Abstract
BackgroundDiabetes mellitus is a common metabolic disorder characterized by dysfunction of insulin-secreting pancreatic beta-cells. MicroRNAs are important regulators of beta-cell activities. These non-coding RNAs have recently been discovered to exert their effects not only inside the cell producing them but, upon exosome-mediated transfer, also in other recipient cells. This novel communication mode remains unexplored in pancreatic beta-cells. In the present study, the microRNA content of exosomes released by beta-cells in physiological and physiopathological conditions was analyzed and the biological impact of their transfer to recipient cells investigated.ResultsExosomes were isolated from the culture media of MIN6B1 and INS-1 derived 832/13 beta-cell lines and from mice, rat or human islets. Global profiling revealed that the microRNAs released in MIN6B1 exosomes do not simply reflect the content of the cells of origin. Indeed, while a subset of microRNAs was preferentially released in exosomes others were selectively retained in the cells. Moreover, exposure of MIN6B1 cells to inflammatory cytokines changed the release of several microRNAs. The dynamics of microRNA secretion and their potential transfer to recipient cells were next investigated. As a proof-of-concept, we demonstrate that if cel-miR-238, a C. Elegans microRNA not present in mammalian cells, is expressed in MIN6B1 cells a fraction of it is released in exosomes and is transferred to recipient beta-cells. Furthermore, incubation of untreated MIN6B1 or mice islet cells in the presence of microRNA-containing exosomes isolated from the culture media of cytokine-treated MIN6B1 cells triggers apoptosis of recipient cells. In contrast, exosomes originating from cells not exposed to cytokines have no impact on cell survival. Apoptosis induced by exosomes produced by cytokine-treated cells was prevented by down-regulation of the microRNA-mediating silencing protein Ago2 in recipient cells, suggesting that the effect is mediated by the non-coding RNAs.ConclusionsTaken together, our results suggest that beta-cells secrete microRNAs that can be transferred to neighboring beta-cells. Exposure of donor cells to pathophysiological conditions commonly associated with diabetes modifies the release of microRNAs and affects survival of recipient beta-cells. Our results support the concept that exosomal microRNAs transfer constitutes a novel cell-to-cell communication mechanism regulating the activity of pancreatic beta-cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-015-0097-7) contains supplementary material, which is available to authorized users.
Highlights
Diabetes mellitus is a common metabolic disorder characterized by dysfunction of insulin-secreting pancreatic beta-cells
We investigated if the release of exosomes from pancreatic beta-cells can affect the surrounding cells and can constitute a cell-to-cell communication mode permitting a concerted adaptation of beta-cells to environmental cues
Isolation and characterization of exosomes released by pancreatic beta-cells Microvesicles released by the pancreatic beta-cell line MIN6B1 cultured in DMEM medium complemented with exosome-depleted FCS were isolated by ultra-centrifugation and characterized for their size and content
Summary
Diabetes mellitus is a common metabolic disorder characterized by dysfunction of insulin-secreting pancreatic beta-cells. MiRNAs act by binding to the 3’UTR of target mRNAs of specific genes leading to translational repression and/or to a decrease in messenger stability [5] Beside their activity accomplished inside the cell producing them, these small RNA molecules can be released in the extracellular environment packaged within microvesicles or in association with proteins or high-density lipoproteins (HDL) [6,7,8]. Exosomes accumulate in the culture media of several cell types, and are present in different body fluids such as blood, urine or saliva [14] These extracellular vesicles carry proteins and nucleic acids, including miRNAs that can be transferred to recipient cells [9,15]. Exosomal miRNAs were reported to be involved in a broad range of biological processes including the immune reaction and in the regulation of the cardiovascular system [19,20]
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