Vasoactive intestinal peptide and inflammatory cytokines enhance vascular endothelial growth factor production from epidermal keratinocytes

Summary Background Overexpression of vascular endothelial growth factor (VEGF) in epidermal lesions of psoriasis is well documented; however, its underlying mechanisms are largely unknown. We have recently demonstrated that vasoactive intestinal peptide (VIP) induces the production of cytokines such as interleukin‐6 and stem cell factor from keratinocytes, thereby contributing to the development of inflammatory dermatoses such as psoriasis. Objectives In this study, we attempted to determine whether VIP could increase the production of VEGF in human keratinocytes. Methods We examined the expression of VEGF using reverse transcription–polymerase chain reaction, immunocytochemistry, enzyme‐linked immunosorbent assay and immunoblotting in normal human epidermal keratinocytes and human epidermal keratinocyte cell line DJM‐1 cultured in the absence or presence of VIP and/or inflammatory cytokines. Results We demonstrate that human keratinocytes produced VEGF in a steady state at both mRNA and protein levels. VIP significantly upregulated the production of VEGF in keratinocytes in a dose‐ and time‐dependent manner. The VIP‐mediated production of VEGF was further enhanced by inflammatory cytokines such as interferon‐γ, tumour necrosis factor‐α and interleukin‐4, with maximum enhancement being observed with the combination of VIP and interferon‐γ. Conclusions VIP and other cytokines from nerve endings, mast cells and local inflammatory cells are capable of enhancing VEGF production from epidermal keratinocytes, which may underlie excessive angiogenesis and vasodilation in skin lesions of psoriasis.