Aβ42 Protofibrils Interact with and Are Trafficked through Microglial-Derived Microvesicles

Effects of MicroRNAs and Long Non-coding RNAs on Beneficial Action of Exercise on Cognition in Degenerative Diseases: A Review

Recent research has exposed a growing body of proof underscoring the importance of microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) in maintaining the physical composition of neurons and influencing cognitive functioning in both standard and atypical circumstances. Extensive research has been conducted on the possible application of miRNAs and lncRNAs as biomarkers for various diseases, with a particular focus on brain disorders, as they possess remarkable durability in cell-free surroundings and can endure repeated freezing and thawing processes. It is intriguing to note that miRNAs and lncRNAs have the ability to function through paracrine mechanisms, thereby playing a role in communication between different organs. Recent research has proposed that the improvement of cognitive abilities through physical exercise in mentally healthy individuals is a valuable method for uncovering potential connections between miRNAs, or microRNAs, and lncRNAs, and human cognitive function. The process of cross-correlating data from disease models and patients with existing data will be crucial in identifying essential miRNAs and lncRNAs, which can potentially act as biomarkers or drug targets in the treatment of cognitive disorders. By combining this method with additional research in animal models, we can determine the function of these molecules and their potential impact on therapy. This article discusses the latest research about the primary miRNAs, lncRNAs, and their exosomes that are affected by physical activity in terms of human cognitive function.

Exosomes in Vascular/Neurological Disorders and the Road Ahead

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), stroke, and aneurysms, are characterized by the abnormal accumulation and aggregation of disease-causing proteins in the brain and spinal cord. Recent research suggests that proteins linked to these conditions can be secreted and transferred among cells using exosomes. The transmission of abnormal protein buildup and the gradual degeneration in the brains of impacted individuals might be supported by these exosomes. Furthermore, it has been reported that neuroprotective functions can also be attributed to exosomes in neurodegenerative diseases. The potential neuroprotective functions may play a role in preventing the formation of aggregates and abnormal accumulation of proteins associated with the disease. The present review summarizes the roles of exosomes in neurodegenerative diseases as well as elucidating their therapeutic potential in AD, PD, ALS, HD, stroke, and aneurysms. By elucidating these two aspects of exosomes, valuable insights into potential therapeutic targets for treating neurodegenerative diseases may be provided.

Hotspots and trends of microglia in Alzheimer's disease: a bibliometric analysis during 2000-2022

BACKGROUND

Alzheimer's disease is one common type of dementia. Numerous studies have suggested a correlation between Alzheimer's disease and inflammation. Microglia mainly participate in the inflammatory response in the brain. Currently, ample evidence has shown that microglia are closely related to the occurrence and development of Alzheimer's disease.

OBJECTIVE

We opted for bibliometric analysis to comprehensively summarize the advancements in the study of microglia in Alzheimer's disease, aiming to provide researchers with current trends and future research directions.

METHODS

All articles and reviews pertaining to microglia in Alzheimer's disease from 2000 to 2022 were downloaded through Web of Science Core Collection. The results were subjected to bibliometric analysis using VOSviewer 1.6.18 and CiteSpace 6.1 R2.

RESULTS

Overall, 7449 publications were included. The number of publications was increasing yearly. The United States has published the most publications. Harvard Medical School has published the most papers of all institutions. Journal of Alzheimer's Disease and Journal of Neuroscience were the journals with the most studies and the most commonly cited, respectively. Mt Heneka is the author with the highest productivity and co-citation. After analysis, the most common keywords are neuroinflammation, amyloid-beta, inflammation, neurodegeneration. Gut microbiota, extracellular vesicle, dysfunction and meta-analysis are the hotspots of research at the present stage and are likely to continue.

CONCLUSION

NLRP3 inflammasome, TREM2, gut microbiota, mitochondrial dysfunction, exosomes are research hotspots. The relationship between microglia-mediated neuroinflammation and Alzheimer's disease have been the focus of current research and the development trend of future research.

The Dual Nature of Microglia in Alzheimer's Disease: A Microglia-Neuron Crosstalk Perspective

Microglia are critical players in the neuroimmune system, and their involvement in Alzheimer's disease (AD) pathogenesis is increasingly being recognized. However, whether microglia play a positive or negative role in AD remains largely controversial and the precise molecular targets for intervention are not well defined. This partly results from the opposing roles of microglia in AD pathology, and is mainly reflected in the microglia-neuron interaction. Microglia can prune synapses resulting in excessive synapse loss and neuronal dysfunction, but they can also promote synapse formation, enhancing neural network plasticity. Neuroimmune crosstalk accelerates microglial activation, which induces neuron death and enhances the microglial phagocytosis of β-amyloid to protect neurons. Moreover, microglia have dual opposing roles in developing the major pathological features in AD, such as amyloid deposition and blood-brain barrier permeability. This review summarizes the dual opposing role of microglia in AD from the perspective of the interaction between neurons and microglia. Additionally, current AD treatments targeting microglia and the advantages and disadvantages of developing microglia-targeted therapeutic strategies are discussed.

Research progress on the role of extracellular vesicles in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease, affect millions of people worldwide. Tremendous efforts have been put into disease-related research, but few breakthroughs have been made in diagnostic and therapeutic approaches. Extracellular vesicles (EVs) are heterogeneous cell-derived membrane structures that arise from the endosomal system or are directly separated from the plasma membrane. EVs contain many biomolecules, including proteins, nucleic acids, and lipids, which can be transferred between different cells, tissues, or organs, thereby regulating cross-organ communication between cells during normal and pathological processes. Recently, EVs have been shown to participate in various aspects of neurodegenerative diseases. Abnormal secretion and levels of EVs are closely related to the pathogenesis of neurodegenerative diseases and contribute to disease progression. Numerous studies have proposed EVs as therapeutic targets or biomarkers for neurodegenerative diseases. In this review, we summarize and discuss the advanced research progress on EVs in the pathological processes of several neurodegenerative diseases. Moreover, we outline the latest research on the roles of EVs in neurodegenerative diseases and their therapeutic potential for the diseases.

P2X7 Receptor and Extracellular Vesicle Release

Extensive evidence indicates that the activation of the P2X₇ receptor (P2X₇R), an ATP-gated ion channel highly expressed in immune and brain cells, is strictly associated with the release of extracellular vesicles. Through this process, P2X₇R-expressing cells regulate non-classical protein secretion and transfer bioactive components to other cells, including misfolded proteins, participating in inflammatory and neurodegenerative diseases. In this review, we summarize and discuss the studies addressing the impact of P2X₇R activation on extracellular vesicle release and their activities.

A new class of monoclonal Aβ antibodies selectively targets and triggers deposition of Aβ protofibrils

Aggregation and accumulation of amyloid-β peptide (Aβ) are a critical trigger for the onset of Alzheimer's disease (AD). While the plaques are the most outstanding Aβ pathological feature, much of the recent research emphasis has been on soluble Aβ species because of their diffusible, proinflammatory, and toxic properties. The focus on soluble aggregated Aβ species has also increased the interest in antibodies that are selective for different Aβ conformations. In the current study, we developed and characterized a new class of monoclonal antibodies (referred to as mAbSL) that are selective for Aβ protofibrils. Cloning and sequencing of the heavy and light chain variable regions for multiple antibodies identified sequence characteristics that may impart the conformational selectivity by the antibodies. Transfection of FreeStyle 293F cells with the plasmids permitted in-house expression and purification of mAbSL antibodies along with non-conformation-selective Aβ monoclonal antibodies (Aβ mAbs). Several of the purified mAbSL antibodies demonstrated significant affinity and selectivity for Aβ42 protofibrils compared with Aβ42 monomers and Aβ42 fibrils. Competition ELISA assays assessing the best overall antibody, mAbSL 113, yielded affinity constants of 7 nM for the antibody-Aβ42 protofibril interaction, while the affinity for either Aβ42 monomers or Aβ42 fibrils was roughly 80 times higher. mAbSL 113 significantly inhibited Aβ42 monomer aggregation by a unique mechanism compared with the inhibition displayed by Aβ mAb 513. Aβ42 protofibril dynamics were also markedly altered in the presence of mAbSL 113, whereby insoluble complex formation and protofibril deposition were stimulated by the antibody at low substoichiometric molar ratios. As the field contemplates the therapeutic effectiveness of Aβ conformation-selective antibodies, the findings presented here demonstrate new information on a monoclonal antibody that selectively targets Aβ protofibrils and impacts Aβ dynamics.

Emerging Roles of Extracellular Vesicles in Alzheimer's Disease: Focus on Synaptic Dysfunction and Vesicle-Neuron Interaction

Alzheimer's disease (AD) is considered by many to be a synaptic failure. Synaptic function is in fact deeply affected in the very early disease phases and recognized as the main cause of AD-related cognitive impairment. While the reciprocal involvement of amyloid beta (Aβ) and tau peptides in these processes is under intense investigation, the crucial role of extracellular vesicles (EVs) released by different brain cells as vehicles for these molecules and as mediators of early synaptic alterations is gaining more and more ground in the field. In this review, we will summarize the current literature on the contribution of EVs derived from distinct brain cells to neuronal alterations and build a working model for EV-mediated propagation of synaptic dysfunction in early AD. A deeper understanding of EV-neuron interaction will provide useful targets for the development of novel therapeutic approaches aimed at hampering AD progression.

Extracellular vesicles, from the pathogenesis to the therapy of neurodegenerative diseases

Extracellular vesicles (EVs) are small bilipid layer-enclosed vesicles that can be secreted by all tested types of brain cells. Being a key intercellular communicator, EVs have emerged as a key contributor to the pathogenesis of various neurodegenerative diseases (NDs) including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease through delivery of bioactive cargos within the central nervous system (CNS). Importantly, CNS cell-derived EVs can be purified via immunoprecipitation, and EV cargos with altered levels have been identified as potential biomarkers for the diagnosis and prognosis of NDs. Given the essential impact of EVs on the pathogenesis of NDs, pathological EVs have been considered as therapeutic targets and EVs with therapeutic effects have been utilized as potential therapeutic agents or drug delivery platforms for the treatment of NDs. In this review, we focus on recent research progress on the pathological roles of EVs released from CNS cells in the pathogenesis of NDs, summarize findings that identify CNS-derived EV cargos as potential biomarkers to diagnose NDs, and comprehensively discuss promising potential of EVs as therapeutic targets, agents, and drug delivery systems in treating NDs, together with current concerns and challenges for basic research and clinical applications of EVs regarding NDs.

Extracellular vesicles: A new paradigm in understanding, diagnosing and treating neurodegenerative disease

Neurodegenerative disorders (NDs) are becoming one of the leading causes of disability and death across the globe due to lack of timely preventions and treatments. Concurrently, intensive research efforts are being carried out to understand the etiology of these age-dependent disorders. Extracellular vesicles (EVs)-biological nanoparticles released by cells-are gaining tremendous attention in understanding their role in pathogenesis and progression of NDs. EVs have been found to transmit pathogenic proteins of NDs between neurons. Moreover, the ability of EVs to exquisitely surmount natural biological barriers, including blood-brain barrier and in vivo safety has generated interest in exploring them as potential biomarkers and function as natural delivery vehicles of drugs to the central nervous system. However, limited knowledge of EV biogenesis, their heterogeneity and lack of adequate isolation and analysis tools have hampered their therapeutic potential. In this review, we cover the recent advances in understanding the role of EVs in neurodegeneration and address their role as biomarkers and delivery vehicles to the brain.

Extracellular vesicles in the study of Alzheimer's and Parkinson's diseases: Methodologies applied from cells to biofluids

Extracellular vesicles (EVs) are gaining increased importance in fundamental research as key players in disease pathogenic mechanisms, but also in translational and clinical research due to their value in biomarker discovery, either for diagnostics and/or therapeutics. In the first research scenario, the study of EVs isolated from neuronal models mimicking neurodegenerative diseases can open new avenues to better understand the pathological mechanisms underlying these conditions or to identify novel molecular targets for diagnosis and/or therapeutics. In the second research scenario, the easy availability of EVs in body fluids and the specificity of their cargo, which can reflect the cell of origin or disease profiles, turn these into attractive diagnostic tools. EVs with exosome-like characteristics, circulating in the bloodstream and other peripheral biofluids, constitute a non-invasive and rapid alternative to study several conditions, including brain-related disorders. In both cases, several EVs isolation methods are already available, but each neuronal model or biofluid presents its own challenges. Herein, a literature overview on EVs isolation methodologies from distinct neuronal models (cellular culture and brain tissue) and body fluids (serum, plasma, cerebrospinal fluid, urine and saliva) was carried out. Focus was given to approaches employed in the context of Alzheimer's and Parkinson's diseases, and the main research findings discussed. The topics here revised will facilitate the choice of EVs isolation methodologies and potentially prompt new discoveries in EVs research and in the neurodegenerative diseases field.

The multiple faces of extracellular vesicles released by microglia: Where are we 10 years after?

As resident component of the innate immunity in the central nervous system (CNS), microglia are key players in pathology. However, they also exert fundamental roles in brain development and homeostasis maintenance. They are extremely sensitive and plastic, as they assiduously monitor the environment, adapting their function in response to stimuli. On consequence, microglia may be defined a heterogeneous community of cells in a dynamic equilibrium. Extracellular vesicles (EVs) released by microglia mirror the dynamic nature of their donor cells, exerting important and versatile functions in the CNS as unbounded conveyors of bioactive signals. In this review, we summarize the current knowledge on EVs released by microglia, highlighting their heterogeneous properties and multifaceted effects.

Review on the roles of specific cell-derived exosomes in Alzheimer's disease

Alzheimer's disease (AD) is the sixth leading cause of death worldwide and cannot be effectively cured or prevented; thus, early diagnosis, and intervention are important. The importance of exosomes, membrane-bound extracellular vesicles produced in the endosome of eukaryotic cells, in the development, diagnosis, and treatment of AD has been recognized; however, their specific functions remain controversial and even unclear. With the development of exosome extraction, isolation, and characterization, many studies have focused on exosomes derived from different cells and body fluids. In this study, we summarized the roles of exosomes derived from different body fluids and cells, such as neuron, glial, stem, and endothelial cells, in the development, diagnosis, monitoring, and treatment of AD. We also emphasize the necessity to focus on exosomes from biological fluids and specific cells that are less invasive to target. Moreover, aside from the concentrations of classic and novel biomarkers in exosomes, the size and number of exosomes may also influence early and differential diagnosis of AD.

Differential Effects of APOE Genotype on MicroRNA Cargo of Cerebrospinal Fluid Extracellular Vesicles in Females With Alzheimer's Disease Compared to Males

Multiple biological factors, including age, sex, and genetics, influence Alzheimer's disease (AD) risk. Of the 6.2 million Americans living with Alzheimer's dementia in 2021, 3.8 million are women and 2.4 million are men. The strongest genetic risk factor for sporadic AD is apolipoprotein E-e4 (APOE-e4). Female APOE-e4 carriers develop AD more frequently than age-matched males and have more brain atrophy and memory loss. Consequently, biomarkers that are sensitive to biological risk factors may improve AD diagnostics and may provide insight into underlying mechanistic changes that could drive disease progression. Here, we have assessed the effects of sex and APOE-e4 on the miRNA cargo of cerebrospinal fluid (CSF) extracellular vesicles (EVs) in AD. We used ultrafiltration (UF) combined with size exclusion chromatography (SEC) to enrich CSF EVs (e.g., Flotillin+). CSF EVs were isolated from female and male AD or controls (CTLs) that were either APOE-e3,4 or -e3,3 positive (n = 7/group, 56 total). MiRNA expression levels were quantified using a custom TaqMan™ array that assayed 190 miRNAs previously found in CSF, including 25 miRNAs that we previously validated as candidate AD biomarkers. We identified changes in the EV miRNA cargo that were affected by both AD and sex. In total, four miRNAs (miR-16-5p, -331-3p, -409-3p, and -454-3p) were significantly increased in AD vs. CTL, independent of sex and APOE-e4 status. Pathway analysis of the predicted gene targets of these four miRNAs with identified pathways was highly relevant to neurodegeneration (e.g., senescence and autophagy). There were also three miRNAs (miR-146b-5p, -150-5p, and -342-3p) that were significantly increased in females vs. males, independent of disease state and APOE-e4 status. We then performed a statistical analysis to assess the effect of APOE genotype in AD within each sex and found that APOE-e4 status affects different subsets of CSF EV miRNAs in females vs. males. Together, this study demonstrates the complexity of the biological factors associated with AD risk and the impact on EV miRNAs, which may contribute to AD pathophysiology.

The microglial membrane receptor TREM2 mediates exosome secretion to promote phagocytosis of amyloid-β by microglia

Considerable evidence links the microglial transmembrane receptor TREM2 to the progression of Alzheimer's disease through its involvement in Aβ phagocytosis by microglia. While previous studies have mainly focused on the phagocytic regulation of microglia itself, the antigen presentation of microglial exosomes in the process of immunity has been less investigated. Here, we identified TREM2 expressed on the membrane of microglial exosomes and found that it controlled exosome secretion without affecting exosome size. Microglial exosomes bind to Aβ in a TREM2-dependent manner, which changes the inflammatory environment around Aβ and promotes microglia to phagocytose Aβ. These findings delineate a novel exosome-mediated mechanism of microglial cell-Aβ crosstalk that facilitates Aβ clearance under either physiological or pathological conditions in the central nervous system.

Exosomes in Age-Related Cognitive Decline: Mechanistic Insights and Improving Outcomes

Aging is the most prominent risk factor for cognitive decline, yet behavioral symptomology and underlying neurobiology can vary between individuals. Certain individuals exhibit significant age-related cognitive impairments, while others maintain intact cognitive functioning with only minimal decline. Recent developments in genomic, proteomic, and functional imaging approaches have provided insights into the molecular and cellular substrates of cognitive decline in age-related neuropathologies. Despite the emergence of novel tools, accurately and reliably predicting longitudinal cognitive trajectories and improving functional outcomes for the elderly remains a major challenge. One promising approach has been the use of exosomes, a subgroup of extracellular vesicles that regulate intercellular communication and are easily accessible compared to other approaches. In the current review, we highlight recent findings which illustrate how the analysis of exosomes can improve our understanding of the underlying neurobiological mechanisms that contribute to cognitive variation in aging. Specifically, we focus on exosome-mediated regulation of miRNAs, neuroinflammation, and aggregate-prone proteins. In addition, we discuss how exosomes might be used to enhance individual patient outcomes by serving as reliable biomarkers of cognitive decline and as nanocarriers to deliver therapeutic agents to the brain in neurodegenerative conditions.

OUP accepted manuscript

Synaptic dysfunction is an early mechanism in Alzheimer’s disease that involves progressively larger areas of the brain over time. However, how it starts and propagates is unknown.

Here we show that amyloid-β released by microglia in association with large extracellular vesicles (Aβ-EVs) alters dendritic spine morphology in vitro, at the site of neuron interaction, and impairs synaptic plasticity both in vitro and in vivo in the entorhinal cortex–dentate gyrus circuitry. One hour after Aβ-EV injection into the mouse entorhinal cortex, long-term potentiation was impaired in the entorhinal cortex but not in the dentate gyrus, its main target region, while 24 h later it was also impaired in the dentate gyrus, revealing a spreading of long-term potentiation deficit between the two regions. Similar results were obtained upon injection of extracellular vesicles carrying Aβ naturally secreted by CHO7PA2 cells, while neither Aβ₄₂ alone nor inflammatory extracellular vesicles devoid of Aβ were able to propagate long-term potentiation impairment. Using optical tweezers combined to time-lapse imaging to study Aβ-EV–neuron interaction, we show that Aβ-EVs move anterogradely at the axon surface and that their motion can be blocked through annexin-V coating. Importantly, when Aβ-EV motility was inhibited, no propagation of long-term potentiation deficit occurred along the entorhinal–hippocampal circuit, implicating large extracellular vesicle motion at the neuron surface in the spreading of long-term potentiation impairment.

Our data indicate the involvement of large microglial extracellular vesicles in the rise and propagation of early synaptic dysfunction in Alzheimer’s disease and suggest a new mechanism controlling the diffusion of large extracellular vesicles and their pathogenic signals in the brain parenchyma, paving the way for novel therapeutic strategies to delay the disease.

The Amyloid-β Pathway in Alzheimer's Disease

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.

Microglial Exosomes in Neurodegenerative Disease

Microglia play an important role in neurodegenerative disease [i.e., Parkinson’s disease (PD), Alzheimer’s disease (AD), and amyotrophic lateral sclerosis (ALS)]. These diseases share some similar pathological changes and several microglia-associated processes, including immune response, neuroinflammation, phagocytosis, elimination of synapses et al. Microglia in the central nervous system (CNS) has been described as having both destructive and protective effects in neurological disorders. Besides, considerable evidence also indicates that microglia play a significant role in neurogenesis, neuronal cell death, and synaptic interactions. The communication between microglia and neurons is of vital role in regulating complex functions which are key to appropriate the activity of the brain. Accumulating studies have also demonstrated that exosomes with sizes ranging from 40–100 nm, released by microglia, could serve as key mediators in intercellular signaling. These exosomes, identified in terms of cellular origin in many kinds of biological fluids, exert their effects by delivering specific cargos such as proteins, microRNAs (miRNAs), and mRNAs. It was shown that microglial exosomes could transport to and be uptake by neurons, which may either be beneficial or instead, detrimental to CNS diseases. The focus of this review is to summarize the involvement of microglial exosomes in critical pathologies associated with neurodegenerative disease and how they contribute to these disorders, including PD, AD, and ALS. We also review the application of microglia exosomes as potential biomarkers in monitoring disease progression, as well as focusing on their roles as drug delivery vehicles in treating neurodegenerative disorders.

Insights Into the Proteomic Profiling of Extracellular Vesicles for the Identification of Early Biomarkers of Neurodegeneration

Extracellular vesicles (EVs) are involved in the development and progression of neurodegenerative diseases, including Alzheimer's and Parkinson's disease. Moreover, EVs have the capacity to modify the physiology of neuronal circuits by transferring proteins, RNA, lipids, and metabolites. The proteomic characterization of EVs (exosomes and microvesicles) from preclinical models and patient samples has the potential to reveal new proteins and molecular networks that affect the normal physiology prior to the appearance of traditional biomarkers of neurodegeneration. Noteworthy, many of the genetic risks associated to the development of Alzheimer's and Parkinson's disease affect the crosstalk between mitochondria, endosomes, and lysosomes. Recent research has focused on determining the role of endolysosomal trafficking in the onset of neurodegenerative diseases. Proteomic studies indicate an alteration of biogenesis and molecular content of EVs as a result of endolysosomal and autophagic dysfunction. In this review, we discuss the status of EV proteomic characterization and their usefulness in discovering new biomarkers for the differential diagnosis of neurodegenerative diseases. Despite the challenges related to the failure to follow a standard isolation protocol and their implementation for a clinical setting, the analysis of EV proteomes has revealed the presence of key proteins with post-translational modifications that can be measured in peripheral fluids.

From inflammasome to Parkinson's disease: Does the NLRP3 inflammasome facilitate exosome secretion and exosomal alpha-synuclein transmission in Parkinson's disease?

A pivotal neuropathological manifestation of synucleinopathies, like Parkinson's disease (PD), is the aggregation of α-synuclein. In a recent cell-to-cell transmission model of α-synuclein, α-synuclein propagation was demonstrated to resemble that of prion proteins in the central nervous system. Furthermore, exosomes, as biomolecule carriers, have been shown to transmit α-synuclein from neuron to neuron. However, the mechanisms underlying exosomal α-synuclein transmission have not been well understood. The NLR family pyrin domain containing 3 protein (NLRP3) inflammasome activation in microglia, and the subsequent release of proinflammatory cytokines, are two crucial pathological events involved in neuroinflammation and PD progression. Research has revealed that the NLRP3 inflammasome may facilitate the secretion of extracellular vesicles, as well as exosomal transmission of proteins like aggregated α-synuclein. However, only a few reports have evaluated these pathogenic mechanisms. Herein we evaluate for the first time the current evidence for the involvement of the NLRP3 inflammasome in microvesicle generation by microglial cells, and the various mechanisms regarding the production, shedding, and content of exosomes in relation to α-synuclein transmission from neuron to neuron. Furthermore, we propose a model of microglial NLRP3 inflammasome-dependent exosome secretion and exosomal α-synuclein transmission in PD. This knowledge may lead to the identification of novel potential targets for drug development and stimulate further research in PD.

Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease

Glia have been implicated in Alzheimer’s disease (AD) pathogenesis. Variants of the microglia receptor TREM2 increase AD risk and activation of “disease-associated microglia” (DAM) is dependent on TREM2 in mouse models of AD. We surveyed gene expression changes associated with AD pathology and TREM2 in 5XFAD mice and human AD by snRNA-seq. We confirmed the presence of Trem2-dependent DAM and identified a novel Serpina3n⁺C4b⁺ reactive oligodendrocyte population in mice. Interestingly, remarkably different glial phenotypes were evident in human AD. Microglia signature was reminiscent of IRF8-driven reactive microglia in peripheral nerve injury. Oligodendrocyte signatures suggested impaired axonal myelination and metabolic adaptation to neuronal degeneration. Astrocyte profiles indicated weakened metabolic coordination with neurons. Notably, the reactive phenotype of microglia was less palpable in TREM2 R47H and R62H carriers than in non-carriers, demonstrating a TREM2 requirement in both mouse and human AD, despite the marked species-specific differences.

Roles of microglial membranes in Alzheimer's disease

The majority of Alzheimer's disease (AD) risk genes are highly and selectively expressed by microglia in the brain. Several of these genes are related to lipid and cholesterol metabolism, lipid synthesis, lipid transport, endocytosis, exocytosis and phagocytosis. Therefore, studying the roles of cellular membrane biophysics in microglial function should improve our understanding of the AD pathology. In this chapter, we discuss how lipid rafts and membrane-cytoskeleton adhesion impact microglial-mediated oxidative stress and clearance of amyloid-β peptide (Aβ). We also discuss potential roles of lipid membrane-bound extracellular vesicles as carriers of pathological factors to promote inflammation and cytotoxicity.

Increased Microglial Exosomal miR-124-3p Alleviates Neurodegeneration and Improves Cognitive Outcome after rmTBI

Repetitive mild traumatic brain injury (rmTBI) is considered to be an important risk factor for long-term neurodegenerative disorders such as Alzheimer's disease, which is characterized by β-amyloid abnormalities and impaired cognitive function. Microglial exosomes have been reported to be involved in the transportation, distribution, and clearance of β-amyloid in Alzheimer's disease. However, their impacts on the development of neurodegeneration after rmTBI are not yet known. The role of miRNAs in microglial exosomes on regulating post-traumatic neurodegeneration was investigated in the present study. We demonstrated that miR-124-3p level in microglial exosomes from injured brain was significantly altered in the acute, sub-acute, and chronic phases after rmTBI. In in vitro experiments, microglial exosomes with upregulated miR-124-3p (EXO-124) alleviated neurodegeneration in repetitive scratch-injured neurons. The effects were exerted by miR-124-3p targeting Rela, an inhibitory transcription factor of ApoE that promotes the β-amyloid proteolytic breakdown, thereby inhibiting β-amyloid abnormalities. In mice with rmTBI, the intravenously injected microglial exosomes were taken up by neurons in injured brain. Besides, miR-124-3p in the exosomes was transferred into hippocampal neurons and alleviated neurodegeneration by targeting the Rela/ApoE signaling pathway. Consequently, EXO-124 treatments improved the cognitive outcome after rmTBI, suggesting a promising therapeutic strategy for future clinical translation.

Inflammatory mechanisms in neurodegeneration

This review discusses the profound connection between microglia, neuroinflammation, and Alzheimer's disease (AD). Theories have been postulated, tested, and modified over several decades. The findings have further bolstered the belief that microglia-mediated inflammation is both a product and contributor to AD pathology and progression. Distinct microglia phenotypes and their function, microglial recognition and response to protein aggregates in AD, and the overall role of microglia in AD are areas that have received considerable research attention and yielded significant results. The following article provides a historical perspective of microglia, a detailed discussion of multiple microglia phenotypes including dark microglia, and a review of a number of areas where microglia intersect with AD and other pathological neurological processes. The overall breadth of important discoveries achieved in these areas significantly strengthens the hypothesis that neuroinflammation plays a key role in AD. Future determination of the exact mechanisms by which microglia respond to, and attempt to mitigate, protein aggregation in AD may lead to new therapeutic strategies.

Neuroimmune Crosstalk through Extracellular Vesicles in Health and Disease

The dynamics of CNS function rely upon omnidirectional communication among CNS cell types. Extracellular vesicles (EVs) have emerged as key mediators of this communication and are actively involved in response to CNS injury, mediating inflammatory response and inflammation-related neuroprotection as they display dual beneficial and detrimental roles. Neuroimmune interactions include communication between neurons and microglia, the resident macrophages within the CNS, and these interactions are a critical mediator of healthy brain functions, mounting an inflammatory response, and disease pathogenesis. This review aims to organize recent research highlighting the role of EVs in health and neurodegenerative disorders, with a specific focus on neuroimmune interactions between neurons and glia in Alzheimer's disease.

Microglia-Derived Microvesicles Affect Microglia Phenotype in Glioma

Extracellular-released vesicles (EVs), such as microvesicles (MV) and exosomes (Exo) provide a new type of inter-cellular communication, directly transferring a ready to use box of information, consisting of proteins, lipids and nucleic acids. In the nervous system, EVs participate to neuron-glial cross-talk, a bidirectional communication important to preserve brain homeostasis and, when dysfunctional, involved in several CNS diseases. We investigated whether microglia-derived EVs could be used to transfer a protective phenotype to dysfunctional microglia in the context of a brain tumor. When MV, isolated from microglia stimulated with LPS/IFNγ were brain injected in glioma-bearing mice, we observed a phenotype switch of tumor associated myeloid cells (TAMs) and a reduction of tumor size. Our findings indicate that the MV cargo, which contains upregulated transcripts for several inflammation-related genes, can transfer information in the brain of glioma bearing mice modifying microglial gene expression, reducing neuronal death and glioma invasion, thus promoting the recovery of brain homeostasis.

Microglia in Alzheimer's disease: A target for immunotherapy

Microglia are resident Mϕs of the CNS that play pleiotropic functions in brain development and homeostasis. Impaired microglial functions are thought to be involved in the onset and progression of various neurodevelopmental and neurodegenerative diseases. Thus, understanding microglia in these settings may indicate new approaches for therapeutic intervention. Here, we review recent evidence implicating microglia in Alzheimer's disease and discuss potential therapeutic strategies targeting microglia and their receptors in this disease.