RasGRP1 is a target for VEGF to induce angiogenesis and involved in the endothelial-protective effects of metformin under high glucose in HUVECs.

Impaired angiogenesis in endothelial cells is a hallmark of diabetes vascular complications. Ras guanine-releasing protein 1 (RasGRP1) is a guanine nucleotide exchange factor for Ras, and its role in endothelial angiogenesis has not been investigated. Given the importance of Ras in vascular endothelial growth factor (VEGF)-induced angiogenesis, we hypothesized that RasGRP1 may be a critical pathway downstream of VEGF and involved in endothelial angiogenesis. Furthermore, we investigate whether RasGRP1-dependent VEGF signaling was downregulated under high glucose conditions mimicking diabetes and required for the endothelial protective action of metformin in human umbilical vein endothelial cells (HUVECs). HUVECs were transfected with either RasGRP1 small interfering RNA (siRNA) or pEnter-RasGRP1 plasmid to down- and upregulate RasGRP1 expression before different treatments, such as added VEGF or not, exposed to high glucose (35 mM) or normal glucose (5 mM) in the presence or absence of metformin. Expression of VEGF, RasGRP1, and their signaling targets were analyzed by Western blot; migration and tube formation were detected by transwell chamber assay and Matrigel angiogenesis assay, respectively. Knockdown of RasGRP1 significantly attenuated VEGF-induced migration and tube formation activities of HUVECs and activation of AKT pathway. The expression of VEGF, RasGRP1, and AKT phosphorylation was downregulated in HUVECs exposed to high glucose compared with normal glucose, whereas metformin upregulated the RasGRP1-dependent VEGF signaling and ameliorates the impaired angiogenesis caused by high glucose. RasGRP1 is involved in the VEGF-induced angiogenesis and the pro-angiogenesis effects of metformin under hyperglycemia.