What are the functions of proteoglycans?

Proteoglycans function as structural components of cartilage, intervertebral discs, brain ECM, tendons, and corneas. Therefore they are important for collagen organization, viscoelastic properties, and corneal transparency. Proteoglycans also provide hydration and swelling pressure of the tissue allowing it to resist compressional forces. Leucine rich proteoglycans (SLRPs) are the largest class of proteoglycans, and function as signaling molecules when tissues are remodeling during diabetes, inflammation, cancer, and atherosclerosis. 

Additionally, proteoglycans function in chemical signaling by binding secreted signal molecules (e.g. growth factors) and altering their signal activity. Proteoglycans can also bind to secreted proteins like proteases and protease inhibitors. This allows for the regulation of proteins by restricting their range of action, altering proteins to allow for more cell surface receptors, protecting it from degradation, or providing an environment of the protein for delayed release.