Figure 3.

The role of the gut microbiota in neurodegeneration is depicted schematically. Bad mood, increasing age, drugs, dietary changes, and circadian rhythms can disrupt gut microbiota homeostasis. When gut dysbiosis occurs, beneficial bacteria in the gut are transformed into pathogenic bacteria, producing a large number of harmful metabolites and proinflammatory molecules, resulting in increased blood–brain barrier permeability and peripheral inflammatory responses, thereby aggravating oxidative stress in the brain. At the same time, dysbiosis can induce bad mood. Increased levels of ROS in neuronal mitochondria, endoplasmic reticulum, and peroxisomes, increased protein and lipid oxidation, and accumulation of neurotoxic proteins lead to neurodegeneration.