Deregulation of excitatory neurotransmission underlying synapse failure in Alzheimer's disease

Abstract

Alzheimer′s disease (AD) is the most common form of dementia in the elderly. Memory loss in AD is increasingly attributed to soluble oligomers of the amyloid-b peptide (AbOs), toxins that accumulate in AD brains and target particular synapses. Glutamate receptors appear to be centrally involved in synaptic targeting by AbOs. Once bound to neurons, AbOs dysregulate the activity and reduce the surface expression of both N-methyl-D-aspartate (NMDA) and 2-amino- 3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA) types of glutamate receptors, impairing signaling pathways involved in synaptic plasticity. In the extracellular milieu, AbOs promote accumulation of the excitatory amino acids, glutamate and D-serine. This leads to overactivation of glutamate receptors, triggering abnormal calcium signals with noxious impacts on neurons. Here, we review key findings linking AbOs to deregulated glutamate neurotransmission and implicating this as a primary mechanism of synapse failure in AD. We also discuss strategies to counteract the impact of AbOs on excitatory neurotransmission. In particular, we review evidence showing that inducing neuronal hyperpolarization via activation of inhibitory GABAA receptors prevents AbOinduced excitotoxicity, suggesting that this could comprise a possible therapeutic approach in AD.