Effect of the Alzheimer amyloid fragment A beta(25-35) on Akt/PKB kinase and survival of PC12 cells

The phosphatidylinositol 3 kinase (PI3K)-Akt/PKB pathway protects neurons f rom apoptosis caused by diverse stress stimuli. However, its protective rol e against the amyloid beta peptide (A beta), a major constituent of Alzheim er's disease plaques, has not been studied. We investigated the effect of t he A beta -derived A beta (25-35) peptide on apoptosis and on the Akt survi val pathway in PC12 cells. Cells submitted to micromolar concentrations of A beta (25-35) exhibited increased production of reactive oxygen species (R OS) and morphological alterations consistent with apoptosis. Akt1 was activ ated shortly after incubation with A beta (25-35) and A beta (1-40) with a kinetics different to that of nerve-derived growth factor. Akt1 activation was blocked by the PI3K inhibitor wortmannin. We tested the hypothesis that Akt1 might modify the vulnerability of neural cells to apoptosis induced b y A beta (25-35). Overexpression of an active version of Akt1 attenuated th e apoptotic effect of A beta (25-35) as determined by flow cytometry. Moreo ver, PC12 cells overexpressing a membrane-targeted N-myristylated fusion pr otein of enhanced green fluorescence protein (EGFP) and mouse Akt1 exhibite d lower levels of ROS than control EGFP-transfected cells. The present find ings demonstrate that Akt1 is activated in response to A beta (25-35) in a PI3K-dependent manner and that active Akt1 protects PC12 cells against the pro-apoptotic action of this peptide.