Male Alzheimer's Disease Mice Research Articles

Sex-specific hypothalamic neuropathology and glucose metabolism in an amyloidosis transgenic mouse model of Alzheimer’s disease

BackgroundAmyloid toxicity and glucose metabolic disorders are key pathological features during the progression of Alzheimer’s disease (AD). While the hypothalamus plays a crucial role in regulating systemic energy balance, the distribution of amyloid plaques in the preoptic, anterior, tuberal, and mammillary regions of the hypothalamus in AD mice, particularly across both sexes, remains largely unclear. Our ongoing research aims to explore hypothalamic neuropathology and glucose metabolic disturbances in a well-described APP/PS1 mouse model of AD.ResultsImmunocytochemical staining revealed that Old-AD-Female mice exhibited a greater hypothalamic Amyloid β (Aβ) burden than their Old-AD-Male counterparts, with the mammillary bodies showing the most severe accumulation. Analysis of ionized calcium binding adaptor molecule 1 (IBA1) immunoreactivity and Iba1 mRNA indicated differential microgliosis based on sex, while tanycytic territory and ZO-1 tight junction protein expression remained stable in AD mice. Moreover, sex-specific peripheral glucose metabolic parameters (random and fasting blood glucose) seemed to be exacerbated by age. Old AD mice of both sexes exhibited limited hypothalamic activation (c-Fos + cells) in response to blood glucose fluctuations. Hypothalamic Glut 1 expression decreased in young but increased in old female AD mice compared with age-matched male AD mice. Pearson correlation analysis further supported a negative correlation between hypothalamic Aβ load and random blood glucose in old AD groups of both genders, shedding light on the mechanisms underlying this amyloidosis mouse model.ConclusionAged APP/PS1 mice exhibit sex-specific hypothalamic neuropathology and differential glucose metabolism, highlighting distinct pathological mechanisms within each gender.

Detection of sex-specific glutamate changes in subregions of hippocampus in an early-stage Alzheimer's disease mouse model using GluCEST MRI.

Regional glucose hypometabolism resulting in glutamate loss has been shown as one of the characteristics of Alzheimer's disease (AD). Because the impact of AD varies between the sexes, we utilized glutamate-weighted chemical exchange saturation transfer (GluCEST) magnetic resonance imaging (MRI) for high-resolution spatial mapping of cerebral glutamate and investigated subregional changes in a sex-specific manner. Eight-month-old male and female AD mice harboring mutant amyloid precursor protein (APPNL-F/NL-F: n = 36) and wild-type (WT: n = 39) mice underwent GluCEST MRI, followed by proton magnetic resonance spectroscopy (1H-MRS) in hippocampus and thalamus/hypothalamus using 9.4T preclinical MR scanner. GluCEST measurements revealed significant (p≤0.02) glutamate loss in the entorhinal cortex (% change ± standard error: 8.73±2.12%), hippocampus (11.29±2.41%), and hippocampal fimbriae (19.15±2.95%) of male AD mice. A similar loss of hippocampal glutamate in male AD mice (11.22±2.33%; p = 0.01) was also observed in 1H-MRS. GluCEST MRI detected glutamate reductions in the fimbria and entorhinal cortex of male AD mice, which was not reported previously. Resilience in female AD mice against these changes indicates an intact status of cerebral energy metabolism. Glutamate levels were monitored in different brain regions of early-stage Alzheimer's disease (AD) and wild-type male and female mice using glutamate-weighted chemical exchange saturation transfer (GluCEST) magnetic resonance imaging (MRI). Male AD mice exhibited significant glutamate loss in the hippocampus, entorhinal cortex, and the fimbriae of the hippocampus. Interestingly, female AD mice did not have any glutamate loss in any brain region and should be investigated further to find the probable cause. These findings demonstrate previously unreported sex-specific glutamate changes in hippocampal sub-regions using high-resolution GluCEST MRI.

Microglial hexokinase 2 deficiency increases ATP generation through lipid metabolism leading to β-amyloid clearance.

Microglial cells consume adenosine triphosphate (ATP) during phagocytosis to clear neurotoxic β-amyloid in Alzheimer's disease (AD). However, the contribution of energy metabolism to microglial function in AD remains unclear. Here, we demonstrate that hexokinase 2 (HK2) is elevated in microglia from an AD mouse model (5xFAD) and AD patients. Genetic deletion or pharmacological inhibition of HK2 significantly promotes microglial phagocytosis, lowers the amyloid plaque burden and attenuates cognitive impairment in male AD mice. Notably, the ATP level is dramatically increased in HK2-deficient or inactive microglia, which can be attributed to a marked upregulation in lipoprotein lipase (LPL) expression and subsequent increase in lipid metabolism. We further show that two downstream metabolites of HK2, glucose-6-phosphate and fructose-6-phosphate, can reverse HK2-deficiency-induced upregulation of LPL, thus supporting ATP production and microglial phagocytosis. Our findings uncover a crucial role for HK2 in phagocytosis through regulation of microglial energy metabolism, suggesting a potential therapeutic strategy for AD by targeting HK2.

Hippocampal neural circuit connectivity alterations in an Alzheimer's disease mouse model revealed by monosynaptic rabies virus tracing

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with growing major health impacts, particularly in countries with aging populations. The examination of neural circuit mechanisms in AD mouse models is a recent focus for identifying new AD treatment strategies. We hypothesize that age-progressive changes of both long-range and local hippocampal neural circuit connectivity occur in AD. Recent advancements in viral-genetic technologies provide new opportunities for semi-quantitative mapping of cell-type-specific neural circuit connections in AD mouse models. We applied a recently developed monosynaptic rabies tracing method to hippocampal neural circuit mapping studies in AD model mice to determine how local and global circuit connectivity to hippocampal CA1 excitatory neurons may be altered in the single APP knock-in (APP-KI) AD mouse model. To determine age-related AD progression, we measured circuit connectivity in age-matched littermate control and AD model mice at two different ages (3–4 vs. 10–11 months old). We quantitatively mapped the connectivity strengths of neural circuit inputs to hippocampal CA1 excitatory neurons from brain regions including hippocampal subregions, medial septum, subiculum and entorhinal cortex, comparing different age groups and genotypes. We focused on hippocampal CA1 because of its clear relationship with learning and memory and that the hippocampal formation shows clear neuropathological changes in human AD. Our results reveal alterations in circuit connectivity of hippocampal CA1 in AD model mice. Overall, we find weaker extrinsic CA1 input connectivity strengths in AD model mice compared with control mice, including sex differences of reduced subiculum to CA1 inputs in aged female AD mice compared with aged male AD mice. Unexpectedly, we find a connectivity pattern shift with an increased proportion of inputs from the CA3 region to CA1 excitatory neurons when comparing young and old AD model mice, as well as old wild-type mice and old AD model mice. These unexpected shifts in CA3-CA1 input proportions in this AD mouse model suggest the possibility that compensatory circuit increases may occur in response to connectivity losses in other parts of the hippocampal circuits. We expect that this work provides new insights into the neural circuit mechanisms of AD pathogenesis.

Elucidating the temperature exposome in Alzheimer's disease.

The etiology of Alzheimer's disease (AD) is multifaceted with both genetic and modifiable environmental exposure (exposome) factors contributing to cognitive decline. Metabolic syndrome, including insulin resistance, increases the risk for developing AD, which we have observed in AβPP/PS1 mice. We hypothesized that altering environmental temperature (eT) exposure would improve the metabolic profile of AD mice thereby alleviating cognitive deficits. Starting at 6 months of age (mild amyloid pathology and cognitive impairment), male and female AβPP/PS1, APPNL-F/NL-F , and genetic background control C57BL/6 mice were chronically housed at either 16, 23, or 30°C for 6 months. At 12 months of age, mice were assayed for insulin sensitivity, glucose tolerance, and cognitive performance using the Morris water maze (MWM) behavioral paradigm. Plasma, hippocampal, and peripheral (adipose, hepatic, and pancreatic) samples were procured postmortem and tissue-specific markers of amyloid accumulation and metabolism were assayed. In male mice, chronic exposure to 16°C eT reduced body weight, but had no effect on metabolism nor cognition (Figure 1). Male AD mice exposed to 30°C eT had reduced body weight, improved glucose tolerance, and better performance on the MWM. Plasma concentrations of insulin-like growth factor 1 (IGF-1) and leptin were also decreased in male AD mice at 30°C eT. In female mice, chronic exposure to either eT did not alter body weight, nor cognition. However, 30°C eT improved insulin sensitivity of female C57BL/6 and AβPP/PS1 mice with an corresponding increase in IGF-1 plasma levels. Despite the known improvements on metabolic factors by increasing thermogenesis, chronic exposure to 16°C did not improve the metabolic profile of control or AD mice. Unexpectedly, 30°C eT improved the metabolic profile of male and female C57BL/6 and AβPP/PS1 mice, but cognitive performance was only improved in male mice. Work is ongoing to elucidate markers of glucose metabolism and amyloid pathology in post mortem tissue to better interpret these sexually dimorphic results. This work was supported by the National Institutes of Health (R01 AG057767, R01 AG061937), the Illinois Department of Public Health (03282005H), CARE, and the Kenneth Stark Endowment.

Anxiety throughout Alzheimer’s disease progression: In mice and (wo)men

Neuropsychiatric disturbances, such as depression and anxiety, are observed in 90% of Alzheimer's disease (AD) patients and are frequent in those at risk for AD (Lyketsos CG, et al. 2012). Similarly, epidemiological studies show that neurodegeneration and clinical symptoms occur more rapidly in females once diagnosed. In addition to cognitive decline and daily anxiety, AD patients (∼50%) become confused, agitated, and anxious in the evening, often referred to as "sundowning"(Canevelli M, et al. 2016). This circadian disruption can also greatly impact AD pathology. Restlessness before and during sleep has been shown to inhibit Ab clearance, increase neurofibrillary tangles, and dysregulate synaptic activity, all of which are characteristic hallmarks of AD (Cordone S, et al. 2019). Using our activity-dependent tagging system, the ArcCreERT2 x (ChR2)-EYFP x AD (APP/PS1), we labeled neurons activated during learning. These neurons can then can be compared with secondary neuronal ensembles activated during memory retrieval. The neurons activated at both time points represent an engram. Here, we aimed to identify the neural ensembles linking anxiety and memory loss following AD progression by utilizing behavioral studies, calcium imaging and whole-brain microscopy, in female and male mice. We found: 1) Female AD mice exhibited anxiety-like behavior at an earlier age compared to controls and male mice, 2) AD female mice displayed memory deficits as early as 2 months of age, 3) Anxiety-like behavior correlated with memory impairment only in AD female mice, 4) Unlike their male counterparts, female AD mice showed a decline in memory traces in the CA3 of the hippocampus, and 5) Male AD mice exhibit sundowning behavior at 2 months which correlates to increased calcium transients in the vCA1. We have also translated these findings to humans using the ADNI dataset. In humans, anxiety predicts transition to dementia and that anxiety has a sex-specific effect on brain atrophy. To use anxiety as a neuropsychiatric biomarker of AD in the human population in combination with current imaging and cognitive testing and to find novel brain areas associated with increased anxiety and memory loss. This could provide new therapeutic targets for those at risk for AD.

Sex Differences in the White Matter and Myelinated Fibers of APP/PS1 Mice and the Effects of Running Exercise on the Sex Differences of AD Mice.

Previous studies have suggested that changes in the white matter might play an important role in the pathogenic processes of Alzheimer's disease (AD). However, no study has investigated sex differences in these changes. Previous studies found that running exercise could delay both the decline in spatial learning and memory abilities as well as the changes in the white matter during early AD in male mice. However, whether exercise also has an effect on the changes in the white matter in female AD mice remains unknown. To address these questions, 6- and 10-month-old male and female APP/PS1 double transgenic AD mice were used. The 6-month-old male and female APP/PS1 double transgenic AD mice underwent a 4-month running exercise regime. The white matter volume and parameters of the myelinated fibers in the white matter of the 10-month-old exercised and non-exercised male and female AD mice were investigated using electron microscopy and stereological methods. There were no significant differences in the mean escape latencies between the male and female AD mice in the non-exercised groups, but after 4 months of treadmill exercise, the mean escape latencies of the female exercised AD mice had significantly shortened compared with those of the male exercised AD mice. The total white matter volume and most of the parameters of the myelinated fibers of the white matter in the female AD mice were significantly lower than those of the male AD mice. The total length of the myelinated fibers with diameters ranging from 0.6 to 0.7 μm, the axonal diameter of the myelinated fibers and the g-ratio of the myelinated fibers in the white matter of the exercised female AD mice were significantly increased compared with those of the non-exercised female AD mice. There were sex-specific differences in the white matter and myelinated fibers of white matter in the AD mice. Running exercise more effectively delayed the decline in spatial learning and memory abilities and delayed the changes in the myelinated fibers of the white matter in female transgenic mice with early AD than in male transgenic mice.

Selenium positively affects the proteome of 3 × Tg-AD mice cortex by altering the expression of various key proteins: unveiling the mechanistic role of selenium in AD prevention.

Selenium (Se) deficiency is believed to be involved in pathogenesis of Alzheimer's disease (AD) due to failure of antioxidant system. Its supplementation may restore the antioxidant system and compensate the impairments caused by AD. Present study reveals the effect of Se on the proteomic changes in cortex within triple transgenic male AD mice (3 × Tg-AD) after 4 months sodium selenate supplementation. Using iTRAQ comparative proteomics approach, 142 proteins found significant alterations with 96 down-regulated and 46 up-regulated proteins in the cortices of AD mice in comparison with the wild non-transgenic type mice. On treatment with sodium selenate, 41 proteins showed reverse expression, that is, thirty three proteins were down-regulated in AD mice but up-regulated in selenate treated AD mice while eight up-regulated proteins in AD mice showed lower expression in selenate treated mice. OmicsBean bioinformatics analysis revealed that Se positively affected the proteins vital in biological process, structural cores, and molecular functions, which include metabolic proteins, structural proteins, signaling molecules, oxidative stress balancers, and proteosomal degradation proteins. Results of mass spectrometry (MS) were further confirmed by Western blot analysis of five important proteins, prompting the authenticity of the MS results. This paper fills the protein-based molecular gap between AD and Se-treatment, and it provides a full view of Se in reversing the change of cortical protein levels during AD formation.

Gender difference in valproic acid-induced neuroprotective effects on APP/PS1 double transgenic mice modeling Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder that causes progressive memory and cognitive impairment with gender difference in specific cognitive ability domains, pathology, and risk of AD. Since valproic acid (VPA) is a widely used mood stabilizer and an antiepileptic drug, which exhibits multiple neuroprotective activities on AD, this study intended to investigate the gender difference in the effect of VPA on APP/PS1 double transgenic mice modeling AD. Behavioral experiments showed that VPA reduced the autonomous behaviors, improved learning and memory, and exhibited gender differences in AD mice compared with the control mice. The decrease in senile plaque, amyloid β (Aβ) 40, and Aβ42 caused by VPA in the male AD mice was more notable than that in the female AD mice. Meanwhile, VPA protected brain cells from dying notably in the male AD mice but only slightly in the female AD mice, and VPA treatment thickened the postsynaptic density and markedly increased the number and density of presynaptic vesicles in both male and female AD mice. However, the effects of rescuing early synaptic structural and functional deficits by VPA were more obvious in the male mice. Overall, these results supported the hypothesis that gender difference significantly influences AD and indicated that VPA may be a promising remedy for AD if basic biological differences and gender specificity were prudently taken into account.