extracellular matrix

WKP

A layer consisting mainly of proteins (especially collagen) and glycosaminoglycans (mostly as proteoglycans) that forms a sheet underlying cells such as endothelial cells and epithelial cells. The proteins are secreted by cells in the vicinity. GO:0005578

The extra-cellualr matrix (ECM) is secreted locally and assembles into a network in the spaces surrounding cells (intercellualr space). The extra-cellualr matrix (ECM) forms a significant proportion of the volume of any tissue.

The ECM serves many functions. For example, matrix proteins sequester water that provides turgor to soft tissues and minerals that give rigidity to skeletal tissues. They also function as a reservoir for growth factors controlling cell proliferation. ECM is important for cell-to-cell interactions and provides a substratum for cells to adhere, migrate, and proliferate, directly modulating cell form and function. Synthesis and degrada-tion of ECM accompanies morphogenesis, wound healing, and chronic fibrotic processes, as well as tumor invasion and metastasis.

Three groups of macromolecules, which are often physically associated, constitute the ECM:

 (1) fibrous structural proteins, such as the collagens and elastins
 (2) a diverse group of adhesive glycoproteins
 (3) proteoglycans and hyaluronic acid (HA or hyaluran).

These macromolecules are present in intercellular junctions and cell surfaces and may assemble into two general organizations: interstitial matrix and basement membrane (BM).

Interstitial matrix

The interstitial matrix is present in spaces between epithelial, endothelial, and smooth muscle cells and in connective tissue. It consists of fibrillar and nonfibrillar collagen, elastin, fibronectin, proteoglycans, hyaluronate, and other components.

Basement membrane

Basement membranes (BMs) are produced by epithelial and mesenchymal cells and are closely associated with the cell surface. They consist of a network of amorphous nonfibrillar collagen (mostly type IV), laminin, heparan sulfate, proteoglycan, and other glycoproteins.

The cells in tissue are in contact with secreted extracellular macromolecules referred to as the extracellular matrix. The matrix helps hold the cells and tissues together and provides a means in which cell can migrate and interact. In many cases cells are held together by cell-cell adhesions.

Components of the extracellular matrix in connective tissue are:

 polysccharide chains of the class called glycosaminoglycans (GAG) which are usually found covalently linked to proteins in the form of proteoglycans.
 fibrous proteins of two functional types which have structural and adhesive types.

• collagen and elastin (structural)
• fibronectin and laminin (adhesive)

Pathology (by molecular groups): impairment of the extracellular matrix

  pathology of collagens
 pathology of matrilins
 pathology of laminin
 pathology of elastins
 pathology of microfibrils (fibrillinopathies)
 pathology of cartilage oligomeric matrix protein
 pathology of extracellular matrix proteases

• pathology of metalloproteases
• pathology of ADAMTSs
• pathology of disintegrins

By localization

 cartilage extracellular matrix
 liver extracellular matrix
 renal extracellular matrix

See also

 extracellular matrix remodeling
 wound healing

References

 Bosman FT, Stamenkovic I. Functional structure and composition of the extracellular matrix. J Pathol. 2003 Jul;200(4):423-8. PMID: 12845610

 Schenk S, Quaranta V. Tales from the crypt[ic] sites of the extracellular matrix. Trends Cell Biol. 2003 Jul;13(7):366-75. PMID: 12837607

 De Arcangelis A, Georges-Labouesse E. Integrin and ECM functions: roles in vertebrate development. Trends Genet. 2000 Sep;16(9):389-95. PMID: 10973067