Expression of gelatinase A, a mediator of extracellular matrix remodeling, by tracheal gland serous cells in culture and in vivo

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Expression of matrix metalloproteinase-2 and matrix metalloproteinase-9 in recurrent chronic rhinosinusitis with nasal polyposis

Matrix metalloproteinase (MMP) is involved in the upper airway remodeling process. We hypothesized that MMP had an additive effect on the formation of recurrent nasal polyp. We also investigated the association between the functional promoter polymorphism of MMPs and the intensity of labeling index. Expressions of MMP-2 and MMP-9 were assessed via immunohistochemical staining and compared between different groups, including recurrent nasal polyps, nonrecurrent nasal polyps, and control nasal mucosa. Two promoter functional single-nucleotide polymorphisms (rs3918242 for MMP-9 and rs243865 for MMP-2) were selected to correlate with staining intensity. Expression of MMP-9 was significantly enhanced in gland for recurrent nasal polyp (p = 0.016) and nonrecurrent nasal polyp (p = 0.005) compared to the control. MMP-2 positivity was significantly increased in surface epithelium for recurrent nasal polyp (p = 0.004) compared to the control (p = 0.061). However, there was no significant difference in MMP-9 and MMP-2 expressions between recurrent and nonrecurrent nasal polyps. Genetic polymorphism of MMP-2 and MMP-9 functional promoters was not associated with the intensity of labeling index. These results suggested that up-regulation of MMP-9 in gland and MMP-2 in surface epithelium was characteristic of both recurrent and nonrecurrent nasal polyps. Pathogenesis of recurrent nasal polyps may involve a mechanism other than MMP.

Corelationship between matrix metalloproteinase 2 and 9 expression and severity of chronic rhinosinusitis with nasal polyposis

BACKGROUND

Matrix metalloproteinase (MMP) is involved in the remodeling process of inflammatory airway diseases and is correlated with the severity of asthma. We hypothesized that MMP was associated with the severity of chronic rhinosinusitis with nasal polyps (CRSwNPs). We also investigated the effect of allergy on the expression of MMP in the polyp.

METHODS

The expression of MMP-2 and -9 was investigated in recurrent nasal polyps of 30 patients and in nonrecurrent nasal polyps of 31 patients undergoing endoscopic sinus surgery. These expressions were then compared with those in control nasal mucosal samples obtained from 32 patients with chronic hypertrophic rhinitis. Demographic data, Lund-Mackay (LM) score, polyp grade, and allergy status were obtained for all patients. Tissue samples were assessed via immunohistochemistry.

RESULTS

MMP-2 and -9 were constantly expressed in recurrent NPs, primary NPs, and control nasal mucosa. The expression of MMP-9 was significantly enhanced in glands and MMP-2 positivity was significantly increased in surface epithelium for patients with NPs when compared with control nasal mucosa. The expression of MMP-9 and -2 was not correlated with polyp grade and LM score. Allergic status is an independent factor in the expression of MMP-2 and -9.

CONCLUSION

These results suggested up-regulation of MMP-9, and MMP-2 in gland and surface epithelium, respectively, were characteristic of NPs. Therefore, patients with allergy will exhibit greater MMP-2 and -9 positivity. However, the MMP-2 and -9 expression intensity was not correlated with the severity of CRS with nasal polyposis.

Loss of matrix metalloproteinase-2 amplifies murine toxin-induced liver fibrosis by upregulating collagen I expression

BACKGROUND AND AIMS

Matrix metalloproteinase-2 (MMP-2), a type IV collagenase secreted by activated hepatic stellate cells (HSCs), is upregulated in chronic liver disease and is considered a profibrotic mediator due to its proliferative effect on cultured HSCs and ability to degrade normal liver matrix. Although associative studies and cell culture findings suggest that MMP-2 promotes hepatic fibrogenesis, no in vivo model has definitively established a pathologic role for MMP-2 in the development and progression of liver fibrosis. We therefore examined the impact of MMP-2 deficiency on liver fibrosis development during chronic CCl(4) liver injury and explored the effect of MMP-2 deficiency and overexpression on collagen I expression.

METHODS

Following chronic CCl(4) administration, liver fibrosis was analyzed using Sirius Red staining with quantitative morphometry and real-time polymerase chain reaction (PCR) in MMP-2-/- mice and age-matched MMP-2+/+ controls. These studies were complemented by analyses of cultured human stellate cells.

RESULTS

MMP-2-/- mice demonstrated an almost twofold increase in fibrosis which was not secondary to significant differences in hepatocellular injury, HSC activation or type I collagenase activity; however, type I collagen messenger RNA (mRNA) expression was increased threefold in the MMP-2-/- group by real-time PCR. Furthermore, targeted reduction of MMP-2 in cultured HSCs using RNA interference significantly increased collagen I mRNA and protein, while overexpression of MMP-2 resulted in decreased collagen I mRNA.

CONCLUSIONS

These findings suggest that increased MMP-2 during the progression of liver fibrosis may be an important mechanism for inhibiting type I collagen synthesis by activated HSCs, thereby providing a protective rather than pathologic role.

Type I collagen is a genetic modifier of matrix metalloproteinase 2 in murine skeletal development

Recessive inactivating mutations in human matrix metalloproteinase 2 (MMP2, gelatinase A) are associated with syndromes that include abnormal facial appearance, short stature, and severe bone loss. Mmp2(-/-) mice have only mild aspects of these abnormalities, suggesting that MMP2 function is redundant during skeletal development in the mouse. Here, we report that Mmp2(-/-) mice with additional mutations that render type I collagen resistant to collagenase-mediated cleavage to TC(A) and TC(B) fragments (Col1a1(r/r) mice) have severe developmental defects resembling those observed in MMP2-null humans. Composite Mmp2(-/-);Col1a1(r/r) mice were born in expected Mendelian ratios but were half the size of wild-type, Mmp2(-/-), and Col1a1(r/r) mice and failed to thrive. Furthermore, composite Mmp2(-/-);Col1a1(r/r) animals had very abnormal craniofacial features with shorter snouts, bulging skulls, incompletely developed calvarial bones and unclosed cranial sutures. In addition, trabecular bone mass was reduced concomitant with increased numbers of bone-resorbing osteoclasts and osteopenia. In vitro, MMP2 had a unique ability among the collagenolytic MMPs to degrade mutant collagen, offering a possible explanation for the genetic interaction between Mmp2 and Col1a1(r). Thus, because mutations in the type I collagen gene alter the phenotype of mice with null mutations in Mmp2, we conclude that type I collagen is an important modifier gene for Mmp2. Developmental Dynamics 236:1683-1693, 2007. (c) 2007 Wiley-Liss, Inc.

Muscle connective tissue content of endurance-trained and inactive individuals

Although it is known that exercise exerts a positive regulatory effect on collagen synthesis, the effects of endurance training on muscle endomysial connective tissue in man are not so well documented. To investigate this, a single muscle biopsy was collected from two groups of volunteers - endurance-trained sports participants and age-matched healthy untrained individuals. Endomysial staining intensity of types I, III and IV collagen was quantified by immunohistochemical staining and image analysis methods. Gelatinase activity in the endomysium was also quantified histochemically. Mean cycling VO2peak values of 53+/-6 (SD) and 32+/-8 mL/kg/min (P<0.01) were recorded for the trained and untrained groups, respectively. The staining intensity of types I, III and IV collagen and gelatinase activity in the trained group were not significantly different from the untrained group. However, when the data for all 11 volunteers were pooled, significant negative correlations were found for type III collagen staining intensity and capillary/fiber ratio; and for the relationship between type IV collagen staining intensity and VO2peak. These results suggest a negative association between aerobic capacity and the intensity of staining for types III and IV collagen in muscle endomysium.

MT1-MMP-dependent neovessel formation within the confines of the three-dimensional extracellular matrix

During angiogenesis, endothelial cells initiate a tissue-invasive program within an interstitial matrix comprised largely of type I collagen. Extracellular matrix–degradative enzymes, including the matrix metalloproteinases (MMPs) MMP-2 and MMP-9, are thought to play key roles in angiogenesis by binding to docking sites on the cell surface after activation by plasmin- and/or membrane-type (MT) 1-MMP–dependent processes. To identify proteinases critical to neovessel formation, an ex vivo model of angiogenesis has been established wherein tissue explants from gene-targeted mice are embedded within a three-dimensional, type I collagen matrix. Unexpectedly, neither MMP-2, MMP-9, their cognate cell-surface receptors (i.e., β₃ integrin and CD44), nor plasminogen are essential for collagenolytic activity, endothelial cell invasion, or neovessel formation. Instead, the membrane-anchored MMP, MT1-MMP, confers endothelial cells with the ability to express invasive and tubulogenic activity in a collagen-rich milieu, in vitro or in vivo, where it plays an indispensable role in driving neovessel formation.

Characterization of gelatinases in bronchoalveolar lavage fluid and gelatinases produced by alveolar macrophages isolated from healthy calves

OBJECTIVE

To characterize gelatinases in bronchoalveolar lavage fluid (BALF) and gelatinases produced by alveolar macrophages of healthy calves.

SAMPLE POPULATION

Samples of BALF and alveolar macrophages obtained from 20 healthy 2-month-old calves.

PROCEDURE

BALF was examined by use of gelatin zymography and immunoblotting to detect gelatinases and tissue inhibitor of metalloproteinase (TIMP)-1 and -2. Cultured alveolar macrophages were stimulated with lipopolysaccharide (LPS), and conditioned medium was subjected to zymography. Alveolar macrophage RNA was used for reverse transcriptase-polymerase chain reaction assay of matrix metalloproteinases (MMPs), cyclooxygenase-2, and inducible nitric oxide synthase.

RESULTS

Gelatinolytic activity in BALF was evident at 92 kd (14/20 calves; latent MMP-9) and 72 kd (18/20; latent MMP-2). Gelatinolytic activity was evident at 82 kd (10/20 calves; active MMP-9) and 62 kd (17/20; active MMP-2). Gelatinases were inhibited by metal chelators but not serine protease inhibitors. Immunoblotting of BALF protein and conditioned medium confirmed the MMP-2 and -9 proteins. Endogenous inhibitors (ie, TIMPs) were detected in BALF from all calves (TIMP-1) or BALF from only 4 calves (TIMP-2). Cultured alveolar macrophages expressed detectable amounts of MMP-9 mRNA but not MMP-2 mRNA.

CONCLUSIONS AND CLINICAL RELEVANCE

Healthy calves have detectable amounts of the gelatinases MMP-2 and -9 in BALF Endogenous inhibitors of MMPs were detected in BALF (ie, TIMP-1, all calves; TIMP-2, 4 calves). Lipopolysaccharide-stimulated alveolar macrophages express MMP-9 but not MMP-2 mRNA. The role of proteases in the pathogenesis of lung injury associated with pneumonia has yet to be determined.

Skeletal muscle collagen content in humans after high-force eccentric contractions

The purpose of this study was to investigate the effects of high-force eccentric muscle contractions on collagen remodeling and on circulating levels of matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) in humans. Nine volunteers [5 men and 4 women, mean age 23 (SD 4) yr] each performed a bout of 100 maximum voluntary eccentric contractions of the knee extensors. Muscle biopsies were taken before exercise and on days 4 and 22 afterward. Image analysis of stained tissue sections was used to quantify endomysial collagen staining intensity. Maximum voluntary contractile isometric force was recorded preexercise and on days 1, 2, 3, 4, 8, 11, and 14 postexercise. Venipuncture blood samples were also drawn on these days for measurement of serum creatine kinase activity and concentrations of MMP-9, TIMP-1, TIMP-2, and the MMP-2/TIMP-2 complex. Maximum voluntary contractile force declined by 39 +/- 23% (mean +/- SD) on day 2 postexercise and recovered thereafter. Serum creatine kinase activity peaked on day 4 postexercise (P < 0.01). Collagen type IV staining intensity increased significantly on day 22 postexercise to 126 +/- 29% (mean +/- SD) of preexercise values (P < 0.05). Serum MMP-9 levels increased on day 8 postexercise (P < 0.01), and serum TIMP-1 was also significantly elevated on days 1, 2, 3, 4, and 14 postexercise (P < 0.05). These results suggest that a single bout of eccentric muscle contractions results in remodeling of endomysial type IV collagen, possibly via the MMP pathway.

Following matrix metalloproteinases activity near the cell boundary by infrared micro-spectroscopy

Matrix Metalloproteinases (MMPs) are cell-secreted soluble and membrane-tethered enzymes that degrade extracellular matrix (ECM) proteins. These proteases play a key role in diverse physiological and pathological processes, including embryonic development, wound repair, inflammatory diseases and cancer. Yet, there is insufficient knowledge on the mode by which cell-produced MMPs conduct their action on the ECM. Specifically, the localization and the mode of the degradation within the pericellular space are of great interest. To provide new insights to these questions we utilized Fourier transform infrared (FTIR) micro-spectroscopy to follow proteolytic processes, induced by invasive cancer cells, on insoluble collagen-based matrices. Here we show that FTIR micro-spectroscopy have a great potential for monitoring degradation events near cells. Using this tool we demonstrate that the net proteolysis is unevenly distributed around the cell boundary. The degradation patterns show different levels of proteolytic activity by MMPs within the pericellular space. In addition, our spectral analysis suggests that the enzymatic proteolysis of the collagen-based matrices induces unwinding of the triple helical structures of the macromolecules within the collagen network.

Basement membrane zone remodeling during appendageal development in human fetal skin. The absence of type VII collagen is associated with gelatinase-A (MMP2) activity

Epithelial cell adhesion, migration, and differentiation are controlled by interactions at the basement membrane zone (BMZ). Type VII collagen is the major collagenous component of anchoring fibrils that are essential for the attachment of the epidermis to the dermis. Gelatinase A (MMP-2) is believed to be necessary for the degradation of type VII collagen. In this study we have examined the in vivo distribution of type VII collagen and gelatinase A (Gel A) in the developing human epidermis and its appendages. At 13-15 wk of gestation a marked decrease in type VII collagen immunoreactivity was seen in the BMZ surrounding invading appendageal buds; however, type VII collagen mRNA was strongly expressed in the budding epidermal keratinocytes adjacent to the BMZ. At these stages, Gel A-positive mesenchymal-like cells were found scattered throughout the stroma with numerous Gel A-containing cells in direct contact with the developing appendageal buds. In situ zymography was used to show Gel A-activity in vivo. Gel A-mediated lysis was present at the interface between the appendageal buds and the underlying BMZ. By 20-25 wk of gestational age, immunostaining for type VII collagen protein was absent from the BMZ surrounding the distal portion of invading appendageal epithelial cords of both hair follicles and sweat glands. In contrast, type VII collagen mRNA was present in the basal keratinocytes adjacent to the BMZ surrounding the distal portion of these invading appendageal epithelial cords. At these stages Gel A-positive cells were present in the stroma directly adjacent to the distal portion of developing appendageal cords that lacked type VII collagen. In situ zymography showed zones of Gel A-mediated stromal lysis at the distal portion of developing appendageal cords. Interestingly, no differences were seen in the distribution of type IV collagen in the BMZ of both budding and resting fetal epidermis. These observations suggest that the absence of type VII collagen protein correlates directly with the presence of Gel A-activity at the BMZ. Gel A appears to play a major role in appendageal development and contributes to remodeling of the BMZ during fetal skin morphogenesis.

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.

Expression of gelatinase A and its activator MT1-MMP in the inflammatory periprosthetic response to polyethylene

Wear debris of polyethylene prosthetic components is known to induce a host granulomatous reaction which recruits numerous macrophages and multinucleated giant cells. By releasing cellular mediators of a nonspecific inflammatory reaction, activated phagocytic cells are thought to play a key role in osteolysis leading to aseptic loosening of the prosthesis. Matrix metalloproteinases (MMPs) have been implicated in this destructive process by their ability to degrade extracellular matrix components of bone and adjacent connective tissue. To investigate the roles of gelatinase A, its activator MT1-MMP, and the MMP inhibitors TIMP-1 and TIMP-2 in aseptic loosening of polyethylene prostheses, immunohistochemistry (IHC) and in situ hybridization (ISH) were performed on periprosthetic pseudosynovial interface tissues. Gelatinase A and MT1-MMP were strongly detected immunohistochemically in macrophages and multinucleated giant cells in contact with polyethylene wear debris. In contrast to MT1-MMP, gelatinase A mRNAs were not found in phagocytic cells but in surrounding fibroblasts, thereby suggesting cooperation between macrophages and fibroblasts in this process. While TIMP-1 was expressed essentially in hyperplastic pseudosynoviocytes as assessed by IHC and ISH, TIMP-2, MT1-MMP, and gelatinase A were colocalized in phagocytic cells. These data support the concept of progelatinase A activation involving a trimolecular complex (MT1-MMP-TIMP-2-gelatinase A) mechanism. Thus, this study demonstrated that gelatinase A and its activator might contribute to the aseptic loosening of polyethylene prostheses.

Cell-matrix interactions modulate 92-kD gelatinase expression by human bronchial epithelial cells

We have previously reported that primary human bronchial epithelial cells (HBECs) cultured on types I + III collagen were able to differentially regulate the production of major constitutive 92-kD gelatinase, minor 72-kD gelatinase, and their tissue-specific inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1) in response to lipopolysaccharide (LPS) or proinflammatory cytokines, suggesting that HBECs may be involved in vivo in the active remodeling of the underlying extracellular matrix (ECM). In this study, we examined the possible effects of specific type IV collagen as compared with types I + III collagen on HBEC behavior and function. We investigated 92-kD gelatinase and TIMP-1 expression with zymography and reverse zymography, respectively, at the protein level, and with quantitative reverse transcription-polymerase chain reaction (RT-PCR) at the mRNA level. Results showed similar morphologic features and identical proliferation rates of HBECs in response to the two matrix substrates. Nevertheless, differences at the protein and mRNA levels between HBEC cultures on type IV collagen and on types I + III collagen included: (1) a lower basal level of 92-kD gelatinase production; (2) less upregulation of 92-kD gelatinase in response to LPS endotoxin or to the proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha); and (3) loss of activation of the proforms of the 92-kD and 72-kD gelatinases. These findings, together with the maintenance of TIMP-1 expression, strongly suggest that type IV collagen used as a matrix substratum is associated with a homeostatic HBEC phenotype, and limits the ability of HBECs to degrade the matrix. In contrast, types I + III collagen may be associated with a matrix resorption phenotype corresponding to active matrix remodeling and repair. Thus, the ECM underlying HBECs may modulate matrix remodeling by HBECs, particularly in response to inflammatory processes during acute lung injury.

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.

Role of the matrixin MMP-2 in multicellular organization of adipocytes cultured in basement membrane components

Primary rat adipocytes cultured in basement membrane component gels migrated and organized into large, three-dimensional, multicellular clusters. Gross morphological changes seen during this reorganization are described. The rate of cluster formation decreased with age of the rats and was stimulated by insulin in older, but not in younger rats. Echistatin, a disintegrin, partially inhibited the formation of multicellular clusters in a concentration-dependent fashion (50% inhibitory concentration approximately 10 nM). The original extracellular matrix was initially remodeled and eventually destroyed by the time large multicellular clusters were observed. This implied that one or more matrix-degrading protease(s) were being secreted. Adipocyte-conditioned medium was found to contain a divalent cation-sensitive gelatinase activity at approximately 72 and/or approximately 62 kDa. The elution profile of this activity from gelatin-Sepharose 4B was similar to matrix metalloproteinase 2 (MMP-2, a 72-kDa matrixin with a 62-kDa mature form), and the dimethyl sulfoxide eluant from these columns contained MMP-2 immunoreactivity. MMP-2 concentration and activity were greater in conditioned medium from young than from older animals; however, insulin did not affect the amount of MMP-2 in adipocyte-conditioned media. The matrixin inhibitor 1,10-phenanthroline not only blocked gelatinase activity in zymograms but also prevented extracellular matrix remodeling and destruction, as well as adipocyte migration and the formation of cell-cell contacts in adipocyte cultures. These observations are consistent with the hypothesis that the matrixin MMP-2 is secreted by adipocytes. Whereas matrixin activity alone may not be sufficient for the formation of multicellular clusters, the data indicate that it may have a requisite role in this process.

Cell-matrix interactions in gland development in the lung

The tubulo-acinar glands of the conducting airways participate in lung host defense and the pathogenesis of chronic inflammatory airway disease. Models of gland development may provide clues to mechanisms that promote hypersecretion in diseases such as chronic bronchitis and cystic fibrosis. The developmental anatomy of airway glands was described 30 years ago, but the regulation of gland formation remains a mystery. During the pseudoglandular stage of lung development, poorly differentiated surface epithelial cells grow radially from the lumen and invade the airway submucosa. The basal lamina is remodeled during this process and animal studies indicate a correlation between the expression of the 72-kD gelatinase (MMP-2) and gland morphogenesis. Cell culture models with lung epithelial and mesenchymal elements mimic early gland morphogenesis. Studies using this model have corroborated the involvement of 72-kD gelatinase in the formation of gland-like structures. While the secretion and activation of 72-kD gelatinase is correlated with epithelial matrix invasion, the presence of activated 72-kD gelatinase is not by itself sufficient to permit epithelial matrix invasion. Whether the 72-kD gelatinase participates in a more complex proteolytic cascade or whether appropriate localization of the enzyme is critical to airway epithelial morphogenesis is the focus of ongoing investigation.

Metalloproteinases regulate parietal endoderm differentiating and migrating in cultured mouse embryos

Extracellular matrix (ECM) adhesion and proteolysis play important roles in embryonic development. In previous work (Behrendtsen et al. [1992] Development 114:447-456) we showed that gelatinase B activity is rate-limiting for trophoblast-mediated invasion and degradation of ECM in culture. In the present study, we show that metalloproteinases (MMPs) have distinct roles in migration along ECM as opposed to invasion through ECM. We investigated the role of ECM proteolysis in the differentiation and migration of parietal endoderm (PE), the first embryonic migratory cell type, adhering to ECM surfaces. Gelatinase B was the major MMP of PE; mRNA and protein were detected in PE of 7.5- and 8.5-day embryos. Using cultures of inner cell masses (ICMs) isolated from mouse blastocysts, we found that inhibitors of metalloproteinases, specifically, tissue inhibitor of metalloproteinases (TIMP)-1 and a peptide hydroxamic acid stimulated outgrowth and differentiation of PE from ICMs cultured on fibronectin, but inhibitors of plasminogen activators did not. TIMP-1 increased the number of PE cells and mean distance migrated and increased expression of the PE differentiation marker vimentin; the increase in cell number was not at the expense of other cell types. The stimulatory effect of TIMP-1 was most marked on low concentrations of substrate fibronectin, decreasing as concentrations of fibronectin increased. TIMP-1 also stimulated the outgrowth of PE in blastocyst cultures and in ICM/trophectoderm co-cultures; in ICM/trophectoderm co-cultures TIMP-1 stimulated PE differentiation on higher concentrations of fibronectin than was permissive for ICMs cultured alone. These data indicate that metalloproteinase inhibitors preserved the migration-inducing status of the ECM. We conclude that metalloproteinases have distinct roles in invasive activity through ECM barriers and migratory activity along ECM surfaces.

Degradation of bradykinin by bovine tracheal epithelium and isolated epithelial cells

1. The degradation of bradykinin (BK) labelled with tritiated proline at positions 2 and 3 ([3H]-BK) was determined on the luminal surface of bovine tracheal epithelium, in supernatants obtained from incubations of the luminal tracheal surface, and in suspensions of isolated tracheal epithelial cells. Peptidase inhibitors and identification of peptide fragments were used for characterization of the metabolic pathways. 2. On the luminal surface of intact bovine trachea, [3H]-BK was degraded with a half life of 12.8 min. [1-7]-BK and [1-5]-BK were the major direct metabolites which were further degraded via [1-3]-BK and [2-3]-BK to proline. Metabolism of [3H]-BK was unaltered in the presence of ramiprilat (250 nM) or phosphoramidon (10 microM). Phenanthroline diminished the formation of [1-7]- and [1-5]-BK and abolished the generation of proline. 3. Supernatants obtained from incubations of tracheal epithelium contained kininase activities which steadily increased when tracheae were incubated for longer than 30 min. After 60 min contact with epithelium, the incubation medium contained higher kininase activities than the epithelium itself. The spectrum of kinin metabolites generated by kininases in the supernatant was comparable to that formed by intact epithelium. 4. In suspensions of isolated epithelial cells, [3H]-BK was degraded with a half life of 70 min. The metabolites [1-3]- and [2-3]-BK were formed in parallel to [1-7]- and [1-5]-BK; however, proline was not generated. Degradation of [3H]-BK was not influenced by ramiprilat, but was inhibited by 85% in the presence of phosphoramidon. Phosporamidon markedly inhibited the generation of [1-7]- and [1-5]-BK and nearly abolished the formation of [1-3]- and [2-3]-BK. 5. In conclusion, angiotensin I-converting enzyme and neutral endopeptidase 24.11 are not significantly involved in [3H]-BK degradation on the luminal side of intact tracheal epithelium. The spectrum of metabolites found may in fact reflect the combined activities of metalloendopeptidase 24.15 and post-proline cleaving enzymes. Enzymes showing similar kininase activities are also released from the epithelium. Isolated epithelial cells contain low activities of these kininases, but a high activity of neutral endopeptidases, which may reflect an exclusively basolateral localization of the latter.

Basement membrane and repair of injury to peripheral nerve: defining a potential role for macrophages, matrix metalloproteinases, and tissue inhibitor of metalloproteinases-1

Injury to a peripheral nerve is followed by a remodeling process consisting of axonal degeneration and regeneration. It is not known how Schwann cell-derived basement membrane is preserved after injury or what role matrix metalloproteinases (MMPs) and their inhibitors play in axonal degeneration and regeneration. We showed that the MMPs gelatinase B (MMP-9), stromelysin-1 (MMP-3), and the tissue inhibitor of MMPs (TIMP)-1 were induced in crush and distal segments of mouse sciatic nerve after injury. TIMP-1 inhibitor activity was present in excess of proteinase activity in extracts of injured nerve. TIMP-1 protected basement membrane type IV collagen from degradation by exogenous gelatinase B in cryostat sections of nerve in vitro. In vivo, during the early phase (1 d after crush) and later phase (4 d after crush) after injury, induction of TNF-alpha and TGF-beta 1 mRNAs, known modulators of TIMP-1 expression, were paralleled by an upregulation of TIMP-1 and gelatinase B mRNAs. At 4 days after injury, TIMP-1, gelatinase B, and TNF-alpha mRNAs were localized to infiltrating macrophages and Schwann cells in the regions of nerve infiltrated by elicited macrophages. TIMP-1 and cytokine mRNA expression was upregulated in undamaged nerve explants incubated with medium conditioned by macrophages or containing the cytokines TGF-beta 1, TNF-alpha, and IL-1 alpha. These results show that TIMP-1 may protect basement membrane from uncontrolled degradation after injury and that cytokines produced by macrophages may participate in the regulation of TIMP-1 levels during nerve repair.

Expression of matrix metalloproteinase gelatinases A and B by cultured epithelial cells from human bronchial explants

To investigate the role of human bronchial epithelial cells (HBECs) in the maintenance and remodeling of the extracellular matrix, we evaluated the expression by HBECs of 72- and 92-kDa gelatinases under basal conditions and after exposure to bacterial lipopolysaccharides (LPS). Confluent HBECs from explants were cultured in plastic dishes coated with type I and III collagens. Gelatin zymography of HBEC-conditioned media showed constitutive major 92-kDa and minor 72-kDa gelatinases recognized by specific human antibodies and totally inhibited by the metalloproteinase inhibitor EDTA. The identification of the two matrix metalloproteinases was confirmed by quantitative reverse transcription-polymerase chain reaction. Identical patterns of gelatinase expression were observed with repetitive primary cultures issued from the same explants. Zymography showed that exposure of HBECs to LPS induced 2- and 20-fold increases in 92-kDa gelatinase production and activation, respectively, as well as a smaller increase in activated 68-kDa gelatinase. With [3H]gelatin substrate, elevated metallogelatinolytic activity (138 microgram of hydrolyzed gelatin/48 h/10(6) cells) was also observed, whereas no activity was detected in the absence of LPS. A human epithelial cell line (16HBE14o-) exhibited the same basal profile of gelatinase activity, but this profile remained unchanged after exposure to LPS. Quantitative reverse transcription-polymerase chain reaction demonstrated only minimal changes in 92-kDa mRNA levels in response to LPS, but the half-life of 92-kDa gelatinase mRNA was increased with exposure to LPS. In contrast, concomitant slight increases in 72-kDa gelatinase protein and mRNA were found, suggesting that the control mechanisms regulating the expression of 92- and 72-kDa gelatinases by HBECs in response to LPS are divergent. All these data allowed us to propose that HBECs may be actively involved in the physiological and physiopathological remodeling of the airway basement membrane.

Transmembrane-deletion mutants of the membrane-type matrix metalloproteinase-1 process progelatinase A and express intrinsic matrix-degrading activity

Membrane-type matrix metalloproteinase-1 (MT-MMP-1) has been proposed to play a critical role in regulating the expression of tissue-invasive phenotypes in normal and neoplastic cells by directly or indirectly mediating the activation of progelatinase A. To begin characterizing MT-MMP-1 structure-function relationships, transmembrane-deletion mutants were constructed, and the processing of the zymogens as well as the enzymic activity of the mature proteinases was analyzed. We now demonstrate that pro-MT-MMP-1 mutants are efficiently processed to active proteinases following post-translational endoproteolysis immediately downstream of an Arg108-Arg-Lys-Arg basic motif by a proprotein convertase-dependent pathway. The secreted form of active MT-MMP-1 not only displays an N terminus identical with that described for the processed wild-type enzyme at Tyr112 (Strongin, A. Y., Collier, I., Bannikov, G., Marmer, B. L., Grants, G. A., and Goldberg, G. I. (1995) J. Biol. Chem. 270, 5331-5338), but also directly mediated progelatinase A activation via a two-step proteolytic cascade indistinguishable from that observed with intact cells. Furthermore, although the only function previously ascribed to MT-MMP-1 is its ability to act as a progelatinase A activator, purified transmembrane deletion mutants also expressed proteolytic activities against a wide range of extracellular matrix molecules. Given recent reports that MT-MMP-1 ectodomains may undergo intercellular transfer in vivo (Okada, A., Bellocq, J.-P., Rouyer, N., Chenard, M.-P., Rio, M.-C., Chambon, P., and Basset, P. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 2730-2734), our data suggest that soluble forms of the proteinase confer recipient cells with the ability to not only process progelatinase A, but also directly degrade extracellular matrix components.

Phagocytosis and intracellular digestion of collagen, its role in turnover and remodelling

Collagens of most connective tissues are subject to continuous remodelling and turnover, a phenomenon which occurs under both physiological and pathological conditions. Degradation of these proteins involves participation of a variety of proteolytic enzymes including members of the following proteinase classes: matrix metalloproteinases (e.g. collagenase, gelatinase and stromelysin), cysteine proteinases (e.g. cathepsin B and L) and serine proteinases (e.g. plasmin and plasminogen activator). Convincing evidence is available indicating a pivotal role for matrix metalloproteinases, in particular collagenase, in the degradation of collagen under conditions of rapid remodelling, e.g. inflammation and involution of the uterus. Under steady state conditions, such as during turnover of soft connective tissues, involvement of collagenase has yet to be demonstrated. Under these circumstances collagen degradation is likely to take place particularly within the lysosomal apparatus after phagocytosis of the fibrils. We propose that this process involves the following steps: (i) recognition of the fibril by membrane-bound receptors (integrins?), (ii) segregation of the fibril, (iii) partial digestion of the fibril and/or its surrounding non-collagenous proteins by matrix metalloproteinases (possibly gelatinase), and finally (iv) lysosomal digestion by cysteine proteinases, such as cathepsin B and/or L. Modulation of this pathway is carried out under the influence of growth factors and cytokines, including transforming growth factor beta and interleukin 1 alpha.