Role of gut microbiota metabolite TMAO in upregulating NLRP3 inflammasome: a study on the pathogenesis of hippocampus-related cognitive impairment

Objective To explore the potential role of the gut microbiota metabolite trimethylamine N-oxide (TMAO) in mediating neuroinflammatory responses in cognitive impairment. Methods Mice were randomly divided into three groups: control, TMAO, and TMAO + DMB. The TMAO group was fed a high-choline, high-fat diet combined with TMAO for six weeks, while the TMAO + DMB group received the same diet along with TMAO inhibitor 4,4'-diamino-3,3'-dimethylbiphenyl (DMB) for six weeks. The levels of NOD-like receptor thermal protein domain associated protein 3 (NLRP3), caspase-1, and interleukin-1β (IL-1β) in the bilateral hippocampus of the mice were detected by Western blot. The morphology and survival of neurons in hippocampal CA1 region was observed by Cresyl violet staining. The Morris water maze test was used to evaluate learning and memory abilities. Results Compared with the control group, the TMAO group showed significantly increased expression of NLRP3, caspase-1, and IL-1β proteins in the hippocampal tissues (P<0.05), and exhibited excessive neuron deaths in the CA1 region, with impaired learning and memory abilities. After TMAO inhibition with DMB, the TMAO + DMB group showed significantly reduced levels of NLRP3, caspase-1, and IL-1β proteins in the hippocampus (P<0.05), and exhibited decreases in neuron death rate, indicating alleviated damage (P<0.05), with improved learning and memory abilities. Conclusions The gut microbiota metabolite TMAO exacerbates chronic inflammatory responses in the hippocampus by upregulating the NLRP3 inflammasome, which lesds to increased neuronal damage in the CA1 region, and impaired learning and memory, ultimately worsening cognitive dysfunction.