A curious link between gut bacteria and Parkinson’s disease
Recent research suggests that the composition of your intestinal bacteria can cause Parkinson’s disease.
Overview
Parkinson’s disease is a degenerative neurological disorder. At present, the pathology of the disease is unknown, but recent research suggests a link between gut bacteria and Parkinson’s.
Researchers have known for a while that a number of physical changes occur in patients with Parkinson’s disease, especially changes in the digestive system, including constipation, bloating, and indigestion. These typically occur long before loss of motor control, the hallmark of the disease.
The biological link between gut bacteria and Parkinson’s disease was first discovered by a group of researchers from Caltech. Over the last couple of years, researchers have found significant additional evidence that the gut bacterial environment and enteric nervous system plays a pivotal role in the pathogenesis of the disease.
Researchers have found that changes in the composition of intestinal bacteria are linked to a number of neurological conditions, including neurodegenerative diseases like Parkinson’s disease. Metabolites produced by intestinal microbes may be either beneficial or pathogenic. An imbalance in the microbial environment of the intestines may lead to the pathogenesis of Parkinson’s disease.
70% of the neurons outside the central nervous system exist in the intestines; this network of neurons is connected to the brain via a nerve known as the vagus nerve. Scientists believe that this nerve could potentially be the link between changes in the gut and changes in the brain. One piece of supporting evidence is that alpha-synuclein, a sticky protein that clumps in the brain of people with Parkinson’s is also present in the gut of people with Parkinson’s.
The role of gut bacteria in other bodily functions also suggests a link to Parkinson’s. The gut microbial environment modulates the immune process in the body and the central nervous system. As part of this function, it may induce oxidative toxicity and related inflammation, which is an underlying mechanism for the progress of Parkinson’s. Gut bacteria also plays a role in removing environmental toxins from the body. Previous studies have shown that environmental toxins are linked to an enhanced risk for Parkinson’s disease.
The gut microbiota has a significant influence on blood-brain barrier (BBB) permeability. Controlled permeability is essential for an integrated BBB structure. The altered microbial environment in the gut of patients upregulates expression of tight junction proteins, such as claudins. Overexpression of these proteins decreases BBB permeability, an effect that is seen in patients with Parkinson’s.
Furthermore, the BBB gene encodes a glycoprotein (P-gp) with ATPase activity, which controls the transport and exchange of a variety of molecules and nutrients between the circulatory system and the brain parenchyma, the functional tissue in the brain. Patients with Parkinson’s have significantly lower activity of this glycoprotein.
Researchers are now trying to characterize the gut bacteria from Parkinson’s patients to determine which microbes predispose people to the disorder. If they can identify certain microbes, scientists can find a way to screen for the disease before symptoms appear and damage to the brain and motor occurs.
Further Reading and References
Yu-Jie Zhang, et al. International Journal of Molecular Science. 2015, 16 (4), 7483–7519.
Houser, MC and Tansey, MG. Nature Partner Journal. 2017. Doi:10, 1038/s41531–016–0002–0.
Rudie Kortekaas et al. Annals of Neurology. 2005, 57, 176–179.
Viorica Braniste et al. Science Translational Medicine. 2014, 6 (263), 263ra 158.
Agata Mulak and Bruno Bonaz. World Journal of Gastroenterology. 2015, 21(37), 10609–10620.
Timothy R. Simpson, et al. Cell. 2016, 167(6), 1469–1480.
