The role of Itgam+ pulmonary macrophage populations in the pathogenesis and long-term effects of bronchopulmonary dysplasia.

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Bronchopulmonary dysplasia (BPD) is the most common neonatal chronic lung disease in premature infants, characterized by an arrest of alveolar and microvascular development. BPD develops following O2 and ventilator therapy for acute respiratory failure and is associated with life-long complications, including asthma, pulmonary hypertension, and emphysema. Currently, BPD lacks curative or preventive strategies. Oxygen-triggered inflammation plays a critical role in BPD pathogenesis. However, the key immune populations driving the injury remain unidentified. Moreover, it is unknown to which extent changes to immune cells persist after recovery and increase susceptibility to lung diseases later in life. The preliminary data show that hyperoxia triggers the trans-differentiation of macrophages (MFs) towards the yet unexplored pro-inflammatory Itgam+/Inhba+ phenotype. We hypothesize that Itgam+/Inhba+ MFs constitute the main source of pro-inflammatory signaling targeting the lung endothelial and stromal cells and play a causal role in BPD pathogenesis. To address this hypothesis, we pursue three specific aims: (1) To profile the long-term effects of hyperoxia on the phenotype and dynamics of Itgam+/Inhba+ MFs and other immune cells during recovery using single cell (sc)RNA-seq. Mice will be exposed to hyperoxia from birth until postnatal day (P)14, followed by recovery in room air until P70. Lung Itgam+ MFs will be isolated and profiled. Importantly, we will create a lung scRNA-seq atlas following the hyperoxia-injury, focusing on the Itgam+ MFs and their communication with other lung cell populations. (2) To Investigate the effects of hyperoxia on Itgam+ MFs and the impact of hyperoxic Itgam+ MFs on alveolar formation in vitro/ex vivo. To study acute effects of hyperoxia we will expose Itgam+ MFs to hyperoxia in vitro and evaluate transcriptional changes and changes in cytokines/chemokines production. Further, we will co-culture precision cut lung slices from healthy developing mice with hyperoxic Itgam+ MFs and evaluate changes in proliferation, cell death, and alveolar growth. (3) To investigate the causal role of Itgam+ MFs in an in vivo model of BPD on histological and functional level. 3a: Determining the functional role of Itgam+ MFs by transplanting primary Itgam+ MFs from hyperoxia-exposed mice to healthy developing mice. 3b: Analysing the causal role of Itgam+ MFs by depletion of Itgam+ cells in hyperoxia-exposed Itgam-cre/ROSA-DTA mice. Lung architecture, vasculature and function, and cell survival will be assessed. The strengths of this proposal include the use of novel scRNA-seq and systems biology approaches together with readily available animal models, well-established techniques, as well as possible clinical implications. Completion of this project will provide new mechanistic insights in macrophage biology in BPD and offer new possible therapeutic strategies, which might also be relevant for adult emphysematous chronic lung diseases.