Abstract
Objective-We evaluated whether phosphatidylinositol 3-kinase gamma (PI3K gamma) plays a role in reparative neovascularization and endothelial progenitor cell (EPC) function.
Methods and Results-Unilateral limb ischemia was induced in mice lacking the PI3K gamma gene (PI3K gamma(-/-)) or expressing a catalytically inactive mutant (PI3K gamma(KD/KD)) and wild-type controls (WT). Capillarization and arteriogenesis were reduced in PI3K gamma(-/-) ischemic muscles resulting in delayed reperfusion compared with WT, whereas reparative neovascularization was preserved in PI3K gamma(KD/KD). In PI3K gamma(-/-) muscles, endothelial cell proliferation was reduced, apoptosis was increased, and interstitial space was infiltrated with leukocytes but lacked cKit(+) progenitor cells that in WT muscles typically surrounded arterioles. PI3K gamma is constitutively expressed by WT EPCs, with expression levels being upregulated by hypoxia. PI3K gamma(-/-) EPCs showed a defect in proliferation, survival, integration into endothelial networks, and migration toward SDF-1. The dysfunctional phenotype was associated with nuclear constraining of FOXO1, reduced Akt and eNOS phosphorylation, and decreased nitric oxide ( NO) production. Pretreatment with an NO donor corrected the migratory defect of PI3K gamma(-/-) EPCs. PI3K gamma(KD/KD) EPCs showed reduced Akt phosphorylation, but constitutive activation of eNOS and preserved proliferation, survival, and migration.
Conclusions-We newly demonstrated that PI3K gamma modulates angiogenesis, arteriogenesis, and vasculogenesis by mechanisms independent from its kinase activity.