Bacterial and host enzymes modulate the pro-inflammatory response elicited by the peptidoglycan of Lyme disease agent Borrelia burgdorferi

• Published in: PLoS pathogens Vol. 21; no. 7; p. e1013324
• Main Authors: McCausland, Joshua W., Kloos, Zachary A., Irnov, Irnov, Sonnert, Nicole D., Zhou, Junhui, Putnik, Rachel, Mueller, Elizabeth A., Steere, Allen C., Palm, Noah W., Grimes, Catherine L., Jacobs-Wagner, Christine
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 07.07.2025; Public Library of Science (PLoS)
• Subjects: Bacterial Proteins - immunology; Bacterial Proteins - metabolism; Biology and Life Sciences; Borrelia burgdorferi - enzymology; Borrelia burgdorferi - immunology; Borrelia burgdorferi - metabolism; Development and progression; Enzymes; Health aspects; Host-bacteria relationships; Host-Pathogen Interactions - immunology; Humans; Immune response; Immunological research; Inflammation; Inflammation - immunology; Lyme disease; Lyme Disease - immunology; Lyme Disease - metabolism; Lyme Disease - microbiology; Medicine and Health Sciences; Peptidoglycan - immunology; Peptidoglycan - metabolism; Peptidoglycans; Physical Sciences; Regulation; Research and Analysis Methods; United States
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1013324

The spirochete Borrelia burgdorferi causes Lyme disease. In some patients, an excessive, dysregulated proinflammatory immune response can develop in joints leading to persistent arthritis even after antibiotic therapy. In such patients, persistence of antigenic B. burgdorferi peptidoglycan (PG Bb ) fragments within joint tissues may contribute to immunopathogenesis pre- and post-antibiotic treatment. In live B. burgdorferi cells, the outer membrane shields the polymeric PG Bb sacculus from exposure to the immune system. However, unlike most diderm bacteria, B. burgdorferi releases PG Bb turnover products into its environment due to the absence of recycling activity. In this study, we identified the released PG Bb fragments using a mass spectrometry-based approach. By characterizing the l , d -carboxypeptidase activity of B. burgdorferi protein BB0605 (renamed DacA), we found that PG Bb turnover largely occurs at sites of PG Bb synthesis. In parallel, we demonstrated that the lytic transglycosylase activity associated with BB0259 (renamed MltS) releases PG Bb fragments with 1,6-anhydro bond on their N -acetylmuramyl residues. Stimulation of human cell lines with various synthetic PG Bb fragments revealed that 1,6-anhydromuramyl-containing PG Bb fragments are poor inducers of a NOD2-dependent immune response relative to their hydrated counterparts found in the polymeric PG Bb isolated from dead bacteria. We also showed that the activity of the human N -acetylmuramyl- l -alanine amidase PGLYRP2, which reduces the immunogenicity of PG Bb material, is low in joint (synovial) fluids relative to serum. Altogether, our findings suggest that MltS activity helps B. burgdorferi evade PG-based immune detection by NOD2 during growth despite shedding PG Bb fragments and that PG Bb -induced immunopathology likely results from host sensing of PG Bb material from dead (lysed) spirochetes. Additionally, our results suggest the possibility that natural variation in PGLYRP2 activity may contribute to differences in susceptibility to PG-induced inflammation across tissues and individuals.