The second most common neurodegenerative disease of the nervous system after Alzheimer's disease, Parkinson's disease affects about 200,000 people in France and more than one million in Europe: 8,000 new cases are reported each year in France.
Yet its causes remain largely unknown. Characterized by a progressive loss of control of movements and the appearance of other motor symptoms such as tremor, Parkinson's disease also causes gastrointestinal disorders, sometimes decades before the onset of the first motor problems.
A new study published Oct. 31 in the journal Science Translational Medicine explains this surprising link between the digestive system and the onset of the disease. According to its authors, the appendix, a small excrescence located in the large intestine, would play the role of triggering this brain disease. Its ablation would thus reduce the risk of developing it by 19%. "Our work suggests that the appendix could play a role in the onset of Parkinson's disease," said Viviane Labrie, of the Van Andel Research Institute in Michigan, during a conference call with the press on Tuesday. October.
The appendix as a reservoir for toxins
Led by a large cohort, the study followed 1.7 million Swedes for decades. They concluded that early appendicectomy reduced the risk of developing Parkinson's disease by 19%. This is particularly true for people living in rural areas: at home, this risk is even reduced by 25%, while no similar decrease was found among Swedes living in urban areas. In addition, the removal of the appendix is also related to a later onset of three and a half years on average of the disease.
How to explain it? For neuroscientists authors of this work, this is due to the specific role played by the appendix. As a reservoir of our intestinal microbiota, it also has the particularity of storing a key protein in the onset of Parkinson's disease: the alpha-synuclein protein, which forms aggregates and whose action progressively destroys nerve cells. "Although its reputation is largely 'useless', the appendix actually plays a major role in our immune system, in regulating the composition of our intestinal bacteria and now, as our work shows, in the onset of Parkinson's disease, "explains Viviane Labrie.
Alpha-synuclein protein has been found in abundance in the digestive system, particularly in the appendix, in people with and without Parkinson's disease. "This protein does not like to stay in one place, it can move from neuron to neuron," says Viviane Labrie.
It moves especially via the vagus nerve, which connects the digestive system to the brain. "If it enters the brain, it can set in and develop until it has neurotoxic effects that could lead to Parkinson's disease," says the researcher.
The role played by pesticides
It remains to be determined to what extent the pathology develops, since aggregates of alpha-synuclein have also been found in the appendix of people not affected by Parkinson's disease. According to the researchers, it is possible that the disease is triggered in case of deficiency mechanisms of elimination of the protein, or dysfunction of those preventing its propagation. "A deeper knowledge of this phenomenon could lead to a better understanding of the disease, but also to find new forms of therapy," said Viviane Labrie.
Another point to clarify is that of the role played by environmental factors in the accumulation of alpha-synuclein and thus the onset of Parkinson's disease. For researchers, the 25% reduction in risk among Swedes living in rural areas highlights the role played by pesticides in triggering neurological disease. "This research reinforces two hypotheses: Parkinson's disease starts early in the digestive tract, and environmental factors, such as pesticide exposure, have a role in the development of pathology in genetically predisposed people," notes Vanessa Fleury. , neurologist at University Hospitals in Geneva (HUG), quoted by Le Temps.
It has just launched a pilot study to compare the oral microbiota and the level of inflammation between patients with Parkinson's disease and healthy subjects. "We believe that these two factors could promote the aggregation of alpha-synuclein and its passage in the brain," says the researcher.
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