Periostin in skin tissue and skin-related diseases.

Extracellular matrix (ECM) is not only involved in the maintenance of normal physiological tissue but also in interactions with other ECM components, tissue remodeling, and modulating immune responses. The skin provides a distinctive environment characterized by rich fibroblasts producing various ECM proteins, epithelial-mesenchymal interactions, and immune responses induced by external stimuli. Recently, periostin-a matricellular protein-has been highlighted for its pivotal functions in the skin. Analysis of periostin null mice has revealed that periostin contributes to collagen fibrillogenesis, collagen cross-linking, and the formation of ECM meshwork via interactions with other ECM components. Periostin expression is enhanced by mechanical stress or skin injury; this is indicative of the physiologically protective functions of periostin, which promotes wound repair by acting on keratinocytes and fibroblasts. Along with its physiological functions, periostin plays pathogenic roles in skin fibrosis and chronic allergic inflammation. In systemic sclerosis (SSc) patients, periostin levels reflect the severity of skin fibrosis. Periostin null mice have shown reduced skin fibrosis in a bleomycin-induced SSc mouse model, indicating a key role of periostin in fibrosis. Moreover, in atopic dermatitis (AD), attenuated AD phenotype has been observed in periostin null mice in a house dust mite extract-induced AD mouse model. Th2 cytokine-induced periostin acts on keratinocytes to produce inflammatory cytokines that further enhance the Th2 response, thereby sustaining and amplifying chronic allergic inflammation. Thus, periostin is deeply involved in the pathogenesis of AD and other inflammation-related disorders affecting the skin. Understanding the dynamic actions of periostin would be key to dissecting pathogenesis of skin-related diseases and to developing novel therapeutic strategies.