THE ESSENTIAL
- Nearly 900,000 French people are affected by Alzheimer’s disease, according to Inserm.
- Alzheimer’s disease is rare before the age of 65.
Alzheimer’s disease is characterized by disorders of memory, temporo-spatial orientation and the execution of simple gestures. This pathology is mainly caused by the degeneration of neurons in the brain. It mainly occurs in people over the age of 65. Women are more commonly affected by Alzheimer’s disease compared to men.
In a recent study published in the journal Science Advancesscientists from the Massachusetts Institute of Technology (MIT) sought to understand why women are more likely to develop Alzheimer’s disease.
Alzheimer’s: a chemical reaction at the origin of neuronal inflammation
As part of this study, the researchers observed 40 brains of men and women, half of which came from people who had died of Alzheimer’s disease. According to the results, 1,449 different types of proteins appear in the brain with age. The authors of the study focused particularly on proteins resulting from a chemical reaction: the S-nitrosylation process. This molecular event would lead to neuronal inflammation at the origin of cognitive decline.
Scientists have observed that this chemical reaction occurs when a molecule bound to nitric oxide (NO) binds tightly to a sulfur (S) atom on a block of amino acids, including proteins, to form a protein SNO -C3 modified. The study showed that levels of the protein SNO-C3 were six times higher in the brains of women with Alzheimer’s disease than in men.
The scientific team also clarified that this protein could activate immune cells in the brain (microglia) to destroy synapses, in other words the connection points through which neurons send signals to each other.
The protective effects of estrogen to fight cognitive decline
As a reminder, estrogens have protective effects at the neuronal level. The American researchers therefore assumed that these female hormones protect the female brain against the S-nitrosylation process. However, this protection disappears at menopause when estrogen levels drop sharply.
Additional experiments conducted on cultured human brain cells confirmed this hypothesis. SNO-C3 increases when estrogen (β-estradiol) levels decrease, due to the activation of an enzyme that makes NO in brain cells. This increase in SNO-C3 activates the microglial destruction of synapses, and therefore leads to the onset of Alzheimer’s disease.
“Why women are more susceptible to Alzheimer’s disease has long been a mystery, but I believe our findings represent an important piece of the puzzle that explains women’s increased vulnerability as they age.”said Dr. Stuart Lipton, lead author of the study and clinical neurologist.