Sex differences between APPswePS1dE9 mice in A-beta accumulation and pancreatic islet function during the development of Alzheimer’s disease

AAV mediated carboxyl terminus of Hsp70 interacting protein overexpression mitigates the cognitive and pathological phenotypes of APP/PS1 mice

JOURNAL/nrgr/04.03/01300535-202501000-00033/figure1/v/2024-05-14T021156Z/r/image-tiff The E3 ubiquitin ligase, carboxyl terminus of heat shock protein 70 (Hsp70) interacting protein (CHIP), also functions as a co-chaperone and plays a crucial role in the protein quality control system. In this study, we aimed to investigate the neuroprotective effect of overexpressed CHIP on Alzheimer's disease. We used an adeno-associated virus vector that can cross the blood-brain barrier to mediate CHIP overexpression in APP/PS1 mouse brain. CHIP overexpression significantly ameliorated the performance of APP/PS1 mice in the Morris water maze and nest building tests, reduced amyloid-β plaques, and decreased the expression of both amyloid-β and phosphorylated tau. CHIP also alleviated the concentration of microglia and astrocytes around plaques. In APP/PS1 mice of a younger age, CHIP overexpression promoted an increase in ADAM10 expression and inhibited β-site APP cleaving enzyme 1, insulin degrading enzyme, and neprilysin expression. Levels of HSP70 and HSP40, which have functional relevance to CHIP, were also increased. Single nuclei transcriptome sequencing in the hippocampus of CHIP overexpressed mice showed that the lysosomal pathway and oligodendrocyte-related biological processes were up-regulated, which may also reflect a potential mechanism for the neuroprotective effect of CHIP. Our research shows that CHIP effectively reduces the behavior and pathological manifestations of APP/PS1 mice. Indeed, overexpression of CHIP could be a beneficial approach for the treatment of Alzheimer's disease.

Aging, sex, metabolic and life experience factors: Contributions to neuro-inflammaging in Alzheimer's disease research

Alzheimer's disease (AD) is prevalent around the world, yet our understanding of the disease is still very limited. Recent work suggests that the cornerstone of AD may include the inflammation that accompanies it. Failure of a normal pro-inflammatory immune response to resolve may lead to persistent central inflammation that contributes to unsuccessful clearance of amyloid-beta plaques as they form, neuronal death, and ultimately cognitive decline. Individual metabolic, and dietary (lipid) profiles can differentially regulate this inflammatory process with aging, obesity, poor diet, early life stress and other inflammatory factors contributing to a greater risk of developing AD. Here, we integrate evidence for the interface between these factors, and how they contribute to a pro-inflammatory brain milieu. In particular, we discuss the importance of appropriate polyunsaturated fatty acids (PUFA) in the diet for the metabolism of specialised pro-resolving mediators (SPMs); raising the possibility for dietary strategies to improve AD outlook.

Impaired Hippocampal Reactivation Preceding Robust Aβ Deposition in a Model of Alzheimer's Disease

Current therapeutic strategies for Alzheimer's disease (AD) target amyloid-beta (Aβ) fibrils and high molecular weight protofibrils associated with plaques, but other bioactive species may directly contribute to neural systems failure in AD. Employing hippocampal electrophysiological recordings and dynamic calcium imaging across the sleep-wake cycle in young mice expressing human Aβ and Aβ oligomers, we reveal marked impairments of hippocampal function long before amyloid plaques predominate. In slow wave sleep (SWS), Aβ increased the proportion of hypoactive cells and reduced place-cell reactivation. During awake behavior, Aβ impaired theta-gamma phase-amplitude coupling (PAC) and drove excessive synchronization of place cell calcium fluctuations with hippocampal theta. Remarkably, the on-line impairment of hippocampal theta-gamma PAC correlated with the SWS impairment of place-cell reactivation. Together, these results identify toxic effects of Aβ on memory encoding and consolidation processes before robust plaque deposition and support targeting soluble Aβ-related species to treat and prevent AD.

Sex differences in luteinizing hormone aggravates Aβ deposition in APP/PS1 and Aβ1-42-induced mouse models of Alzheimer's disease

Alzheimer's disease (AD) exhibits a higher incidence rate among older women, and dysregulation of the hypothalamic-pituitary-gonadal (HPG) axis during aging is associated with cognitive impairments and the development of dementia. luteinizing hormone (LH) has an important role in CNS function, such as mediating neuronal pregnenolone production, and modulating neuronal plasticity and cognition. The sex differences in LH and its impact on Aβ deposition in AD individuals remain unclear, with no reported specific mechanisms. Here, we show through data mining that LH-related pathways are significantly enriched in female AD patients. Additionally, LH levels are elevated in female AD patients and exhibit a negative correlation with cognitive levels but a positive correlation with AD pathology levels, and females exhibit a greater extent of AD pathology, such as Aβ deposition. In vivo, we observed that the exogenous injection of LH exacerbated behavioral impairments induced by Aβ1-42 in mice. LH injection resulted in worsened neuronal damage and increased Aβ deposition. In SH-SY5Y cells, co-administration of LH with Aβ further exacerbated Aβ-induced neuronal damage. Furthermore, LH can dose-dependently decrease the levels of NEP and LHR proteins while increasing the expression of GFAP and IBA1 in vivo and in vitro. Taken together, these results indicate that LH can exacerbate cognitive impairment and neuronal damage in mice by increasing Aβ deposition. The potential mechanism may involve the reduction of NEP and LHR expression, along with the exacerbation of Aβ-induced inflammation.

Mechanisms of sex differences in Alzheimer's disease

Alzheimer's disease (AD) and the mechanisms underlying its etiology and progression are complex and multifactorial. The higher AD risk in women may serve as a clue to better understand these complicated processes. In this review, we examine aspects of AD that demonstrate sex-dependent effects and delve into the potential biological mechanisms responsible, compiling findings from advanced technologies such as single-cell RNA sequencing, metabolomics, and multi-omics analyses. We review evidence that sex hormones and sex chromosomes interact with various disease mechanisms during aging, encompassing inflammation, metabolism, and autophagy, leading to unique characteristics in disease progression between men and women.

Akt activation ameliorates deficits in hippocampal-dependent memory and activity-dependent synaptic protein synthesis in an Alzheimer's disease mouse model

Protein kinase-B (Akt) and the mechanistic target of rapamycin (mTOR) signaling pathways are implicated in Alzheimer's disease (AD) pathology. Akt/mTOR signaling pathways, activated by external inputs, enable new protein synthesis at the synapse and synaptic plasticity. The molecular mechanisms impeding new protein synthesis at the synapse in AD pathogenesis remain elusive. Here, we aimed to understand the molecular mechanisms prior to the manifestation of histopathological hallmarks by characterizing Akt1/mTOR signaling cascades and new protein synthesis in the hippocampus of WT and amyloid precursor protein/presenilin-1 (APP/PS1) male mice. Intriguingly, compared to those in WT mice, we found significant decreases in pAkt1, pGSK3β, pmTOR, pS6 ribosomal protein, and p4E-BP1 levels in both post nuclear supernatant and synaptosomes isolated from the hippocampus of one-month-old (presymptomatic) APP/PS1 mice. In synaptoneurosomes prepared from the hippocampus of presymptomatic APP/PS1 mice, activity-dependent protein synthesis at the synapse was impaired and this deficit was sustained in young adults. In hippocampal neurons from C57BL/6 mice, downregulation of Akt1 precluded synaptic activity-dependent protein synthesis at the dendrites but not in the soma. In three-month-old APP/PS1 mice, Akt activator (SC79) administration restored deficits in memory recall and activity-dependent synaptic protein synthesis. C57BL/6 mice administered with an Akt inhibitor (MK2206) resulted in memory recall deficits compared to those treated with vehicle. We conclude that dysregulation of Akt1/mTOR and its downstream signaling molecules in the hippocampus contribute to memory recall deficits and loss of activity-dependent synaptic protein synthesis. In AD mice, however, Akt activation ameliorates deficits in memory recall and activity-dependent synaptic protein synthesis.

APOE genotype and sex modulate Alzheimer's disease pathology in aged EFAD transgenic mice

Increasing evidence supports that age, APOE and sex interact to modulate Alzheimer's disease (AD) risk, however the underlying pathways are unclear. One way that AD risk factors may modulate cognition is by impacting amyloid beta (Aβ) accumulation as plaques, and/or neuroinflammation Therefore, the goal of the present study was to evaluate the extent to which age, APOE and sex modulate Aβ pathology, neuroinflammation and behavior in vivo. To achieve this goal, we utilized the EFAD mice, which express human APOE3 or APOE4 and have five familial AD mutations (FAD) that result in Aβ42 overproduction. We assessed Aβ levels, reactive glia and Morris water maze performance in 6-, 10-, 14-, and 18-month-old EFAD mice. Female APOE4 mice had the highest Aβ deposition, fibrillar amyloid deposits and neuroinflammation as well as earlier behavior deficits. Interestingly, we found that female APOE3 mice and male APOE4 mice had similar levels of pathology. Collectively our data support that the combination of APOE4 and female sex is the most detrimental combination for AD, and that at older ages, female sex may be equivalent to APOE4 genotype.

Tranexamic acid in a mouse model of cerebral amyloid angiopathy: setting the stage for a novel stroke treatment approach

Background

Symptomatic intracerebral hemorrhage (sICH) commonly occurs in patients with cerebral amyloid angiopathy (CAA). Amyloid also initiates plasminogen activation and might promote sICH.

Objectives

As amyloid-driven plasmin formation can be blocked by tranexamic acid (TXA), we aimed to evaluate the biodistribution and long-term consequences of TXA on brain amyloid-beta (Aβ) levels, inflammation, and neurologic function in APP/PS1 mice.

Methods

APP/PS1 mice overexpressing the mutant human amyloid precursor protein and wild-type littermates were randomized to TXA (20 mg/mL) or placebo in the drinking water for 6 months. TXA in plasma and various organs was determined by liquid chromatography-mass spectrometry. Plasmin activity assays were performed to evaluate changes in fibrinolytic activity. Neurologic function was evaluated by Y-maze and parallel rod floor testing. Proximity ligation-based immunoassays were used to quantitate changes of 92 biomarkers of inflammation. Brain Aβ levels were assessed by immunohistochemistry.

Results

Long-term oral TXA administration inhibited fibrinolysis. TXA accumulated in the kidney (19.4 ± 11.2 μg/g) with 2- to 5-fold lower levels seen in the lung, spleen, and liver. TXA levels were lowest in the brain (0.28 ± 0.01 μg/g). Over 6 months, TXA had no discernible effect on motor coordination, novelty preference, or brain Aβ levels. TXA reduced plasma levels of epithelial cell adhesion molecule and increased CCL20.

Conclusion

Long-term TXA treatment does not alter brain Aβ levels or impact neurologic behavior in mice predisposed to amyloid deposition and had minor effects on the levels of inflammatory mediators. This finding supports the safety of TXA and lays the foundation for TXA as a novel treatment to reduce sICH in patients with CAA.

Reduction in GABAB on glia induce Alzheimer's disease related changes

Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by beta-amyloid plaques (Aβ), neurofibrillary tangles (NFT), and neuroinflammation. Data have demonstrated that neuroinflammation contributes to Aβ and NFT onset and progression, indicating inflammation and glial signaling is vital to understanding AD. A previous investigation demonstrated a significant decrease of the GABAB receptor (GABABR) in APP/PS1 mice (Salazar et al., 2021). To determine if changes in GABABR restricted to glia serve a role in AD, we developed a mouse model with a reduction of GABABR restricted to macrophages, GAB/CX3ert. This model exhibits changes in gene expression and electrophysiological alterations similar to amyloid mouse models of AD. Crossing the GAB/CX3ert mouse with APP/PS1 resulted in significant increases in Aβ pathology. Our data demonstrates that decreased GABABR on macrophages leads to several changes observed in AD mouse models, as well as exacerbation of AD pathology when crossed with existing models. These data suggest a novel mechanism in AD pathogenesis.

Pre-symptomatic synaptic dysfunction and longitudinal decay of hippocampal synaptic function in APPPS1 mouse model of Alzheimer's disease is sex-independent

Alzheimer's disease (AD) is an incurable, age-related and progressive neurodegenerative disease characterized by cognitive impairments. Deficits in synaptic plasticity were reported in various models of AD-like pathology and are considered as an early contributing factor of cognitive impairment. However, the majority of previous studies were focused on overt, symptomatic stages of pathology and assessed long-term potentiation (LTP), whereas long-term depression (LTD) was much less investigated and the precise nature of its involvement remains poorly defined. To better understand the earliest synaptic dysfunctions along the pre-symptomatic stage of AD-like pathology, we performed a detailed analysis of underlying mechanisms and quantified basal synaptic activity, presynaptic release probability, and synaptic plasticity such as post-tetanic potentiation (PTP), as well as LTP and LTD. These parameters were studied in APPPS1 mouse model at two time points (early- and mid-) along the pre-symptomatic stage, which were compared with alterations monitored at two later time-points, i.e. the onset of cognitive deficits and the overt stage of full-blown pathology. Because sex is known to be an instrumental biological parameter in AD pathophysiology, all alterations were assessed in both males and females. Our data show that, as compared to wild-type (WT) littermates, initial neuronal hyperexcitability, seen at early pre-symptomatic stage shifts subsequently towards hypoexcitability at mid-pre-symptomatic stage and remains impaired at advanced stages. The pre-symptomatic changes also involve increased synaptic plasticity as assessed by paired-pulse facilitation (PPF), which returns to basal level at the onset of pathology and remains stable afterwards. Synaptic plasticity is impaired by mid-pre-symptomatic stage and manifests as lowered LTP and absence of LTD induction, the latter being reported here for the first time. Observed LTP and LTD impairments both persist in older APPPS1 mice. Remarkably, none of the observed differences was gender-dependent. Altogether, our data evidence that major impairments in basal synaptic efficacy and plasticity are detectable already during mid-pre-symptomatic stage of AD-like pathogenesis and likely involve hyperexcitability as the underlying mechanism. Our study also uncovers synaptic alterations that may become critical read-outs for testing the efficiency of novel, pre-symptomatic stage-targeted therapies for AD.

Systematic review of brain and blood lipidomics in Alzheimer's disease mouse models

Alzheimer's disease (AD) diagnosis is based on invasive and expensive biomarkers. Regarding AD pathophysiological mechanisms, there is evidence of a link between AD and aberrant lipid homeostasis. Alterations in lipid composition have been observed in blood and brain samples, and transgenic mouse models represent a promising approach. Nevertheless, there is great variability among studies in mice for the determination of different types of lipids in targeted and untargeted methods. It could be explained by the different variables (model, age, sex, analytical technique), and experimental conditions used. The aim of this work is to review the studies on lipid alteration in brain tissue and blood samples from AD mouse models, focusing on different experimental parameters. As result, great disparity has been observed among the reviewed studies. Brain studies showed an increase in gangliosides, sphingomyelins, lysophospholipids and monounsaturated fatty acids and a decrease in sulfatides. In contrast, blood studies showed an increase in phosphoglycerides, sterols, diacylglycerols, triacylglycerols and polyunsaturated fatty acids, and a decrease in phospholipids, lysophospholipids and monounsaturated fatty acids. Thus, lipids are closely related to AD, and a consensus on lipidomics studies could be used as a diagnostic tool and providing insight into the mechanisms involved in AD.

Interleukin-17 Promotes the Infiltration of CD8+ T Cells into the Brain in a Mouse Model for Alzheimer's Disease

BACKGROUND

Interleukin-17 (IL-17) family cytokines play critical roles in inflammation and pathogen resistance. Inflammation in the central nervous system, denoted as neuroinflammation, promotes the onset and progression of Alzheimer's disease (AD). Previous studies showed that IL-17A neutralizing antibody treatment alleviated Amyloid β (Aβ) burden in rodent models of AD, while overexpression of IL-17A in mouse lateral ventricles rescued part of the AD pathology. However, the involvement of IL-17 in AD and its mechanism of action remain largely unknown.

METHODS

To investigate the role of IL-17 in AD, we crossed mice lacking the common receptor of IL-17 signaling (IL-17RA knockout mice) to the APP/PS1 mouse model of AD. We then analyzed the composition of immune cells and cytokines/chemokines during different phases of AD pathology, and interrogated the underlying mechanism by which IL-17 may regulate immune cell infiltration into AD brains.

RESULTS

Ablation of IL-17RA in APP/PS1 mice decreased infiltration of CD8+ T cells and myeloid cells to mouse brain. IL-17 was able to promote the production of myeloid- and T cell-attracting chemokines CXCL1 and CXCL9/10 in primary glial cells. We also observed that IL-17 is upregulated in the late stage of AD development, and ectopic expression of IL-17 via adenoviral infection to the cortex trended towards worsened cognition in APP/PS1 mice, suggesting a pathogenic role of excessive IL-17 in AD.

CONCLUSION

Our data show that IL-17 signaling promotes neuroinflammation in AD by accelerating the infiltration of CD8+ T lymphocytes and Gr1+ CD11b+ myeloid cells.

Immune-mediated platelet depletion augments Alzheimer's disease neuropathological hallmarks in APP-PS1 mice

In Alzheimer's disease (AD), platelets become dysfunctional and might contribute to amyloid beta deposition. Here, we depleted platelets in one-year-old APP Swedish PS1 dE9 (APP-PS1) transgenic mice for five days, using intraperitoneal injections of an anti-CD42b antibody, and assessed changes in cerebral amyloidosis, plaque-associated neuritic dystrophy and gliosis. In APP-PS1 female mice, platelet depletion shifted amyloid plaque size distribution towards bigger plaques and increased neuritic dystrophy in the hippocampus. In platelet-depleted females, plaque-associated Iba1+ microglia had lower amounts of fibrillar amyloid beta cargo and GFAP+ astrocytic processes showed a higher overlap with thioflavin S+ amyloid plaques. In contrast to the popular hypothesis that platelets foster plaque pathology, our data suggest that platelets might limit plaque growth and attenuate plaque-related neuritic dystrophy at advanced stages of amyloid plaque pathology in APP-PS1 female mice. Whether the changes in amyloid plaque pathology are due to a direct effect on amyloid beta deposition or are a consequence of altered glial function needs to be further elucidated.

Exogenous Oxytocin Administration Restores Memory in Female APP/PS1 Mice

BACKGROUND

Current treatment options for Alzheimer's disease (AD) are limited, inefficient, and often have serious side effects. Oxytocin is a neuropeptide implicated in a variety of central processes, such as social and reproductive behaviors. Among others, it has garnered attention in various domains of psychiatric research, while its role in the development and course of neurodegenerative disorders like AD is rather unknown.

OBJECTIVE

This study aimed to investigate the role of exogenous oxytocin administration on memory, specifically in view of AD, as a potential novel treatment option.

METHODS

We describe a novel treatment approach by using a relatively low dose of long-term intranasal oxytocin treatment, to restore memory deficits in female APPswePS1dE9 mice.

RESULTS

Female APPswePS1dE9 mice treated with oxytocin showed increased spatial memory performance in the object location task and improved working memory in the Y-Maze, while indicating decreased sociability.

CONCLUSIONS

These results indicate that oxytocin is able to reverse acquired cognitive deficits in female APPswePS1dE9 mice.

The hibernation-derived compound SUL-138 shifts the mitochondrial proteome towards fatty acid metabolism and prevents cognitive decline and amyloid plaque formation in an Alzheimer's disease mouse model

BACKGROUND

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide and remains without effective cure. Increasing evidence is supporting the mitochondrial cascade hypothesis, proposing that loss of mitochondrial fitness and subsequent ROS and ATP imbalance are important contributors to AD pathophysiology.

METHODS

Here, we tested the effects of SUL-138, a small hibernation-derived molecule that supports mitochondrial bioenergetics via complex I/IV activation, on molecular, physiological, behavioral, and pathological outcomes in APP/PS1 and wildtype mice.

RESULTS

SUL-138 treatment rescued long-term potentiation and hippocampal memory impairments and decreased beta-amyloid plaque load in APP/PS1 mice. This was paralleled by a partial rescue of dysregulated protein expression in APP/PS1 mice as assessed by mass spectrometry-based proteomics. In-depth analysis of protein expression revealed a prominent effect of SUL-138 in APP/PS1 mice on mitochondrial protein expression. SUL-138 increased the levels of proteins involved in fatty acid metabolism in both wildtype and APP/PS1 mice. Additionally, in APP/PS1 mice only, SUL-138 increased the levels of proteins involved in glycolysis and amino acid metabolism pathways, indicating that SUL-138 rescues mitochondrial impairments that are typically observed in AD.

CONCLUSION

Our study demonstrates a SUL-138-induced shift in metabolic input towards the electron transport chain in synaptic mitochondria, coinciding with increased synaptic plasticity and memory. In conclusion, targeting mitochondrial bioenergetics might provide a promising new way to treat cognitive impairments in AD and reduce disease progression.

Females exhibit higher GluA2 levels and outperform males in active place avoidance despite increased amyloid plaques in TgF344-Alzheimer's rats

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is most prevalent in females. While estrogen provides neuroprotection in females, sex mediated differences in the development of AD pathology are not fully elucidated. Therefore, comparing events between sexes in early-stage AD pathology may reveal more effective therapeutic targets of intervention. To address sex differences, we analyzed early-stage 9-month male and female TgF344-AD (Tg-AD) rats, an AD model carrying the APPswe and Presenilin 1 (PS1ΔE9) mutations that develops progressive age-dependent AD pathology similar to humans. Tg-AD females significantly outperformed Tg-AD males in the active place avoidance (aPAT) test that assesses hippocampal-dependent spatial learning and memory. However, comparisons between Tg-AD male or female rats and their WT counterparts showed significant deficits for female but not male rats. Nevertheless, Tg-AD females experienced significantly less hippocampal neuronal loss with higher GluA2 subunit levels than Tg-AD males. Unexpectedly, Tg-AD females displayed higher levels of hippocampal amyloid plaques than Tg-AD males. Thus, we propose that GluA2 may provide a neuroprotective function for Tg-AD females in our rat model by mitigating cognitive impairment independently of amyloid plaques. Elucidating this protective mechanism in AD could lead to new targets for early intervention.

Adult-Onset Deficiency of Mitochondrial Complex III in a Mouse Model of Alzheimer's Disease Decreases Amyloid Beta Plaque Formation

For decades, mitochondrial dysfunctions and the generation of reactive oxygen species have been proposed to promote the development and progression of the amyloid pathology in Alzheimer's disease, but this association is still debated. It is unclear whether different mitochondrial dysfunctions, such as oxidative phosphorylation deficiency and oxidative stress, are triggers or rather consequences of the formation of amyloid aggregates. Likewise, the role of the different mitochondrial oxidative phosphorylation complexes in Alzheimer's patients' brain remains poorly understood. Previous studies showed that genetic ablation of oxidative phosphorylation enzymes from early age decreased amyloid pathology, which were unexpected results. To better model oxidative phosphorylation defects in aging, we induced the ablation of mitochondrial Complex III (CIIIKO) in forebrain neurons of adult mice with amyloid pathology. We found that mitochondrial Complex III dysfunction in adult neurons induced mild oxidative stress but did not increase amyloid beta accumulation. On the contrary, CIIIKO-AD mice showed decreased plaque number, decreased Aβ42 toxic fragment, and altered amyloid precursor protein clearance pathway. Our results support the hypothesis that mitochondrial dysfunctions alone, caused by oxidative phosphorylation deficiency, is not the cause of amyloid accumulation.

(D-Ser2) oxyntomodulin recovers hippocampal synaptic structure and theta rhythm in Alzheimer's disease transgenic mice

In our previous studies, we have shown that (D-Ser2) oxyntomodulin (Oxm), a glucagon-like peptide 1 (GLP-1) receptor (GLP1R)/glucagon receptor (GCGR) dual agonist peptide, protects hippocampal neurons against Aβ_1–42 -induced cytotoxicity, and stabilizes the calcium homeostasis and mitochondrial membrane potential of hippocampal neurons. Additionally, we have demonstrated that (D-Ser2) Oxm improves cognitive decline and reduces the deposition of amyloid-beta in Alzheimer's disease model mice. However, the protective mechanism remains unclear. In this study, we showed that 2 weeks of intraperitoneal administration of (D-Ser2) Oxm ameliorated the working memory and fear memory impairments of 9-month-old 3×Tg Alzheimer's disease model mice. In addition, electrophysiological data recorded by a wireless multichannel neural recording system implanted in the hippocampal CA1 region showed that (D-Ser2) Oxm increased the power of the theta rhythm. In addition, (D-Ser2) Oxm treatment greatly increased the expression level of synaptic-associated proteins SYP and PSD-95 and increased the number of dendritic spines in 3×Tg Alzheimer's disease model mice. These findings suggest that (D-Ser2) Oxm improves the cognitive function of Alzheimer's disease transgenic mice by recovering hippocampal synaptic function and theta rhythm.

Selective reduction of astrocyte apoE3 and apoE4 strongly reduces Aβ accumulation and plaque-related pathology in a mouse model of amyloidosis

Background

One of the key pathological hallmarks of Alzheimer disease (AD) is the accumulation of the amyloid-β (Aβ) peptide into amyloid plaques. The apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset AD and has been shown to influence the accumulation of Aβ in the brain in an isoform-dependent manner. ApoE can be produced by different cell types in the brain, with astrocytes being the largest producer of apoE, although reactive microglia also express high levels of apoE. While studies have shown that altering apoE levels in the brain can influence the development of Aβ plaque pathology, it is not fully known how apoE produced by specific cell types, such as astrocytes, contributes to amyloid pathology.

Methods

We utilized APOE knock-in mice capable of having APOE selectively removed from astrocytes in a tamoxifen-inducible manner and crossed them with the APP/PS1-21 mouse model of amyloidosis. We analyzed the changes to Aβ plaque levels and assessed the impact on cellular responses to Aβ plaques when astrocytic APOE is removed.

Results

Tamoxifen administration was capable of strongly reducing apoE levels in the brain by markedly reducing astrocyte apoE, while microglial apoE expression remained. Reduction of astrocytic apoE3 and apoE4 led to a large decrease in Aβ plaque deposition and less compact plaques. While overall Iba1⁺ microglia were unchanged in the cortex after reducing astrocyte apoE, the expression of the disease-associated microglial markers Clec7a and apoE were lower around amyloid plaques, indicating decreased microglial activation. Additionally, astrocyte GFAP levels are unchanged around amyloid plaques, but overall GFAP levels are reduced in the cortex of female apoE4 mice after a reduction in astrocytic apoE. Finally, while the amount of neuritic dystrophy around remaining individual plaques was increased with the removal of astrocytic apoE, the overall amount of cortical amyloid-associated neuritic dystrophy was significantly decreased.

Conclusion

This study reveals an important role of astrocytic apoE3 and apoE4 on the deposition and accumulation of Aβ plaques as well as on certain Aβ-associated downstream effects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-022-00516-0.

Centella asiatica Alters Metabolic Pathways Associated With Alzheimer's Disease in the 5xFAD Mouse Model of ß-Amyloid Accumulation

Centella asiatica is an herb used in Ayurvedic and traditional Chinese medicine for its beneficial effects on brain health and cognition. Our group has previously shown that a water extract of Centella asiatica (CAW) elicits cognitive-enhancing effects in animal models of aging and Alzheimer's disease, including a dose-related effect of CAW on memory in the 5xFAD mouse model of ß-amyloid accumulation. Here, we endeavor to elucidate the mechanisms underlying the effects of CAW in the brain by conducting a metabolomic analysis of cortical tissue from 5xFAD mice treated with increasing concentrations of CAW. Tissue was collected from 8-month-old male and female 5xFAD mice and their wild-type littermates treated with CAW (0, 200, 500, or 1,000 mg/kg/d) dissolved in their drinking water for 5 weeks. High-performance liquid chromatography coupled to high-resolution mass spectrometry analysis was performed and relative levels of 120 annotated metabolites were assessed in the treatment groups. Metabolomic analysis revealed sex differences in the effect of the 5xFAD genotype on metabolite levels compared to wild-type mice, and variations in the metabolomic response to CAW depending on sex, genotype, and CAW dose. In at least three of the four treated groups (5xFAD or wild-type, male or female), CAW (500 mg/kg/d) significantly altered metabolic pathways related to purine metabolism, nicotinate and nicotinamide metabolism, and glycerophospholipid metabolism. The results are in line with some of our previous findings regarding specific mechanisms of action of CAW (e.g., improving mitochondrial function, reducing oxidative stress, and increasing synaptic density). Furthermore, these findings provide new information about additional, potential mechanisms for the cognitive-enhancing effect of CAW, including upregulation of nicotinamide adenine dinucleotide in the brain and modulation of brain-derived neurotrophic factor. These metabolic pathways have been implicated in the pathophysiology of Alzheimer's disease, highlighting the therapeutic potential of CAW in this neurodegenerative disease.

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.

Liver Bile Acid Changes in Mouse Models of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive cognitive impairment. It is hypothesized to develop due to the dysfunction of two major proteins, amyloid-β (Aβ) and microtubule-associated protein, tau. Evidence supports the involvement of cholesterol changes in both the generation and deposition of Aβ. This study was performed to better understand the role of liver cholesterol and bile acid metabolism in the pathophysiology of AD. We used male and female wild-type control (C57BL/6J) mice to compare to two well-characterized amyloidosis models of AD, APP/PS1, and App^NL-G-F. Both conjugated and unconjugated primary and secondary bile acids were quantified using UPLC-MS/MS from livers of control and AD mice. We also measured cholesterol and its metabolites and identified changes in levels of proteins associated with bile acid synthesis and signaling. We observed sex differences in liver cholesterol levels accompanied by differences in levels of synthesis intermediates and conjugated and unconjugated liver primary bile acids in both APP/PS1 and App^NL-G-F mice when compared to controls. Our data revealed fundamental deficiencies in cholesterol metabolism and bile acid synthesis in the livers of two different AD mouse lines. These findings strengthen the involvement of liver metabolism in the pathophysiology of AD.

Chronic sleep deprivation exacerbates cognitive and synaptic plasticity impairments in APP/PS1 transgenic mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive deficits. Sleep deprivation (SD) could lead to memory deficits, and it was a candidate risk factor for AD. However, the effects of chronic SD on the cognitive functions of AD model mice and its possible mechanism are still unclear. In the present study, 8-month-old male APP/PS1 transgenic mice and wild type (WT) littermates were subjected to chronic SD by using the modified multiple platform method (MMPM), with 20 h of SD each day for 21 days. Then, the effects of chronic SD on cognitive functions in APP/PS1 mice were tested by using behavioral tests, the potential mechanisms were investigated by in vivo electrophysiological recording, western blot and immunochemistry. The results showed that chronic SD obviously aggravated the cognitive impairments, exacerbated in vivo hippocampal long-term potentiation (LTP) suppression, reduced the expression level of PSD95, increased amyloid-β (Aβ) protein deposition and overactivated microglia in the hippocampus of APP/PS1 mice. These results indicate that chronic SD exacerbates the cognitive deficits in APP/PS1 mice by accelerating the development of AD pathologies, reducing the expression of PSD95 and aggravating the LTP suppression in hippocampus. At the same time, chronic SD also impaired cognitive functions and synaptic plasticity in WT mice through down-regulating the level of PSD95 and activating microglia. These findings further clarify the electrophysiological and molecular mechanisms of exacerbated cognitive deficits in AD caused by chronic SD.

Sex differences in the IntelliCage and the Morris water maze in the APP/PS1 mouse model of amyloidosis

Transgenic rodent models were created to decipher pathogenic mechanisms associated with Alzheimer’s disease (AD), and behavioral apparatuses such as the Morris water maze (MWM) are used to assess cognition in mice. The IntelliCage was designed to circumvent issues of traditional behavioral tests, such as frequent human handling. The motivation to complete IntelliCage tasks is water consumption, which is less stressful than escaping from a pool in the MWM. Here, we examined behavioral performances of mice in the IntelliCage and MWM tasks. Twelve-month-old male and female APP/PS1 and non-transgenic mice first underwent 42 days of IntelliCage testing to assess prefrontal cortical and hippocampal function followed by MWM testing for six days. We found that females performed better in the IntelliCage while males performed superiorly in the MWM. Mechanistically, female APP/PS1 mice had a higher Amyloid-β plaque load throughout the brain, which is inconsistent with their performance in the IntelliCage. Collectively, these results inform scientists about the sex-based differences when testing animals in different behavioral paradigms that tap similar cognitive functions.

Gender Differences of NLRP1 Inflammasome in Mouse Model of Alzheimer's Disease

Background: There is a significant gender difference in the incidence and symptoms of Alzheimer's disease (AD), but its mechanisms are not completely understood. Recent studies showed that NLRP1 inflammasome was overexpressed in females under some pathological conditions such as nodular melanoma. Whether NLRP1 signals have a gender difference in AD has not been elucidated. This study was designed to investigate gender difference on the expressions of NLRP1 signals including NLRP1, Capase-1 and IL-1β in the brains of APP/PS1^+/- mice. Methods: Female and male APP/PS1^+/- mice (30-weeks-old) were used in this study. Amyloid-β (Aβ) plaques were stained with Congo red dye and cell apoptosis was detected by TUNEL staining. Expressions of NLRP1, Capase-1 and IL-1β were measured by immunofluorescent staining and Western blotting assay. Results: The numbers of Aβ plaques in cortex and hippocampus and neuronal apoptosis in cortex were 4 and 2-folds in females than males, respectively (P < 0.001). The average size of Aβ plaques in both cortex (females: 3527.11 ± 539.88 μm² vs. males: 1920.44 ± 638.49 μm²) and hippocampus (females: 1931 ± 308.61 μm² vs. males: 1038.55 ± 220.40 μm²) were also larger in females than males (P < 0.01). More interestingly, expressions of NLRP1, Caspase-1, and IL-1β were markedly increased in the cortex of females as compared with males. Conclusions: These findings show that NLRP1 signals are higher in brains of female APP/PS1^+/- mice than males, which may be related to the gender differences of AD.

Huntingtin-associated protein 1 plays an essential role in the pathogenesis of type 2 diabetes by regulating the translocation of GLUT4 in mouse adipocytes

OBJECTIVE

Glucose disposal by insulin-responsive tissues maintains the body glucose homeostasis and insulin resistance leads to a risk of developing type 2 diabetes (T2DM). Insulin stimulates the translocation of glucose transporter isoform 4 (GLUT4) vesicles from intracellular compartments to the plasma membrane to facilitate glucose uptake. However, the underlying mechanisms of GLUT4 vesicle translocation are not well defined. Here we show the role of huntingtin-associated protein 1 (HAP1) in GLUT4 translocation in adipocytes and the pathogenesis of T2DM.

RESEARCH DESIGN AND METHODS

The parameters for glucose metabolism including body weight, glucose tolerance and insulin tolerance were assessed in wild-type (WT) and Hap1^+/- mice. HAP1 protein expression was verified in adipose tissue. Hap1 mRNA and protein expression was monitored in adipose tissue of high-fat diet (HFD)-induced diabetic mice. Insulin-stimulated GLUT4 vesicle translocation and glucose uptake were detected using immunofluorescence techniques and quantified in primary adipocytes from Hap1^-/- mice. The interaction between HAP1 and GLUT4 was assessed by immunofluorescence colocalization and co-immunoprecipitation in HEK293 cells and adipose tissue. The role of sortilin in HAP1 and GLUT4 interaction was approved by co-immunoprecipitation and RNA interference.

RESULTS

The expression of Hap1 mRNA and protein was detected in WT mouse adipose tissue and downregulated in adipose tissue of HFD-induced diabetic mice. Hap1^+/- mice exhibited increased body weight, pronounced glucose tolerance and significant insulin intolerance compared with the WT mice. HAP1 colocalized with GLUT4 in mouse adipocytes and cotransfected HEK293 cells. Furthermore, the insulin-stimulated GLUT4 vesicle translocation and glucose uptake were defective in Hap1^-/- adipocytes. Finally, sortilin mediated the interaction of HAP1 and GLUT4.

CONCLUSIONS

Our study showed that HAP1 formed a protein complex with GLUT4 and sortilin, and played a critical role in insulin-stimulated GLUT4 translocation in adipocytes. Its downregulation may contribute to the pathogenesis of diabetes.

Microglial-associated responses to comorbid amyloid pathology and hyperhomocysteinemia in an aged knock-in mouse model of Alzheimer's disease

BACKGROUND

Elevated blood homocysteine levels, termed hyperhomocysteinemia (HHcy), is a prevalent risk factor for Alzheimer's disease (AD) in elderly populations. While dietary supplementation of B-vitamins is a generally effective method to lower homocysteine levels, there is little if any benefit to cognition. In the context of amyloid pathology, dietary-induced HHcy is known to enhance amyloid deposition and certain inflammatory responses. Little is known, however, about whether there is a more specific effect on microglia resulting from combined amyloid and HHcy pathologies.

METHODS

The present study used a knock-in mouse model of amyloidosis, aged to 12 months, given 8 weeks of B-vitamin deficiency-induced HHcy to better understand how microglia are affected in this comorbidity context.

RESULTS

We found that HHcy-inducing diet increased amyloid plaque burden, altered the neuroinflammatory milieu, and upregulated the expression of multiple damage-associated and "homeostatic" microglial genes.

CONCLUSIONS

Taken together, these data indicate complex effects of comorbid pathologies on microglial function that are not driven solely by increased amyloid burden. Given the highly dynamic nature of microglia, their central role in AD pathology, and the frequent occurrence of various comorbidities in AD patients, it is increasingly important to understand how microglia respond to mixed pathological processes.

Sex-specific hippocampal metabolic signatures at the onset of systemic inflammation with lipopolysaccharide in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Systemic inflammation enhances the risk and progression of Alzheimer's disease (AD). Lipopolysaccharide (LPS), a potent pro-inflammatory endotoxin produced by the gut, is found in excess levels in AD where it associates with neurological hallmarks of pathology. Sex differences in susceptibility to inflammation and AD progression have been reported, but how this impacts on LPS responses remains under investigated. We previously reported in an APP/PS1 model of AD that systemic LPS administration rapidly altered hippocampal metabolism in males. Here, we used untargeted metabolomics to comprehensively identify hippocampal metabolic processes occurring at onset of systemic inflammation with LPS (100 µg/kg, i.v.) in APP/PS1 mice, at an early pathological stage, and investigated the sexual dimorphism in this response. Four hours after LPS administration, pathways regulating energy metabolism, immune and oxidative stress responses were simultaneously recruited in the hippocampi of 4.5-month-old mice with a more protective response in females despite their pro-inflammatory and pro-oxidant metabolic signature in the absence of immune stimulation. LPS induced comparable behavioural sickness responses in male and female wild-type and APP/PS1 mice and comparable activation of both the serotonin and nicotinamide pathways of tryptophan metabolism in their hippocampi. Elevations in N-methyl-2-pyridone-5-carboxamide, a major toxic metabolite of nicotinamide, correlated with behavioural sickness regardless of sex, as well as with the LPS-induced hypothermia seen in males. Males also exhibited a pro-inflammatory-like downregulation of pyruvate metabolism, exacerbated in APP/PS1 males, and methionine metabolism whereas females showed a greater cytokine response and anti-inflammatory-like downregulation of hippocampal methylglyoxal and methionine metabolism. Metabolic changes were not associated with morphological markers of immune cell activation suggesting that they constitute an early event in the development of LPS-induced neuroinflammation and AD exacerbation. These data suggest that the female hippocampus is more tolerant to acute systemic inflammation.

The Ethyl Acetate Extract of Leaves of Ugni molinae Turcz. Improves Neuropathological Hallmarks of Alzheimer's Disease in Female APPswe/PS1dE9 Mice Fed with a High Fat Diet

The most common type of dementia is Alzheimer's disease (AD), a progressive neurodegenerative disease characterized by impairment in cognitive performance in aged individuals. Currently, there is no effective pharmacological treatment that cures the disease due to the lack of knowledge on the actual mechanisms involved in its pathogenesis. In the last decades, the amyloidogenic hypothesis has been the most studied theory trying to explain the origin of AD, yet it does not address all the concerns relating to its development. In the present study, a possible new preclinical treatment of AD was evaluated using the ethyl acetate extract (EAE) of leaves of Ugni molinae Turcz. (synonym Myrtus ugni Molina Family Myrtacea). The effects were assessed on female transgenic mice from a preclinical model of familial AD (APPswe/PS1dE9) combined with a high fat diet. This preclinical model was selected due to the already available experimental and observational data proving the relationship between obesity, gender, metabolic stress, and cognitive dysfunction; related to characteristics of sporadic AD. According to chemical analyses, EAE would contain polyphenols such as tannins, flavonoid derivatives, and phenolic acids, as well as pentacyclic triterpenoids that exhibit neuroprotective, anti-inflammatory, and antioxidant effects. In addition, the treatment evidenced its capacity to prevent deterioration of memory capacity and reduction of progression speed of AD neuropathology.

The APMAP interactome reveals new modulators of APP processing and beta-amyloid production that are altered in Alzheimer's disease

The adipocyte plasma membrane-associated protein APMAP is expressed in the brain where it associates with γ-secretase, a protease responsible for the generation of the amyloid-β peptides (Aβ) implicated in the pathogenesis of Alzheimer's disease (AD). In this study, behavioral investigations revealed spatial learning and memory deficiencies in our newly generated mouse line lacking the protein APMAP. In a mouse model of AD, the constitutive deletion of APMAP worsened the spatial memory phenotype and led to increased Aβ production and deposition into senile plaques. To investigate at the molecular level the neurobiological functions of APMAP (memory and Aβ formation) and a possible link with the pathological hallmarks of AD (memory impairment and Aβ pathology), we next developed a procedure for the high-grade purification of cellular APMAP protein complexes. The biochemical characterization of these complexes revealed a series of new APMAP interactomers. Among these, the heat shock protein HSPA1A and the cation-dependent mannose-6-phosphate receptor (CD-M6PR) negatively regulated APP processing and Aβ production, while clusterin, calnexin, arginase-1, PTGFRN and the cation-independent mannose-6-phosphate receptor (CI-M6PR/IGF2R) positively regulated APP and Aβ production. Several of the newly identified APMAP interactomers contribute to the autophagy-lysosome system, further supporting an emergent agreement that this pathway can modulate APP metabolism and Aβ generation. Importantly, we have also demonstrated increased alternative splicing of APMAP and lowered levels of the Aβ controllers HSPA1A and CD-M6PR in human brains from neuropathologically verified AD cases.

Age-related deterioration of motor function in male and female 5xFAD mice from 3 to 16 months of age

Alzheimer's disease (AD) is a neurodegenerative disorder that leads to age-related cognitive and sensori-motor dysfunction. There is an increased understanding that motor dysfunction contributes to overall AD severity, and a need to ameliorate these impairments. The 5xFAD mouse develops the neuropathology, cognitive and motor impairments observed in AD, and thus may be a valuable animal model to study motor deficits in AD. Therefore, we assessed age-related changes in motor ability of male and female 5xFAD mice from 3 to 16 months of age, using a battery of behavioral tests. At 9-10 months, 5xFAD mice showed reduced body weight, reduced rearing in the open-field and impaired performance on the rotarod compared to wild-type controls. At 12-13 months, 5xFAD mice showed reduced locomotor activity on the open-field, and impaired balance on the balance beam. At 15-16 months, impairments were also seen in grip strength. Although sex differences were observed at specific ages, the development of motor dysfunction was similar in male and female mice. Given the 5xFAD mouse is commonly on a C57BL/6 × SJL hybrid background, a subset of mice may be homozygous recessive for the Dysf ^im mutant allele, which leads to muscular weakness in SJL mice and may exacerbate motor dysfunction. We found small effects of Dysf ^im on motor function, suggesting that Dysf ^im contributes little to motor dysfunction in 5xFAD mice. We conclude that the 5xFAD mouse may be a useful model to study mechanisms that produce motor dysfunction in AD, and to assess the efficacy of therapeutics on ameliorating motor impairment.