Abstract
Background: Hypoxia-inducible factor (HIF)-1α regulates the transcription of lines of genes including vascular endothelial growth factor (VEGF), a major gene responsible for the angiogenesis. Several recent studies have demonstrated that a nonhypoxic pathway via nitric oxide (NO) is involved in activation of HIF-1α. However, there is no direct evidence demonstrating that the release of angiogenic factors by cardiomyocytes through the nonhypoxic induction pathway of HIF-1α in the heart. Therefore, we assessed the effects of a NO donor, S-nitroso-N-acetylpenicillamine (SNAP), on the induction of VEGF via HIF-1α under normoxia using primary cultured rat cardiomyocytes (PRCMs). Methods and Results: PRCMs treated with acetylcholine (ACh) or SNAP exhibited a significant production of NO. SNAP activated induction of HIF-1α protein expression in PRCMs during normoxia. Phosphatidylinositol 3-kinase (PI3K)–dependent Akt phosphorylation was induced by SNAP, and was completely blocked by wortmannin, a PI3K inhibitor, and NG-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor. The SNAP treatment also increased VEGF protein expression in PRCMs. Furthermore, conditioned medium derived from SNAP-treated cardiomyocytes phosphorylated VEGF type2 receptor (Flk-1) of human umbilical vein endothelial cells (4-fold increase compare to the control group, p < 0.001, n = 5) and accelerated angiogenesis. Conclusion: Our results suggest that cardiomyocytes produce VEGF through a nonhypoxic HIF-1α induction pathway activated by NO, resulting in angiogenesis.
