Bacterial peptidoglycan as a pro-inflammatory cofactor in MS: functional assessment in vivo and in vitro
01 / 2005 - 01 / 2006
Stichting MS Research
Mounting recent evidence from both longitudinal MS patient cohorts and EAE models strongly supports a role for infectious agents in disease activity. Importantly, viral as well as bacterial agents such as Chlamydia pneumoniae are associated with MS and precipitate EAE. This suggests a common disease influencing mechanism for diverse microbial agents. Indeed, the recent identification of the molecular families of Toll-like receptors (TLR) (O'Neill, 2004) and NOD/CARD recognizing molecular patterns of diverse microbial agents is a fundamental and major breakthrough in our understanding how infectious agents engage innate as well as adaptive immunity. Ligands such as LPS (engaging TLR4) and CpG dinucleotides (TLR9) have been shown to stimulate EAE. In the current pilot project we focus on the potently pro-inflammatory bacterial cell wall compound, peptidoglycan (PG), which is a TLR2 ligand. We previously demonstrated that PG is present in antigen presenting cells (APC) in MS postmortem brain, and we functionally demonstrated that PG is a pro-inflammatory stimulus for EAE induction in mice (submitted). This project aims to test the hypothesis that PG uses TLR2 and NOD2 to act as a cofactor in EAE, to determine how human and mouse APC recognize and respond to PG, and to assess how modulation of PG burden and persistence by specific enzymes impacts on EAE in vivo and APC function in vitro. We will take full advantage of recently developed mice genetically deficient for TLR2, the main membrane signaling receptor for PG, NOD2, an intracelluar PG receptor, and mice deficient for lysozyme, a major enzyme for intracellular degradation of PG by macrophages, dendritic cells (DC) and neutrophils. This in vivo approach will be complemented by functional in vitro studies modulating both human and mouse APC by exposure to PG, including assessment of treatment with lysozyme and NAMLAA/PGRP-L, the second major enzyme involved in PG degradation. This pilot project is designed to provide crucial insight into PG action in vivo and its functional role in MS. The results will provide the basis for a full project proposal in which these findings can potentially be further exploited for clinical applications, for instance by modulating PG burden by improved mucosal barrier function, by stimulation of PG degradation, and by interference with TLR2 signaling pathways.