Exosome Secretion - More Than Simple Waste Disposal? Implications for Physiology, Diagnostics and Therapeutics

Neural stem cell-derived exosomes and regeneration: cell-free therapeutic strategies for traumatic brain injury

Regenerative repair of the brain after traumatic brain injury (TBI) remains an extensive clinical challenge, inspiring intensified interest in therapeutic approaches to explore superior repair strategies. Exosome therapy is another research hotspot following stem cell alternative therapy. Prior research verified that exosomes produced by neural stem cells can participate in the physiological and pathological changes associated with TBI and have potential neuroregulatory and repair functions. In comparison with their parental stem cells, exosomes have superior stability and immune tolerance and lower tumorigenic risk. In addition, they can readily penetrate the blood‒brain barrier, which makes their treatment efficiency superior to that of transplanted stem cells. Exosomes secreted by neural stem cells present a promising strategy for the development of novel regenerative therapies. Their tissue regeneration and immunomodulatory potential have made them encouraging candidates for TBI repair. The present review addresses the challenges, applications and potential mechanisms of neural stem cell exosomes in regenerating damaged brains.

Application of stem cells in regeneration medicine

Regeneration is a complex process affected by many elements independent or combined, including inflammation, proliferation, and tissue remodeling. Stem cells is a class of primitive cells with the potentiality of differentiation, regenerate with self-replication, multidirectional differentiation, and immunomodulatory functions. Stem cells and their cytokines not only inextricably linked to the regeneration of ectodermal and skin tissues, but also can be used for the treatment of a variety of chronic wounds. Stem cells can produce exosomes in a paracrine manner. Stem cell exosomes play an important role in tissue regeneration, repair, and accelerated wound healing, the biological properties of which are similar with stem cells, while stem cell exosomes are safer and more effective. Skin and bone tissues are critical organs in the body, which are essential for sustaining life activities. The weak repairing ability leads a pronounced impact on the quality of life of patients, which could be alleviated by stem cell exosomes treatment. However, there are obstacles that stem cells and stem cells exosomes trough skin for improved bioavailability. This paper summarizes the applications and mechanisms of stem cells and stem cells exosomes for skin and bone healing. We also propose new ways of utilizing stem cells and their exosomes through different nanoformulations, liposomes and nanoliposomes, polymer micelles, microspheres, hydrogels, and scaffold microneedles, to improve their use in tissue healing and regeneration.

Protocatechuic acid boosts continual efferocytosis in macrophages by derepressing KLF4 to transcriptionally activate MerTK

Macrophages clear apoptotic cells through a process called continual efferocytosis. We found that protocatechuic acid (PCA), a polyphenolic compound abundant in fruits and vegetables, increased the continual efferocytic capacity of macrophages and inhibited the progression of advanced atherosclerosis. PCA reduced the intracellular amounts of microRNA-10b (miR-10b) by promoting its secretion in extracellular vesicles, which led to an increase in the abundance of the miR-10b target Krüppel-like factor 4 (KLF4). In turn, KLF4 transcriptionally induced the gene encoding Mer proto-oncogene tyrosine kinase (MerTK), an efferocytic receptor for the recognition of apoptotic cells, resulting in increased continual efferocytic capacity. However, in naive macrophages, the PCA-induced secretion of miR-10b did not affect KLF4 and MerTK protein abundance or efferocytic capacity. In mice, oral administration of PCA increased continual efferocytosis in macrophages residing in the peritoneal cavities, thymi, and advanced atherosclerotic plaques through the miR-10b-KLF4-MerTK pathway. In addition, pharmacological inhibition of miR-10b with antagomiR-10b also increased the efferocytic capacity of efferocytic but not naive macrophages in vitro and in vivo. Together, these data describe a pathway that promotes continual efferocytosis in macrophages through miR-10b secretion and a KLF4-dependent increase in MerTK abundance, which can be activated by dietary PCA and which has implications for understanding the regulation of continual efferocytosis in macrophages.

Exosomes from bacteria (Streptococcus parauberis) challenged olive flounder (Paralichthys olivaceus): Isolation, molecular characterization, wound healing, and regeneration activities

Exosomes are a group of extracellular vesicles carrying membrane proteins, lipids, RNAs, and, cytosolic proteins, which play key role in intercellular communication and homeostasis. This study describes the isolation, physicochemical, morphological and molecular characterization, toxicity, wound healing, and regeneration properties of plasma derived exosomes from naive (phosphate-buffered saline [PBS]-injected; PBS-Exo) and Streptococcus parauberis-challenged (Sp-Exo) olive flounder (Paralichthys olivaceus). The average diameters of PBS-Exo and Sp-Exo were 120.5 ± 6.1 and 113.1 ± 9.3 nm, respectively, and they presented unique cup shape morphologies. Both exosomes exhibited classical tetraspanin surface markers (CD81, CD9, and CD63) and were enriched with acetylcholinesterase. High-throughput miRNA profiling revealed differentially expressed miRNAs (log₂ fold change ≥1; P < 0.05), including 14 known and 22 novel miRNAs, in Sp-Exo. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that the target genes of the miRNAs contribute towards various physiological and immunological functions, including wound healing and fin regeneration. Sp-Exo exhibited a rapid wound healing (cell migration) capacity in human fibroblast cells, and its mRNA and protein expression patterns corroborated its activity. Higher larval fin regeneration was more prevalent in Sp-Exo than in PBS-Exo, which further confirmed its functional significance. Our study provides the first basic physiochemical, morphometric, molecular (miRNA profiling), and wound healing evidences of Sp-Exo in olive flounder and highlights important miRNA cargoes in exosomes that may be potential therapeutic candidates in wound healing.

Exosomes and ultrasound: The future of theranostic applications

Biomaterials and pertaining formulations have been very successful in various diagnostic and therapeutic applications because of its ability to overcome pharmacological limitations. Some of them have gained significant focus in the recent decade for their theranostic properties. Exosomes can be grouped as biomaterials, since they consist of various biological micro/macromolecules and possess all the properties of a stable biomaterial with size in nano range. Significant research has gone into isolation and exploitation of exosomes as potential theranostic agent. However, the limitations in terms of yield, efficacy, and target specificity are continuously being addressed. On the other hand, several nano/microformulations are responsive to physical or chemical alterations and were successfully stimulated by tweaking the physical characteristics of the surrounding environment they are in. Some of them are termed as photodynamic, sonodynamic or thermodynamic therapeutic systems. In this regard, ultrasound and acoustic systems were extensively studied for its ability towards altering the properties of the systems to which they were applied on. In this review, we have detailed about the diagnostic and therapeutic applications of exosomes and ultrasound separately, consisting of their conventional applications, drawbacks, and developments for addressing the challenges. The information were categorized into various sections that provide complete overview of the isolation strategies and theranostic applications of exosomes in various diseases. Then the ultrasound-based disease diagnosis and therapy were elaborated, with special interest towards the use of ultrasound in enhancing the efficacy of nanomedicines and nanodrug delivery systems, Finally, we discussed about the ability of ultrasound in enhancing the diagnostic and therapeutic properties of exosomes, which could be the future of theranostics.

Extracellular Vesicles Derived From Ex Vivo Expanded Regulatory T Cells Modulate In Vitro and In Vivo Inflammation

Extracellular vehicles (EVs) are efficient biomarkers of disease and participate in disease pathogenesis; however, their use as clinical therapies to modify disease outcomes remains to be determined. Cell-based immune therapies, including regulatory T cells (Tregs), are currently being clinically evaluated for their usefulness in suppressing pro-inflammatory processes. The present study demonstrates that ex vivo expanded Tregs generate a large pool of EVs that express Treg-associated markers and suppress pro-inflammatory responses in vitro and in vivo. Intravenous injection of Treg EVs into an LPS-induced mouse model of inflammation reduced peripheral pro-inflammatory transcripts and increased anti-inflammatory transcripts in myeloid cells as well as Tregs. Intranasal administration of enriched Treg EVs in this model also reduced pro-inflammatory transcripts and the associated neuroinflammatory responses. In a mouse model of amyotrophic lateral sclerosis, intranasal administration of enriched Treg EVs slowed disease progression, increased survival, and modulated inflammation within the diseased spinal cord. These findings support the therapeutic potential of expanded Treg EVs to suppress pro-inflammatory responses in human disease.

Hypoxia Induced Changes of Exosome Cargo and Subsequent Biological Effects

Exosomes are small extracellular vesicles that are secreted by almost all types of cells and exist in almost all extracellular spaces. As an important mediator of intercellular communication, exosomes encapsulate the miRNA, lncRNA, cirRNA, mRNA, cytokine, enzyme, lipid, and other components from the cytoplasm into its closed single membrane structure and transfer them to recipient units in an autocrine, paracrine, or endocrine manner. Hypoxia is a state of low oxygen tension and is involved in many pathological processes. Hypoxia influences the size, quantity, and expression of exosome cargos. Exosomes derived from hypoxic tumor cells transfer genetics, proteins, and lipids to the recipient units to exert pleiotropic effects. Different donor cells produce different cargo contents, target different recipient units and lead to different biological effects. Hypoxic exosomes derived from tumor cells uptaken by normoxic tumor cells lead to promoted proliferation, migration, and invasion; uptaken by extracellular space or liver lead to promoted metastasis; uptaken by endothelial cells lead to promoted angiogenesis; uptaken by immune cells lead to promoted macrophage polarization and changed tumor immune microenvironment. In addition to various types of tumors, hypoxic exosomes also participate in the development of diseases in the cardiovascular system, neuron system, respiratory system, hematology system, endocrine system, urinary system, reproduction system, and skeletomuscular system. Understanding the special characteristics of hypoxic exosomes provide new insight into elaborating the pathogenesis of hypoxia related disease. This review summarizes hypoxia induced cargo changes and the biological effects of hypoxic exosomes in tumors and non-malignant diseases in different systems.

Internalization and trafficking of CSPG-bound recombinant VAR2CSA lectins in cancer cells

Proteoglycans are proteins that are modified with glycosaminoglycan chains. Chondroitin sulfate proteoglycans (CSPGs) are currently being exploited as targets for drug-delivery in various cancer indications, however basic knowledge on how CSPGs are internalized in tumor cells is lacking. In this study we took advantage of a recombinant CSPG-binding lectin VAR2CSA (rVAR2) to track internalization and cell fate of CSPGs in tumor cells. We found that rVAR2 is internalized into cancer cells via multiple internalization mechanisms after initial docking on cell surface CSPGs. Regardless of the internalization pathway used, CSPG-bound rVAR2 was trafficked to the early endosomes in an energy-dependent manner but not further transported to the lysosomal compartment. Instead, internalized CSPG-bound rVAR2 proteins were secreted with exosomes to the extracellular environment in a strictly chondroitin sulfate-dependent manner. In summary, our work describes the cell fate of rVAR2 proteins in tumor cells after initial binding to CSPGs, which can be further used to inform development of rVAR2-drug conjugates and other therapeutics targeting CSPGs.

The Function of Astrocyte Mediated Extracellular Vesicles in Central Nervous System Diseases

Astrocyte activation plays an important role during disease-induced inflammatory response in the brain. Exosomes in the brain could be released from bone marrow (BM)-derived stem cells, neuro stem cells (NSC), mesenchymal stem cells (MSC), etc. We summarized that exosomes release and transport signaling to the target cells, and then produce function. Furthermore, we discussed the pathological interactions between astrocytes and other brain cells, which are related to brain diseases such as stroke, Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) disease, multiple sclerosis (MS), psychiatric, traumatic brain injury (TBI), etc. We provide up-to-date, comprehensive and valuable information on the involvement of exosomes in brain diseases, which is beneficial for basic researchers and clinical physicians.

Advances in extracellular vesicles analysis

Extracellular vesicles (EVs) play an important role in intercellular communication in normal cellular process and pathological conditions by facilitating the transport of cellular content from one cell to another. EVs as conveyors of various biological molecules with their ability to redirect effects on a target cell physiological function in cell type-specific manner makes EVs an excellent candidate for drug delivery vehicle in disease therapy. Moreover, unique characteristics and contents of EVs which differ depends on cellular origin and physiological state make them a valuable source of diagnostic biomarker. Herein, we review the current progress in extracellular vesicle (EV) analysis, its transition from biomedical research to advancing therapy, and recent pioneered approaches to characterize and quantify EVs' subclasses with an emphasis on the integration of advanced technologies for both qualitative and quantitative analysis of EVs in different clinical tissue/body fluid samples.

RPE Cells Engulf Microvesicles Secreted by Degenerating Rod Photoreceptors

Rhodopsin is mislocalized to the inner segment plasma membrane (IS PM) in various blinding disorders including autosomal-dominant retinitis pigmentosa caused by class I rhodopsin mutations. In these disorders, rhodopsin-laden microvesicles are secreted into the extracellular milieu by afflicted photoreceptor cells. Using a Xenopus laevis model expressing class I mutant rhodopsin or Na+/K+-ATPase (NKA) fused to Dendra2, we fluorescently labeled the microvesicles and found retinal pigment epithelial (RPE) cells are capable of engulfing microvesicles containing rhodopsin. A unique sorting mechanism allows class I mutant rhodopsin, but not NKA, to be packaged into the microvesicles. Under normal physiological conditions, NKA is not shed as microvesicles to the extracellular space, but is degraded intracellularly. Those studies provide novel insights into protein homeostasis in the photoreceptor IS PM.

The Course of Circulating Small Extracellular Vesicles in Patients Undergoing Surgical Aortic Valve Replacement

In the last years, increasing efforts have been devoted to investigating the role of small extracellular vesicles (sEVs) in cardiovascular diseases. These nano-sized particles (30-150 nm), secreted by different cell types, contain signalling molecules that enable participation in intercellular communication processes. In this study, we examined the course of circulating sEVs in patients undergoing surgical aortic valve replacement (SAVR) and correlated them with echocardiographic and standard blood parameters. Peripheral blood samples were collected from 135 patients undergoing SAVR preoperatively and at three follow-up points. Circulating sEVs were precipitated using Exoquick™ exosome isolation reagent and analyzed by nanoparticle tracking analysis (NTA). Our findings indicate that no more than 7 days after SAVR, there was a marked increase of circulating sEVs before returning to initial values after 3 months. Further, shear stress is not a trigger for the formation and release of circulating sEVs. Moreover, we pointed out a correlation between circulating sEVs and erythrocytes as well as LDH and creatinine levels in peripheral blood. Finally, all patients with a moderate prosthesis-patient mismatch as well as with an impaired left ventricular mass regression had lower levels of circulating sEVs 3 months after SAVR compared to their respective status before surgery. We conclude that in patients with aortic valve stenosis (AVS), sEVs may play an important part in mediating cell-cell communication and SAVR may have a crucial and lasting impact on their circulating levels. Besides, lower levels of sEVs portend to be associated with inferior recovery after major surgical interventions. The additional use of circulating sEVs beyond echocardiographic and laboratory parameters could have a prognostic value to estimate adverse outcomes in patients undergoing SAVR.

Proteomic Analysis on Exosomes Derived from Patients' Sera Infected with Echinococcus granulosus

Cystic echinococcosis (CE), a zoonotic disease caused by Echinococcus granulosus at the larval stage, predominantly develops in the liver and lungs of intermediate hosts and eventually results in organ malfunction or even death. The interaction between E. granulosus and human body is incompletely understood. Exosomes are nanosized particles ubiquitously present in human body fluids. Exosomes carry biomolecules that facilitate communication between cells. To the best of our knowledge, the role of exosomes in patients with CE is not reported. Here, we isolated exosomes from the sera of patients with CE (CE-exo) and healthy donors and subjected them to liquid chromatography-tandem mass spectrometry analysis. Proteomic analysis identified 49 proteins specifically expressed in CE-exo, including 4 proteins of parasitic origin. The most valuable parasitic proteins included tubulin alpha-1C chain and histone H4. And 8 proteins were differentially regulated in CE-exo (fold change>1.5), as analyzed with bioinformatic methods such as annotation and functional enrichment analyses. These findings may improve our understanding about the interaction between E. granulosus and human body, and may contribute to the diagnosis and prevention of CE.

Identification of serum exosomal microRNAs in acute spinal cord injured rats

It is important to find specific and easily detectable diagnostic markers in acute stage of spinal cord injury for guiding treatment and estimating prognosis. Although, microRNAs are attractive biomarkers, there is still no uniform standard for clinical evaluation of spinal cord injury based on “free circulation” miRNA spectrum. The reason may be that miRNA analysis from biological fluids is influenced by many pre-analysis variables. Exosome miRNAs are widely distributed in body fluids and have many advantages comparing with free miRNAs. The specific miRNAs in the central nervous system can be transported to the peripheral circulation and concentrated in exosomes. Therefore, we hypothesized that there might be some physiological changes associated with spinal cord injury in serum exosomal miRNAs. Using next-generation sequencing, miRNA profiles in serum exosomes of sham and acute spinal cord injury rats were analyzed, and integrative bioinformatics were used to analyze the function and regulation of putative target genes. The results showed that acute spinal cord injury can lead to changes in miRNA expression in the circulating exosomes. The changed miRNAs and their associated pathways may explain the pathology of acute spinal cord injury. More importantly, we determined serum exosomal miR-125b-5p, miR-152-3p, and miR-130a-3p are specific and easily detectable diagnostic markers in acute spinal cord injury. More interestingly, we also found some valuable known and novel miRNAs. Further bioinformatics analysis and functional research will be of great help to make clear their role in the pathological process of spinal cord injury and judging whether they can be used as diagnostic markers.

Impact statement

This research hypothesized that there might be some physiological changes associated with SCI in serum exosomal miRNAs. Using next-generation sequencing, miRNA profiles in serum exosomes of sham and acute SCI rats were analyzed, and integrative bioinformatics were used to analyze the function and regulation of putative target genes. The results showed that acute SCI can lead to changes in miRNA expression in the circulating exosomes. The changed miRNAs and their associated pathways may explain the pathology of acute SCI. More importantly, we determined serum exosomal miR-125b-5p, miR-152-3p, and miR-130a-3p are specific and easily detectable diagnostic markers in acute SCI.

Interaction with hyaluronan matrix and miRNA cargo as contributors for in vitro potential of mesenchymal stem cell-derived extracellular vesicles in a model of human osteoarthritic synoviocytes

BACKGROUND

Osteoarthritis (OA) is the most prevalent joint disease, and to date, no options for effective tissue repair and restoration are available. With the aim of developing new therapies, the impact of mesenchymal stem cells (MSCs) has been explored, and the efficacy of MSCs started to be deciphered. A strong paracrine capacity relying on both secreted and vesicle-embedded (EVs) protein or nucleic acid-based factors has been proposed as the principal mechanism that contributes to tissue repair. This work investigated the mechanism of internalization of extracellular vesicles (EVs) released by adipose-derived MSCs (ASCs) and the role of shuttled miRNAs in the restoration of homeostasis in an in vitro model of human fibroblast-like synoviocytes (FLSs) from OA patients.

METHODS

ASC-EVs were isolated by differential centrifugation and validated by flow cytometry and nanoparticle tracking analysis. ASC-EVs with increased hyaluronan (HA) receptor CD44 levels were obtained culturing ASCs on HA-coated plastic surfaces. OA FLSs with intact or digested HA matrix were co-cultured with fluorescent ASC-EVs, and incorporation scored by flow cytometry and ELISA. ASC-EV complete miRNome was deciphered by high-throughput screening. In inflamed OA FLSs, genes and pathways potentially regulated by ASC-EV miRNA were predicted by bioinformatics. OA FLSs stimulated with IL-1β at physiological levels (25 pg/mL) were treated with ASC-EVs, and expression of inflammation and OA-related genes was measured by qRT-PCR over a 10-day time frame with modulated candidates verified by ELISA.

RESULTS

The data showed that HA is involved in ASC-EV internalization in FLSs. Indeed, both removal of HA matrix presence on FLSs and modulation of CD44 levels on EVs affected their recruitment. Bioinformatics analysis of EV-embedded miRNAs showed their ability to potentially regulate the main pathways strictly associated with synovial inflammation in OA. In this frame, ASC-EVs reduced the expression of pro-inflammatory cytokines and chemokines in a chronic model of FLS inflammation.

CONCLUSIONS

Given their ability to affect FLS behavior in a model of chronic inflammation through direct interaction with HA matrix and miRNA release, ASC-EVs confirm their role as a novel therapeutic option for osteoarthritic joints.

Proteomic analysis of synovial fluid: current and potential uses to improve clinical outcomes

INTRODUCTION

Synovial fluid (SF) is in close proximity to tissues which are primarily altered during articular disease and has significant potential to better understand the underlying disease pathogeneses of articular pathologies and biomarker discovery. Although development of mass spectrometry-based methods has allowed faster and higher sensitivity techniques, interrogation of the SF proteome has been hindered by its large protein concentration dynamic range, impeding quantification of lower abundant proteins. Areas covered: Recent advances have developed methodologies to reduce the large protein concentration dynamic range of SF and subsequently allow deeper exploration of the SF proteome. This review concentrates on methods to overcome biofluid complexity, mass spectrometry proteomics methodologies, extracellular vesicles proteomics and the application of advances within the field in clinical disease, including osteoarthritis, rheumatoid arthritis, spondyloarthritis and juvenile arthritis. A narrative review was conducted with articles searched using PubMed, 1991-2018. Expert opinion: The SF proteomics field faces various challenges, including the requirement for rigorous and standardised methods of sample collection/storage, the sensitivity and specificity of proteomic assays, techniques to combat the large protein concentration dynamic range and comprehensive data analysis to reduce falsely identified markers. Additionally, there are challenges in developing multi 'omic' integration techniques, with computational integration enhancing analysis.

Monitoring wastewater for assessing community health: Sewage Chemical-Information Mining (SCIM)

Timely assessment of the aggregate health of small-area human populations is essential for guiding the optimal investment of resources needed for preventing, avoiding, controlling, or mitigating human exposure risks, as well as for maintaining or promoting health. Seeking those interventions yielding the greatest benefit with respect to the allocation of resources is critical for making progress toward community sustainability, reducing health disparities, promoting social justice, and maintaining or improving collective health and well-being. More informative, faster, and less-costly approaches are needed for guiding investigation of cause-effect linkages involving communities and stressors originating from both the built and natural environments. One such emerging approach involves the continuous monitoring of sewage for chemicals that serve as indicators of the collective status of human health (or stress/disease) or any other facet relevant to gauging time-trends in community-wide health. This nascent approach can be referred to as Sewage Chemical-Information Mining (SCIM) and involves the monitoring of sewage for the information that resides in the form of natural and anthropogenic chemicals that enter sewers as a result of the everyday actions, activities, and behaviors of humans. Of particular interest is a specific embodiment of SCIM that would entail the targeted monitoring of a broad suite of endogenous biomarkers of key physiologic processes (as opposed to xenobiotics or their metabolites). This application is termed BioSCIM-an approach roughly analogous to a hypothetical community-wide collective clinical urinalysis, or to a hypothetical en masse human biomonitoring program. BioSCIM would be used for gauging the status or time-trends in community-wide health on a continuous basis. This paper presents an update on the progress made with the development of the BioSCIM concept in the period of time since its original publication in 2012, as well as the next steps required for its continued development.