Collagens, Elastic Fibers and Other Extracellular Matrix Proteins of the Dermis at a Glance
- The extracellular matrix (ECM) is a complex network composed of a large number of components, which determines tissue stiffness, compliance, and resilience.
- ECM proteins (i.e., collagens, proteoglycans, glycoproteins) consist of structural domains with different biological functions.
- ECM signals control cell differentiation, polarity, migration, survival, and expression of specific genes.
- There are many ECM-associated heritable diseases. The molecular mechanisms responsible for the resulting phenotypes are often complex and involve several different cellular pathways.
- The dynamic balance between ECM synthesis and degradation is critical for many acquired disease processes, i.e., tumor invasion and metastasis, fibrosis, and inflammatory pathologies.
The extracellular matrix (ECM) is a complex network of different components, responsible for determining and maintaining tissue architecture, and for mediating a number of important biological events. It is composed of a large number of diverse protein families, each constituted by many different individual members. These include the collagens, encoded by 42 different genes, elastin and associated microfibrillar proteins, fibronectin, proteoglycans, and many more molecules. (See Table 63-1.)
Table 63-1 Major Genes and Proteins of the Extracellular Matrix ||Download (.pdf)
Table 63-1 Major Genes and Proteins of the Extracellular Matrix
Number of Genes
Number and Name of Proteins
28; collagens type I to XXVIII
Several splice variants
1; 20 splice variants
7; Fibulin 1–7
3; Fibrillin 1–3
15; LM-111, LM-332, LM-511, etc.
4; Matrilins 1–4
2; Nidogen 1 and 2
4; Tenascin-C, -X, -R, and -W
5; Thrombospondin 1–5
Although all of these proteins are genetically, structurally, and biologically diverse, a common denominator is that most of them have a modular structure, and they are composed of one, a few, or several copies of a limited set of individual structural modules, also called domains.1 These can be combined in multiple ways giving rise to proteins as diverse as fibrillin and laminin (Fig. 63-1). Specific functions have been unraveled for some of these domains, for instance, interaction with other ECM proteins, cell adhesion-promoting activity, cytokine trapping, and regulation. Therefore, the ECM has a critical role for many cellular functions, including proliferation, survival, polarity, differentiation, expression of specific genes, and migration.2–4 All different cell types, such as mesenchymal, epithelial, and endothelial cells, and also inflammatory and tumor cells, participate in the production of distinct ECM macromolecules, and are all influenced by interactions with these compounds. It is well established that the ECM determines the biophysical properties of connective tissues. More recently it became clear that, conversely, stiffness and compliance of connective tissues are important factors for the regulation of cellular functions.5–8