Nutrition

Parkinson’s, Alzheimer’s: the track of intestinal bacteria is confirmed

The secretion of amyloid proteins by our intestinal flora would lead to the appearance of proteins of the same kind in the brain. However, clusters of amyloid proteins in neurons are involved in neurodegenerative diseases such as Parkinson’s or Alzheimer’s.

Parkinson’s disease, Alzheimer’s disease, fronto-temporal degeneration, amyotrophic lateral sclerosis, all these pathologies have one thing in common. The death of neurons associated with the accumulation of so-called amyloid proteins in the brain. Abnormal proteins aggregate into sorts of “balls of wool” which fill the neurons, and are transmitted from neurons to neurons, between different brain regions and even between different organs. They probably cause inflammation (a reaction of the immune system) and cell death. But where do they come from? Shu Chen, from Case Western Reserve University in Cleveland, and his colleagues have shown that they come from our intestines, and more specifically from bacteria in the intestinal flora.

Amyloid proteins are formed in the intestine

In different neurodegenerative diseases, neurons present this type of amyloid protein aggregates that disrupt their functioning. Until now, we did not know how the first abnormal proteins appear, which fold badly and accumulate in neurons. A significant inflammatory reaction was also observed around the brain regions where these proteins aggregate, without it being known whether or not it causes the death of neurons. On the other hand, it was known that amyloid proteins are already present in the intestines and intestinal neurons of patients sometimes 20 years before Parkinson’s disease is diagnosed.

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Our intestines contain more than 1.5 kilograms of bacteria. This intestinal flora or microbiota has many roles in digestion, against inflammation, etc. These bacteria are mostly not only harmless, but also essential to our survival. But since 2002, we know that some of them produce amyloid proteins, useful for their proliferation, adhesion and resistance. The most studied are the “curli” proteins, secreted by Escherichia coli bacteria. Chen and his colleagues speculated that these gut flora amyloid proteins cause other amyloid proteins to appear in brain neurons.

Inflammation of the brain

They chose to study the aggregation of one of these proteins, alpha-synuclein, which accumulates in the neurons of patients suffering from Parkinson’s disease. To do this, they fed 344 aged rats and C. elegans worms (genetically modified to express human alpha-synuclein) for two or three months with curli-producing Escherichia coli bacteria, other animals receiving modified bacteria to no longer produce curli.

Result: the rats having received the E. coli secreting the curli showed aggregated alpha-synuclein proteins in the intestine and in the intestinal neurons, but also in the neurons of the brain. The worms developed clusters of alpha-synuclein proteins in their muscle cells. Conversely, animals exposed to non-curli-producing bacteria developed very few amyloid aggregates. In addition, the appearance of amyloid proteins caused an intense local inflammatory reaction in the brains of rats, comparable to that observed in the brains of patients suffering from neurodegenerative diseases.

Prebiotics and probiotics

This study is one of the first to demonstrate that the microbiota is capable of causing the aggregation of abnormal proteins in brain neurons. But here is a new avenue of research to better understand neurodegenerative diseases, or even treat them, given that we now have many tools to study and act on the intestinal flora, such as the regular intake of pre- and pro-biotics.

[HighProtein-Foods.com]

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