New research has uncovered a relationship between the brain inflammation and motor problems associated with Parkinson’s Disease, and the balance of intestinal microbes in the gut microbiome. The microbes appear to send signals that cause the inflammation, which could mean doctors could eventually treat the disease by fixing the bacterial imbalance.

The research, which was conducted on mice, was published in the December 1st issue of the journal Cell.

70 percent of Parkinson’s patients also show gastrointestinal symptoms such as constipation, which often appear years before symptoms like muscle weakness and neurological problems. While other recent studies have shown a link between Parkinson’s and the intestinal microbiome, it was unclear that gut microbes were directly causing the disease. According to Sarkis Mazmanian, a microbiologist at Caltech, who coauthored the study, “What our study adds is a functional, mechanistic role for the microbiome.”

The research studied mice whose brain’s produced an excess of alpha-synuclein, which is the protein thought to cause Parkinson’s as it builds up in the brain. The mice behaved as you would expect them to if they had Parkinson’s, underperforming at tasks that involve motor functions. The brains of the mice also showed signs of inflammation. However, when the researchers raised these mice to not have any gut microbes at all, they behaved in healthier ways. While they still produced excessive alpha-synuclein, it did not build up in their brains, and did not lead to muscle weakness and unsteady gait.

Furthermore, the researchers took gut microbes from Parkinson’s patients and transferred them to the germ-free mice who were producing an excess of alpha-synuclein. These mice developed the characteristic motor problems weeks later, while mice with microbes transferred from healthy humans remained healthy.

“Even though the mice that received the healthy microbiota received hundreds of bacteria, they didn’t get the disease,” according to Mazmanian.

These results suggest that it is the specific combination of microbes that lead to Parkinson’s, rather the presence of bacteria in general. The next step for researchers will be to determine precisely which microbes are causing the problems.

Mice who had received bacteria from Parkinson’s patients had unusually high levels of certain intestinal microbes. According to one of the researchers, Caltech microbiologist Tim Sampson, these higher than normal levels of certain bacteria may be causing symptoms associated with Parkinson’s.

“I’m interested in trying to understand if there are potential pathogenic microbes that might be individually driving the disease. Once we’ve figured that out we’ll be able to understand whether we can remove that group of organisms or block them,” according to Sampson.

Researchers also report that lower than normal levels of certain microbes may be a factor in causing Parkinson’s, although more research would be necessary to determine which bacteria are leading to problems as a result of low levels.

According to Mazmanian, targeted probiotic therapy to replace helpful microbes may be a treatment option in the future.

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