PGLYRP-1 mediated intracellular peptidoglycan detection promotes mucosal protection

Peptidoglycan recognition proteins (PGRPs or PGLYRPs) are implicated in the control of the intestinal microbiota; however, molecular requirements for peptidoglycan (PGN) binding and receptor signaling mechanisms remain poorly understood. We identified PGLYRP-1 as a receptor for the disaccharide motif of lysine N-acetylglucosamine N-acetylmuramic tripeptide (GMTriP-K) with a newly constructed PGN microarray. Surprisingly, PGLYRP-1 was required for innate immune activation of macrophages by GMTriP-K but not N-acetylglucosamine N-acetylmuramic dipeptide (GMDiP) or muramyl dipeptide (MDP). In macrophages, intracellular PGLYRP-1 complexed with NOD2 and GEF-H1, both of which were required for GMTriP-K-regulated gene expression. PGLYRP-1 localized to the endoplasmic reticulum and interacted at the Golgi with NOD2 upon GMTriP-K stimulation. PGLYRP-1 upregulation and its dependent gene expression signatures were induced in both mouse intestinal inflammation and human ulcerative colitis. Importantly, PGLYRP-1 activation by GMTriP-K resulted in innate immune activation and protection of mice from colitis. Our results show that PGLYRPs can function as intracellular PGN pattern recognition receptors for the control of host defense responses in the intestine.