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. Here, MAPT is linked to Alzheimer disease.