Activation of Lung Macrophages in Hypoxic Pulmonary Hypertension. Mus musculus

Studies in various animal models suggest an important role for pulmonary macrophages in the pathogenesis of pulmonary hypertension (PH). Yet, the molecular mechanisms characterizing the functional macrophage phenotype relative to time and pulmonary localization/compartmentalization remain largely unknown. Here, we utilized a hypoxic murine model of PH in combination with flow cytometry assisted cell sorting (FACS) to quantify and isolate lung macrophages from two compartments over time and characterized their programing via RNA sequencing (RNAseq) approaches. In response to hypoxia, we found an early increase in macrophage number that was restricted to the interstitial/perivascular compartment, without recruitment of macrophages to the alveolar compartment or changes in the number of resident alveolar macrophages. Principle component analysis demonstrated significant differences in overall gene expression between alveolar (AMs) and interstitial macrophages (IMs) at baseline and after 4 and 14 days hypoxic exposure. AM’s at both day 4 and 14 and IM’s at day 4 shared a conserved “hypoxia program” characterized by mitochondrial dysfunction, pro-inflammatory gene activation and mTORC1 signaling, while IM’s at day 14 demonstrated a unique anti-inflammatory/ pro-reparative programming state. We conclude that the pathogenesis of vascular remodeling in hypoxic PH involves an early compartment independent activation of lung macrophages towards a conserved hypoxia program, with the development of compartment specific programs later on in the course of disease. Thus, harnessing time and compartment specific differences in lung macrophage polarization needs to be considered in the therapeutic targeting of macrophages in hypoxic PH and potentially other inflammatory lung diseases. Overall design: FACS sorting of lung macrophages from hypoxic mouse lung