Role of Arginase‐I in Capillary Tube Formation and Ischemia‐induced Angiogenesis

Abstract

Studies have shown that arginase-I (Arg-I), an enzyme which utilizes L-arginine to form urea and ornithine for subsequent synthesis of polyamines, is up-regulated under various pathophysiological conditions such as tissue ischemia, cancer metastasis, wound healing and inflammation, which are known to promote angiogenesis. However, the role of Arg-I in angiogenesis remains unclear. Herein, we propose that Arg-I can promote angiogenesis. To test this hypothesis, adenoviral vector encoding Arg-I with GFP reporter gene (AdArg-IeGFP) was reconstructed for Arg-I over-expression in human umbilical vein endothelial cells (HUVEC), cultured mouse aortic rings, and mouse ischemic hindlimb by femoral artery ligation. Adenoviral vector (109 particles in 100 μl) were injected to the ischemic tissue at multiple sites distal to the ligation. Results showed that Arg-I protein expression and activity in HUVEC were increased by 4.5- and 9-fold, respectively, at day-4 after transfection. Over-expression of Arg-1 increased HUVEC proliferation and promoted tube-like morphogenesis. Both number and length of capillary outgrowth were significantly higher in the aortic explants over-expressed with Arg-1. Transfection of AdArg-IeGFP to ischemic tissue caused over-expression of Arg-1 significantly increased capillary density and blood flow with time. Inhibition of arginase activity by nor-Nw-hydroxy-L-arginine abolished capillary tube formation in vitro and reduced the angiogenic effect of Arg-I in vivo. These results suggest that Arg-I plays an important role in the process of angiogenesis. Supported by NIH grant: HL-71761