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 proteog lycans, basement membrane proteoglycans, small leucine-rich proteoglyc ans, large proteoglycans aggregating with hyaluronan, and intracellula r granule proteoglycans. They have a wide range of functions, but litt le is known of the proteoglycans that are present in the epithelial an d stromal compartments of hair follicles. However, the transmembrane p roteoglycan 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 gr owth factors as well as fibronectin and interstitial collagens, and ca n associate in a transmembrane relationship with the cellular cytoskel eton. It is strongly expressed in mesenchymal cells coincident with st romal-epithelial interactions during tissue morphogenesis. Proteoglyca ns 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 proteogly can, BM-CSPG. The function of this proteoglycan is not known, but deve lopmental studies indicate that it may have a role in stabilizing base ment membranes. In the hair cycle, BM-CSPG decreases through catagen a nd is virtually absent from the telogen papilla. One or more heparansu lfate proteoglycans, including perlecan, are also present in papilla a nd follicular basement membranes. Some of the leucine-rich proteoglyca ns, such as decorin, are associated with interstitial collagens, and m ay influence fibrillogenesis. Because small amounts of types I and III collagens may be present in anagen papillae, decorin may also be a co nstituent.