The biology of nematode- and IL4Rα-dependent murine macrophage polarization in vivo as defined by RNA-Seq and targeted lipidomics

Abstract

Abstract Alternatively activated macrophages (AAMφ) are a major component of the response to helminth infection; however, their functions remain poorly defined. To better understand the helminth-induced AAMφ phenotype, we performed a systems-level analysis of in vivo derived AAMφ using an established mouse model. With next-generation RNA sequencing, we characterized the transcriptomes of peritoneal macrophages from BALB/c and IL4Rα−/− mice elicited by the nematode Brugia malayi, or via intraperitoneal thioglycollate injection. We defined expression profiles of AAMφ-associated cytokines, chemokines, and their receptors, providing evidence that AAMφ contribute toward recruitment and maintenance of eosinophilia. Pathway analysis highlighted complement as a potential AAMφ-effector function. Up-regulated mitochondrial genes support in vitro evidence associating mitochondrial metabolism with alternative activation. We mapped macrophage transcription start sites, defining over-represented cis-regulatory motifs within AAMφ-associated promoters. These included the binding site for PPAR transcription factors, which maintain mitochondrial metabolism. Surprisingly PPARγ, implicated in the maintenance of AAMφ, was down-regulated on infection. PPARδ expression, however, was maintained. To explain how PPAR-mediated transcriptional activation could be maintained, we used lipidomics to quantify AAMφ-derived eicosanoids, potential PPAR ligands. We identified the PPARδ ligand PGI2 as the most abundant AAMφ-derived eicosanoid and propose a PGI2-PPARδ axis maintains AAMφ during B malayi implantation.