An expression screen for aged-dependent microRNAs identifies miR-30a as a key regulator of aging features in human epidermis

The mechanisms affecting epidermal homeostasis during aging remain poorly understood. To identify age-related microRNAs, a class of non-coding RNAs known to play a key role in the regulation of epidermal homeostasis, an exhaustive miRNA expression screen was performed in human keratinocytes from young or elderly subjects. Many microRNAs modulated by aging were identified, including miR-30a, in which both strands were overexpressed in aged cells and epidermal tissue. Stable MiR-30a over-expression strongly impaired epidermal differentiation, inducing severe barrier function defects in an organotypic culture model. A significant increase was also observed in the level of apoptotic cells in epidermis over-expressing miR-30a. Several gene targets of miR-30a were identified in keratinocytes, including LOX (encoding lysyl oxidase, a regulator of the proliferation/differentiation balance of keratinocytes), IDH1 (encoding isocitrate dehydrogenase, an enzyme of cellular metabolism) and AVEN (encoding a caspase inhibitor). Direct regulation of LOX, IDH1 and AVEN by miR-30a was confirmed in human keratinocytes. They were, moreover, observed to be repressed in aged skin, suggesting a possible link between miR-30a induction and skin-aging phenotype. This study revealed a new miRNA actor and deciphered new molecular mechanisms to explain certain alterations observed in epidermis during aging and especially those concerning keratinocyte differentiation and apoptosis.