Human adipocyte extracellular vesicles in reciprocal signaling between adipocytes and macrophages

Androgen receptor deficiency in monocytes/macrophages does not alter adiposity or glucose homeostasis in male mice

Androgen deprivation in men leads to increased adiposity, but the mechanisms underlying androgen regulation of fat mass have not been fully defined. Androgen receptor (AR) is expressed in monocytes/macrophages, which are resident in key metabolic tissues and influence energy metabolism in surrounding cells. Male mice bearing a cell-specific knockout of the AR in monocytes/macrophages (M-ARKO) were generated to determine whether selective loss of androgen signaling in these cells would lead to altered body composition. Wild-type (WT) and M-ARKO mice (12–22 weeks of age, n = 12 per group) were maintained on a regular chow diet for 8 weeks and then switched to a high-fat diet for 8 additional weeks. At baseline and on both the regular chow and high-fat diets, no differences in lean mass or fat mass were observed between groups. Consistent with the absence of differential body weight or adiposity, no differences in food intake (3.0 ± 0.5 g per day for WT mice vs 2.8 ± 0.4 g per day for M-ARKO mice) or total energy expenditure (0.6 ± 0.1 Kcal h⁻¹ for WT mice vs 0.5 ± 0.1 Kcal h⁻¹ for M-ARKO mice) were evident between groups during high-fat feeding. Liver weight was greater in M-ARKO than that in WT mice (1.5 ± 0.1 g vs 1.3 ± 0.0 g, respectively, P = 0.02). Finally, M-ARKO mice did not exhibit impairments in glucose tolerance or insulin sensitivity relative to WT mice at any study time point. In aggregate, these findings suggest that AR signaling specifically in monocytes/macrophages does not contribute to the regulation of systemic energy balance, adiposity, or insulin sensitivity in male mice.

Adipose Tissue Exosomal Proteomic Profile Reveals a Role on Placenta Glucose Metabolism in Gestational Diabetes Mellitus

CONTEXT

Molecules produced by adipose tissue (AT) function as an endocrine link between maternal AT and fetal growth by regulating placental function in normal women and women with gestational diabetes mellitus (GDM).

OBJECTIVE

We hypothesized that AT-derived exosomes (exo-AT) from women with GDM would carry a specific set of proteins that influences glucose metabolism in the placenta.

DESIGN

Exosomes were isolated from omental AT-conditioned media from normal glucose tolerant (NGT) pregnant women (n = 65) and pregnant women with GDM (n = 82). Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry was used to construct a small ion library from AT and exosomal proteins, followed by ingenuity pathway analysis to determine the canonical pathways and biofunctions. The effect of exosomes on human placental cells was determined using a Human Glucose Metabolism RT2 Profiler PCR array.

RESULTS

The number of exosomes (vesicles/μg of tissue/24 hours) was substantially (1.7-fold) greater in GDM than in NGT, and the number of exosomes correlated positively with the birthweight Z score. Ingenuity pathway analysis of the exosomal proteins revealed differential expression of the proteins targeting the sirtuin signaling pathway, oxidative phosphorylation, and mechanistic target of rapamycin signaling pathway in GDM compared with NGT. GDM exo-AT increased the expression of genes associated with glycolysis and gluconeogenesis in placental cells compared with the effect of NGT exo-AT.

CONCLUSIONS

Our findings are consistent with the possibility that AT exosomes play an important role in mediating the changes in placental function in GDM and might be responsible for some of the adverse consequences in this pregnancy complication, such as fetal overgrowth.

Exosomes secreted by mesenchymal stromal/stem cell-derived adipocytes promote breast cancer cell growth via activation of Hippo signaling pathway

Objective

Although adipocytes are the most abundant stromal cell component in breast cancer tissues, their interaction with breast cancer cells has been less investigated compared to cancer-associated fibroblasts or macrophages. Exosomes are a novel way of cell-cell communication and have been demonstrated to play an important role in various biological processes. However, to our knowledge, only a few studies have reported the effects of adipocyte exosomes on tumor development. Here, utilizing exosomes isolated from in vitro mesenchymal stromal/stem cell (MSC)-differentiated adipocytes, we systematically investigated this issue in a breast cancer model.

Material and methods

Exosomes were isolated from MSC-differentiated adipocytes and added to breast cancer cells MCF7. Cell proliferation was detected by MTS, and migration was analyzed by wound healing and transwell assay. An in vivo mouse xenograft model was used to evaluate MSC-differentiated adipocyte exosomes’ contribution to tumor growth. Signaling pathway activation was evaluated by western blot and immunofluorescence staining.

Results

We found MSC-differentiated adipocyte-derived exosomes are actively incorporated by breast cancer cell MCF7 and subsequently promote MCF7 proliferation and migration as well as protect MCF7 from serum derivation or chemotherapeutic drug-induced apoptosis in vitro. In the in vivo mouse xenograft model, depletion of exosomes reduces tumor-promoting effects of adipocytes. Transcriptomic analysis of MSC-differentiated adipocyte exosome-treated MCF7 identified several activated signaling pathways, among which we confirm the Hippo signaling pathway and found a blockade of this pathway leads to a reduced growth-promoting effect of adipocyte exosomes.

Conclusion

Taken together, our findings provide new insights into the role of adipocyte exosomes in the tumor microenvironment.

Exosomes and diabetes

Diabetes is a group of metabolic diseases characterized by elevated blood glucose levels that drive the development of life-threatening complications. Diabetes results from a situation of insufficient insulin action, either by deficient production of the hormone by the pancreas, or by the development of insulin resistance in peripheral tissues such as liver, muscle, or the adipose depots. Communication between organs is thus central to the maintenance of glucose homoeostasis. Recently, several studies are evidencing that small vesicles called exosomes released by, amongst other, the adipose tissue can regulate gene expression in other tissues, hence modulating interorgan crosstalk. Therefore, exosomes participate in the development of diabetes and its associated complications. Their study holds the potential of providing us with novel biomarkers for the early diagnosis and stratification of patients at risk of developing diabetes, hence allowing the timely implementation of more personalized therapies. On the other hand, the molecular dissection of the pathways initiated by exosomes under situations of metabolic stress could help to gain a deeper knowledge of the pathophysiology of diabetes and its associated metabolic diseases.

Adipose-derived exosomes: A novel adipokine in obesity-associated diabetes

Dysfunction of the adipose tissue is a central driver for obesity-associated diabetes. It is characterized by dysregulated adipokine secretion, which contributes to insulin resistance of key metabolic tissues, including the liver, skeletal muscles, and fat itself. The inter-organ cross talk between the adipose tissue and the other organs as well as the intra-organ cross talk between adipocytes and macrophages within the adipose tissue, traditionally mediated by hormones, was recently evidenced to be regulated by adipose-derived exosomes. Exosomes are nano-sized membrane-bound vesicles secreted by the donor cells to modify intercellular communication by translating constituent nucleic acids and proteins to the target cells. Herein, we reviewed the latest progress in understanding the role of adipose-derived exosomes in the development of insulin resistance, a key mechanism that underpins diabetes and diabetic complications, with a special focus on the role of exosomal miRNAs (micro RNAs) and proteins, and discusses the potential implications of targeting adipose tissue-derived exosomes for diabetic therapeutics.

Shedding Perspective on Extracellular Vesicle Biology in Diabetes and Associated Metabolic Syndromes

The etiology of diabetes and associated metabolic derailments is a complex process that relies on crosstalk between metabolically active tissues. Dysregulation of secreted factors and metabolites from islets, adipose tissue, liver, and skeletal muscle contributes to the overall progression of diabetes and metabolic syndrome. Extracellular vesicles (EVs) are circulating nanovesicles secreted by most cell types and are comprised of bioactive cargoes that are horizontally transferred to targeted cells/tissues. Accumulating evidence from the past decade implicates the role of EVs as mediators of islet cell dysfunction, inflammation, insulin resistance, and other metabolic consequences associated with diabetes. This review covers a broad spectrum of basic EV biology (i.e., biogenesis, secretion, and uptake), including a comprehensive investigation of the emerging role of EVs in β-cell autocrine/paracrine interactions and the multidirectional crosstalk in metabolically active tissues. Understanding the utility of this novel means of intercellular communication could impart insight into the development of new treatment regimens and biomarker detection to treat diabetes.

Inflammatory adipocyte-derived extracellular vesicles promote leukocyte attachment to vascular endothelial cells

BACKGROUND AND AIMS

Obesity is associated with an increased risk of cardiovascular disease, but the mechanisms involved are not completely understood. In obesity, the adipocyte microenvironment is characterised by both hypoxia and inflammation. Therefore, we sought to determine whether extracellular vesicles (EVs) derived from adipocytes in this setting might be involved in mediating cardiovascular disease, specifically by promoting leukocyte attachment to vascular endothelial cells.

METHODS

Mature 3T3-L1 adipocytes were incubated for 24 h under control, TNF-α (30 ng/mL), hypoxia (1% O₂), or TNF-α+hypoxia (30 ng/mL, 1% O₂) conditions. EVs were isolated by differential ultracentrifugation and analysed by nanoparticle tracking analysis. Primary human umbilical vein endothelial cells (HUVECs) were treated with EVs for 6 h before being lysed for Western blotting to investigate changes in adhesion molecule production, or for use in leukocyte attachment assays.

RESULTS

EVs from adipocytes treated with TNF-α and TNF-α+hypoxia increased vascular cell adhesion molecule (VCAM-1) production in HUVECs compared to basal level (4.2 ± 0.6 and 3.8 ± 0.3-fold increase, respectively (p < 0.05)), an effect that was inhibited by an anti-TNF-α neutralising antibody. Production of other adhesion molecules (E-selectin, P-selectin, platelet endothelial cell adhesion molecule and VE-Cadherin) was unchanged. Pre-incubating HUVECs with TNF-α+hypoxia EVs significantly increased leukocyte attachment compared to basal level (3.0 ± 0.4-fold increase (p < 0.05)).

CONCLUSIONS

Inflammatory adipocyte EVs induce VCAM-1 production in vascular endothelial cells, accompanied by enhanced leukocyte attachment. Preventing adipocyte derived EV-induced VCAM-1 upregulation may offer a novel therapeutic target in the prevention of obesity-driven cardiovascular disease.

Fatty acids: Adiposity and breast cancer chemotherapy, a bad synergy?

Globally, breast cancer continues to be a major concern in women's health. Lifestyle related risk factors, specifically excess adipose tissue (adiposity) has reached epidemic proportions and has been identified as a major risk factor in the development of breast cancer. Dysfunctional adipose tissue has evoked research focusing on its association with metabolic-related conditions, breast cancer risk and progression. Adipose dysfunction in coordination with immune cells and inflammation, are responsible for accelerated cell growth and survival of cancer cells. Recently, evidence also implicates adiposity as a potential risk factor for chemotherapy resistance. Chemotherapeutic agents have been shown to negatively impact adipose tissue. Since adipose tissue is a major storage site for fatty acids, it is not unlikely that these negative effects may disrupt adipose tissue homeostasis. It is therefore argued that fatty acid composition may be altered due to the chemotherapeutic pharmacokinetics, which in turn could have severe health related outcomes. The underlying molecular mechanisms elucidating the effects of fatty acid composition in adiposity-linked drug resistance are still unclear and under explored. This review focuses on the potential role of adiposity in breast cancer and specifically emphasizes the role of fatty acids in cancer progression and treatment resistance.

Obesity May Accelerate the Aging Process

Lines of evidence from several studies have shown that increases in life expectancy are now accompanied by increased disability rate. The expanded lifespan of the aging population imposes a challenge on the continuous increase of chronic disease. The prevalence of overweight and obesity is increasing at an alarming rate in many parts of the world. Further to increasing the onset of metabolic imbalances, obesity leads to reduced life span and affects cellular and molecular processes in a fashion resembling aging. Nine key hallmarks of the aging process have been proposed. In this review, we will review these hallmarks and discuss pathophysiological changes that occur with obesity, that are similar to or contribute to those that occur during aging. We present and discuss the idea that obesity, in addition to having disease-specific effects, may accelerate the rate of aging affecting all aspects of physiology and thus shortening life span and health span.

Exosome-Like Vesicles as New Mediators and Therapeutic Targets for Treating Insulin Resistance and β-Cell Mass Failure in Type 2 Diabetes Mellitus

Exosome-like vesicles (ELVs), the smallest class of extracellular vesicles released from cells, function in cellular crosstalk and therefore profoundly affect physiologic responses and pathologic progression. A growing body of evidence supports a novel role for ELVs as important mediators and therapeutic targets due to their effects on regulation of both insulin signaling and β-cell mass. Pathologic conditions associated with type 2 diabetes (such as high blood glucose, inflammation, hypoxia, and fatty acids) can alter the quantity and components of ELVs secreted from the pancreas or peripheral insulin-targeting tissues. These released ELVs can either enter the blood circulation or be taken up by neighboring cells or macrophages, which can lead to insulin resistance or β-cell apoptosis. This review focuses on the roles of ELVs in insulin resistance and β-cell failure and also highlights the potential use of ELVs and exosome-based delivery systems in therapeutic interventions aimed at treating type 2 diabetes mellitus as well as the challenges associated with exosome-targeting therapeutics.

Vésicules extracellulaires, biomarqueurs et bioeffecteurs du syndrome métabolique

Les vésicules extracellulaires (VE) suscitent un intérêt croissant lié à leur capacité à transférer du contenu biologique entre cellules. Les VE, émises dans l’espace extracellulaire, circulent via les différents fluides de l’organisme et modulent localement ou à distance les réponses des cellules avec lesquelles elles ont interagi. Des données cliniques et expérimentales étayent leur rôle dans les maladies liées au syndrome métabolique. Les VE bousculent la vision traditionnelle de la communication intercellulaire et représentent ainsi un mode de communication alternatif et versatile, qui ouvre la porte à de nouveaux concepts et opportunités tant biologiques que thérapeutiques.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Extracellular Vesicles: A Potential Novel Regulator of Obesity and Its Associated Complications

Childhood obesity continues to be a major public health concern. Obesity causes various metabolic complications, including insulin resistance, type 2 diabetes mellitus (T2DM), non-alcoholic fatty liver disease (NAFLD), dyslipidemia, and cardiovascular disease. However, currently, we have a limited understanding of the pathophysiology in the development of these processes. Extracellular vesicles (EVs) are nano-sized vesicles secreted by different cell types that travel to various organ systems carrying molecular and genetic information. These vesicles have been proposed as a novel intercellular communication mode in systemic metabolic regulation and in several pathophysiologic processes. In particular, recent studies indicate that EVs play a critical role in the pathogenesis of obesity and its metabolic complications. In this study, we reviewed the current literature that supports the role of EVs in the regulation of metabolic homeostasis and pathogenesis of obesity and its associated metabolic complications, with a short discussion about future directions in the EV research field.

Altered Extracellular Vesicle Concentration, Cargo, and Function in Diabetes

Type 2 diabetes is a chronic age-associated degenerative metabolic disease that reflects relative insulin deficiency and resistance. Extracellular vesicles (EVs) (exosomes, microvesicles, and apoptotic bodies) are small (30-400 nm) lipid-bound vesicles capable of shuttling functional proteins, nucleic acids, and lipids as part of intercellular communication systems. Recent studies in mouse models and in cell culture suggest that EVs may modulate insulin signaling. Here, we designed cross-sectional and longitudinal cohorts of euglycemic participants and participants with prediabetes or diabetes. Individuals with diabetes had significantly higher levels of EVs in their circulation than euglycemic control participants. Using a cell-specific EV assay, we identified that levels of erythrocyte-derived EVs are higher with diabetes. We found that insulin resistance increases EV secretion. Furthermore, the levels of insulin signaling proteins were altered in EVs from individuals with high levels of insulin resistance and β-cell dysfunction. Moreover, EVs from individuals with diabetes were preferentially internalized by circulating leukocytes. Cytokine levels in the media and in EVs were higher from monocytes incubated with diabetic EVs. Microarray of these leukocytes revealed altered gene expression pathways related to cell survival, oxidative stress, and immune function. Collectively, these results suggest that insulin resistance increases the secretion of EVs, which are preferentially internalized by leukocytes, and alters leukocyte function.

Exosome and Macrophage Crosstalk in Sleep-Disordered Breathing-Induced Metabolic Dysfunction

Obstructive sleep apnea (OSA) is a highly prevalent worldwide public health problem that is characterized by repetitive upper airway collapse leading to intermittent hypoxia, pronounced negative intrathoracic pressures, and recurrent arousals resulting in sleep fragmentation. Obesity is a major risk factor of OSA and both of these two closely intertwined conditions result in increased sympathetic activity, oxidative stress, and chronic low-grade inflammation, which ultimately contribute, among other morbidities, to metabolic dysfunction, as reflected by visceral white adipose tissue (VWAT) insulin resistance (IR). Circulating extracellular vesicles (EVs), including exosomes, are released by most cell types and their cargos vary greatly and reflect underlying changes in cellular homeostasis. Thus, exosomes can provide insights into how cells and systems cope with physiological perturbations by virtue of the identity and abundance of miRNAs, mRNAs, proteins, and lipids that are packaged in the EVs cargo, and are secreted from the cells into bodily fluids under normal as well as diseased states. Accordingly, exosomes represent a novel pathway via which a cohort of biomolecules can travel long distances and result in the modulation of gene expression in selected and targeted recipient cells. For example, exosomes secreted from macrophages play a critical role in innate immunity and also initiate the adaptive immune response within specific metabolic tissues such as VWAT. Under normal conditions, phagocyte-derived exosomes represent a large portion of circulating EVs in blood, and carry a protective signature against IR that is altered when secreting cells are exposed to altered physiological conditions such as those elicited by OSA, leading to emergence of IR within VWAT compartment. Consequently, increased understanding of exosome biogenesis and biology should lead to development of new diagnostic biomarker assays and personalized therapeutic approaches. Here, the evidence on the major biological functions of macrophages and exosomes as pathophysiological effectors of OSA-induced metabolic dysfunction is discussed.

Phenotyping of circulating extracellular vesicles (EVs) in obesity identifies large EVs as functional conveyors of Macrophage Migration Inhibitory Factor

Objective

Obesity-associated metabolic dysfunctions are linked to dysregulated production of adipokines. Accumulating evidence suggests a role for fat-derived extracellular vesicles (EVs) in obesity-metabolic disturbances. Since EVs convey numerous proteins we aimed to evaluate their contribution in adipokine secretion.

Methods

Plasma collected from metabolic syndrome patients were used to isolate EV subtypes, namely microvesicles (MVs) and exosomes (EXOs). Numerous soluble factor concentrations were measured successively on total, MV- and EXO-depleted plasma by multiplexed immunoassays.

Results

Circulating MVs and EXOs were significantly increased with BMI, supporting a role of EVs as metabolic relays in obesity. Obesity was associated with dysregulated soluble factor production. Sequential depletion of plasma MVs and EXOs did not modify plasma levels of these molecules, with the exception of Macrophage Migration Inhibitory Factor (MIF). Half of plasma MIF circulated within MVs, and this MV secretory pathway was conserved over different MIF-producing cells. Although MV-associated MIF triggered rapid ERK1/2 activation in macrophages, these functional MV-MIF effects specifically relied on MIF tautomerase activity.

Conclusion

Our results emphasize the importance of reconsidering MIF-metabolic actions with regard to its MV-associated form and opening new EV-based strategies for therapeutic MIF approaches.

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Plasma EV subtypes are significantly increased with obesity.

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Plasma EV subtypes carry adipokines.

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MV (large EV subtype) constitute a major secretory pathway for MIF.

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MV-associated MIF transduces metabolic responses through its tautomerase activity.

Evidence for Adipocyte-Derived Extracellular Vesicles in the Human Circulation

Adipocyte-derived extracellular vesicles (EVs) may serve as novel endocrine mediators of adipose tissue and impact upon vascular health. However, it is unclear whether adipocyte-derived EVs are present in the human circulation. Therefore, the purpose of this study was to seek evidence for the presence of adipocyte-derived EVs in circulating plasma. Size-exclusion chromatography of platelet-free plasma identified fractions 5 to 10 as containing EVs by a peak in particle concentration, which corresponded with the presence of EV and adipocyte proteins. Pooling fractions 5 to 10 and subjecting to ultracentrifugation yielded a plasma EV sample, as verified by transmission electron microscopy (TEM) showing EV structures and Western blotting for EV (e.g., CD9 and Alix) and adipocyte markers. Magnetic beads and a solid-phase assay were used to deplete the EV sample of the four major families of circulating EVs: platelet-derived, leukocyte-derived, endothelial-derived, and erythrocyte-derived EVs. Postdepletion samples from both techniques contained EV structures as visualized by TEM, as well as CD9, Alix, and classic adipocyte proteins. Postdepletion samples also contained a range of other adipocyte proteins from an adipokine array. Adipocyte proteins and adipokines are expressed in optimally processed plasma EV samples, suggesting that adipocyte-derived EVs are secreted into the human circulation.

Fed-EXosome: extracellular vesicles and cell-cell communication in metabolic regulation

Extracellular vesicles (EVs) have emerged as a novel messaging system of the organism, mediating cell-cell and interorgan communication. Through their content of proteins and nucleic acids, as well as membrane proteins and lipid species, EVs can interact with and modulate the function of their target cells. The regulation of whole-body metabolism requires cross-talk between key metabolic tissues including adipose tissue (AT), the liver and skeletal muscle. Furthermore, the regulation of nutrient/energy allocation during pregnancy requires co-ordinated communication between the foetus and metabolic organs of the mother. A growing body of evidence is suggesting that EVs play a role in communication between and within key metabolic organs, both physiologically during metabolic homoeostasis but also contributing to pathophysiology during metabolic dysregulation observed in metabolic diseases such as obesity and diabetes. As obesity and its associated metabolic complications are reaching epidemic proportions, characterization of EV-mediated communication between key metabolic tissues may offer important insights into the regulation of metabolic functions during disease and offer global therapeutic opportunities. Here, we focus on the role of EVs in metabolic regulation and, in particular, EV-mediated cross-talk between cells of the AT.

Effects of exosomes from LPS-activated macrophages on adipocyte gene expression, differentiation, and insulin-dependent glucose uptake

Obesity is usually associated with low-grade inflammation, which determines the appearance of comorbidities like atherosclerosis and insulin resistance. Infiltrated macrophages in adipose tissue are partly responsible of this inflammatory condition. Numerous studies point to the existence of close intercommunication between macrophages and adipocytes and pay particular attention to the proinflammatory cytokines released by both cell types. However, it has been recently described that in both, circulation and tissue level, there are extracellular vesicles (including microvesicles and exosomes) containing miRNAs, mRNAs, and proteins that can influence the inflammatory response. The objective of the present research is to investigate the effect of exosomes released by lipopolysaccharide (LPS)-activated macrophages on gene expression and cell metabolism of adipocytes, focusing on the differential exosomal miRNA pattern between LPS- and non-activated macrophages. The results show that the exosomes secreted by the macrophages do not influence the preadipocyte-to-adipocyte differentiation process, fat storage, and insulin-mediated glucose uptake in adipocytes. However, exosomes induce changes in adipocyte gene expression depending on their origin (LPS- or non-activated macrophages), including genes such as CXCL5, SOD, TNFAIP3, C3, and CD34. Some of the pathways or metabolic processes upregulated by exosomes from LPS-activated macrophages are related to inflammation (complement activation, regulation of reactive oxygen species, migration and activation of leukocyte, and monocyte chemotaxis), carbohydrate catabolism, and cell activation. miR-530, chr9_22532, and chr16_34840 are more abundant in exosomes from LPS-activated macrophages, whereas miR-127, miR-143, and miR-486 are more abundant in those secreted by non-activated macrophages.

Chemoresistance: Intricate Interplay Between Breast Tumor Cells and Adipocytes in the Tumor Microenvironment

Excess adipose tissue is a hallmark of an overweight and/or obese state as well as a primary risk factor for breast cancer development and progression. In an overweight/obese state adipose tissue becomes dysfunctional due to rapid hypertrophy, hyperplasia, and immune cell infiltration which is associated with sustained low-grade inflammation originating from dysfunctional adipokine synthesis. Evidence also supports the role of excess adipose tissue (overweight/obesity) as a casual factor for the development of chemotherapeutic drug resistance. Obesity-mediated effects/modifications may contribute to chemotherapeutic drug resistance by altering drug pharmacokinetics, inducing chronic inflammation, as well as altering tumor-associated adipocyte adipokine secretion. Adipocytes in the breast tumor microenvironment enhance breast tumor cell survival and decrease the efficacy of chemotherapeutic agents, resulting in chemotherapeutic resistance. A well-know chemotherapeutic agent, doxorubicin, has shown to negatively impact adipose tissue homeostasis, affecting adipose tissue/adipocyte functionality and storage. Here, it is implied that doxorubicin disrupts adipose tissue homeostasis affecting the functionality of adipose tissue/adipocytes. Although evidence on the effects of doxorubicin on adipose tissue/adipocytes under obesogenic conditions are lacking, this narrative review explores the potential role of obesity in breast cancer progression and treatment resistance with inflammation as an underlying mechanism.

The Emerging Roles of Microparticles in Diabetic Nephropathy

Microparticles (MPs) are a type of extracellular vesicles (EVs) shed from the outward budding of plasma membranes during cell apoptosis and/or activation. These microsized particles then release specific contents (e.g., lipids, proteins, microRNAs) which are active participants in a wide range of both physiological and pathological processes at the molecular level, e.g., coagulation and angiogenesis, inflammation, immune responses. Research limitations, such as confusing nomenclature and overlapping classification, have impeded our comprehension of these tiny molecules. Diabetic nephropathy (DN) is currently the greatest contributor to end-stage renal diseases (ESRD) worldwide, and its public health impact will continue to grow due to the persistent increase in the prevalence of diabetes mellitus (DM). MPs have recently been considered as potentially involved in DN onset and progression, and this review juxtaposes some of the research updates about the possible mechanisms from several relevant aspects and insights into the therapeutic perspectives of MPs in clinical management and pharmacological treatment of DN patients.

Exosomes as new players in metabolic organ cross-talk

Blood glucose homeostasis requires a constant communication between insulin-secreting and insulin-sensitive cells. A wide variety of circulating factors, including hormones, cytokines and chemokines work together to orchestrate the systemic response of metabolic organs to changes in the nutritional state. Failure in the coordination between these organs can lead to a rise in blood glucose levels and to the appearance of metabolic disorders such as diabetes mellitus. Exosomes are small extracellular vesicles (EVs) that are produced via the endosomal pathway and are released from the cells upon fusion of multivesicular bodies with the plasma membrane. There is emerging evidence indicating that these EVs play a central role in cell-to-cell communication. The interest in exosomes exploded when they were found to transport bioactive proteins, messenger RNA (mRNAs) and microRNA (miRNAs) that can be transferred in active form to adjacent cells or to distant organs. In this review, we will first outline the mechanisms governing the biogenesis, the cargo upload and the release of exosomes by donor cells as well as the uptake by recipient cells. We will then summarize the studies that support the novel concept that miRNAs and other exosomal cargo components are new important vehicles for metabolic organ cross-talk.

The Micro-Managing Fat: Exosomes as a New Messenger

Brown fat secretes endocrine factors and exerts metabolic effects beyond thermogenesis. In addition to protein factors and bioactive lipids, recent work has revealed brown fat-derived miRNAs carried by exosomes as a new means of interorgan crosstalk, with potentially important implications for metabolic physiology and disease.

Extracellular Vesicles as a Source of Urological Biomarkers: Lessons Learned From Advances and Challenges in Clinical Applications to Major Diseases

Extracellular vesicles (EVs) not only eliminate unwanted molecular components, but also carry molecular cargo essential for specific intercellular communication mechanisms. As the molecular characteristics and biogenetical mechanisms of heterogeneous EVs are different, many studies have attempted to purify and characterize EVs. In particular, exosomal molecules, including proteins, lipids, and nucleic acids, have been suggested as disease biomarkers or therapeutic targets in various diseases. However, several unresolved issues and challenges remain despite these promising results, including source variability before the isolation of exosomes from body fluids, the contamination of proteins during isolation, and methodological issues related to the purification of exosomes. This paper reviews the general characteristics of EVs, particularly microvesicles and exosomes, along with their physiological roles and contribution to the pathogenesis of major diseases, several widely used methods to isolate exosomes, and challenges in the development of disease biomarkers using the molecular contents of EVs isolated from body fluids.

Characterisation of adipocyte-derived extracellular vesicle subtypes identifies distinct protein and lipid signatures for large and small extracellular vesicles

Extracellular vesicles (EVs) are biological vectors that can modulate the metabolism of target cells by conveying signalling proteins and genomic material. The level of EVs in plasma is significantly increased in cardiometabolic diseases associated with obesity, suggesting their possible participation in the development of metabolic dysfunction. With regard to the poor definition of adipocyte-derived EVs, the purpose of this study was to characterise both qualitatively and quantitatively EVs subpopulations secreted by fat cells. Adipocyte-derived EVs were isolated by differential centrifugation of conditioned media collected from 3T3-L1 adipocytes cultured for 24 h in serum-free conditions. Based on morphological and biochemical properties, as well as quantification of secreted EVs, we distinguished two subpopulations of adipocyte-derived EVs, namely small extracellular vesicles (sEVs) and large extracellular vesicles (lEVs). Proteomic analyses revealed that lEVs and sEVs exhibit specific protein signatures, allowing us not only to define novel markers of each population, but also to predict their biological functions. Despite similar phospholipid patterns, the comparative lipidomic analysis performed on these EV subclasses revealed a specific cholesterol enrichment of the sEV population, whereas lEVs were characterised by high amounts of externalised phosphatidylserine. Enhanced secretion of lEVs and sEVs is achievable following exposure to different biological stimuli related to the chronic low-grade inflammation state associated with obesity. Finally, we demonstrate the ability of primary murine adipocytes to secrete sEVs and lEVs, which display physical and biological characteristics similar to those described for 3T3-L1. Our study provides additional information and elements to define EV subtypes based on the characterisation of adipocyte-derived EV populations. It also underscores the need to distinguish EV subpopulations, through a combination of multiple approaches and markers, since their specific composition may cause distinct metabolic responses in recipient cells and tissues.

The isolation of morphologically intact and biologically active extracellular vesicles from the secretome of cancer-associated adipose tissue

Breast cancer cells closely interact with different cell types of the surrounding adipose tissue to favor invasive growth and metastasis. Extracellular vesicles (EVs) are nanometer-sized vesicles secreted by different cell types that shuttle proteins and nucleic acids to establish cell-cell communication. To study the role of EVs released by cancer-associated adipose tissue in breast cancer progression and metastasis a standardized EV isolation protocol that obtains pure EVs and maintains their functional characteristics is required. We implemented differential ultracentrifugation as a pre-enrichment step followed by OptiPrep density gradient centrifugation (dUC-ODG) to isolate EVs from the conditioned medium of cancer-associated adipose tissue. A combination of immune-electron microscopy, nanoparticle tracking analysis (NTA) and Western blot analysis identified EVs that are enriched in flotillin-1, CD9 and CD63, and sized between 20 and 200 nm with a density of 1.076-1.125 g/ml. The lack of protein aggregates and cell organelle proteins confirmed the purity of the EV preparations. Next, we evaluated whether dUC-ODG isolated EVs are functionally active. ZR75.1 breast cancer cells treated with cancer-associated adipose tissue-secreted EVs from breast cancer patients showed an increased phosphorylation of CREB. MCF-7 breast cancer cells treated with adipose tissue-derived EVs exhibited a stronger propensity to form cellular aggregates. In conclusion, dUC-ODG purifies EVs from conditioned medium of cancer-associated adipose tissue, and these EVs are morphologically intact and biologically active.

Extracellular Vesicles from Adipose Tissue-A Potential Role in Obesity and Type 2 Diabetes?

Adipose tissue plays a key role in the development of insulin resistance and its pathological sequelae, such as type 2 diabetes and non-alcoholic fatty liver disease. Dysfunction in the adipose tissue response to storing excess fatty acids as triglyceride can lead to adipose tissue inflammation and spillover of fatty acids from this tissue and accumulation of fatty acids as lipid droplets in ectopic sites, such as liver and muscle. Extracellular vesicles (EVs) are released from adipocytes and have been proposed to be involved in adipocyte/macrophage cross talk and to affect insulin signaling and transforming growth factor β expression in liver cells leading to metabolic disease. Furthermore EV produced by adipose tissue-derived mesenchymal stem cells (ADSC) can promote angiogenesis and cancer cell migration and have neuroprotective and neuroregenerative properties. ADSC EVs have therapeutic potential in vascular and neurodegenerative disease and may also be used to target specific functional miRNAs to cells. Obesity is associated with an increase in adipose-derived EV which may be related to the metabolic complications of obesity. In this review, we discuss our current knowledge of EV produced by adipose tissue and the potential impact of adipose tissue-derived EV on metabolic diseases associated with obesity.

Cross Talk between Adipose Tissue and Placenta in Obese and Gestational Diabetes Mellitus Pregnancies via Exosomes

Obesity is an important public health issue worldwide, where it is commonly associated with the development of metabolic disorders, especially insulin resistance (IR). Maternal obesity is associated with an increased risk of pregnancy complications, especially gestational diabetes mellitus (GDM). Metabolism is a vital process for energy production and the maintenance of essential cellular functions. Excess energy storage is predominantly regulated by the adipose tissue. Primarily made up of adipocytes, adipose tissue acts as the body's major energy reservoir. The role of adipose tissue, however, is not restricted to a "bag of fat." The adipose tissue is an endocrine organ, secreting various adipokines, enzymes, growth factors, and hormones that take part in glucose and lipid metabolism. In obesity, the greater portion of the adipose tissue comprises fat, and there is increased pro-inflammatory cytokine secretion, macrophage infiltration, and reduced insulin sensitivity. Obesity contributes to systemic IR and its associated metabolic complications. Similar to adipose tissue, the placenta is also an endocrine organ. During pregnancy, the placenta secretes various molecules to maintain pregnancy physiology. In addition, the placenta plays an important role in metabolism and exchange of nutrients between mother and fetus. Inflammation at the placenta may contribute to the severity of maternal IR and her likelihood of developing GDM and may also mediate the adverse consequences of obesity and GDM on the fetus. Interestingly, studies on maternal insulin sensitivity and secretion of placental hormones have not shown a positive correlation between these phenomena. Recently, a great interest in the field of extracellular vesicles (EVs) has been observed in the literature. EVs are produced by a wide range of cells and are present in all biological fluids. EVs are involved in cell-to-cell communication. Recent evidence points to an association between adipose tissue-derived EVs and metabolic syndrome in obesity. In this review, we will discuss the changes in human placenta and adipose tissue in GDM and obesity and summarize the findings regarding the role of adipose tissue and placenta-derived EVs, with an emphasis on exosomes in obesity, and the contribution of obesity to the development of GDM.

Extracellular Vesicles: Novel Mediators of Cell Communication In Metabolic Disease

Metabolic homeostasis emerges from the complex, multidirectional crosstalk between key metabolic tissues including adipose tissue, liver, and skeletal muscle. This crosstalk, traditionally mediated by hormones and metabolites, becomes dysregulated in human diseases such as obesity and diabetes. Extracellular vesicles (EVs; including exosomes) are circulating, cell-derived nanoparticles containing proteins and nucleic acids that interact with and modify local and distant cellular targets. Accumulating evidence, reviewed herein, supports a role for extracellular vesicles in obesity-associated metabolic disturbance, particularly the local and systemic inflammation characteristic of adipose and hepatic stress. As the practical and conceptual challenges facing the field are tackled, this emerging and versatile mode of intercellular communication may afford valuable insights and therapeutic opportunities in combatting these major threats to modern human health.

Adipocyte-derived microvesicles from obese mice induce M1 macrophage phenotype through secreted miR-155

The pro-inflammatory profile of M1 macrophage accumulation in adipose tissue is a central event leading to the metabolic complications of obesity. However, the mechanisms by which M1 macrophages are enriched in adipose tissue during weight gain remain incompletely understood. Here, we investigated the effects of adipocyte-derived microvesicles (ADM) on modulating macrophage phenotype in mice and explored the involved molecular signalling pathways. We found that, compared with ADM from lean mice (SD ADM), ADM from obese mice (HFD ADM) significantly enhanced M1 marker expression. The quantitative RT-PCR assay demonstrated that miR-155 was upregulated in both HFD ADM and HFD ADM-treated macrophages. By depleting miR-155 expression in HFD ADM and increasing miR-155 level in SD ADM, we further illustrated that miR-155 in ADM-induced M1 macrophage polarization. Functionally, in contrast to SD ADM, HFD ADM significantly decreased the protein level of SOCS1, a proven miR-155 target, leading to activation of STAT1, and suppression of STAT6 signalling; these effects were reversed by silencing miR-155 in HFD ADM. Furthermore, the supernatant of bone marrow-derived macrophages pre-stimulated with miR-155-bearing ADM interfered with insulin signalling and insulin-induced glucose uptake in adipocytes. Collectively, these results provide the first evidence that M1 macrophage polarization can be mediated by miR-155-bearing ADM, which reciprocally regulates insulin signalling and glucose uptake in adipocytes. Our study reveals a novel mechanism through which obesity induces an imbalance in the M1-to-M2 macrophage ratio in adipose tissue, thus causing chronic inflammation and local insulin resistance.

Physiological and pathological impact of exosomes of adipose tissue

Exosomes are nanovesicles that have emerged as a new intercellular communication system for transporting proteins and RNAs; recent studies have shown that they play a role in many physiological and pathological processes such as immune regulation, cell differentiation, infection and cancer. By transferring proteins, mRNAs and microRNAs, exosomes act as information vehicles that alter the behavior of recipient cells. Compared to direct cell-cell contact or secreted factors, exosomes can affect recipient cells in more efficient ways. In whole adipose tissues, it has been shown that exosomes exist in supernatants of adipocytes and adipose stromal cells (ADSCs). Adipocyte exosomes are linked to lipid metabolism and obesity-related insulin resistance and exosomes secreted by ADSCs are involved in angiogenesis, immunomodulation and tumor development. This review introduces characteristics of exosomes in adipose tissue, summarizes their functions in different physiological and pathological processes and provides the further insight into potential application of exosomes to disease diagnosis and treatment.

Characterisation of adipocyte-derived extracellular vesicles released pre- and post-adipogenesis

Extracellular vesicles (EVs) are submicron vesicles released from many cell types, including adipocytes. EVs are implicated in the pathogenesis of obesity-driven cardiovascular disease, although the characteristics of adipocyte-derived EVs are not well described. We sought to define the characteristics of adipocyte-derived EVs before and after adipogenesis, hypothesising that adipogenesis would affect EV structure, molecular composition and function. Using 3T3-L1 cells, EVs were harvested at day 0 and day 15 of differentiation. EV and cell preparations were visualised by electron microscopy and EVs quantified by nanoparticle tracking analysis (NTA). EVs were then assessed for annexin V positivity using flow cytometry; lipid and phospholipid composition using 2D thin layer chromatography and gas chromatography; and vesicular protein content by an immuno-phenotyping assay. Pre-adipogenic cells are connected via a network of protrusions and EVs at both time points display classic EV morphology. EV concentration is elevated prior to adipogenesis, particularly in exosomes and small microvesicles. Parent cells contain higher proportions of phosphatidylserine (PS) and show higher annexin V binding. Both cells and EVs contain an increased proportion of arachidonic acid at day 0. PREF-1 was increased at day 0 whilst adiponectin was higher at day 15 indicating EV protein content reflects the stage of adipogenesis of the cell. Our data suggest that EV production is higher in cells before adipogenesis, particularly in vesicles <300 nm. Cells at this time point possess a greater proportion of PS (required for EV generation) whilst corresponding EVs are enriched in signalling fatty acids, such as arachidonic acid, and markers of adipogenesis, such as PREF-1 and PPARγ.

Extracellular Vesicles: Evolving Factors in Stem Cell Biology

Stem cells are proposed to continuously secrete trophic factors that potentially serve as mediators of autocrine and paracrine activities, associated with reprogramming of the tumor microenvironment, tissue regeneration, and repair. Hitherto, significant efforts have been made to understand the level of underlying paracrine activities influenced by stem cell secreted trophic factors, as little is known about these interactions. Recent findings, however, elucidate this role by reporting the effects of stem cell derived extracellular vesicles (EVs) that mimic the phenotypes of the cells from which they originate. Exchange of genetic information utilizing persistent bidirectional communication mediated by stem cell-EVs could regulate stemness, self-renewal, and differentiation in stem cells and their subpopulations. This review therefore discusses stem cell-EVs as evolving communication factors in stem cell biology, focusing on how they regulate cell fates by inducing persistent and prolonged genetic reprogramming of resident cells in a paracrine fashion. In addition, we address the role of stem cell-secreted vesicles in shaping the tumor microenvironment and immunomodulation and in their ability to stimulate endogenous repair processes during tissue damage. Collectively, these functions ensure an enormous potential for future therapies.

Minireview: Emerging Roles for Extracellular Vesicles in Diabetes and Related Metabolic Disorders

Extracellular vesicles (EVs), membrane-contained vesicles released by most cell types, have attracted a large amount of research interest over the past decade. Because of their ability to transfer cargo via regulated processes, causing functional impacts on recipient cells, these structures may play important roles in cell-cell communication and have implications in the physiology of numerous organ systems. In addition, EVs have been described in most human biofluids and have wide potential as relatively noninvasive biomarkers of various pathologic conditions. Specifically, EVs produced by the pancreatic β-cell have been demonstrated to regulate physiologic and pathologic responses to β-cell stress, including β-cell proliferation and apoptosis. β-Cell EVs are also capable of interacting with immune cells and may contribute to the activation of autoimmune processes that trigger or propagate β-cell inflammation and destruction during the development of diabetes. EVs from adipose tissue have been shown to contribute to the development of the chronic inflammation and insulin resistance associated with obesity and metabolic syndrome via interactions with other adipose, liver, and muscle cells. Circulating EVs may also serve as biomarkers for metabolic derangements and complications associated with diabetes. This minireview describes the properties of EVs in general, followed by a more focused review of the literature describing EVs affecting the β-cell, β-cell autoimmunity, and the development of insulin resistance, which all have the potential to affect development of type 1 or type 2 diabetes.

Inflamed macrophage microvesicles induce insulin resistance in human adipocytes

BACKGROUND

Cytokines secreted by adipose tissue macrophages (ATMs) significantly alter adipocyte function, inducing inflammatory responses and decreasing insulin sensitivity. However, little relevant information is available regarding the role of microvesicles (MVs) derived from ATMs in macrophage-adipocyte crosstalk.

METHODS

MVs were generated by stimulation of M1 or M2 phenotype THP-1 macrophages and incubated with human primary mature adipocytes and differentiated adipocytes. Subsequently, insulin-stimulated phosphorylation of Akt (pAkt) and glucose uptake were determined. Glucose transporter 4 (GLUT4) translocation and nuclear translocation of nuclear factor (NF)-kappa B were also analyzed in treated adipocytes.

RESULTS

M1 macrophage-derived MVs (M1 MVs) significantly reduced protein abundance of insulin-induced Akt phosphorylation in human primary mature adipocytes and differentiated adipocytes, when compared with the same concentration of M2 macrophage-derived MVs (M2 MVs). In contrast to M2 MVs, which enhanced the insulin-induced glucose uptake measured by 2-NBDG, M1 MVs decreased this effect in treated adipocytes. M1 MVs treatment also brought about a significant increase in the nuclear translocation of nuclear factor (NF)-kappa B, coupled with a decrease in pAkt level and GLUT4 translocation compared with M2 MVs-treated adipocytes. These effects were reversed by BAY 11-7085, a NF- kappa B specific inhibitor.

CONCLUSIONS

MVs derived from proinflammatory (M1) macrophages may, at least in part, contribute to the pathogenesis of obesity-induced insulin resistance, reducing insulin signal transduction and decreasing glucose uptake in human adipocytes, through NF-kappa B activation. Therefore, these MVs may be potential therapy candidates for the management of type 2 diabetes mellitus.

Interaction of differentiated human adipocytes with macrophages leads to trogocytosis and selective IL-6 secretion

Obesity leads to adipose tissue inflammation that is characterized by increased release of proinflammatory molecules and the recruitment of activated immune cells. Although macrophages are present in the highest number among the immune cells in obese adipose tissue, not much is known about their direct interaction with adipocytes. We have introduced an ex vivo experimental system to characterize the cellular interactions and the profile of secreted cytokines in cocultures of macrophages and human adipocytes differentiated from either mesenchymal stem cells or a preadipocyte cell line. As observed by time-lapse microscopy, flow, and laser-scanning cytometry, macrophages phagocytosed bites of adipocytes (trogocytosis), which led to their de novo, phagocytosis and NF-κB-dependent synthesis, then release of interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1. IL-6 secretion was not accompanied by secretion of other proinflammatory cytokines, such as tumor necrosis factor (TNF)-α and IL-8, except MCP-1. LPS-induced release of TNF-α, IL-8 and MCP-1 was decreased in the presence of the differentiated adipocytes but the IL-6 level did not subside suggesting that phagocytosis-dependent IL-6 secretion may have significant regulatory function in the inflamed adipose tissue.

Secretion of fatty acid binding protein aP2 from adipocytes through a nonclassical pathway in response to adipocyte lipase activity

Adipocyte fatty acid binding protein 4, aP2, contributes to the pathogenesis of several common diseases including type 2 diabetes, atherosclerosis, fatty liver disease, asthma, and cancer. Although the biological functions of aP2 have classically been attributed to its intracellular action, recent studies demonstrated that aP2 acts as an adipokine to regulate systemic metabolism. However, the mechanism and regulation of aP2 secretion remain unknown. Here, we demonstrate a specific role for lipase activity in aP2 secretion from adipocytes in vitro and ex vivo. Our results show that chemical inhibition of lipase activity, genetic deficiency of adipose triglyceride lipase and, to a lesser extent, hormone-sensitive lipase blocked aP2 secretion from adipocytes. Increased lipolysis and lipid availability also contributed to aP2 release as determined in perilipin1-deficient adipose tissue explants ex vivo and upon treatment with lipids in vivo and in vitro. In addition, we identify a nonclassical route for aP2 secretion in exosome-like vesicles and show that aP2 is recruited to this pathway upon stimulation of lipolysis. Given the effect of circulating aP2 on glucose metabolism, these data support that targeting aP2 or the lipolysis-dependent secretory pathway may present novel mechanistic and translational opportunities in metabolic disease.

Lipid signaling in adipose tissue: Connecting inflammation & metabolism

Obesity-associated low-grade inflammation of white adipose tissue (WAT) contributes to development of insulin resistance and other disorders. Accumulation of immune cells, especially macrophages, and macrophage polarization from M2 to M1 state, affect intrinsic WAT signaling, namely anti-inflammatory and proinflammatory cytokines, fatty acids (FA), and lipid mediators derived from both n-6 and n-3 long-chain PUFA such as (i) arachidonic acid (AA)-derived eicosanoids and endocannabinoids, and (ii) specialized pro-resolving lipid mediators including resolvins derived from both eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), lipoxins (AA metabolites), protectins and maresins (DHA metabolites). In this respect, potential differences in modulating adipocyte metabolism by various lipid mediators formed by inflammatory M1 macrophages typical of obese state, and non-inflammatory M2 macrophages typical of lean state remain to be established. Studies in mice suggest that (i) transient accumulation of M2 macrophages could be essential for the control of tissue FA levels during activation of lipolysis, (ii) currently unidentified M2 macrophage-borne signaling molecule(s) could inhibit lipolysis and re-esterification of lipolyzed FA back to triacylglycerols (TAG/FA cycle), and (iii) the egress of M2 macrophages from rebuilt WAT and removal of the negative feedback regulation could allow for a full unmasking of metabolic activities of adipocytes. Thus, M2 macrophages could support remodeling of WAT to a tissue containing metabolically flexible adipocytes endowed with a high capacity of both TAG/FA cycling and oxidative phosphorylation. This situation could be exemplified by a combined intervention using mild calorie restriction and dietary supplementation with EPA/DHA, which enhances the formation of "healthy" adipocytes. This article is part of a Special Issue entitled Oxygenated metabolism of PUFA: analysis and biological relevance."

Effect of extracellular vesicles of human adipose tissue on insulin signaling in liver and muscle cells

OBJECTIVE

Insulin resistance (IR) is a key mechanism in obesity-induced cardiovascular disease. To unravel mechanisms whereby human adipose tissue (AT) contributes to systemic IR, the effect of human AT-extracellular vesicles (EVs) on insulin signaling in liver and muscle cells was determined.

METHODS

EVs released from human subcutaneous (SAT) and omental AT (OAT)-explants ex vivo were used for stimulation of hepatocytes and myotubes in vitro. Subsequently, insulin-induced Akt phosphorylation and expression of gluconeogenic genes (G6P, PEPCK) was determined. AT-EV adipokine levels were measured by multiplex immunoassay, and AT-EVs were quantified by high-resolution flow cytometry.

RESULTS

In hepatocytes, AT-EVs from the majority of patients inhibited insulin-induced Akt phosphorylation, while EVs from some patients stimulated insulin-induced Akt phosphorylation. In myotubes AT-EVs exerted an ambiguous effect on insulin signaling. Hepatic Akt phosphorylation related negatively to G6P-expression by both SAT-EVs (r = -0.60, P = 0.01) and OAT-EVs (r = -0.74, P = 0.001). MCP-1, IL-6, and MIF concentrations were higher in OAT-EVs compared to SAT-EVs and differently related to lower Akt phosphorylation in hepatocytes. Finally, the number of OAT-EVs correlated positively with liver enzymes indicative for liver dysfunction.

CONCLUSIONS

Human AT-EVs can stimulate or inhibit insulin signaling in hepatocytes- possibly depending on their adipokine content- and may thereby contribute to systemic IR.

Extracellular vesicle markers in relation to obesity and metabolic complications in patients with manifest cardiovascular disease

Background

Alterations in extracellular vesicles (EVs), including exosomes and microparticles, contribute to cardiovascular disease. We hypothesized that obesity could favour enhanced release of EVs from adipose tissue, and thereby contribute to cardiovascular risk via obesity-induced metabolic complications. The objectives of this study were: 1) to investigate the relation between the quantity, distribution and (dys) function of adipose tissue and plasma concentrations of atherothrombotic EV-markers; 2) to determine the relation between these EV-markers and the prevalence of the metabolic syndrome; and 3) to assess the contribution of EV markers to the risk of incident type 2 diabetes.

Methods

In 1012 patients with clinically manifest vascular disease, subcutaneous and visceral fat thickness was measured ultrasonographically. Plasma EVs were isolated and levels of cystatin C, serpin G1, serpin F2 and CD14 were measured, as well as fasting metabolic parameters, hsCRP and adiponectin. The association between adiposity, EV-markers, and metabolic syndrome was tested by multivariable linear and logistic regression analyses. As sex influences body fat distribution, sex-stratified analyses between adipose tissue distribution and EV-markers were performed. The relation between EV-markers and type 2 diabetes was assessed with Cox regression analyses.

Results

Higher levels of hsCRP (β 5.59; 95% CI 3.00–8.18) and lower HDL-cholesterol levels (β-11.26; 95% CI −18.39 – -4.13) were related to increased EV-cystatin C levels, and EV-cystatin C levels were associated with a 57% higher odds of having the metabolic syndrome (OR 1.57; 95% CI 1.19–2.27). HDL-cholesterol levels were positively related to EV-CD14 levels (β 5.04; 95% CI 0.07–10.0), and EV-CD14 levels were associated with a relative risk reduction of 16% for development of type 2 diabetes (HR 0.84, 95% CI 0.75–0.94), during a median follow up of 6.5 years in which 42 patients developed type 2 diabetes.

Conclusions

In patients with clinically manifest vascular disease, EV-cystatin C levels were positively related, and EV-CD14 levels were negatively related to metabolic complications of obesity.