Signals from the gut and bacteria have an impact on brain function (Lynch and Pedersen, 2016), and Aβ or Tau proteogen fibers injected into the colon or brain lysates from AD patients propagate from the gut to the brain via the vagus nerve, where inflammation activates C/EBPβ/δ-secretase and triggers AD-related pathological changes and cognitive dysfunction in the gut (Chen et al., 2021). This evidence concerns the gene MAPT and Alzheimer disease.