SIRT1 Is Essential for Normal Cognitive Function and Synaptic Plasticity

The lack of SIRT1 does not affect exploratory behavior but leads to deficits in immediate memory. A, B , SIRT1-KO mice showed normal exploratory behavior in the open field compared with WT as revealed by distance traveled ( A ) and time spent in the center of the arena ( B ) (n = 4 per genotype; WT, 3.6 ± 1. 05%; KO, 3.4 ± 1.5%). C , Novel object recognition test shows normal discriminatory ability to a novel object in SIRT1-KO mice (n = 4 per genotype; training WT, 7 ± 5; training KO, 12 ± 6; test WT, 30 ± 12; KO test, 40 ± 13; p > 0.5). D , Decreased spontaneous alternation in the Y maze compared with WT mice (n = 16 per genotype; WT 58 ± 4 vs KO 48 ± 2%; *p < 0.05). Data represent means ± SEM. E , Cross sections of retinas from SIRT1-KO and WT mice show normal morphology of all retinal layers (ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer) by hematoxylin and eosin staining as well as by isolectin (red), GFAP (green), and DAPI (blue) staining ( F ). Scale bars, 100 μM.

SIRT-KO mice are markedly impaired in associative memory. A , SIRT1-KO mice show slightly higher activity (n = 4 per genotype; WT, 5.5 ± 0.6 cm/s; KO, 8 ± 1.2 cm/s; *p < 0.05) yet similar responses to electric shock than WT mice during training. B, C , Conditioning to context short term ( B ) (n = 4 per genotype; WT, 49 ± 7%; KO, 14 ± 9%; *p < 0.05) and long term ( C ) (WT, n = 13, 48 ± 6%; KO, n = 10, 4 ± 1.5%; **p < 0.001). D , Freezing to altered context did not reveal differences between genotypes (WT, n = 13; KO, n = 10). In contrast to SIRT1-KO, wild-type mice show significantly decreased fear responses in the altered context compared with that in the training context (6 ± 3 vs 48 ± 6%, respectively; p < 0.001). E , In conditioning to tone, SIRT1-KO mice (n = 10; 14 ± 4%) also displayed decreased performance compared with WT mice (n = 13; 31 ± 6%; *p < 0.05). Data represent means ± SEM.

SIRT1-KO mice show spatial learning and memory impairment. A , Success of SIRT1-KO mice (n = 5; open circles) to find the escape box in the Barnes maze was lower than for WT mice (n = 6; *p < 0.001; filled circles). B , Latency to find the escape box significantly decreased in WT mice compared with SIRT1-KO (*p < 0.001). C, D , Number of total errors ( C ) and deviations from the first error ( D ) (*p < 0.001) were both higher in SIRT1-KO mice than WT mice. E, F , Search strategy of WT ( E ) and SIRT1-KO ( F ) mice (serial strategy, yellow; spatial strategy, green; random strategy, red). Data represent means ± SEM. Statistical significance values correspond to the differences between curves analyzed all over the acquisition phase. *p < 0.05, days with statistical significance.

Lack of SIRT1 decreases hippocampal synaptic plasticity. A , I/O plots of field EPSP slopes versus current input (microamperes) were similar in WT (n = 7; filled circles) and SIRT1-KO (n = 8; open circles) mice, indicating that lack of SIRT1 does not alter baseline synaptic transmission. B , Paired-pulse facilitation (n = 3 each genotype) shows similar presynaptic plasticity in WT and SIRT1-KO mice. C , LTP in hippocampal CA1 field elicited by 5 × 3 and 10 × 10 TBS (EPSP slopes; WT, n = 5, filled circles; SIRT1-KO mice, n = 7, open circles). Five burst of 3 × 100 Hz stimulation evokes LTP in both genotypes, whereas 10 bursts of 10 × 100 Hz trains stimulation leads to a long-lasting form of LTP in control but not in SIRTI-KO mouse. D , EPSP slopes averages during the first 2 min after TBS (short-term potentiation) were similar in both genotypes. E , EPSP slopes averages 30–40 min after applying the 10 × 10 TBS protocol show significant differences in LTP induction in WT animals compared with SIRT1-KO mice (*p < 0.05, t test). Data represent means ± SEM.

Burst responses in field CA1 of hippocampal slices from SIRT1-KO and NeSTO mice. Two different protocols of TBS, followed by 40 min of test-pulse recording were used. A , 5 × 3 TBS, five bursts at 5 Hz (theta burst), each burst consisting of three pulses at 100 Hz. B , 10 × 10 TBS, 10 theta bursts, each burst consisting of 10 pulses at 100 Hz. The duration of each pulse within TBS was double that of the test pulse. For each burst response during LTP induction, the area under the curve was measured and each burst area was normalized to the first burst area. (The bottom panels of simulated responses were not scaled.) C, D SIRT1-KO (open circles) and WT (filled circles) burst responses elicited by 5 × 3 TBS ( C ) and 10 × 10 TBS ( D ). E, F , NeSTO (gray bars) and Nestin–Cre (black bars) burst responses elicited by 5 × 3 TBS ( E ) and 10 × 10 TBS ( F ) (p < 0.005, two-way ANOVA). Data represent mean ± SEM.

Neuronal dendritic trees from SIRT1-KO mice show less branching and complexity than WT mice. A , Sholl analysis shows significantly less dendritic material over the entire neuronal tree in SIRT1-KO mice; p < 0.0001. B , Dendritic branch length was 22% lower in SIRT1-KO (100 ± 5.1%) than WT mice (122 ± 10%; p < 0.05). C , Neuronal dendritic arbors show less complexity in SIRT-KO mice (p < 0.05). SIRT1-KO and WT for all analysis correspond to n = 4 brain and n = 20 neurons (5 neurons per brain). Data represent mean ± SEM. Statistical significance values correspond to the differences between curves analyzed over the entire neuronal trees. Asterisks show the shells from the soma with statistical significance of p < 0.05.