Pulmonary Microbial Dysbiosis Leads to Redox Imbalance Through the Nrf2 Pathway in Neonatal Murine Models

Abstract

Background Distinct airway microbial dysbiosis is seen in infants with severe bronchopulmonary dysplasia (BPD). In addition to dysbiosis, oxidative stress has been shown to exacerbate BPD, and upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent antioxidants are protective. Previous studies revealed protected lung structure in germ free (GF) mice. In order to understand the protective mechanisms in GF mice, we analyzed Nrf2 dependent genes heme-oxygenase-1 (Hmox1) and NADPH quinone oxidoreducase-1 (Nqo1), which both neutralize reactive oxygen species and maintain redox balance. In addition, we analyzed pulmonary mechanics in an Nrf2 knockout murine model after colonization with E. coli, respiratory probiotic, or E. coli followed by respiratory probiotic. Methods 1. GF mice were intranasally inoculated with three separate doses of E. coli at P3, P6, and P9. Phosphate buffered saline (PBS) treated GF mice as well as non-germ free mice (NGF) were used as controls. All groups were exposed to normoxia (21% FiO2) or hyperoxia (85% FiO2). The expression of Hmox1 and Nqo1 in lung tissue harvested at P14 was measured by qPCR. 2. C57BL/6 mice with an Nrf2 knockout were colonized through intranasal inoculation with PBS, E. coli, respiratory probiotic, or E. coli followed by respiratory probiotic on P3, P6, and P9. All groups were exposed to normoxia (21% FiO2) or hyperoxia (85% FiO2) from P3-P14. On P14, pulmonary function tests were performed. Results GF mice colonized with E. coli show a significant increase in Hmox1 and Nqo1 expression independent of hyperoxia exposure. In an Nrf2 knockout model, treatment with E. coli resulted in worsening pulmonary function in both normoxia and hyperoxia (high resistance P<0.001, low compliance). Treatment with a respiratory probiotic resulted in improvement in pulmonary function even in hyperoxic conditions (decreased resistance P<0.05, increased compliance). Conclusion Our results suggest the presence of an interaction between airway microbiome and Nrf2-dependent antioxidant responses in the lung. Through these studies, we hope to lay the foundation for microbiome related therapeutics development for BPD.