Paracrine regulation of epidermal growth via Smad3

Skin is the largest organ in the body and it serves as a protective barrier. It is made up of an outermost epidermal layer and an underlying dermal layer. The formation and maintenance of the epidermis depend on the precise regulation of keratinocyte proliferation, differentiation and apoptosis. This homeostasis relies on a network of cytokines and growth factors, one of the most important being transforming growth factor β (TGFβ). TGFβ regulates cell growth, apoptosis, differentiation, migration and extracellular matrix production. TGFβ signals via Smad proteins in the canonical signaling pathway (Figure 1). TGFβ is an important growth inhibitor of epithelial cells, but it is also one of the most pro-fibrotic cytokine in vivo. However, the role of TGFβ signaling in fibroblasts in the dermis and the paracrine regulation of keratinocytes in the epidermis remain unclear. [1st Award