Apolipoprotein E Regulates Amyloid Formation within Endosomes of Pigment Cells

Single Extracellular Vesicle Imaging and Computational Analysis Identifies Inherent Architectural Heterogeneity

Evaluating the heterogeneity of extracellular vesicles (EVs) is crucial for unraveling their complex actions and biodistribution. Here, we identify consistent architectural heterogeneity of EVs using cryogenic transmission electron microscopy (cryo-TEM), which has an inherent ability to image biological samples without harsh labeling methods while preserving their native conformation. Imaging EVs isolated using different methodologies from distinct sources, such as cancer cells, normal cells, immortalized cells, and body fluids, we identify a structural atlas of their dominantly consistent shapes. We identify EV architectural attributes by utilizing a segmentation neural network model. In total, 7,576 individual EVs were imaged and quantified by our computational pipeline. Across all 7,576 independent EVs, the average eccentricity was 0.5366 ± 0.2, and the average equivalent diameter was 132.43 ± 67 nm. The architectural heterogeneity was consistent across all sources of EVs, independent of purification techniques, and compromised of single spherical, rod-like or tubular, and double shapes. This study will serve as a reference foundation for high-resolution images of EVs and offer insights into their potential biological impact.

Possible Roles of Extracellular Vesicles in the Pathogenesis and Interventions of Immune-Mediated Central Demyelinating Diseases

Multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) are two of the most devastating immune-mediated central demyelinating disorders. NMOSD was once considered as a variant of MS until the discovery of an antibody specific to the condition. Despite both MS and NMOSD being considered central demyelinating disorders, their pathogenesis and clinical manifestations are distinct, however the exact mechanisms associated with each disease remain unclear. Extracellular vesicles (EVs) are nano-sized vesicles originating in various cells which serve as intercellular communicators. There is a large body of evidence to show the possible roles of EVs in the pathogenesis of several diseases, including the immune-mediated central demyelinating disorders. Various types of EVs are found across disease stages and could potentially be used as a surrogate marker, as well as acting by carrying a cargo of biochemical molecules. The possibility for EVs to be used as a next-generation targeted treatment for the immune-mediated central demyelinating disorders has been investigated. The aim of this review was to comprehensively identify, compile and discuss key findings from in vitro, in vivo and clinical studies. A summary of all findings shows that: 1) the EV profiles of MS and NMOSD differ from those of healthy individuals, 2) the use of EV markers as liquid biopsy diagnostic tools appears to be promising biomarkers for both MS and NMOSD, and 3) EVs are being studied as a potential targeted therapy for MS and NMOSD. Any controversial findings are also discussed in this review.

Enrichment, Characterization, and Proteomic Profiling of Small Extracellular Vesicles Derived from Human Limbal Mesenchymal Stromal Cells and Melanocytes

Limbal epithelial progenitor cells (LEPC) rely on their niche environment for proper functionality and self-renewal. While extracellular vesicles (EV), specifically small EVs (sEV), have been proposed to support LEPC homeostasis, data on sEV derived from limbal niche cells like limbal mesenchymal stromal cells (LMSC) remain limited, and there are no studies on sEVs from limbal melanocytes (LM). In this study, we isolated sEV from conditioned media of LMSC and LM using a combination of tangential flow filtration and size exclusion chromatography and characterized them by nanoparticle tracking analysis, transmission electron microscopy, Western blot, multiplex bead arrays, and quantitative mass spectrometry. The internalization of sEV by LEPC was studied using flow cytometry and confocal microscopy. The isolated sEVs exhibited typical EV characteristics, including cell-specific markers such as CD90 for LMSC-sEV and Melan-A for LM-sEV. Bioinformatics analysis of the proteomic data suggested a significant role of sEVs in extracellular matrix deposition, with LMSC-derived sEV containing proteins involved in collagen remodeling and cell matrix adhesion, whereas LM-sEV proteins were implicated in other cellular bioprocesses such as cellular pigmentation and development. Moreover, fluorescently labeled LMSC-sEV and LM-sEV were taken up by LEPC and localized to their perinuclear compartment. These findings provide valuable insights into the complex role of sEV from niche cells in regulating the human limbal stem cell niche.

APOE from patient-derived astrocytic extracellular vesicles alleviates neuromyelitis optica spectrum disorder in a mouse model

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune astrocytopathy of the central nervous system, mediated by antibodies against aquaporin-4 water channel protein (AQP4-Abs), resulting in damage of astrocytes with subsequent demyelination and axonal damage. Extracellular communication through astrocyte-derived extracellular vesicles (ADEVs) has received growing interest in association with astrocytopathies. However, to what extent ADEVs contribute to NMOSD pathogenesis remains unclear. Here, through proteomic screening of patient-derived ADEVs, we observed an increase in apolipoprotein E (APOE)-rich ADEVs in patients with AQP4-Abs-positive NMOSD. Intracerebral injection of the APOE-mimetic peptide APOE130-149 attenuated microglial reactivity, neuroinflammation, and brain lesions in a mouse model of NMOSD. The protective effect of APOE in NMOSD pathogenesis was further established by the exacerbated lesion volume in APOE-deficient mice, which could be rescued by exogenous APOE administration. Genetic knockdown of the APOE receptor lipoprotein receptor-related protein 1 (LRP1) could block the restorative effects of APOE130-149 administration. The transfusion ADEVs derived from patients with NMOSD and healthy controls also alleviated astrocyte loss, reactive microgliosis, and demyelination in NMOSD mice. The slightly larger beneficial effect of patient-derived ADEVs as compared to ADEVs from healthy controls was further augmented in APOE-/- mice. These results indicate that APOE from astrocyte-derived extracellular vesicles could mediate disease-modifying astrocyte-microglia cross-talk in NMOSD.

Unveiling the mechanistic link between extracellular amyloid fibrils, mechano-signaling and YAP activation in cancer

The tumor microenvironment is a complex ecosystem that plays a critical role in cancer progression and treatment response. Recently, extracellular amyloid fibrils have emerged as novel components of the tumor microenvironment; however, their function remains elusive. In this study, we establish a direct connection between the presence of amyloid fibrils in the secretome and the activation of YAP, a transcriptional co-activator involved in cancer proliferation and drug resistance. Furthermore, we uncover a shared mechano-signaling mechanism triggered by amyloid fibrils in both melanoma and pancreatic ductal adenocarcinoma cells. Our findings highlight the crucial role of the glycocalyx protein Agrin which binds to extracellular amyloid fibrils and acts as a necessary factor in driving amyloid-dependent YAP activation. Additionally, we reveal the involvement of the HIPPO pathway core kinase LATS1 in this signaling cascade. Finally, we demonstrate that extracellular amyloid fibrils enhance cancer cell migration and invasion. In conclusion, our research expands our knowledge of the tumor microenvironment by uncovering the role of extracellular amyloid fibrils in driving mechano-signaling and YAP activation. This knowledge opens up new avenues for developing innovative strategies to modulate YAP activation and mitigate its detrimental effects during cancer progression.

The Contributions of the Endolysosomal Compartment and Autophagy to APOEɛ4 Allele-Mediated Increase in Alzheimer's Disease Risk

Apolipoprotein E4 (APOE4), although yet-to-be fully understood, increases the risk and lowers the age of onset of Alzheimer's disease (AD), which is the major cause of dementia among elderly individuals. The endosome-lysosome and autophagy pathways, which are necessary for homeostasis in both neurons and glia, are dysregulated even in early AD. Nonetheless, the contributory roles of these pathways to developing AD-related pathologies in APOE4 individuals and models are unclear. Therefore, this review summarizes the dysregulations in the endosome-lysosome and autophagy pathways in APOE4 individuals and non-human models, and how these anomalies contribute to developing AD-relevant pathologies. The available literature suggests that APOE4 causes endosomal enlargement, increases endosomal acidification, impairs endosomal recycling, and downregulates exosome production. APOE4 impairs autophagy initiation and inhibits basal autophagy and autophagy flux. APOE4 promotes lysosome formation and trafficking and causes ApoE to accumulate in lysosomes. APOE4-mediated changes in the endosome, autophagosome and lysosome could promote AD-related features including Aβ accumulation, tau hyperphosphorylation, glial dysfunction, lipid dyshomeostasis, and synaptic defects. ApoE4 protein could mediate APOE4-mediated endosome-lysosome-autophagy changes. ApoE4 impairs vesicle recycling and endosome trafficking, impairs the synthesis of autophagy genes, resists being dissociated from its receptors and degradation, and forms a stable folding intermediate that could disrupt lysosome structure. Drugs such as molecular correctors that target ApoE4 molecular structure and enhance autophagy may ameliorate the endosome-lysosome-autophagy-mediated increase in AD risk in APOE4 individuals.

Single extracellular vesicle imaging and computational analysis identifies inherent architectural heterogeneity

Evaluating the heterogeneity of extracellular vesicles (EVs) is crucial for unraveling their complex actions and biodistribution. Here, we identify consistent architectural heterogeneity of EVs using cryogenic transmission electron microscopy (cryo-TEM) which has an inherent ability to image biological samples without harsh labeling methods and while preserving their native conformation. Imaging EVs isolated using different methodologies from distinct sources such as cancer cells, normal cells, and body fluids, we identify a structural atlas of their dominantly consistent shapes. We identify EV architectural attributes by utilizing a segmentation neural network model. In total, 7,576 individual EVs were imaged and quantified by our computational pipeline. Across all 7,576 independent EVs, the average eccentricity was 0.5366, and the average equivalent diameter was 132.43 nm. The architectural heterogeneity was consistent across all sources of EVs, independent of purification techniques, and compromised of single spherical (S. Spherical), rod-like or tubular, and double shapes. This study will serve as a reference foundation for high-resolution EV images and offer insights into their potential biological impact.

The effects of intracellular and exosomal ncRNAs on cancer progression

Altered gene expression as well as mislocalization of a gene's encoded product (proteins or noncoding RNAs (ncRNAs)) can lead to disease and cancer formation. Multiple studies have indicated that exosomes and their contents act as cell-to-cell communicators and play a key role in cancer progression. Moreover, exosomes contain several functional molecules, including ncRNAs. NcRNAs function as master regulators to coordinate cell growth, cell motility and drug resistance. However, intracellular ncRNAs, which can be transferred to recipient cells via exosomes (exosomal ncRNAs), mediate common/distinct downstream molecules, signaling pathways and functions that are less emphasized concepts in cancer development research. In this study, by using exosomes as a model, we comprehensively discuss the current knowledge regarding (1) the functional role of ncRNAs, both their intracellular and exosomal forms, in cancer progression, (2) the possible mechanism of ncRNA incorporation into exosomes and (3) the therapeutic applications and limitations of exosomes based on current knowledge.

Host defense amyloids: Biosensors of the immune system?

There is considerable evidence showing that highly ordered aggregate structures known as amyloids carry out essential biological roles in species ranging from bacteria to humans. Indeed, many antimicrobial peptides/proteins form amyloids to carry out their host defense functions and many amyloids are antimicrobial. The similarity of host defense amyloids from bacterial biofilms to the mammalian epididymal amyloid matrix implies highly conserved host defense structures/functions. With an emphasis on the epididymal amyloid matrix, here we review the common properties of host defense amyloids including unique traits that would allow them to function as powerful biosensors of the immune system.

NPC1 plays a role in the trafficking of specific cargo to melanosomes

Niemann-Pick type C1 (NPC1) protein is a multimembrane spanning protein of the lysosome limiting membrane that facilitates intracellular cholesterol and sphingolipid transport. Loss-of-function mutations in the NPC1 protein cause Niemann-Pick disease type C1, a lysosomal storage disorder characterized by the accumulation of cholesterol and sphingolipids within lysosomes. To investigate whether the NPC1 protein could also play a role in the maturation of the endolysosomal pathway, here, we have investigated its role in a lysosome-related organelle, the melanosome. Using a NPC1-KO melanoma cell model, we found that the cellular phenotype of Niemann-Pick disease type C1 is associated with a decreased pigmentation accompanied by low expression of the melanogenic enzyme tyrosinase. We propose that the defective processing and localization of tyrosinase, occurring in the absence of NPC1, is a major determinant of the pigmentation impairment in NPC1-KO cells. Along with tyrosinase, two other pigmentation genes, tyrosinase-related protein 1 and Dopachrome-tautomerase have lower protein levels in NPC1 deficient cells. In contrast with the decrease in pigmentation-related protein expression, we also found a significant intracellular accumulation of mature PMEL17, the structural protein of melanosomes. As opposed to the normal dendritic localization of melanosomes, the disruption of melanosome matrix generation in NPC1 deficient cells causes an accumulation of immature melanosomes adjacent to the plasma membrane. Together with the melanosomal localization of NPC1 in WT cells, these findings suggest that NPC1 is directly involved in tyrosinase transport from the trans-Golgi network to melanosomes and melanosome maturation, indicating a novel function for NPC1.

ApoE expression in macrophages communicates immunometabolic signaling that controls hyperlipidemia-driven hematopoiesis & inflammation via extracellular vesicles

While apolipoprotein E (apoE) expression by myeloid cells is recognized to control inflammation, whether such benefits can be communicated via extracellular vesicles is not known. Through the study of extracellular vesicles produced by macrophages derived from the bone marrow of Wildtype (WT-BMDM-EV) and ApoE deficient (EKO-BMDM-EV) mice, we uncovered a critical role for apoE expression in regulating their cell signaling properties. WT-BMDM-EV communicated anti-inflammatory properties to recipient myeloid cells by increasing cellular levels of apoE and miR-146a-5p, that reduced NF-κB signalling. They also downregulated cellular levels of miR-142a-3p, resulting in increased levels of its target carnitine palmitoyl transferase 1A (CPT1A) which improved fatty acid oxidation (FAO) and oxidative phosphorylation (OxPHOS) in recipient cells. Such favorable metabolic polarization enhanced cell-surface MerTK levels and the phagocytic uptake of apoptotic cells. In contrast, EKO-BMDM-EV exerted opposite effects by reducing cellular levels of apoE and miR-146a-5p, which increased NF-κB-driven GLUT1-mediated glucose uptake, aerobic glycolysis, and oxidative stress. Furthermore, EKO-BMDM-EV increased cellular miR-142a-3p levels, which reduced CPT1A levels and impaired FAO and OxPHOS in recipient myeloid cells. When cultured with naïve CD4+ T lymphocytes, EKO-BMDM-EV drove their activation and proliferation, and fostered their transition to a Th1 phenotype. While infusions of WT-BMDM-EV into hyperlipidemic mice resolved inflammation, infusions of EKO-BMDM-EV increased hematopoiesis and drove inflammatory responses in myeloid cells and T lymphocytes. ApoE-dependent immunometabolic signaling by macrophage extracellular vesicles was dependent on transcriptional axes controlled by miR-146a-5p and miR-142a-3p that could be reproduced by infusing miR-146a mimics & miR-142a antagonists into hyperlipidemic apoE-deficient mice. Together, our findings unveil a novel property for apoE expression in macrophages that modulates the immunometabolic regulatory properties of their secreted extracellular vesicles.

A tale of exosomes and their implication in cancer

Cancer is a cause of high deaths worldwide and also a huge burden for the health system. Cancer cells have unique properties such as a high rate of proliferation, self-renewal, metastasis, and treatment resistance, therefore, the development of novel diagnoses of cancers is a tedious task. Exosomes are secreted by virtually all cell types and have the ability to carry a multitude of biomolecules crucial for intercellular communication, hence, contributing a crucial part in the onset and spread of cancer. These exosomal components can be utilized in the development of markers for diagnostic and prognostic purposes for various cancers. This review emphasized primarily the following topics: exosomes structure and functions, isolation and characterization strategies of exosomes, the role of exosomal contents in cancer with a focus in particular on noncoding RNA and protein, exosomes, and the cancer microenvironment interactions, cancer stem cells, and tumor diagnosis and prognosis based on exosomes.

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.

The Ebola virus VP40 matrix layer undergoes endosomal disassembly essential for membrane fusion

Ebola viruses (EBOVs) assemble into filamentous virions, whose shape and stability are determined by the matrix viral protein 40 (VP40). Virus entry into host cells occurs via membrane fusion in late endosomes; however, the mechanism of how the remarkably long virions undergo uncoating, including virion disassembly and nucleocapsid release into the cytosol, remains unknown. Here, we investigate the structural architecture of EBOVs entering host cells and discover that the VP40 matrix disassembles prior to membrane fusion. We reveal that VP40 disassembly is caused by the weakening of VP40-lipid interactions driven by low endosomal pH that equilibrates passively across the viral envelope without a dedicated ion channel. We further show that viral membrane fusion depends on VP40 matrix integrity, and its disassembly reduces the energy barrier for fusion stalk formation. Thus, pH-driven structural remodeling of the VP40 matrix acts as a molecular switch coupling viral matrix uncoating to membrane fusion during EBOV entry.

In Vitro Interaction of Melanoma-Derived Extracellular Vesicles with Collagen

Extracellular vesicles are now considered as active contributors to melanoma progression through their capacity to modify the tumor microenvironment and to favor the formation of a pre-metastatic niche. These prometastatic roles of tumor-derived EVs would pass through their interaction with the extracellular matrix (ECM) and its remodeling, in turn providing a substrate favoring persistent tumor cell migration. Nevertheless, the capacity of EVs to directly interact with ECM components is still questionable. In this study, we use electron microscopy and a pull-down assay to test the capacity of sEVs, derived from different melanoma cell lines, to physically interact with collagen I. We were able to generate collagen fibrils coated with sEVs and to show that melanoma cells release subpopulations of sEVs that can differentially interact with collagen.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

CAR-T-Derived Extracellular Vesicles: A Promising Development of CAR-T Anti-Tumor Therapy

Extracellular vesicles (EVs) are a heterogenous population of plasma membrane-surrounded particles that are released in the extracellular milieu by almost all types of living cells. EVs are key players in intercellular crosstalk, both locally and systemically, given that they deliver their cargoes (consisting of proteins, lipids, mRNAs, miRNAs, and DNA fragments) to target cells, crossing biological barriers. Those mechanisms further trigger a wide range of biological responses. Interestingly, EV phenotypes and cargoes and, therefore, their functions, stem from their specific parental cells. For these reasons, EVs have been proposed as promising candidates for EV-based, cell-free therapies. One of the new frontiers of cell-based immunotherapy for the fight against refractory neoplastic diseases is represented by genetically engineered chimeric antigen receptor T (CAR-T) lymphocytes, which in recent years have demonstrated their effectiveness by reaching commercialization and clinical application for some neoplastic diseases. CAR-T-derived EVs represent a recent promising development of CAR-T immunotherapy approaches. This crosscutting innovative strategy is designed to exploit the advantages of genetically engineered cell-based immunotherapy together with those of cell-free EVs, which in principle might be safer and more efficient in crossing biological and tumor-associated barriers. In this review, we underlined the potential of CAR-T-derived EVs as therapeutic agents in tumors.

Macromolecular sheets direct the morphology and orientation of plate-like biogenic guanine crystals

Animals precisely control the morphology and assembly of guanine crystals to produce diverse optical phenomena in coloration and vision. However, little is known about how organisms regulate crystallization to produce optically useful morphologies which express highly reflective crystal faces. Guanine crystals form inside iridosome vesicles within chromatophore cells called iridophores. By following iridosome formation in developing scallop eyes, we show that pre-assembled, fibrillar sheets provide an interface for nucleation and direct the orientation of the guanine crystals. The macromolecular sheets cap the (100) faces of immature guanine crystals, inhibiting growth along the π-stacking growth direction. Crystal growth then occurs preferentially along the sheets to generate highly reflective plates. Despite their different physical properties, the morphogenesis of iridosomes bears a striking resemblance to melanosome morphogenesis in vertebrates, where amyloid sheets template melanin deposition. The common control mechanisms for melanin and guanine formation inspire new approaches for manipulating the morphologies and properties of molecular materials.

Identification of Alternative Splicing in Proteomes of Human Melanoma Cell Lines without RNA Sequencing Data

Alternative splicing is one of the main regulation pathways in living cells beyond simple changes in the level of protein expression. Most of the approaches proposed in proteomics for the identification of specific splicing isoforms require a preliminary deep transcriptomic analysis of the sample under study, which is not always available, especially in the case of the re-analysis of previously acquired data. Herein, we developed new algorithms for the identification and validation of protein splice isoforms in proteomic data in the absence of RNA sequencing of the samples under study. The bioinformatic approaches were tested on the results of proteome analysis of human melanoma cell lines, obtained earlier by high-resolution liquid chromatography and mass spectrometry (LC-MS). A search for alternative splicing events for each of the cell lines studied was performed against the database generated from all known transcripts (RefSeq) and the one composed of peptide sequences, which included all biologically possible combinations of exons. The identifications were filtered using the prediction of both retention times and relative intensities of fragment ions in the corresponding mass spectra. The fragmentation mass spectra corresponding to the discovered alternative splicing events were additionally examined for artifacts. Selected splicing events were further validated at the mRNA level by quantitative PCR.

The Roles of Exosomes in the Diagnose, Development and Therapeutic Resistance of Oral Squamous Cell Carcinoma

Oral cancer is one of the most common cancers worldwide, of which more than half of patients are diagnosed at a locally advanced stage with poor prognosis due to recurrence, metastasis and resistant to treatment. Thus, it is imperative to further explore the potential mechanism of development and drug resistance of oral cancer. Exosomes are small endosome-derived lipid nanoparticles that are released by cells. Since the cargoes of exosomes were inherited from their donor cells, the cargo profiles of exosomes can well recapitulate that of their donor cells. This is the theoretical basis of exosome-based liquid biopsy, providing a tool for early diagnosis of oral cancer. As an important intracellular bioactive cargo delivery vector, exosomes play a critical role in the development of oral cancer by transferring their cargoes to receipt cells. More importantly, recent studies have revealed that exosomes could induce therapy-resistance in oral cancer through multiple ways, including exosome-mediated drug efflux. In this review, we summarize and compare the role of exosomes in the diagnosis, development and therapy-resistant of oral cancer. We also highlight the clinical application of exosomes, and discuss the advantages and challenges of exosomes serving as predictive biomarker, therapy target and therapy vector in oral cancer.

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.

OCA7 is a melanosome membrane protein that defines pigmentation by regulating early stages of melanosome biogenesis

Mutations in C10orf11 (oculocutaneous albinism type 7 [OCA7]) cause OCA, a disorder that presents with hypopigmentation in skin, eyes, and hair. The OCA7 pathophysiology is unknown, and there is virtually no information on the OCA7 protein and its cellular function. Here, we discover that OCA7 localizes to the limiting membrane of melanosomes, the specialized pigment cell organelles where melanin is synthesized. We demonstrate that OCA7 is recruited through interaction with a canonical effector-binding surface of melanosome proteins Rab32 and Rab38. Using newly generated OCA7-KO MNT1 cells, we show OCA7 regulates overall melanin levels in a melanocyte autonomous manner by controlling melanosome maturation. Importantly, we found that OCA7 regulates premelanosome protein (PMEL) processing, impacting fibrillation and the striations that define transition from melanosome stage I to stage II. Furthermore, the melanosome lumen of OCA7-KO cells displays lower pH than control cells. Together, our results reveal that OCA7 regulates pigmentation through two well-established determinants of melanosome biogenesis and function, PMEL processing, and organelle pH.

Extracellular signals regulate the biogenesis of extracellular vesicles

Extracellular vesicles (EVs) are naturally released membrane vesicles that act as carriers of proteins and RNAs for intercellular communication. With various biomolecules and specific ligands, EV has represented a novel form of information transfer, which possesses extremely outstanding efficiency and specificity compared to the classical signal transduction. In addition, EV has extended the concept of signal transduction to intercellular aspect by working as the collection of extracellular information. Therefore, the functions of EVs have been extensively characterized and EVs exhibit an exciting prospect for clinical applications. However, the biogenesis of EVs and, in particular, the regulation of this process by extracellular signals, which are essential to conduct further studies and support optimal utility, remain unclear. Here, we review the current understanding of the biogenesis of EVs, focus on the regulation of this process by extracellular signals and discuss their therapeutic value.

Relationships of APOE Genotypes With Small RNA and Protein Cargo of Brain Tissue Extracellular Vesicles From Patients With Late-Stage AD

Background and Objectives

Variants of the apolipoprotein E (APOE) gene are the greatest known risk factors for sporadic Alzheimer disease (AD). Three major APOE isoform alleles, ε2, ε3, and ε4, encode and produce proteins that differ by only 1-2 amino acids but have different binding partner interactions. Whereas APOE ε2 is protective against AD relative to ε3, ε4 is associated with an increased risk for AD development. However, the role of APOE in gene regulation in AD pathogenesis has remained largely undetermined. Extracellular vesicles (EVs) are lipid bilayer-delimited particles released by cells to dispose of unwanted materials and mediate intercellular communication, and they are implicated in AD pathophysiology. Brain-derived EVs (bdEVs) could act locally in the tissue and reflect cellular changes. To reveal whether APOE genotype affects EV components in AD brains, bdEVs were separated from patients with AD with different APOE genotypes for parallel small RNA and protein profile.

Methods

bdEVs from late-stage AD brains (BRAAK stages 5-6) from patients with APOE genotypes ε2/3 (n = 5), ε3/3 (n = 5), ε3/4 (n = 6), and ε4/4 (n = 6) were separated using our published protocol into a 10,000g pelleted extracellular fraction (10K) and a further purified EV fraction. Counting, sizing, and multiomic characterization by small RNA sequencing and proteomic analysis were performed for 10K, EVs, and source tissue.

Results

Comparing APOE genotypes, no significant differences in bdEV total particle concentration or morphology were observed. Overall small RNA and protein profiles of 10K, EVs, and source tissue also did not differ substantially between different APOE genotypes. However, several differences in individual RNAs (including miRNAs and tRNAs) and proteins in 10K and EVs were observed when comparing the highest and lowest risk groups (ε4/4 and ε2/3). Bioinformatic analysis and previous publications indicate a potential regulatory role of these molecules in AD.

Discussion

For patients with late-stage AD in this study, only a few moderate differences were observed for small RNA and protein profiles between APOE genotypes. Among these, several newly identified 10K and EV-associated molecules may play roles in AD progression. Possibly, larger genotype-related differences exist and are more apparent in or before earlier disease stages.

Extracellular vesicles from pristane-treated CD38-deficient mice express an anti-inflammatory neutrophil protein signature, which reflects the mild lupus severity elicited in these mice

In CD38-deficient (Cd38-/-) mice intraperitoneal injection of pristane induces a lupus-like disease, which is milder than that induced in WT mice, showing significant differences in the inflammatory and autoimmune processes triggered by pristane. Extracellular vesicles (EV) are present in all body fluids. Shed by cells, their molecular make-up reflects that of their cell of origin and/or tissue pathological situation. The aim of this study was to analyze the protein composition, protein abundance, and functional clustering of EV released by peritoneal exudate cells (PECs) in the pristane experimental lupus model, to identify predictive or diagnostic biomarkers that might discriminate the autoimmune process in lupus from inflammatory reactions and/or normal physiological processes. In this study, thanks to an extensive proteomic analysis and powerful bioinformatics software, distinct EV subtypes were identified in the peritoneal exudates of pristane-treated mice: 1) small EV enriched in the tetraspanin CD63 and CD9, which are likely of exosomal origin; 2) small EV enriched in CD47 and CD9, which are also enriched in plasma-membrane, membrane-associated proteins, with an ectosomal origin; 3) small EV enriched in keratins, ECM proteins, complement/coagulation proteins, fibrin clot formation proteins, and endopetidase inhibitor proteins. This enrichment may have an inflammation-mediated mesothelial-to-mesenchymal transition origin, representing a protein corona on the surface of peritoneal exudate EV; 4) HDL-enriched lipoprotein particles. Quantitative proteomic analysis allowed us to identify an anti-inflammatory, Annexin A1-enriched pro-resolving, neutrophil protein signature, which was more prominent in EV from pristane-treated Cd38-/- mice, and quantitative differences in the protein cargo of the ECM-enriched EV from Cd38-/- vs WT mice. These differences are likely to be related with the distinct inflammatory outcome shown by Cd38-/- vs WT mice in response to pristane treatment. Our results demonstrate the power of a hypothesis-free and data-driven approach to transform the heterogeneity of the peritoneal exudate EV from pristane-treated mice in valuable information about the relative proportion of different EV in a given sample and to identify potential protein markers specific for the different small EV subtypes, in particular those proteins defining EV involved in the resolution phase of chronic inflammation.

Exosomal MicroRNAs as Novel Cell-Free Therapeutics in Tissue Engineering and Regenerative Medicine

Extracellular vesicles (EVs) are membrane-bound vesicles (50–1000 nm) that can be secreted by all cell types. Microvesicles and exosomes are the major subsets of EVs that exhibit the cell–cell communications and pathological functions of human tissues, and their therapeutic potentials. To further understand and engineer EVs for cell-free therapy, current developments in EV biogenesis and secretion pathways are discussed to illustrate the remaining gaps in EV biology. Specifically, microRNAs (miRs), as a major EV cargo that exert promising therapeutic results, are discussed in the context of biological origins, sorting and packing, and preclinical applications in disease progression and treatments. Moreover, advanced detection and engineering strategies for exosomal miRs are also reviewed. This article provides sufficient information and knowledge for the future design of EVs with specific miRs or protein cargos in tissue repair and regeneration.

Overcoming the blood-brain barrier: Exosomes as theranostic nanocarriers for precision neuroimaging

Exosomes are cell-derived vesicles with a lipid bilayer membrane that play important roles in intercellular communication. They provide an unprecedented opportunity for the development of drug delivery nanoplatforms due to their low immunogenicity, low toxicity, biocompatibility, stability, and ability to change the functions of recipient cells. In addition, exosomes can penetrate the blood-brain barrier and then target and accumulate in relevant pathological brain regions. However, few studies have focused on the applications of exosomes as nanocarriers for use in precision neuroimaging studies. Thus, this report presents the feasibility of fabricating specific exosome-based diagnostic reagents for the application of personalized/precision radiology in the central nervous system based on important recent fundamental discoveries and technological advances.

Chick cranial neural crest cells release extracellular vesicles that are critical for their migration

The content and activity of extracellular vesicles purified from cell culture media or bodily fluids have been studied extensively; however, the physiological relevance of exosomes within normal biological systems is poorly characterized, particularly during development. Although exosomes released by invasive metastatic cells alter migration of neighboring cells in culture, it is unclear whether cancer cells misappropriate exosomes released by healthy differentiated cells or reactivate dormant developmental programs that include exosome cell-cell communication. Using chick cranial neural fold cultures, we show that migratory neural crest cells, a developmentally critical cell type and model for metastasis, release and deposit CD63-positive 30-100 nm particles into the extracellular environment. Neural crest cells contain ceramide-rich multivesicular bodies and produce larger vesicles positive for migrasome markers as well. We conclude that neural crest cells produce extracellular vesicles including exosomes and migrasomes. When Rab27a plasma membrane docking is inhibited, neural crest cells become less polarized and rounded, leading to a loss of directional migration and reduced speed. These results indicate that neural crest cell exosome release is critical for migration.

KIBRA regulates amyloid β metabolism by controlling extracellular vesicles secretion

Background

Previous research has revealed that KIBRA controls secretion of extracellular vesicles (EVs) by inhibiting the proteasomal degradation of Rab27a and EVs play an important role in amyloid β (Aβ) metabolism and transmission during Alzheimer's disease (AD) pathogenesis. Here, we further test the hypothesis that KIBRA regulates Aβ metabolism via the endosomal-lysosomal system.

Methods

We generated KIBRA knockout mice on a 5XFAD background and KIBRA knockdown cells in murine HT22 cells with stably overexpressing APP. Various forms of Aβ and quantification of EVs were analyzed by biochemical methods and nanoparticle tracking analysis, respectively. Multivesicular bodies (MVBs) were visualized by electron microscopy and confocal fluorescent microscopy. In a population-based cohort (n = 1419), KIBRA genotypes and plasma Aβ levels were analyzed using multiple-PCR amplification and Simoa, respectively.

Findings

Multiple forms of Aβ were dramatically attenuated in KIBRA knockout mouse brain, including monomers, oligomers, and extracellular deposition, but KIBRA knockout had no effect on intraneuronal APP C-terminal fragment β (APP-CTFβ)/Aβ levels. KIBRA depletion also decreased APP-CTFβ/Aβ-associated EVs secretion and subsequently enhanced MVBs number. Furthermore, we found that excessive accumulation of MVBs harboring APP-CTFβ/Aβ promoted the MVBs-lysosome fusion for degradation and inhibition of lysosomal function rescued secretion of APP-CTFβ/Aβ-associated EVs. More importantly, whole exon sequencing of KIBRA in a large population-based cohort identified the association of KIBRA rs28421695 polymorphism with plasma Aβ levels.

Interpretation

These results demonstrate that KIBRA regulates Aβ metabolism via controlling the secretion of APP-CTFβ/Aβ-associated EVs.

Funding

National Key R&D Program of China, and National Natural Science Foundation of China.

Apolipoprotein E, a Crucial Cellular Protein in the Lifecycle of Hepatitis Viruses

Apolipoprotein E (ApoE) is a multifunctional protein expressed in several tissues, including those of the liver. This lipoprotein component is responsible for maintaining lipid content homeostasis at the plasma and tissue levels by transporting lipids between the liver and peripheral tissues. The ability of ApoE to interact with host-cell surface receptors and its involvement in several cellular pathways raised questions about the hijacking of ApoE by hepatotropic viruses. Hepatitis C virus (HCV) was the first hepatitis virus reported to be dependent on ApoE for the completion of its lifecycle, with ApoE being part of the viral particle, mediating its entry into host cells and contributing to viral morphogenesis. Recent studies of the hepatitis B virus (HBV) lifecycle have revealed that this virus and its subviral envelope particles also incorporate ApoE. ApoE favors HBV entry and is crucial for the morphogenesis of infectious particles, through its interaction with HBV envelope glycoproteins. This review summarizes the data highlighting the crucial role of ApoE in the lifecycles of HBV and HCV and discusses its potential role in the lifecycle of other hepatotropic viruses.

[Tetraspanins and syndecans: Partners in crime for 'dealing' exosomes?]

Exosomes are small extracellular vesicles derived from endosomal compartments. The molecular mechanisms supporting the biology of exosomes, from their biogenesis to their internalization by target cells, rely on 'dedicated' membrane proteins. These mechanisms of action need to be further clarified. This will help to better understand how exosome composition and heterogeneity are established. This would also help to rationalize their use as source of biomarkers and therapeutic tools. Here we discuss how syndecans and tetraspanins, two families of membrane scaffold proteins, cooperate to regulate different steps of exosome biology.

Extracellular WNTs: Trafficking, Exosomes, and Ligand-Receptor Interaction

WNT signaling is a key developmental pathway in tissue organization. A recent focus of research is the secretion of WNT proteins from source cells. Research over the past decade on how WNTs are produced and released into the extracellular space has unravelled very specific control mechanisms in the early secretory pathway, specialized trafficking routes, and redundant forms of packaging for delivery to target cells. In this review I discuss the findings that WNT proteins have been found on extracellular vesicles (EVs) such as exosomes and possible functional implications. There is an ongoing debate in the WNT signaling field whether EV are relevant in vivo and can fulfill specific functions, also fueled by the general preconception of EV secretion as cellular garbage disposal. As part of the EV research community, I want to give an overview of what we know and don't know about WNT secretion on EVs and offer a more unifying model that can explain current discrepancies in observations regarding WNT secretion.

Extracellular vesicles in cardiovascular disease: Biological functions and therapeutic implications

Extracellular vesicles (EVs), including exosomes and microvesicles, are lipid bilayer particles naturally released from the cell. While exosomes are formed as intraluminal vesicles (ILVs) of the multivesicular endosomes (MVEs) and released to extracellular space upon MVE-plasma membrane fusion, microvesicles are generated through direct outward budding of the plasma membrane. Exosomes and microvesicles have same membrane orientation, different yet overlapping sizes; their cargo contents are selectively packed and dependent on the source cell type and functional state. Both exosomes and microvesicles can transfer bioactive RNAs, proteins, lipids, and metabolites from donor to recipient cells and influence the biological properties of the latter. Over the last decade, their potential roles as effective inter-tissue communicators in cardiovascular physiology and pathology have been increasingly appreciated. In addition, EVs are attractive sources of biomarkers for the diagnosis and prognosis of diseases, because they acquire their complex cargoes through cellular processes intimately linked to disease pathogenesis. Furthermore, EVs obtained from various stem/progenitor cell populations have been tested as cell-free therapy in various preclinical models of cardiovascular diseases and demonstrate unequivocally encouraging benefits. Here we summarize the findings from recent research on the biological functions of EVs in the ischemic heart disease and heart failure, and their potential as novel diagnostic biomarkers and therapeutic opportunities.

Proinflammatory Extracellular Vesicle-Mediated Signaling Contributes to the Induction of Neuroinflammation in Animal Models of Endotoxemia and Peripheral Surgical Stress

Peripheral inflammation induced by endotoxemia or surgical stress induces neuroinflammation thereby causing neurological symptoms ranging from sickness behavior to delirium. Thus, proinflammatory signaling must be operative between the periphery and the central nervous system (CNS). In the present study, we tested whether nanometer-sized extracellular vesicles (EVs) that were produced during the peripheral inflammatory process have the capacity to induce neuroinflammation. Conditions of endotoxemia or surgical intervention were simulated in rats by lipopolysaccharide (LPS) injection or partial hepatectomy (HpX). EVs were concentrated from these animals and tested for their proinflammatory action (I) in a microglial cell line and (II) by intracerebroventricular and (III) by intravenous injections into healthy rats. EVs from both conditions induced the secretion of cytokines from the glial cell line. Intracerebroventricular injection of the EVs caused the release of inflammatory cytokines to the cerebrospinal fluid indicating their pro-neuroinflammatory capacity. Finally, proinflammatory EVs were shown to pass the blood-brain barrier and induce neuroinflammation after their intravenous injection. Based on these data, we suggest that EV-associated proinflammatory signaling contributes to the induction of neuroinflammation in endotoxemia and peripheral surgical stress. Preliminary results suggest that peripheral cholinergic signals might be involved in the control of proinflammatory EV-mediated signaling from the periphery to the brain.

The impaired unfolded protein-premelanosome protein and transient receptor potential channels-autophagy axes in apoptotic melanocytes in vitiligo

Vitiligo is an autoimmune skin disease, characterized by depigmentation and epidermal melanocytes loss. The specific mechanisms underlying vitiligo have not been fully understood. As a result, treating vitiligo is a dermatological challenge. Recently, much attention has been paid to the dysfunction and interaction of organelles under environmental stress. The impaired organelles could generate misfolded proteins, particularly accumulated toxic premelanosome protein (PMEL) amyloid oligomers, activating the autoimmune system and cause melanocyte damage. Unfolded protein response (UPR) dysfunction accelerates toxic PMEL accumulation. Herein, we presented a narrative review on UPR's role in vitiligo, the misfolded PMEL-induced attack of the autoimmune system under autophagy dysfunction caused by abnormal activation of transient receptor potential (TRP) channels and the background of UPR system defects in melanocytes. All of these mechanisms were integrated to form UPR/PMEL-TRP channels/autophagy axis, providing a new understanding of vitiligo pathogenesis.

Melanosome biogenesis in the pigmentation of mammalian skin

Melanins, the main pigments of the skin and hair in mammals, are synthesized within membrane-bound organelles of melanocytes called melanosomes. Melanosome structure and function are determined by a cohort of resident transmembrane proteins, many of which are expressed only in pigment cells, that localize specifically to melanosomes. Defects in the genes that encode melanosome-specific proteins or components of the machinery required for their transport in and out of melanosomes underlie various forms of ocular or oculocutaneous albinism, characterized by hypopigmentation of the hair, skin and eyes and by visual impairment. We review major components of melanosomes, including the enzymes that catalyze steps in melanin synthesis from tyrosine precursors, solute transporters that allow these enzymes to function, and structural proteins that underlie melanosome shape and melanin deposition. We then review the molecular mechanisms by which these components are biosynthetically delivered to newly forming melanosomes-many of which are shared by other cell types that generate cell type-specific lysosome-related organelles. We also highlight unanswered questions that need to be addressed by future investigation.

Rapid separation of blood plasma exosomes from low-density lipoproteins via a hydrophobic interaction chromatography method on a polyester capillary-channeled polymer fiber phase

Exosomes are membrane-bound, cell-secreted vesicles, with sizes ranging from 30 to 150 nm. Exosomes in blood plasma have become proposed targets as measurable indicators of disease conditions. Current methods for plasma-based exosome isolation are time-consuming, complex, and have high operational costs. One of the most commonly reported shortcomings of current isolation protocols is the co-extraction of lipoproteins (e.g. low-density lipoproteins, LDLs) with the target exosomes. This report describes the use of a rapid, single-operation hydrophobic interaction chromatography (HIC) procedure on a polyester (PET) capillary-channeled polymer (C-CP) fiber column, demonstrating the ability to efficiently purify exosomes. The method has previously been demonstrated for isolation of exosomes from diverse biological matrices, but questions were raised about the potential co-elution of LDLs. In the method described herein, a step-gradient procedure sequentially elutes spiked lipoproteins and blood plasma-originating exosomes in 10 min, with the LDLs excluded from the desired exosome fraction. Mass spectrometry (MS) was used to characterize an impurity in the primary LDL material, identifying the presence of exosomal material. Transmission electron microscopy (TEM) and an enzyme-linked immunosorbent assay (ELISA) were used to identify the various elution components. The method serves both as a rapid means of high purity exosome isolation as well as a screening tool for the purity of LDL samples with respect to extracellular vesicles.

The emerging role of β-secretases in cancer

BACE1 and BACE2 belong to a class of proteases called β-secretases involved in ectodomain shedding of different transmembrane substrates. These enzymes have been extensively studied in Alzheimer's disease as they are responsible for the processing of APP in neurotoxic Aβ peptides. These proteases, especially BACE2, are overexpressed in tumors and correlate with poor prognosis. Recently, different research groups tried to address the role of BACE1 and 2 in cancer development and progression. In this review, we summarize the latest findings on β-secretases in cancer, highlighting the mechanisms that build the rationale to propose inhibitors of these proteins as a new line of treatment for different tumor types.

The exosome journey: from biogenesis to uptake and intracellular signalling

The use of exosomes in clinical settings is progressively becoming a reality, as clinical trials testing exosomes for diagnostic and therapeutic applications are generating remarkable interest from the scientific community and investors. Exosomes are small extracellular vesicles secreted by all cell types playing intercellular communication roles in health and disease by transferring cellular cargoes such as functional proteins, metabolites and nucleic acids to recipient cells. An in-depth understanding of exosome biology is therefore essential to ensure clinical development of exosome based investigational therapeutic products. Here we summarise the most up-to-date knowkedge about the complex biological journey of exosomes from biogenesis and secretion, transport and uptake to their intracellular signalling. We delineate the major pathways and molecular players that influence each step of exosome physiology, highlighting the routes of interest, which will be of benefit to exosome manipulation and engineering. We highlight the main controversies in the field of exosome research: their adequate definition, characterisation and biogenesis at plasma membrane. We also delineate the most common identified pitfalls affecting exosome research and development. Unravelling exosome physiology is key to their ultimate progression towards clinical applications.

Identification of critical amino acid residues in the regulatory N-terminal domain of PMEL

The pigment cell-specific protein PMEL forms a functional amyloid matrix in melanosomes onto which the pigment melanin is deposited. The amyloid core consists of a short proteolytic fragment, which we have termed the core-amyloid fragment (CAF) and perhaps additional parts of the protein, such as the PKD domain. A highly O-glycosylated repeat (RPT) domain also derived from PMEL proteolysis associates with the amyloid and is necessary to establish the sheet-like morphology of the assemblies. Excluded from the aggregate is the regulatory N-terminus, which nevertheless must be linked in cis to the CAF in order to drive amyloid formation. The domain is then likely cleaved away immediately before, during, or immediately after the incorporation of a new CAF subunit into the nascent amyloid. We had previously identified a 21 amino acid long region, which mediates the regulatory activity of the N-terminus towards the CAF. However, many mutations in the respective segment caused misfolding and/or blocked PMEL export from the endoplasmic reticulum, leaving their phenotype hard to interpret. Here, we employ a saturating mutagenesis approach targeting the motif at single amino acid resolution. Our results confirm the critical nature of the PMEL N-terminal region and identify several residues essential for PMEL amyloidogenesis.

Extracellular Vesicles from Red Blood Cells and Their Evolving Roles in Health, Coagulopathy and Therapy

Red blood cells (RBCs) release extracellular vesicles (EVs) including both endosome-derived exosomes and plasma-membrane-derived microvesicles (MVs). RBC-derived EVs (RBCEVs) are secreted during erythropoiesis, physiological cellular aging, disease conditions, and in response to environmental stressors. RBCEVs are enriched in various bioactive molecules that facilitate cell to cell communication and can act as markers of disease. RBCEVs contribute towards physiological adaptive responses to hypoxia as well as pathophysiological progression of diabetes and genetic non-malignant hematologic disease. Moreover, a considerable number of studies focus on the role of EVs from stored RBCs and have evaluated post transfusion consequences associated with their exposure. Interestingly, RBCEVs are important contributors toward coagulopathy in hematological disorders, thus representing a unique evolving area of study that can provide insights into molecular mechanisms that contribute toward dysregulated hemostasis associated with several disease conditions. Relevant work to this point provides a foundation on which to build further studies focused on unraveling the potential roles of RBCEVs in health and disease. In this review, we provide an analysis and summary of RBCEVs biogenesis, composition, and their biological function with a special emphasis on RBCEV pathophysiological contribution to coagulopathy. Further, we consider potential therapeutic applications of RBCEVs.

Functional Amyloids Are the Rule Rather Than the Exception in Cellular Biology

Amyloids are a class of protein aggregates that have been historically characterized by their relationship with human disease. Indeed, amyloids can be the result of misfolded proteins that self-associate to form insoluble, extracellular plaques in diseased tissue. For the first 150 years of their study, the pathogen-first definition of amyloids was sufficient. However, new observations of amyloids foster an appreciation for non-pathological roles for amyloids in cellular systems. There is now evidence from all domains of life that amyloids can be non-pathogenic and functional, and that their formation can be the result of purposeful and controlled cellular processes. So-called functional amyloids fulfill an assortment of biological functions including acting as structural scaffolds, regulatory mechanisms, and storage mechanisms. The conceptual convergence of amyloids serving a functional role has been repeatedly confirmed by discoveries of additional functional amyloids. With dozens already known, and with the vigorous rate of discovery, the biology of amyloids is robustly represented by non-pathogenic amyloids.

Transcriptomic Profiling of Human Pluripotent Stem Cell-derived Retinal Pigment Epithelium over Time

Human pluripotent stem cell (hPSC)-derived progenies are immature versions of cells, presenting a potential limitation to the accurate modelling of diseases associated with maturity or age. Hence, it is important to characterise how closely cells used in culture resemble their native counterparts. In order to select appropriate time points of retinal pigment epithelium (RPE) cultures that reflect native counterparts, we characterised the transcriptomic profiles of the hPSC-derived RPE cells from 1- and 12-month cultures. We differentiated the human embryonic stem cell line H9 into RPE cells, performed single-cell RNA-sequencing of a total of 16,576 cells to assess the molecular changes of the RPE cells across these two culture time points. Our results indicate the stability of the RPE transcriptomic signature, with no evidence of an epithelial–mesenchymal transition, and with the maturing populations of the RPE observed with time in culture. Assessment of Gene Ontology pathways revealed that as the cultures age, RPE cells upregulate expression of genes involved in metal binding and antioxidant functions. This might reflect an increased ability to handle oxidative stress as cells mature. Comparison with native human RPE data confirms a maturing transcriptional profile of RPE cells in culture. These results suggest that long-term in vitro culture of RPE cells allows the modelling of specific phenotypes observed in native mature tissues. Our work highlights the transcriptional landscape of hPSC-derived RPE cells as they age in culture, which provides a reference for native and patient samples to be benchmarked against.

Extracellular Vesicles in Viral Infections: Two Sides of the Same Coin?

Extracellular vesicles are small membrane structures containing proteins and nucleic acids that are gaining a lot of attention lately. They are produced by most cells and can be detected in several body fluids, having a huge potential in therapeutic and diagnostic approaches. EVs produced by infected cells usually have a molecular signature that is very distinct from healthy cells. For intracellular pathogens like viruses, EVs can have an even more complex function, since the viral biogenesis pathway can overlap with EV pathways in several ways, generating a continuum of particles, like naked virions, EVs containing infective viral genomes and quasi-enveloped viruses, besides the classical complete viral particles that are secreted to the extracellular space. Those particles can act in recipient cells in different ways. Besides being directly infective, they also can prime neighbor cells rendering them more susceptible to infection, block antiviral responses and deliver isolated viral molecules. On the other hand, they can trigger antiviral responses and cytokine secretion even in uninfected cells near the infection site, helping to fight the infection and protect other cells from the virus. This protective response can also backfire, when a massive inflammation facilitated by those EVs can be responsible for bad clinical outcomes. EVs can help or harm the antiviral response, and sometimes both mechanisms are observed in infections by the same virus. Since those pathways are intrinsically interlinked, understand the role of EVs during viral infections is crucial to comprehend viral mechanisms and respond better to emerging viral diseases.

Analysis of the regenerative capacity of human serum exosomes after a simple multistep separation from lipoproteins

Due to the abundance of lipoproteins in blood, it is challenging to characterize the biological functions and components of blood-derived extracellular vesicles. The aim of this study was to develop a multiple-step purification protocol to separate serum exosomes from serum proteins and lipoproteins and assess their regenerative potential. Exosomes were isolated by concentrating them in human serum using ultracentrifugation (UC), followed sequentially by density gradient (DG) UC and size exclusion chromatography (SEC). Purity and characterization were assessed by western blots, Lipoprint®, enzyme-linked immunosorbent assay, electron microscopy, mass spectrometry, and nanoparticle tracking analysis. Functionality was assessed by cell proliferation analysis and with an in vivo subcutaneous angiogenesis model. SEC alone isolated nano-sized vesicles possessing vesicle markers TSG101 and CD9, but there was a substantial presence of apolipoprotein B, predominantly derived from very-low- and intermediate-density lipoprotein particles. This was reduced to an undetectable level using the combined UC DG SEC approach. Mass spectrometry identified 224 proteins in UC DG SEC isolates relative to the 135 from SEC, with considerable increases in exosome-related proteins and reductions in lipoproteins. A consistent but limited increase in human dermal fibroblast proliferation and evidence of neovascularization enhancement were observed after exposure to UC DG SEC exosomes. An UC DG SEC purification protocol considerably improved the removal of lipoproteins during isolation of serum exosomes. The purified exosomes stimulated cell proliferation and potentially increased an in vivo angiogenic response. This multistep purification allows for more accurate identification of serum exosome functional activity and composition.

ALIX- and ESCRT-III-dependent sorting of tetraspanins to exosomes

The intraluminal vesicles (ILVs) of endosomes mediate the delivery of activated signaling receptors and other proteins to lysosomes for degradation, but they also modulate intercellular communication when secreted as exosomes. The formation of ILVs requires four complexes, ESCRT-0, -I, -II, and -III, with ESCRT-0, -I, and -II presumably involved in cargo sorting and ESCRT-III in membrane deformation and fission. Here, we report that an active form of the ESCRT-associated protein ALIX efficiently recruits ESCRT-III proteins to endosomes. This recruitment occurs independently of other ESCRTs but requires lysobisphosphatidic acid (LBPA) in vivo, and can be reconstituted on supported bilayers in vitro. Our data indicate that this ALIX- and ESCRT-III-dependent pathway promotes the sorting and delivery of tetraspanins to exosomes. We conclude that ALIX provides an additional pathway of ILV formation, secondary to the canonical pathway, and that this pathway controls the targeting of exosomal proteins.

Amyloid aggregates accumulate in melanoma metastasis modulating YAP activity

Melanoma progression is generally associated with increased transcriptional activity mediated by the Yes-associated protein (YAP). Mechanical signals from the extracellular matrix are sensed by YAP, which then activates the expression of proliferative genes, promoting melanoma progression and drug resistance. Which extracellular signals induce mechanotransduction, and how this is mediated, is not completely understood. Here, using secretome analyses, we reveal the extracellular accumulation of amyloidogenic proteins, i.e. premelanosome protein (PMEL), in metastatic melanoma, together with proteins that assist amyloid maturation into fibrils. We also confirm the accumulation of amyloid-like aggregates, similar to those detected in Alzheimer disease, in metastatic cell lines, as well as in human melanoma biopsies. Mechanistically, beta-secretase 2 (BACE2) regulates the maturation of these aggregates, which in turn induce YAP activity. We also demonstrate that recombinant PMEL fibrils are sufficient to induce mechanotransduction, triggering YAP signaling. Finally, we demonstrate that BACE inhibition affects cell proliferation and increases drug sensitivity, highlighting the importance of amyloids for melanoma survival, and the use of beta-secretase inhibitors as potential therapeutic approach for metastatic melanoma.

Transmissible Endosomal Intoxication: A Balance between Exosomes and Lysosomes at the Basis of Intercellular Amyloid Propagation

In Alzheimer′s disease (AD), endolysosomal dysfunctions are amongst the earliest cellular features to appear. Each organelle of the endolysosomal system, from the multivesicular body (MVB) to the lysosome, contributes to the homeostasis of amyloid precursor protein (APP) cleavage products including β-amyloid (Aβ) peptides. Hence, this review will attempt to disentangle how changes in the endolysosomal system cumulate to the generation of toxic amyloid species and hamper their degradation. We highlight that the formation of MVBs and the generation of amyloid species are closely linked and describe how the molecular machineries acting at MVBs determine the generation and sorting of APP cleavage products towards their degradation or release in association with exosomes. In particular, we will focus on AD-related distortions of the endolysomal system that divert it from its degradative function to favour the release of exosomes and associated amyloid species. We propose here that such an imbalance transposed at the brain scale poses a novel concept of transmissible endosomal intoxication (TEI). This TEI would initiate a self-perpetuating transmission of endosomal dysfunction between cells that would support the propagation of amyloid species in neurodegenerative diseases.