Influence of heparan sulfate chains in proteoglycan at the dermal-epidermal junction on epidermal homeostasis

: Basement membrane (BM) plays important roles in skin morphogenesis and homeostasis by controlling dermal–epidermal interactions. However, it remains unclear whether heparan sulfate (HS) chains of proteoglycan in epidermal BM contribute to epidermal homeostasis. To explore the function of HS chains at the dermal–epidermal junction (DEJ), we used a skin equivalent (SE) model. This model lacked HS at the DEJ and showed abnormal expression of the differentiation markers filaggrin and loricrin; similar changes were seen in ultraviolet B‐irradiated human skin. Perlecan (core‐protein of HS proteoglycan) remained localized at the DEJ in both SE and UV‐irradiated human skin. Heparanase, which degrades HS, was increased in epidermis of UV‐irradiated skin, compared with unirradiated skin. We found that deposition of HS at the DEJ in the SE model was markedly augmented by a synthetic heparanase inhibitor, and release of HS into conditioned medium was suppressed. The inhibitor also increased filaggrin and loricrin expression. Moreover, the recovery of HS was associated with an increase of Ki67‐positive basal cells, compared with control SE cultured without inhibitor. Comparative gene expression analysis in epidermis of SE cultured in the presence and absence of heparanase inhibitor, using DNA microarrays, showed that recovery of HS was associated with increased expression of differentiation‐related genes and down‐regulation of degradation‐enzyme‐related genes. These results indicate that degradation of HS at the DEJ by heparanase impairs epidermal homeostasis in SE, leading to abnormal differentiation and proliferation behaviour. Thus, HS chains in epidermal BM appear to play an important role in epidermal homeostasis.