Biogenesis and function of ESCRT-dependent extracellular vesicles

A toolbox for the immunomagnetic purification of signaling organelles

Homeostasis and the complex functions of organisms and cells rely on the sophisticated spatial and temporal regulation of signaling in different intra- and extracellular compartments and via different mediators. We here present a set of fast and easy to use protocols for the target-specific immunomagnetic enrichment of receptor containing endosomes (receptosomes), plasma membranes, lysosomes and exosomes. Isolation of subcellular organelles and exosomes is prerequisite for and will advance their detailed subsequent biochemical and functional analysis. Sequential application of the different subprotocols allows isolation of morphological and functional intact organelles from one pool of cells. The enrichment is based on a selective labelling using receptor ligands or antibodies together with superparamagnetic microbeads followed by separation in a patented matrix-free high-gradient magnetic purification device. This unique magnetic chamber is based on a focusing system outside of the empty separation column, generating an up to 3 T high-gradient magnetic field focused at the wall of the column.

Exosomes: fighting cancer with cancer

Exosomes are nanovesicles secreted by many cells, including cancer cells. Extensive research has been carried out to validate potential applications of exosomes and to evaluate their efficiency in a wide range of diseases, including cancer. The current knowledge on the origin, biogenesis and composition of exosomes is described. This review then focuses on the use of exosomes in cancer diagnostics and therapeutics.

Exosome as a Novel Shuttle for Delivery of Therapeutics across Biological Barriers

The effective delivery of target-specific siRNA to the brain by exploiting the exosomes derived from dendritic cells renders the paradigm shift for the prospective use of nanosized exosomes as a delivery system. Although the in vivo targeting strategies by other nanovesicles like liposomes exist, still this novel exosome-based delivery approach holds an inclusive dominance of in vivo security and reduced immunogenicity. Achieving promising exosome-based delivery strategies warrants more desirable exploration of their biology. Over the years, the invention of novel production, characterization, targeting strategies, and cargo loading techniques of exosome improved its ability to reach clinics. Essentially, exosome-based delivery of therapeutics assures to conquer the major hurdles, like delivery of cargos across impermeable biological barriers, like the blood-brain barrier, biocompatibility, increased solubility, metabolic stability, improved circulation time, target specific delivery, and pharmacokinetics, and thereby enhanced the efficacy of loaded therapeutic agents. In this article, we cover the current status of exosome as a delivery vehicle for therapeutics and the challenges that need to be overcome, and we also discuss future perspectives of this exciting field of research to transform it from bench to clinical reality.

Post-translational and transcriptional dynamics - regulating extracellular vesicle biology

Introduction: Extracellular vesicles (EVs) are secreted into their extracellular environment, contain a specific repertoire of cellular cargo, and represent a novel vehicle for cell-cell communication. Protein post-translational modifications (PTMs) are emerging as major effectors of EV biology and function, and in turn, regulate cellular signaling. Areas covered: Discovery and investigation of PTMs such as methylation, glycosylation, acetylation, phosphorylation, sumoylation, and many others has established fundamental roles for PTMs within EVs and associated EV function. The application of enrichment strategies for modifications, high-resolution quantitative mass spectrometry-based proteomics, and improved technological approaches have provided key insights into identification and characterization of EV-based PTMs. Recently, an overwhelming appreciation for the diversity of modifications, including post-transcriptional modifications, dynamic roles of these modifications, and their emerging interplay, including protein-protein, protein-lipid, protein-RNA, and variable RNA modifications, is emerging. At a cellular level, such interplay is essential for gene expression/genome organization, protein function and localization, RNA metabolism, cell division, and cell signaling. Expert commentary: The understanding of these modifications and interactions will provide strategies toward how distinct cargo is localized, sorted, and delivered through EVs to mediate intercellular function, with further understanding of such modifications and intermolecular interactions will provide advances in EV-based therapeutic strategies.

Candida albicans biofilm-induced vesicles confer drug resistance through matrix biogenesis

Cells from all kingdoms of life produce extracellular vesicles (EVs). Their cargo is protected from the environment by the surrounding lipid bilayer. EVs from many organisms have been shown to function in cell–cell communication, relaying signals that impact metazoan development, microbial quorum sensing, and pathogenic host–microbe interactions. Here, we have investigated the production and functional activities of EVs in a surface-associated microbial community or biofilm of the fungal pathogen Candida albicans. Crowded communities like biofilms are a context in which EVs are likely to function. Biofilms are noteworthy because they are encased in an extracellular polymeric matrix and because biofilm cells exhibit extreme tolerance to antimicrobial compounds. We found that biofilm EVs are distinct from those produced by free-living planktonic cells and display strong parallels in composition to biofilm matrix material. The functions of biofilm EVs were delineated with a panel of mutants defective in orthologs of endosomal sorting complexes required for transport (ESCRT) subunits, which are required for normal EV production in diverse eukaryotes. Most ESCRT-defective mutations caused reduced biofilm EV production, reduced matrix polysaccharide levels, and greatly increased sensitivity to the antifungal drug fluconazole. Matrix accumulation and drug hypersensitivity of ESCRT mutants were reversed by addition of wild-type (WT) biofilm EVs. Vesicle complementation showed that biofilm EV function derives from specific cargo proteins. Our studies indicate that C. albicans biofilm EVs have a pivotal role in matrix production and biofilm drug resistance. Biofilm matrix synthesis is a community enterprise; prior studies of mixed cell biofilms have demonstrated extracellular complementation. Therefore, EVs function not only in cell–cell communication but also in the sharing of microbial community resources.

Candida albicans—the most common fungal pathogen in humans—often grows as a biofilm, resulting in an infection that is difficult to treat. These adherent communities tolerate extraordinarily high concentrations of antifungals due in large part to the protective extracellular matrix. The present study identifies extracellular vesicles (EVs) that are distinct to biofilms. These EVs deliver the functional extracellular matrix and are essential for resistance to antifungals. Our findings not only reveal a coordinated mechanism by which the defining trait of the biofilm lifestyle arises but also identify a number of potential therapeutic targets.

Structures, Functions, and Dynamics of ESCRT-III/Vps4 Membrane Remodeling and Fission Complexes

The endosomal sorting complexes required for transport (ESCRT) pathway mediates cellular membrane remodeling and fission reactions. The pathway comprises five core complexes: ALIX, ESCRT-I, ESCRT-II, ESCRT-III, and Vps4. These soluble complexes are typically recruited to target membranes by site-specific adaptors that bind one or both of the early-acting ESCRT factors: ALIX and ESCRT-I/ESCRT-II. These factors, in turn, nucleate assembly of ESCRT-III subunits into membrane-bound filaments that recruit the AAA ATPase Vps4. Together, ESCRT-III filaments and Vps4 remodel and sever membranes. Here, we review recent advances in our understanding of the structures, activities, and mechanisms of the ESCRT-III and Vps4 machinery, including the first high-resolution structures of ESCRT-III filaments, the assembled Vps4 enzyme in complex with an ESCRT-III substrate, the discovery that ESCRT-III/Vps4 complexes can promote both inside-out and outside-in membrane fission reactions, and emerging mechanistic models for ESCRT-mediated membrane fission.

Varicella-Zoster Virus and the Enteric Nervous System

Varicella zoster virus (VZV) infects and becomes latent in sensory, enteric, and other autonomic neurons during the viremia of varicella. Reactivation of VZV in neurons that project to the skin causes the rash of zoster; however, reactivation of VZV in enteric neurons can cause a painful gastrointestinal disorder ("enteric zoster") without cutaneous manifestations. Detection of VZV DNA in saliva of patients with gastrointestinal symptoms may suggest enteric zoster. This diagnosis is reinforced by observing a response to antiviral therapy and can be confirmed by detecting VZV gene products in intestinal mucosal biopsies. We developed an in vivo guinea pig model that may be useful in studies of VZV latency and reactivation. VZV-infected lymphocytes are used to induce latent infection in sensory and enteric neurons; evidence suggests that exosomes and stimulator of interferon genes (STING) may, by preventing proliferation play roles in the establishment of neuronal latency.

The ESCRT protein CHMP2B acts as a diffusion barrier on reconstituted membrane necks

Endosomal sorting complexes required for transport (ESCRT)-III family proteins catalyze membrane remodeling processes that stabilize and constrict membrane structures. It has been proposed that stable ESCRT-III complexes containing CHMP2B could establish diffusion barriers at the post-synaptic spine neck. In order to better understand this process, we developed a novel method based on fusion of giant unilamellar vesicles to reconstitute ESCRT-III proteins inside GUVs, from which membrane nanotubes are pulled. The new assay ensures that ESCRT-III proteins polymerize only when they become exposed to physiologically relevant membrane topology mimicking the complex geometry of post-synaptic spines. We establish that CHMP2B, both full-length and with a C-terminal deletion (ΔC), preferentially binds to membranes containing phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Moreover, we show that CHMP2B preferentially accumulates at the neck of membrane nanotubes, and provide evidence that CHMP2B-ΔC prevents the diffusion of PI(4,5)P2 lipids and membrane-bound proteins across the tube neck. This indicates that CHMP2B polymers formed at a membrane neck may function as a diffusion barrier, highlighting a potential important function of CHMP2B in maintaining synaptic spine structures.

Ceramide and Exosomes: A Novel Target in Cancer Biology and Therapy

Exosomes are secreted extracellular vesicles (EVs) that carry micro RNAs and other factors to reprogram cancer cells and tissues affected by cancer. Exosomes are exchanged between cancer cells and other tissues, often to prepare a premetastatic niche, escape immune surveillance, or spread multidrug resistance. Only a few studies investigated the function of lipids in exosomes although their lipid composition is different from that of the secreting cells. Ceramide is one of the lipids critical for exosome formation, and it is also enriched in these EVs. New research suggests that lipids in the exosomal membrane may organize and transmit "mobile rafts" that turn exosomes into extracellular signalosomes spreading activation of cell signaling pathways in oncogenesis and metastasis. Ceramide may modulate the function of mobile rafts and their effect on these cell signaling pathways. The critical role of lipids and, in particular, ceramide for formation, secretion, and function of exosomes may lead to a radically new understanding of cancer biology and therapy.

Role of sphingolipids in the biogenesis and biological activity of extracellular vesicles

Extracellular vesicles (EVs) are membrane vesicles released by both eukaryotic and prokaryotic cells; they not only serve physiological functions, such as disposal of cellular components, but also play pathophysiologic roles in inflammatory and degenerative diseases. Common molecular mechanisms for EV biogenesis are evident in different cell biological contexts across eukaryotic phyla, and inhibition of this biogenesis may provide an avenue for therapeutic research. The involvement of sphingolipids (SLs) and their enzymes on EV biogenesis and release has not received much attention in current research. Here, we review how SLs participate in EV biogenesis by shaping membrane curvature and how they contribute to EV action in target cells. First, we describe how acid and neutral SMases, by generating the constitutive SL, ceramide, facilitate biogenesis of EVs at the plasma membrane and inside the endocytic compartment. We then discuss the involvement of other SLs, such as sphingosine-1-phosphate and galactosyl-sphingosine, in EV formation and cargo sorting. Last, we look ahead at some biological effects of EVs mediated by changes in SL levels in recipient cells.

From intra- to extracellular vesicles: extracellular vesicles in developmental signalling

Signalling from cell-to-cell is fundamental for determining differentiation and patterning. This communication can occur between adjacent and distant cells. Extracellular vesicles (EVs) are membrane-based structures thought to facilitate the long-distance movement of signalling molecules. EVs have recently been found to allow the transport of two major developmental signalling pathways: Hedgehog and Wnt. These signalling molecules undergo crucial post-translational lipid modifications, which anchor them to membranes and impede their free release into the extracellular space. Preparation of these ligands in EVs involves intracellular vesicle sorting in an endocytosis-dependent recycling process before secretion. In the present review, we discuss the most recent advances with regard to EV involvement in developmental signalling at a distance. We focus on the role of the protein complexes involved in EV genesis, and provide a comprehensive perspective of the contribution of these complexes to intracellular vesicle sorting of developmental signals for their extracellular secretion, reception and transduction.

Regulation and mechanisms of extracellular vesicle biogenesis and secretion

EV (extracellular vesicle) biology is a rapidly expanding field. These heterogeneous membrane vesicles, which are shed from virtually all cell types, collectively represent a new dimension of intercellular communication in normal physiology and disease. They have been shown to deliver infectious and pathogenic agents to non-infected cells whereas in cancers they are thought to condition the tumor microenvironment. Their presence in body fluids and inherent capacity for systemic delivery point to their clinical promise. All of the above only intensifies the need to better understand the classification, mode of biogenesis, and contents of the different subtypes of EVs. This article focusses on vesicle subtypes labeled as exosomes and MVs (microvesicles) and discusses the biogenesis and release of these vesicles from cells.

Exosomal cargo-loading and synthetic exosome-mimics as potential therapeutic tools

Exosomes are nano-sized vesicles that serve as mediators for intercellular communication through the delivery of cargo, including protein, lipids, nucleic acids or other cellular components, to neighboring or distant cells. Exosomal cargo may vary in response to different physiological or pathological conditions. The endosomal sorting complex required for transport (ESCRT) family has been widely accepted as a key mechanism in biogenesis and cargo sorting. On the other hand, accumulating evidence show that ESCRT-independent pathways exist. Due to the critical role of exosomes in intercellular communications in delivering cargo to recipient cells, exosomes have been investigated as a vector for the delivery of endogenous or exogenous cargo for therapeutic purposes. But the number of exosomes produced by cells is limited, which hampers their application. Synthetic exosome-mimics have been fabricated and investigated as a therapeutic tool for drug delivery. This review focuses on ESCRT-independent regulation of cargo loading into exosomes, including lipid raft and ceramide-mediated mechanisms, and reported exosomes or exosome-mimics with therapeutic effects.

Serum exosomes can restore cellular function in vitro and be used for diagnosis in dysferlinopathy

Purpose: It is challenging to deliver the full-length dysferlin gene or protein to restore cellular functions of dysferlin-deficient (DYSF^-/-) myofibres in dysferlinopathy, a disease caused by the absence of dysferlin, which is currently without effective treatment. Exosomes, efficient membranous nanoscale carriers of biological cargoes, could be useful.

Experimental design: Myotube- and human serum-derived exosomes were investigated for their capabilities of restoring dysferlin protein and cellular functions in murine and human DYSF^-/- cells. Moreover, dysferlinopathic patient serum- and urine-derived exosomes were assessed for their abilities as diagnostic tools for dysferlinopathy.

Results: Here we show that exosomes from dysferlin-expressing myotubes carry abundant dysferlin and enable transfer of full-length dysferlin protein to DYSF^-/- myotubes. Exogenous dysferlin correctly localizes on DYSF^-/- myotube membranes, enabling membrane resealing in response to injury. Human serum exosomes also carry dysferlin protein and improve membrane repair capabilities of human DYSF^-/- myotubes irrespective of mutations. Lack of dysferlin in dysferlinopathic patient serum and urine exosomes enables differentiation between healthy controls and dysferlinopathic patients.

Conclusions: Our findings provide evidence that exosomes are efficient carriers of dysferlin and can be employed for the treatment and non-invasive diagnosis of dysferlinopathy.

Incidence of hypothyroidism after 131I therapy for hyperthyroidism. Relation to pretherapy serum levels of T3, T4 and thyroid antibodies

A correlation is reported between serum levels of triiodothyronine (S-T3) and thyroxine (S-T4) before treatment, as well as levels of thyroid antibodies before treatment, and the development of hypothyroidism following 131I therapy in 86 patients with hyperthyroidism. Patients with marked elevation of S-T3 or S-T4 had demonstrable antibodies to thyroid cytoplasmic antigen more often than those with normal or moderately elevated levels, and patients with markedly elevated levels of S-T3 also had a higher incidence of hypothyroidism after treatment. Patients with nodular thyroid glands and with markedly elevated levels of S-T3 required a larger number of 131I doses before no signs of hyperthyroidism persisted in comparison to those with moderately elevated levels.