MAPT and Cognitive impairment: Metabolites from Bacteroides Fragile and Neuroinflammation: Stool samples from AD patients contain Bacteroides fragilis and its metabolites, including 12-hydroxy-heptatridecanoic acid (12-HHTrE) and prostaglandin E2 (PGE2). These metabolites upregulate the C/EBP-β/Asparagine endopeptidase (AEP) pathway, which is associated with microglial activation. This leads to the aggregation of Aβ and tau proteins and widespread neuroinflammation, accelerating cognitive impairment.