Extracellular matrix

The extracellular matrix (ECM) is the totality of macromolecules that fill the space outside the plasma membrane of cells of different tissues and that are essential for their integrity.

The variety of different demands placed on ECMs results in a structure that is complex in terms of its structure and function, which differs according to tissue and organ and determines the typical histoarchitecture. In early embryonic development it develops from the middle cotyledon, the mesoderm.

In some tissues, the extracellular matrix occupies only a narrow space (muscles, liver, etc.), while in others it represents the actual functional carrier of the tissue (bone, cartilage, tendons, etc.). On the one hand, it fulfils various mechanical functions such as the formation of a supporting framework for the attachment and migration of cells or the formation of sliding bearings in joints and tendon sheaths. On the other hand there are regulatory tasks. Thus, the ECMC supplies the cells with certain biological information and thus influences cell activities such as adhesion, cell proliferation and differentiation, migration and apoptosis.

This mutual influence between cells and ECM takes place either directly via cell receptor-matrix binding or indirectly via associated factors, which are of utmost importance in this interaction. These factors include chemokines, growth factors and the enzymes acting on the matrix as well as their inhibitors. Functionally, this group of ECM, cells and the aforementioned associated factors form a unit that plays an important role in both physiological and pathological mechanisms.

Examples of pathological processes of ECM are organ fibrosis, tumor growth, metastasis and autoimmune diseases.

The main components of ECM are collagens. In addition, non-collagenous glycoproteins, proteoglycans and glycosaminoglycans contribute to the structure and function of ECM. However, it is not always possible to clearly distinguish the structural groups from one another, as some collagens, for example, have glycosaminoglycan side chains or very long non-collagen domains.