Neu differentiation factor upregulates epidermal migration and integrin expression in excisional wounds

Abstract

Neu differentiation factor (NDF) is a 44-kD glycoprotein which was isolated from ras-transformed rat fibroblasts and indirectly induces tyrosine phosphorylation of the HER-2/neu receptor via binding to either the HER-3 or HER-4 receptor. NDF contains a receptor binding epidermal growth factor (EGF)-like domain and is a member of the EGF family. There are multiple different isoforms of NDF which arise by alternative splicing of a single gene. To date, in vivo biologic activities have not been demonstrated for any NDF isoform. Since NDF, HER-2/neu, and HER-3 are present in skin, and other EGF family members can influence wound keratinocytes in vivo, we investigated whether NDF would stimulate epidermal migration and proliferation in a rabbit ear model of excisional wound repair. In this model, recombinant human NDF- α2 (rhNDF-α2), applied once at the time of wounding, induced a highly significant increase in both epidermal migration and epidermal thickness at doses ranging from 4 to 40 μg/cm2. In contrast, rhNDF-α1, rhNDF-β1, and rhNDF-β2 had no apparent biologic effects in this model. rhNDF-α2 also induced increased neoepidermal expression of α5 and α6 integrins, two of the earliest integrins to appear during epidermal migration. In addition, rhNDF-α2-treated wounds exhibited increased neoepidermal expression of cytokeratin 10 and filaggrin, both epidermal differentiation markers. NDF α isoforms were expressed in dermal fibroblasts of wounded and un-wounded skin, while both HER-2/neu and HER-3 were expressed in unwounded epidermis and dermal adnexa. In wounds, HER-2/neu expression was markedly decreased in the wound neoepidermis while neoepidermal HER-3 expression was markedly upregulated. Taken together, these results suggest that endogenous NDF-α2 may function as a paracrine mediator directing initial epidermal migration during cutaneous tissue repair.