Isolation of microglia-derived extracellular vesicles: towards miRNA signatures and neuroprotection

Therapeutic potential of microglia-derived extracellular vesicles in ischemic stroke

Ischemic stroke (IS) is a debilitating neurological disorder with limited treatment options. Extracellular vesicles (EVs) have emerged as crucial lipid bilayer particles derived from various cell types that facilitate intercellular communication and enable the exchange of proteins, lipids, and genetic material. Microglia are resident brain cells that play a crucial role in brain development, maintenance of neuronal networks, and injury repair. They secrete numerous extracellular vesicles in different states. Recent evidence indicates that microglia-derived extracellular vesicles (M-EVs) actively participate in mediating various biological processes, such as neuroprotection and neurorepair, in stroke, making them an excellent therapeutic approach for treating this condition. This review comprehensively summarizes the latest research on M-EVs in stroke and explores their potential as novel therapeutic targets for this disorder. Additionally, it provides an overview of the effects and functions of M-EVs on stroke recovery to facilitate the development of clinically relevant therapies for IS.

Extracellular Vesicles: The Next Generation of Biomarkers and Treatment for Central Nervous System Diseases

It has been widely established that the characterization of extracellular vesicles (EVs), particularly small EVs (sEVs), shed by different cell types into biofluids, helps to identify biomarkers and therapeutic targets in neurological and neurodegenerative diseases. Recent studies are also exploring the efficacy of mesenchymal stem cell-derived extracellular vesicles naturally enriched with therapeutic microRNAs and proteins for treating various diseases. In addition, EVs released by various neural cells play a crucial function in the modulation of signal transmission in the brain in physiological conditions. However, in pathological conditions, such EVs can facilitate the spread of pathological proteins from one brain region to the other. On the other hand, the analysis of EVs in biofluids can identify sensitive biomarkers for diagnosis, prognosis, and disease progression. This review discusses the potential therapeutic use of stem cell-derived EVs in several central nervous system diseases. It lists their differences and similarities and confers various studies exploring EVs as biomarkers. Further advances in EV research in the coming years will likely lead to the routine use of EVs in therapeutic settings.

FGFR3 drives Aβ-induced tau uptake

The amyloid cascade hypothesis suggests that amyloid beta (Aβ) contributes to initiating subsequent tau pathology in Alzheimer's disease (AD). However, the underlying mechanisms through which Aβ contributes to tau uptake and propagation remain poorly understood. Here, we show that preexisting amyloid pathology accelerates the uptake of extracellular tau into neurons. Using quantitative proteomic analysis of endocytic vesicles, we reveal that Aβ induces the internalization of fibroblast growth factor receptor 3 (FGFR3). Extracellular tau binds to the extracellular domain of FGFR3 and is internalized by the FGFR3 ligand, fibroblast growth factor 2 (FGF2). Aβ accelerates FGF2 secretion from neurons, thereby inducing the internalization of tau-attached FGFR3. Knockdown of FGFR3 in the hippocampus reduces tau aggregation by decreasing tau uptake and improving memory function in AD model mice. These data suggest FGFR3 in neurons as a novel tau receptor and a key mediator of Aβ-induced tau uptake in AD.

Effect of General Anesthetic Agents on Microglia

The effects of general anesthetic agents (GAAs) on microglia and their potential neurotoxicity have attracted the attention of neuroscientists. Microglia play important roles in the inflammatory process and in neuromodulation of the central nervous system. Microglia-mediated neuroinflammation is a key mechanism of neurocognitive dysfunction during the perioperative period. Microglial activation by GAAs induces anti-inflammatory and pro-inflammatory effects in microglia, suggesting that GAAs play a dual role in the mechanism of postoperative cognitive dysfunction. Understanding of the mechanisms by which GAAs regulate microglia may help to reduce the incidence of postoperative adverse effects. Here, we review the actions of GAAs on microglia and the consequent changes in microglial function. We summarize clinical and animal studies associating microglia with general anesthesia and describe how GAAs interact with neurons via microglia to further explore the mechanisms of action of GAAs in the nervous system.

Microglia-derived extracellular vesicles in homeostasis and demyelination/remyelination processes

Microglia (MG) play a crucial role as the predominant myeloid cells in the central nervous system and are commonly activated in multiple sclerosis. They perform essential functions under normal conditions, such as actively surveying the surrounding parenchyma, facilitating synaptic remodeling, engulfing dead cells and debris, and protecting the brain against infectious pathogens and harmful self-proteins. Extracellular vesicles (EVs) are diverse structures enclosed by a lipid bilayer that originate from intracellular endocytic trafficking or the plasma membrane. They are released by cells into the extracellular space and can be found in various bodily fluids. EVs have recently emerged as a communication mechanism between cells, enabling the transfer of functional proteins, lipids, different RNA species, and even fragments of DNA from donor cells. MG act as both source and recipient of EVs. Consequently, MG-derived EVs are involved in regulating synapse development and maintaining homeostasis. These EVs also directly influence astrocytes, significantly increasing the release of inflammatory cytokines like IL-1β, IL-6, and TNF-α, resulting in a robust inflammatory response. Furthermore, EVs derived from inflammatory MG have been found to inhibit remyelination, whereas Evs produced by pro-regenerative MG effectively promote myelin repair. This review aims to provide an overview of the current understanding of MG-derived Evs, their impact on neighboring cells, and the cellular microenvironment in normal conditions and pathological states, specifically focusing on demyelination and remyelination processes.

Development of microRNA-based therapeutics for central nervous system diseases

MicroRNA (miRNA)-mediated gene silencing is a method of RNA interference in which a miRNA binds to messenger RNA sequences and regulates target gene expression. MiRNA-based therapeutics have shown promise in treating a variety of central nervous system diseases, as verified by results from diverse preclinical model organisms. Over the last decade, several miRNA-based therapeutics have entered clinical trials for various kinds of diseases, such as tumors, infections, and inherited diseases. However, such clinical trials for central nervous system diseases are scarce, and many central nervous system diseases, including hemorrhagic stroke, ischemic stroke, traumatic brain injury, intractable epilepsy, and Alzheimer's disease, lack effective treatment. Considering its effectiveness for central nervous system diseases in preclinical experiments, microRNA-based intervention may serve as a promising treatment for these kinds of diseases. This paper reviews basic principles and recent progress of miRNA-based therapeutics and summarizes general procedures to develop such therapeutics for treating central nervous system diseases. Then, the current obstacles in drug development are discussed. This review also provides a new perspective on possible solutions to these obstacles in the future.

Current aspects of small extracellular vesicles in pain process and relief

Small extracellular vesicles (sEVs) have been identified as a noteworthy paracrine mechanism of intercellular communication in diagnosing and managing neurological disorders. Current research suggests that sEVs play a pivotal role in the pathological progression of pain, emphasizing their critical function in the pathological progression of pain in acute and chronic pain models. By facilitating the transfer of diverse molecules, such as proteins, nucleic acids, and metabolites, sEVs can modulate pain signaling transmission in both the central and peripheral nervous systems. Furthermore, the unique molecules conveyed by sEVs in pain disorders indicate their potential as diagnostic biomarkers. The application of sEVs derived from mesenchymal stem cells (MSCs) in regenerative pain medicine has emerged as a promising strategy for pain management. Moreover, modified sEVs have garnered considerable attention in the investigation of pathological processes and therapeutic interventions. This review presents a comprehensive overview of the current knowledge regarding the involvement of sEVs in pain pathogenesis and treatment. Nevertheless, additional research is imperative to facilitate their clinical implementation. Schematic diagram of sEVs in the biogenesis, signal transmission, diagnosis, and treatment of pain disorders. Small extracellular vesicles (sEVs) are secreted by multiple cells, loading with various biomolecules, such as miRNAs, transmembrane proteins, and amino acids. They selectively target other cells and regulating pain signal transmission. The composition of sEVs can serve as valuable biomarkers for pain diagnosis. In particular, mesenchymal stem cell-derived sEVs have shown promise as regenerative medicine for managing multiple pain disorders. Furthermore, by modifying the structure or contents of sEVs, they could potentially be used as a potent analgesic method.

Microglial exosomes alleviate intermittent hypoxia-induced cognitive deficits by suppressing NLRP3 inflammasome

Intermittent hypoxia is the best predictor of developing cognitive decline and Alzheimer's disease progression in patients with obstructive sleep apnea. The nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome has been poorly studied as a regulator of neuroinflammation in cognitive impairment caused by intermittent hypoxia. As critical inflammatory cells, exosomes secreted by microglia have been found to affect the spread of pathologic proteins and neuropathology in neurodegenerative diseases. However, the effects of microglial exosomes on neuroinflammation and cognitive outcomes after intermittent hypoxia remain unclear. In this study, the role of miRNAs in microglial exosomes in improving cognitive deficits in mice exposed to intermittent hypoxia was investigated. We demonstrated that miR-146a-5p fluctuated over time in microglial exosomes of mice exposed to intermittent hypoxia for different periods of time, which could regulate neuronal NLRP3 inflammasome and neuroinflammation. In primary neurons, we found that miR-146a-5p regulated mitochondrial reactive oxygen species by targeting HIF1α, thus affecting the NLRP3 inflammasome and secretion of inflammatory factors. Similarly, further studies showed that inhibition of NLRP3 by administering overexpressed miR-146a-5p in microglial exosomes and MCC950 has improved neuroinflammation and cognitive dysfunction in mice after intermittent hypoxia. In conclusion, NLRP3 inflammasome may be a regulatory target for ameliorating cognitive impairment caused by intermittent hypoxia, and microglial exosomal miR-146a-5p may be a promising therapeutic strategy.

A Whole-Course-Repair System Based on Neurogenesis-Angiogenesis Crosstalk and Macrophage Reprogramming Promotes Diabetic Wound Healing

Diabetic wound (DW) therapy is currently a big challenge in medicine and strategies to enhance neurogenesis and angiogenesis have appeared to be a promising direction. However, the current treatments have failed to coordinate neurogenesis and angiogenesis simultaneously, leading to an increased disability rate caused by DWs. Herein, a whole-course-repair system is introduced by a hydrogel to concurrently achieve a mutually supportive cycle of neurogenesis-angiogenesis under a favorable immune-microenvironment. This hydrogel can first be one-step packaged in a syringe for later in situ local injections to cover wounds long-termly for accelerated wound healing via the synergistic effect of magnesium ions (Mg²⁺ ) and engineered small extracellular vesicles (sEVs). The self-healing and bio-adhesive properties of the hydrogel make it an ideal physical barrier for DWs. At the inflammation stage, the formulation can recruit bone marrow-derived mesenchymal stem cells to the wound sites and stimulate them toward neurogenic differentiation, while providing a favorable immune microenvironment via macrophage reprogramming. At the proliferation stage of wound repair, robust angiogenesis occurs by the synergistic effect of the newly differentiated neural cells and the released Mg²⁺ , allowing a regenerative neurogenesis-angiogenesis cycle to take place at the wound site. This whole-course-repair system provides a novel platform for combined DW therapy.

Biomarkers for parkinsonian disorders in CNS-originating EVs: promise and challenges

Extracellular vesicles (EVs), including exosomes, microvesicles, and oncosomes, are nano-sized particles enclosed by a lipid bilayer. EVs are released by virtually all eukaryotic cells and have been shown to contribute to intercellular communication by transporting proteins, lipids, and nucleic acids. In the context of neurodegenerative diseases, EVs may carry toxic, misfolded forms of amyloidogenic proteins and facilitate their spread to recipient cells in the central nervous system (CNS). CNS-originating EVs can cross the blood-brain barrier into the bloodstream and may be found in other body fluids, including saliva, tears, and urine. EVs originating in the CNS represent an attractive source of biomarkers for neurodegenerative diseases, because they contain cell- and cell state-specific biological materials. In recent years, multiple papers have reported the use of this strategy for identification and quantitation of biomarkers for neurodegenerative diseases, including Parkinson's disease and atypical parkinsonian disorders. However, certain technical issues have yet to be standardized, such as the best surface markers for isolation of cell type-specific EVs and validating the cellular origin of the EVs. Here, we review recent research using CNS-originating EVs for biomarker studies, primarily in parkinsonian disorders, highlight technical challenges, and propose strategies for overcoming them.

Transcriptome Analysis Unveils That Exosomes Derived from M1-Polarized Microglia Induce Ferroptosis of Neuronal Cells

Microglia play a vital role in neurodegenerative diseases. However, the effects of microglia-derived exosomes on neuronal cells are poorly understood. This study aimed to explore the role of M1-polarized microglia exosomes in neuronal cells by transcriptome analysis. Exosomes isolated from resting M0-phenotype BV2 (M0-BV2) microglia and M1-polarized BV2 (M1-BV2) microglia were analyzed using high-throughput sequencing of the transcriptome. Differentially expressed genes (DEGs) between the two types of exosomes were identified by analyzing the sequencing data. The biological functions and pathways regulated by the identified DEGs were then identified using bioinformatics analyses. Finally, we evaluated the effects of exosomes on neuronal cells by coculturing M0-BV2 and M1-BV2 exosomes with primary neuronal cells. Enrichment analyses revealed that DEGs were significantly enriched in the ferroptosis pathway (p = 0.0137). M0-BV2 exosomes had no distinct effects on ferroptosis in neuronal cells, whereas M1-BV2 exosomes significantly reduced ferroptosis suppressor proteins (GPX4, SLC7A11, and FTH1) and elevated the levels of intracellular and mitochondrial ferrous iron and lipid peroxidation in neuronal cells. Polarized M1-BV2 microglia exosomes can induce ferroptosis in neuronal cells, thereby aggravating neuronal damage. Taken together, these findings enhance knowledge of the pathogenesis of neurological disorders and suggest potential therapeutic targets against neurodegenerative diseases.

Microglial Extracellular Vesicles as Modulators of Brain Microenvironment in Glioma

Microglial cells represent the resident immune elements of the central nervous system, where they exert constant monitoring and contribute to preserving neuronal activity and function. In the context of glioblastoma (GBM), a common type of tumor originating in the brain, microglial cells deeply modify their phenotype, lose their homeostatic functions, invade the tumoral mass and support the growth and further invasion of the tumoral cells into the surrounding brain parenchyma. These modifications are, at least in part, induced by bidirectional communication among microglial and tumoral cells through the release of soluble molecules and extracellular vesicles (EVs). EVs produced by GBM and microglial cells transfer different kinds of biological information to receiving cells, deeply modifying their phenotype and activity and could represent important diagnostic markers and therapeutic targets. Recent evidence demonstrates that in GBM, microglial-derived EVs contribute to the immune suppression of the tumor microenvironment (TME), thus favoring GBM immune escape. In this review, we report the current knowledge on EV formation, biogenesis, cargo and functions, with a focus on the effects of microglia-derived EVs in GBM. What clearly emerges from this analysis is that we are at the beginning of a full understanding of the complete picture of the biological effects of microglial-derived EVs and that further investigations using multidisciplinary approaches are necessary to validate their use in GBM diagnosis and therapy.

Exosomes as CNS Drug Delivery Tools and Their Applications

Central nervous system (CNS) diseases threaten the health of people all over the world. However, due to the structural and functional particularities of the brain and spinal cord, CNS-targeted drug development is rather challenging. Exosomes are small cellular vesicles with lipid bilayers that can be secreted by almost all cells and play important roles in intercellular communication. The advantages of low immunogenicity, the ability to cross the blood-brain barrier, and the flexibility of drug encapsulation make them stand out among CNS drug delivery tools. Herein, we reviewed the research on exosomes in CNS drug delivery over the past decade and outlined the impact of the drug loading mode, administration route, and engineered modification on CNS targeting. Finally, we highlighted the problems and prospects of exosomes as CNS drug delivery tools.

Multiple roles of neuronal extracellular vesicles in neurological disorders

Neuropathy is a growing public health problem in the aging, adolescent, and sport-playing populations, and the number of individuals at risk of neuropathy is growing; its risks include aging, violence, and conflicts between players. The signal pathways underlying neuronal aging and damage remain incompletely understood and evidence-based treatment for patients with neuropathy is insufficiently delivered; these are two of the reasons that explain why neuropathy is still not completely curable and why the progression of the disease cannot be inhibited. Extracellular vesicles (EVs) shuttling is an important pathway in disease progression. Previous studies have focused on the EVs of cells that support and protect neurons, such as astrocytes and microglia. This review aims to address the role of neuronal EVs by delineating updated mechanisms of neuronal damage and summarizing recent findings on the function of neuronal EVs. Challenges and obstacles in isolating and analyzing neuronal EVs are discussed, with an emphasis on neuron as research object and modification of EVs on translational medicine.

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

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

Small Extracellular Vesicles of M1-BV2 Microglia Induce Neuronal PC12 Cells Apoptosis via the Competing Endogenous Mechanism of CircRNAs

Polarized microglia play a vital role in neurodegenerative diseases. However, the effects of polarized microglia-derived small extracellular vesicles (SEVs) on neuronal cells and the regulatory mechanisms of circular RNAs (circRNAs) in SEVs remain incompletely defined. In the present study, we carried out high-throughput sequencing and differential expression analysis of circRNAs in the SEVs of M0-phenotype BV2 microglia (M0-BV2) and polarized M1-phenotype BV2 microglia (M1-BV2). Hub circRNAs in the SEVs and their functions were screened using multiple bioinformatics methods. We further validated the effects of SEVs on neuronal PC12 cells by co-culturing M0-BV2 SEVs and M1-BV2 SEVs with neuronal PC12 cells. Among the differentially expressed circRNAs, the target mRNAs of six hub circRNAs (circ_0000705, circ_0001313, circ_0000229, circ_0001123, circ_0000621, and circ_0000735) were enriched in apoptosis-related biological processes. Furthermore, western blot and flow cytometry analysis demonstrated that M0-BV2 SEVs had no distinct effect on apoptosis of neuronal PC12 cells, while M1-BV2 SEVs remarkably increased the apoptosis of neuronal PC12 cells. We then constructed the competing endogenous RNA (ceRNA) networks of the six hub circRNAs. Taken together, the results suggest that polarized M1-BV2 microglia can induce apoptosis of neuronal PC12 cells through secreted SEVs, and this regulatory effect may be achieved by the circRNAs circ_0000705, circ_0001313, circ_0000229, circ_0001123, circ_0000621, and circ_0000735 through ceRNAs regulatory networks. These findings provide new potential targets for the treatment of neurodegenerative diseases.

Neurovascular Unit-Derived Extracellular Vesicles: From Their Physiopathological Roles to Their Clinical Applications in Acute Brain Injuries

Extracellular vesicles (EVs) form a heterogeneous group of membrane-enclosed structures secreted by all cell types. EVs export encapsulated materials composed of proteins, lipids, and nucleic acids, making them a key mediator in cell–cell communication. In the context of the neurovascular unit (NVU), a tightly interacting multicellular brain complex, EVs play a role in intercellular communication and in maintaining NVU functionality. In addition, NVU-derived EVs can also impact peripheral tissues by crossing the blood–brain barrier (BBB) to reach the blood stream. As such, EVs have been shown to be involved in the physiopathology of numerous neurological diseases. The presence of NVU-released EVs in the systemic circulation offers an opportunity to discover new diagnostic and prognostic markers for those diseases. This review outlines the most recent studies reporting the role of NVU-derived EVs in physiological and pathological mechanisms of the NVU, focusing on neuroinflammation and neurodegenerative diseases. Then, the clinical application of EVs-containing molecules as biomarkers in acute brain injuries, such as stroke and traumatic brain injuries (TBI), is discussed.

miR-214-3p Deficiency Enhances Caspase-1-Dependent Pyroptosis of Microglia in White Matter Injury

White matter injury (WMI) is the most frequent impairment of neurodevelopment in preterm infants. Here, we report that the caspase-1 inflammasome is abundantly activated in the microglia of WMI mice and results in increased pyroptosis of microglia. Pharmacology inhibition of caspase-1 cleavage alleviated the pathogenesis of WMI mice. The expression of microRNA miR-214-3p was largely reduced in the microglia of WMI mice compared to controls. Compromised expression of miR-214-3p on microglia gives rise to the inflammasome activation and microglial pyroptosis. Treatment with miR-214-3p agomir is sufficient to relieve the white matter lesion and demyelination in WMI mice. miR-214-3p is able to bind to the 3' region of the NLRP-3 inflammasome compartment NEK7, preventing the transcription of NEK7 mRNA. As a result, in WMI mice, the lack of miR-214-3p leads to the accumulation of NEK7 which supports NLRP 3 inflammasome activation, microglial pyroptosis, and white matter pathogenesis.

Cell-Derived Exosomes as Therapeutic Strategies and Exosome-Derived microRNAs as Biomarkers for Traumatic Brain Injury

Traumatic brain injury (TBI) is a complex, life-threatening condition that causes mortality and disability worldwide. No effective treatment has been clinically verified to date. Achieving effective drug delivery across the blood–brain barrier (BBB) presents a major challenge to therapeutic drug development for TBI. Furthermore, the field of TBI biomarkers is rapidly developing to cope with the many aspects of TBI pathology and enhance clinical management of TBI. Exosomes (Exos) are endogenous extracellular vesicles (EVs) containing various biological materials, including lipids, proteins, microRNAs, and other nucleic acids. Compelling evidence exists that Exos, such as stem cell-derived Exos and even neuron or glial cell-derived Exos, are promising TBI treatment strategies because they pass through the BBB and have the potential to deliver molecules to target lesions. Meanwhile, Exos have decreased safety risks from intravenous injection or orthotopic transplantation of viable cells, such as microvascular occlusion or imbalanced growth of transplanted cells. These unique characteristics also create Exos contents, especially Exos-derived microRNAs, as appealing biomarkers in TBI. In this review, we explore the potential impact of cell-derived Exos and exosome-derived microRNAs on the diagnosis, therapy, and prognosis prediction of TBI. The associated challenges and opportunities are also discussed.

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

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

Engineering extracellular vesicles for Alzheimer's disease: An emerging cell-free approach for earlier diagnosis and treatment

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder affecting over five million people globally and has no established cure. Current AD-related treatments only alleviate cognitive and behavioral symptoms and do not address disease onset or progression, underlining the unmet need to create an effective, innovative AD therapeutic. Extracellular vesicles (EVs) have emerged as a new class of nanotherapeutics. These secreted, lipid-bound cellular signaling carriers show promise for potential clinical applications for neurodegenerative diseases like AD. Additionally, analyzing contents and characteristics of patient-derived EVs may address the unmet need for earlier AD diagnostic techniques, informing physicians of altered genetic expression or cellular communications specific to healthy and diseased physiological states. There are numerous recent advances in regenerative medicine using EVs and include bioengineering perspectives to modify EVs, target glial cells in neurodegenerative diseases like AD, and potentially use EVs to diagnose and treat AD earlier. This article is categorized under: Neurological Diseases > Biomedical Engineering Neurological Diseases > Molecular and Cellular Physiology Neurological Diseases > Stem Cells and Development.

[Extracellular vesicles in the central nervous system]

Extracellular Vesicles (EVs) are released by a wide diversity of cells. They contain proteins, RNAs and lipids that will be exchanged between these cells. They represent therefore a major form of intercellular communication in both physiological and pathological conditions. This is particularly relevant in the nervous system where neurons and glial cells form a very dense network where billions of connections are made. In this review, the different roles played by the EVs in a healthy brain to maintain cerebral homeostasis during development, synaptic transmission or axonal myelination will be discussed. In addition, the pathological aspects of EVs presence will also be addressed. In recent years, the EVs have emerged as major players in the spread of neurodegenerative diseases, in neuroinflammation and in tumor development, although they may also be beneficial in some conditions.

Cell-derived extracellular vesicles and membranes for tissue repair

Humans have a limited postinjury regenerative ability. Therefore, cell-derived biomaterials have long been utilized for tissue repair. Cells with multipotent differentiation potential, such as stem cells, have been administered to patients for the treatment of various diseases. Researchers expected that these cells would mediate tissue repair and regeneration through their multipotency. However, increasing evidence has suggested that in most stem cell therapies, the paracrine effect but not cell differentiation or regeneration is the major driving force of tissue repair. Additionally, ethical and safety problems have limited the application of stem cell therapies. Therefore, nonliving cell-derived techniques such as extracellular vesicle (EV) therapy and cell membrane-based therapy to fulfil the unmet demand for tissue repair are important. Nonliving cell-derived biomaterials are safer and more controllable, and their efficacy is easier to enhance through bioengineering approaches. Here, we described the development and evolution from cell therapy to EV therapy and cell membrane-based therapy for tissue repair. Furthermore, the latest advances in nonliving cell-derived therapies empowered by advanced engineering techniques are emphatically reviewed, and their potential and challenges in the future are discussed.

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.

Functionalized nanoparticles with monocyte membranes and rapamycin achieve synergistic chemoimmunotherapy for reperfusion-induced injury in ischemic stroke

BACKGROUND

Ischemic stroke is an acute and severe neurological disease, and reperfusion is an effective way to reverse brain damage after stroke. However, reperfusion causes secondary tissue damage induced by inflammatory responses, called ischemia/reperfusion (I/R) injury. Current therapeutic strategies that control inflammation to treat I/R are less than satisfactory.

RESULTS

We report a kind of shield and sword nano-soldier functionalized nanoparticles (monocyte membranes-coated rapamycin nanoparticles, McM/RNPs) that can reduce inflammation and relieve I/R injury by blocking monocyte infiltration and inhibiting microglia proliferation. The fabricated McM/RNPs can actively target and bind to inflammatory endothelial cells, which inhibit the adhesion of monocytes to the endothelium, thus acting as a shield. Subsequently, McM/RNPs can penetrate the endothelium to reach the injury site, similar to a sword, and release the RAP drug to inhibit the proliferation of inflammatory cells. In a rat I/R injury model, McM/RNPs exhibited improved active homing to I/R injury areas and greatly ameliorated neuroscores and infarct volume. Importantly, in vivo animal studies revealed good safety for McM/RNPs treatment.

CONCLUSION

The results demonstrated that the developed McM/RNPs may serve as an effective and safe nanovehicles for I/R injury therapy.

Extracellular vesicles derived from CD73 modified human umbilical cord mesenchymal stem cells ameliorate inflammation after spinal cord injury

BACKGROUND

Spinal cord injury (SCI) is an inflammatory condition, and excessive adenosine triphosphate (ATP) is released into the extracellular space, which can be catabolized into adenosine by CD73. Extracellular vesicles have been designed as nano drug carriers in many diseases. However, their impacts on delivery of CD73 after SCI are not yet known. We aimed to construct CD73 modified extracellular vesicles and explore the anti-inflammatory effects after SCI.

METHODS

CD73 engineered extracellular vesicles (CD73+ hucMSC-EVs) were firstly established, which were derived from human umbilical cord mesenchymal stem cells (hucMSCs) transduced by lentiviral vectors to upregulate the expression of CD73. Effects of CD73+ hucMSC-EVs on hydrolyzing ATP into adenosine were detected. The polarization of M2/M1 was verified by immunofluorescence. Furthermore, A2aR and A_2bR inhibitors and A2bR knockdown cells were used to investigate the activated adenosine receptor. Biomarkers of microglia and levels of cAMP/PKA were also detected. Repetitively in vivo study, morphology staining, flow cytometry, cytokine analysis, and ELISA assay, were also applied for verifications.

RESULTS

CD73+ hucMSC-EVs reduced concentration of ATP and promoted the level of adenosine. In vitro experiments, CD73+ hucMSC-EVs increased macrophages/microglia M2:M1 polarization, activated adenosine 2b receptor (A2bR), and then promoted cAMP/PKA signaling pathway. In mice using model of thoracic spinal cord contusion injury, CD73+ hucMSC-EVs improved the functional recovery after SCI through decreasing the content of ATP in cerebrospinal fluid and improving the polarization from M1 to M2 phenotype. Thus, the cascaded pro-inflammatory cytokines were downregulated, such as TNF-α, IL-1β, and IL-6, while the anti-inflammatory cytokines were upregulated, such as IL-10 and IL-4.

CONCLUSIONS

CD73+ hucMSC-EVs ameliorated inflammation after spinal cord injury by reducing extracellular ATP, promoting A2bR/cAMP/PKA pathway and M2/M1 polarization. CD73+ hucMSC-EVs might be promising nano drugs for clinical application in SCI therapy.

Neonatal stroke enhances interaction of microglia-derived extracellular vesicles with microglial cells

Microglial cells support brain homeostasis under physiological conditions and modulate brain injury in a context-dependent and brain maturation-dependent manner. Microglial cells protect neonatal brain from acute stroke. While microglial signaling via direct cell-cell interaction and release of variety of molecules is intensely studied, less is known about microglial signaling via release and uptake of extracellular vesicles (EVs). We asked whether neonatal stroke alters release of microglial EVs (MEV) and MEV communication with activated microglia. We pulled down and plated microglia from ischemic-reperfused and contralateral cortex 24 h after transient middle cerebral artery occlusion (tMCAO) in postnatal day 9 mice, isolated and characterized microglia-derived microvesicles (P3-MEV) and exosomes (P4-MEV), and determined uptake of fluorescently labeled P3-MEV and P4-MEV by plated microglia derived from ischemic-reperfused and contralateral cortex. We then examined how reducing EVs release in neonatal brain-by intra-cortical injection of CRISPR-Cas9-Smpd3/KO (Smpd3/KD) to downregulate Smpd3 gene to disrupt neutral sphingomyelinase-2 (N-SMase2)-impacts P3-MEV and P4-MEV release and stroke injury. Both size and protein composition differed between P3-MEV and P4-MEV. tMCAO further altered protein composition of P3-MEV and P4-MEV and significantly, up to 5-fold, increased uptake of both vesicle subtypes by microglia from ischemic-reperfused regions. Under physiological conditions neurons were the predominant cell type expressing N-SMase-2, an enzyme involved in lipid signaling and EVs release. After tMCAO N-SMase-2 expression was diminished in injured neurons but increased in activated microglia/macrophages, leading to overall reduced N-SMase-2 activity. Compared to intracerebral injection of control plasmid, CRISPR-Cas9-Smpd3/Ct, Smpd3/KD injection further reduced N-SMase-2 activity and significantly reduced injury. Smpd3 downregulation decreased MEV release from injured regions, reduced Smpd3/KD-P3-MEV uptake and abolished Smpd3/KD-P4-MEV uptake by microglia from ischemic-reperfused region. Cumulatively, these data demonstrate that microglial cells release both microvesicles and exosomes in naïve neonatal brain, that the state of microglial activation determines both properties of released EVs and their recognition/uptake by microglia in ischemic-reperfused and control regions, suggesting a modulatory role of MEV in neonatal stroke, and that sphingosine/N-SMase-2 signaling contributes both to EVs release and uptake (predominantly P4-MEV) after neonatal stroke.

Microglia extracellular vesicles: focus on molecular composition and biological function

Extracellular vesicles (EVs) are a heterogeneous family of cell-derived lipid bounded vesicles comprising exosomes and microvesicles. They are potentially produced by all types of cells and are used as a cell-to-cell communication method that allows protein, lipid, and genetic material exchange. Microglia cells produce a large number of EVs both in resting and activated conditions, in the latter case changing their production and related biological effects. Several actions of microglia in the central nervous system are ascribed to EVs, but the molecular mechanisms by which each effect occurs are still largely unknown. Conflicting functions have been ascribed to microglia-derived EVs starting from the neuronal support and ending with the propagation of inflammation and neurodegeneration, confirming the crucial role of these organelles in tuning brain homeostasis. Despite the increasing number of studies reported on microglia-EVs, there is also a lot of fragmentation in the knowledge on the mechanism at the basis of their production and modification of their cargo. In this review, a collection of literature data about the surface and cargo proteins and lipids as well as the miRNA content of EVs produced by microglial cells has been reported. A special highlight was given to the works in which the EV molecular composition is linked to a precise biological function.

Advances in microglia cellular models: focus on extracellular vesicle production

Microglia are the major component of the innate immune system in the central nervous system. They promote the maintenance of brain homeostasis as well as support inflammatory processes that are often related to pathological conditions such as neurodegenerative diseases. Depending on the stimulus received, microglia cells dynamically change their phenotype releasing specific soluble factors and largely modify the cargo of their secreted extracellular vesicles (EVs). Despite the mechanisms at the basis of microglia actions have not been completely clarified, the recognized functions exerted by their EVs in patho-physiological conditions represent the proof of the crucial role of these organelles in tuning cell-to-cell communication, promoting either protective or harmful effects. Consistently, in vitro cell models to better elucidate microglia EV production and mechanisms of their release have been increased in the last years. In this review, the main microglial cellular models that have been developed and validated will be described and discussed, with particular focus on those used to produce and derive EVs. The advantages and disadvantages of their use will be evidenced too. Finally, given the wide interest in applying EVs in diagnosis and therapy too, the heterogeneity of available models for producing microglia EVs is here underlined, to prompt a cross-check or comparison among them.

Microglial Extracellular Vesicles as Vehicles for Neurodegeneration Spreading

Microglial cells are the neuroimmune competent cells of the central nervous system. In the adult, microglia are responsible for screening the neuronal parenchyma searching for alterations in homeostasis. Chronic neuroinflammation plays a role in neurodegenerative disease. Indeed, microglia-mediated neuroinflammation is involved in the onset and progression of several disorders in the brain and retina. Microglial cell reactivity occurs in an orchestrated manner and propagates across the neural parenchyma spreading the neuroinflammatory signal from cell to cell. Extracellular vesicles are important vehicles of intercellular communication and act as message carriers across boundaries. Extracellular vesicles can be subdivided in several categories according to their cellular origin (apoptotic bodies, microvesicles and exosomes), each presenting, different but sometimes overlapping functions in cell communication. Mounting evidence suggests a role for extracellular vesicles in regulating microglial cell action. Herein, we explore the role of microglial extracellular vesicles as vehicles for cell communication and the mechanisms that trigger their release. In this review we covered the role of microglial extracellular vesicles, focusing on apoptotic bodies, microvesicles and exosomes, in the context of neurodegeneration and the impact of these vesicles derived from other cells in microglial cell reactivity.

Prospects for the application of Müller glia and their derivatives in retinal regenerative therapies

Neural cell death is the main feature of all retinal degenerative disorders that lead to blindness. Despite therapeutic advances, progression of retinal disease cannot always be prevented, and once neuronal cell damage occurs, visual loss cannot be reversed. Recent research in the stem cell field, and the identification of Müller glia with stem cell characteristics in the human eye, have provided hope for the use of these cells in retinal therapies to restore vision. Müller glial cells, which are the major structural cells of the retina, play a very important role in retinal homeostasis during health and disease. They are responsible for the spontaneous retinal regeneration observed in zebrafish and lower vertebrates during early postnatal life, and despite the presence of Müller glia with stem cell characteristics in the adult mammalian retina, there is no evidence that they promote regeneration in humans. Like many other stem cells and neurons derived from pluripotent stem cells, Müller glia with stem cell potential do not differentiate into retinal neurons or integrate into the retina when transplanted into the vitreous of experimental animals with retinal degeneration. However, despite their lack of integration, grafted Müller glia have been shown to induce partial restoration of visual function in spontaneous or induced experimental models of photoreceptor or retinal ganglion cell damage. This improvement in visual function observed after Müller cell transplantation has been ascribed to the release of neuroprotective factors that promote the repair and survival of damaged neurons. Due to the development and availability of pluripotent stem cell lines for therapeutic uses, derivation of Müller cells from retinal organoids formed by iPSC and ESC has provided more realistic prospects for the application of these cells to retinal therapies. Several opportunities for research in the regenerative field have also been unlocked in recent years due to a better understanding of the genomic and proteomic profiles of the developing and regenerating retina in zebrafish, providing the basis for further studies of the human retina. In addition, the increased interest on the nature and function of cellular organelle release and the characterization of molecular components of exosomes released by Müller glia, may help us to design new approaches that could be applied to the development of more effective treatments for retinal degenerative diseases.

Decreased Level of Exosomal miR-5121 Released from Microglia Suppresses Neurite Outgrowth and Synapse Recovery of Neurons Following Traumatic Brain Injury

Activated microglia can suppress neurite outgrowth and synapse recovery in the acute stage following traumatic brain injury (TBI). However, the underlying mechanism has not been clearly elucidated. Exosomes derived from microglia have been reported to play a critical role in microglia-neuron interaction in healthy and pathological brains. Here, we aimed to investigate the role of microglia-derived exosomes in regulating neurite outgrowth and synapse recovery following TBI. In our study, exosomes derived from microglia were co-cultured with stretch-injured neurons in vitro and intravenously injected into mice that underwent fluid percussion injury (FPI) by tail vein injection in vivo. The results showed that microglia-derived exosomes could be absorbed by neurons in vitro and in vivo. Moreover, exosomes derived from stretch-injured microglia decreased the protein levels of GAP43, PSD-95, GluR1, and Synaptophysin and dendritic complexity in stretch-injured neurons in vitro, and reduced GAP43+ NEUN cell percentage and apical dendritic spine density in the pericontusion region in vivo. Motor coordination was also impaired in mice treated with stretch-injured microglia-derived exosomes after FPI. A microRNA microarray showed that the level of miR-5121 was decreased most greatly in exosomes derived from stretch-injured microglia. Overexpression of miR-5121 in stretch-injured microglia-derived exosomes partly reversed the suppression of neurite outgrowth and synapse recovery of neurons both in vitro and in vivo. Moreover, motor coordination in miR-5121 overexpressed exosomes treated mice was significantly improved after FPI. Following mechanistic study demonstrated that miR-5121 might promote neurite outgrowth and synapse recovery by directly targeting RGMa. In conclusion, our finding revealed a novel exosome-mediated mechanism of microglia-neuron interaction that suppressed neurite outgrowth and synapse recovery of neurons following TBI.

Emerging Roles of Extracellular Vesicles in the Central Nervous System: Physiology, Pathology, and Therapeutic Perspectives

Extracellular vesicles or EVs are secreted by most, if not all, eukaryote cell types and recaptured by neighboring or distant cells. Their cargo, composed of a vast diversity of proteins, lipids, and nucleic acids, supports the EVs' inter-cellular communication. The role of EVs in many cellular processes is now well documented both in physiological and pathological conditions. In this review, we focus on the role of EVs in the central nervous system (CNS) in physiological as well as pathological conditions such as neurodegenerative diseases or brain cancers. We also discuss the future of EVs in clinical research, in particular, their value as biomarkers as well as innovative therapeutic agents. While an increasing number of studies reveal EV research as a promising field, progress in the standardization of protocols and innovation in analysis as well as in research tools is needed to make a breakthrough in our understanding of their impact in the pathophysiology of the brain.

Epigenetics and Communication Mechanisms in Microglia Activation with a View on Technological Approaches

Microglial cells, the immune cells of the central nervous system (CNS), play a crucial role for the proper brain development and function and in CNS homeostasis. While in physiological conditions, microglia continuously check the state of brain parenchyma, in pathological conditions, microglia can show different activated phenotypes: In the early phases, microglia acquire the M2 phenotype, increasing phagocytosis and releasing neurotrophic and neuroprotective factors. In advanced phases, they acquire the M1 phenotype, becoming neurotoxic and contributing to neurodegeneration. Underlying this phenotypic change, there is a switch in the expression of specific microglial genes, in turn modulated by epigenetic changes, such as DNA methylation, histones post-translational modifications and activity of miRNAs. New roles are attributed to microglial cells, including specific communication with neurons, both through direct cell–cell contact and by release of many different molecules, either directly or indirectly, through extracellular vesicles. In this review, recent findings on the bidirectional interaction between neurons and microglia, in both physiological and pathological conditions, are highlighted, with a focus on the complex field of microglia immunomodulation through epigenetic mechanisms and/or released factors. In addition, advanced technologies used to study these mechanisms, such as microfluidic, 3D culture and in vivo imaging, are presented.

Inhibition of PDE1-B by Vinpocetine Regulates Microglial Exosomes and Polarization Through Enhancing Autophagic Flux for Neuroprotection Against Ischemic Stroke

Exosomes contribute to cell–cell communications. Emerging evidence has shown that microglial exosomes may play crucial role in regulation of neuronal functions under ischemic conditions. However, the underlying mechanisms of microglia-derived exosome biosynthesis are largely unknown. Herein, we reported that the microglial PDE1-B expression was progressively elevated in the peri-infarct region after focal middle cerebral artery occlusion. By an oxygen-glucose-deprivation (OGD) ischemic model in cells, we found that inhibition of PDE1-B by vinpocetine in the microglial cells promoted M2 and inhibited M1 phenotype. In addition, knockdown or inhibition of PDE1-B significantly enhanced the autophagic flux in BV2 cells, and vinpocetine-mediated suppression of M1 phenotype was dependent on autophagy in ischemic conditions. Co-culture of BV2 cells and neurons revealed that vinpocetine-treated BV2 cells alleviated OGD-induced neuronal damage, and treatment of BV2 cells with 3-MA abolished the observed effects of vinpocetine. We further demonstrated that ischemia and vinpocetine treatment significantly altered microglial exosome biogenesis and release, which could be taken up by recipient neurons and regulated neuronal damage. Finally, we showed that the isolated exosome per se from conditioned BV2 cells is sufficient to regulate cortical neuronal survival in vivo. Taken together, these results revealed a novel microglia-neuron interaction mediated by microglia-derived exosomes under ischemic conditions. Our findings further suggest that PDE1-B regulates autophagic flux and exosome biogenesis in microglia which plays a crucial role in neuronal survival under cerebral ischemic conditions.

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.

Proteomic examination of the neuroglial secretome: lessons for the clinic

Introduction: Glial cells are closely associated with neurons located throughout the nervous system and regulate neuronal activity and function through various mechanisms including the secretion of proteins and other signaling molecules. Glia-secreted proteins play crucial roles in modulating neuronal function in physiological and pathological conditions. Aberrant activation of glial cells leading to neuroinflammation is a common phenomenon observed in various neurological disorders. Aberrantly activated glial cells secrete proteins in disease-specific manner and can be exploited as a repository for novel biomarker discovery.Areas covered: In this review, we describe the recent advances in proteomic techniques, highlighting the need for their application to the secretomic field. Studies regarding the secretome profile of glial cells published within the last 5 years are discussed in detail. The use of glia-based biomarkers in various neuroinflammatory and neurodegenerative diseases is also discussed.Expert opinion: Precise diagnosis and timely treatment of neurological disorders remains a challenge and glia-focused research to identify specific biomarkers appears to be a promising approach to combat these disorders. Recent technological advancement in proteomic research would open new frontiers for more rigorous analysis of glial secretome variations over time and the discovery/development of novel biomarkers for neurological disorders.

Liquid biopsies for diagnosing and monitoring primary tumors of the central nervous system

Obtaining diagnostic specimens, notably to monitor disease course in cancer patients undergoing therapy, is an emerging area of research, however, with few clinical implications so far in the field of Neuro-oncology. Specifically for patients with primary brain tumors where repeat biosampling from the tumor and clinical decision making based on neuroimaging alone remain challenging, this area may assume a central role. In principle, sampling could focus on blood, cerebrospinal fluid or urine with differential sensitivities and specificities of findings that differ between specific parameters and target molecules. These include protein, mRNA, miRNA, cell-free DNA, either freely circulating or as cargo of extracellular vesicles, as well circulating tumor cells. The most solid biomarkers are those directly reflecting neoplastic disease, e.g., in the case of primary brain tumors isocitrate dehydrogenase mutation or epidermal growth factor receptor variant III. Importantly, the main goals of liquid biopsy marker development are to better understand response to therapy, natural evolution and emergence of resistant clones, rather than obviating the need for surgical interventions which remain to be a mainstay of therapy for the vast majority of primary brain tumors.

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.