Altered Angiogenesis in Caveolin-1 Gene–Deficient Mice Is Restored by Ablation of Endothelial Nitric Oxide Synthase

Abstract

Caveolin-1 is an essential structural protein of caveolae, specialized plasma membrane organelles highly abundant in endothelial cells, where they regulate multiple functions including angiogenesis. Caveolin-1 exerts a tonic inhibition of endothelial nitric oxide synthase (eNOS) activity. Accordingly, caveolin-1 gene-disrupted mice have enhanced eNOS activity as well as increased systemic nitric oxide (NO) levels. We hypothesized that excess eNOS activity, secondary to caveolin deficiency, would mediate the decreased angiogenesis observed in caveolin-1 gene-disrupted mice. We tested tumor angiogenesis in mice lacking either one or both proteins, using in vitro, ex vivo, and in vivo assays. We show that endothelial cell migration, tube formation, cell sprouting from aortic rings, tumor growth, and angiogenesis are all significantly impaired in both caveolin-1-null and eNOSnull mice. We further show that these parameters were either partially or fully restored in double knockout mice that lack both caveolin-1 and eNOS. Furthermore, the effects of genetic ablation of eNOS are mimicked by the administration of the NOS inhibitor N-nitro-L-arginine methyl ester hydrochloride (L-NAME), including the reversal of the caveolin-1-null mouse angiogenic phenotype. This study is the first to demonstrate the detrimental effects of unregulated eNOS activity on angiogenesis, and shows that impaired tumor angiogenesis in caveolin-1-null mice is, at least in part, the result of enhanced eNOS activity.

Liver X Receptor Activation Reduces Angiogenesis by Impairing Lipid Raft Localization and Signaling of Vascular Endothelial Growth Factor Receptor-2

“…As knockout of caveolin-1 inhibits angiogenesis by impairing VEGFR2 compartmentation and by causing a detrimental deregulation of endothelial NO synthase, LXR activation may restrain angiogenesis by altering the physiological conditions of caveolin-1 expression and internalization, and possibly endothelial NO synthase activity. 38,39 Furthermore, as lipid rafts/caveolae are membrane microdomains harboring multiple signaling platforms, we cannot exclude that the effects of LXR activation may extend to other relevant receptors and pathways, such as those of fibroblast growth factor or transforming growth factor-β.…”

PEDF expression regulates the proangiogenic and proinflammatory phenotype of the lung endothelium

“…NO is a major player in VEGF-mediated angiogenesis, and eNOS is the major source of NO production in the endothelium. Inhibition of eNOS activity attenuates capillary morphogenesis in vitro and VEGF-mediated angiogenesis in vivo (26,39). Although iNOS is more efficient in NO production, it is generally associated with inflammatory conditions, and it is recognized as a marker of inflammation.…”

Caveolins and caveolae in ocular physiology and pathophysiology

“…Outside of the eye, studies on the effect of caveolae on angiogenesis have been confounding with some studies suggesting that Cav-1 promotes angiogenesis (Chang et al, 2009; Sonveaux et al, 2004; Woodman et al, 2003) while others indicate anti-angiogenic activity (Bauer et al, 2005; Lin et al, 2007). A study using the corneal VEGF pocket assay in Cav-1 −/− mice showed that Cav-1 expression promotes VEGF-induced corneal angiogenesis (Morais et al, 2012). In these studies, Cav-1 −/− mice had a significantly blunted angiogenic response to VEGF.…”