Transcriptional Analysis Reveals Alteration of Lung Macrophages Following Mesenchymal Stem Cell Therapy in Neonatal Mice With Hyperoxia-Induced Injury

Abstract

Background Lung immaturity is one of the most serious consequences of growth restriction and premature birth. Preterm babies often require mechanical ventilation to survive, but exposure to high levels of oxygen can permanently damage the lungs and interrupts normal development. As lung macrophages play an important role in hyperoxic lung injury and repair, our objective was to use next generation sequencing (NGS) to identify changes in the macrophage transcriptome following neonatal hyperoxia, with and without treatment with human mesenchymal stem cells (hMSCs). We provide the first report of RNA-sequencing of lung macrophages following neonatal hyperoxia and hMSCs therapy. Methods Neonatal mice exposed to normoxia (21%O2) or hyperoxia (90% O2) from birth to postnatal day 4 were randomized to receive either hMSCs or vehicle via intratracheal delivery on postnatal day 4. Mouse lungs from normoxia and hyperoxia groups with and without hMSCs therapy were examined at day 14. RNA-sequencing was performed on flow-cytometric CD45+CD11b+CD11c+ sorted lung macrophages. Purified total RNA was used to construct barcoded multiplex-compatible sequencing libraries using: 1) Illumina Stranded mRNA Sample Preparation chemistry (for transcriptomics) and 2) Bio Scientific NEXTFlex Small RNA chemistry (for small RNA). Results Sorted CD45+CD11b+CD11c+ lung macrophages from hyperoxia-exposed neonatal mice showed differentially expressed macrophage genes and miRNA compared to mice exposed to normoxia or hyperoxia+hMSCs. The administration of hMSCs was found to differentially upregulate 421 genes and downregulate 651 genes in CD45+CD11b+CD11c+ lung macrophages from neonatal mice exposed to hyperoxia, compared to normoxia. Integrity pathway analysis (IPA) analysis of macrophage-specific gene pathways revealed the effectiveness of hMSCs in altering macrophage function towards an anti-inflammatory ‘M2’ phenotype. Small-RNA sequencing provided further evidence on the effects of hMSCs, where 1,098 small RNAs transcriptomes were expressed as either significantly up- or down-regulated in response to hMSCs therapy following hyperoxia-induced lung damage. Conclusions Pathway analysis of the predicted mRNA targets of differentially expressed genes provides insight into miRNAs that preferentially target several important pathways. These miRNAs will be functionally relevant for lung macrophages, and will provide a greater understanding of the interaction between macrophage genotype and the associated phenotypes in the setting of inflammation or tissue repair.