APP-KO neurons exhibit alterations in spine density and spine type distribution that are rescued in CA1 neurons of APPsα-KI mice. (a) Scheme depicting the genotypes analyzed and selected proteolytic APP fragments. Note that APPsα-KI neurons lack transmembrane APP and express solely the secreted APPsα ectodomain, recognized by m3.2 antibody. Bottom: scheme of the modified genomic APPsα-KI locus. (b) Western blot analysis of soluble APPs expressed in APPsα-KI brain probed with the APPsα-specific antibody m3.2. APP-KO brain was used as a negativ control, β-tubulin staining as a loading control (c) left panel: Spine density of basal and apical dendrites of APP-KO CA1 neurons is severely reduced compared to WT neurons (One-way ANOVA with Bonferroni multiple comparison, ***p ≤ 0.001) whereas no significant alterations were detectable for APPsα-KI neurons (One-way ANOVA with Bonferroni multiple comparison, n.s.). Number of neurons used for spine density determination: WT n = 20, APP-KO n = 15, APPsα-KI n = 14. Right panel: Representative images of apical dendrites from the indicated genotypes (Scale bar: 5 μm). (d) Spine length was not significantly altered between WT, APP-KO and APPsα-KI (One-way ANOVA, n.s.). (e) Comparison of the relative frequency of spine types. Note that APP-KO neurons show a significant reduction in the number of mushroom spines and increased numbers of stubby spines (see results for details). Spine type distribution of APPsα-KI neurons was not significantly different from WT neurons. For spine type distribution analysis the number of neurons per genotype was: WT n = 15, APP-KO n = 15, APPsα-KI n = 14. Values represent mean ± SEM; One-way ANOVA with Bonferroni multiple comparison test, *p < 0.05, **p < 0.01, ***p < 0.001.