[Akt activation mediates estrogen-induced neuroprotection against beta amyloid]

To investigate the effects of estrogen 17beta-estradiol on beta-amyloid protein 25-35 (Abeta25-35) -induced neurotoxicity and possible mechanism thereof.

Primary cortical neurons were obtained from the brain of a SD rat and cultured and treated with Abeta25-35 and 17beta-estradiol. I order to investigate the possible mechanism of antagonism of estrogen against the neurotoxicity of Abeta25-35, Akt- I, a specific Akt inhibitor and ICI-182780, an inhibitor of estrogen receptor were added before the addition of estrogen. The Abeta32-35 induced cell viability and lactate dehydrogenase (LDH) release into the cell media was detected with spectrophotometer. Western blotting was used to detect the level of phosphorylated Akt, a cell-protecting factor, and level of nonphosphorylated Akt in different conditions.

20 micromol/L Abeta25-35 decreased the cell viability of the rat cortical neurons to 40.4% (P < 0.01) as compared with the control group and the cell viability of the group with the addition of 17beta-estradiol was 84.2%, significantly higher than that of the Abeta25-35 group (P < 0.01). The LDH secretion level of the Abeta25-35 was 172.5% as high as that of the control group (P < 0.01), while that of the 17beta-estradiol preincubation group was only 118.5% that of the control group (P < 0.01). Both Akt inhibitor and estrogen receptor antagonist partially antagonized estrogen's protective effects against Abeta25-35 in cell viability. Abeta25-35 decreased the phosphorylated Akt level to 69.5% (P < 0.01), while estrogen 17beta-estradiol pretreatment antagonized this effect to 94.7% (P < 0.01), and the addition of Akt inhibitor partially blocked the estrogen's rescue effect (75.4%, P < 0.05). Estrogen treatment alone increased Akt phosphorylation, but this phosphorylation could be partially blocked by the estrogen receptor antagonist, the latter alone had no effect on Akt phosphorylation. Under all circumstances, the amount of nonphosphorylated Akt didn't change significantly.

The estrogen 17beta-estradiol partially alleviates the Abeta25-35-induced neurotoxicity and Akt activation may be involved in estrogen's neuroprotective effect. Estrogen receptor may play a role in estrogen induced Akt activation.