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Urotensin-II (U-II) has been considered as one of the most potent vasoactive peptides, although its physiological and pathophysiological role is still not finally resolved. Recent evidence suggests that it promotes angiogenic responses in endothelial cells, although the underlying signalling mechanisms are unclear. Reactive oxygen species derived from NADPH oxidases are major signalling molecules in the vasculature. Because NOX2 is functional in endothelial cells, we investigated the role of the NOX2-containing NADPH oxidase in U-II-induced angiogenesis and elucidated a possible contribution of hypoxia-inducible factor-1 (HIF-1), the master regulator of hypoxic angiogenesis, in the response to U-II. We found that U-II increases angiogenesis in vitro and in vivo, and these responses were prevented by antioxidants, NOX2 knockdown and in Nox2(-/-) mice. In addition, U-II-induced angiogenesis was dependent on HIF-1. Interestingly, U-II increased NOX2 transcription involving HIF-1, and chromatin immunoprecipitation confirmed NOX2 as a target gene of HIF-1. In support, NOX2 levels were greatly diminished in U-II-stimulated isolated vessels derived from mice deficient in endothelial HIF-1. Conversely, reactive oxygen species derived from NOX2 were required for U-II activation of HIF and upregulation of HIF-1. In line with this, U-II-induced upregulation of HIF-1 was absent in Nox2(-/-) vessels. Collectively, these findings identified HIF-1 and NOX2 as partners acting in concert to promote angiogenesis in response to U-II. Because U-II has been found to be elevated in cardiovascular disorders and in tumour tissues, this feed-forward mechanism could be an interesting anti-angiogenic therapeutic option in these disorders.

The vasoactive peptide urotensin-II (U-II) has been associated with vascular remodeling in different cardiovascular disorders. Although U-II can induce reactive oxygen species (ROS) by the NADPH oxidase NOX4 and stimulate smooth muscle cell (SMC) proliferation, the precise mechanisms linking U-II to vascular remodeling processes remain unclear. Forkhead Box O (FoxO) transcription factors have been associated with redox signaling and control of proliferation and apoptosis. We thus hypothesized that FoxOs are involved in the SMC response toward U-II and NOX4. We found that U-II and NOX4 stimulated FoxO activity and identified matrix metalloproteinase-2 (MMP2) as target gene of FoxO3a. FoxO3a activation by U-II was preceded by NOX4-dependent phosphorylation of c-Jun NH(2)-terminal kinase and 14-3-3 and decreased interaction of FoxO3a with its inhibitor 14-3-3, allowing MMP2 transcription. Functional studies in FoxO3a-depleted SMCs and in FoxO3a(-/-) mice showed that FoxO3a was important for basal and U-II-stimulated proliferation and vascular outgrowth, whereas treatment with an MMP2 inhibitor blocked these responses. Our study identified U-II and NOX4 as new activators of FoxO3a, and MMP2 as a novel target gene of FoxO3a, and showed that activation of FoxO3a by this pathway promotes vascular growth. FoxO3a may thus contribute to progression of cardiovascular diseases associated with vascular remodeling.