Background and Objective The suppression of angiogenesis associated with cardiac growth has been reported to be essential for the transition from cardiac hypertrophy to heart failure. It is well established that angiotension II (Ang II) is an important regulator in vascular homeostasis. Under certain conditions, Ang II could exert directly anti-angiogenic effects in cardiovascular system. However, the potential mechanisms are unclear. This present study was conducted to determine the underlying mechanisms for the anti-angiogenic effect of Ang II.
Methods and Results Angiogenesis was determined by tube formation from the cardiac microvascular endothelial cells (ECs). Microvessel density and cardiac function were analysed in mice subjected to Ang II infusion (200 ng/kg/min) or vehicle for 2 weeks. Ang II (1μM) greatly inhibited tube formation and stimulated phosphorylation and upregulation of P53 in cultured cardiac ECs. P53 inhibitor, pifithrin-α (PFT-α, 3.0mg/kg), significantly reversed the inhibitory effect of Ang II on tube formation. Vascular endothelial growth factor (VEGF) and Hif-1α has been reported as important pro-angiogenetic factors. The present study indicated that Ang II decreased VEGF concentration in cultured medium and downregulated HIF-1 expression in cultured ECs. Interestingly, Ang II also stimulated the upregulation of Jagged 1, a ligand of Notch, but it didn’t affect the Delta-like 4 (Dll 4), another ligand of Notch, expression in cardiac ECs. However, PFT-α partly abolished these effects of Ang II. These results were consistent with the study in vivo. Further research revealed that siRNA-Jagged 1 transfection in cultured ECs dramatically abolished the phosphorylation of P53 and the downregulation of HIF1 induced by Ang II. Additionally, Ang II- induced inhibitory effect on capillary formation was blocked by siRNA-Jagged 1 transfection in cultured cardiac ECs.
Conclusions Ang II promoted the phosphorylation and upregulation of P53, and increased Jagged 1 expression, the upregulation of Jagged 1 in turn stimulated the phosphorylation of P53, which resulted in the downregulation of Hif-1α and VEGF, then induced the inhibitory effects of Ang II on capillary formation. The present data suggest that Ang II exerts anti-angiogenesis via the cooperation of P53 and Jagged 1 in vitro and in vivo.