[Cartilage proteoglycan aggregate: structure and function].

The proteoglycan aggregate is the major structural component of the extracellular matrix of the cartilage, composed of aggrecan, hyaluronan (HA) and link protein (LP). The aggregates provide cartilage with unique gel-like property and resistance to deformation through water absorption. Natural knockout mice of aggrecan, termed cartilage matrix deficiency, and LP-null mice exhibit decreased levels of aggrecan depositon in cartilage and correspond well with their phenotypes such as dwarfism and spinal misalignment, demonstrating in vivo roles of the aggregate in cartilage development and homeostasis. Our recent studies demonstrate that versican/PG-M, another member of aggrecan family with a similar domain structure, binds both HA and LP, forming an aggregate. Further functional analyses of domains and subdomains showed distinct interaction of versican/PG-M with LP from aggrecan, suggesting that the versican/PG-M aggregate may have different function in cartilage.