MicroRNA-mediated keratinocyte hyperproliferation in psoriasis vulgaris

Abstract

Psoriasis is a chronic inflammatory skin disease characterized by intense proliferation and abnormal differentiation of keratinocytes, although the pathogenesis is still not completely clarified. We investigated the mechanism of keratinocyte proliferation seen in psoriasis, focusing on microRNA (miRNA). miRNAs were extracted from tissues and sera of psoriasis, atopic dermatitis and healthy control. To determine pathogenic miRNAs, we performed miRNA polymerase chain reaction (PCR) array analysis. The results were confirmed with quantitative real-time PCR, in situ hybridization, immunohistochemistry, transient transfection of siRNA and inhibitor in cultured keratinocytes and Western blotting. PCR array analysis using tissue miRNA demonstrated miR-424 level was markedly decreased in psoriasis skin in vivo. Protein expression of mitogen-activated protein kinase kinase 1 (MEK1) or cyclin E1, predicted target genes of miR-424, was increased in psoriatic skin, although their mRNA levels were not. The transfection of specific inhibitor of miR-424 in normal human keratinocytes led to upregulation of MEK1 or cyclin E1 protein, and resulted in increased cell proliferation. On the other hand, cell number was significantly decreased when cells were transfected with siRNA for MEK1 or cyclin E1. Furthermore, we first investigated serum miRNA levels in psoriasis. Although not significant, serum miR-424 concentration tended to be decreased in patients with psoriasis compared with healthy controls. Decreased miR-424 expression and subsequently increased MEK1 or cyclin E1 may play a key role in the pathogenesis of psoriasis. Investigation of the regulatory mechanisms of keratinocyte proliferation by miRNA may lead to new treatments and a disease activity marker.