Psoriasis is a chronic skin disease characterized by abnormal keratinocyte proliferation and differentiation, inflammation, and angiogenesis. Although dysfunction of the immune system is known to be an important factor in the pathogenesis of psoriasis, there is also strong evidence that psychological stresses are involved. Neuropeptides are thought to be main mediators of neurogenic inflammation, presumably involved in the pathogenesis of psoriasis. Vasoactive intestinal peptide (VIP) is one of the major neuropeptides in human and rodent skin. In the present study, we examined the effect and mechanism of VIP on vascular endothelial growth factor (VEGF) production by HaCaT cells which is a spontaneous, immortalized, human keratinocyte cell line. Our data indicate the mRNA and protein levels of VEGF by VIP were increased in a concentration-dependent manner. However, this increase was abrogated by pretreatment with an extracellular signal-regulated kinase (ERK) inhibitor PD98059 or p38MAPK inhibitor SB203580; pretreatment with c-Jun N-terminal kinase (JNK) inhibitor SP600125 did not attenuate the effects of VIP on the expression of VEGF. In addition, VIP treatment induced rapid phosphorylation of ERK1/2 and p38MAPK, and PD98059 and SB203580 were able to inhibit VIP-induced phosphorylation of ERK1/2 and p38MAPK, respectively. These results suggest that VIP increases the expression of VEGF through the ERK1/2 and p38MAPK signaling pathway in human HaCaT cells.
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