Protective role of Galectin-7 for skin barrier impairment in atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) patients have a barrier disorder in association with Th2 dominant skin inflammation. Galectin-7 (Gal-7), a soluble unglycosylated lectin, is highly expressed in the stratum corneum of AD patients. However, the biological significance of increased Gal-7 expression in AD skin lesions remains unclear. OBJECTIVE: We aimed to investigate the production mechanism and functional role of Gal-7 in AD patients and IL-4/IL-13-stimulated epidermal keratinocytes. METHODS: We assessed the Gal-7 expression levels in skin lesions and sera from AD patients. Gal-7 levels were also measured in monolayered normal human epidermal keratinocytes (NHEKs) and 3-dimensional (3D)-reconstructed epidermis in the presence or absence of IL-4/IL-13 with or without Stat3, Stat6 or Gal-7 gene silencing. RESULTS: Gal-7 was highly expressed in the stratum corneum or intercellular space of AD lesional epidermis as assessed by the stratum corneum proteome analysis and immunohistochemistry. A positive correlation was noted between serum Gal-7 level and transepidermal water loss in patients with AD. These clinical findings were corroborated by our in vitro data, which showed that IL-4/IL-13 facilitated the extracellular release of endogenous Gal-7 in both monolayered NHEKs and 3D-reconstructed epidermis. This machinery was caused by IL-4/IL-13-induced cell damage and inhibited by knockdown of Stat6 but not Stat3 in NHEKs. Moreover, we performed Gal-7 knockdown experiment on 3D-reconstructed epidermis and the result suggested that endogenous Gal-7 serves as a protector from IL-4/IL-13-induced disruption of cell-to-cell adhesion and/or cell-to-extracellular matrix adhesion. CONCLUSION AND CLINICAL RELEVANCE: Our study unveils the characteristic of Gal-7 and its possible role as an alarmin that reflects the IL-4/IL-13-induced skin barrier impairment in AD.