Jongshin Kim,¹ Yoo Hyung Kim,^1,2 Jaeryung Kim,^1,2 Do Young Park,^1,2 Hosung Bae,^1,2 Da-Hye Lee,³ Kyun Hoo Kim,^1,2 Seon Pyo Hong,^1,2 Seung Pil Jang,^1,2 Yoshiaki Kubota,⁴ Young-Guen Kwon,⁵ Dae-Sik Lim,^3,* and Gou Young Koh<sup>1,2,*

1</sup> Center for Vascular Research, Institute for Basic Science, Daejeon, Korea. ²Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea. ³National Creative Research Initiatives Center for Cell Division and Differentiation, Department of Biological Science, KAIST, Daejeon, Korea. ⁴Department of Vascular Biology, The Sakaguchi Laboratory, Keio University School of Medicine, Tokyo, Japan. ⁵Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea.

Authorship note: Jo. Kim and Y.H. Kim contributed equally to this work.

^*Address correspondence to: Gou Young Koh, Center for Vascular Research, IBS, Graduate School of Medical Science and Engineering, KAIST, 291 Daehak-ro, Daejeon 34141, Korea. ; Or to: Dae-Sik Lim, National Creative Research Initiatives Center for Cell Division and Differentiation, Department of Biological Science, KAIST, 291 Daehak-ro, Daejeon 34141, Korea.

Angiogenesis is a multistep process that requires coordinated migration, proliferation, and junction formation of vascular endothelial cells (ECs) to form new vessel branches in response to growth stimuli. Major intracellular signaling pathways that regulate angiogenesis have been well elucidated, but key transcriptional regulators that mediate these signaling pathways and control EC behaviors are only beginning to be understood. Here, we show that YAP/TAZ, a transcriptional coactivator that acts as an end effector of Hippo signaling, is critical for sprouting angiogenesis and vascular barrier formation and maturation. In mice, endothelial-specific deletion of Yap/Taz led to blunted-end, aneurysm-like tip ECs with fewer and dysmorphic filopodia at the vascular front, a hyper-pruned vascular network, reduced and disarranged distributions of tight and adherens junction proteins, disrupted barrier integrity, subsequent hemorrhage in growing retina and brain vessels, and reduced pathological choroidal neovascularization. Mechanistically, YAP/TAZ activates actin cytoskeleton remodeling, an important component of filopodia formation and junction assembly. Moreover, YAP/TAZ coordinates EC proliferation and metabolic activity by upregulating MYC signaling. Overall, these results show that YAP/TAZ plays multifaceted roles for EC behaviors, proliferation, junction assembly, and metabolism in sprouting angiogenesis and barrier formation and maturation and could be a potential therapeutic target for treating neovascular diseases.