"Unfolding Parkinson's Disease Through the Microbiome-Gut-Brain Axis"

Parkinson's disease (PD) is a progressive and multifactorial neurodegenerative disorder primarily caused by the loss of dopaminergic neurons in the substantia nigra. This neuronal loss leads to characteristic motor symptoms such as tremors, rigidity, and slowness of movement. Although PD has long been regarded as a disorder originating in the brain, recent findings suggest that the gut-brain axis, the intricate communication network between the gastrointestinal tract and the central nervous system also plays an important role in the development and progression of PD. Interestingly, early non-motor symptoms such as constipation and other bowel irregularities often appear several years before the onset of motor symptoms, indicating that changes in gut function may precede and even contribute to neurodegeneration. The gut microbiota influences neuronal signaling, immune activity, and metabolic balance through neuroactive molecules such as neurotransmitters, short-chain fatty acids (SCFAs), and cytokines. In PD, microbial imbalance, intestinal barrier dysfunction, and chronic inflammation are closely linked to the misfolding and accumulation of α-synuclein (α-syn), which can spread from the gut to the brain through the vagus nerve in a prion-like manner. Current therapeutic approaches are increasingly exploring ways to restore gut microbial balance using probiotics, prebiotics, dietary interventions, fecal microbiota transplantation (FMT), and SCFA supplementation. These strategies not only aim to relieve symptoms but may also have the potential to slow disease progression. This review discusses the mechanisms through which the gut-brain axis contributes to PD, summarizes key clinical and preclinical findings, and highlights emerging gut-targeted therapeutic approaches.