Activated double-stranded RNA-dependent protein kinase and neuronal death in models of Alzheimer's disease

Neuronal death is a pathological hallmark of Alzheimer's Disease. We have shown previously that phosphorylated double-stranded RNA-dependent protein kinase is present in degenerating hippocampal neurons and in senile plaques of Alzheimer's Disease brains and that genetically down-regulating double-stranded RNA-dependent protein kinase activity protects against in vitro beta-amyloid peptide neurotoxicity. In this report, we showed that two double-stranded RNA-dependent protein kinase blockers attenuate, in human Neuroblastoma cells, beta-amyloid peptide toxicity evaluated by Caspase 3 assessment. In addition, we have used the newly engineered APP(SL)/presenilin 1 knock-in transgenic mice, which display a severe neuronal loss in hippocampal regions, to analyze the activation of double-stranded RNA-dependent protein kinase. Western blots revealed the increased levels of activated double-stranded RNA-dependent protein kinase and the inhibition of eukaryotic initiation factor 2 Alpha activity in the Brains of these double transgenic mice. Phosphorylated RNA-dependent protein kinase-like endoplasmic reticulum-resident kinase was also increased in the Brains of these mice. The levels of activated double-stranded RNA-dependent protein kinase were also increased in the Brains of patients with Alzheimer's Disease. At 3, 6 and 12 months, hippocampal neurons display double stranded RNA-dependent protein kinase labelings in both the nucleus and the cytoplasm. Confocal microscopy showed that almost constantly activated double-stranded RNA-dependent protein kinase co-localized with DNA strand breaks in apoptotic nuclei of CA1 hippocampal neurons. Taken together these results demonstrate that double-stranded RNA-dependent protein kinase is associated with neurodegeneration in APP(SL)/presenilin 1 knock-in mice and could represent a new therapeutic target for neuroprotection.