Microglial activation and tau propagate jointly across Braak stages

The mitochondrial translocator protein (TSPO) in Alzheimer's disease: Therapeutic and immunomodulatory functions

The translocator protein (TSPO) has been widely investigated as a PET-imaging biomarker of neuroinflammation and, more recently, as a therapeutic target for the treatment of neurodegenerative disease. TSPO ligands have been shown to exert neuroprotective effects in vivo and in vitro models of Alzheimer's disease (AD), by reducing toxic beta amyloid peptides, and attenuating brain atrophy. Recent transcriptomic and proteomic analyses, and the generation of TSPO-KO mice, have enabled new insights into the mechanistic function of TSPO in AD. Using a multi-omics approach in both TSPO-KO- and TSPO ligand-treated mice, we have demonstrated a key role for TSPO in microglial respiratory metabolism and phagocytosis in AD. In this review, we discuss emerging evidence for therapeutic and immunomodulatory functions of TSPO in AD, and new tools for studying TSPO in the brain.

Yishen Huazhuo decoction regulates microglial polarization to reduce Alzheimer's disease-related neuroinflammation through TREM2

Background

Aging is the primary risk factor for the onset of Alzheimer's disease (AD). Inflamma-aging is a major feature in the process of aging, and the chronic neuroinflammation caused by inflamma-aging is closely related to AD. As the main participant of neuroinflammation, the polarization of microglia (MG) could influence the development of neuroinflammation.

Objective

This study aims to observe the impact of YHD on microglia (MG) polarization and neuroinflammation to delay the onset and progression of AD.

Methods

In vivo experiment, four-month senescence accelerated mouse prone 8 (SAMP8) were used as the model group, the SAMR1 mice of the same age were used as the control group. In YHD group, 6.24 g/kg YHD was intragastrically administrated continuously for 12 weeks, and Ibuprofen 0.026 g/kg in positive control group. Morris Water Maze test was used to evaluate the learning and memory ability, Nissl's staining and immunofluorescence double staining for neuron damage and MG M1/M2 polarization, Enzyme-Linked Immunosorbent Assay (ELISA) for neuroinflammation biomarkers in hippocampus, Western blot for key protein expression of TREM2/NF-κB signaling pathway. In vitro experiments, 10 μM/l Aβ1-42 induced BV-2 cell model was used to re-verify the effect of YHD regulating MG polarization to reduce neuroinflammation. Also, TREM2 small interfering RNA (siRNA) was used to clarify the key target of YHD.

Results

YHD could improve the learning and memory ability of SAMP8 mice evaluated by the Morris Water Maze test. Like Ibuprofen, YHD could regulate the M1/M2 polarization of MG and the levels of neuroinflammatory markers TNF-α and IL-10 in hippocampus, and relieve neuroinflammation and neuron loss. In addition, YHD could also regulate the expression of PU.1, TREM2, p-NF-κB P65 in the TREM2/NF-κB signaling pathway. Further in vitro experiments, we found that YHD had a significant regulatory effect on Aβ1-42-induced BV-2 cell polarization, and it could significantly increase PU.1, TREM2, decrease p-NF-κB P65, p-IKKβ, TNF-α, IL-6, IL-1β. At the same time, using siRNA to inhibit TREM2, it proved that TREM2 was a key target for YHD to promote Aβ1-42-induced BV-2 cell M2 polarization to reduce neuroinflammation.

Conclusions

YHD could regulate the TREM2/NF-κB signaling pathway through TREM2, thereby to adjust MG polarization and reduce AD-related neuroinflammation.

Hybrid Amyloid Quantum Dot Nano-Bio Assemblies to Probe Neuroinflammatory Damage

Various oligomeric species of amyloid-beta have been proposed to play different immunogenic roles in the cellular pathology of Alzheimer's Disease. The dynamic interconversion between various amyloid oligomers and fibrillar assemblies makes it difficult to elucidate the role each potential aggregation state may play in driving neuroinflammatory and neurodegenerative pathology. The ability to identify the amyloid species that are key and essential drivers of these pathological hallmarks of Alzheimer's Disease is of fundamental importance for also understanding downstream events including tauopathies that mediate neuroinflammation with neurologic deficits. Here, we report the design and construction of a quantum dot mimetic for larger spherical oligomeric amyloid species as an "endogenously" fluorescent proxy for this cytotoxic assembly of amyloid to investigate its role in inducing inflammatory and stress response states in neuronal and glial cell types. The design parameters and construction protocol developed here may be adapted for developing quantum dot nano-bio assemblies for other biological systems of interest, particularly neurodegenerative diseases involving other protein aggregates.

Glial reactivity is linked to synaptic dysfunctionacross the aging and Alzheimer's disease spectrum

Previous studies have shown that glial and neuronal changes may trigger synaptic dysfunction in Alzheimer's disease(AD). However, the link between glial and neuronal markers and synaptic abnormalities in the living brain is poorly understood. Here, we investigated the association between biomarkers of astrocyte and microglial reactivity and synaptic dysfunction in 478 individuals across the aging and AD spectrum from two cohorts with available CSF measures of amyloid-β(Aβ), phosphorylated tau(pTau181), astrocyte reactivity(GFAP), microglial activation(sTREM2), and synaptic biomarkers(GAP43 and neurogranin). Elevated CSF GFAP levels were linked to presynaptic and postsynaptic dysfunction, regardless of cognitive status or Aβ presence. CSF sTREM2 levels were associated with presynaptic biomarkers in cognitively unimpaired and impaired Aβ + individuals and postsynaptic biomarkers in cognitively impaired Aβ + individuals. Notably, CSF pTau181 levels mediated all associations between GFAP or sTREM2 levels and synaptic dysfunction biomarkers. These results suggest that neuronal-related synaptic biomarkers could be used in clinical trials targeting glial reactivity in AD.

TLR2 immunotherapy suppresses neuroinflammation, tau spread, and memory loss in rTg4510 mice

In Alzheimer's disease, chronic neuroinflammation is accompanied by amyloid and tau pathologies. Especially, aberrant microglial activation is known to precede the regional tau pathology development, but the mechanisms how microglia affect tau spread remain largely unknown. Here, we found that toll-like receptor 2 (TLR2) in microglia recognizes oligomeric tau as a pathogenic ligand and induces inflammatory responses. Knockout of TLR2 reduced tau pathology and microglial activation in rTg4510 tau transgenic mice. Treatment of oligomeric tau induced TLR2 activation and increased inflammatory responses in microglial cells. TLR2 further mediated the tau-induced microglial activation and promoted tau uptake into neurons in neuron-microglia co-culture system and in mouse hippocampus after intracranial tau injection. Importantly, treatment with anti-TLR2 monoclonal antibody Tomaralimab blocked TLR2 activation and inflammatory responses in a dose-dependent manner, and significantly reduced tau spread and memory loss in rTg4510 mice. These results suggest that TLR2 plays a crucial role in tau spread by causing aberrant microglial activation in response to pathological tau, and blocking TLR2 with immunotherapy may ameliorate tau pathogenesis in Alzheimer's disease.

Evidence for reduced anti-inflammatory microglial phagocytic response in late-life major depression

Major depressive disorder (MDD) is associated with Alzheimer's disease (AD) but the precise mechanisms underlying this relationship are not understood. While it is well established that cerebrospinal fluid (CSF) soluble levels of triggering receptor expressed on myeloid cells 2 (sTREM2) increase during early stages of AD, how sTREM2 levels behave in subjects with MDD is not known. In a longitudinal study, we measured CSF sTREM2 levels in 27 elderly cognitively intact individuals with late-life major depression (LLMD) and in 19 healthy controls. We tested the hypothesis that, similarly to what happens in early stages of AD, CSF sTREM2 would be elevated in MDD. In addition, we compared the associations of CSF sTREM2, pro- and anti- inflammatory, and AD biomarkers in LLMD and control subjects. Surprisingly, we found that mean CSF sTREM2 levels were significantly reduced in LLMD compared to controls. This reduction was no longer significant at the 3-year follow-up visit when depression severity improved. In addition, we found that CSF sTREM2 was associated with AD biomarkers and proinflammatory cytokines in controls but not in LLMD. These findings suggest that impaired microglia phagocytic response to AD pathology may be a novel link between MDD and AD.

Complement receptor 4 mediates the clearance of extracellular tau fibrils by microglia

Tauopathies exhibit a characteristic accumulation of misfolded tau aggregates in the brain. Tau pathology shows disease-specific spatiotemporal propagation through intercellular transmission, which is closely correlated with the progression of clinical manifestations. Therefore, identifying molecular mechanisms that prevent tau propagation is critical for developing therapeutic strategies for tauopathies. The various innate immune receptors, such as complement receptor 3 (CR3) and complement receptor 4 (CR4), have been reported to play a critical role in the clearance of various extracellular toxic molecules by microglia. However, their role in tau clearance has not been studied yet. In the present study, we investigated the role of CR3 and CR4 in regulating extracellular tau clearance. We found that CR4 selectively binds to tau fibrils but not to tau monomers, whereas CR3 does not bind to either of them. Inhibiting CR4, but not CR3, significantly reduces the uptake of tau fibrils by BV2 cells and primary microglia. By contrast, inhibiting CR4 has no effect on the uptake of tau monomers by BV2 cells. Furthermore, inhibiting CR4 suppresses the clearance of extracellular tau fibrils, leading to more seed-competent tau fibrils remaining in the extracellular space relative to control samples. We also provide evidence that the expression of CR4 is upregulated in the brains of human Alzheimer's disease patients and the PS19 mouse model of tauopathy. Taken together, our data strongly support that CR4 is a previously undescribed receptor for the clearance of tau fibrils in microglia and may represent a novel therapeutic target for tauopathy.

In a circuit necessary for cognition and emotional affect, Alzheimer's-like pathology associates with neuroinflammation, cognitive and motivational deficits in the young adult TgF344-AD rat

In addition to extracellular amyloid plaques, intracellular neurofibrillary tau tangles, and inflammation, cognitive and emotional affect perturbations are characteristic of Alzheimer's disease (AD). The cognitive and emotional domains impaired by AD include several forms of decision making (such as intertemporal choice), blunted motivation (increased apathy), and impaired executive function (such as working memory and cognitive flexibility). However, the interaction between these domains of the mind and their supporting neurobiological substrates at prodromal stages of AD, or whether these interactions can be predictive of AD severity (individual variability), remain unclear. In this study, we employed a battery of cognitive and emotional tests in the young adult (5-7 mo) transgenic Fisher-344 AD (TgF344-AD; TgAD) rat model of AD. We also assessed whether markers of inflammation or AD-like pathology in the prelimbic cortex (PrL) of the medial prefrontal cortex (mPFC), basolateral amygdala (BLA), or nucleus accumbens (NAc), all structures that directly support the aforementioned behaviors, were predictive of behavioral deficits. We found TgAD rats displayed maladaptive decision making, greater apathy, and impaired working memory that was indeed predicted by AD-like pathology in the relevant brain structures, even at an early age. Moreover, we report that the BLA is an early epicenter of inflammation, and notably, AD-like pathology in the PrL, BLA, and NAc was predictive of BLA inflammation. These results suggest that operant-based battery testing may be sensitive enough to determine pathology trajectories, including neuroinflammation, from early stages of AD.

Sequence of Molecular Events in the Development of Alzheimer's Disease: Cascade Interactions from Beta-Amyloid to Other Involved Proteins

Alzheimer's disease is the primary neurodegenerative disease affecting the elderly population. Despite the first description of its pathology over a century ago, its precise cause and molecular mechanism remain unknown. Numerous factors, including beta-amyloid, tau protein, the APOEε4 gene, and different metals, have been extensively investigated in relation to this disease. However, none of them have been proven to have a decisive causal relationship. Furthermore, no single theory has successfully integrated these puzzle pieces thus far. In this review article, we propose the most probable molecular mechanism for AD, which clearly shows the relationship between the main aspects of the disease, and addresses fundamental questions such as: Why is aging the major risk factor for the disease? Are amyloid plaques and tau tangles the causes or consequences of AD? Why are the distributions of senile plaques and tau tangles in the brain different and independent of each other? Why is the APOEε4 gene a risk factor for AD? Finally, why is the disease more prevalent in women?

A High-Carbohydrate Diet Induces Cognitive Impairment and Promotes Amyloid Burden and Tau Phosphorylation via PI3K/Akt/GSK-3β Pathway in db/db Mice

BACKGROUND

Cognitive impairment is a prevalent complication of type 2 diabetes, influenced significantly by various dietary patterns. High-carbohydrate diets (HCDs) are commonly consumed nowadays; however, the specific impact of HCDs on cognitive function in diabetes remains unclear.

METHODS

The objective of this study was to investigate whether an HCD has effects on cognition in diabetes. Eight-week-old diabetic (db/db) mice and wild-type (WT) mice underwent a twelve-week dietary intervention, including a normal diet (ND), an HCD, or a high-fat diet (HFD). Following this, behavioral tests were conducted, and related hippocampal pathology was evaluated.

RESULTS

Our results demonstrated that an HCD exacerbated cognitive decline in db/db mice compared to an ND. Additionally, an HCD increased amyloid-β burden and expression of β-site APP cleaving enzyme-1. An HCD was also found to promote the phosphorylation of tau protein via the PI3K/Akt/GSK-3β pathway. Furthermore, an HCD markedly induced neuroinflammation and increased the quantity of microglia and astrocytes. However, these damages induced by an HCD were less severe than those caused by an HFD.

CONCLUSIONS

Collectively, our findings indicate that a high intake of carbohydrates can have an adverse impact on cognitive function in diabetes.

Nanoligomers targeting NF-κB and NLRP3 reduce neuroinflammation and improve cognitive function with aging and tauopathy

Neuroinflammation contributes to impaired cognitive function in brain aging and neurodegenerative disorders like Alzheimer's disease, which is characterized by the aggregation of pathological tau. One major driver of both age- and tau-associated neuroinflammation is the NF-κB and NLRP3 signaling axis. However, current treatments targeting NF-κB or NLRP3 may have adverse/systemic effects, and most have not been clinically translatable. In this study, we tested the efficacy of a novel, nucleic acid therapeutic (Nanoligomer) cocktail specifically targeting both NF-κB and NLRP3 in the brain for reducing neuroinflammation and improving cognitive function in old (aged 19 months) wildtype mice, and in rTg4510 tau pathology mice (aged 2 months). We found that 4 weeks of NF-κB/NLRP3-targeting Nanoligomer treatment strongly reduced neuro-inflammatory cytokine profiles in the brain and improved cognitive-behavioral function in both old and rTg4510 mice. These effects of NF-κB/NLRP3-targeting Nanoligomers were also associated with reduced glial cell activation and pathology, favorable changes in transcriptome signatures of glia-associated inflammation (reduced) and neuronal health (increased), and positive systemic effects. Collectively, our results provide a basis for future translational studies targeting both NF-κB and NLRP3 in the brain, perhaps using Nanoligomers, to inhibit neuroinflammation and improve cognitive function with aging and neurodegeneration.

Chuanxiong Renshen Decoction Inhibits Alzheimer's Disease Neuroinflammation by Regulating PPARγ/NF-κB Pathway

Background and Aim

Previous studies of our research group have shown that Chuanxiong Renshen Decoction (CRD) has the effect of treating AD, but the exact mechanism of its effect is still not clarified. The aim of this study was to investigate the effect and mechanism of CRD on AD neuroinflammation.

Materials and Methods

Morris Water Maze (MWM) tests were employed to assess the memory and learning capacity of AD mice. HE and Nissl staining were used to observe the neural cells of mice. The expression of Iba-1 and CD86 were detected by immunohistochemical staining. Utilize UHPLC-MS/MS metabolomics techniques and the KEGG to analyze the metabolic pathways of CRD against AD. Lipopolysaccharide (LPS) induced BV2 microglia cells to construct a neuroinflammatory model. The expression of Iba-1 and CD86 were detected by immunofluorescence and flow cytometry. The contents of TNF-α and IL-1β were detected by ELISA. Western blot assay was used to detect the expression of PPARγ, p-NF-κB p65, NF-κB p65 proteins and inflammatory cytokines iNOS and COX-2 in PPARγ/NF-κB pathway with and without PPARγ inhibitor GW9662.

Results

CRD ameliorated the learning and memory ability of 3×Tg-AD mice, repaired the damaged nerve cells in the hippocampus, reduced the area of Iba-1 and CD86 positive areas in both the hippocampus and cortex regions, as well as attenuated serum levels of IL-1β and TNF-α in mice. CRD-containing serum significantly decreased the expression level of Iba-1, significantly reduced the levels of TNF-α and IL-1β, significantly increased the protein expression of PPARγ, and significantly decreased the proteins expression of iNOS, COX-2 and p-NF-κB p65 in BV2 microglia cells. After addition of PPARγ inhibitor GW9662, the inhibitory effect of CRD-containing serum on NF-κB activation was significantly weakened.

Conclusion

CRD can activate PPARγ, regulating PPARγ/NF-κB signaling pathway, inhibiting microglia over-activation and reducing AD neuroinflammation.

Herpes simplex virus 1 accelerates the progression of Alzheimer's disease by modulating microglial phagocytosis and activating NLRP3 pathway

Accumulating evidence implicates that herpes simplex virus type 1 (HSV-1) has been linked to the development and progression of Alzheimer's disease (AD). HSV-1 infection induces β-amyloid (Aβ) deposition in vitro and in vivo, but the effect and precise mechanism remain elusive. Here, we show that HSV-1 infection of the brains of transgenic 5xFAD mice resulted in accelerated Aβ deposition, gliosis, and cognitive dysfunction. We demonstrate that HSV-1 infection induced the recruitment of microglia to the viral core to trigger microglial phagocytosis of HSV-GFP-positive neuronal cells. In addition, we reveal that the NLRP3 inflammasome pathway induced by HSV-1 infection played a crucial role in Aβ deposition and the progression of AD caused by HSV-1 infection. Blockade of the NLRP3 inflammasome signaling reduces Aβ deposition and alleviates cognitive decline in 5xFAD mice after HSV-1 infection. Our findings support the notion that HSV-1 infection is a key factor in the etiology of AD, demonstrating that NLRP3 inflammasome activation functions in the interface of HSV-1 infection and Aβ deposition in AD.

Neuroinflammation Parallels 18F-PI-2620 Positron Emission Tomography Patterns in Primary 4-Repeat Tauopathies

BACKGROUND

Preclinical, postmortem, and positron emission tomography (PET) imaging studies have pointed to neuroinflammation as a key pathophysiological hallmark in primary 4-repeat (4R) tauopathies and its role in accelerating disease progression.

OBJECTIVE

We tested whether microglial activation (1) progresses in similar spatial patterns as the primary pathology tau spreads across interconnected brain regions, and (2) whether the degree of microglial activation parallels tau pathology spreading.

METHODS

We examined in vivo associations between tau aggregation and microglial activation in 31 patients with clinically diagnosed 4R tauopathies, using 18F-PI-2620 PET and 18F-GE180 (translocator protein [TSPO]) PET. We determined tau epicenters, defined as subcortical brain regions with highest tau PET signal, and assessed the connectivity of tau epicenters to cortical regions of interest using a 3-T resting-state functional magnetic resonance imaging template derived from age-matched healthy elderly controls.

RESULTS

In 4R tauopathy patients, we found that higher regional tau PET covaries with elevated TSPO-PET across brain regions that are functionally connected to each other (β = 0.414, P < 0.001). Microglial activation follows similar distribution patterns as tau and distributes primarily across brain regions strongly connected to patient-specific tau epicenters (β = -0.594, P < 0.001). In these regions, microglial activation spatially parallels tau distribution detectable with 18F-PI-2620 PET.

CONCLUSIONS

Our findings indicate that the spatial expansion of microglial activation parallels tau distribution across brain regions that are functionally connected to each other, suggesting that tau and inflammation are closely interrelated in patients with 4R tauopathies. The combination of in vivo tau and inflammatory biomarkers could therefore support the development of immunomodulatory strategies for disease-modifying treatments in these conditions. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Alzheimer's disease pathophysiology in the Retina

The retina is an emerging CNS target for potential noninvasive diagnosis and tracking of Alzheimer's disease (AD). Studies have identified the pathological hallmarks of AD, including amyloid β-protein (Aβ) deposits and abnormal tau protein isoforms, in the retinas of AD patients and animal models. Moreover, structural and functional vascular abnormalities such as reduced blood flow, vascular Aβ deposition, and blood-retinal barrier damage, along with inflammation and neurodegeneration, have been described in retinas of patients with mild cognitive impairment and AD dementia. Histological, biochemical, and clinical studies have demonstrated that the nature and severity of AD pathologies in the retina and brain correspond. Proteomics analysis revealed a similar pattern of dysregulated proteins and biological pathways in the retina and brain of AD patients, with enhanced inflammatory and neurodegenerative processes, impaired oxidative-phosphorylation, and mitochondrial dysfunction. Notably, investigational imaging technologies can now detect AD-specific amyloid deposits, as well as vasculopathy and neurodegeneration in the retina of living AD patients, suggesting alterations at different disease stages and links to brain pathology. Current and exploratory ophthalmic imaging modalities, such as optical coherence tomography (OCT), OCT-angiography, confocal scanning laser ophthalmoscopy, and hyperspectral imaging, may offer promise in the clinical assessment of AD. However, further research is needed to deepen our understanding of AD's impact on the retina and its progression. To advance this field, future studies require replication in larger and diverse cohorts with confirmed AD biomarkers and standardized retinal imaging techniques. This will validate potential retinal biomarkers for AD, aiding in early screening and monitoring.

FGFR3 drives Aβ-induced tau uptake

The amyloid cascade hypothesis suggests that amyloid beta (Aβ) contributes to initiating subsequent tau pathology in Alzheimer's disease (AD). However, the underlying mechanisms through which Aβ contributes to tau uptake and propagation remain poorly understood. Here, we show that preexisting amyloid pathology accelerates the uptake of extracellular tau into neurons. Using quantitative proteomic analysis of endocytic vesicles, we reveal that Aβ induces the internalization of fibroblast growth factor receptor 3 (FGFR3). Extracellular tau binds to the extracellular domain of FGFR3 and is internalized by the FGFR3 ligand, fibroblast growth factor 2 (FGF2). Aβ accelerates FGF2 secretion from neurons, thereby inducing the internalization of tau-attached FGFR3. Knockdown of FGFR3 in the hippocampus reduces tau aggregation by decreasing tau uptake and improving memory function in AD model mice. These data suggest FGFR3 in neurons as a novel tau receptor and a key mediator of Aβ-induced tau uptake in AD.

Multi-strain probiotics ameliorate Alzheimer's-like cognitive impairment and pathological changes through the AKT/GSK-3β pathway in senescence-accelerated mouse prone 8 mice

BACKGROUND

Alzheimer's disease (AD), the most prevalent type of dementia, still lacks disease-modifying treatment strategies. Recent evidence indicates that maintaining gut microbiota homeostasis plays a crucial role in AD. Targeted regulation of gut microbiota, including probiotics, is anticipated to emerge as a potential approach for AD treatment. However, the efficacy and mechanism of multi-strain probiotics treatment in AD remain unclear.

METHODS

In this study, 6-month-old senescence-accelerated-mouse-prone 8 (SAMP8) and senescence-accelerated-mouse-resistant 1 (SAMR1) were utilized. The SAMP8 mice were treated with probiotic-2 (P2, a probiotic mixture of Bifidobacterium lactis and Lactobacillus rhamnosus) and probiotic-3 (P3, a probiotic mixture of Bifidobacterium lactis, Lactobacillus acidophilus, and Lactobacillus rhamnosus) (1 × 109 colony-forming units) once daily for 8 weeks. Morris water maze (MWM) and novel object recognition (NOR) tests were employed to assess the memory ability. 16S sequencing was applied to determine the composition of gut microbiota, along with detecting serum short-chain fatty acids (SCFAs) concentrations. Neural injury, Aβ and Tau pathology, and neuroinflammation level were assessed through western blot and immunofluorescence. Finally, potential molecular mechanisms was explored through transcriptomic analysis and western blotting.

RESULTS

The MWM and NOR test results indicated a significant improvement in the cognitive level of SAMP8 mice treated with P2 and P3 probiotics compared to the SAMP8 control group. Fecal 16S sequencing revealed an evident difference in the α diversity index between SAMP8 and SAMR1 mice, while the α diversity of SAMP8 mice remained unchanged after P2 and P3 treatment. At the genus level, the relative abundance of ten bacteria differed significantly among the four groups. Multi-strain probiotics treatment could modulate serum SCFAs (valeric acid, isovaleric acid, and hexanoic acid) concentration. Neuropathological results demonstrated a substantial decrease in neural injury, Aβ and Tau pathology and neuroinflammation in the brain of SAMP8 mice treated with P3 and P2. Transcriptomic analysis identified the chemokine signaling pathway as the most significantly enriched signaling pathway between SAMP8 and SAMR1 mice. Western blot test indicated a significant change in the phosphorylation level of downstream AKT/GSK-3β between the SAMP8 and SAMR1 groups, which could be reversed through P2 and P3 treatment.

CONCLUSIONS

Multi-strain probiotics treatment can ameliorate cognitive impairment and pathological change in SAMP8 mice, including neural damage, Aβ and Tau pathology, and neuroinflammation. This effect is associated with the regulation of the phosphorylation of the AKT/GSK-3β pathway.

Targeting Microglia in Neuroinflammation: H3 Receptor Antagonists as a Novel Therapeutic Approach for Alzheimer's Disease, Parkinson's Disease, and Autism Spectrum Disorder

Histamine performs dual roles as an immune regulator and a neurotransmitter in the mammalian brain. The histaminergic system plays a vital role in the regulation of wakefulness, cognition, neuroinflammation, and neurogenesis that are substantially disrupted in various neurodegenerative and neurodevelopmental disorders. Histamine H3 receptor (H3R) antagonists and inverse agonists potentiate the endogenous release of brain histamine and have been shown to enhance cognitive abilities in animal models of several brain disorders. Microglial activation and subsequent neuroinflammation are implicated in impacting embryonic and adult neurogenesis, contributing to the development of Alzheimer's disease (AD), Parkinson's disease (PD), and autism spectrum disorder (ASD). Acknowledging the importance of microglia in both neuroinflammation and neurodevelopment, as well as their regulation by histamine, offers an intriguing therapeutic target for these disorders. The inhibition of brain H3Rs has been found to facilitate a shift from a proinflammatory M1 state to an anti-inflammatory M2 state, leading to a reduction in the activity of microglial cells. Also, pharmacological studies have demonstrated that H3R antagonists showed positive effects by reducing the proinflammatory biomarkers, suggesting their potential role in simultaneously modulating crucial brain neurotransmissions and signaling cascades such as the PI3K/AKT/GSK-3β pathway. In this review, we highlight the potential therapeutic role of the H3R antagonists in addressing the pathology and cognitive decline in brain disorders, e.g., AD, PD, and ASD, with an inflammatory component.

Tau follows principal axes of functional and structural brain organization in Alzheimer's disease

Alzheimer's disease (AD) is a brain network disorder where pathological proteins accumulate through networks and drive cognitive decline. Yet, the role of network connectivity in facilitating this accumulation remains unclear. Using in-vivo multimodal imaging, we show that the distribution of tau and reactive microglia in humans follows spatial patterns of connectivity variation, the so-called gradients of brain organization. Notably, less distinct connectivity patterns ("gradient contraction") are associated with cognitive decline in regions with greater tau, suggesting an interaction between reduced network differentiation and tau on cognition. Furthermore, by modeling tau in subject-specific gradient space, we demonstrate that tau accumulation in the frontoparietal and temporo-occipital cortices is associated with greater baseline tau within their functionally and structurally connected hubs, respectively. Our work unveils a role for both functional and structural brain organization in pathology accumulation in AD, and supports subject-specific gradient space as a promising tool to map disease progression.

Chronic inflammation with microglia senescence at basal forebrain: impact on cholinergic deficit in Alzheimer's brain haemodynamics

Cholinergic innervation in the brain is involved in modulating neurovascular function including cerebral blood flow haemodynamics in response to neuronal activity. Cholinergic deficit is associated with pathophysiology in Alzheimer's disease, albeit the aetiology remains to be clarified. In the current study, neocortex cerebral blood flow response to acetylcholine was evaluated by Laser-Doppler Flowmetry (LDF) in 3xTgAD Alzheimer's disease model) and wild-type mice of two age groups. The peak of cerebral blood flow to acetylcholine (i.v.) from baseline levels (% ΔrCBF) was higher in young 3xTgAD versus in wild-type mice (48.35; 95% CI:27.03-69.67 versus 22.70; CI:15.5-29.91, P < 0.05); this was reversed in old 3xTgAD mice (21.44; CI:2.52-40.35 versus 23.25; CI:23.25-39). Choline acetyltransferase protein was reduced in neocortex, while cerebrovascular reactivity to acetylcholine was preserved in young 3×TgAD mice. This suggests endogenous acetylcholine deficit and possible cholinergic denervation from selected cholinergic nuclei within the basal forebrain. The early deposition of tauopathy moieties (mutant hTau and pTau181) and its coincidence in cholinergic cell clusters (occasionaly), were observed at the basal forebrain of 3xTgAD mice including substantia innominate, nucleus Basalis of Meynert and nucleus of horizontal limb diagonal band of Broca. A prominent feature was microglia interacting tauopathy and demonstrated a variety of morphology changes particularly when located in proximity to tauopathy. The microglia ramified phenotype was reduced as evaluated by the ramification index and Fractal analysis. Increased microglia senescence, identified as SASP (senescence-associated secretory phenotype), was colocalization with p16Ink4ɑ, a marker of irreversible cell-cycle arrest in old 3xTgAD versus wild-type mice (P = 0.001). The p16Ink4ɑ was also observed in neuronal cells bearing tauopathy within the basal forebrain of 3xTgAD mice. TNF-ɑ, the pro-inflammatory cytokine elevated persistently in microglia (Pearson's correlation coefficient = 0.62) and the loss of cholinergic cells in vulnerable basal forebrain environment, was indicated by image analysis in 3xTgAD mice, which linked to the cholinergic deficits in neocortex rCBF haemodynamics. Our study revealed the early change of CBF haemodynamics to acetylcholine in 3xTgAD model. As a major effector of brain innate immune activation, microglia SASP with age-related disease progression is indicative of immune cell senescence, which contributes to chronic inflammation and cholinergic deficits at the basal forebrain. Targeting neuroinflammation and senescence may mitigate cholinergic pathophysiology in Alzheimer's disease.

Decoding sTREM2: its impact on Alzheimer's disease - a comprehensive review of mechanisms and implications

Soluble Triggering Receptor Expressed on Myeloid Cells 2 (sTREM2) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). This review comprehensively examines sTREM2's involvement in AD, focusing on its regulatory functions in microglial responses, neuroinflammation, and interactions with key pathological processes. We discuss the dynamic changes in sTREM2 levels in cerebrospinal fluid and plasma throughout AD progression, highlighting its potential as a therapeutic target. Furthermore, we explore the impact of genetic variants on sTREM2 expression and its interplay with other AD risk genes. The evidence presented in this review suggests that modulating sTREM2 activity could influence AD trajectory, making it a promising avenue for future research and drug development. By providing a holistic understanding of sTREM2's multifaceted role in AD, this review aims to guide future studies and inspire novel therapeutic strategies.

Nanoligomers targeting NF-κB and NLRP3 reduce neuroinflammation and improve cognitive function with aging and tauopathy

Neuroinflammation contributes to impaired cognitive function in brain aging and neurodegenerative disorders like Alzheimer's disease, which is characterized by the aggregation of pathological tau. One major driver of both age- and tau-associated neuroinflammation is the NF-κB and NLRP3 signaling axis. However, current treatments targeting NF-κB or NLRP3 may have adverse/systemic effects, and most have not been clinically translatable. In this study, we tested the efficacy of a novel, nucleic acid therapeutic (Nanoligomer) cocktail specifically targeting both NF-κB and NLRP3 in the brain for reducing neuroinflammation and improving cognitive function in old (aged 19 months) wildtype mice, and in rTg4510 tau pathology mice (aged 2 months). We found that 4 weeks of NF-κB/NLRP3-targeting Nanoligomer treatment strongly reduced neuro-inflammatory cytokine profiles in the brain and improved cognitive-behavioral function in both old and rTg4510 mice. These effects of NF-κB/NLRP3-targeting Nanoligomers were also associated with reduced glial cell activation and pathology, favorable changes in transcriptome signatures of glia-associated inflammation (reduced) and neuronal health (increased), and positive systemic effects. Collectively, our results provide a basis for future translational studies targeting both NF-κB and NLRP3 in the brain, perhaps using Nanoligomers, to inhibit neuroinflammation and improve cognitive function with aging and neurodegeneration.

Identification of senescent, TREM2-expressing microglia in aging and Alzheimer's disease model mouse brain

Alzheimer's disease (AD) and dementia in general are age-related diseases with multiple contributing factors, including brain inflammation. Microglia, and specifically those expressing the AD risk gene TREM2, are considered important players in AD, but their exact contribution to pathology remains unclear. In this study, using high-throughput mass cytometry in the 5×FAD mouse model of amyloidosis, we identified senescent microglia that express high levels of TREM2 but also exhibit a distinct signature from TREM2-dependent disease-associated microglia (DAM). This senescent microglial protein signature was found in various mouse models that show cognitive decline, including aging, amyloidosis and tauopathy. TREM2-null mice had fewer microglia with a senescent signature. Treating 5×FAD mice with the senolytic BCL2 family inhibitor ABT-737 reduced senescent microglia, but not the DAM population, and this was accompanied by improved cognition and reduced brain inflammation. Our results suggest a dual and opposite involvement of TREM2 in microglial states, which must be considered when contemplating TREM2 as a therapeutic target in AD.

Progress on early diagnosing Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects both cognition and non-cognition functions. The disease follows a continuum, starting with preclinical stages, progressing to mild cognitive and behavioral impairment, ultimately leading to dementia. Early detection of AD is crucial for better diagnosis and more effective treatment. However, the current AD diagnostic tests of biomarkers using cerebrospinal fluid and/or brain imaging are invasive or expensive, and mostly are still not able to detect early disease state. Consequently, there is an urgent need to develop new diagnostic techniques with higher sensitivity and specificity during the preclinical stages of AD. Various non-cognitive manifestations, including behavioral abnormalities, sleep disturbances, sensory dysfunctions, and physical changes, have been observed in the preclinical AD stage before occurrence of notable cognitive decline. Recent research advances have identified several biofluid biomarkers as early indicators of AD. This review focuses on these non-cognitive changes and newly discovered biomarkers in AD, specifically addressing the preclinical stages of the disease. Furthermore, it is of importance to explore the potential for developing a predictive system or network to forecast disease onset and progression at the early stage of AD.

Translocator protein (TSPO) genotype does not change cerebrospinal fluid levels of glial activation, axonal and synaptic damage markers in early Alzheimer's disease

BACKGROUND

PET imaging of the translocator protein (TSPO) is used to assess in vivo brain inflammation. One of the main methodological issues with this method is the allelic dependence of the radiotracer affinity. In Alzheimer's disease (AD), previous studies have shown similar clinical and patho-biological profiles between TSPO genetic subgroups. However, there is no evidence regarding the effect of the TSPO genotype on cerebrospinal-fluid biomarkers of glial activation, and synaptic and axonal damage.

METHOD

We performed a trans-sectional study in early AD to compare cerebrospinal-fluid levels of GFAP, YKL-40, sTREM2, IL-6, IL-10, NfL and neurogranin between TSPO genetic subgroups.

RESULTS

We recruited 33 patients with early AD including 16 (48%) high affinity binders, 13 (39%) mixed affinity binders, and 4/33 (12%) low affinity binders. No difference was observed in terms of demographics, and cerebrospinal fluid levels of each biomarker for the different subgroups.

CONCLUSION

TSPO genotype is not associated with a change in glial activation, synaptic and axonal damage in early AD. Further studies with larger numbers of participants will be needed to confirm that the inclusion of specific TSPO genetic subgroups does not introduce selection bias in studies and trials of AD that combine TSPO imaging with cerebrospinal fluid biomarkers.

Association of soluble TREM2 with Alzheimer's disease and mild cognitive impairment: a systematic review and meta-analysis

Objective

Soluble triggering receptor expressed on myeloid cells 2 (sTREM2) is a potential neuroinflammatory biomarker linked to the pathogenesis of Alzheimer's disease (AD) and mild cognitive impairment (MCI). Previous studies have produced inconsistent results regarding sTREM2 levels in various clinical stages of AD. This study aims to establish the correlation between sTREM2 levels and AD progression through a meta-analysis of sTREM2 levels in cerebrospinal fluid (CSF) and blood.

Methods

Comprehensive searches were conducted in PubMed, Embase, Web of Science, and the Cochrane Library to identify observational studies reporting CSF and blood sTREM2 levels in AD patients, MCI patients, and healthy controls. A random effects meta-analysis was used to calculate the standardized mean difference (SMD) and 95% confidence intervals (CIs).

Results

Thirty-six observational studies involving 3,016 AD patients, 3,533 MCI patients, and 4,510 healthy controls were included. CSF sTREM2 levels were significantly higher in both the AD [SMD = 0.28, 95% CI (0.15, 0.41)] and MCI groups [SMD = 0.30, 95% CI (0.13, 0.47)] compared to the healthy control group. However, no significant differences in expression were detected between the AD and MCI groups [SMD = 0.09, 95% CI (-0.09, 0.26)]. Furthermore, increased plasma sTREM2 levels were associated with a higher risk of AD [SMD = 0.42, 95% CI (0.01, 0.83)].

Conclusion

CSF sTREM2 levels are positively associated with an increased risk of AD and MCI. Plasma sTREM2 levels were notably higher in the AD group than in the control group and may serve as a promising biomarker for diagnosing AD. However, sTREM2 levels are not effective for distinguishing between different disease stages of AD. Further investigations are needed to explore the longitudinal changes in sTREM2 levels, particularly plasma sTREM2 levels, during AD progression.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42024514593.

Microglia and amyloid plaque formation in Alzheimer's disease - Evidence, possible mechanisms, and future challenges

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that severely affects patients and their families. Genetic and environmental risk factors, such as viral infections, synergize to accelerate the aging-associated neurodegeneration. Genetic risk factors for late-onset AD (LOAD), which accounts for most AD cases, are predominantly implicated in microglial and immune cell functions. As such, microglia play a major role in formation of amyloid beta (Aβ) plaques, the major pathological hallmark of AD. This review aims to provide an overview of the current knowledge regarding the role of microglia in Aβ plaque formation, as well as their impact on morphological and functional diversity of Aβ plaques. Based on this discussion, we seek to identify challenges and opportunities in this field with potential therapeutic implications.

Personalized whole-brain neural mass models reveal combined Aβ and tau hyperexcitable influences in Alzheimer's disease

Neuronal dysfunction and cognitive deterioration in Alzheimer's disease (AD) are likely caused by multiple pathophysiological factors. However, mechanistic evidence in humans remains scarce, requiring improved non-invasive techniques and integrative models. We introduce personalized AD computational models built on whole-brain Wilson-Cowan oscillators and incorporating resting-state functional MRI, amyloid-β (Aβ) and tau-PET from 132 individuals in the AD spectrum to evaluate the direct impact of toxic protein deposition on neuronal activity. This subject-specific approach uncovers key patho-mechanistic interactions, including synergistic Aβ and tau effects on cognitive impairment and neuronal excitability increases with disease progression. The data-derived neuronal excitability values strongly predict clinically relevant AD plasma biomarker concentrations (p-tau217, p-tau231, p-tau181, GFAP) and grey matter atrophy obtained through voxel-based morphometry. Furthermore, reconstructed EEG proxy quantities show the hallmark AD electrophysiological alterations (theta band activity enhancement and alpha reductions) which occur with Aβ-positivity and after limbic tau involvement. Microglial activation influences on neuronal activity are less definitive, potentially due to neuroimaging limitations in mapping neuroprotective vs detrimental activation phenotypes. Mechanistic brain activity models can further clarify intricate neurodegenerative processes and accelerate preventive/treatment interventions.

Microbial infection promotes amyloid pathology in a mouse model of Alzheimer's disease via modulating γ-secretase

Microbial infection as a type of environmental risk factors is considered to be associated with long-term increased risk of dementia, including Alzheimer's disease (AD). AD is characterized by two neuropathologically molecular hallmarks of hyperphosphorylated tau and amyloid-β (Aβ), the latter generated by several biochemically reactive enzymes, including γ-secretase. However, how infectious risk factors contribute to pathological development of the AD core molecules remains to be addressed. In this work, we utilized a modified herpes simplex virus type 1 (mHSV-1) and found that its hippocampal infection locally promotes Aβ pathology in 5 × FAD mice, the commonly used amyloid model. Mechanistically, we identified HSV-1 membrane glycoprotein US7 (Envelope gI) that interacts with and modulates γ-secretase and consequently facilitates Aβ production. Furthermore, we presented evidence that adenovirus-associated virus-mediated locally hippocampal overexpression of the US7 aggravates Aβ pathology in 5 × FAD mice. Collectively, these findings identify a herpesviral factor regulating γ-secretase in the development and progression of AD and represent a causal molecular link between infectious pathogens and neurodegeneration.

Microglial Reactivity Correlates with Presynaptic Loss Independent of β-Amyloid and Tau

OBJECTIVE

Triggering receptor expressed on myeloid cells-2 (TREM2) and progranulin (PGRN) are critical regulators of microglia activation and can be detected in cerebrospinal fluid (CSF). However, whether microglial reactivity is detrimental or neuroprotective for Alzheimer disease (AD) is still debatable.

METHODS

We identified 663 participants with baseline β-amyloid (Aβ) positron emission tomography (PET) and CSF biomarker data, including phosphorylated tau181 (p-Tau181), soluble TREM2 (sTREM2), PGRN, and growth-associated protein-43 (GAP-43). Among them, 254 participants had concurrent longitudinal CSF biomarkers. We used multivariate regression analysis to study the associations of CSF microglial biomarkers with Aβ PET, CSF p-Tau181, and CSF GAP-43 cross-sectionally and longitudinally. A Chinese aging cohort's independent CSF samples (n = 65) were analyzed as a validation.

RESULTS

Higher baseline levels of CSF microglial biomarkers were related to faster rates of CSF sTREM2 increase and CSF PGRN decrease. Elevated CSF p-Tau181 was associated with higher levels of CSF microglial biomarkers and faster rates of CSF sTREM2 increase and CSF PGRN decrease. In both cohorts, higher Aβ burden was associated with attenuated CSF p-Tau181 effects on CSF microglial biomarker increases. Independent of Aβ PET and CSF p-Tau181 pathologies, higher levels of CSF sTREM2 but not CSF PGRN were related to elevated CSF GAP-43 levels and faster rates of CSF GAP-43 increase.

INTERPRETATION

These findings suggest that higher Aβ burden may attenuate the p-Tau-associated microglial responses, and TREM2-related microglial reactivity may independently correlate with GAP-43-related presynaptic loss. This study highlights the two-edged role of microglial reactivity in AD and other neurodegenerative diseases. ANN NEUROL 2024;95:917-928.

Characterization of tau propagation pattern and cascading hypometabolism from functional connectivity in Alzheimer's disease

Tau pathology and its spatial propagation in Alzheimer's disease (AD) play crucial roles in the neurodegenerative cascade leading to dementia. However, the underlying mechanisms linking tau spreading to glucose metabolism remain elusive. To address this, we aimed to examine the association between pathologic tau aggregation, functional connectivity, and cascading glucose metabolism and further explore the underlying interplay mechanisms. In this prospective cohort study, we enrolled 79 participants with 18F-Florzolotau positron emission tomography (PET), 18F-fluorodeoxyglucose PET, resting-state functional, and anatomical magnetic resonance imaging (MRI) images in the hospital-based Shanghai Memory Study. We employed generalized linear regression and correlation analyses to assess the associations between Florzolotau accumulation, functional connectivity, and glucose metabolism in whole-brain and network-specific manners. Causal mediation analysis was used to evaluate whether functional connectivity mediates the association between pathologic tau and cascading glucose metabolism. We examined 22 normal controls and 57 patients with AD. In the AD group, functional connectivity was associated with Florzolotau covariance (β = .837, r = 0.472, p < .001) and glucose covariance (β = 1.01, r = 0.499, p < .001). Brain regions with higher tau accumulation tend to be connected to other regions with high tau accumulation through functional connectivity or metabolic connectivity. Mediation analyses further suggest that functional connectivity partially modulates the influence of tau accumulation on downstream glucose metabolism (mediation proportion: 49.9%). Pathologic tau may affect functionally connected neurons directly, triggering downstream glucose metabolism changes. This study sheds light on the intricate relationship between tau pathology, functional connectivity, and downstream glucose metabolism, providing critical insights into AD pathophysiology and potential therapeutic targets.

Neuritic Plaques - Gateways to Understanding Alzheimer's Disease

Extracellular deposits of amyloid-β (Aβ) in the form of plaques are one of the main pathological hallmarks of Alzheimer's disease (AD). Over the years, many different Aβ plaque morphologies such as neuritic plaques, dense cored plaques, cotton wool plaques, coarse-grain plaques, and diffuse plaques have been described in AD postmortem brain tissues, but correlation of a given plaque type with AD progression or AD symptoms is not clear. Furthermore, the exact trigger causing the development of one Aβ plaque morphological subtype over the other is still unknown. Here, we review the current knowledge about neuritic plaques, a subset of Aβ plaques surrounded by swollen or dystrophic neurites, which represent the most detrimental and consequential Aβ plaque morphology. Neuritic plaques have been associated with local immune activation, neuronal network dysfunction, and cognitive decline. Given that neuritic plaques are at the interface of Aβ deposition, tau aggregation, and local immune activation, we argue that understanding the exact mechanism of neuritic plaque formation is crucial to develop targeted therapies for AD.

VSP-2 attenuates secretion of inflammatory cytokines induced by LPS in BV2 cells by mediating the PPARγ/NF-κB signaling pathway

Neuroinflammation, characterized by microglial activation and the subsequent secretion of inflammatory cytokines, plays a pivotal role in neurodegenerative diseases and brain injuries, often leading to neuronal damage and death. Alleviating neuroinflammation has thus emerged as a promising strategy to protect neurons and ameliorate neurodegenerative disorders. While peroxisome proliferator-activated receptor gamma (PPARγ) agonists have demonstrated potential therapeutic actions on neuroinflammation, their prolonged use, such as with rosiglitazone, can lead to cardiac risks and lipid differentiation disorders. In this study, we investigated the effects of a newly synthesized PPARγ agonist, VSP-2, on secretion of inflammatory cytokines in BV2 cells. Treatment with VSP-2 significantly reduced the mRNA and protein levels of proinflammatory cytokines such as interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α). Furthermore, VSP-2 attenuated the phosphorylation of nuclear factor kappa B (NF-κB) (65 kD) and IκBα, as well as the nuclear translocation of NF-κB (65 kD). Additionally, the use of PPARγ small interfering RNA was able to attenuate the effects of VSP-2 on proinflammatory cytokines and the NF-κB pathway. In conclusion, our findings suggest that VSP-2 effectively suppressed the expressions of IL-1β, IL-6, and TNF-α via the PPARγ/NF-κB signaling pathway. Given its potential therapeutic benefits, VSP-2 may emerge as a promising candidate for the treatment of neurodegenerative diseases or brain injuries associated with neuroinflammation.

Onset of Alzheimer disease in apolipoprotein ɛ4 carriers is earlier in butyrylcholinesterase K variant carriers

BACKGROUND

The authors sought to examine the impact of the K-variant of butyrylcholinesterase (BCHE-K) carrier status on age-at-diagnosis of Alzheimer disease (AD) in APOE4 carriers.

METHODS

Patients aged 50-74 years with cerebrospinal fluid (CSF) biomarker-confirmed AD, were recruited to clinical trial (NCT03186989 since June 14, 2017). Baseline demographics, disease characteristics, and biomarkers were evaluated in 45 patients according to BCHE-K and APOE4 allelic status in this post-hoc study.

RESULTS

In APOE4 carriers (N = 33), the mean age-at-diagnosis of AD in BCHE-K carriers (n = 11) was 6.4 years earlier than in BCHE-K noncarriers (n = 22, P < .001, ANOVA). In APOE4 noncarriers (N = 12) there was no observed influence of BCHE-K. APOE4 carriers with BCHE-K also exhibited slightly higher amyloid and tau accumulations compared to BCHE-K noncarriers. A predominantly amyloid, limited tau, and limbic-amnestic phenotype was exemplified by APOE4 homozygotes with BCHE-K. In the overall population, multiple regression analyses demonstrated an association of amyloid accumulation with APOE4 carrier status (P < .029), larger total brain ventricle volume (P < .021), less synaptic injury (Ng, P < .001), and less tau pathophysiology (p-tau181, P < .005). In contrast, tau pathophysiology was associated with more neuroaxonal damage (NfL, P = .002), more synaptic injury (Ng, P < .001), and higher levels of glial activation (YKL-40, P = .01).

CONCLUSION

These findings have implications for the genetic architecture of prognosis in early AD, not the genetics of susceptibility to AD. In patients with early AD aged less than 75 years, the mean age-at-diagnosis of AD in APOE4 carriers was reduced by over 6 years in BCHE-K carriers versus noncarriers. The functional status of glia may explain many of the effects of APOE4 and BCHE-K on the early AD phenotype.

TRIAL REGISTRATION

NCT03186989 since June 14, 2017.

Innate immune activation in neurodegenerative diseases

Activation of the innate immune system following pattern recognition receptor binding has emerged as one of the major pathogenic mechanisms in neurodegenerative disease. Experimental, epidemiological, pathological, and genetic evidence underscores the meaning of innate immune activation during the prodromal as well as clinical phases of several neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal dementia. Importantly, innate immune activation and the subsequent release of inflammatory mediators contribute mechanistically to other hallmarks of neurodegenerative diseases such as aberrant proteostatis, pathological protein aggregation, cytoskeleton abnormalities, altered energy homeostasis, RNA and DNA defects, and synaptic and network disbalance and ultimately to the induction of neuronal cell death. In this review, we discuss common mechanisms of innate immune activation in neurodegeneration, with particular emphasis on the pattern recognition receptors (PRRs) and other receptors involved in the detection of damage-associated molecular patterns (DAMPs).

Characterization of monoamine oxidase-B (MAO-B) as a biomarker of reactive astrogliosis in Alzheimer's disease and related dementias

Reactive astrogliosis accompanies the two neuropathological hallmarks of Alzheimer's disease (AD)-Aβ plaques and neurofibrillary tangles-and parallels neurodegeneration in AD and AD-related dementias (ADRD). Thus, there is growing interest in developing imaging and fluid biomarkers of reactive astrogliosis for AD/ADRD diagnosis and prognostication. Monoamine oxidase-B (MAO-B) is emerging as a target for PET imaging radiotracers of reactive astrogliosis. However, a thorough characterization of MAO-B expression in postmortem control and AD/ADRD brains is lacking. We sought to: (1) identify the primary cell type(s) expressing MAO-B in control and AD brains; (2) quantify MAO-B immunoreactivity in multiple brain regions of control and AD donors as a proxy for PET radiotracer uptake; (3) correlate MAO-B level with local AD neuropathological changes, reactive glia, and cortical atrophy; (4) determine whether the MAOB rs1799836 SNP genotype impacts MAO-B expression level; (5) compare MAO-B immunoreactivity across AD/ADRD, including Lewy body diseases (LBD) and frontotemporal lobar degenerations with tau (FTLD-Tau) and TDP-43 (FTLD-TDP). We found that MAO-B is mainly expressed by subpial and perivascular cortical astrocytes as well as by fibrous white matter astrocytes in control brains, whereas in AD brains, MAO-B is significantly upregulated by both cortical reactive astrocytes and white matter astrocytes across temporal, frontal, and occipital lobes. By contrast, MAO-B expression level was unchanged and lowest in cerebellum. Cortical MAO-B expression was independently associated with cortical atrophy and local measures of reactive astrocytes and microglia, and significantly increased in reactive astrocytes surrounding Thioflavin-S+ dense-core Aβ plaques. MAO-B expression was not affected by the MAOB rs1799836 SNP genotype. MAO-B expression was also significantly increased in the frontal cortex and white matter of donors with corticobasal degeneration, Pick's disease, and FTLD-TDP, but not in LBD or progressive supranuclear palsy. These findings support ongoing efforts to develop MAO-B-based PET radiotracers to image reactive astrogliosis in AD/ADRD.

Silencing Apoe with divalent-siRNAs improves amyloid burden and activates immune response pathways in Alzheimer's disease

INTRODUCTION

The most significant genetic risk factor for late-onset Alzheimer's disease (AD) is APOE4, with evidence for gain- and loss-of-function mechanisms. A clinical need remains for therapeutically relevant tools that potently modulate APOE expression.

METHODS

We optimized small interfering RNAs (di-siRNA, GalNAc) to potently silence brain or liver Apoe and evaluated the impact of each pool of Apoe on pathology.

RESULTS

In adult 5xFAD mice, siRNAs targeting CNS Apoe efficiently silenced Apoe expression and reduced amyloid burden without affecting systemic cholesterol, confirming that potent silencing of brain Apoe is sufficient to slow disease progression. Mechanistically, silencing Apoe reduced APOE-rich amyloid cores and activated immune system responses.

DISCUSSION

These results establish siRNA-based modulation of Apoe as a viable therapeutic approach, highlight immune activation as a key pathway affected by Apoe modulation, and provide the technology to further evaluate the impact of APOE silencing on neurodegeneration.

Microglia measured by TSPO PET are associated with Alzheimer's disease pathology and mediate key steps in a disease progression model

INTRODUCTION

Evidence suggests microglial activation precedes regional tau and neurodegeneration in Alzheimer's disease (AD). We characterized microglia with translocator protein (TSPO) positron emission tomography (PET) within an AD progression model where global amyloid beta (Aβ) precedes local tau and neurodegeneration, resulting in cognitive impairment.

METHODS

Florbetaben, PBR28, and MK-6240 PET, T1 magnetic resonance imaging, and cognitive measures were performed in 19 cognitively unimpaired older adults and 22 patients with mild cognitive impairment or mild AD to examine associations among microglia activation, Aβ, tau, and cognition, adjusting for neurodegeneration. Mediation analyses evaluated the possible role of microglial activation along the AD progression model.

RESULTS

Higher PBR28 uptake was associated with higher Aβ, higher tau, and lower MMSE score, independent of neurodegeneration. PBR28 mediated associations between tau in early and middle Braak stages, between tau and neurodegeneration, and between neurodegeneration and cognition.

DISCUSSION

Microglia are associated with AD pathology and cognition and may mediate relationships between subsequent steps in AD progression.

Long-Term High-Fat Diet Consumption Aggravates β-Amyloid Deposition and Tau Pathology Accompanied by Microglial Activation in an Alzheimer's Disease Model

Alzheimer's disease (AD) is the most prevailing form of dementia, with long-term high-fat diet (HFD) consumption being a pivotal contributor to AD pathogenesis. As microglial dysfunction is a crucial factor in the AD onset, it becomes imperative to explore the effects of HFD on microglial function and AD pathogenesis. In the present study, 3xTg-AD model mice at the age of 9-month are subjected to random allocation, with one group receiving a standard diet (ND) and the other an HFD for 3 months. Subsequently, transcriptomic profiling of microglia unveils that HFD alters fatty acid metabolism and mediates T cell infiltration. Within the hippocampus, microglia exhibit aberrant morphology and lipid accretion in response to the HFD, evidenced by conspicuously enlarged microglial cell bodies and accumulation of lipid droplets. These lipid-droplet-accumulating microglia exhibit diminished migratory capacity and compromise plaque consolidation, thereby exacerbating the accumulation of β-amyloid. Noteworthy, the HFD induces T cell infiltration, thereby aggravating neuroinflammation and Tau phosphorylation. Morris water maze test reveals that HFD-consuming mice display marked impairment in memory performance. In summary, this study demonstrates that prolonged HFD consumption exacerbates amyloid deposition, tau pathology, and cognitive deficits, which is associated with the accumulation of lipid droplets within microglia.

Different inflammatory signatures based on CSF biomarkers relate to preserved or diminished brain structure and cognition

Neuroinflammation is a hallmark of Alzheimer's disease (AD) and both positive and negative associations of individual inflammation-related markers with brain structure and cognitive function have been described. We aimed to identify inflammatory signatures of CSF immune-related markers that relate to changes of brain structure and cognition across the clinical spectrum ranging from normal aging to AD. A panel of 16 inflammatory markers, Aβ42/40 and p-tau181 were measured in CSF at baseline in the DZNE DELCODE cohort (n = 295); a longitudinal observational study focusing on at-risk stages of AD. Volumetric maps of gray and white matter (GM/WM; n = 261) and white matter hyperintensities (WMHs, n = 249) were derived from baseline MRIs. Cognitive decline (n = 204) and the rate of change in GM volume was measured in subjects with at least 3 visits (n = 175). A principal component analysis on the CSF markers revealed four inflammatory components (PCs). Of these, the first component PC1 (highly loading on sTyro3, sAXL, sTREM2, YKL-40, and C1q) was associated with older age and higher p-tau levels, but with less pathological Aβ when controlling for p-tau. PC2 (highly loading on CRP, IL-18, complement factor F/H and C4) was related to male gender, higher body mass index and greater vascular risk. PC1 levels, adjusted for AD markers, were related to higher GM and WM volumes, less WMHs, better baseline memory, and to slower atrophy rates in AD-related areas and less cognitive decline. In contrast, PC2 related to less GM and WM volumes and worse memory at baseline. Similar inflammatory signatures and associations were identified in the independent F.ACE cohort. Our data suggest that there are beneficial and detrimental signatures of inflammatory CSF biomarkers. While higher levels of TAM receptors (sTyro/sAXL) or sTREM2 might reflect a protective glia response to degeneration related to phagocytic clearance, other markers might rather reflect proinflammatory states that have detrimental impact on brain integrity.

Mitochondrial Dysfunction as the Major Basis of Brain Aging

The changes in the properties of three biological events that occur with cerebral aging are discussed. These adverse changes already begin to develop early in mid-life and gradually become more pronounced with senescence. Essentially, they are reflections of the progressive decline in effectiveness of key processes, resulting in the deviation of essential biochemical trajectories to ineffective and ultimately harmful variants of these programs. The emphasis of this review is the major role played by the mitochondria in the transition of these three important processes toward more deleterious variants as brain aging proceeds. The immune system: the shift away from an efficient immune response to a more unfocused, continuing inflammatory condition. Such a state is both ineffective and harmful. Reactive oxygen species are important intracellular signaling systems. Additionally, microglial phagocytic activity utilizing short lived reactive oxygen species contribute to the removal of aberrant or dead cells and bacteria. These processes are transformed into an excessive, untargeted, and persistent generation of pro-oxidant free radicals (oxidative stress). The normal efficient neural transmission is modified to a state of undirected, chronic low-level excitatory activity. Each of these changes is characterized by the occurrence of continuous activity that is inefficient and diffused. The signal/noise ratio of several critical biological events is thus reduced as beneficial responses are gradually replaced by their impaired and deleterious variants.

Neuroinflammation of Microglial Regulation in Alzheimer's Disease: Therapeutic Approaches

Alzheimer's disease (AD) is a complex degenerative disease of the central nervous system that is clinically characterized by a progressive decline in memory and cognitive function. The pathogenesis of AD is intricate and not yet fully understood. Neuroinflammation, particularly microglial activation-mediated neuroinflammation, is believed to play a crucial role in increasing the risk, triggering the onset, and hastening the progression of AD. Modulating microglial activation and regulating microglial energy metabolic disorder are seen as promising strategies to intervene in AD. The application of anti-inflammatory drugs and the targeting of microglia for the prevention and treatment of AD has emerged as a new area of research interest. This article provides a comprehensive review of the role of neuroinflammation of microglial regulation in the development of AD, exploring the connection between microglial energy metabolic disorder, neuroinflammation, and AD development. Additionally, the advancements in anti-inflammatory and microglia-regulating therapies for AD are discussed.

Mechanisms linking cerebrovascular dysfunction and tauopathy: Adding a layer of epiregulatory complexity

Intracellular accumulation of hyperphosphorylated misfolded tau proteins are found in many neurodegenerative tauopathies, including Alzheimer's disease (AD). Tau pathology can impact cerebrovascular physiology and function through multiple mechanisms. In vitro and in vivo studies have shown that alterations in the blood-brain barrier (BBB) integrity and function can result in synaptic abnormalities and neuronal damage. In the present review, we will summarize how tau proteostasis dysregulation contributes to vascular dysfunction and, conversely, we will examine the factors and pathways leading to tau pathological alterations triggered by cerebrovascular dysfunction. Finally, we will highlight the role epigenetic and epitranscriptomic factors play in regulating the integrity of the cerebrovascular system and the progression of tauopathy including a few observartions on potential therapeutic interventions. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

The relationship between inflammation, impaired glymphatic system, and neurodegenerative disorders: A vicious cycle

The term "glymphatic" emerged roughly a decade ago, marking a pivotal point in neuroscience research. The glymphatic system, a glial-dependent perivascular network distributed throughout the brain, has since become a focal point of investigation. There is increasing evidence suggesting that impairment of the glymphatic system appears to be a common feature of neurodegenerative disorders, and this impairment exacerbates as disease progression. Nevertheless, the common factors contributing to glymphatic system dysfunction across most neurodegenerative disorders remain unclear. Inflammation, however, is suspected to play a pivotal role. Dysfunction of the glymphatic system can lead to a significant accumulation of protein and waste products, which can trigger inflammation. The interaction between the glymphatic system and inflammation appears to be cyclical and potentially synergistic. Yet, current research is limited, and there is a lack of comprehensive models explaining this association. In this perspective review, we propose a novel model suggesting that inflammation, impaired glymphatic function, and neurodegenerative disorders interconnected in a vicious cycle. By presenting experimental evidence from the existing literature, we aim to demonstrate that: (1) inflammation aggravates glymphatic system dysfunction, (2) the impaired glymphatic system exacerbated neurodegenerative disorders progression, (3) neurodegenerative disorders progression promotes inflammation. Finally, the implication of proposed model is discussed.

De Novo Generation and Identification of Novel Compounds with Drug Efficacy Based on Machine Learning

One of the main challenges in small molecule drug discovery is finding novel chemical compounds with desirable activity. Traditional drug development typically begins with target selection, but the correlation between targets and disease remains to be further investigated, and drugs designed based on targets may not always have the desired drug efficacy. The emergence of machine learning provides a powerful tool to overcome the challenge. Herein, a machine learning-based strategy is developed for de novo generation of novel compounds with drug efficacy termed DTLS (Deep Transfer Learning-based Strategy) by using dataset of disease-direct-related activity as input. DTLS is applied in two kinds of disease: colorectal cancer (CRC) and Alzheimer's disease (AD). In each case, novel compound is discovered and identified in in vitro and in vivo disease models. Their mechanism of actionis further explored. The experimental results reveal that DTLS can not only realize the generation and identification of novel compounds with drug efficacy but also has the advantage of identifying compounds by focusing on protein targets to facilitate the mechanism study. This work highlights the significant impact of machine learning on the design of novel compounds with drug efficacy, which provides a powerful new approach to drug discovery.

Interactions between vascular burden and amyloid-β pathology on trajectories of tau accumulation

Cerebrovascular pathology often co-exists with Alzheimer's disease pathology and can contribute to Alzheimer's disease-related clinical progression. However, the degree to which vascular burden contributes to Alzheimer's disease pathological progression is still unclear. This study aimed to investigate interactions between vascular burden and amyloid-β pathology on both baseline tau tangle load and longitudinal tau accumulation. We included 1229 participants from the Swedish BioFINDER-2 Study, including cognitively unimpaired and impaired participants with and without biomarker-confirmed amyloid-β pathology. All underwent baseline tau-PET (18F-RO948), and a subset (n = 677) underwent longitudinal tau-PET after 2.5 ± 1.0 years. Tau-PET uptake was computed for a temporal meta-region-of-interest. We focused on four main vascular imaging features and risk factors: microbleeds; white matter lesion volume; stroke-related events (infarcts, lacunes and haemorrhages); and the Framingham Heart Study Cardiovascular Disease risk score. To validate our in vivo results, we examined 1610 autopsy cases from an Arizona-based neuropathology cohort on three main vascular pathological features: cerebral amyloid angiopathy; white matter rarefaction; and infarcts. For the in vivo cohort, primary analyses included age-, sex- and APOE ɛ4-corrected linear mixed models between tau-PET (outcome) and interactions between time, amyloid-β and each vascular feature (predictors). For the neuropathology cohort, age-, sex- and APOE ɛ4-corrected linear models between tau tangle density (outcome) and an interaction between plaque density and each vascular feature (predictors) were performed. In cognitively unimpaired individuals, we observed a significant interaction between microbleeds and amyloid-β pathology on greater baseline tau load (β = 0.68, P < 0.001) and longitudinal tau accumulation (β = 0.11, P < 0.001). For white matter lesion volume, we did not observe a significant independent interaction effect with amyloid-β on tau after accounting for microbleeds. In cognitively unimpaired individuals, we further found that stroke-related events showed a significant negative interaction with amyloid-β on longitudinal tau (β = -0.08, P < 0.001). In cognitively impaired individuals, there were no significant interaction effects between cerebrovascular and amyloid-β pathology at all. In the neuropathology dataset, the in vivo observed interaction effects between cerebral amyloid angiopathy and plaque density (β = 0.38, P < 0.001) and between infarcts and plaque density (β = -0.11, P = 0.005) on tau tangle density were replicated. To conclude, we demonstrated that cerebrovascular pathology-in the presence of amyloid-β pathology-modifies tau accumulation in early stages of Alzheimer's disease. More specifically, the co-occurrence of microbleeds and amyloid-β pathology was associated with greater accumulation of tau aggregates during early disease stages. This opens the possibility that interventions targeting microbleeds may attenuate the rate of tau accumulation in Alzheimer's disease.

Exosomes secreted from induced pluripotent stem cell ameliorate the lipopolysaccharide induced neuroinflammatory response via lncRNA-0949

PURPOSE

To study the effect of exosomes derived from the induced pluripotent stem cells (iPSCs) in the neuroinflammatory response of microglia caused by lipopolysaccharide (LPS) and reveal the potential underlying mechanism.

METHODS

A permanent microglia cell line HMO6 was activated by LPS. The features of exosomes were analyzed by nano flow cytometry, Western blot and transmission electron microscope. The RNA-seq was used to analyze the difference of noncoding RNA profiles between iPSC-Exos and HMO6 derived exosomes and proved that long no-coding RNA (lncRNA-0949) was highly expressed in the iPSC-Exos. Activated HMO6 cells were cocultured with iPSC-Exos in which lncRNA-0949 was overexpressed, knocked down or normally expressed. Quantitative real-time polymerase chain reaction (RT-qPCR), Enzyme-Linked Immunosorbent Assay and Western blot assay were adopted to analyze RNA and protein expression of inflammatory factors in HMO6 cells.

RESULTS

The oxidative stress and inflammatory response of microglia were significantly attenuated with the iPSC derived exosomes treatment. LncRNA-0949 was effectively delivered into the HMO6 cells through the iPSC-Exos, which largely alleviated the production of malondialdehyde, IL-6, IL-1β and TNF-α in HMO6 cells. Overexpression of lncRNA-0949 could enhance the anti-inflammatory effect of the iPSC-Exos, and knock-down of lncRNA-0949 impaired this availability.

CONCLUSION

According to our results, lncRNA-0949 enriched exosomes from iPSC could potentially be used as a therapeutic strategy to prevent/treat neuroinflammatory diseases.

Microglia in brain aging: An overview of recent basic science and clinical research developments

Aging is characterized by progressive degeneration of tissues and organs, and it is positively associated with an increased mortality rate. The brain, as one of the most significantly affected organs, experiences age-related changes, including abnormal neuronal activity, dysfunctional calcium homeostasis, dysregulated mitochondrial function, and increased levels of reactive oxygen species. These changes collectively contribute to cognitive deterioration. Aging is also a key risk factor for neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. For many years, neurodegenerative disease investigations have primarily focused on neurons, with less attention given to microglial cells. However, recently, microglial homeostasis has emerged as an important mediator in neurological disease pathogenesis. Here, we provide an overview of brain aging from the perspective of the microglia. In doing so, we present the current knowledge on the correlation between brain aging and the microglia, summarize recent progress of investigations about the microglia in normal aging, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, and then discuss the correlation between the senescent microglia and the brain, which will culminate with a presentation of the molecular complexity involved in the microglia in brain aging with suggestions for healthy aging.

Interleukin 10 (IL10) promoter region polymorphism is associated with IL10 serum concentrations and processing speed in healthy community-dwelling older adults

Inflammation is repressed by interleukin 10 (IL10), a potent anti-inflammatory cytokine, and unchecked inflammation can have detrimental effects on cognition. In healthy older adults enrolled in the Australian Research Council Longevity Intervention (ARCLI) cohort we explored whether a known functional single nucleotide polymorphism (SNP) in the promoter region of IL10, -1082 G/A (rs1800896), was associated with reaction times on computerized cognitive testing that included elements of processing speed (i.e., reaction time). Participants were aged 60-75 years (240 females, 158 males), free of dementia and psychiatric disorders, and provide a blood sample. Processing speed was measured using the Swinburne University Computerized Cognitive Assessment Battery (SUCCAB), which includes measures of reaction time (in milliseconds, ms) on six tasks. Blood-derived DNA was genotyped for the IL10 rs1800896 SNP and presence of the APOE E4 allele. General linear models for each SUCCAB subtest were fitted, with age, sex, education (years), APOE E4 carrier status, and IL10 genotype as independent variables. Carriers of the IL10 AA genotype had significantly slower reaction times on multiple tests compared to carriers of the minor allele (AG, GG) and lower IL10 serum levels. Although IL10 SNPs have not been detected in Alzheimer's disease genome-wide associated studies, these results support further exploration of IL10 mechanisms as a possible resilience factor.

Human stem cell transplantation models of Alzheimer's disease

Alzheimer's disease (AD) is the most frequent form of dementia. It is characterized by pronounced neuronal degeneration with formation of neurofibrillary tangles and deposition of amyloid β throughout the central nervous system. Animal models have provided important insights into the pathogenesis of AD and they have shown that different brain cell types including neurons, astrocytes and microglia have important functions in the pathogenesis of AD. However, there are difficulties in translating promising therapeutic observations in mice into clinical application in patients. Alternative models using human cells such as human induced pluripotent stem cells (iPSCs) may provide significant advantages, since they have successfully been used to model disease mechanisms in neurons and in glial cells in neurodegenerative diseases in vitro and in vivo. In this review, we summarize recent studies that describe the transplantation of human iPSC-derived neurons, astrocytes and microglial cells into the forebrain of mice to generate chimeric transplantation models of AD. We also discuss opportunities, challenges and limitations in using differentiated human iPSCs for in vivo disease modeling and their application for biomedical research.