Broad-based nutritional supplementation in 3xTg mice corrects mitochondrial function and indicates sex-specificity in response to Alzheimer's disease intervention

Abstract

Nutrition has been highlighted as a potential factor in Alzheimer's disease (AD) risk and decline and has been investigated as a therapeutic target. Broad-based combination diet therapies have the potential to simultaneously effect numerous protective and corrective processes, both directly (e.g., neuroprotection) and indirectly (e.g., improved vascular health). Here we administered either normal mouse chow with a broad-based nutritional supplement or mouse chow alone to aged male and female 3xTg mice and wildtype (WT) controls. After approximately 4 months of feeding, mice were given a battery of cognitive tasks and then injected with a radiolabeled glucose analog. Brains were assessed for differences in regional glucose uptake and mitochondrial cytochrome oxidase activity, AD pathology, and inflammatory markers. Supplementation induced behavioral changes in the 3xTg, but not WT, mice, and the mode of these changes was influenced by sex. Subsequent analyses indicated that differential response to supplementation by male and female 3xTg mice highlighted brain regional strategies for the preservation of function. Several regions involved have been shown to mediate responses to steroid hormones, indicating a mechanism for sex-based vulnerability. Thus, these findings may have broad implications for the human response to future therapeutics.

Fig. 1

Flowchart summarizing each stage of the study. The same animals were used for each analysis throughout the study, with tissues distributed from the behaviorally-tested animals.

Fig. 2

Mean (±standard deviation) chow consumed and body weight change during the protocol was not significantly different between 3×Tg and WT nor supplemented versus nonsupplemented. A) Mean chow consumption (g/day) for each group during the first three weeks of supplementation. B) Mean starting and ending body weights (g) for each group.

Fig. 3

Mean error scores for total errors (±SE) on the delayed match to position for regular testing days 1–10, separated into learning (days 1–5) and asymptotic (days 6–10) phases.

Fig. 4

Mean distance scores in centimeters (±SE) on Morris maze days 1–6.

Fig. 5

Mean (±standard deviation) cytochrome oxidase activity in select regions. A) ROIs demonstrating significant effects of supplementation, where supplementation significantly prevented or restored the region-specific cytochrome oxidase activity decline in 3×Tg mice. B) 3×Tg hippocampal ROIs demonstrated supplementation-driven differential sex effects, wherein the female 3×Tg mice decreased further from the WT means and the 3×Tg males improved toward the WT mean. Abbreviations as in Table 2.

Fig. 6

Mean (±SE) ELISA results. A) Female 3×Tg mice demonstrated significantly higher human Aβ levels than males. Supplementation only significantly reduced Aβ₄₂ levels in female 3×Tg mice, with Aβ₄₀ trending similarly. WT mice were not analyzed for human Aβ. B) Synaptophysin ELISA demonstrated no significant differences. C) GFAP (glial fibrillary acidic protein) ELISA demonstrated no significant differences.

Fig. 7

Mean (±SE) Western blotting results, normalized to β-actin. A) IBA1 (ionized calcium binding adaptor molecule 1) demonstrated no significant differences. B) ARG1 (arginase 1) demonstrated a significant increase in female 3×Tg mice after supplementation (2-tailed t -test, p<0.05). C) YM1 (chitinase 3-like 3) demonstrated no significant differences. D) MMR (macrophage mannose receptor) demonstrated no significant differences. *Significantly different from nonsupplemented 3×Tg females, 2-tailed t -test, p < 0.05.