Susceptibility of hippocampal neurons to Aβ peptide toxicity is associated with perturbation of Ca 2+ homeostasis

Abstract

Neuritic dystrophy, loss of synapses and neuronal death in the cerebral cortex and hippocampus are hallmarks of Alzheimer's disease. The aim of the present study was to investigate the differential susceptibility of cortical and hippocampal neurons to amyloid-beta (Aβ)-induced toxicity. For that, we have used primary neuronal cultures prepared from rat brain cortex and hippocampus which were treated with the synthetic peptides Aβ25-35 or Aβ1-40. Aβ-induced apoptotic cell death was analyzed by determining caspase-3-like activity. Neuritic dystrophy was evaluated by cobalt staining and MAP2 immunoreactivity. Perturbation of Ca 2+ homeostasis caused by exposure to Aβ was evaluated by determining basal cytosolic calcium levels in the whole neuronal population and by single cell calcium imaging under basal and KCl-depolarization conditions. Finally, levels of GluR2 subunit of glutamate AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-proprionate) receptors were quantified by western blotting. Our results demonstrated that hippocampal neurons in culture are more susceptible than cortical neurons to Aβ-induced apoptosis and also that this mechanism involves the perturbation of Ca 2+ homeostasis. Accordingly, the exposure of hippocampal neurons to Aβ peptides decreases the protein levels of the GluR2 subunit of glutamate AMPA receptors that may be associated with a significant rise of cytosolic Ca 2+ concentration, leading to dendritic dystrophy and activation of apoptotic neuronal death.