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13: Extracellular Matrix and Cell Adhesion - Biology

13: Extracellular Matrix and Cell Adhesion - Biology


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Interactions between a cell and its environment or with other cells are governed by cell-surface proteins. This chapter examines a subset of those interactions: direct cell contact with either other cells or extracellular matrix (ECM). Extracellular matrix is a general term for the extremely large proteins and polysaccharides that are secreted by some cells in a multicellular organism, and which acts as connective material to hold cells in a defined space. Cell density can vary greatly between different tissues of an animal, from tightly-packed muscle cells with many direct cell-to-cell contacts to liver tissue, in which some of the cells are only loosely organized, suspended in a web of extracellular matrix.

  • 13.1: Introduction to Extracellular Matrix and Cell Adhesion
    The extracellular matrix is a generic term encompassing mixtures of polysaccharides and proteins, including collagens, bronectins, laminins, and proteoglycans, all secreted by the cell. The proportions of these components can vary greatly depending on tissue type. Two, quite different, examples of extracellular matrices are the basement membrane underlying the epidermis of the skin.
  • 13.2: Collagen
    The largest and most prominent of the extracellular matrix proteins, constituting a quarter of the dry mass of the human body, are the members of the collagen family. Collagens are polymers that can be categorized into fibrillar and non fibrillar types. The fibrillar collagens are made up of triple helical monomers of either identical (homotrimer) or different (heterotrimer) subunits.
  • 13.3: Proteoglycans
    The protein component of proteoglycans are not as large as fibrillar collagens in general, but they often ll a massive volume because of heavy glycosylation. The sugars, many of which are sulfated or carboxylated, are hygroscopic to begin with, but being negatively charged, attract positive ions, which in turn brings in more water. Sugars attached to the core proteins are usually repeating disaccharide units such as chondroitin, chondroitin sulfate, heparin, heparan sulfate, keratan sulfate, or
  • 13.4: Fibronectins
    Fibronectin and laminin are significantly smaller than either collagens or proteoglycans, and play different roles in the extracellular matrix. Fibronectin is formed by the joining of two similar polypeptide subunits via a pair of disulfide bonds near the C-terminal of each (fig. 5). Each subunit is arranged as a linear sequence of 30 functional domains (varies slightly by species). Within each subunit, each domain acts as a semi-independent unit with respect to secondary and even tertiary struc
  • 13.5: Laminins
    Although there are many other less abundant proteins in the extracellular matrix, laminin is the final ECM molecule to be discussed in this chapter. Laminins are a family of secreted glycoproteins that are found in many ECM formations, and like fibronectin, bind to cells via integrin receptors. The laminin protein is composed of three subunits (α, β, γ) arranged in a cruciform shape. There are multiple isoforms of each subunit yielding the variety (15) of laminin proteins catalogued to date.
  • 13.6: Integrins
    The integrins have thus far been introduced as receptors for fibronectin and laminin, but it is a large family with a wide variety of substrates. For example, the focal adhesion (fig. 8) shows an an integrin receptor bound to collagen. Focal adhesions are usually transient, and seen as points of contact as fibroblasts or other migratory cells crawl on a culture dish or slide coated with ECM proteins.
  • 13.7: Hemidesmosomes
    Hemidesmosomes, particularly those attaching epithelial cells to their basement membrane, are the tightest adhesive interactions in an animal body. This close contact, and the reinforced structure of these contacts, is crucial for the protective resilience of epithelial layers. Remember the α6β4 integrin? That would be the one that links with intermediate filaments instead of f-actin. Intermediate filaments, as we’ve already noted, are not dynamic, but about as stable as a cellular component can
  • 13.8: Dystrophin Glycoprotein Complex
    Another type of cell-ECM connection is the dystrophin glycoprotein complex (DGC) of skeletal muscle cells. Similar complexes are found in smooth muscle and in some non-muscle tissues. Muscle cells, of course are subject to frequent mechanical stress, and connectivity to the ECM is important in supporting the cell integrity. The DGC uses the large transmembrane glycoprotein, dystroglycan, as its primary binding partner to basal lamina laminin
  • 13.9: Desmosomes
    An example of a cell-cell interaction with many similarities to a cell-ECM interaction, but using different adhesion molecules, is the desmosome. Like its basal-lamina-attached counterpart, the hemidesmosome, the desmosome is found in epithelial sheets, and its purpose is to link cells together so that pressure is spread across many cells rather than concentrated on one or a few. Desmosomes are necessary for the structural integrity of epithelial layers, and are the most common cell-cell junctio
  • 13.10: Cadherins
    The cadherin superfamily is comprised of the desmogleins (of which 4 have been identified in humans) and desmocollins (3 in humans), the cadherins (>20), and the protocadherins (~20) as well as other related proteins. They share structural similarity and a dependence on Ca2+ for adhesive activity, and they can be found in most tissues, and for that matter, most metazoan species. Cadherins are single-transmembrane modular proteins.
  • 13.11: Tight Junctions
    Sometimes, holding cells together, even with great strength, is not enough. In epithelia especially, a layer of cells may need to not only hold together but form a complete seal to separate whatever is in contact with the apical side from whatever is in contact with the basal side. That would be a job for The Tight Junction! Well, more accurately, for many tight junctions in an array near the apical surface. Perhaps the best example of the utility of tight junctions is in the digestive tract.
  • 13.12: Ig Superfamily CAMs
    Junction adhesion molecules (JAMs) have recently been found in tight junctions. These molecules are members of a gigantic superfamily of cell adhesion molecules known as the Ig (immunoglobulin domain) superfamily because all of these proteins contain an immunoglobulin loop domain that plays an important part in the adhesion mechanism. The purpose of immunoglobulins (antibodies) is to recognize and adhere to other molecules.
  • 13.13: Selectins
    The last major cell adhesion molecule family to discuss is the selectins. Selectins bind heterophilically to oligosaccharide moieties on glycoproteins. In fact the name of the family is based on lectin, a generic term for proteins that bind sugars. The selectins, like cadherins and IgSF molecules are modular glycoproteins that pass through the membrane once.
  • 13.14: Gap Junctions
    Unlike the other types of cell-cell adhesion, the gap junction (sometimes called a nexus) connects not only the outside of two cells, it connects their cytoplasm as well. Each cell has a connexon (aka hemichannel) made of six connexin proteins. The connexins may be all of the same type, or combinations of different ones, of which there are 20 known in humans and mice. The connexon interacts with a connexon on an adjacent cell to connect the cytoplasm of both cells in a gap junction.

Thumbnail: Illustration depicting extracellular matrix (basement membrane and interstitial matrix) in relation to epithelium, endothelium and connective tissue. (Public Domain; Twooars via Wikipedia).


Summary

Tissue repair involves a close interplay between growth factors and cell adhesion molecules. The normal healing process may be disrupted by pathophysiological states such as inflammation, due to loss of growth factors, cell adhesion molecules, or both, which results in a reduced rate of healing. Such events may occur in inflammatory bowel disease during mucosal restitution. We postulate that the beneficial response to heparin observed in inflammatory bowel disease may result from mechanisms in addition to anticoagulation. These include the restoration of high-affinity receptor binding by antiulcerogenic growth factors, such as basic fibroblast growth factor, that normally rely on the presence of heparan sulphate proteoglycans, such as syndecan-1, as coreceptors. Loss of syndecan-1 has been observed in the ulcerated mucosa of patients with inflammatory bowel disease. This loss may lead to impaired binding of basic fibroblast growth factor and a reduced rate of ulcer healing. We suggest that heparin restores high-affinity receptor binding of basic fibroblast growth, and so increases the rate of mucosal recovery.


Cysteine Cathepsins and their Extracellular Roles: Shaping the Microenvironment

: For a long time, cysteine cathepsins were considered primarily as proteases crucial for nonspecific bulk proteolysis in the endolysosomal system. However, this view has dramatically changed, and cathepsins are now considered key players in many important physiological processes, including in diseases like cancer, rheumatoid arthritis, and various inflammatory diseases. Cathepsins are emerging as important players in the extracellular space, and the paradigm is shifting from the degrading enzymes to the enzymes that can also specifically modify extracellular proteins. In pathological conditions, the activity of cathepsins is often dysregulated, resulting in their overexpression and secretion into the extracellular space. This is typically observed in cancer and inflammation, and cathepsins are therefore considered valuable diagnostic and therapeutic targets. In particular, the investigation of limited proteolysis by cathepsins in the extracellular space is opening numerous possibilities for future break-through discoveries. In this review, we highlight the most important findings that establish cysteine cathepsins as important players in the extracellular space and discuss their roles that reach beyond processing and degradation of extracellular matrix (ECM) components. In addition, we discuss the recent developments in cathepsin research and the new possibilities that are opening in translational medicine.

Keywords: cancer cathepsin extracellular matrix inflammation associated disease osteoporosis.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Cysteine cathepsin structures and specificities.…

Cysteine cathepsin structures and specificities. ( A ) Crystal structure of the two-chain…

Cysteine cathepsin secretion and their…

Cysteine cathepsin secretion and their extracellular roles. ( A ) Secretion of extracellular…

Extracellular cathepsins as diagnostic targets,…

Extracellular cathepsins as diagnostic targets, prodrug activators, and targets for targeted drug delivery.…


Fibronectin receptor functions in embryonic cells deficient in alpha 5 beta 1 integrin can be replaced by alpha V integrins.

alpha 5 beta 1 integrin mediates cell adhesion to extracellular matrix by interacting with fibronectin (FN). Mouse lines carrying null mutations in genes encoding either the alpha 5 integrin subunit or FN have been generated previously. Both mutations are embryonic lethal with overlapping defects, but the defects of alpha 5-null embryos are less severe. Primary embryonic cells lacking alpha 5 beta 1 are able to adhere to FN, form focal contacts, migrate on FN, and assemble FN matrix. These results suggest the involvement of (an)other FN receptors(s). In this study, we examined functions of alpha 4 beta 1 and alpha V integrins in embryonic cells lacking alpha 5 beta 1. Our analysis of cells lacking both alpha 4 beta 1 and alpha 5 beta 1 showed that alpha 4 beta 1 is also not required for these FN-dependent functions. Using alpha V-specific blocking reagents, we showed that alpha V integrins are required for alpha 5-null cells, but not wild-type cells, to adhere and spread on FN. Our data also showed that, although the expression levels of alpha V integrins on the wild-type and alpha 5-null cells are similar, there is an increase in recruitment of alpha V integrins into focal contacts in alpha 5-null cells plated on FN, indicating that alpha V integrins can compensate functionally for the loss of alpha 5 beta 1 in focal contacts of alpha 5-null cells. Finally, our data suggested possible roles for alpha V integrins in replacing the role of alpha 5 beta 1 in FN matrix assembly in vitro and in FN-dependent embryonic functions in vivo.


The Caenorhabditis elegans homologue of the extracellular calcium binding protein SPARC/osteonectin affects nematode body morphology and mobility.

The extracellular matrix-associated protein, SPARC (osteonectin [Secreted Protein Acidic and Rich in Cysteine]), modulates cell adhesion and induces a change in cell morphology. SPARC expression in mammals is developmentally regulated and is highest at sites of extracellular matrix assembly and remodeling such as parietal endoderm and bone. We have isolated cDNA and genomic DNA clones encoding the Caenorhabditis elegans homologue of SPARC. The gene organization is highly conserved, and the proteins encoded by mouse, human, and nematode genes are about 38% identical. SPARC consists of four domains (I-IV) based on predicted secondary structure. Using bacterial fusion proteins containing nematode domain I or the domain IV EF-hand motif, we show that, like the mammalian proteins, both domains bind calcium. In transgenic nematodes expressing a SPARC-lacZ fusion gene, beta-galactosidase staining accumulated in a striated pattern in the more heavily stained muscle cells along the body. Comparison of the pattern of transgene expression to unc-54-lacZ animals demonstrated that SPARC is expressed by body wall and sex muscle cells. Appropriate levels of SPARC are essential for normal C. elegans development and muscle function. Transgenic nematodes overexpressing the wild-type SPARC gene were abnormal. Embryos were deformed, and adult hermaphrodites had vulval protrusions and an uncoordinated (Unc) phenotype with reduced mobility and paralysis.


Author information

Affiliations

Vascular Program, Institute for Cell Engineering, and McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, 21205, Maryland, USA

Daniele M. Gilkes & Gregg L. Semenza

Johns Hopkins Physical Sciences-Oncology Center, The Johns Hopkins University, Baltimore, 21218, Maryland, USA

Daniele M. Gilkes & Gregg L. Semenza

Departments of Pediatrics, Oncology, Medicine, Radiation Oncology and Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, 21205, Maryland, USA

Johns Hopkins Physical Sciences-Oncology Center, The Johns Hopkins University, Baltimore, 21218, Maryland, USA

Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, Baltimore, 21218, Maryland, USA

Departments of Oncology and Pathology and Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, 21205, Maryland, USA


Esophageal Cancer Development: Crucial Clues Arising from the Extracellular Matrix

In the last years, the extracellular matrix (ECM) has been reported as playing a relevant role in esophageal cancer (EC) development, with this compartment being related to several aspects of EC genesis and progression. This sounds very interesting due to the complexity of this highly incident and lethal tumor, which takes the sixth position in mortality among all tumor types worldwide. The well-established increase in ECM stiffness, which is able to trigger mechanotransduction signaling, is capable of regulating several malignant behaviors by converting alteration in ECM mechanics into cytoplasmatic biochemical signals. In this sense, it has been shown that some molecules play a key role in these events, particularly the different collagen isoforms, as well as enzymes related to its turnover, such as lysyl oxidase (LOX) and matrix metalloproteinases (MMPs). In fact, MMPs are not only involved in ECM stiffness, but also in other events related to ECM homeostasis, which includes ECM remodeling. Therefore, the crucial role of distinct MMPs isoform has already been reported, especially MMP-2, -3, -7, and -9, along EC development, thus strongly associating these proteins with the control of important cellular events during tumor progression, particularly in the process of invasion during metastasis establishment. In addition, by distinct mechanisms, a vast diversity of glycoproteins and proteoglycans, such as laminin, fibronectin, tenascin C, galectin, dermatan sulfate, and hyaluronic acid exert remarkable effects in esophageal malignant cells due to the activation of oncogenic signaling pathways mainly involved in cytoskeleton alterations during adhesion and migration processes. Finally, the wide spectrum of interactions potentially mediated by ECM may represent a singular intervention scenario in esophageal carcinogenesis natural history and, due to the scarce knowledge on the cellular and molecular mechanisms involved in EC development, the growing body of evidence on ECM's role along esophageal carcinogenesis might provide a solid base to improve its management in the future.

Keywords: adhesion esophageal carcinogenesis extracellular matrix glycoproteins metalloproteinases proteoglycans remodeling stiffness.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Extracellular matrix (ECM) and esophageal…

Extracellular matrix (ECM) and esophageal carcinogenesis. The figure schematically represents how ECM may…

Mechanistic pathways involved in the…

Mechanistic pathways involved in the reciprocal interactions between esophageal cancer (EC) cells and…


YL implemented phagocyte sorting, flow cytometry detecting phagocytotic ability, and confocal microscopy imaging the phenomenon. YL, XZ, and KL analyzed the data of flow cytometry, while the fluorescence of pictures were calculated by ZX, JL, and SX. HM and MH performed RNA extraction for transcriptome. YZ and FM carried out bioinformatics analyses of transcriptomic data. YZ and ZY designed the research. YZ, YL, and N-KW wrote the manuscript and language proof.

This work was supported by the National Key Rɭ Program of China (2018YFC1406505), the National Science Foundation of China (Nos. 31572640 and 31572661), Science and Technology Program of Guangzhou, China (No. 201804020073), the Guangdong Special Support Program of Youth Scientific and Technological Innovation (No. 2015TQ01N139), the Program of the Pearl River Young Talents of Science and Technology in Guangzhou of China (201806010003), Institution of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences (ISEE2018PY01, ISEE2018PY03, ISEE2018ZD01), Science and Technology Planning Project of Guangdong Province, China (2017B030314052, 201707010177).


1. Introduction

Pancreatic ductal adenocarcinoma (PDAC), the most aggressive type of pancreatic cancer, is characterized by its very important fibro-inflammatory stromal reaction and low vascularity [1], findings that can be considered pathognomonic for the disease. This feature, known as a desmoplastic reaction, creates a stroma that does not allow the arrival of chemotherapeutic drugs to malignant cells and is one of the fundamental reasons for treatment failures [2]. The desmoplastic reaction entails a fibroblast-rich stroma with an increased dense extracellular matrix (ECM). PDAC stroma provides “protection” to malignant epithelial cells and participates in cancer progression [3]. The intense desmoplastic reaction originates in pancreatic stellate cells (PSCs) that proliferate and produce extracellular matrix proteins, namely fibronectin and collagen creating a particularly dense environment surrounding the malignant cells [4,5]. The unique features of the ECM in pancreatic cancer go beyond “protection” modulating cancer growth through angiogenesis and growth factors [6]. Table 1 shows the evidence that sustains the pro-tumoral concept of the desmoplastic reaction.

Table 1

Evidence of pro-tumoral effects of the desmoplastic reaction.

Ref.Finding
[7]Gemcitabine resistance was promoted by collagen I through a metalloproteases
(MT1-MMP) expression that in turn increases high mobility group AT 2 (HMGA2) protein which is an indirect transcription promoter.
[8]Extracellular matrix proteins showed pro-proliferative activity in PDAC in vitro.
[9]Pancreatic stromal fibroblasts showed the ability to promote cancer progression.
[10]Matrix collagen significantly increased the production of MMPs in PDAC impacting cell migration and invasive potential.
[11]Suppressing the desmoplastic process with metformin inhibited pancreatic cancer progression.
[12]Desmoplasia promoted pancreatic cancer progression.
[13]Extracellular matrix composition modulated PDAC and stem cells. An increased in collagen I introduced a switch in rapidly growing CSCs to a slower-growing avascular niche endothelial-type of cells, creating a supportive mechanism for tumor progression and mainly for tumor invasion. An active cross-talk between PDAC cells, CSCs, and matrix was carried out through the secretome. This process led to less proliferation but more invasion of PDAC cells into the CSCs derived vascular network.
[14]The extracellular matrix of PDAC and focal adhesion kinase (FAK) were found to regulate CSCs
[15]When PDAC cells were co-cultured with fibroblast, the latter acquired a myofibroblastic morphology expressing desmoplastic markers.
[16]Adding stellate cells to a PDAC 3D cell culture generated a rich stroma similar to that found in vivo.

Conclusions of Table 1 : There are an intense interrelation and cross-talk between PDAC cells and fibroblasts that adopt the form of stellate cells which results in the production of a rich desmoplastic reaction that favors invasion and cancer progression.

Originally, the cancer cell was thought to be the main producer of the ECM [17], however, now it is evident that specialized cells, stellate cells, are the main ECM source. PSCs are in a quiescent stage surrounding pancreatic acini but when malignancy develops, they adopt active participation. A symbiotic relationship between malignant and stellate cells was proposed [9,18,19].

Figure 1 shows a surgically removed PDAC specimen where the relationship between tumor cells (ducts and acini) and the high levels of the intense desmoplastic stroma can be seen.

Tissue specimen of a pancreatic ductal adenocarcinoma (PDAC). Intense stromal reaction surrounding tumoral ducts and acini (from the personal collection of TK). Magnification 150×.

Recently, Ogawa et al. [20] have distinguished three types of ECMs that differentially influence survival and molecular characteristics. These stromas had different fibroblast populations and transcriptome signatures. Thus, the PDAC matrix is a complex and heterogeneous issue that has direct implications in tumor progression and patient survival [21]. Furthermore, different types of fibroblasts have also been found in the normal pancreas which expands during carcinogenesis with a different prevalence according to subtypes [22].

Interestingly, there are drugs with the ability to inhibit fibroblastic proliferation and their production of collagen and pro-inflammatory cytokines. Pirfenidone is one of such drugs that have been FDA approved for the treatment of pulmonary fibrosis [23]. On the other hand, there are also non-toxic drugs that inhibit the enzymes intervening in hyaluronan production and drugs that decrease the expression of its receptor, CD44.

Targeting pancreatic extracellular environment has been investigated and proposed by many authors [24,25,26,27,28,29,30]. Many “repurposable” drugs with stromal inhibiting abilities have been identified, including metformin [31], all-trans retinoic acid [32], curcumin [33], glutamine analogs such as 6-diazo-5-oxo- l -norleucine (DON) [34], among others.

This manuscript will analyze separately the characteristics of these drugs and finally propose a unified vision of how they should act on the tumor stroma.

We strongly believe that there will be no real breakthrough in PDAC treatment unless the stroma is simultaneously targeted. Pancreatic stroma and tumor should be viewed as one pathological entity in which even if we can separate the parts, functionally they represent a non-divisible unit and so it should be treated.


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Pivotal role of matrix metalloproteinase 13 in extracellular matrix turnover in idiopathic pulmonary fibrosis. / Nkyimbeng, Takwi Ruppert, Clemens Shiomi, Takayuki Dahal, Bhola Lang, György Seeger, Werner Okada, Yasunori D'Armiento, Jeanine Günther, Andreas.

In: PloS one , Vol. 8, No. 9, e73279, 2013.

Research output : Contribution to journal › Article › peer-review

T1 - Pivotal role of matrix metalloproteinase 13 in extracellular matrix turnover in idiopathic pulmonary fibrosis.

N2 - Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by excessive deposition of extracellular matrix (ECM). We investigated the regulation of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) in lung fibrosis. MMP and TIMP expression, collagenolytic activity and collagen content was assessed in IPF (n=16) versus donor (n=6) lung homogenates and accomplished by in-situ-zymography for gelatinolytic and collagenolytic activities, combined with MMP antigen detection. Role of MMP13 was assessed employing the bleomycin model of lung fibrosis in MMP-13(-/-) versus wild-type mice. In IPF, MMPs-1, 2, 7, 9 and 13, but not MMP-8, were significantly upregulated, whereas none of the TIMPs (1-4) were significantly altered. Collagen content was slightly increased and collagenolytic activity was most prominent in the airways and co-localized with MMP-13. We observed an exaggerated early inflammatory response and an augmented lung fibrosis in bleomycin-challenged MMP-13(-/-) versus wild-type mice, with elevated lung collagen content 28d after bleomycin challenge in the MMP-13(-/-) mice. Our data suggest that i) collagen deposition in IPF lungs is not primarily due to excessive TIMP production, but rather due to overwhelming ECM production in face of an overall increased, but spatially imbalanced collagenolytic activity, ii) preferential distribution of collagenolytic activity, largely MMP-13, in the airways offers an explanation for the development of honeycomb cysts and iii) despite an overall increase in inflammatory cell content the presence of MMP-13 seems to limit the overall extent of ECM deposition in lung fibrosis.

AB - Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by excessive deposition of extracellular matrix (ECM). We investigated the regulation of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) in lung fibrosis. MMP and TIMP expression, collagenolytic activity and collagen content was assessed in IPF (n=16) versus donor (n=6) lung homogenates and accomplished by in-situ-zymography for gelatinolytic and collagenolytic activities, combined with MMP antigen detection. Role of MMP13 was assessed employing the bleomycin model of lung fibrosis in MMP-13(-/-) versus wild-type mice. In IPF, MMPs-1, 2, 7, 9 and 13, but not MMP-8, were significantly upregulated, whereas none of the TIMPs (1-4) were significantly altered. Collagen content was slightly increased and collagenolytic activity was most prominent in the airways and co-localized with MMP-13. We observed an exaggerated early inflammatory response and an augmented lung fibrosis in bleomycin-challenged MMP-13(-/-) versus wild-type mice, with elevated lung collagen content 28d after bleomycin challenge in the MMP-13(-/-) mice. Our data suggest that i) collagen deposition in IPF lungs is not primarily due to excessive TIMP production, but rather due to overwhelming ECM production in face of an overall increased, but spatially imbalanced collagenolytic activity, ii) preferential distribution of collagenolytic activity, largely MMP-13, in the airways offers an explanation for the development of honeycomb cysts and iii) despite an overall increase in inflammatory cell content the presence of MMP-13 seems to limit the overall extent of ECM deposition in lung fibrosis.


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