Extracellular Vesicles (EVs) are gaining interest as central players in liquid biopsies, with potential applications in diagnosis, prognosis and therapeutic guidance in most pathological conditions. These nanosized particles transmit signals determined by their protein, lipid, nucleic acid and sugar content, and the unique molecular pattern of EVs dictates the type of signal to be transmitted to recipient cells. However, their small sizes and the limited quantities that can usually be obtained from patient-derived samples pose a number of challenges to their isolation, study and characterization. These challenges and some possible options to overcome them are discussed in this review.

Background: Cardiovascular risk in diabetes remains elevated despite glucose lowering therapies. We hypothesised that hyperglycaemia induces trained immunity in macrophages, promoting persistent pro-atherogenic characteristics. Methods: Bone marrow derived macrophages from control and mice with diabetes were grown in physiological glucose (5 mM) and subject to RNA-sequencing (n=6), ATAC-sequencing (n=6) and ChIP-sequencing (n=6) for determination of hyperglycaemia-induced trained immunity. Bone marrow transplantation from mice with (n=9) or without (n=6) diabetes into [normoglycaemic] Ldlr -/- mice was used to assess its functional significance in vivo . Evidence of hyperglycaemia-induced trained immunity was sought in human peripheral blood mononuclear cells (PBMCs) from patients with diabetes (n=8) compared with case controls (n=16) and in human atherosclerotic plaque macrophages excised by laser capture microdissection. Results: In macrophages, high extracellular glucose promoted pro-inflammatory gene expression and pro-atherogenic functional characteristics, through glycolysis-dependent mechanisms. Bone marrow-derived macrophages (BMDM) from diabetic mice, retained these characteristics, even when cultured in physiological glucose, indicating hyperglycaemia-induced trained immunity. Bone marrow transplantation from diabetic mice into [normoglycaemic] Ldlr -/- mice increased aortic root atherosclerosis, confirming a disease-relevant and persistent form of trained innate immunity. Integrated ATAC-seq, ChIP-seq and RNA-seq analyses of haematopoietic stem cells and BMDM revealed a pro-inflammatory "priming effect" in diabetes. The pattern of open chromatin implicated transcription factor, RUNX1, while transcriptomes of atherosclerotic plaque macrophages and peripheral leukocytes in patients with type 2 diabetes were enriched for RUNX1 targets, consistent with a potential role in human disease. Pharmacological inhibition of RUNX1 in vitro inhibited the trained phenotype. Conclusions: Hyperglycaemia-induced trained immunity may explain why targeting elevated glucose is ineffective in reducing macrovascular risk in diabetes and suggests new targets for disease prevention and therapy.

Transcriptionally activated monocytes are recruited to the heart after acute myocardial infarction (AMI). After AMI in mice and humans, the number of extracellular vesicles (EVs) increased acutely. In humans, EV number correlated closely with the extent of myocardial injury. We hypothesized that EVs mediate splenic monocyte mobilization and program transcription following AMI. Some plasma EVs bear endothelial cell (EC) integrins, and both proinflammatory stimulation of ECs and AMI significantly increased VCAM-1–positive EV release. Injected EC-EVs localized to the spleen and interacted with, and mobilized, splenic monocytes in otherwise naive, healthy animals. Analysis of human plasma EV-associated miRNA showed 12 markedly enriched miRNAs after AMI; functional enrichment analyses identified 1,869 putative mRNA targets, which regulate relevant cellular functions (e.g., proliferation and cell movement). Furthermore, gene ontology termed positive chemotaxis as the most enriched pathway for the miRNA-mRNA targets. Among the identified EV miRNAs, EC-associated miRNA-126-3p and -5p were highly regulated after AMI. miRNA-126-3p and -5p regulate cell adhesion– and chemotaxis-associated genes, including the negative regulator of cell motility, plexin-B2. EC-EV exposure significantly downregulated plexin-B2 mRNA in monocytes and upregulated motility integrin ITGB2. These findings identify EVs as a possible novel signaling pathway by linking ischemic myocardium with monocyte mobilization and transcriptional activation following AMI.

Extracellular vesicles (EVs) are submicron-sized lipid envelopes that are produced and released from a parent cell and can be taken up by a recipient cell. EVs are capable of mediating cellular signalling by carrying nucleic acids, proteins, lipids and cellular metabolites between cells and organs. Metabolic dysfunction is associated with changes in plasma concentrations of EVs as well as alterations in their EV cargo. Since EVs can act as messengers between parent and recipient cells, they could be involved in cell-to-cell and organ-to-organ communication in metabolic diseases. Recent literature has shown that EVs are produced by cells within metabolic tissues, such as adipose tissue, pancreas, muscle and liver. These vesicles have therefore been proposed as a novel intercellular communication mode in systemic metabolic regulation. In this review, we will describe and discuss the current literature that investigates the role of adipose-derived EVs in the regulation of obesity-associated metabolic disease. We will particularly focus on the EV-dependent communication between adipocytes, the vasculature and immune cells in type 2 diabetes.Electronic supplementary materialThe online version of this article (10.1007/s00125-019-05014-5) contains a slide of the figure for download, which is available to authorised users.