Impact of prematurity on rabbit lung development: a key factor for mimicking chronic neonatal lung disease

Background: Preterm birth and postnatal insults alter normal lung development, leading to bronchopulmonary dysplasia (BPD). Preterm rabbit is being recognized as a relevant BPD model, but a deeper molecular characterization is needed. Aims and objectives: To characterize rabbit lung development in order to evaluate its translational potential as a BPD model. Methods: Lung samples were collected at multiple gestational ages (GA) comprised between day 20 and day 42, and from preterm pups delivered at GA 28th, at birth, and postnatal days 3 and 7. Histological and transcriptomic analyses were performed. Radial alveolar count (RAC), tissue density (TD%), and arteries medial thickness (MT%) were assessed. A network-based analysis was performed to identify modules of co-expressed genes, and to monitor time-dependent gene expression (GE) modulation in correlation with histological data. Results: RAC values increased from 0.75±0.5 to 9±1.3 during lung development, while TD and MT decreased from 81.5±6.9% to 18.2±2.7% and from 61.9±7.9% to 35.8±17.2%, respectively. Foetal GE modules are enriched in pathways such as cell cycle, epithelium morphogenesis, and VEGF signalling, positively correlated with TD and MT (p-val<0.001). Surfactant metabolism was upregulated from late-foetal up to postnatal stages and positively correlated with RAC (p-val<0.001). Postnatally upregulated modules showed complement system and lymphocyte activation. Immune system activation and developmental patterns were delayed in preterm pups compared with age-matched term ones. Conclusions: Our in-depth characterization of normal rabbit lung development highlights the specific impact of prematurity on such process.