In utero exposure to second-hand smoke activates pro-asthmatic and oncogenic miRNAs in adult asthmatic mice

Exposures to environmental pollutants contribute to dysregulated microRNA (miRNA) expression profiles, which have been implicated in various diseases. Previously, we reported aggravated asthmatic responses in ovalbumin (OVA)-challenged adult mice that had been exposed in utero to second-hand smoke (SHS). Whether in utero SHS exposure dysregulates miRNA expression patterns in the adult asthma model has not been investigated. Pregnant BALB/c mice were exposed (days 6-19 of pregnancy) to SHS (10 mg/m(3)) or HEPA-filtered air. All offspring were sensitized and challenged with OVA (19-23 weeks) before sacrifice. RNA samples extracted from lung homogenates, were subjected to RNA sequencing (RNA-seq). RNA-seq identified nine miRNAs that were most significantly up-regulated by in utero SHS exposure. Among these nine, miR-155-5p, miR-21-3p, and miR-18a-5p were also highly correlated with pro-asthmatic Th2 cytokine levels in bronchoalveolar lavage fluid. Further analysis indicated that these up-regulated miRNAs shared common chromosome locations, particularly Chr 11C, with pro-asthmatic genes. These three miRNAs have also been characterized as oncogenic miRNAs (oncomirs). We cross-referenced miRNA-mRNA expression profiles and identified 16 tumor suppressor genes that were down-regulated in the in utero-exposed offspring and that are predicted targets of the up-regulated oncomirs. In conclusion, in utero SHS exposure activates pro-asthmatic genes and miRNAs, which colocalize at specific chromosome locations, in OVA-challenged adult mice. The oncogenic characteristics of the miRNAs and putative miRNA-mRNA regulatory networks suggest that the synergistic effect of in utero SHS exposure and certain adult irritants may promote an oncogenic milieu in mouse lungs via inhibition of miRNA-regulated tumor suppressor genes