AMP-Activated Protein Kinase &agr;2 in Neutrophils Regulates Vascular Repair via Hypoxia-Inducible Factor-1&agr; and a Network of Proteins Affecting Metabolism and Apoptosis

Randa Abdel Malik, Nina Zippel, Timo Frömel, Juliana Heidler, Sven Zukunft, Barbara Walzog, Nariman Ansari, Francesco Pampaloni, Susanne Wingert, Michael A. Rieger, Ilka Wittig, Beate Fisslthaler, Ingrid Fleming

The AMP-activated protein kinase (AMPK) is stimulated by hypoxia and while the AMPKα1 catalytic subunit has been implicated in angiogenesis, little is known about the role played by the AMPKα2 subunit in vascular repair. To determine the role of the AMPKα2 subunit in vascular repair. Recovery of blood flow after femoral artery ligation was impaired (>80%) in AMPKα2(-/-) versus wild-type mice, a phenotype reproduced in mice lacking AMPKα2 in myeloid cells (AMPKα2(ΔMC)). Three days after ligation neutrophil infiltration into ischemic limbs of AMPKα2(ΔMC) mice was lower than in wild-type mice despite being higher after 24 hours. Neutrophil survival in ischemic tissue is required to attract monocytes which contribute to the angiogenic response. Indeed, apoptosis was increased in hypoxic neutrophils from AMPKα2(ΔMC) mice, fewer monocytes were recruited, and gene array analysis revealed attenuated expression of pro-angiogenic proteins in ischemic AMPKα2(ΔMC) hindlimbs. Many angiogenic growth factors are regulated by hypoxia-inducible factor (HIF)-1α, and HIF-1α induction was attenuated in AMPKα2-deficient cells and accompanied by its enhanced hydroxylation. Also, fewer proteins were regulated by hypoxia in neutrophils from AMPKα2(ΔMC) mice. Mechanistically, isocitrate dehydrogenase expression and the production of α-ketoglutarate, which negatively regulate HIF-1α stability, were attenuated in neutrophils from wild-type mice but remained elevated in cells from AMPKα2(ΔMC) mice. AMPKα2 regulates α-ketoglutarate generation, HIF-1α stability and neutrophil survival which in turn determine further myeloid cell recruitment and repair potential. The activation of AMPKα2 in neutrophils is a decisive event in the initiation of vascular repair after ischemia.