How are proteoglycans distributed?
Proteoglycans are synthesized by all connective tissue cells. They can remain associated with these cells on their cell surface (syndecan, betaglycan), intracellularly (serglycin), or in the basement membrane (perlecan). These cell-associated proteoglycans commonly contain heparin/heparan sulfate or chondroitin sulfate as their major GAGs. Alternatively, proteoglycans can be secreted into the extracellular matrix (aggrecan, decorin, biglycan, fibromodulin, lumican). These matrix proteoglycans usually contain chondroitin sulfate, dermatan sulfate, or keratan sulfate as their major GAGs. Aggrecan binds to central hyaluronic acid filaments in cartilage. Decorin helps bind type II collagen fibers together in cartilage, whereas fibromodulin and lumican bind type II collagen to type IX.