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Event: 1501

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Increased, extracellular matrix deposition

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
Increased extracellular matrix deposition
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization

Organ term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
ACE2 inhibition, liver fibrosis KeyEvent Evgeniia Kazymova (send email) Under development: Not open for comment. Do not cite Under Development
AHR activation leading to lung fibrosis via TGF-β dependent fibrosis tox path KeyEvent Allie Always (send email) Under development: Not open for comment. Do not cite
AHR activation leading to lung fibrosis via IL-6 tox path KeyEvent Evgeniia Kazymova (send email) Under development: Not open for comment. Do not cite
AhR and chronic liver diseases KeyEvent Cataia Ives (send email) Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Sex Applicability

An indication of the the relevant sex for this KE. More help

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

ECM is a macromolecular structure that provides physical support to tissues and is essential for organ function. The composition of ECM is tissue specific and consists mainly of fibrous proteins, glycoproteins, and proteoglycans. The ECM in lung is compartmentalised to basement membrane and the interstitial space. Fibroblasts found in the interstitial space are the main sources of ECM in lung (White, 2015). Altered composition of ECM is observed in several lung diseases of inflammatory origin in humans including chronic obstructive pulmonary disease, asthma and idiopathic lung fibrosis. The composition and architecture of the ECM determines 1) the open sites of attachment that are available to cells, 2) the mechanical properties of the ECM and 3) the mechanical loading (breathing) experienced by the cells. Thus, changes in the ECM composition during the exaggerated wound healing process determines if an organism commits to fibrotic process or completes the wound healing (Blaauboer et al., 2014).

Evidence for its perturbation in the context of pulmonary fibrosis:

In lung fibrosis, an exaggerated amount of ECM is distributed in the alveolar parenchyma in a non-heterogenous manner, leading to lower spirometry readings implying occlusion of alveolar regions and reduced gas exchange. Collagen 1 and Collagen III are suggested to be the main components of the ECM in the thickened alveolar septa in fibrosis with other constituents such as fibronectin, elastin and tenacin C (Zhang et al., 1994; Hinz, 2006; Kuhn & McDonald, 1991; Crabb et al., 2006; Bensadoun et al., 1996; Klingberg et al., 2012; McKleroy et al., 2013). It is suggested that ECM composition dramatically changes during the fibrotic process. The early fibrotic process is characterised by collagen III deposition and collagen 1 predominates the later stages of the fibrosis. Excessive collagen production by myofibroblasts is necessary for the development of fibrosis (scarred tissue), with established areas of scar formation containing almost exclusively Type I collagen (Bateman et al., 1981; McKleroy et al., 2013; Zhang et al., 1994). Studies have demonstrated that while total collagen increases in IPF, there is also a shift toward the less elastic type I collagen, which contributes to the stiffness of the scar tissue within the lung (Nimni, 1983; Rozin et al., 2005; McKleroy et al., 2013).

The fibrotic ECM contains characteristic accumulation of fibroblasts and myofibroblasts, which are the major contributors of ECM synthesised. The proliferation of fibroblasts and their differentiation into myofibroblasts is, in turn, guided by the composition and structure of the ECM. For example, studies have demonstrated that cytokines secreted in response to inflammation are capable of activating fibroblasts, and that these changes could cause alterations in the fibroblasts that lead to excessive proliferation and ECM deposition (Sivakumar et al., 2012; Wynn, 2011).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

qRT-PCR, Immunosorbant assays, and immunohistochemistry:

The qRT-PCR, ELISA, and immunohistochemistry are routinely used to assess the levels of protein and mRNA levels. The various genes and proteins that are assessed include, collagen I, collagen III, elastin and tenacin C. Histological staining with stains such as Masson Trichrome, Picro-sirius red are used to identify the tissue/cellular distribution of collagen, which can be quantified using morphometric analysis both in vivo and in vitro. The assays are routinely used and are quantitative.

Sircol Collagen Assay for collagen quantification:

The Serius dye has been used for many decades to detect collagen in histology samples. The Serius Red F3BA selectively binds to collagen and the signal can be read at 540 nm (Chen & Raghunath, 2009; Nikota et al., 2017).

Hydroxyproline assay:

Hydroxyproline is a non-proteinogenic amino acid formed by the prolyl-4-hydroxylase. Hydroxyproline is only found in collagen and thus, it serves as a direct measure of the amount of collagen present in cells or tissues. Colorimetric methods are readily available and have been extensively used to quantify collagen using this assay (Chen & Raghunath, 2009; Nikota et al., 2017).

Ex vivo and in vitro models of ECM deposition:

No models currently exist which allow for in vitro assessment of ECM deposition. Using single, or co-cultures containing fibroblasts, the production of soluble ECM components can be assessed after exposure to a stressor of interest using either ELISA or qRT-PCR experiments as a proxy. 

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help


List of the literature that was cited for this KE description. More help

1. Bateman, E., Turner-Warwick, M. and Adelmann-Grill, B. (1981). Immunohistochemical study of collagen types in human foetal lung and fibrotic lung disease. Thorax, 36(9), pp.645-653.

2. Bensadoun, E., Burke, A., Hogg, J. and Roberts, C. (1996). Proteoglycan deposition in pulmonary fibrosis. American Journal of Respiratory and Critical Care Medicine, 154(6), pp.1819-1828.

3. Blaauboer M et al. Extracellular matrix proteins: A positive feedback loop in lung fibrosis. Matrix Biology, 2014, 34, 170-178

4. Chen, C. and Raghunath, M. (2009). Focus on collagen: in vitro systems to study fibrogenesis and antifibrosis _ state of the art. Fibrogenesis & Tissue Repair, 2(1).

5. Crabb, R., Chau, E., Decoteau, D. and Hubel, A. (2006). Microstructural Characteristics of Extracellular Matrix Produced by Stromal Fibroblasts. Annals of Biomedical Engineering, 34(10), pp.1615-1627.

6. HINZ, B. (2006). Masters and servants of the force: The role of matrix adhesions in myofibroblast force perception and transmission. European Journal of Cell Biology, 85(3-4), pp.175-181.

7. Kuhn C, McDonald JA. The roles of the myofibroblast in idiopathic pulmonary fibrosis. Ultrastructural and immunohistochemical features of sites of active extracellular matrix synthesis. Am J Pathol. 1991;138(5):1257–1265.

8. Klingberg, F., Hinz, B. and White, E. (2012). The myofibroblast matrix: implications for tissue repair and fibrosis. The Journal of Pathology, 229(2), pp.298-309.

9. McKleroy, W., Lee, T. and Atabai, K. (2013). Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis. American Journal of Physiology-Lung Cellular and Molecular Physiology, 304(11), pp.L709-L721.

10. Nikota, J., Banville, A., Goodwin, L., Wu, D., Williams, A., Yauk, C., Wallin, H., Vogel, U. and Halappanavar, S. (2017). Stat-6 signaling pathway and not Interleukin-1 mediates multi-walled carbon nanotube-induced lung fibrosis in mice: insights from an adverse outcome pathway framework. Particle and Fibre Toxicology, 14(1).

11. Nimni, M. (1983). Collagen: Structure, function, and metabolism in normal and fibrotic tissues. Seminars in Arthritis and Rheumatism, 13(1), pp.1-86.

12. Rozin, G., Gomes, M., Parra, E., Kairalla, R., de Carvalho, C. and Capelozzi, V. (2005). Collagen and elastic system in the remodelling process of major types of idiopathic interstitial pneumonias (IIP). Histopathology, 46(4), pp.413-421.

13. Sivakumar, P., Ntolios, P., Jenkins, G. and Laurent, G. (2012). Into the matrix. Current Opinion in Pulmonary Medicine, 18(5), pp.462-469.

14. White, E. (2015). Lung Extracellular Matrix and Fibroblast Function. Annals of the American Thoracic Society, 12(Supplement 1), pp.S30- S33.

15. Wynn, T. (2011). Integrating mechanisms of pulmonary fibrosis. The Journal of Experimental Medicine, 208(7), pp.1339-1350.

16. Zhang K, Rekhter MD, Gordon D, Phan SH. Myofibroblasts and their role in lung collagen gene expression during pulmonary fibrosis. A combined immunohistochemical and in situ hybridization study. Am J Pathol. 1994;145(1):114–125