Background:
Angiogenesis and neovascularization are essential processes that follow ischemia insults. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) not only induces endothelial cell (EC) death and inhibits angiogenesis, but also promotes EC migration, invasion and proliferation
in vitro
. These seemingly opposite effects make its role in angiogenesis
in vivo
unclear. Using TRAIL
-/-
and wild-type mice, we sought to determine the role of TRAIL in angiogenesis and neovascularisation. We also sought mechanisms
in vitro
.
Methods and Results:
Reduced vascularisation assessed by real-time
in vivo
3D Vevo ultrasound imaging and CD31 staining was observed in TRAIL
-/-
mice 28 d after hindlimb ischemia. Moreover, reduced capillary formation and increased apoptosis was evident in TRAIL
-/-
muscles even at 3 d after ischemic surgery. We have previously shown that fibroblast growth factor-2 (FGF-2), a potent angiogenic factor, regulates TRAIL gene expression in vascular smooth muscle cells. Indeed, FGF-2 also regulates TRAIL expression in ECs, and FGF-2-inducible proliferation, migration and tubule formation was inhibited with siRNA targeting TRAIL. Notably, both FGF-2 and TRAIL significantly increased NOX4 expression. TRAIL-inducible angiogenic activity in ECs was inhibited with siRNAs targeting NOX4, and consistent with these, NOX4 mRNA was reduced in 3 d ischemic hindlimbs of TRAIL
-/-
mice. TRAIL stimulated intracellular H
2
O
2
levels in ECs, and TRAIL-inducible proliferation, migration and tubule formation was inhibited with not only PEG-catalase, a H
2
O
2
scavenger, but also blocked with L-NAME, a nitric oxide synthase inhibitor.
Conclusions:
This is the first demonstration showing that TRAIL promotes angiogenesis
in vivo
. We show for the first time that the TRAIL stimulates NOX4 expression to mediate nitric oxide-dependent angiogenic effects. This has significant therapeutic implications such that TRAIL may improve the angiogenic response to ischemia and increase perfusion recovery in patients with CVD and diabetes.
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