Findings from the team point to the gut as the origin of Parkinson’s disease, not only in the brain as previously thought.
Gastrointestinal problems such as constipation often precede the decline in motor skills seen in patients with Parkinson's.
The team used mice bred to produce high levels of alpha-synuclein. This protein is associated with brain damage in Parkinson's sufferers.
However, only mice with bacteria in their gut developed Parkinson's symptoms - an observation not seen in sterile mice.
When bacteria from individuals with Parkinson's were transplanted into these mice, more symptoms were observed when compared to bacteria taken from healthy people.
Bacterial species from Parkinson’s donors included Proteus, Bilophila, and Roseburia, with a loss of members of families Lachnospiraceae, Rikenellaceae, and Peptostreptococcaceae, as well as Butyricicoccus.
According to the European Parkinson's Disease Association, 1.2 million people in Europe have Parkinson’s.
The disease sees the brain become progressively damaged over many years, with the main symptoms being involuntary shaking, slow movement and stiff and inflexible muscles.
“We have discovered for the first time a biological link between the gut microbiome and Parkinson's disease,” said senior study author and professor of Microbiology at Caltech, Dr Sarkis Mazmanian.
The gut: target for therapy?
The use of pre- and probiotics in the treatment of Parkinson’s has been touted as an effective therapy for managing the condition’s symptoms.
One study, which used milk fermented with the probiotic strain Lactobacillus casei to treat constipation as a secondary symptom of the condition, resulted in improvements to stool consistency and bowel habits in Parkinson's patients.
These latest study findings appear to deal with the molecular hallmarks of the condition. However, the authors acknowledged there was some way to go before antibiotics or faecal microbe transplants become viable therapies.
“Long-term, high-strength antibiotic use, like we utilised in this study, comes with significant risk to humans, such as defects in immune and metabolic function," said co-author Dr Timothy Sampson, postdoctoral scholar at Caltech.
"Gut bacteria provide immense physiological benefit, and we do not yet have the data to know which particular species are problematic or beneficial in Parkinson's disease."
Dr Arthur Roach, director of research and development at charity Parkinson’s UK added further studies were required in other model systems and in humans to confirm the connection.
Published online ahead of print, DOI: 10.1016/j.cell.2016.11.018
“Gut Microbiota Regulate Motor Deficits and Neuroinflammation in a Model of Parkinson’s Disease.”
Authors: Timothy Sampson et al.