Expression and potential function of beta-amyloid precursor proteins during cutaneous wound repair

sAPP, the secretory domain of the beta-amyloid precursor protein (APP), exerts a growth promoting and motogenic activity on keratinocytes. Here we report on the expression of APP and its homologue, the amyloid precursor like protein 2 (APLP2), during cutaneous wound repair using a full-thickness excisional wound healing model in mice. In unwounded skin APP was predominantly expressed in the basal cell layer. During wound healing increased suprabasal expression of APP was observed in all cell layers of the hyperproliferative epithelium at the wound margin. APP mRNA was increased up to 2.3-fold, whereas the APLP2 mRNA was decreased. Immunocytochemically, all proliferation competent keratinocytes of the normal as well as the wound site epidermis showed increased expression of APP but not of APLP2. Using culture models of keratinocyte differentiation the release of sAPP was found to be significantly higher in proliferating cells, i.e., when cultured at subconfluency or at low [Ca(2+)], than in quiescent, partially differentiated keratinocytes cultured at confluency or at high [Ca(2+)]. Our results suggest that sAPP secretion is presumably also increased in proliferation competent keratinocytes of the wound margin and that sAPP due to its growth promoting and motogenic function might participate in the control of epidermal wound repair.