Background/Aims: Dysfunction of endothelial progenitor cell (EPCs) contributes to diabetic vascular disease. We reported that downregulated miR-126 in diabetic patients causes EPC dysfunction. The study was designed to investigate how high glucose (HG) and advanced glycation end products (AGEs) regulate miR-126 expression and whether miR-126 mediates the effects of HG and AGEs on EPCs. Methods: We first tested the effects of glucose (5.5-50 mM) and AGEs at 50-200 mg/l on EPC proliferation and selected HG at 50 mM and AGEs at 50 mg/l for further experiments. EPCs were stimulated with HG and AGEs, and miR-126 expression was measured by real-time PCR. Reactive oxygen species (ROS) were measured by immunofluorescence microscopy and flow cytometry. IL-6 and TNF-α levels in EPC supernatants were determined by ELISA. The effects of miR-126 on ROS and inflammatory markers under stimulation of HG and AGEs were also assessed. Finally, the effects of inhibitors of PI3K and Akt on AGE-mediated miR-126 expression were examined. Results: HG and AGEs increased IL-6, TNF-α and ROS and decreased miR-126 expression in EPCs. miR-126 negatively regulated IL-6, TNF-α and ROS. miR-126 overexpression reduced and miR-126 inhibition further increased the inflammatory markers and ROS induced by HG and AGEs. Inhibitors of PI3K and Akt further decreased miR-126 expression in the presence of AGEs. Conclusions: In conclusion, hyperglycemia and AGEs decrease miR-126 expression in EPCs. Recovering miR-126 expression may protect EPCs against dysfunction induced by HG and AGEs.

Background: Endothelial progenitor cells (EPCs) contribute to reendothelialization and neovascularization and protect against vascular injury and ischemia of various organs. We have previously shown downregulation of microRNA (miR)-126 in EPCs from diabetic patients, which contributes to dysfunction of EPCs including impaired migratory ability. The aims of the present study were to examine (1) in vitro the effects of miR-126 on the homing and stemness of late outgrowth EPCs (LOCs), along with relevant signaling pathways, and (2) in vivo the effects of modulating LOCs by manipulating miR-126 expression on LOC homing and reendothelialization of injured arteries in GK rats (a non-obese diabetes model). Methods: Rat bone marrow-derived LOCs were transfected with miR-126 inhibitor or lentiviral vectors expressing miR-126. LOC migration was determined by transwell migration assay. CXCR4 expression was measured by real-time PCR, Western blotting, and confocal microscopy while related signaling pathway proteins were measured by Western Blotting. Stemness gene expression, and gene and protein expression and promoter activity of KLF-8 were also measured. LOCs transfected with lenti-miR-126 or miR-126 inhibitor were injected into GK rats with carotid artery injury, and then vascular reendothelialization and the extent of intimal hyperplasia were examined. Results: Lenti-miR-126 increased while miR-126 inhibitor decreased LOC migration and CXCR4 expression on LOCs. miR-126 positively regulated pERK , VEGF, p-Akt, and eNOS protein expression, and inhibitors of these proteins blocked miR-126-induced CXCR4 expression and also reduced LOC migration. Overexpression of miR-126 promoted while inhibition of miR-126 suppressed stemness gene expression in LOCs. miR-126 also inhibited gene and protein expression and promoter activity of KLF-8 while shRNA-mediated knockdown of KLF-8 increased stemness gene expression. Upregulation of stemness gene expression by miR-126 overexpression was completely abrogated by cotransfection of lenti-KLF-8 and lenti-miR-126 into LOCs. In GK rats, transplantation of LOCs overexpressing miR-126 enhanced LOC homing and reendothelialization and decreased intimal hyperplasia of injured arteries. Conclusion: Our results indicate that miR-126 protects against vascular injury by promoting CXCR4 expression and LOC homing via ERK/VEGF and Akt/eNOS signaling pathways and maintaining stemness via targeting KLF-8.