P3–343: Effect of abeta (25–35) peptide on rat cultured hippocampal neurons: A neuroprotective response?

Alzheimer disease (AD) is characterized by the accumulation of brain extracellular plaques composed of Abeta peptide and by hyperphosphorylation of Tau protein, leading to intracellular neurofibrillary tangles. Abeta, and its toxic 25–35 fragment, plays a central role in neuronal death, inducing apoptosis. During brain development, neurotrophins (NTs), in particular nerve growth factor (NGF), brain–derived neurotrophic factor, neurotrophin–3 (NT–3) and neurotrophin–4/5 (NT–4/5), antagonize cell death by promoting neuronal survival acting on a set of high affinity tyrosine kinase receptors (i.e. TrkA, TrkB, and TrkC), that, when activated, are the docking sites for different kinases such as phosphatidylinositol 3–kinase (PI–3K). For these reasons neurotrophins may represent a potential candidate for therapeutic treatment of neurobiological disorders. In the present study we are investigating the effect of Abeta peptide (fragment 25–35) on protein expression and phosphorylation, The investigation has been carried out using cultured rat primary hippocampal neurons. After incubation for different times (3 min to 48 hours) with 25μM Abeta, cells were subjected to RT–PCR and EF/WB experiments. RT–PCR results indicate that treatments with Abeta induce an increased expression of TrkA ≫ NGF > p75, and of the Bcl2 family–Bcl–XL genes. Interestingly, an unidentified 50 KDa protein is present after Abeta treatments. Assessment of protein phosphorylation reveals, 1–3 hours after Abeta treatment, an increase of protein phosphorylation, in particular within the 75–200 and 15–25 KDa range. Moreover, a 2–fold increase of anti–apoptotic phospho–Akt and of its substrate, phospho–GSK–3β, was observed. Since it is known that TrkA/NGF–PI3K/Akt cell survival pathway affects GSK–3 beta phosphorylation, reducing tau hyperphosphorylation, it could be hypothesized that at least in a first stage, hippocampal cells exposed to Abeta try to activate survival mechanisms through the modification of protein expression/phosphorylation.