Increased Release of Apolipoprotein E in Extracellular Vesicles Following Amyloid-β Protofibril Exposure of Neuroglial Co-Cultures

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.

The enhancer RNA, AANCR, regulates APOE expression in astrocytes and microglia

Enhancers, critical regulatory elements within the human genome, are often transcribed into enhancer RNAs. The dysregulation of enhancers leads to diseases collectively termed enhanceropathies. While it is known that enhancers play a role in diseases by regulating gene expression, the specific mechanisms by which individual enhancers cause diseases are not well understood. Studies of individual enhancers are needed to fill this gap. This study delves into the role of APOE-activating noncoding RNA, AANCR, in the central nervous system, elucidating its function as a genetic modifier in Alzheimer's Disease. We employed RNA interference, RNaseH-mediated degradation, and single-molecule RNA fluorescence in situ hybridization to demonstrate that mere transcription of AANCR is insufficient; rather, its transcripts are crucial for promoting APOE expression. Our findings revealed that AANCR is induced by ATM-mediated ERK phosphorylation and subsequent AP-1 transcription factor activation. Once activated, AANCR enhances APOE expression, which in turn imparts an inflammatory phenotype to astrocytes. These findings demonstrate that AANCR is a key enhancer RNA in some cell types within the nervous system, pivotal for regulating APOE expression and influencing inflammatory responses, underscoring its potential as a therapeutic target in neurodegenerative diseases.

Proteomic Profile of Circulating Extracellular Vesicles in the Brain after Δ9-Tetrahydrocannabinol Inhalation

Given the increasing use of cannabis in the US, there is an urgent need to better understand the drug's effects on central signaling mechanisms. Extracellular vesicles (EVs) have been identified as intercellular signaling mediators that contain a variety of cargo, including proteins. Here, we examined whether the main psychoactive component in cannabis, Δ9-tetrahydrocannabinol (THC), alters EV protein signaling dynamics in the brain. We first conducted in vitro studies, which found that THC activates signaling in choroid plexus epithelial cells, resulting in transcriptional upregulation of the cannabinoid 1 receptor and immediate early gene c-fos, in addition to the release of EVs containing RNA cargo. Next, male and female rats were examined for the effects of either acute or chronic exposure to aerosolized ('vaped') THC on circulating brain EVs. Cerebrospinal fluid was extracted from the brain, and EVs were isolated and processed with label-free quantitative proteomic analyses via high-resolution tandem mass spectrometry. Interestingly, circulating EV-localized proteins were differentially expressed based on acute or chronic THC exposure in a sex-specific manner. Taken together, these findings reveal that THC acts in the brain to modulate circulating EV signaling, thereby providing a novel understanding of how exogenous factors can regulate intercellular communication in the brain.

Amyloid-β deposits in human astrocytes contain truncated and highly resistant proteoforms

Alzheimer's disease (AD) is a neurodegenerative disorder that develops over decades. Glial cells, including astrocytes are tightly connected to the AD pathogenesis, but their impact on disease progression is still unclear. Our previous data show that astrocytes take up large amounts of aggregated amyloid-beta (Aβ) but are unable to successfully degrade the material, which is instead stored intracellularly. The aim of the present study was to analyze the astrocytic Aβ deposits composition in detail in order to understand their role in AD propagation. For this purpose, human induced pluripotent cell (hiPSC)-derived astrocytes were exposed to sonicated Aβ42 fibrils and magnetic beads. Live cell imaging and immunocytochemistry confirmed that the ingested Aβ aggregates and beads were transported to the same lysosomal compartments in the perinuclear region, which allowed us to successfully isolate the Aβ deposits from the astrocytes. Using a battery of experimental techniques, including mass spectrometry, western blot, ELISA and electron microscopy we demonstrate that human astrocytes truncate and pack the Aβ aggregates in a way that makes them highly resistant. Moreover, the astrocytes release specifically truncated forms of Aβ via different routes and thereby expose neighboring cells to pathogenic proteins. Taken together, our study establishes a role for astrocytes in mediating Aβ pathology, which could be of relevance for identifying novel treatment targets for AD.

Emergence of Extracellular Vesicles as "Liquid Biopsy" for Neurological Disorders: Boom or Bust

Extracellular vesicles (EVs) have emerged as an attractive liquid biopsy approach in the diagnosis and prognosis of multiple diseases and disorders. The feasibility of enriching specific subpopulations of EVs from biofluids based on their unique surface markers has opened novel opportunities to gain molecular insight from various tissues and organs, including the brain. Over the past decade, EVs in bodily fluids have been extensively studied for biomarkers associated with various neurological disorders, such as Alzheimer's disease, Parkinson's disease, schizophrenia, bipolar disorder, major depressive disorders, substance use disorders, human immunodeficiency virus-associated neurocognitive disorder, and cancer/treatment-induced neurodegeneration. These studies have focused on the isolation and cargo characterization of either total EVs or brain cells, such as neuron-, astrocyte-, microglia-, oligodendrocyte-, pericyte-, and endothelial-derived EVs from biofluids to achieve early diagnosis and molecular characterization and to predict the treatment and intervention outcomes. The findings of these studies have demonstrated that EVs could serve as a repetitive and less invasive source of valuable molecular information for these neurological disorders, supplementing existing costly neuroimaging techniques and relatively invasive measures, like lumbar puncture. However, the initial excitement surrounding blood-based biomarkers for brain-related diseases has been tempered by challenges, such as lack of central nervous system specificity in EV markers, lengthy protocols, and the absence of standardized procedures for biological sample collection, EV isolation, and characterization. Nevertheless, with rapid advancements in the EV field, supported by improved isolation methods and sensitive assays for cargo characterization, brain cell-derived EVs continue to offer unparallel opportunities with significant translational implications for various neurological disorders. SIGNIFICANCE STATEMENT: Extracellular vesicles present a less invasive liquid biopsy approach in the diagnosis and prognosis of various neurological disorders. Characterizing these vesicles in biofluids holds the potential to yield valuable molecular information, thereby significantly impacting the development of novel biomarkers for various neurological disorders. This paper has reviewed the methodology employed to isolate extracellular vesicles derived from various brain cells in biofluids, their utility in enhancing the molecular understanding of neurodegeneration, and the potential challenges in this research field.

Extracellular Vesicles in the Central Nervous System: A Novel Mechanism of Neuronal Cell Communication

Cell-to-cell communication is essential for the appropriate development and maintenance of homeostatic conditions in the central nervous system. Extracellular vesicles have recently come to the forefront of neuroscience as novel vehicles for the transfer of complex signals between neuronal cells. Extracellular vesicles are membrane-bound carriers packed with proteins, metabolites, and nucleic acids (including DNA, mRNA, and microRNAs) that contain the elements present in the cell they originate from. Since their discovery, extracellular vesicles have been studied extensively and have opened up new understanding of cell-cell communication; they may cross the blood-brain barrier in a bidirectional way from the bloodstream to the brain parenchyma and vice versa, and play a key role in brain-periphery communication in physiology as well as pathology. Neurons and glial cells in the central nervous system release extracellular vesicles to the interstitial fluid of the brain and spinal cord parenchyma. Extracellular vesicles contain proteins, nucleic acids, lipids, carbohydrates, and primary and secondary metabolites. that can be taken up by and modulate the behaviour of neighbouring recipient cells. The functions of extracellular vesicles have been extensively studied in the context of neurodegenerative diseases. The purpose of this review is to analyse the role extracellular vesicles extracellular vesicles in central nervous system cell communication, with particular emphasis on the contribution of extracellular vesicles from different central nervous system cell types in maintaining or altering central nervous system homeostasis.

Extracellular Vesicle and Lipoprotein Interactions

Extracellular vesicles and lipoproteins are lipid-based biological nanoparticles that play important roles in (patho)physiology. Recent evidence suggests that extracellular vesicles and lipoproteins can interact to form functional complexes. Such complexes have been observed in biofluids from healthy human donors and in various in vitro disease models such as breast cancer and hepatitis C infection. Lipoprotein components can also form part of the biomolecular corona that surrounds extracellular vesicles and contributes to biological identity. Potential mechanisms and the functional relevance of extracellular vesicle-lipoprotein complexes remain poorly understood. This Review addresses the current knowledge of the extracellular vesicle-lipoprotein interface while drawing on pre-existing knowledge of liposome interactions with biological nanoparticles. There is an urgent need for further research on the lipoprotein-extracellular vesicle interface, which could return important mechanistic, therapeutic, and diagnostic findings.

Emerging Role of Astrocyte-Derived Extracellular Vesicles as Active Participants in CNS Neuroimmune Responses

Astrocyte-derived extracellular vesicles (ADEVs) have garnered attention as a fundamental mechanism of intercellular communication in health and disease. In the context of neurological diseases, for which prodromal diagnosis would be advantageous, ADEVs are also being explored for their potential utility as biomarkers. In this review, we provide the current state of data supporting our understanding on the manifold roles of ADEVs in several common neurological disorders. We also discuss these findings from a unique emerging perspective that ADEVs represent a means by which the central nervous system may broadcast influence over other systems in the body to affect neuroinflammatory processes, with both dual potential to either propagate illness or restore health and homeostasis.

Recommendations for reproducibility of cerebrospinal fluid extracellular vesicle studies

Cerebrospinal fluid (CSF) is a clear, transparent fluid derived from blood plasma that protects the brain and spinal cord against mechanical shock, provides buoyancy, clears metabolic waste and transports extracellular components to remote sites in the brain. Given its contact with the brain and the spinal cord, CSF is the most informative biofluid for studies of the central nervous system (CNS). In addition to other components, CSF contains extracellular vesicles (EVs) that carry bioactive cargoes (e.g., lipids, nucleic acids, proteins), and that can have biological functions within and beyond the CNS. Thus, CSF EVs likely serve as both mediators of and contributors to communication in the CNS. Accordingly, their potential as biomarkers for CNS diseases has stimulated much excitement for and attention to CSF EV research. However, studies on CSF EVs present unique challenges relative to EV studies in other biofluids, including the invasive nature of CSF collection, limited CSF volumes and the low numbers of EVs in CSF as compared to plasma. Here, the objectives of the International Society for Extracellular Vesicles CSF Task Force are to promote the reproducibility of CSF EV studies by providing current reporting and best practices, and recommendations and reporting guidelines, for CSF EV studies. To accomplish this, we created and distributed a world-wide survey to ISEV members to assess methods considered 'best practices' for CSF EVs, then performed a detailed literature review for CSF EV publications that was used to curate methods and resources. Based on responses to the survey and curated information from publications, the CSF Task Force herein provides recommendations and reporting guidelines to promote the reproducibility of CSF EV studies in seven domains: (i) CSF Collection, Processing, and Storage; (ii) CSF EV Separation/Concentration; (iii) CSF EV Size and Number Measurements; (iv) CSF EV Protein Studies; (v) CSF EV RNA Studies; (vi) CSF EV Omics Studies and (vii) CSF EV Functional Studies.

Context-specific regulation of extracellular vesicle biogenesis and cargo selection

To coordinate, adapt and respond to biological signals, cells convey specific messages to other cells. An important aspect of cell-cell communication involves secretion of molecules into the extracellular space. How these molecules are selected for secretion has been a fundamental question in the membrane trafficking field for decades. Recently, extracellular vesicles (EVs) have been recognized as key players in intercellular communication, carrying not only membrane proteins and lipids but also RNAs, cytosolic proteins and other signalling molecules to recipient cells. To communicate the right message, it is essential to sort cargoes into EVs in a regulated and context-specific manner. In recent years, a wealth of lipidomic, proteomic and RNA sequencing studies have revealed that EV cargo composition differs depending upon the donor cell type, metabolic cues and disease states. Analyses of distinct cargo 'fingerprints' have uncovered mechanistic linkages between the activation of specific molecular pathways and cargo sorting. In addition, cell biology studies are beginning to reveal novel biogenesis mechanisms regulated by cellular context. Here, we review context-specific mechanisms of EV biogenesis and cargo sorting, focusing on how cell signalling and cell state influence which cellular components are ultimately targeted to EVs.

Altered Distribution of SNARE Proteins in Primary Neurons Exposed to Different Alpha-Synuclein Proteoforms

Growing evidence indicates that the pathological alpha-synuclein (α-syn) aggregation in Parkinson's disease (PD) and dementia with Lewy bodies (DLB) starts at the synapses. Physiologic α-syn is involved in regulating neurotransmitter release by binding to the SNARE complex protein VAMP-2 on synaptic vesicles. However, in which way the SNARE complex formation is affected by α-syn pathology remains unclear. In this study, primary cortical neurons were exposed to either α-syn monomers or preformed fibrils (PFFs) for different time points and the effect on SNARE protein distribution was analyzed with a novel proximity ligation assay (PLA). Short-term exposure to monomers or PFFs for 24 h increased the co-localization of VAMP-2 and syntaxin-1, but reduced the co-localization of SNAP-25 and syntaxin-1, indicating a direct effect of the added α-syn on SNARE protein distribution. Long-term exposure to α-syn PFFs for 7 d reduced VAMP-2 and SNAP-25 co-localization, although there was only a modest induction of ser129 phosphorylated (pS129) α-syn. Similarly, exposure to extracellular vesicles collected from astrocytes treated with α-syn PFFs for 7 d influenced VAMP-2 and SNAP-25 co-localization despite only low levels of pS129 α-syn being formed. Taken together, our results demonstrate that different α-syn proteoforms have the potential to alter the distribution of SNARE proteins at the synapse.

A novel regulator in Alzheimer's disease progression: The astrocyte-derived extracellular vesicles

Alzheimer's disease (AD) is known as an age-related irreversible neurodegenerative disease. AD seriously endangers the health of the elderly, but there is still no effective treatment. In the past several decades, the significant role of astrocytes in the process of AD has been universally acknowledged. In addition, extracellular vesicles (EVs) have been recognized as an essential mediator in intercellular communication and participate in various pathophysiological processes by carrying and transporting diverse cargoes. Moreover, specific conditions and stimuli can modulate the amount and properties of astrocyte-derived EVs (ADEVs) to affect AD progression. Thus, recent studies focused on the involvement of ADEVs in the pathogenesis of AD and the potential application of ADEVs in the diagnosis and treatment of AD, which provides a new direction and possibility for revealing the mystery of AD. Interestingly, it can be concluded that ADEVs have both pathogenic and protective effects in the process of AD through a comprehensive generalization. In this review, we aim to summarize the multi-faces of ADEVs effects on AD development, which can provide a novel strategy to investigate the underlying mechanism in AD. We also summarize the current ADEVs clinically relevant studies to raise the potential use of ADEVs in the discovery of novel biomarkers for diagnosis and therapeutic targets for AD.

Amyloid-β accumulation in human astrocytes induces mitochondrial disruption and changed energy metabolism

BACKGROUND

Astrocytes play a central role in maintaining brain energy metabolism, but are also tightly connected to the pathogenesis of Alzheimer's disease (AD). Our previous studies demonstrate that inflammatory astrocytes accumulate large amounts of aggregated amyloid-beta (Aβ). However, in which way these Aβ deposits influence their energy production remain unclear.

METHODS

The aim of the present study was to investigate how Aβ pathology in astrocytes affects their mitochondria functionality and overall energy metabolism. For this purpose, human induced pluripotent cell (hiPSC)-derived astrocytes were exposed to sonicated Aβ₄₂ fibrils for 7 days and analyzed over time using different experimental approaches.

RESULTS

Our results show that to maintain stable energy production, the astrocytes initially increased their mitochondrial fusion, but eventually the Aβ-mediated stress led to abnormal mitochondrial swelling and excessive fission. Moreover, we detected increased levels of phosphorylated DRP-1 in the Aβ-exposed astrocytes, which co-localized with lipid droplets. Analysis of ATP levels, when blocking certain stages of the energy pathways, indicated a metabolic shift to peroxisomal-based fatty acid β-oxidation and glycolysis.

CONCLUSIONS

Taken together, our data conclude that Aβ pathology profoundly affects human astrocytes and changes their entire energy metabolism, which could result in disturbed brain homeostasis and aggravated disease progression.

Intracellular deposits of amyloid-beta influence the ability of human iPSC-derived astrocytes to support neuronal function

BACKGROUND

Astrocytes are crucial for maintaining brain homeostasis and synaptic function, but are also tightly connected to the pathogenesis of Alzheimer's disease (AD). Our previous data demonstrate that astrocytes ingest large amounts of aggregated amyloid-beta (Aβ), but then store, rather than degrade the ingested material, which leads to severe cellular stress. However, the involvement of pathological astrocytes in AD-related synaptic dysfunction remains to be elucidated.

METHODS

In this study, we aimed to investigate how intracellular deposits of Aβ in astrocytes affect their interplay with neurons, focusing on neuronal function and viability. For this purpose, human induced pluripotent stem cell (hiPSC)-derived astrocytes were exposed to sonicated Αβ₄₂ fibrils. The direct and indirect effects of the Αβ-exposed astrocytes on hiPSC-derived neurons were analyzed by performing astrocyte-neuron co-cultures as well as additions of conditioned media or extracellular vesicles to pure neuronal cultures.

RESULTS

Electrophysiological recordings revealed significantly decreased frequency of excitatory post-synaptic currents in neurons co-cultured with Aβ-exposed astrocytes, while conditioned media from Aβ-exposed astrocytes had the opposite effect and resulted in hyperactivation of the synapses. Clearly, factors secreted from control, but not from Aβ-exposed astrocytes, benefited the wellbeing of neuronal cultures. Moreover, reactive astrocytes with Aβ deposits led to an elevated clearance of dead cells in the co-cultures.

CONCLUSIONS

Taken together, our results demonstrate that inclusions of aggregated Aβ affect the reactive state of the astrocytes, as well as their ability to support neuronal function.

MCP-1 levels in astrocyte-derived exosomes are changed in preclinical stage of Alzheimer's disease

Background

Alzheimer's disease (AD) is the most common form of dementia in older adults. There is accumulating evidence that inflammatory processes play a critical role in AD pathogenesis. In this study, we investigated whether inflammatory factors in plasma and astrocyte-derived exosomes (ADEs) from plasma are differentially expressed in the early stages of AD and their potential role in pathological processes in the AD continuum.

Method

We included 39 normal controls (NCs), 43 participants with subjective cognitive decline (SCD), and 43 participants with amnestic mild cognitive impairment (aMCI)/AD. IL-6, IL-8, and MCP-1 in plasma and ADEs from plasma were evaluated using a commercial multiplex Luminex-based kit.

Results

Pairwise comparisons between the groups showed no significant differences in plasma levels of IL-6, IL-8, or MCP-1. However, ADEs in the SCD group showed an increase in MCP-1 levels compared to the NC group. To differentiate the preclinical group, discriminant analysis was performed using sex, age, years of education, and genotype. This revealed a difference between the SCD and NC groups (area under the curve: 0.664). A Spearman correlation analysis of MCP-1 in plasma and ADEs showed no or weak correlation in the SCD (R = 0.150, p = 0.350) and aMCI/AD (R = 0.310, p = 0.041) groups, while a positive correlation in the NC group (R = 0.360, p = 0.026).

Conclusion

Plasma IL-6, IL-8, and MCP-1 levels were not significantly different. However, the concentration of MCP-1 in ADEs is slightly altered during the preclinical phase of AD, which could be a potential role of the central neuron system (CNS) immune response in the AD continuum.

Clinical trial registration

www.ClinicalTrials.gov, identifier: NCT03370744.

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.

Relationships of APOE Genotypes With Small RNA and Protein Cargo of Brain Tissue Extracellular Vesicles From Patients With Late-Stage AD

Background and Objectives

Variants of the apolipoprotein E (APOE) gene are the greatest known risk factors for sporadic Alzheimer disease (AD). Three major APOE isoform alleles, ε2, ε3, and ε4, encode and produce proteins that differ by only 1-2 amino acids but have different binding partner interactions. Whereas APOE ε2 is protective against AD relative to ε3, ε4 is associated with an increased risk for AD development. However, the role of APOE in gene regulation in AD pathogenesis has remained largely undetermined. Extracellular vesicles (EVs) are lipid bilayer-delimited particles released by cells to dispose of unwanted materials and mediate intercellular communication, and they are implicated in AD pathophysiology. Brain-derived EVs (bdEVs) could act locally in the tissue and reflect cellular changes. To reveal whether APOE genotype affects EV components in AD brains, bdEVs were separated from patients with AD with different APOE genotypes for parallel small RNA and protein profile.

Methods

bdEVs from late-stage AD brains (BRAAK stages 5-6) from patients with APOE genotypes ε2/3 (n = 5), ε3/3 (n = 5), ε3/4 (n = 6), and ε4/4 (n = 6) were separated using our published protocol into a 10,000g pelleted extracellular fraction (10K) and a further purified EV fraction. Counting, sizing, and multiomic characterization by small RNA sequencing and proteomic analysis were performed for 10K, EVs, and source tissue.

Results

Comparing APOE genotypes, no significant differences in bdEV total particle concentration or morphology were observed. Overall small RNA and protein profiles of 10K, EVs, and source tissue also did not differ substantially between different APOE genotypes. However, several differences in individual RNAs (including miRNAs and tRNAs) and proteins in 10K and EVs were observed when comparing the highest and lowest risk groups (ε4/4 and ε2/3). Bioinformatic analysis and previous publications indicate a potential regulatory role of these molecules in AD.

Discussion

For patients with late-stage AD in this study, only a few moderate differences were observed for small RNA and protein profiles between APOE genotypes. Among these, several newly identified 10K and EV-associated molecules may play roles in AD progression. Possibly, larger genotype-related differences exist and are more apparent in or before earlier disease stages.

Characterising extracellular vesicles from individual low volume cerebrospinal fluid samples, isolated by SmartSEC

Extracellular vesicles (EVs) are suggested to have a role in the progression of neurodegeneration, and are able to transmit pathological proteins from one cell to another. One of the biofluids from which EVs can be isolated is cerebrospinal fluid (CSF). However, so far, few studies have been performed on small volumes of CSF. Since pooling of patient samples possibly leads to the loss of essential individual patient information, and CSF samples are precious, it is important to have efficient techniques for the isolation of EVs from smaller volumes. In this study, the SmartSEC HT isolation kit from System Biosciences has been evaluated for this purpose. The SmartSEC HT isolation kit was used for isolation of EVs from 500 μL starting volumes of CSF, resulting in two possible EV fractions of 500 μL. Both fractions were characterised and compared to one another using a whole range of characterisation techniques. Results indicated the presence of EVs in both fractions, albeit fraction 1 showed more reproducible results over the different characterisation methods. For example, CMG (CellMask Green membrane stain) fluorescence nanotracking analysis (NTA), ExoView, and the particles/μg ratio demonstrated a clear difference between fraction 1 and 2, where fraction 1 came out as the one where most EVs were eluted with the least contamination. In the other methods, this difference was less noticeable. We successfully performed complementary characterisation tests using only 500 μL of CSF starting volume, and, conclude that fraction 1 consisted of sufficiently pure EVs for further biomarker studies. This means that future EV extractions may be based upon smaller CSF quantities, such as from individual patients. In that way, patient samples do not have to be pooled and individual patient information can be included in forthcoming studies, potentially linking EV content, size and distribution to individualised neurological diagnoses.

The envelope protein of Zika virus interacts with apolipoprotein E early in the infectious cycle and this interaction is conserved on the secreted viral particles

Background

Zika virus (ZIKV), a member of the Flaviviridae family, has caused massive outbreaks of infection in tropical areas over the last decade and has now begun spreading to temperate countries. Little is currently known about the specific host factors involved in the intracellular life cycle of ZIKV. Flaviviridae viruses interact closely with host-cell lipid metabolism and associated secretory pathways. Another Flaviviridae, hepatitis C virus, is highly dependent on apolipoprotein E (ApoE) for the completion of its infectious cycle. We therefore investigated whether ZIKV also interacted with this protein.

Methods

ZIKV infections were performed on both liver and microglia derived cell lines in order to proceed to colocalization analysis and immunoprecipitation assays of ApoE and Zika envelope glycoprotein (Zika E). Transmission electron microscopy combined to immunogold labeling was also performed on the infected cells and related supernatant to study the association of ApoE and Zika E protein in the virus-induced membrane rearrangements and secreted particles, respectively. Finally, the potential of neutralization of anti-ApoE antibodies on ZIKV particles was studied.

Result

We demonstrated an interaction between ApoE and the Zika E protein. This specific interaction was observed in virus-induced host-cell membrane rearrangements, but also on newly formed intracellular particles. The partial neutralizing effect of anti-ApoE antibody and the immunogold labeling of the two proteins on secreted virions indicates that this interaction is conserved during ZIKV intracellular trafficking and release.

Conclusions

These data suggest that another member of the Flaviviridae also interacts with ApoE, indicating that this could be a common mechanism for the viruses from this family.

Stem Cell-based Therapeutic and Diagnostic Approaches in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative impairment mainly recognized by memory loss and cognitive deficits. However, the current therapies against AD are mostly limited to palliative medications, prompting researchers to investigate more efficient therapeutic approaches for AD, such as stem cell therapy. Recent evidence has proposed that extensive neuronal and synaptic loss and altered adult neurogenesis, which is perceived pivotal in terms of plasticity and network maintenance, occurs early in the course of AD, which exacerbates neuronal vulnerability to AD. Thus, regeneration and replenishing the depleted neuronal networks by strengthening the endogenous repair mechanisms or exogenous stem cells and their cargoes is a rational therapeutic approach. Currently, several stem cell-based therapies as well as stem cell products like exosomes, have shown promising results in the early diagnosis of AD.

OBJECTIVE

This review begins with a comparison between AD and normal aging pathophysiology and a discussion on open questions in the field. Next, summarizing the current stem cell-based therapeutic and diagnostic approaches, we declare the advantages and disadvantages of each method. Also, we comprehensively evaluate the human clinical trials of stem cell therapies for AD.

METHODOLOGY

Peer-reviewed reports were extracted through Embase, PubMed, and Google Scholar until 2021.

RESULTS

With several ongoing clinical trials, stem cells and their derivatives (e.g., exosomes) are an emerging and encouraging field in diagnosing and treating neurodegenerative diseases. Although stem cell therapies have been successful in animal models, numerous clinical trials in AD patients have yielded unpromising results, which we will further discuss.

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.

Role of Extracellular Vesicles in Glia-Neuron Intercellular Communication

Cross talk between glia and neurons is crucial for a variety of biological functions, ranging from nervous system development, axonal conduction, synaptic transmission, neural circuit maturation, to homeostasis maintenance. Extracellular vesicles (EVs), which were initially described as cellular debris and were devoid of biological function, are now recognized as key components in cell-cell communication and play a critical role in glia-neuron communication. EVs transport the proteins, lipids, and nucleic acid cargo in intercellular communication, which alters target cells structurally and functionally. A better understanding of the roles of EVs in glia-neuron communication, both in physiological and pathological conditions, can aid in the discovery of novel therapeutic targets and the development of new biomarkers. This review aims to demonstrate that different types of glia and neuronal cells secrete various types of EVs, resulting in specific functions in intercellular communications.

Concordance of Alzheimer’s Disease Subtypes Produced from Different Representative Morphological Measures: A Comparative Study

Background: Gray matter (GM) density and cortical thickness (CT) obtained from structural magnetic resonance imaging are representative GM morphological measures that have been commonly used in Alzheimer’s disease (AD) subtype research. However, how the two measures affect the definition of AD subtypes remains unclear. Methods: A total of 180 AD patients from the ADNI database were used to identify AD subgroups. The subtypes were identified via a data-driven strategy based on the density features and CT features, respectively. Then, the similarity between the two features in AD subtype definition was analyzed. Results: Four distinct subtypes were discovered by both density and CT features: diffuse atrophy AD, minimal atrophy AD (MAD), left temporal dominant atrophy AD (LTAD), and occipital sparing AD. The matched subtypes exhibited relatively high similarity in atrophy patterns and neuropsychological and neuropathological characteristics. They differed only in MAD and LTAD regarding the carrying of apolipoprotein E ε2. Conclusions: The results verified that different representative morphological GM measurement methods could produce similar AD subtypes. Meanwhile, the influences of apolipoprotein E genotype, asymmetric disease progression, and their interactions should be considered and included in the AD subtype definition. This study provides a valuable reference for selecting features in future studies of AD subtypes.

In sickness and in health: The functional role of extracellular vesicles in physiology and pathology in vivo: Part II: Pathology: Part II: Pathology

It is clear from Part I of this series that extracellular vesicles (EVs) play a critical role in maintaining the homeostasis of most, if not all, normal physiological systems. However, the majority of our knowledge about EV signalling has come from studying them in disease. Indeed, EVs have consistently been associated with propagating disease pathophysiology. The analysis of EVs in biofluids, obtained in the clinic, has been an essential of the work to improve our understanding of their role in disease. However, to interfere with EV signalling for therapeutic gain, a more fundamental understanding of the mechanisms by which they contribute to pathogenic processes is required. Only by discovering how the EV populations in different biofluids change-size, number, and physicochemical composition-in clinical samples, may we then begin to unravel their functional roles in translational models in vitro and in vivo, which can then feedback to the clinic. In Part II of this review series, the functional role of EVs in pathology and disease will be discussed, with a focus on in vivo evidence and their potential to be used as both biomarkers and points of therapeutic intervention.

Traumatic brain injury in the presence of Aβ pathology affects neuronal survival, glial activation and autophagy

Traumatic brain injury (TBI) presents a widespread health problem in the elderly population. In addition to the acute injury, epidemiological studies have observed an increased probability and earlier onset of dementias in the elderly following TBI. However, the underlying mechanisms of the connection between TBI and Alzheimer's disease in the aged brain and potential exacerbating factors is still evolving. The aim of this study was to investigate cellular injury-induced processes in the presence of amyloid β (Aβ) pathology. For this purpose, a co-culture system of cortical stem-cell derived astrocytes, neurons and oligodendrocytes were exposed to Aβ₄₂ protofibrils prior to a mechanically induced scratch injury. Cellular responses, including neurodegeneration, glial activation and autophagy was assessed by immunoblotting, immunocytochemistry, ELISA and transmission electron microscopy. Our results demonstrate that the combined burden of Aβ exposure and experimental TBI causes a decline in the number of neurons, the differential expression of the key astrocytic markers glial fibrillary acidic protein and S100 calcium-binding protein beta, mitochondrial alterations and prevents the upregulation of autophagy. Our study provides valuable information about the impact of TBI sustained in the presence of Aβ deposits and helps to advance the understanding of geriatric TBI on the cellular level.

Role of Glia-Derived Extracellular Vesicles in Neurodegenerative Diseases

Extracellular vesicles (EVs), as nano-sized vesicles secreted by almost all cells, have been recognized as the essential transmitter for cell-to-cell communication and participating in multiple biological processes. Neurodegenerative diseases (ND), such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, share common mechanisms of the aggregation and propagation of distinct pathologic proteins among cells in the nervous systems and neuroinflammatory reactions mediated by glia during the pathogenic process. This feature indicates the vital role of crosstalk between neurons and glia in the pathogenesis of ND. In recent years, glia-derived EVs have been investigated as potential mediators of signals between neurons and glia, which provides a new direction and strategy for understanding ND. By a comprehensive summary, it can be concluded that glia-derived EVs have both a beneficial and/or a detrimental effect in the process of ND. Therefore, this review article conveys the role of glia-derived EVs in the pathogenesis of ND and raises current limitations of their potential application in the diagnosis and treatment of ND.

Extracellular Vesicle Proteomes Shed Light on the Evolutionary, Interactive, and Functional Divergence of Their Biogenesis Mechanisms

Extracellular vesicles (EVs) are membranous structures containing bioactive molecules, secreted by most cells into the extracellular environment. EVs are classified by their biogenesis mechanisms into two major subtypes: ectosomes (enriched in large EVs; lEVs), budding directly from the plasma membrane, which is common in both prokaryotes and eukaryotes, and exosomes (enriched in small EVs; sEVs) generated through the multivesicular bodies via the endomembrane system, which is unique to eukaryotes. Even though recent proteomic analyses have identified key proteins associated with EV subtypes, there has been no systematic analysis, thus far, to support the general validity and utility of current EV subtype separation methods, still largely dependent on physical properties, such as vesicular size and sedimentation. Here, we classified human EV proteomic datasets into two main categories based on distinct centrifugation protocols commonly used for isolating sEV or lEV fractions. We found characteristic, evolutionarily conserved profiles of sEV and lEV proteins linked to their respective biogenetic origins. This may suggest that the evolutionary trajectory of vesicular proteins may result in a membership bias toward specific EV subtypes. Protein-protein interaction (PPI) network analysis showed that vesicular proteins formed distinct clusters with proteins in the same EV fraction, providing evidence for the existence of EV subtype-specific protein recruiters. Moreover, we identified functional modules enriched in each fraction, including multivesicular body sorting for sEV, and mitochondria cellular respiration for lEV proteins. Our analysis successfully captured novel features of EVs embedded in heterogeneous proteomics studies and suggests specific protein markers and signatures to be used as quality controllers in the isolation procedure for subtype-enriched EV fractions.

Crosstalk between astrocytes and microglia results in increased degradation of α-synuclein and amyloid-β aggregates

Background

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are characterized by brain accumulation of aggregated amyloid-beta (Aβ) and alpha-synuclein (αSYN), respectively. In order to develop effective therapies, it is crucial to understand how the Aβ/αSYN aggregates can be cleared. Compelling data indicate that neuroinflammatory cells, including astrocytes and microglia, play a central role in the pathogenesis of AD and PD. However, how the interplay between the two cell types affects their clearing capacity and consequently the disease progression remains unclear.

Methods

The aim of the present study was to investigate in which way glial crosstalk influences αSYN and Aβ pathology, focusing on accumulation and degradation. For this purpose, human-induced pluripotent cell (hiPSC)-derived astrocytes and microglia were exposed to sonicated fibrils of αSYN or Aβ and analyzed over time. The capacity of the two cell types to clear extracellular and intracellular protein aggregates when either cultured separately or in co-culture was studied using immunocytochemistry and ELISA. Moreover, the capacity of cells to interact with and process protein aggregates was tracked using time-lapse microscopy and a customized “close-culture” chamber, in which the apical surfaces of astrocyte and microglia monocultures were separated by a <1 mm space.

Results

Our data show that intracellular deposits of αSYN and Aβ are significantly reduced in co-cultures of astrocytes and microglia, compared to monocultures of either cell type. Analysis of conditioned medium and imaging data from the “close-culture” chamber experiments indicate that astrocytes secrete a high proportion of their internalized protein aggregates, while microglia do not. Moreover, co-cultured astrocytes and microglia are in constant contact with each other via tunneling nanotubes and other membrane structures. Notably, our live cell imaging data demonstrate that microglia, when attached to the cell membrane of an astrocyte, can attract and clear intracellular protein deposits from the astrocyte.

Conclusions

Taken together, our data demonstrate the importance of astrocyte and microglia interactions in Aβ/αSYN clearance, highlighting the relevance of glial cellular crosstalk in the progression of AD- and PD-related brain pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02158-3.

CD5L as an Extracellular Vesicle-Derived Biomarker for Liquid Biopsy of Lung Cancer

Cancer screening and diagnosis can be achieved by analyzing specific molecules within serum-derived extracellular vesicles (EVs). This study sought to profile EV-derived proteins to identify potential lung cancer biomarkers. EVs were isolated from 80 serum samples from healthy individuals and cancer patients via polyethylene glycol (PEG)-based precipitation and immunoaffinity separation using antibodies against CD9, CD63, CD81, and EpCAM. Proteomic analysis was performed using 2-D gel electrophoresis and matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–TOF MS). The expression of proteins that were differentially upregulated in the EVs or tissue of lung cancer samples was validated by Western blotting. The area under the curve (AUC) was calculated to assess the predictability of each differentially expressed protein (DEP) for lung cancer. A total of 55 upregulated protein spots were selected, seven of which (CD5L, CLEC3B, ITIH4, SERFINF1, SAA4, SERFINC1, and C20ORF3) were found to be expressed at high levels in patient-derived EVs by Western blotting. Meanwhile, only the expression of EV CD5L correlated with that in cancer tissues. CD5L also demonstrated the highest AUC value (0.943) and was found to be the core regulator in a pathway related to cell dysfunction. Cumulatively, these results show that EV-derived CD5L may represent a potential biomarker—detected via a liquid biopsy—for the noninvasive diagnosis of lung cancer.

Glia-Derived Extracellular Vesicles: Role in Central Nervous System Communication in Health and Disease

Glial cells are crucial for the maintenance of correct neuronal functionality in a physiological state and intervene to restore the equilibrium when environmental or pathological conditions challenge central nervous system homeostasis. The communication between glial cells and neurons is essential and extracellular vesicles (EVs) take part in this function by transporting a plethora of molecules with the capacity to influence the function of the recipient cells. EVs, including exosomes and microvesicles, are a heterogeneous group of biogenetically distinct double membrane-enclosed vesicles. Once released from the cell, these two types of vesicles are difficult to discern, thus we will call them with the general term of EVs. This review is focused on the EVs secreted by astrocytes, oligodendrocytes and microglia, aiming to shed light on their influence on neurons and on the overall homeostasis of the central nervous system functions. We collect evidence on neuroprotective and homeostatic effects of glial EVs, including neuronal plasticity. On the other hand, current knowledge of the detrimental effects of the EVs in pathological conditions is addressed. Finally, we propose directions for future studies and we evaluate the potential of EVs as a therapeutic treatment for neurological 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.

Extracellular vesicles from amyloid-β exposed cell cultures induce severe dysfunction in cortical neurons

Alzheimer’s disease (AD) is characterized by a substantial loss of neurons and synapses throughout the brain. The exact mechanism behind the neurodegeneration is still unclear, but recent data suggests that spreading of amyloid-β (Aβ) pathology via extracellular vesicles (EVs) may contribute to disease progression. We have previously shown that an incomplete degradation of Aβ₄₂ protofibrils by astrocytes results in the release of EVs containing neurotoxic Aβ. Here, we describe the cellular mechanisms behind EV-associated neurotoxicity in detail. EVs were isolated from untreated and Aβ₄₂ protofibril exposed neuroglial co-cultures, consisting mainly of astrocytes. The EVs were added to cortical neurons for 2 or 4 days and the neurodegenerative processes were followed with immunocytochemistry, time-lapse imaging and transmission electron microscopy (TEM). Addition of EVs from Aβ₄₂ protofibril exposed co-cultures resulted in synaptic loss, severe mitochondrial impairment and apoptosis. TEM analysis demonstrated that the EVs induced axonal swelling and vacuolization of the neuronal cell bodies. Interestingly, EV exposed neurons also displayed pathological lamellar bodies of cholesterol deposits in lysosomal compartments. Taken together, our data show that the secretion of EVs from Aβ exposed cells induces neuronal dysfunction in several ways, indicating a central role for EVs in the progression of Aβ-induced pathology.

Long-Term Effects of Traumatic Brain Injury in a Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is the leading cause of dementia worldwide, affecting over 10% of the elderly population. Epidemiological evidence indicates that traumatic brain injury (TBI) is an important risk factor for developing AD later in life. However, which injury-induced processes that contribute to the disease onset remains unclear. The aim with the present study was to identify cellular processes that could link TBI to AD development, by investigating the chronic impact of two different injury models, controlled cortical impact (CCI) and midline fluid percussion injury (mFPI). The trauma was induced in 3-month-old tg-ArcSwe mice, carrying the Arctic mutation along with the Swedish mutation, and the influence of TBI on AD progression was analyzed at 12- and 24-weeks post-injury. The long-term effect of the TBI on memory deficiency, amyloid-β (Aβ) pathology, neurodegeneration and inflammation was investigated by Morris water maze, PET imaging, immunohistochemistry, and biochemical analyses. Morris water maze analysis demonstrated that mice subjected to CCI or mFPI performed significantly worse than uninjured tg-ArcSwe mice, especially at the later time point. Moreover, the injured mice showed a late upregulation of reactive gliosis, which concurred with a more pronounced Aβ pathology, compared to uninjured AD mice. Our results suggest that the delayed glial activation following TBI may be an important link between the two diseases. However, further studies in both experimental models and human TBI patients will be required to fully elucidate the reasons why TBI increases the risk of neurodegeneration.

Diagnostic and therapeutic potential of exosomes in Alzheimer's disease

Exosomes are small extracellular vesicles released by almost all cell types in physiological and pathological conditions. The exosomal potential to unravel disease mechanisms, or to be used as a source of biomarkers, is being explored, in particularly in the field of neurodegenerative diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the world and exosomes appear to have a relevant role in disease pathogenesis. This review summarizes the current knowledge on exosome contributions to AD as well as their use as disease biomarker resources or therapeutic targets. The most recent findings with respect to both protein and miRNA biomarker candidates for AD, herein described, highlight the state of the art in this field and encourage the use of exosomes derived from biofluids in clinical practice in the near future.

Astrocyte-derived extracellular vesicles: Neuroreparative properties and role in the pathogenesis of neurodegenerative disorders

Extracellular vesicles (EVs) released by neural cells play an essential role in brain homeostasis and the crosstalk between neural cells and the periphery. EVs are diverse, nano-sized vesicles, which transport proteins, nucleic acids, and lipids between cells over short and long expanses and hence are proficient for modulating the target cells. EVs released from neural cells are implicated in synaptic plasticity, neuron-glia interface, neuroprotection, neuroregeneration, and the dissemination of neuropathological molecules. This review confers the various properties of EVs secreted by astrocytes and their potential role in health and disease with a focus on evolving concepts. Naïve astrocytes shed EVs containing a host of neuroprotective compounds, which include fibroblast growth factor-2, vascular endothelial growth factor, and apolipoprotein-D. Stimulated astrocytes secrete EVs with neuroprotective molecules including heat shock proteins, synapsin 1, unique microRNAs, and glutamate transporters. Well-characterized astrocyte-derived EVs (ADEVs) generated in specific culture conditions and ADEVs that are engineered to carry the desired miRNAs or proteins are likely useful for treating brain injury and neurogenerative diseases. On the other hand, in conditions such as Alzheimer's disease (AD), stroke, Parkinson's disease, Amyotrophic lateral sclerosis (ALS), and other neuroinflammatory conditions, EVs released by activated astrocytes appear to mediate or exacerbate the pathological processes. The examples include ADEVs spreading the dysregulated complement system in AD, mediating motoneuron toxicity in ALS, and stimulating peripheral leukocyte migration into the brain in inflammatory conditions. Strategies restraining the release of EVs by activated astrocytes or modulating the composition of ADEVs are likely beneficial for treating neurodegenerative diseases. Also, periodic analyses of ADEVs in the blood is useful for detecting astrocyte-specific biomarkers in different neurological conditions and for monitoring disease progression and remission with distinct therapeutic approaches.

Glia-Derived Extracellular Vesicles: Role in Central Nervous System Communication in Health and Disease

Glial cells are crucial for the maintenance of correct neuronal functionality in a physiological state and intervene to restore the equilibrium when environmental or pathological conditions challenge central nervous system homeostasis. The communication between glial cells and neurons is essential and extracellular vesicles (EVs) take part in this function by transporting a plethora of molecules with the capacity to influence the function of the recipient cells. EVs, including exosomes and microvesicles, are a heterogeneous group of biogenetically distinct double membrane-enclosed vesicles. Once released from the cell, these two types of vesicles are difficult to discern, thus we will call them with the general term of EVs. This review is focused on the EVs secreted by astrocytes, oligodendrocytes and microglia, aiming to shed light on their influence on neurons and on the overall homeostasis of the central nervous system functions. We collect evidence on neuroprotective and homeostatic effects of glial EVs, including neuronal plasticity. On the other hand, current knowledge of the detrimental effects of the EVs in pathological conditions is addressed. Finally, we propose directions for future studies and we evaluate the potential of EVs as a therapeutic treatment for neurological disorders.

Glia-derived exosomes: Promising therapeutic targets

Glia is an important component of the nervous system that is involved in neurotransmitter uptake, signal transduction, myelin synthesis, neurodevelopment, and immune response. Exosomes are extracellular vesicles that are secreted from certain types of cells, and are known to mediate glia function. Glia-derived exosomes (GDEs) can transport proteins, nucleotides and cellular waste, and exert both protective and toxic effects on the nervous system. GDEs promote glia-neuron communication, anti-stress responses, anti-inflammation and neurite outgrowth, and may also be involved in neurological disease such as glioma, glioblastoma, Alzheimer's disease, Parkinson disease and neuronal HIV infections. This review summarizes the current research on GDEs and their functions, with emphasis on their therapeutic potential.

Subtypes Based on Six Apolipoproteins in Non-Demented Elderly Are Associated with Cognitive Decline and Subsequent Tau Accumulation in Cerebrospinal Fluid

Apolipoproteins (APOs) have been implicated in the pathogenesis of Alzheimer's disease (AD). In the present study, we aimed to investigate if patterns of cerebrospinal fluid (CSF) APOs (APOA-I, APOC-III, APOD, APOE, APOH, and APOJ) levels are associated with changes over time in cognition, memory performance, neuroimaging markers, and AD-related pathologies (CSF Aβ42, t-tau, and p-tau) in non-demented older adults. At baseline, a total of 241 non-demented older adults with CSF APOs data was included in the present analysis. Hierarchical agglomerative cluster analysis including the six CSF APOs was carried out. Among non-demented older adults, we identified two clusters. Compare with the first cluster, the second cluster had higher levels of APOs in CSF. Additionally, the second cluster showed a more benign disease course, including slower cognitive decline and slower p-tau accumulation in CSF. Our data highlight the importance of APOs in the pathogenesis of AD.

α-synuclein-lipoprotein interactions and elevated ApoE level in cerebrospinal fluid from Parkinson's disease patients

Two of the most important issues in Parkinson’s disease (PD) research are the identification of mechanisms underlying α-synuclein cell-to-cell transfer in the nervous system and the discovery of early diagnostic biomarkers. Both of these issues are addressed in our current manuscript. Using multiple approaches, we present that α-synuclein interacts with lipoproteins within human cerebrospinal fluid and can be taken up by cells in such a state. Moreover, using cerebrospinal fluid samples from 3 large and independent cohorts of patients, we demonstrate that apolipoprotein E is elevated in early, not yet medicated, patients with PD. Finally, using postmortem brain tissue, we provide preliminary histological evidence that apolipoprotein E is enriched in a subpopulation of dopaminergic neurons of human substantia nigra.

The progressive accumulation, aggregation, and spread of α-synuclein (αSN) are common hallmarks of Parkinson’s disease (PD) pathology. Moreover, numerous proteins interact with αSN species, influencing its toxicity in the brain. In the present study, we extended analyses of αSN-interacting proteins to cerebrospinal fluid (CSF). Using coimmunoprecipitation, followed by mass spectrometry, we found that αSN colocalize with apolipoproteins on lipoprotein vesicles. We confirmed these interactions using several methods, including the enrichment of lipoproteins with a recombinant αSN, and the subsequent uptake of prepared vesicles by human dopaminergic neuronal-like cells. Further, we report an increased level of ApoE in CSF from early PD patients compared with matched controls in 3 independent cohorts. Moreover, in contrast to controls, we observed the presence of ApoE-positive neuromelanin-containing dopaminergic neurons in substantia nigra of PD patients. In conclusion, the cooccurrence of αSN on lipoprotein vesicles, and their uptake by dopaminergic neurons along with an increase of ApoE in early PD, proposes a mechanism(s) for αSN spreading in the extracellular milieu of PD.

Changes to the Human Serum Proteome in Response to High Intensity Interval Exercise: A Sequential Top-Down Proteomic Analysis

Exercise has been shown to improve health status and prevent chronic diseases. In contrast, overtraining can lead to maladaptation and detrimental health outcomes. These outcomes appear to be mediated in part by released peptides and, potentially, alterations in protein abundances and their modified forms, termed proteoforms. Proteoform biomarkers that either predict the beneficial effects of exercise or indicate (mal)adaptation are yet to be elucidated. Thus, we assessed the influence of high-intensity interval exercise (HIIE) on the human serum proteome to identify novel exercise-regulated proteoforms. To this end, a top-down proteomics approach was used, whereby two-dimensional gel electrophoresis was used to resolve and differentially profile intact proteoforms, followed by protein identification via liquid chromatography-tandem mass spectrometry. Blood was collected from six young-adult healthy males, pre-exercise and 5 min and 1 h post-exercise. Exercise consisted of a maximal cycle ergometer test followed by 8 min × 1 min high-intensity intervals at 90% W max, with 1 min non-active recovery between intervals. Twenty resolved serum proteoforms changed significantly in abundance at 5 min and/or 1 h post-HIIE, including apolipoproteins, serpins (protease inhibitors), and immune system proteins, known to have broad anti-inflammatory and antioxidant effects, involvement in lipid clearance, and cardio-/neuro-protective effects. This initial screening for potential biomarkers indicates that a top-down analytical proteomic approach may prove useful in further characterizing the response to exercise and in understanding the molecular mechanisms that lead to health benefits, as well as identifying novel biomarkers for exercise (mal)adaptation.

Lipidomic characterization of extracellular vesicles in human serum

There is a wide variety of extracellular vesicles (EVs) that differ in size and cargo composition. EVs isolated from human plasma or serum carry lipid, protein, and RNA cargo that provides insights to the regulation of normal physiological processes, and to pathological states. Specific populations of EVs have been proposed to contain protein and RNA cargo that are biomarkers for neurologic and systemic diseases. Although there is a considerable amount of evidence that circulating lipids are biomarkers for multiple disease states, it not clear if these lipid biomarkers are enriched in EVs, or if specific populations of EVs are enriched for particular classes of lipid. A highly reproducible workflow for the analysis of lipid content in EVs isolated from human plasma or serum would facilitate this area of research. Here we optimized an MS/MSALL workflow for the untargeted analysis of the lipid content in EVs isolated from human serum. A simple sequential ultracentrifugation protocol isolated three distinct types of serum EVs that were identified based on size, targeted protein, and untargeted lipidomic analyses. EVs in the upper and middle fractions were approximately 140 nm in diameter, while EVs in the pellet were approximately 110 nm in diameter. EVs in the upper most buoyant fractions contained the highest concentration of lipids, were enriched with phospholipids, and immunopositive for the cytoskeletal markers actin, α-actinin, and the mitochondrial protein mitofillin, but negative for the typical EV markers CD63, TSG101, and flotillin. A central fraction of EVs was devoid of cytoskeletal and mitochondrial markers, and positive for CD63, and TSG101, but negative for flotillin. The EV pellet contained no cytoskeletal or mitochondrial markers, but was positive for CD63, TSG101, and flotillin. The EV pellet contained the lowest concentration of most lipids, but was enriched with ceramide. These results provided new insights into the lipid composition of EVs isolated from serum using a simple ultracentrifugation isolation method suitable for lipidomic analysis by mass spectrometry.

Potential Effects of MSC-Derived Exosomes in Neuroplasticity in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of dementia affecting regions of the central nervous system that exhibit synaptic plasticity and are involved in higher brain functions such as learning and memory. AD is characterized by progressive cognitive dysfunction, memory loss and behavioral disturbances of synaptic plasticity and energy metabolism. Cell therapy has emerged as an alternative treatment of AD. The use of adult stem cells, such as neural stem cells and Mesenchymal Stem Cells (MSCs) from bone marrow and adipose tissue, have the potential to decrease cognitive deficits, possibly by reducing neuronal loss through blocking apoptosis, increasing neurogenesis, synaptogenesis and angiogenesis. These processes are mediated primarily by the secretion of many growth factors, anti-inflammatory proteins, membrane receptors, microRNAs (miRNA) and exosomes. Exosomes encapsulate and transfer several functional molecules like proteins, lipids and regulatory RNA which can modify cell metabolism. In the proteomic characterization of the content of MSC-derived exosomes, more than 730 proteins have been identified, some of which are specific cell type markers and others are involved in the regulation of binding and fusion of exosomes with adjacent cells. Furthermore, some factors were found that promote the recruitment, proliferation and differentiation of other cells like neural stem cells. Moreover, within exosomal cargo, a wide range of miRNAs were found, which can control functions related to neural remodeling as well as angiogenic and neurogenic processes. Taking this into consideration, the use of exosomes could be part of a strategy to promote neuroplasticity, improve cognitive impairment and neural replacement in AD. In this review, we describe how exosomes are involved in AD pathology and discuss the therapeutic potential of MSC-derived exosomes mediated by miRNA and protein cargo.