Various applications of microRNAs in skin diseases

microRNA (miRNA) is a family of non-coding RNAs, which consists of 19-25 nucleotides and regulates the expression of approximately 30% of human protein-coding mRNAs. miRNAs can bind to complementary sequences of the three prime untranslated regions of target mRNAs, leading to the modulation of gene expression. By altering target expression, miRNAs can affect various cellular activities including cell proliferation and cell development in vitro or carcinogenesis and immune response in vivo. A lot of researches have paid attention to the possibility that miRNAs play a role in the pathogenesis of various human disorders including skin diseases. For example, miR-29a down-regulation is thought to mediate the posttranscriptional up-regulation of collagens, which contributes to the tissue fibrosis in scleroderma. In addition, recent studies indicate that extracellular miRNA levels may be useful for the diagnosis and/or the estimation of disease activity of skin diseases. miR-150 levels were significantly decreased in sera of scleroderma patients, and were inversely correlated with the prevalence of pitting scars/ulcers and the incidence of anti-topoisomerase I antibody. Currently, the therapeutic value of miRNAs for the treatment of human diseases is under evaluation in animal models. let-7a can be overexpressed in the mouse skin by intermittent intraperitoneal miRNA injection, and skin fibrosis induced by bleomycin in mice can be improved by the supplementation of let-7a. This paper discusses the possible applications of miRNAs in the clarification of pathogenesis, diagnosis, evaluation of disease activity and treatment of skin diseases.