The microbiota-gut-brain axis: from dysbiosis to neurodegenerative disease

Abstract

The relation between the gut and the brain has been discussed for years, but the concept of gut microbiota (GM) has not been linked for so long. Having suggested its involvement in neurodegenerative disorders, this literature review aims to summarise the current knowledge on the possible bidirectional pathways that could explain it, while discussing the composition and alterations of the GM and the main pathological features that characterise neurodegeneration. It also presents the existing scientific evidence on the use of GM as a therapeutic target, accompanied by a systematic review-meta-analysis that evaluates the indication of one of the possible interventions: the faecal microbiota transplantation (FMT). GM is made up of the trillions of microorganisms in the gut, mostly bacteria, which interact dynamically with the host, contributing to both health and disease. These, through neural, endocrine and immune pathways, based on mechanisms that require further research, can modify the gut-brain axis promoting neurodegenerative processes such as neuroinflammation, protein misfolding and loss of integrity of the intestinal and blood-brain barriers, thus facilitating the passage of components derived from a deregulated GM that has been characterised in Alzheimer's and Parkinson's patients. Although more studies are needed, the promising results obtained in animal and more limited human trials, using GM modulating interventions such as oral bacteriotherapy or FMT, give hope for the cure and early detection of these increasingly prevalent diseases.