GSK-3 Inhibition Ameliorates Ab Pathology Figure 11. Inhibiting Shaggy activity reduces amyloid levels of Arctic Ab42 flies. (A) Protein levels of UAS-ArcAb42/UAS-gfp;elavGS/+ and UAS-ArcAb42/+;elavGS/UAS-SggS9E flies on +RU486 SY medium, and UAS-ArcAb42/UAS-gfp;elavGS/+ flies on +RU +Lithium (Li), were measured by ELISA at 15 days post-induction (see Materials and Methods). Data were compared using one-way ANOVA, number of independent tests (n) = 3. P,0.01, and P,0.0001 when comparing UAS-ArcAb42/UAS-gfp;elavGS/+ to UAS-ArcAb42/+;elavGS/UAS-SggS9E flies on +RU486 SY medium, and UAS-ArcAb42/UAS-gfp;elavGS/+ +RU to UAS-ArcAb42/UAS-gfp;elavGS/+ +RU +Li respectively. (B) RNA levels of UAS-ArcAb42/UAS-gfp;elavGS/+, UAS- ArcAb42/+;elavGS/UAS-SggS9E +RU486 SY medium and UAS-ArcAb42/UAS-gfp;elavGS/+ +RU + lithium flies were measured at day 5. No significant difference was seen in the levels of RNA expression, number of independent tests (n) = 3. doi:10.1371/journal.pgen.1001087.g011 using constitutive expression systems may, therefore, represent abnormal neuronal development in addition to the response to AD pathology in the adult period. Hence, we confined GSK-3 inhibition to the adult neurons of Arctic Ab42-expressing flies, by over-expressing a dominant negative form of the Drosophila orthologue Sgg, using our inducible expression system, or we treated whole adult flies with the GSK-3 inhibitor, lithium. GSK-3 inhibition extended lifespan of Arctic Ab42-expressing flies and suppressed the locomotor dysfunction caused by expression of the peptide in adult neurons. This is an important finding because it demonstrates a definitive role for GSK-3 in Ab42 pathogenesis in adult flies. Moreover, we found that inhibiting Sgg in adulthood had no adverse effect on wild type flies. Hence, our study provides further support for the therapeutic potential of GSK-3 inhibitors in treating Alzheimer’s disease. Further studies are required to test this potential in mammalian models, firstly to confirm the relevance of GSK-3 for direct regulation of Ab42 toxicity and secondly to establish a therapeutic index for GSK-3 inhibition in the treatment of AD. Ab42 has been shown previously to increase tau phosphoryla- tion in cells [45] and in mice [5,43]. Correlative evidence has suggested that GSK-3 may mediate the effects of Ab on tau PLoS Genetics | www.plosgenetics.org 13 September 2010 | Volume 6 | Issue 9 | e1001087