Hyperoxia-exposed preterm rabbit BPD models biomolecular characterization

Abstract

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that represents the most common complication in preterm babies with adverse consequences in adulthood. BPD is a complex and multifactorial disease, and its development relies on several prenatal and postnatal causal factors which alter alveolar growth, pulmonary vascular development, and inflammation. This complex etiology, and the scarcity of human pathology specimens available, hamper the development of effective therapies, therefore BPD animal models are key tools to investigate the precise mechanisms leading to BPD. The preterm rabbit model incorporates the positive aspects of both small (mice and rats) and large animal (baboons and lambs) models used to study BPD pathophysiology so far. Continuous exposure to high oxygen concentration (95% O2) for 7 days induces functional and morphological lung changes in preterm rabbits that resemble those observed in BPD-affected babies. To date, the molecular characterization of the BPD onset in this model is missing, therefore the main aim of this thesis was to characterize the 95% hyperoxia exposed preterm rabbit model for 7 days (post-natal day = PND7) by a multi-disciplinary approach to i) characterize the histological and molecular changes during BPD development and ii) confirm the translational potential of the preterm rabbit as BPD model for new therapeutic strategies development. We found hyperoxia exposure induced the arrest of lung and vasculature development and lung injury compared to normoxia at day 7. Moreover, several processes have been found dysregulated by hyperoxia exposure. Inflammatory and cell death processes were up-regulated whereas lung and vasculature development ones were down-regulated. We have also identified 42 genes as strongly correlated with BPD development, whose signature would be useful for future evaluations of new pharmacological treatments' therapeutic effects. An extended version (up to 14 days) of the PND7 preterm rabbit model has been set up and validated in Chiesi Farmaceutici, using 70% of oxygen instead of 95%. This long-term BPD model would bypass the high oxygen concentrations (O2> 40%) no longer used in the Neonatal Intensive Care Unit (NICU). Additionally, the short experimental timeframe of the PND7 BPD model impedes testing any therapeutic treatments, since a preventative approach is the only feasible. For these reasons, we characterized the histological features and gene expression patterns of the previously selected 42 genes on day 14. The histological and gene expression analysis showed that normoxic preterm pups, and even more those hyperoxia-exposed, have a lung growth delay when compared to their age-matched controls born at term. Moreover, comparison analyses have been performed in order to highlight the different phenotypes between days 7 and 14 models. Both histology and gene expression analysis revealed that the PND14 model has a milder phenotype than the PND7 one, and we identified a preterm influence on lung development in PND14 pups that was missed in the PND7 one. The overall of these analyses demonstrated the high translational value of our preterm rabbit models to study BPD development and pathophysiology. Finally, deep molecular characterization of both animal models will be crucial for identifying new targets and pathways that can be used to build novel BPD preventative and therapeutic treatments.