Does therapeutic intervention in atopic dermatitis normalize epidermal Notch deficiency?

This viewpoint presents a unifying concept for the treatment of atopic dermatitis (AD) that is based on the improvement of deficient Notch signalling, which appears to represent the fundamental epithelial defect of AD resulting in epidermal and immunological barrier dysfunction. One study of AD patients demonstrated a marked epidermal deficiency of Notch receptors and several mouse models with genetically suppressed Notch signalling exhibit dry skin, signs of scratching, skin barrier abnormalities, increased transepidermal water loss and Th2 cell-mediated immunological changes closely resembling human AD. Notch signalling is critically involved in the differentiation of regulatory T cells, in the feedback inhibition of activated innate immunity, in the repression of activating protein-1 (AP-1), the regulation of late epidermal differentiation associated with filaggrin- and stratum corneum barrier lipid processing, in aquaporin 3- and claudin-1 expression and in keratinocyte-mediated release of thymic stromal lymphopoietin (TSLP), which promotes Th2-driven immune responses with TSLP- and IL-31-mediated stimulation of cutaneous sensory neurons involved in the induction of itch. Translational evidence will be provided that all major therapeutic regimens employed for the treatment of AD such as glucocorticoids, calcineurin inhibitors and UV radiation may converge in the upregulation of impaired Notch signalling, the proposed pathogenic defect of AD.