Autocrine VEGF maintains endothelial survival through regulation of metabolism and autophagy

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.

Stealing VEGF from thy neighbor

The distribution and patterning of blood vessels is controlled by vascular endothelial growth factor (VEGF), which is precisely regulated throughout its life cycle. Okabe et al. show that VEGF is titrated away from the endothelium by adjacent neurons via endocytosis, regulating density and trajectory of blood vessels.

Canonical and noncanonical vascular endothelial growth factor pathways: new developments in biology and signal transduction

The past 5 years have witnessed a significant expansion in our understanding of vascular endothelial growth factor (VEGF) signaling. In particular, the process of canonical activation of VEGF receptor tyrosine kinases by homodimeric VEGF molecules has now been broadened by the realization that heterodimeric ligands and receptors are also active participants in the signaling process. Although heterodimer receptors were described 2 decades ago, their impact, along with the effect of additional cell surface partners and novel autocrine VEGF signaling pathways, are only now starting to be clarified. Furthermore, ligand-independent signaling (noncanonical) has been identified through galectin and gremlin binding and upon rise of intracellular levels of reactive oxygen species. Activation of the VEGF receptors in the absence of ligand holds immediate implications for therapeutic approaches that exclusively target VEGF. The present review provides a concise summary of the recent developments in both canonical and noncanonical VEGF signaling and places these findings in perspective to their potential clinical and biological ramifications.

Abstract 168: Contribution of Vascular Endothelial Growth Factor Signaling to Fate Specification in Cardiomyocytes

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.

Progesterone receptor in the vascular endothelium triggers physiological uterine permeability preimplantation

Vascular permeability is frequently associated with inflammation and is triggered by a cohort of secreted permeability factors such as vascular endothelial growth factor (VEGF). Here, we show that the physiological vascular permeability that precedes implantation is directly controlled by progesterone receptor (PR) and is independent of VEGF. Global or endothelial-specific deletion of PR blocks physiological vascular permeability in the uterus, whereas misexpression of PR in the endothelium of other organs results in ectopic vascular leakage. Integration of an endothelial genome-wide transcriptional profile with chromatin immunoprecipitation sequencing revealed that PR induces an NR4A1 (Nur77/TR3)-dependent transcriptional program that broadly regulates vascular permeability in response to progesterone. Silencing of NR4A1 blocks PR-mediated permeability responses, indicating a direct link between PR and NR4A1. This program triggers concurrent suppression of several junctional proteins and leads to an effective, timely, and venous-specific regulation of vascular barrier function that is critical for embryo implantation.