The Influence of Gut Microbiome on Alpha-Synuclein Aggregation: Implications for Parkinson's Disease Pathogenesis.

Parkinson's disease (PD) is a progressive neurodegenerative disorder traditionally characterized by dopaminergic neuronal loss in the substantia nigra and the accumulation of misfolded α-synuclein (α-syn) aggregates. While genetic susceptibility and environmental exposures are well-recognized contributors to PD, growing evidence indicates that disease initiation and progression may also involve peripheral mechanisms originating in the gastrointestinal (GI) tract. Early non-motor symptoms such as constipation, along with the presence of α-syn pathology in the enteric nervous system, have led to increasing interest in the gut-brain axis as a critical modulator of PD pathogenesis. Recent literatures reveal that gut microbiota dysbiosis can influence neurodegeneration through immune activation, intestinal barrier dysfunction, and altered production of microbial metabolites, including short-chain fatty acids, bile acids, lipopolysaccharides, and tryptophan-derived compounds. However, the precise molecular mechanisms by which these microbial factors modulate α-syn aggregation, propagation, and clearance remain incompletely understood. In this article, we review current clinical and experimental literature linking gut microbiota alterations to α-syn pathology, with particular emphasis on inflammatory signaling, microbial metabolites, and impaired proteostatic pathways that promote α-syn misfolding. We further integrate emerging concepts of "body-first" and "brain-first" PD subtypes and discuss proposed routes of α-syn transmission from the enteric to the central nervous system, including vagal, hematogenous, and immune-mediated pathways. By highlighting underexplored mechanistic connections between gut dysbiosis and α-syn biology, this review underscores the potential of microbiome-targeted strategies for early diagnosis and disease modification. A deeper understanding of gut-brain communication may ultimately enable personalized therapeutic approaches and reshape current paradigms of PD pathogenesis.