Microbiota-derived metabolite Indoles induced aryl hydrocarbon receptor activation and inhibited neuroinflammation in APP/PS1 mice

Gut microbiota alterations might affect the development of Alzheimer's disease (AD) through microbiota-derived metabolites. For example, microbiota-derived Indoles via tryptophan metabolism prevented Aβ accumulation and Tau hyperphosphorylation, restored synaptic plasticity, and then promoted the cognitive and behavioral ability of APP/PS1 mice. The imbalanced compositions of Indoles-producing bacteria with tryptophan deficiency were found in male APP/PS1 mice, but the molecular mechanisms remained unclear. Our current study revealed that Indoles (including indole, indole-3-acetic acid and indole-3-propionic acid) upregulated the production of aryl hydrocarbon receptor (AhR), inhibited the activation of the NF-κB signal pathway as well as the formation of the NLRP3 inflammasome, reduced the release of inflammatory cytokines, including TNF-α, IL-6, IL-1β and IL-18, alleviating the inflammatory response of APP/PS1 mice. These findings demonstrated the roles of Indoles-producing bacteria in activating the AhR pathway to regulate neuroinflammation of AD through gut microbiota-derived Indoles, which implied a novel way for AD treatment.