Toxic events of beta-amyloid oligomers on cortical neurons and protective effect of beta-Estradiol: A mechanistic study (Neuro-Sys, SfN 2014)

Alzheimer disease (AD) affects mainly people over the age of 65 years, suffering from different clinical symptoms such as progressive decline in memory, thinking, language, and learning capacity. The toxic role of β amyloid peptide (Ab) has now shifted from insoluble Ab fibrils to smaller, soluble oligomeric Ab aggregates (AβO). Many evidences suggest that the neurodegenerative process would be due to the interaction of AβO with binding targets, activation of stress kinases, hyperphosphorylation of tau protein, caspase activation, loss of synapse, neuronal death, loss of cholinergic function, generation of reactive intermediates of oxygen (oxidative stress), or glutamate excitotoxicity. Urgent need for efficient new therapies is high, but could only be successful with an extensively comprehension of AβO degeneration process. In the present work, based on an in vitro primary cell culture treated with AβO preparation, we have carefully studied the cytopathological effects of AβO on neuronal death and then we have investigated the effect of 17-β Estradiol (β-estr) on the degeneration process induced by AβO. Briefly we used rat cortical neurons (from E15). The cells were seeded in 96-well plates and intoxicated with AβO solution after 11 days of culture for 24 hours. β-estr was used at 100 nM (final concentration) and was added as pretreatment (1h before injuries). A co-incubation with selective inhibitors was performed for the mechanistic study. In parallel, western blotting (WB) analysis was done to quantify protein levels and their activation. We showed that β-estr was able to significantly protect neurons as well as glial cells from degeneration decreasing the caspase 3 activation and the massive mitochondrial stress (induced by AβO). Preservation of neurite network and synapsis integrity was also observed. Moreover, the large hyperphosphorylation of tau protein induced by AβO was significantly reduced with β-Estr. A mechanistic study was also performed co-incubating inhibitors of main survival pathways to try to better understand the mode of action of β-estr and the pathway involved in the AβO toxicity. We showed that the effects of -Estr were fully abolished blocking the MEK pathway as well as the DNA repair pathway (PARP-g) or the mitochondrial anti-apoptotic pathway (Bcl2). Interestingly the effect was inexisting coincubating β-estr with TrK receptor or Ras/Raf inhibitors showing the predominant role of growth factors paythway in its neuroprotective effect. Finally, we showed a large inactivation of AKT protein in presence of AβO that was reversed even over activated in presence of β-Estr.