Rat hair follicle dermal papillae have an extracellular matrix containing basement membrane components

Dermal papillae are small mesenchymally derived zones at the bases of hair follicles which have an important role in hair morphogenesis in the embryo and control of the hair growth cycle in postnatal mammals. The cells of the papilla are enmeshed in a dense extracellular matrix which undergoes extensive changes in concert with the hair cycle. Here it is shown that this matrix in anagen pelage follicles of postnatal rats contains an abundance of basement membrane components rather than dermal components such as interstitial collagens. In particular, type IV collagen, laminin, and basement membrane types of chondroitin sulfate and heparan sulfate proteoglycans are present as matrix components. Dermal papilla cells, when initially isolated from adult rat vibrissae and cultured in vitro, retained the potential to synthesize this spectrum of matrix components, but this was gradually lost, to be replaced by synthesis of other components including type I and III collagens. It seems likely therefore that the dermal papilla cells in vivo synthesize a basement membrane type of extracellular matrix, although a contribution from epithelial, and in some cases capillary endothelial, cells cannot be ruled out.