FOXO1 couples metabolic activity and growth state in the vascular endothelium

© 2016 Macmillan Publishers Limited. All rights reserveEndothelial cells (ECs) are plastic cells that can switch between growth states with different bioenergetic and biosynthetic requirements. Although quiescent in most healthy tissues, ECs divide and migrate rapidly upon proangiogenic stimulation. Adjusting endothelial metabolism to the growth state is central to normal vessel growth and function, yet it is poorly understood at the molecular level. Here we report that the forkhead box O (FOXO) transcription factor FOXO1 is an essential regulator of vascular growth that couples metabolic and proliferative activities in ECs. Endothelial-restricted deletion of FOXO1 in mice induces a profound increase in EC proliferation that interferes with coordinated sprouting, thereby causing hyperplasia and vessel enlargement. Conversely, forced expression of FOXO1 restricts vascular expansion and leads to vessel thinning and hypobranching. We find that FOXO1 acts as a gatekeeper of endothelial quiescence, which decelerates metabolic activity by reducing glycolysis and mitochondrial respiration. Mechanistically, FOXO1 suppresses signalling by MYC (also known as c-MYC), a powerful driver of anabolic metabolism and growth. MYC ablation impairs glycolysis, mitochondrial function and proliferation of ECs while its EC-specific overexpression fuels these processes. Moreover, restoration of MYC signalling in FOXO1-overexpressing endothelium normalizes metabolic activity and branching behaviour. Our findings identify FOXO1 as a critical rheostat of vascular expansion and define the FOXO1-MYC transcriptional network as a novel metabolic checkpoint during endothelial growth and proliferation.The research of M.P. is supported by the Max Planck Society, the European Research Council (ERC) Starting Grant ANGIOMET (311546), the Deutsche Forschungsgemeinschaft (SFB 834), the Excellence Cluster Cardiopulmonary System (EXC 147/1), the Cluster of Excellence Macromolecular Complexes (EXC115), the Foundation Leducq Transatlantic Network (ARTEMIS), the LOEWE grant Ub-Net, and the European Molecular Biology Organization Young Investigator Programme. S.S. was supported by a PhD fellowship of the Belgian Science Policy (IWT) and I.M.A. is a recipient of a DOC-fFORTE fellowship of the Austrian Academy of Sciences. C.A.F was supported by a European Union FP7 Marie Curie Post-doctoral Fellowship and a FCT grant (IF/00412/2012). The research of K.R. is supported by an ERC Advanced Grant (268921) and C.K. received support from the National Institutes of Health K08CA090438. The research of H.G. is supported by Cancer Research UK, an ERC consolidator grant (REshape), the Foundation Leducq Transatlantic Network (ARTEMIS), the Lister Institute of Preventive Medicine and the British Council under the BIRAX Initiative. The work of P.C. is funded by long-term structural funding: Methusalem Funding by the Flemish Government, ERC Advanced Research Grant (269073), and FWO G.0834.13N from the Flanders Science Fund.