Supplemental oxygen exposure is a risk factor for the development of bronchopulmonary dysplasia (BPD). Reactive oxygen species may damage lung tissue, but hyperoxia also has the potential to alter genome activity via changes in DNA methylation. Understanding the epigenetic potential of hyperoxia would enable further improvement of the therapeutic strategies for BPD.
Here we aimed to identify hyperoxia-related alterations in DNA methylation, which could affect the activity of crucial genetic pathways involved in the development of hyperoxic lung injury.
Newborn mice (n=24) were randomized to hyperoxia (85% O2) or normoxia groups for 14 days, followed by normoxia for the subsequent 14 days. The mice were sacrificed on day 28, and lung tissue was analyzed using microarrays developed for the assessment of genome methylation and expression profiles.
The mean DNA methylation level was higher in the hyperoxia group than the normoxia group. The analysis of specific DNA fragments revealed hypermethylation of >1000 gene promoters in the hyperoxia group, confirming the presence of the DNA-hypermethylation effect of hyperoxia.
Further analysis showed significant enrichment of the TGF-β signaling pathway (p=0.0013). The hypermethylated genes included Tgfbr1, Crebbp, and Creb1, which play central roles in the TGF-β signaling pathway and cell cycle regulation.
Genome expression analysis revealed in the hyperoxia group complementary downregulation of genes that are crucial for cell cycle regulation (Crebbp, Smad2, and Smad3).
These results suggest the involvement of the methylation of TGF-β pathway genes in lung tissue reaction to hyperoxia. The data also suggest that hyperoxia may be a programming factor in newborn mice.