Sex differences in metabolic phenotype and hypothalamic inflammation in the 3xTg-AD mouse model of Alzheimer's disease

Abstract

Background: Alzheimer's disease (AD) is notably associated with cognitive decline resulting from impaired function of hippocampal and cortical areas; however, several other domains and corresponding brain regions are affected. One such brain region is the hypothalamus, shown to atrophy and develop amyloid and tau pathology in AD patients. The hypothalamus controls several functions necessary for survival, including energy and glucose homeostasis. Changes in appetite and body weight are common in AD, often seen several years prior to the onset of cognitive symptoms. Therefore, altered metabolic processes may serve as a biomarker for AD, as well as a target for treatment, considering they are likely both a result of pathological changes and contributor to disease progression. Previously, we reported sexually dimorphic metabolic disturbances in ~ 7-month-old 3xTg-AD mice, accompanied by differences in systemic and hypothalamic inflammation.

Methods: In the current study, we investigated metabolic outcomes and hypothalamic inflammation in 3xTg-AD males and females at 3, 6, 9, and 12 months of age to determine when these sex differences emerge.

Results: In agreement with our previous study, AD males displayed less weight gain and adiposity, as well as reduced blood glucose levels following a glucose challenge, compared to females. These trends were apparent by 6-9 months of age, coinciding with increased expression of inflammatory markers (Iba1, GFAP, TNF-α, and IL-1β) in the hypothalamus of AD males.

Conclusions: These findings provide additional evidence for sex-dependent effects of AD pathology on energy and glucose homeostasis, which may be linked to hypothalamic inflammation.

Keywords: Alzheimer’s disease; Gender; Hypothalamus; Inflammation; Metabolic; Sex.

Fig. 1

Sex and age interact to influence body mass and adiposity in 3xTg-AD mice. A Raw body mass in male and female 3xTg-AD mice at 3, 6, 9, and 12 months of age. n = 6–10/group. B Body mass normalized to same-sex mice at 3 months of age in male and female 3xTg-AD mice n = 6–10/group. C Subcutaneous adiposity, as calculated by percent body mass, in male and female 3xTg-AD mice at 3, 6, 9, and 12 months of age. n = 4–10/group. D Visceral adiposity, as calculated by percent body mass, in male and female 3xTg-AD mice at 3, 6, 9, and 12 months of age. n = 5–10/group. **p < 0.01 vs. opposite sex of same age, ***p < 0.001 vs. opposite sex of same age, ****p < 0.0001 vs. opposite sex of same age, ^ = p < 0.05 vs. same-sex 3 month; ^^ = p < 0.01 vs. same-sex 3 month; ^^^ = p < 0.001 vs. same-sex 3 month; ^^^^ = p < 0.0001 vs. same-sex 3 month. Data are presented as mean ± SEM

Fig. 2

Sex and age interact to influence glucose intolerance in 3xTg-AD mice. A–D Blood glucose levels were measured following overnight fasting (t = 0), then mice were subjected to a glucose tolerance test (GTT). Mice were injected with glucose challenge and blood glucose levels were measured at 15, 30, 60, 90, and 120 min post-injection. Graphs show results of the glucose tolerance test in 3xTg-AD male and female mice at A 3, B 6, C 9, and D 12 months of age. E Area under the curve for GTT testing was computed as a measure of total glucose exposure. n = 4–10/group. *p < .05 vs. opposite sex of same age, **p < 0.01 vs. opposite sex of same age, ****p < 0.0001 vs. opposite sex of same age, ^ = p < 0.05 vs. same-sex 3 month; ^^^^ = p < 0.0001 vs. same-sex 3 month. GTT = glucose tolerance test, AUC = area under the curve, min = minutes. Data are presented as mean ± SEM

Fig. 3

Sex and age interact to influence hypothalamic expression of inflammation-related genes in 3xTg-AD mice. Gene expression levels in homogenate of the whole hypothalamus related to inflammation in male and female 3xTg-AD mice at 3, 6, 9, and 12 months of age. Hypothalamus was collected and assayed for A Iba1, B GFAP, C TNF-α, D IL-1β, E IL-6, and F Ikbkb. Relative normalized expression levels are shown as fold-change compared to a reference sample (Ref), which was a homogenate of hypothalamic samples collected from five 3-month-old wild-type mice. n = 3–6/group. *p < 0.05 vs. opposite sex of same age; **p < 0.01 vs. opposite sex of same age; ^ = p < 0.05 vs. same-sex 3 month; ^^ = p < 0.01 vs. same-sex 3 month. Data are presented as mean ± SEM. Iba1 = ionized calcium-binding adaptor molecule 1, GFAP = glial fibrillary acidic protein, TNF-α = tumor necrosis factor alpha, IL-1β = interleukin-1 beta; IL6 = interleukin-6, Ikbkb = inhibitor of nuclear factor kappa-B kinase subunit beta