1 x 10^5 HUVECs were seeded in 6-well plates and 24 h. later were transfected with 24 pmoles of siRNA, miRNA mimics, inhibitors or the nonsense controls. For each transfection, oligonucleotides were mixed with 8 ul of transfection reagent in 200 ul of DMEM medium without FBS and antibiotics for 10 min. The mixture was then added to each well in a final volume of 2 ml of medium. Cells were analysed 24h later.

Endothelial dysfunction is one of the main pathophysiological processes involved in renal ischemia reperfusion injury. Our previous microarray study demonstrated that miR-98 was upregulated in the kidney with ischemia reperfusion injury (IRI). The present study was performed to investigate whether miR-98 was involved in the regulation of endothelial apoptosis under hypoxia and re-oxygenation (H/R) conditions. The dynamic changes of miR-98 in mouse IRI kidney and H/R HUVECs was measured. HUVECs were treated with HIF-1alpha siRNA to investigate the role of HIF-1alpha on miR-98 expression. The potential target genes of miR-98 were predicted by bioinformatics analyses. HUVECs were transfected with miR-98 mimics or inhibitor to confirm the role of miR-98 on the expression of target genes and hypoxia-induced apoptosis. The target gene was finally confirmed by dual-luciferase reporter assay. Both of IRI and H/R induced significantly up-regulation of miR-98 in the ischemic kidney and hypoxic HUVECs. HIF-1alpha siRNA remarkably down-regulated the expression of miR-98 in both normal and hypoxic HUVECs. The putative target genes of miR-98 included IL-6, IL-10 and caspase-3. MiR-98 mimics significantly inhibit caspase-3 expression in HUVECs, while anti-miR-98 significantly up-regulated it. But no change of IL-6 and IL-10 levels was observed after miRNA transfection. miR-98 protected HUVECs against apoptosis induced by hypoxia, while anti-miR-98 had the reverse effect. Furthermore, the dual-luciferase reporter assay confirmed that miR-98 decreased the luciferase activity by targeting the 3' untranslated region of caspase-3. In conclusion, Renal IRI induces up-regulation of miR-98 dependent on HIF-1alpha, which protects endothelial cells against apoptosis by targeting caspase-3.