Fig 1: Wnt3a binds to and regulates APP expression through changing its intracellular trafficking.(A) Co-immunoprecipitation (co-IP) of Wnt3a-V5 with full-length proteins mAPP-flag or mAPPLΔCRD. The tagged proteins were co-expressed in HEK293T cells and immunoprecipitated with ant-flag and anti-v5 antibodies. Wild-type mAPP could pull down Wnt3a and vice versa, while mAPP lacking the CRD domain showed impaired ability to pull down Wnt3a even with higher protein levels compared to wild type mAPP in the input. (B) mAPP localization after 4 hr PBS/BSA or Wnt3a treatment. Immunofluorescence for APP (red), Rab5 (green), Golgin97 (green), and Lamp1 (green) revealed mAPP localization in different intracellular compartments. The inset showed zoomed in images of the area in the white box and arrows indicated the overlap of mAPP with respective cellular compartment markers. Scale bar = 10 um. (C–E) Quantification of the overlap of mAPP with early endosome (C), TGN (D) or lysosome (E), respectively, after Wnt3a treatment. (n=33–54 cells, t-test). (F) Western blots of mAPP and Actin on the lysates of DIV7 primary cultured cortical neurons showed that mAPP protein expression level was altered after Wnt3a treatment. (G) Quantification of the western blots results for figure F. (n=three biological independent repeat, t-test). (H) qPCR results showed that mApp mRNA expression was not affected after Wnt3a treatment on DIV7. App-/- mice derived primary neurons were used as a negative control. (n=three biological independent repeat, one-way ANOVA). (I and J) Western blots for APP showed that the Retromer inhibitor Ly294002 (J) could rescue Wnt3a-induced mAPP increase compared with control groups (I). (K and L) Quantification of the western blots results for figure I and J. (n=three biological independent repeat, t-test). (M) Western blots for mAPP expression 4 hr after Wnt3a and Wnt5a treatment at the same time on DIV7. PBS/BSA group acted as control group. (N) Quantification of the western blots results for figure M. (n=three biological independent repeat, t-test). (O) qPCR results for mApp mRNA expression in mApp knockout neurons (negative control), PBS/BSA treated control group neurons and Wnt3a+Wnt5a-treated group neurons. (n=three biological independent repeat, one-way ANOVA). Bars represent the mean ± S.E.M. Samples collected from at least two independent experiments. *p<0.05, **p<0.01. Figure 4—source data 1.Co-immunoprecipitation (co-IP) of Wnt3a-V5 with full-length proteins mAPP-flag or mAPPLΔCRD. Figure 4—source data 2.Western blots for mAPP and Actin after Wnt3a treatment on DIV7 primary cortical neurons. Figure 4—source data 3.Western blots for mAPP and Actin after Wnt3a treatment on DIV7 primary cortical neurons. Figure 4—source data 4.Western blots for mAPP and Actin after adding Ly294002 followed by Wnt3a treatment on DIV7 primary cortical neurons. Figure 4—source data 5.Western blots for mAPP and Actin after Wnt3a + Wnt5a treatment on DIV7 primary cortical neurons.