Acetylation-dependent regulation of endothelial Notch signalling by the SIRT1 deacetylase

Abstract

Notch signalling coordinates angiogenesis by controlling the specification of endothelial cells into tip cells that lead the way in growing blood vessels and the stalk cells that follow. Michael Potente and colleagues have identified a previously unknown component in Notch signalling regulation in endothelial cells that may provide a mechanism for fine-tuning angiogenesis in response to metabolic requirements and angiogenic stress. They show that the metabolism- and redox-sensing deacetylase SIRT1 deacetylates the Notch1 intracellular domain directly, thereby controlling its stability and turnover and negatively modulating Notch signalling. Inactivation of SIRT1 impairs angiogenesis in zebrafish and mice. Notch signalling is a key intercellular communication mechanism that is essential for cell specification and tissue patterning, and which coordinates critical steps of blood vessel growth1,2,3 . Although subtle alterations in Notch activity suffice to elicit profound differences in endothelial behaviour and blood vessel formation2,3 , little is known about the regulation and adaptation of endothelial Notch responses. Here we report that the NAD+-dependent deacetylase SIRT1 acts as an intrinsic negative modulator of Notch signalling in endothelial cells. We show that acetylation of the Notch1 intracellular domain (NICD) on conserved lysines controls the amplitude and duration of Notch responses by altering NICD protein turnover. SIRT1 associates with NICD and functions as a NICD deacetylase, which opposes the acetylation-induced NICD stabilization. Consequently, endothelial cells lacking SIRT1 activity are sensitized to Notch signalling, resulting in impaired growth, sprout elongation and enhanced Notch target gene expression in response to DLL4 stimulation, thereby promoting a non-sprouting, stalk-cell-like phenotype. In vivo, inactivation of Sirt1 in zebrafish and mice causes reduced vascular branching and density as a consequence of enhanced Notch signalling. Our findings identify reversible acetylation of the NICD as a molecular mechanism to adapt the dynamics of Notch signalling, and indicate that SIRT1 acts as rheostat to fine-tune endothelial Notch responses.