Aromatic amino acid metabolites influence interferon signaling and Influenza infectivity

Abstract The gut microbiota extensively metabolizes the three aromatic amino acids. Previously we found that a tyrosine metabolite can alter type I interferon (IFN) signaling. Herein we screened 17 metabolites of these amino acids for effects on IFN signaling alone and with LPS, IFN-β, and Influenza utilizing IFN reporter human lung epithelial cells (A549) and monocytes (THP1). While the tryptophan metabolites reduced IFN signaling in both cell types, tyrosine and phenylalanine metabolites had varied effects, depending on cell type. The cells were also treated with pooled metabolites from each family and a composite treatment with all three family metabolites. The composite treatment reduced IFN signaling in both cell types, suggesting a tryptophan metabolite effect dominance. Strikingly, when pretreated with composite treatment and infected with influenza, cells had reduced viral recovery and IFN signaling in both cell types. RNA sequencing validated earlier observation of reduced viral loads and IFN signaling. Gene silencing utilizing single siRNAs for upregulated genes identified (EGR2, ATP6V0D2, SPOCK1, and IL31RA) did not completely abrogate the repressed IFN signaling. However, these targets demonstrated linkage to TGF-beta signaling, and treatment with a TGF-beta inhibitor and gene silencing of all four gene targets led to a significant reversal of IFN signaling suppression. Our in vivo work demonstrated that intranasal administration of these metabolites prior to influenza infection leads to reduced animal weight loss, viral titers, and histological inflammation. Our work implicates that microbial metabolites alter IFN signaling through TGF-beta signaling and can promote beneficial outcomes during influenza infection. The study was supported by grant from NIH (K08 AI135097-02) and Burroughs Wellcome Fund, awarded to Dr. Ashley L. Steed