Endothelial PHACTR1 Promotes Endothelial Activation and Atherosclerosis by Repressing PPAR & gamma; Activity Under Disturbed Flow in Mice

BACKGROUND:Numerous genome-wide association studies revealed that SNPs (single nucleotide polymorphisms) at the PHACTR1 (phosphatase and actin regulator 1) locus strongly correlate with coronary artery disease. However, the biological function of PHACTR1 remains poorly understood. Here, we identified the proatherosclerotic effect of endothelial PHACTR1, contrary to macrophage PHACTR1. METHODS:We generated global (Phactr1(-/-)) and endothelial cell (EC)-specific (Phactr1(ECKO)) Phactr1 KO (knockout) mice and crossed these mice with apolipoprotein E-deficient (Apoe(-/-)) mice. Atherosclerosis was induced by feeding the high-fat/high-cholesterol diet for 12 weeks or partially ligating carotid arteries combined with a 2-week high-fat/high-cholesterol diet. PHACTR1 localization was identified by immunostaining of overexpressed PHACTR1 in human umbilical vein ECs exposed to different types of flow. The molecular function of endothelial PHACTR1 was explored by RNA sequencing using EC-enriched mRNA from global or EC-specific Phactr1 KO mice. Endothelial activation was evaluated in human umbilical vein ECs transfected with siRNA targeting PHACTR1 and in Phactr1(ECKO) mice after partial carotid ligation. RESULTS:Global or EC-specific Phactr1 deficiency significantly inhibited atherosclerosis in regions of disturbed flow. PHACTR1 was enriched in ECs and located in the nucleus of disturbed flow areas but shuttled to cytoplasm under laminar flow in vitro. RNA sequencing showed that endothelial Phactr1 depletion affected vascular function, and PPAR & gamma; (peroxisome proliferator-activated receptor gamma) was the top transcription factor regulating differentially expressed genes. PHACTR1 functioned as a PPAR & gamma; transcriptional corepressor by binding to PPAR & gamma; through the corepressor motifs. PPAR & gamma; activation protects against atherosclerosis by inhibiting endothelial activation. Consistently, PHACTR1 deficiency remarkably reduced endothelial activation induced by disturbed flow in vivo and in vitro. PPAR & gamma; antagonist GW9662 abolished the protective effects of Phactr1 KO on EC activation and atherosclerosis in vivo. CONCLUSIONS:Our results identified endothelial PHACTR1 as a novel PPAR & gamma; corepressor to promote atherosclerosis in disturbed flow regions. Endothelial PHACTR1 is a potential therapeutic target for atherosclerosis treatment.