Expression profiling of the developing rabbit lung

Abstract

Bronchopulmonary dysplasia (BPD) is the most common respiratory morbidity in preterm neonates with an incidence of 5–68%, which increases significantly with declining gestational age (GA). Despite advances in neonatal care having resulted in improved survival rates of premature infants, limited progress has been made in reducing BPD rates. The clinical BPD phenotype is the result of a complex multifactorial process in which various pre- and postnatal factors compromise normal development of the immature lung. Understanding how the alveoli and capillary network develop and how these mechanisms are disrupted in BPD is critical for developing efficient therapies. In this scenario, animal models are essential tools for the preclinical development of pharmacological treatments. In the last years, in Chiesi laboratories, a hyperoxia-exposed preterm rabbit model of BPD has been validated. This model represents a suitable lab preclinical tool for mimicking the clinical BPD phenotype to test new pharmacological treatments. However, the molecular characterization of rabbit lung development is lacking. The main aim of this study was to demonstrate the translational power of the preterm rabbit as BPD model by a multi-disciplinary approach to i) characterize histological and molecular changes during the physiological rabbit lung development ii) evaluate the prematurity impact on rabbit lung development, and iii) compare rabbit and mouse lung developmental expression. During the PhD project, we have finalized RNA sequencing analysis of lung samples collected at different time points of GA that correspond to different lung developmental stages of rabbit (canalicular, saccular and alveolar phases). We identified genes and pathways related to processes involved in lung development. Weighted correlation network analysis (WCNA) showed a progressive transcriptomic development profile, starting from pseudo glandular up to the alveolar phase. These results were confirmed by histological analysis and showed a significant similarity of our data with the main gene/protein-set involved in the normal lung development of humans. Prematurity impact on rabbit lung physiological gene expression was evaluated comparing the transcriptomic profiles of preterm and age-matched term pups. Pathway enrichment analysis of differentially expressed genes (DEG) lists highlighted that genes up-regulated in the preterm animals in comparison to the age-matched term pups were mainly enriched in terms of immune system related-pathways. In addition, immune system activation and developmental patterns are delayed as a result of premature delivery in comparison to the term birth. In order to demonstrate the translational power of the preterm rabbit as a BPD model, we compared rabbit data with currently literature-available records from a preclinical transcriptomic study on lung development in mice, the most used animals for preclinical study on BPD. The results showed that the expression profile at preterm and term birth in both species was similar. Common enriched pathways are present in mice and rabbits born in both preterm and term conditions, despite their different lung developmental phases. No enriched common pathways emerged from the comparison between preterm rabbits and term mice. Rodents born at term in the saccular phase have structurally immature lungs, but they are functionally mature and fully capable of extrauterine survival, contrary to preterm rabbits that have structurally and functionally immature lungs as preterm neonates. This result supports the high translational power of the preterm rabbit as a suitable animal model for studying the dysregulation of lung development-related pathways, leading to BPD.