Butyrate-Producing Bacteria and Neuroinflammation: The absence of anti-inflammatory butyrate-producing bacteria in the AD gut microbiota, combined with elevated inflammatory PGE2 metabolites in the brain, increases microglial activation. This leads to chronic neuroinflammation and activates the C/EBP-β/AEP pathway, enhancing APP and tau expression levels and AEPδ-secretase activity, contributing to AD pathogenesis. This evidence concerns the gene APP and Alzheimer disease.