Signal transduction during amyloid-beta-peptide neurotoxicity: role in Alzheimer disease

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive dementia accompanied by two main structural changes in the brain: intracellular protein deposits termed neurofibrillary tangles (NFT) and extracellular amyloid protein deposits surrounded by dystrophic neurites that constitutes the senile plaques. Currently, it is widely accepted that amyloid beta-peptide (A beta) metabolism disbalance is crucial for AD progression. A beta deposition may be enhanced by molecular chaperones, including metals like copper and proteins like acetylcholinesterase (AChE). At the neuronal level, several AD-related proteins interact with transducers of the Wnt/beta-catenin signaling pathway, including beta-catenin and glycogen synthase kinase 3 beta (GSK-3 beta) and both in vitro and in vivo studies suggest that Wnt/beta-catenin signaling is a target for A beta toxicity. Accordingly, activation of this signaling by lithium or Wnt ligands in AD-experimental animal models or in primary hippocampal neurons attenuate A beta neurotoxicity by recovering beta-catenin levels and Wnt-target gene expression of survival genes such as bcl-2. On the other hand, peroxisomal proliferator-activated receptor gamma (PPAR gamma) and muscarinic acetylcholine receptor (mAChR) agonists also activate Wnt/beta-catenin signaling and they have neuroprotective effects on hippocampal neurons. Our studies are consistent with the idea that a sustained loss of function of Wnt signaling components would trigger a series of events, determining the onset and development of AD and that modulation of this pathway through the activation of cross-talking signaling cascades should be considered as a possible therapeutic strategy for AD treatment.