Dysregulation of MicroRNA biogenesis in diabetic skin

Clinical skin manifestations are common in diabetes, often being the first sign of the metabolic disorder. Molecular mechanisms underlying such defects are largely unknown. We investigated whether microRNAs (miRNAs), small non coding RNAs regulating gene expression at post-transcriptional level and playing a role in skin homeostasis, are differentially expressed in diabetic and non-diabetic skin. miRNA profiling by microarray analysis was performed on RNA extracted from the skin of streptozotocin-induced diabetic mice, a model of type I diabetes. More than 400 different mouse miRNA species were identified; expression analysis revealed a general downmodulation in diabetic skin. In detail, among the 30 most significantly modulated miRNAs, 27 were downregulated and 3 were upregulated in diabetic mice. Pathway analysis using Tarbase showed an enrichment of signature-miRNA target genes related to TGF-beta and Wnt signaling. We investigated whether miRNA alteration in diabetic skin associates with changes in the expression of genes involved in miRNA biogenesis. Dicer1, DCGR8, Drosha, Exportin 5, and Ago2 were analyzed by real time-PCR; all, but Ago2, were expressed at significantly lower levels in the skin of diabetic mice compared to non-diabetic controls. Reduction in selected miRNA expression levels and in miRNA biogenesis genes was confirmed in RNA extracted from the skin of db/db mice, a model of type 2 diabetes, in which also Ago2 was significantly reduced. In vitro experiments with human dermal fibroblasts showed that hypoxia (250 mM CoCl2 or 1% O2, for 24 hours), but not hyperglycemia (35 mM D-Glucose, for three weeks), induces Dicer and Drosha downregulation. These findings indicate decreased expression of the majority of modulated miRNAs in diabetic skin associated to reduced levels of genes responsible for miRNA biogenesis, and suggest that miRNA dysregulation is linked to the hypoxic condition of diabetic skin.