Quantifying exosome secretion from single cells reveals a modulatory role for GPCR signaling

LS, Saftics A, Shodubi O, Raghunandan S, Xu J, Tsai SJ, Dong Y, Li R, Jovanovic-Talisman T, Gould SJ. Endocytosis blocks the vesicular secretion of exosome marker proteins

Exosomes are secreted vesicles of ~30 to 150 nm diameter that play important roles in human health and disease. To better understand how cells release these vesicles, we examined the biogenesis of the most highly enriched human exosome marker proteins, the exosomal tetraspanins CD81, CD9, and CD63. We show here that endocytosis inhibits their vesicular secretion and, in the case of CD9 and CD81, triggers their destruction. Furthermore, we show that syntenin, a previously described exosome biogenesis factor, drives the vesicular secretion of CD63 by blocking CD63 endocytosis and that other endocytosis inhibitors also induce the plasma membrane accumulation and vesicular secretion of CD63. Finally, we show that CD63 is an expression-dependent inhibitor of endocytosis that triggers the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These results suggest that the vesicular secretion of exosome marker proteins in exosome-sized vesicles occurs primarily by an endocytosis-independent pathway.

Insights into membrane interactions and their therapeutic potential

Recent research into membrane interactions has uncovered a diverse range of therapeutic opportunities through the bioengineering of human and non-human macromolecules. Although the majority of this research is focussed on fundamental developments, emerging studies are showcasing promising new technologies to combat conditions such as cancer, Alzheimer's and inflammatory and immune-based disease, utilising the alteration of bacteriophage, adenovirus, bacterial toxins, type 6 secretion systems, annexins, mitochondrial antiviral signalling proteins and bacterial nano-syringes. To advance the field further, each of these opportunities need to be better understood, and the therapeutic models need to be further optimised. Here, we summarise the knowledge and insights into several membrane interactions and detail their current and potential uses therapeutically.

Multiparametric Single-Vesicle Flow Cytometry Resolves Extracellular Vesicle Heterogeneity and Reveals Selective Regulation of Biogenesis and Cargo Distribution

Mammalian cells release a heterogeneous array of extracellular vesicles (EVs) that contribute to intercellular communication by means of the cargo that they carry. To resolve EV heterogeneity and determine if cargo is partitioned into select EV populations, we developed a method named "EV Fingerprinting" that discerns distinct vesicle populations using dimensional reduction of multiparametric data collected by quantitative single-EV flow cytometry. EV populations were found to be discernible by a combination of membrane order and EV size, both of which were obtained through multiparametric analysis of fluorescent features from the lipophilic dye Di-8-ANEPPS incorporated into the lipid bilayer. Molecular perturbation of EV secretion and biogenesis through respective ablation of the small GTPase Rab27a and overexpression of the EV-associated tetraspanin CD63 revealed distinct and selective alterations in EV populations, as well as cargo distribution. While Rab27a disproportionately affects all small EV populations with high membrane order, the overexpression of CD63 selectively increased the production of one small EV population of intermediate membrane order. Multiplexing experiments subsequently revealed that EV cargos have a distinct, nonrandom distribution with CD63 and CD81 selectively partitioning into smaller vs larger EVs, respectively. These studies not only present a method to probe EV biogenesis but also reveal how the selective partitioning of cargo contributes to EV heterogeneity.

Methods, Mechanisms, and Application Prospects for Enhancing Extracellular Vesicle Uptake

Extracellular vesicles (EVs) are considered to be a new generation of bioinspired nanoscale drug delivery systems due to their low immunogenicity, natural functionality, and excellent biocompatibility. However, limitations such as low uptake efficiency, insufficient production, and inhomogeneous performance undermine their potential. To address these issues, numerous researchers have put forward various methods and applications for enhancing EV uptake in recent decades. In this review, we introduce various methods for the cellular uptake of EVs and summarize recent advances on the methods and mechanisms for enhancing EV uptake. In addition, we provide further understanding regarding enhancing EV uptake and put forward prospects and challenges for the development of EV-based therapy in the future.

A solution for highly efficient electroporation of primary cytotoxic T lymphocytes

BACKGROUND

Cytotoxic T lymphocytes (CTLs) are central players in the adaptive immune response. Their functional characterization and clinical research depend on efficient and reliable transfection. Although various methods have been utilized, electroporation remains the preferred technique for transient gene over-expression. However, the efficiency of electroporation is reduced for human and mouse primary CTLs. Lonza offers kits that effectively improve plasmid DNA transfection quality. Unfortunately, the removal of key components of the cell recovery medium considerably reduced the efficiency of their kit for CTLs. Our aim was to develop a new recovery medium to be used with Lonza's Nucleofector system that would significantly enhance transfection rates.

RESULTS

We assessed the impact of different media in which the primary CTLs were placed to recover after electroporation on cell survival, transfection rate and their ability to form an immunological synapse and to perform exocytosis. We transfected the cells with pmax-GFP and large constructs encoding for either CD81-super ecliptic pHluorin or granzyme B-pHuji. The comparison of five different media for mouse and two for human CTLs demonstrated that our new recovery medium composed of Opti-MEM-GlutaMAX supplemented with HEPES, DMSO and sodium pyruvate gave the best result in cell survival (> 50%) and transfection rate (> 30 and 20% for mouse and human cells, respectively). More importantly, the functionality of CTLs was at least twice as high as with the original Lonza recovery medium. In addition, our RM significantly improved transfection efficacy of natural killer cells that are notoriously hard to electroporate.

CONCLUSION

Our results show that successful transfection depends not only on the electroporation medium and pulse sequence but also on the medium applied for cell recovery. In addition, we have reduced our reliance on proprietary products by designing an effective recovery medium for both mouse and human primary CTLs and other lymphocytes that can be easily implemented by any laboratory. We expect that this recovery medium will have a significant impact on both fundamental and applied research in immunology.

Extracellular-Vesicle Catch-and-Release Isolation System Using a Net-Charge Invertible Curvature-Sensing Peptide

Extracellular vesicles (EVs) carry various informative components, including signaling proteins, transcriptional regulators, lipids, and nucleic acids. These components are utilized for cell-cell communication between donor and recipient cells. EVs have shown great promise as pharmaceutical-targeting vesicles and have attracted the attention of researchers in the fields of biological and medical science because of their importance as diagnostic and prognostic markers. However, the isolation and purification of EVs from cell-cultured media remain challenging. Ultracentrifugation is the most widely used method, but it requires specialized and expensive equipment. In the present study, we proposed a novel methodology to isolate EVs using a simple and convenient method, i.e., an EV catch-and-release isolation system (EV-CaRiS) using a net-charge invertible curvature-sensing peptide (NIC). Curvature-sensing peptides recognize vesicles by binding to lipid-packing defects on highly curved membranes regardless of the expression levels of biomarkers. NIC was newly designed to reversibly capture and release EVs in a pH-dependent manner. NIC allowed us to achieve reproducible EV isolation from three human cell lines on resin using a batch method and single-particle imaging of EVs containing the ubiquitous exosome markers CD63 and CD81 by total internal reflection fluorescence microscopy (TIRFM). EV-CaRiS was demonstrated as a simple and convenient methodology for EV isolation, and NIC is promising for applications in the single-particle analysis of EVs.

Exosomes define a local and systemic communication network in healthy pancreas and pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC), a lethal disease, requires a grasp of its biology for effective therapies. Exosomes, implicated in cancer, are poorly understood in living systems. Here we use the genetically engineered mouse model (ExoBow) to map the spatiotemporal distribution of exosomes from healthy and PDAC pancreas in vivo to determine their biological significance. We show that, within the PDAC microenvironment, cancer cells establish preferential communication routes through exosomes with cancer associated fibroblasts and endothelial cells. The latter being a conserved event in the healthy pancreas. Inhibiting exosomes secretion in both scenarios enhances angiogenesis, underscoring their contribution to vascularization and to cancer. Inter-organ communication is significantly increased in PDAC with specific organs as most frequent targets of exosomes communication occurring in health with the thymus, bone-marrow, brain, and intestines, and in PDAC with the kidneys, lungs and thymus. In sum, we find that exosomes mediate an organized intra- and inter- pancreas communication network with modulatory effects in vivo.

Directional Endothelial Communication by Polarized Extracellular Vesicle Release

BACKGROUND

Extracellular vesicles (EVs) contain bioactive cargo including miRNAs and proteins that are released by cells during cell-cell communication. Endothelial cells (ECs) form the innermost lining of all blood vessels, interfacing with cells in the circulation and vascular wall. It is unknown whether ECs release EVs capable of governing recipient cells within these 2 separate compartments. Given their boundary location, we propose ECs use bidirectional release of distinct EV cargo in quiescent (healthy) and activated (atheroprone) states to communicate with cells within the circulation and blood vessel wall.

METHODS

EVs were isolated from primary human aortic ECs (plate and transwell grown; ±IL [interleukin]-1β activation), quantified, visualized, and analyzed by miRNA transcriptomics and proteomics. Apical and basolateral EC-EV release was determined by miRNA transfer, total internal reflection fluorescence and electron microscopy. Vascular reprogramming (RNA sequencing) and functional assays were performed on primary human monocytes or smooth muscle cells±EC-EVs.

RESULTS

Activated ECs increased EV release, with miRNA and protein cargo related to atherosclerosis. EV-treated monocytes and smooth muscle cells revealed activated EC-EV altered pathways that were proinflammatory and atherogenic. ECs released more EVs apically, which increased with activation. Apical and basolateral EV cargo contained distinct transcriptomes and proteomes that were altered by EC activation. Notably, activated basolateral EC-EVs displayed greater changes in the EV secretome, with pathways specific to atherosclerosis. In silico analysis determined compartment-specific cargo released by the apical and basolateral surfaces of ECs can reprogram monocytes and smooth muscle cells, respectively, with functional assays and in vivo imaging supporting this concept.

CONCLUSIONS

Demonstrating that ECs are capable of polarized EV cargo loading and directional EV secretion reveals a novel paradigm for endothelial communication, which may ultimately enhance the design of endothelial-based therapeutics for cardiovascular diseases such as atherosclerosis where ECs are persistently activated.

The ins-and-outs of exosome biogenesis, secretion, and internalization

Exosomes are specialized cargo delivery vesicles secreted from cells by fusion of multivesicular bodies (MVBs) with the plasma membrane (PM). While the function of exosomes during physiological and pathological events has been extensively reported, there remains a lack of understanding of the mechanisms that regulate exosome biogenesis, secretion, and internalization. Recent technological and methodological advances now provide details about MVB/exosome structure as well as the pathways of exosome biogenesis, secretion, and uptake. In this review, we outline our current understanding of these processes and highlight outstanding questions following on recent discoveries in the field.

Small RNA-big impact: exosomal miRNAs in mitochondrial dysfunction in various diseases

Mitochondria are multitasking organelles involved in maintaining the cell homoeostasis. Beyond its well-established role in cellular bioenergetics, mitochondria also function as signal organelles to propagate various cellular outcomes. However, mitochondria have a self-destructive arsenal of factors driving the development of diseases caused by mitochondrial dysfunction. Extracellular vesicles (EVs), a heterogeneous group of membranous nano-sized vesicles, are present in a variety of bodily fluids. EVs serve as mediators for intercellular interaction. Exosomes are a class of small EVs (30-100 nm) released by most cells. Exosomes carry various cargo including microRNAs (miRNAs), a class of short noncoding RNAs. Recent studies have closely associated exosomal miRNAs with various human diseases, including diseases caused by mitochondrial dysfunction, which are a group of complex multifactorial diseases and have not been comprehensively described. In this review, we first briefly introduce the characteristics of EVs. Then, we focus on possible mechanisms regarding exosome-mitochondria interaction through integrating signalling networks. Moreover, we summarize recent advances in the knowledge of the role of exosomal miRNAs in various diseases, describing how mitochondria are changed in disease status. Finally, we propose future research directions to provide a novel therapeutic strategy that could slow the disease progress mediated by mitochondrial dysfunction.

Secretome Analysis: Reading Cellular Sign Language to Understand Intercellular Communication

A significant portion of mammalian proteomes is secreted to the extracellular space to fulfill crucial roles in cell-to-cell communication. To best recapitulate the intricate and multi-faceted crosstalk between cells in a live organism, there is an ever-increasing need for methods to study protein secretion in model systems that include multiple cell types. In addition, posttranslational modifications further expand the complexity and versatility of cellular communication. This review aims to summarize recent strategies and model systems that employ cellular coculture, chemical biology tools, protein enrichment, and proteomic methods to characterize the composition and function of cellular secretomes. This is all geared towards gaining better understanding of organismal biology in vivo mediated by secretory signaling.

A surfactant lipid layer of endosomal membranes facilitates airway gas filling in Drosophila

The mechanisms underlying the construction of an air-liquid interface in respiratory organs remain elusive. Here, we use live imaging and genetic analysis to describe the morphogenetic events generating an extracellular lipid lining of the Drosophila airways required for their gas filing and animal survival. We show that sequential Rab39/Syx1A/Syt1-mediated secretion of lysosomal acid sphingomyelinase (Drosophila ASM [dASM]) and Rab11/35/Syx1A/Rop-dependent exosomal secretion provides distinct components for lipid film assembly. Tracheal inactivation of Rab11 or Rab35 or loss of Rop results in intracellular accumulation of exosomal, multi-vesicular body (MVB)-derived vesicles. On the other hand, loss of dASM or Rab39 causes luminal bubble-like accumulations of exosomal membranes and liquid retention in the airways. Inactivation of the exosomal secretion in dASM mutants counteracts this phenotype, arguing that the exosomal secretion provides the lipid vesicles and that secreted lysosomal dASM organizes them into a continuous film. Our results reveal the coordinated functions of extracellular vesicle and lysosomal secretions in generating a lipid layer crucial for airway gas filling and survival.

Emerging technologies for engineering of extracellular vesicles

Extracellular vesicles (EVs) are lipid-bilayer membrane-enclosed vesicles that are secreted by all cell types. Natural EVs contain biological information such as proteins, nucleic acids, and lipids from their parent cells. Therefore, EVs have been extensively studied as diagnostic biomarkers and therapeutic tools under normal and pathological conditions. However, some drawbacks, including low yield, poor therapeutic effects, lack of imaging, and targeting capacity of natural EVs, still need to be improved. Emerging engineering technologies have rendered EVs new properties or functionalities that broadened their applications in the biomedical field. Herein, in this review, we gave a brief overview of advanced strategies for EV engineering. We focused on pre-treatment of parent cells to regulate their released EVs. Meanwhile, we summarized and discussed the direct modification of EVs to achieve drug loading, imaging, and targeting functionalities for downstream applications.

A phosphoinositide switch mediates exocyst recruitment to multivesicular endosomes for exosome secretion

Exosomes are secreted to the extracellular milieu when multivesicular endosomes (MVEs) dock and fuse with the plasma membrane. However, MVEs are also known to fuse with lysosomes for degradation. How MVEs are directed to the plasma membrane for exosome secretion rather than to lysosomes is unclear. Here we report that a conversion of phosphatidylinositol-3-phosphate (PI(3)P) to phosphatidylinositol-4-phosphate (PI(4)P) catalyzed sequentially by Myotubularin 1 (MTM1) and phosphatidylinositol 4-kinase type IIα (PI4KIIα) on the surface of MVEs mediates the recruitment of the exocyst complex. The exocyst then targets the MVEs to the plasma membrane for exosome secretion. We further demonstrate that disrupting PI(4)P generation or exocyst function blocked exosomal secretion of Programmed death-ligand 1 (PD-L1), a key immune checkpoint protein in tumor cells, and led to its accumulation in lysosomes. Together, our study suggests that the PI(3)P to PI(4)P conversion on MVEs and the recruitment of the exocyst direct the exocytic trafficking of MVEs for exosome secretion.

VAMP5 and distinct sets of cognate Q-SNAREs mediate exosome release

Small extracellular vesicles (sEVs) are largely classified into two types, plasma-membrane derived sEVs and endomembrane-derived sEVs. The latter type (referred to as exosomes herein) is originated from late endosomes or multivesicular bodies (MVBs). In order to release exosomes extracellularly, MVBs must fuse with the plasma membrane, not with lysosomes. In contrast to the mechanism responsible for MVB-lysosome fusion, the mechanism underlying the MVB-plasma membrane fusion is poorly understood. Here, we systematically analyze soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family proteins and identify VAMP5 as an MVB-localized SNARE protein required for exosome release. Depletion of VAMP5 in HeLa cells impairs exosome release. Mechanistically, VAMP5 mediates exosome release by interacting with SNAP47 and plasma membrane SNARE Syntaxin 1 (STX1) or STX4 to release exosomes. VAMP5 is also found to mediate asymmetric exosome release from polarized Madin-Darby canine kidney (MDCK) epithelial cells through interaction with the distinct sets of Q-SNAREs, suggesting that VAMP5 is a general exosome regulator in both polarized cells and non-polarized cells.Key words: exosome, small extracellular vesicle (sEV), multivesicular body, SNARE, VAMP5.

Extracellular release in the quality control of the mammalian mitochondria

Mammalian cells release a wealth of materials to their surroundings. Emerging data suggest these materials can even be mitochondria with perturbed morphology and aberrant function. These dysfunctional mitochondria are removed by migrating cells through membrane shedding. Neuronal cells, cardiomyocytes, and adipocytes send dysfunctional mitochondria into the extracellular space for nearby cells to degrade. Various studies also indicate that there is an interplay between intracellular mitochondrial degradation pathways and mitochondrial release in handling dysfunctional mitochondria. These observations, in aggregate, suggest that extracellular release plays a role in quality-controlling mammalian mitochondria. Future studies will help delineate the various types of molecular machinery mammalian cells use to release dysfunctional mitochondria. Through the studies, we will better understand how mammalian cells choose between intracellular degradation and extracellular release for the quality control of mitochondria.

Acute joint inflammation induces a sharp increase in the number of synovial fluid EVs and modifies their phospholipid profile

Inflammation is the hallmark of most joint disorders. However, the precise regulation of induction, perpetuation, and resolution of joint inflammation is not entirely understood. Since extracellular vesicles (EVs) are critical for intercellular communication, we aim to unveil their role in these processes. Here, we investigated the EVs' dynamics and phospholipidome profile from synovial fluid (SF) of healthy equine joints and from horses with lipopolysaccharide (LPS)-induced synovitis. LPS injection triggered a sharp increase of SF-EVs at 5-8 h post-injection, which started to decline at 24 h post-injection. Importantly, we identified significant changes in the lipid profile of SF-EVs after synovitis induction. Compared to healthy joint-derived SF-EVs (0 h), SF-EVs collected at 5, 24, and 48 h post-LPS injection were strongly increased in hexosylceramides. At the same time, phosphatidylserine, phosphatidylcholine, and sphingomyelin were decreased in SF-EVs at 5 h and 24 h post-LPS injection. Based on the lipid changes during acute inflammation, we composed specific lipid profiles associated with healthy and inflammatory state-derived SF-EVs. The sharp increase in SF-EVs during acute synovitis and the correlation of specific lipids with either healthy or inflamed states-derived SF-EVs are findings of potential interest for unveiling the role of SF-EVs in joint inflammation, as well as for the identification of EV-biomarkers of joint inflammation.

Identification of the SNARE complex that mediates the fusion of multivesicular bodies with the plasma membrane in exosome secretion

Exosomes play crucial roles in local and distant cellular communication and are involved in various physiological and pathological processes. Tumour-derived exosomes are pivotal to tumorigenesis, but the precise mechanisms underlying their secretion remain elusive. In particular, the SNARE proteins that mediate the fusion of multivesicular bodies (MVBs) with the plasma membrane (PM) in tumour cells are subject to debate. In this study, we identified syntaxin-4, SNAP-23, and VAMP-7 as the SNAREs responsible for exosome secretion in MCF-7 breast cancer cells and found that a SNARE complex consisting of these SNAREs can drive membrane fusion in vitro. Deletion of any of these SNAREs in MCF-7 cells did not affect MVB biogenesis and transportation, indicating their specific involvement in MVB-PM fusion. In addition, syntaxin-4, SNAP-23, and VAMP-7 play equivalent roles in exosome secretion in both HeLa cervical cancer cells and A375 melanoma cells, suggesting their conserved function in exosome secretion. Furthermore, deletion of VAMP-7 in 4T1 mammary carcinoma cells efficiently inhibited exosome secretion and led to significant attenuation of tumour growth and lung metastasis in mouse models, implying that VAMP-7 may hold promise as a novel therapeutic target for breast cancer.

Rational Engineering of an Improved Genetically Encoded pH Sensor Based on Superecliptic pHluorin

Genetically encoded pH sensors based on fluorescent proteins are valuable tools for the imaging of cellular events that are associated with pH changes, such as exocytosis and endocytosis. Superecliptic pHluorin (SEP) is a pH-sensitive green fluorescent protein (GFP) variant widely used for such applications. Here, we report the rational design, development, structure, and applications of Lime, an improved SEP variant with higher fluorescence brightness and greater pH sensitivity. The X-ray crystal structure of Lime supports the mechanistic rationale that guided the introduction of beneficial mutations. Lime provides substantial improvements relative to SEP for imaging of endocytosis and exocytosis. Furthermore, Lime and its variants are advantageous for a broader range of applications including the detection of synaptic release and neuronal voltage changes.

Novel Multi-Ingredient Supplement Facilitates Weight Loss and Improves Body Composition in Overweight and Obese Individuals: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

BACKGROUND

Despite the growing recognition of the obesity crisis, its rates continue to rise. The current first-line therapies, such as dietary changes, energy restriction, and physical activity, are typically met with poor adherence. Novel nutritional interventions can address the root causes of obesity, including mitochondrial dysfunction, and facilitate weight loss.

OBJECTIVE

The objective of this study was to investigate the effects of a multi-ingredient nutritional supplement designed to facilitate mitochondrial function and metabolic health outcomes over a 12 wk period.

METHODS

Fifty-five overweight and/or obese participants (age (mean ± SEM): 26 ± 1; body mass index (BMI) (kg/m2): 30.5 ± 0.6) completed this double-blind, placebo-controlled clinical trial. Participants were randomized to 12 wks of daily consumption of multi-ingredient supplement (MIS; n = 28; containing 50 mg forskolin, 500 mg green coffee bean extract, 500 mg green tea extract, 500 mg beet root extract, 400 mg α-lipoic acid, 200 IU vitamin E, and 200 mg CoQ10) or control placebo (PLA, n = 27; containing microcrystalline cellulose) matched in appearance. The co-primary outcomes were bodyweight and fat mass (kg) changes. The secondary outcomes included other body composition measures, plasma markers of obesity, fatty liver disease biomarkers, resting energy metabolism, blood pressure, physical performance, and quality of life. The post-intervention differences between MIS and PLA were examined via ANCOVA which was adjusted for the respective pre-intervention variables.

RESULTS

After adjustment for pre-intervention data, there was a significant difference in weight (p < 0.001) and fat mass (p < 0.001) post-intervention between the PLA and MIS treatment arms. Post-intervention weight and fat mass were significantly lower in MIS. Significant post-intervention differences corrected for baseline were found in markers of clinical biochemistry (AST, p = 0.017; ALT, p = 0.008), molecular metabolism (GDF15, p = 0.028), and extracellular vesicle-associated miRNA species miR-122 and miR-34a in MIS (p < 0.05).

CONCLUSIONS

Following the 12 wks of MIS supplementation, weight and body composition significantly improved, concomitant with improvements in molecular markers of liver health and metabolism.

Extracellular vesicles stimulate smooth muscle cell migration by presenting collagen VI

The extracellular matrix (ECM) supports blood vessel architecture and functionality and undergoes active remodelling during vascular repair and atherogenesis. Vascular smooth muscle cells (VSMCs) are essential for vessel repair and, via their secretome, are able to invade from the vessel media into the intima to mediate ECM remodelling. Accumulation of fibronectin (FN) is a hallmark of early vascular repair and atherosclerosis and here we show that FN stimulates VSMCs to secrete small extracellular vesicles (sEVs) by activating the β1 integrin/FAK/Src pathway as well as Arp2/3-dependent branching of the actin cytoskeleton. Spatially, sEV were secreted via filopodia-like cellular protrusions at the leading edge of migrating cells. We found that sEVs are trapped by the ECM in vitro and colocalise with FN in symptomatic atherosclerotic plaques in vivo. Functionally, ECM-trapped sEVs induced the formation of focal adhesions (FA) with enhanced pulling forces at the cellular periphery. Proteomic and GO pathway analysis revealed that VSMC-derived sEVs display a cell adhesion signature and are specifically enriched with collagen VI. In vitro assays identified collagen VI as playing the key role in cell adhesion and invasion. Taken together our data suggests that the accumulation of FN is a key early event in vessel repair acting to promote secretion of collage VI enriched sEVs by VSMCs. These sEVs stimulate migration and invasion by triggering peripheral focal adhesion formation and actomyosin contraction to exert sufficient traction forces to enable VSMC movement within the complex vascular ECM network.

Exosomal release of the virus-encoded chemokine receptor US28 contributes to chemokine scavenging

The human cytomegalovirus (HCMV)-encoded chemokine receptor US28 contributes to various aspects of the viral life cycle and promotes immune evasion by scavenging chemokines from the microenvironment of HCMV-infected cells. In contrast to the plasma membrane localization of most human chemokine receptors, US28 has a predominant intracellular localization. In this study, we used immunofluorescence and electron microscopy to determine the localization of US28 upon exogenous expression, as well as in HCMV-infected cells. We observed that US28 localizes to late endosomal compartments called multivesicular bodies (MVBs), where it is sorted in intraluminal vesicles. Live-cell total internal reflection fluorescence (TIRF) microscopy revealed that US28-containing MVBs can fuse with the plasma membrane, resulting in the secretion of US28 on exosomes. Exosomal US28 binds the chemokines CX3CL1 and CCL5, and US28-containing exosomes inhibited the CX3CL1-CX3CR1 signaling axis. These findings suggest that exosomal release of US28 contributes to chemokine scavenging and immune evasion by HCMV.

Context-specific regulation of extracellular vesicle biogenesis and cargo selection

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

Endosomal egress and intercellular transmission of hepatic ApoE-containing lipoproteins and its exploitation by the hepatitis C virus

Liver-generated plasma Apolipoprotein E (ApoE)-containing lipoproteins (LPs) (ApoE-LPs) play central roles in lipid transport and metabolism. Perturbations of ApoE can result in several metabolic disorders and ApoE genotypes have been associated with multiple diseases. ApoE is synthesized at the endoplasmic reticulum and transported to the Golgi apparatus for LP assembly; however, the ApoE-LPs transport pathway from there to the plasma membrane is largely unknown. Here, we established an integrative imaging approach based on a fully functional fluorescently tagged ApoE. We found that newly synthesized ApoE-LPs accumulate in CD63-positive endosomes of hepatocytes. In addition, we observed the co-egress of ApoE-LPs and CD63-positive intraluminal vesicles (ILVs), which are precursors of extracellular vesicles (EVs), along the late endosomal trafficking route in a microtubule-dependent manner. A fraction of ApoE-LPs associated with CD63-positive EVs appears to be co-transmitted from cell to cell. Given the important role of ApoE in viral infections, we employed as well-studied model the hepatitis C virus (HCV) and found that the viral replicase component nonstructural protein 5A (NS5A) is enriched in ApoE-containing ILVs. Interaction between NS5A and ApoE is required for the efficient release of ILVs containing HCV RNA. These vesicles are transported along the endosomal ApoE egress pathway. Taken together, our data argue for endosomal egress and transmission of hepatic ApoE-LPs, a pathway that is hijacked by HCV. Given the more general role of EV-mediated cell-to-cell communication, these insights provide new starting points for research into the pathophysiology of ApoE-related metabolic and infection-related disorders.

Extracellular Vesicles in Hepatobiliary Health and Disease

Extracellular vesicles (EVs) are membrane-bound nanoparticles released by cells and are an important means of intercellular communication in physiological and pathological states. We provide an overview of recent advances in the understanding of EV biogenesis, cargo selection, recipient cell effects, and key considerations in isolation and characterization techniques. Studies on the physiological role of EVs have relied on cell-based model systems due to technical limitations of studying endogenous nanoparticles in vivo . Several recent studies have elucidated the mechanistic role of EVs in liver diseases, including nonalcoholic fatty liver disease, viral hepatitis, cholestatic liver disease, alcohol-associated liver disease, acute liver injury, and liver cancers. Employing disease models and human samples, the biogenesis of lipotoxic EVs downstream of endoplasmic reticulum stress and microvesicles via intracellular activation stress signaling are discussed in detail. The diverse cargoes of EVs including proteins, lipids, and nucleic acids can be enriched in a disease-specific manner. By carrying diverse cargo, EVs can directly confer pathogenic potential, for example, recruitment and activation of monocyte-derived macrophages in NASH and tumorigenicity and chemoresistance in hepatocellular carcinoma. We discuss the pathogenic role of EVs cargoes and the signaling pathways activated by EVs in recipient cells. We review the literature that EVs can serve as biomarkers in hepatobiliary diseases. Further, we describe novel approaches to engineer EVs to deliver regulatory signals to specific cell types, and thus use them as therapeutic shuttles in liver diseases. Lastly, we identify key lacunae and future directions in this promising field of discovery and development. © 2023 American Physiological Society. Compr Physiol 13:4631-4658, 2023.

siRNA screening reveals that SNAP29 contributes to exosome release

Cells release extracellular vesicles (EVs) of different sizes. Small EVs (< 200 nm) can originate from the fusion of multivesicular bodies with the plasma membrane, i.e. exosomes, and from budding of the plasma membrane, i.e. small ectosomes. To investigate the molecular machinery required for the release of small EVs, we developed a sensitive assay based on incorporation of radioactive cholesterol in EV membranes and used it in a siRNA screening. The screening showed that depletion of several SNARE proteins affected the release of small EVs. We focused on SNAP29, VAMP8, syntaxin 2, syntaxin 3 and syntaxin 18, the depletion of which reduced the release of small EVs. Importantly, this result was verified using gold standard techniques. SNAP29 depletion resulted in the largest effect and was further investigated. Immunoblotting analysis of small EVs showed that the release of several proteins considered to be associated with exosomes like syntenin, CD63 and Tsg101 was reduced, while the level of several proteins that have been shown to be released in ectosomes (annexins) or by secretory autophagy (LC3B and p62) was not affected by SNAP29 depletion. Moreover, these proteins appeared in different fractions when the EV samples were further separated by a density gradient. These results suggest that SNAP29 depletion mainly affects the secretion of exosomes. To investigate how SNAP29 affects exosome release, we used microscopy to study the distribution of MBVs using CD63 labelling and CD63-pHluorin to detect fusion events of MVBs with the plasma membrane. SNAP29 depletion caused a redistribution of CD63-labelled compartments but did not change the number of fusion events. Further experiments are therefore needed to fully understand the function of SNAP29. To conclude, we have developed a novel screening assay that has allowed us to identify several SNAREs involved in the release of small EVs.

Inhibition of endolysosome fusion increases exosome secretion

Exosomes are small vesicles that are secreted from cells to dispose of undegraded materials and mediate intercellular communication. A major source of exosomes is intraluminal vesicles within multivesicular endosomes that undergo exocytic fusion with the plasma membrane. An alternative fate of multivesicular endosomes is fusion with lysosomes, resulting in degradation of the intraluminal vesicles. The factors that determine whether multivesicular endosomes fuse with the plasma membrane or with lysosomes are unknown. In this study, we show that impairment of endolysosomal fusion by disruption of a pathway involving the BLOC-one-related complex (BORC), the small GTPase ARL8, and the tethering factor HOPS increases exosome secretion by preventing the delivery of intraluminal vesicles to lysosomes. These findings demonstrate that endolysosomal fusion is a critical determinant of the amount of exosome secretion and suggest that suppression of the BORC-ARL8-HOPS pathway could be used to boost exosome yields in biotechnology applications.

Autolysosomal exocytosis of lipids protect neurons from ferroptosis

During oxidative stress neurons release lipids that are internalized by glia. Defects in this coordinated process play an important role in several neurodegenerative diseases. Yet, the mechanisms of lipid release and its consequences on neuronal health are unclear. Here, we demonstrate that lipid-protein particle release by autolysosome exocytosis protects neurons from ferroptosis, a form of cell death driven by lipid peroxidation. We show that during oxidative stress, peroxidated lipids and iron are released from neurons by autolysosomal exocytosis which requires the exocytic machinery VAMP7 and syntaxin 4. We observe membrane-bound lipid-protein particles by TEM and demonstrate that these particles are released from neurons using cryoEM. Failure to release these lipid-protein particles causes lipid hydroperoxide and iron accumulation and sensitizes neurons to ferroptosis. Our results reveal how neurons protect themselves from peroxidated lipids. Given the number of brain pathologies that involve ferroptosis, defects in this pathway likely play a key role in the pathophysiology of neurodegenerative disease.

Extracellular vesicle-matrix interactions

The extracellular matrix in microenvironments harbors a variety of signals to control cellular functions and the materiality of tissues. Most efforts to synthetically reconstitute the matrix by biomaterial design have focused on decoupling cell-secreted and polymer-based cues. Cells package molecules into nanoscale lipid membrane-bound extracellular vesicles and secrete them. Thus, extracellular vesicles inherently interact with the meshwork of the extracellular matrix. In this Review, we discuss various aspects of extracellular vesicle-matrix interactions. Cells receive feedback from the extracellular matrix and leverage intracellular processes to control the biogenesis of extracellular vesicles. Once secreted, various biomolecular and biophysical factors determine whether extracellular vesicles are locally incorporated into the matrix or transported out of the matrix to be taken up by other cells or deposited into tissues at a distal location. These insights can be utilized to develop engineered biomaterials where EV release and retention can be precisely controlled in host tissue to elicit various biological and therapeutic outcomes.

Extracellular vesicles - on the cusp of a new language in the biological sciences

Extracellular vesicles (EVs) play a key role both in physiological balance and homeostasis and in disease processes through their ability to participate in intercellular signaling and communication. An ever-expanding knowledge pool and a myriad of functional properties ascribed to EVs point to a new language of communication in biological systems that has opened a path for the discovery and implementation of novel diagnostic applications. EVs originate in the endosomal network and via non-random shedding from the plasma membrane by mechanisms that allow the packaging of functional cargoes, including proteins, lipids, and genetic materials. Deciphering the molecular mechanisms that govern packaging, secretion and targeted delivery of extracellular vesicle-borne cargo will be required to establish EVs as important signaling entities, especially when ascribing functional properties to a heterogeneous population of vesicles. Several molecular cascades operate within the endosomal network and at the plasma membrane that recognize and segregate cargos as a prelude to vesicle budding and release. EVs are transferred between cells and operate as vehicles in biological fluids within tissues and within the microenvironment where they are responsible for short- and long-range targeted information. In this review, we focus on the remarkable capacity of EVs to establish a dialogue between cells and within tissues, often operating in parallel to the endocrine system, we highlight selected examples of past and recent studies on the functions of EVs in health and disease.

Fluorescence labeling of extracellular vesicles for diverse bio-applications in vitro and in vivo

Extracellular vesicles (EVs) are nanosized vesicles enclosed in a lipid membrane that are sustainably released by nearly all cell types. EVs have been deemed as valuable biomarkers for diagnostics and effective drug carriers, owing to the physiological function of transporting biomolecules for intercellular communication. To investigate their biological properties, efficient labeling strategies have been constructed for EV research, among which fluorescence labeling exerts a powerful function due to the capability of visualizing the nanovesicles with high sensitivity both in vitro and in vivo. In one aspect, with the help of functional fluorescence tags, EVs could be differentiated and categorized in vitro by various analytical techniques, which exert vital roles in disease diagnosis, prognosis, and treatment monitoring. Additionally, innovative EV reporters have been utilized for visualizing EVs, in combination with powerful microscopy techniques, which provide potential tools for investigating the dynamic events of EV release and intercellular communication in suitable animal models. In this feature article, we survey the latest advances regarding EV fluorescence labeling strategies and their application in biomedical application and in vivo biology investigation, highlighting the progresses in individual EV imaging. Finally, the challenges and future perspectives in unravelling EV physiological properties and further biomedical application are discussed.

Exploiting the biogenesis of extracellular vesicles for bioengineering and therapeutic cargo loading

Extracellular vesicles (EVs) are gaining increasing attention for diagnostic and therapeutic applications in various diseases. These natural nanoparticles benefit from favorable safety profiles and unique biodistribution capabilities, rendering them attractive drug-delivery modalities over synthetic analogs. However, the widespread use of EVs is limited by technological shortcomings and biological knowledge gaps that fail to unravel their heterogeneity. An in-depth understanding of their biogenesis is crucial to unlocking their full therapeutic potential. Here, we explore how knowledge about EV biogenesis can be exploited for EV bioengineering to load therapeutic protein or nucleic acid cargos into or onto EVs. We summarize more than 75 articles and discuss their findings on the formation and composition of exosomes and microvesicles, revealing multiple pathways that may be stimulation and/or cargo dependent. Our analysis further identifies key regulators of natural EV cargo loading and we discuss how this knowledge is integrated to develop engineered EV biotherapeutics.

Bioengineered exosomal-membrane-camouflaged abiotic nanocarriers: neurodegenerative diseases, tissue engineering and regenerative medicine

A bio-inspired strategy has recently been developed for camouflaging nanocarriers with biomembranes, such as natural cell membranes or subcellular structure-derived membranes. This strategy endows cloaked nanomaterials with improved interfacial properties, superior cell targeting, immune evasion potential, and prolonged duration of systemic circulation. Here, we summarize recent advances in the production and application of exosomal membrane-coated nanomaterials. The structure, properties, and manner in which exosomes communicate with cells are first reviewed. This is followed by a discussion of the types of exosomes and their fabrication methods. We then discuss the applications of biomimetic exosomes and membrane-cloaked nanocarriers in tissue engineering, regenerative medicine, imaging, and the treatment of neurodegenerative diseases. Finally, we appraise the current challenges associated with the clinical translation of biomimetic exosomal membrane-surface-engineered nanovehicles and evaluate the future of this technology.

Identifying signatures of EV secretion in metastatic breast cancer through functional single-cell profiling

Extracellular vesicles (EVs) regulate the tumor microenvironment by facilitating transport of biomolecules. Despite extensive investigation, heterogeneity in EV secretion among cancer cells and the mechanisms that support EV secretion are not well characterized. We developed an integrated method to identify individual cells with differences in EV secretion and performed linked single-cell RNA-sequencing on cloned single cells from the metastatic breast cancer cells. Differential gene expression analyses identified a four-gene signature of breast cancer EV secretion: HSP90AA1, HSPH1, EIF5, and DIAPH3. We functionally validated this gene signature by testing it across cell lines with different metastatic potential in vitro. Analysis of the TCGA and METABRIC datasets showed that this signature is associated with poor survival, invasive breast cancer types, and poor CD8⁺ T cell infiltration in human tumors. We anticipate that our method for directly identifying the molecular determinants of EV secretion will have broad applications across cell types and diseases.

Exosome secretion kinetics are controlled by temperature

When multivesicular endosomes (MVEs) fuse with the plasma membrane, exosomes are released into the extracellular space where they can affect other cells. The ability of exosomes to regulate cells nearby or further away depends on whether they remain attached to the secreting cell membrane. The regulation and kinetics of exosome secretion are not well characterized, but probes for directly imaging single MVE fusion events have allowed for visualization of the fusion and release process. In particular, the design of an exosome marker with a pH-sensitive dye in the middle of the tetraspanin protein CD63 has facilitated studies of individual MVE fusion events. Using TIRF microscopy, single fusion events were measured in A549 cells held at 23-37°C and events were identified using an automated detection algorithm. Stable docking precedes fusion almost always and a decrease in temperature was accompanied by decrease in the rate of content loss and in the frequency of fusion events. The loss of CD63-pHluorin fluorescence was measured at fusion sites and fit with a single or double exponential decay, with most events requiring two components and a plateau because the loss of fluorescence was typically incomplete. To interpret the kinetics, fusion events were simulated as a localized release of tethered/untethered exosomes coupled with the membrane diffusion of CD63. The experimentally observed decay required three components in the simulation: 1) free exosomes, 2) CD63 membrane diffusion from the endosomal membrane into the plasma membrane, and 3) tethered exosomes. Modeling with slow diffusion of the tethered exosomes (0.0015-0.004 μm2/s) accurately fits the experimental data for all temperatures. However, simulating with immobile tethers or the absence of tethers fails to replicate the data. Our model suggests that exosome release from the fusion site is incomplete due to postfusion, membrane attachment.

From Exosome Biogenesis to Absorption: Key Takeaways for Cancer Research

Exosomes are mediators of intercellular communication in normal physiology and diseases. While many studies have emerged on the function of exosomal cargoes, questions remain regarding the origin of these exosomes. The packaging and secretion of exosomes in different contexts modify exosomal composition, which may in turn impact delivery, uptake and cargo function in recipient cells. A mechanistic understanding of exosome biology is therefore crucial to investigating exosomal function in complex biological systems and to the development of novel therapeutic approaches. Here, we outline the steps in exosome biogenesis, including endosome formation, MVB formation, cargo sorting and extracellular release, as well as exosome absorption, including targeting, interaction with recipient cells and the fate of internalized exosomes. In addition to providing a framework of exosome dynamics, we summarize current evidence on major pathways and regulatory mechanisms. We also highlight the various mechanisms observed in cancer and point out directions to improve study design in exosome biology. Further research is needed to illuminate the relationship between exosome biogenesis and function, which will aid the development of translational applications.

Application of small extracellular vesicles in the diagnosis and prognosis of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant tumor originating from the epithelium of the nasopharynx. The disease is insidious, and most patients are diagnosed at the advanced stage, resulting in poor prognosis. Early diagnosis is important to reduce NPC mortality. Small extracellular vesicles (sEVs) are rich in a variety of bioactive molecules, such as proteins, nucleic acids, and lipids, which can participate in the physiological and pathological regulation of the body by affecting the function of target cells. Numerous studies have shown that some RNAs and proteins in sEVs of tumor origin have a key role in the development of NPC and are potential candidates for malignancy detection. Studying the relationship between the cargoes of these sEVs and NPC may help in the diagnosis of the disease. Here in this review, we summarize the application of sEVs as biomarkers in the diagnosis of NPC and their role in NPC metastasis and prognosis. In addition, we discuss possible future applications and limitations of sEVs as biomarkers.

Spatial organization of lysosomal exocytosis relies on membrane tension gradients

Lysosomal exocytosis is involved in many key cellular processes but its spatiotemporal regulation is poorly known. Using total internal reflection fluorescence microscopy (TIRFM) and spatial statistics, we observed that lysosomal exocytosis is not random at the adhesive part of the plasma membrane of RPE1 cells but clustered at different scales. Although the rate of exocytosis is regulated by the actin cytoskeleton, neither interfering with actin or microtubule dynamics by drug treatments alters its spatial organization. Exocytosis events partially co-appear at focal adhesions (FAs) and their clustering is reduced upon removal of FAs. Changes in membrane tension following a hypo-osmotic shock or treatment with methyl-β-cyclodextrin were found to increase clustering. To investigate the link between FAs and membrane tension, cells were cultured on adhesive ring-shaped micropatterns, which allow to control the spatial organization of FAs. By using a combination of TIRFM and fluorescence lifetime imaging microscopy (FLIM), we revealed the existence of a radial gradient in membrane tension. By changing the diameter of micropatterned substrates, we further showed that this gradient as well as the extent of exocytosis clustering can be controlled. Together, our data indicate that the spatial clustering of lysosomal exocytosis relies on membrane tension patterning controlled by the spatial organization of FAs.

Extracellular Vesicles and Particles Modulate Proton Secretion in a Model of Human Parietal Cells

The secretion of extracellular vesicles and particles (EVPs) is an important mechanism of cellular communication. In this work, we demonstrate a functional role of EVPs in mechanisms regulating gastric acid secretion. HGT-1 cells were used as a model system to assess proton secretion. First, in order to prove EVP secretion by HGT-1 cells, EVPs were isolated by size exclusion chromatography and characterized by nanoparticle tracking analysis, Western blot, and cryo transmission electron microscopy. For examination of the potential role of EVPs in proton secretion, HGT-1 cells were treated with pharmacological EV-inhibitors, resulting in a reduction of histamine-induced proton secretion. To demonstrate the functional role of EVPs in the mechanism of proton secretion, EVP-conditioned supernatant was collected after stimulation of HGT-1 cells with histamine, fractionated, and subjected to an activity screening. The results revealed constituents of the HGT-1-derived secretome with an MW of >100 kDa (including EVPs) to modulate proton secretion, while smaller constituents had no effect. Finally, a dose-dependent modulatory effect on proton secretion of HGT-1 cells was demonstrated by isolated HGT-1-derived EVPs. Hence, this study presents first results on the potential function of EVPs as a previously undiscovered mechanism of regulation of gastric acid secretion by parietal cells.

Exosomes mediated fibrogenesis in dilated cardiomyopathy through a MicroRNA pathway

Cardiac fibrosis is a hallmark in late-stage familial dilated cardiomyopathy (DCM) patients, although the underlying mechanism remains elusive. Cardiac exosomes (Exos) have been reported relating to fibrosis in ischemic cardiomyopathy. Thus, we investigated whether Exos secreted from the familial DCM cardiomyocytes could promote fibrogenesis. Using human iPSCs differentiated cardiomyocytes we isolated Exos of angiotensin II stimulation conditioned media from either DCM or control (CTL) cardiomyocytes. Of interest, cultured cardiac fibroblasts had increased fibrogenesis following exposure to DCM-Exos rather than CTL-Exos. Meanwhile, injecting DCM-Exos into mouse hearts enhanced cardiac fibrosis and impaired cardiac function. Mechanistically, we identified the upregulation of miRNA-218-5p in the DCM-Exos as a critical contributor to fibrogenesis. MiRNA-218-5p activated TGF-β signaling via suppression of TNFAIP3, a master inflammation inhibitor. In conclusion, our results illustrate a profibrotic effect of cardiomyocytes-derived Exos that highlights an additional pathogenesis pathway for cardiac fibrosis in DCM.

Extracellular vesicles in the retina - putative roles in physiology and disease

The retina encompasses a network of neurons, glia and epithelial and vascular endothelia cells, all coordinating visual function. Traditionally, molecular information exchange in this tissue was thought to be orchestrated by synapses and gap junctions. Recent findings have revealed that many cell types are able to package and share molecular information via extracellular vesicles (EVs) and the technological advancements in visualisation and tracking of these delicate nanostructures has shown that the role of EVs in cell communication is pleiotropic. EVs are released under physiological conditions by many cells but they are also released during various disease stages, potentially reflecting the health status of the cells in their cargo. Little is known about the physiological role of EV release in the retina. However, administration of exogenous EVs in vivo after injury suggest a neurotrophic role, whilst photoreceptor transplantation in early stages of retina degeneration, EVs may facilitate interactions between photoreceptors and Müller glia cells. In this review, we consider some of the proposed roles for EVs in retinal physiology and discuss current evidence regarding their potential impact on ocular therapies via gene or cell replacement strategies and direct intraocular administration in the diseased eye.

The Machinery of Exosomes: Biogenesis, Release, and Uptake

Exosomes are a subtype of membrane-contained vesicles 40-200 nm in diameter that are secreted by cells into their surroundings. By transporting proteins, lipids, mRNA, miRNA, lncRNA, and DNA, exosomes are able to perform such vital functions as maintaining cellular homeostasis, removing cellular debris, and facilitating intercellular and interorgan communication. Exosomes travel in all body fluids and deliver their molecular messages in autocrine, paracrine as well as endocrine manners. In recent years, there has been an increased interest in studying exosomes as diagnostic markers and therapeutic targets, since in many disease conditions this machinery becomes dysregulated or hijacked by pathological processes. Additionally, delivery of exosomes and exosomal miRNA has already been shown to improve systemic metabolism and inhibit progression of cancer development in mice. However, the subcellular machinery of exosomes, including their biogenesis, release and uptake, remains largely unknown. This review will bring molecular details of these processes up to date with the goal of expanding the knowledge basis for designing impactful exosome experiments in the future.

Isolation and characterization of extracellular vesicles and future directions in diagnosis and therapy

Extracellular vesicles (EVs) are a unique and heterogeneous class of lipid bilayer nanoparticles secreted by most cells. EVs are regarded as important mediators of intercellular communication in both prokaryotic and eukaryotic cells due to their ability to transfer proteins, lipids and nucleic acids to recipient cells. In addition to their physiological role, EVs are recognized as modulators in pathological processes such as cancer, infectious diseases, and neurodegenerative disorders, providing new potential targets for diagnosis and therapeutic intervention. For a complete understanding of EVs as a universal cellular biological system and its translational applications, optimal techniques for their isolation and characterization are required. Here, we review recent progress in those techniques, from isolation methods to characterization techniques. With interest in therapeutic applications of EVs growing, we address fundamental points of EV-related cell biology, such as cellular uptake mechanisms and their biodistribution in tissues as well as challenges to their application as drug carriers or biomarkers for less invasive diagnosis or as immunogens. This article is categorized under: Diagnostic Tools > Biosensing Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Metabolites as extracellular vesicle cargo in health, cancer, pleural effusion, and cardiovascular diseases: An emerging field of study to diagnostic and therapeutic purposes

Extracellular vesicles (EVs) are highly diverse nanoscale membrane-bound structures released from different cell types into the extracellular environment. They play essential functions in cell signaling by transporting their cargo, such as proteins, RNA, DNA, lipids, metabolites, and small molecules, to recipient cells. It has recently been shown that EVs might modulate carcinogenesis by delivering cargo to recipient cells. Furthermore, recent discoveries revealed that changes in plasma-derived EV levels and cargo in subjects with metabolic diseases were documented by many researchers, suggesting that EVs might be a promising source of disease biomarkers. One of the cargos of EVs that has recently attracted the most attention is metabolites. The metabolome of these vesicles introduces a plethora of disease indicators; hence, examining the metabolomics of EVs detected in human biofluids would be an effective approach. On the other hand, metabolites have various roles in biological systems, including the production of energies, synthesizing macromolecules, and serving as signaling molecules and hormones. Metabolome rewiring in cancer and stromal cells is a characteristic of malignancy, but the current understanding of how this affects the metabolite composition and activity of tumor-derived EVs remains in its infancy. Since new findings and studies in the field of exosome biology and metabolism are constantly being published, it is likely that diagnostic and treatment techniques, including the use of exosome metabolites, will be launched in the coming years. Recent years have seen increased interest in the EV metabolome as a possible source for biomarker development. However, our understanding of the role of these molecules in health and disease is still immature. In this work, we have provided the latest findings regarding the role of metabolites as EV cargoes in the pathophysiology of diseases, including cancer, pleural effusion (PE), and cardiovascular disease (CVD). We also discussed the significance of metabolites as EV cargoes of microbiota and their role in host-microbe interaction. In addition, the latest findings on metabolites in the form of EV cargoes as biomarkers for disease diagnosis and treatment are presented in this study.

Phospholipase D and cancer metastasis: A focus on exosomes

In mammals, phospholipase D (PLD) enzymes involve 6 isoforms, of which only three have established lipase activity to produce the signaling lipid phosphatidic acid (PA). This phospholipase activity has been postulated to contribute to cancer progression for over three decades now, but the exact mechanisms involved have yet to be uncovered. Indeed, using various models, an altered PLD activity has been proposed altogether to increase cell survival rate, promote angiogenesis, boost rapamycin resistance, and favor metastasis. Although for some part, the molecular pathways by which this increase in PA is pro-oncogenic are partially known, the pleiotropic functions of PA make it quite difficult to distinguish which among these simple signaling pathways is responsible for each of these PLD facets. In this review, we will describe an additional potential contribution of PA generated by PLD1 and PLD2 in the biogenesis, secretion, and uptake of exosomes. Those extracellular vesicles are now viewed as membrane vehicles that carry informative molecules able to modify the fate of receiving cells at distance from the original tumor to favor homing of metastasis. The perspectives for a better understanding of these complex role of PLDs will be discussed.

Live-Imaging Detection of Multivesicular Body-Plasma Membrane Fusion and Exosome Release in Cultured Primary Neurons

Exosomes represent a class of extracellular vesicles (EVs) derived from the endocytic pathway that is important for cell-cell communication and implicated in the spread of pathogenic protein aggregates associated with neurological diseases. Exosomes are released extracellularly when multivesicular bodies (also known as late endosomes) fuse with the plasma membrane (PM). An important breakthrough in exosome research is the ability to capture MVB-PM fusion and exosome release simultaneously in individual cells using live-imaging microscopy techniques. Specifically, researchers have created a construct fusing CD63, a tetraspanin enriched in exosomes, with the pH-sensitive reporter pHluorin whereby CD63-pHluorin fluorescence is quenched in the acidic MVB lumen and only fluoresces when released into the less acidic extracellular environment. Here, we describe a method using this CD63-pHluorin construct to visualize MVB-PM fusion/exosome secretion in primary neurons using total internal reflection fluorescence (TIRF) microscopy.

Endothelial ACKR1 is induced by neutrophil contact and down-regulated by secretion in extracellular vesicles

Atypical chemokine receptor-1 (ACKR1), previously known as the Duffy antigen receptor for chemokines, is a widely conserved cell surface protein that is expressed on erythrocytes and the endothelium of post-capillary venules. In addition to being the receptor for the parasite causing malaria, ACKR1 has been postulated to regulate innate immunity by displaying and trafficking chemokines. Intriguingly, a common mutation in its promoter leads to loss of the erythrocyte protein but leaves endothelial expression unaffected. Study of endothelial ACKR1 has been limited by the rapid down-regulation of both transcript and protein when endothelial cells are extracted and cultured from tissue. Thus, to date the study of endothelial ACKR1 has been limited to heterologous over-expression models or the use of transgenic mice. Here we report that exposure to whole blood induces ACKR1 mRNA and protein expression in cultured primary human lung microvascular endothelial cells. We found that contact with neutrophils is required for this effect. We show that NF-κB regulates ACKR1 expression and that upon removal of blood, the protein is rapidly secreted by extracellular vesicles. Finally, we confirm that endogenous ACKR1 does not signal upon stimulation with IL-8 or CXCL1. Our observations define a simple method for inducing endogenous endothelial ACKR1 protein that will facilitate further functional studies.

Visualization of Exosome Release and Uptake During Cell Migration Using the Live Imaging Reporter pHluorin_M153R-CD63

Exosome secretion and uptake regulate cell migration through autocrine and paracrine mechanisms. Monitoring exosome secretion and uptake during cell migration is critical for investigation of these mechanisms. Exosomes can be visualized by direct labeling with fluorescent dyes or by tagging intrinsic markers with fluorescent proteins for live imaging. Due to several limitations of fluorescent dye-labeled exosomes, we created two bright genetically encoded reporters of exosome secretion, pHluorin_M153R-CD63 and pHluorin_M153R-CD63-mScarlet. Here, we describe how to visualize secretion and uptake of exosomes labeled with these pH-sensitive and pH-insensitive fluorescent protein-tagged exosomal markers during cell migration using time-lapse fluorescent microscopy.

ER-endosome contacts master the ins and outs of secretory endosomes

What defines whether an endosome follows the degradative pathway or fuses with the plasma membrane to release exosomes? In this issue of JCB, Fredrik Verweij and colleagues (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202112032) demonstrate how secretory endosomes are guided by ER-endosome contacts to take a cellular detour and several identity transitions for efficient exosome release.

ER membrane contact sites support endosomal small GTPase conversion for exosome secretion

Exosomes are endosome-derived extracellular vesicles involved in intercellular communication. They are generated as intraluminal vesicles within endosomal compartments that fuse with the plasma membrane (PM). The molecular events that generate secretory endosomes and lead to the release of exosomes are not well understood. We identified a subclass of non-proteolytic endosomes at prelysosomal stage as the compartment of origin of CD63 positive exosomes. These compartments undergo a Rab7a/Arl8b/Rab27a GTPase cascade to fuse with the PM. Dynamic endoplasmic reticulum (ER)-late endosome (LE) membrane contact sites (MCS) through ORP1L have the distinct capacity to modulate this process by affecting LE motility, maturation state, and small GTPase association. Thus, exosome secretion is a multi-step process regulated by GTPase switching and MCS, highlighting the ER as a new player in exosome-mediated intercellular communication.