Evidence for Altered Wnt Signaling in Psoriatic Skin

The Wnt gene family encodes a set of highly conserved secreted signaling proteins that have major roles in embryogenesis and tissue homeostasis. Yet the expression of this family of important mediators in psoriasis, a disease characterized by marked changes in keratinocyte growth and differentiation, is incompletely understood. We subjected 58 paired biopsies from lesional and uninvolved psoriatic skin and 64 biopsies from normal skin to global gene expression profiling. WNT5A transcripts were upregulated fivefold in lesional skin, accompanied by increased Wnt-5a protein levels. Notably, WNT5A mRNA was markedly induced by IL-1 alpha, tumor necrosis factor-alpha, IFN-gamma, and transforming growth factor-alpha in cultured keratinocytes. Frizzled 2 (FZD2) and FZD5, which encode receptors for Wnt5A, were also increased in lesional psoriatic skin. In contrast, expression of WIF1 mRNA, encoding a secreted antagonist of the Wnt proteins, was downregulated 410-fold in lesional skin, along with decreased WNT inhibitory factor (WIF)-1 immunostaining. Interestingly, pathway analysis along with reduced AXIN2 expression and lack of nuclear translocation of beta-catenin indicated a suppression of canonical Wnt signaling in lesional skin. The results of our study suggest a shift away from canonical Wnt signaling toward noncanonical pathways driven by interactions between Wnt-5a and its cognate receptors in psoriasis, accompanied by impaired homeostatic inhibition of Wnt signaling by WIF-1 and dickkopf.