Fra‐1 Signaling both in Lung Resident and Myeloid Cells Is Required for Hyperoxia‐Induced Bronchopulmonary Dysplasia in Mice
Authors: Tamatam Chandramohan R , Reddy Narsa M , Potteti Haranatha R , Elangovan Indira , Reddy Sekhar P 
Published: November 2023

RationaleBronchopulmonary dysplasia (BPD) is a chronic disease of preterm babies. While current clinical care has largely improved the survival of preterm babies, incidence of BPD and poor health outcomes associated with this disease remain major clinical problems. Lung cellular stress and inflammation have been linked to BPD pathogenesis in humans and experimental models. Fra‐1 (Fosl1) is a heterodimeric partner of Jun/AP‐1 transcription factor and is known to differentially regulate gene expression involved in various cellular processes, including cellular stress and inflammation, which are known to contribute to BPD pathogenesis. We examine whether Fra‐1/AP1 transcription factor is a critical modulator of BPD pathogenesis.MethodsTo test our hypothesis, we have used Fra‐1 floxed (Fra‐1FF or WT) and Fra‐1 null (Fra‐1−/−) mice, and mice with a conditional deletion of Fra‐1 in myeloid cells. Fra‐1 in myeloid cells was deleted by crossing Fra‐1 floxed mice with a transgenic mice bearing Cre under the control of the LyzM promoter (hereafter notated as Fra‐1−/−LysM mice). Fra‐1F/F, Fra‐1−/− and Fra‐1−/−LysM pups (1‐day‐old) (n = 3–5/group) with mothers were exposed to 95% O2 for 72 h and allowed to recover in room air for two weeks. Mice were sacrificed, the left lungs were fixed, sectioned, and stained with H&E to visualize alveolar simplification and to quantify mean chord length (MCL) by morphometry analysis. Fra‐1F/F, Fra‐1−/− and Fra‐1−/−LysM pups exposed to 95% O2 for 72 h were immediately sacrificed and the left lung was collected for RNA isolation, and right lobe was used for protein analysis. Expression levels of several pro‐inflammatory mediators and antioxidant genes in the lungs of WT (Fra‐1F/F) and Fra‐1−/− pups exposed to 95% O2 for 72 h were analyzed by qPCR.ResultsWe found increased expression of Fra‐1 in the lungs of pups exposed to hypeorixia. Fra‐1 null pups showed markedly reduced levels of hyperoxia‐induced alveoli simplification (or MCL) as compared to WT pups (33% vs 6%, WT vs Fra1−/−), suggesting that Fra‐1 signaling is required for BPD development. Alveoli simplification in the lungs of Fra‐1−/−LysM pups exposed to hyperoxia was 12% lower than WT counterparts (33% vs 21%, WT vs Fra‐1−/−LysM), suggesting that Fra‐1 signaling in myeloid cells partly contributes to BPD. The expression levels of inflammatory mediators (IL‐1β, TNF‐α, and IL‐6) were markedly lower in the lungs of Fra1−/− pups exposed to 72 h hyperoxia than in WT counterparts. Surprisingly, antioxidant gene expression in the lungs of hyperoxia exposed Fra‐1−/− pups was also markedly lower than in WT counterparts.ConclusionOur findings suggest that Fra‐1 signaling both in lung resident and inflammatory cells play an important role in promoting hyperoxia‐induced BPD, and that Fra‐1 regulates this process at least in part by modulating inflammatory cytokine and antioxidant gene expression in the lung.Support or Funding InformationPartly supported by NIH grants, HL66109 and ES11863 (to SPR)