Stimulation of G‐proteins in human control and Alzheimer's disease brain by FAD mutants of APP 714–723 : Implication of oxidative mechanisms

We report the effects of amyloid precursor protein (APP) fragment 714–723 (APP 714–723 ; peptide P1) and its V717F and V717G mutants (peptides P2 and P3, respectively) on G‐protein activity ([ 35 S]GTPγS binding) in membranes from postmortem human control and Alzheimer's disease (AD) brains. The peptides P1, P2, and P3 revealed a significant stimulatory effect on [ 35 S]GTPγS binding in control temporal cortex. The most potent stimulator, P3, at 10 μM concentration enhanced [ 35 S]GTPγS binding by 500%. The effect was threefold stronger than that for wild‐type P1 and twofold stronger than that for P2. In sporadic AD, the stimulatory effect of P1, P2, and P3 on G‐proteins was reduced significantly whereas in Swedish familial AD (SFAD), only P1 elicited marked stimulation (at 10 μM by 50%). In control sensory postcentral cortex, the stimulation of G‐proteins by P3 was 1.5‐fold lower than that in control temporal cortex, whereas in AD and SFAD the effect showed no remarkable regional difference. Treatment of membranes with H 2 O 2 produced 1.5‐fold higher stimulation in [ 35 S]GTPγS binding to temporal cortex than that in binding to sensory postcentral cortex. In AD and SFAD, the stimulation by H 2 O 2 revealed no significant regional difference. Glutathione, desferrioxamine (DFO), and 17β‐estradiol markedly decreased the strong stimulatory effect by P3 on [ 35 S]GTPγS binding to control temporal cortex, with the protective effect by DFO being most potent. The G αo ‐protein levels were not changed in AD or SFAD brain membranes as compared to levels in control membranes. We suggest that strong G‐protein stimulation by P3 in the human brain implies the specific (per)oxidation mechanism that might be affected by regional content of peroxidizing substrates and antioxidants. © 2004 Wiley‐Liss, Inc.