microRNA-223 suppresses histone deacetylase 2 in chronic obstructive pulmonary disease

Background: Histone Deacetylase 2 (HDAC2) is a key epigenetic modifier whose expression and activity have been found downregulated in patients with chronic obstructive pulmonary disease (COPD). MicroRNAs (miRNAs) are a group of small, non-coding RNA molecules that have emerged as gene silencers. We hypothesized that miRNAs are involved in the regulation of HDAC2 activity and expression. Methods: Levels of miRNA and mRNA were quantified by quantitative PCR. Protein expression and activity of HDAC2 were measured by Western Blotting and HDAC-Glo assay. Manipulation of miRNA levels in human pulmonary endothelial cells (HPAEC) was achieved by using electroporation with either miRNA inhibitors or miRNA mimics. Interaction between miRNA-223 and HDAC2 promoter was assessed with a reporter gene assay. Results: Prediction software (miRWalk ®) identified miRNA-223 as a potential repressor of HDAC2 (miRNA-223 was recently found to be upregulated in COPD patients (Ezzie, M.E. et al., Thorax 2012; 67(2):122-131)). Stimulation experiments with inflammatory cytokines involved in the pathogenesis of COPD (e.g. IL-1β, IL-6 and TNF-α) induced the expression of miRNA-223 in HPAEC. Subsequent functional experiments demonstrated that overexpression of miRNA-223 decreased both HDAC2 expression levels and its activity in HPAEC. Direct miRNA-target interaction was confirmed by reporter gene assay. Conclusion: Our data suggest that miRNA-223, the most prevalent miRNA in COPD, controls expression and activity of HDAC2 in pulmonary cells. This pathway provides a novel pathogenetic link between dysregulated miRNA expression and epigenetic activity in COPD.