Abstract Rationale Cellular senescence, a stable cell cycle arrest, is critical for organ development. Our previous work noted a transient spike in senescent markers in the developing murine lung during the saccular phase, which was disrupted by hyperoxia, a driver of bronchopulmonary dysplasia (BPD), resulting in lung simplification. This suggests a critical, yet undefined, role for a developmental senescence program (DSP) in normal alveolarization. Objectives 1) Precisely map the DSP timeline across species; 2) identify senescent cell lineages during lung development; 3) determine their transcriptional programs; and 4) establish how hyperoxia/BPD disrupts these populations and programs. Methods We collected lung tissue from mice (P3, P7, P10, P60) and lambs (GD115-GD150) at developmental stages to quantify p21, a senescence marker. To map the DSP, we used public scRNA-seq data from murine (E15-P64, GSE160876, GSE165063) and Rhesus Macaque (E45-P7, GSE158440) lungs covering embryonic through alveolar stages and from hyperoxia-induced BPD mouse models. Senescence was scored using established (SenMayo) and internally curated gene lists. Results A post-natal increase in senescent markers was observed in mouse and lamb. In mice, scRNA-seq revealed a senescence score peak between P7-P14, during peak alveolarization. This DSP was predominantly restricted to the mesenchyme, originating from four cell populations (∼80% of high-scoring cells), contrasting with BPD models where senescence is predominantly in alveolar macrophages (∼75%). Notably, in alveolar fibroblast 2 cells (AF2, ∼30%), the senescent peak (P14) was associated with transient upregulation (Sox9, Gata6, Pparg, Id2, Klf4) and downregulation (Snai2, Foxm1, Etv4, Tbx4, Foxf1) of key developmental transcription factors (TFs). Hyperoxia exposure (P0-P3) led to a decreased senescent score in AF2 at P7, not p60 and a 3-4 fold decrease in Sox9-expressing epithelial cells. Conclusions Developmental senescence is an active, transcriptionally-driven cellular reprogramming, not passive decay. This program co-opts developmental TFs to drive cell cycle arrest (Gata6, Klf4) and redefine cell identity (Sox9, Pparg) towards an altered, embryonic-like state crucial for tissue remodeling. Hyperoxia alters this DSP by modifying lung cell composition and senescent cell identity. Further Rhesus Macaque analysis is ongoing because understanding this DSP across higher species may enable therapies that selectively prevent pathological senescence in BPD while sparing the DSP required for healthy lung development. This abstract is funded by: NIH
Ouonkap et al. (2026) studied this question.