Identification and characterization of hADSC-derived exosome proteins from different isolation methods

Exosomes are secreted into the extracellular space by most cell types and contain various molecular constituents, which play roles in many biological processes. Adipose-derived mesenchymal stem cells (ADSCs) can differentiate into a variety of cell types and secrete a series of paracrine factors through exosomes. ADSC-derived exosomes have shown diagnostic and therapeutic potential in many clinical diseases. The molecular components are critical for their mechanisms. Several methods have been developed for exosome purification, including ultracentrifugation, ultrafiltration, density gradient purification, size-based isolation, polymer precipitation and immuno-affinity purification. Thus, we employed four methods to isolate exosomes from the hADSC culture medium, including ultracentrifugation, size exclusion chromatography, ExoQuick-TC precipitation and ExoQuick-TC ULTRA isolation. Following exosome isolation, we performed quantitative proteomic analysis of the exosome proteins using isobaric tags for relative and absolute quantification (iTRAQ) labelling, combined with 2D-LC-MS/MS. There were 599 universal and 138 stably expressed proteins in hADSC-derived exosomes. We proved that these proteins were potential hADSC-derived exosomes markers, including CD109, CD166, HSPA4, TRAP1, RAB2A, RAB11B and RAB14. From the quantitative proteomic analysis, we demonstrated that hADSC-derived exosome protein expression varied, with lipopolysaccharide (LPS) treatment, in the different isolation methods. Pathway analysis and proliferation, migration and endothelial tube formation assays showed varying effects in cells stimulated with hADSC-derived exosomes from different isolation methods. Our study revealed that different isolation methods might introduce variations in the protein composition in exosomes, which reflects their effects on biological function. The pros and cons of these methods are important points to consider for downstream research applications.     

Visualizing of the cellular uptake and intracellular trafficking of exosomes by live‐cell microscopy

Cells release exosomes to transfer various molecules to other cells. Exosomes are involved in a number of physiological and pathological processes. They are emerging great potential utility for diseases diagnosis and treatment recently. However, the internalization and intracellular trafficking of exosomes have not been described clearly. In this work, exosomes were isolated from the culture medium of PC12 cells, labeled by lipophilic dye and amino‐reactive fluorophore, incubated with resting PC12 cells. The results of live‐cell microscopy indicated that exosomes were internalized through endocytosis pathway, trapped in vesicles, and transported to perinuclear region. Particle tracking fluorescent vesicles suggested that the active transport of exosomes may be mediated by cytoskeleton. The proteins on exosome membrane were found to be released from exosomes and trapped in lysosome. The inverted transport of lipophilic dye from perinuclear region to cell peripheries was revealed, possibly caused by recycling of the exosome lipids. This study provides new sight into the mechanisms of exosome uptake and intracellular fate. J. Cell. Biochem. 111: 488–496, 2010. © 2010 Wiley‐Liss, Inc.     

Exosomes Released from Breast Cancer Carcinomas Stimulate Cell Movement

For metastasis to occur cells must communicate with to their local environment to initiate growth and invasion. Exosomes have emerged as an important mediator of cell-to-cell signalling through the transfer of molecules such as mRNAs, microRNAs, and proteins between cells. Exosomes have been proposed to act as regulators of cancer progression. Here, we study the effect of exosomes on cell migration, an important step in metastasis. We performed cell migration assays, endocytosis assays, and exosome proteomic profiling on exosomes released from three breast cancer cell lines that model progressive stages of metastasis. Results from these experiments suggest: (1) exosomes promote cell migration and (2) the signal is stronger from exosomes isolated from cells with higher metastatic potentials; (3) exosomes are endocytosed at the same rate regardless of the cell type; (4) exosomes released from cells show differential enrichment of proteins with unique protein signatures of both identity and abundance. We conclude that breast cancer cells of increasing metastatic potential secrete exosomes with distinct protein signatures that proportionally increase cell movement and suggest that released exosomes could play an active role in metastasis.     

Exosome-based immunotherapy

Exosomes are small membrane vesicles originating from late endosomes and secreted by hematopoietic and epithelial cells in culture. Exosome proteic and lipid composition is unique and might shed some light into exosome biogenesis and function. Exosomes secreted from professional antigen-presenting cells (i.e., B lymphocytes and dendritic cells) are enriched in MHC class I and II complexes, costimulatory molecules, and hsp70–90 chaperones, and have therefore been more extensively studied for their immunomodulatory capacities in vitro and in vivo. This review will present the main biological features pertaining to tumor or DC-derived exosomes, will emphasize their immunostimulatory function, and will discuss their implementation in cancer immunotherapy.Abbreviations APC antigen-presenting cell - ASI active specific immunotherapy - CTL cytotoxic T lymphocyte - DC dendritic cell - FDC follicular dendritic cell - MD-DC monocyte-derived dendritic cell - GMP good manufacturing procedure - HLA human leukocyte antigen - HSP heat shock protein - MHC major histocompatibility complex - MVB multivesicular body - ExAs ascitis-derived exosomes - DEX DC-derived exosome - TEX tumor cell–derived exosome This work was presented at the first Cancer Immunology and Immunotherapy Summer School, 8–13 September 2003, Ionian Village, Bartholomeio, Peloponnese, Greece.     

Myotube-derived exosomal miRNAs downregulate Sirtuin1 in myoblasts during muscle cell differentiation

It has recently been established that exosomes can mediate intercellular cross-talk under normal and pathological conditions through the transfer of specific miRNAs. As muscle cells secrete exosomes, we addressed the question of whether skeletal muscle (SkM) exosomes contained specific miRNAs, and whether they could act as “endocrine signals” during myogenesis. We compared the miRNA repertoires found in exosomes released from C2C12 myoblasts and myotubes and found that 171 and 182 miRNAs were exported into exosomes from myoblasts and myotubes, respectively. Interestingly, some miRNAs were expressed at higher levels in exosomes than in their donor cells and vice versa, indicating a selectivity in the incorporation of miRNAs into exosomes. Moreover miRNAs from C2C12 exosomes were regulated during myogenesis. The predicted target genes of regulated exosomal miRNAs are mainly involved in the control of important signaling pathways for muscle cell differentiation (e.g., Wnt signaling pathway). We demonstrated that exosomes from myotubes can transfer small RNAs (C. elegans miRNAs and siRNA) into myoblasts. Moreover, we present evidence that exosome miRNAs secreted by myotubes are functionally able to silence Sirt1 in myoblasts. As Sirt1 regulates muscle gene expression and differentiation, our results show that myotube–exosome miRNAs could contribute to the commitment of myoblasts in the process of differentiation. Until now, myokines in muscle cell secretome provided a conceptual basis for communication between muscles. Here, we show that miRNA exosomal transfer would be a powerful means by which gene expression is orchestrated to regulate SkM metabolic homeostasis.     

Protein profile of exosomes from trabecular meshwork cells

To better understand the role of exosomes in the trabecular meshwork (TM), the site of intraocular pressure control, the exosome proteome from primary cultures of human TM cell monolayers was analyzed. Exosomes were purified from urine and conditioned media from primary cultures of human TM cell monolayers and subjected to a two dimensional HPLC separation and MS/MS analyses using the MudPIT strategy. Spectra were searched against a human protein database using Sequest. Protein profiles were compared to each other and the Exocarta database and the presence of specific protein markers confirmed by Western blot analyses of exosomes from aqueous humor and human TM cell strains (n=5) that were untreated, or exposed to dexamethasone and/or ionomycin. TM cell exosomes contained 108 of the 143 most represented exosome proteins in ExoCarta, including previously characterized markers such as membrane organizing and tetraspanin proteins. Several cell-specific proteins in TM exosomes were identified including myocilin, emilin-1 and neuropilin-1. All TM exosome proteins had flotation densities on sucrose gradients and release responses to ionomycin typical for exosomes. Taken together, TM exosomes have a characteristic exosome protein profile plus contain unique proteins, including the glaucoma-causing protein, myocilin; suggesting a role for exosomes in the control of intraocular pressure.     

Microenvironmental pH Is a Key Factor for Exosome Traffic in Tumor Cells

Exosomes secreted by normal and cancer cells carry and deliver a variety of molecules. To date, mechanisms referring to tumor exosome trafficking, including release and cell-cell transmission, have not been described. To gain insight into this, exosomes purified from metastatic melanoma cell medium were labeled with a lipid fluorescent probe, R18, and analyzed by spectrofluorometry and confocal microscopy. A low pH condition is a hallmark of tumor malignancy, potentially influencing exosome release and uptake by cancer cells. Using different pH conditions as a modifier of exosome traffic, we showed (i) an increased exosome release and uptake at low pH when compared with a buffered condition and (ii) exosome uptake by melanoma cells occurred by fusion. Membrane biophysical analysis, such as fluidity and lipid composition, indicated a high rigidity and sphingomyelin/ganglioside GM3 (N-acetylneuraminylgalactosylglucosylceramide) content in exosomes released at low pH. This was likely responsible for the increased fusion efficiency. Consistent with these results, pretreatment with proton pump inhibitors led to an inhibition of exosome uptake by melanoma cells. Fusion efficiency of tumor exosomes resulted in being higher in cells of metastatic origin than in those derived from primary tumors or normal cells. Furthermore, we found that caveolin-1, a protein involved in melanoma progression, is highly delivered through exosomes released in an acidic condition. The results of our study provide the evidence that exosomes may be used as a delivery system for paracrine diffusion of tumor malignancy, in turn supporting the importance of both exosomes and tumor pH as key targets for future anti-cancer strategies.     

Exosome-mediated transduction of mechanical force regulates prostate cancer migration via microRNA

Physical cues in the extracellular microenvironment regulate cancer cell metastasis. Functional microRNA (miRNA) carried by cancer derived exosomes play a critical role in extracellular communication between cells and the extracellular microenvironment. However, little is known about the role of exosomes loaded miRNAs in the mechanical force transmission between cancer cells and extracellular microenvironment. Herein, our results suggest that stiff extracellular matrix (ECM) induced exosomes promote cancer cell migration. The ECM mechanical force regulated the exosome miRNA cargo of prostate cancer cells. Exosome miRNAs regulated by the ECM mechanical force modulated cancer cell metastasis by regulating cell motility, ECM remodeling and the interaction between cancer cells and nerves. Focal adhesion kinase mediated-ECM mechanical force regulated the intracellular miRNA expression, and F-actin mediate-ECM mechanical force regulated miRNA packaging into exosomes. The above results demonstrated that the exosome miRNA cargo promoted cancer metastasis by transmitting the ECM mechanical force. The ECM mechanical force may play multiple roles in maintaining the microenvironment of cancer metastasis through the exosome miRNA cargo.     

外泌体分泌在1,4-苯醌诱导的HL-60细胞凋亡中起保护作用

慢性苯暴露损害造血系统,可引起再生障碍性贫血,甚至白血病。外泌体(exosomes)是细胞分泌的纳米级膜泡,在许多生理和病理过程中发挥重要作用。然而,苯及其代谢产物对外泌体分泌的影响仍不清楚。本研究旨在观察苯的活性代谢产物1,4-苯醌(1,4-benzoquinone,1,4-BQ)能否引起人早幼粒白血病细胞HL-60外泌体分泌量的变化以及外泌体释放在1,4-BQ诱导的细胞凋亡中的作用。应用不同浓度1,4-BQ处理细胞24 h,超高速离心法提取细胞培养基中的外泌体,结果发现1,4-BQ能促进外泌体分泌,呈剂量反应关系。进一步应用外泌体抑制剂GW4869抑制外泌体分泌,流式细胞仪检测细胞凋亡率、蛋白质免疫印迹法检测抑凋亡蛋白质Bcl-2、凋亡通路关键蛋白质cleaved caspase-9和cleaved caspase-3的表达,探讨外泌体分泌对1,4-BQ所致细胞凋亡的影响。结果显示:与对照组相比,1,4-BQ单独处理组的凋亡率、Bcl-2、cleaved caspase-9和cleaved caspase-3的表达均显著增高(P<0.05),而1,4-BQ+GW4869组的凋亡率及凋亡相关蛋白质的表达均显著高于1,4-BQ单独处理组(P<0.05),表明抑制外泌体分泌可增加1,4-BQ诱导的细胞凋亡。综上表明,1,4-BQ能促进外泌体分泌,并在1,4-BQ诱导的细胞凋亡中起保护作用。本研究为了解苯的毒性效应和毒性机制提供了新的实验证据。     

The therapeutic potential of immune cell-derived exosomes as an alternative to adoptive cell transfer

Adoptive cell transfer (ACT), a form of cell-based immunotherapy that eliminates cancer by restoring and strengthening the body’s immune system, has revolutionized cancer treatment. ACT entails intravenous transfer of either tumor-resident or peripheral blood-modified immune cells into cancer patients to mediate anti-tumor response. Although these immune cells control and eradicate cancer via enhanced cytotoxicity against specific tumor antigens, several side effects have been frequently reported in clinical trials. Recently, exosomes, potential cell-free therapeutics, have emerged as an alternative to cell-based immunotherapies, due to their higher stability under same storage condition, lower risk of GvHD and CRS, and higher resistance to immunosuppressive tumor microenvironment. Exosomes, which are nano-sized lipid vesicles, are secreted by living cells, including immune cells. Exosomes contain proteins, lipids, and nucleic acids, and the functional role of each exosome is determined by the specific cargo derived from parental cells. Exosomes derived from cytotoxic effectors including T cells and NK cells exert anti-tumor effects via proteins such as granzyme B and FasL. In this mini-review, we describe the current understanding of the ACT and immune cell-derived exosomes and discuss the limitations of ACT and the opportunities for immune cell-derived exosomes as immune therapies.     

Molecular characterization of dendritic cell-derived exosomes. Selective accumulation of the heat shock protein hsc73.

Exosomes are membrane vesicles secreted by hematopoietic cells upon fusion of late multivesicular endosomes with the plasma membrane. Dendritic cell (DC)-derived exosomes induce potent antitumor immune responses in mice, resulting in the regression of established tumors (Zitvogel, L., A. Regnault, A. Lozier, J. Wolfers, C. Flament, D. Tenza, P. Ricciardi-Castagnoli, G. Raposo, and S. Amigorena. 1998. Nat. Med. 4:594-600). To unravel the molecular basis of exosome-induced immune stimulation, we now analyze the regulation of their production during DC maturation and characterize extensively their protein composition by peptide mass mapping. Exosomes contain several cytosolic proteins (including annexin II, heat shock cognate protein hsc73, and heteromeric G protein Gi2alpha), as well as different integral or peripherally associated membrane proteins (major histocompatibility complex class II, Mac-1 integrin, CD9, milk fat globule-EGF-factor VIII [MFG-E8]). MFG-E8, the major exosomal component, binds integrins expressed by DCs and macrophages, suggesting that it may be involved in exosome targeting to these professional antigen-presenting cells. Another exosome component is hsc73, a cytosolic heat shock protein (hsp) also present in DC endocytic compartments. hsc73 was shown to induce antitumor immune responses in vivo, and therefore could be involved in the exosome's potent antitumor effects. Finally, exosome production is downregulated upon DC maturation, indicating that in vivo, exosomes are produced by immature DCs in peripheral tissues. Thus, DC-derived exosomes accumulate a defined subset of cellular proteins reflecting their endosomal biogenesis and accounting for their biological function.     

Exosomes released from Mycoplasma infected tumor cells activate inhibitory B cells

Mycoplasmas cause numerous human diseases and are common opportunistic pathogens in cancer patients and immunocompromised individuals. Mycoplasma infection elicits various host immune responses. Here we demonstrate that mycoplasma-infected tumor cells release exosomes (myco+ exosomes) that specifically activate splenic B cells and induce splenocytes cytokine production. Induction of cytokines, including the proinflammatory IFN-γ and the anti-inflammatory IL-10, was largely dependent on the presence of B cells. B cells were the major IL-10 producers. In splenocytes from B cell deficient μMT mice, induction of IFN-γ+ T cells by myco+ exosomes was greatly increased compared with wild type splenocytes. In addition, anti-CD3-stimulated T cell proliferation was greatly inhibited in the presence of myco+ exosome-treated B cells. Also, anti-CD3-stimulated T cell signaling was impaired by myco+ exosome treatment. Proteomic analysis identified mycoplasma proteins in exosomes that potentially contribute to the effects. Our results demonstrate that mycoplasma-infected tumor cells release exosomes carrying mycoplasma components that preferentially activate B cells, which in turn, are able to inhibit T cell activity. These results suggest that mycoplasmas infecting tumor cells can exploit the exosome pathway to disseminate their own components and modulate the activity of immune cells, in particular, activate B cells with inhibitory activity.     

The role of exosomes in hepatitis,liver cirrhosis and hepatocellular carcinoma

Exosomes are small vesicles that were initially thought to be a mechanism for discarding unneeded membrane proteins from reticulocytes. Their mediation of intercellular communication appears to be associated with several biological functions. Current studies have shown that most mammalian cells undergo the process of exosome formation and utilize exosome‐mediated cell communication. Exosomes contain various microRNAs, mRNAs and proteins. They have been reported to mediate multiple functions, such as antigen presentation, immune escape and tumour progression. This concise review highlights the findings regarding the roles of exosomes in liver diseases, particularly hepatitis B, hepatitis C, liver cirrhosis and hepatocellular carcinoma. However, further elucidation of the contributions of exosomes to intercellular information transmission is needed. The potential medical applications of exosomes in liver diseases seem practical and will depend on the ingenuity of future investigators and their insights into exosome‐mediated biological processes.     

Cellular Internalization of Exosomes Occurs Through Phagocytosis

Exosomes play important roles in many physiological and pathological processes. However, the exosome–cell interaction mode and the intracellular trafficking pathway of exosomes in their recipient cells remain unclear. Here, we report that exosomes derived from K562 or MT4 cells are internalized more efficiently by phagocytes than by non‐phagocytic cells. Most exosomes were observed attached to the plasma membrane of non‐phagocytic cells, while in phagocytic cells these exosomes were found to enter via phagocytosis. Specifically, they moved to phagosomes together with phagocytic polystyrene carboxylate‐modified latex beads (biospheres) and were further sorted into phagolysosomes. Moreover, exosome internalization was dependent on the actin cytoskeleton and phosphatidylinositol 3‐kinase, and could be inhibited by the knockdown of dynamin2 or overexpression of a dominant‐negative form of dynamin2. Further, antibody pretreatment assays demonstrated that tim4 but not tim1 was involved in exosomes uptake. We also found that exosomes did not enter the internalization pathway involving caveolae, macropinocytosis and clathrin‐coated vesicles. Our observation that the cellular uptake of exosomes occurs through phagocytosis has important implications for exosome–cell interactions and the exosome intracellular trafficking pathway.     

Tumour‐derived exosomal miR‐3473b promotes lung tumour cell intrapulmonary colonization by activating the nuclear factor‐κB of local fibroblasts

Tumour‐derived exosomes have been shown to induce pre‐metastatic niche formation, favoring metastatic colonization of tumour cells, but the underlying molecular mechanism is still not fully understood. In this study, we showed that exosomes derived from the LLC cells could indeed significantly enhance their intrapulmonary colonization. Circulating LLC‐derived exosomes were mainly engulfed by lung fibroblasts and led to the NF‐κB signalling activation. Further studies indicated that the exosomal miR‐3473b was responsible for that by hindering the NFKB inhibitor delta's (NFKBID) function. Blocking miR‐3473b could reverse the exosome‐mediated NF‐κB activation of fibroblasts and decrease intrapulmonary colonization of lung tumour cells. Together, this study demonstrated that the miR‐3473b in exosomes could mediate the interaction of lung tumour cells and local fibroblasts in metastatic sites and, therefore, enhance the metastasis of lung tumour cells.     

Sequences within RNA coding for HIV‐1 Gag p17 are efficiently targeted to exosomes

HIV budding requires the interaction with cell factors involved in the biogenesis of exosomes. This implies the possibility that viral products undergo exosome incorporation. While this has been already described for both Gag and Nef HIV‐1 proteins, no conclusive results on HIV genome have been produced so far. Here, we report that unspliced, but not single or double spliced, HIV‐1 RNA species are incorporated in exosomes. Deletion mutant analysis indicated that the presence of a stretch of sequences within the 5′ end of the Gag p17 open reading frame is sufficient for HIV‐1 RNA exosome incorporation. These sequences were found associating with exosomes also out of the HIV‐1 context, thus indicating that the diversion towards the vesicular compartment can occur without need of additional HIV‐1 sequences. Finally, the incorporation of genomic HIV‐1 RNA in exosomes significantly increased when producer cells express HIV‐1 defective for viral genome packaging. Manipulating infected cells to favour the selective incorporation in exosomes of genomic HIV‐1 RNA might have therapeutic implications.     

Inhibiting Extracellular Vesicle Release from Human Cardiosphere Derived Cells with Lentiviral Knockdown of nSMase2 Differentially Effects Proliferation and Apoptosis in Cardiomyocytes,Fibroblasts and Endothelial Cells In Vitro

Numerous studies have shown a beneficial effect of cardiosphere-derived cell (CDC) therapy on regeneration of injured myocardium. Paracrine signaling by CDC secreted exosomes may contribute to improved cardiac function. However, it has not yet been demonstrated by a genetic approach that exosome release contributes to the therapeutic effect of transplanted CDCs. By employing a lentiviral knockdown (KD) strategy against neutral spingomyelinase 2 (nSMase2), a crucial gene in exosome secretion, we have defined the role of physiologically secreted human CDC-derived exosomes on cardiac fibroblast, endothelial cell and primary cardiomyocyte proliferation, cell death, migration and angiogenesis using a series of in vitro coculture assays. We found that secretion of hCDC-derived exosomes was effectively inhibited by nSMase2 lentiviral KD and shRNAi expression was stable and constitutive. hCDC exosome release contributed to the angiogenic and pro-migratory effects of hCDCs on HUVECs, decreased proliferation of fibroblasts, and decreased apoptosis of cardiomyocytes. These in vitro reactions support a role for exosome secretion as a paracrine mechanism of stem cell-mediated cardiac repair in vivo. Importantly, we have established a novel tool to test constitutive inhibition of exosome secretion in stem cell populations in animal models of cardiac disease.     

Exosomes derived from mature dendritic cells increase endothelial inflammation and atherosclerosis via membrane TNF‐α mediated NF‐κB pathway

Whether dendritic cell (DC) derived exosomes play a role in the progression of endothelial inflammation and atherosclerosis remains unclear. Using a transwell system and exosome release inhibitor GW4869, we demonstrated that mature DCs contributed to endothelial inflammation and exosomes were involved in the process. To further confirm this finding, we isolated exosomes from bone marrow dendritic cell (BMDC) culture medium (named DC‐exos) and stimulated human umbilical vein endothelial cell (HUVEC) with these DC‐exos. We observed that mature DC‐exos increased HUVEC inflammation through NF‐κB pathway in a manner similar to that of lipopolysaccharide. After a protein array analysis of exosomes, we identified and confirmed tumour necrosis factor (TNF)‐α on exosome membrane being the trigger of NF‐κB pathway in HUVECs. We then performed an in vivo study and found that the aorta endothelial of mice could uptake intravenously injected exosomes and was activated by these exosomes. After a period of 12 weeks of mature DC‐exos injection into ApoE?/? mice, the atherosclerotic lesions significantly increased. Our study demonstrates that mature DCs derived exosomes increase endothelial inflammation and atherosclerosis via membrane TNF‐α mediated NF‐κB pathway. This finding extends our knowledge on how DCs affect inflammation and provides a potential method to prevent endothelial inflammation and atherosclerosis.     

Oncogenic and Non‐Malignant Pancreatic Exosome Cargo Reveal Distinct Expression of Oncogenic and Prognostic Factors Involved in Tumor Invasion and Metastasis

Exosomes are small extracellular membrane vesicles important in intercellular communication, with their oncogenic cargo attributed to tumor progression and pre‐metastatic niche formation. To gain an insight into key differences in oncogenic composition of exosomes, human non‐malignant epithelial and pancreatic cancer cell models and purified and characterized resultant exosome populations are utilized. Proteomic analysis reveals the selective enrichment of known exosome markers and signaling proteins in comparison to parental cells. Importantly, valuable insights into oncogenic exosomes (362 unique proteins in comparison to non‐malignant exosomes) of key metastatic regulatory factors and signaling molecules fundamental to pancreatic cancer progression (KRAS, CD44, EGFR) are provided. It is reported that oncogenic exosomes contain factors known to regulate the pre‐metastatic niche (S100A4, F3, ITGβ5, ANXA1), clinically‐relevant proteins which correlate with poor prognosis (CLDN1, MUC1) as well as protein networks involved in various cancer hallmarks including proliferation (CLU, CAV1), invasion (PODXL, ITGA3), metastasis (LAMP1, ST14) and immune surveillance escape (B2M). The presence of these factors in oncogenic exosomes offers an understanding of select differences in exosome composition during tumorigenesis, potential components as prognostic and diagnostic biomarkers in pancreatic cancer, and highlights the role of exosomes in mediating crosstalk between tumor and stromal cells.     

Sphingolipid-modulated exosome secretion promotes clearance of amyloid-β by microglia

Amyloid β-peptide (Aβ), the pathogenic agent of Alzheimer disease, is a physiological metabolite whose levels are constantly controlled in normal brain. Recent studies have demonstrated that a fraction of extracellular Aβ is associated with exosomes, small membrane vesicles of endosomal origin, although the fate of Aβ in association with exosome is largely unknown. In this study, we identified novel roles for neuron-derived exosomes acting on extracellular Aβ, i.e. exosomes drive conformational changes in Aβ to form nontoxic amyloid fibrils and promote uptake of Aβ by microglia. The Aβ internalized together with exosomes was further transported to lysosomes and degraded. We also found that blockade of phosphatidylserine on the surface of exosomes by annexin V not only prevented exosome uptake but also suppressed Aβ incorporation into microglia. In addition, we demonstrated that secretion of neuron-derived exosomes was modulated by the activities of sphingolipid-metabolizing enzymes, including neutral sphingomyelinase 2 (nSMase2) and sphingomyelin synthase 2 (SMS2). In transwell experiments, up-regulation of exosome secretion from neuronal cells by treatment with SMS2 siRNA enhanced Aβ uptake into microglial cells and significantly decreased extracellular levels of Aβ. Our findings indicate a novel mechanism responsible for clearance of Aβ through its association with exosomes. The modulation of the vesicle release and/or elimination may alter the risk of AD.