Transforming growth factor-β-activated kinase 1 regulates angiogenesis via AMP-activated protein kinase-α1 and redox balance in endothelial cells.

Objective: Transforming growth factor-β-activated kinase 1 (TAK1) is a mitogen-activated protein 3-kinase and an AMP-activated protein kinase (AMPK) kinase in some cell types. Although TAK1(-/-) mice display defects in developmental vasculogenesis, the role of TAK1 in endothelial cells has not been investigated in detail.

Approach And Results: TAK1 downregulation (small interfering RNA) in human endothelial cells attenuated proliferation without inducing apoptosis and diminished endothelial cell migration, as well as tube formation. Cytokine- and vascular endothelial growth factor (VEGF)-induced endothelial cell sprouting in a modified spheroid assay were abrogated by TAK1 downregulation. Moreover, VEGF-induced endothelial sprouting was impaired in aortic rings from mice lacking TAK1 in endothelial cells (TAK(ΔEC)). TAK1 inhibition and downregulation also inhibited VEGF-stimulated phosphorylation of several kinases, including AMPK. Proteomic analyses revealed that superoxide dismutase 2 (SOD2) expression was reduced in TAK1-deficient endothelial cells, resulting in attenuated hydrogen peroxide production but increased mitochondrial superoxide production. Endothelial cell SOD2 expression was also attenuated by AMPK inhibition and in endothelial cells from AMPKα1(-/-) mice but was unaffected by inhibitors of c-Jun N-terminal kinase, p38, extracellular signal-regulated kinase 1/2, or phosphatidylinositol 3-kinase/Akt. Moreover, the impaired endothelial sprouting from TAK(ΔEC) aortic rings was abrogated in the presence of polyethylene glycol-SOD, and tube formation was normalized by the overexpression of SOD2. A similar rescue of angiogenesis was observed in polyethylene glycol-SOD-treated aortic rings from mice with endothelial cell-specific deletion of the AMPKα1.

Conclusions: These results establish TAK1 as an AMPKα1 kinase that regulates vascular endothelial growth factor-induced and cytokine-induced angiogenesis by modulating SOD2 expression and the superoxide anion:hydrogen peroxide balance.