Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Substance interaction with the cell membrane leading to lung fibrosis||KeyEvent|
Key Event Description
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. 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 (reviewed in White 2015).
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. 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, 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 ME, 2014). 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, P., 2012; Wynn, T.A., 2011).
In lung fibrosis, an exaggerated amount of ECM is distributed in the alveolar parenchyma in a non-heterogenous manner, occluding alveolar regions leading to 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, K., 1994; Hinz, B., 2006; Kuhn, C., 1991; Crabb, R.A., 2006; Bensadoun, E.S., 1996; Klingberg, F., 2013; McKleroy, W., 2013). Excessive collagen production by myofibroblasts forms the basis of scar formation containing almost exclusively Type I collagen (Bateman, ED, 1981; McKleroy, W., 2013; Zhang, K., 1994). Several types of collagen exist, with differences based on their tissue localisation and function. However, type I collagen is the most abundant throughout the body, as well as in lung scar tissue. 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, M.E.1983; Rozin, G.F., 2005; McKleroy, W., 2013).
How It Is Measured or Detected
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.
SircolTM 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 (Clarice ZC, 2009).
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 (Clarice ZC, 2009).
Domain of Applicability
- Eric S. White. Lung Extracellular Matrix and Fibroblast Function. Ann Am Thorac Soc. 2015 Vol 12, Supplement 1, pp S30–S33.
- Marjolein E. Blaauboer, Fee R. Boeijen, Claire L. Emson, Scott M. Turner, Behrouz Zandieh-Doulabi, Roeland Hanemaaijer, Theo H. Smit, Reinout Stoop, Vincent Everts, Extracellular matrix proteins: A positive feedback loop in lung fibrosis?, In Matrix Biology, Volume 34, 2014, Pages 170-178, ISSN 0945-053X,
- Sivakumar, Pitchumania; Ntolios, Paschalisb; Jenkins, Gislic; Laurent, Geoffreyb. Into the matrix: targeting fibroblasts in pulmonary fibrosis. Current Opinion in Pulmonary Medicine: September 2012 - Volume 18 - Issue 5 - p 462–469.
- Thomas A. Wynn. Integrating mechanisms of lung fibrosis. Journal of Experimental Medicine Jul 2011, 208 (7) 1339-1350.
- Zhang, K., Rekhter, M.D., Gordon, D., and Phan, S.H.: Co-Expression of o-smooth muscle actin and type I collagen in fibroblast-like cells of rat lungs with bleomycininduced pulmonary fibrosis: a combined immuno-histochemical and in situ hybridization study. Am. J. Pathol. 1994; 145:114-125
- 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, 175-181.
- 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;138:1257–1265.
- Crabb RA, EP Chau, DM Decoteau, A Hubel. Multifunctional polymeric microfibers with prolonged drug delivery and structural support capabilities. Annals of Biomedical Engineering 34 (10), 1615-1627, 2006. 19, 2006.
- Bensadoun E, Burke AK, Hogg JC, Roberts CR. Proteoglycan deposition in pulmonary fibrosis. Am J. Respir. Crit. Care Med. 1996;154:1819–1828.
- Klingberg F, Hinz B, White ES. The myofibroblast matrix: implications for tissue repair and fibrosis. The Journal of pathology. 2013;229(2):298-309.
- McKleroy W, Lee TH, Atabai K.Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis. Am J Physiol Lung Cell Mol Physiol 304:L709-L721.
- Bateman, E., Turner-Warwick, M., and Adelmann-Grill, B. C. Immunohistochemical study of collagen types in human foetal lung and fibrotic lung disease. Thorax 1981 ;36:645-653.
- Zhang, K., Rekhter, M.D., Gordon, D., and Phan, S.H.: Co-Expression of o-smooth muscle actin and type I collagen in fibroblast-like cells of rat lungs with bleomycininduced pulmonary fibrosis: a combined immuno-histochemical and in situ hybridization study. Am. J. Pathol. 1994; 145:114-125.
- Nimni ME. Collagen: Structure, function, and metabolism in normal and fibrotic tissues Seminars in arthritis and rheumatism; 1983 Aug ; 13(1) 1-86.
- Rozin GF, Gomes MM, Parra ER, Kairalla RA, de Carvalho CR, Capelozzi VL. Collagen and elastic system in the remodelling process of major types of idiopathic interstitial pneumonias (IIP) Histopathology. 2005;46:413–421.
- Clarice ZC Chen and Michael Raghunath. Focus on collagen: in vitro systems to study fibrogenesis and antifibrosis - state of the art. Fibrogenesis & Tissue Repair 2009, 2:7.