HAIR FOLLICLE PROTEOGLYCANS

Proteoglycans are polymorphic macromolecules present in all mammalian tissues, including the skin and its appendages. They consist of a core protein to which one or more glycosaminoglycan chains are covalently attached. Broadly, they can be divided into classes based on location and core protein structure. These classes include cell surface proteoglycans, basement membrane proteoglycans, small leucine-rich proteoglycans, large proteoglycans aggregating with hyaluronan, and intracellular granule proteoglycans. They have a wide range of functions, but little is known of the proteoglycans that are present in the epithelial and stromal compartments of hair follicles. However, the transmembrane proteoglycan syndecan may be important in follicle morphogenesis, both with respect to the epithelium and dermal papilla cells. Syndecan may possess both heparan and chondroitin sulfate chains, interacts with growth factors as well as fibronectin and interstitial collagens, and can associate in a transmembrane relationship with the cellular cytoskeleton. It is strongly expressed in mesenchymal cells coincident with stromal-epithelial interactions during tissue morphogenesis. Proteoglycans are present in all basement membranes, including those surrounding the epithelial compartment of hair follicles. Additionally, and quite unlike the dermis, the dermal papilla is enriched in basement-membrane components, especially a chondroitin 6-sulfate - containing proteoglycan, BM-CSPG. The function of this proteoglycan is not known, but developmental studies indicate that it may have a role in stabilizing basement membranes. In the hair cycle, BM-CSPG decreases through catagen and is virtually absent from the telogen papilla. One or more heparansulfate proteoglycans, including perlecan, are also present in papilla and follicular basement membranes. Some of the leucine-rich proteoglycans, such as decorin, are associated with interstitial collagens, and may influence fibrillogenesis. Because small amounts of types I and III collagens may be present in anagen papillae, decorin may also be a constituent.