Fisetin Reduces the Impact of Aging on Behavior and Physiology in the Rapidly Aging SAMP8 Mouse

Abstract

Alzheimer's disease (AD) is rarely addressed in the context of aging even though there is an overlap in pathology. We previously used a phenotypic screening platform based on old age-associated brain toxicities to identify the flavonol fisetin as a potential therapeutic for AD and other age-related neurodegenerative diseases. Based on earlier results with fisetin in transgenic AD mice, we hypothesized that fisetin would be effective against brain aging and cognitive dysfunction in rapidly aging senescence-accelerated prone 8 (SAMP8) mice, a model for sporadic AD and dementia. An integrative approach was used to correlate protein expression and metabolite levels in the brain with cognition. It was found that fisetin reduced cognitive deficits in old SAMP8 mice while restoring multiple markers associated with impaired synaptic function, stress, and inflammation. These results provide further evidence for the potential benefits of fisetin for the treatment of age-related neurodegenerative diseases.

Figure 1.

Fisetin improves cognitive function and locomotor activity in old SAMP8 mice. Spatial learning/memory and recognition memory were evaluated by the Barnes maze (A) and object recognition (B) assays, respectively. The elevated plus maze (C) was used to measure disinhibition. Average velocity (D), number of vertical events (E), and vertical time (F) were assessed in young mice and old SAMP8 mice fed with control or fisetin diets with the open-field test. One-way ANOVA followed by Tukey–Kramer post-hoc test and two-way repeated-measures ANOVA and post-hoc Bonferroni-corrected t test (n = 12–13/group). All data are mean ± SD. *p < .05, ***p < .001. ANOVA = analysis of variance; SAMP8 = senescence-accelerated prone 8.

Figure 2.

Dysregulation of neuronal homeostasis and stress responses in the hippocampus of old SAMP8 mice is partially restored by fisetin. RIPA-soluble fractions from hippocampal tissue were analyzed by Western blotting for relevant markers of neuronal homeostasis and stress and are presented relative to actin. Arc (A), Homer 1 (B), SAP102 (C), HSP40 (D), HSP60 (E), and HSP90 (F). One-way ANOVA followed by Tukey–Kramer post-hoc test (n = 6/group). All data are mean ± SD. *p < .05, **p < .01, ***p < .001. ANOVA = analysis of variance; SAMP8 = senescence-accelerated prone 8.

Figure 3.

Markers of increased inflammation in the hippocampus of old SAMP8 mice are partially prevented by fisetin. (A) Astrocyte activation measured by Western blot of GFAP levels. (B) Ratio of the p25 and p35 forms of the Cdk5 activator was measured by Western blotting. (C) Activation of the stress/inflammation-associated SAPK/JNK was measured by Western blot analysis of its phosphorylation at Thr183/Tyr185. (D) Quantification of microglia in the hippocampus. One-way ANOVA followed by Tukey–Kramer post-hoc test (n = 6/group). All data are mean ± SD. *p < .05, **p < .01, ***p < .001. ANOVA = analysis of variance; GFAP = glial fibrillary acidic protein; SAMP8 = senescence-accelerated prone 8; APK/JNK = stress-activated protein kinase/Jun-amino-terminal kinase.

Figure 4.

Analysis of eicosanoid metabolism in the cortex of young SAMP8, old SAMP8, and old SAMP8 mice fed with fisetin. Significant changes in the metabolites of arachidonic acid, docosahexaenoic acid, and linoleic acid derived from the actions of COX, LOXs, cytochrome P450, and nonenzymatic oxidation, with aging and fisetin treatment. With the exception of eicosanoids derived from linoleic acid, whose levels were not quantified in this study, levels of all other eicosanoids were normalized to their respective fatty acid precursor. Boxes are: white = young; black = old; gray = old + fisetin. One-way ANOVA followed by Tukey–Kramer post-hoc test (n = 5/group). *p < .05, **p < .01, ***p < .001. ANOVA = analysis of variance; SAMP8 = senescence-accelerated prone 8.

Figure 5.

Global metabolomic profiling of plasma and cortex demonstrate that alterations in biological pathways between young SAMP8 and old SAMP8 mice are partially rescued by fisetin. Plasma and cortex biochemicals found significantly modified. Boxes are: white = young; black = old; gray = old + fisetin. Welch’s two-sample t test was used to identify biochemicals that differed significantly between experimental groups (n = 5/group). *p < .05, **p < .01, ***p < .001. SAMP8 = senescence-accelerated prone 8.