A novel circRNA-miRNA-mRNA regulatory axis as a sex-specific biological variable in bronchopulmonary dysplasia.

Babies born prematurely with gestational age <28 weeks usually develop a severe pulmonary complication called Bronchopulmonary Dysplasia (BPD) in response to hyperoxia. BPD is a sexually dimorphic pediatric disease with no curative options. Several micro RNAs (miRNAs) are implicated in BPD and are expressed differentially in males and females. Circular (circ) RNAs serve as sponges for their dedicated miRNAs to influence transcription and translation. We tested the dimorphism of these circular RNAs in BPD to assess their biological significance and unravel a circRNA-miRNA-mRNA regulatory axis in response to hyperoxia. Our RNA-Sequencing assay identified approximately 33 000 circRNAs at the alveolar stage of development with only a handful of them being expressed differentially between males and females in the control room air (RA) and hyperoxia-treated (BPD) groups. One circRNA, i.e circNfix was found to be associated with miR204-5p that targets the downstream mRNA target Ntrk2. To prove that circNfix regulates Ntrk2, we silenced circNfix using a GapmeR and found that Ntrk2 was also suppressed, leading to an improved alveolar phenotype in BPD male pups. From the results of our study, we can propose circNfix and Ntrk2 as novel key regulators in the pathogenesis and sexual dimorphism of BPD, while simultaneously proposing the use of circNfix GapmeR towards a potential therapeutic application.