Proteoglycan expression patterns in human hair follicle

Summary Background Proteoglycans (PGs) are known to play key roles in many cellular signalling pathways involved in hair follicle biology. Although some PG core proteins have previously been described in adult human hair follicles, their glycosaminoglycan (GAG) moieties have been less studied. Objectives To add knowledge about PG core protein and GAG distributions in human anagen hair follicle and, for selected follicles, during catagen. Methods We used immunohistochemistry and immunohistofluorescence to revisit the expression pattern of GAG chains and core proteins in human hair follicle. The studied epitopes included CD44v3, syndecan‐1, perlecan, versican, aggrecan, biglycan, heparan sulphate (HS), chondroitin sulphate (CS), dermatan sulphate (DS) and keratan sulphate (KS). Results The membrane PGs syndecan‐1 and CD44v3 were respectively detected in the epithelial part of whole hair and in the outer root sheath basal layer. The dermal part of the hair follicle contained high amounts of extracellular PGs such as perlecan, versican, aggrecan, biglycan and their saccharidic moieties, namely HS, CS, DS and KS. We also observed a variable distribution of these components along the hair follicle. Especially, we noted a PG impoverishment at the very bottom of the anagen bulb. Moreover, while type D chondroitin expression remained unaffected, 4C3‐CS and PG4‐CS/DS epitopes respectively decreased in the dermal papilla and the connective tissue sheath, at the onset of catagen. Conclusions GAG and PG expression along the human anagen hair follicle was characterized by (i) discontinuities mainly affecting the basement membrane and (ii) disappearance of some epitopes at catagen onset. These results are discussed in term of functionalities in nutrient diffusion, cell proliferation and differentiation, and hair protection.