Strain of gut bacteria contributes to the development of Parkinson’s disease

Researchers say they are on the brink of alleviating and slowing the symptoms of patients with Parkinson’s disease.

Affecting more than 100,000 Australians, Parkinson’s disease (PD) is a progressive neurodegenerative disease wherein a neuronal protein called α-synuclein aggregates to form toxic Lewy bodies and Lewy neurites in nerve cells.

The cause is unknown, but a 2021 study found that bacteria of the Desulfovibrio genus in the gut correlate with the disease, and that a higher number also correlates with the severity of the symptoms of the disease.

Now, building on their previous study, Finnish researchers have found that the bacterial strains in patients with Parkinson’s cause aggregation of α-synuclein protein in a model organism – the worm Caenorhabditis elegans.

The findings, published in the journal Frontiers in Cellular and Infection Microbiology, open up the possibility of screening for carriers of these harmful bacteria and targeting them to treat the disease.

“Our findings are significant, as the cause of Parkinson’s disease has gone unknown despite attempts to identify it throughout the last two centuries. The findings indicate that specific strains of Desulfovibrio bacteria are likely to cause Parkinson’s disease,” says Per Saris, Professor in the Department of Microbiology at the University of Helsinki and leader of the study.

“The disease is primarily caused by environmental factors, that is, environmental exposure to the Desulfovibrio bacterial strains that cause Parkinson’s disease. Only a small share, or roughly 10%, of Parkinson’s disease is caused by individual genes.”

Saris’ group investigated whether the Desulfovibrio strains found in patients can result in progress towards Parkinson’s disease by taking faecal samples from ten PD patients and their healthy spouses, and isolated Desulfovibrio species.

These strains were then used to feed C. elegans nematodes genetically edited to produce human α-synuclein fused with yellow fluorescence protein.

Imaging the head sections of the worms revealed that Desulfovibrio strains isolated from healthy individuals do not cause α-synuclein aggregation to the same degree as strains isolated from PD patients.

The aggregates caused by strains isolated from PD patients were also larger.

Saris says that their findings make it possible to screen for the carriers of these harmful Desulfovibrio bacteria.

“Consequently, they can be targeted by measures to remove these strains from the gut, potentially alleviating and slowing the symptoms of patients with Parkinson’s disease,” says Saris.

“Once the Desulfovibrio bacteria are eliminated from the gut, α-synuclein aggregates are no longer formed in intestinal cells, from which they travel towards the brain via the vagus nerve like prion proteins.”

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