Internalization of Exosomes through Receptor-Mediated Endocytosis

Oral cancer cell‑derived exosomes modulate natural killer cell activity by regulating the receptors on these cells

Oral cancer (OC) is the most common type of head and neck malignant tumor. Tumor‑derived exosomes induce a complex extracellular environment that affects tumor immunity. In the present study, exosomes were isolated from OC cell lines (WSU‑HN4 and SCC‑9) by ultrafiltration and the protein content of these oral cancer‑derived exosomes (OCEXs) was analyzed by mass spectrometry, which revealed the enrichment of transforming growth factor (TGF)‑β1. Natural killer (NK) cells were examined by flow cytometry following co‑culture with OCEXs. The expression of killer cell lectin like receptor K1 (KLRK1; also known as NKG2D, as used herein) and natural cytotoxicity triggering receptor 3 (NCR3; also known as NKp30, as used herein) in NK cells was found to be significantly upregulated following co‑culture with the OCEXs for 1 day, whereas this expression decreased at 7 days. Killer cell lectin like receptor C1 (KLRC1; also known as NKG2A; as used herein) expression exhibited an opposite trend at 1 day. In addition, NK cell cytotoxicity against the OC cells was enhanced at 1 day, but was attenuated at 7 days. TGF‑β1 inhibited the function of NK cells at 7 days, whereas it had no obvious effects at 1 and 3 days. On the whole, the findings of the present study reveal changes in NK cell function and provide new insight into NK cell dysfunction.

Interactions of childhood maltreatment and genetic variations in adult depression: A systematic review

Background Childhood maltreatment (CM) significantly increases the risk of adulthood psychopathology. Interplay between susceptible genetic variations and CM contributes to the occurrence of depression. This review aims to systematically synthesize the relationships between genetic variations and depression among those exposed to CM. Methods Electronic databases and gray literature to March 31st, 2020 were searched for literature on the topic of depression and CM limited to English-language. Data extraction and quality assessment of key study characteristics were conducted. Qualitative approaches were used to synthesize the findings. Results The initial search resulted in 9185 articles. A total of 29 articles that met the eligibility criteria were included in this review. High heterogeneity was identified regarding the study sample ages, candidate genes and SNPs, the categorization of CM and depression. The findings of this review include several frequently studied genes (5-HTTLPR, CRHR1, BDNF, CREB1, FKBP5, IL1B, NTRK2, and OXTR). Both consistent and inconsistent findings were identified. Overall, the interplay of CM with CREB1-rs2253206 significantly increased the risk of depression. In contrast, CRHR1-TCA haplotype (rs7209436, rs4792887, rs110402), CRHR1-rs17689882, and CRHR1-rs110402 showed protective effects on depression and depressive symptoms among individuals with a history of maltreatment. Limitations Due to clinical and methodological diversity of the studies a qualitative approach was used. Conclusion This review firstly provides a comprehensive overview of the interplay between CM and genetic variations in adult depression. Future etiological explorations should focus on the above-identified genes for down-stream exploration and address the issues and challenges of gene by environment studies.

New Insights on the Mobility of Viral and Host Non-Coding RNAs Reveal Extracellular Vesicles as Intriguing Candidate Antiviral Targets

Intercellular communication occurring by cell-to-cell contacts and via secreted messengers trafficked through extracellular vehicles is critical for regulating biological functions of multicellular organisms. Recent research has revealed that non-coding RNAs can be found in extracellular vesicles consistent with a functional importance of these molecular vehicles in virus propagation and suggesting that these essential membrane-bound bodies can be highjacked by viruses to promote disease pathogenesis. Newly emerging evidence that coronaviruses generate non-coding RNAs and use extracellular vesicles to facilitate viral pathogenicity may have important implications for the development of effective strategies to combat COVID-19, a disease caused by infection with the novel coronavirus, SARS-CoV-2. This article provides a short overview of our current understanding of the interactions between non-coding RNAs and extracellular vesicles and highlights recent research which supports these interactions as potential therapeutic targets in the development of novel antiviral therapies.

Advances in Exosomes-Based Drug Delivery Systems

Exosomes, a subgroup of extracellular vesicles, are important mediators of long-distance intercellular communication and are involved in a diverse range of biological processes such as the transport of lipids, proteins, and nucleic acids. Researchers, seeing the problems caused by the toxic effects and clearance of synthetic nanoparticles, consider exosomes as an interesting alternative to such nanoparticles in the specific and controlled transport of drugs. In recent years, there have been remarkable advances in the use of exosomes in cancer therapeutics or for treating neurological diseases, among other applications. The objective of this work is to analyze studies focused on exosomes used in drug delivery system, present and future applications in this field of research are discussed based on the results obtained.

High frequency acoustic cell stimulation promotes exosome generation regulated by a calcium-dependent mechanism

Exosomes are promising disease diagnostic markers and drug delivery vehicles, although their use in practice is limited by insufficient homogeneous quantities that can be produced. We reveal that exposing cells to high frequency acoustic irradiation stimulates their generation without detriment to cell viability by exploiting their innate membrane repair mechanism, wherein the enhanced recruitment of calcium ions from the extracellular milieu into the cells triggers an ESCRT pathway known to orchestrate exosomal production. Given the high post-irradiation cell viabilities (≈95%), we are able to recycle the cells through iterative irradiation and post-excitation incubation steps, which facilitate high throughput production of a homogeneous population of exosomes-a particular challenge for translating exosome therapy into clinical practice. In particular, we show that approximately eight- to ten-fold enrichment in the number of exosomes produced can be achieved with just 7 cycles over 280 mins, equivalent to a yield of around 1.7-2.1-fold/h.

Electrostatic Surface Properties of Blood and Semen Extracellular Vesicles: Implications of Sialylation and HIV-Induced Changes on EV Internalization

Although extracellular vesicle (EV) surface electrostatic properties (measured as zeta potential, ζ-potential) have been reported by many investigators, the biophysical implications of charge and EV origin remains uncertain. Here, we compared the ζ-potential of human blood EVs (BEVs) and semen EVs (SEVs) from 26 donors that were HIV-infected (HIV+, n = 13) or HIV uninfected (HIV-, n = 13). We found that, compared to BEVs that bear neutral surface charge, SEVs were significantly more negatively charged, even when BEVs and SEVs were from the same individual. Comparison of BEVs and SEVs from HIV- and HIV+ groups revealed subtle HIV-induced alteration in the ζ-potential of EVs, with the effect being more significant in SEVs (∆ζ-potential = -8.82 mV, p-value = 0.0062) than BEVs (∆ζ-potential = -1.4 mV, p-value = 0.0462). These observations were validated by differences in the isoelectric point (IEP) of EVs, which was in the order of HIV + SEV ≤ HIV-SEV ≪ HIV + BEV ≤ HIV-BEV. Functionally, the rate and efficiency of SEV internalization by the human cervical epithelial cell line, primary peripheral blood lymphocytes, and primary blood-derived monocytes were significantly higher than those of BEVs. Mechanistically, removal of sialic acids from the surface of EVs using neuraminidase treatment significantly decreased SEV's surface charge, concomitant with a substantial reduction in SEV's internalization. The neuraminidase effect was independent of HIV infection and insignificant for BEVs. Finally, these results were corroborated by enrichment of glycoproteins in SEVs versus BEVs. Taken together, these findings uncover fundamental tissue-specific differences in surface electrostatic properties of EVs and highlight the critical role of surface charge in EV/target cell interactions.

The Protective Effect of Exercise in Neurodegenerative Diseases: The Potential Role of Extracellular Vesicles

Physical activity has systemic effects on the body, affecting almost every organ. It is important not only for general health and wellbeing, but also in the prevention of diseases. The mechanisms behind the therapeutic effects of physical activity are not completely understood; however, studies indicate these benefits are not confined to simply managing energy balance and body weight. They also include systemic factors which are released into the circulation during exercise and which appear to underlie the myriad of benefits exercise can elicit. It was shown that along with a number of classical cytokines, active tissues also engage in inter-tissue communication via extracellular vesicles (EVs), specifically exosomes and other small EVs, which are able to deliver biomolecules to cells and alter their metabolism. Thus, EVs may play a role in the acute and systemic adaptations that take place during and after physical activity, and may be therapeutically useful in the treatment of a range of diseases, including metabolic disorders such as type 2 diabetes and obesity; and the focus of this review, neurological disorders such as Alzheimer's disease.

Proteomic Approach for Searching for Universal, Tissue-Specific, and Line-Specific Markers of Extracellular Vesicles in Lung and Colorectal Adenocarcinoma Cell Lines

Tumor-derived extracellular vesicles (EVs), including exosomes, contain proteins that mirror the molecular landscape of producer cells. Being potentially detectible in biological fluids, EVs are of great interest for the screening of cancer biomarkers. To reveal universal, tissue-specific, and line-specific markers, we performed label-free mass spectrometric profiling of EVs originating from the human colon cancer cell lines Caco-2, HT29, and HCT-116, as well as from the lung cancer cell lines NCI-H23 and A549. A total of 651 proteins was identified in the EV samples using at least two peptides. These proteins were highly enriched in exosome markers. We found 11 universal, eight tissue-specific, and 29 line-specific markers, the levels of which were increased in EVs compared to the whole lysates. The EV proteins were involved in the EGFR, Rap1, integrin, and microRNA signaling associated with metastasis and cancer progression. An EV protein-based assay could be developed as a liquid biopsy tool.

Myeloid Cell Modulation by Tumor-Derived Extracellular Vesicles

Extracellular vesicles (EV) can carry proteins, RNA and DNA, thus serving as communication tools between cells. Tumor cells secrete EV, which can be taken up by surrounding cells in the tumor microenvironment as well as by cells in distant organs. Tumor-derived EV (TEV) contain factors induced by tumor-associated hypoxia such as heat shock proteins or a variety of microRNA (miRNA). The interaction of TEV with tumor and host cells can promote cancer angiogenesis, invasion and metastasis. Myeloid cells are widely presented in tissues, comprise the majority of immune cells and play an essential role in immune reactions and tissue remodeling. However, in cancer, the differentiation of myeloid cells and their functions are impaired, resulting in tumor promotion. Such alterations are due to chronic inflammatory conditions associated with cancer and are mediated by the tumor secretome, including TEV. A high capacity of myeloid cells to clear EV from circulation put them in the central position in EV-mediated formation of pre-metastatic niches. The exposure of myeloid cells to TEV could trigger numerous signaling pathways. Progenitors of myeloid cells alter their differentiation upon the contact with TEV, resulting in the generation of myeloid-derived suppressor cells (MDSC), inhibiting anti-tumor function of T and natural killer (NK) cells and promoting thereby tumor progression. Furthermore, TEV can augment MDSC immunosuppressive capacity. Different subsets of mature myeloid cells such as monocytes, macrophages, dendritic cells (DC) and granulocytes take up TEV and acquire a protumorigenic phenotype. However, the delivery of tumor antigens to DC by TEV was shown to enhance their immunostimulatory capacity. The present review will discuss a diverse and complex EV-mediated crosstalk between tumor and myeloid cells in the context of the tumor type, TEV-associated cargo molecules and type of recipient cells.

Exploiting Manipulated Small Extracellular Vesicles to Subvert Immunosuppression at the Tumor Microenvironment through Mannose Receptor/CD206 Targeting

Immunosuppression at tumor microenvironment (TME) is one of the major obstacles to be overcome for an effective therapeutic intervention against solid tumors. Tumor-associated macrophages (TAMs) comprise a sub-population that plays multiple pro-tumoral roles in tumor development including general immunosuppression, which can be identified in terms of high expression of mannose receptor (MR or CD206). Immunosuppressive TAMs, like other macrophage sub-populations, display functional plasticity that allows them to be re-programmed to inflammatory macrophages. In order to mitigate immunosuppression at the TME, several efforts are ongoing to effectively re-educate pro-tumoral TAMs. Extracellular vesicles (EVs), released by both normal and tumor cells types, are emerging as key mediators of the cell to cell communication and have been shown to have a role in the modulation of immune responses in the TME. Recent studies demonstrated the enrichment of high mannose glycans on the surface of small EVs (sEVs), a subtype of EVs of endosomal origin of 30–150 nm in diameter. This characteristic renders sEVs an ideal tool for the delivery of therapeutic molecules into MR/CD206-expressing TAMs. In this review, we report the most recent literature data highlighting the critical role of TAMs in tumor development, as well as the experimental evidences that has emerged from the biochemical characterization of sEV membranes. In addition, we propose an original way to target immunosuppressive TAMs at the TME by endogenously engineered sEVs for a new therapeutic approach against solid tumors.

Extracellular Vesicles in the Development of Cancer Therapeutics

Extracellular vesicles (EVs) are small lipid bilayer-delimited nanoparticles released from all types of cells examined thus far. Several groups of EVs, including exosomes, microvesicles, and apoptotic bodies, have been identified according to their size and biogenesis. With extensive investigations on EVs over the last decade, it is now recognized that EVs play a pleiotropic role in various physiological processes as well as pathological conditions through mediating intercellular communication. Most notably, EVs have been shown to be involved in cancer initiation and progression and EV signaling in cancer are viewed as potential therapeutic targets. Furthermore, as membrane nanoparticles, EVs are natural products with some of them, such as tumor exosomes, possessing tumor homing propensity, thus leading to strategies utilizing EVs as drug carriers to effectively deliver cancer therapeutics. In this review, we summarize recent reports on exploring EVs signaling as potential therapeutic targets in cancer as well as on developing EVs as therapeutic delivery carriers for cancer therapy. Findings from preclinical studies are primarily discussed, with early phase clinical trials reviewed. We hope to provide readers updated information on the development of EVs as cancer therapeutic targets or therapeutic carriers.

Uptake and Fate of Extracellular Membrane Vesicles: Nucleoplasmic Reticulum-Associated Late Endosomes as a New Gate to Intercellular Communication

Extracellular membrane vesicles (EVs) are emerging as new vehicles in intercellular communication, but how the biological information contained in EVs is shared between cells remains elusive. Several mechanisms have been described to explain their release from donor cells and the initial step of their uptake by recipient cells, which triggers a cellular response. Yet, the intracellular routes and subcellular fate of EV content upon internalization remain poorly characterized. This is particularly true for EV-associated proteins and nucleic acids that shuttle to the nucleus of host cells. In this review, we will describe and discuss the release of EVs from donor cells, their uptake by recipient cells, and the fate of their cargoes, focusing on a novel intracellular route wherein small GTPase Rab7⁺ late endosomes containing endocytosed EVs enter into nuclear envelope invaginations and deliver their cargo components to the nucleoplasm of recipient cells. A tripartite protein complex composed of (VAMP)-associated protein A (VAP-A), oxysterol-binding protein (OSBP)-related protein-3 (ORP3), and Rab7 is essential for the transfer of EV-derived components to the nuclear compartment by orchestrating the particular localization of late endosomes in the nucleoplasmic reticulum.

Exosomes in Angiogenesis and Anti-angiogenic Therapy in Cancers

Angiogenesis is the process through which new blood vessels are formed from pre-existing ones. Exosomes are involved in angiogenesis in cancer progression by transporting numerous pro-angiogenic biomolecules like vascular endothelial growth factor (VEGF), matrix metalloproteinases (MMPs), and microRNAs. Exosomes promote angiogenesis by suppressing expression of factor-inhibiting hypoxia-inducible factor 1 (HIF-1). Uptake of tumor-derived exosomes (TEX) by normal endothelial cells activates angiogenic signaling pathways in endothelial cells and stimulates new vessel formation. TEX-driven cross-talk of mesenchymal stem cells (MSCs) with immune cells blocks their anti-tumor activity. Effective inhibition of tumor angiogenesis may arrest tumor progression. Bevacizumab, a VEGF-specific antibody, was the first antiangiogenic agent to enter the clinic. The most important clinical problem associated with cancer therapy using VEGF- or VEFGR-targeting agents is drug resistance. Combined strategies based on angiogenesis inhibitors and immunotherapy effectively enhances therapies in various cancers, but effective treatment requires further research.

Decoy ACE2-expressing extracellular vesicles that competitively bind SARS-CoV-2 as a possible COVID-19 therapy

The novel strain of coronavirus that appeared in 2019, SARS-CoV-2, is the causative agent of severe respiratory disease, COVID-19, and the ongoing pandemic. As for SARS-CoV that caused the SARS 2003 epidemic, the receptor on host cells that promotes uptake, through attachment of the spike (S) protein of the virus, is angiotensin-converting enzyme 2 (ACE2). In a recent article published by Batlle et al. (Clin. Sci. (Lond.) (2020) 134, 543-545) it was suggested that soluble recombinant ACE2 could be used as a novel biological therapeutic to intercept the virus, limiting the progression of infection and reducing lung injury. Another way, discussed here, to capture SARS-CoV-2, as an adjunct or alternative, would be to use ACE2+-small extracellular vesicles (sEVs). A competitive inhibition therapy could therefore be developed, using sEVs from engineered mesenchymal stromal/stem cells (MSCs), overexpressing ACE2.

In vitro cultured human endometrial cells release extracellular vesicles that can be uptaken by spermatozoa

Extracellular vesicles (EVs) derived from different parts of the male reproductive tract can be internalized by human spermatozoa affecting their maturation and regulating their functions. Here we demonstrate that EVs derived from the female tract can be uptaken by sperm and affect their competence. Primary endometrial cells release EVs with a diameter between 50 and 350 nm and bear the standard vesicle and exosome marker proteins CD63, CD9, TSG101 and ALIX. The uptake of dye-labelled endometrial cell-derived EVs by spermatozoa, quantified as fluorescence intensity, was significantly higher when EVs were derived from cells in the proliferative phase. Vital, motile fluorescent sperm could be appreciated after a 48-hour co-incubation with endometrial cells previously labelled with the Vybrant™ DiO dye. EV internalization by sperm was blocked at 4 °C and by incubation with filipin, suggesting an energy-dependent process probably attributable to the lipid-raft domain mediated-endocytosis. Sperm ability to undergo capacitation and acrosome reaction was stimulated by endometrial cell-derived EVs as manifested by the increased protein tyrosine phosphorylation and evident reactivity when stimulated with a calcium ionophore. Based on these findings, EVs exchange may be suggested as an emerging way through which female reproductive tract cells can interact with the passing spermatozoa.

Tumor-Derived Exosomes in Immunosuppression and Immunotherapy

Tumor-derived exosomes (TEX) are involved in cancer development, metastasis, and disease progression. They can modulate angiogenesis to elevate the malignant degree of tumor cells. TEX carry immunosuppressive factors affecting the antitumor activities of immune cells. Tumor cells as well as immune cells secrete immunologically active exosomes which affect intercellular communication, antigen presentation, activation of immune cells, and immune surveillance. Cell proliferation and immune response suppression create a favorable microenvironment for tumor. TEX can inhibit immune cell proliferation, induce apoptosis of activated CD8+ Teffs, suppress NK cell activity, interfere with monocyte differentiation, and promote Treg as well as MDSC expansion. Exosomes of microenvironment cells may also contribute to the development of drug resistance in cancer therapy. An important role of TEX in modulating the sensitivity of tumor cells to immunotherapy is a promising area of research to make the cancer therapy more successful.

Exosomes as Mediators of Chemical-Induced Toxicity

PURPOSE OF REVIEW

This review provides information regarding how exosomes may contribute to environmental chemical-induced pathogenesis of chronic diseases. In connecting exosome biology to environmental toxicology and disease pathogenesis, we address vital questions regarding what constitutes exosomal cargo, how toxicants influence exosomal cargo, and how environmental stimuli influence exosomal physiological and pathological functions.

RECENT FINDINGS

Recent studies in the field demonstrate that exosomal cargo changes depending on external stimuli, which has consequences for the microenvironment of recipient cells. Based on recent findings, it is evident that exosomal cargo comprises various biological molecules including proteins, nucleic acids, and lipid molecules. Misfolded proteins and miRNA are examples of exosomal cargo molecules that can be altered by toxicants, ultimately changing the microenvironment of recipient cells in ways that are conducive to pathological processes. It will be crucial to map out the key signaling pathways that toxicants target to modulate exosomal cargo and their release.

Free and hydrogel encapsulated exosome-based therapies in regenerative medicine

Over the last few decades, mesenchymal stem cells-derived exosomes (MSCs-Ex) have attracted a lot of attention as a therapeutic tool in regenerative medicine. Exosomes are extracellular vehicles (EVs) that play important roles in cell-cell communication through various processes such as stress response, senescence, angiogenesis, and cell differentiation. Success in the field of regenerative medicine sparked exploration of the potential use of exosomes as key therapeutic effectors of MSCs to promote tissue regeneration. Various approaches including direct injection, intravenous injection, intraperitoneal injection, oral administration, and hydrogel-based encapsulation have been exploited to deliver exosomes to target tissues in different disease models. Despite significant advances in exosome therapy, it is unclear which approach is more effective for administering exosomes. Herein, we critically review the emerging progress in the applications of exosomes in the form of free or association with hydrogels as therapeutic agents for applications in regenerative medicine.

Exosomes as a storehouse of tissue remodeling proteases and mediators of cancer progression

Rapidly increasing scientific reports of exosomes and their biological effects have improved our understanding of their cellular sources and their cell-to-cell communication. These nano-sized vesicles act as potent carriers of regulatory bio-macromolecules and can induce regulatory functions by delivering them from its source to recipient cells. The details of their communication network are less understood. Recent studies have shown that apart from delivering its cargo to the cells, it can directly act on extracellular matrix (ECM) proteins and growth factors and can induce various remodeling events. More importantly, exosomes carry many surface-bound proteases, which can cleave different ECM proteins and carbohydrates and can shed cell surface receptors. These local extracellular events can modulate signaling cascades, which consequently influences the whole tissue and organ. This review aims to highlight the critical roles of exosomal proteases and their mechanistic insights within the cellular and extracellular environment.

Cutting edge approaches for rapid characterization of airway exosomes

Exosomes have been described as promising biomarkers for understanding disease progression and prognosis. These lipid membrane nanoparticles derived from airway cells have been shown to have immunomodulatory effects, such as driving inflammatory responses in asthma. These emerging evidences demonstrating an important pathophysiological role of exosomes warrants the development of novel approaches for isolation and rapid characterization of exosomes, which would be applicable for both translational and clinical studies. In this review article, we describe two methods of rapid exosomes characterization: (1) imaging flow cytometry using ImageStream; and (2) conventional flow cytometry using the BD Symphony A5 platform. We also explore sorting of exosomes using the BD Aria.

Engineered stem cells targeting multiple cell surface receptors in tumors

Multiple stem cell types exhibit inherent tropism for cancer, and engineered stem cells have been used as therapeutic agents to specifically target cancer cells. Recently, stem cells have been engineered to target multiple surface receptors on tumor cells, as well as endothelial and immune cells in the tumor microenvironment. In this review, we discuss the rationales and strategies for developing multiple receptor-targeted stem cells, their mechanisms of action, and the promises and challenges they hold as cancer therapeutics.

Engineering Extracellular Vesicles as Nanotherapeutics for Regenerative Medicine

Long thought of to be vesicles that primarily recycled waste biomolecules from cells, extracellular vesicles (EVs) have now emerged as a new class of nanotherapeutics for regenerative medicine. Recent studies have proven their potential as mediators of cell proliferation, immunomodulation, extracellular matrix organization and angiogenesis, and are currently being used as treatments for a variety of diseases and injuries. They are now being used in combination with a variety of more traditional biomaterials and tissue engineering strategies to stimulate tissue repair and wound healing. However, the clinical translation of EVs has been greatly slowed due to difficulties in EV isolation and purification, as well as their limited yields and functional heterogeneity. Thus, a field of EV engineering has emerged in order to augment the natural properties of EVs and to recapitulate their function in semi-synthetic and synthetic EVs. Here, we have reviewed current technologies and techniques in this growing field of EV engineering while highlighting possible future applications for regenerative medicine.

Exosomes from mesenchymal stromal cells reduce murine colonic inflammation via a macrophage-dependent mechanism

Conventional treatments for inflammatory bowel disease (IBD) have multiple potential side effects. Therefore, alternative treatments are desperately needed. This work demonstrated that systemic administration of exosomes from human bone marrow-derived mesenchymal stromal cells (MSC-Exos) substantially mitigated colitis in various models of IBD. MSC-Exos treatment downregulated inflammatory responses, maintained intestinal barrier integrity, and polarized M2b macrophages but did not favor intestinal fibrosis. Mechanistically, infused MSC-Exos acted mainly on colonic macrophages, and macrophages from colitic colons acquired obvious resistance to inflammatory restimulation when prepared from mice treated with MSC-Exos versus untreated mice. The beneficial effect of MSC-Exos was blocked by macrophage depletion. Also, the induction of IL-10 production from macrophages was partially involved in the beneficial effect of MSC-Exos. MSC-Exos were enriched in proteins involved in regulating multiple biological processes associated with the anticolitic benefit of MSC-Exos. Particularly, metallothionein-2 in MSC-Exos was required for the suppression of inflammatory responses. Taken together, MSC-Exos are critical regulators of inflammatory responses and may be promising candidates for IBD treatment.

Physiologic constraints of using exosomes in vivo as systemic delivery vehicles

Systemic delivery of exosomes meets hurdles which had not been elucidated using live molecular imaging for their biodistribution. Production and uptake of endogenous exosomes are expected to be nonspecific and specific, respectively, where external stimuli of production of exosomes and their quantitative degree of productions are not understood. Despite this lack of understanding of basic physiology of in vivo behavior of exosomes including their possible paracrine or endocrine actions, many engineering efforts are taken to develop therapeutic vehicles. Especially, the fraction of exosomes’ taking the routes of waste disposal and exerting target actions are not characterized after systemic administration. Here, we reviewed the literature about in vivo distribution and disposal/excretion of exogenous or endogenous exosomes and, from these limited resources of knowledge currently available, summarized the knowledge and the uncertainties of exosomes on physiologic standpoints. An eloquent example of the investigations to understand the roles and confounders of exosomes’ action in the brain was highlighted with emphasis on the recent discovery of brain lymphatics and hypothesis of glymphatic/lymphatic clearance pathways in diseases as well as in physiologic processes. The possibility of delivering therapeutic exosomes through the systemic circulation, across blood-brain barriers and finally to target cells such as microglia, astrocytes and/or neurons is a good testbed in which the investigators can formulate problems to solve for both understanding (science) and application (engineering).

Circulating microRNAs and Their Role in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by bone marrow infiltration of clonal plasma cells. The recent literature has clearly demonstrated clonal heterogeneity in terms of both the genomic and transcriptomic signature of the tumor. Of note, novel studies have also highlighted the importance of the functional cross-talk between the tumor clone and the surrounding bone marrow milieu, as a relevant player of MM pathogenesis. These findings have certainly enhanced our understanding of the underlying mechanisms supporting MM pathogenesis and disease progression. Within the specific field of small non-coding RNA-research, recent studies have provided evidence for considering microRNAs as a crucial regulator of MM biology and, in this context, circulating microRNAs have been shown to potentially contribute to prognostic stratification of MM patients. The present review will summarize the most recent studies within the specific topic of microRNAs and circulating microRNAs in MM.

Connexins and Integrins in Exosomes

Connexins and integrins, the two structurally and functionally distinct families of transmembrane proteins, have been shown to be inter-connected by various modes of cross-talk in cells, such as direct physical coupling via lateral contact, indirect physical coupling via actin and actin-binding proteins, and functional coupling via signaling cascades. This connexin-integrin cross-talk exemplifies a biologically important collaboration between channels and adhesion receptors in cells. Exosomes are biological lipid-bilayer nanoparticles secreted from virtually all cells via endosomal pathways into the extracellular space, thereby mediating intercellular communications across a broad range of health and diseases, including cancer progression and metastasis, infection and inflammation, and metabolic deregulation. Connexins and integrins are embedded in the exosomal membranes and have emerged as critical regulators of intercellular communication. This concise review article will explain and discuss recent progress in better understanding the roles of connexins, integrins, and their cross-talk in cells and exosomes.