Junctions and inflammation in the skin.

The skin forms a life-sustaining barrier between the organism and physical environment. The physical barrier of skin is mainly localized in the stratum corneum (SC); however, nucleated epidermis also contributes to the barrier through tight, gap, and adherens junctions (AJs), as well as through desmosomes and cytoskeletal elements. Many inflammatory diseases, such as atopic dermatitis (AD) and psoriasis, are associated with barrier dysfunction. It is becoming increasingly clear that the skin barrier function is not only affected by inflammatory signals but that defects in structural components of the barrier may be the initiating event for inflammatory diseases. This view is supported by findings that mutations in filaggrin, a key structural epidermal barrier protein, cause the inflammatory skin disease AD, and that a loss of AJ components, namely epidermal p120 catenin or α-catenin results in skin inflammation.