Accelerated human epidermal turnover driven by increased hyaluronan production

•Hyaluronan (HA) is an essential component of extracellular matrix in the skin.•1-ethyl-β-N-acetylglucosaminide (β-NAG2) is a selective inducer of HA production.•β-NAG2 increased epidermal HA and thickness in reconstructed human skin equivalents.•Epidermal proliferation and differentiation were promoted via enhanced HA production.•Epidermal HA production plays a key role in epidermal morphogenesis and homeostasis. Hyaluronan (HA) is an essential component of extracellular matrix in the skin, but its functions in the epidermis remain elusive. We examined the interaction of increased HA production mediated by 1-ethyl-β-N-acetylglucosaminide (β-NAG2), a newly developed highly selective inducer of HA production which is intracellularly converted to UDP-N-acetylglucosamine, a substrate of HA, with epidermal proliferation and differentiation. The amount, molecular size and epidermal tissue distribution of HA and expression of CD44, a cell surface receptor for HA, were analyzed in β-NAG2-treated organ cultured human skin, reconstructed human skin equivalents or cultured human skin keratinocytes. The relationship between HA and epidermal proliferation or differentiation was examined. β-NAG2 significantly increased HA production in the epidermis of skin explants or skin equivalents without affecting molecular size of HA (>2000 kDa) or CD44 mRNA expression. Histochemical experiments revealed that β-NAG2 enhances HA signals in the basal to granular layers of the epidermis of skin equivalents, accompanying increased epidermal stratification. Immunohistochemical experiments demonstrated that signals of Ki67, transglutaminase 1 and filaggrin are increased in β-NAG2-treated skin equivalents, and these observations were confirmed by the data showing that mRNA expression of PCNA, transglutaminase 1 (TGM1) and filaggrin (FLG) is significantly up-regulated by β-NAG2 in skin equivalents. Importantly, blockade of HA production by inhibiting conversion of β-NAG2 to UDP-NAG abolished β-NAG2-mediated up-regulation of PCNA, TGM1 and FLG mRNA expression in cultured keratinocytes. These results suggest that increased epidermal HA production plays a key role in epidermal morphogenesis and homeostasis by accelerating keratinocyte proliferation and differentiation.