Surfactant Protein Receptor Sp-R210 Isoforms Play A Role In Regulating Macrophage Immune Response In Conjunction With Epigenetic Changes During Influenza A Infection

Abstract Alveolar macrophages (AMs) and surfactant proteins are critical for host defense and regulation of immune responses to airborne pathogens like influenza A virus (IAV). Previous findings showed that the surfactant protein A receptor SP-R210 regulates macrophage responses to LPS and phagocytic flux. Our goal is to understand how the long (L) and short (S) isoforms of SP-R210 alter macrophage responses to respiratory pathogens. Here we investigated how altering expression of the L isoform changes macrophage epigenetic landscape during IAV infection. Chromatin immunoprecipitation and sequencing were used to identify alterations in H3K4me3, H3K9me3, and H3K27me3 histone methylation and PU.1 transcription factor binding in L knockdown (KD) cells at baseline and after IAV infection. The UCSC genome browser was used to identify spatial relations of enriched binding regions, revealing reduced PU.1 binding at genes associated with macrophage differentiation and signaling between innate and adaptive immune cells, such as interleukin 18 (IL-18) and colony-stimulating factor receptors (CSF1R, CSF2RB) in KD cells. These changes were mirrored with decreased H3K4me3 marks in KD macrophages. Further analysis with ChIPseeker revealed enrichment in Toll-like receptor and interferon signaling pathways in KDmacrophages. IAV infection upregulated PU.1 binding to genes associated with IL-3, IL-5 and TLR4 signaling pathways among others. RNA sequencing confirmed increased TLR4 and TLR6 and decreased IL-18 transcripts in KDmacrophages. These findings support the idea that the L isoform of SP-R210 regulates chromatin architecture and accessibility of transcription factors at genes with roles in macrophage differentiation and activation.