According to a new French study, proteins specific to Alzheimer’s disease behave like pathogenic prions, transmitting their abnormal form to healthy prion proteins. In the case of cattle, prions are also responsible for the transmission of Mad Cow disease.
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A Woman With Alzheimer
Alzheimer’s disease is the leading cause of dementia in the world. It affects 8 million new people every year. From a clinical point of view, it progressively affects the patient’s cognitive functions (memory, language, reasoning, learning, problem-solving, decision-making, perception, and attention.) leading to a loss of autonomy. From a physiological point of view, it has been known for thirty years that two proteins play a central role in their formation: the beta-amyloid protein and the tau protein. According to a French study published in Acta Neuropathologica Communications, these proteins behave as pathogenic prions, transmitting their abnormal form to healthy prion proteins and thus multiplying the degeneration of neurons in the brain.
To carry out their study, researchers at the François Jacob Institute of Biology (France) examined samples of patients who died of Alzheimer’s disease. By inoculating extracts in healthy animals, they observed that this eventually led to memory and speech disorders, loss of neurons, and a reduction in brain size.
They also observed the appearance of lesions characteristic of Alzheimer’s disease: amyloidosis and tauopathy. Thus, transmission of disease damage suggests that β-amyloid and Tau proteins behave as pathogenic prions, the researchers observed.
The first such experimental demonstration
On its website, Inserm explains that “prion diseases are rare diseases characterized by a degeneration of the central nervous system and the formation of aggregates of a specific protein”. They are due to the accumulation in the brain of a normal but malformed protein, the prion protein. These diseases are characterized by a rapid and fatal course and absence of treatment. The best known is Creutzfeldt-Jakob disease”.
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Although this study is not the first to study the “prion hypothesis” in Alzheimer’s disease (a theory already advanced for other degenerative diseases such as Parkinson’s), it is the first experimental demonstration in which clinical signs associated with a neurodegenerative process were inoculated through the sample from one brain to another.
“Our results indicate that inoculation of brain homogenate of Alzheimer’s disease induces encephalopathy characterized by neuronal loss, progressive atrophy, changes in neuronal activity and cognitive deficits, as well as rare deposits of β-amyloid and tau. The clinical signs are explained by neuronal loss, brain atrophy, and neuronal network dysfunction. Tau lesions may be a strong, but not the only, decisive induction of neuronal loss and clinical outcomes. Further studies are needed to assess the nature of the relationships between the different lesions induced by the inoculation of the Alzheimer’s gene and to evaluate the mechanisms leading to encephalopathy induced by these inoculations,” the researchers conclude.
A disease that is spreading
This discovery reinforces the Alzheimer’s prion hypothesis, paving the way for the exploration of new mechanisms to understand neuronal and memory loss. In the US, Alzheimer’s disease affects about 5.8 million people and more than 50 million worldwide.
References
Mudher, A., Colin, M., Dujardin, S. et al. What is the evidence that tau pathology spreads through prion-like propagation?. acta neuropathol commun 5, 99 (2017). https://doi.org/10.1186/s40478-017-0488-7
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