Alzheimer's disease: How amyloid aggregates alter neuronal function

Alzheimer's disease: How amyloid aggregates alter neuronal function
Rat hippocampal neurons in primary culture, showing a fluorescent soluble protein (left) and trajectories corresponding to the movement of the glutamate receptors on its surface, measured by following individual molecules. Credit: Patricio Opazo/Daniel Choquet/IINS

While the harmful effects of amyloid peptide aggregates observed in Alzheimer's disease are well established, the mechanism through which they act on brain cells remains ill-defined. Researchers from CNRS and universite de Bordeaux have just revealed that they alter the usual functioning of connections between neurons by interacting with a key enzyme of synaptic plasticity. The results will be published on June 12, 2018 in the journal Cell Reports.

Alzheimer's disease, which affects nearly 1 million French people, is characterized by a premature alteration of the patient's cognitive faculties, followed by in late stages. Three types of brain lesions are characteristic of the illness: , fibrillar degeneration, and the accumulation of amyloid peptides that form on . The respective involvement of these different elements in developing the symptoms of the illness is still poorly understood.

Researchers knew, for instance, that amyloid peptides disrupt synapses-the area of contact and chemical communication between neurons-but did not understand how they did so until the research conducted by teams from l'Institut interdisciplinaire de neurosciences (CNRS/universite de Bordeaux). Their findings have revealed the molecular mechanism that links amyloid aggregates and deficient synaptic function observed in animal models of Alzheimer's disease: peptide oligomers interact with a key enzyme in synaptic balance, thereby preventing its normal mobilization.

Alzheimer's disease: How amyloid aggregates alter neuronal function
The measure of the activity of the CaMKII enzyme, triggered by the application of amyloid peptide oligomers in rat hippocampal neurons in culture. Image on left: basic level of CaMKII activity. Image on right: activation of CaMKII by the amyloid peptide. Credit: Patricio Opazo/Daniel Choquet/IINS

The molecule, called CamKII, usually orchestrates , an aspect of neuronal adaptability that enables neurons to reinforce their responses to the signals they exchange. Groups of neurons that code for an information to be memorized are connected by synapses, which are themselves under the control of mechanisms of synaptic plasticity. When the connection between two neurons must be reinforced in order to memorize information, for instance during intense stimulation, CamKII is activated and leads to a chain of reactions that strengthen the capacity to transmit messages between these . Synaptic plasticity is central to memory and learning. Amyloid peptides prevent CamKII from participating to this process of synaptic plasticity, and this blockage eventually leads to the disappearance of the synapse. This discovery could find an application in early phases of Alzheimer's disease when initial cognitive deficiencies are observed, which could be linked to this synaptic malfunction.

The goal for researchers now is to continue studying aggregates, especially by trying to prevent their interaction with CamKII and the loss of synapses observed during the disease.


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Journal information: Cell Reports

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Jun 12, 2018
Amyloid oligomers and dozens of other factors (inlcuding various environmental toxins, a diet high in sugar, high fructose corn syrup, carbohydrates, and salt, and psychological stress) prevents the calmodulin-dependent protein kinase II from helping to regenerate neurons and synapses in the hippocampus via the phosphatidlinositol 3-kinase. The nitration of the latter kinase leads to the death of synapses and neurons rather than to their regeneration.

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