

Bovine chondrocytes were cultured in alginate gel beads. Cells were treated with IL-1alpha in the presence of vehicle or drugs at various concentrations. After 48 h mRNA expression of MMP-1, MMP-3, and of the tissue inhibitor of metalloproteinases (TIMP-1) was analysed by RT-PCR-ELISA. The protein synthesis of TIMP-1 and MMP-3 was determined by immunoprecipitation. The activity of enzymes and inhibitors was measured by functional assays.

RESULTS

IL-1 increased the expression and activity of MMPs. In contrast, TIMP activity remained unchanged although TIMP-1 expression was down-regulated. All tested NSAIDs and dexamethasone inhibited collagenase activity induced by IL-1. Transcript levels of MMP-1, however, were only reduced by indomethacin, meloxicam, naproxen and dexamethasone. Proteoglycanase activity was only reduced by indomethacin, meloxicam and dexamethasone. These effects were pre-translational as confirmed by immunoprecipitation. The IL-1 decreased expression of TIMP-1 was further reduced by dexamethasone, which resulted in a significant loss of TIMP activity. No effects on TIMP activity or TIMP-1 biosynthesis were observed after treatment of chondrocytes with NSAIDs.

CONCLUSION

Our studies clearly demonstrate that marked differences exist between individual NSAIDs with respect to their ability to modulate the imbalance between proteases and inhibitors during OA and RA, suggesting that the respective modes of action are independent of the inhibition of cyclooxygenases. Due to their co-regulation of MMPs and TIMP(s) glucocorticoids should be carefully studied for their overall effect on ECM proteolysis.

Nitric oxide mediates cyclosporine-induced apoptosis in cultured renal cells

BACKGROUND

The clinical use of cyclosporine (CsA) is limited by its nephrotoxicity. Apoptosis, perhaps instigated by increased nitric oxide synthase (NOS) activity, may play a role in such toxicity.

METHODS

Human mesangial cells, human tubular cells, human umbilical vein endothelial cells, or murine endothelial cells were cultured with CsA at final concentrations of 0 to 1000 ng/mL for 4 to 24 hours. As inhibitors of apoptosis, 0.01 mol/L L-nitromethylarginine (L-NAME) or 1 microg/mL cycloheximide (CHX) was added, whereas 0.01 mol/L sodium nitroprusside (as a nitric oxide donor) was used as a positive control. Apoptosis was assessed by using TUNEL method and by DNA fragmentation by electrophoresis. In addition, NOS enzymatic activity, Northern blots for inducible NOS (iNOS) mRNA, and immunohistochemically demonstrable iNOS protein were evaluated.

RESULTS

Within 12 to 24 hours, CsA significantly increased the fraction (8 to 35%) of apoptotic cells in each cell line, according to the dose. Fragmentation of DNA confirmed apoptosis. L-NAME and CHX inhibited the phenomenon, whereas sodium nitroprusside enhanced it. Each cell line significantly increased NOS activity in response to CsA, an effect blunted by L-NAME and CHX. Neither inhibitor modified the increased iNOS mRNA expression elicited by CsA. Positive staining for both iNOS and p53 proteins was observed in all cell lines incubated with CsA that were inhibited by CHX; L-NAME inhibited only p53 staining.

CONCLUSIONS

CsA induces apoptosis in various renal cell lines, and this effect is mediated by the induction of iNOS via p53. These effects may contribute to the acellular fibrosis characteristic of late CsA nephrotoxicity.

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.

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.

Collagenase-3 induction in rat lung fibroblasts requires the combined effects of tumor necrosis factor-alpha and 12-lipoxygenase metabolites: a model of macrophage-induced, fibroblast-driven extracellular matrix remodeling during inflammatory lung injury

The mechanisms responsible for the induction of matrix-degrading proteases during lung injury are ill defined. Macrophage-derived mediators are believed to play a role in regulating synthesis and turnover of extracellular matrix at sites of inflammation. We find a localized increase in the expression of the rat interstitial collagenase (MMP-13; collagenase-3) gene from fibroblastic cells directly adjacent to macrophages within silicotic rat lung granulomas. Conditioned medium from macrophages isolated from silicotic rat lungs was found to induce rat lung fibroblast interstitial collagenase gene expression. Conditioned medium from primary rat lung macrophages or J774 monocytic cells activated by particulates in vitro also induced interstitial collagenase gene expression. Tumor necrosis factor-alpha (TNF-alpha) alone did not induce interstitial collagenase expression in rat lung fibroblasts but did in rat skin fibroblasts, revealing tissue specificity in the regulation of this gene. The activity of the conditioned medium was found to be dependent on the combined effects of TNF-alpha and 12-lipoxygenase-derived arachidonic acid metabolites. The fibroblast response to this conditioned medium was dependent on de novo protein synthesis and involved the induction of nuclear activator protein-1 activity. These data reveal a novel requirement for macrophage-derived 12-lipoxygenase metabolites in lung fibroblast MMP induction and provide a mechanism for the induction of resident cell MMP gene expression during inflammatory lung processes.

Posttranscriptional regulation of collagenase-1 gene expression in synoviocytes by adenosine receptor stimulation

OBJECTIVE

To characterize the transcriptional and posttranscriptional regulation of collagenase-1 by adenosine receptor stimulation in interleukin-1 (IL-1)-stimulated fibroblast-like synoviocytes (FLS).

METHODS

FLS were stimulated with IL-1 and either the nonselective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) or the adenylate cyclase activator forskolin. Electrophoretic mobility shift assays were performed to determine AP-1 and cAMP-responsive element binding protein (CREB) activation. Transcriptional activation was determined by transfecting HS68 dermal fibroblasts with a collagenase-chloramphenicol acetyltransferase construct. Finally, collagenase messenger RNA (mRNA) half-life was determined by activating cells in the presence of IL-1, IL-1 + NECA, or IL-1 + forskolin and culturing cells in the presence of actinomycin D.

RESULTS

NECA and forskolin had no effect on AP-1 activation, c-jun or c-fos gene expression, or CREB phosphorylation. IL-1 markedly increased collagenase promoter activity, and neither NECA nor forskolin blocked this action. Studies of mRNA half-life showed that both NECA and forskolin decreased the half-life of collagenase mRNA in IL-1-stimulated FLS and HS68 cells.

CONCLUSION

The findings of this study demonstrate that NECA and forskolin decrease collagenase gene expression in FLS and dermal fibroblasts due to enhanced mRNA degradation.

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.

Inhibition of synoviocyte collagenase gene expression by adenosine receptor stimulation

OBJECTIVE

To characterize the regulation of matrix metalloproteinases (MMPs) by adenosine.

METHODS

Cultured fibroblast-like synoviocytes (FLS) were stimulated with interleukin-1 (IL-1) in the presence or absence of adenosine receptor agonists. Immunoreactive MMPs were measured using specific enzyme-linked immunosorbent assays, and gene expression was assessed by Northern blot analysis.

RESULTS

The nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) decreased collagenase production by IL-1-stimulated synoviocytes from 196 +/- 28 ng/ml (mean +/- SEM) to 66 +/- 9 ng/ml (P < 0.001). There was minimal effect on stromelysin production (decrease from 107 +/- 16 ng/ml to 97 +/- 15 ng/ml). Selective adenosine receptor agonists implicated the A2b adenosine receptor in this activity, and reverse transcriptase-polymerase chain reaction studies confirmed that FLS express this receptor. Northern blot analysis demonstrated that the mechanism of action was pre-translational since NECA decreased collagenase, but not stromelysin or tissue inhibitor of metalloproteinases 1 (TIMP-1), messenger RNA levels. Cyclic AMP levels were increased by NECA, and a direct adenylate cyclase activator (forskolin) also suppressed collagenase gene expression. These data suggest that cAMP mediates the inhibitory effect of NECA on collagenase production.

CONCLUSION

Stimulation of the A2b receptor on FLS decreases collagenase gene expression, with little or no effect on stromelysin and TIMP-1. The combination of antiinflammatory and MMP-regulating properties of adenosine or adenosine-regulating agents suggest that treatment based on this approach might be useful in rheumatoid arthritis.

Minocycline impairment of both osteoid tissue removal and osteoclastic resorption in a synchronized model of remodeling in the rat

In addition to their antibacterial effects, tetracyclines may inhibit interstitial collagenase activity and bone resorption. These properties were assessed morphometrically using minocycline (25 and 50 mg/kg/day given by the IM route) in a rat model of synchronized remodeling in which osteoclastic resorption peaks 4 days after the activating event (the extractions of the upper molars) along the antagonist mandibular cortex, a zone undergoing physiologically active formation. During the first 2 days of activation, minocycline at the two doses impaired very significantly the disorganization of both the osteoid seam and the layer of osteoblasts, a prerequisite to give osteoclasts access to the mineralized bone surface. The number of readily identifiable osteoblasts decreased slightly during this period, suggesting that minocycline prevented their transformation into lining cells. Their synthetic activity, as estimated by the size of the cells and their nucleus, appeared relatively preserved too, mostly with the higher dose. AT the peak of osteoclasia, the bone surfaces undergoing remodeling were significantly decreased in the minocycline-treated groups. The resorption surface was reduced (P < 0.0003) as well as the number of osteoclasts (P < 0.0007), which were also significantly smaller. Their resorbing activity was dramatically affected as well: they excavated lacunae whose area was significantly reduced by over 70%. In addition, formation was still a prominent activity in the treated animals. These data are compatible with the inhibition at the early stages of activation of an osteoblast-secreted collagenase whose action may be the elimination of the osteoid seam. The inhibition of an osteoclast collagenase and/or of a bone matrix bound-collagenase may be responsible for the reduction in lacunar size. A direct effect of minocycline on osteoclast resorptive activity may also participate in the low resorption profile, as tetracyclines are known to interfere with the intracellular [Ca2+].

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.

Cortisol increases interstitial collagenase expression in osteoblasts by post-transcriptional mechanisms

Glucocorticoids regulate both bone formation and bone resorption. In osteoblasts, they inhibit type I collagen synthesis; however, there is limited information about their effects on interstitial collagenase, the enzyme that degrades type I collagen. We used primary cultures of osteoblast-enriched cells from fetal rat calvariae (Ob cells) to study the effects of cortisol on collagenase expression. Northern blot analysis showed that cortisol increased collagenase transcript levels in a dose- and time-dependent manner, which was paralleled by an increase in immunoreactive metalloproteinase in the culture medium. Cortisol increased the half-life of collagenase mRNA from 6 to 12 h in transcription-arrested Ob cells. In contrast, cortisol modestly decreased collagenase gene transcription after 24 h of treatment. The up-regulation of collagenase by cortisol is osteoblast-specific, since the glucocorticoid decreased phorbol 12-myristate 13-acetate-induced collagenase mRNA expression in rat fibroblasts, a result that agrees with other studies of collagenase gene regulation in fibroblastic cells. In conclusion, cortisol increases interstitial collagenase transcript levels by post-transcriptional mechanisms in osteoblastic cells. Our data demonstrate that glucocorticoids regulate collagenase gene expression in a novel tissue-specific manner, further highlighting the differences in gene regulation between osteoblastic and fibroblastic cells.