Endothelial KLF15/VASN axis inhibits angiogenesis via activation of Notch1 signaling

Angiogenesis is a dynamic process fine-tuned by transcription factors in endothelial cells. The Krüpple-like factor 15 (KLF15)-mediated transcriptional regulation mechanism is critical for cardiovascular diseases. However, the role of endothelial KLF15 in governing angiogenesis remains unknown.KLF15 and vasorin (VASN) were deleted from endothelial cells using tamoxifen-inducible Cdh5-promoter-driven Cre recombinase in EC-KLF15 KO and EC-VASN KO mice, respectively. EC-KLF15 KO, EC-VASN KO and control mice were subjected to retinal angiogenesis or tumor cell transplantation. The RNA sequencing (RNA-seq), ATAC-seq, and ChIP-seq were conducted to identify VASN as a downstream effector of KLF15. Cell proliferation, wound healing, tube formation, and sprouting assays were performed to delineate endothelial cell function. In EC-KLF15 KO mice and adenovirus-mediated KLF15 overexpression mice, we showed that KLF15 negatively regulated retinal angiogenesis, as confirmed in cultured endothelial cells. KLF15 opened chromatin, bound to the promoters of GC-rich sequences, and transactivated the expression of VASN. Subsequently, VASN suppressed endothelial angiogenic function which was essential for Dll4-induced Notch1 signaling activation. Moreover, increased expression of VASN in EC-KLF15 KO mice suppressed retinal angiogenesis, which was attenuated by γ-secretase inhibitor. EC-VASN KO mice recapitulated the promotion of retinal angiogenesis in EC-KLF15 KO mice. Finally, the EGF-like domain of VASN was essential for its interaction with Notch1, and VASN EGF-like domain-derived peptides activated Notch1 signaling and suppressed angiogenesis.The KLF15/VASN axis negatively regulates angiogenesis by activating Notch1 signaling. KLF15 and VASN in endothelial cells might represent novel therapeutic targets for the treatment of impaired angiogenesis-related diseases and tumors.