ABSTRACT
Title
Down-regulation of endogenous FGF-2 in endothelium is responsible for impaired angiogenesis in experimental model of metabolic syndrome
Authors
E. Bocci
Doctorate School in Molecular Medicine
Dept. of Biothecnology, Section Pharmacology, Toxicology and Chemotherapy - University of Siena, Italy
Doctorate School in Molecular Medicine
Dept. of Biothecnology, Section Pharmacology, Toxicology and Chemotherapy - University of Siena, Italy
Abstract
During inflammation the endothelium, inflammatory cells and stromal cells produce prostanoids, molecules that are released into the extracellular space where they exert autocrine or paracrine effects. Prostaglandin (PG)E2, the principal prostanoid synthetized by Cyclooxygenase-2, has been demonstrated to contribute to angiogenesis and tumor progression. PGE2 exerts its effects through G protein coupled receptors, and the transactivation of some tyrosine kinase receptors. Indeed, we showed that PGE2 is capable to induce the angiogenic phenotype in microvascular endothelial cells by the interaction with the fibroblast growth factor (FGF) receptor-1, FGFR1 [1,2].
FGF-2 plays an essential role in the maintenance of blood vessels. Different molecular isoforms of FGF-2 have been characterized and only the 18 kDa isoform is secreted by an unconventional mechanism. The down-regulation of FGF-2 in endothelium is responsible for impaired angiogenesis in experimental model of metabolic syndrome [3].
The metabolic syndrome, a common cause of cardiovascular disease, promotes endothelial dysfunction by increased free radical production and an impaired ability of cells to detoxify the radicals and repair damaged molecules. In patients with metabolic syndrome the production of vasodilator and antithrombotic substances is reduced, while the reactive oxygen and nitrative species (ROS/RNS) are enhanced [4].
We hypothesized that impairment of endothelial function in the metabolic syndrome is caused by oxidative-mediated downregulation of FGF-2 protein. First, we examined the ability of abdominal aorta vessels, explanted from zucker obese rats (OZR), an animal model of metabolic syndrome, and from their lean counterparts (LZR), to form sprouting in vitro, in response to the pro-angiogenic stimuli, VEGF, FGF-2 and PGE-2. While all the stimuli examined produced vigorous sprouting from vessels isolated from LZR, in OZR vessels the angiogenic response was curtailed for VEGF and PGE-2, but not for FGF-2 ,which retained its ability to promote neo-vessel formation. Since the pro-angiogenic activity of VEGF and PGE-2 is mediated by FGF-2 availability in endothelial cells [2], our results suggested a reduced FGF-2 expression in vessels from ZOF rats. In fact, a decreased expression of the endogenous FGF-2 and an increase production of ROS due to the decrease of both antioxidant enzymes SOD-1 and catalase, was measured in vessels from ZOF rats.
To analyze the role of oxidative stress on FGF-2 signaling, we used the coronary venular endothelial cells (CVEC) treated with DMNQ, a redoxcycling agent known to induce intracellular superoxide anion formation. DMNQ induced a significant decrease of FGF-2 expression, which corresponded to an increased FGF-2 release in the conditioned medium.
The caspase-1 activity is an important regulator of unconventional protein secretion and it is know that its activity is mediated by a cytosolic molecular complex, the “inflammasome” [4]. In CVEC, DMNQ significantly reduced the intracellular caspase-1 expression, while increased the release of FGF-2/caspase-1 complex.
In conclusion, in vitro and in vivo studies showed that metabolic syndrome linked oxidative stress to decrease intracellular FGF-2 availability, leading to failure of VEGF and PGE2 pro-angiogenic effects, while it increased the FGF-2 release on extracellular space mediated by FGF-2/caspase-1 complex formation.
1. Finetti F et al. (2008) J Biol Chem. 283(4):2139-46.
2. Finetti F et al (2009) Circ Res.105(7):657-66.
3. Taverna et al. (2003) J Biol Chem. 278(51):51911-9.
4. Keller et al. (2008) Cell. 132(5):818-31.
FGF-2 plays an essential role in the maintenance of blood vessels. Different molecular isoforms of FGF-2 have been characterized and only the 18 kDa isoform is secreted by an unconventional mechanism. The down-regulation of FGF-2 in endothelium is responsible for impaired angiogenesis in experimental model of metabolic syndrome [3].
The metabolic syndrome, a common cause of cardiovascular disease, promotes endothelial dysfunction by increased free radical production and an impaired ability of cells to detoxify the radicals and repair damaged molecules. In patients with metabolic syndrome the production of vasodilator and antithrombotic substances is reduced, while the reactive oxygen and nitrative species (ROS/RNS) are enhanced [4].
We hypothesized that impairment of endothelial function in the metabolic syndrome is caused by oxidative-mediated downregulation of FGF-2 protein. First, we examined the ability of abdominal aorta vessels, explanted from zucker obese rats (OZR), an animal model of metabolic syndrome, and from their lean counterparts (LZR), to form sprouting in vitro, in response to the pro-angiogenic stimuli, VEGF, FGF-2 and PGE-2. While all the stimuli examined produced vigorous sprouting from vessels isolated from LZR, in OZR vessels the angiogenic response was curtailed for VEGF and PGE-2, but not for FGF-2 ,which retained its ability to promote neo-vessel formation. Since the pro-angiogenic activity of VEGF and PGE-2 is mediated by FGF-2 availability in endothelial cells [2], our results suggested a reduced FGF-2 expression in vessels from ZOF rats. In fact, a decreased expression of the endogenous FGF-2 and an increase production of ROS due to the decrease of both antioxidant enzymes SOD-1 and catalase, was measured in vessels from ZOF rats.
To analyze the role of oxidative stress on FGF-2 signaling, we used the coronary venular endothelial cells (CVEC) treated with DMNQ, a redoxcycling agent known to induce intracellular superoxide anion formation. DMNQ induced a significant decrease of FGF-2 expression, which corresponded to an increased FGF-2 release in the conditioned medium.
The caspase-1 activity is an important regulator of unconventional protein secretion and it is know that its activity is mediated by a cytosolic molecular complex, the “inflammasome” [4]. In CVEC, DMNQ significantly reduced the intracellular caspase-1 expression, while increased the release of FGF-2/caspase-1 complex.
In conclusion, in vitro and in vivo studies showed that metabolic syndrome linked oxidative stress to decrease intracellular FGF-2 availability, leading to failure of VEGF and PGE2 pro-angiogenic effects, while it increased the FGF-2 release on extracellular space mediated by FGF-2/caspase-1 complex formation.
1. Finetti F et al. (2008) J Biol Chem. 283(4):2139-46.
2. Finetti F et al (2009) Circ Res.105(7):657-66.
3. Taverna et al. (2003) J Biol Chem. 278(51):51911-9.
4. Keller et al. (2008) Cell. 132(5):818-31.