Rationale: Idiopathic pulmonary fibrosis (IPF) is a disease of progressive lung fibrosis with a high mortality rate. In organ repair and remodeling, epigenetic events are important. MicroRNAs (miRNAs) regulate gene expression post-transcriptionally and can target epigenetic molecules important in DNA methylation. The miR-17∼92 miRNA cluster is critical for lung development and lung epithelial cell homeostasis and is predicted to target fibrotic genes and DNA methyltransferase (DNMT)-1 expression.

Objectives: We investigated the miR-17∼92 cluster expression and its role in regulating DNA methylation events in IPF lung tissue.

Methods: Expression and DNA methylation patterns of miR-17∼92 were determined in human IPF lung tissue and fibroblasts and fibrotic mouse lung tissue. The relationship between the miR-17∼92 cluster and DNMT-1 expression was examined in vitro. Using a murine model of pulmonary fibrosis, we examined the therapeutic potential of the demethylating agent, 5′-aza-2′-deoxycytidine.

Measurements and Main Results: Compared with control samples, miR-17∼92 expression was reduced in lung biopsies and lung fibroblasts from patients with IPF, whereas DNMT-1 expression and methylation of the miR-17∼92 promoter was increased. Several miRNAs from the miR-17∼92 cluster targeted DNMT-1 expression resulting in a negative feedback loop. Similarly, miR-17∼92 expression was reduced in the lungs of bleomycin-treated mice. Treatment with 5′-aza-2′-deoxycytidine in a murine bleomycin-induced pulmonary fibrosis model reduced fibrotic gene and DNMT-1 expression, enhanced miR-17∼92 cluster expression, and attenuated pulmonary fibrosis.

Conclusions: This study provides insight into the pathobiology of IPF and identifies a novel epigenetic feedback loop between miR-17∼92 and DNMT-1 in lung fibrosis.