Direct extraction and assay of bone tissue collagenase and its relation to parathyroid-hormone-induced bone resorption

Dietary zinc reduces osteoclast resorption activities and increases markers of osteoblast differentiation, matrix maturation, and mineralization in the long bones of growing rats

The nutritional influence of zinc on markers of bone extracellular matrix resorption and mineralization was investigated in growing rats. Thirty male weanling rats were randomly assigned to consume AIN-93G based diets containing 2.5, 5, 7.5, 15 or 30 microg Zn/g diet for 24 days. Femur zinc increased substantially as zinc increased from 5 to 15 microg/g diet and modestly between 15 and 30 microg/g (P<.05). By morphological assessment, trabecular bone increased steadily as dietary zinc increased to 30 microg/g. Increasing dietary zinc tended to decrease Zip2 expression nonsignificantly and elevated the relative expression of metallothionen-I at 15 but not 30 microg Zn/g diet. Femur osteoclastic resorption potential, indicated by matrix metalloproteinases (MMP-2 and MMP-9) and carbonic anhydrase-2 activities decreased with increasing dietary zinc. In contrast to indicators of extracellular matrix resorption, femur tartrate-resistant acid and alkaline phosphatase activities increased fourfold as dietary zinc increased from 2.5 to 30 microg Zn/g. Likewise, 15 or 30 microg Zn/g diet resulted in maximum relative expression of osteocalcin, without influencing expression of core-binding factor alpha-1, collagen Type 1 alpha-1, or nuclear factor of activated T cells c1. In conclusion, increased trabecular bone with additional zinc suggests that previous requirement estimates of 15 microg Zn/g diet may not meet nutritional needs for optimal bone development. Overall, the up-regulation of extracellular matrix modeling indexes and concomitant decrease in resorption activities as dietary zinc increased from 2.5 to 30 microg/g provide evidence of one or more physiological roles for zinc in modulating the balance between bone formation and resorption.

Triphasic pattern in the ex vivo response of human proliferative phase endometrium to oestrogens

The aim of this study was to evaluate the ex vivo oestrogen responsiveness of human proliferative phase endometrium using short-term explant cultures. The effects of oestrogen (17beta-E2) on proliferation and the expression of oestrogen-responsive genes known to be involved in regulating endometrial function were evaluated. Three distinct response patterns could be distinguished: (1) the menstrual (M) phase pattern (cycle days 2-5), which is characterised by a complete lack in the proliferative response to 17beta-E2, while an increased expression of AR (2.6-fold, P<0.01), PR (2.7-fold, P<0.01) and COX-2 (3.5-fold, P<0.01) at the mRNA level was observed and a similar upregulation was also found for AR, PR and COX-2 at the protein level; (2) the early proliferative (EP) phase pattern (cycle days 6-10) with 17beta-E2 enhanced proliferation in the stroma (1.7-fold, P<0.05), whereas the expression of AR, PR and COX-2 were not affected at the mRNA and protein levels and ER-alpha mRNA and protein levels were significantly reduced by 17beta-E2; (3) the late proliferative (LP) phase pattern (cycle days 11-14), which is characterised by a moderate stimulation of proliferation (1.4-fold, P<0.05) and PR mRNA expression (1.7-fold, P<0.01) by 17beta-E2. In conclusion, three distinct response patterns to 17beta-E2 could be identified with respect to proliferation and the expression of known oestrogen-responsive genes in human proliferative phase endometrium explant cultures.

Low molecular weight inhibitors of matrix metalloproteinases can enhance the expression of matrix metalloproteinase-2 (gelatinase A) without inhibiting its activation

BACKGROUND

In the current study, the authors investigated the effects of synthetic low molecular weight inhibitors of matrix metalloproteinases (MMPs) on the expression and activation of MMP-2 in a three-dimensional tissue system.

METHODS

Rabbit periosteal explants were cultured with or without various concentrations of the MMP inhibitors CT1166, CT1399, or CT1746, and conditioned media and tissue extracts were analyzed for the expression and activity of MMP-2.

RESULTS

The data showed that blocking the activity of all MMPs with relatively high inhibitor concentrations completely prevented the conversion of pro-MMP-2 into its active form and that the level of protein was decreased. Selective inhibition of the activity of gelatinases (MMP-2 and MMP-9) by using low inhibitor concentrations, however, induced a higher level of active MMP-2 and increased its expression significantly.

CONCLUSIONS

The current observations indicate that selective inhibitors of MMPs affect the expression and activity of MMP-2, thus providing clues regarding the differing effects such inhibitors appear to have when applied in vivo.

Ectopic localization of matrix metalloproteinase-9 in chronic cutaneous wounds

It has been hypothesized that excessive activity of matrix metalloproteinases (MMPs), in particular the gelatinases MMP-9 and MMP-2, contributes to poor healing of chronic skin ulcers. We compared MMP-9 and MMP-2 in wound margin biopsies of standardized acute partial-thickness wounds in healthy volunteers (n = 6) and in venous leg ulcer patients (n = 12) with those of chronic wounds of different etiologies (n = 34) by a combination of specific analyses of activity and protein localization. We also studied MMP-14 by immunohistochemistry and in situ hybridization in parallel. Neither MMP-9 (P =.814) nor MMP-2 (P =.742) endogenous activities differed significantly between acute and chronic wound tissues. Acute wound healing was characterized by induction of MMP-9 in the advancing epithelium. In chronic wounds, prominent MMP-9 immunostaining was seen in neutrophils and macrophages in the ulcer bed, but virtually no MMP-9 was detected in wound edge keratinocytes. MMP-2 was increased and activated with acute wound age. MMP-2 was found abundantly in dermal fibroblasts and endothelial cells beneath, but not in new epithelium of acute and chronic wounds. MMP-14 mRNA or protein was detected solely in the stroma of both acute and chronic wounds. In conclusion, the overall activity of gelatinases MMP-9 and MMP-2 was not increased in chronic wounds compared to normally healing wound tissues. Chronic nonhealing wounds may not be caused by excessive gelatinase activity, but are distinguished from healing wounds by an unfavorable distribution and persistance of MMP-9.

Matrix metalloproteinase inhibitor BB-3103 unlike the serine proteinase inhibitor aprotinin abrogates epidermal healing of human skin wounds ex vivo

Several matrix metalloproteinases and serine proteinases are upregulated in migrating keratinocytes during cutaneous wound repair. Single cell culture studies indicate the necessity for matrix metalloproteinases but not for serine proteinases in keratinocyte locomotion. To account for epithelial-mesenchymal interactions, an ex vivo human skin wound model was used to investigate the contribution of matrix metalloproteinases and serine proteinases to wound healing by treatment with broad-spectrum inhibitors of matrix metalloproteinases (BB-3103) or serine proteinases (aprotinin). Human skin explants with circular 3 mm superficial defects were incubated in culture medium without (controls) or with the proteinase inhibitors for 7 d. BB-3103 abrogated epithelialization (p < 0.001), whereas aprotinin-treated wounds and controls were covered with new epithelium. Lack of epithelialization was unlikely due to cytotoxicity because the matrix metalloproteinase inhibitor did neither influence viability of cultured epidermal keratinocytes nor apoptosis in wounds. Involvement of specific matrix metalloproteinases in epithelialization was analyzed by gelatin zymography, western blotting, immunohistochemistry, and in situ hybridization. Wound healing was accompanied by active matrix metalloproteinase-1 and increased active matrix metalloproteinase-2 but irrespectively of active matrix metalloproteinase-9. BB-3103 blocked activation of matrix metalloproteinase-2 and matrix metalloproteinase-9 but not of matrix metalloproteinase-1. Active matrix metalloproteinase-2 localized solely to the dermis, whereas matrix metalloproteinase-9 was consistently found in new epithelium. Membrane-type 1 matrix metalloproteinase was undetectable in wound keratinocytes. BB-3103 and aprotinin reduced tumor necrosis factor-alpha in media but did not appreciably alter amounts of other soluble regulators of matrix metalloproteinases and epithelialization. Our findings demonstrate that keratinocyte migration is associated with active matrix metalloproteinase-2 but occurs independently of serine proteinases and active matrix metalloproteinase-9 in fibrin-deficient skin wound healing.

Topical synthetic inhibitor of matrix metalloproteinases delays epidermal regeneration of human wounds

Matrix metalloproteinases (MMPs) degrade extracellular proteins during epithelialization of wounds. To evaluate the biological significance of MMPs in epidermal healing, the synthetic broad-spectrum MMP inhibitor GM 6001 (also called Galardin and Ilomastat) was applied topically to standardized human wounds. GM 6001 (10 microg/microl) or vehicle alone was applied every second day onto 4 de-roofed 6 mm suction blister wounds on the volar forearm of healthy male volunteers for 12 days. GM 6001 delayed healing by 2-4 days as assessed macroscopically and microscopically. In situ hybridization or immunohistochemistry showed that MMP-1 (interstitial collagenase) was present in and MMP-2 (gelatinase A) close to laterally migrating keratinocytes whereas MMP-9 (gelatinase B) was seen during maturation of new epidermis. MMP-1 was undetectable in blister roofs (normal epidermis) and found in low levels in normal skin. Total MMP-1 activities increased about 100-fold in wounds, independent of treatment, compared to normal skin as analyzed by specific ELISA-based activity assay. By gelatin zymography, MMP-2, but not MMP-9, was detected in blister roofs and wound healing was associated with increased active MMP-2 and latent MMP-9 levels. GM 6001 prevented activation of MMP-2 and increased latent MMP-9 levels. GM 6001 delayed re-appearance of laminin-5, the synthesis of which correlated with epidermal regeneration. Restoration of stratum corneum, measured indirectly by transepidermal water loss, was also impaired (P<0.05) in the GM 6001 group. In conclusion, pharmacological MMP inhibition delayed epidermal regeneration in vivo, suggesting that MMPs are required to restore epidermis after epidermal ablation in humans.

In vivo perimenstrual activation of progelatinase B (proMMP-9) in the human endometrium and its dependence on stromelysin 1 (MMP-3) ex vivo

Most matrix metalloproteinases (MMPs) are secreted as inactive proenzymes. Their expression is well documented in several human tissues, but their activators in vivo are still unknown. To address this question, the activation of progelatinase B (proMMP-9) in the human endometrium was selected as a model system. ProMMP-9 was detected by gelatin zymography in homogenates of fresh endometrial tissue sampled during all phases of the menstrual cycle, whereas its active form was observed only during the late secretory and menstrual phases. Furthermore, proMMP-9 was expressed and activated in endometrial explants sampled outside the perimenstrual phase and cultured in the absence of both progesterone and oestradiol, mimicking the menstrual condition in vivo. Analysis of such tissue cultures by gelatin zymography and Western blotting showed that activation of proMMP-9 depended on a secreted factor and was selectively inhibited by either a synthetic inhibitor of stromelysin 1 (MMP-3) or a monoclonal antibody that specifically blocks MMP-3, thus providing strong evidence for the activation of proMMP-9 in vivo by MMP-3. The activation of proMMP-3 was itself inhibited by a broad-range MMP inhibitor in most cultures, but seemed to involve multiple pathways, implying both serine proteinases and metalloproteinases, which could operate in parallel or sequentially.

Involvement of fibronectin type II repeats in the efficient inhibition of gelatinases A and B by long-chain unsaturated fatty acids

The matrix metalloproteinases gelatinase A (MMP-2) and gelatinase B (MMP-9) are implicated in the physiological and pathological breakdown of several extracellular matrix proteins. In the present study, we show that long-chain fatty acids (e.g. oleic acid, elaidic acid, and cis- and trans-parinaric acids) inhibit gelatinase A as well as gelatinase B with K(i) values in the micromolar range but had only weak inhibitory effect on collagenase-1 (MMP-1), as assessed using synthetic or natural substrates. The inhibition of gelatinases depended on fatty acid chain length (with C18 > C16, C14, and C10), and the presence of unsaturations increased their inhibitory capacity on both types of gelatinase. Ex vivo experiments on human skin tissue sections have shown that micromolar concentrations of a long-chain unsaturated fatty acid (elaidic acid) protect collagen and elastin fibers against degradation by gelatinases A and B, respectively. In order to understand why gelatinases are more susceptible than collagenase-1 to inhibition by long-chain fatty acids, the possible role of the fibronectin-like domain (a domain unique to gelatinases) in binding inhibitory fatty acids was investigated. Affinity and kinetic studies with a recombinant fibronectin-like domain of gelatinase A and with a recombinant mutant of gelatinase A from which this domain had been deleted pointed to an interaction of long-chain fatty acids with the fibronectin-like domain of the protease. Surface plasmon resonance studies on the interaction of long-chain fatty acids with the three individual type II modules of the fibronectin-like domain of gelatinase A revealed that the first type II module is primarily responsible for binding these compounds.

Matrix metalloproteinase 9 and vascular endothelial growth factor are essential for osteoclast recruitment into developing long bones

Bone development requires the recruitment of osteoclast precursors from surrounding mesenchyme, thereby allowing the key events of bone growth such as marrow cavity formation, capillary invasion, and matrix remodeling. We demonstrate that mice deficient in gelatinase B/matrix metalloproteinase (MMP)-9 exhibit a delay in osteoclast recruitment. Histological analysis and specialized invasion and bone resorption models show that MMP-9 is specifically required for the invasion of osteoclasts and endothelial cells into the discontinuously mineralized hypertrophic cartilage that fills the core of the diaphysis. However, MMPs other than MMP-9 are required for the passage of the cells through unmineralized type I collagen of the nascent bone collar, and play a role in resorption of mineralized matrix. MMP-9 stimulates the solubilization of unmineralized cartilage by MMP-13, a collagenase highly expressed in hypertrophic cartilage before osteoclast invasion. Hypertrophic cartilage also expresses vascular endothelial growth factor (VEGF), which binds to extracellular matrix and is made bioavailable by MMP-9 (Bergers, G., R. Brekken, G. McMahon, T.H. Vu, T. Itoh, K. Tamaki, K. Tanzawa, P. Thorpe, S. Itohara, Z. Werb, and D. Hanahan. 2000. Nat. Cell Biol. 2:737-744). We show that VEGF is a chemoattractant for osteoclasts. Moreover, invasion of osteoclasts into the hypertrophic cartilage requires VEGF because it is inhibited by blocking VEGF function. These observations identify specific actions of MMP-9 and VEGF that are critical for early bone development.

Mouse fibroblasts in long-term culture within collagen three-dimensional scaffolds: influence of crosslinking with diphenylphosphorylazide on matrix reorganization, growth, and biosynthetic and proteolytic activities

With the rapid development of tissue engineering and gene therapy, collagen-based biomaterials frequently are used as cell transplant devices. In this study we determined the behavior of mouse fibroblasts cultured for up to 6 weeks in control sponges treated by severe dehydration and used commercially as hemostatic agents and in two sponges (DPPA 2 and 3) crosslinked by diphenylphosphorylazide, a method developed in our laboratory. Growth capacity, biosynthetic and proteolytic activities, and matrix reorganization were followed over time in cultures and compared with similar data for fibroblasts in monolayer culture on plastic and in floating or attached collagen gels. Control sponges with and without seeded mouse fibroblasts showed rapid partial denaturation or contraction, weight loss, and severe calcification (13-18% Ca) after 6 weeks. In contrast, the crosslinked sponges showed only slightly decreased size and weight, and the calcification was inhibited (0.2% Ca) in the presence of cells. Mouse fibroblasts seeded on the crosslinked sponge surface at 50,000-200,000 cells/cm(2) progressively penetrated the matrix and proliferated to give the same constant cell density after 3 weeks (around 600,000 cells/sponge). A specific, two- to threefold decrease in collagen synthesis was observed between 1 and 3 or 6 weeks, due mainly to a decrease in the fraction secreted into the medium (25-30% instead of 45-50%). No collagenase 3 activity was detected in the culture medium under any condition or time whereas 25% gelatinase A was found by gelatin zymography to be in an active form in cultures within sponges as compared with less than 10% in monolayers and more than 50% in floating collagen gel. A small amount of gelatinase B was observed after 1 week in sponge cultures and was completely absent thereafter. These results show that the biosynthetic and proteolytic behavior of mouse fibroblasts cultured in crosslinked collagen scaffolds is different from that in monolayers or in floating collagen gels and more similar to that previously described in attached collagen gels.

In situ hybridization for matrix metalloproteinase-1 and cathepsin K in rat root-resorbing tissue induced by tooth movement

The movement of teeth during orthodontic treatment occasionally induces undesirable root resorption. Although high collagenolytic activity has been detected in resorbing tissue of deciduous teeth, the cellular origin of collagenolytic enzymes in root-resorbing tissue caused by tooth movement has not been identified. Here, rats were subject to 7 days of experimental tooth movement to induce root resorption. In situ hybridization with digoxigenin-labelled RNA probes was performed on sections of the maxillary bone to detect the mRNAs that encode matrix metalloproteinase-1 (MMP-1) and cathepsin K in root-resorbing tissue. MMP-1 mRNA was detected in fibroblastic cells, cementoblasts and osteoblasts, but not in odontoclasts nor osteoclasts. Moreover, MMP-1 mRNA was highly expressed in some cementocytes located near odontoclasts and in many osteocytes. In contrast, cathepsin K mRNA was expressed only in odontoclasts and osteoclasts. These results suggest that MMP-1 and cathepsin K are important in root resorption during tooth movement in a mode similar to bone resorption.

Collagen breakdown in soft connective tissue explants is associated with the level of active gelatinase A (MMP-2) but not with collagenase

Recent data suggest that gelatinase A (matrix metalloproteinase-2, MMP-2) plays an important role in the degradation of collagen of soft connective tissues. In an attempt to investigate its participation in more detail we assessed the digestion of collagen in cultured rabbit periosteal explants and compared this with the level of active MMP-2 and collagenases. The data demonstrated that both collagen degradation and MMP activity increased with time. Conditioned medium obtained from explants cultured for 72 h showed that the level of active MMP-2 correlated with collagen degradation (r = 0.80, d.f. = 23, P < 0.0001). Such a relationship was not found with collagenase activity (r = -0.08, d.f. = 21, NS). The possible involvement of MMP-2 in collagen degradation was investigated further by incubating explants with selective gelatinase inhibitors (CT1166, CT1399 and CT1746). In the presence of these compounds breakdown of collagen was almost completely abolished (approximately 80%). Finally we assessed whether periosteal fibroblasts had the capacity to degrade collagen type I that conferred resistance to collagenase activity. Breakdown of this collagen did not differ from degradation of normal collagen. Taken together, our data provide support for the view that MMP-2 plays a crucial role in collagen degradation of soft connective tissue.

The role of the plasminogen system in bone resorption in vitro

The plasminogen/plasmin proteolytic cascade plays an important role in extracellular matrix remodeling. The presence of the two plasminogen activators (PAs), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA), and their inhibitor type 1 (PAI-1) in bone cells, suggests a role in one or more aspects of bone resorption such as osteoclast formation, mineral dissolution, and degradation of the organic matrix. These different processes were assayed in vitro using cells derived from mice with either tPA (tPA-/-), uPA (uPA-/-), PAI-1 (PAI-1-/-) inactivation or with a combined inactivation (tPA-/-:uPA-/-) and compared with wild-type mice (WT). First, osteoclast formation, assessed by investigating the number and characteristics of tartrate-resistant acid phosphatase-positive multinucleated cells formed in cocultures of primary osteoblasts and bone marrow cells treated with 1alpha,25-dihydroxyvitamin D3, was not different between the different cell types. Second, dentine resorption, an assay for osteoclast activity, was not affected by the combined deficiency of both tPA and uPA. Finally, the ability to degrade nonmineralized bone-like matrix was however, significantly reduced in tPA-/-:uPA-/- cells compared with WT cells (28.1 +/- 0.6%, n = 6 vs. 56.4 +/- 3.1%, n = 6, respectively, p < 0.0001). Surprisingly, collagen proteolysis by bone cells was not dependent on the presence of plasmin as suggested by degradation assays performed on type I 3H-collagen films. Taken together, these data suggest that the plasminogen activator/plasmin system is not required for osteoclast formation, nor for the resorption of the mineral phase, but is involved in the removal of noncollagenous proteins present in the nonmineralized bone matrix.

Effects of continuous infusion of PTH on experimental tooth movement in rats

Development of new methods for accelerating orthodontic tooth movement has been strongly desired for shortening of the treatment period. The rate of orthodontic tooth movement is dependent on the rate of bone resorption occurring in the compressed periodontium in the direction of orthodontic force applied to the tooth. In the present study, we examined the effects of continuous infusion of parathyroid hormone (PTH) on tooth movement. Male rats weighing 350-400 g were treated with subcutaneous of vehicle or hPTH(1-84) at 1-10 micrograms/100 g of body weight/day. When the upper right first molar (M1) was moved mesially for 72 h by the insertion of an elastic band between the first and second molars, M1 movement was accelerated by PTH infusion at 10 micrograms. PTH infusion caused a 2- to 3-fold increase in the number of osteoclasts in the compressed periodontium of M1, indicating that such treatment accelerated tooth movement by enhancing bone resorptive activity induced in the compressed periodontium. When M1 was moved mesially by an orthodontic coil spring ligated between upper incisors and M1 for 12 days, PTH(1-84) infusion at 10 micrograms caused a 2-fold increase in the rate of M1 movement. PTH(1-34) infusion at 4 micrograms had an effect comparable to that of PTH(1-84). However, intermittent injection of PTH(1-34) did not accelerate M1 movement. PTH infusion for 13 days did not affect either bone mineral measurements or the serum calcium level. These findings suggest that continuous administration of PTH is applicable to accelerate orthodontic tooth movement.

Local cytokines induce differential expression of matrix metalloproteinases but not their tissue inhibitors in human endometrial fibroblasts

The endometrium is the only human tissue to undergo cyclic breakdown and regeneration. This physiological alternation renders it an advantageous system for studying tissue remodelling. Our previous observations indicate that menstrual endometrial breakdown is initiated by matrix metalloproteinases (MMPs), which are controlled overall by ovarian steroids but are also locally regulated by cytokines. We have therefore compared the effect of several endometrial cytokines on the gene expression of eight MMPs and their tissue inhibitors (TIMP)-1, -2 and -3, in primary cultures of human endometrial fibroblasts. Three categories of gene expression were identified: (a) MMP-13, -15 and -16 mRNAs were not detected despite stimulation by various cytokines; (b) MMP-2 and -14 as well as TIMP-1, -2 and -3 mRNAs were constitutively expressed but not markedly affected by the six cytokines tested; (c) mRNAs for MMP-1, -9 and -11 were selectively induced by specific cytokines: insulin-like growth factor-II, epidermal growth factor (EGF), platelet derived growth factor (PDGF)-BB and interleukin (IL)-6 stimulated MMP-11 expression; MMP-1 was induced by EGF, PDGF-BB, tumour necrosis factor (TNF)alpha and IL-1alpha, which also exerted additive effects. In contrast with MMP-1 and MMP-11 gene expression, which was sustained for 48 h, MMP-9 mRNA was quickly induced by TNFalpha, but disappeared within 12 h despite continuing stimulation. These results show that several cytokines are able to induce the selective expression of MMPs in cultured human endometrial fibroblasts and are thus good candidates for involvement in local triggering of menstrual tissue breakdown.

Differential regulation of MMP-13 (collagenase-3) and MMP-3 (stromelysin-1) in mouse calvariae

Bone resorption in mice involves the degradation of extracellular matrix. Whereas several proteases seem to be implicated in this process, it becomes increasingly clear that matrix metalloproteinases (MMPs), amongst them especially MMP-13 and MMP-3, play an essential role. We have purified MMP-13 and MMP-3 from mouse calvariae-conditioned media by differential fractionation and analyzed their collagenolytic, caseinolytic, gelatinolytic and proteoglycanolytic activities. It could be shown that in mouse calvariae-conditioned media most of the measured enzyme activities were due to MMP-13, although zymographies revealed that MMP-3, MMP-2, MMP-9 as well as TIMPs were present too. MMP-13 and MMP-3 proteins were detected and their enzyme activities were neutralized by specific polyclonal antisera. Furthermore, it was demonstrated that in cultures of mouse calvariae the production of MMP-13 was induced by the potent MMP-stimulator heparin and by parathyroid hormone (PTH), whereas the levels of MMP-3 remained unchanged. Although PTH-induced bone resorption was inhibited by calcitonin treatment, MMP-13 mRNA and protein expression were not significantly altered by this hormone. Together with previous observations, these results indicate that PTH regulates bone resorption through MMP-13, but not by MMP-3, and that its reversion by calcitonin involves neither of the two enzymes.

Involvement of V-ATPases in the digestion of soft connective tissue collagen

The contribution of vacuolar H+-ATPases (V-ATPases) to collagen degradation was investigated in soft connective tissue explants (periosteum). Immunolocalisation showed faint to intense staining of cells throughout the periosteum. The V-ATPase inhibitors, bafilomycin A1 and folimycin, decreased overall collagen degradation by 40 and 50% after 24 and 48 h, respectively. The participation of V-ATPases in intracellular degradation of collagen was demonstrated by the decrease of the amount of phagocytosed collagen in fibroblasts upon inhibition of pump activity. The inhibition of degradation was not due to a reduction in activity of gelatinase A, an enzyme previously found to mediate collagen degradation, as assessed by zymographic analysis of tissue and conditioned medium. Bafilomycin A1 even induced an increase of gelatinase A and B levels in both fractions. In conclusion, acidification by V-ATPases may represent an important mechanism in extracellular and intracellular collagen degradation in soft connective tissue.

Gelatinase A (MMP-2) and cysteine proteinases are essential for the degradation of collagen in soft connective tissue

The degradation of soft connective tissue collagen is considered to depend on the activity of various proteolytic enzymes, particularly those belonging to the group of matrix metalloproteinases and cysteine proteinases. In the present study, we investigated the contribution of these enzymes to this process. Using a general inhibitor of MMPs (SC44463), collagen degradation was strongly inhibited, by about 40% after 24 h and up to 80% after 72 h of culturing. Blockage of cysteine proteinase activity (with leupeptin or E-64) reduced breakdown at these time intervals by 50% and 20%, respectively. Given the abundant presence of gelatinases--in particular gelatinase A (MMP-2)--in the tissue, the effect of an inhibitor selective for gelatinases (CT1166) was studied. Gelatinase inhibition resulted in a dose-dependent decrease of collagen breakdown up to 90% after 48 h. The ability of gelatinase A to degrade collagens was demonstrated by the induction of breakdown in devitalized explants by addition of activated gelatinase A, or by activation of endogenous enzyme with 4-aminophenylmercuric acetate. This latter effect was not found with plasmin, an activator of MMPs other than gelatinase A. Finally, the relevance of gelatinase A to the in vivo degradation of soft connective tissue collagen was implicated by the significant correlation found between its activity and the collagen turnover rates of four soft connective tissues (tooth pulp, periodontal ligament, molar gingiva and skin). We conclude that collagen degradation in soft connective tissue is mediated by MMPs and to a lesser extent by cysteine proteinases. Our data are the first to attach a key role to gelatinase A in this process.

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.

Paracrine stimulation of interstitial collagenase (MMP-1) in the human endometrium by interleukin 1alpha and its dual block by ovarian steroids

In the cycling human endometrium, the expression of interstitial collagenase (MMP-1) and of several related matrix metalloproteinases (MMPs) follows the late-secretory fall in sex steroid plasma concentrations and is thought to be a critical step leading to menstruation. The rapid and extensive lysis of interstitial matrix that precedes menstrual shedding requires a strict control of these proteinases. However, the mechanism by which ovarian steroids regulate endometrial MMPs remains unclear. We report here that, in the absence of ovarian steroids, MMP-1 expression in endometrial fibroblasts is markedly stimulated by medium conditioned by endometrial epithelial cells. This stimulation can be prevented by antibodies directed against interleukin 1alpha (IL-1alpha) but not against several other cytokines. Ovarian steroids inhibit the release of IL-1alpha and repress MMP-1 production by IL-1alpha-stimulated fibroblasts. In short-term cultures of endometrial explants obtained throughout the menstrual cycle, the release of both IL-1alpha and MMP-1 is essentially limited to the perimenstrual phase. We conclude that epithelium-derived IL-1alpha is the key paracrine inducer of MMP-1 in endometrial fibroblasts. However, MMP-1 production in the human endometrium is ultimately blocked by ovarian steroids, which act both upstream and downstream of IL-1alpha, thereby exerting an effective control via a "double-block" mechanism.

Expression of gelatinases within the trabecular bone compartment of ovariectomized and parathyroidectomized adult female rats

Ovariectomized (ovx) and parathyroidectomized (ptx) rat models of disturbed bone metabolism have been widely used in evaluating bone changes resulting from hormonal depletion, and are characterized by elevated and depressed bone turnover, respectively. We report here the expression of gelatinases extracted from native trabecular bone in these models. Nine-month-old female Sprague-Dawley rats were sacrificed after 3 weeks following ovx or 10 days post ptx to determine the influence of these procedures on the levels of proximal tibial bone tissue gelatinases. Identification and quantitation of these enzymes were performed via gelatin gel zymography of native tissue extracts and laser densitometry of developed gels, respectively. In the ptx model, a reduction in tissue levels of pro- and active-MMP-2 and a 45 kDa activated fragment was seen, whereas ovx exhibited significant increases in these enzymes. The MMPs are therefore clearly under the influence of factors known to modulate bone remodeling in vivo. The study of MMP levels directly extracted from bone using these experimental models may assist in developing management regimes for metabolic bone diseases through the use of drugs aimed at controlling turnover.

The recombinant catalytic domain of mouse collagenase-3 depolymerizes type I collagen by cleaving its aminotelopeptides

The sequence coding for the catalytic domain of mouse collagenase-3 (MMP-13) was amplified by polymerase chain reaction and expressed in Escherichia coli. The recombinant catalytic domain (CCD), mainly recovered as inclusion bodies, was renatured and purified to homogeneity by preparative SDS-PAGE. The purified CCD degraded gelatin, casein and a synthetic peptide. CCD was not able to cleave the triple-helical domain of type I collagen but conserved the specific property of full-length collagenase-3 to cleave the N-telopeptides. These results show that residues involved in the recognition and cleavage of the aminotelopeptides of type I collagen are located in the catalytic domain of mouse collagenase-3 and that the C-terminal domain is not required for this activity.

Cytokine-induced endogenous procollagenase stored in the extracellular matrix of soft connective tissue results in a burst of collagen breakdown following its activation

Numerous data strongly suggest the involvement of cytokines and the matrix metalloproteinase collagenase (MMP-1) in the pathogenesis of periodontitis. Recently, we have demonstrated that, upon culturing under the influence of IL-1 alpha + EGF, a large amount of inactive procollagenase (MMP-1) is stored in the extracellular matrix of periosteal tissue. We now show that this endogenous reservoir of proenzyme can be operative after activation with plasmin and is able to induce a rapid and almost complete breakdown of the collagenous extracellular matrix. The level of collagen degradation following activation showed a strong correlation with the amount of proenzyme that was incorporated in the tissue. The highest level of degradation (70% of the total amount of collagenous proteins) was found with the IL-1 alpha + EGF-treated explants, followed by those treated with IL-1 alpha alone (35%). Explants cultured with EGF or in the absence of cytokines, containing only small amounts of procollagenase, showed little collagen breakdown following plasmin activation (7%). Inhibition of metalloproteinases by EDTA, or blockage of plasmin by PMSF, prevented the degradation in all explants irrespective of the amount of proenzyme present in the tissue. Our findings demonstrate that endogenous proenzyme stored in a native connective tissue matrix can be activated at a later time interval which results in a massive breakdown of the tissue. This study shows a possible pathway of collagenase-induced breakdown without recent de novo synthesis of the enzyme. Such a sequence may be operative in chronic inflammatory diseases, such as periodontitis, where production of procollagenase under the influence of cytokines spans a longer time period, whereas breakdown is often characterized by a cyclic behaviour.

Expression of matrix metalloproteinase 9 (96-kd gelatinase B) in human rheumatoid arthritis

OBJECTIVE

To determine the expression of matrix metalloproteinase 9/gelatinase B (MMP-9) in synovial fluid (SF), plasma, and synovial tissue from individuals with rheumatoid arthritis (RA), inflammatory arthritis (IA), and osteoarthritis (OA), using specific monoclonal antibody reagents.

METHODS

Gelatinolytic activity in the SF and plasma of patients with RA, IA, and OA was assessed by gelatin zymography. A mouse monoclonal antiserum, 277.13, which selectively recognizes soluble latent forms of human MMP-9, was used to quantitate MMP-9 levels in patient synovial effusions, plasma, and synovial tissue with a capture sandwich enzyme-linked immunosorbent assay (ELISA). Fifty-one SF samples (31 RA, 9 OA, 11 IA) were analyzed. Immunolocalization of MMP-9 in RA, OA, and normal synovium was investigated using MMP-9-specific antisera.

RESULTS

MMP-9 antigen levels in synovial effusions were elevated 67-fold in RA samples compared with OA samples. In addition, although MMP-9 antigen levels in IA synovial effusions were 2.7-fold less than the values in RA samples, they were elevated 34-fold over the values in OA samples. These data indicate an association between increased MMP-9 levels and inflammatory arthritis. A predominant 92-kd gelatinolytic activity (specifically inhibited by EDTA) was evident in RA and IA samples, but no activity was observed in OA samples. Among 86 plasma samples (17 RA, 9 IA, 60 normal controls) analyzed for MMP-9 antigen levels by immunocapture ELISA, MMP-9 antigen levels were elevated 7-fold in RA plasma compared with normal plasma. RA synovial tissue extracts demonstrated elevated levels of MMP-9 antigen compared with OA synovial tissue. MMP-9 immunolocalization studies demonstrated expression in infiltrating leukocytes (neutrophils and macrophages), endothelial cells, and synovial fibroblasts in RA synovium.

CONCLUSION

Latent MMP-9 and/or MMP-9-tissue inhibitor of metalloproteinases 1 (TIMP-1) complexes are elevated in RA and IA SF compared with OA SF. In addition, MMP-9 is increased in RA plasma versus normal control plasma. Synovial tissue levels of MMP-9 antigen are also elevated in RA versus OA. The tissue distribution of MMP-9 within RA synovium is localized to sites of inflammation comprising surface synovial lining cells, endothelium, and leukocytes. Taken together, these observations suggest that connective tissue turnover occurs as a result of excessive MMP activity over TIMP action in the invading pannus, periarticular tissue, or SF. Further studies such as those used in the present investigation will help elucidate the role of a number of different enzymes and inhibitors in the destructive arthropathies.

Cytokines modulate phagocytosis and intracellular digestion of collagen fibrils by fibroblasts in rabbit periosteal explants. Inverse effects on procollagenase production and collagen phagocytosis

Degradation of fibrillar collagen may occur in the extracellular space by enzymes, such as the metalloproteinase collagenase, or in the lysosomal apparatus of fibroblasts following phagocytosis. As the mechanisms involved in the regulation of the latter process are unknown, we investigated possible modulating effects of the cytokines epidermal growth factor (EGF), platelet-derived growth factor (PDGF), interleukin-1 alpha (IL-1 alpha) and transforming growth factor-beta (TGF-beta) on both collagen phagocytosis and the release of collagenase in an in vitro model employing periosteal tissue explants. The data demonstrated that the level of intracellular collagen digestion could be influenced by cytokines: IL-1 alpha inhibited and TGF-beta enhanced phagocytosis of fibrillar collagen by periosteal fibroblasts, whereas the cytokines had an opposite effect on the release of procollagenase. In combination, IL-1 alpha and TGF-beta proved to have an antagonizing effect on either parameter. PDGF and EGF had no effect on phagocytosis or collagenase release. The level of phagocytosed collagen correlated positively with the actual breakdown of collagen as assessed by the release of hydroxyproline but negatively with the level of released procollagenase. Our findings demonstrated that cytokines are able to modulate both the phagocytosis of collagen fibrils by fibroblasts and their subsequent intracellular breakdown, as well as the release of procollagenase, an enzyme considered crucial for extracellular collagenolysis. Moreover, our data show a negative correlation between these two parameters. It is concluded that IL-1 alpha, EGF and TGF-beta may be important in modulating the contribution of the intracellular and extracellular route of collagen breakdown.

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.

Cloning and complete coding sequence of a novel human cathepsin expressed in giant cells of osteoclastomas

A gene encoding a possible novel human cathepsin, a cysteine proteinase that is distinct from previously characterized enzymes, has been identified by differential screening of a human osteoclastoma cDNA library. This molecule, termed cathepsin X, appears to represent the human homolog of the osteoclast-expressed rabbit cathepsin OC-2. Cathepsin X (GenBank accession number U20280) is 93.9% identical to OC-2 at the amino acid level, and is 92% identical at the nucleotide level within the coding region. Cathepsin X is 52.2 and 46.9% identical to cathepsins S and L, respectively, and is therefore clearly distinct from these enzymes. Cathepsin X mRNA was localized to multinucleated giant cells within the osteoclastoma tumor by in situ hybridization. These data strongly support the hypothesis that cathepsin X represents a novel cysteine proteinase which is expressed at high levels in osteoclasts.

Localisation of mRNA for collagenase in osteocytic, bone surface and chondrocytic cells but not osteoclasts

Osteoclasts resorb the extracellular matrix of bone by secreting protons and enzymes into a circumpherentially sealed compartment between the osteoclast and the bone surface. Although the lysosomal cysteine proteinases play a major role in matrix degradation by osteoclasts, collagenase (matrix metalloproteinase-1, EC 3.4.24.7) is also required for osteoclastic bone resorption, and may be directly involved in collagen degradation in the hemivacuole. We assessed the effects of inhibitors of cysteine proteinases and collagenase on bone resorption by osteoclasts isolated from rodent bone. We found that while inhibition of cysteine proteinases strongly suppressed osteoclastic resorption, inhibitors of collagenase were without effect on the number, size, or demineralised fringe of excavations. We could find no evidence of expression of mRNA for collagenase in rat osteoclasts by in situ hybridisation, but found that it was expressed by chondrocytes, bone surface cells and osteocytes adjacent to osteoclasts. The distribution of these cells, and the correlation between increased collagenase production and increased stimulation of osteoclastic resorption in vitro by bone cells, suggests that these cells might be involved in the regulation of bone resorption in situ, and that collagenase production might play a role in this process.

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.

Expression of interstitial collagenase is restricted to skeletal tissue during mouse embryogenesis

Collagenases are thought to be involved in physiological and pathological processes that require extracellular matrix remodeling. Using the in situ hybridization technique, we describe the expression of interstitial collagenase gene during mouse embryogenesis between E6.5 and E17. We demonstrate that interstitial collagenase expression is exclusively detected in one event, namely the onset of bone formation. Transcripts accumulate in hypertrophied chondrocytes, found in the mature cartilaginous matrix of long-bone growth plates or ribs, and in osteoblasts and/or in endothelial cells that have migrated into the shafts of developing long bones. The expression of the tissue inhibitor of metalloproteinases (TIMP-2) gene precedes the expression of interstitial collagenase in developing bones. These data suggest that interstitial collagenase plays a specific role in bone development and that the tight regulation of its activity during development is achieved not only by post-translational mechanisms with TIMPs, as previously suggested, but also at the transcriptional level.

The expression of interstitial collagenase in human endometrium is controlled by progesterone and by oestradiol and is related to menstruation

Human endometrial tissue, sampled at different periods of the reproductive cycle, expressed interstitial collagenase mRNA, protein and activity only just before and during the menstrual period. This clear-cut correlation and the inhibition of collagenase expression by progesterone and oestradiol in tissue culture point to a pivotal role of this proteinase in the mechanism of menstrual tissue breakdown and bleeding.

Action of metalloproteinases on porcine dentin mineralization

Samples containing predentin and mineralized dentin involving the mineralized front (newly formed dentin) were prepared by scraping developing porcine teeth after odontoblastic cell debris had been removed from the predentin surfaces. An extract was obtained separately from the matrices of predentin and of the newly formed dentin with a 4 M guanidine solution before and after demineralization with acetic acid solution. Enzymography detected 56 and 61 kDa gelatinases and 25 kDa proteoglycanase as neutral metalloproteinases in both extracts and proved them to be in an active form. Approximately half of the 56 and 61 kDa gelatinases binds to collagen fibers in predentin matrix. Three high molecular weight proteoglycans (70-85 kDa, 130-180 kDa, and 290 kDa) were found in the predentin matrix, but not in the newly formed dentin. The proteoglycanases in predentin degraded 290 kDa proteoglycan, if incubated together with calcium (Ca) ions. The results of this investigation indicate that active proteoglycanases which existed in the predentin perform no substantial work in proteoglycan degradation because the Ca ions are masked in the predentin matrix by coexisting proteoglycans. When mineralization occurs, however, they can degrade the proteoglycan at the mineralization front because excess Ca ions may be supplied via odontoblastic processes.

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 &lt; 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.

Immunolocalisation of collagenase in rabbit periosteal tissue explants and extraction of the enzyme. The effect of the cytokines IL-1 alpha and EGF

The effect of interleukin-1 alpha (IL-1 alpha) and murine epidermal growth factor (EGF) on incorporation of endogenously produced collagenase in the extracellular matrix of soft connective tissue was studied in an in vitro model system using periosteal explants obtained from rabbit calvariae. Immunohistochemical analysis indicated the highest level of collagenase in explants cultured for 72 hours with IL-1 alpha in combination with EGF. Most enzyme appeared to be associated with the extracellular matrix, but labeling was also found in numerous fibroblast-like cells. Explants cultured in the presence of IL-1 alpha alone contained less enzyme and in periostea treated without cytokines, or with EGF alone, only a faint label, if any, was seen. Freshly isolated, non-cultured periostea contained no detectable enzyme. Extraction of collagenase from periostea revealed that: (1) non-cultured periosteum did not contain detectable levels of enzyme. (2) The amount of total activatable enzyme synergistically increased (10-fold) under the influence of IL-1 alpha and EGF, whereas IL-1 alpha alone showed a 4-fold enhancement compared to control or EGF-incubated explants. (3) The latent fraction of the enzyme was synergistically increased (up to 100-fold or more) in periostea cultured in the presence of IL-1 alpha + EGF (21.17 mU/explant versus 0.05 mU/explant in controls). (4) Active collagenase, on the other hand, appeared to be present in a relatively high concentration in explants cultured without cytokines (2.45 mU/explant versus 0.36 mU/explant in IL-1 alpha + EGF-treated explants).(ABSTRACT TRUNCATED AT 250 WORDS)

(Pro)collagenase (matrix metalloproteinase-1) is present in rodent osteoclasts and in the underlying bone-resorbing compartment

Osteoclasts resorb the extracellular matrix of bone by secreting enzymes and acid into a sealed-off compartment that they form upon attachment to the bone surface. Although the lysosomal cysteine proteinases can degrade collagen after the demineralization of bone at low pH, several lines of evidence suggest that collagenase (matrix metalloproteinase-1, EC 3.4.24.7) may also be involved in this process. The question of whether collagenase is present in the osteoclast and/or in the bone-resorbing compartment has however not been resolved. We have prepared an anti-mouse collagenase antiserum and affinity-purified an IgG fraction that specifically immunoblots and immunoprecipitates (pro)collagenase. Using these antibodies, we demonstrate by immunolocalization the presence of (pro)collagenase both in the osteoclasts and in the extracellular subosteoclastic bone-resorbing compartment. These specific localizations were observed not only in mice but also in rat and rabbit osteoclasts and using not only the antibody we have prepared but also antibodies raised in other laboratories against rat (Jeffrey et al., J. Cell. Physiol. 143, 396–403, 1990) and rabbit (Brinckerhoff et al., J. Biol. Chem. 265, 22262–22269, 1990) collagenase. Intracellular collagenase was observed in the osteoclasts whether the cells were plated on bone or cultured on glass coverslips. It is proposed that osteoclastic collagenase is secreted in the resorbing compartment where it may cooperate with the lysosomal cysteine proteinases in the degradation of the collagen component of the matrix during the resorption of bone.

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

Recombinant human TIMP-1 and TIMP-2 (tissue inhibitors of metalloproteinases) inhibited bone resorption induced by either parathyroid hormone or 1,25-dihydroxyvitamin D3 in cultured neonatal mouse calvariae. The inhibition was reversible, dose-dependent and complete at 1 microgram/ml inhibitor concentration. TIMP-2 was more potent than TIMP-1. TIMP-1 and TIMP-2 also inhibited basal bone resorption. Neither metalloproteinase inhibitor affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase or the spontaneous release of lactate dehydrogenase. These results suggest that endogenous TIMPs play a central role in regulating both physiological and pathological bone resorption.

Progesterone regulates the activity of collagenase and related gelatinases A and B in human endometrial explants

Explants of human endometrium were cultured to study the release of matrix metalloproteinases (MMPs). Analysis of conditioned media by zymography revealed latent and active forms of collagenase (MMP-1, EC 3.4.24.7), 72-kDa gelatinase A (MMP-2, EC 3.4.24.24), and 92-kDa gelatinase B (MMP-9, EC 3.4.24.35). These proteinases were identified by their M(r), their inhibition by tissue inhibitor of metalloproteinases, and the activation of their zymogens by trypsin or aminophenylmercuric acetate. In the absence of sex hormone, explants released large amounts of enzyme activities, as measured by densitometry of zymograms or in soluble assays. Physiological concentrations of progesterone (10-200 nM) almost totally abolished the release of collagenase, of total gelatinase activity, and of the active form of gelatinase B and largely inhibited the release of the active form of gelatinase A. These effects, which were antagonized by mifepristone (RU 38486), suggest that progesterone restrains endometrial tissue breakdown by blocking the secretion and activation of MMPs.

An active neutral metalloproteinase bound to the insoluble collagen in the mineralized phase matrix of adult rat calvaria

Two kinds of proteinases were found in the mineralized phase matrix of 24-week-old rat calvaria by means of enzymography using gelatin as a substrate. One proteinase was a neutral thiol 58kD proteinase as shown in a previous paper [2]. The other was a neutral metalloproteinase that had a molecular mass of 56kD and was detected only when calcium (Ca) ions were added to the incubation buffer. It is believed that the 56kD proteinase is bound to the insoluble collagen of the bone matrix, as it is solubilized by 4 M guanidine HC1 solution from the insoluble collagen fraction, when prepared by removing extractable proteins of the mineralized phase matrix. The insoluble collagen fraction could also be solubilized and prepared as gelatin by heating at 65 degrees C for 5 minutes. The gelatin was then incubated at 37 degrees C without further treatment and became degraded without an activation of 4-aminophenylmercuric acetate (APMA). This nonactivated degradation was enhanced by adding Ca ions. These results suggest that the 56kD metalloproteinase bound to the insoluble collagen of bone matrix is in an active form and may participate in the rapid degradation of collagen during bone resorption. As partially purified 56kD metalloproteinase degraded cartilage type proteoglycan, but not type I, IV, and V collagens, it is possibly related to the degradation of proteoglycans before it binds to collagen fibers during bone formation.

Degradation of collagen in the bone-resorbing compartment underlying the osteoclast involves both cysteine-proteinases and matrix metalloproteinases

The site of action of cysteine-proteinases (CPs) and matrix metalloproteinases (MMPs) in the degradation of bone collagen by osteoclasts was investigated by evaluating the effects of the CP-inhibitor trans-epoxy-succinyl-L-leucylamido (4-guanidino)-butane (E-64) and the MMP-inhibitor N-(3-N-benzyloxycarbonyl amino-1-R-carboxypropyl)-L-leucyl-O-methyl-L-tyrosine N-methylamide (Cl-1) in an in vitro model system of PTH-stimulated mouse calvaria. In the presence of each of the two inhibitors a large area of collagen free of mineral crystallites was seen adjacent to the ruffled border of the osteoclasts. Following a culture period of 24 h this area proved to be about 10 times larger in inhibitor-treated explants than in controls. Moreover the percentage of osteoclasts in close contact with such demineralized bone areas appeared to be significantly higher in inhibitor-treated explants than in control specimens (60% and 5%, respectively). These effects were not apparent when the osteoclastic activity was inhibited with calcitonin. No significant differences were found between the effects of the two inhibitors, E-64 and Cl-1. Our observations indicate that under the influence of inhibitors of MMPs and CPs demineralization of bone by osteoclasts proceeded up to a certain point whereas matrix degradation was strongly inhibited. It is concluded that within the osteoclastic resorption lacuna both CPs and MMPs participate in the degradation of the collagenous bone matrix.

Tissue and urokinase plasminogen activators in bone tissue and their regulation by parathyroid hormone

The identification of the plasminogen activator (PA) types present in bone and the regulation of their activity by parathyroid hormone (PTH) were investigated in cultures of fetal mouse calvariae with the use of either a chromogenic substrate or a zymographic assay. PA was detected essentially in the tissue extracts of the explanted bones, with only 1-2% of the total activity released in the surrounding culture media. From their electrophoretic behavior compared to PAs of other mouse tissues and from their response to a specific antibody raised against the tissue type PA (tPA), two major molecular species, of 70 and 48 kD were identified as tPA and urokinase (uPA), respectively, a third minor species of 105 kD being likely to correspond to complexes between tPA and an inhibitor; the culture fluids, moreover, contained enzymatically active degradation products of uPA of 42 and 29 kD. The PA activity of the bone extracts was only minimally affected by the addition of fibrinogen fragments to the chromogenic assays. PTH induced bone resorption and stimulated in parallel the accumulation of PA in the tissue; other bone-resorbing agents, 1,25-dihydroxyvitamin D3 and prostaglandin E2, had similar effects. Densitometric scanning of the zymograms of the bone extracts indicated that PTH stimulated only the production of tPA and had no effect on that of uPA. However, PTH also enhanced the release of uPA (both the 48 kD and the 29 kD forms) from the bones into the media. Although inhibiting bone resorption, calcitonin had no effect on the PTH-induced accumulation of PA in bone or on the release of tPA, but it prevented the PTH-induced accumulation of 29 kD uPA in the culture fluids. Thus these studies support the view that tPA and possibly also uPA may have a role in the physiology of bone; the nature of this role remains to be elucidated, however.

Production of gelatin-degrading matrix metalloproteinases ('type IV collagenases') and inhibitors by articular chondrocytes during their dedifferentiation by serial subcultures and under stimulation by interleukin-1 and tumor necrosis factor alpha

The gelatin-degrading matrix metalloproteinase (MMP) activities and their inhibitors produced by rabbit articular chondrocytes have been characterized by gel substrate analysis ('zymography') after electrophoresis on non-reducing sodium dodecyl sulfate-polyacrylamide gels containing gelatin. Differentiated chondrocytes in confluent primary culture produced constitutively only one gelatinase which presented the main characteristics of proMMP-2 ('72 kDa type IV procollagenase'). It had an apparent Mr of 66,000 (unreduced), which was partially or totally converted to 61,000 by, respectively, trypsin or APMA treatment; exogenous TIMP (tissue inhibitor or metalloproteinases) inhibited the conversion triggered by APMA but not that induced by trypsin. This proMMP-2 was also the predominant gelatinase found, together with its 61 kDa activation product, in extracts of articular cartilage. Differentiated chondrocytes simultaneously produced MMP inhibitors which on reverse zymograms were distributed over two bands with Mr of 27,500 and 20,400, resistant to both pH 2 and 100 degrees C, corresponding, respectively, presumably, to TIMP and TIMP-2. Interleukin-1 (IL1) and tumor necrosis factor alpha (TNF alpha) did not affect the production of the proMMP-2 nor of the two species of TIMP. However, IL1 induced the coordinated production of 91 and 55 kDa gelatinases. The 91 kDa activity is likely to correspond to proMMP-9. It could be converted to a 81 kDa gelatinase by trypsin or APMA treatment, in a process that was inhibited in both cases by exogenous TIMP. The 55 kDa gelatinolytic activity most probably represents the sum of the activities of proMMP-1 (procollagenase) and proMMP-3 (prostromelysin). It was sequentially converted to lower size forms (49 to 35 kDa) by either trypsin or APMA; that conversion was inhibited by TIMP, with the exception, however, of the first steps (from 55 to 49, then to 42 kDa) induced by trypsin. The 55 kDa and its conversion forms were all active on both gelatin and casein. TNF alpha did also stimulate the production of proMMP-9, although less efficiently than IL1, but it did not induce, or very poorly, that of the 55 kDa proMMP-1/proMMP-3 activity. Low levels of proMMP-9 and of its 81 kDa product of activation were also found in extracts of cartilage. With increasing passage number and cell dedifferentiation, confluent chondrocytes produced increasing amounts of proMMP-2 and of the two species of TIMP. A spontaneous low production of proMMP-9 and proMMP-1/proMMP-3 was only occasionally observed in cultures of dedifferentiated chondrocytes, accompanying a spontaneous low production of procollagenase.(ABSTRACT TRUNCATED AT 400 WORDS)

Age-related thermal stability and susceptibility to proteolysis of rat bone collagen

The shrinkage temperature (Ts) and the pepsin-solubilizability of collagen fibrils in bone matrix obtained from decalcified femur diaphysis from 2-, 5-, 15- and 25-month-old rats were found to decrease with age. Digestion with human fibroblast collagenase dissolved less than half of the collagen, whereas sequential treatment by pepsin followed by collagenase resulted in its complete dissolution. This result shows that collagenase and a telopeptide-cleaving enzyme, when acting in an appropriate sequence, have a great potential for the degradation of bone collagen. The 'melting' profile of the pepsin-solubilized collagen showed a biphasic transition with transition peak at 35.9 degrees C and 40.8 degrees C. With increasing age an increasing proportion of the collagen 'melted' in the transition peak at 35.9 degrees C (pre-transition), and the 'melting' temperature (Tm) of the collagen decreased in parallel with Ts in relation to age. Both Ts and Tm decreased by 3 degrees C in the age span investigated. The age-related change in Ts could therefore be accounted for by the decrease in molecular stability. The collagenase-cleavage products of the bone collagen obtained by the sequential treatment with pepsin and collagenase showed only one peak transition (at 35.1 degrees C), and the Tm for the products was independent of age. The results indicate that the pre-transition for the pepsin-solubilized collagen is due to an age-related decrease in thermal stability may have implications for the mechanical strength and turnover of the bone collagen. In contrast with bone collagen, soft-tissue collagen showed neither the age-dependency of thermal stability nor the characteristic biphasic 'melting' profile.

Possible role and mechanism of action of dissolved calcium in the degradation of bone collagen by lysosomal cathepsins and collagenase

Equilibrium experiments with bone powder, at pH values ranging from 6.3 to 3.5, show a linear relation between log([Ca2+]/[Ca2+]0) (where [Ca2+]0 = 1 M-Ca2+) and pH, indicating that [Ca2+] could reach levels of 25 mM at pH 5 and 90 mM at pH 4. These elevated Ca2+ concentrations stimulated the lysis of insoluble bone collagen in vitro by purified lysosomes and by mouse bone collagenase, whose activities were additive at acid pH. At neutral pH, the addition of 10-100 mM-CaCl2 did not influence the susceptibility of acid-soluble skin collagen in solution towards bone collagenase, but increased it markedly towards collagen in the fibrillar form. Increasing the [Ca2+] did not influence the susceptibility of collagen to trypsin. Elevated [Ca2+] and a co-operation between lysosomal cysteine proteinases and matrix collagenase could thus participate in the osteoclastic breakdown of bone collagen.

The effect of phenytoin on collagenase and gelatinase activities in UMR 106-01 rat osteoblastic osteosarcoma cells

Phenytoin (PHT), a widely used anticonvulsant, has been shown to inhibit bone resorption in rodent organ cultures. The drug also has complex effects on bone metabolism including chronic clinical symptoms of osteomalacia. However, the precise mechanism of PHT action in bone is still unclear. Neutral collagenases that specifically cleave native collagen have been implicated in the turnover of connective tissue. The effect of PHT was assessed on collagenase and gelatinase activities from UMR 106-01 rat osteoblastic osteosarcoma cells. Semiconfluent cells were treated with PHT (50 and 10 micrograms/ml) in the presence of bovine parathyroid hormone, b-PTH-(1-34), at 10(-7) M for 24, 48, 72 and 96 h. The media were assayed following concentration, APMA activation, and incubation with native or denatured [3H]-methyl collagen substrate (approximately 100,000 dpm) at 27 degrees C for 18 h and 35 degrees C for 2 h, respectively. Enzyme activities were presented as primary counts per minute for each time point and calculated as % activity of PTH at 10(-7) M. Parathyroid hormone (10(-7) M) stimulated collagenase activity (approximately 65-fold) and gelatinase activity (approximately 400-fold). PHT (50 micrograms/ml) reduced the PTH-stimulated collagenase activity by 18-53% and the gelatinase activity by 58-72%. SDS PAGE and fluorography following PHT treatment indicated a PHT-induced partial inhibition of PTH-stimulated degradation to alpha A chains of Type I collagen. Phenytoin may inhibit bone resorption through its action on the transcription, synthesis, and/or secretion of the collagenolytic enzymes, collagenase and gelatinase.

The induction of specific metabolic alterations in mouse calvarial organ cultures by glycosaminoglycans

Glycosaminoglycans specifically regulate the amount of calcium released from bone cultures; the mechanisms responsible for this regulation are not known. Media from glycosaminoglycan-stimulated bone organ cultures were analysed to determine (1) if specific calcium-releasing substances were selectively produced, and (2) if protein synthesis was differentially affected by glycosaminoglycans. Chondroitin sulphate B, hyaluronic acid and keratan sulphate at 100 micrograms/ml significantly increased prostaglandin release when compared with control cultures. In combination with suboptimal concentrations of PTH, chondroitin sulphate B, heparin and keratan sulphate significantly stimulated prostaglandin release. When indomethacin was included in the test assays, the stimulated prostaglandin release was abolished. Heparin-treated cultures released the greatest percentage of latent collagenase activity followed by hyaluronic acid-treated cultures. Organ cultures treated with heparin and PTH amount of active collagenase. Stimulation increased interleukin-1 above control levels but with no significant difference among the glycosaminoglycans except for keratan sulphate cultures with which had the greatest amount of interleukin-1. Collagen protein decreased between 48 and 72 h under both control and experimental conditions. Examination of the predominant [35S]-methionine labelled proteins revealed that prostaglandin E2 treatment resulted in a relative shift in labelling to higher molecular-weight proteins as time in culture increased (up to 144 h). After 48 h, when equal amounts of labelled protein were analysed, there was a predominance in labelling of a 200,000 Da protein in the prostaglandin-treated cultures. These findings demonstrate that modulation of calcium release by glycosaminoglycans results in the selective release of molecules capable of stimulating calcium release.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct extraction and assay of collagenase from human osteoarthritic articular cartilage

A method has been developed for the direct extraction of collagenase from small quantities (5 mg) of human osteoarthritic articular cartilage. The enzyme, which was not detected in normal cartilage, was entirely in a latent form and demonstrated typical properties of mammalian collagenase after activation by trypsin.

Collagenolytic activity extracted from intestinal anastomoses of the rat

The post-operative degradation of collagen has been postulated to play an important role in the development of anastomotic leakage in the intestine. However, collagenolytic activity in intestinal anastomoses has hardly been studied so far. We have measured collagenolytic activity, after extraction in an urea-containing medium, in both ileal and colonic anastomoses in the rat, from 12 hours to 31 days after operation. In ileum collagenolytic activity increased significantly, from 2 to 4 (average 2.7) times the control value, at 12 hours post-operatively followed by a steady decline to original levels. Four weeks after surgery the activity was still slightly, but significantly, enhanced. In colon collagenolytic activity also increased up to 4 times the pre-operative level (average 3.0) 12 hours after operation. Return to original levels was delayed in colon compared to ileum but here activities were similar to control values after one month. In both parts of the intestine there was only a small increase in activity at a segment proximal to the anastomosis during the first 24 hours after operation. The amount of protein extracted did not vary significantly between control and anastomotic samples. These data are the first to show a transiently increased extractable collagenolytic activity in intestinal anastomoses.