Galactocerebroside and not glucocerebroside or ceramide stimulate epidermal β-glucocerebrosidase activity

Glycosphingolipids including glucocerebroside (GluCer) and galactocerebroside (GalCer) have been recognized as bioreguratory lipids by our group and others. In addition, our recent study demonstrated that GalCer corrects dry skin conditions in humans. The processing of stratum corneum lipids, which occurs when β-glucocerebrosidase (β-GluCer'ase) changes GluCer to ceramide (Cer), is required to form the epidermal permeability barrier. We herein investigated the effects of GluCer, GalCer and Cer on the processing of GluCer to Cer by assaying epidermal β-CluCer'ase in mice (155%, P < 0.01) when compared to vehicle treated controls, while neither GluCer nor Cer had this effect. Studies using inhibitors of β-GluCer'ase or β-galactosidase and measuring the optimum pH of the enzyme verified that GalCer specifically activated β-GluCer'ase. We confirmed that GalCer significantly increased β-GluCer'ase activity in the outer epidermal fraction (172%, P < 0.01) and that the activation of β-GluCer'ase is not due to a direct activating effect of GalCer on the enzyme. Furthermore, the induction of β-GluCer'ase activity by GalCer was also observed in cultured normal human deratinocytes (123%, P < 0.01). Finally, acylceramide content in stratum corneum was increased in mice treated with GalCer (194%, P < 0.0005). These results indicate that GalCer appears to affect the Cer construct in the stratum corneum by the activation of β-GluCer'ase, which ultimately contribute to an enhancement of barrier formation.