Autocrine VEGF is necessary for endothelial survival, although the cellular mechanisms supporting this function are unknown. Here, we show that -even after full differentiation and maturation -continuous expression of VEGF by endothelial cells is needed to sustain vascular integrity and cellular viability. Depletion of VEGF from the endothelium results in mitochondria fragmentation and suppression of glucose metabolism, leading to increased autophagy that contributes to cell death. Gene-expression profiling showed that endothelial VEGF contributes to the regulation of cell cycle and mitochondrial gene clusters, as well as several -but not all -targets of the transcription factor FOXO1. Indeed, VEGF-deficient endothelium in vitro and in vivo showed increased levels of FOXO1 protein in the nucleus and cytoplasm. Silencing of FOXO1 in VEGF-depleted cells reversed expression profiles of several of the gene clusters that were de-regulated in VEGF knockdown, and rescued both cell death and autophagy phenotypes. Our data suggest that endothelial VEGF maintains vascular homeostasis through regulation of FOXO1 levels, thereby ensuring physiological metabolism and endothelial cell survival.
Autocrine VEGF is necessary for endothelial survival, although the cellular mechanisms supporting this function are unknown. Here, we show that -even after full differentiation and maturation -continuous expression of VEGF by endothelial cells is needed to sustain vascular integrity and cellular viability. Depletion of VEGF from the endothelium results in mitochondria fragmentation and suppression of glucose metabolism, leading to increased autophagy that contributes to cell death. Gene-expression profiling showed that endothelial VEGF contributes to the regulation of cell cycle and mitochondrial gene clusters, as well as several -but not all -targets of the transcription factor FOXO1. Indeed, VEGF-deficient endothelium in vitro and in vivo showed increased levels of FOXO1 protein in the nucleus and cytoplasm. Silencing of FOXO1 in VEGF-depleted cells reversed expression profiles of several of the gene clusters that were de-regulated in VEGF knockdown, and rescued both cell death and autophagy phenotypes. Our data suggest that endothelial VEGF maintains vascular homeostasis through regulation of FOXO1 levels, thereby ensuring physiological metabolism and endothelial cell survival.
Vascular endothelial growth factor (VEGF) is one of the pivotal proangiogenic growth factors that has long contributed to our knowledge of blood vessel and circulatory maintenance as well as angiogenesis in both pathology and pathophysiology. However, the non-canonical functions of VEGF in cardiac morphogenesis have not been well characterized. Here, we examined how VEGF regulates cardiomyocyte cell fate. Using chimeric embryos harboring both wild type and VEGF-null embryonic stem cells, we observed that derivatives of VEGF null cells were preferentially recruited to the atrium of the heart in comparison to the ventricles. To further provide physiologic context of this finding, we used reporter-LacZ staining and RT-PCR and found that endogenous VEGF was indeed expressed at much lower levels in the atrium but highly expressed in the ventricle early in cardiac morphogenesis. These data lead to our hypothesis that cell-autonomous expression of VEGF is a determinant of atrial vs. ventricular cardiomyocyte cell fate. To test this hypothesis, we used a VEGF knock-in mouse model of Sm22Cre x Rosa 26 VEGF. VEGF overexpression in cardiomyocytes (and smooth muscle) at E8.5 resulted in lethality by P1 and thickened atrial and ventricular walls in mutant embryos as characterized by histology (H&E, IF). We further explored the molecular changes underlying this phenotype via microarray and RT-PCR and find disruptions in molecular markers necessary for wall development, specifically: Notch-1, BMP10, Nrg-1. Taken together, our data indicates that aberrant embryonic VEGF signaling disrupts several critical signaling pathways and that overexpression leads to disruption of cardiomyocyte proliferation and cardiac morphogenesis. These findings add to the foundation of better understanding heart development, laying the groundwork for future therapy of congenital and acquired cardiac disease.
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