Fig. 1.

Amyloid β neurotoxicity is IDO1-Kyn-AhR dependent and blocked by IDO1 inhibitor. a–d SD rat primary hippocampal neurons were treated with Aβ (1 μM) or Aβ (1 μM) plus RY101 (1 or 10 nM), 1-L-MT (100 μM), or RY103 (10 nM) for 24 h. a Expressions of IDO1-Kyn-AhR, Wnt/β-catenin signaling pathway proteins, and p-Tau determined by western blot. b mRNA expression of CYP1A1 quantified by qPCR. c Apoptosis of neurons evaluated by flow cytometry. Annexin V-FITC is used for cytomembrane staining and PI is used for nucleus staining. d Immunostaining of postsynaptic marker PSD95 (green), neuronal nuclei (DAPI, blue), and β-tubulin (red) (×400 magnification, scale bar = 50 μm). The upright panel exhibited an enlarged view of the representative region in the white box. e The effect of Kyn (200 μM, 24 h) on the expressions of Wnt/β-catenin signaling pathway proteins and p-Tau in wild-type, IDO1 stable knockdown (IDO1 KD), and AhR stable knockdown (AhR KD) HT22 cells determined by western blot. f Expressions of DKK1 in IDO1 stable overexpressing (IDO1 OE) or AhR stable overexpressing (AhR OE) HT22 cells determined by western blot. Con group represents wild-type HT22 cells without treatment, OE-NC group represents wild-type HT22 cells transfected with empty vector. g The effect of Kyn (200 μM, 24 h) on DKK1 expression in IDO1 stable knockdown (IDO1 KD) or AhR stable knockdown (AhR KD) HT22 cells determined by western blot. h ChIP analysis of AhR binding to DKK1 promoter in HT22 cells treated with Kyn (200 μM, 24 h) or Aβ (5 μM, 24 h). ChIP assay was performed with control IgG or anti-AhR antibodies. Immunoprecipitated DNA was examined using qPCR and primers specific for the DKK1 promoter. i Morris water maze (MWM) test for the number of platform location crossings. (n = 8–15 mice in each group). j Concentrations of Trp and Kyn in serum were determined by HPLC and Kyn/Trp ratio was calculated (n = 5–9 mice in each group). k–m Expressions of IDO1-Kyn-AhR, DKK1, and Wnt/β-catenin signaling pathway proteins in the hippocampus determined by western blot. (n ≥ 3 mice in each group). n Schematic of Aβ neurotoxicity regulates Wnt/β-catenin signaling pathway via IDO1-Kyn-AhR pathway. Results shown in a–h are representative of at least three independent experiments. Results shown in i–m, n ≥ 3 mice in each group. The data of e and g were analyzed by Student’s t test, the other data were analyzed by one-way ANOVA followed by Dunnett’s post hoc test. The data of i and j were expressed as the mean ± SD. The data of b and h were expressed as the mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001. The mRNA values are normalized to the level of actin mRNA