CNS-Derived Blood Exosomes as a Promising Source of Biomarkers: Opportunities and Challenges

Several miRNAs derived from serum extracellular vesicles are potential biomarkers for early diagnosis and progression of Parkinson's disease

Background

Blood-based test for predicting disease progression and early diagnosis of Parkinson’s disease (PD) is an unmet need in the clinic. The profiles of microRNAs (miRNAs) are regarded as potential diagnostic biomarkers for human diseases, whereas miRNAs in the periphery are susceptible to the influence of various components. MiRNAs enriched in serum extracellular vesicles (EVs) have demonstrated disease-specific advantages in diagnosis due to their high abundance, stability and resistance to degradation. This study was aimed to screen differentially expressed EV-derived miRNAs between healthy controls and PD patients to aid in diagnosis of PD.

Methods

A total of 31 healthy controls and 72 patients with a diagnosis of PD at different Hoehn and Yahr stages in Tangdu Hospital were included. In total, 185 differentially expressed miRNAs were obtained through RNA sequencing of serum EVs as well as edgeR and t-test analyses. Subsequently, the weighted gene co-expression network analysis (WGCNA) was utilized to identify the commonly expressed miRNAs in all stages of PD by constructing connections between modules, and specifically expressed miRNAs in each stage of PD by functional enrichment analysis. After aligning these miRNAs with PD-related miRNAs in Human miRNA Disease Database, the screened miRNAs were further validated by receiver operating characteristic (ROC) curves and quantitative real-time polymerase chain reaction (qRT-PCR) using peripheral blood EVs from 40 more participants.

Results

WGCNA showed that 4 miRNAs were commonly associated with all stages of PD and 13 miRNAs were specifically associated with different stages of PD. Of the 17 obtained miRNAs, 7 were validated by ROC curve analysis and 7 were verified in 40 more participants by qRT-PCR. Six miRNAs were verified by both methods, which included 2 miRNAs that were commonly expressed in all stages of PD and 4 miRNAs that were specifically expressed in different stages of PD.

Conclusions

The 6 serum EV-derived miRNAs, hsa-miR-374a-5p, hsa-miR-374b-5p, hsa-miR-199a-3p, hsa-miR-28-5p, hsa-miR-22-5p and hsa-miR-151a-5p, may potentially be used as biomarkers for PD progression and for early diagnosis of PD in populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00249-y.

Genomic Mosaicism Formed by Somatic Variation in the Aging and Diseased Brain

Over the past 20 years, analyses of single brain cell genomes have revealed that the brain is composed of cells with myriad distinct genomes: the brain is a genomic mosaic, generated by a host of DNA sequence-altering processes that occur somatically and do not affect the germline. As such, these sequence changes are not heritable. Some processes appear to occur during neurogenesis, when cells are mitotic, whereas others may also function in post-mitotic cells. Here, we review multiple forms of DNA sequence alterations that have now been documented: aneuploidies and aneusomies, smaller copy number variations (CNVs), somatic repeat expansions, retrotransposons, genomic cDNAs (gencDNAs) associated with somatic gene recombination (SGR), and single nucleotide variations (SNVs). A catch-all term of DNA content variation (DCV) has also been used to describe the overall phenomenon, which can include multiple forms within a single cell’s genome. A requisite step in the analyses of genomic mosaicism is ongoing technology development, which is also discussed. Genomic mosaicism alters one of the most stable biological molecules, DNA, which may have many repercussions, ranging from normal functions including effects of aging, to creating dysfunction that occurs in neurodegenerative and other brain diseases, most of which show sporadic presentation, unlinked to causal, heritable genes.

Brain-Derived Exosomal Proteins as Effective Biomarkers for Alzheimer's Disease: A Systematic Review and Meta-Analysis

Alzheimer's disease (AD), a progressive neurodegenerative disease, affects approximately 50 million people worldwide, which warrants the search for reliable new biomarkers for early diagnosis of AD. Brain-derived exosomal (BDE) proteins, which are extracellular nanovesicles released by all cell lineages of the central nervous system, have been focused as biomarkers for diagnosis, screening, prognosis prediction, and monitoring in AD. This review focused on the possibility of BDE proteins as AD biomarkers. The articles published prior to 26 January 2021 were searched in PubMed, EMBASE, Web of Science, and Cochrane Library to identify all relevant studies that reported exosome biomarkers in blood samples of patients with AD. From 342 articles, 20 studies were selected for analysis. We conducted a meta-analysis of six BDE proteins and found that levels of amyloid-β42 (standardized mean difference (SMD) = 1.534, 95% confidence interval [CI]: 0.595-2.474), total-tau (SMD = 1.224, 95% CI: 0.534-1.915), tau phosphorylated at threonine 181 (SMD = 4.038, 95% CI: 2.312-5.764), and tau phosphorylated at serine 396 (SMD = 2.511, 95% CI: 0.795-4.227) were significantly different in patients with AD compared to those in control. Whereas, those of p-tyrosine-insulin receptor substrate-1 and heat shock protein 70 did not show significant differences. This review suggested that Aβ42, t-tau, p-T181-tau, and p-S396-tau could be effective in diagnosing AD as blood biomarkers, despite the limitation in the meta-analysis based on the availability of data. Therefore, certain BDE proteins could be used as effective biomarkers for AD.

The emerging role of exosomes in Alzheimer's disease

Alzheimer's disease (AD), manifested by memory loss and a decline in cognitive functions, is the most prevalent neurodegenerative disease accounting for 60-80 % of dementia cases. But, to-date, there is no effective treatment available to slow or stop the progression of AD. Exosomes are small extracellular vesicles that carry constituents, such as functional messenger RNAs, non-coding RNAs, proteins, lipids, DNA, and other bioactive substances of their source cells. In the brain, exosomes are likely to be sourced by almost all cell types and involve in cell communication to regulate cellular functions. The yet, accumulated evidence on the roles of exosomes and their constituents in the AD pathological process suggests their significance as additional biomarkers and therapeutic targets for AD. This review summarizes the current reported research findings on exosomes roles in the pathogenesis, diagnosis, and treatment of AD.

Biophotonics for diagnostic detection of extracellular vesicles

Extracellular Vesicles (EVs) are versatile carriers for biomarkers involved in the pathogenesis of multiple human disorders. Despite the increasing scientific and commercial interest in EV application in diagnostics, traditional biomolecular techniques usually require consistent sample amount, rely on operator-dependent and time- consuming procedures and cannot cope with the nano-size range of EVs, limiting both sensitivity and reproducibility of results. The application of biophotonics, i.e. light-based methods, for the diagnostic detection of EVs has brought to the development of innovative platforms with excellent sensitivity. In this review, we propose an overview of the most promising and emerging technologies used in the field of EV-related biomarker discovery. When tested on clinical samples, the reported biophotonic approaches in most cases have managed to discriminate between nanovesicles and contaminants, achieved much higher resolution compared to traditional procedures, and reached moderate to excellent diagnostic accuracy, thus demonstrating great potentialities for their clinical translation.

Extracellular vesicles (exosomes and ectosomes) play key roles in the pathology of brain diseases

Last century, neurons and glial cells were mostly believed to play distinct functions, relevant for the brain. Progressively, however, it became clear that neurons, astrocytes and microglia co-operate intensely with each other by release/binding of signaling factors, direct surface binding and generation/release of extracellular vesicles, the exosomes and ectosomes, called together vesicles in this abstract. The present review is focused on these vesicles, fundamental in various brain diseases. Their properties are extraordinary. The specificity of their membrane governs their fusion with distinct target cells, variable depending on the state and specificity of their cells of origin and target. Result of vesicle fusion is the discharge of their cargos into the cytoplasm of target cells. Cargos are composed of critical molecules, from proteins (various nature and function) to nucleotides (especially miRNAs), playing critical roles in immune and neurodegenerative diseases. Among immune diseases is multiple sclerosis, affected by extensive dysregulation of co-trafficking neural and glial vesicles, with distinct miRNAs inducing severe or reducing effects. The vesicle-dependent differences between progressive and relapsing-remitting forms of the disease are relevant for clinical developments. In Alzheimer’s disease the vesicles can affect the brain by changing their generation and inducing co-release of effective proteins, such Aβ and tau, from neurons and astrocytes. Specific miRNAs can delay the long-term development of the disease. Upon their traffic through the blood-brainbarrier, vesicles of various origin reach fluids where they are essential for the identification of biomarkers, important for diagnostic and therapeutic innovations, critical for the future of many brain patients.

Thrombospondin 1-induced exosomal proteins attenuate hypoxia-induced paraptosis in corneal epithelial cells and promote wound healing

Thrombospondin-1 (TSP1) is involved in corneal wound healing caused by chemical injury. Herein, we examined the effects of TSP1 on hypoxia-induced damages and wound-healing activity in human corneal epithelial (HCE) cells. Exosomal protein expression was determined using liquid chromatography-tandem mass spectrometry, and HCE cell migration and motility were examined through wound-healing assay and time-lapse microscopy. Reestablishment of cell junctions by TSP1 was assessed through confocal microscopy and 3D image reconstruction. Our results show that CoCl₂ -induced hypoxia promoted HCE cell death by paraptosis. TSP1 protected these cells against paraptosis by attenuating mitochondrial membrane potential depletion, swelling and dilation of endoplasmic reticulum and mitochondria, and mitochondrial fission. Exosomes isolated from HCE cells treated with TSP1 contained wound healing-associated proteins that were taken up by HCE cells to promote tissue remodeling and repair. TSP1 protected HCE cells against hypoxia-induced damages and inhibited paraptosis progression by promoting cell migration, cell-cell adhesion, and extracellular matrix remodeling. These findings indicate that TSP1 ameliorates hypoxia-induced paraptosis in HCE cells and promotes wound healing and remodeling by regulating exosomal protein expression. TSP1 may, therefore, play important roles in the treatment of hypoxia-associated corneal diseases.

Atremorine in Parkinson's disease: From dopaminergic neuroprotection to pharmacogenomics

Atremorine is a novel bioproduct obtained by nondenaturing biotechnological processes from a genetic species of Vicia faba. Atremorine is a potent dopamine (DA) enhancer with powerful effects on the neuronal dopaminergic system, acting as a neuroprotective agent in Parkinson's disease (PD). Over 97% of PD patients respond to a single dose of Atremorine (5 g, p.o.) 1 h after administration. This response is gender-, time-, dose-, and genotype-dependent, with optimal doses ranging from 5 to 20 g/day, depending upon disease severity and concomitant medication. Drug-free patients show an increase in DA levels from 12.14 ± 0.34 pg/ml to 6463.21 ± 1306.90 pg/ml; and patients chronically treated with anti-PD drugs show an increase in DA levels from 1321.53 ± 389.94 pg/ml to 16,028.54 ± 4783.98 pg/ml, indicating that Atremorine potentiates the dopaminergic effects of conventional anti-PD drugs. Atremorine also influences the levels of other neurotransmitters (adrenaline, noradrenaline) and hormones which are regulated by DA (e.g., prolactin, PRL), with no effect on serotonin or histamine. The variability in Atremorine-induced DA response is highly attributable to pharmacogenetic factors. Polymorphic variants in pathogenic (SNCA, NUCKS1, ITGA8, GPNMB, GCH1, BCKDK, APOE, LRRK2, ACMSD), mechanistic (DRD2), metabolic (CYP2D6, CYP2C9, CYP2C19, CYP3A4/5, NAT2), transporter (ABCB1, SLC6A2, SLC6A3, SLC6A4) and pleiotropic genes (APOE) influence the DA response to Atremorine and its psychomotor and brain effects. Atremorine enhances DNA methylation and displays epigenetic activity via modulation of the pharmacoepigenetic network. Atremorine is a novel neuroprotective agent for dopaminergic neurons with potential prophylactic and therapeutic activity in PD.

Pregnancy-Related Extracellular Vesicles Revisited

Extracellular vesicles (EVs) are small vesicles ranging from 20–200 nm to 10 μm in diameter that are discharged and taken in by many different types of cells. Depending on the nature and quantity of their content—which generally includes proteins, lipids as well as microRNAs (miRNAs), messenger-RNA (mRNA), and DNA—these particles can bring about functional modifications in the receiving cells. During pregnancy, placenta and/or fetal-derived EVs have recently been isolated, eliciting interest in discovering their clinical significance. To date, various studies have associated variations in the circulating levels of maternal and fetal EVs and their contents, with complications including gestational diabetes and preeclampsia, ultimately leading to adverse pregnancy outcomes. Furthermore, EVs have also been identified as messengers and important players in viral infections during pregnancy, as well as in various congenital malformations. Their presence can be detected in the maternal blood from the first trimester and their level increases towards term, thus acting as liquid biopsies that give invaluable insight into the status of the feto-placental unit. However, their exact roles in the metabolic and vascular adaptations associated with physiological and pathological pregnancy is still under investigation. Analyzing peer-reviewed journal articles available in online databases, the purpose of this review is to synthesize current knowledge regarding the utility of quantification of pregnancy related EVs in general and placental EVs in particular as non-invasive evidence of placental dysfunction and adverse pregnancy outcomes, and to develop the current understanding of these particles and their applicability in clinical practice.

Extracellular vesicles and intercellular communication in the central nervous system

Neurons and glial cells of the central nervous system (CNS) release extracellular vesicles (EVs) to the interstitial fluid of the brain and spinal cord parenchyma. EVs contain proteins, nucleic acids and lipids that can be taken up by, and modulate the behaviour of, neighbouring recipient cells. The functions of EVs have been extensively studied in the context of neurodegenerative diseases. However, mechanisms involved in EV-mediated neuron-glial communication under physiological conditions or healthy ageing remain unclear. A better understanding of the myriad roles of EVs in CNS homeostasis is essential for the development of novel therapeutics to alleviate and reverse neurological disturbances of ageing. Proteomic studies are beginning to reveal cell type-specific EV cargo signatures that may one day allow us to target specific neuronal or glial cell populations in the treatment of debilitating neurological disorders. This review aims to synthesise the current literature regarding EV-mediated cell-cell communication in the brain, predominantly under physiological conditions.

Function of exosomes in neurological disorders and brain tumors

Exosomes are a subtype of extracellular vesicles released from different cell types including those in the nervous system, and are enriched in a variety of bioactive molecules such as RNAs, proteins and lipids. Numerous studies have indicated that exosomes play a critical role in many physiological and pathological activities by facilitating intercellular communication and modulating cells' responses to external environments. Particularly in the central nervous system, exosomes have been implicated to play a role in many neurological disorders such as abnormal neuronal development, neurodegenerative diseases, epilepsy, mental disorders, stroke, brain injury and brain cancer. Since exosomes recapitulate the characteristics of the parental cells and have the capacity to cross the blood-brain barrier, their cargo can serve as potential biomarkers for early diagnosis and clinical assessment of disease treatment. In this review, we describe the latest findings and current knowledge of the roles exosomes play in various neurological disorders and brain cancer, as well as their application as promising biomarkers. The potential use of exosomes to deliver therapeutic molecules to treat diseases of the central nervous system is also discussed.

Proteomics Profiling of Neuron-Derived Small Extracellular Vesicles from Human Plasma: Enabling Single-Subject Analysis

Small extracellular vesicles have been intensively studied as a source of biomarkers in neurodegenerative disorders. The possibility to isolate neuron-derived small extracellular vesicles (NDsEV) from blood represents a potential window into brain pathological processes. To date, the absence of sensitive NDsEV isolation and full proteome characterization methods has meant their protein content has been underexplored, particularly for individual patients. Here, we report a rapid method based on an immunoplate covalently coated with mouse monoclonal anti-L1CAM antibody for the isolation and the proteome characterization of plasma-NDsEV from individual Parkinson’s disease (PD) patients. We isolated round-shaped vesicles with morphological characteristics consistent with exosomes. On average, 349 ± 38 protein groups were identified by liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis, 20 of which are annotated in the Human Protein Atlas as being highly expressed in the brain, and 213 were shared with a reference NDsEV dataset obtained from cultured human neurons. Moreover, this approach enabled the identification of 23 proteins belonging to the Parkinson disease KEGG pathway, as well as proteins previously reported as PD circulating biomarkers.

News about the Role of Fluid and Imaging Biomarkers in Neurodegenerative Diseases

Biomarkers are molecules that are variable in their origin, nature, and mechanism of action; they are of great relevance in biology and also in medicine because of their specific connection with a single or several diseases. Biomarkers are of two types, which in some cases are operative with each other. Fluid biomarkers, started around 2000, are generated in fluid from specific proteins/peptides and miRNAs accumulated within two extracellular fluids, either the central spinal fluid or blood plasma. The switch of these proteins/peptides and miRNAs, from free to segregated within extracellular vesicles, has induced certain advantages including higher levels within fluids and lower operative expenses. Imaging biomarkers, started around 2004, are identified in vivo upon their binding by radiolabeled molecules subsequently revealed in the brain by positron emission tomography and/or other imaging techniques. A positive point for the latter approach is the quantitation of results, but expenses are much higher. At present, both types of biomarker are being extensively employed to study Alzheimer’s and other neurodegenerative diseases, investigated from the presymptomatic to mature stages. In conclusion, biomarkers have revolutionized scientific and medical research and practice. Diagnosis, which is often inadequate when based on medical criteria only, has been recently improved by the multiplicity and specificity of biomarkers. Analogous results have been obtained for prognosis. In contrast, improvement of therapy has been limited or fully absent, especially for Alzheimer’s in which progress has been inadequate. An urgent need at hand is therefore the progress of a new drug trial design together with patient management in clinical practice.

Extracellular mitochondria in the cerebrospinal fluid (CSF): Potential types and key roles in central nervous system (CNS) physiology and pathogenesis

The cerebrospinal fluid (CSF) has an important role in the transport of nutrients and signaling molecules to the central nervous and immune systems through its circulation along the brain and spinal cord tissues. The mitochondrial activity in the central nervous system (CNS) is essential in processes such as neuroplasticity, neural differentiation and production of neurotransmitters. Interestingly, extracellular and active mitochondria have been detected in the CSF where they act as a biomarker for the outcome of pathologies such as subarachnoid hemorrhage and delayed cerebral ischemia. Additionally, cell-free-circulating mitochondrial DNA (ccf-mtDNA) has been detected in both the CSF of healthy donors and in that of patients with neurodegenerative diseases. Key questions arise as there is still much debate regarding if ccf-mtDNA detected in CSF is associated with a diversity of active or inactive extracellular mitochondria coexisting in distinct pathologies. Additionally, it is of great scientific and medical importance to identify the role of extracellular mitochondria (active and inactive) in the CSF and the difference between them being damage associated molecular patterns (DAMPs) or factors that promote homeostasis. This review analyzes the different types of extracellular mitochondria, methods for their identification and their presence in CSF. Extracellular mitochondria in the CSF could have an important implication in health and disease, which may lead to the development of medical approaches that utilize mitochondria as therapeutic agents.

Exosomes as Emerging Biomarker Tools in Neurodegenerative and Neuropsychiatric Disorders-A Proteomics Perspective

Exosomes are synthesized and secreted by different cell types and contain proteins, lipids, metabolites and RNA species that reflect the physiological status of the cell of origin. As such, exosomes are increasingly being used as a novel reservoir for disease biomarker discovery. However, isolation of exosomes can be challenging due to their nonuniformity of shape and variable tissue of origin. Moreover, various analytical techniques used for protein detection and quantitation remain insensitive to the low amounts of protein isolated from exosomes. Despite these challenges, techniques to improve proteomic yield and increase protein dynamic range continue to improve at a rapid rate. In this review, we highlight the importance of exosome proteomics in neurodegenerative and neuropsychiatric disorders and the associated technical difficulties. Furthermore, current progress and technological advancements in exosome proteomics research are discussed with an emphasis on disease-associated protein biomarkers.

Extracellular Vesicles: Novel Roles in Neurological Disorders

Exosomes are small extracellular vesicles (EVs) secreted by almost all cells, which have been recognized as a novel platform for intercellular communication in the central nervous system (CNS). Exosomes are capable of transferring proteins, nucleic acids, lipids, and metabolites between neurons and glial cells, contributing to CNS development and maintenance of homeostasis. Evidence shows that exosomes originating from CNS cells act as suppressors or promoters in the initiation and progression of neurological disorders. Moreover, these exosomes have been shown to transfer molecules associated with diseases through the blood-brain barrier (BBB) and thus can be detected in blood. This unique feature enables exosomes to act as potential diagnostic biomarkers for neurological disorders. In addition, a substantial number of researches have indicated that exosomes derived from mesenchymal stem cells (MSCs) have repair effects on neurological disorders. Herein, we briefly introduce the roles of exosomes under physiological and pathological conditions. In particular, novel roles of exosomes as potential diagnostic biomarkers and therapeutic tools for neurological disorders are highlighted.

Neural cell-derived plasma exosome protein abnormalities implicate mitochondrial impairment in first episodes of psychosis

Neuroprotective and other functional proteins of mitochondria were quantified in extracts of plasma neural-derived exosomes from ten first-episode psychosis (FP) patients and ten matched psychiatrically normal controls (ctls). Astrocyte-derived extracellular vesicles (ADEVs) and neuron-derived extracellular vesicles (NDEVs) were immunoabsorbed separately from physically precipitated plasma total EVs. Extracted mitochondrial ATP synthase was specifically immunofixed to plastic wells for quantification of catalytic activity based on conversion of NADH to NAD+ . Other extracted mitochondrial functional proteins were quantified by ELISAs. All protein levels were normalized with EV content of the CD81 exosome marker. FP patient ADEV level but not NDEV level of mitochondrial ATP synthase activity was significantly lower than that of ctls. FP patient ADEV and NDEV levels of the functionally critical mitochondrial proteins mitofusin 2 and cyclophilin D, but not of transcription factor A of mitochondria, and of the mitochondrial short open-reading frame neuroprotective and metabolic regulatory peptides humanin and MOTS-c were significantly lower than those of ctls. In contrast, FP patient NDEV, but not ADEV, level of the mitochondrial-tethering protein syntaphilin, but not of myosin VI, was significantly higher than that of ctls. The distinctively different neural levels of some mitochondrial proteins in FP patients than ctls now should be correlated with diverse clinical characteristics. Drugs that increase depressed levels of proteins and mimetics of deficient short open-reading frame peptides may be of therapeutic value in early phases of schizophrenia.

Extracellular Vesicle Transportation and Uptake by Recipient Cells: A Critical Process to Regulate Human Diseases

Emerging evidence highlights the relevance of extracellular vesicles (EVs) in modulating human diseases including but not limited to cancer, inflammation, and neurological disorders. EVs can be found in almost all types of human body fluids, suggesting that their trafficking may allow for their targeting to remote recipient cells. While molecular processes underlying EV biogenesis and secretion are increasingly elucidated, mechanisms governing EV transportation, target finding and binding, as well as uptake into recipient cells remain to be characterized. Understanding the specificity of EV transport and uptake is critical to facilitating the development of EVs as valuable diagnostics and therapeutics. In this mini review, we focus on EV uptake mechanisms and specificities, as well as their implications in human diseases.

Extracellular Vesicles in Neuroinflammation

Extracellular vesicles (EVs) are a heterogenous group of membrane-bound particles that play a pivotal role in cell–cell communication, not only participating in many physiological processes, but also contributing to the pathogenesis of several diseases. The term EVs defines many and different vesicles based on their biogenesis and release pathway, including exosomes, microvesicles (MVs), and apoptotic bodies. However, their classification, biological function as well as protocols for isolation and detection are still under investigation. Recent evidences suggest the existence of novel subpopulations of EVs, increasing the degree of heterogeneity between EV types and subtypes. EVs have been shown to have roles in the CNS as biomarkers and vehicles of drugs and other therapeutic molecules. They are known to cross the blood brain barrier, allowing CNS EVs to be detectable in peripheral fluids, and their cargo may give information on parental cells and the pathological process they are involved in. In this review, we summarize the knowledge on the function of EVs in the pathogenesis of multiple sclerosis (MS) and discuss recent evidences for their potential applications as diagnostic biomarkers and therapeutic targets.

Biofluidic material-based carriers: Potential systems for crossing cellular barriers

Biofluids act as a repository for disease biomarkers and are excellent diagnostic tools applied in establishing a disease profile based on clinical testing, evaluation and monitoring the progression of patients suffering from various conditions. Furthermore, biofluids and their derived components such proteins, pigments, enzymes, hormones and cells carry a potential in the development of therapeutic drug delivery systems or as cargo materials for targeting the drug to the site of action. The presence of biofluids with respect to their specific location reveals the information of disease progression and mechanism, delivery aspects such as routes of administration as well as pharmacological factors such as binding affinity, rate of kinetics, efficacy, bioavailability and patient compliance. This review focuses on the properties and functional benefits of some biofluids, namely blood, saliva, bile, urine, amniotic fluid, synovial fluid and cerebrospinal fluid. It also covers the therapeutic and targeting action of fluid-derived substances in various micro- or nano-systems like nanohybrids, nanoparticles, self-assembled micelles, microparticles, cell-based systems, etc. The formulation of such biologically-oriented systems demonstrate the advantages of natural origin, biocompatibility and biodegradability and offer new techniques for overcoming the challenges experienced in conventional therapies.

The molecular tweezer CLR01 improves behavioral deficits and reduces tau pathology in P301S-tau transgenic mice

BACKGROUND

Molecular tweezers (MTs) are broad-spectrum inhibitors of abnormal protein aggregation. A lead MT, called CLR01, has been demonstrated to inhibit the aggregation and toxicity of multiple amyloidogenic proteins in vitro and in vivo. Previously, we evaluated the effect of CLR01 in the 3 × Tg mouse model of Alzheimer's disease, which overexpresses mutant human presenilin 1, amyloid β-protein precursor, and tau and found that subcutaneous administration of the compound for 1 month led to a robust reduction of amyloid plaques, neurofibrillary tangles, and microgliosis. CLR01 also has been demonstrated to inhibit tau aggregation in vitro and tau seeding in cell culture, yet because in Alzheimer's disease (AD) and in the 3 × Tg model, tau hyperphosphorylation and aggregation are thought to be downstream of Aβ insults, the study in this model left open the question whether CLR01 affected tau in vivo directly or indirectly.

METHODS

To determine if CLR01 could ameliorate tau pathology directly in vivo, we tested the compound similarly using the P301S-tau (line PS19) mouse model. Mice were administered 0.3 or 1.0 mg/kg per day CLR01 and tested for muscle strength and behavioral deficits, including anxiety- and disinhibition-like behavior. Their brains then were analyzed by immunohistochemical and biochemical assays for pathological forms of tau, neurodegeneration, and glial pathology.

RESULTS

CLR01 treatment ameliorated muscle-strength deterioration, anxiety-, and disinhibition-like behavior. Improved phenotype was associated with decreased levels of pathologic tau forms, suggesting that CLR01 exerts a direct effect on tau in vivo. Limitations of the study included a relatively short treatment period of the mice at an age in which full pathology is not yet developed. In addition, high variability in this model lowered the statistical significance of the findings of some outcome measures.

CONCLUSIONS

The findings suggest that CLR01 is a particularly attractive candidate for the treatment of AD because it targets simultaneously the two major pathogenic proteins instigating and propagating the disease, amyloid β-protein (Aβ), and tau, respectively. In addition, our study suggests that CLR01 can be used for the treatment of other tauopathies in the absence of amyloid pathology.

The Evolving Landscape of Exosomes in Neurodegenerative Diseases: Exosomes Characteristics and a Promising Role in Early Diagnosis

Neurodegenerative diseases (ND) remains to be one of the biggest burdens on healthcare systems and serves as a leading cause of disability and death. Alzheimer's disease (AD) is among the most common of such disorders, followed by Parkinson's disease (PD). The basic molecular details of disease initiation and pathology are still under research. Only recently, the role of exosomes has been linked to the initiation and progression of these neurodegenerative diseases. Exosomes are small bilipid layer enclosed extracellular vesicles, which were once considered as a cellular waste and functionless. These nano-vesicles of 30-150 nm in diameter carry specific proteins, lipids, functional mRNAs, and high amounts of non-coding RNAs (miRNAs, lncRNAs, and circRNAs). As the exosomes content is known to vary as per their originating and recipient cells, these vesicles can be utilized as a diagnostic biomarker for early disease detection. Here we review exosomes, their biogenesis, composition, and role in neurodegenerative diseases. We have also provided details for their characterization through an array of available techniques. Their updated role in neurodegenerative disease pathology is also discussed. Finally, we have shed light on a novel field of salivary exosomes as a potential candidate for early diagnosis in neurodegenerative diseases and compared the biomarkers of salivary exosomes with other blood/cerebrospinal fluid (CSF) based exosomes within these neurological ailments.

Multi-Omics Analysis of Microglial Extracellular Vesicles From Human Alzheimer's Disease Brain Tissue Reveals Disease-Associated Signatures

Alzheimer's disease (AD) is the most common cause of dementia, yet there is no cure or diagnostics available prior to the onset of clinical symptoms. Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are released from almost all types of cell. Genome-wide association studies have linked multiple AD genetic risk factors to microglia-specific pathways. It is plausible that microglia-derived EVs may play a role in the progression of AD by contributing to the dissemination of insoluble pathogenic proteins, such as tau and Aβ. Despite the potential utility of EVs as a diagnostic tool, our knowledge of human brain EV subpopulations is limited. Here we present a method for isolating microglial CD11b-positive small EVs from cryopreserved human brain tissue, as well as an integrated multiomics analysis of microglial EVs enriched from the parietal cortex of four late-stage AD (Braak V-VI) and three age-matched normal/low pathology (NL) cases. This integrated analysis revealed 1,000 proteins, 594 lipids, and 105 miRNAs using shotgun proteomics, targeted lipidomics, and NanoString nCounter technology, respectively. The results showed a significant reduction in the abundance of homeostatic microglia markers P2RY12 and TMEM119, and increased levels of disease-associated microglia markers FTH1 and TREM2, in CD11b-positive EVs from AD brain compared to NL cases. Tau abundance was significantly higher in AD brain-derived microglial EVs. These changes were accompanied by the upregulation of synaptic and neuron-specific proteins in the AD group. Levels of free cholesterol were elevated in microglial EVs from the AD brain. Lipidomic analysis also revealed a proinflammatory lipid profile, endolysosomal dysfunction, and a significant AD-associated decrease in levels of docosahexaenoic acid (DHA)-containing polyunsaturated lipids, suggesting a potential defect in acyl-chain remodeling. Additionally, four miRNAs associated with immune and cellular senescence signaling pathways were significantly upregulated in the AD group. Our data suggest that loss of the homeostatic microglia signature in late AD stages may be accompanied by endolysosomal impairment and the release of undigested neuronal and myelin debris, including tau, through extracellular vesicles. We suggest that the analysis of microglia-derived EVs has merit for identifying novel EV-associated biomarkers and providing a framework for future larger-scale multiomics studies on patient-derived cell-type-specific EVs.

Exosomes and exosomal microRNA in non-targeted radiation bystander and abscopal effects in the central nervous system

Localized cranial radiotherapy is a dominant treatment for brain cancers. After being subjected to radiation, the central nervous system (CNS) exhibits targeted effects as well as non-targeted radiation bystander effects (RIBE) and abscopal effects (RIAE). Radiation-induced targeted effects in the CNS include autophagy and various changes in tumor cells due to radiation sensitivity, which can be regulated by microRNAs. Non-targeted radiation effects are mainly induced by gap junctional communication between cells, exosomes containing microRNAs can be transduced by intracellular endocytosis to regulate RIBE and RIAE. In this review, we discuss the involvement of microRNAs in radiation-induced targeted effects, as well as exosomes and/or exosomal microRNAs in non-targeted radiation effects in the CNS. As a target pathway, we also discuss the Akt pathway which is regulated by microRNAs, exosomes, and/or exosomal microRNAs in radiation-induced targeted effects and RIBE in CNS tumor cells. As the CNS-derived exosomes can cross the blood-brain-barrier (BBB) into the bloodstream and be isolated from peripheral blood, exosomes and exosomal microRNAs can emerge as promising minimally invasive biomarkers and therapeutic targets for radiation-induced targeted and non-targeted effects in the CNS.

CSF and Blood Biomarkers in Neuroinflammatory and Neurodegenerative Diseases: Implications for Treatment

Neuroinflammatory and neurodegenerative diseases are characterized by the interplay of a number of molecular pathways that can be assessed through biofluids, especially cerebrospinal fluid and blood. Accordingly, the definition and classification of these disorders will move from clinical and pathological to biological criteria. The consequences of this biomarker-based diagnostic and prognostic approach are highly relevant to the field of drug development. Indeed, in view of the availability of disease-modifying drugs, fluid biomarkers offer a unique opportunity for improving the quality and applicability of results from clinical trials. Herein, we discuss the benefits of using fluid biomarkers for patient stratification, target engagement, and outcome assessment, as well as the most recent developments in neuroinflammatory and neurodegenerative diseases.

Advances in Exosomes-Based Drug Delivery Systems

Exosomes, a subgroup of extracellular vesicles, are important mediators of long-distance intercellular communication and are involved in a diverse range of biological processes such as the transport of lipids, proteins, and nucleic acids. Researchers, seeing the problems caused by the toxic effects and clearance of synthetic nanoparticles, consider exosomes as an interesting alternative to such nanoparticles in the specific and controlled transport of drugs. In recent years, there have been remarkable advances in the use of exosomes in cancer therapeutics or for treating neurological diseases, among other applications. The objective of this work is to analyze studies focused on exosomes used in drug delivery system, present and future applications in this field of research are discussed based on the results obtained.

The Role of Exosomal microRNAs and Oxidative Stress in Neurodegenerative Diseases

Neurodegenerative diseases including Alzheimer's disease and Parkinson's disease are aging-associated diseases with irreversible damage of brain tissue. Oxidative stress is commonly detected in neurodegenerative diseases and related to neuronal injury and pathological progress. Exosome, one of the extracellular vesicles, is demonstrated to carry microRNAs (miRNAs) and build up a cell-cell communication in neurons. Recent research has found that exosomal miRNAs regulate the activity of multiple physiological pathways, including the oxidative stress response, in neurodegenerative diseases. Here, we review the role of exosomal miRNAs and oxidative stress in neurodegenerative diseases. Firstly, we explore the relationship between oxidative stress and neurodegenerative diseases. Secondly, we introduce the characteristics of exosomes and roles of exosome-related miRNAs. Thirdly, we summarized the crosstalk between exosomal miRNAs and oxidative stress in neurodegenerative diseases. Fourthly, we discuss the potential of exosomes to be a biomarker in neurodegenerative diseases. Finally, we summarize the advantages of exosome-based delivery and present situation of research on exosome-based delivery of therapeutic miRNA. Our work is aimed at probing and reinforcing the recognition of the pathomechanism of neurodegenerative diseases and providing the basis for novel strategies of clinical diagnosis and treatment.

A Brief History of Adherons: The Discovery of Brain Exosomes

Although exosomes were first described in reticulocytes in 1983, many people do not realize that similar vesicles had been studied in the context of muscle and nerve, beginning in 1980. At the time of their discovery, these vesicles were named adherons, and they were found to play an important role in both cell–substrate and cell–cell adhesion. My laboratory described several molecules that are present in adherons, including heparan sulfate proteoglycans (HSPGs) and purpurin. HSPGs have since been shown to play a variety of key roles in brain physiology. Purpurin has a number of important functions in the retina, including a role in nerve cell differentiation and regeneration. In this review, I discuss the discovery of adherons and how that led to continuing studies on their role in the brain with a particular focus on HSPGs.

Exosomal miRNAs as Potential Diagnostic Biomarkers in Alzheimer's Disease

Alzheimer’s disease (AD), a neurodegenerative disease, is linked to a variety of internal and external factors present from the early stages of the disease. There are several risk factors related to the pathogenesis of AD, among these exosomes and microRNAs (miRNAs) are of particular importance. Exosomes are nanocarriers released from many different cell types, including neuronal cells. Through the transfer of bioactive molecules, they play an important role both in the maintenance of physiological and in pathological conditions. Exosomes could be carriers of potential biomarkers useful for the assessment of disease progression and for therapeutic applications. miRNAs are small noncoding endogenous RNA sequences active in the regulation of protein expression, and alteration of miRNA expression can result in a dysregulation of key genes and pathways that contribute to disease development. Indeed, the involvement of exosomal miRNAs has been highlighted in various neurodegenerative diseases, and this opens the possibility that dysregulated exosomal miRNA profiles may influence AD disease. The advances in exosome-related biomarker detection in AD are summarized. Finally, in this review, we highlight the use of exosomal miRNAs as essential biomarkers in preclinical and clinical studies in Alzheimer’s disease, also taking a look at their potential clinical value.

Extracellular Vesicles: From Biomarkers to Therapeutic Tools

Intercellular communication is an essential hallmark of multicellular organisms and can be mediated through direct cell–cell contact or transfer of secreted molecules. In the last two decades, a third mechanism for intercellular communication has emerged that involves intercellular transfer of extracellular vesicles (EVs). EVs are membranous vesicles of 30–5000 nm in size. Based on their dimension and biogenesis, EVs can be divided into different categories, such as microvesicles, apoptotic bodies, ectosomes, and exosomes. It has already been demonstrated that protein changes, expressed on the surfaces or in the content of these vesicles, may reflect the status of producing cells. For this reason, EVs, and exosomes in particular, are considered ideal biomarkers in several types of disease—from cancer diagnosis to heart rejection. This aspect opens different opportunities in EVs clinical application, considering the importance given to liquid biopsy in the recent years. Furthermore, extracellular vesicles can be natural or engineered carriers of cytoprotective or cytotoxic factors and applied, as a therapeutic tool, from regenerative medicine to target cancer therapy. This is of pivotal importance in the so called “era of the 4P medicine”. This Editorial focuses on recent findings pertaining to EVs in different medical areas, from biomarkers to therapeutic applications.

Advancing medicine for Alzheimer's disease: A plasma neural exosome platform

Enrichment of neurally derived extracellular vesicles of several cell-types from plasma for protein quantification longitudinally in living patients with Alzheimer's disease has permitted the development of a tentative temporal framework of initiating events, progression mechanisms, and amplification processes. Interactions of beta-amyloid peptides with an elevated level of their normal prion protein dendritic receptor and of phospho-tau species with their synaptogyrin-3 synaptic vesicle receptor replace excessive production and accumulation of neuropathic proteins as the major initiating events. Synaptic dysfunction and microvascular angiopathy are confirmed as early progression mechanisms of decreased neuronal network connectivity, hypoxia, altered blood-brain barrier, and neurocellular degeneration. Neurally derived extracellular vesicle protein abnormalities also reveal a range of later amplification processes that encompasses insulin resistance, lysosomal defects, decreased survival factors, increased reactive oxygen species, and excessive neuroinflammation. New potential therapeutic targets also are suggested as well as the likely timing of their pathogenic engagement.

Extracellular vesicles and amyotrophic lateral sclerosis: from misfolded protein vehicles to promising clinical biomarkers

Extracellular vesicles (EVs) are small reservoirs of different molecules and important mediators of cell-to-cell communication. As putative vehicles of misfolded protein propagation between cells, they have drawn substantial attention in the field of amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Moreover, exosome-mediated non-coding RNA delivery may play a crucial role in ALS, given the relevance of RNA homeostasis in disease pathogenesis. Since EVs can enter the systemic circulation and are easily detectable in patients’ biological fluids, they have generated broad interest both as diagnostic and prognostic biomarkers and as valuable tools in understanding disease pathogenesis. Here, after a brief introduction on biogenesis and functions of EVs, we aim to investigate their role in neurodegenerative disorders, especially ALS. Specifically, we focus on the main findings supporting EV-mediated protein and RNA transmission in ALS in vitro and in vivo models. Then, we provide an overview of clinical applications of EVs, summarizing the most relevant studies able to detect EVs in blood and cerebrospinal fluid (CSF) of ALS patients, underlying their potential use in aiding diagnosis and prognosis. Finally, we explore the therapeutic applications of EVs in ALS, either as targets or as vehicles of proteins, nucleic acids and molecular drugs.

Vesicular Transport of Encapsulated microRNA between Glial and Neuronal Cells

Exosomes (EXs) and extracellular microvesicles (EMVs) represent a diverse assortment of plasma membrane-derived nanovesicles, 30–1000 nm in diameter, released by all cell lineages of the central nervous system (CNS). They are examples of a very active and dynamic form of extracellular communication and the conveyance of biological information transfer essential to maintain homeostatic neurological functions and contain complex molecular cargoes representative of the cytoplasm of their cells of origin. These molecular cargoes include various mixtures of proteins, lipids, proteolipids, cytokines, chemokines, carbohydrates, microRNAs (miRNA) and messenger RNAs (mRNA) and other components, including end-stage neurotoxic and pathogenic metabolic products, such as amyloid beta (Aβ) peptides. Brain microglia, for example, respond to both acute CNS injuries and degenerative diseases with complex reactions via the induction of a pro-inflammatory phenotype, and secrete EXs and EMVs enriched in selective pathogenic microRNAs (miRNAs) such as miRNA-34a, miRNA-125b, miRNA-146a, miRNA-155, and others that are known to promote neuro-inflammation, induce complement activation, disrupt innate–immune signaling and deregulate the expression of neuron-specific phosphoproteins involved in neurotropism and synaptic signaling. This communication will review our current understanding of the trafficking of miRNA-containing EXs and EMVs from astrocytes and “activated pro-inflammatory” microglia to target neurons in neurodegenerative diseases with an emphasis on Alzheimer’s disease wherever possible.

Circulating exosomal long non-coding RNAs in patients with acute myocardial infarction

Exosomes are attracting considerable interest in the cardiovascular field as the wide range of their functions is recognized in acute myocardial infarction (AMI). However, the regulatory role of exosomal long non-coding RNAs (lncRNAs) in AMI remains largely unclear. Exosomes were isolated from the plasma of AMI patients and controls, and the sequencing profiles and twice qRT-PCR validations of exosomal lncRNAs were performed. A total of 518 differentially expressed lncRNAs were detected over two-fold change, and 6 kinds of lncRNAs were strikingly elevated in AMI patients with top fold change and were selected to perform subsequent validation. In the two validations, lncRNAs ENST00000556899.1 and ENST00000575985.1 were significantly up-regulated in AMI patients compared with controls. ROC curve analysis revealed that circulating exosomal lncRNAs ENST00000556899.1 and ENST00000575985.1 yielded the area under the curve values of 0.661 and 0.751 for AMI, respectively. Moreover, ENST00000575985.1 showed more significant relationship with clinical parameters, including inflammatory biomarkers, prognostic indicators and myocardial damage markers. Multivariate logistic model exhibited positive association of ENST00000575985.1 with the risk of heart failure in AMI patients. In summary, our data demonstrated that circulating exosomal lncRNAs ENST00000556899.1 and ENST00000575985.1 are elevated in patients with AMI, functioning as potential biomarkers for predicting the prognosis of pateints with AMI.

Biomarker Organization in Circulating Extracellular Vesicles: New Applications in Detecting Neurodegenerative Diseases

Neurodegenerative diseases are heterogeneous disorders characterized by a progressive loss of function and/or death of nerve cells, leading to severe cognitive and functional decline. Due to the complex pathology, early detection and intervention are critical to the development of successful treatments; however, current diagnostic approaches are limited to subjective, late-stage clinical findings. Extracellular vesicles (EVs) have recently emerged as a promising circulating biomarker for neurodegenerative diseases. Actively released by diverse cells, EVs are nanoscale membrane vesicles. They abound in blood, readily cross the blood-brain barrier, and carry diverse molecular cargoes in different organizational states: these molecular cargoes are inherited from the parent cells or bound to the EV membrane through surface associations. Specifically, EVs have been found to be associated with several important pathogenic proteins of neurodegenerative diseases, and their involvement could alter disease progression. This article provides an overview of EVs as circulating biomarkers of neurodegenerative diseases and introduces new technological advances to characterize the biophysical properties of EV-associated biomarkers for accurate, blood-based detection of neurodegenerative diseases.