The role of the gut microbiota and microbial metabolites in neuroinflammation

Recent literature indicates a potential importance of the gut microbiota for immune-mediated diseases. For instance, decreased diversity of commensals or an outgrowth of some bacterial strains, referred to as gut dysbiosis, was recently linked to hypertension, colitis, lupus, rheumatoid arthritis, and multiple sclerosis (MS). Studies in experimental autoimmune encephalomyelitis (EAE) as pivotal animal model of MS revealed a potential importance of microbial metabolites, including short-chain fatty acids or tryptophan metabolites. Both metabolites may influence the disease by modulation of the immune system, mainly by inducing Treg. These studies prompted researchers to investigate the contribution of the gut microbiota and microbial metabolites in the pathogenesis of MS. This review summarizes recent findings on the gut microbiota in MS patients and discusses the potential mechanisms how microbial metabolites may affect neuroinflammation. Many of these studies have been performed in the EAE model and were later reversely translated to humans. We also give a short summary on dietary high-salt effects on microbiota components and discuss the potential relevance of high-salt as a risk factor in MS.