P2RX7 inhibitor suppresses exosome secretion and disease phenotype in P301S tau transgenic mice

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

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

Brain incoming call from glia during neuroinflammation: Roles of extracellular vesicles

The functionality of the central nervous system (CNS) relies on the connection, integration, and the exchange of information among neural cells. The crosstalk among glial cells and neurons is pivotal for a series of neural functions, such as development of the nervous system, electric conduction, synaptic transmission, neural circuit establishment, and brain homeostasis. Glial cells are crucial players in the maintenance of brain functionality in physiological and disease conditions. Neuroinflammation is a common pathological process in various brain disorders, such as neurodegenerative diseases, and infections. Glial cells, including astrocytes, microglia, and oligodendrocytes, are the main mediators of neuroinflammation, as they can sense and respond to brain insults by releasing pro-inflammatory or anti-inflammatory factors. Recent evidence indicates that extracellular vesicles (EVs) are pivotal players in the intercellular communication that underlies physiological and pathological processes. In particular, glia-derived EVs play relevant roles in modulating neuroinflammation, either by promoting or inhibiting the activation of glial cells and neurons, or by facilitating the clearance or propagation of pathogenic proteins. The involvement of EVs in neurodegenerative diseases such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Huntington's Disease (HD), and Multiple Sclerosis (MS)- which share hallmarks such as neuroinflammation and oxidative stress to DNA damage, alterations in neurotrophin levels, mitochondrial impairment, and altered protein dynamics- will be dissected, showing how EVs act as pivotal cell-cell mediators of toxic stimuli, thereby propagating degeneration and cell death signaling. Thus, this review focuses on the EVs secreted by microglia, astrocytes, oligodendrocytes and in neuroinflammatory conditions, emphasizing on their effects on neurons and on central nervous system functions, considering both their beneficial and detrimental effects.

Exosomes: A Cellular Communication Medium That Has Multiple Effects On Brain Diseases

Exosomes, as membranous vesicles generated by multiple cell types and secreted to extracellular space, play a crucial role in a range of brain injury-related brain disorders by transporting diverse proteins, RNA, DNA fragments, and other functional substances. The nervous system's pathogenic mechanisms are complicated, involving pathological processes like as inflammation, apoptosis, oxidative stress, and autophagy, all of which result in blood-brain barrier damage, cognitive impairment, and even loss of normal motor function. Exosomes have been linked to the incidence and progression of brain disorders in recent research. As a result, a thorough knowledge of the interaction between exosomes and brain diseases may lead to the development of more effective therapeutic techniques that may be implemented in the clinic. The potential role of exosomes in brain diseases and the crosstalk between exosomes and other pathogenic processes were discussed in this paper. Simultaneously, we noted the delicate events in which exosomes as a media allow the brain to communicate with other tissues and organs in physiology and disease, and compiled a list of natural compounds that modulate exosomes, in order to further improve our understanding of exosomes and propose new ideas for treating brain disorders.

Aberrant regulation of serine metabolism drives extracellular vesicle release and cancer progression

Cancer cells secrete extracellular vesicles (EVs) to regulate cells in the tumor microenvironment to benefit their own growth and survive in the patient's body. Although emerging evidence has demonstrated the molecular mechanisms of EV release, regulating cancer-specific EV secretion remains challenging. In this study, we applied a microRNA library to reveal the universal mechanisms of EV secretion from cancer cells. Here, we identified miR-891b and its direct target gene, phosphoserine aminotransferase 1 (PSAT1), which promotes EV secretion through the serine-ceramide synthesis pathway. Inhibition of PSAT1 affected EV secretion in multiple types of cancer, suggesting that the miR-891b/PSAT1 axis shares a common mechanism of EV secretion from cancer cells. Interestingly, aberrant PSAT1 expression also regulated cancer metastasis via EV secretion. Our data link the PSAT1-controlled EV secretion mechanism and cancer metastasis and show the potential of this mechanism as a therapeutic target in multiple types of cancer.

Extracellular vesicle therapy in neurological disorders

Extracellular vesicles (EVs) are vital for cell-to-cell communication, transferring proteins, lipids, and nucleic acids in various physiological and pathological processes. They play crucial roles in immune modulation and tissue regeneration but are also involved in pathogenic conditions like inflammation and degenerative disorders. EVs have heterogeneous populations and cargo, with numerous subpopulations currently under investigations. EV therapy shows promise in stimulating tissue repair and serving as a drug delivery vehicle, offering advantages over cell therapy, such as ease of engineering and minimal risk of tumorigenesis. However, challenges remain, including inconsistent nomenclature, complex characterization, and underdeveloped large-scale production protocols. This review highlights the recent advances and significance of EVs heterogeneity, emphasizing the need for a better understanding of their roles in disease pathologies to develop tailored EV therapies for clinical applications in neurological disorders.

Microglial modulation as a therapeutic strategy in Alzheimer's disease: Focus on microglial preconditioning approaches

Alzheimer's disease (AD) is a progressive disease that causes an impairment of learning and memory. Despite the highly complex pathogenesis of AD, amyloid beta (Aβ) deposition and neurofibrillary tangles (NFTs) formation are the main hallmarks of AD. Neuroinflammation also has a crucial role in the development of AD. As the central nervous system's innate immune cells, microglial cells are activated in AD and induce inflammation by producing pro-inflammatory mediators. However, microglial activation is not always deleterious. M2-activated microglial cells are considered anti-inflammatory cells, which develop neuroprotection. Various approaches are proposed for managing AD, yet no effective therapy is available for this disorder. Considering the potential protective role of M2 microglia in neurodegenerative disorders and the improvement of these disorders by preconditioning approaches, it can be suggested that preconditioning of microglial cells may be beneficial for managing AD progression. Therefore, this study review microglial preconditioning approaches for preventing and improving AD.

Unlocking the therapeutic potential of P2X7 receptor: a comprehensive review of its role in neurodegenerative disorders

The P2X7 receptor (P2X7R), an ATP-gated ion channel, has emerged as a crucial player in neuroinflammation and a promising therapeutic target for neurodegenerative disorders. This review explores the current understanding of P2X7R's structure, activation, and physiological roles, focusing on its expression and function in microglial cells. The article examines the receptor's involvement in calcium signaling, microglial activation, and polarization, as well as its role in the pathogenesis of Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis. The review highlights the complex nature of P2X7R signaling, discussing its potential neuroprotective and neurotoxic effects depending on the disease stage and context. It also addresses the development of P2X7R antagonists and their progress in clinical trials, identifying key research gaps and future perspectives for P2X7R-targeted therapy development. By providing a comprehensive overview of the current state of knowledge and future directions, this review serves as a valuable resource for researchers and clinicians interested in exploring the therapeutic potential of targeting P2X7R for the treatment of neurodegenerative disorders.

Unveiling the role of exosomes as cellular messengers in neurodegenerative diseases and their potential therapeutic implications

Exosomes are a subgroup of extracellular vesicles that function as transmitters, allowing cells to communicate more effectively with each other. However, exosomes may have both beneficial and harmful impacts on central nervous system disorders. Hence, the fundamental molecular mechanisms of the origin of illness and its progression are currently being investigated. The involvement of exosomes in the origin and propagation of neurodegenerative illness has been demonstrated recently. Exosomes provide a representation of the intracellular environment since they include various essential bioactive chemicals. The latest studies have demonstrated that exosomes transport several proteins. Additionally, these physiological vesicles are important in the regeneration of nervous tissue and the healing of neuronal lesions. They also offer a microenvironment to stimulate the conformational variation of concerning proteins for aggregation, resulting in neurodegenerative diseases. The biosynthesis, composition, and significance of exosomes as extracellular biomarkers in neurodegenerative disorders are discussed in this article, with a particular emphasis on their neuroprotective effects.

Complicated Role of Post-translational Modification and Protease-Cleaved Fragments of Tau in Alzheimer's Disease and Other Tauopathies

Tau, a microtubule-associated protein predominantly localized in neuronal axons, plays a crucial role in promoting microtubule assembly, stabilizing their structure, and participating in axonal transport. Perturbations in tau's structure and function are implicated in the pathogenesis of neurodegenerative diseases collectively known as tauopathies, the most common disorder of which is Alzheimer's disease (AD). In tauopathies, it has been found that tau has a variety of post-translational modification (PTM) abnormalities and/or tau is cleaved into a variety of fragments by some specific proteolytic enzymes; however, the precise contributions of these abnormal modifications and fragments to disease onset and progression remain incompletely understood. Herein, we provide an overview about the involvement of distinctive abnormal tau PTMs and different tau fragments in the pathogenesis of AD and other tauopathies and discuss the involvement of proteolytic enzymes such as caspases, calpains, and asparagine endopeptidase in mediating tau cleavage while also addressing the intercellular transmission role played by tau. We anticipate that further exploration into PTMs and fragmented forms of tau will yield valuable insights for diagnostic approaches and therapeutic interventions targeting AD and other related disorders.

P2RX7 plays a critical role in extracellular vesicle-mediated secretion of pathogenic molecules from microglia and astrocytes

Extracellular vesicle (EV) secretion is mediated by purinergic receptor P2X7 (P2RX7), an ATP-gated cation channel highly expressed in microglia. We have previously shown that administration of GSK1482160, a P2RX7 selective inhibitor, suppresses EV secretion from murine microglia and prevents tauopathy development, leading to the recovery of the hippocampal function in PS19 mice, expressing P301S tau mutant. It is yet unknown, however, whether the effect of GSK1482160 on EV secretion from glial cells is specifically regulated through P2RX7. Here we tested GSK1482160 on primary microglia and astrocytes isolated from C57BL/6 (WT) and P2rx7-/- mice and evaluated their EV secretion and phagocytotic activity of aggregated human tau (hTau) under ATP stimulation. GSK1482160 treatment and deletion of P2rx7 significantly reduced secretion of small and large EVs in microglia and astrocytes in both ATP stimulated or unstimulated condition as determined by nanoparticle tracking analysis, CD9 ELISA and immunoblotting of Tsg101 and Flotilin 1 using isolated EVs. GSK1482160 treatment had no effect on EV secretion from P2rx7 -/- microglia while we observed significant reduction in the secretion of small EVs from P2rx7 -/- astrocytes, suggesting its specific targeting of P2RX7 in EV secretion except small EV secretion from astrocytes. Finally, deletion of P2rx7 suppressed IL-1β secretion and phagocytosed misfolded tau from both microglia and astrocytes. Together, these findings show that GSK1482160 suppresses EV secretion from microglia and astrocytes in P2RX7-dependment manner, and P2RX7 critically regulates secretion of IL-1β and misfolded hTau, demonstrating as the viable target of suppressing EV-mediated neuroinflammation and tau propagation.

Microglial purinergic signaling in Alzheimer's disease

Alzheimer's disease (AD) is a progressive and fatal neurodegenerative disease. The prevalent features of AD pathogenesis are the appearance of β-amyloid (Aβ) plaques and neurofibrillary tangles, which cause microglial activation, synaptic deficiency, and neuronal loss. Microglia accompanies AD pathological processes and is also linked to cognitive deficits. Purinergic signaling has been shown to play a complex and tight interplay with the chemotaxis, phagocytosis, and production of pro-inflammatory factors in microglia, which is an important mechanism for regulating microglia activation. Here, we review recent evidence for interactions between AD, microglia, and purinergic signaling and find that the purinergic P2 receptors pertinently expressed on microglia are the ionotropic receptors P2X4 and P2X7, and the subtypes of P2YRs expressed by microglia are metabotropic receptors P2Y2, P2Y6, P2Y12, and P2Y13. The adenosine P1 receptors expressed in microglia include A1R, A2AR, and A2BR. Among them, the activation of P2X4, P2X7, and adenosine A1, A2A receptors expressed in microglia can aggravate the pathological process of AD, whereas P2Y2, P2Y6, P2Y12, and P2Y13 receptors expressed by microglia can induce neuroprotective effects. However, A1R activation also has a strong neuroprotective effect and has a significant anti-inflammatory effect in chronic neuroinflammation. These receptors regulate a variety of pathophysiological processes in AD, including APP processing, Aβ production, tau phosphorylation, neuroinflammation, synaptic dysfunction, and mitochondrial dysfunction. This review also provides key pharmacological advances in purinergic signaling receptors.

Unveiling the Complex Role of Exosomes in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative illness, characterized by memory loss and cognitive decline, accounting for 60-80% of dementia cases. AD is characterized by senile plaques made up of amyloid β (Aβ) protein, intracellular neurofibrillary tangles caused by hyperphosphorylation of tau protein linked with microtubules, and neuronal loss. Currently, therapeutic treatments and nanotechnological developments are effective in treating the symptoms of AD, but a cure for the illness has not yet been found. Recently, the increased study of extracellular vesicles (EVs) has led to a growing awareness of their significant involvement in neurodegenerative disorders, including AD. Exosomes are small extracellular vesicles that transport various components including messenger RNAs, non-coding RNAs, proteins, lipids, DNA, and other bioactive compounds from one cell to another, facilitating information transmission and material movement. There is growing evidence indicating that exosomes have complex functions in AD. Exosomes may have a dual role in Alzheimer's disease by contributing to neuronal death and also helping to alleviate the pathological progression of the disease. Therefore, the primary aim of this review is to outline the updated understandings on exosomes biogenesis and many functions of exosomes in the generation, conveyance, distribution, and elimination of hazardous proteins related to Alzheimer's disease. This review is intended to provide novel insights for understanding the development, specific treatment, and early detection of Alzheimer's disease.

Single-cell sequencing of the substantia nigra reveals microglial activation in a model of MPTP

Background

N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin widely used to induce PD models, but the effect of MPTP on the cells and genes of PD has not been fully elucidated.

Methods

Single-nucleus RNA sequencing was performed in the Substantia Nigra (SN) of MPTP mice. UMAP analysis was used for the dimensionality reduction visualization of the SN in the MPTP mice. Known marker genes highly expressed genes in each cluster were used to annotate most clusters. Specific Differentially Expressed Genes (DEGs) and PD risk genes analysis were used to find MPTP-associated cells. GO, KEGG, PPI network, GSEA and CellChat analysis were used to reveal cell type-specific functional alterations and disruption of cell-cell communication networks. Subset reconstruction and pseudotime analysis were used to reveal the activation status of the cells, and to find the transcription factors with trajectory characterized.

Results

Initially, we observed specific DEGs and PD risk genes enrichment in microglia. Next, We obtained the functional phenotype changes in microglia and found that IGF, AGRN and PTN pathways were reduced in MPTP mice. Finally, we analyzed the activation state of microglia and revealed a pro-inflammatory trajectory characterized by transcription factors Nfe2l2 and Runx1.

Conclusion

Our work revealed alterations in microglia function, signaling pathways and key genes in the SN of MPTP mice.

Increased Cerebral Level of P2X7R in a Tauopathy Mouse Model by PET Using [18F]GSK1482160

Neuroinflammation plays an important role in Alzheimer's disease and primary tauopathies. The aim of the current study was to map [18F]GSK1482160 for imaging of purinergic P2X7R in Alzheimer's disease and primary tauopathy mouse models. Small animal PET was performed using [18F]GSK1482160 in widely used mouse models of Alzheimer's disease (APP/PS1, 5×FAD, and 3×Tg), 4-repeat tauopathy (rTg4510) mice, and age-matched wild-type mice. Increased uptake of [18F]GSK1482160 was observed in the brains of 7-month-old rTg4510 mice compared to wild-type mice and compared to 3-month-old rTg4510 mice. A positive correlation between hippocampal tau [18F]APN-1607 and [18F]GSK1482160 uptake was found in rTg4510 mice. No significant differences in the uptake of [18F]GSK1482160 was observed for APP/PS1 mice, 5×FAD mice, or 3×Tg mice. Immunofluorescence staining further indicated the distribution of P2X7Rs in the brains of 7-month-old rTg4510 mice with accumulation of tau inclusion. These findings provide in vivo imaging evidence for an increased level of P2X7R in the brains of tauopathy mice.

P2X7 Receptor: an Emerging Target in Alzheimer's Disease

Alzheimer's disease (AD) is a major cause of age-related dementia, which is becoming a global health crisis. However, the pathogenesis and etiology of AD are still not fully understood. And there are no valid treatment methods or precise diagnostic tools for AD. There is increasing evidence that P2X7R expression is upregulated in AD and is involved in multiple related pathological processes such as Aβ plaques, neurogenic fiber tangles, oxidative stress, and chronic neuroinflammation. This suggests that P2X7R may be a key player in the development of AD. P2X7R is a member of the ligand-gated purinergic receptor (P2X) family. It has received attention in neuroscience due to its role in a wide range of aging and age-related neurological disorders. In this review, we summarize current information on the roles of P2X7R in AD and suggest potential pharmacological interventions to slow down AD progression.

P2X7 receptors: a bibliometric review from 2002 to 2023

For many years, there has been ongoing research on the P2X7 receptor (P2X7R). A comprehensive, systematic, and objective evaluation of the scientific output and status of P2X7R will be instrumental in guiding future research directions. This study aims to present the status and trends of P2X7R research from 2002 to 2023. Publications related to P2X7R were retrieved from the Web of Science Core Collection database. Quantitative analysis and visualization tools were Microsoft Excel, VOSviewer, and CiteSpace software. The analysis content included publication trends, literature co-citation, and keywords. 3282 records were included in total, with the majority of papers published within the last 10 years. Based on literature co-citation and keyword analysis, neuroinflammation, neuropathic pain, gastrointestinal diseases, tumor microenvironment, rheumatoid arthritis, age-related macular degeneration, and P2X7R antagonists were considered to be the hotspots and frontiers of P2X7R research. Researchers will get a more intuitive understanding of the status and trends of P2X7R research from this study.

Comorbidity Genes of Alzheimer's Disease and Type 2 Diabetes Associated with Memory and Cognitive Function

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are comorbidities that result from the sharing of common genes. The molecular background of comorbidities can provide clues for the development of treatment and management strategies. Here, the common genes involved in the development of the two diseases and in memory and cognitive function are reviewed. Network clustering based on protein-protein interaction network identified tightly connected gene clusters that have an impact on memory and cognition among the comorbidity genes of AD and T2DM. Genes with functional implications were intensively reviewed and relevant evidence summarized. Gene information will be useful in the discovery of biomarkers and the identification of tentative therapeutic targets for AD and T2DM.

The Neuro-Inflammatory Microenvironment: An Important Regulator of Stem Cell Survival in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, characterized by progressive memory loss and cognitive impairment due to excessive accumulation of extracellular amyloid-β plaques and intracellular neurofibrillary tangles. Although decades of research efforts have been put into developing disease-modifying therapies for AD, no "curative" drug has been identified. As a central player in neuro-inflammation, microglia play a key role inbrain homeostasis by phagocytosing debris and regulating the balance between neurotoxic and neuroprotective events. Typically, the neurotoxic phenotype of activated microglia is predominant in the impaired microenvironment of AD. Accordingly, transitioning the activity state of microglia from pro-inflammatory to anti-inflammatory can restore the disrupted homeostatic microenvironment. Recently, stem cell therapy holds great promise as a treatment for AD; however, the diminished survival of transplanted stem cells has resulted in a disappointing long-term outcome for this treatment. This article reviews the functional changes of microglia through the course of AD-associated homeostatic deterioration. We summarize the possible microglia-associated therapeutic targets including TREM2, IL-3Rα, CD22, C5aR1, CX3CR1, P2X7R, CD33, Nrf2, PPAR-γ, CSF1R, and NLRP3, each of which has been discussed in detail. The goal of this review is to put forth the notion that microglia could be targeted by either small molecules or biologics to make the brain microenvironment more amenable to stem cell implantation and propose a novel treatment strategy for future stem cell interventions in AD.

ApoE4 expression disrupts tau uptake, trafficking, and clearance in astrocytes

Tauopathies are a collection of neurodegenerative diseases characterized by the accumulation of pathogenic aggregates of the microtubule-associated protein tau. Despite the prevalence and diversity of tau astrogliopathy in tauopathies, the interactions between astrocytes and tau in the brain, and the influence of neurodegenerative genetic risk factors like the apolipoprotein E4 (apoE4) isoform, are largely unknown. Here, we leveraged primary and immortalized astrocytes expressing humanized apoE isoforms to characterize the mechanisms by which astrocytes interact with and eliminate extracellular tau, and the influence of apoE genotype on these processes. Our work indicates that astrocytes rapidly internalize, process, and release tau via an exosomal secretory mechanism under physiological conditions. However, we found that apoE4 disrupted these processes in comparison to apoE3, resulting in an astrocytic phenotype prone to intracellular tau accumulation. Furthermore, exposure to repetitive mild traumatic brain injuries exacerbated the apoE4-induced impairments in tau processing and elimination by astrocytes in apoE4 targeted-replacement mice. The diminished ability of apoE4 astrocytes to eliminate extracellular tau can lead to an accumulation of pathogenic tau, which induces mitochondrial dysfunction, as demonstrated by our studies. In total, our findings suggest that the apoE4 isoform lowers the threshold of astrocytic resilience to pathogenic tau, rendering them susceptible to bioenergetic deficits in the early stages of neurodegenerative diseases such as traumatic brain injury, potentially contributing to neurological decline.

Novel method for collecting hippocampal interstitial fluid extracellular vesicles (EVISF ) reveals sex-dependent changes in microglial EV proteome in response to Aβ pathology

Brain-derived extracellular vesicles (EVs) play an active role in Alzheimer's disease (AD), relaying important physiological information about their host tissues. The internal cargo of EVs is protected from degradation, making EVs attractive AD biomarkers. However, it is unclear how circulating EVs relate to EVs isolated from disease-vulnerable brain regions. We developed a novel method for collecting EVs from the hippocampal interstitial fluid (ISF) of live mice. EVs (EVISF ) were isolated via ultracentrifugation and characterized by nanoparticle tracking analysis, immunogold labelling, and flow cytometry. Mass spectrometry and proteomic analyses were performed on EVISF cargo. EVISF were 40-150 nm in size and expressed CD63, CD9, and CD81. Using a model of cerebral amyloidosis (e.g., APPswe, PSEN1dE9 mice), we found protein concentration increased but protein diversity decreased with Aβ deposition. Genotype, age, and Aβ deposition modulated proteostasis- and immunometabolic-related pathways. Changes in the microglial EVISF proteome were sexually dimorphic and associated with a differential response of plaque associated microglia. We found that female APP/PS1 mice have more amyloid plaques, less plaque associated microglia, and a less robust- and diverse- EVISF microglial proteome. Thus, in vivo microdialysis is a novel technique for collecting EVISF and offers a unique opportunity to explore the role of EVs in AD.

P2X7R influences tau aggregate burden in human tauopathies and shows distinct signalling in microglia and astrocytes

The purinoceptor P2X7R is a promising therapeutic target for tauopathies, including Alzheimer's disease (AD). Pharmacological inhibition or genetic knockdown of P2X7R ameliorates cognitive deficits and reduces pathological tau burden in mice that model aspects of tauopathy, including mice expressing mutant human frontotemporal dementia (FTD)-causing forms of tau. However, disagreements remain over which glial cell types express P2X7R and therefore the mechanism of action is unresolved. Here, we show that P2X7R protein levels increase in human AD post-mortem brain, in agreement with an upregulation of P2RX7 mRNA observed in transcriptome profiles from the AMP-AD consortium. P2X7R protein increases mirror advancing Braak stage and coincide with synapse loss. Using RNAScope we detect P2RX7 mRNA in microglia and astrocytes in human AD brain, including in the vicinity of senile plaques. In cultured microglia, P2X7R activation modulates the NLRP3 inflammasome pathway by promoting the formation of active complexes and release of IL-1β. In astrocytes, P2X7R activates NFκB signalling and increases production of the cytokines CCL2, CXCL1 and IL-6 together with the acute phase protein Lcn2. To further explore the role of P2X7R in a disease-relevant context, we expressed wild-type or FTD-causing mutant forms of tau in mouse organotypic brain slice cultures. Inhibition of P2X7R reduces insoluble tau levels without altering soluble tau phosphorylation or synaptic localisation, suggesting a non-cell autonomous role of glial P2X7R on pathological tau aggregation. These findings support further investigations into the cell-type specific effects of P2X7R-targeting therapies in tauopathies.

Exosomes Derived from M2 Microglial Cells Modulated by 1070-nm Light Improve Cognition in an Alzheimer's Disease Mouse Model

Near-infrared photobiomodulation has been identified as a potential strategy for Alzheimer's disease (AD). However, the mechanisms underlying this therapeutic effect remain poorly characterize. Herein, it is illustrate that 1070-nm light induces the morphological alteration of microglia from an M1 to M2 phenotype that secretes exosomes, which alleviates the β-amyloid burden to improve cognitive function by ameliorating neuroinflammation and promoting neuronal dendritic spine plasticity. The results show that 4 J cm-2 1070-nm light at a 10-Hz frequency prompts microglia with an M1 inflammatory type to switch to an M2 anti-inflammatory type. This induces secretion of M2 microglial-derived exosomes containing miR-7670-3p, which targets activating transcription factor 6 (ATF6) during endoplasmic reticulum (ER) stress. Moreover, it is found that miR-7670-3p reduces ATF6 expression to further ameliorate ER stress, thus attenuating the inflammatory response and protecting dendritic spine integrity of neurons in the cortex and hippocampus of 5xFAD mice, ultimately leading to improvements in cognitive function. This study highlights the critical role of exosomes derive from 1070-nm light-modulated microglia in treating AD mice, which may provide a theoretical basis for the treatment of AD with the use of near-infrared photobiomodulation.

Microglia in neurodegenerative diseases: mechanism and potential therapeutic targets

Microglia activation is observed in various neurodegenerative diseases. Recent advances in single-cell technologies have revealed that these reactive microglia were with high spatial and temporal heterogeneity. Some identified microglia in specific states correlate with pathological hallmarks and are associated with specific functions. Microglia both exert protective function by phagocytosing and clearing pathological protein aggregates and play detrimental roles due to excessive uptake of protein aggregates, which would lead to microglial phagocytic ability impairment, neuroinflammation, and eventually neurodegeneration. In addition, peripheral immune cells infiltration shapes microglia into a pro-inflammatory phenotype and accelerates disease progression. Microglia also act as a mobile vehicle to propagate protein aggregates. Extracellular vesicles released from microglia and autophagy impairment in microglia all contribute to pathological progression and neurodegeneration. Thus, enhancing microglial phagocytosis, reducing microglial-mediated neuroinflammation, inhibiting microglial exosome synthesis and secretion, and promoting microglial conversion into a protective phenotype are considered to be promising strategies for the therapy of neurodegenerative diseases. Here we comprehensively review the biology of microglia and the roles of microglia in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple system atrophy, amyotrophic lateral sclerosis, frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies and Huntington's disease. We also summarize the possible microglia-targeted interventions and treatments against neurodegenerative diseases with preclinical and clinical evidence in cell experiments, animal studies, and clinical trials.

Application of exosome engineering modification in targeted delivery of therapeutic drugs

Cancer is the leading cause of premature death in humans. Scientists have developed several therapeutic drugs for cancer treatment. However, drug delivery faces many problems. First, traditional drugs do not target tumors and are prone to causing significant toxic side effects. Second, suitable drug carriers are essential for improving drug delivery to tumors or circulating cancer cells. Exosomes are natural extracellular vesicles with low immunogenicity and prolonged blood circulation in vivo. These characteristics render exosomes ideal drug carriers. This review highlights the properties of exosomes and mechanisms of exosome biogenesis. It also summarizes the engineering modification methods for enhancing exosome yield, targeting, and drug-loading capacity.

Comprehensive characterization of human brain-derived extracellular vesicles using multiple isolation methods: Implications for diagnostic and therapeutic applications

Extracellular vesicles (EVs) have emerged as critical mediators of intercellular communication and promising biomarkers and therapeutics in the central nervous system (CNS). Human brain-derived EVs (BDEVs) provide a comprehensive snapshot of physiological changes in the brain's environment, however, the isolation of BDEVs and the comparison of different methods for this purpose have not been fully investigated. In this study, we compared the yield, morphology, subtypes and protein cargo composition of EVs isolated from the temporal cortex of aged human brains using three established separation methods: size-exclusion chromatography (SEC), phosphatidylserine affinity capture (MagE) and sucrose gradient ultracentrifugation (SG-UC). Our results showed that SG-UC method provided the highest yield and collected larger EVs compared to SEC and MagE methods as assessed by transmission electron microscopy and nanoparticle tracking analysis (NTA). Quantitative tandem mass-tag (TMT) mass spectrometry analysis of EV samples from three different isolation methods identified a total of 1158 proteins, with SG-UC showing the best enrichment of common EV proteins with less contamination of non-EV proteins. In addition, SG-UC samples were enriched in proteins associated with ATP activity and CNS maintenance, and were abundant in neuronal and oligodendrocytic molecules. In contrast, MagE samples were more enriched in molecules related to lipoproteins, cell-substrate junction and microglia, whereas SEC samples were highly enriched in molecules related to extracellular matrix, Alzheimer's disease and astrocytes. Finally, we validated the proteomic results by performing single-particle analysis using the super-resolution microscopy and flow cytometry. Overall, our findings demonstrate the differences in yield, size, enrichment of EV cargo molecules and single EV assay by different isolation methods, suggesting that the choice of isolation method will have significant impact on the downstream analysis and protein discovery.

The P2X7 Receptor, a Multifaceted Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by impaired episodic memory and two pathological lesions: amyloid plaques and neurofibrillary tangles. In AD, damaged neurons and the accumulation of amyloid β (Aβ) peptides cause a significant release of high amounts of extracellular ATP, which acts as a danger signal. The purinergic receptor P2X7 is the main sensor of high concentrations of ATP, and P2X7 has been shown to be upregulated in the brains of AD patients, contributing to the disease's pathological processes. Further, there are many polymorphisms of the P2X7 gene that impact the risk of developing AD. P2X7 can directly modulate Aβ plaques and Tau protein lesions as well as the inflammatory response by regulating NLRP3 inflammasome and the expression of several chemokines. The significant role of microglial P2X7 in AD has been well established, although other cell types may also be important in P2X7-mediated mechanisms. In this review, we will discuss the different P2X7-dependent pathways involved in the development of AD.

Tau and neuroinflammation in Alzheimer's disease: interplay mechanisms and clinical translation

Alzheimer's Disease (AD) contributes to most cases of dementia. Its prominent neuropathological features are the extracellular neuritic plaques and intercellular neurofibrillary tangles composed of aggregated β-amyloid (Aβ) and hyperphosphorylated tau protein, respectively. In the past few decades, disease-modifying therapy targeting Aβ has been the focus of AD drug development. Even though it is encouraging that two of these drugs have recently received accelerated US Food and Drug Administration approval for AD treatment, their efficacy or long-term safety is controversial. Tau has received increasing attention as a potential therapeutic target, since evidence indicates that tau pathology is more associated with cognitive dysfunction. Moreover, inflammation, especially neuroinflammation, accompanies AD pathological processes and is also linked to cognitive deficits. Accumulating evidence indicates that inflammation has a complex and tight interplay with tau pathology. Here, we review recent evidence on the interaction between tau pathology, focusing on tau post-translational modification and dissemination, and neuroinflammatory responses, including glial cell activation and inflammatory signaling pathways. Then, we summarize the latest clinical trials targeting tau and neuroinflammation. Sustained and increased inflammatory responses in glial cells and neurons are pivotal cellular drivers and regulators of the exacerbation of tau pathology, which further contributes to its worsening by aggravating inflammatory responses. Unraveling the precise mechanisms underlying the relationship between tau pathology and neuroinflammation will provide new insights into the discovery and clinical translation of therapeutic targets for AD and other tau-related diseases (tauopathies). Targeting multiple pathologies and precision therapy strategies will be the crucial direction for developing drugs for AD and other tauopathies.

The emerging double-edged sword role of exosomes in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by progressive loss of memory and cognitive dysfunction. The primary pathological hallmarks of AD are senile plaques formed by deposition of amyloid β (Aβ) protein, intracellular neurofibrillary tangles resulting from hyperphosphorylation of microtubule-associated protein tau, and loss of neurons. At present, although the exact pathogenesis of AD is still unclear and there is a lack of effective treatment for AD in clinical practice, researchers have never stopped exploring the pathogenic mechanism of AD. In recent years, with the rise of the research of extracellular vesicles (EVs), people gradually realize that EVs also play important roles in neurodegenerative diseases. Exosomes, as a member of the small EVs, are regarded as carriers for information exchange and material transport between cells. Many cells of the central nervous system can release exosomes in both physiological and pathological conditions. Exosomes derived from damaged nerve cells can not only participate in Aβ production and oligomerization, but also disseminate the toxic proteins of Aβ and tau to neighboring neurons, thereby acting as "seeds" to amplify the toxic effects of misfolded proteins. Furthermore, exosomes may also be involved in the degradation and clearance process of Aβ. There is increasing evidence to suggest that exosomes play multiple roles in AD. Just like a double-edged sword, exosomes can participate in AD pathology in a direct or indirect way, causing neuronal loss, and can also participate in alleviating the pathological progression of AD. In this review, we summarize and discuss the current reported research findings on this double-edged role of exosomes in AD.

Ectopic ATP synthase stimulates the secretion of extracellular vesicles in cancer cells

ABSTARCT

Ectopic ATP synthase on the plasma membrane (eATP synthase) has been found in various cancer types and is a potential target for cancer therapy. However, whether it provides a functional role in tumor progression remains unclear. Here, quantitative proteomics reveals that cancer cells under starvation stress express higher eATP synthase and enhance the production of extracellular vesicles (EVs), which are vital regulators within the tumor microenvironment. Further results show that eATP synthase generates extracellular ATP to stimulate EV secretion by enhancing P2X7 receptor-triggered Ca2+ influx. Surprisingly, eATP synthase is also located on the surface of tumor-secreted EVs. The EVs-surface eATP synthase increases the uptake of tumor-secreted EVs in Jurkat T-cells via association with Fyn, a plasma membrane protein found in immune cells. The eATP synthase-coated EVs uptake subsequently represses the proliferation and cytokine secretion of Jurkat T-cells. This study clarifies the role of eATP synthase on EV secretion and its influence on immune cells.

P2X7 receptor inhibition ameliorates ubiquitin-proteasome system dysfunction associated with Alzheimer's disease

BACKGROUND

Over recent years, increasing evidence suggests a causal relationship between neurofibrillary tangles (NFTs) formation, the main histopathological hallmark of tauopathies, including Alzheimer's disease (AD), and the ubiquitin-proteasome system (UPS) dysfunction detected in these patients. Nevertheless, the mechanisms underlying UPS failure and the factors involved remain poorly understood. Given that AD and tauopathies are associated with chronic neuroinflammation, here, we explore if ATP, one of the danger-associated molecules patterns (DAMPs) associated with neuroinflammation, impacts on AD-associated UPS dysfunction.

METHODS

To evaluate if ATP may modulate the UPS via its selective P2X7 receptor, we combined in vitro and in vivo approaches using both pharmacological and genetic tools. We analyze postmortem samples from human AD patients and P301S mice, a mouse model that mimics pathology observed in AD patients, and those from the new transgenic mouse lines generated, such as P301S mice expressing the UPS reporter Ub^G76V-YFP or P301S deficient of P2X7R.

RESULTS

We describe for the first time that extracellular ATP-induced activation of the purinergic P2X7 receptor (P2X7R) downregulates the transcription of β5 and β1 proteasomal catalytic subunits via the PI3K/Akt/GSK3/Nfr2 pathway, leading to their deficient assembly into the 20S core proteasomal complex, resulting in a reduced proteasomal chymotrypsin-like and postglutamyl-like activities. Using UPS-reported mice (UbGFP mice), we identified neurons and microglial cells as the most sensitive cell linages to a P2X7R-mediated UPS regulation. In vivo pharmacological or genetic P2X7R blockade reverted the proteasomal impairment developed by P301S mice, which mimics that were detected in AD patients. Finally, the generation of P301S;UbGFP mice allowed us to identify those hippocampal cells more sensitive to UPS impairment and demonstrate that the pharmacological or genetic blockade of P2X7R promotes their survival.

CONCLUSIONS

Our work demonstrates the sustained and aberrant activation of P2X7R caused by Tau-induced neuroinflammation contributes to the UPS dysfunction and subsequent neuronal death associated with AD, especially in the hippocampus.

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.

Extracellular vesicles as personalized medicine

Extracellular vesicles (EVs) are released from all cells in the body, forming an important intercellular communication network that contributes to health and disease. The contents of EVs are cell source-specific, inducing distinct signaling responses in recipient cells. The specificity of EVs and their accumulation in fluid spaces that are accessible for liquid biopsies make them highly attractive as potential biomarkers and therapies for disease. The duality of EVs as favorable (therapeutic) or unfavorable (pathological) messengers is context dependent and remains to be fully determined in homeostasis and various disease states. This review describes the use of EVs as biomarkers, drug delivery vehicles, and regenerative therapeutics, highlighting examples involving viral infections, cancer, and neurological diseases. There is growing interest to provide personalized therapy based on individual patient and disease characteristics. Increasing evidence suggests that EV biomarkers and therapeutic approaches are ideal for personalized medicine due to the diversity and multifunctionality of EVs.

The human neurosecretome: extracellular vesicles and particles (EVPs) of the brain for intercellular communication, therapy, and liquid-biopsy applications

Emerging evidence suggests that brain derived extracellular vesicles (EVs) and particles (EPs) can cross blood-brain barrier and mediate communication among neurons, astrocytes, microglial, and other cells of the central nervous system (CNS). Yet, a complete understanding of the molecular landscape and function of circulating EVs & EPs (EVPs) remain a major gap in knowledge. This is mainly due to the lack of technologies to isolate and separate all EVPs of heterogeneous dimensions and low buoyant density. In this review, we aim to provide a comprehensive understanding of the neurosecretome, including the extracellular vesicles that carry the molecular signature of the brain in both its microenvironment and the systemic circulation. We discuss the biogenesis of EVPs, their function, cell-to-cell communication, past and emerging isolation technologies, therapeutics, and liquid-biopsy applications. It is important to highlight that the landscape of EVPs is in a constant state of evolution; hence, we not only discuss the past literature and current landscape of the EVPs, but we also speculate as to how novel EVPs may contribute to the etiology of addiction, depression, psychiatric, neurodegenerative diseases, and aid in the real time monitoring of the "living brain". Overall, the neurosecretome is a concept we introduce here to embody the compendium of circulating particles of the brain for their function and disease pathogenesis. Finally, for the purpose of inclusion of all extracellular particles, we have used the term EVPs as defined by the International Society of Extracellular Vesicles (ISEV).

Increased level of RAB39B leads to neuronal dysfunction and behavioural changes in mice

Duplications of the Xq28 region are a common cause of X-linked intellectual disability (XLID). The RAB39B gene locates in Xq28 and has been implicated in disease pathogenesis. However, whether increased dosage of RAB39B leads to cognitive impairment and synaptic dysfunction remains elusive. Herein, we overexpressed RAB39B in mouse brain by injecting AAVs into bilateral ventricles of neonatal animals. We found that at 2 months of age, neuronal overexpression of RAB39B impaired the recognition memory and the short-term working memory in mice and resulted in certain autism-like behaviours, including social novelty defect and repetitive grooming behaviour in female mice. Moreover, overexpression of RAB39B decreased dendritic arborization of primary neurons in vitro and reduced synaptic transmission in female mice. Neuronal overexpression of RAB39B also altered autophagy without affecting levels and PSD distribution of synaptic proteins. Our results demonstrate that overexpression of RAB39B compromises normal neuronal development, thereby resulting in dysfunctional synaptic transmission and certain intellectual disability and behavioural abnormalities in mice. These findings identify a molecular mechanism underlying XLID with increased copy numbers of Xq28 and provide potential strategies for disease intervention.

Astrocyte adaptation in Alzheimer's disease: a focus on astrocytic P2X7R

Astrocytes are key homeostatic and defensive cells of the central nervous system (CNS). They undertake numerous functions during development and in adulthood to support and protect the brain through finely regulated communication with other cellular elements of the nervous tissue. In Alzheimer's disease (AD), astrocytes undergo heterogeneous morphological, molecular and functional alterations represented by reactive remodelling, asthenia and loss of function. Reactive astrocytes closely associate with amyloid β (Aβ) plaques and neurofibrillary tangles in advanced AD. The specific contribution of astrocytes to AD could potentially evolve along the disease process and includes alterations in their signalling, interactions with pathological protein aggregates, metabolic and synaptic impairments. In this review, we focus on the purinergic receptor, P2X7R, and discuss the evidence that P2X7R activation contributes to altered astrocyte functions in AD. Expression of P2X7R is increased in AD brain relative to non-demented controls, and animal studies have shown that P2X7R antagonism improves cognitive and synaptic impairments in models of amyloidosis and tauopathy. While P2X7R activation can induce inflammatory signalling pathways, particularly in microglia, we focus here specifically on the contributions of astrocytic P2X7R to synaptic changes and protein aggregate clearance in AD, highlighting cell-specific roles of this purinoceptor activation that could be targeted to slow disease progression.

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 and Alzheimer's disease in the novel era of Precision Medicine: implications for disease progression, diagnosis and treatment

Extracellular vesicles (EVs), secreted membranous nano-sized particles, are critical intercellular messengers participating in nervous system homeostasis, while recent evidence implicates EVs in Alzheimer's disease (AD) pathogenesis. Specifically, small EVs have been shown to spread toxic proteins, induce neuronal loss, and contribute to neuroinflammation and AD progression. On the other hand, EVs can reduce amyloid-beta deposition and transfer neuroprotective substances between cells, mitigating disease mechanisms. In addition to their roles in AD pathogenesis, EVs also exhibit great potential for the diagnosis and treatment of other brain disorders, representing an advantageous tool for Precision Medicine. Herein, we summarize the contribution of small EVs to AD-related mechanisms and disease progression, as well as their potential as diagnostic and therapeutic agents for AD.

Interpretable deep learning translation of GWAS and multi-omics findings to identify pathobiology and drug repurposing in Alzheimer's disease

Translating human genetic findings (genome-wide association studies [GWAS]) to pathobiology and therapeutic discovery remains a major challenge for Alzheimer's disease (AD). We present a network topology-based deep learning framework to identify disease-associated genes (NETTAG). We leverage non-coding GWAS loci effects on quantitative trait loci, enhancers and CpG islands, promoter regions, open chromatin, and promoter flanking regions under the protein-protein interactome. Via NETTAG, we identified 156 AD-risk genes enriched in druggable targets. Combining network-based prediction and retrospective case-control observations with 10 million individuals, we identified that usage of four drugs (ibuprofen, gemfibrozil, cholecalciferol, and ceftriaxone) is associated with reduced likelihood of AD incidence. Gemfibrozil (an approved lipid regulator) is significantly associated with 43% reduced risk of AD compared with simvastatin using an active-comparator design (95% confidence interval 0.51-0.63, p < 0.0001). In summary, NETTAG offers a deep learning methodology that utilizes GWAS and multi-genomic findings to identify pathobiology and drug repurposing in AD.

P2X7 Receptor and Purinergic Signaling: Orchestrating Mitochondrial Dysfunction in Neurodegenerative Diseases

Mitochondrial dysfunction is one of the basic hallmarks of cellular pathology in neurodegenerative diseases. Since the metabolic activity of neurons is highly dependent on energy supply, nerve cells are especially vulnerable to impaired mitochondrial function. Besides providing oxidative phosphorylation, mitochondria are also involved in controlling levels of second messengers such as Ca2+ ions and reactive oxygen species (ROS). Interestingly, the critical role of mitochondria as producers of ROS is closely related to P2XR purinergic receptors, the activity of which is modulated by free radicals. Here, we review the relationships between the purinergic signaling system and affected mitochondrial function. Purinergic signaling regulates numerous vital biological processes in the CNS. The two main purines, ATP and adenosine, act as excitatory and inhibitory neurotransmitters, respectively. Current evidence suggests that purinergic signaling best explains how neuronal activity is related to neuronal electrical activity and energy homeostasis, especially in the development of Alzheimer's and Parkinson's diseases. In this review, we focus on the mechanisms underlying the involvement of the P2RX7 purinoreceptor in triggering mitochondrial dysfunction during the development of neurodegenerative disorders. We also summarize various avenues by which the purine signaling pathway may trigger metabolic dysfunction contributing to neuronal death and the inflammatory activation of glial cells. Finally, we discuss the potential role of the purinergic system in the search for new therapeutic approaches to treat neurodegenerative diseases.

Exosomal and vesicle-free tau seeds-propagation and convergence in endolysosomal permeabilization

In Alzheimer's disease (AD), β-amyloid peptides aggregate to form amyloid plaques, and the microtubule-associated protein tau forms neurofibrillary tangles. However, severity and duration of AD correlate with the stereotypical emergence of tau tangles throughout the brain, suggestive of a gradual region-to-region spreading of pathological tau. The current notion in the field is that misfolded tau seeds propagate transsynaptically and corrupt the proper folding of soluble tau in recipient neurons. This is supported by accumulating evidence showing that in AD, functional connectivity and not proximity predicts the spreading of tau pathology. Tau seeds can be found in two flavors, vesicle-free, that is, naked as in oligomers and fibrils, or encapsulated by membranes of secreted vesicles known as exosomes. Both types of seeds have been shown to propagate between interconnected neurons. Here, we describe potential ways of how their propagation can be controlled in several subcellular compartments by manipulating mechanisms affecting production, neuron-to-neuron transmission, internalization, endosomal escape, and autophagy. We emphasize that although vesicle-free tau seeds and exosomes differ, they share the ability to trigger endolysosomal permeabilization. Such a mechanistic convergence in endolysosomal permeabilization presents itself as a unique opportunity to target both types of tau seeding. We discuss the cellular response to endolysosomal damage that might be key to control permeabilization, and the significant overlap in the seeding mechanism of proteopathic agents other than tau, which suggests that targeting the endolysosomal pathway could pave the way toward developing broad-spectrum treatments for neurodegenerative diseases.

Cathepsin L-containing exosomes from α-synuclein-activated microglia induce neurotoxicity through the P2X7 receptor

Uncontrolled microglial activation is pivotal to the pathogenesis of Parkinson's disease (PD), which can secrete Cathepsin L (CTSL) to affect the survival of neurons in the PD patients; however, the precise mechanism has yet to be determined. We demonstrated for the first time that CTSL was mostly released by exosomes derived from α-Syn-activated microglia, resulting in neuronal damage and death. The elevation of CTSL activity was blocked by GW4869, suggesting a critical role for exosomes in mediating CTSL release. Furthermore, the P2X7R/PI3K/AKT signalling pathway was identified as the underlying molecular mechanism since specific antagonists of this signalling pathway, P2X7R knockdown and exosome release inhibitors significantly reduced the injury to cultured mouse cortical neurons. Our study suggests that increased extracellular release of CTSL from α-Syn-activated microglia through exosomes amplifies and aggravates of the neurotoxic effect of microglia, implying that CTSL may be involved in a fresh mechanism of PD pathogenesis, and serve as a potential biomarker and a target for PD drug development.

Spatial decrease of synaptic density in amnestic mild cognitive impairment follows the tau build-up pattern

Next to amyloid and tau, synaptic loss is a key pathological hallmark in Alzheimer's disease, closely related to cognitive dysfunction and neurodegeneration. Tau is thought to cause synaptic loss, but this has not been experimentally verified in vivo. In a 2-year follow-up study, dual tracer PET-MR was performed in 12 amnestic MCI patients using ¹⁸F-MK-6240 for tau and ¹¹C-UCB-J for SV2A as a proxy for synaptic density. Tau already accumulated in the neocortex at baseline with progression in Braak V/VI at follow-up. While synaptic loss was limited to limbic regions at baseline, it followed the specific tau pattern to stage IV/V regions two years later, indicating that tau spread might drive synaptic vulnerability. Moreover, synaptic density changes correlated to changes in cognitive function. This study shows for the first time in vivo that synaptic loss regionally follows tau accumulation after two years, providing a disease-modifying window of opportunity for (combined) tau-targeting therapies.

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.

Pathogenesis, therapeutic strategies and biomarker development based on "omics" analysis related to microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease and the most common cause of dementia. Among various pathophysiological aspects, microglia are considered to play important roles in the pathogenesis of AD. Genome wide association studies (GWAS) showed that the majority of AD risk genes are highly or exclusively expressed in microglia, underscoring the critical roles of microglia in AD pathogenesis. Recently, omics technologies have greatly advanced our knowledge of microglia biology in AD. Omics approaches, including genomics, epigenomics, transcriptomics, proteomics, and metabolomics/lipidomics, present remarkable opportunities to delineate the underlying mechanisms, discover novel diagnostic biomarkers, monitor disease progression, and shape therapeutic strategies for diseases. In this review, we summarized research based on microglial "omics" analysis in AD, especially the recent research advances in the identification of AD-associated microglial subsets. This review reinforces the important role of microglia in AD and advances our understanding of the mechanism of microglia in AD pathogenesis. Moreover, we proposed the value of microglia-based omics in the development of therapeutic strategies and biomarkers for AD.

Trem2 deletion enhances tau dispersion and pathology through microglia exosomes

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder that manifests sequential Aβ and tau brain pathology with age-dependent onset. Variants in the microglial immune receptor TREM2 are associated with enhanced risk of onset in sporadic Alzheimer's disease (AD). While recent studies suggest TREM2 dysfunction can aggravate tau pathology, mechanisms underlying TREM2-dependent modulation of tau pathology remains elusive.

METHODS

Here, we characterized differences in progressive tau spreading from the medial entorhinal cortex (MEC) to the hippocampus in wildtype (WT) and Trem2 knockout (KO) mice by injection of AAV-P301L tau into the MEC, and correlated changes in hippocampal tau histopathology with spatial and fear memory. We also compared effects of intraneuronal dispersion between cultured microglia and neurons using a microfluidic dispersion assay, analyzed differences in microglial tau trafficking following uptake, and quantified exosomal tau secretion and pathogenicity from purified WT and Trem2 KO exosomes.

RESULTS

Trem2 deletion in mice (Trem2 KO) can enhance tau spreading from the medial entorhinal cortex (MEC) to the hippocampus, which coincides with impaired synaptic function and memory behavior. Trem2 deletion in microglia enhances intraneuronal dispersion of tau in vitro between neuronal layers cultured in a microfluidic chamber, and the presence of exosome inhibitors can significantly reduce tau in exosomes and extracellular media from tau-loaded microglia. Although microglial Trem2 deletion has no effect on tau uptake, Trem2 deletion enhances distribution to endosomal and cellular pre-exosomal compartments following internalization. Trem2 deletion has little effect on exosome size, however, proteomic analysis indicates that Trem2 deletion can modulate changes in the microglial proteomic landscape with tau and LPS/ATP treatment conditions associated with exosome induction. Furthermore, exosomes from Trem2 KO microglia show elevated tau levels, and feature enhanced tau-seeding capacity in a tau FRET reporter line compared to exosomes from WT microglia.

CONCLUSION

Together, our results reveal a role for Trem2 in suppressing exosomal tau pathogenicity, and demonstrates that Trem2 deletion can enhance tau trafficking, distribution and seeding through microglial exosomes.

LRP1 is a neuronal receptor for α-synuclein uptake and spread

BACKGROUND

The aggregation and spread of α-synuclein (α-Syn) protein and related neuronal toxicity are the key pathological features of Parkinson's disease (PD) and Lewy body dementia (LBD). Studies have shown that pathological species of α-Syn and tau can spread in a prion-like manner between neurons, although these two proteins have distinct pathological roles and contribute to different neurodegenerative diseases. It is reported that the low-density lipoprotein receptor-related protein 1 (LRP1) regulates the spread of tau proteins; however, the molecular regulatory mechanisms of α-Syn uptake and spread, and whether it is also regulated by LRP1, remain poorly understood.

METHODS

We established LRP1 knockout (LRP1-KO) human induced pluripotent stem cells (iPSCs) isogenic lines using a CRISPR/Cas9 strategy and generated iPSC-derived neurons (iPSNs) to test the role of LRP1 in α-Syn uptake. We treated the iPSNs with fluorescently labeled α-Syn protein and measured the internalization of α-Syn using flow cytometry. Three forms of α-Syn species were tested: monomers, oligomers, and pre-formed fibrils (PFFs). To examine whether the lysine residues of α-Syn are involved in LRP1-mediated uptake, we capped the amines of lysines on α-Syn with sulfo-NHS acetate and then measured the internalization. We also tested whether the N-terminus of α-Syn is critical for LRP1-mediated internalization. Lastly, we investigated the role of Lrp1 in regulating α-Syn spread with a neuronal Lrp1 conditional knockout (Lrp1-nKO) mouse model. We generated adeno-associated viruses (AAVs) that allowed for distinguishing the α-Syn expression versus spread and injected them into the hippocampus of six-month-old Lrp1-nKO mice and the littermate wild type (WT) controls. The spread of α-Syn was evaluated three months after the injection.

RESULTS

We found that the uptake of both monomeric and oligomeric α-Syn was significantly reduced in iPSNs with LRP1-KO compared with the WT controls. The uptake of α-Syn PFFs was also inhibited in LRP1-KO iPSNs, albeit to a much lesser extent compared to α-Syn monomers and oligomers. The blocking of lysine residues on α-Syn effectively decreased the uptake of α-Syn in iPSNs and the N-terminus of α-Syn was critical for LRP1-mediated α-Syn uptake. Finally, in the Lrp1-nKO mice, the spread of α-Syn was significantly reduced compared with the WT littermates.

CONCLUSIONS

We identified LRP1 as a key regulator of α-Syn neuronal uptake, as well as an important mediator of α-Syn spread in the brain. This study provides new knowledge on the physiological and pathological role of LRP1 in α-Syn trafficking and pathology, offering insight for the treatment of synucleinopathies.

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.

Interplay between purinergic signalling and extracellular vesicles in health and disease

Purinergic signalling is a receptor-mediated process characterized by the binding of extracellular nucleotides and nucleosides to purinergic receptors, which results in the activation intracellular signalling pathways, and, ultimately, leads to changes in cell physiology. Purinergic signalling has been related to the regulation of important physiological processes (e.g., renal electrolyte reabsorption; platelet aggregation; immune response). In addition, it has been associated with pathophysiological situations such as cancer and inflammation. Extracellular vesicles (EVs) are nanoparticles released by all cells of the organism, which play a key role in cell-cell communication. In this regard, EVs can mediate effects on target cells located at distant locations. Within their cargo, EVs contain molecules with the potential to affect purinergic signalling at the target cells and tissues. Here, we review the studies addressing the regulation of purinergic signalling by EVs based on the cell type or tissue where the regulation takes place. In this regard, EVs are found to play a major role in modulating the extracellular ATP levels and, specially, adenosine. This has a clear impact on, for instance, the inflammatory and immune response against cancer cells. Furthermore, we discuss the data available on the regulation of EV secretion and its cargo by purinergic signalling. Here, a major role of the purinergic receptor P2X7 and again, an impact on processes such as inflammation, immune response and cancer pathogenesis has been established. Finally, we highlight uninvestigated aspects of these two regulatory networks and address their potential as therapeutic targets.

Functional genome-wide short hairpin RNA library screening identifies key molecules for extracellular vesicle secretion from microglia

Activated microglia release extracellular vesicles (EVs) as modulators of brain homeostasis and innate immunity. However, the molecules critical for regulating EV production from microglia are poorly understood. Here we establish a murine microglial cell model to monitor EV secretion by measuring the fluorescence signal of tdTomato, which is linked to tetraspanin CD63. Stimulation of tdTomato⁺ cells with ATP induces rapid secretion of EVs and a reduction in cellular tdTomato intensity, reflecting EV secretion. We generate a GFP⁺ tdTomato⁺ cell library expressing TurboGFP and barcoded short hairpin RNAs for genome-wide screening using next-generation sequencing. We identify Mcfd2, Sepp1, and Sdc1 as critical regulators of ATP-induced EV secretion from murine microglia. Small interfering RNA (siRNA-based) silencing of each of these genes suppresses lipopolysaccharide- and ATP-induced inflammasome activation, as determined by interleukin-1β release from primary cultured murine microglia. These molecules are critical for microglial EV secretion and are potential therapeutic targets for neuroinflammatory disorders.

Ruan et al. report genome-wide shRNA library screening on a tdTomato-CD63⁺ microglia cell model to identify factors implicated in the process of extracellular vesicle (EV) release. The molecules Sepp1, Mcfd2, and Sdc1 are critical for ATP-induced secretion of EV and EV-associated interleukin-1β from murine microglia.

Small but Mighty-Exosomes, Novel Intercellular Messengers in Neurodegeneration

Simple Summary

Exosomes are biological nanoparticles recently recognized as intercellular messengers. They contain a cargo of lipids, proteins, and RNA. They can transfer their content to not only cells in the vicinity but also to cells at a distance. This unique ability empowers them to modulate the physiology of recipient cells. In brain, exosomes play a role in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease and amyotrophic lateral sclerosis.

Abstract

Exosomes of endosomal origin are one class of extracellular vesicles that are important in intercellular communication. Exosomes are released by all cells in our body and their cargo consisting of lipids, proteins and nucleic acids has a footprint reflective of their parental origin. The exosomal cargo has the power to modulate the physiology of recipient cells in the vicinity of the releasing cells or cells at a distance. Harnessing the potential of exosomes relies upon the purity of exosome preparation. Hence, many methods for isolation have been developed and we provide a succinct summary of several methods. In spite of the seclusion imposed by the blood–brain barrier, cells in the CNS are not immune from exosomal intrusive influences. Both neurons and glia release exosomes, often in an activity-dependent manner. A brief description of exosomes released by different cells in the brain and their role in maintaining CNS homeostasis is provided. The hallmark of several neurodegenerative diseases is the accumulation of protein aggregates. Recent studies implicate exosomes’ intercellular communicator role in the spread of misfolded proteins aiding the propagation of pathology. In this review, we discuss the potential contributions made by exosomes in progression of Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Understanding contributions made by exosomes in pathogenesis of neurodegeneration opens the field for employing exosomes as therapeutic agents for drug delivery to brain since exosomes do cross the blood–brain barrier.