GSK-3 Inhibition Ameliorates Ab Pathology Figure 10. Lithium treatment alone has a greater protective effect against Ab42 toxicity than loss of tau function alone. (A) Loss of tau partially suppressed the locomotor dysfunction phenotype of Arctic Ab42 flies. Expression of Arctic Ab42 peptide in a tau heterozygous background in the adult fly nervous system caused locomotor dysfunction. This phenotype was suppressed when Arctic Ab42 peptide was expressed in a homozygous tau mutant background. Climbing ability of UAS-ArcAb42/+;elavGS Tau EP3203/TM6 and UAS-ArcAb42/+;elavGS Tau EP3203/Tau Dfc flies on +RU486 SY medium was assessed at the indicated time-points (see Materials and Methods). Data are presented as the average performance index (PI) 6 SEM (number of independent tests (n) = 3, number of flies per group (nt) = 45). P,0.0001 comparing the PI of UAS-ArcAb42/ +;elavGS Tau EP3203/Tau Dfc to UAS-ArcAb42/+;elavGS Tau EP3203/TM6 flies (two-way ANOVA). The crosses were performed at 27uC. Western blotting analysis, using a non-phosphorylation dependent antibody to Drosophila tau, confirmed that endogenous tau protein levels were greatly reduced in UAS-ArcAb42/+;elavGS tau EP3203/tau Dfc flies in comparison to tau heterozygous flies (UAS-ArcAb42/+;elavGS tau EP3203/TM6) and control w1118 flies. (B) Arctic Ab42 toxicity was suppressed when the peptide was expressed in a homozygous tau mutant background or when flies were treated with lithium. Lithium treatment alone had a greater protective effect against Ab42 toxicity than did loss of tau function alone, and was not dependent on tau. Climbing ability of UAS-ArcAb42/+;elavGS/+ and UAS-ArcAb42/+;elavGS tau EP3203/tau Dfc flies on 2 or +RU486 SY medium, in the presence or absence of lithium, was assessed at the indicated time-points. Data are presented as the average PI 6 SEM and were analysed by two-way ANOVA (number of independent tests (n) = 4, number of flies per group (nt) = 60). Comparing PI of UAS-ArcAb42/UAS-gfp;elavGS/+ and UAS-ArcAb42/+;elavGS tau EP3203/tau Dfc flies on 2RU, significant differences between genotypes (P,0.0001) were observed. P = 0.0002 comparing PI of UAS-ArcAb42/UAS-gfp;elavGS/+ and UAS-ArcAb42/+;elavGS tau EP3203/tau Dfc flies on +RU food. No significant differences were observed comparing UAS-ArcAb42/+;elavGS/+ and UAS-ArcAb42/+;elavGS tau EP3203/tau Dfc flies on +RU +lithium (P = 0.692). doi:10.1371/journal.pgen.1001087.g010 however, one other study has shown that WT Ab42 expression does not alter phosphorylation of Sgg in flies [55]. These differences may reflect varying mechanisms by which Arctic mutant Ab42 and WT Ab42 peptides modulate GSK-3 activity, or a distinction in the effect of expressing Ab42 throughout development compared to adult-only expression. Hence, our observed increase in Sgg activity may reflect an age-dependent effect. We aimed, therefore, to further investigate the functional role of this kinase in mediating Ab toxicity in our adult-onset AD model. GSK-3 plays an important role in neuronal development [56,57]. Previous analyses of the role of GSK-3 in amyloid toxicity PLoS Genetics | www.plosgenetics.org 12 September 2010 | Volume 6 | Issue 9 | e1001087