Figure 4: GSK-3β activity is inhibited by different mechanisms in retinal neurons. (A) LiCl significantly upregulated p-GSK-3β (Ser9) expression in serum-deprived retinal neurons, but did not affect GSK-3β expression. (B) Relative protein expression of p-GSK-3β and GSK-3β are presented as histograms. (C) SB216763 not only directly decreased expression of GSK-3β but also dramatically inhibited its phosphorylation. (D) Relative protein expression of p-GSK-3β and GSK-3β is presented as histograms. Data are expressed as mean ± SEM compared with the control group. n = 3 for each group. *P < 0.05, **P < 0.01, vs. control (Con) group (Student's t-test). Gapdh: Glyceraldehyde 3-phosphate dehydrogenase; GSK-3β: glycogen synthase kinase-3β; LiCl: lithium chloride; p-GSK-3β: phosphorylated glycogen synthase kinase-3β; SB216763: a GSK-3β inhibitor.