Abstract 886: Modulation of Angiogenesis and Postnatal Vascular Growth by the NAD-Dependent Histone Deacetylase SIRT1
The NAD-dependent histone deacetylase Sir2 regulates organismal life-span in various species in response to caloric restriction. Mammalian homologues of Sir2 are called sirtuins, among which SIRT1 is the closest homologue of Sir2. In an effort to define the role of sirtuins for endothelial cell function and vascular homeostasis, we found that specifically SIRT1 plays a key role in the regulation of angiogenesis signaling. Here, we show that SIRT1 is highly expressed in various cultured endothelial cells and displays especially robust expression in the postnatal endothelium in vivo. Treatment of endothelial cells with the small molecule weight inhibitors of sirtuins, sirtinol and nicotinamide, inhibited endothelial sprout formation and migration in a three-dimensional spheroidal assay of angiogenesis and endothelial differentiation (856±86μm vs. 86±38μm and 675±183μm vs. 311±119μm, respectively), whereas the sirtuin activator resveratrol enhanced the angiogenic response. Small interfering RNA-mediated silencing of endogenous SIRT1, but not SIRT2, SIRT3 or SIRT5 abolished the outgrowth of capillary-like structures (935±39μm vs. 202±58μm) and inhibited vessel growth in a Matrigel plug assay in vivo. This anti-angiogenic effect of SIRT1 gene silencing was unlikely the consequence of excessive apoptosis or increased cell cycle arrest, since knock down of SIRT1 had only a minor effect on apoptosis and cell cycle progression. Consistent with these data, overexpression of wild type SIRT1, but not of a catalytically inactive mutant, enhanced sprout formation and migration in vitro. Microarray analysis revealed that loss of SIRT1 expression leads to the downregulation of genes involved in vascular differentiation and remodeling such as Fli1, hHex, Tal1, Flt1, CXCR4 and MMP14. Moreover, SIRT1 binds and deacetylates the Foxo transcription factor Foxo1, which is a negative regulator of postnatal vascular growth. Knock down of Foxo1 partially rescued the inhibitory effects of SIRT1 gene silencing on sprout formation suggesting that SIRT1 is a negative regulator of Foxo1 in endothelial cells. We conclude that SIRT1 acts as a novel epigenetic regulator of endothelial gene expression governing postnatal vascular growth and differentiation.