Keratinocyte Integrin α3β1 Promotes Secretion of IL-1α to Effect Paracrine Regulation of Fibroblast Gene Expression and Differentiation

After cutaneous injury, keratinocytes secrete paracrine factors that regulate wound cell functions; dysregulation of this signaling can lead to wound pathologies. Previously, we established that keratinocyte integrin alpha 3 beta 1 promotes wound angiogenesis through paracrine stimulation of endothelial cells. We hypothesize here that alpha 3 beta 1-dependent paracrine signaling from keratinocytes regulates the differentiation state of myofibroblasts. We report that epidermal a3-knockout mice exhibit more wound myofibroblasts and fewer cyclooxygenase 2 (Cox-2)-positive dermal cells than controls. We also found that conditioned medium from a3-expressing mouse keratinocytes (MKa3 thorn), but not from a3-null MK cells (MKa3 e), induces expression of Cox-2 in fibroblasts in a time-and dose-dependent manner and that this induction is mediated by IL-1a. Compared with MKa3 e cells, MKa3 thorn cells secrete more IL-1a and less IL-1RA, a natural IL-1 receptor antagonist. Treatment with an IL-1a neutralizing antibody, recombinant IL-1RA, or IL-1 receptoretargeting small interfering RNA suppresses MKa3 thorn conditioned medium-dependent induction of Cox-2 expression in fibroblasts. Finally, active recombinant IL-1a is sufficient to induce Cox-2 in fibroblasts and to inhibit transforming growth factor-beinduced a-SMA expression. Our findings support a role for keratinocyte integrin a3b1 in controlling the secretion of IL-1a, a paracrine factor that regulates the wound myofibroblast phenotype.