Figure 1

BACEi treatment decreases Aβ40 and Sez6 family protein ectodomain levels in the mouse brain and reduces cortical mushroom spine density. (A) The molecular structure of BACEi Compound H. (B) Aβ40 levels after 30 mg/kg/day BACEi treatment are reduced in WT and Sez6 TKO brains by 67% and 77% respectively as detected by Meso Scale Discovery assay. n = 15–16 per group; 2-way ANOVA: genotype p = 0.21, treatment p < 0.0001, interaction p = 0.21. (C) Sez6, Sez6L and Sez6L2 ectodomain protein fragments in brains from BACEi treated WT mice were decreased by 95%, 96% and 36% respectively compared to vehicle treated WTs as detected by Western blot. Representative Western blot (i) and quantitation of all samples (ii). n = 4–9/treatment; unpaired t-test: Sez6 p = 0.0012, Sez6L p = 0.0032, Sez6L2 p = 0.0018. Full-length blots are presented in Supplementary Figs. 2–4. (Di) Representative image of hippocampal dendrite segment used for analysis of dendritic spines. (Image shows a single Z plane however individual spines were examined in multiple planes as described in “Methods”). (Dii) BACEi treatment did not affect the density of dendritic spines on oblique apical secondary branches of hippocampal CA1 pyramidal neurons. The overall density and densities of individual spine classes were not altered by treatment in either WT or Sez6 TKO mice. n = 35 neurons (from 7 brains) per genotype/treatment; 2-way nested ANOVA of overall density: genotype p = 0.71, treatment p = 0.18, interaction p = 0.16. (Ei) Representative image of a cortical dendrite segment used for analysis of dendritic spines. (Eii) BACEi treatment did not affect the overall density of dendritic spines on basal secondary dendrites of layer V pyramidal neurons in the somatosensory cortex. However, BACE inhibition specifically reduced mushroom spine density in both WT and Sez6 TKO cortical neurons. WT vehicle: 0.41 ± 0.02 spines/µm, WT BACEi: 0.35 ± 0.02, TKO vehicle: 0.4 ± 0.02, TKO BACEi: 0.32 ± 0.02. n = 35 neurons (from 7 brains) per genotype/treatment; 2-way nested ANOVA of overall density: genotype p = 0.27, treatment p = 0.3, interaction p = 0.11; mushroom spine density: genotype p = 0.4, treatment p = 0.01, interaction p = 0.56. All graphs show mean ± SEM. **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001.