So far it was thought to be due to an accumulation of Tau and amyloid proteins in the brain. But US researchers are putting forward a new lead: the appearance of Alzheimer's disease could be linked to an obsolescence of lysosomes, which are the cellular recycling centers.
Alzheimer's disease, the most common cause of dementia in the elderly, is characterized by plaques and tangles in the brain due to accumulation of Tau and beta-amyloid proteins. This accumulation is observed in all patients and is identified as the cause of the progressive degeneration and death of neurons. It would be due to repeated attacks of the brain related to viruses, bacteria or certain lifestyle
Wrong way ?
What if we went wrong? "Dozens of clinical trials based on this theory have failed," says Ryan R. Julian, a chemistry professor who led the work of a team of scientists at the University of California Riverside that proposes in a study published in the ACS Central Science Journal another explanation for the onset of the disease.
"The other" cause of Alzheimer's is the lysosome. Explanation: The lysosome, an organelle in the cell, serves as a bin to it. Older proteins and lipids are sent to the lysosome to be broken down into their constituent elements, which are then returned to the cell for incorporation into new proteins and lipids. To maintain functionality, protein synthesis is balanced by protein degradation.
The weak point of the lysosome
But the lysosome has a weak point: if that does not break down into small pieces, they can not leave the lysosome either. The cell decides that the lysosome does not work and "stores" it, meaning that the cell pushes the lysosome to the side and proceeds to create a new one. If the new lysosome also fails, the process is repeated, resulting in storage of the lysosome.
And Ryan R. Julian recalls that "the brains of people with lysosomal storage disorder, another well-studied disease, and that of people with Alzheimer's disease are similar in terms of lysosomal storage." CQFD!
Alzheimer's disease occurs later in life
But we can not consider that this work will quickly revolutionize the care of Alzheimer's patients: "The symptoms of lysosomal storage disorder appear after a few weeks after birth and are often fatal after a few years. Alzheimer's disease occurs much later in life, so the delays are very different, "says Professor Julian.
His team offers an explanation: long-lived proteins can undergo spontaneous changes that can make them indigestible by lysosomes. "Long-lived proteins become more problematic as they get older and may explain the lysosomal storage observed in Alzheimer's disease, an age-related disease," concludes Professor Julian. "If we are right, it would open new avenues for the treatment and prevention of this disease."
900,000 patients in France
Alzheimer's disease affects, according to the National Institute of Health and Medical Research (INSERM) 900,000 people in France. It is observed almost exclusively in elderly people. Patients gradually lose their cognitive abilities, their physical integrity and their autonomy.