Microglial malfunction: the third rail in the development of Alzheimer's disease

Trait-anxiety and glial-related neuroinflammation of the amygdala and its associated regions in Alzheimer's disease: A significant correlation

Background

Positron emission tomography, which assesses the binding of translocator protein radiotracers, 11C-DPA-713, may be a sensitive method for determining glial-mediated neuroinflammation levels. This study investigated the relationship between regional 11C-DPA713 binding potential (BPND) and anxiety in patients with Alzheimer's disease (AD) continuum.

Methods

Nineteen patients with AD continuum determined to be amyloid-/p-tau 181-positive via cerebrospinal fluid analysis were included in this cross-sectional study (mild cognitive impairment [MCI, n = 5] and AD [n = 14]). Anxiety was evaluated using the State-Trait Anxiety Inventory (STAI). A whole-brain voxel-based analysis was performed to examine the relationship between 11C-DPA-713-BPND values at each voxel and the STAI score. Stepwise multiple regression analysis was performed to determine the predictors of STAI scores using independent variables, including 11C-DPA-713-BPND values within significant clusters. 11C-DPA-713-BPND values were compared between patients with AD continuum with low-to-moderate and high STAI scores.

Results

Voxel-based analysis revealed a positive correlation between trait anxiety severity and 11C-DPA713-BPND values in the centromedial amygdala and the left inferior occipital area [P < 0.001 (uncorrected) at the voxel-level]. 11C-DPA713-BPND values in these regions were a strong predictor of the STAI trait anxiety score. Specifically, patients with AD continuum and high trait anxiety had increased 11C-DPA713-BPND values in these regions.

Conclusions

The amygdala-occipital lobe circuit influences the control of emotional generation, and disruption of this network by AD pathology-induced inflammation may contribute to the expression of anxiety. Our findings suggest that suppression of inflammation can help effectively treat anxiety by attenuating damage to the amygdala and its associated areas.

Single-cell biclustering for cell-specific transcriptomic perturbation detection in AD progression

The pathogenesis of Alzheimer disease (AD) involves complex gene regulatory changes across different cell types. To help decipher this complexity, we introduce single-cell Bayesian biclustering (scBC), a framework for identifying cell-specific gene network biomarkers in scRNA and snRNA-seq data. Through biclustering, scBC enables the analysis of perturbations in functional gene modules at the single-cell level. Applying the scBC framework to AD snRNA-seq data reveals the perturbations within gene modules across distinct cell groups and sheds light on gene-cell correlations during AD progression. Notably, our method helps to overcome common challenges in single-cell data analysis, including batch effects and dropout events. Incorporating prior knowledge further enables the framework to yield more biologically interpretable results. Comparative analyses on simulated and real-world datasets demonstrate the precision and robustness of our approach compared to other state-of-the-art biclustering methods. scBC holds potential for unraveling the mechanisms underlying polygenic diseases characterized by intricate gene coexpression patterns.

Erythrocyte membrane-coated nanocarriers modified by TGN for Alzheimer's disease

Alzheimer's disease (AD) is an aging-related neurodegenerative disease, and the main pathological feature was β-amyloid protein (Aβ) deposition. Recently, bioactive materials-based drug delivery system has been widely investigated for the treatment of AD. In this study, we developed a red blood cells (RBC) membrane-coated polycaprolactone (PCL) nanoparticles (NPs) loading with a therapeutic agent for AD, curcumin (Cur). A functional peptide TGNYKALHPHN (TGN) was conjugated to the surface of membrane for blood-brain barrier (BBB) transport (TGN-RBC-NPs-Cur). TGN peptide can be recognized by receptors on the BBB and has great potential for brain transport. To confirm the targeted delivery of Cur to the brain, a cell co-culturing immortalized human cerebral microvascular endothelial cells and human brain astrocytes glioblastoma (hCMEC/D3 and U-118MG) in vitro model was established. As a result, the BBB transporting ratio of TGN-RBC-NPs-FITC was 29.64% at 12 h which was approximately eight-fold than RBC-NPs-FITC. The improvement of drug accumulation in the AD lesion was confirmed by the NPs modified with the BBB-penetrating peptide in the fluorescence imaging and quantitative analysis with UPLC-MS/MS in vivo. The neuroprotective effects were evaluated with new object recognition behavioral test, in vitro AD cell model, dendritic spine stain, GFAP and IBA1 immunofluorescence stain. The spatial learning and memory abilities of the AD model mice treated with TGN-RBC-NPs-Cur were obviously enhanced compared with the AD control mice and were also better than Cur at the same dosage. These results were consistent with the values of protection index of rat adrenal pheochromocytoma cells (PC12 cells) treated by Aβ25-35. TGN-RBC-NPs-Cur increased the dendritic segments densities and restrained activation of microglia and astrocytes of AD mice, as well as reversed cognitive function of AD mice. All of the results demonstrated TGN-RBC-NPs-Cur a promising therapeutic strategy for delaying the progression of AD by designing biomimetic nanosystems to deliver drugs into the brain.

Integrating TSPO PET imaging and transcriptomics to unveil the role of neuroinflammation and amyloid-β deposition in Alzheimer's disease

PURPOSE

Despite the revealed role of immunological dysfunctions in the development and progression of Alzheimer's disease (AD) through animal and postmortem investigations, direct evidence regarding the impact of genetic factors on microglia response and amyloid-β (Aβ) deposition in AD individuals is lacking. This study aims to elucidate this mechanism by integrating transcriptomics and TSPO, Aβ PET imaging in clinical AD cohort.

METHODS

We analyzed 85 patients with PET/MR imaging for microglial activation (TSPO, [18F]DPA-714) and Aβ ([18F]AV-45) within the prospective Alzheimer's Disease Immunization and Microbiota Initiative Study Cohort (ADIMIC). Immune-related differentially expressed genes (IREDGs), identified based on AlzData, were screened and verified using blood samples from ADIMIC. Correlation and mediation analyses were applied to investigate the relationships between immune-related genes expression, TSPO and Aβ PET imaging.

RESULTS

TSPO uptake increased significantly both in aMCI (P < 0.05) and AD participants (P < 0.01) and showed a positive correlation with Aβ deposition (r = 0.42, P < 0.001). Decreased expression of TGFBR3, FABP3, CXCR4 and CD200 was observed in AD group. CD200 expression was significantly negatively associated with TSPO PET uptake (r =-0.33, P = 0.013). Mediation analysis indicated that CD200 acted as a significant mediator between TSPO uptake and Aβ deposition (total effect B = 1.92, P = 0.004) and MMSE score (total effect B =-54.01, P = 0.003).

CONCLUSION

By integrating transcriptomics and TSPO PET imaging in the same clinical AD cohort, this study revealed CD200 played an important role in regulating neuroinflammation, Aβ deposition and cognitive dysfunction.

Interactions of Cellular Energetic Gene Clusters in the Alzheimer's Mouse Brain

Alzheimer's disease (AD) is the most common cause of dementia in the aging population. The pathological characteristics include extracellular senile plaques and intracellular neurofibrillary tangles. In addition, mitochondrial dysfunction, oxidative stress, and neuroinflammation contribute to AD pathogenesis. In this study, we sought to determine the crosstalk between different pathways in the brain of 5XFAD mice, a mouse model for amyloid pathology, by RNA-seq analysis. We observed significant changes in the expression of genes (1288 genes; adj p value < 0.05; log2-fold > 1 and < 1) related to pathways including oxidation-reduction, oxidative phosphorylation, innate immune response, ribosomal protein synthesis, and ubiquitin proteosome system. The most striking feature was the downregulation of genes related to oxidation-reduction process with changes in the expression of a large number of mitochondrial genes. We also observed an upregulation of several immune response genes. Gene interaction network of oxidation-reduction related genes further confirmed a tight cluster of mitochondrial genes. Furthermore, gene interaction analysis of all the 1288 genes showed at least three distinct interaction clusters, with the predominant one relating to cellular energetics. In summary, we identified 1288 genes distinctly different in the 5XFAD brain compared to the WT brain and found cellular energetics to be the most distinct gene cluster in the AD mouse brain.

Extracellular vesicles from hiPSC-NSCs can prevent peripheral inflammation-induced cognitive dysfunction with inflammasome inhibition and improved neurogenesis in the hippocampus

Extracellular vesicles (EVs) released by human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs) are enriched with miRNAs and proteins capable of mediating robust antiinflammatory activity. The lack of tumorigenic and immunogenic properties and ability to permeate the entire brain to incorporate into microglia following intranasal (IN) administrations makes them an attractive biologic for curtailing chronic neuroinflammation in neurodegenerative disorders. We tested the hypothesis that IN administrations of hiPSC-NSC-EVs can alleviate chronic neuroinflammation and cognitive impairments induced by the peripheral lipopolysaccharide (LPS) challenge. Adult male, C57BL/6J mice received intraperitoneal injections of LPS (0.75 mg/kg) for seven consecutive days. Then, the mice received either vehicle (VEH) or hiPSC-NSC-EVs (~ 10 × 109 EVs/administration, thrice over 6 days). A month later, mice in all groups were investigated for cognitive function with behavioral tests and euthanized for histological and biochemical studies. Mice receiving VEH after LPS displayed deficits in associative recognition memory, temporal pattern processing, and pattern separation. Such impairments were associated with an increased incidence of activated microglia presenting NOD-, LRR-, and pyrin domain containing 3 (NLRP3) inflammasomes, elevated levels of NLRP3 inflammasome mediators and end products, and decreased neurogenesis in the hippocampus. In contrast, the various cognitive measures in mice receiving hiPSC-NSC-EVs after LPS were closer to naive mice. Significantly, these mice displayed diminished microglial activation, NLRP3 inflammasomes, proinflammatory cytokines, and a level of neurogenesis matching age-matched naïve controls. Thus, IN administrations of hiPSC-NSC-EVs are an efficacious approach to reducing chronic neuroinflammation-induced cognitive impairments.

Salvianolic acid B exerts protective effects against Aβ-induced neuroinflammation through the inhibition of NLRP3 inflammasome activation and switching of M1/M2 polarization

BACKGROUND

Salvianolic acid B (SalB) is a bioactive extract of Salvia miltiorrhiza with the ability to ameliorate amyloid beta (Aβ)-induced neuronal degeneration and neuroinflammation in Alzheimer's disease (AD). However, the underlying mechanisms of this action have not been elucidated. Herein, we aimed to investigate whether the neuroprotective effect of SalB is attributable to the modulation of microglial polarization and NLRP3 inflammasome-mediated neuroinflammation.

METHODS

Based on the TMT-labeled proteomics analysis, immunofluorescence, western blot and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were employed to investigate the effects of SalB on neuroinflammation in Aβ1-42-stimulated BV2 microglia cells.

RESULTS

At the proteomic level, a total of 6631 proteins were quantified, and of these, 104 were significantly influenced under Aβ1-42 treatment. The expression of 36 Aβ1-42-induced differentially expressed proteins were significantly recovered by SalB treatment (13 upregulated and 23 downregulated). NLRP3 was significantly recovered and was identified as one of the hub proteins. Consistent with the result of the proteomic analysis, western blot and qRT-PCR demonstrated that SalB reduced Aβ1-42-induced NLRP3 upregulation at both the protein and mRNA levels. In addition, SalB significantly blocked M1 microglia polarization, enhanced M2 microglial polarization, and inhibited the production of caspase-1 and interleukin-1β in BV2 microglia cells.

CONCLUSION

our study demonstrated, for the first time, that the anti-inflammatory effects of SalB were mediated by the regulation of NLRP3 activation and promotion of microglial M2 polarization, indicating the potential of SalB as a novel therapeutic candidate for AD.

Network analysis identifies strain-dependent response to tau and tau seeding-associated genes

Previous research demonstrated that genetic heterogeneity is a critical factor in modeling amyloid accumulation and other Alzheimer's disease phenotypes. However, it is unknown what mechanisms underlie these effects of genetic background on modeling tau aggregate-driven pathogenicity. In this study, we induced tau aggregation in wild-derived mice by expressing MAPT. To investigate the effect of genetic background on the action of tau aggregates, we performed RNA sequencing with brains of C57BL/6J, CAST/EiJ, PWK/PhJ, and WSB/EiJ mice (n = 64) and determined core transcriptional signature conserved in all genetic backgrounds and signature unique to wild-derived backgrounds. By measuring tau seeding activity using the cortex, we identified 19 key genes associated with tau seeding and amyloid response. Interestingly, microglial pathways were strongly associated with tau seeding activity in CAST/EiJ and PWK/PhJ backgrounds. Collectively, our study demonstrates that mouse genetic context affects tau-mediated alteration of transcriptome and tau seeding. The gene modules associated with tau seeding provide an important resource to better model tauopathy.

Neuroimaging biomarkers of glial activation for predicting the annual cognitive function decline in patients with Alzheimer's disease

BACKGROUND

Glial activation is central to the pathogenesis of Alzheimer's disease (AD). However, researchers have not demonstrated its relationship to longitudinal cognitive deterioration. We aimed to compare the prognostic effects of baseline positron emission tomography (PET) imaging of glial activation and amyloid/tau pathology on the successive annual cognitive decline in patients with AD.

METHODS

We selected 17 patients diagnosed with mild cognitive impairment or AD. We assessed the annual changes in global cognition and memory. Furthermore, we assessed the predictive effects of baseline amyloid and tau pathology indicated by cerebrospinal fluid (CSF) concentrations and PET imaging of glial activation (11C-DPA-713-binding potential in the area of Braak 1-3 [11C-DPA-713-BPND]) on global cognition and memory using a stepwise regression analysis.

RESULTS

The final multiple regression model of annual changes in global cognition and memory scores included 11C-DPA-713-BPND as the predictor. The CSF Aβ42/40 ratios and p-tau concentrations were removed from the final model. In stepwise Bayesian regression analysis, the Bayes factor-based model comparison suggested that the best model included 11C-DPA-713-BPND as the predictor of decline in global cognition and memory.

CONCLUSIONS

Translocator protein-PET imaging of glial activation is a stronger predictor of AD clinical progression than the amount of amyloid/tau pathology measured using CSF concentrations. Glial activation is the primary cause of tau-induced neuronal toxicity and cognitive deterioration, thereby highlighting the potential of blocking maladaptive microglial responses as a therapeutic strategy for AD treatment.

Emerging roles for ITAM and ITIM receptor signaling in microglial biology and Alzheimer's disease-related amyloidosis

Microglia are critical responders to amyloid beta (Aβ) plaques in Alzheimer's disease (AD). Therefore, the therapeutic targeting of microglia in AD is of high clinical interest. While previous investigation has focused on the innate immune receptors governing microglial functions in response to Aβ plaques, how microglial innate immune responses are regulated is not well understood. Interestingly, many of these microglial innate immune receptors contain unique cytoplasmic motifs, termed immunoreceptor tyrosine-based activating and inhibitory motifs (ITAM/ITIM), that are commonly known to regulate immune activation and inhibition in the periphery. In this review, we summarize the diverse functions employed by microglia in response to Aβ plaques and also discuss the innate immune receptors and intracellular signaling players that guide these functions. Specifically, we focus on the role of ITAM and ITIM signaling cascades in regulating microglia innate immune responses. A better understanding of how microglial innate immune responses are regulated in AD may provide novel therapeutic avenues to tune the microglial innate immune response in AD pathology.

BAC Transgenic Expression of Human TREM2-R47H Remodels Amyloid Plaques but Unable to Reprogram Plaque-associated Microglial Reactivity in 5xFAD Mice

Background

Genetic study of late-onset Alzheimer's disease (AD) reveals that a rare Arginine-to-Histamine mutation at amino acid residue 47 (R47H) in Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) results in increased disease risk. TREM2 plays critical roles in regulating microglial response to amyloid plaques in AD, leading to their clustering and activation surrounding the plaques. We previously showed that increasing human TREM2 gene dosage exerts neuroprotective effects against AD-related deficits in amyloid depositing mouse models of AD. However, the in vivo effects of the R47H mutation on human TREM2-mediated microglial reprogramming and neuroprotection remains poorly understood.

Method

Here we created a BAC transgenic mouse model expressing human TREM2 with the R47H mutation in its cognate genomic context (BAC-TREM2-R47H). Importantly, the BAC used in this study was engineered to delete critical exons of other TREM-like genes on the BAC to prevent confounding effects of overexpressing multiple TREM-like genes. We crossed BAC-TREM2- R47H mice with 5xFAD [1], an amyloid depositing mouse model of AD, to evaluate amyloid pathologies and microglial phenotypes, transcriptomics and in situ expression of key TREM2 -dosage dependent genes. We also compared the key findings in 5xFAD/BAC-TREM2-R47H to those observed in 5xFAD/BAC-TREM2 mice.

Result

Both BAC-TREM2 and BAC-TREM2-R47H showed proper expression of three splicing isoforms of TREM2 that are normally found in human. In 5xFAD background, elevated TREM2-R47H gene dosages significantly reduced the plaque burden, especially the filamentous type. The results were consistent with enhanced phagocytosis and altered NLRP3 inflammasome activation in BAC- TREM2-R47H microglia in vitro. However, unlike TREM2 overexpression, elevated TREM2- R47H in 5xFAD failed to ameliorate cognitive and transcriptomic deficits. In situ analysis of key TREM2 -dosage dependent genes and microglial morphology uncovered that TREM2-R47H showed a loss-of-function phenotype in reprogramming of plaque-associated microglial reactivity and gene expression in 5xFAD.

Conclusion

Our study demonstrated that the AD-risk variant has a previously unknown, mixture of partial and full loss of TREM2 functions in modulating microglial response in AD mouse brains. Together, our new BAC-TREM2-R47H model and prior BAC-TREM2 mice are invaluable resource to facilitate the therapeutic discovery that target human TREM2 and its R47H variant to ameliorate AD and other neurodegenerative disorders.

Amyloid-β Pathology-Specific Cytokine Secretion Suppresses Neuronal Mitochondrial Metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease (AD) brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in AD patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of AD at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10/CXCL10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

We identify a pattern of cytokine secretion predictive of progressing amyloid-β pathology in the 5xFAD mouse model of AD that reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in AD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00782-y.

Recapitulation of pathophysiological features of AD in SARS-CoV-2-infected subjects

Infection with the etiological agent of COVID-19, SARS-CoV-2, appears capable of impacting cognition in some patients with post-acute sequelae of SARS-CoV-2 (PASC). To evaluate neuropathophysiological consequences of SARS-CoV-2 infection, we examine transcriptional and cellular signatures in the Brodmann area 9 (BA9) of the frontal cortex and the hippocampal formation (HF) in SARS-CoV-2, Alzheimer's disease (AD), and SARS-CoV-2-infected AD individuals compared to age- and gender-matched neurological cases. Here, we show similar alterations of neuroinflammation and blood-brain barrier integrity in SARS-CoV-2, AD, and SARS-CoV-2-infected AD individuals. Distribution of microglial changes reflected by the increase in Iba-1 reveals nodular morphological alterations in SARS-CoV-2-infected AD individuals. Similarly, HIF-1α is significantly upregulated in the context of SARS-CoV-2 infection in the same brain regions regardless of AD status. The finding may help in informing decision-making regarding therapeutic treatments in patients with neuro-PASC, especially those at increased risk of developing AD.

CARD9 attenuates Aβ pathology and modifies microglial responses in an Alzheimer's disease mouse model

Recent advances have highlighted the importance of several innate immune receptors expressed by microglia in Alzheimer's disease (AD). In particular, mounting evidence from AD patients and experimental models indicates pivotal roles for TREM2, CD33, and CD22 in neurodegenerative disease progression. While there is growing interest in targeting these microglial receptors to treat AD, we still lack knowledge of the downstream signaling molecules used by these receptors to orchestrate immune responses in AD. Notably, TREM2, CD33, and CD22 have been described to influence signaling associated with the intracellular adaptor molecule CARD9 to mount downstream immune responses outside of the brain. However, the role of CARD9 in AD remains poorly understood. Here, we show that genetic ablation of CARD9 in the 5xFAD mouse model of AD results in exacerbated amyloid beta (Aβ) deposition, increased neuronal loss, worsened cognitive deficits, and alterations in microglial responses. We further show that pharmacological activation of CARD9 promotes improved clearance of Aβ deposits from the brains of 5xFAD mice. These results help to establish CARD9 as a key intracellular innate immune signaling molecule that regulates Aβ-mediated disease and microglial responses. Moreover, these findings suggest that targeting CARD9 might offer a strategy to improve Aβ clearance in AD.

Alzheimer's disease-specific cytokine secretion suppresses neuronal mitochondrial metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in Alzheimer's disease patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of Alzheimer's disease at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

An Alzheimer's disease-specific pattern of cytokine secretion reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in Alzheimer's disease.

Network analysis reveals strain-dependent response to misfolded tau aggregates

Mouse genetic backgrounds have been shown to modulate amyloid accumulation and propagation of tau aggregates. Previous research into these effects has highlighted the importance of studying the impact of genetic heterogeneity on modeling Alzheimer's disease. However, it is unknown what mechanisms underly these effects of genetic background on modeling Alzheimer's disease, specifically tau aggregate-driven pathogenicity. In this study, we induced tau aggregation in wild-derived mice by expressing MAPT (P301L). To investigate the effect of genetic background on the action of tau aggregates, we performed RNA sequencing with brains of 6-month-old C57BL/6J, CAST/EiJ, PWK/PhJ, and WSB/EiJ mice (n=64). We also measured tau seeding activity in the cortex of these mice. We identified three gene signatures: core transcriptional signature, unique signature for each wild-derived genetic background, and tau seeding-associated signature. Our data suggest that microglial response to tau seeds is elevated in CAST/EiJ and PWK/PhJ mice. Together, our study provides the first evidence that mouse genetic context influences the seeding of tau.

SUMMARY

Seeding of tau predates the phosphorylation and spreading of tau aggregates. Acri and colleagues report transcriptomic responses to tau and elevated tau seeds in wild-derived mice. This paper creates a rich resource by combining genetics, tau biosensor assays, and transcriptomics.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

Molecular and spatial signatures of mouse brain aging at single-cell resolution

The diversity and complex organization of cells in the brain have hindered systematic characterization of age-related changes in its cellular and molecular architecture, limiting our ability to understand the mechanisms underlying its functional decline during aging. Here, we generated a high-resolution cell atlas of brain aging within the frontal cortex and striatum using spatially resolved single-cell transcriptomics and quantified changes in gene expression and spatial organization of major cell types in these regions over the mouse lifespan. We observed substantially more pronounced changes in cell state, gene expression, and spatial organization of non-neuronal cells over neurons. Our data revealed molecular and spatial signatures of glial and immune cell activation during aging, particularly enriched in the subcortical white matter, and identified both similarities and notable differences in cell-activation patterns induced by aging and systemic inflammatory challenge. These results provide critical insights into age-related decline and inflammation in the brain.

Acquired immunity and Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive defects. The role of the central immune system dominated by microglia in the progression of AD has been extensively investigated. However, little is known about the peripheral immune system in AD pathogenesis. Recently, with the discovery of the meningeal lymphatic vessels and glymphatic system, the roles of the acquired immunity in the maintenance of central homeostasis and neurodegenerative diseases have attracted an increasing attention. The T cells not only regulate the function of neurons, astrocytes, microglia, oligodendrocytes and brain microvascular endothelial cells, but also participate in the clearance of β-amyloid (Aβ) plaques. Apart from producing antibodies to bind Aβ peptides, the B cells affect Aβ-related cascades via a variety of antibody-independent mechanisms. This review systemically summarizes the recent progress in understanding pathophysiological roles of the T cells and B cells in AD.

Microglia PTK2B/Pyk2 in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a highly hereditary disease with complex genetic susceptibility factors. Extensive genome-wide association studies have established a distinct susceptibility link between the protein tyrosine kinase 2β (PTK2B) gene and late-onset Alzheimer's disease (LOAD), but the specific pathogenic mechanisms remain incompletely understood. PTK2B is known to be expressed in neurons, and recent research has revealed its more important significance in microglia. Elucidating the role of PTK2B high expression in microglia in AD's progression is crucial for uncovering novel pathogenic mechanisms of the disease. Our review of existing studies suggests a close relationship between PTK2B/proline-rich tyrosine kinase 2 (Pyk2) and tau pathology, and this process might be β-amyloid (Aβ) dependence. Pyk2 is hypothesized as a pivotal target linking Aβ and tau pathologies. Concurrently, Aβ-activated Pyk2 participates in the regulation of microglial activation and its proinflammatory functions. Consequently, it is reasonable to presume that Pyk2 in microglia contributes to amyloid-induced tau pathology in AD via a neuroinflammatory pathway. Furthermore, many things remain unclear, such as identifying the specific pathways that lead to the release of downstream inflammatory factors due to Pyk2 phosphorylation and whether all types of inflammatory factors can activate neuronal kinase pathways. Additionally, further in vivo experiments are essential to validate this hypothesized pathway. Considering PTK2B/Pyk2's potential role in AD pathogenesis, targeting this pathway may offer innovative and promising therapeutic approaches for AD.

Identification and Prioritization of PET Neuroimaging Targets for Microglial Phenotypes Associated with Microglial Activity in Alzheimer's Disease

Activation of microglial cells accompanies the progression of many neurodegenerative disorders, including Alzheimer's disease (AD). Development of molecular imaging tools specific to microglia can help elucidate the mechanism through which microglia contribute to the pathogenesis and progression of neurodegenerative disorders. Through analysis of published genetic, transcriptomic, and proteomic data sets, we identified 19 genes with microglia-specific expression that we then ranked based on association with the AD characteristics, change in expression, and potential druggability of the target. We believe that the process we used to identify and rank microglia-specific genes is broadly applicable to the identification and evaluation of targets in other disease areas and for applications beyond molecular imaging.

Nanoparticles-based anti-aging treatment of Alzheimer's disease

Age is the strongest risk factor for Alzheimer's disease (AD). In recent years, the relationship between aging and AD has been widely studied, with anti-aging therapeutics as the treatment for AD being one of the mainstream research directions. Therapeutics targeting senescent cells have shown improvement in AD symptoms and cerebral pathological changes, suggesting that anti-aging strategies may be a promising alternative for AD treatment. Nanoparticles represent an excellent approach for efficiently crossing the blood-brain barrier (BBB) to achieve better curative function and fewer side effects. Thereby, nanoparticles-based anti-aging treatment may exert potent anti-AD therapeutic efficacy. This review discusses the relationship between aging and AD and the application and prospect of anti-aging strategies and nanoparticle-based therapeutics in treating AD.

Molecular and cellular similarities in the brain of SARS-CoV-2 and Alzheimer's disease individuals

Infection with the etiological agent of COVID-19, SARS-CoV-2, appears capable of impacting cognition, which some patients with Post-acute Sequelae of SARS-CoV-2 (PASC). To evaluate neuro-pathophysiological consequences of SARS-CoV-2 infection, we examine transcriptional and cellular signatures in the Broadman area 9 (BA9) of the frontal cortex and the hippocampal formation (HF) in SARS-CoV-2, Alzheimer's disease (AD) and SARS-CoV-2 infected AD individuals, compared to age- and gender-matched neurological cases. Here we show similar alterations of neuroinflammation and blood-brain barrier integrity in SARS-CoV-2, AD, and SARS-CoV-2 infected AD individuals. Distribution of microglial changes reflected by the increase of Iba-1 reveal nodular morphological alterations in SARS-CoV-2 infected AD individuals. Similarly, HIF-1α is significantly upregulated in the context of SARS-CoV-2 infection in the same brain regions regardless of AD status. The finding may help to inform decision-making regarding therapeutic treatments in patients with neuro-PASC, especially those at increased risk of developing AD.

TEASER

SARS-CoV-2 and Alzheimer's disease share similar neuroinflammatory processes, which may help explain neuro-PASC.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address two factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Recent Treatment Strategies in Alzheimer's Disease and Chronic Traumatic Encephalopathy

Neurotrauma has been well linked to the progression of neurodegenerative disease. Much work has been done characterizing chronic traumatic encephalopathy, but less has been done regarding the contribution to Alzheimer's Disease. This review focuses on AD and its association with neurotrauma. Emerging clinical trials are discussed as well as novel mechanisms. We then address how some of these mechanisms are shared with CTE and emerging pre-clinical studies. This paper is a user-friendly resource that summarizes the emerging findings and proposes further investigation into key areas of interest. It is intended to serve as a catalyst for both research teams and clinicians in the quest to improve effective treatment and diagnostic options.

Role of aging in Blood-Brain Barrier dysfunction and susceptibility to SARS-CoV-2 infection: impacts on neurological symptoms of COVID-19

COVID-19, which is caused by Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2), has resulted in devastating morbidity and mortality worldwide due to lethal pneumonia and respiratory distress. In addition, the central nervous system (CNS) is well documented to be a target of SARS-CoV-2, and studies detected SARS-CoV-2 in the brain and the cerebrospinal fluid of COVID-19 patients. The blood-brain barrier (BBB) was suggested to be the major route of SARS-CoV-2 infection of the brain. Functionally, the BBB is created by an interactome between endothelial cells, pericytes, astrocytes, microglia, and neurons, which form the neurovascular units (NVU). However, at present, the interactions of SARS-CoV-2 with the NVU and the outcomes of this process are largely unknown. Moreover, age was described as one of the most prominent risk factors for hospitalization and deaths, along with other comorbidities such as diabetes and co-infections. This review will discuss the impact of SARS-CoV-2 on the NVU, the expression profile of SARS-CoV-2 receptors in the different cell types of the CNS and the possible role of aging in the neurological outcomes of COVID-19. A special emphasis will be placed on mitochondrial functions because dysfunctional mitochondria are also a strong inducer of inflammatory reactions and the "cytokine storm" associated with SARS-CoV-2 infection. Finally, we will discuss possible drug therapies to treat neural endothelial function in aged patients, and, thus, alleviate the neurological symptoms associated with COVID-19.

MS4A6A is a new prognostic biomarker produced by macrophages in glioma patients

MS4A6A has been recognized as being associated with aging and the onset of neurodegenerative disease. However, the mechanisms of MS4A6A in glioma biology and prognosis are ill-defined. Here, we show that MS4A6A is upregulated in glioma tissues, resulting in unfavorable clinical outcomes and poor responses to adjuvant chemotherapy. Multivariate Cox regression analysis suggested that MS4A6A expression can act as a strong and independent predictor for glioma outcomes (CGGA1: HR: 1.765, p < 0.001; CGGA2: HR: 2.626, p < 0.001; TCGA: HR: 1.415, p < 0.001; Rembrandt: HR: 1.809, p < 0.001; Gravendeel: HR: 1.613, p < 0.001). A protein–protein interaction (PPI) network revealed that MS4A6A might be coexpressed with CD68, CD163, and macrophage-specific signatures. Enrichment analysis showed the innate immune response and inflammatory response to be markedly enriched in the high MS4A6A expression group. Additionally, single-cell RNA sequencing (scRNA-seq) analysis revealed distinctive expression features for MS4A6A in macrophages in the glioma immune microenvironment (GIME). Immunofluorescence staining confirmed colocalization of CD68/MS4A6A and CD163/MS4A6A in macrophages. Correlation analysis revealed that MS4A6A expression is positively related to the tumor mutation burden (TMB) of glioma, displaying the high potential of applying MS4A6A to evaluate responsiveness to immunotherapy. Altogether, our research indicates that MS4A6A upregulation may be used as a promising and effective indicator for adjuvant therapy and prognosis assessment.

Promising Role of Oral Cavity Mesenchymal Stem Cell-Derived Extracellular Vesicles in Neurodegenerative Diseases

Mesenchymal stem cells (MSCs) and mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been regarded as the beneficial and available tools to treat various hereditary, multifactorial, acute, and chronic diseases. Mesenchymal stem cells can be extracted from numerous sources for clinical purposes while oral cavity-derived mesenchymal stem cells seem to be more effective in neuroregeneration than other sources due to their similar embryonic origins to neuronal tissues. In various studies and different neurodegenerative diseases (NDs), oral cavity mesenchymal stem cells have been applied to prove their promising capacities in disease improvement. Moreover, oral cavity mesenchymal stem cells' secretion is regarded as a novel and practical approach to neuroregeneration; hence, extracellular vesicles (EVs), especially exosomes, may provide promising results to improve CNS defects. This review article focuses on how oral cavity-derived stem cells and their extracellular vesicles can improve neurodegenerative conditions and tries to show which molecules are involved in the recovery process.

High frequency repetitive transcranial magnetic stimulation alleviates cognitive deficits in 3xTg-AD mice by modulating the PI3K/Akt/GLT-1 Axis

Objective

Glutamate mediated excitotoxicity, such as oxidative stress, neuroinflammation, synaptic loss and neuronal death, is ubiquitous in Alzheimer's disease (AD). Our previous study found that 15 Hz repetitive transcranial magnetic stimulation (rTMS) could reduce cortical excitability. The purpose of this study was to explore the therapeutic effect of higher frequency rTMS on 3xTg-AD model mice and further explore the mechanisms of rTMS.

Methods

First, WT and 3xTg-AD model mice received 25 Hz rTMS treatment for 21 days. The Morris water maze test was used to evaluate the cognitive function. The levels of Aβ and neuroinflammation were assessed by ELISA and immunofluorescence. Oxidative stress was quantified by biochemical assay kits. Brain glucose metabolism was assessed by ¹⁸F-FDG PET. Apoptosis was assessed by western blot and TUNEL staining. Synaptic plasticity and PI3K/Akt/GLT-1 pathway related protein expression were assessed by western blot. Next, to explore the activity of PI3K/Akt in the therapeutic effect of rTMS, 3xTg-AD model mice were given LY294002 intervention and rTMS treatment for 21 days, the experimental method was the same as before.

Results

We found that 25 Hz rTMS could improve cognitive function of 3xTg-AD model mice, reduce hippocampal Aβ1-42 levels, ameliorate oxidative stress and improve glucose metabolism. rTMS alleviated neuroinflammatory response, enhanced synaptic plasticity and reduced neuronal loss and cell apoptosis, accompanied by activation of PI3K/Akt/GLT-1 pathway. After administration of PI3K/Akt inhibitor LY294002, 25 Hz rTMS could not improve the cognitive function and reduce neuron damage of 3xTg-AD model mice, nor could it upregulate the expression of GLT-1, indicating that its therapeutic and protective effects required the involvement of PI3K/Akt/GLT-1 pathway.

Conclusion

rTMS exerts protective role for AD through regulating multiple pathological processes. Meanwhile, this study revealed the key role of PI3K/Akt/GLT-1 pathway in the treatment of AD by rTMS, which might be a new target.

Proficiency of Extracellular Vesicles From hiPSC-Derived Neural Stem Cells in Modulating Proinflammatory Human Microglia: Role of Pentraxin-3 and miRNA-21-5p

Extracellular vesicles (EVs) shed by human-induced pluripotent stem cell (hiPSC)-derived neural stem cells (hNSC-EVs) have shown potent antiinflammatory properties in a mouse macrophage assay and a mouse model of acute neuroinflammation. They can also quickly permeate the entire brain after intranasal administration, making them attractive as an autologous or allogeneic off-the-shelf product for treating neurodegenerative diseases. However, their ability to modulate activated human microglia and specific proteins and miRNAs mediating antiinflammatory effects of hNSC-EVs are unknown. We investigated the proficiency of hNSC-EVs to modulate activated human microglia and probed the role of the protein pentraxin 3 (PTX3) and the miRNA miR-21-5p within hNSC-EVs in mediating the antiinflammatory effects. Mature microglia generated from hiPSCs (iMicroglia) expressed multiple microglia-specific markers. They responded to lipopolysaccharide (LPS) or interferon-gamma challenge by upregulating tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) mRNA expression and protein release. iMicroglia also exhibited proficiency to phagocytose amyloid-beta (Aβ). The addition of hNSC-EVs decreased TNF-α and IL-1β mRNA expression and the release of TNF-α and IL-1β by LPS-stimulated iMicroglia (proinflammatory human Microglia). However, the antiinflammatory activity of hNSC-EVs on LPS-stimulated microglia was considerably diminished when the PTX3 or miR-21-5p concentration was reduced in EVs. The results demonstrate that hNSC-EVs are proficient for modulating the proinflammatory human microglia into non-inflammatory phenotypes, implying their utility to treat neuroinflammation in neurodegenerative diseases. Furthermore, the role of PTX3 and miR-21-5p in the antiinflammatory activity of hNSC-EVs provides a new avenue for improving the antiinflammatory effects of hNSC-EVs through PTX3 and/or miR-21-5p overexpression.

p38 activation occurs mainly in microglia in the P301S Tauopathy mouse model

Tauopathies are a group of neurodegenerative diseases characterized by the accumulation of hyperphosphorylated tau protein in the brain. Many of these pathologies also present an inflammatory component determined by the activation of microglia, the resident immune cells of the brain. p38 MAPK is one of the molecular pathways involved in neuroinflammation. Although this kinase is expressed mainly in glia, its activation in certain neurodegenerative diseases such as Alzheimer's Disease has been associated with its ability to phosphorylate tau in neurons. Using the P301S Tauopathy mouse model, here we show that p38 activation increases during aging and that this occurs mainly in microglia of the hippocampus rather than in neurons. Furthermore, we have observed that these mice present an activated microglial variant called rod microglia. Interestingly, p38 activation in this subpopulation of microglia is decreased. On the basis of our findings, we propose that rod microglia might have a neuroprotective phenotype in the context of tau pathology.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.

Deletion of Abi3 gene locus exacerbates neuropathological features of Alzheimer's disease in a mouse model of Aβ amyloidosis

Recently, large-scale human genetics studies identified a rare coding variant in the ABI3 gene that is associated with an increased risk of Alzheimer’s disease (AD). However, pathways by which ABI3 contributes to the pathogenesis of AD are unknown. To address this question, we determined whether loss of ABI3 function affects pathological features of AD in the 5XFAD mouse model. We demonstrate that the deletion of Abi3 locus significantly increases amyloid β (Aβ) accumulation and decreases microglia clustering around the plaques. Furthermore, long-term potentiation is impaired in 5XFAD;Abi3 knockout (“Abi3−/−”) mice. Moreover, we identified marked changes in the proportion of microglia subpopulations in Abi3−/− mice using a single-cell RNA sequencing approach. Mechanistic studies demonstrate that Abi3 knockdown in microglia impairs migration and phagocytosis. Together, our study provides the first in vivo functional evidence that loss of ABI3 function may increase the risk of developing AD by affecting Aβ accumulation and neuroinflammation.

microRNA-425 loss mediates amyloid plaque microenvironment heterogeneity and promotes neurodegenerative pathologies

Different cellular and molecular changes underlie the pathogenesis of Alzheimer's disease (AD). Among these, neuron‐specific dysregulation is a necessary event for accumulation of classic pathologies including amyloid plaques. Here, we show that AD‐associated pathophysiology including neuronal cell death, inflammatory signaling, and endolysosomal dysfunction is spatially colocalized to amyloid plaques in regions with abnormal microRNA‐425 (miR‐425) levels and this change leads to focal brain microenvironment heterogeneity, that is, an amyloid plaque‐associated microenvironment (APAM). APAM consists of multiple specific neurodegenerative signature pathologies associated with senile plaques that contribute to the heterogeneity and complexity of AD. Remarkably, miR‐425, a neuronal‐specific regulator decreased in AD brain, maintains a normal spatial transcriptome within brain neurons. We tested the hypothesis that miR‐425 loss correlates with enhanced levels of mRNA targets downstream, supporting APAM and AD progression. A miR‐425‐deficient mouse model has enhanced APP amyloidogenic processing, neuroinflammation, neuron loss, and cognitive impairment. In the APP/PS1 mouse model, intervening with miR‐425 supplementation ameliorated APAM changes and memory deficits. This study reveals a novel mechanism of dysregulation of spatial transcriptomic changes in AD brain, identifying a probable neuronal‐specific microRNA regulator capable of staving off amyloid pathogenesis. Moreover, our findings provide new insights for developing AD treatment strategies with miRNA oligonucleotide(s).

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address 2 factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Infusion of hESC derived Immunity-and-matrix regulatory cells improves cognitive ability in early-stage AD mice

Objectives

In this study, we administered immunity‐and‐matrix regulatory cells (IMRCs) via tail vein (IV) and intracerebroventricular (ICV) injection to 3‐month‐old 5×FAD transgenic mice to assess the effects of IMRC transplantation on the behaviour and pathology of early‐stage Alzheimer's disease (AD).

Materials and methods

Clinical‐grade human embryonic stem cell (hESC)‐derived IMRCs were produced under good manufacturing practice (GMP) conditions. Three‐month‐old 5×FAD mice were administered IMRCs via IV and ICV injection. After 3 months, the mice were subjected to behavioural tests and electrophysiological analysis to evaluate their cognitive function, memory ability and synaptic plasticity. The effect of IMRCs on amyloid‐beta (Aβ)‐related pathology was detected by thioflavin‐S staining and Western blot. Quantitative real‐time PCR, ELISA and immunostaining were used to confirm that IMRCs inhibit neuroinflammation. RNA‐seq analysis was performed to measure changes in gene expression and perform a pathway analysis in response to IMRC treatment.

Results

IMRC administration via tail vein injection significantly ameliorated cognitive deficits in early‐stage AD (5×FAD) mice. However, no significant change was observed in the characteristic pathology of AD in the ICV group. Plaque analysis revealed that IMRCs did not influence either plaque deposition or BACE1 expression. In addition, IMRCs inhibited inflammatory responses and reduced microglial activation in vivo.

Conclusions

We have shown that peripheral administration of IMRCs can ameliorate AD pathology and associated cognitive deficits.

Prodromal neuroinflammatory, cholinergic and metabolite dysfunction detected by PET and MRS in the TgF344-AD transgenic rat model of AD: a collaborative multi-modal study

Mouse models of Alzheimer's disease (AD) are valuable but do not fully recapitulate human AD pathology, such as spontaneous Tau fibril accumulation and neuronal loss, necessitating the development of new AD models. The transgenic (TG) TgF344-AD rat has been reported to develop age-dependent AD features including neuronal loss and neurofibrillary tangles, despite only expressing APP and PSEN1 mutations, suggesting an improved modelling of AD hallmarks. Alterations in neuronal networks as well as learning performance and cognition tasks have been reported in this model, but none have combined a longitudinal, multimodal approach across multiple centres, which mimics the approaches commonly taken in clinical studies. We therefore aimed to further characterise the progression of AD-like pathology and cognition in the TgF344-AD rat from young-adults (6 months (m)) to mid- (12 m) and advanced-stage (18 m, 25 m) of the disease. Methods: TgF344-AD rats and wild-type (WT) littermates were imaged at 6 m, 12 m and 18 m with [¹⁸F]DPA-714 (TSPO, neuroinflammation), [¹⁸F]Florbetaben (Aβ) and [¹⁸F]ASEM (α7-nicotinic acetylcholine receptor) and with magnetic resonance spectroscopy (MRS) and with (S)-[¹⁸F]THK5117 (Tau) at 15 and 25 m. Behaviour tests were also performed at 6 m, 12 m and 18 m. Immunohistochemistry (CD11b, GFAP, Aβ, NeuN, NeuroChrom) and Tau (S)-[¹⁸F]THK5117 autoradiography, immunohistochemistry and Western blot were also performed. Results: [¹⁸F]DPA-714 positron emission tomography (PET) showed an increase in neuroinflammation in TG vs wildtype animals from 12 m in the hippocampus (+11%), and at the advanced-stage AD in the hippocampus (+12%), the thalamus (+11%) and frontal cortex (+14%). This finding coincided with strong increases in brain microgliosis (CD11b) and astrogliosis (GFAP) at these time-points as assessed by immunohistochemistry. In vivo [¹⁸F]ASEM PET revealed an age-dependent increase uptake in the striatum and pallidum/nucleus basalis of Meynert in WT only, similar to that observed with this tracer in humans, resulting in TG being significantly lower than WT by 18 m. In vivo [¹⁸F]Florbetaben PET scanning detected Aβ accumulation at 18 m, and (S)-[¹⁸F]THK5117 PET revealed subsequent Tau accumulation at 25m in hippocampal and cortical regions. Aβ plaques were low but detectable by immunohistochemistry from 6 m, increasing further at 12 and 18 m with Tau-positive neurons adjacent to Aβ plaques at 18 m. NeuroChrom (a pan neuronal marker) immunohistochemistry revealed a loss of neuronal staining at the Aβ plaques locations, while NeuN labelling revealed an age-dependent decrease in hippocampal neuron number in both genotypes. Behavioural assessment using the novel object recognition task revealed that both WT & TgF344-AD animals discriminated the novel from familiar object at 3 m and 6 m of age. However, low levels of exploration observed in both genotypes at later time-points resulted in neither genotype successfully completing the task. Deficits in social interaction were only observed at 3 m in the TgF344-AD animals. By in vivo MRS, we showed a decrease in neuronal marker N-acetyl-aspartate in the hippocampus at 18 m (-18% vs age-matched WT, and -31% vs 6 m TG) and increased Taurine in the cortex of TG (+35% vs age-matched WT, and +55% vs 6 m TG). Conclusions: This multi-centre multi-modal study demonstrates, for the first time, alterations in brain metabolites, cholinergic receptors and neuroinflammation in vivo in this model, validated by robust ex vivo approaches. Our data confirm that, unlike mouse models, the TgF344-AD express Tau pathology that can be detected via PET, albeit later than by ex vivo techniques, and is a useful model to assess and longitudinally monitor early neurotransmission dysfunction and neuroinflammation in AD.

Spreading of Beta-Amyloid in Organotypic Mouse Brain Slices and Microglial Elimination and Effects on Cholinergic Neurons

The extracellular deposition of β-amyloid (Aβ) is one of the major characteristics in Alzheimer´s disease (AD). The "spreading hypothesis" suggests that a pathological protein (similar to prions) spreads over the entire brain. The aim of the present study was to use organotypic brain slices of postnatal day 8-10 mice. Using collagen hydrogels, we applied different Aβ peptides onto brain slices and analyzed spreading as well as glial reactions after eight weeks of incubation. Our data showed that from all tested Aβ peptides, human Aβ42 had the most potent activity to spread over into adjacent "target" areas. This effect was potentiated when brain slices from transgenic AD mice (APP_SweDI) were cultured. When different brain areas were connected to the "target slice" the spreading activity was more intense, originating from ventral striatum and brain stem. Reactive glial-fibrillary acidic protein (GFAP) astrogliosis increased over time, but Aβ depositions co-localized only with Iba1+ microglia but not with astrocytes. Application of human Aβ42 did not cause a degeneration of cholinergic neurons. We concluded that human Aβ42 spreads over into other "target areas", causing activation of glial cells. Most of the spread Aβ42 was taken up by microglia, and thus toxic free Aβ could not damage cholinergic neurons.

Neuronal mitochondria-targeted therapy for Alzheimer's disease by systemic delivery of resveratrol using dual-modified novel biomimetic nanosystems

Reactive oxygen species (ROS)-induced neuronal mitochondrial dysfunction is a key pathologic factor in sporadic Alzheimer’s disease (AD). Neuronal mitochondria have been proposed to be a promising therapeutic target for AD, especially for the failures of phase III clinical trials on conventional amyloid-β (Aβ) targeted therapy. However, the efficient intravenous delivery of therapeutic agents to neuronal mitochondria in the brain remains a major challenge due to the complicated physiological environment. Recently, biomaterials-based nanomedicine has been widely investigated for the treatment of AD. Herein, we devised a strategy for functional antioxidant delivery to neuronal mitochondria by loading antioxidants into red blood cell (RBC) membrane-coated nanostructured lipid carriers (NLC) bearing rabies virus glycoprotein (RVG29) and triphenylphosphine cation (TPP) molecules attached to the RBC membrane surface (RVG/TPP NPs@RBCm). With the advantage of suitable physicochemical properties of NLC and unique biological functions of the RBC membrane, RVG/TPP NPs@RBCm are stabilized and enabled sustained drug release, providing improved biocompatibility and long-term circulation. Under the synergistic effects of RVG29 and TPP, RVG/TPP NPs@RBCm can not only penetrate the blood–brain barrier (BBB) but also target neuron cells and further localize in the mitochondria. After encapsulating Resveratrol (RSV) as the model antioxidant, the data demonstrated that RVG/TPP-RSV NPs@RBCm can relieve AD symptoms by mitigating Aβ-related mitochondrial oxidative stress both in vitro and in vivo. The memory impairment in APP/PS1 mice is significantly improved following the systemic administration of RVG/TPP-RSV NPs@RBCm. In conclusion, intravenous neuronal mitochondria-targeted dual-modified novel biomimetic nanosystems are a promising therapeutic candidate for ROS-induced mitochondrial dysfunction in AD.

Restoring metabolism of myeloid cells reverses cognitive decline in ageing

Ageing is characterized by the development of persistent pro-inflammatory responses that contribute to atherosclerosis, metabolic syndrome, cancer and frailty^1-3. The ageing brain is also vulnerable to inflammation, as demonstrated by the high prevalence of age-associated cognitive decline and Alzheimer's disease^4-6. Systemically, circulating pro-inflammatory factors can promote cognitive decline^7,8, and in the brain, microglia lose the ability to clear misfolded proteins that are associated with neurodegeneration^9,10. However, the underlying mechanisms that initiate and sustain maladaptive inflammation with ageing are not well defined. Here we show that in ageing mice myeloid cell bioenergetics are suppressed in response to increased signalling by the lipid messenger prostaglandin E₂ (PGE₂), a major modulator of inflammation¹¹. In ageing macrophages and microglia, PGE₂ signalling through its EP2 receptor promotes the sequestration of glucose into glycogen, reducing glucose flux and mitochondrial respiration. This energy-deficient state, which drives maladaptive pro-inflammatory responses, is further augmented by a dependence of aged myeloid cells on glucose as a principal fuel source. In aged mice, inhibition of myeloid EP2 signalling rejuvenates cellular bioenergetics, systemic and brain inflammatory states, hippocampal synaptic plasticity and spatial memory. Moreover, blockade of peripheral myeloid EP2 signalling is sufficient to restore cognition in aged mice. Our study suggests that cognitive ageing is not a static or irrevocable condition but can be reversed by reprogramming myeloid glucose metabolism to restore youthful immune functions.

APP/PS1 Gene-Environment Noise Interaction Aggravates AD-like Neuropathology in Hippocampus Via Activation of the VDAC1 Positive Feedback Loop

BACKGROUND

Environmental risk factors, including environmental noise stress, and genetic factors, have been associated with the occurrence and development of Alzheimer's disease (AD). However, the exact role and mechanism of AD-like pathology induced by environment-gene interactions between environmental noise and APP/PS1 gene remain elusive.

METHODS

Herein, we investigated the impact of chronic noise exposure on AD-like neuropathology in APP/PS1 transgenic mice. The Morris water maze (MWM) task was conducted to evaluate AD-like changes. The hippocampal phosphorylated Tau, amyloid-β (Aβ), and neuroinflammation were assessed. We also assessed changes in positive feedback loop signaling of the voltage-dependent anion channel 1 (VDAC1) to explore the potential underlying mechanism linking AD-like neuropathology to noise-APP/PS1 interactions.

RESULTS

Long-term noise exposure significantly increased the escape latency and the number of platform crossings in the MWM task. The Aβ overproduction was induced in the hippocampus of APP/PS1 mice, along with the increase of Tau phosphorylation at Ser396 and Thr231 and the increase of the microglia and astrocytes markers expression. Moreover, the VDAC1-AKT (protein kinase B)-GSK3β (glycogen synthase kinase 3 beta)-VDAC1 signaling pathway was abnormally activated in the hippocampus of APP/PS1 mice after noise exposure.

CONCLUSION

Chronic noise exposure and APP/PS1 overexpression may synergistically exacerbate cognitive impairment and neuropathological changes that occur in AD. This interaction may be mediated by the positive feedback loop of the VDAC1-AKT-GSK3β-VDAC1 signaling pathway.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

Non-genetic Heterogeneity of Macrophages in Diseases-A Medical Perspective

Macrophages are sessile immune cells with a high functional plasticity. Initially considered as a uniform population of phagocytic scavengers, it is now widely accepted that these cells also assume developmental and metabolic functions specific of their tissue of residence. Hence, the paradigm is shifting while our comprehension of macrophage heterogeneity improves. Accordingly, exploiting this intrinsic versatility appears more and more promising for the establishment of innovative therapeutic strategies. Nevertheless, identifying relevant therapeutic targets remains a considerable challenge. Herein, we discuss various features of macrophage heterogeneity in five main categories of human diseases: infectious, inflammatory, metabolic, age-related, and neoplastic disorders. We summarize the current understanding of how macrophage heterogeneity may impact the pathogenesis of these diseases and propose a comprehensive overview with the aim to help in establishing future macrophage-targeted therapies.

ROS-responsive and multifunctional anti-Alzheimer prodrugs: Tacrine-ibuprofen hybrids via a phenyl boronate linker

Current drugs available in clinic for Alzheimer's disease (AD) treatment can only alleviate disease symptoms without clearly curing or delaying the process of AD. And some AD drugs failed in Phase III clinical trials are only focused on targeting amyloid-β (Aβ). Therefore, an alternative strategy in AD drug design is meaningful to be involved in the multiple pathogenic factors which can affect each other at multiple levels. Herein, we report a series of ROS-responsive prodrugs based on multi-target-directed ligands (MTDLs) approach, which can specifically release tacrine derivatives and ibuprofen under oxidation of ROS and show acetylcholinesterase (AChE)-inhibiting, neuron-protective and anti-inflammatory effects in extracellular or intracellular assays. Related biological study illustrated that compound 22 was able to permeate blood-brain-barrier (BBB) showing little hepatotoxicity in comparison to tacrine. Besides, 22 hinted a therapeutic clue in AD-treatment by regulating proinflammatory factors (IL-1β and TNF-α) and apoptosis related proteins (Bax, Bcl-2 and cleaved caspase-3). Further spatial memory assays in Aβ-induced AD model showed that 22 enhanced the ability of learning and memory. Our study proves that the strategy of ROS-responsive prodrugs has promise for AD treatments in future and offers a way for AD drug development.

Profiling Microglia From Alzheimer's Disease Donors and Non-demented Elderly in Acute Human Postmortem Cortical Tissue

Microglia are the tissue-resident macrophages of the central nervous system (CNS). Recent studies based on bulk and single-cell RNA sequencing in mice indicate high relevance of microglia with respect to risk genes and neuro-inflammation in Alzheimer's disease (AD). Here, we investigated microglia transcriptomes at bulk and single-cell levels in non-demented elderly and AD donors using acute human postmortem cortical brain samples. We identified seven human microglial subpopulations with heterogeneity in gene expression. Notably, gene expression profiles and subcluster composition of microglia did not differ between AD donors and non-demented elderly in bulk RNA sequencing nor in single-cell sequencing.

Isoorientin, a GSK-3β inhibitor, rescues synaptic dysfunction, spatial memory deficits and attenuates pathological progression in APP/PS1 model mice

β-Amyloid (Aβ) elevation, tau hyperphosphorylation, and neuroinflammation are major hallmarks of Alzheimer's disease (AD). Glycogen synthase kinase-3β (GSK-3β) is a key protein kinase implicated in the pathogenesis of AD. Blockade of GSK-3β is an attractive therapeutic strategy for AD. Isoorientin, a 6-C-glycosylflavone, was previously shown to be a highly selective inhibitor of GSK-3β, while exerting neuroprotective effects in neuronal models of AD. In the present study, we evaluated the in vivo effects of isoorientin on GSK-3β, tau phosphorylation, Aβ deposition, neuroinflammatory response, long-term potentiation, and spatial memory in amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice using biochemical, electrophysiological, and behavioral tests. Chronic oral administration of isoorientin to APP/PS1 mice at 8 months of age attenuated multiple AD pathogenic hallmarks in the brains, including GSK-3β overactivation, tau hyperphosphorylation, Aβ deposition, and neuroinflammation. For neuroinflammation, isoorientin treatment reduced the number of activated microglia associated with Aβ-positive plaques, and in parallel reduced the levels of pro-inflammatory factors in the brains of APP/PS1 mice. Strikingly, isoorientin reversed deficits in synaptic long-term potentiation and spatial memory relevant to cognitive functions. Together, the findings suggest that isoorientin is a brain neuroprotector and may be a promising drug lead for treatment of AD and related neurodegenerative disorders.

Evaluation of Associations of Alzheimer's Disease Risk Variants that Are Highly Expressed in Microglia with Neuropathological Outcome Measures

A number of Alzheimer's disease (AD) susceptibility loci are expressed abundantly in microglia. We examined associations between AD risk variants in genes that are highly expressed in microglia and neuropathological outcomes, including cerebral amyloid angiopathy (CAA) and microglial activation, in 93 AD patients. We observed significant associations of CAA pathology with APOEɛ4 and PTK2B rs28834970. Nominally significant associations with measures of microglial activation in white matter were observed for variants in PTK2B, PICALM, and CR1. Our findings suggest that several AD risk variants may also function as disease modifiers through amyloid-β metabolism and white matter microglial activity.

Neuroinflammation in Alzheimer's Disease: Microglia, Molecular Participants and Therapeutic Choices

Alzheimer's disease is the world's most common dementing illness. It is pathologically characterized by β-amyloid accumulation, extracellular senile plaques and intracellular neurofibrillary tangles formation, and neuronal necrosis and apoptosis. Neuroinflammation has been widely recognized as a crucial process that participates in AD pathogenesis. In this review, we briefly summarized the involvement of microglia in the neuroinflammatory process of Alzheimer's disease. Its roles in the AD onset and progression are also discussed. Numerous molecules, including interleukins, tumor necrosis factor alpha, chemokines, inflammasomes, participate in the complex process of AD-related neuroinflammation and they are selectively discussed in this review. In the end of this paper from an inflammation- related perspective, we discussed some potential therapeutic choices.

Tumour necrosis factor induces increased production of extracellular amyloid-β- and α-synuclein-containing aggregates by human Alzheimer's disease neurons

In addition to increased aberrant protein aggregation, inflammation has been proposed as a key element in the pathogenesis and progression of Alzheimer’s disease. How inflammation interacts with other disease pathways and how protein aggregation increases during disease are not clear. We used single-molecule imaging approaches and membrane permeabilization assays to determine the effect of chronic exposure to tumour necrosis factor, a master proinflammatory cytokine, on protein aggregation in human-induced pluripotent stem cell-derived neurons harbouring monogenic Alzheimer’s disease mutations. We report that exposure of Alzheimer’s disease neurons, but not control neurons, to tumour necrosis factor induces substantial production of extracellular protein aggregates. Aggregates from Alzheimer’s disease neurons are composed of amyloid-β and α-synuclein and induce significant permeabilization of lipid membranes in an assay of pathogenicity. These findings provide support for a causal relationship between two crucial processes in Alzheimer’s disease pathogenesis and suggest that targeting inflammation, particularly tumour necrosis factor, may have beneficial downstream effects on ameliorating aberrant protein aggregation and accumulation.

Macrophage membrane-coated nanocarriers Co-Modified by RVG29 and TPP improve brain neuronal mitochondria-targeting and therapeutic efficacy in Alzheimer's disease mice

Neuronal mitochondrial dysfunction caused by excessive reactive oxygen species (ROS) is an early event of sporadic Alzheimer's disease (AD), and considered to be a key pathologic factor in the progression of AD. The targeted delivery of the antioxidants to mitochondria of injured neurons in brain is a promising therapeutic strategy for AD. A safe and effective drug delivery system (DDS) which is able to cross the blood-brain barrier (BBB) and target neuronal mitochondria is necessary. Recently, bioactive materials-based DDS has been widely investigated for the treatment of AD. Herein, we developed macrophage (MA) membrane-coated solid lipid nanoparticles (SLNs) by attaching rabies virus glycoprotein (RVG29) and triphenylphosphine cation (TPP) molecules to the surface of MA membrane (RVG/TPP-MASLNs) for functional antioxidant delivery to neuronal mitochondria. According to the results, MA membranes camouflaged the SLNs from being eliminated by RES-rich organs by inheriting the immunological characteristics of macrophages. The unique properties of the DDS after decoration with RVG29 on the surface was demonstrated by the ability to cross the BBB and the selective targeting to neurons. After entering the neurons in CNS, TPP further lead the DDS to mitochondria driven by electric charge. The Genistein (GS)- encapsulated DDS (RVG/TPP-MASLNs-GS) exhibited the most favorable effects on reliveing AD symptoms in vitro and in vivo by the synergies gained from the combination of MA membranes, RVG29 and TPP. These results demonstrated a promising therapeutic candidate for delaying the progression of AD via neuronal mitochondria-targeted delivery by the designed biomimetic nanosystems.

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MA membranes inherited the immunological properties of macrophages, providing RVG/TPP-MASLNs with enhanced RES evasion.

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RVG/TPP-MASLNs combined the advantages of RVG29, TPP and MA, greatly improving the efficiency for brain targeting delivery.

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The biomimetic nanosystems effectively improve the curative effect of genistein on the symptoms of AD mice with biosafety.