Exosomal miRNAs: Biological Properties and Therapeutic Potential

MicroRNAs (miRNAs), small non-coding regulatory RNAs that regulate gene expression at the post-transcriptional level, are master regulators of a wide array of cellular processes. Altered miRNA expression could be a determinant of disease development and/or progression and manipulation of miRNA expression represents a potential avenue of therapy. Exosomes are cell-derived extracellular vesicles that promote cell–cell communication and immunoregulatory functions. These “bioactive vesicles” shuttle various molecules, including miRNAs, to recipient cells. Inappropriate release of miRNAs from exosomes may cause significant alterations in biological pathways that affect disease development, supporting the concept that miRNA-containing exosomes could serve as targeted therapies for particular diseases. This review briefly summarizes recent advances in the biology, function, and therapeutic potential of exosomal miRNAs

Engineered Extracellular Vesicles Loaded With miR-124 Attenuate Cocaine-Mediated Activation of Microglia

MicroRNA-124 (miR-124), a brain-enriched microRNA, is known to regulate microglial quiescence. Psychostimulants such as cocaine have been shown to activate microglia by downregulating miR-124, leading, in turn, to neuroinflammation. We thus rationalized that restoring the levels of miR-124 could function as a potential therapeutic approach for cocaine-mediated neuroinflammation. Delivering miRNA based drugs in the brain that are effective and less invasive, however, remains a major challenge in the field. Herein we engineered extracellular vesicles (EVs) and loaded them with miR-124 for delivery in the brain. Approach involved co-transfection of mouse dendritic cells with Dicer siRNA and RVG-Lamp2b plasmid to deplete endogenous miRNAs and for targeting the CNS, respectively. Mouse primary microglia (mPm) were treated with purified engineered EVs loaded with either Cy5-miR-124 or Cy5-scrambled miRNA oligos in the presence or absence of cocaine followed by assessing EV uptake and microglial activation. In vivo studies involved pretreating mice intranasally with engineered EVs followed by cocaine injection (20 mg/kg, i.p.). mPm exposed to EV-miR-124 exhibited reduced expression of miR-124 targets - TLR4 and STAT3 as well as ERK-1/2 and Iba1. In cocaine administered mice, EV-Cy5-miR-124 delivered intranasally were detected in the CNS and significantly reduced the expression of inflammatory markers TLR4, MYD88, STAT3 and NF-kB p65 while also downregulating the microglial activation marker, Iba1. Collectively, these findings suggest that engineered EVs can deliver miR-124 into the CNS, thereby alleviating cocaine-mediated microglial activation. Manipulating EV miRNAs can thus be envisioned as an efficient means for delivery of RNA-based therapeutics to target organs

Engineering Neurotoxin-Functionalized Exosomes for Targeted Delivery to the Peripheral Nervous System

The administration of therapeutics to peripheral nerve tissue is challenging due to the complexities of peripheral neuroanatomy and the limitations imposed by the blood–nerve barrier (BNB). Therefore, there is a pressing need to enhance delivery effectiveness and implement targeted delivery methods. Recently, erythrocyte-derived exosomes (Exos) have gained widespread attention as biocompatible vehicles for therapeutics in clinical applications. However, engineering targeted Exos for the peripheral nervous system (PNS) is still challenging. This study aims to develop a targeted Exo delivery system specifically designed for presynaptic terminals of peripheral nerve tissue. The clostridium neurotoxin, tetanus toxin-C fragment (TTC), was tethered to the surface of red blood cell (RBC)-derived Exos via a facile and efficient bio-orthogonal click chemistry method without a catalyst. Additionally, Cyanine5 (Cy5), a reactive fluorescent tag, was also conjugated to track Exo movement in both in vitro and in vivo models. Subsequently, Neuro-2a, a mouse neuronal cell line, was treated with dye-labeled Exos with/without TTC in vitro, and the results indicated that TTC-Exos exhibited more efficient accumulation along the soma and axonal circumference, compared to their unmodified counterparts. Further investigation, using a mouse model, revealed that within 72 h of intramuscular administration, engineered TTC-Exos were successfully transported into the neuromuscular junction and sciatic nerve tissues. These results indicated that TTC played a crucial role in the Exo delivery system, improving the affinity to peripheral nerves. These promising results underscore the potential of using targeted Exo carriers to deliver therapeutics for treating peripheral neuropathies

MiR-9 promotes microglial activation by targeting MCPIP1

Microglia participate in innate inflammatory responses within the central nervous system. The highly conserved microRNA-9 (miR-9) plays critical roles in neurogenesis as well as axonal extension. Its role in microglial inflammatory responses, however, remains poorly understood. Here we identify a unique role of miR-9 in mediating the microglial inflammatory response via distinct signalling pathways. MiR-9-mediated regulation of cellular activation involved downregulated expression of the target protein, monocyte chemotactic protein-induced protein 1 (MCPIP1) that is crucial for controlling inflammation. Results indicate that miR-9-mediated cellular activation involved signalling via the NF-kappa B pathway, but not the beta-catenin pathway

Neuronal-Derived Extracellular Vesicles are Enriched in the Brain and Serum of HIV-1 Transgenic Rats

Despite the efficacy of combination antiretroviral therapy (ART) in controlling human immunodeficiency virus (HIV-1) replication, cytotoxic viral proteins such as HIV-1 transactivator of transcription (Tat) persist in tissues such as the brain. Although HIV-1 does not infect neuronal cells, it is susceptible to viral Tat protein-mediated toxicity, leading to neuroinflammation that underlies HIV-associated neurocognitive disorders (HAND). Given the role of extracellular vesicles (EVs) in both cellular homoeostasis and under pathological conditions, we sought to investigate the alterations in the quantity of neuronal-derived EVs in the brain–as defined by the presence of cell adhesion molecule L1 (L1CAM) and to evaluate the presence of L1CAM+ EVs in the peripheral circulation of HIV-1 transgenic (HIV-1 Tg) rats. The primary goal of this study was to investigate the effect of long-term exposure of HIV-1 viral proteins on the release of neuronal EVs in the brain and their transfer in the systemic compartment. Brain and serum EVs were isolated from both wild type and HIV-1 Tg rats using differential ultracentrifugation with further purification using the Optiprep gradient method. The subpopulation of neuronal EVs was further enriched using immunoprecipitation. The current findings demonstrated increased presence of L1CAM+ neuronal-derived EVs both in the brain and serum of HIV-1 Tg rats. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The International Society for Extracellular Vesicles

Exosomes derived from differentiated human ADMSC with the Schwann cell phenotype modulate peripheral nerve-related cellular functions

Peripheral nerve regeneration remains a significant clinical challenge due to the unsatisfactory functional recovery and public health burden. Exosomes, especially those derived from mesenchymal stem cells (MSCs), are promising as potential cell-free therapeutics and gene therapy vehicles for promoting neural regeneration. In this study, we reported the differentiation of human adipose derived MSCs (hADMSCs) towards the Schwann cell (SC) phenotype (hADMSC-SCs) and then isolated exosomes from hADMSCs with and without differentiation (i.e., dExo vs uExo). We assessed and compared the effects of uExo and dExo on antioxidative, angiogenic, antiinflammatory, and axon growth promoting properties by using various peripheral nerve-related cells. Our results demonstrated that hADMSC-SCs secreted more neurotrophic factors and other growth factors, compared to hADMSCs without differentiation. The dExo isolated from hADMSC-SCs protected rat SCs from oxidative stress and enhanced HUVEC migration and angiogenesis. Compared to uExo, dExo also had improved performances in downregulating pro-inflammatory gene expressions and cytokine secretions and promoting axonal growth of sensory neurons differentiated from human induced pluripotent stem cells. Furthermore, microRNA (miRNA) sequencing analysis revealed that exosomes and their parent cells shared some similarities in their miRNA profiles and exosomes displayed a distinct miRNA signature. Many more miRNAs were identified in dExo than in uExo. Several upregulated miRNAs, like miRNA-132-3p and miRNA-199b-5p, were highly related to neuroprotection, anti-inflammation, and angiogenesis. The dExo can effectively modulate various peripheral nerverelated cellular functions and is promising for cell-free biological therapeutics to enhance neural regeneration

SERS spectroscopy with machine learning to analyze human plasma derived sEVs for coronary artery disease diagnosis and prognosis

Coronary artery disease (CAD) is one of the major cardiovascular diseases and represents the leading causes of global mortality. Developing new diagnostic and therapeutic approaches for CAD treatment are critically needed, especially for an early accurate CAD detection and further timely intervention. In this study, we successfully isolated human plasma small extracellular vesicles (sEVs) from four stages of CAD patients, that is, healthy control, stable plaque, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction. Surface-enhanced Raman scattering (SERS) measurement in conjunction with five machine learning approaches, including Quadratic Discriminant Analysis, Support Vector Machine (SVM), K-Nearest Neighbor, Artificial Neural network, were then applied for the classification and prediction of the sEV samples. Among these five approaches, the overall accuracy of SVM shows the best predication results on both early CAD detection (86.4%) and overall prediction (92.3%). SVM also possesses the highest sensitivity (97.69%) and specificity (95.7%). Thus, our study demonstrates a promising strategy for noninvasive, safe, and high accurate diagnosis for CAD early detection

Astrocyte EV-Induced lincRNA-Cox2 Regulates Microglial Phagocytosis: Implications for Morphine-Mediated Neurodegeneration

Impairment of microglial functions, such as phagocytosis and/ or dysregulation of immune responses, has been implicated as an underlying factor involved in the pathogenesis of various neurodegenerative disorders. Our previous studies have demonstrated that long intergenic noncoding RNA (lincRNA)-Cox2 expression is influenced by nuclear factor kB (NF-kB) signaling and serves as a coactivator of transcriptional factors to regulate the expression of a vast array of immune- related genes in microglia. Extracellular vesicles (EVs) have been recognized as primary facilitators of cell-to-cell communication and cellular regulation. Herein, we show that EVs derived from astrocytes exposed to morphine can be taken up by microglial endosomes, leading, in turn, to activation of Toll-like receptor 7 (TLR7) with a subsequent upregulation of lincRNA-Cox2 expression, ultimately resulting in impaired microglial phagocytosis. This was further validated in vivo, wherein inhibition of microglial phagocytic activity was also observed in brain slices isolated from morphine-administrated mice compared with control mice. Additionally, we also showed that intranasal delivery of EVs containing lincRNA-Cox2 siRNA (small interfering RNA) was able to restore microglial phagocytic activity in mice administered morphine. These findings have ramifications for the development of EV-loaded RNA-based therapeutics for the treatment of various disorders involving functional impairment of microglia

Binding of NF-kappaB p65 subunit to the promoter elements is involved in LPS-induced transactivation of miRNA genes in human biliary epithelial cells

The majority of human miRNA genes is transcribed by polymerase II and can be classified as class II genes similar to protein-coding genes. Whereas current research on miRNAs has focused on the physiological and pathological functions, the molecular mechanisms underlying their transcriptional regulation are largely unknown. We recently reported that lipopolysaccharide (LPS) alters mature miRNA expression profile in human biliary epithelial cells. In this study, we tested the role of transcription factor NF-κB in LPS-induced transcription of select miRNA genes. Of the majority of LPS-up-regulated mature miRNAs in cultured human biliary epithelial cells, potential NF-κB binding sites were identified in the putative promoter elements of their corresponding genes. Inhibition of NF-κB activation by SC-514, an IKK2 inhibitor, blocked LPS-induced up-regulation of a subset of pri-miRNAs, including pri-miR-17-92, pri-miR-125b-1, pri-miR-21, pri-miR-23b-27b-24-1, pri-miR-30b, pri-miR-130a and pri-miR-29a. Moreover, direct binding of NF-κB p65 subunit to the promoter elements of mir-17-92, mir-125b-1, mir-21, mir-23b-27b-24-1, mir-30b and mir-130a genes was identified by chromatin immunoprecipitation analysis and confirmed by the luciferase reporter assay. Thus, a subset of miRNA genes is regulated in human biliary epithelial cells through NF-κB activation induced by LPS, suggesting a role of the NF-κB pathway in the transcriptional regulation of miRNA genes

miR-16 Targets Transcriptional Corepressor SMRT and Modulates NF-kappaB-Regulated Transactivation of Interleukin-8 Gene

The signaling pathways associated with the Toll-like receptors (TLRs) and nuclear factor-kappaB (NF-κB) are essential to pro-inflammatory cytokine and chemokine expression, as well as initiating innate epithelial immune responses. The TLR/NF-κB signaling pathways must be stringently controlled through an intricate network of positive and negative regulatory elements. MicroRNAs (miRNAs) are non-coding small RNAs that regulate the stability and/or translation of protein-coding mRNAs. Herein we report that miR-16 promotes NF-κB-regulated transactivation of the IL-8 gene by suppression of the silencing mediator for retinoid and thyroid hormone receptor (SMRT). LPS stimulation activated miR-16 gene transcription in human monocytes (U937) and biliary epithelial cells (H69) through MAPK-dependent mechanisms. Transfection of cells with the miR-16 precursor promoted LPS-induced production of IL-8, IL-6, and IL-1α, without a significant effect on their RNA stability. Instead, an increase in NF-κB-regulated transactivation of the IL-8 gene was confirmed in cells following transfection of miR-16 precursor. Importantly, miR-16 targeted the 3′-untranslated region of SMRT and caused translational suppression of SMRT. LPS decreased SMRT expression via upregulation of miR-16. Moreover, functional manipulation of SMRT altered NF-κB-regulated transactivation of LPS-induced IL-8 expression. These data suggest that miR-16 targets SMRT and modulates NF-κB-regulated transactivation of the IL-8 gene