The interleukin-1α stimulated expression of the wrinkle-inducing elastase neprilysin in adult human dermal fibroblasts is mediated via the intracellular signaling axis of ERK/JNK/c-Jun/c-Fos/AP-1

Neprilysin is a skin wrinkle-inducing membrane bound elastase that is expressed abundantly in UV-exposed and in aged dermal fibroblasts. The overexpression of neprilysin is closely associated with enhanced epithelial-mesenchymal cytokine interactions mainly via interleukin (IL)-1 alpha, which has the distinct potential to stimulate the expression of neprilysin by human dermal fibroblasts (HDFs). The over-expression of neprilysin also accelerates the formation of wrinkles, accompanied by disruptions of the three-dimensional architecture of dermal elastic fibers that are responsible for the loss of skin elasticity. Because the signaling pathway(s) that lead to the IL-1 alpha-stimulated expression of neprilysin in HDFs remain unclear, we characterized the signaling pathway involved, including their related transcription factors, in IL-1 alpha-treated HDFs. Since qRT-PCR analysis revealed that the mRNA expression level of neprilysin is stimulated to a stronger extent in adult HDFs (aHDFs) by IL-1 alpha than in neonatal HDFs, we used aHDFs for the signaling analysis. Western blotting analysis of the phosphorylation of signaling factors revealed that IL-1 alpha significantly stimulated the phosphorylation of ERK1/2, RSK, JNK, p38, MSK1, NFkB, c-Jun, ATF-2, CREB, and STAT3. Analysis using various signaling inhibitors demonstrated that inhibiting ERK and JNK but not p38, MSK1, NFkB, or STAT3 significantly abrogated the IL-1 alpha stimulated expression of neprilysin at the mRNA, protein, and enzyme activity levels. Furthermore, silencing c-Fos significantly down-regulated the IL-1 alpha-increased expression of neprilysin at the protein and enzyme activity levels. These findings strongly suggest that the IL-1 alpha-stimulated expression of neprilysin in aHDFs is mediated via the intracellular signaling axis of ERK/JNK/c-Jun/c-Fos/AP-1.