S reduced significantly at E12.5. Of note, there is significantly increased endothelial branching by the R1 CKO endocardial cells at E11.5. n = 5 ventricular explants per group, *p,0.01, error bars = SD. doi:10.1371/journal.pone.0070570.gEndocardial Vegfr1 Negatively Regulates Coronary AngiogenesisTo reveal if Vegfr1 also negatively regulated the angiogenic process, we performed an ex vivo embryonic coronary angiogenesis assay. In this assay, we isolated the ventricles from the E11.5 Nfatc1Cre;R26fsEGFP (control) or Nfatc1Cre;R26fsEGFP;Vegfr1f/f (R1 CKO) embryos and cultured them in the matrigel. We used Vegf120 to induce the angiogenesis by the ventricular endocardial cells and visualized their angiogenic movement by EGFP, including invasion of the ventricular wall and subsequently Title Loaded From File formation of endothelial networks confirmed by their expression of Pecam1 (Fig. 6A). Using this approach, we showed that the angiogenesis 16574785 by the endocardial cells occurred Title Loaded From File mostly at E11.5 (Fig. 6B, 6C) and the process subsided by E12.5 in either group (Fig. 6B, 6D), the R1 CKO cells formed increased vascular networks (Fig. 6D, 6E). Quantitative analysis confirmed that the R1 CKO endocardial cells generated significantly more endothelial branches compared to the control cells at E11.5; the difference was diminished at E12.5 when the angiogenic process was greatly weakened (Fig. 6F). These results support that sVegfr1 inhibits the Vegfa-induced Vegfr2 signaling in the endocardial cells for the onset of coronary angiogenesis [27]; removal of Vegfr1 results in the premature coronary angiogen-esis by these cells. The data also reveal a narrow developmental window for the Vegf signaling and Vegfr1 action on the initiation of coronary vessel formation.Vegfr1 Limits the Vegf-Notch Signaling Required for Coronary AngiogenesisTo explore the mechanisms by which Vegfr1 inhibits the coronary angiogenesis, we examined expression of angiogenic or endothelial genes in the E11.5 control and R1 CKO ventricles using qRT-PCR and found that, among 23 genes examined (Table S1), expressions of Aplnr, Depp, Dll4, Nrp1, and Nrp2 were significantly increased in the R1 CKO ventricles (Fig. 7A). Of note, Dll4 functions in the Notch pathway and interact with Vegf signaling to regulate vascular endothelial differentiation and angiogenesis [38,39,40,41]. To determine whether Notch signaling is responsible for the increased embryonic coronary angiogenesis by the R1 CKO endocardial cells, we blocked the Notch signaling in the ex vivo coronary angiogenesis assay by using DAPT [41]. We found that DAPT treatment abolished the Vegf120-induced coronary angiogenesis by either by either control or R1 CKO endocardial cells (Fig. 7B-F). Taken together, these results suggest that Notch signaling is essential for the Vegfa-induced coronary angiogenesis and suggest thatVegfr1 Regulates Coronary AngiogenesisFigure 7. Notch signaling mediates Vegf120-induced coronary angiogenesis by the ventricular endocardial cells. A. A graph showing increased expression of 5 angiogenic/vascular endothelial genes in the E11.5 R1 CKO hearts. B-E, Images of E11.5 ventricular explants showing that 23977191 Notch signaling inhibitor DAPT abolished the Vegf120-induced angiogenic branching (arrows) by the control (B, D) and R1 CKO endocardial cells (C, E). F, Statistical analysis showing that DAPT treatment significantly inhibits the endothelial branching by the control or R1 CKO endocardial cells. n = 5 ventricles, *p,0.05, error ba.S reduced significantly at E12.5. Of note, there is significantly increased endothelial branching by the R1 CKO endocardial cells at E11.5. n = 5 ventricular explants per group, *p,0.01, error bars = SD. doi:10.1371/journal.pone.0070570.gEndocardial Vegfr1 Negatively Regulates Coronary AngiogenesisTo reveal if Vegfr1 also negatively regulated the angiogenic process, we performed an ex vivo embryonic coronary angiogenesis assay. In this assay, we isolated the ventricles from the E11.5 Nfatc1Cre;R26fsEGFP (control) or Nfatc1Cre;R26fsEGFP;Vegfr1f/f (R1 CKO) embryos and cultured them in the matrigel. We used Vegf120 to induce the angiogenesis by the ventricular endocardial cells and visualized their angiogenic movement by EGFP, including invasion of the ventricular wall and subsequently formation of endothelial networks confirmed by their expression of Pecam1 (Fig. 6A). Using this approach, we showed that the angiogenesis 16574785 by the endocardial cells occurred mostly at E11.5 (Fig. 6B, 6C) and the process subsided by E12.5 in either group (Fig. 6B, 6D), the R1 CKO cells formed increased vascular networks (Fig. 6D, 6E). Quantitative analysis confirmed that the R1 CKO endocardial cells generated significantly more endothelial branches compared to the control cells at E11.5; the difference was diminished at E12.5 when the angiogenic process was greatly weakened (Fig. 6F). These results support that sVegfr1 inhibits the Vegfa-induced Vegfr2 signaling in the endocardial cells for the onset of coronary angiogenesis [27]; removal of Vegfr1 results in the premature coronary angiogen-esis by these cells. The data also reveal a narrow developmental window for the Vegf signaling and Vegfr1 action on the initiation of coronary vessel formation.Vegfr1 Limits the Vegf-Notch Signaling Required for Coronary AngiogenesisTo explore the mechanisms by which Vegfr1 inhibits the coronary angiogenesis, we examined expression of angiogenic or endothelial genes in the E11.5 control and R1 CKO ventricles using qRT-PCR and found that, among 23 genes examined (Table S1), expressions of Aplnr, Depp, Dll4, Nrp1, and Nrp2 were significantly increased in the R1 CKO ventricles (Fig. 7A). Of note, Dll4 functions in the Notch pathway and interact with Vegf signaling to regulate vascular endothelial differentiation and angiogenesis [38,39,40,41]. To determine whether Notch signaling is responsible for the increased embryonic coronary angiogenesis by the R1 CKO endocardial cells, we blocked the Notch signaling in the ex vivo coronary angiogenesis assay by using DAPT [41]. We found that DAPT treatment abolished the Vegf120-induced coronary angiogenesis by either by either control or R1 CKO endocardial cells (Fig. 7B-F). Taken together, these results suggest that Notch signaling is essential for the Vegfa-induced coronary angiogenesis and suggest thatVegfr1 Regulates Coronary AngiogenesisFigure 7. Notch signaling mediates Vegf120-induced coronary angiogenesis by the ventricular endocardial cells. A. A graph showing increased expression of 5 angiogenic/vascular endothelial genes in the E11.5 R1 CKO hearts. B-E, Images of E11.5 ventricular explants showing that 23977191 Notch signaling inhibitor DAPT abolished the Vegf120-induced angiogenic branching (arrows) by the control (B, D) and R1 CKO endocardial cells (C, E). F, Statistical analysis showing that DAPT treatment significantly inhibits the endothelial branching by the control or R1 CKO endocardial cells. n = 5 ventricles, *p,0.05, error ba.
