Exploring Th2 cytokine-driven ceramide enzyme expression and epidermal barrier dysfunction in an atopic dermatitis explant model

Atopic dermatitis (AD) is a chronic inflammatory skin disorder linked to immune dysregulation and ceramide deficiency. We used human skin explant models to investigate the role of the de novo ceramide synthesis pathway in AD pathogenesis. Skin explants were maintained at an air-liquid interface and treated for seven days with cytokines that drive the inflammation and itch of AD: IL-4/IL-13 alone, IL-4/IL-13 with IL-33 or IL-31, or IL-33/IL-31 alone. Epidermal spongiosis, a histological characteristic of AD, was increased in explant cultures treated with IL-4/IL-13, IL-33, and the combination of IL-4/IL-13 with IL-33 or IL-31, but not with IL-31 alone. Across all treatments leading to spongiosis, gene and protein expression of the early (DSG1) and late (FLG) differentiation markers was decreased, as in AD, as shown by real-time polymerase chain reactions and immunostaining, respectively. Gene expression of AD markers POSTN (encoding periostin) and CAII (encoding carbonic anhydrase) were dramatically increased by IL4/13 alone but not when IL-31 or IL-33 was added. SPTLC3 and SPTSSB expression, key enzymes for ceramide synthesis required for skin differentiation, were decreased by treatment with IL-4/IL-13 or IL-33 but not IL-31. These results suggest a role for the reduction of differentiation-related SPT complex components in AD and highlight explant cultures as models for inflammatory skin disease research and therapeutic testing.