Mirnas In Lung Damage And Repair Mechanisms

The molecular mechanisms of lung injury are incompletely understood, especially in the fields of lung fibrosis and immune complex induced acute lung injury. MiRNAs are short (about 22 bp in length), single-stranded, and non-coding RNAs that inhibit the production of target proteins or induce degradation of mRNAs by binding target mRNAs at complementary sites in 3'-untranslated regions (3'-UTRs) or coding sequences and thereby suppressing target gene expression. 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 microarray with 1810 miRNA probes was performed thereafter. MiRNAs expressed in lungs with bleomycin treatment at different time points were compared to 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-127, 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- signaling. In addition, we found that miR-127 appeared down-regulated during lung injury. We set out to investigate the role of miR-127 in lung injury and inflammation. Expression of miR-127 significantly reduced cytokine release by macrophages. Looking into the mechanisms of the regulation of inflammation by miR-127, we found that IgG FeγReceptorⅠ(FcγRI/CD64) was a target of miR-127, as evidenced by reduced CD64 protein expression in macrophages over-expressing miR-127. Furthermore, miR-127 significantly reduced the luciferase activity with a reporter construct containing the native 3'-UTR of CD64. Importantly, we demonstrated that miR-127 attenuated lung inflammation in an IgG immune complex (IgG IC) model in vivo. As accessed by lung histology, cytokine release in bronchoalveolar lavage fluid, including interleukin-6 (IL-6), Tumor necrosis factor-α(TNF-α), macrophage inflammatory protein-1β(MIP-1β), macrophage inflammatory protein-2 (MIP-2), Monocyte chemotactic protein-1 (MCP-1) and chemokine (C-X-C motif) ligand-1 (KC), lung permeability assay, compliment component 5a (C5a) and signal transducer and activator of transcription 3 (STAT3) protein assays. Therefore, these data suggested that miR-127 targets macrophage CD64 leading to reduction of lung inflammation.Altogether, we investigated the miRNA expression patterns in lung tissues of bleomycin model, and found the differentially expressed miRNAs during distinct pathologic phases of lung fibrosis. We also predicted gene regulation by differentially expressed miRNAs during lung fibrosis, and cross-referenced to the molecular pathways in distinct pathologic phases of lung fibrosis. We identified for the first time that miR-127 was involved in acute lung inflammation. In particular, we found that CD64 is a bona fide target of miR-127. MiR-127 administration inhibited the inflammatory response of IgG IC induced acute lung injury. We believe that by understanding how miRNAs regulate lung fibrosis and inflammation would pave the way to develop a novel therapeutic approach to the treatment of infectious or non-infectious lung injury.