Exosomal miR-27a-5p attenuates inflammation through Toll-like receptor 7 in foodborne Salmonella infections

Salmonella is a common food-borne pathogen that is highly pathogenic and infectious, causing serious harm to livestock breeding and food safety. Uncovering the mechanisms of Salmonella infection and immune evasion can effectively prevent Salmonella contamination of livestock and poultry food. Here, small RNA sequencing results showed that exosomes produced by naïve murine macrophages RAW 264.7 cells contained a unique enrichment of a set of microRNAs (miRNAs) after Salmonella infection. Quantitative real-time polymerase chain reaction (qPCR) analysis verified that the tested miRNA (i.e. miR-27a-5p, miR-92a-1-5p and miR-1249-5p) showed similar expression patterns, consistent with small RNA sequencing data. TargetScan database predicted that the most promising targets for the differentially expressed miRNAs were abundant in the immune system, infectious diseases, and signal transduction pathways. Dual-luciferase reporter assays confirmed that Toll-like receptor 7 (TLR7) was the target of miR-27a-5p. Western blotting and enzyme-linked immunosorbent assay (ELISA) results revealed that overexpression of miR-27a-5p suppressed inflammation by targeting TLR7/nuclear factor kappa-B (NF-κB) signaling pathway and leading interleukin-6 (IL-6) and IL-1β cytokines slightly reduction in recipient macrophages, suggesting that exosomal miR-27a-5p uptake by naïve macrophages may inhibit pro-inflammatory macrophage differentiation. Therefore, these results contribute to our systematic understanding of the mechanism of exosomal miRNA in Salmonella infection, providing a potential target for preventing immune escape from Salmonella.