APP23 Mice Research Articles

Alzheimer's Disease Enhanced Tonic Inhibition is Correlated With Upregulated Astrocyte GABA Transporter-3/4 in a Knock-In APP Mouse Model.

Cognitive decline is a major symptom in Alzheimer’s disease (AD), which is strongly associated with synaptic excitatory-inhibitory imbalance. Here, we investigated whether astrocyte-specific GABA transporter 3/4 (GAT3/4) is altered in APP knock-in mouse model of AD and whether this is correlated with changes in principal cell excitability. Using the APP NL-F/NL-F knock-in mouse model of AD, aged-matched to wild-type mice, we performed in vitro electrophysiological whole-cell recordings combined with immunohistochemistry in the CA1 and dentate gyrus (DG) regions of the hippocampus. We observed a higher expression of GAD67, an enzyme that catalyses GABA production, and GAT3/4 in reactive astrocytes labelled with GFAP, which correlated with an enhanced tonic inhibition in the CA1 and DG of 12–16 month-old APP NL-F/NL-F mice compared to the age-matched wild-type animals. Comparative neuroanatomy experiments performed using post-mortem brain tissue from human AD patients, age-matched to healthy controls, mirrored the results obtained using mice tissue. Blocking GAT3/4 associated tonic inhibition recorded in CA1 and DG principal cells resulted in an increased membrane input resistance, enhanced firing frequency and synaptic excitation in both wild-type and APP NL-F/NL-F mice. These effects exacerbated synaptic hyperactivity reported previously in the APP NL-F/NL-F mice model. Our data suggest that an alteration in astrocyte GABA homeostasis is correlated with increased tonic inhibition in the hippocampus, which probably plays an important compensatory role in restoring AD-associated synaptic hyperactivity. Therefore, reducing tonic inhibition through GAT3/4 may not be a good therapeutic strategy for AD

The Transglutaminase-2 Interactome in the APP23 Mouse Model of Alzheimer's Disease.

Amyloid-beta (Aβ) deposition in the brain is closely linked with the development of Alzheimer’s disease (AD). Unfortunately, therapies specifically targeting Aβ deposition have failed to reach their primary clinical endpoints, emphasizing the need to broaden the search strategy for alternative targets/mechanisms. Transglutaminase-2 (TG2) catalyzes post-translational modifications, is present in AD lesions and interacts with AD-associated proteins. However, an unbiased overview of TG2 interactors is lacking in both control and AD brain. Here we aimed to identify these interactors using a crossbreed of the AD-mimicking APP23 mouse model with wild type and TG2 knock-out (TG2−/−) mice. We found that absence of TG2 had no (statistically) significant effect on Aβ pathology, soluble brain levels of Aβ1–40 and Aβ1–42, and mRNA levels of TG family members compared to APP23 mice at 18 months of age. Quantitative proteomics and network analysis revealed a large cluster of TG2 interactors involved in synaptic transmission/assembly and cell adhesion in the APP23 brain typical of AD. Comparative proteomics of wild type and TG2−/− brains revealed a TG2-linked pathological proteome consistent with alterations in both pathways. Our data show that TG2 deletion leads to considerable network alterations consistent with a TG2 role in (dys)regulation of synaptic transmission and cell adhesion in APP23 brains.

High Level Forebrain Expression of Active Tau Kinase p38γ Exacerbates Cognitive Dysfunction in Aged APP-transgenic Alzheimer’s Mice

Persistent improvement of cognitive deficits in Alzheimer’s disease (AD), a common form of dementia, is an unattained therapeutic objective. Gene therapy holds promise for treatment of familial and sporadic forms of AD. p38γ, a member of the p38 mitogen-activated protein (MAP) kinase family, inhibits amyloid-β toxicity through regulation of tau phosphorylation. We recently showed that a gene delivery approach increasing p38γ resulted in markedly better learning and memory performance in mouse models of AD at advanced stages of amyloid-β- and tau-mediated cognitive impairment. Notably, low-to-moderate expression of p38γ had beneficial outcomes on cognition. The impact of high levels of p38γ on neuronal function remain unclear. Therefore, we addressed the outcomes of high levels of active p38γ on brain function, by direct injection of p38γ-encoding adeno-associated virus (AAV) into the forebrain of aged mice of an APP transgenic AD mouse model. While motor function in p38γ-expressing APP transgenic mice 2 months post-injection was comparable to control treated APP mice, their activity was markedly reduced in the open field test and included frequent bouts of immobility. Moreover, their learning and memory function was markedly impaired compared to control-treated aged APP mice. These results suggest that high neuronal levels of active p38γ emphasize a stress kinase role of p38γ, perturbing circuit function in motivation, navigation, and spatial learning. Overall, this work shows excessive neuronal p38γ levels can aggravate circuit dysfunction and advises adjustable expression systems will be required for sustainable AD gene therapy based on p38γ activity.

Accelerated Aging Characterizes the Early Stage of Alzheimer's Disease.

For Alzheimer’s disease (AD), aging is the main risk factor, but whether cognitive impairments due to aging resemble early AD deficits is not yet defined. When working with mouse models of AD, the situation is just as complicated, because only a few studies track the progression of the disease at different ages, and most ignore how the aging process affects control mice. In this work, we addressed this problem by comparing the aging process of PS2APP (AD) and wild-type (WT) mice at the level of spontaneous brain electrical activity under anesthesia. Using local field potential recordings, obtained with a linear probe that traverses the posterior parietal cortex and the entire hippocampus, we analyzed how multiple electrical parameters are modified by aging in AD and WT mice. With this approach, we highlighted AD specific features that appear in young AD mice prior to plaque deposition or that are delayed at 12 and 16 months of age. Furthermore, we identified aging characteristics present in WT mice but also occurring prematurely in young AD mice. In short, we found that reduction in the relative power of slow oscillations (SO) and Low/High power imbalance are linked to an AD phenotype at its onset. The loss of SO connectivity and cortico-hippocampal coupling between SO and higher frequencies as well as the increase in UP-state and burst durations are found in young AD and old WT mice. We show evidence that the aging process is accelerated by the mutant PS2 itself and discuss such changes in relation to amyloidosis and gliosis.

Analysis of the dynamics of primary cilia in a humanized APP mouse model

Analysis of the dynamics of primary cilia in a humanized APP mouse model

Histone Deacetylase Inhibitor Improves the Dysfunction of Hippocampal Gamma Oscillations and Fast Spiking Interneurons in Alzheimer's Disease Model Mice.

The hippocampal gamma oscillation is important for cognitive function, and its deficit is related to cognitive impairment in Alzheimer’s disease (AD). Recently, it has been recognized that post-translational modification via histone acetylation is a fundamental molecular mechanism for regulating synaptic plasticity and cognitive function. However, little is known regarding the regulation of hippocampal gamma oscillation by histone acetylation. We investigated whether histone acetylation regulated kainate-induced gamma oscillations and their important regulator, fast-spiking interneurons, using acute hippocampal slices of AD model mice (PSAPP transgenic mice). We found a decrease in kainate-induced gamma oscillations in slices from PSAPP mice, accompanied with the increased activity of fast spiking interneurons in basal state and the decreased activity in activated state. The histone deacetylase (HDAC) inhibitor (SAHA, named vorinostat) restored deficits of gamma oscillation in PSAPP mice, accompanied with rescue of activity of fast spiking interneurons in basal and activated state. The effect of SAHA was different from that of the clinical AD drug donepezil, which rescued only function of fast spiking interneurons in basal state. Besides, activator of nuclear receptor family 4a (NR4a) receptor (cytosporone B), as one of the epigenetic modification related to HDAC inhibition, rescued the deficits in gamma oscillations in PSAPP mice. These results suggested a novel mechanism in which HDAC inhibition improved impairment of gamma oscillations in PSAPP mice by restoring the activity of fast spiking interneurons both in basal and activated state. The reversal of gamma oscillation deficits by HDAC inhibition and/or NR4a activation appears to be a potential therapeutic target for treating cognitive impairment in AD patients.

Gut microbiota-driven brain Aβ amyloidosis in mice requires microglia.

We previously demonstrated that lifelong antibiotic (ABX) perturbations of the gut microbiome in male APPPS1-21 mice lead to reductions in amyloid β (Aβ) plaque pathology and altered phenotypes of plaque-associated microglia. Here, we show that a short, 7-d treatment of preweaned male mice with high-dose ABX is associated with reductions of Aβ amyloidosis, plaque-localized microglia morphologies, and Aβ-associated degenerative changes at 9 wk of age in male mice only. More importantly, fecal microbiota transplantation (FMT) from transgenic (Tg) or WT male donors into ABX-treated male mice completely restored Aβ amyloidosis, plaque-localized microglia morphologies, and Aβ-associated degenerative changes. Transcriptomic studies revealed significant differences between vehicle versus ABX-treated male mice and FMT from Tg mice into ABX-treated mice largely restored the transcriptome profiles to that of the Tg donor animals. Finally, colony-stimulating factor 1 receptor (CSF1R) inhibitor-mediated depletion of microglia in ABX-treated male mice failed to reduce cerebral Aβ amyloidosis. Thus, microglia play a critical role in driving gut microbiome-mediated alterations of cerebral Aβ deposition.

Vaccination against the broadly expressed microbial antigen PNAG prevents cognitive decline in the APP-PS1 mouse model of Alzheimer's disease.

While there is ample evidence for a role of the microbiota in cognitive decline in Alzheimer's Disease (AD), there is little insight into how the microbiota mediates neuronal dysfunction and cognitive decline. A conserved surface polysaccharide, poly-N-acetyl glucosamine (PNAG) is produced by a broad range of microbial cells, but not mammals. We have detected the presence of PNAG-positive, likely microbiota-derived cells or fragments closely associated with amyloid-ß deposits in the brains of deceased AD individuals and cognitively impaired APP-PS1 mice, but not non-AD controls. These fragments potentially provide an inflammatory stimulus critical for neural tissue destruction and cognitive impairment. We tested whether vaccination against PNAG prevented microbial access to brains of APP-PS1 mice and impacted cognitive decline. Microbial factors were detected with a human IgG monoclonal antibody (MAb) to PNAG in brain tissues from human AD and APP/PS1 mice. Two cohorts of APP/PS1 mice and wild type (WT) littermate controls were vaccinated with either a PNAG vaccine (5GlcNH2 -TT) or TT (tetanus toxin) only as a control, five times starting at either 5 weeks or 5 months of age. Only PNAG-immunized mice made specific antibodies over the experimental period. Water T maze testing of mice was performed at 12-15 months of age. Brains were harvested to detect both PNAG and amyloid-ß immunohistochemically. PNAG-positive microbial factors were elevated in areas with amyloid-ß deposits in brain tissue from human AD cases and APP/PS1 mice. Non-AD age- and sex-matched controls had little detectable brain PNAG, even around amyloid-ß deposits. Active PNAG vaccination at both 5 weeks and 5 months of age prevented cognitive decline in APP-PS1 mice. Only 10% or 30% of non-immune APP/PS1 mice reached criteria by day 5 of reversal, respectively, compared to 90% and 100% of PNAG vaccinated APP/PS1 mice. Immunohistochemistry indicated decreased presence of PNAG-positive material in PNAG vaccinated mice and a modest reduction in amyloid-ß deposits. Antibodies to PNAG induced at 5 weeks or 5 months of age prevented cognitive decline and brain pathology in APP/PS1 mice, suggesting that microbial factors that enter the brain are critical for cognitive decline that may be prevented by vaccination.

Glitter in the darkness? Non‐fibrillar β‐amyloid plaque components significantly impact the β‐amyloid PET signal

AbstractBackgroundβ‐amyloid PET (Aβ‐PET) is an important tool for quantification of amyloidosis in the brain of suspected Alzheimer’s disease (AD) patients and transgenic AD mouse models. Despite the excellent correlation of Aβ‐PET with gold standard immunohistochemical assessments, the relative contributions of fibrillar and non‐fibrillar Aβ components to the in vivo Aβ‐PET signal remain unclear. Thus, we obtained two murine cerebral amyloidosis models that present with distinct Aβ plaque compositions and performed regression analysis between immunohistochemistry and Aβ PET to determine the biochemical contributions to Aβ‐PET signal in vivo.MethodWe investigated groups of AppNL‐G‐F and APPPS1 mice three, six and 12 months of age by longitudinal [18F]‐florbetaben Aβ‐PET and with immunohistochemical analysis of the fibrillar and total Aβ burdens. We then applied group level inter‐modality regression models using age and genotype matched sets of fibrillar/ non‐fibrillar Aβ data (predictors) and Aβ‐PET results (outcome) for both transgenic models. An independent group of double‐hit APPPS1 mice with dysfunctional microglia due to knock‐out of triggering receptor expression on myeloid cells 2 (Trem2‐/‐) served for validation and evaluation of translational impact.ResultNeither fibrillar nor non‐fibrillar Aβ content alone sufficed to explain the Aβ‐PET findings in either transgenic AD model (Figure 1). A regression model compiling fibrillar and non‐fibrillar Aβ together with the estimate of individual heterogeneity and age at scanning could explain a 93% of variance of the Aβ‐PET signal (p<0.001; Figure 2). Fibrillar Aβ burden had a 16‐fold higher contribution to the Aβ‐PET signal when compared to non‐fibrillar Aβ. However, given the relatively greater abundance of non‐fibrillar Aβ, we estimate that non‐fibrillar Aβ produced 79±25% of the net in vivo Aβ‐PET signal in AppNL‐G‐F mice, and 25±12% in the APPPS1 mice. Corresponding results in groups of APPPS1/Trem2‐/‐ and APPPS1/Trem2+/+ mice validated the calculated regression factors and revealed that the altered fibrillarity due to Trem2 knockout impacts the Aβ‐PET signal (Figure 3).ConclusionTaken together, the in vivo Aβ‐PET signal derives from the composite of fibrillar and non‐fibrillar Aβ plaque components. While fibrillar Aβ has inherently higher PET tracer binding, the greater abundance of non‐fibrillar Aβ plaque in AD model mice contributes importantly to the PET signal.

Disruptions in sleep‐dependent brain rhythms contribute to Alzheimer’s pathogenesis

Sleep-dependent brain rhythms are important for memory consolidation during sleep, and Alzheimer's disease (AD) patients experience memory disturbances. We sought to examine sleep-dependent brain rhythms, slow oscillations, in an animal model of AD (APP mice). The power of slow oscillations was decreased early in the disease progression. Soluble amyloid-beta was sufficient to disrupt the slow waves. Cortical GABA levels were low in APP mice and application of exogenous GABA restored the slow oscillations, indicating that aberrant excitatory activity within the cortical circuit was responsible for slow oscillation dysfunction. Next we sought to manipulate slow waves in APP mice with optogenetics. Driving slow oscillations at normal frequency with light activation of channelrhodopsin-2 (ChR2) expressed in cortical neurons restored slow wave power by synchronizing neuronal activity. Using multiphoton microscopy, we performed longitudinal imaging of senile plaques and monitored intracellular calcium. Cytosolic calcium is a surrogate marker of neuronal activity and is normally tightly regulated. We had previously demonstrated that resting calcium levels measured with the genetically encoded calcium sensor YellowCameleon 3.6 were elevated in a subset of neurons in APP transgenics, and hypothesized that an effective treatment would restore calcium to control levels. Driving slow oscillation activity with optogenetics halted amyloid plaque deposition and prevented calcium overload associated with this pathology. On the other hand, driving slow oscillation activity at twice the normal frequency resulted in increased amyloid production, increased amyloid plaque deposition, disruptions in neuronal calcium homeostasis, and loss of synaptic spines. Therefore, while restoration of physiological circuit dynamics is sufficient to abrogate the progression of Alzheimer's disease pathology and should be considered an avenue for clinical treatment of patients with sleep disorders, pathophysiological stimulation of neuronal circuits leads to activity dependent acceleration of amyloid production, aggregation and downstream neuronal dysfunction.

Activity‐dependent dysfunctional gene expression patterns are normalized by in vivo treatment of late‐stage Aβ pathology mice with a TrkB/C small molecule ligand

AbstractBackgroundNeurotrophin signaling via TrkB and TrkC receptors participates in long‐term potentiation (LTP), a biological substrate of memory formation that is disrupted by amyloid‐β (Aβ) in APP mice. In this study, we ask whether there are alterations in activity‐dependent gene expression signatures in APP mice, and if so, could elements of these alterations be restored by prior treatment with a small molecule TrkB/C partial agonist, PTX‐BD10‐2.MethodWe administered PTX‐BD10‐2 (50 mg/kg) or vehicle (VEH) orally once daily to male wild type (WT) and APP mice expressing London and Swedish mutations (APP‐L/S) for 3 months starting at 13 months of age. Paired‐pulse ratios (PPR) and Theta Burst Stimulation (TBS) were applied to acute hippocampal slices, in absence of drug, to induce short and long‐term synaptic plasticity. Upon completion of recordings, we examined whole tissue transcriptomic profiles for differential gene expression and enrichment of ontological terms and pathways.ResultPronounced deficits in PPR (at 10 and 20 ms) and LTP were found in APP‐L/S relative to WT slices, and entirely restored in slices from APP‐L/S mice treated with PTX‐BD10‐2 (Fig. 1). To identify candidate mechanisms of this pre/post synaptic plasticity rescue, we examined activity (TBS)‐dependent transcriptomic signatures. Analysis of TBS‐only slices demonstrated alterations in gene expression between WT_VEH_TBS and APP‐L/S_VEH_TBS mice. In particular, significant downregulation of genes in pathways known to be important for synapse function: axoneme, glutamatergic/GABAergic synaptic signaling, neurotransmitter release/transmission and neuronal action potential; and upregulation of gene pathways that are candidates contributing to degeneration in AD and in APP‐L/S_VEH_TBS mice: immune system processes, inflammatory responses, aging and neuron death; when compared to WT_VEH_TBS. Remarkably, the altered expression levels of most of the genes from these pathways were reverted to WT pattern in APP‐L/S_BD10‐2_TBS mice (Fig. 2), thus revealing candidate mechanisms to restore PPR and LTP deficits in APP‐L/S mice.ConclusionPTX‐BD10‐2 treatment mitigates Aβ‐related synapse dysfunction and alterations in synapse‐relevant gene expression profiles in APP‐L/S mice in the context of stimulation. These findings point to therapeutic potential of targeting TrkB/C, and moreover, provide a cellular model to identify candidate signaling modules for understanding synaptic impairment and revealing novel therapeutic targets.

A time-restricted feeding intervention reduces alterations in circadian behaviors and pathology in a mouse model of Alzheimer's disease.

Circadian rhythm disruptions impact nearly all Alzheimer's disease (AD) patients, with daytime sleepiness, sundowning, sleep fragmentation, and night-time insomnia being common disturbances. These early and progressive declines support the role of circadian dysfunction as a driver of AD pathology, hence the therapeutic potential of circadian-modulating interventions needs to be investigated. One of the most powerful regulators of the circadian system is the daily feed/fast cycle. We have recently shown that early, presymptomatic time-restricted feeding (TRF) can ameliorate a range of symptoms related to neurodegenerative conditions, including improving sleep/wake timing and circadian rhythmicity. At 12 months of age, the APP23 mouse model of AD (expressing the human APP gene containing the Swedish mutation) exhibits disrupted behavior resembling sundowning. We hypothesized that imposing early-age TRF in APP23 mice would improve circadian rhythmicity and deter the disruptions observed to emerge and progress with advancing neuropathology. Adult male and female APP23 transgenic (AD) and littermate non-transgenic (control) mice were housed individually and subjected to ab libitum (ALF) feeding or a TRF protocol consisting of 6-hours feeding in the middle of the active phase followed by 18-hours fasting for 3 months. Behavioral sleep (48 hours) and ongoing cage locomotor activity were recorded from an early age. Our analysis shows that AD mice exhibit disruptions in total sleep (P < 0.001) and the emergence of excessive wakefulness (P < 0.001). AD mice also show significant active-phase agitation (P < 0.05) accompanied by excessive sleep-phase fragmentation (P < 0.05). TRF induced nutritional ketosis (β-Hydroxybutyrate > 0.5 mM) accompanied by reduced blood glucose when compared to ALF mice, although mice consumed equivalent volumes of food in both experimental groups. Importantly, TRF improved total and sleep-phase sleep in AD mice (P < 0.05) and significantly reduced agitation and fragmentation (P < 0.05). Early application of TRF can forestall circadian disruptions in AD mice. TRF has been reported to modulate expression of clock and clock-controlled genes, transcriptional regulators, metabolism related genes, BDNF, and other neurotrophic factors. Our results suggest that these changes may also impact sleep, circadian behaviors, and agitation associated with AD.

GM6 attenuates Alzheimer's disease pathology through a reduction in fibrinogen levels and by regulation of Aβ, p-tau and inflammation.

Alzheimer's disease (AD) is characterized by cerebral amyloid-b (Ab) deposition, vascular alterations, tau pathology, microglia activation, and inflammation. Vascular dysfunction and amyloid burden are independent and equal predictors of cognitive decline in the elderly, with an additive adverse effect on cognition. Fibrinogen, a blood coagulation protein, is deposited in the AD brain; co-localizes with amyloid plaques, pericyte loss, dystrophic neurites, and activated microglia; and its increased concentrations in plasma and cerebrospinal fluid correlate with brain atrophy in AD patients. GM6 is a derivative of motoneuronotrophic factor (MNTF) which functions as a regulator of key biomarkers and acts upon multiple extracellular receptors to modulate a series of signaling pathways. This study evaluates the effects of GM6 on fibrinogen levels in two animal models of AD. APP and h-tau transgenic mice were treated with GM6 daily for up to 4 months and examined for changes in fibrinogen, Aβ peptide levels, plaques, inflammation, phosphorylated tau (p-tau) as well as behavioral changes associated with disease progression. Fibrinogen levels were determined by ELISA and western blot analysis. When we studied APP transgenic mice treated with GM6 compared to placebo, fibrinogen levels were significantly decreased (75%) along with diminished Aβ peptide levels, attenuation of plaque load, and a reduction in inflammatory biomarkers. In another study of the p-tau formation in the h-tau mice treated with GM6 compared to placebo, again a reduction in fibrinogen was observed along with reduction in p-tau and inflammation biomarker levels. In both transgenic mice, behavioral changes were attenuated with GM6 treatment. In both APP and h-tau mice, inflammation cytokines TNF-α, IL-1β, IL-6, and TGF-β were reduced by 80-90% as previously reported. In conclusion, to counter the additive adverse effect on cognition from vascular dysfunction and amyloid burden, GM6 may be a feasible approach to attenuate Alzheimer's disease pathology through a reduction in fibrinogen levels and by regulation of Ab, p-tau and inflammation.

Identification of the neuroprotective Shc target in Alzheimer's and validation of the neuroprotective benefit of a set of small‐molecule Shc blockers

AbstractBackgroundIncreased Shc expression has recently been linked to human AD progression. The human Shc locus has recently been identified as extremely important in the conversion from Mild Cognitive Impairment (MCI) to full Alzheimer's Disease (AD) [1]. Shc is more highly expressed in Hippocampus of human AD cases vs. Controls [2], and A‐beta increases Shc activity and gene expression in cells, and Shc knockdown reduces A‐beta toxicity [3]. Mice with Shc reduction resist AD and age‐related cerebrovascular dysfunction. It has been demonstrated that there is a significant benefit to PSAPP mice when Shc is genetically reduced, they have improved memory and cognition relative to PSAPP mice, and survive longer. Furthermore this improvement is with the same amyloid burden–thus Shc underexpression appears to neuroprotect downstream of the toxic A‐beta signal[4]. Furthermore, Shc reduced mice resist age‐related cerebrovascular dysfunction [5]. Under MTA we have received small molecules from Buto Corp, to identify their relative efficacy in cell and animal models of disease.MethodWe tested the neuroprotective potency of Shc blockers challenged with A‐beta in 384‐well plates. We also tested the anti‐inflammatory potency of Shc blockers, by measuring post A‐beta or LPS challenge to human microglial cells the expression of multiple inflammatory genes, including IL‐6, IL‐10, and Nos. We also tested the impact of Shc Blockers on memory loss in the ApoE4 mouse model of ADResultWe observe significant protection of several Shc blockers from A‐beta neurotoxicity. We observe significant protection of multiple Shc blockers from A‐beta or LPS mediated microglial inflammation. We observe significant protection from memory loss in the ApoE4 mouse model of AD by a molecule observed to be neuroprotective in Results 1 and 2.ConclusionThe data above suggest that small‐molecule Shc blockers are a novel therapeutic strategy for AD.

The Histone H3 K4me3, K27me3, and K27ac Genome-Wide Distributions Are Differently Influenced by Sex in Brain Cortexes and Gastrocnemius of the Alzheimer's Disease PSAPP Mouse Model.

Background: Women represent the majority of Alzheimer’s disease patients and show typical symptoms. Genetic, hormonal, and behavioral mechanisms have been proposed to explain sex differences in dementia prevalence. However, whether sex differences exist in the epigenetic landscape of neuronal tissue during the progression of the disease is still unknown. Methods: To investigate the differences of histone H3 modifications involved in transcription, we determined the genome-wide profiles of H3K4me3, H3K27ac, and H3K27me3 in brain cortexes of an Alzheimer mouse model (PSAPP). Gastrocnemius muscles were also tested since they are known to be different in the two sexes and are affected during the disease progression. Results: Correlation analysis distinguished the samples based on sex for H3K4me3 and H3K27me3 but not for H3K27ac. The analysis of transcription starting sites (TSS) signal distribution, and analysis of bounding sites revealed that gastrocnemius is more influenced than brain by sex for the three histone modifications considered, exception made for H3K27me3 distribution on the X chromosome which showed sex-related differences in promoters belonging to behavior and cellular or neuronal spheres in mice cortexes. Conclusions: H3K4me3, H3K27ac, and H3K27me3 signals are slightly affected by sex in brain, with the exception of H3K27me3, while a higher number of differences can be found in gastrocnemius.

Distinct Aβ pathology in the olfactory bulb and olfactory deficits in a mouse model of Aβ and α-syn co-pathology.

Several degenerative brain disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are characterized by the simultaneous appearance of amyloid‐β (Aβ) and α‐synuclein (α‐syn) pathologies and symptoms that are similar, making it difficult to differentiate between these diseases. Until now, an accurate diagnosis can only be made by postmortem analysis. Furthermore, the role of α‐syn in Aβ aggregation and the arising characteristic olfactory impairments observed during the progression of these diseases is still not well understood. Therefore, we assessed Aβ load in olfactory bulbs of APP‐transgenic mice expressing APP695 KM670/671NL and PSEN1 L166P under the control of the neuron‐specific Thy‐1 promoter (referred to here as APPPS1) and APPPS1 mice co‐expressing SNCA A30P (referred to here as APPPS1 × [A30P]aSYN). Furthermore, the olfactory capacity of these mice was evaluated in the buried food and olfactory avoidance test. Our results demonstrate an age‐dependent increase in Aβ load in the olfactory bulb of APP‐transgenic mice that go along with exacerbated olfactory performance. Our study provides clear evidence that the presence of α‐syn significantly diminished the endogenous and seed‐induced Aβ deposits and significantly ameliorated olfactory dysfunction in APPPS1 × [A30P]aSYN mice.

IKK2/NF-κB Activation in Astrocytes Reduces amyloid β Deposition: A Process Associated with Specific Microglia Polarization.

Alzheimer’s disease (AD) is a common neurodegenerative disease that is accompanied by pronounced neuroinflammatory responses mainly characterized by marked microgliosis and astrogliosis. However, it remains open as to how different aspects of astrocytic and microglial activation affect disease progression. Previously, we found that microglia expansion in the spinal cord, initiated by IKK2/NF-κB activation in astrocytes, exhibits stage-dependent beneficial effects on the progression of amyotrophic lateral sclerosis. Here, we investigated the impact of NF-κB-initiated neuroinflammation on AD pathogenesis using the APP23 mouse model of AD in combination with conditional activation of IKK2/NF-κB signaling in astrocytes. We show that NF-κB activation in astrocytes triggers a distinct neuroinflammatory response characterized by striking astrogliosis as well as prominent microglial reactivity. Immunohistochemistry and Congo red staining revealed an overall reduction in the size and number of amyloid plaques in the cerebral cortex and hippocampus. Interestingly, isolated primary astrocytes and microglia cells exhibit specific marker gene profiles which, in the case of microglia, point to an enhanced plaque clearance capacity. In contrast, direct IKK2/NF-κB activation in microglia results in a pro-inflammatory polarization program. Our findings suggest that IKK2/NF-κB signaling in astrocytes may activate paracrine mechanisms acting on microglia function but also on APP processing in neurons.

Synapsin-Promoted Caveolin-1 Overexpression Maintains Mitochondrial Morphology and Function in PSAPP Alzheimer's Disease Mice.

Mitochondrial dysfunction plays a pivotal role in the Alzheimer’s Disease (AD) pathology. Disrupted mitochondrial dynamics (i.e., fusion/fission balance), which are essential for normal mitochondria structure and function, are documented in AD. Caveolin-1 (Cav-1), a membrane/lipid raft (MLR) scaffolding protein regulates metabolic pathways in several different cell types such as hepatocytes and cancer cells. Previously, we have shown decreased expression of Cav-1 in the hippocampus of 9-month (m) old PSAPP mice, while hippocampal overexpression of neuron-targeted Cav-1 using the synapsin promoter (i.e., SynCav1) preserved cognitive function, neuronal morphology, and synaptic ultrastructure in 9 and 12 m PSAPP mice. Considering the central role of energy production in maintaining normal neuronal and synaptic function and survival, the present study reveals that PSAPP mice exhibit disrupted mitochondrial distribution, morphometry, and respiration. In contrast, SynCav1 mitigates mitochondrial damage and loss and enhances mitochondrial respiration. Furthermore, by examining mitochondrial dynamics, we found that PSAPP mice showed a significant increase in the phosphorylation of mitochondrial dynamin-related GTPase protein (DRP1), resulting in excessive mitochondria fragmentation and dysfunction. In contrast, hippocampal delivery of SynCav1 significantly decreased p-DRP1 and augmented the level of the mitochondrial fusion protein, mitofusin1 (Mfn1) in PSAPP mice, a molecular event, which may mechanistically explain for the preserved balance of mitochondria fission/fusion and metabolic resilience in 12 m PSAPP-SynCav1 mice. Our data demonstrate the critical role for Cav-1 in maintaining normal mitochondrial morphology and function through affecting mitochondrial dynamics and explain a molecular and cellular mechanism underlying the previously reported neuroprotective and cognitive preservation induced by SynCav1 in PSAPP mouse model of AD.

MFG-E8 (LACTADHERIN): a novel marker associated with cerebral amyloid angiopathy

Brain accumulation of amyloid-beta (Aβ) is a crucial feature in Alzheimer´s disease (AD) and cerebral amyloid angiopathy (CAA), although the pathophysiological relationship between these diseases remains unclear. Numerous proteins are associated with Aβ deposited in parenchymal plaques and/or cerebral vessels. We hypothesized that the study of these proteins would increase our understanding of the overlap and biological differences between these two pathologies and may yield new diagnostic tools and specific therapeutic targets. We used a laser capture microdissection approach combined with mass spectrometry in the APP23 transgenic mouse model of cerebral-β-amyloidosis to specifically identify vascular Aβ-associated proteins. We focused on one of the main proteins detected in the Aβ-affected cerebrovasculature: MFG-E8 (milk fat globule-EGF factor 8), also known as lactadherin. We first validated the presence of MFG-E8 in mouse and human brains. Immunofluorescence and immunoblotting studies revealed that MFG-E8 brain levels were higher in APP23 mice than in WT mice. Furthermore, MFG-E8 was strongly detected in Aβ-positive vessels in human postmortem CAA brains, whereas MFG-E8 was not present in parenchymal Aβ deposits. Levels of MFG-E8 were additionally analysed in serum and cerebrospinal fluid (CSF) from patients diagnosed with CAA, patients with AD and control subjects. Whereas no differences were found in MFG-E8 serum levels between groups, MFG-E8 concentration was significantly lower in the CSF of CAA patients compared to controls and AD patients. Finally, in human vascular smooth muscle cells MFG-E8 was protective against the toxic effects of the treatment with the Aβ40 peptide containing the Dutch mutation. In summary, our study shows that MFG-E8 is highly associated with CAA pathology and highlights MFG-E8 as a new CSF biomarker that could potentially be used to differentiate cerebrovascular Aβ pathology from parenchymal Aβ deposition.

Abstract P391: Inhalation Of Airborne Particulate Matter Alters Cardiovascular Function Of Alzheimer-prone Mice

Air pollution has detrimental effects on cardiovascular and lung function, and the extent of its pathological consequences continues to be uncovered. Recently, air pollution has been implicated in the development of Alzheimer Disease (AD) progression. AD and heart failure are common co-morbidities, giving reason to believe that cardiovascular dysfunction may contribute to AD. A known contributor to cardiovascular dysfunction-particulate matter (PM 2.5 , &lt; 2.5 μm diameter)—is a critical component of air pollution and is considered a risk factor for heart failure and AD development. This co-morbidity pattern and shared environmental risk factor prompted the hypothesis that PM 2.5 contributes to cardiovascular dysfunction in a transgenic mouse model of AD. We tested our hypothesis by subjecting 6-month-old transgenic (APP) and non-carrier wildtype (WT) male mice to filtered air (FA) or PM 2.5 for 5 days/week, 6 hours/day for 3 months (n = 34). Following exposure, echocardiography, pressure-volume (PV) loops, and respiratory mechanics were performed to detect cardiac and pulmonary changes associated with genotype and exposure conditions among the 3-month group. Echocardiography revealed left ventricular anterior wall thickness in systole was significantly elevated among PM-exposed APP mice compared to FA-exposed APP controls. PV data demonstrated significant reduced end-systolic elastance in PM-exposed mice compared to FA-exposed mice in both WT and APP mouse models, demonstrating impaired contractility. PV loops also showed that the time constant of isovolumetric relaxation was increased in PM-exposed compared to FA-exposed WT mice. APP mice experienced higher lung resistance and central airway resistance with an increasing dose of methacholine. Taken together, these findings indicate airborne particulate matter exposure causes cardiac and pulmonary dysfunction in a transgenic mouse model of AD.