Obesity is recognized as a significant risk factor for Alzheimer’s disease (AD). Studies have supported the notion that obesity accelerates AD-related pathophysiology in mouse models of AD. The ...majority of studies, to date, have focused on the use of early-onset AD models. Here, we evaluate the impact of genetic risk factors on late-onset AD (LOAD) in mice fed with a high fat/high sugar diet (HFD). We focused on three mouse models created through the IU/JAX/PITT MODEL-AD Center. These included a combined risk model with
APOE4
and a variant in triggering receptor expressed on myeloid cells 2 (
Trem2
R47H
). We have termed this model, LOAD1. Additional variants including the M28L variant in phospholipase C Gamma 2 (
Plcg2
M28L
) and the 677C > T variant in methylenetetrahydrofolate reductase (
Mthfr
677C >
T
) were engineered by CRISPR onto LOAD1 to generate LOAD1.
Plcg2
M28L
and LOAD1.
Mthfr
677C >
T
. At 2 months of age, animals were placed on an HFD that induces obesity or a control diet (CD), until 12 months of age. Throughout the study, blood was collected to assess the levels of cholesterol and glucose. Positron emission tomography/computed tomography (PET/CT) was completed prior to sacrifice to image for glucose utilization and brain perfusion. After the completion of the study, blood and brains were collected for analysis. As expected, animals fed a HFD, showed a significant increase in body weight compared to those fed a CD. Glucose increased as a function of HFD in females only with cholesterol increasing in both sexes. Interestingly, LOAD1.
Plcg2
M28L
demonstrated an increase in microglia density and alterations in regional brain glucose and perfusion on HFD. These changes were not observed in LOAD1 or LOAD1.
Mthfr
677C >
T
animals fed with HFD. Furthermore, LOAD1.
Plcg2
M28L
but not LOAD1.
Mthfr
677C >
T
or LOAD1 animals showed transcriptomics correlations with human AD modules. Our results show that HFD affects the brain in a genotype-specific manner. Further insight into this process may have significant implications for the development of lifestyle interventions for the treatment of AD.
Introduction
Alzheimer's disease (AD) is the most common form of dementia. Beta‐secretase (BACE) inhibitors have been proposed as potential therapeutic interventions; however, initiating treatment ...once disease has significantly progressed has failed to effectively stop or treat disease. Whether BACE inhibition may have efficacy when administered prophylactically in the early stages of AD has been under‐investigated. The present studies aimed to evaluate prophylactic treatment of the BACE inhibitor verubecestat in an AD mouse model using the National Institute on Aging (NIA) resources of the Model Organism Development for Late‐Onset Alzheimer's Disease (MODEL‐AD) Preclinical Testing Core (PTC) Drug Screening Pipeline.
Methods
5XFAD mice were administered verubecestat ad libitum in chow from 3 to 6 months of age, prior to the onset of significant disease pathology. Following treatment (6 months of age), in vivo imaging was conducted with 18F‐florbetapir (AV‐45/Amyvid) (18F‐AV45) and 18‐FDG (fluorodeoxyglucose)–PET (positron emission tomography)/MRI (magnetic resonance imaging), brain and plasma amyloid beta (Aβ) were measured, and the clinical and behavioral characteristics of the mice were assessed and correlated with the pharmacokinetic data.
Results
Prophylactic verubecestat treatment resulted in dose‐ and region‐dependent attenuations of 18F‐AV45 uptake in male and female 5XFAD mice. Plasma Aβ40 and Aβ42 were also dose‐dependently attenuated with treatment. Across the dose range evaluated, side effects including coat color changes and motor alterations were reported, in the absence of cognitive improvement or changes in 18F‐FDG uptake.
Discussion
Prophylactic treatment with verubecestat resulted in attenuated amyloid plaque deposition when treatment was initiated prior to significant pathology in 5XFAD mice. At the same dose range effective at attenuating Aβ levels, verubecestat produced side effects in the absence of improvements in cognitive function. Taken together these data demonstrate the rigorous translational approaches of the MODEL‐AD PTC for interrogating potential therapeutics and provide insight into the limitations of verubecestat as a prophylactic intervention for early‐stage AD.
Background
As research efforts to discover and develop promising future therapeutics continues, the necessity to develop clinically significant Alzheimer’s disease (AD) mouse models and analysis is ...more important than ever.
Method
The study utilizes a novel MODEL‐AD (Model Organism Development and Evaluation for Late‐onset AD) mouse model that incorporates APOE4, Trem2*R47H, and humanized amyloid‐beta (Aβ) allele into C57BL/6J (B6) mice to produce LOAD2. Two cohorts of male and female LOAD2 mice received either control or high fat diet (HFD) followed by brain metabolism imaging using 18F‐FDG PET/CT. Brain regions were segmented using the Paxinos‐Franklin atlas and analyzed using a whole brain neurovascular uncoupling and connectivity approach. To do this, we computed z‐score statistics for all mice relative their control diet group, and conducted hierarchical modularization of all 28 brain regions and statically compared results across sex and high‐risk diet in 12‐month‐old mice.
Result
An initial network analysis detected metabolic hypo‐perfusion and metabolism for female mice, while males showed neurovascular uncoupling. Hierarchical analysis revealed primary modules within the whole brain network. These primary modules were then further modularized to yield a final breakdown of six secondary sub‐modules consisting of 3‐7 brain regions. Predominate functional associations of the sub‐modules’ brain regions were sensory (S) and learning (L), while sub‐module 2.1 had the strongest visual (V) representation. Statistical analysis of the six sub‐modules exhibited significant, module‐, sex‐, and dietary‐dependent effect for LOAD2 mice on high fat diet (HFD) by 12mo.
Conclusion
The incorporation of APOE4, Trem2*R47H, and humanized Ab sequence in combination with HFD induced age‐dependent LOAD‐relevant changes in neurovascular coupling and whole brain network connectivity consistent with known brain circuit variations observed clinically. These findings support application of this newer LOAD2 mouse model to improve knowledge regarding disease mechanism. Additionally, our connectivity analysis approach shows promise for implementation in future therapeutic development and testing.
Background
The Model Organism Development and Evaluation for Late‐Onset Alzheimer’s Disease (MODEL‐AD) Consortium seeks to develop the next generation of AD models based on human data. A popular ...model of familial AD is the 5xFAD mouse. It is characterized by early amyloid‐β deposition and cognitive decrements. Despite numerous studies, the 5xFAD mouse has not been comprehensively phenotyped for vascular and metabolic aspects over its lifespan.
Method
Males and females 5xFAD and WT littermates underwent in vivo 18F‐FDG‐PET imaging at 4, 6, and 12 months to evaluate regional glucose metabolism. A separate cohort of mice (4, 8, 12 months) underwent “vessel painting” that labels all cerebral vessels with a fluorescent dye. Brains were analyzed for vascular characteristics such as vessel and junction density, vessel length, network complexity, number and diameter of collaterals.
Result
Our analyses revealed that vessel length, vessel and junction densities increased from 4 to 12 months on the cortical surface in both 5xFAD and WT mice. The number of collateral vessels between the middle cerebral artery (MCA) and the anterior and posterior cerebral arteries decreased with age but interestingly their diameters were significantly increased only in 5xFAD mice. MCA average vessel length was significantly decreased at 8 and 12 months in 5xFAD mice compared to WT; primarily driven by males. Analysis of 18F‐FDG cortical uptake found significant interactions between WT and 5xFAD mice spanning 4‐12 months of age in retrosplenial somatosensory and visual cortices. Broadly, 5xFAD males had increased 18F‐FDG uptake at 12 months of age compared to WT mice. In most cortical regions, female 5xFAD mice had reduced FDG uptake compared to WT across the lifespan. In males these metabolic increases coincided with decreased vessel characteristics.
Conclusion
The 5xFAD mouse exhibits AD‐like cognitive deficits with age that are associated with increasing amyloid‐β deposition. No significant differences were found in cortical vascular features although males and females exhibited opposite effects in 18F‐FDG uptake. The MCA supplies blood to large portions of the motor cortex and increased vessel lengths and decreased collaterals along with higher metabolic rates in 5xFAD mice may be related to increasing behavioral deficits via metabolic insufficiency or other mechanisms.
Background
The Model Organism Development and Evaluation for Late‐Onset Alzheimer’s Disease (MODEL‐AD) Consortium has been established to develop the next generation of Alzheimer’s disease (AD) ...models based on human genomic findings. As new models are developed, phenotypic data are compared to established models, including the 5xFAD mouse model. We undertook measurements of diffusion metrics to characterize the temporal alterations in brain structure in male and female 5xFAD mice, including connectivity analysis between the hippocampus and infralimbic prefrontal cortex (PFC).
Method
5xFAD mice were compared to age‐matched littermates (C57BL/6J, WT) at 4, 8, and 12 months (mo). Mice underwent high resolution diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) at 9.4T (5 B0, 30 directions b=3000 mm2/sec) to assess regional white and gray matter. Regional tissue features were extracted from fractional anisotropy (FA), radial (RD), axial (AxD) and mean diffusivity (MD) parametric maps. Tractography was performed based on the AMBMC mouse atlas. 18F‐AV45 PET was performed in a separate cohort at 4, 6, and 12mo to quantitate amyloid β (Aβ) load.
Result
Elevated FA within hippocampal CA1 was first observed in 5xFAD males at 8mo, but at 12mo 5xFAD females had increased FA in bilateral CA1 compared to WT mice. Connectivity between CA1 and PFC found 12mo 5xFAD females had significantly increased RD along the tract with concomitant increases in MD and AxD. AV45‐PET uptake was increased at 6mo (∼20%) and remained elevated at 12mo (∼25%) in the PFC in male and female 5xFAD compared to WT. In the hippocampus there was a ∼20% increase in AV45 binding at 6mo, that then declines by 12mo in 5xFAD mice.
Conclusion
Phenotyping of mouse models using DTI identifies altered brain connectivity and regional tissue modifications that may be indicative of increasing Aβ deposition. These data support that increasing Aβ deposition results in altered DTI metrics and connectivity using clinically relevant imaging modalities.
Vascular contributions to cognitive impairment and dementia (VCID) particularly Alzheimer’s disease and related dementias (ADRDs) are increasing; however, mechanisms driving cerebrovascular decline ...are poorly understood. Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in the folate and methionine cycles. Variants in MTHFR, notably 677 C > T, are associated with dementias, but no mouse model existed to identify mechanisms by which MTHFR677C > T increases risk. Therefore, MODEL-AD created a novel knock-in (KI) strain carrying the Mthfr677C > T allele on the C57BL/6J background (Mthfr677C > T) to characterize morphology and function perturbed by the variant. Consistent with human clinical data, Mthfr677C > T mice have reduced enzyme activity in the liver and elevated plasma homocysteine levels. MTHFR enzyme activity is also reduced in the Mthfr677C > T brain. Mice showed reduced tissue perfusion in numerous brain regions by PET/CT as well as significantly reduced vascular density, pericyte number and increased GFAP-expressing astrocytes in frontal cortex. Electron microscopy revealed cerebrovascular damage including endothelial and pericyte apoptosis, reduced luminal size, and increased astrocyte and microglial presence in the microenvironment. Collectively, these data support a mechanism by which variations in MTHFR perturb cerebrovascular health laying the foundation to incorporate our new Mthfr677C > T mouse model in studies examining genetic susceptibility for cerebrovascular dysfunction in ADRDs.
Background
The MODEL‐AD Consortium seeks to develop the next generation of Alzheimer’s Disease models based on human data. A popular model of familial AD is the 5xFAD mouse, characterized by early ...amyloid‐β deposition and cognitive decrements. Despite numerous studies, the 5xFAD mouse has not been comprehensively phenotyped for vascular and metabolic features over its lifespan.
Method
Male and female 5xFAD and WT littermates underwent in vivo 18F‐FDG‐PET imaging at 4, 6, and 12 months of age to evaluate regional glucose metabolism. A separate cohort of mice (4, 8, 12 months) underwent “vessel painting” that labels all cerebral vessels with a fluorescent dye. “Vessel painted” brains were analyzed for vascular characteristics such as vessel density, junction density, vessel length, network complexity, number of collaterals and vessel diameter.
Results
Our analyses revealed that vessel length, vessel and junction densities increased from 4 to 12 months on the cortical surface in both 5xFAD and WT mice. The number of collateral vessels between the middle cerebral artery (MCA) and the anterior and posterior cerebral arteries decreased with age but their diameters were significantly increased only in 5xFAD mice. MCA average vessel length was decreased in 5xFAD mice compared to WT. Analysis of 18F‐FDG cortical uptake found significant interactions between WT and 5xFAD mice spanning 4‐12 months of age in retrosplenial, somatosensory and visual cortices. Broadly, 5xFAD males had increased 18F‐FDG uptake at 12 months of age compared to WT mice. In most cortical regions, female 5xFAD mice had reduced FDG uptake compared to WT across the lifespan. In males these metabolic increases coincided with decreased vessel characteristics.
Conclusion
The 5xFAD mouse exhibits AD‐like cognitive deficits with age that are associated with increasing amyloid‐β deposition. No significant differences were found in cortical vascular features although males and females exhibited opposite effects in 18F‐FDG uptake. The MCA supplies blood to large portions of the motor cortex and increased vessel lengths and decreased collaterals along with higher metabolic rates in 5xFAD mice may be related to increasing behavioral deficits via metabolic insufficiency or other mechanisms.
Background
The MODEL‐AD Consortium seeks to develop the next generation of Alzheimer’s Disease models based on human data. A popular model of familial AD is the 5xFAD mouse, characterized by early ...amyloid‐ß deposition and cognitive decrements. Despite numerous studies, the 5xFAD mouse has not been comprehensively phenotyped for vascular and metabolic features over its lifespan.
Method
Male and female 5xFAD and WT littermates underwent in vivo 18F‐FDG‐PET imaging at 4, 6, and 12 months of age to evaluate regional glucose metabolism. A separate cohort of mice (4, 8, 12 months) underwent “vessel painting” that labels all cerebral vessels with a fluorescent dye. “Vessel painted” brains were analyzed for vascular characteristics such as vessel density, junction density, vessel length, network complexity, number of collaterals and vessel diameter.
Result
Our analyses revealed that vessel length, vessel and junction densities increased from 4 to 12 months on the cortical surface in both 5xFAD and WT mice. The number of collateral vessels between the middle cerebral artery (MCA) and the anterior and posterior cerebral arteries decreased with age but their diameters were significantly increased only in 5xFAD mice. MCA average vessel length was decreased in 5xFAD mice compared to WT. Analysis of 18F‐FDG cortical uptake found significant interactions between WT and 5xFAD mice spanning 4‐12 months of age in retrosplenial, somatosensory and visual cortices. Broadly, 5xFAD males had increased 18F‐FDG uptake at 12 months of age compared to WT mice. In most cortical regions, female 5xFAD mice had reduced FDG uptake compared to WT across the lifespan. In males these metabolic increases coincided with decreased vessel characteristics.
Conclusion
The 5xFAD mouse exhibits AD‐like cognitive deficits with age that are associated with increasing amyloid‐ß deposition. No significant differences were found in cortical vascular features although males and females exhibited opposite effects in 18F‐FDG uptake. The MCA supplies blood to large portions of the motor cortex and increased vessel lengths and decreased collaterals along with higher metabolic rates in 5xFAD mice may be related to increasing behavioral deficits via metabolic insufficiency or other mechanisms.
Lead (Pb) is an environmental factor has been suspected of contributing to the dementia including Alzheimer’s disease (AD). Our previous studies have shown that Pb exposure at the subtoxic dose ...increased brain levels of beta-amyloid (Aβ) and amyloid plaques, a pathological hallmark for AD, in amyloid precursor protein (APP) transgenic mice, and is hypothesized to inhibit Aβ clearance in the blood- cerebrospinal fluid (CSF) barrier. However, it remains unclear how different levels of Pb affect Aβ clearance in the whole blood-brain barrier system. This study was designed to investigate whether chronic exposure of Pb affected the permeability of the blood-brain barrier system by using the Dynamic Contrast-Enhanced Computerized Tomography (DCE-CT) method.
DEC-CT was used to investigate whether chronic exposure of toxic Pb affected the permeability of the real-time blood brain barrier system.
Data showed that Pb exposure increased permeability surface area product, and also significantly induced brain perfusion. However, Pb exposure did not alter extracellular volumes or fractional blood volumes of mouse brain.
Our data suggest that Pb exposure at subtoxic and toxic levels directly targets the brain vasculature and damages the blood brain barrier system.
Background
Alzheimer’s disease (AD) is the most common cause of dementia in the United States. Approximately 95% of patients have sporadic Late‐Onset AD (LOAD) which lacks an inheritance pattern. ...Therefore, identifying phenotypic patterns is critical for understanding disease progression.
Among all the genetic markers which being identified as AD risks, and APOE4 confers the strongest one. The GWAS analysis also revealed a LOAD‐associated locus on the gene of TREM2. As the microglial receptor of APOE, the R47H variant on TREM2 increases the AD risk. In this study, how these risk alleles affect the brain phenotypes were assessed by MODEL‐AD.
Method
We established an analytical scheme which elucidates the cerebral perfusion and metabolism profiles across 27 brain regions by using 64Cu‐PTSM and 18F‐FDG PET imaging platform in the mice with wild‐type, humanized APOE3 (hAPOε3/ ε3), humanized APOE4 (hAPOε4/ ε4), TREM2 risk (Trem2R47H/R47H), and doubled risks (hAPOε4/ ε4:Trem2R47H/R47H) alleles.
Also, RNA‐seq results from the hemisphere samples were used to conduct the correlation between PET measurements and the gene expression changes from each animal cohort.
Result
Longitudinal analysis (4mo animals as reference) revealed aging effects in each cohort. The male hAPOE4 mice and both sexes of Trem2 risk animals had hypo‐perfusion and metabolism, while female hAPOE4 mice showed an uncoupled hyper‐perfusion and hypo‐metabolism phenotype. In the doubled risks mice, perfusion and metabolism showed a mixed regional‐dependent phenotype.
Cross‐sectional analysis (wildtype mice as reference) showed the effects of humanized genes. A reduction in glucose metabolism was discovered. Intriguingly, male risks mice also showed reduced in perfusion, while the female mice showed a metabolic uncoupling profile.
Cross‐sectional analysis (hAPOE3 mice as reference) showed the effects of risk alleles. An overall reduction in both perfusion and metabolism was discovered in all animal cohorts.
To confirm these findings, RNAseq showed the genes involved in cerebral perfusion, glucose transportation, and metabolism regulation were altered, which are consistent with the findings.
Conclusion
These data suggest that the new perfusion‐metabolism strategy may help to identify AD‐related patterns. Moreover, they replicate clinical manifestations of subjects with the same variants. Finally, additional studies are needed to elucidate the mechanisms and etiology of this uncoupling phenomenon.
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