Role of the Gut Microbiome and Bacterial Amyloids in the Development of Synucleinopathies (Review)

Less than ten years ago, evidence began to accumulate about the association between changes in the composition of the gut microbiota and the development of human synucleinopathies, in particular the sporadic form of Parkinson’s disease. We collected data from more than one hundred and thirty experimental studies that reported similar results and summarized the frequencies of detection of different groups of bacteria in these studies. It is important to note that it is extremely rare that a unidirectional change in the abundance of one or another group of microorganisms (only an increase or only a decrease) was detected in patients with Parkinson’s disease. However, we were able to identify several groups of bacteria that were overrepresented in patients with Parkinson’s disease in the studies analyzed. There are various hypotheses about the molecular mechanisms that explain such relationships. Usually, α-synuclein aggregation is associated with the development of inflammatory processes that occur in response to changes in the microbiome. However, experimental evidence is accumulating on the influence of bacterial proteins, including amyloids (curli), as well as various metabolites on aSyn aggregation. In the review, we provided up-to-date information about such examples.