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Event: 1501

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. 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. The short name should be less than 80 characters in length. More help
Increased extracellular matrix deposition

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help
Level of Biological Organization

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.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. More help

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). 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 signalling 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. 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
Substance interaction with the lung cell membrane leading to lung fibrosis KeyEvent Cataia Ives (send email) Under development: Not open for comment. Do not cite EAGMST Under Review
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


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. 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

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. 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. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. 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

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. 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).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

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

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). 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