S100A12 Induced in the Epidermis by Reduced Hydration Activates Dermal Fibroblasts and Causes Dermal Fibrosis

Disruption of the barrier function of skin increases transepidermal water loss and up-regulates inflammatory pathways in the epidermis. Consequently, sustained expression of proinflammatory cytokines from the epidermis is associated with dermal scarring. We found increased expression of S100A12 in the epidermis of human hypertrophic and keloid scar. Exposing a stratified keratinocyte culture to a reduced-hydration environment increased the expression and secretion of S100A12 by nearly 70%, which in turn activated dermal fibroblasts in vitro. Direct treatment of fibroblasts with conditioned medium collected from stratified keratinocyte culture under reduced-hydration conditions activated fibroblasts, shown by up-regulation of alpha-smooth muscle actin, pro-collagen 1, and F-actin expression. However, this fibroblast activation was not found when S100A12 was knocked down by RNA interference in keratinocytes. Pharmacological blockade of S100A12 receptors, RAGE, or TLR4 inhibited S100A12-induced fibroblast activation. Local delivery of S100A12 resulted in a marked hypertrophic scar formation in a validated rabbit hypertrophic scar model compared with saline control. Our findings indicate that S100A12 functions as a proinflammatory cytokine and suggest that S100A12 is a potential therapeutic target for dermal scarring.