Research Paper Volume 16, Issue 11 pp 9309—9333

Figure 4. Dietary sucrose modulates lithium’s influence on the GSK-3 phosphorylation ratio. Whole-body protein extracts of w¹¹¹⁸ females treated with the experimental diet were obtained for Western blot analysis. (A) 1 mM LiCl supplemented to the 1% sucrose diet elevated total levels of GSK-3 (Dunn’s multiple comparisons test, *p ≤ 0.05) as did elevating the dietary sucrose content up to 5% (Dunnett’s T3 multiple comparisons test, **p ≤ 0.005). (B) Lithium supplemented to the 5% sucrose diet elevated levels of p-GSK-3 similar to the 1% sucrose diet compared to the 5% and 1% sucrose diets (Dunnett’s T3 multiple comparisons test, *p ≤ 0.05). (C) Lithium significantly lowers the pGSK-3/GSK-3 ratio when added to the 1% sucrose diet (Dunn’s multiple comparisons test, ***p ≤ 0.001). In contrast, added to the 5% sucrose diet, lithium slightly elevated the pGSK-3/GSK-3 ratio. Co-administered to 10% sucrose, lithium had no significant impact on the pGSK-3/GSK-3 ratio. In general, pGSK-3/GSK-3 ratios of flies treated with the 1% sucrose diet were significantly higher than that of those receiving the 5% and 10% sucrose diets. Two known Drosophila GSK-3 isoforms were detected at 52 kDa (G, major isoform) and 58 kDa (SGG39). Overall, feeding the non-supplemented 5% sucrose diet generated the lowest levels of pGSK-3/GSK-3 ratio (Tukey’s multiple comparisons test, **p ≤ 0.005). All data are reported as mean ± SD.