Abstract. Degradation of type I collagen, the most abundant collagen, is initiated by collagenase cleavage at a highly conserved site between Gly775 and I1e776 of the od(I) chain. Mutations at or around this site render type I collagen resistant to collagenase digestion in vitro. We show here that mice carrying a collagenaseresistant mutant Colla-1 transgene die late in embryogenesis, ascribable to overexpression of the transgene, since the same mutation introduced into the endogenous Colla-1 gene by gene targeting permitted normal development of mutant mice to young adulthood. With increasing age, animals carrying the targeted mutation developed marked fibrosis of the dermis similar to that in human scleroderma. Postpartum involution of the uterus in the mutant mice was also impaired, with persistence of collagenous nodules in the uterine wall. AIthough type I collagen from the homozygous mutant mice was resistant to cleavage by human or rat fibroblast collagenases at the helical site, only the rat collagenase cleaved collagen trimers at an additional, novel site in the nonhelical N-telopeptide domain. Our results suggest that cleavage by murine collagenase at the N-telopeptide site could account for resorption of type I collagen during embryonic and early adult life. During intense collagen resorption, however, such as in the immediate postpartum uterus and in the dermis later in life, cleavage at the helical site is essential for normal collagen turnover. Thus, type I collagen is degraded by at least two differentially controlled mechanisms involving collagenases with distinct, but overlapping, substrate specificities.T YPE I collagen is among the most abundant components of the extracellular matrix of many tissues, particularly in skin, tendons, ligaments, uterus, large blood vessels and bone. The helical trimeric molecules of type I collagen comprise two al(I) chains and one ~2(I) chain, encoded by two separate genes, Colla-1 and Colla-2, respectively (50). In mice, type I collagen is first synthesized in the mesenchymal stroma of the head, heart and somites at day 8 of gestation (E8) and its production continues throughout development and postnatal life (27). It has been demonstrated that type I collagen is critical for bone development (9, 10), hematopoiesis (29, 37), integrity of the vascular system (29) and for mesenchymal-epithelial induction in organogenesis (6).The collagen content of different tissues during development and in adult animals is tightly regulated by coordinated processes of synthesis and degradation (2,8,57 teoporosis or inflammatory joint diseases) or excessive deposition (e.g. pulmonary fibrosis or scleroderma) (32, 39). The degradation of type I collagen requires the action of specific collagenases since native, triple-helical molecules are resistant to attack by proteolytic enzymes at 37°C and neutral pH. The collagenases are members of a family of proteinases, the metalloproteinases or matrixins, all of which contain a catalytic zinc-binding domain that includes the sequence moti...

Osteoclasts form an acidic compartment at their attachment site in which bone demineralization and matrix degradation occur. Although both the cysteine proteinases and neutral collagenases participate in bone resorption, their roles have remained unclear. Here we show that interstitial collagenase has an essential role in initiating bone resorption, distinct from that of the cysteine proteinases. Treatment of osteoclasts with cysteine proteinase inhibitors did not affect the number of resorption lacunae ("pits") formed on the surface of dentine slices, but it generated abnormal pits that were demineralized but filled with undegraded matrix. Treatment with metalloproteinase inhibitors did not alter the qualitative features of lacunae, but it greatly reduced the number of pits and surface area resorbed. Treatment of bone cells with an inhibitory anti-rat interstitial collagenase antiserum reduced bone resorption markedly. In the presence of collagenase inhibitors, resorption was restored by pretreatment of dentine slices with rat interstitial collagenase or by precoating the dentine slices with collagenase-derived gelatin peptides or heatgelatinized collagen. Immunostaining revealed that interstitial collagenase is produced at high levels by stromal cells and osteoblasts adjacent to osteoclasts. These results indicate that interstitial collagenase can function as a "coupling factor," allowing osteoblasts to initiate bone resorption by generating collagen fragments that activate osteoclasts.Normal bone turnover is highly regulated. Osteoclasts, the cells that degrade bone, require activation to trigger their boneresorptive capacity. Once activated, osteoclasts secrete both protons and proteinases at their attachment site, resulting in dissolution of bone mineral and degradation of the matrix (1). Osteoclasts produce several cysteine proteinases (2-4), enzymes with acidic pH optima, of which cathepsin K appears to be essential for normal bone resorption (5, 6). Studies indicate that the major function of secreted cysteine proteinases is matrix degradation (3, 7).The role of neutral metalloproteinases, a second class of proteinase produced in bone tissue (3,8), is less clear. Members of the metalloproteinase family have neutral pH optima, are secreted as proenzymes, and contain a zinc atom at the active site (9, 10). Although some prior studies suggested that neutral metalloproteinases contribute to osteoclast matrix degradation (11), recent evidence indicates that osteoclasts do not produce collagenase (12). Collagenase is produced by cells of osteoblastic lineage and may be required for resorption of intact bone tissue (13)(14)(15)(16). Observations that isolated osteoclasts that had no detectable collagenase activity were able to resorb bone prompted the suggestion that collagenase promotes resorption by removing unmineralized matrix from the bone surface, facilitating osteoclast attachment (8,17,18).In this study we have examined the qualitative and quantitative roles of acid cysteine proteinases and interstitial...

Human skin procollagenase has been isolated, in pure form, from the medium of fibroblasts cultured in the presence or absence of added serum. Purification was achieved using a combination of cation-exchange (phosphocellulose or carboxymethylcellulose) and gel-filtration chromatography. Two forms (60 000 and 55 000 daltons) of the procollagenase were detected by electrophoresis in sodium dodecyl sulfatepolyacrylamide gels and could be separated by chromatography on Ultrogel AcA-44. Each form was converted to active enzyme by trypsin, producing species of 50 000 and 45 000 daltons, respectively. An autoactivation process also occurred, which yielded active enzyme without a detectable change in molecular weight. Procollagenase also was found in organ cultures of human skin but only when serum was added to the medium. This suggests that a serum-inhibitable proteolytic system is present in these cultures which, like trypsin, converts procollagenase to the active enzyme forms that can be isolated from serum-free organ culture medium. The collagenase species obtained from either fibroblast or organ culture medium were chromatographically and electrophoretically identical.

Abstract. Osteoclasts are the principal resorptive cells of bone, yet their capacity to degrade collagen, the major organic component of bone matrix, remains unexplored. Accordingly, we have studied the bone resorptive activity of highly enriched populations of isolated chicken osteoclasts, using as substrate devitalized rat bone which had been labeled in vivo with L-[5-3H]proline or 45Ca, and bone-like matrix produced and mineralized in vitro by osteoblast-like rat osteosarcoma cells.When co-cultured with a radiolabeled substrate, osteoclast-mediated mineral mobilization reached a maximal rate within 2 h, whereas organic matrix degradation appeared more slowly, reaching maximal rate by 12-24 h. Thereafter, the rates of organic and inorganic matrix resorption were essentially linear and parallel for at least 6 d when excess substrate was available.Osteoclast-mediated degradation of bone collagen was confirmed by amino acid analysis. 39% of the solubilized tritium was recovered as trans-4-hydroxyproline, 47% as proline. 10,000 osteoclasts solubilized 70% of the total radioactivity and 65% of the [3H]-trans-4-hydroxyproline from 100/~g of 25-50-/~m bone fragments within 5 d. Virtually all released tritium-labeled protein was of low molecular weight, 99% with Mr -10,000, and 65% with Mr _< 1,000. Moreover, when the 14% of resorbed [3H]proline-labeled peptides with Mr ~ 2,000 were examined for the presence of TC A and TC B, the characteristic initial products of mammalian collagenase activity, none was detected by SDS PAGE. In addition, osteoclast-conditioned medium had no collagenolytic activity, and exogenous TC A and TC B fragments were not degraded by osteoclasts. On the other hand, osteoclast lysates have collagenolytic enzyme activity in acidic but not in neutral buffer, with maximum activity at pH 4.0. These data indicate that osteoclasts have the capacity to resorb the organic phase of bone by a process localized to the osteoclast and its attachment site. This process appears to be independent of secretion of neutral collagenase and probably reflects acid protease activity.

Manganese-superoxide dismutase (Sod2) removes mitochondrially derived superoxide (O 2 . ) at near-diffusion limiting rates and is the only antioxidant enzyme whose expression is regulated by numerous stimuli. Here it is shown that Sod2 also serves as a source of the intracellular signaling molecule H 2 O 2 . Sod2-dependent increases in the steady-state levels of H 2 O 2 led to ERK1/2 activation and subsequent downstream transcriptional increases in matrix metalloproteinase-1 (MMP-1) expression, which were reversed by expression of the H 2 O 2 -detoxifying enzyme, catalase. In addition, a single nucleotide polymorphism has recently been identified (1G/2G) at base pair ؊1607 that creates an Ets site adjacent to an AP-1 site at base pair ؊1602 and has been shown to dramatically enhance transcription of the MMP-1 promoter. Luciferase promoter constructs containing either the 1G or 2G variation were 25-or 1000-fold more active when transiently transfected into Sod2-overexpressing cell lines, respectively. The levels of MMP-2, -3, and -7 were also increased in the Sod2-overexpressing cell lines, suggesting that Sod2 may function as a "global" redox regulator of MMP expression. In addition, Sod2 ؊/؉ mouse embryonic fibroblasts failed to respond to the cytokine-mediated induction of the murine functional analog of MMP-1, MMP-13. This study provides evidence that the modulation of Sod2 activity by a wide array of pathogenic and inflammatory stimuli may be utilized by the cell as a primary signaling mechanism leading to matrix metalloproteinase expression.