Regulation of Angiogenesis by Vascular Endothelial Growth Factor and Angiopoietin-1 in the Rat Aorta Model

Abstract

Vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1) promote the spontaneous angiogenic response of freshly cut rat aortic rings. When VEGF and Ang-1 were tested in cultures of 14-day-old rings, which are quiescent and unable to spontaneously produce neovessels, only VEGF was capable of inducing an angiogenic response. Ang-1 failed to initiate angiogenesis in this system, but significantly potentiated VEGF-induced neovessel sprouting. Potential differences in cell signaling triggered by VEGF and Ang-1 were evaluated in cultures of quiescent rings. VEGF induced biphasic and prolonged (15 minutes and 4 to 24 hours) phosphorylation of p44/42 MAPK and Akt, while the effect of Ang-1 was transient and monophasic (15 minutes). Both VEGF and Ang-1 induced rapid, monophasic (15 minutes) phosphorylation of p38 MAPK. When VEGF and Ang-1 were administered together, the second peak of VEGF-induced p44/42 MAPK phosphorylation was markedly reduced. The effect of the VEGF/Ang-1 combination on AKT phosphorylation was, instead, additive over time, and sustained over a 24-hour period. The VEGF/Ang-1 combination caused an additive effect also on p38 MAPK phosphorylation at 1 hour. Confocal microscopy of VEGF-, Ang-1, or VEGF/Ang-1-stimulated aortic rings double stained at time points of maximal phosphorylation for cell markers and signal transduction proteins demonstrated phosphorylated p44/42 MAPK, p38 MAPK, and Akt predominantly in endothelial cells. Experiments with specific inhibitors demonstrated that p44/42 MAPK and Akt, but not p38 MAPK, are necessary for neovessel sprouting. These results identify p44/42 MAPK and Akt as critical intracellular mediators of angiogenesis, whose transient phosphorylation is, however, not sufficient for the initiation of this process. The observation that sustained phosphorylation of these signaling pathways, particularly of Akt, correlates with induction of angiogenesis suggests that the duration of phosphorylation signals influences critical cellular events required for the induction of angiogenic sprouting.

15(S)-Hydroxyeicosatetraenoic Acid–Induced Angiogenesis Requires STAT3-Dependent Expression of VEGF

“…Because the inhibition of either the PI3/Akt/mTOR/S6K1 or STAT3 signaling resulted in almost complete suppression of 15(S)-HETE-induced angiogenesis, it is possible that these two signaling pathways play stage-specific events of angiogenesis. It was reported that PI3K/AKT signaling plays an important role in the sprouting of endothelial cells (46,47). On the other hand, VEGF is needed for the survival and maintenance of the plasticity of the vessel (48,49).…”

Suppression of UVB-induced phosphorylation of mitogen-activated protein kinases and nuclear factor kappa B by green tea polyphenol in SKH-1 hairless mice

“…The involvement of the MAPK pathway in tumor proliferation is well documented. Activation of the MAPK pathway occurs in response to integrin-mediated cellular adhesion to the extracellular matrix, which plays a critical role in both tumor metastasis and angiogenesis (Chen et al, 1998;Zhu et al, 2002). Previously, we have demonstrated that Figure 6 Inhibitory effect of green tea polyphenol on UVB-induced phosphorylation of p38 in SKH-1 hairless mice.…”

Loss of Collagen XVIII Enhances Neovascularization and Vascular Permeability in Atherosclerosis

“…3,15 Aorta rings from age-matched WT, Het, and knockout (KO) mice were embedded in rat collagen I (2 mg/mL) and cultured with serum-free media (Invitrogen, No. 17601) and vascular endothelial cell growth factor (VEGF) (0, 2, 4, or 8 ng/mL, nϭ4 rings per dose).…”

“…17601) and vascular endothelial cell growth factor (VEGF) (0, 2, 4, or 8 ng/mL, nϭ4 rings per dose). 3,15 We measured sprout area in images captured through a Nikon SMZ microscope (50ϫ magnification). Maximum sprout area was normalized to a valueϭ1.…”