The Formation of Cartilage Extracellular Matrix

Abstract

Normal cartilage function is dependent upon the unique structural properties of the extensive extracellular matrix (ECM). In final assembled form, the ECM of hyaline cartilage is composed of abundant amounts of proteoglycan (PG) and type II collagen. Additional collagens and glycoproteins may be important structural components as well. Through their concentration of negative charges, PGs confer upon the cartilage ECM the ability to retain high levels of hydration and thereby resist compression. Type II collagen fibers contribute to the tensile strength of cartilage.In the cartilage ECM, PG monomers associate with hyaluronic acid and link protein to form large aggregates. In turn, PG aggregates are associated with the fibrous meshwork of type II collagen. Interactions with other ECM molecules may occur as well. The cartilage matrix constituents are themselves large and complex. For example, the PG monomer is 1-5 x 106 daltons in size and contains a core protein of Mr >300K (comprising only 8-10% of the complete monomer).