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Background: A case study on a PSEN1 (E280A) carrier with APOECh (R136S) mutation revealed changes in APOE protein function led to a protective effect on AD outcomes. Notably, there is an intriguing disparity between the two hallmark pathologies: a reduction in tauopathy but no change in plaque burden. Given that the APOE protein is predominantly produced by astrocytes and activated microglia, and the APOE gene is among the disease-associated microglia (DAM) genes, it is conceivable that the variance in pathological outcomes may be rooted in the glial response. Therefore, studying the APOEch mutation will provide a unique opportunity to investigate the role of APOE in tau and Aβ plaque development, with a particular emphasis on the proposed link: neuroinflammation., Method: We used CRIPSR-Cas9 to introduce ApoeCh into the mouse genome. Mice were then bred and crossed to homozygosity with the 5xFAD and PS19 transgenic mouse models to study the effect of the variant on amyloid plaque and tauopathy, respectively. Brain slices were immunolabeled for microglia and reactive astrocytes, and single-cell spatial transcriptomics/proteomics was investigated using multiplexed error-robust fluorescence in situ (MERFISH) technology. Plasma neurofilament light chain (NfL) along with Ab and tau protein levels were measured via MSD technology., Result: In the 5xFAD mouse model, analysis of confocal images reveals reduction in plaque load in the 5xFAD mice at 12 months of age that is reflected in the global decrease in microglia and astrocyte number with ApoeCh. However, there is an increase in DAM response to plaque observed through elevated CD11c + staining along with upregulation of DAM genes and protein levels via spatial transcriptomics and proteomics. In the PS19 mice, although there is an increase in phospho-tau level, there is a stark reduction in microgliosis to tauopathy. Plasma neurofilament light chain levels reveal that ApoeCh reduces plasma NfL level in response to plaques but not tau., Conclusion: ApoeCh mutation has differential effects on glial responses to plaque and tau. ApoeCh decreases plaque load and plasma NfL but increases inflammatory response to plaques. Whereas in a tau model, ApoeCh increases phosphorylated tau level but decreases microgliosis and inflammatory response to tau pathology., (© 2024 The Alzheimer's Association. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Background: Genome-Wide Association Studies (GWAS) identified ApoE4 and Trem2*R47H as two of the strongest genetic risk factors for late-onset Alzheimer's Disease (LOAD). As part of our efforts to develop mouse models that better recapitulate LOAD, at Model Organism Development & Evaluation for Late-Onset Alzheimer's Disease (MODEL-AD) consortium at University of California - Irvine, we have created a triple homozygous mouse model that combines our previously developed hAb-KI loxP mice (Jackson Lab #031050), Trem2 R47H NSS (Jackson Lab #034036) and a humanized ApoE4 (Jackson Lab #027894), to evaluate the interactions between aging, hAPOE4, TREM2*R47H, and hAb., Method: By breeding the hAb-KI loxP , hApoE4 and Trem2 R47H NSS , we obtained triple homozygous (HO) mice and we then generated four different groups: WT (C57BL6/J), hAb-KI loxP HO, hAb-KI loxP HO;hApoE4 HO and hAb-KI loxP HO;hApoE4 HO;Trem2 R47H NSS HO. All four groups were then aged to 4, 12, 18 and 24 months of age, when coronal hippocampal slices were prepared, and long-term potentiation recordings were obtained. Additionally, we also measured soluble and insoluble Ab40 and Ab42 as well as plasma neurofilament light chain (NfL)., Result: hAb-KI loxP mice showed a significant reduction in mean potentiation 50-60 minutes post TBS, when compared to WT mice at 4, 12, 18 and 24 months of age, indicative of an LTP deficit associated to human Ab. Interestingly, both hAPOE4 and Trem2 R47H NSS variants completely prevent the LTP deficits observed on the hAb-KI loxP mice from 4 months of age. In addition, cortical soluble Ab40, Ab42 and the Ab42/Ab40 ratio were significantly decreased in hAb-KI loxP ;hAPOE4 and hAb-KI loxP ;hAPOE4;Trem2 R47H NSS mice at 24 m of age, when compared to hAb-KI loxP . However, plasma NfL levels were significantly increased in hAb-KI loxP ;hAPOE4;Trem2 R47H NSS mice at 24 months of age, indicative of axonal damage in this mouse model., Conclusion: hAb induces robust LTP deficits that are prevent by either hAPOE4 or TREM2*R47H, contrary to expectations. However, hAPOE4 and Trem2 R47H NSS variants have a cumulative detrimental effect on axonal damage when combined with aging., (© 2024 The Alzheimer's Association. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Background: In several large genome-wide association studies (GWAS), genetic polymorphisms of Abi3 have been identified as a risk factor for late-onset Alzheimer's Disease (LOAD). ABI3 along with ABI1 and ABI2, regulate the formation of the WAVE complex which in turn, regulates actin dynamics. ABI3 is highly expressed in microglia in the brain, however, the function of ABI3 in microglia is relatively unknown. In recent studies knock-out of ABI3 has been shown to exacerbate amyloid beta (Aβ) pathology and associated inflammation. To date, there have been no studies on variant specific effects on amyloid beta pathology., Methods: To study the effects of ABI3 on the development of Alzheimer's disease (AD) relevant pathologies we introduced an equivalent coding sequence change that has been identified as a risk variant for LOAD (S212F) into the C57BL/6 mouse genome using CRISPR/Cas9 (S209F). We set out to characterize the Abi3 S209 F variant and investigate its impact on AD pathology when crossed with 5xFAD transgenic mice, generating four distinct groups: WT, Abi3 S209 F homozygous, 5xFAD, and 5xFAD/Abi3 S209 F homozygous. Characterization was performed using histological staining and biochemical approaches at 4-, 12- and 18-months of age., Results: 5xFAD/Abi3 S209 mice displayed an age-related decrease in dense core-Aβ plaque burden, characterized by reduced Thioflavin-S staining, accompanied by changes in fibrillar Aβ (OC) staining, in confocal images of both subiculum and visual cortical regions of 5xFAD/Abi3 F mice displayed an age-related decrease in dense core-Aβ plaque burden, characterized by reduced Thioflavin-S staining, accompanied by changes in fibrillar Aβ (OC) staining, in confocal images of both subiculum and visual cortical regions of 5xFAD/Abi3 S209F mice compared to 5xFAD mice. Broadly, microglial numbers mimic plaque load, however by 18-months of age 5xFAD/Abi3 S209F mice display dramatic reductions in IBA1+ microglia number - to levels comparable to WT/Abi3 S209F homozygous mice, suggesting a general loss of plaque associated microglia. By 12 months of age, Abi3 S209F homozygous and 5xFAD/ Abi3 S209F mice displayed increased synaptic density, independent of pathology in visual cortex, subiculum and CA1 regions., Conclusions: Together, these results characterize the effects of the Abi3 S209F missense mutation on 5xFAD-mediated pathology, specifically in Aβ plaque development, glial morphology, and synapses. Our data suggests that this mutation may affect microglia dynamics in an age-dependent manner and may result in dysfunctional microglia at later stages of disease., (© 2024 The Alzheimer's Association. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Background: Genome-Wide Association Studies (GWAS) implicate SPI1 (PU.1) as a risk factor for late-onset Alzheimer's Disease (LOAD). Within the brain, SPI1 encodes a microglia-specific transcription factor, necessary for microglial proliferation and activation. SPI1 rs1377416 has been identified as a non-coding GWAS risk variant for AD. We have developed a novel mouse model with the SPI1 rs1377416 variant to explore its impacts on AD pathogenesis., Method: By using CRISPR/Cas9, we have generated SPI1*rs1377416 mice that carry a non-coding mutation corresponding to the rs1377416 SNP found in human SPI1. We crossed the SPI1 mice with the 5xFAD mouse model of AD and aged them to 4 and 12 months of age. Coronal brain sections were then obtained and immunolabeled with several markers to visualize amyloid plaques, glial cells and assess axonal and neuritic damage. Confocal images were then obtained and quantified in subiculum and cortex., Result: We found an age-related increase in dense core plaque number and size in the subiculum of 5xFAD;SPI1 mice. Microglial volume as well as astrocytic activation were reduced in 5xFAD;SPI1 compared to 5xFAD mice in both brain areas at 12 months. Correspondingly, neuritic dystrophy and axonal damage were also diminished. Significant sex difference was observed in different analyses with males being affected less than females (with the exception of plaque deposition), and mainly detected in subiculum., Conclusion: Our results indicate that the rs1377416 variant of SPI1 induces an age-dependent increase in amyloid deposition in the 5xFAD model of AD. Moreover, this SPI1 variant exerts a protective effect by suppressing astrocytic response and preventing neuritic and axonal damage. There is a strong sex difference observed between males and females when the variant is present and requires further investigation., (© 2024 The Alzheimer's Association. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Introduction: Emerging evidence links changes in the gut microbiome to late-onset Alzheimer's disease (LOAD), necessitating examination of AD mouse models with consideration of the microbiome., Methods: We used shotgun metagenomics and untargeted metabolomics to study the human amyloid beta knock-in (hAβ-KI) murine model for LOAD compared to both wild-type (WT) mice and a model for early-onset AD (3xTg-AD)., Results: Eighteen-month female (but not male) hAβ-KI microbiomes were distinct from WT microbiomes, with AD genotype accounting for 18% of the variance by permutational multivariate analysis of variance (PERMANOVA). Metabolomic diversity differences were observed in females, however no individual metabolites were differentially abundant. hAβ-KI mice microbiomes were distinguishable from 3xTg-AD animals (81% accuracy by random forest modeling), with separation primarily driven by Romboutsia ilealis and Turicibacter species. Microbiomes were highly cage specific, with cage assignment accounting for more than 40% of the PERMANOVA variance between the groups., Discussion: These findings highlight a sex-dependent variation in the microbiomes of hAβ-KI mice and underscore the importance of considering the microbiome when designing studies that use murine models for AD., Highlights: Microbial diversity and the abundance of several species differed in human amyloid beta knock-in (hAβ-KI) females but not males. Correlations to Alzheimer's disease (AD) genotype were stronger for the microbiome than the metabolome. Microbiomes from hAβ-KI mice were distinct from 3xTg-AD mice. Cage effects accounted for most of the variance in the microbiome and metabolome., (© 2024 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Background: Variants in ABCA7, a member of the ABC transporter superfamily, have been associated with increased risk for developing late onset Alzheimer's disease (LOAD)., Methods: CRISPR-Cas9 was used to generate an Abca7 V1613M variant in mice, modeling the homologous human ABCA7 V1599M variant, and extensive characterization was performed., Results: Abca7 V1613M microglia show differential gene expression profiles upon lipopolysaccharide challenge and increased phagocytic capacity. Homozygous Abca7 V1613M mice display elevated circulating cholesterol and altered brain lipid composition. When crossed with 5xFAD mice, homozygous Abca7 V1613M mice display fewer Thioflavin S-positive plaques, decreased amyloid beta (Aβ) peptides, and altered amyloid precursor protein processing and trafficking. They also exhibit reduced Aβ-associated inflammation, gliosis, and neuronal damage., Discussion: Overall, homozygosity for the Abca7 V1613M variant influences phagocytosis, response to inflammation, lipid metabolism, Aβ pathology, and neuronal damage in mice. This variant may confer a gain of function and offer a protective effect against Alzheimer's disease-related pathology., Highlights: ABCA7 recognized as a top 10 risk gene for developing Alzheimer's disease. Loss of function mutations result in increased risk for LOAD. V1613M variant reduces amyloid beta plaque burden in 5xFAD mice. V1613M variant modulates APP processing and trafficking in 5xFAD mice. V1613M variant reduces amyloid beta-associated damage in 5xFAD mice., (© 2024 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Introduction: The BIN1 coding variant rs138047593 (K358R) is linked to Late-Onset Alzheimer's Disease (LOAD) via targeted exome sequencing., Methods: To elucidate the functional consequences of this rare coding variant on brain amyloidosis and neuroinflammation, we generated BIN1 K358R knock-in mice using CRISPR/Cas9 technology. These mice were subsequently bred with 5xFAD transgenic mice, which serve as a model for Alzheimer's pathology., Results: The presence of the BIN1 K358R variant leads to increased cerebral amyloid deposition, with a dampened response of astrocytes and oligodendrocytes, but not microglia, at both the cellular and transcriptional levels. This correlates with decreased neurofilament light chain in both plasma and brain tissue. Synaptic densities are significantly increased in both wild-type and 5xFAD backgrounds homozygous for the BIN1 K358R variant., Discussion: The BIN1 K358R variant modulates amyloid pathology in 5xFAD mice, attenuates the astrocytic and oligodendrocytic responses to amyloid plaques, decreases damage markers, and elevates synaptic densities., Highlights: BIN1 rs138047593 (K358R) coding variant is associated with increased risk of LOAD. BIN1 K358R variant increases amyloid plaque load in 12-month-old 5xFAD mice. BIN1 K358R variant dampens astrocytic and oligodendrocytic response to plaques. BIN1 K358R variant decreases neuronal damage in 5xFAD mice. BIN1 K358R upregulates synaptic densities and modulates synaptic transmission., (© 2024 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Introduction: Alzheimer's disease (AD) is a neurodegenerative disorder with multifactorial etiology, including genetic factors that play a significant role in disease risk and resilience. However, the role of genetic diversity in preclinical AD studies has received limited attention., Methods: We crossed five Collaborative Cross strains with 5xFAD C57BL/6J female mice to generate F1 mice with and without the 5xFAD transgene. Amyloid plaque pathology, microglial and astrocytic responses, neurofilament light chain levels, and gene expression were assessed at various ages., Results: Genetic diversity significantly impacts AD-related pathology. Hybrid strains showed resistance to amyloid plaque formation and neuronal damage. Transcriptome diversity was maintained across ages and sexes, with observable strain-specific variations in AD-related phenotypes. Comparative gene expression analysis indicated correlations between mouse strains and human AD., Discussion: Increasing genetic diversity promotes resilience to AD-related pathogenesis, relative to an inbred C57BL/6J background, reinforcing the importance of genetic diversity in uncovering resilience in the development of AD., Highlights: Genetic diversity's impact on AD in mice was explored. Diverse F1 mouse strains were used for AD study, via the Collaborative Cross. Strain-specific variations in AD pathology, glia, and transcription were found. Strains resilient to plaque formation and plasma neurofilament light chain (NfL) increases were identified. Correlations with human AD transcriptomics were observed., (© 2024 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Alzheimer's disease (AD) is among the most prevalent age-related neurodegenerative diseases. Endothelial cell (EC) senescence was discovered in the AD brain, but its function in AD pathogenesis was unidentified. Here we created an AD mouse model with EC senescence (APP/PS1;TERF2DN mice) by intercrossing APP/PS1 mice with Tie2 promoter-driven dominant negative telomeric repeat-binding factor 2 transgenic mice (TERF2DN-Tg mice). We evaluated cognitive functions and AD brain pathology in APP/PS1;TERF2DN mice. Surprisingly, compared with the control APP/PS1 mice, APP/PS1;TERF2DN mice demonstrated the attenuation of cognitive impairment and amyloid-β (Aβ) pathology, accompanied by the compaction of Aβ plaques with increased microglial coverage and reduced neurite dystrophy. Moreover, we evaluated whether EC senescence could affect microglial morphology and phagocytosis of Aβ. Compared with wild-type mice, microglia in TERF2DN-Tg mice display increased numbers of endpoints (a morphometric parameter to quantify the number of processes) and Aβ phagocytosis and related gene expression. Single-cell RNA-sequencing analysis showed that compared with APP/PS1 mouse microglia, APP/PS1;TERF2DN mouse microglia displayed a modest decline in disease-associated microglia, accompanied by an altered direction of biological process branching from antigen synthesis and arrangement to ribonucleoprotein complex biogenesis. Our outcomes indicate that EC senescence alters microglia toward a protective phenotype with a rise in phagocytic and barrier roles, and may offer a clue to create a novel preventive/therapeutic method to treat AD., (© 2023 Wiley Periodicals LLC.)

Background: The TREM2 R47H variant is one of the strongest genetic risk factors for late-onset Alzheimer's Disease (AD). Unfortunately, many current Trem2 R47H mouse models are associated with cryptic mRNA splicing of the mutant allele that produces a confounding reduction in protein product. To overcome this issue, we developed the Trem2 R47H NSS (Normal Splice Site) mouse model in which the Trem2 allele is expressed at a similar level to the wild-type Trem2 allele without evidence of cryptic splicing products., Methods: Trem2 R47H NSS mice were treated with the demyelinating agent cuprizone, or crossed with the 5xFAD mouse model of amyloidosis, to explore the impact of the TREM2 R47H variant on inflammatory responses to demyelination, plaque development, and the brain's response to plaques., Results: Trem2 R47H NSS mice display an appropriate inflammatory response to cuprizone challenge, and do not recapitulate the null allele in terms of impeded inflammatory responses to demyelination. Utilizing the 5xFAD mouse model, we report age- and disease-dependent changes in Trem2 R47H NSS mice in response to development of AD-like pathology. At an early (4-month-old) disease stage, hemizygous 5xFAD/homozygous Trem2 R47H NSS (5xFAD/Trem2 R47H NSS ) mice have reduced size and number of microglia that display impaired interaction with plaques compared to microglia in age-matched 5xFAD hemizygous controls. This is associated with a suppressed inflammatory response but increased dystrophic neurites and axonal damage as measured by plasma neurofilament light chain (NfL) level. Homozygosity for Trem2 R47H NSS suppressed LTP deficits and loss of presynaptic puncta caused by the 5xFAD transgene array in 4-month-old mice. At a more advanced (12-month-old) disease stage 5xFAD/Trem2 R47H NSS mice no longer display impaired plaque-microglia interaction or suppressed inflammatory gene expression, although NfL levels remain elevated, and a unique interferon-related gene expression signature is seen. Twelve-month old Trem2 R47H NSS mice also display LTP deficits and postsynaptic loss., Conclusions: The Trem2 R47H NSS mouse is a valuable model that can be used to investigate age-dependent effects of the AD-risk R47H mutation on TREM2 and microglial function including its effects on plaque development, microglial-plaque interaction, production of a unique interferon signature and associated tissue damage., (© 2023. The Author(s).)

Mouse models of human diseases are invaluable tools for studying pathogenic mechanisms and testing interventions and therapeutics. For disorders such as Alzheimer's disease in which numerous models are being generated, a challenging first step is to identify the most appropriate model and age to effectively evaluate new therapeutic approaches. Here we conducted a detailed phenotypic characterization of the 5xFAD model on a congenic C57BL/6 J strain background, across its lifespan - including a seldomly analyzed 18-month old time point to provide temporally correlated phenotyping of this model and a template for characterization of new models of LOAD as they are generated. This comprehensive analysis included quantification of plaque burden, Aβ biochemical levels, and neuropathology, neurophysiological measurements and behavioral and cognitive assessments, and evaluation of microglia, astrocytes, and neurons. Analysis of transcriptional changes was conducted using bulk-tissue generated RNA-seq data from microdissected cortices and hippocampi as a function of aging, which can be explored at the MODEL-AD Explorer and AD Knowledge Portal. This deep-phenotyping pipeline identified novel aspects of age-related pathology in the 5xFAD model., (© 2021. The Author(s).)