FIGURE 1.

Microbiome-gut-brain axis and neurodegenerative disease. Several risk factors have been associated with the etiology of microbial dysbiosis and neurodegenerative disorders. The balance between normobiosis and dysbiosis within the gut microbiome is preserved by the presence or absence of high-abundant species (Lachnospiracea, Clostridiaceae, Ruminococcaceae, Eubacterium, Butyriciccocaceae, Lactobacillus, Bifidobacterium, Faecalibacterium, Roseburia, and Bacteroides) and low-abundant species (Enterobacteriaceae, Alistipes, and Akkermansia). In the presence of beneficial microbes, homeostatic mechanisms such as neuropeptide synthesis, promotion of intestinal barrier integrity and immune cell regulatory functions are maintained. Higher abundances of microbes are associated with dysbiosis, degrade mucin, dysregulate intestinal barrier, and enable pathogenic microbes and their metabolites and endotoxins to infiltrate, promoting local immune cell recruitment and triggering systemic inflammation.