Microglia mediate the clearance of soluble Abeta through fluid phase macropinocytosis

Unraveling the complex role of microglia in Alzheimer's disease: amyloid β metabolism and plaque formation

BACKGROUND

Alzheimer's disease (AD) is characterized by amyloid β (Aβ) accumulation in the brain. Recent genome-wide association studies have identified numerous AD risk genes highly expressed in microglia, highlighting their potential role in AD pathogenesis. Although microglia possess phagocytic capacity and have been implicated in Aβ clearance, accumulating evidence suggests their contribution to AD pathogenesis is more complex than initially anticipated.

MAIN BODY

This review synthesizes current knowledge on microglial Aβ metabolism in AD, reconciling conflicting data from various studies. We examine evidence supporting the role of microglia in Aβ clearance, including studies on AD risk genes like TREM2 and their impact on microglial phagocytosis. Conversely, we explore findings that challenge this view, such as microglial depletion experiments resulting in unchanged or decreased Aβ accumulation. We propose that the contribution of microglia to Aβ metabolism is context-dependent, varying with disease progression, genetic background, and experimental conditions. Notably, microglia may promote parenchymal amyloid accumulation in early disease stages, while this accumulation-promoting effect may diminish in later stages. We discuss potential mechanisms for this paradoxical effect, including intracellular Aβ aggregation and release of pro-aggregation factors. Additionally, we explore the interplay between microglia-mediated Aβ metabolism and other clearance pathways, such as the glymphatic system, highlighting a potential compensatory relationship between parenchymal amyloid deposition and cerebral amyloid angiopathy.

CONCLUSION

Our review underscores the complex and dynamic role of microglia in AD pathogenesis. Understanding the stage-specific functions of microglia in Aβ metabolism is crucial for developing targeted interventions. Future research should focus on elucidating the mechanisms of microglial functional changes throughout disease progression and determining the pathological significance of these changes. Exploring potential therapeutic strategies that selectively enhance beneficial microglial functions while mitigating their detrimental effects remains an important goal.

Amyloid-β induces lipid droplet-mediated microglial dysfunction via the enzyme DGAT2 in Alzheimer's disease

Microglial phagocytosis genes have been linked to increased risk for Alzheimer's disease (AD), but the mechanisms translating genetic association to cellular dysfunction remain unknown. Here, we showed that microglia formed lipid droplets (LDs) upon amyloid-β (Aβ) exposure and that LD loads increased with proximity to amyloid plaques in brains from individuals with AD and the 5xFAD mouse model. LD-laden microglia exhibited defects in Aβ phagocytosis, and unbiased lipidomic analyses identified a parallel decrease in free fatty acids (FFAs) and increase in triacylglycerols (TGs) as the key metabolic transition underlying LD formation. Diacylglycerol O-acyltransferase 2 (DGAT2)-a key enzyme that converts FFAs to TGs-promoted microglial LD formation and was increased in mouse 5xFAD and human AD brains. Pharmacologically targeting DGAT2 improved microglial uptake of Aβ and reduced plaque load and neuronal damage in 5xFAD mice. These findings identify a lipid-mediated mechanism underlying microglial dysfunction that could become a therapeutic target for AD.

Organelle perturbation in Alzheimer's disease: do intracellular amyloid-ß and the fragmented Golgi mediate early intracellular neurotoxicity?

Alzheimer's disease is a devastating and incurable neurological disease. Most of the current research has focused on developing drugs to clear the extracellular amyloid plaques in the brain of Alzheimer's disease patients. However, this approach is limited as it does not treat the underlying cause of the disease. In this review, we highlight the evidence in the field showing that the accumulation of intracellular toxic amyloid-ß could underpin very early events in neuronal death in both familial early-onset and sporadic late-onset alzheimer's disease. Indeed, intracellular amyloid-ß, which is produced within intracellular compartments, has been shown to perturb endosomal and secretory organelles, in different neuronal models, and the brain of Alzheimer's patients, leading to membrane trafficking defects and perturbation of neuronal function associated with cognition defects. The Golgi apparatus is a central transport and signaling hub at the crossroads of the secretory and endocytic pathways and perturbation of the Golgi ribbon structure is a hallmark of Alzheimer's disease. Here, we discuss the role of the Golgi as a major player in the regulation of amyloid-β production and propose that the Golgi apparatus plays a key role in a cellular network which can seed the onset of Alzheimer's disease. Moreover, we propose that the Golgi is central in an intracellular feedback loop leading to an enhanced level of amyloid-β production resulting in early neuronal defects before the appearance of clinical symptoms. Further advances in defining the molecular pathways of this intracellular feedback loop could support the design of new therapeutic strategies to target a primary source of neuronal toxicity in this disease.

Downregulation of Fidgetin-Like 2 Increases Microglial Function: The Relationship Between Microtubules, Morphology, and Activity

The microtubule cytoskeleton regulates microglial morphology, motility, and effector functions. The microtubule-severing enzyme, fidgetin-like 2 (FL2), negatively regulates cell motility and nerve regeneration, making it a promising therapeutic target for central nervous system injury. Microglia perform important functions in response to inflammation and injury, but how FL2 affects microglia is unclear. In this study, we investigated the role of FL2 in microglial morphology and injury responses in vitro. We first determined that the pro-inflammatory stimulus, lipopolysaccharide (LPS), induced a dose- and time-dependent reduction in FL2 expression associated with reduced microglial ramification. We then administered nanoparticle-encapuslated FL2 siRNA to knockdown FL2 and assess microglial functions compared to negative control siRNA and vehicle controls. Time-lapse live-cell microscopy showed that FL2 knockdown increased the velocity of microglial motility. After incubation with fluorescently labeled IgG-opsonized beads, FL2 knockdown increased phagocytosis. Microglia were exposed to low-dose LPS after nanoparticle treatment to model injury-induced cytokine secretion. FL2 knockdown enhanced LPS-induced cytokine secretion of IL-1α, IL-1β, and TNFα. These results identify FL2 as a regulator of microglial morphology and suggest that FL2 can be targeted to increase or accelerate microglial injury responses.

Quantification and correlation of amyloid-β plaque load, glial activation, GABAergic interneuron numbers, and cognitive decline in the young TgF344-AD rat model of Alzheimer's disease

Background

Animal models of Alzheimer's disease (AD) are essential tools for investigating disease pathophysiology and conducting preclinical drug testing. In this study, we examined neuronal and glial alterations in the hippocampus and medial prefrontal cortex (mPFC) of young TgF344-AD rats and correlated these changes with cognitive decline and amyloid-β plaque load.

Methods

We compared TgF344-AD and non-transgenic littermate rats aged 7-8 months of age. We systematically quantified β-amyloid plaques, astrocytes, microglia, four different subtypes of GABAergic interneurons (calretinin-, cholecystokinin-, parvalbumin-, and somatostatin-positive neurons), and newly generated neurons in the hippocampus. Spatial learning and memory were assessed using the Barnes maze test.

Results

Young TgF344-AD rats had a large number of amyloid plaques in both the hippocampus and mPFC, together with a pronounced increase in microglial cell numbers. Astrocytic activation was significant in the mPFC. Cholecystokinin-positive cell numbers were decreased in the hippocampus of transgenic rats, but calretinin-, parvalbumin-, and somatostatin-positive cell numbers were not altered. Adult neurogenesis was not affected by genotype. TgF344-AD rats had spatial learning and memory impairments, but this cognitive deficit did not correlate with amyloid plaque number or cellular changes in the brain. In the hippocampus, amyloid plaque numbers were negatively correlated with cholecystokinin-positive neuron and microglial cell numbers. In the mPFC, amyloid plaque number was negatively correlated with the number of astrocytes.

Conclusion

Pronounced neuropathological changes were found in the hippocampus and mPFC of young TgF344-AD rats, including the loss of hippocampal cholecystokinin-positive interneurons. Some of these neuropathological changes were negatively correlated with amyloid-β plaque load, but not with cognitive impairment.

Ketamine does not rescue plaque load or gap detection in the 5XFAD mouse model of Alzheimer's disease

Ketamine has received growing attention for its effects on neuroplasticity and neuroinflammation, and as a treatment for depression and other mental health disorders. Recent evidence suggests that early sensory and behavioral deficits in Alzheimer's disease could be caused by synaptic disruption that occurs before irreversible neuropathology. This raises the possibility that ketamine could slow down or prevent network disruption and the ensuing sensory and behavioral deficits in Alzheimer's. Here we tested this idea in the 5XFAD mouse model of Alzheimer's, using either an acute single injection of ketamine, or chronic daily injections over 15 weeks. We tested the effects of ketamine on both amyloid plaque load and on a behavioral auditory gap detection task that is an early Alzheimer's biomarker in both mice and humans. We found that ketamine had no effect on plaque load, nor any effect on gap detection, for either acute or chronic dosing. Chronic ketamine facilitated startle responses specifically in 5XFAD mice, but this could simply be related to experience-dependent effects on stress or habituation rather than any rescue effect of ketamine on Alzheimer's-related deficits. We did find robust correlations between gap detection deficits and plaque load in auditory cortex and in the caudal pontine reticular nucleus, demonstrating that the behavioral deficits seen in 5XFAD mice are directly related to amyloid accumulation in these brain regions, and confirming the validity of gap detection as an early biomarker of Alzheimer's. Ketamine, however, had no effect on the strength of these correlations. We conclude that ketamine has no beneficial effect on the development of behavioral gap detection deficits or plaque load in the 5XFAD Alzheimer's mouse model, following either an acute single dose or a chronic daily dose regimen.

Exosomes and non-coding RNAs: bridging the gap in Alzheimer's pathogenesis and therapeutics

Alzheimer's disease (AD) is a neurodegenerative disease that primarily affects the elderly population and is the leading cause of dementia. Meanwhile, the vascular hypothesis suggests that vascular damage occurs in the early stages of the disease, leading to neurodegeneration and hindered waste clearance, which in turn triggers a series of events including the accumulation of amyloid plaques and Tau protein tangles. Non-coding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), have been found to be involved in the regulation of AD. Furthermore, lncRNAs and circRNAs can act as competitive endogenous RNAs to inhibit miRNAs, and their interactions can form a complex regulatory network. Exosomes, which are extracellular vesicles (EVs), are believed to be able to transfer ncRNAs between cells, thus playing a regulatory role in the brain by crossing the blood-brain barrier (BBB). Exosomes are part of the intercellular carrier system; therefore, utilizing exosomes to deliver drugs to recipient cells might not activate the immune system, making it a potential strategy to treat central nervous system diseases. In this review, we review that AD is a multifactorial neurological disease and that ncRNAs can regulate its multiple pathogenic mechanisms to improve our understanding of the etiology of AD and to simultaneously regulate multiple pathogenic mechanisms of AD through the binding of ncRNAs to exosomes to improve the treatment of AD.

Microglial Lyzl4 Facilitates β-Amyloid Clearance in Alzheimer's Disease

Alzheimer's Disease (AD) is a neurodegenerative condition characterized by the accumulation and deposition of amyloid-β (Aβ) aggregates in the brain. Despite a wealth of research on the toxicity of Aβ and its role in synaptic damage, the mechanisms facilitating Aβ clearance are not yet fully understood. However, microglia, the primary immune cells of the central nervous system, are known to maintain homeostasis through the phagocytic clearance of protein aggregates and cellular debris. In this study, RNA sequencing analysis and live cell functional screens are employed to uncover microglial genetic modifiers related to AD. Lyzl4 is identified, which encodes a c-type lysozyme-like enzyme primarily localized to microglial lysosomes, as a gene significantly upregulated in AD microglia with aging and propose that Lyzl4 upregulation acts as a positive regulator of Aβ clearance. Furthermore, it is found that Lyzl4 overexpression boosts Aβ clearance both in vitro and in vivo, underscoring its potential for mitigating Aβ burden. These novel insights position Lyzl4 as a promising therapeutic target for Alzheimer's disease, paving the way for further exploration into potential AD treatments.

Microglia degrade Alzheimer's amyloid-beta deposits extracellularly via digestive exophagy

How microglia digest Alzheimer's fibrillar amyloid-beta (Aβ) plaques that are too large to be phagocytosed is not well understood. Here, we show that primary microglial cells create acidic extracellular compartments, lysosomal synapses, on model plaques and digest them with exocytosed lysosomal enzymes. This mechanism, called digestive exophagy, is confirmed by electron microscopy in 5xFAD mouse brains, which shows that a lysosomal enzyme, acid phosphatase, is secreted toward the plaques in structures resembling lysosomal synapses. Signaling studies demonstrate that the PI3K-AKT pathway modulates the formation of lysosomal synapses, as inhibition of PI3K1β or AKT1/2 reduces both lysosome exocytosis and actin polymerization, both required for the formation of the compartments. Finally, we show that small fibrils of Aβ previously internalized and trafficked to lysosomes are exocytosed toward large Aβ aggregates by microglia. Thus, the release of lysosomal contents during digestive exophagy may also contribute to the spread and growth of fibrillar Aβ.

Amyloid β Induces Lipid Droplet-Mediated Microglial Dysfunction in Alzheimer's Disease

Several microglia-expressed genes have emerged as top risk variants for Alzheimer's disease (AD). Impaired microglial phagocytosis is one of the main proposed outcomes by which these AD-risk genes may contribute to neurodegeneration, but the mechanisms translating genetic association to cellular dysfunction remain unknown. Here we show that microglia form lipid droplets (LDs) upon exposure to amyloid-beta (Aβ), and that their LD load increases with proximity to amyloid plaques in brains from human patients and the AD mouse model 5xFAD. LD formation is dependent on age and disease progression and is prominent in the hippocampus in mice and humans. Despite differences in microglial LD load between brain regions and sexes in mice, LD-laden microglia exhibited a deficit in Aβ phagocytosis. Unbiased lipidomic analysis identified a decrease in free fatty acids (FFAs) and a parallel increase in triacylglycerols (TGs) as the key metabolic transition underlying LD formation. DGAT2, a key enzyme for converting FFAs to TGs, promotes microglial LD formation and is increased in 5xFAD and human AD brains. Inhibition or degradation of DGAT2 improved microglial uptake of Aβ and drastically reduced plaque load in 5xFAD mice, respectively. These findings identify a new lipid-mediated mechanism underlying microglial dysfunction that could become a novel therapeutic target for AD.

Lipid-nanoparticle-induced vacuolization in microglia

Lipid-containing vacuoles in microglia were discovered more than one hundred years ago in the brain of patients showing neurodegenerative processes. Recently, molecular-biological studies demonstrated specific changes in lipid-metabolism related to neurodegeneration. Despite that already Alzheimer described a distinct glia phenotype having large, lipid-containing vacuoles (Gitterzellen), little is known about how microglia convert lipid metabolites into a vacuolated phenotype. We studied the impact of liver-derived, insoluble, lipid-enriched nanoparticles (Lef-NP) ( ~ 20 nm) and of ceramide-coated Percoll-nanoparticles (Cer-NP) ( ~ 20 nm) on vacuolization in microglia. Lipidomic analysis of Lef-NP revealed numerous distinct lipids, including pro-inflammatory ceramides, which are enriched in the brain of Alzheimer patients. Video microscopy revealed that hepatocyte-derived Lef-NP and Cer-NP enhanced macropinocytosis, followed by macropinosome swelling and formation of the Gitterzellen phenotype. Neither ceramide nor Percoll-nanoparticles induced Gitterzellen-formation. Electron-tomography visualized membrane contact-sites between nanoparticle-loaded endosomes, endoplasmic reticulum cisternae and mitochondria. Suppression of lipid-nanoparticle-induced Gitterzellen-formation by amiloride, which supresses macropinocytosis, and bafilomycin A, an endosomal acidification inhibitor, further confirmed a pinocytotic pathway in Gitterzellen-formation. Bafilomycin A also reversed Gitterzellen to a ramified microglia phenotype. Our experimental findings suggest that lipid-nanoparticles but not emulsified lipids provoke vacuolization in microglia, and provide a simple in-vitro model for a pathogenic process taking years in the human brain.

The Mechanistic Link Between Tau-Driven Proteotoxic Stress and Cellular Senescence in Alzheimer's Disease

In Alzheimer's disease (AD), tau dissociates from microtubules (MTs) due to hyperphosphorylation and misfolding. It is degraded by various mechanisms, including the 20S proteasome, chaperone-mediated autophagy (CMA), 26S proteasome, macroautophagy, and aggrephagy. Neurofibrillary tangles (NFTs) form upon the impairment of aggrephagy, and eventually, the ubiquitin chaperone valosin-containing protein (VCP) and heat shock 70 kDa protein (HSP70) are recruited to the sites of NFTs for the extraction of tau for the ubiquitin-proteasome system (UPS)-mediated degradation. However, the impairment of tau degradation in neurons allows tau to be secreted into the extracellular space. Secreted tau can be monomers, oligomers, and paired helical filaments (PHFs), which are seeding competent pathological tau that can be endocytosed/phagocytosed by healthy neurons, microglia, astrocytes, oligodendrocyte progenitor cells (OPCs), and oligodendrocytes, often causing proteotoxic stress and eventually triggers senescence. Senescent cells secrete various senescence-associated secretory phenotype (SASP) factors, which trigger cellular atrophy, causing decreased brain volume in human AD. However, the molecular mechanisms of proteotoxic stress and cellular senescence are not entirely understood and are an emerging area of research. Therefore, this comprehensive review summarizes pertinent studies that provided evidence for the sequential tau degradation, failure, and the mechanistic link between tau-driven proteotoxic stress and cellular senescence in AD.

The deficient CLEC5A ameliorates the behavioral and pathological deficits via the microglial Aβ clearance in Alzheimer's disease mouse model

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease that causes cognitive dysfunction in older adults. One of the AD pathological factors, β-Amyloid (Aβ), triggers inflammatory responses and phagocytosis of microglia. C-type lectin domain family 5 member A (CLEC5A) induces over-reactive inflammatory responses in several virus infections. Yet, the role of CLEC5A in AD progression remains unknown. This study aimed to elucidate the contribution of CLEC5A to Aβ-induced microglial activation and behavioral deficits.

METHODS

The AD mouse model was crossed with Clec5a knockout mice for subsequent behavioral and pathological tests. The memory deficit was revealed by the Morris water maze, while the nociception abnormalities were examined by the von Frey filament and hotplate test. The Aβ deposition and microglia recruitment were identified by ELISA and immunohistochemistry. The inflammatory signals were identified by ELISA and western blotting. In the Clec5a knockdown microglial cell model and Clec5a knockout primary microglia, the microglial phagocytosis was revealed using the fluorescent-labeled Aβ.

RESULTS

The AD mice with Clec5a knockout improved Aβ-induced memory deficit and abnormal nociception. These mice have reduced Aβ deposition and increased microglia coverage surrounding the amyloid plaque, suggesting the involvement of CLEC5A in AD progression and Aβ clearance. Moreover, the phagocytosis was also increased in the Aβ-stressed Clec5a knockdown microglial cell lines and Clec5a knockout primary microglia.

CONCLUSION

The Clec5a knockout ameliorates AD-like deficits by modulating microglial Aβ clearance. This study implies that targeting microglial Clec5a could offer a promising approach to mitigate AD progression.

How do HCN channels play a part in Alzheimer's and Parkinson's disease?

Neurodegenerative diseases like Alzheimer's and Parkinson's disease (AD and PD) are well-known, yet their underlying causes remain unclear. Recent studies have suggested that disruption of ion channels contribute to their pathogenesis. Among these channels, the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, encoded by HCN1-4 genes, are of particular interest due to their role in generating hyperpolarization-activated current (Ih), which is crucial in various neural activities impacting memory and motor functions. A growing body of evidence underscores the pivotal role of HCN in Aβ generation, glial cell function, and ischemia-induced dementia; while HCN is expressed in various regions of the basal ganglia, modulating their functions and influencing motor disorders in PD; neuroinflammation triggered by microglial activation represents a shared pathological mechanism in both AD and PD, in which HCN also plays a significant part. This review delves into the neuronal functions governed by HCN, its roles in the aforementioned pathogenesis, its expression patterns in AD and PD, and discusses potential therapeutic drugs targeting HCN for the treatment of these diseases, aiming to offer a novel perspective and inspire future research endeavors.

Cognitive Effects of Simulated Galactic Cosmic Radiation Are Mediated by ApoE Status, Sex, and Environment in APP Knock-In Mice

Cosmic radiation experienced during space travel may increase the risk of cognitive impairment. While simulated galactic cosmic radiation (GCRsim) has led to memory deficits in wildtype (WT) mice, it has not been investigated whether GCRsim in combination with genetic risk factors for Alzheimer's disease (AD) worsens memory further in aging mice. Here, we investigated the central nervous system (CNS) effects of 0 Gy (sham) or 0.75 Gy five-ion GCRsim or 2 Gy gamma radiation (IRR) in 14-month-old female and male APPNL-F/NL-F knock-in (KI) mice bearing humanized ApoE3 or ApoE4 (APP;E3F and APP;E4F). As travel to a specialized facility was required for irradiation, both traveled sham-irradiated C57BL/6J WT and KI mice and non-traveled (NT) KI mice acted as controls for potential effects of travel. Mice underwent four behavioral tests at 20 months of age and were euthanized for pathological and biochemical analyses 1 month later. Fecal samples were collected pre- and post-irradiation at four different time points. GCRsim seemed to impair memory in male APP;E3F mice compared to their sham counterparts. Travel tended to improve cognition in male APP;E3F mice and lowered total Aβ in female and male APP;E3F mice compared to their non-traveled counterparts. Sham-irradiated male APP;E4F mice accumulated more fibrillar amyloid than their APP;E3F counterparts. Radiation exposure had only modest effects on behavior and brain changes, but travel-, sex-, and genotype-specific effects were seen. Irradiated mice had immediate and long-term differences in their gut bacterial composition that correlated to Alzheimer's disease phenotypes.

Switch to phagocytic microglia by CSFR1 inhibition drives amyloid-beta clearance from glutamatergic terminals rescuing LTP in acute hippocampal slices

Microglia, traditionally regarded as innate immune cells in the brain, drive neuroinflammation and synaptic dysfunctions in the early phases of Alzheimer disease (AD), acting upstream to Aβ accumulation. Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its levels are significantly increased in neurodegenerative diseases, possibly contributing to the chronic inflammatory microglial response. On the other hand, CSF-1R inhibitors confer neuroprotection in preclinical models of neurodegenerative diseases. Here, we determined the effects of the CSF-1R inhibitor PLX3397 on the Aβ-mediated synaptic alterations in ex vivo hippocampal slices. Electrophysiological findings show that PLX3397 rescues LTP impairment and neurotransmission changes induced by Aβ. In addition, using confocal imaging experiments, we demonstrate that PLX3397 stimulates a microglial transition toward a phagocytic phenotype, which in turn promotes the clearance of Aβ from glutamatergic terminals. We believe that the selective pruning of Aβ-loaded synaptic terminals might contribute to the restoration of LTP and excitatory transmission alterations observed upon acute PLX3397 treatment. This result is in accordance with the mechanism proposed for CSF1R inhibitors, that is to eliminate responsive microglia and replace it with newly generated, homeostatic microglia, capable of promoting brain repair. Overall, our findings identify a connection between the rapid microglia adjustments and the early synaptic alterations observed in AD, possibly highlighting a novel disease-modifying target.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fused in sarcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic Frontotemporal lobar degeneration (FTLD). Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fu sed in s arcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic FTLD. Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

Co-aggregation with Apolipoprotein E modulates the function of Amyloid-β in Alzheimer's disease

Which isoforms of apolipoprotein E (apoE) we inherit determine our risk of developing late-onset Alzheimer's Disease (AD), but the mechanism underlying this link is poorly understood. In particular, the relevance of direct interactions between apoE and amyloid-β (Aβ) remains controversial. Here, single-molecule imaging shows that all isoforms of apoE associate with Aβ in the early stages of aggregation and then fall away as fibrillation happens. ApoE-Aβ co-aggregates account for ~50% of the mass of diffusible Aβ aggregates detected in the frontal cortices of homozygotes with the higher-risk APOE4 gene. We show how dynamic interactions between apoE and Aβ tune disease-related functions of Aβ aggregates throughout the course of aggregation. Our results connect inherited APOE genotype with the risk of developing AD by demonstrating how, in an isoform- and lipidation-specific way, apoE modulates the aggregation, clearance and toxicity of Aβ. Selectively removing non-lipidated apoE4-Aβ co-aggregates enhances clearance of toxic Aβ by glial cells, and reduces secretion of inflammatory markers and membrane damage, demonstrating a clear path to AD therapeutics.

Modulation of Oxidative Stress and Neuroinflammation by Cannabidiol (CBD): Promising Targets for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of dementia globally. Although the direct cause of AD remains under debate, neuroinflammation and oxidative stress are critical components in its pathogenesis and progression. As a result, compounds like cannabidiol (CBD) are being increasingly investigated for their ability to provide antioxidant and anti-inflammatory neuroprotection. CBD is the primary non-psychotropic phytocannabinoid derived from Cannabis sativa. It has been found to provide beneficial outcomes in a variety of medical conditions and is gaining increasing attention for its potential therapeutic application in AD. CBD is not psychoactive and its lipophilic nature allows its rapid distribution throughout the body, including across the blood-brain barrier (BBB). CBD also possesses anti-inflammatory, antioxidant, and neuroprotective properties, making it a viable candidate for AD treatment. This review outlines CBD's mechanism of action, the role of oxidative stress and neuroinflammation in AD, and the effectiveness and limitations of CBD in preclinical models of AD.

An integrated toolkit for human microglia functional genomics

BACKGROUND

Microglia, the brain's resident immune cells, play vital roles in brain development, and disorders like Alzheimer's disease (AD). Human iPSC-derived microglia (iMG) provide a promising model to study these processes. However, existing iMG generation protocols face challenges, such as prolonged differentiation time, lack of detailed characterization, and limited gene function investigation via CRISPR-Cas9.

METHODS

Our integrated toolkit for in-vitro microglia functional genomics optimizes iPSC differentiation into iMG through a streamlined two-step, 20-day process, producing iMG with a normal karyotype. We confirmed the iMG's authenticity and quality through single-cell RNA sequencing, chromatin accessibility profiles (ATAC-Seq), proteomics and functional tests. The toolkit also incorporates a drug-dependent CRISPR-ON/OFF system for temporally controlled gene expression. Further, we facilitate the use of multi-omic data by providing online searchable platform that compares new iMG profiles to human primary microglia: https://sherlab.shinyapps.io/IPSC-derived-Microglia/ .

RESULTS

Our method generates iMG that closely align with human primary microglia in terms of transcriptomic, proteomic, and chromatin accessibility profiles. Functionally, these iMG exhibit Ca2 + transients, cytokine driven migration, immune responses to inflammatory signals, and active phagocytosis of CNS related substrates including synaptosomes, amyloid beta and myelin. Significantly, the toolkit facilitates repeated iMG harvesting, essential for large-scale experiments like CRISPR-Cas9 screens. The standalone ATAC-Seq profiles of our iMG closely resemble primary microglia, positioning them as ideal tools to study AD-associated single nucleotide variants (SNV) especially in the genome regulatory regions.

CONCLUSIONS

Our advanced two-step protocol rapidly and efficiently produces authentic iMG. With features like the CRISPR-ON/OFF system and a comprehensive multi-omic data platform, our toolkit equips researchers for robust microglial functional genomic studies. By facilitating detailed SNV investigation and offering a sustainable cell harvest mechanism, the toolkit heralds significant progress in neurodegenerative disease drug research and therapeutic advancement.

Novel histone post-translational modifications in Alzheimer's disease: current advances and implications

Alzheimer's disease (AD) has a complex pathogenesis, and multiple studies have indicated that histone post-translational modifications, especially acetylation, play a significant role in it. With the development of mass spectrometry and proteomics, an increasing number of novel HPTMs, including lactoylation, crotonylation, β-hydroxybutyrylation, 2-hydroxyisobutyrylation, succinylation, and malonylation, have been identified. These novel HPTMs closely link substance metabolism to gene regulation, and an increasing number of relevant studies on the relationship between novel HPTMs and AD have become available. This review summarizes the current advances and implications of novel HPTMs in AD, providing insight into the deeper pathogenesis of AD and the development of novel drugs.

Investigation of Antibody Pharmacokinetics in the Brain Following Intra-CNS Administration and Development of PBPK Model to Characterize the Data

Despite the promising potential of direct central nervous system (CNS) antibody administration to enhance brain exposure, there remains a significant gap in understanding the disposition of antibodies following different intra-CNS injection routes. To bridge this knowledge gap, this study quantitatively investigated the brain pharmacokinetics (PK) of antibodies following intra-CNS administration. The microdialysis samples from the striatum (ST), cerebrospinal fluid (CSF) samples through cisterna magna (CM) puncture, plasma, and brain homogenate samples were collected to characterize the pharmacokinetics (PK) profiles of a non-targeting antibody, trastuzumab, following intracerebroventricular (ICV), intracisternal (ICM), and intrastriatal (IST) administration. For a comprehensive analysis, these intra-CNS injection datasets were juxtaposed against our previously acquired intravenous (IV) injection data obtained under analogous experimental conditions. Our findings highlighted that direct CSF injections, either through ICV or ICM, resulted in ~ 5-6-fold higher interstitial fluid (ISF) drug exposure than IV administration. Additionally, the low bioavailability observed following IST administration indicates the existence of a local degradation process for antibody elimination in the brain ISF along with the ISF bulk flow. The study further refined a physiologically based pharmacokinetic (PBPK) model based on new observations by adding the perivascular compartments, oscillated CSF flow, and the nonspecific uptake and degradation of antibodies by brain parenchymal cells. The updated model can well characterize the antibody PK following systemic and intra-CNS administration. Thus, our research offers quantitative insight into antibody brain disposition pathways and paves the way for determining optimal dosing and administration strategies for antibodies targeting CNS disorders.

Effects of early tooth loss on chronic stress and progression of neuropathogenesis of Alzheimer's disease in adult Alzheimer's model AppNL-G-F mice

Introduction

Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by accumulated amyloid-β (Aβ) plaques, aggregated phosphorylated tau protein, gliosis-associated neuroinflammation, synaptic dysfunction, and cognitive impairment. Many cohort studies indicate that tooth loss is a risk factor for AD. The detailed mechanisms underlying the association between AD and tooth loss, however, are not yet fully understood.

Methods

We explored the involvement of early tooth loss in the neuropathogenesis of the adult AppNL-G-F mouse AD model. The maxillary molars were extracted bilaterally in 1-month-old male mice soon after tooth eruption.

Results

Plasma corticosterone levels were increased and spatial learning memory was impaired in these mice at 6 months of age. The cerebral cortex and hippocampus of AD mice with extracted teeth showed an increased accumulation of Aβ plaques and phosphorylated tau proteins, and increased secretion of the proinflammatory cytokines, including interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α), accompanied by an increased number of microglia and astrocytes, and decreased synaptophysin expression. AD mice with extracted teeth also had a shorter lifespan than the control mice.

Discussion

These findings revealed that long-term tooth loss is a chronic stressor, activating the recruitment of microglia and astrocytes; exacerbating neuroinflammation, Aβ deposition, phosphorylated tau accumulation, and synaptic dysfunction; and leading to spatial learning and memory impairments in AD model mice.

Endocytosis and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia. The pathogenesis of AD still remains unclear, including two main hypotheses: amyloid cascade and tau hyperphosphorylation. The hallmark neuropathological changes of AD are extracellular deposits of amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Endocytosis plays an important role in a number of cellular processes including communication with the extracellular environment, nutrient uptake, and signaling by the cell surface receptors. Based on the results of genetic and biochemical studies, there is a link between neuronal endosomal function and AD pathology. Taking this into account, we can state that in the results of previous research, endolysosomal abnormality is an important cause of neuronal lesions in the brain. Endocytosis is a central pathway involved in the regulation of the degradation of amyloidogenic components. The results of the studies suggest that a correlation between alteration in the endocytosis process and associated protein expression progresses AD. In this article, we discuss the current knowledge about endosomal abnormalities in AD.

How brain 'cleaners' fail: Mechanisms and therapeutic value of microglial phagocytosis in Alzheimer's disease

Microglia are the resident phagocytes of the brain, where they primarily function in the clearance of dead cells and the removal of un- or misfolded proteins. The impaired activity of receptors or proteins involved in phagocytosis can result in enhanced inflammation and neurodegeneration. RNA-seq and genome-wide association studies have linked multiple phagocytosis-related genes to neurodegenerative diseases, while the knockout of such genes has been demonstrated to exert protective effects against neurodegeneration in animal models. The failure of microglial phagocytosis influences AD-linked pathologies, including amyloid β accumulation, tau propagation, neuroinflammation, and infection. However, a precise understanding of microglia-mediated phagocytosis in Alzheimer's disease (AD) is still lacking. In this review, we summarize current knowledge of the molecular mechanisms involved in microglial phagocytosis in AD across a wide range of pre-clinical, post-mortem, ex vivo, and clinical studies and review the current limitations regarding the detection of microglia phagocytosis in AD. Finally, we discuss the rationale of targeting microglial phagocytosis as a therapeutic strategy for preventing AD or slowing its progression.

Proposed mechanisms of tau: relationships to traumatic brain injury, Alzheimer's disease, and epilepsy

Traumatic brain injury (TBI), Alzheimer's disease (AD), and epilepsy share proposed mechanisms of injury, including neuronal excitotoxicity, cascade signaling, and activation of protein biomarkers such as tau. Although tau is typically present intracellularly, in tauopathies, phosphorylated (p-) and hyper-phosphorylated (hp-) tau are released extracellularly, the latter leading to decreased neuronal stability and neurofibrillary tangles (NFTs). Tau cleavage at particular sites increases susceptibility to hyper-phosphorylation, NFT formation, and eventual cell death. The relationship between tau and inflammation, however, is unknown. In this review, we present evidence for an imbalanced endoplasmic reticulum (ER) stress response and inflammatory signaling pathways resulting in atypical p-tau, hp-tau and NFT formation. Further, we propose tau as a biomarker for neuronal injury severity in TBI, AD, and epilepsy. We present a hypothesis of tau phosphorylation as an initial acute neuroprotective response to seizures/TBI. However, if the underlying seizure pathology or TBI recurrence is not effectively treated, and the pathway becomes chronically activated, we propose a "tipping point" hypothesis that identifies a transition of tau phosphorylation from neuroprotective to injurious. We outline the role of amyloid beta (Aβ) as a "last ditch effort" to revert the cell to programmed death signaling, that, when fails, transitions the mechanism from injurious to neurodegenerative. Lastly, we discuss targets along these pathways for therapeutic intervention in AD, TBI, and epilepsy.

Approaches for Increasing Cerebral Efflux of Amyloid-β in Experimental Systems

Amyloid protein-β (Aβ) concentrations are increased in the brain in both early onset and late onset Alzheimer's disease (AD). In early onset AD, cerebral Aβ production is increased and its clearance is decreased, while increased Aβ burden in late onset AD is due to impaired clearance. Aβ has been the focus of AD therapeutics since development of the amyloid hypothesis, but efforts to slow AD progression by lowering brain Aβ failed until phase 3 trials with the monoclonal antibodies lecanemab and donanemab. In addition to promoting phagocytic clearance of Aβ, antibodies lower cerebral Aβ by efflux of Aβ-antibody complexes across the capillary endothelia, dissolving Aβ aggregates, and a "peripheral sink" mechanism. Although the blood-brain barrier is the main route by which soluble Aβ leaves the brain (facilitated by low-density lipoprotein receptor-related protein-1 and ATP-binding cassette sub-family B member 1), Aβ can also be removed via the blood-cerebrospinal fluid barrier, glymphatic drainage, and intramural periarterial drainage. This review discusses experimental approaches to increase cerebral Aβ efflux via these mechanisms, clinical applications of these approaches, and findings in clinical trials with these approaches in patients with AD or mild cognitive impairment. Based on negative findings in clinical trials with previous approaches targeting monomeric Aβ, increasing the cerebral efflux of soluble Aβ is unlikely to slow AD progression if used as monotherapy. But if used as an adjunct to treatment with lecanemab or donanemab, this approach might allow greater slowing of AD progression than treatment with either antibody alone.

Roles in Innate Immunity

Microglia are best known as the resident phagocytes of the central nervous system (CNS). As a resident brain immune cell population, microglia play key roles during the initiation, propagation, and resolution of inflammation. The discovery of resident adaptive immune cells in the CNS has unveiled a relationship between microglia and adaptive immune cells for CNS immune-surveillance during health and disease. The interaction of microglia with elements of the peripheral immune system and other CNS resident cells mediates a fine balance between neuroprotection and tissue damage. In this chapter, we highlight the innate immune properties of microglia, with a focus on how pattern recognition receptors, inflammatory signaling cascades, phagocytosis, and the interaction between microglia and adaptive immune cells regulate events that initiate an inflammatory or neuroprotective response within the CNS that modulates immune-mediated disease exacerbation or resolution.

VEGF controls microglial phagocytic response to amyloid-β

Microglial cells are well known to be implicated in the pathogenesis of Alzheimer's disease (AD), due to the impaired clearance of amyloid-β (Aβ) protein. In AD, Aβ accumulates in the brain parenchyma as soluble oligomers and protofibrils, and its aggregation process further give rise to amyloid plaques. Compelling evidence now indicate that Aβ oligomers (Aβo) are the most toxic forms responsible for neuronal and synaptic alterations. Recently, we showed that the Vascular Endothelial Growth Factor (VEGF) counteracts Aβo-induced synaptic alterations and that a peptide derived from VEGF is able to inhibit Aβ aggregation process. Moreover, VEGF has been reported to promote microglial chemotaxis to Aβ brain deposits. We therefore investigated whether VEGF could influence microglial phagocytic response to Aβ, using in vitro and ex vivo models of amyloid accumulation. We report here that VEGF increases Aβo phagocytosis by microglial cells and further characterized the molecular basis of the VEGF effect. VEGF is able to control α-secretase activity in microglial cells, resulting in the increased cleavage of the Triggering Receptor Expressed on Myeloid cells 2 (TREM2), a major microglial Aβ receptor. Consistently, the soluble form sTREM2 also increases Aβo phagocytosis by microglial cells. Taken together, these findings propose VEGF as a new regulator of Aβ clearance and suggest its potential role in rescuing compromised microglial function in AD.

LRPAP1 is released from activated microglia and inhibits microglial phagocytosis and amyloid beta aggregation

Low-density lipoprotein receptor-related protein-associated protein 1 (LRPAP1), also known as receptor associated protein (RAP), is an endoplasmic reticulum (ER) chaperone and inhibitor of LDL receptor related protein 1 (LRP1) and related receptors. These receptors have dozens of physiological ligands and cell functions, but it is not known whether cells release LRPAP1 physiologically at levels that regulate these receptors and cell functions. We used mouse BV-2 and human CHME3 microglial cell lines, and found that microglia released nanomolar levels of LRPAP1 when inflammatory activated by lipopolysaccharide or when ER stressed by tunicamycin. LRPAP1 was found on the surface of live activated and non-activated microglia, and anti-LRPAP1 antibodies induced internalization. Addition of 10 nM LRPAP1 inhibited microglial phagocytosis of isolated synapses and cells, and the uptake of Aβ. LRPAP1 also inhibited Aβ aggregation in vitro. Thus, activated and stressed microglia release LRPAP1 levels that can inhibit phagocytosis, Aβ uptake and Aβ aggregation. We conclude that LRPAP1 release may regulate microglial functions and Aβ pathology, and more generally that extracellular LRPAP1 may be a physiological and pathological regulator of a wide range of cell functions.

Inhibition of Sirt2 Decreases ApoE Secretion in Astrocytes and Microglial Cells

Amyloid-β (Aβ) accumulation caused by an imbalance of the production and clearance of Aβ in the brain is associated with the development of Alzheimer's disease (ad). Apolipoprotein E (ApoE) (the strongest genetic risk factor) enhances Aβ clearance, preventing Aβ deposition. Sirtuin 2 (Sirt2) is an NAD+-dependent histone deacetylase and its inhibition has been reported to ameliorate memory impairment in ad-like model mice. However, the role of Sirt2 in ApoE secretion is unknown. Here, we found that inhibition of Sirt2 activity in primary cultured astrocytes and BV2 cells decreased ApoE secretion, resulting in the accumulation of intracellular ApoE and inhibiting extracellular Aβ degradation. However, the reduction of Sirt2 protein level by Sirt2 siRNA decreased ApoE protein level, which ultimately reduces ApoE secretion. In addition, the knockdown of Sirt2 in the HEK293-APP cells also decreased levels of intracellular ApoE leading to reduction of its secretion, which is accompanied by increased Aβ levels without altering APP and APP processing enzymes. Our findings provide a novel role of Sirt2 in ApoE secretion.

Stress regulates Alzheimer's disease progression via selective enrichment of CD8+ T cells

This study investigates stress's impact on Alzheimer's disease (AD) using male APP/PS1 transgenic mice. Negative stressors (chronic social defeat, restraint) and positive hedonia (environmental enrichment, EE) were applied. Stress worsens AD pathology, while EE slows progression. Brain RNA sequencing reveals interleukin-6 (IL-6) and IL-10 as key stress-related AD regulators. Flow cytometry shows that the CD8+/CD4+ T cell ratio shifts in response to stress exposure and EE. Stress exposure increases CD8+/CD4+ ratio, opposite to EE. Depletion and enrichment of CD8+ T cells both accelerate AD, indicating immune intervention's negative impact. Stress management and balanced immunity may aid AD therapy, highlighting novel potential treatment.

Insulin-degrading enzyme (IDE) as a modulator of microglial phenotypes in the context of Alzheimer's disease and brain aging

The insulin-degrading enzyme (IDE) is an evolutionarily conserved zinc-dependent metallopeptidase highly expressed in the brain, where its specific functions remain poorly understood. Besides insulin, IDE is able to cleave many substrates in vitro, including amyloid beta peptides, making this enzyme a candidate pathophysiological link between Alzheimer's disease (AD) and type 2 diabetes (T2D). These antecedents led us to address the impact of IDE absence in hippocampus and olfactory bulb. A specific induction of microgliosis was found in the hippocampus of IDE knockout (IDE-KO) mice, without any effects in neither hippocampal volume nor astrogliosis. Performance on hippocampal-dependent memory tests is influenced by IDE gene dose in 12-month-old mice. Furthermore, a comprehensive characterization of the impact of IDE haploinsufficiency and total deletion in metabolic, behavioral, and molecular parameters in the olfactory bulb, a site of high insulin receptor levels, reveals an unambiguous barcode for IDE-KO mice at that age. Using wildtype and IDE-KO primary microglial cultures, we performed a functional analysis at the cellular level. IDE absence alters microglial responses to environmental signals, resulting in impaired modulation of phenotypic states, with only transitory effects on amyloid-β management. Collectively, our results reveal previously unknown physiological functions for IDE in microglia that, due to cell-compartment topological reasons, cannot be explained by its enzymatic activity, but instead modulate their multidimensional response to various damaging conditions relevant to aging and AD conditions.

Advances in Amyloid-β Clearance in the Brain and Periphery: Implications for Neurodegenerative Diseases

This review examines the role of impaired amyloid-β clearance in the accumulation of amyloid-β in the brain and the periphery, which is closely associated with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). The molecular mechanism underlying amyloid-β accumulation is largely unknown, but recent evidence suggests that impaired amyloid-β clearance plays a critical role in its accumulation. The review provides an overview of recent research and proposes strategies for efficient amyloid-β clearance in both the brain and periphery. The clearance of amyloid-β can occur through enzymatic or non-enzymatic pathways in the brain, including neuronal and glial cells, blood-brain barrier, interstitial fluid bulk flow, perivascular drainage, and cerebrospinal fluid absorption-mediated pathways. In the periphery, various mechanisms, including peripheral organs, immunomodulation/immune cells, enzymes, amyloid-β-binding proteins, and amyloid-β-binding cells, are involved in amyloid-β clearance. Although recent findings have shed light on amyloid-β clearance in both regions, opportunities remain in areas where limited data is available. Therefore, future strategies that enhance amyloid-β clearance in the brain and/or periphery, either through central or peripheral clearance approaches or in combination, are highly encouraged. These strategies will provide new insight into the disease pathogenesis at the molecular level and explore new targets for inhibiting amyloid-β deposition, which is central to the pathogenesis of sporadic AD (amyloid-β in parenchyma) and CAA (amyloid-β in blood vessels).

Concussion: Beyond the Cascade

Sport concussion affects millions of athletes each year at all levels of sport. Increasing evidence demonstrates clinical and physiological recovery are becoming more divergent definitions, as evidenced by several studies examining blood-based biomarkers of inflammation and imaging studies of the central nervous system (CNS). Recent studies have shown elevated microglial activation in the CNS in active and retired American football players, as well as in active collegiate athletes who were diagnosed with a concussion and returned to sport. These data are supportive of discordance in clinical symptomology and the inflammatory response in the CNS upon symptom resolution. In this review, we will summarize recent advances in the understanding of the inflammatory response associated with sport concussion and broader mild traumatic brain injury, as well as provide an outlook for important research questions to better align clinical and physiological recovery.

Folate Deficiency Increased Microglial Amyloid-β Phagocytosis via the RAGE Receptor in Chronic Unpredictable Mild-Stress Rat and BV2 Cells

Depression is often considered one of the prevalent neuropsychiatric symptoms of Alzheimer's disease (AD). β-amyloid (Aβ) metabolism disorders and impaired microglia phagocytosis are potential pathological mechanisms between depression and AD. Folate deficiency (FD) is a risk factor for depression and AD. In this study, we used a chronic unpredictable mild stress (CUMS) rat model and a model of Aβ phagocytosis by BV2 cells to explore the potential mechanisms by which FD affects depression and AD. The results revealed that FD exacerbated depressive behavior and activated microglia in CUMS rats, leading to an increase in intracellular Aβ and phagocytosis-related receptors for advanced glycation end products (RAGE). Then, in vitro results showed that the expression of the RAGE receptor and M2 phenotype marker (CD206) were upregulated by FD treatment in BV2 cells, leading to an increase in Aβ phagocytosis. However, there was no significant difference in the expression of toll-like receptor 4 (TLR4) and clathrin heavy chain (CHC). Furthermore, when using the RAGE-specific inhibitor FPS-ZM1, there was no significant difference in Aβ uptake between folate-normal (FN) and FD BV2 cell groups. In conclusion, these findings suggest FD may promote microglia phagocytosis Aβ via regulating the expression of RAGE or microglia phenotype under Aβ treatment.

Effect of Curcumin on Cognitive Behavior and Pathological Characteristics of the Hippocampus in Mice with Inherent Alzheimer's Disease

This study examined the effect of curcumin on pathological manifestations and clearance of amyloid β peptide (Aβ) in the hippocampus of 8-month-old transgenic APP/PS1 mice with inherent Alzheimer's disease. APP/PS1 mice and the age-matched wild-type controls were subjected to 3 behavioral tests: open field, new object recognition, and Morris water maze. Expression of Aβ, APP, CTF, BACE1, IDE, NEP, and LRP1 proteins in the extracted hippocampal tissue was evaluated by Western blotting. The distribution and the quantity of amyloid plaques and the spread of microglia in the hippocampus were determined by immunofluorescence. The contents of Aβ40 and Aβ42 in the hippocampus were assayed and analyzed on Simoa HD-1 analyzer. The proteins interacting with Aβ in the hippocampus of APP/PS1 mice were detected by co-immunoprecipitation. Curcumin significantly reduced motor hyperactivity in the open-field test, improved short-term recognition memory, spatial learning, and reference memory in APP/PS1 mice. In the hippocampus of APP/PS1 mice, curcumin significantly diminished the elevated Aβ levels and inhibited microglia proliferation. At the same time, curcumin had no effect on Aβ production, extracellular enzymatic hydrolysis, and LRP1-mediated outward transport, but enhanced Aβ clearance by activation of the intracellular ubiquitin-proteasome system and related peripheral mechanisms. Thus, curcumin improves the learning and memory abilities of APP/PS1 mice and reduces the pathological accumulation of Aβ in the brain.

Elevated Galectin-3 Is Associated with Aging, Multiple Sclerosis, and Oxidized Phosphatidylcholine-Induced Neurodegeneration

Aging is a significant risk factor associated with the progression of CNS neurodegenerative diseases including multiple sclerosis (MS). Microglia, the resident macrophages of the CNS parenchyma, are a major population of immune cells that accumulate in MS lesions. While they normally regulate tissue homeostasis and facilitate the clearance of neurotoxic molecules including oxidized phosphatidylcholines (OxPCs), their transcriptome and neuroprotective functions are reprogrammed by aging. Thus, determining the factors that instigate aging associated microglia dysfunction can lead to new insights for promoting CNS repair and for halting MS disease progression. Through single-cell RNA sequencing (scRNAseq), we identified Lgals3, which encodes for galectin-3 (Gal3), as an age upregulated gene by microglia responding to OxPC. Consistently, excess Gal3 accumulated in OxPC and lysolecithin-induced focal spinal cord white matter (SCWM) lesions of middle-aged mice compared with young mice. Gal3 was also elevated in mouse experimental autoimmune encephalomyelitis (EAE) lesions and more importantly in MS brain lesions from two male and one female individuals. While Gal3 delivery alone into the mouse spinal cord did not induce damage, its co-delivery with OxPC increased cleaved caspase 3 and IL-1β within white matter lesions and exacerbated OxPC-induced injury. Conversely, OxPC-mediated neurodegeneration was reduced in Gal3-/- mice compared with Gal3+/+ mice. Thus, Gal3 is associated with increased neuroinflammation and neurodegeneration and its overexpression by microglia/macrophages may be detrimental for lesions within the aging CNS.SIGNIFICANCE STATEMENT Aging accelerates the progression of neurodegenerative diseases such as multiple sclerosis (MS). Understanding the molecular mechanisms of aging that increases the susceptibility of the CNS to damage could lead to new strategies to manage MS progression. Here, we highlight that microglia/macrophage-associated galectin-3 (Gal3) was upregulated with age exacerbated neurodegeneration in the mouse spinal cord white matter (SCWM) and in MS lesions. More importantly, co-injection of Gal3 with oxidized phosphatidylcholines (OxPCs), which are neurotoxic lipids found in MS lesions, caused greater neurodegeneration compared with injection of OxPC alone, whereas genetic loss of Gal3 reduced OxPC damage. These results demonstrate that Gal3 overexpression is detrimental to CNS lesions and suggest its deposition in MS lesions may contribute to neurodegeneration.

Unraveling the Connection of Epstein-Barr Virus and Its Glycoprotein M146-157 Peptide with Neurological Ailments

Epstein-Barr virus (EBV) is known to be associated with several cancers along with neurological modalities like Alzheimer's disease (AD) and multiple sclerosis (MS). Previous study from our group revealed that a 12 amino acid peptide fragment (₁₄₆SYKHVFLSAFVY₁₅₇) of EBV glycoprotein M (gM) exhibits amyloid-like self-aggregative properties. In the current study, we have investigated its effect on Aβ₄₂ aggregation along with its effect on neural cell immunology and disease markers. EBV virion was also considered for the above-mentioned investigation. An increase in the aggregation of Aβ₄₂ peptide was observed upon incubation with gM_146-157. Further, the exposure of EBV and gM_146-157 onto neuronal cells indicated the upregulation of inflammatory molecules like IL-1β, IL-6, TNF-α, and TGF-β that suggested neuroinflammation. Besides, host cell factors like mitochondrial potential and calcium ion signaling play a crucial role in cellular homeostasis and alterations in these factors aid in neurodegeneration. Changes in mitochondrial membrane potential manifested a decrease while elevation in the level of total Ca²⁺ ions was observed. Amelioration of Ca²⁺ ions triggers excitotoxicity in neurons. Subsequently, neurological disease-associated genes APP, ApoE4, and MBP were found to be increased at the protein level. Additionally, demyelination of neurons is a hallmark of MS and the myelin sheath consists of ∼70% of lipid/cholesterol-associated moieties. Hereby, genes associated with cholesterol metabolism indicated changes at the mRNA level. Enhanced expression of neurotropic factors like NGF and BDNF was discerned postexposure to EBV and gM_146-157. Altogether, this study delineates a direct connection of EBV and its peptide gM_146-157 with neurological illnesses.

Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

lncRNA NEAT1: Key player in neurodegenerative diseases

Neurodegenerative diseases are the most common causes of disability worldwide. Given their high prevalence, devastating symptoms, and lack of definitive diagnostic tests, there is an urgent need to identify potential biomarkers and new therapeutic targets. Long non-coding RNAs (lncRNAs) have recently emerged as powerful regulatory molecules in neurodegenerative diseases. Among them, lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) has been reported to be upregulated in Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). However, whether this is part of a protective or harmful mechanism is still unclear. This review summarizes our current knowledge of the role of NEAT1 in neurodegenerative diseases and its association with the characteristic aggregation of misfolded proteins: amyloid-β and tau in AD, α-synuclein in PD, mutant huntingtin in HD, and TAR DNA-binding protein-43 fused in sarcoma/translocated in liposarcoma in ALS. The aim of this review is to stimulate further research on more precise and effective treatments for neurodegenerative diseases.

Retinal pathological features and proteome signatures of Alzheimer's disease

Alzheimer's disease (AD) pathologies were discovered in the accessible neurosensory retina. However, their exact nature and topographical distribution, particularly in the early stages of functional impairment, and how they relate to disease progression in the brain remain largely unknown. To better understand the pathological features of AD in the retina, we conducted an extensive histopathological and biochemical investigation of postmortem retina and brain tissues from 86 human donors. Quantitative examination of superior and inferior temporal retinas from mild cognitive impairment (MCI) and AD patients compared to those with normal cognition (NC) revealed significant increases in amyloid β-protein (Aβ42) forms and novel intraneuronal Aβ oligomers (AβOi), which were closely associated with exacerbated retinal macrogliosis, microgliosis, and tissue atrophy. These pathologies were unevenly distributed across retinal layers and geometrical areas, with the inner layers and peripheral subregions exhibiting most pronounced accumulations in the MCI and AD versus NC retinas. While microgliosis was increased in the retina of these patients, the proportion of microglial cells engaging in Aβ uptake was reduced. Female AD patients exhibited higher levels of retinal microgliosis than males. Notably, retinal Aβ42, S100 calcium-binding protein B+ macrogliosis, and atrophy correlated with severity of brain Aβ pathology, tauopathy, and atrophy, and most retinal pathologies reflected Braak staging. All retinal biomarkers correlated with the cognitive scores, with retinal Aβ42, far-peripheral AβOi and microgliosis displaying the strongest correlations. Proteomic analysis of AD retinas revealed activation of specific inflammatory and neurodegenerative processes and inhibition of oxidative phosphorylation/mitochondrial, and photoreceptor-related pathways. This study identifies and maps retinopathy in MCI and AD patients, demonstrating the quantitative relationship with brain pathology and cognition, and may lead to reliable retinal biomarkers for noninvasive retinal screening and monitoring of AD.

Cardiolipin released by microglia can act on neighboring glial cells to facilitate the uptake of amyloid-β (1-42)

Cardiolipin is a mitochondrial phospholipid that is also detected in serum inferring its extracellular release; however, this process has not been directly demonstrated for any of the brain cell types. Nevertheless, extracellular cardiolipin has been shown to modulate several neuroimmune functions of microglia and astrocytes, including upregulation of their endocytic activity. Low cardiolipin levels are associated with brain aging, and may thus hinder uptake of amyloid-β (Αβ) in Alzheimer's disease. We hypothesized that glial cells are one of the sources of extracellular cardiolipin in the brain parenchyma where this phospholipid interacts with neighboring cells to upregulate the endocytosis of Αβ. Liquid chromatography-mass spectrophotometry identified 31 different species of cardiolipin released from murine BV-2 microglial cells and revealed this process was accelerated by exposure to Aβ42. Extracellular cardiolipin upregulated internalization of fluorescently-labeled Aβ42 by primary murine astrocytes, human U118 MG astrocytic cells, and murine BV-2 microglia. Increased endocytic activity in the presence of extracellular cardiolipin was also demonstrated by studying uptake of Aβ42 and pHrodo™ Bioparticles™ by human induced pluripotent stem cells (iPSCs)-derived microglia, as well as iPSC-derived human brain organoids containing microglia, astrocytes, oligodendrocytes and neurons. Our observations indicate that Aβ42 augments the release of cardiolipin from microglia into the extracellular space, where it can act on microglia and astrocytes to enhance their endocytosis of Aβ42. Our observations suggest that the reduced glial uptake of Aβ due to the decreased levels of cardiolipin could be at least partially responsible for the extracellular accumulation of Aβ in aging and Alzheimer's disease.

Neuronal vulnerability to brain aging and neurodegeneration in cognitively impaired marmoset monkeys (Callithrix jacchus)

The investigation of neurobiological and neuropathological changes that affect synaptic integrity and function with aging is key to understanding why the aging brain is vulnerable to Alzheimer's disease. We investigated the cellular characteristics in the cerebral cortex of behaviorally characterized marmosets, based on their trajectories of cognitive learning as they transitioned to old age. We found increased astrogliosis, increased phagocytic activity of microglial cells and differences in resting and reactive microglial cell phenotypes in cognitively impaired compared to nonimpaired marmosets. Differences in amyloid beta deposition were not related to cognitive trajectory. However, we found age-related changes in density and morphology of dendritic spines in pyramidal neurons of layer 3 in the dorsolateral prefrontal cortex and the CA1 field of the hippocampus between cohorts. Overall, our data suggest that an accelerated aging process, accompanied by neurodegeneration, that takes place in cognitively impaired aged marmosets and affects the plasticity of dendritic spines in cortical areas involved in cognition and points to mechanisms of neuronal vulnerability to aging.

Molecular Imaging of Neuroinflammation in Alzheimer's Disease and Mild Cognitive Impairment

Alzheimer's disease (AD) is the most prevalent neurocognitive disorder. Due to the ineffectiveness of treatments targeting the amyloid cascade, molecular biomarkers for neuroinflammation are attracting attention with increasing knowledge about the role of neuroinflammation in the pathogenesis of AD. This chapter will explore the results of studies using molecular imaging for diagnosing AD and mild cognitive impairment (MCI). Because it is critical to interpreting the data to understand which substances are targeted in molecular imaging, this chapter will discuss the two most significant targets, microglia and astrocytes, as well as the best-known radioligands for each. Then, neuroimaging results with PET neuroinflammation imaging will be reviewed for AD and MCI. Although a growing body of evidence has suggested that these molecular imaging biomarkers for neuroinflammation may have a role in the diagnosis of AD and MCI, the findings are inconsistent or cross-sectional, which indicates that it is difficult to apply the contents in practice due to the need for additional study. In particular, because the results of multiple interventions targeting neuroinflammation were inconclusive, molecular imaging markers for neuroinflammation can be used in combination with conventional markers to select appropriate patients for early intervention for neuroinflammation rather than as a single marker.

Pathological Roles of INPP5D in Alzheimer's Disease

Current hypothesis of Alzheimer's disease (AD) postulates that amyloid β (Aβ) deposition in the brain causes tau inclusion in neurons and leads to cognitive decline. The discovery of the genetic association between triggering receptor expressed on myeloid cells 2 (TREM2) with increased AD risk points to a causal link between microglia and AD pathogenesis, and revealed a crucial role of TREM2-dependent clustering of microglia around amyloid plaques that prevents Aβ toxicity to facilitate tau deposition near the plaques. Here we review the physiological and pathological roles of another AD risk gene expressed in microglia, inositol polyphosphate-5-polyphosphatase D (INPP5D), which encodes a phosphoinositide phosphatase. Evidence suggests that its risk polymorphisms alter the expression level and/or function of INPP5D, while concomitantly affecting tau levels in cerebrospinal fluids. In β-amyloidosis mice, INPP5D was upregulated upon Aβ deposition and negatively regulated the microglial clustering toward amyloid plaques. INPP5D seems to exert its function by acting antagonistically at downstream of the TREM2 signaling pathway, suggesting that it is a novel regulator of the protective barrier by microglia. Further studies to elucidate INPP5D's role in AD may help in developing new therapeutic targets for AD treatment.

Dietary fish oil increases catalase activity in patients with probable Alzheimer's disease

Background: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of neuritic plaques and neurofibrillary tangles that finally result in synaptic and neuronal loss. Oxidative stress accompanies pathological changes in AD. Objective: to assess the efficacy of dietary omega 3 polyunsaturated fatty acids supplementation on the levels of proteins oxidation, hydroperoxides and enzymatic activities of catalase and superoxide dismutase in AD patients. Methods: clinical, controlled, randomized, double-blind trial. Patients consumed fish oil or placebo for one year. Oxidative stress markers were assessed in plasma using spectrophotometric methods. Results: carbonyl groups in proteins and hydroperoxides in plasma have similar values in both treatment groups at the beginning of the study. At six and 12 months of treatment, these values decreased significantly in the fish oil group, while in the placebo group no changes were observed in both oxidative stress markers. Catalase activity increased significantly at six and twelve months after treatment in patients treated with fish oil. While the superoxide dismutase activity was not modified in both study groups. Conclusions: patients who consume omega 3 polyunsaturated fatty acids at a stable dose of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) show decreased oxidation of proteins and lipids in plasma. In addition, an increase in catalase activity was detected. Thus, the presented data warrants further studies evaluating the antioxidant effect of omega 3 polyunsaturated fatty acids.

New Insights into lncRNAs in Aβ Cascade Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia, but its pathogenesis is not fully understood, and effective drugs to treat or reverse the progression of the disease are lacking. Long noncoding RNAs (lncRNAs) are abnormally expressed and deregulated in AD and are closely related to the occurrence and development of AD. In addition, the high tissue specificity and spatiotemporal specificity make lncRNAs particularly attractive as diagnostic biomarkers and specific therapeutic targets. Therefore, an in-depth understanding of the regulatory mechanisms of lncRNAs in AD is essential for developing new treatment strategies. In this review, we discuss the unique regulatory functions of lncRNAs in AD, ranging from Aβ production to clearance, with a focus on their interaction with critical molecules. Additionally, we highlight the advantages and challenges of using lncRNAs as biomarkers for diagnosis or therapeutic targets in AD and present future perspectives in clinical practice.

Assaying Microglia Functions In Vitro

Microglia, the main immune modulators of the central nervous system, have key roles in both the developing and adult brain. These functions include shaping healthy neuronal networks, carrying out immune surveillance, mediating inflammatory responses, and disposing of unwanted material. A wide variety of pathological conditions present with microglia dysregulation, highlighting the importance of these cells in both normal brain function and disease. Studies into microglial function in the context of both health and disease thus have the potential to provide tremendous insight across a broad range of research areas. In vitro culture of microglia, using primary cells, cell lines, or induced pluripotent stem cell derived microglia, allows researchers to generate reproducible, robust, and quantifiable data regarding microglia function. A broad range of assays have been successfully developed and optimised for characterizing microglial morphology, mediation of inflammation, endocytosis, phagocytosis, chemotaxis and random motility, and mediation of immunometabolism. This review describes the main functions of microglia, compares existing protocols for measuring these functions in vitro, and highlights common pitfalls and future areas for development. We aim to provide a comprehensive methodological guide for researchers planning to characterise microglial functions within a range of contexts and in vitro models.