Composition of the Extracellular Matrix

Following extraction, purification, and in-depth biochemical and functional characterization of a large number of the constituting proteins, it is well established that extracellular matrices provide anchorage points to cells, relay force transmission to cells (mechanotransduction), and activate signaling pathways by interacting with cell surface receptors. This results in the control of the activities of resident cells and of the immune response. In addition, structural or chemical motifs embedded in the extracellular matrix sequester growth factors that can be released upon appropriate triggers. Alternatively, bioactive molecules can be released upon enzymatic remodeling of certain extracellular matrix proteins. More recently, gene sequencing led to the identification of many additional components, representing about 300 different secreted proteins forming the matrisome. Based on their nature, structure, and chemistry, extracellular matrix proteins are classified into three groups – collagens, glycoproteins, and proteoglycans – that will be described in this chapter.