Discovery of bioactive peptidoglycan fragments from Lactobacillaceae that confer intestinal protection in hosts

Gut bacteria-derived peptidoglycan fragments (PGNs) are key signaling molecules in mammalian hosts. However, the production and functional roles of soluble PGNs secreted by individual gut bacterial species have not been systematically explored. Herein, we used a targeted LC-MS/MS approach to profile PGNs released by bacteria, identifying Lactobacillaceae as the predominant producers of disaccharide PGNs in culture supernatants. We then chemically synthesized such disaccharide PGNs and confirmed their activation of the mammalian sensor NOD2. Notably, priming murine macrophages with disaccharide PGNs induced tolerance to subsequent stimulation by TLR2/4 ligands, suggesting that sustained exposure to bioactive PGNs in the gut may shape host immune responses. Consistently, the administration of the disaccharide PGN, GM-AQK, effectively alleviated gut inflammation in a DSS-induced colitis mouse model. Together, these findings deepen our understanding of PGN-mediated gut microbiota-host crosstalk and position natural disaccharide PGNs as promising postbiotic candidates for the therapeutic modulation of intestinal inflammation.