Abstract
BACKGROUND: Bronchiolitis exposes infants to both acute burdens (e.g., hospitalization in cases of severe bronchiolitis) and increased risks for chronic respiratory sequelae (e.g., asthma). In severe bronchiolitis, recent evidence suggests distinct pathobiological roles of microbiota (e.g., viruses, bacteria) and host responses influenced by genetic and epigenetic factors. However, the relationship of airway microbiota with host DNA methylation (DNAm) in infants with severe bronchiolitis remains unknown. METHODS: In a multi-center prospective cohort of 504 multi-ethnic infants with severe bronchiolitis (age < 1 year), using nasopharyngeal microbiome (exposure) and blood DNAm (outcome, Infinium MethylationEPIC BeadChip, Illumina) data within 24 h of the hospitalization, we conducted microbiome-epigenome-wide association studies (mbEWAS). We examined microbiota-associated differentially methylated CpGs (mbDMCs, false discovery rate [FDR] < 0.05), regions (mbDMRs, FDR < 0.05), and DNAm age acceleration. We also determined the associations of DNAm age acceleration with asthma development by age 6 years. Furthermore, we focused on asthma-related pathogenic bacteria-Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae-for functional analyses by examining serum mbDMR-related proteins (Proseek Multiplex, Olink) and their enriched pathways (FDR < 0.10). RESULTS: Across 23 common taxa-observed at least in 25% of the infants, we identified 1 mbDMC (S. pneumoniae, cg16594639, chr20: 39528675) and 96 mbDMRs (e.g., S. pneumoniae, chr5:27038497-27038802, CDH9; chr6:48068669-48068940, PTCHD4). A higher H. influenzae abundance was associated with DNAm age deceleration, and the deceleration was associated with a higher risk of developing asthma. In 29 mbDMRs of the asthma-related pathogenic bacteria, we identified 156 mbDMR-related proteins (e.g., MMP9, XCL1). These proteins were enriched in immune response-related pathways (e.g., regulation of ERBB signaling and eosinophil chemotaxis and migration pathways). CONCLUSIONS: In this multi-center prospective cohort study of severe bronchiolitis, our mbEWAS suggested the microbiota-host associations that regulate immune responses.