Comprehensive microRNA analysis in bleomycin-induced pulmonary fibrosis identifies multiple sites of molecular regulation

The molecular mechanisms of lung injury and fibrosis are incompletely understood. MicroRNAs (miRNAs) are crucial biological regulators that act by suppressing their target genes and are involved in a variety of pathophysiological processes. To gain insight into miRNAs in the regulation of lung fibrosis, total RNA was isolated from mouse lungs harvested at different days after bleomycin treatment, and miRNA array with 1,810 miRNA probes was performed thereafter. MiRNAs expressed in lungs with bleomycin treatment at different time points were compared with miRNAs expressed in lungs without bleomycin treatment, resulting in 161 miRNAs differentially expressed. Furthermore, miRNA expression patterns regulated in initial and late periods after bleomycin were identified. Target genes were predicted in silico for differentially expressed miRNAs, including let-7f, let-7g, miR-196b, miR-16, miR-195, miR-25, miR-144, miR-351, miR-153, miR-468, miR-449b, miR-361, miR-700, miR-704, miR-717, miR-10a, miR-211, miR-34a, miR-367, and miR-21. Target genes were then cross-referenced to the molecular pathways, suggesting that the differentially expressed miRNAs regulate apoptosis, Wnt, Toll-like receptor, and TGF-β signaling. Our study demonstrated a relative abundance of miRNA levels in bleomycin-induced lung fibrosis. The miRNAs and their potential target genes identified may contribute to the understanding of the complex transcriptional program of lung fibrosis.