TLR4 and Parkinson disease: According to Braak’s hypothesis (144), α-synuclein aggregates have been reported to travel from the gut to the brain via the vagus nerve, where α-synuclein aggregates ultimately trigger Toll-like receptor 2- and Toll-like receptor 4-mediated inflammation and microglial activation leading to neurodegenerative and motion injury in Parkinson’s disease patients.