Article Figures & Data
Figures
- Figure 1.
Diet-induced obesity leads to impaired hippocampus-dependent spatial memory, synaptic plasticity, and aberrant basal hippocampus gene expression. A, Schematic depicting the experimental time course. The mice subjected to DIO were fed a high-fat diet for 20 week, whereas control mice were maintained on a standard chow diet. Mice were then subjected to behavioral testing, before down-steam serum and molecular analysis. B, Representative experiment of diet-induced body weight gain of DIO and control mice throughout the 20 week time period. DIO mice weighed significantly more than their chow-fed control counterparts in the weeks immediately following the onset of high-fat feeding, as determined by body weight (n = 12–14 per group, Student's t test, t(24) = 7.209). *p < 0.0001 (t test). C, DIO mice had a significantly higher concentration of serum insulin than controls (n = 12–14 per group, Student's t test, t(24) = 4.735). ****p < 0.0001 (t test). D, During the 30 min open field trail, DIO mice ambulated for a significantly lesser distance than control mice (n = 12–14 per group, Student's t test, t(24) = 2.302). *p < 0.05 (t test). E, Control and DIO mice did not significantly differ in terms of their performance on the 24 h test of ORM. F, DIO mice exhibited impaired OLM that was significantly different from that of control mice (n = 12–14 per group, Student's t test, t(24) = 3.186). **p < 0.01 (t test). G, Impaired performance in OLM exhibited by DIO mice is not attributed to a deficit in object exploration during the OLM training trial, as DIO mice did not differ significantly from control mice. H, I, Control and DIO do not differ in terms of their baseline synaptic transmission, measured by input/output curves and paired-pulse facilitation. J, DIO mice show decreased levels of early- and late-phase LTP after θ burst stimulation (TBS; Control: n = 48 slices from 6 mice; DIO: n = 50 slices from 6 mice; one-tailed Student's t test, *p < 0.05 at t = 20, 40, 120, 140, 160, 180 min). K, Diet-induced obesity decreases basal hippocampus expression of peroxisome proliferator-activated receptor gamma coactivator 1-α (Ppargc1a) mRNA (n = 6–9 per group, Student's t test, t(13) = 2.591, *p < 0.05), protein phosphatase 1, catalytic subunit, β isozyme (Ppp1cb) (n = 6–9 per group, Student's t test, t(13) = 3.020, **p < 0.01), reelin (Reln) (n = 6–9 per group, Student's t test, t(13) = 2.854, *p < 0.05), sirtuin 1 (Sirt1) (n = 6–9 per group, Student's t test, t(13) = 2.948, *p < 0.05), compared with that detected in chow-fed controls. E, F, The perforated lines indicate performance indicative of random chance (50%). Error bars indicate SEM.
- Figure 2.
Evidence of high-fat diet induced aberrations in basal hippocampus DNA methylation. A, Gene targets for MeDIP assay. Lines below genes indicate loci for genomic DNA primer pairs. TSS, Transcription start site. B, MeDIP reveals high-fat diet-induced alterations in DNA methylation at Ppp1cb (n = 8 per group, Student's t test, t(14) = 4.773; **p < 0.001), Reln (n = 8 per group, Student's t test, t(14) = 2.265; *p < 0.05), and Sirt1 (n = 8 per group, Student's t test, t(14) = 2.197; *p < 0.05). C, No difference in the percentage of global 5mC genomic DNA was detected.
- Figure 3.
Evidence of high-fat diet-induced aberrations in basal hippocampus DNA hydroxymethylation. A, hMeDIP reveals high-fat diet-induced alterations in DNA hydroxymethylation at Sirt1 (n = 8 per group, Student's t test, t(13) = 2.983). *p < 0.05. B, No difference in the percentage of global 5hmC genomic DNA was detected.
- Figure 4.
Evidence that obesity-induced transcriptional and epigenetic modifications are temporally regulated. A, Sixteen-week-fed DIO mice weighted more at the time of tissue collection (n = 7 or 8 per group, Student's t test, t(13) = 10.35; one Control weight was not recorded). ****p < 0.0001. B, Sixteen-week-fed DIO mice exhibit hyperinsulinemia (n = 7 or 8 per group, Student's t test, t(13) = 3.614; one DIO insulin sample was lost during processing). **p < 0.01. C, Thirteen-week-fed Control and DIO mice did not significantly differ in terms of their performance on the 24 h test of object location memory. D, Measurement of gene expression within the hippocampus of DIO and control mice maintained on their respective diets for the shorter time period of 16 weeks revealed that diet-induced obesity decreases basal hippocampus expression of Ppargc1a mRNA (n = 8 per group, Student's t test, t(14) = 2.499) but failed to alter the expression of other genes. *p < 0.05. E, MeDIP failed to reveal significant high-fat diet-induced alterations in DNA methylation at any of the target gene loci in the 16 week DIO mice compared with control mice. F, In the DIO group, the only gene promoter with evidence of reduced hydroxymethylation was Ppargc1a (n = 8 per group, Student's t test, t(14) = 2.255). *p < 0.05.
- Figure 5.
Sirt1 depletion within the forebrain is sufficient to recapitulate the memory deficit exhibited by DIO mice. A, SIRT1 protein expression was measured from the hippocampus of mice rendered obese at The Jackson Laboratory (DIO) and their chow-fed counterparts (control). SIRT1 protein expression is reduced in the hippocampus of DIO mice relative to that of control mice (n = 6 or 7 per group, Student's t test, t(11) = 2.250, p < 0.05). B, There is also a corresponding reduction in expression the SIRT1 substrate Ac-p53 in the hippocampus of DIO mice compared with that of controls (n = 6 or 7 per group, Student's t test, t(11) = 2.312, p < 0.05). We generated mice in which we could inducibly and conditionally delete exon 4 of the Sirt1 gene, thus forming a truncated, less stable, and catalytically inactive form of Sirt1 (sicko). C, To disrupt Sirt1 function in forebrain neurons, Camk2a-driven CreERt2 expressed selectively in the forebrain was used to excise the Sirt1, exon 4, catalytic domain upon a 5 d of IP tamoxifen injection. D, Using qPCR primers, specific for exon 4 of Sirt1, it was shown that sicko mice have reduced Sirt1 mRNA expression in dorsal hippocampus compared with their control littermates (n = 10–12 per group, Student's t test, t(20) = 8.339). ****p < 0.0001. E, Western blot analysis of SIRT1 in hippocampus tissue isolated from control and sicko mice revealed that sicko mice have reduced SIRT1 protein expression compared with their control littermates (n = 10–12 per group, Student's t test, t(20) = 2.220). *p < 0.05. F, During the 30 min open field trail, control and sicko mice ambulated for a similar distance (n = 14–19 per group, Student's t test, t(31) = 0.9593, p = 0.3463). G, Control and sicko mice did not significantly differ in terms of their performance on the 24 h test of ORM (n = 14–19 per group, Student's t test, t(31) = 0.0123, p = 0.9903). H, sicko mice exhibited impaired OLM that was significantly different from that of control mice (n = 14–19 per group, Student's t test, t(31) = 2.058). *p < 0.05. B, C, The perforated lines indicate performance indicative of random chance (50%). Error bars indicate SEM.
- Figure 6.
Resveratrol-fed obese mice (DRES) exhibit increased hippocampus SIRT1 activity and preserved hippocampus-dependent memory. A, Representative experiment of diet-induced body weight gain of all groups throughout the experiment. Arrow indicates the start of resveratrol diet supplementation. B, Dietary resveratrol administration did not alter serum insulin levels of obese mice (n = 7–10 per group; one-way ANOVA: main effect of diet on insulin expression; F(3,30) = 5.314, p = 0.0047). *p < 0.05, significant differences between control compared with either DIO or DRES mice (Tukey post hoc tests). **p < 0.01, significant differences between control compared with either DIO or DRES mice (Tukey post hoc tests). C, Dietary resveratrol administration in obese mice led to a reduction in a surrogate marker whose expression is inversely related to Sirt1 activity (n = 4 per group; one-way ANOVA: main effect of diet on acetyl-p53 levels; F(2,9) = 12.80, p = 0.0023). *p < 0.05, significant differences between DIO compared with either control or DRES mice (Tukey post hoc tests). **p < 0.01, significant differences between DIO compared with either control or DRES mice (Tukey post hoc tests). D, Distance traveled in the 15 min open field test of locomotion was reduced in the resveratrol-treated mice (n = 12–14 per group; one-way ANOVA: main effect of diet on distance traveled; F(3,48) = 3.984, p = 0.0130). *p < 0.05, significant differences between control and DRES mice (Tukey post hoc tests). E, Neither of the groups differed in their performance on the 24 h test of ORM. F, Dietary resveratrol administration prevented the development of memory impairment observed in obese mice (n = 12–14 per group; one-way ANOVA: main effect of diet on OLM performance; F(3,48) = 3.562, p = 0.0208). *p < 0.05, significant differences between DIO compared with either control or DRES mice (Tukey post hoc tests). E, F, The perforated lines indicate performance indicative of random chance (50%). Error bars indicate SEM. n.s., Not significant.
