The MicroRNA-21 signaling pathway is involved in prorenin receptor (PRR) –induced VEGF expression in ARPE-19 cells under a hyperglycemic condition

PURPOSE: MicroRNAs (miRNAs/miRs) are involved in a large number of biological functions and diseases, such as cancer, cardiovascular diseases, and diabetes. MiR-21 has been reported to target Sprouty homolog 1 (SPRY1), SMAD7, and PTEN. In this study, we examined the underlying role of miR-21 in the regulation of prorenin receptor (PRR)-mediated induction of vascular endothelial growth factor (VEGF) expression via targeting SMAD7, SPRY1, and PTEN in a hyperglycemic condition. METHODS: PRR-mediated induction of VEGF under a hyperglycemic condition (high glucose, 33mM) was studied by treating ARPE-19 cells with perindopril (10 µmol/l), which inhibits angiotensin II-mediated signaling. ARPE-19 cells exposed to normal glucose (NG, 5.5 mM) were considered as the control. To examine the role of miR-21 in the regulation of SPRY1, SMAD7, PTEN, and VEGF, ARPE-19 cells cultured in NG or high glucose were transfected with scramble negative control (Scr), a miR-21 mimic, or a miR-21 antagomir. To investigate the role of PRR and the small GTP-binding protein RAC1 in the regulation of miR-21, the expression of PRR and RAC1 was silenced by transfecting ARPE-19 cells with their corresponding siRNAs. RESULTS: Compared with the NG control, high glucose significantly induced the expression of PRR, VEGF, VEGFR2, and miR-21 but significantly suppressed the expression of SPRY1, SMAD7, and PTEN at the transcript and protein levels. In contrast, silencing the expression of PRR significantly abolished the high glucose–induced expression of VEGF, VEGFR2, and miR-21. Knockdown of RAC1 significantly attenuated the high glucose–induced expression of LOX, CTGF, and miR-21, suggesting that PRR and RAC1 are involved in the CTGF/LOX-mediated regulation of miR-21. Furthermore, high glucose dramatically increased the levels of pERK (p44), hypoxia-inducible factor (HIF-1α), and VEGF. However, this effect was antagonized by the miR-21 antagomir, indicative of the involvement of high glucose–induced miR-21 in the regulation of VEGF through ERK signaling. CONCLUSIONS: Our findings, for the first time, showed that the pleiotropic action of miR-21 induced the expression of pERK, HIF-1α, and VEGF in the high glucose condition by simultaneously targeting SPRY1, SMAD7, and PTEN in ARPE-19 cells. Therefore, miR-21 may serve as a potential therapeutic target for diabetes-induced retinal pathology.