The gut-brain axis affecting TLR4 in Parkinson’s diseases: Gut-brain axis in Parkinson's disease

Parkinson’s disease (PD) is a chronic neurodegenerative illness, which is increasing in developing countries and creating a burden on these economies. Multiple motor and non-motor symptoms have been connected to PD, and patients are diagnosed using clinical observations. Unfortunately, clinical symptoms are found in the late stages of the disease, when preventing is no longer an option. The gastrointestinal system, and more specifically the gut microbiota have an important role in the bidirectional communication taking place between the gut and brain. As a result, the gut microbiota dysbiosis and its effect on the brain-gut axis are among important factors to be considered in PD pathology. In addition, the role of Toll-like receptors (TLRs) in recognizing pathogenic molecules and creating immune responses can affect PD pathogenesis. In this review, we have tried to better understand the effect of TLR4 on the gut microbiota and their dysbiosis, creating a bidirectional feedback loop. Even though the effect of blocking TLR4 signaling on PD is still not well known, it affects PD, and brings hope of using microbial based medications to control this chronic neurodegenerative disease.