A Novel Role for Vascular Endothelial Growth Factor as an Autocrine Survival Factor for Embryonic Stem Cells during Hypoxia

Abstract

Vascular endothelial growth factor (VEGF) is best known for its angiogenic activity on endothelial cells, but it also affects neurons, pneumocytes, and other mature cell types as well as endothelial, neural, and hematopoietic progenitors. Here, we examined its effect on pluripotential embryonic stem (ES) cells under hypoxic stress. ES cells were found to produce VEGF and to express VEGF receptor-2 and neuropilin-1 (Nrp-1), a VEGF 165 isoform-specific receptor. During hypoxia, expression levels of VEGF, Flk-1, and Nrp-1 were elevated. Inhibition or targeted gene inactivation of VEGF increased ES cell apoptosis during prolonged hypoxia (48 h) by about 10-fold. The survival activity of VEGF was specific since inhibition of other growth factors (including basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor, platelet-derived growth factor, and placental growth factor) had no effect. Neuropilin-1 was involved in the VEGF-survival activity since overexpression of Nrp-1 decreased hypoxiainduced apoptosis about 3-fold. The hypoxia-response element, via which hypoxia-inducible transcription factors up-regulate VEGF expression under hypoxic conditions, was critical since targeted deletion of this element in the VEGF promoter enhanced hypoxia-induced ES cell apoptosis to the same extent as VEGF inhibition or gene inactivation. Thus, VEGF plays a critical role in survival of ES cells during prolonged hypoxia.

Vascular Endothelial Growth Factor Directly Inhibits Primitive Neural Stem Cell Survival But Promotes Definitive Neural Stem Cell Survival

“…However, our observation of VEGF-A and Flk1 mRNA expression in undifferentiated ES cells suggests even earlier embryonic effects, in which VEGF-A signaling is part of the mechanism (in addition to TGF␤ signaling) (Tropepe et al, 2001) that suppresses p-NSC formation and survival in vitro before neural plate formation of Nestin ϩ cells is first detected at E7.5. Although undifferentiated ES cells in hypoxic conditions respond to VEGF-A as a survival factor (Brusselmans et al, 2005), this finding is different from the present results. The previous effects were seen only under hypoxic conditions and only on undifferentiated ES cells, whereas the present results were specific to primitive neural stem cells under nonhypoxic conditions.…”

Hypoxia-inducible Factor-1α Inhibits Self-renewal of Mouse Embryonic Stem Cells in Vitro via Negative Regulation of the Leukemia Inhibitory Factor-STAT3 Pathway

“…Previously, Carmeliet et al (25) suggested that hypoxia reduces stem cell proliferation and increases apoptosis through HIF-1␣. Accordantly, a recent report (26) suggested that ESC apoptosis is found to be dependent on the cel- lular differentiation and on the duration and degree of hypoxia. In this context, it is interesting to note that low O 2 tension inhibits differentiation of hESCs (27) and human marrow stromal cells (28).…”

Targeting neuropilin-1 in human leukemia and lymphoma

“…31 In addition to its function as an essential coreceptor in neuronal guidance and angiogenesis, [23][24][25][26][27][28] NRP-1 has also been implicated as a novel mediator of the primary immune response. 32,33 Moreover, the expression of NRP-1 can be stimulated in response to tissue injury or hypoxic conditions, 34,35 and it is highly expressed in diverse solid tumors, such as prostate, breast, pancreatic, lung, ovarian, and gastrointestinal carcinomas. 10,28,36,37 Increased expression of NRP-1 has been correlated with tumor growth and vascularization in vivo and with invasiveness in human cancer.…”