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Event: 68

Key Event Title

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

Accumulation, Collagen

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
Accumulation, Collagen
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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
Organ term
connective tissue

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
Process Object Action
collagen biosynthetic process collagen increased

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
Protein Alkylation to Liver Fibrosis KeyEvent Brigitte Landesmann (send email) Open for citation & comment WPHA/WNT Endorsed
Latent TGFbeta1 activation leads to pulmonary fibrosis KeyEvent Marvin Martens (send email) Under development: Not open for comment. Do not cite
lysosomal uptake induced liver fibrosis KeyEvent Marina Kuburic (send email) Under development: Not open for comment. Do not cite EAGMST Under Review
Binding to ACE2 leads to lung fibrosis KeyEvent Young Jun Kim (send email) Open for comment. Do not cite Under Development
AT1R, lung fibrosis KeyEvent Young Jun Kim (send email) Under development: Not open for comment. Do not cite Under Development
Substance interaction with the lung cell membrane leading to lung fibrosis KeyEvent Sabina Halappanavar (send email) Under development: Not open for comment. Do not cite EAGMST Under Review

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
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
Rattus norvegicus Rattus norvegicus High NCBI
mouse Mus musculus High NCBI

Life Stages

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

Sex Applicability

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

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

Collagen is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs, and the dentin in teeth. In muscle tissue, it serves as a major component of the endomysium. Collagen is the main structural protein in the extracellular space in the various connective tissues, making up from 25% to 35% of the whole-body protein content. In normal tissues, collagen provides strength, integrity, and structure. When tissues are disrupted following injury, collagen is needed to repair the defect. If too much collagen is deposited, normal anatomical structure is lost, function is compromised, and fibrosis results.

The fibroblast is the most common collagen producing cell.Collagen-producing cells may also arise from the process of transition of differentiated epithelial cells into mesenchymal cells (EMT). This has been observed e.g. during renal fibrosis (transformation of tubular epithelial cells into fibroblasts) and in liver injury (transdifferentiation of hepatocytes and cholangiocytes into fibroblasts) (Henderson and Iredale, 2007).

There are close to 20 different types of collagen found with the predominant form being type I collagen. This fibrillar form of collagen represents over 90 percent of our total collagen and is composed of three very long protein chains which are wrapped around each other to form a triple helical structure called a collagen monomer. Collagen is produced initially as a larger precursor molecule called procollagen. As the procollagen is secreted from the cell, procollagen proteinases remove the extension peptides from the ends of the molecule. The processed molecule is referred to as collagen and is involved in fiber formation. In the extracellular spaces the triple helical collagen molecules line up and begin to form fibrils and then fibers. Formation of stable crosslinks within and between the molecules is promoted by the enzyme lysyl oxidase and gives the collagen fibers tremendous strength (Diegelmann,2001). The overall amount of collagen deposited by fibroblasts is a regulated balance between collagen synthesis and collagen catabolism. Disturbance of this balance leads to changes in the amount and composition of collagen. Changes in the composition of the extracellular matrix initiate positive feedback pathways that increase collagen production.

Normally, collagen in connective tissues has a slow turn over; degradating enzymes are collagenases, belonging to the family of matrix metalloproteinases (MMPs).Other cells that can synthesize and release collagenase are macrophages, neutrophils, osteoclasts, and tumor cells (Di Lullo et al., 2001; Prockop and Kivirikko, 1995; Miller and Gay, 1987;Kivirikko  and  Risteli, 1976).

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

Determination of the amount of collagen produced in vitro can be done in a variety of ways ranging from simple colorimetric assays to elaborate chromatographic procedures using radioactive and non-radioactive material. What most of these procedures have in common is the need to destroy the cell layer to obtain solubilized collagen from the pericellular matrix. Rishikof et al describe several methods to assess the in vitro production of type I collagen: Western immunoblotting of intact alpha1(I) collagen using antibodies directed to alpha1(I) collagen amino and carboxyl propeptides, the measurement of alpha1(I) collagen mRNA levels using real-time polymerase chain reaction, and methods to determine the transcriptional regulation of alpha1(I) collagen using a nuclear run-on assay (Rishikof et al., (2005) . 

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 precision cut tissue slices

Precision cut tissue slices mimic the whole organ response and allow histological assessment, an endpoint of interest in regulatory decision making. While this technique uses animals, the number of animals required to conduct a dose-response study can be reduced to 1/4th of what will be used in whole animal exposure studies (Rahman et al., 2020). 


Domain of Applicability

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

Humans: Bataller and  Brenner, 2005; Decaris et al., 2015.  

Mice: Dalton et al., 2009; Leung et al., 2008; Nan et al., 2013.

Rats: Hamdy and El-Demerdash, 2012; Li, Li et al., 2012; Natajaran et al., 2006; Luckey and Petersen, 2001.


List of the literature that was cited for this KE description. More help
  • Henderson, N.C. and J.P. Iredale (2007), Liver fibrosis: cellular mechanisms of progression and resolution, Clin Sci (Lond), vol. 112, no. 5, pp. 265-280.
  • Diegelmann, R.F. (2001), Collagen Metabolism, Wounds, vol. 13, no. 5, available at (accessed on 20 Jamuary 2016).
  • Di Lullo, G.A. et al. (2001), Mapping the Ligand-binding Sites and Disease-associated Mutations on the Most Abundant Protein in the Human, Type I Collagen, J. Biol. Chem, vol. 277, no. 6, pp. 4223–4231.
  • Prockop, D.J. and K.I. Kivirikko (1995), Collagens: molecular biology, diseases, and potentials for therapy, Annu Rev Biochem, vol. 64, pp. 403-434.
  • Miller, E.J. and S. Gay (1987), The collagens: an overview and update, Methods Enzymol, vol. 144, pp. 3-41.
  • Kivirikko, K.I. and L. Risteli (1976), Biosynthesis of collagen and its alterations in pathological states, Med Biol, vol. 54, no. 3, pp. 159-186.
  • Rishikof, D.C. et al. (2005), Methods for measuring type I collagen synthesis in vitro, Methods, Mol Med, vol. 117, pp.129-140.
  • Bataller, R. and D.A. Brenner (2005), Liver Fibrosis, J.Clin. Invest, vol. 115, no. 2, pp. 209-218.
  • Decaris, M.L. et al. (2015), Turnover rates of hepatic collagen and circulating collagen- associated proteins in humans with chronic liver disease, PLoS One, vol. 10, no. 4, e0123311.
  • Dalton, S.R. et al. (2009), Carbon tetrachloride-induced liver damage in asialoglycoprotein receptor-deficient mice, Biochem Pharmacol, vol. 77, no. 7, pp. 1283-1290.
  • Leung, T.M. et al. (2008), Endothelial nitric oxide synthase is a critical factor in experimental liver fibrosis, Int J Exp Pathol, vol. 89, no. 4, pp. 241-250.
  • Nan, Y.M. et al. (2013), Activation of peroxisome proliferator activated receptor alpha ameliorates ethanol mediated liver fibrosis in mice, Lipids in Health and Disease, vol. 12, p. 11.
  • Hamdy, N. and E. El-Demerdash. (2012), New therapeutic aspect for carvedilol: antifibrotic effects of carvedilol in chronic carbon tetrachloride-induced liver damage, Toxicol Appl Pharmacol, vol. 261, no. 3, pp. 292-299.
  • Li, Li et al. (2012), Establishment of a standardized liver fibrosis model with different pathological stages in rats, Gastroenterol Res Pract; vol. 2012, Article ID 560345.Natajaran, S.K. et al. (2006), Oxidative stress in the development of liver cirrhosis: a comparison of two different experimental models, J Gastroenterol Hepatol, vol. 21, no. 6, pp. 947-957.
  • Natarajan SK, Thomas S, Ramamoorthy P, et al. Oxidative stress in the development of liver cirrhosis: a comparison of two different experimental models. J Gastroenterol Hepatol. 2006;21:947–957. doi: 10.1111/j.1440-1746.2006.04231.x
  • Luckey, S.W., and D.R. Petersen (2001), Activation of Kupffer cells during the course of carbon tetrachloride-induced liver injury and fibrosis in rats, Exp Mol Pathol, vol. 71, no. 3, pp. 226-240.
  • 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).

    Rahman, L., Williams, A., Gelda, K., Nikota, J., Wu, D., Vogel, U., & Halappanavar, S. (2020). 21st Century Tools for Nanotoxicology: Transcriptomic Biomarker Panel and Precision-Cut Lung Slice Organ Mimic System for the Assessment of Nanomaterial-Induced Lung Fibrosis. Small, 16(36), e2000272.

  • 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).