Microbiome ssRNA as an environmental cue to activate TLR13-dependent tissue-protective programs in CD5Lhihepatic macrophages

Hepatic macrophages maintain liver homeostasis, but little is known about the signals that activate the hepatoprotective programs within macrophages. Here, we show that toll-like receptor 13 (TLR13), a sensor of bacterial 23S ribosomal RNA (rRNA), senses microbiome RNAs to drive tissue-protective responses in CD5Lhihepatic macrophages. Splenomegaly and hepatomegaly developed in the absence of the endosomal RNase, RNaseT2, via TLR13-dependent macrophage proliferation. Furthermore, TLR13 in hepatic Ly6Clomacrophages activated the transcription factors LXRα and MafB, leading to expression of tissue-clearance molecules, such as CD5L, C1qb, and Axl. Consequently,Rnaset2−/−mice developed resistance to acute liver injury caused by challenges with acetaminophen and lipopolysaccharide + D-galactosamine. TLR13 responses inRnaset2−/−mice were impaired by antibiotics, suggesting that TLR13 were activated by microbiome rRNAs, which was detected in the sera and hepatic macrophages. Repeated administration of wild-type mice with the TLR13 ligand, rather than other TLR ligands, selectively increased the number of Kupffer cells, which expressed immunoregulatory and tissue-clearance genes as hepatic macrophages inRnaset2−/−mice did. Our results suggest that microbiome ssRNA serves as an environmental cue for initiating tissue-protective TLR13 responses in hepatic macrophages.Graphical AbstractIn the absence of an endosomal RNase, RNase T2, microbiome RNAs circulating in the vasculature activate TLR13 in hepatic macrophages to drive hepatoprotective responses through expression of immunoregulatory and tissue-clearance molecules. Consequently, mice lacking RNase T2 are resistant against acute liver injuries caused by acetaminophen and LPS + D-galactosamine.