Figure 2The timeline of GFP-lentivirus and CSP or CSP-TTK21 (one injection, 500 μg/mouse) injection is shown. (Left) The total number of spines was significantly decreased in TAU VEH compared to WT VEH mice. TAU MOL hippocampi showed a significant increase in the total number of spines compared to TAU VEH (One-way ANOVA p=0.0011, post hoc Holm Sidak's multiple comparisons test F(2,243) = 7.03; WT VEH vs. TAU VEH, p < 0.0009; TAU MOL vs. TAU VEH, p=0.0455). (Middle) Based on spine type, the number of head spines (Mushrooms, thins) was significantly lower in both TAU VEH and TAU MOL than in WT VEH controls (One-way ANOVA p=0.0018, post hoc Holm Sidak's multiple comparisons test F(2,243) = 6.467; WT VEH vs. TAU VEH, p=0.0013; WT VEH vs. TAU MOL, p=0.0272. Stubby spine density was significantly increased in TAU MOL compared to TAU VEH mice (One-way ANOVA F(2,243) = 4.311, p = 0.0145, post hoc Holm Sidak's multiple comparisons test: TAU MOL vs. TAU VEH, p=0.0109), as the number of filopodia (One-way ANOVA F(2,243) = 3.845, p = 0.0227, post hoc Holm Sidak's multiple comparisons test TAU MOL vs. TAU VEH, p=0.0179). (Right) Typical images are presented showing a dendrite fragment for each condition. White arrowhead depicts stubby spines. Scale bar, 2 μm. Number of dendritc segments: WT VEH, n=67; TAU VEH, n=93, TAU MOL, n=87; Number of neurons: WT VEH, n=20; TAU VEH, n=28, TAU MOL, n=16; Number of mice: WT VEH, n=2; TAU VEH, n=3, TAU MOL, n=3 CSP-TTK21 injection into THY-Tau22 mice rescues mature dendritic spines formation in response to learning. (Top left) The time line of injections is shown: Mice were injected 3 times (1 per week) with Vehicle (WT mice, WT VEH, NaCl 0.9%), Vehicle (THY-Tau22 mice (TAU VEH), CSP 500 μg /mouse) or Molecule (THY-Tau22 mice (TAU MOL), 500 μg/mice) and either trained over a 4-day acquisition period in the MWM ("learning" group) or left in their home cage ("basal" group). Mushroom-shaped spines were counted in dorsal CA1, four days post-training. (Bottom left) The number of mature spines was significantly increased by learning in WT VEH and TAU MOL mice. Bar graphs are mean ± SEM. (Two-way ANOVA; Learning effect, F(1, 139)=54.18; p< 0.0001; ### post hoc Holm Sidak's multiple comparisons test: Learning vs. Basal in WT VEH (p=0.0001) and in TAU MOL mice; (p=0.0001). After learning, WT VEH and TAU MOL mice displayed significantly higher number of mature spines than TAU VEH mice (Genotype X Treatment effect, F(2,139)= 9.704; p=0.0001; *** post hoc Holm Sidak's multiple comparisons test: TAU MOL vs. TAU VEH (p=0.0001), WT VEH vs. TAU VEH (p=0.0001). (Right) Typical examples of a dendritic fragment bearing mushroom spines (arrows) are shown for each sub-group in response to learning. Number of dendritc segments: Learning: WT VEH, n=27; TAU VEH, n=27, TAU MOL, n=30; WT VEH_HC, n=27; Number of mice: WT VEH, n=3; TAU VEH, n=3, TAU MOL, n=3. Basal: WT VEH, n=27; TAU VEH, n=7, TAU MOL, n=15; Number of mice: WT VEH, n=3; TAU VEH, n=3, TAU MOL, n=2 Mice were injected 3 times (1 per week) with saline (WT VEH), CSP (Vehicle, VEH) or CSP-TTK21 (Molecule, MOL) (500 μg/mice; THY-Tau22 mice (TAU) before euthanasia. Long Term Depression measurements were performed on hippocampal slices. (Top left) Examples of analog traces recorded 10 min before (a) and 55 min after LTD induction (b; dotted line) in the three groups of mice. (Bottom left) Time course of LTD; LTD is expressed as a percent change in fEPSP (field excitatory postsynaptic potentials) slope over time. After the 20-min baseline recording, a low-frequency stimulation (LFS, 2Hz for 10 min) was applied (arrow). Recording was stopped during the 10-min conditioning stimulation and resumed after completion of LFS. LFS induced a strong depression of the fEPSP slope, which recovered partially to reach a stable level of depression about 20 min after stimulation. (Right) Average depression measured in the last 10 min of LTD. LTD was significantly different in TAU VEH (88.4 ± 4.1% of the baseline, n=10) compared to controls (WT VEH, 71.1 ± 4.4%, n=9) (F(1,17)=8.8, p=0.008). CSP-TTK21 treatment restored LTD to control levels (64.9 ± 5.2%, n=10) (WT VEH vs. TAU MOL: F(1,17)=0.83, p=0.37, ns; TAU VEH vs. TAU MOL: F(1,18)=13.2. p=0.0019). Bar graphs are mean ± SEM