MicroRNAs in Skin Diseases

MicroRNAs (miRNAs) comprise a class of small noncoding RNA molecules that are involved in the epigenetic modulation of gene expression. miRNAs act primarily within the cell; however, recent evidence has also shown the presence of miRNAs in cell-free environments, including serum and plasma. The role of miRNAs in skin biology is still incomplete; however, it is now evident that miRNAs indeed are involved in various cellular processes in both normal and diseased skin. Only a few skin-specific miRNAs have been described, e.g., miR-203. Until now the majority of studies have characterized specific patterns of miRNA expression levels in lesional diseased skin relative to nonlesional and healthy skin. Thus, both benign inflammatory skin diseases such as psoriasis, atopic dermatitis (AD), and allergic contact dermatitis (ACD) and malignant skin diseases including basal cell carcinoma and melanoma have been associated with specific miRNA signatures. Some miRNAs appear to be consistently deregulated across several skin diseases indicating a common role in fundamental cellular processes in these pathologies. For instance, aberrant expression of miR-21, -142-3p, and -155 has been reported for psoriasis, AD, and ACD. In this chapter, we summarize the current knowledge on the aberrant expression and biological role of miRNAs in skin diseases. In addition, we present the most recent progress within the clinical utility of miRNAs as biomarkers for various skin diseases.