APPswe/PS1dE9 Research Articles

Nitric oxide donors rescue metabolic and mitochondrial dysfunction in obese Alzheimer’s model

Reduced nitric oxide (NO) bioavailability is a pathological link between obesity and Alzheimer’s disease (AD). Obesity-associated metabolic and mitochondrial bioenergetic dysfunction are key drivers of AD pathology. The hypothalamus is a critical brain region during the development of obesity and dysfunction is an area implicated in the development of AD. NO is an essential mediator of blood flow and mitochondrial bioenergetic function, but the role of NO in obesity-AD is not entirely clear. We investigated diet-induced obesity in female APPswe/PS1dE9 (APP) mouse model of AD, which we treated with two different NO donors (sodium nitrite or L-citrulline). After 26 weeks of a high-fat diet, female APP mice had higher adiposity, insulin resistance, and mitochondrial dysfunction (hypothalamus) than non-transgenic littermate (wild type) controls. Treatment with either sodium nitrite or L-citrulline did not reduce adiposity but improved whole-body energy expenditure, substrate oxidation, and insulin sensitivity. Notably, both NO donors restored hypothalamic mitochondrial respiration in APP mice. Our findings suggest that NO is an essential mediator of whole-body metabolism and hypothalamic mitochondrial function, which are severely impacted by the dual insults of obesity and AD pathology.

Intestinal homeostasis disrupted by Periodontitis exacerbates Alzheimer’s Disease in APP/PS1 mice

Periodontitis exacerbates Alzheimer’s disease (AD) through multiple pathways. Both periodontitis and AD are intricately correlated to intestinal homeostasis, yet there is still a lack of direct evidence regarding whether periodontitis can regulate the progression of AD by modulating intestinal homeostasis. The current study induced experimental periodontitis in AD mice by bilaterally ligating the maxillary second molars with silk and administering Pg-LPS injections in APPswe/PS1ΔE9 (APP/PS1) mice. Behavioral tests and histological analyses of brain tissue were conducted after 8 weeks. Gut microbiota was analyzed and colon tissue were also evaluated. Then, fecal microbiota from mice with periodontitis was transplanted into antibiotic-treated mice to confirm the effects of periodontitis on AD and the potential mechanism was explored. The results indicated periodontitis exacerbated cognitive impairment and anxious behaviour in APP/PS1 mice, with increased Aβ deposition, microglial overactivation and neuroinflammation in brain. Moreover, the intestinal homeostasis of AD mice was altered by periodontitis, including affecting gut microbiota composition, causing colon inflammation and destroyed intestinal epithelial barrier. Furthermore, AD mice that underwent fecal transplantation from mice with periodontitis exhibited worsened AD progression and disrupted intestinal homeostasis. It also impaired intestinal barrier function, elevated peripheral inflammation, damaged blood-brain barrier (BBB) and caused neuroinflammation and synapses impairment. Taken together, the current study demonstrated that periodontitis could disrupt intestinal homeostasis to exacerbate AD progression potential via causing gut microbial dysbiosis, intestinal inflammation and intestinal barrier impairment to induce peripheral inflammation and damage BBB, ultimately leading to neuroinflammation and synapse impairment. It underscores the importance of maintaining both periodontal health and intestinal homeostasis to reduce the risk of AD.

Optogenetic targeting of cortical astrocytes selectively improves NREM sleep in an Alzheimer’s disease mouse model

Alzheimer’s disease (AD) is a progressive neurodegenerative condition marked by memory impairments and distinct histopathological features such as amyloid-beta (Aβ) accumulations. Alzheimer’s patients experience sleep disturbances at early stages of the disease. APPswe/PS1dE9 (APP) mice exhibit sleep disruptions, including reductions in non-rapid eye movement (NREM) sleep, that contribute to their disease progression. In addition, astrocytic calcium transients associated with a sleep-dependent brain rhythm, slow oscillations prevalent during NREM sleep, are disrupted in APP mice. However, at present it is unclear whether restoration of circuit function by targeting astrocytic activity could improve sleep in APP mice. To that end, APP mice expressing channelrhodopsin-2 (ChR2) targeted to astrocytes underwent optogenetic stimulation at the slow oscillation frequency. Optogenetic stimulation of astrocytes significantly increased NREM sleep duration but not duration of rapid eye movement (REM) sleep. Optogenetic treatment increased delta power and reduced sleep fragmentation in APP mice. Thus, optogenetic activation of astrocytes increased sleep quantity and improved sleep quality in an AD mouse model. Astrocytic activity provides a novel therapeutic avenue to pursue for enhancing sleep and slowing AD progression.

Encapsulated lactiplantibacillus plantarum improves Alzheimer’s symptoms in APP/PS1 mice

BackgroundAlzheimer’s disease (AD) is a neurodegenerative disorder that can result in neurotoxicity and an imbalance in gut microbiota. Probiotics have been shown to play an important role in regulating the gut microbiota, but their viability and bioactivity are often compromised as they traverse the gastrointestinal tract, thereby reducing their efficacy and limiting their clinical utility.ResultsIn this work, layer-by-layer (LbL) encapsulation technology was used to encapsulate Lactiplantibacillus plantarum (LP) to improve the above shortcomings. Studies in APPswe/PS1dE9 (APP/PS1) transgenic mice show that LbL-encapsulated LP ((CS/SP)2-LP) protects LP from gastrointestinal damage while (CS/SP)2-LP treatment It improves brain neuroinflammation and neuronal damage in AD mice, reduces Aβ deposition, improves tau protein phosphorylation levels, and restores intestinal barrier damage in AD mice. In addition, post-synaptic density protein 95 (PSD-95) expression increased in AD mice after treatment, indicating enhanced synaptic plasticity. Fecal metabolomic and microbiological analyzes showed that the disordered intestinal microbiota composition of AD mice was restored and short-chain fatty acids (SCFAs) levels were significantly increased after (CS/SP)2-LP treatment.ConclusionOverall, the above evidence suggests that (CS/SP)2-LP can improve AD symptoms by restoring the balance of intestinal microbiota, and (CS/SP)2-LP treatment will provide a new method to improve the symptoms of AD patients.

Gut microbiota and inflammation analyses reveal the protective effect of medium-chain triglycerides combined with docosahexaenoic acid on cognitive function in APP/PS1 and SAMP8 mice

Accumulating evidence has demonstrated that medium-chain triglycerides (MCTs) and docosahexaenoic acid (DHA) positively affect cognitive function. However, it remains unclear whether the improvement is related to the alterations of gut microbiota and inflammation and the impact of the combined intervention. In this study, we hypothesized that the supplementation of MCTs combined with DHA could modulate gut microbiota, inflammation, and improve cognitive function in APPswe/PS1De9 (APP/PS1) model mice and senescence-accelerated mouse prone-8 (SAMP8), which are two different mouse models used in neurodegeneration research. The mice were divided into four groups: Control group, MCTs group, DHA group and MCTs+DHA group. The study assessed cognitive function, inflammatory cytokines, and gut microbiota composition. The results showed that supplementation of MCTs+DHA improved spatial learning ability, memory capacity, exploratory behavior; decreased the relative abundance of Proteobacteria; reduced the ratio of Firmicutes/Bacteroidetes (F/B); decreased the concentrations of serum interleukin (IL)-2, IL-6, monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), while increasing the concentration of IL-10. Furthermore, supplementation with MCTs+DHA exhibited significantly superior effects compared to MCTs or DHA alone in reducing inflammation, optimizing gut microbiota composition, and improving cognitive function. In conclusion, supplementation with MCTs+DHA improved cognition function, accompanied with favorable alterations in gut microbiota and inflammation in APP/PS1 and SAMP8 mice.

BOK-engaged mitophagy alleviates neuropathology in Alzheimer's disease.

Mitochondrial malfunction associated with impaired mitochondrial quality control and self-renewal machinery, known as mitophagy, is an under-appreciated mechanism precipitating synaptic loss and cognitive impairments in Alzheimer's disease (AD). Promoting mitophagy has been shown to improve cognitive function in AD animals. However, the regulatory mechanism was unclear, which formed the aim of this study. Here, we found that a neuron-specific loss of Bcl-2 family member BOK in AD patients and APPswe/PS1dE9 (APP/PS1) mice is closely associated with mitochondrial damage and mitophagy defects. We further revealed that BOK is the key to the Parkin-mediated mitophagy through competitive binding to the MCL1/Parkin complex, resulting in Parkin release and translocation to damaged mitochondria to initiate mitophagy. Furthermore, overexpressing bok in hippocampal neurons of APP/PS1 mice alleviated mitophagy and mitochondrial malfunction, resulting in improved cognitive function. Conversely, the knockdown of bok worsened the aforementioned AD-related changes. Our findings uncover a novel mechanism of BOK signaling through regulating Parkin-mediated mitophagy to mitigate amyloid pathology, mitochondrial and synaptic malfunctions, and cognitive decline in AD, thus representing a promising therapeutic target.

Qifu-yin activates the Keap1/Nrf2/ARE signaling and ameliorates synaptic injury and oxidative stress in APP/PS1 mice

Ethnopharmacological relevanceThe traditional medicinal formulation, Qifu-yin (QFY), has been widely prescribed for Alzheimer's disease (AD) treatment in China, yet the comprehensive mechanisms through which QFY mitigates AD pathology remain to be fully delineated. Aim of the studyThis study aimed to explore the therapeutic implications of QFY on the synaptic injury and oxidative stress in the hippocampus of APPswe/PS1dE9 (APP/PS1) mice, with a concerted effort to elucidate the molecular mechanisms related to synaptic preservation and memory improvement. Materials and methodsThe components of QFY were identified by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The neuroprotective effects of QFY was evaluated using six-month-old male APP/PS1 mice. Subsequent to a 15 days of QFY regimen, spatial memory was assessed utilizing the Morris water maze (MWM) test. Amyloid-beta (Aβ) aggregation was detected via immunostaining, while the quantification of Aβ1-40 and Aβ1-42 was achieved through enzyme-linked immunosorbent assay (ELISA). Transmission electron microscopy (TEM) was used to investigate the synaptic structure and mitochondrial morphology. Golgi staining was applied to examine dendritic spine density. Reactive oxygen species (ROS), 3-nitrotyrosine (3-NT) and 4-hydroxy-nonenal (4-HNE) assays were employed to assess oxidative stress. The expression profiles of Aβ metabolism-associated enzymes and the Keap1/Nrf2/ARE signaling pathway were determined by Western blot. ResultsA total of 20 principal compounds in QFY were identified. QFY mitigated memory deficits of APP/PS1 mice, including reducing escape latency and search distance and increasing the time and distance spent in the target quadrant. In addition, QFY increased platform crossings of APP/PS1 mice in the probe trial of MWM tests. TEM analysis showed that QFY increased synapse number in the CA1 region of APP/PS1 mice. Further studies indicated that QFY elevated the expression levels of Post synaptic density protein 95 (PSD95) and synaptophysin, and mitigated the loss of dendritic spine density in the hippocampus of APP/PS1 mice. QFY has been shown to ameliorated the structural abnormalities of mitochondria, including mitochondrial dissolution and degradation, up-regulate ATP synthesis and membrane potential in the hippocampus of APP/PS1 mice. Moreover, QFY activated the Keap1/Nrf2/ARE signaling pathway in the hippocampus of APP/PS1 mice, which might contribute to the neuroprotective effects of QFY. ConclusionQFY activates the Keap1/Nrf2/ARE signaling, and protects against synaptic and mitochondrial dysfunction in APP/PS1 mice, proposing a potential alternative therapeutic strategy for AD management.

Loss of Cholinergic and Monoaminergic Afferents in APPswe/PS1ΔE9 Transgenic Mouse Model of Cerebral Amyloidosis Preferentially Occurs Near Amyloid Plaques.

Alzheimer's disease (AD) is characterized by a loss of neurons in the cortex and subcortical regions. Previously, we showed that the progressive degeneration of subcortical monoaminergic (MAergic) neurons seen in human AD is recapitulated in the APPswe/PS1ΔE9 (APP/PS) transgenic mouse model. Because degeneration of cholinergic (Ach) neurons is also a prominent feature of AD, we examined the integrity of the Ach system in the APP/PS model. The overall density of Ach fibers is reduced in APP/PS1 mice at 12 and 18 months of age but not at 4 months of age. Analysis of basal forebrain Ach neurons shows no loss of Ach neurons in the APP/PS model. Thus, since MAergic systems show overt cell loss at 18 months of age, the Ach system is less vulnerable to neurodegeneration in the APP/PS1 model. We also examined whether the proximity to Aβ deposition affected the degeneration of Ach and 5-HT afferents. We found that the areas closer to the edges of compact Aβ deposits exhibit a more severe loss of afferents than the areas that are more distal to Aβ deposits. Collectively, the results indicate that the APP/PS model recapitulates the degeneration of multiple subcortical neurotransmitter systems, including the Ach system. In addition, the results indicate that Aβ deposits cause global as well as local toxicity to subcortical afferents.

Early amyloid-induced changes in microglia gene expression in male APP/PS1 mice.

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia, characterized by deposition of extracellular amyloid-beta (Aβ) aggregates and intraneuronal hyperphosphorylated Tau. Many AD risk genes, identified in genome-wide association studies (GWAS), are expressed in microglia, the innate immune cells of the central nervous system. Specific subtypes of microglia emerged in relation to AD pathology, such as disease-associated microglia (DAMs), which increased in number with age in amyloid mouse models and in human AD cases. However, the initial transcriptional changes in these microglia in response to amyloid are still unknown. Here, to determine early changes in microglia gene expression, hippocampal microglia from male APPswe/PS1dE9 (APP/PS1) mice and wild-type littermates were isolated and analyzed by RNA sequencing (RNA-seq). By bulk RNA-seq, transcriptomic changes were detected in hippocampal microglia from 6-months-old APP/PS1 mice. By performing single-cell RNA-seq of CD11c-positive and negative microglia from 6-months-old APP/PS1 mice and analysis of the transcriptional trajectory from homeostatic to CD11c-positive microglia, we identified a set of genes that potentially reflect the initial response of microglia to Aβ.

IL-17A promotes the progression of Alzheimer’s disease in APP/PS1 mice

BackgroundAlzheimer’s disease (AD), which is the most common cause of dementia in elderly individuals, is a progressive neurodegenerative disorder. Neuroinflammation, which is an immune response that is activated by glial cells in the central nervous system, plays an important role in neurodegenerative diseases. Many studies have shown that interleukin-17A (IL-17A) plays an important role in AD, but research on the pathological effects of IL-17A on AD is limited.MethodsWe report the effect of IL-17A on AD progression in APPswe/PS1dE9 (APP/PS1) mice, which are the most widely used AD model mice. The BV2 cell line, which is a microglial cell line derived from C57/BL6 mice, was used to establish a cell model to verify the role of IL-17A in neuroinflammation at the cellular level. The HT22 hippocampal neuronal cell line was used to investigate the relationship between IL-17A and Aβ deposition.ResultsIn this research, we found that IL-17A promotes the progression of AD in the APP/PS1 mouse model. The role of IL-17A in neuroinflammation is related to tumour necrosis factor (TNF)-α. Circulating IL-17A stimulates the secretion of TNF-α by microglia through the Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signalling pathway, thus exacerbating neuroinflammation. In addition, intraperitoneal injection of IL-17A antibody (IL17Ab) significantly improved the cognitive function of APP/PS1 mice.ConclusionsIL-17A increased TNF-α levels in the brain and exacerbated neuroinflammation through the TLR4/NF-κB signalling pathway and microglial activation in APP/PS1 mice. Moreover, IL-17A promoted the progression of AD by enhancing neuroinflammation, inhibiting microglial phagocytosis, and promoting the deposition of β-amyloid 42 in AD model mice.

MiR‐431 attenuates synaptic plasticity and memory deficits in APPswe/PS1dE9 mice

AbstractBackgroundSynaptic plasticity impairment plays a critical role in the pathogenesis of Alzheimer’s disease (AD), and emerging evidence has shown that microRNAs (miRNAs) are alternative biomarkers and therapeutic targets for synaptic dysfunctions in AD. Our previous miRNA assay data have shown that miR‐431 is downregulated in the hippocampus of APPswe/PS1dE9 (APP/PS1) mice. However, the potential role of miR‐431 in AD has not been fully defined.MethodLv‐miR‐431 (1×109 TU/ml, 2 µl), Lv‐Smad4 (1×109 TU/ml, 2 µl) or AAV‐sh‐Smad4 (5×1012 GC/ml, 200 nl) was slowly injected into the bilateral hippocampus of APP/PS1 mice. The behavioral or electrophysiological tests were performed 1 month following the injection, and the mice were then sacrificed for other experiments. QRT‐PCR was used to detect the expression of miR‐431 in plasma and hippocampus. Golgi staining and electron microscopy were performed to evaluate the synaptic structure. Western blot was employed to test the levels of synaptic associated proteins. Immunofluorescence staining and ELISA were utilized to assess hippocampal Aβ levels. Cut&Tag assay and ChIP were used to explore and confirm the potential targets of Smad4.ResultThe level of miR‐431 was downregulated in the plasma of amnestic mild cognitive impairment (aMCI) and AD patients, and it was also decreased in the hippocampus and plasma of APP/PS1 mice. MiR‐431 overexpression in the hippocampus ameliorated synaptic plasticity and memory deficits of APP/PS1 mice, while it didn’t affect the Aβ levels. Smad4 was identified as a target of miR‐431, and Smad4 overexpression reversed the protective effects of miR‐431 in APP/PS1 mice. Furthermore, Smad4 knockdown modulated the expression of synaptic proteins including SAP102, and protected against synaptic plasticity and memory dysfunctions in APP/PS1 mice.ConclusionMiR‐431 attenuates synaptic impairment at least partially by Smad4 inhibition and miR‐431/Smad4 may be a potential therapeutic target for AD treatment.

Memory interference in APPswe/PS1dE9 mice: Role of astrocytic β‐adrenoreceptors

AbstractBackgroundPrevious studies have reported that long‐term β‐adrenoceptor (β‐AR) agonist, isoproterenol hydrochloride (IPE), treatment brings about beneficial effects in an induced model of Alzheimer’s disease (AD) by neutralizing microglial inflammatory morphology against soluble amyloid β oligomers (PMID: 30093491). However, we do not have a clear understanding of how such treatment impacts astrocyte morphology, and whether that afford beneficial effects. Introducing a proactive memory interference step to the classical novel object recognition (NOR) paradigm impairs long‐term memory formation in 2‐month‐old familial model of AD ‐ APPswe/PS1dE9 (APP/PS1) mice. Long‐term IPE treatment rescued long‐term memory. In this study we attempt to understand the impact of long‐term IPE treatment on astrocyte morphology, and how they bring about the reversal in cognitive deficits.Method(1) Mice were taken through a proactive interference step in which they were exposed to objects of varied shape, size and colour before taking them through NOR paradigm. (2) Mice were treated with β‐AR agonist IPE at P26 (0.05g/litre) in drinking water for 21 days till P47. (3) They were sacrificed at 2‐months of age by transcardial perfusion and 100µm coronal sections of hippocampus were stained with astrocytic markers GFAP and S100β by immunohistochemistry. The number and morphology of astrocytes were analysed using ImageJ, SMorph (PMID: 34137444) and Imaris software.ResultOur observations suggest that NOR memory is intact in 2‐month‐old APP/PS1. However, introducing an object‐based short‐term interference before NOR leads to recognition memory deficits in APP/PS1 but not in wild‐type mice. Treatment with IPE restored long‐term memory of APP/PS1 mice to normal levels, thereby protecting them from the effects of interference during the NOR task. Our preliminary findings indicate that IPE impacts the morphology of astrocytes and thus contribute to the reversal of recognition deficits in APP/PS1 at 2 months of age.Conclusionβ‐AR activation can bring about morphological changes in astrocytes that in turn can modulate memory representations.

Early locus coeruleus degeneration impairs the longevity of fear memory in APPswe/PS1dE9 mice

AbstractBackgroundThe locus coeruleus (LC), a brainstem noradrenergic nucleus is known to modulate cognitive functions and behaviour. LC is one the first sites of appearance of misfolded tau protein which later develops into neurofibrillary tangles. Hyperphosphorylated tau and amyloid β are best protein correlates of cognitive decline in Alzheimer’s disease (AD). In early onset AD, subtle cognitive deficits develop <25 years before the patients develop dementia. Loss of LC neurons and its innervation has been found to be significantly associated with behavioural deficits observed during prodromal stage of AD. However, the extent and consequences of LC‐noradrenergic system degeneration during early stages of AD pathogenesis are still under investigation.MethodTo address this question, we have performed contextual fear conditioning (cFC) behavioural task to test fear memory in 2‐month‐old APPswe/PS1dE9 (APP/PS1) mice, a transgenic amyloidogenic model of AD. We further investigated the status of LC terminals and the distribution of β‐adrenoceptors (β‐AR) in the hippocampus using dopamine‐β‐hydroxylase (DBH), tyrosine hydroxylase (TH), and β‐AR immunohistochemistry respectively. Finally, we checked if stereotaxic delivery of β‐AR agonist to the hippocampus could rescue the impairments in long‐term fear memory.ResultOur study demonstrates that 2‐month‐old male but not female APP/PS1 mice exhibit impaired long‐term fear memory in cFC task. Immunohistochemical analysis of DBH and TH positive nerve terminals revealed loss of noradrenergic and dopaminergic terminals in male but not female APP/PS1 mice hippocampus. Further, male APP/PS1 mice were found to have low levels of β‐AR in the hippocampus and intra‐hippocampal administration of isoproterenol hydrochloride, a β‐AR agonist, immediately before cFC could restore long‐term contextual fear memory.ConclusionLC‐noradrenergic system degeneration displayed an inherent sex‐specific difference on longevity of fear memory with deficits occurring only in male APP/PS1 mice during early stages of AD.

Activation of Wnt/β‐catenin pathway in the brain endothelium mitigates Aβ‐induced blood‐brain barrier dysfunction in Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease (AD) is the leading cause of age‐related neurological and cognitive decline. As the mechanisms of this disease are yet to be fully understood, the treatments for AD pose a significant challenge. Dysfunction of the blood‐brain barrier (BBB) is increasingly recognized as a major contributor to the pathophysiology of AD, especially at the early stages of the disease. However, underlying mechanisms remain poorly characterized, while few molecules can directly target and improve BBB function in the context of AD.MethodHere using both AD patients and APPswe/PS1dE9 (APP/PS1) mouse model of AD, BBB damage and the underlying molecular mechanism were examined.Resultwe showed dysfunctional BBB in AD patients indicated by perivascular accumulation of blood‐derived fibrinogen in the hippocampus and cortex, accompanied by decreased tight junction proteins Claudin‐5 and glucose transporter Glut‐1 in the brain endothelial cells (BECs). In the APP/PS1 mice, BBB dysfunction started at 4 months and became severe at 9 months. In the cerebral microvessels of APP/PS1 mice and Aβ‐treated BECs, we found suppressed Wnt/β‐catenin pathway triggered by an increase of GSK3β activation, but not an inhibition of the AKT pathway or switch to the Wnt/planar cell polarity pathway. Furthermore, using our newly developed optogenetic tool for controlled regulation of LRP6 (upstream regulator of the Wnt signaling) to activate Wnt/β‐catenin pathway, Aβ‐inhibited BBB function was restored by promoting the barrier repair and preventing Aβ‐induced BEC impairments.ConclusionTargeting LRP6 in the Wnt/β‐catenin pathway in the brain endothelium can alleviate BBB dysfunction induced by Aβ, which may be a potential treatment strategy for AD.

Correction of mTORC1‐mediated brain protein synthesis rescues memory in mouse models of Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease (AD) is a neurodegenerative disorder characterized by synapse failure and cognitive decline. Brain mRNA translation is central to synaptic plasticity and cognition, and converging evidence indicates it is impaired in AD. The mammalian target of rapamycin complex 1 (mTORC1) pathway plays a key role in regulating protein synthesis, and mTORC1 signaling has received considerable attention in AD research. In this current work, we investigated whether stimulating mTORC1‐mediated protein synthesis can alleviate the impairments in synaptic plasticity and memory in AD mice.MethodTo address this question, we used two different approaches: 1. genetic reduction of the translational repressors, Fragile X messenger ribonucleoprotein (FMRP) or eukaryotic initiation factor 4E (eIF4E)‐binding protein 2 (4E‐BP2); and 2. pharmacological treatment with (2R,6R)‐hydroxynorketamine (HNK), an active metabolite of the antidepressant ketamine that stimulates mTORC1 signaling.ResultOur results showed that genetic reduction of FMRP and 4E‐BP2 prevented the inhibition of hippocampal protein synthesis and memory impairment induced by amyloid‐β oligomers (AβOs) in mice. Reduction of 4E‐BP2 further rescued memory deficits in the APPswe/PS1dE9 (APP/PS1) transgenic mouse model of AD. Moreover, HNK treatment prevented deficits in long‐term potentiation (LTP) and fear memory in AbO‐infused and APP/PS1 mice.ConclusionTaken together, our findings indicate that strategies targeting mRNA translation correct hippocampal protein synthesis, synaptic plasticity and memory deficits in AD models, and raise the prospect that HNK could emerge as a therapeutic approach in AD.

Sleep restoration by optogenetic targeting of GABAergic neurons reprograms microglia and ameliorates pathological phenotypes in an Alzheimer’s disease model

BackgroundAlzheimer’s disease (AD) patients exhibit memory disruptions and profound sleep disturbances, including disruption of deep non-rapid eye movement (NREM) sleep. Slow-wave activity (SWA) is a major restorative feature of NREM sleep and is important for memory consolidation.MethodsWe generated a mouse model where GABAergic interneurons could be targeted in the presence of APPswe/PS1dE9 (APP) amyloidosis, APP-GAD-Cre mice. An electroencephalography (EEG) / electromyography (EMG) telemetry system was used to monitor sleep disruptions in these animals. Optogenetic stimulation of GABAergic interneurons in the anterior cortex targeted with channelrhodopsin-2 (ChR2) allowed us to examine the role GABAergic interneurons play in sleep deficits. We also examined the effect of optogenetic stimulation on amyloid plaques, neuronal calcium as well as sleep-dependent memory consolidation. In addition, microglial morphological features and functions were assessed using confocal microscopy and flow cytometry. Finally, we performed sleep deprivation during optogenetic stimulation to investigate whether sleep restoration was necessary to slow AD progression.ResultsAPP-GAD-Cre mice exhibited impairments in sleep architecture including decreased time spent in NREM sleep, decreased delta power, and increased sleep fragmentation compared to nontransgenic (NTG) NTG-GAD-Cre mice. Optogenetic stimulation of cortical GABAergic interneurons increased SWA and rescued sleep impairments in APP-GAD-Cre animals. Furthermore, it slowed AD progression by reducing amyloid deposition, normalizing neuronal calcium homeostasis, and improving memory function. These changes were accompanied by increased numbers and a morphological transformation of microglia, elevated phagocytic marker expression, and enhanced amyloid β (Aβ) phagocytic activity of microglia. Sleep was necessary for amelioration of pathophysiological phenotypes in APP-GAD-Cre mice.ConclusionsIn summary, our study shows that optogenetic targeting of GABAergic interneurons rescues sleep, which then ameliorates neuropathological as well as behavioral deficits by increasing clearance of Aβ by microglia in an AD mouse model.

Omaveloxolone ameliorates cognitive dysfunction in APP/PS1 mice by stabilizing the STAT3 pathway

AimsTo determine the availability and the potential molecular mechanisms underlying the therapeutic effect of omaveloxolone (RTA408) on Alzheimer's Disease (AD). Materials and methodsThis study employed network pharmacology to assess the feasibility of drug treatment of AD. To determine the cognitive status and emotional state of APPswe/PS1dE9 (APP/PS1) mice after the RTA408 treatment, three classical behavioral experiments (water maze, Y-maze, and open field test) were conducted. Immunofluorescence and immunohistochemical staining were utilized to evaluate hippocampal neuronal status and amyloid (Aβ) deposition in mice. RNA-seq and transcription factor prediction analyses were performed to explore the potential molecular mechanisms regulating the therapeutic effects of RTA408. Molecular docking was employed to predict the direct drug targets. To validate these molecular mechanisms, quantitative reverse transcription PCR (qRT-PCR), Western blotting, and immunofluorescence analyses were performed in two instrumental cell lines, i.e., mouse hippocampal neuronal cells (HT22) and microglia (BV2). ResultsRTA408 was revealed with the capability to reduce Aβ plaque deposition and to restore damaged neurons in the hippocampal region of APP/PS1 mice, ultimately leading to an improvement in cognitive function. This beneficial effect was achieved by balancing the STAT3 pathway. Specifically, RTA408 facilitated the activations of both STAT3/OXR1 and NRF2/ARE axes, thereby enhancing the compromised resistance in neurons to oxidative stress. RTA408 inhibited the NFκB/IL6/STAT3 pathway, effectively countering the neuroinflammation triggered by microglial activation. ConclusionRTA408 is revealed with promising potential in the treatment of AD based on preclinical data.

Magnetic resonance spectroscopy in the hippocampus of adult APP/PS1 mice following chronic vitamin D deficiency

Vitamin D (VitD) deficiency can exacerbate AD progression and may cause changes in brain metabolite levels that can be detected by magnetic resonance spectroscopy (MRS). The purpose of this study was to determine whether chronic VitD deficiency in an AD mouse model caused persistent metabolite levels changes in the hippocampus associated with memory performance. Six-month-old APPSwe/PS1ΔE9 (APP/PS1) mice (N = 14 mice/group) were fed either a VitD deficient (VitD-) diet or a control diet. Metabolite level changes in the hippocampus were evaluated by 1H MRS using a 9.4 T MRI. Ventricle volume was assessed by imaging and spatial memory was evaluated using the Barnes maze. All measurements were made at 6, 9, 12, and 15 months of age. At 15 months of age, amyloid plaque load and astrocyte number were evaluated histologically (N = 4 mice/group). Levels of N-acetyl aspartate and creatine were lower in VitD- mice compared to control diet mice at 12 months of age. VitD deficiency did not change ventricle volume. Lactate levels increased over time in VitD- mice and increases from 12 to 15 months were negatively correlated with changes in primary latency to the target hole in the Barns Maze. VitD- mice showed improved spatial memory performance compared to control diet mice. VitD- mice also had more astrocytes in the cortex and hippocampus at 15 months than control diet mice. This study suggests that severe VitD deficiency in APP/PS1 mice may lead to compensatory changes in metabolite and astrocyte levels that contribute to improved performance on spatial memory tasks.

Mettl1-mediated internal m7G methylation of Sptbn2 mRNA elicits neurogenesis and anti-alzheimer’s disease

BackgroundN7-methylguanosine (m7G) is one of the most conserved modifications in nucleosides impacting mRNA export, splicing, and translation. However, the precise function and molecular mechanism of internal mRNA m7G methylation in adult hippocampal neurogenesis and neurogenesis-related Alzheimer’s disease (AD) remain unknown.ResultsWe profiled the dynamic Mettl1/Wdr4 expressions and m7G modification during neuronal differentiation of neural stem cells (NSCs) in vitro and in vivo. Adult hippocampal neurogenesis and its molecular mechanisms were examined by morphology, biochemical methods and biological sequencing. The translation efficiency of mRNA was detected by polysome profiling. The stability of Sptbn2 mRNA was constructed by RNA stability assay. APPswe/PS1ΔE9 (APP/PS1) double transgenic mice were used as model of AD. Morris water maze was used to detect the cognitive function.MethodsWe found that m7G methyltransferase complex Mettl1/Wdr4 as well as m7G was significantly elevated in neurons. Functionally, silencing Mettl1 in neural stem cells (NSCs) markedly decreased m7G modification, neuronal genesis and proliferation in addition to increasing gliogenesis, while forced expression of Mettl1 facilitated neuronal differentiation and proliferation. Mechanistically, the m7G modification of Sptbn2 mRNA by Mettl1 enhanced its stability and translation, which promoted neurogenesis. Importantly, genetic defciency of Mettl1 reduced hippocampal neurogenesis and spatial memory in the adult mice. Furthermore, Mettl1 overexpression in the hippocampus of APP/PS1 mice rescued neurogenesis and behavioral defects.ConclusionOur findings unravel the pivotal role of internal mRNA m7G modification in Sptbn2-mediated neurogenesis, and highlight Mettl3 regulation of neurogenesis as a novel therapeutic target in AD treatment.

Ligustilide-loaded liposome ameliorates mitochondrial impairments and improves cognitive function via the PKA/AKAP1 signaling pathway in a mouse model of Alzheimer's disease.

Oxidative stress is an early event in the development of Alzheimer's disease (AD) and maybe a pivotal point of interaction governing AD pathogenesis; oxidative stress contributes to metabolism imbalance, protein misfolding, neuroinflammation and apoptosis. Excess reactive oxygen species (ROS) are a major contributor to oxidative stress. As vital sources of ROS, mitochondria are also the primary targets of ROS attack. Seeking effective avenues to reduce oxidative stress has attracted increasing attention for AD intervention. We developed liposome-packaged Ligustilide (LIG) and investigated its effects on mitochondrial function and AD-like pathology in the APPswe/PS1dE9 (APP/PS1) mouse model of AD, and analyzed possible mechanisms. We observed that LIG-loaded liposome (LIG-LPs) treatment reduced oxidative stress and β-amyloid (Aβ) deposition and mitigated cognitive impairment in APP/PS1 mice. LIG management alleviated the destruction of the inner structure in the hippocampal mitochondria and ameliorated the imbalance between mitochondrial fission and fusion in the APP/PS1 mouse brain. We showed that the decline in cAMP-dependent protein kinase A (PKA) and A-kinase anchor protein 1 for PKA (AKAP1) was associated with oxidative stress and AD-like pathology. We confirmed that LIG-mediated antioxidant properties and neuroprotection were involved in upregulating the PKA/AKAP1 signaling in APPswe cells in vitro. Liposome packaging for LIG is relatively biosafe and can overcome the instability of LIG. LIG alleviates mitochondrial dysfunctions and cognitive impairment via the PKA/AKAP1 signaling pathway. Our results provide experimental evidence that LIG-LPs may be a promising agent for AD therapy.