CircRNAs in exosomes from high glucose-treated glomerular endothelial cells activate mesangial cells.

Understanding the relationships between glomerular endothelial cells (GECs) and glomerular mesangial cells (GMCs) is important to identify the molecular mechanisms underlying diabetic nephropathy (DN). Exosomes carried with mRNA, microRNA, and protein play important roles in cell-to-cell communication. In this study, we showed that high glucose (HG)-treated GECs secreted a higher number of exosomes enriched in circRNAs compared with normal glucose (NG)-treated GECs. Differentially expressed circRNAs (DECs) were obtained by high-throughput sequencing. Of these DECs, the expressions of 217 DECs and 484 DECs in HG-treated GEC exosomes were significantly downregulated and upregulated, respectively, compared with NG-treated GEC exosomes. The functions of the DEC target genes were involved in the PI3K/AKT and MAPK pathways. Five DECs were randomly selected for identification by quantitative real-time PCR (qRT-PCR). Two DECs (circRNF169 and circSTRN3) were further selected for functional validation. Moreover, we demonstrated that exosomes released by HG-treated GECs promoted alpha-smooth muscle actin (alpha-SMA) expression. It also inhibited proliferation and promoted epithelial-mesenchymal transition (EMT) in GMCs. In addition, cell functional studies indicated that the knockdown and over-expression of two DECs (circRNF169 and circSTRN3) effectively inhibited or promoted cell proliferation and promoted or inhibited EMT, respectively. Thus, the results of this study provide new insights into the pathogenesis of DN that involves the intercellular transfer of circRNAs from GECs to GMCs via exosomes.