Mouse Model Of Amyloidosis Research Articles

Modulation of hippocampal protein expression by a brain penetrant biologic TNF‐α inhibitor in the 3xTg Alzheimer’s disease mice

AbstractBackgroundAlzheimer’s disease (AD) is a chronic neuroinflammatory condition and the proinflammatory cytokine, tumor necrosis factor alpha (TNF‐α), is a key mediator of neuroinflammation in AD. Biologic TNF‐α inhibitors (bTNFIs) can block cerebral TNF‐α if these large molecules cross the blood‐brain barrier (BBB). Thus, a model bTNFI, the extracellular domain of type II TNF‐α receptor (TNFR) which can bind to and sequester TNF‐α, has been reengineered to enable brain delivery by fusion with a mouse transferrin receptor antibody (TfRMAb). TfRMAb binds to the BBB TfR to deliver the TNFR into the brain via receptor‐mediated transcytosis. Previously, we found the TfRMAb‐TNFR to be protective in a mouse model of amyloidosis (APP/PS1) and tauopathy (PS19), and the aim of the current study was to investigate its effects in a mouse model that combines both amyloidosis and tauopathy (3xTg‐AD mice).MethodEight‐month‐old female triple transgenic 3xTg‐AD mice were injected intraperitoneally with saline (n = 11) or TfRMAb‐TNFR (3 mg/kg; n = 11) three days per week for 12 weeks. At the end of treatment, brains were processed for hippocampal immunohistochemistry and high‐resolution multiplex NanoString spatial proteomics using the GeoMx protein assays for neuroscience.ResultTfRMAb‐TNFR treatment significantly reduced mature β‐sheet rich Aβ plaques and increased plaque‐associated microglial localization around larger plaques in the 3xTg mice. Further, TfRMAb‐TNFR increased plaque‐associated microglial TREM2 compared with saline‐treated 3xTg mice. From a total of 64 target proteins studied using spatial proteomics (comparing protein expression in the Aβ‐plaque bearing vs. plaque‐free regions), 39 (61%) differentially expressed proteins (DEP) were identified in the 11‐month‐old 3xTg mice, comprising of proteins related to neurodegeneration (10% of DEP), neuroinflammation (41% of DEP), amyloid (21% of DEP) and tau (10% of DEP) pathology, autophagy (10% of DEP) and other pathways (8% of DEP). TfRMAb‐TNFR treatment modulated proteins involved in Aβ clearance and processing, microglial function, RNA processing, and neurodegeneration. Majority of these proteins were relevant to microglial function (∼ 40%).ConclusionThe study highlights that TfRMAb‐TNFR modulates several proteins involved in AD pathology and progression and largely suggests a microglia‐centric mechanism of action of this treatment in the 3xTg mice.

Seizures exacerbate tau spread in the 5XFAD mouse model

AbstractBackgroundCentral to the progression of Alzheimer’s disease (AD) is the spread of pathological tau along neuronal connections. This aspect of pathological progression can be recapitulated in WT mice by intracerebral injection of human AD brain derived tau lysate (AD‐tau). AD‐tau spread is enhanced in the amyloidosis mouse model, five times familial AD (5XFAD), suggesting that tau propagation is facilitated by β‐amyloid (Aβ) plaques. Once assumed to simply be a biproduct of Aβ‐induced hyperexcitability, a bidirectional relationship between seizures and AD progression has been established. Our lab has demonstrated worsened tau and Aβ pathology and cognitive deficits in AD patients with seizure history and in seizure‐kindled 5XFAD mice. Thus, we hypothesized that seizures would exacerbate the spread of AD‐tau in the 5XFAD mouse model and that 5XFAD mice would show increased seizure susceptibility and related neuronal activity.MethodTo investigate seizure‐pathology interactions, we crossed the 5XFAD mouse model with targeted recombination in active populations (TRAP; 5X‐TRAP) mice to permanently label seizure‐activated neurons. We injected AD‐tau unilaterally into the hippocampus and overlying cortex (1 µg/site) at 3 months of age in 5X‐TRAP and WT‐TRAP littermates. Seizures were induced with pentylenetetrazol (PTZ) kindling 2‐3 weeks following surgery and seizure‐activated neurons were labeled (tdTomato) on the final day of kindling via 4‐hydroxytamoxifen administration (50 mg/kg). Mice were euthanized three months post AD‐tau injection and immunohistochemistry for phospho‐tau (AT8) was performed.ResultWe found that kindled 5X‐TRAP mice show increased pathological tau (% AT8 coverage) in the dentate gyrus (DG) and CA1 contralateral to injection site compared to non‐kindled mice (p<0.05). We also found a trend towards elevated AT8 in the ipsilateral DG across seizure kindled groups (p = 0.083) and that 5X‐TRAP mice showed increased AT8 in the ipsilateral CA1 compared to WT‐TRAP (p<0.05). Further, we found a trend towards increased seizure susceptibility (0.059) in 5X‐TRAP mice and significantly increased seizure activated neurons (tdTomato+) in the DG of kindled 5X‐TRAP mice compared to WT‐TRAP (p<0.05).ConclusionOverall, our data further indicate a bidirectional relationship between seizures and AD. We also demonstrate that seizures facilitate the spread of pathological tau, thus suggesting that targeting seizure activity may slow AD progression.

Progressive dysregulation of circular RNAs in the hippocampus of a transgenic mouse model of amyloidosis

AbstractBackgroundCircular RNAs (circRNAs) are a class of RNAs that act as transcriptional regulators. They have a circular structure and are produced from back‐splicing events, which makes them more stable than linear RNAs. In Alzheimer’s disease (AD), the role of circRNAs remains elusive. Here, we aimed to evaluate whether the transcription of circRNAs is altered in the hippocampus, a region highly vulnerable to AD, of a transgenic amyloid mouse model.MethodWe selected hippocampal RNA‐sequencing or microarray datasets of circRNAs of the APPswe/PSEN1dE9, a widely used transgenic amyloid mouse model, from the NCBI databases. CircRNAs were detected with the CIRI2 algorithm by using the gene symbol of the parent transcript and the transcript ID. We identified the differently expressed circRNAs between APPswe/PSEN1dE9 and age‐matched wild‐types using the DESeq2 method (p‐value < 0.01). The packages UpSetR and VennDiagram were used to uncover the circRNAs commonly altered between the studies. All analyses were performed in R.ResultFrom 12 databases, three had hippocampal circRNA data of 4, 6, and 8‐month‐old APPswe/PSEN1dE9 mice (GSE166393; GSE158995; and PRJNA712946, n = 3 per group). Amyloid‐beta (Aβ) starts to deposit at six months in the APPswe/PSEN1dE9 hippocampus. The number of dysregulated circRNAs increased with age: 41 (4‐month‐old), 82 (6‐month‐old), and 425 (8‐month‐old) (Figure 1). Interestingly, only one circRNA was shared between the three studies at all time points, originating from the CCDC141 gene. Additionally, 15 circRNAs were shared in at least two ages, such as CD2AP, FMN1, HOMER1, IL1RAP, NDST3, and TET1 (Please, see the full list of intersections in Figure 2). By dividing groups into pre‐plaque (4‐month‐old) and amyloid (6 and 8‐month‐old) phases, we found that four altered circRNAs were shared in both stages, 37 exclusively in pre‐amyloid stage and 490 in amyloid stage (Figure 3).ConclusionOur results demonstrate an increasing dysregulation in circRNAs profiles in the hippocampus of the APP/PS1 mice. Considering the role of circRNAs as transcriptional regulators, one could argue that these progressive changes may impact gene expression in AD‐related brain regions.

Age‐Dependent Changes in Perineuronal Nets and Associated Parvalbumin Interneurons in the 5xFAD Amyloidosis Mouse Model

AbstractBackgroundPerineuronal nets (PNNs) are extracellular matrix structures that surround neurons and proximal dendrites and regulate synaptic transmission, plasticity, and several facets of memory. PNNs are commonly associated with parvalbumin‐positive (PV+) fast‐spiking interneurons which are hypothesized to play physiological roles in memory and cognition. Despite a growing literature related to PNNs and PV+ neurons’ roles in synaptic maintenance and memory, much remains unknown regarding how these structures are affected in neurodegenerative diseases such as Alzheimer’s Disease (AD). In this study, we used the 5xFAD amyloidosis mouse model to investigate how AD‐like pathology affects PNNs and PV+ neuronsMethodUsing immunofluorescence microscopy, we stained 5xFAD and Wild Type (WT) mice at 1.8, 3, 6, and 10 months of age. We stained for PV+ neurons (using anti‐PV antibody), PNNs (using a WFA antibody), and for Amyloid‐Beta (Aβ) plaques (using a 4G8 antibody). Images were then processed using ImageJ to quantify the presence of PV+ neurons, PNNs, and the association between them in several regions of interest across genotypes and age groups.ResultWe found that PNNs, but not PV+ neurons, are significantly depleted in the anterior cortex, posterior cortex, and subiculum of the 5XFAD mice in early amyloidosis (3‐6 month old 5XFAD mice). Furthermore, analyses investigating the co‐localization of PNNs and PV+ neurons in these regions found that PNNs were depleted surrounding PV+ neurons in an age‐dependent manner in the 5XFAD mice compared to WT. Specifically, in early amyloidosis (3‐6 months) there was a general depletion of PNNs, but in later amyloidosis (6 ‐10 months) the depletion of PNNs was preferentially surrounding PV+ neurons. Finally, assessing the relationship between Aβ plaque proximity and the co‐localization between PNNs and PV+ neurons revealed that PNNs closer to Aβ plaques were more likely to be associated with PV+ neuronsConclusionCollectively, these findings may indicate the time‐dependent impact of Aβ pathology on PNNs, both in general and specifically surrounding PV+ neurons. Our ongoing studies will further characterize PNN and PV changes across a wider age spectrum.

Effects of Low-Intensity Pulsed Ultrasound-Induced Blood-Brain Barrier Opening in P301S Mice Modeling Alzheimer's Disease Tauopathies.

Alzheimer's disease (AD) is the leading cause of dementia. No treatments have led to clinically meaningful impacts. A major obstacle for peripherally administered therapeutics targeting the central nervous system is related to the blood-brain barrier (BBB). Ultrasounds associated with microbubbles have been shown to transiently and safely open the BBB. In AD mouse models, the sole BBB opening with no adjunct drugs may be sufficient to reduce lesions and mitigate cognitive decline. However, these therapeutic effects are for now mainly assessed in preclinical mouse models of amyloidosis and remain less documented in tau lesions. The aim of the present study was therefore to evaluate the effects of repeated BBB opening using low-intensity pulsed ultrasounds (LIPU) in tau transgenic P301S mice with two main readouts: tau-positive lesions and microglial cells. Our results show that LIPU-induced BBB opening does not decrease tau pathology and may even potentiate the accumulation of pathological tau in selected brain regions. In addition, LIPU-BBB opening in P301S mice strongly reduced microglia densities in brain parenchyma, suggesting an anti-inflammatory action. These results provide a baseline for future studies using LIPU-BBB opening, such as adjunct drug therapies, in animal models and in AD patients.

Replacing microglia to treat Alzheimer's disease.

In this issue of Cell Stem Cell, Yoo etal.1 report that replacing Trem2 knockout microglia with Trem2 wild-type microglia-like cells derived from systemically transplanted hematopoietic cells rectifies microglial dysfunction in a mouse model of amyloidosis. These findings highlight the potential of microglia replacement therapy for Alzheimer's disease treatment.

Aquaporin 4 is associated with cerebral amyloid‐beta and tau deposits in mouse models

AbstractBackgroundEmerging evidence indicates that the glymphatic system plays an important role in Alzheimer’s disease. Aquaporin 4 (AQP4) constitutes a critical part of the glymphatic system in the clearance of accumulated amyloid‐beta and tau from the brain. Here, we aimed to establish the association between AQP4 and tau as well as amyloid‐beta (Aβ).MethodPerfusion and susceptibility weighted imaging (SWI) magnetic resonance imaging (MRI, at 7 or 9.4 T) were performed in arcAβ mouse model of amyloidosis (aged 16‐18 months), P301L mouse model of 4‐repeat tau (pR5 line) and respective nontransgenic littermates (aged 10‐12 months). Immunofluorescence staining was performed using antibodies against AQP4, CD31, astrogliosis (GFAP, s100β), microgliosis (Iba1, CD68), Aβ (6E10), and tau (AT‐8 and AT‐100) in brain tissue slices from transgenic arcAβ mice and wild‐type littermates.ResultCerebral microbleeds were detected in the cortex and subcortical regions in arcAβ mice. Cerebral blood flow was reduced in the cortex and hippocampus of arcAβ compared to nontransgenic mice but preserved in P301L mice. Increased AQP4 levels were observed surrounding tau deposits in the forebrain of P301L mice and parenchymal amyloid plaques/cerebral amyloid angiopathy in the cortex and hippocampus of arcAβ mice. Depolarization of AQP4 was detected in both arcAβ and P301L mice compared to their respective nontransgenic littermates. Increased s100b‐GFAP and CD68‐Iba1 fluorescence intensities indicative of atrogliosis and microgliosis were detected around tau deposits in P301L mice and amyloid plaques in arcAβ mice.ConclusionWe observed impaired perfusion in arcAβ mice but not in P301L mice, and a spatial association of AQP4 with both tau and Aβ in the brain.

0089 Chronic sleep disruption increases amyloid beta deposition and gliosis in the 5xFAD mouse model

Abstract Introduction Recent studies have found that mid-life sleep disruption is associated with the development of Alzheimer’s disease-related neuropathology, including the deposition of amyloid beta. Yet, the mechanism connecting sleep disruption, particularly over chronic timescales, and downstream Alzheimer’s pathology remains unclear. Methods In this study, we evaluated the impact chronic sleep disruption has on the development of neuroinflammation and amyloid beta plaques in the 5xFAD amyloidosis mouse model. Chronic sleep disruption in male and female C57BL/6 and 5xFAD+ mice was performed in Lafayette sleep fragmentation cages from 10-18 weeks of age. Glymphatic function was assessed by measuring the influx of fluorescent cerebrospinal fluid tracers into brain tissue. Aquaporin-4 localization, amyloid-beta plaque deposition, and markers of astroglial and microglial activation were assessed by immunofluorescence. Results We observed that chronic sleep disruption increased neuropathological outcomes in 5xFAD+ and littermate controls. This was evident in significantly increased amyloid-beta plaque deposition and significantly increased gliosis, indicated by increases in both astrocyte (GFAP) and microglial (Iba1) expression. The impact on glymphatic function, evaluated through both cerebrospinal fluid tracer distribution and assessment of aquaporin-4 mislocalization, was assessed in parallel and correlated with neuropathological outcomes. Conclusion These findings highlight the critical association between dysfunctional sleep and the development of Alzheimer’s-related amyloid beta pathology. They indicate that there is an interaction between chronic sleep disruption, neuroinflammation, and amyloid □ deposition. Support (if any)

Mitochondrial Dysfunction Links to Impaired Hippocampal Serotonin Release in a Mouse Model of Alzheimer's Disease.

Deprivation of extracellular serotonin has been linked to cognitive decline and neuropsychiatric disturbances in Alzheimer's disease (AD). However, despite degeneration of serotonin-producing neurons, whether serotonin release is affected in AD-sensitive brain regions is unknown. This study investigated the impact of mitochondrial dysfunction in decreased hippocampal serotonin release in AD amyloidosis mouse model 5xFAD mice. Electrochemical assays were applied to examine hippocampal serotonin release. We also employed multidisciplinary techniques to determine the role of oligomeric amyloid-β (Aβ) in hippocampal mitochondrial deficits and serotonin release deficiency. 5xFAD mice exhibited serotonin release decrease and relatively moderate downregulation of serotonergic fiber density as well as serotonin content in the hippocampal region. Further experiments showed an inhibitory effect of oligomeric amyloid-β (Aβ) on hippocampal serotonin release without affecting the density of serotonergic fibers. Pharmaceutical uncoupling of mitochondrial oxidative phosphorylation (OXPHOS) disrupted hippocampal serotonin release in an ex vivo setting. This echoes the mitochondrial defects in serotonergic fibers in 5xFAD mice and oligomeric Aβ-challenged primary serotonergic neuron cultures and implicates a link between mitochondrial dysfunction and serotonin transmission defects in AD-relevant pathological settings. The most parsimonious interpretation of our findings is that mitochondrial dysfunction is a phenotypic change of serotonergic neurons, which potentially plays a role in the development of serotonergic failure in AD-related conditions.

Acute stressors do not impair short-term memory or attention in an aged mouse model of amyloidosis.

Memory impairment in Alzheimer's disease patients is thought to be associated with the accumulation of amyloid-beta peptides and tau proteins. However, inconsistent reports of cognitive deficits in pre-clinical studies have raised questions about the link between amyloid-beta and cognitive decline. One possible explanation may be that studies reporting memory deficits often involve behavioral assessments that entail a high stress component. In contrast, in tasks without a high stress component transgenic mice do not consistently show declines in memory. The glucocorticoid cascade hypothesis of aging and the vicious cycle of stress framework suggest that stress exacerbates dementia progression by initiating a cycle of hypothalamic-pituitary-adrenal axis activation and subsequent brain deterioration. Using the APPswe/PS1dE9 mouse model of amyloidosis, we assessed whether stressor exposure prior to testing differentially impaired cognitive performance of aged male and female mice. As part of a larger study, mice performed a delayed match-to-position (DMTP) or a 3-choice serial-reaction time (3CSRT) task. Unexpectedly, these mice did not exhibit cognitive declines during aging. Therefore, at 73 and 74 weeks of age, we exposed mice to a predator odor or forced swim stressor prior to testing to determine if stress revealed cognitive deficits. We predicted stressor exposure would decrease performance accuracy more robustly in transgenic vs. non-transgenic mice. Acute stressor exposure increased accuracy in the DMTP task, but not in the 3CSRT task. Our data suggest that acute stressor exposure prior to testing does not impair cognitive performance in APPswe/PS1dE9 mice.

The Effects of a Blood-Brain Barrier Penetrating Erythropoietin in a Mouse Model of Tauopathy.

Erythropoietin (EPO), a hematopoietic neurotrophin, is a potential therapeutic for Alzheimer's disease (AD) but has limited blood-brain barrier (BBB) permeability. EPO fused to a chimeric transferrin receptor monoclonal antibody (cTfRMAb) enters the brain via TfR-mediated transcytosis across the BBB. We previously showed that cTfRMAb-EPO is protective in a mouse model of amyloidosis, but its effects on tauopathy are not known. Given that amyloid and tau pathology are characteristics of AD, the effects of cTfRMAb-EPO were studied in a tauopathy mouse model (PS19). Six-month-old PS19 mice were injected intraperitoneally with either saline (PS19-Saline; n = 9) or cTfRMAb-EPO (PS19-cTfRMAb-EPO, 10 mg/kg; n = 10); every two or three days on alternate weeks for 8 weeks. Age-matched, saline-treated, wildtype littermates (WT-Saline; n = 12) were injected using the same protocol. After 8 weeks, locomotion, hyperactivity, and anxiety were assessed via the open-field test, and brains were harvested and sectioned. Cerebral cortex, hippocampus, amygdala, and entorhinal cortex sections were analyzed for phospho-tau (AT8) and microgliosis (Iba1). Hippocampal cellular density (H&E) was also assessed. PS19-Saline mice were hyperactive and less anxious compared to WT-Saline mice, and these behavioral phenotypes were significantly reduced in the PS19-cTfRMAb-EPO mice compared to the PS19-Saline mice. cTfRMAb-EPO significantly reduced AT8 load by ≥50% in all of the brain regions analyzed and microgliosis in the entorhinal cortex and amygdala compared to the PS19-Saline mice. Hippocampal pyramidal and granule cell layer density did not differ significantly between the PS19-cTfRMAb-EPO and PS19-Saline mice. This proof-of-concept study demonstrates the therapeutic effects of the BBB-penetrating cTfRMAb-EPO in PS19 mice.

Aquaporin 4 is differentially increased and dislocated in association with tau and amyloid-beta

AimsNeurovascular-glymphatic dysfunction plays an important role in Alzheimer's disease and has been analysed mainly in relation to amyloid-beta (Aβ) pathology. Here, we aim to investigate the neurovascular alterations and mapping of aquaporin 4 (AQP4) distribution and dislocation associated with tau and Aβ. Materials and methodsPerfusion, susceptibility weighted imaging and structural magnetic resonance imaging (MRI) were performed in the pR5 mouse model of 4-repeat tau and the arcAβ mouse model of amyloidosis. Immunofluorescence staining was performed using antibodies against AQP4, vessel, astroglia, microglia, phospho-tau and Aβ in brain tissue slices from pR5, arcAβ and non-transgenic mice. Key findingspR5 mice showed regional atrophy, preserved cerebral blood flow, and reduced cerebral vessel density compared to non-transgenic mice, while arcAβ mice showed cerebral microbleeds and reduced cerebral vessel density. AQP4 dislocation and peri-tau enrichment in the hippocampus and increased AQP4 levels in the cortex and hippocampus were detected in pR5 mice compared to non-transgenic mice. In comparison, cortical AQP4 dislocation and cortical/hippocampal peri-plaque increases were observed in arcAβ mice. Increased expression of reactive astrocytes were detected around the tau inclusions in pR5 mice and Aβ plaques in arcAβ mice. SignificanceWe demonstrated the neurovascular alterations, microgliosis, astrogliosis and increased AQP4 regional expression in pR5 tau and arcAβ mice. We observed a divergent region-specific AQP4 dislocation and association with phospho-tau and Aβ pathologies.

A Trem2R47H mouse model without cryptic splicing drives age- and disease-dependent tissue damage and synaptic loss in response to plaques

BackgroundThe TREM2 R47H variant is one of the strongest genetic risk factors for late-onset Alzheimer’s Disease (AD). Unfortunately, many current Trem2R47H 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 Trem2R47H 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.MethodsTrem2R47H 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.ResultsTrem2R47H 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 Trem2R47H NSS mice in response to development of AD-like pathology. At an early (4-month-old) disease stage, hemizygous 5xFAD/homozygous Trem2R47H NSS (5xFAD/Trem2R47H 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 Trem2R47H 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/Trem2R47H 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 Trem2R47H NSS mice also display LTP deficits and postsynaptic loss.ConclusionsThe Trem2R47H 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.

Altered dynamics of glymphatic flow in a mature-onset Tet-off APP mouse model of amyloidosis

BackgroundAlzheimer’s disease (AD) is an incurable neurodegenerative disorder characterised by the progressive buildup of toxic amyloid-beta (Aβ) and tau protein aggregates eventually leading to cognitive decline. Recent lines of evidence suggest that an impairment of the glymphatic system (GS), a brain waste clearance pathway, plays a key role in the pathology of AD. Moreover, a relationship between GS function and neuronal network integrity has been strongly implicated. Here, we sought to assess the efficacy of the GS in a transgenic Tet-Off APP mouse model of amyloidosis, in which the expression of mutant APP was delayed until maturity, mimicking features of late-onset AD—the most common form of dementia in humans.MethodsTo evaluate GS function, we used dynamic contrast-enhanced MRI (DCE-MRI) in 14-month-old Tet-Off APP (AD) mice and aged-matched littermate controls. Brain-wide transport of the Gd-DOTA contrast agent was monitored over time after cisterna magna injection. Region-of-interest analysis and computational modelling were used to assess GS dynamics while characterisation of brain tissue abnormalities at the microscale was performed ex vivo by immunohistochemistry.ResultsWe observed reduced rostral glymphatic flow and higher accumulation of the contrast agent in areas proximal to the injection side in the AD group. Clustering and subsequent computational modelling of voxel time courses revealed significantly lower influx time constants in AD relative to the controls. Ex vivo evaluation showed abundant amyloid plaque burden in the AD group coinciding with extensive astrogliosis and microgliosis. The neuroinflammatory responses were also found in plaque-devoid regions, potentially impacting brain-fluid circulation.ConclusionsIn a context resembling late-onset AD in humans, we demonstrate the disruption of glymphatic function and particularly a reduction in brain-fluid influx in the AD group. We conjecture that the hindered circulation of cerebrospinal fluid is potentially caused by wide-spread astrogliosis and amyloid-related obstruction of the normal routes of glymphatic flow resulting in redirection towards caudal regions. In sum, our study highlights the translational potential of alternative approaches, such as targeting brain-fluid circulation as potential therapeutic strategies for AD.

Beneficial Effect of ACI-24 Vaccination on Aβ Plaque Pathology and Microglial Phenotypes in an Amyloidosis Mouse Model.

Amyloid-β (Aβ) deposition is an initiating factor in Alzheimer's disease (AD). Microglia are the brain immune cells that surround and phagocytose Aβ plaques, but their phagocytic capacity declines in AD. This is in agreement with studies that associate AD risk loci with genes regulating the phagocytic function of immune cells. Immunotherapies are currently pursued as strategies against AD and there are increased efforts to understand the role of the immune system in ameliorating AD pathology. Here, we evaluated the effect of the Aβ targeting ACI-24 vaccine in reducing AD pathology in an amyloidosis mouse model. ACI-24 vaccination elicited a robust and sustained antibody response in APPPS1 mice with an accompanying reduction of Aβ plaque load, Aβ plaque-associated ApoE and dystrophic neurites as compared to non-vaccinated controls. Furthermore, an increased number of NLRP3-positive plaque-associated microglia was observed following ACI-24 vaccination. In contrast to this local microglial activation at Aβ plaques, we observed a more ramified morphology of Aβ plaque-distant microglia compared to non-vaccinated controls. Accordingly, bulk transcriptomic analysis revealed a trend towards the reduced expression of several disease-associated microglia (DAM) signatures that is in line with the reduced Aβ plaque load triggered by ACI-24 vaccination. Our study demonstrates that administration of the Aβ targeting vaccine ACI-24 reduces AD pathology, suggesting its use as a safe and cost-effective AD therapeutic intervention.

Deletion of the Alzheimer's disease risk gene Abi3 locus results in obesity and systemic metabolic disruption in mice.

Alzheimer's disease (AD) genetics studies have identified a coding variant within ABI3 gene that increases the risk of developing AD. Recently, we demonstrated that deletion of the Abi3 gene locus dramatically exacerbates AD neuropathology in a transgenic mouse model of amyloidosis. In the course of this AD project, we unexpectedly found that deletion of the Abi3 gene locus resulted in a dramatic obese phenotype in non-transgenic mice. Here, we report our investigation into this serendipitous metabolic finding. Specifically, we demonstrate that mice with deletion of the Abi3 gene locus (Abi3-/- ) have dramatically increased body weight and body fat. Further, we determined that Abi3-/- mice have impaired energy expenditure. Additionally, we found that deletion of the Abi3 gene locus altered gene expression within the hypothalamus, particularly within immune-related pathways. Subsequent immunohistological analysis of the central nervous system (CNS) revealed that microglia number and area were decreased specifically within the mediobasal hypothalamus of Abi3-/- mice. Altogether, this investigation establishes the functional importance of the Abi3 gene locus in the regulation of systemic metabolism and maintenance of healthy body weight. While our previous findings indicated the importance of Abi3 in neurodegeneration, this study indicates that Abi3 related functions are also essential for metabolic regulation.

INPP5D deficiency attenuates amyloid pathology in a mouse model of Alzheimer's disease.

Inositol polyphosphate-5-phosphatase (INPP5D) is a microglia-enriched lipid phosphatase in the central nervous system. A non-coding variant (rs35349669) in INPP5D increases the risk for Alzheimer's disease (AD), and elevated INPP5D expression is associated with increased plaque deposition. INPP5D negatively regulates signaling via several microglial cell surface receptors, including triggering receptor expressed on myeloid cells 2 (TREM2); however, the impact of INPP5D inhibition on AD pathology remains unclear. We used the 5xFAD mouse model of amyloidosis to assess how Inpp5d haplodeficiency regulates amyloid pathogenesis. Inpp5d haplodeficiency perturbs the microglial intracellular signaling pathways regulating the immune response, including phagocytosis and clearing of amyloid beta (Aβ). It is important to note that Inpp5d haploinsufficiency leads to the preservation of cognitive function. Spatial transcriptomic analysis revealed that pathways altered by Inpp5d haploinsufficiency are related to synaptic regulation and immune cell activation. These data demonstrate that Inpp5d haplodeficiency enhances microglial functions by increasing plaque clearance and preserves cognitive abilities in 5xFAD mice. Inhibition of INPP5D is a potential therapeutic strategy for AD.

Reduced excitatory neuron activity and interneuron-type-specific deficits in a mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is characterized by progressive memory loss and cognitive decline. These impairments correlate with early alterations in neuronal network activity in AD patients. Disruptions in the activity of individual neurons have been reported in mouse models of amyloidosis. However, the impact of amyloid pathology on the spontaneous activity of distinct neuronal types remains unexplored in vivo. Here we use in vivo calcium imaging with multiphoton microscopy to monitor and compare the activity of excitatory and two types of inhibitory interneurons in the cortices of APP/PS1 and control mice under isoflurane anesthesia. We also determine the relationship between amyloid accumulation and the deficits in spontaneous activity in APP/PS1 mice. We show that somatostatin-expressing (SOM) interneurons are hyperactive, while parvalbumin-expressing interneurons are hypoactive in APP/PS1 mice. Only SOM interneuron hyperactivity correlated with proximity to amyloid plaque. These inhibitory deficits were accompanied by decreased excitatory neuron activity in APP/PS1 mice. Our study identifies cell-specific neuronal firing deficits in APP/PS1 mice driven by amyloid pathology. These findings highlight the importance of addressing the complexity of neuron-specific deficits to ameliorate circuit dysfunction in Alzheimer’s disease.

BCI‐838, an orally active mGluR2/3 antagonist pro‐drug, mimics the beneficial effects of physical exercise on neurogenesis, behavior and exercise‐related molecular pathways in an Alzheimer’s disease mouse model

AbstractBackgroundModulation of physical exercise (PE) represents an intervention that may delay, slow, or prevent mild cognitive impairment (MCI) or dementia due to Alzheimer’s disease (AD). One mechanism proposed to underlie beneficial effects of PE involves the apparent stimulation of adult hippocampal neurogenesis (AHNG). BCI‐838 is a pro‐drug whose metabolite BCI‐632 is one of the most active proneurogenic agents known and is an antagonist at group II metabotropic receptors (mGluR2/3). The drug stimulates AHNG while enhancing learning behavior and exerting anxiolytic and antidepressant properties. We previously demonstrated that the administration of BCI‐838 to a mouse model of cerebral and cerebrovascular accumulation of oligomeric AbE22Q (APPE693Q = “Dutch”) reduced learning behavior impairment and anxiety, both of which are associated with the phenotype of Thy1.1‐Dutch APP mice (Kim et al., Mol Psych 2014). Herein, we sought to determine whether BCI‐838 might substitute for PE, and/or whether treatment with a BCI‐838+PE combination might demonstrate synergistic effects in a mouse model of amyloidosis (APPKM670/671NL/PSEN1Δexon9 = APP/PS1).Method3‐month‐old APP/PS1 mice were treated with either BCI‐838, PE (running wheels), or a combination of BCI‐838+PE for 1 month. We performed learning behavior tests (novel object recognition and Barnes maze), biochemical, and transcriptomic analyses on the hippocampal dentate gyrus (DG) of APP/PS1 mice. We performed gene set enrichment analysis, drug repurposing, and chemogenomic enrichment analyses to reveal molecular pathways of interest and investigated compounds with transcriptomically similar profiles as well as drug targets and side effects.ResultWe report that: (i) BCI‐838, PE, or BCI‐838+PE combination enhanced AHNG, (ii) BCI‐838 alone or associated with PE led to improvement in both spatial and recognition learning behaviors, (iii) BCI‐838 treatment increased mRNA levels of BDNF, metabotropic glutamate receptors, and PIK3C2A of the PI3K‐MTOR pathway, and decreased EIF5A of ketamine‐modulating mTOR activity in the hippocampal DG. qPCR results validated the statistical significance of the association between BCI‐838 treatment and increased levels of BDNF.ConclusionOur study points to BCI‐838 as a safe and orally active compound capable of mimicking the beneficial effect of exercise on AHNG, learning behavior, and anxiety in the APP/PS1 mouse model.

Metabolome-wide association study on ABCA7 indicates a role of ceramide metabolism in Alzheimer’s disease

Genome-wide association studies (GWASs) have identified genetic loci associated with the risk of Alzheimer's disease (AD), but the molecular mechanisms by which they confer risk are largely unknown. We conducted a metabolome-wide association study (MWAS) of AD-associated loci from GWASs using untargeted metabolic profiling (metabolomics) by ultraperformance liquid chromatography-mass spectrometry (UPLC-MS). We identified an association of lactosylceramides (LacCer) with AD-related single-nucleotide polymorphisms (SNPs) in ABCA7 (P = 5.0 × 10-5 to 1.3 × 10-44). We showed that plasma LacCer concentrations are associated with cognitive performance and genetically modified levels of LacCer are associated with AD risk. We then showed that concentrations of sphingomyelins, ceramides, and hexosylceramides were altered in brain tissue from Abca7 knockout mice, compared with wild type (WT) (P = 0.049-1.4 × 10-5), but not in a mouse model of amyloidosis. Furthermore, activation of microglia increases intracellular concentrations of hexosylceramides in part through induction in the expression of sphingosine kinase, an enzyme with a high control coefficient for sphingolipid and ceramide synthesis. Our work suggests that the risk for AD arising from functional variations in ABCA7 is mediated at least in part through ceramides. Modulation of their metabolism or downstream signaling may offer new therapeutic opportunities for AD.