The Neuroprotective Effects of Exercise Against Menopause Induced Alterations in Alzheimer’s Disease Neuropathogenesis

Williams, Christina L

Bilbo, Staci D

Williams-Doria, Janai

2023-10-03T13:35:29Z

2023-10-03T13:35:29Z

2023

Psychology and Neuroscience

Alzheimer’s Disease (AD) disproportionately impacts women; and the loss of ovarian hormones during the perimenopausal transition has been identified as a sex-specific risk factor. Previous studies have shown that the ovarian hormone, estrogen, utilizes its neuroprotective effects on tissues in the brain by aiding in cognitive function, exerting anti-inflammatory effects, promoting neuronal synaptic activity, and regulating energy biosynthesis. These effects are lost when circulating ovarian hormones are decreased. Additionally, during the perimenopausal transition women are experiencing similar neurological deficits found in AD patients such as reduced verbal acuity, memory deficits, delayed speech, etc. making early diagnosis of AD, if present, difficult. As a result, the window for therapeutic intervention is limited. Studies have shown that long-term physical exercise has been associated with a reduction in the rates of cognitive decline, dementia, and other related-neurodegenerative diseases. However, despite the strong evidence for greater female vulnerability, studies aiming to unravel the mechanisms that influence female susceptibility and the potential beneficial effects of exercise on cognitive function, menopause, and AD, are lacking.Here we sought to identify how hormonal changes during the perimenopausal transition influences the susceptibility of females to age-related cognitive decline and the effectiveness of physical exercise during this period in mouse models of AD. Based on a well-characterized neuropathological progression of the CVN-AD (APPSwDI/mNos2-/-) mouse model, we assessed mice at 24 weeks of age (WoA; mid AD-neuropathology) and at 36 WoA (late AD-neuropathology). Mice were treated with either the oil vehicle or 4-vinylcyclohexene diepoxide (VCD) to induce gradual ovarian failure. All mice were given pre- and post-cardiovascular tests at two timepoints, to assess the effects of exercise or being sedentary for 12 weeks. All 24 WoA mice remained sedentary throughout the study. Half of the 36 WoA CVN-AD mice remained sedentary while the other half were exercised with both voluntary wheel running and treadmill training for 12 weeks beginning at 24 WOA. Additionally, all mice were given a novel object recognition test (NOR) 1 week prior to sacrifice to assess short-term episodic memory. After sacrifice, uterine weights, body weights and total follicular counts were assessed. We found that VCD-treatment was effective in reducing uterine weights in all CVN-AD mouse models. Additionally, we found that at 36 WoA CVN-AD have a natural gradual loss in ovarian function. Exercise prior to the exacerbation of AD neuropathology and during the perimenopausal transition increased cardiovascular fitness, improved memory function, and increased the number of healthy ovarian follicles in comparison to sedentary 36 WoA CVN-AD mice. We then investigated the changes in forebrain metabolite levels in 36 WoA CVN-AD mice to identify whether metabolic changes in menopause-like ovarian failure were linked to AD progression and if exercise intervention could modify these effects. As a control, we used forebrain homogenates of sedentary 36 WoA NOS-/- (mNos2-/-) mice that were subjected to the same timelines of VCD- or oil-treatment. Forebrain samples were analyzed using the Biocrates MxP Quant 500 kit, 3 Flow-Injection-Analysis (FIA-MS) and 2 Ultra-High-Pressure Liquid Chromatography (UPLC). The CVN-AD genotype had significantly lower metabolite levels in comparison to NOS-/- mice and this effect was exacerbated by VCD-treatment. When evaluating the effects of exercise on the CVN-AD genotype we found that exercise significantly shifted the brain metabolome and increased metabolite levels in comparison to sedentary CVN-AD and NOS-/- mice. We then compared the interaction between exercise and VCD-treatment and found that exercise was able to reduce some of the negative effects associated with VCD. Within the sedentary CVN-AD treatment group, we found that VCD-treatment significantly increased the number of metabolite changes in comparison to Oil-treated mice. Whereas in the exercise CVN-AD treatment and NOS-/- control groups, VCD’s effects were dampened. These findings indicate that exercise was effective in reducing the effects of VCD-treatment, so much so, there was no difference in the number of metabolite changes between exercised CVN-AD and NOS-/- mice. We then sought to examine the potential role of menopause-like ovarian failure on the neuroinflammatory response and β-amyloid plaque deposition through the evaluation of overall microglial expression, homeostatic microglial expression, and β-amyloid plaque deposition in subregions of the hippocampus. We performed a triple immuno-fluorescence stain (Iba1, Tmem119 and β-amyloid) on brain slices through CA1, CA3 and dentate gyrus (DG) regions of sedentary and exercised 36 WoA CVN-AD mice and 36 WoA NOS-/- control mice. We used confocal microscopy to image the subregions of the hippocampus. Images were then analyzed in the ilastik software program to output cell and area counts of Iba1, Tmem119 and β-amyloid. VCD-treatment in sedentary CVN-AD mice significantly increased microglial proliferation in all subregions of the hippocampus. In comparison, exercise significantly reduced this effect. When evaluating Tmem119 expression, we found that in the CA1 region the CVN-AD genotype has significantly fewer healthy microglia in comparison to sedentary Oil-treated NOS-/- mice. When evaluating Tmem119 expression in the exercised CVN-AD mice we found that in the CA1 region, exercise was able to stave off some of the effects of the genotype and VCD-treatment, however, these effects did not occur in the CA3 and DG. Lastly, when evaluating how microglial expression coupled with exercise intervention and VCD-treatment affected β-amyloid plaque deposition in the CVN-AD mice we found no significant differences within any of the subregions. Taken together, these findings indicate that Aβ plaque deposition may occur independently from microglial expression and that regardless of exercise intervention and VCD-treatment, once Aβ plaques in the CVN-AD pathology occurs they will continue to persist. Collectively these data suggest that the CVN-AD neuropathology drastically impacts cognitive function, the brain metabolome and microglial response. Additionally, exercise as an early intervention during the perimenopausal transition period can prevent some, but not all the deleterious effects of the loss of estrogens and AD neuropathology. Overall, these findings will be significant in contributing to the AD field, especially in evaluating AD as a multiomic disease with sex-specific risk factors that can be modulated by early non-invasive exercise intervention.

https://hdl.handle.net/10161/29113

Neurosciences

Psychology

Alzheimer's disease

Cognitive function

Estrogen

Exercise

Menopause

Neuroprotective

The Neuroprotective Effects of Exercise Against Menopause Induced Alterations in Alzheimer’s Disease Neuropathogenesis

Dissertation