Phosphoinositide 3-kinase γ-deficient hearts are protected from the PAF-dependent depression of cardiac contractility

Objectives: Following an ischemic insult, cardiac contractile recovery might be perturbed by the release of autacoids, like platelet-activating factor (PAF), that depress heart function by acting through G protein-coupled receptors (GPCRs). The signaling events downstream the PAF receptor that lead to the negative inotropic effect are still obscure. We thus investigated whether the GPCR-activated phosphoisositide 3-kinase γ (PI3Kγ) could play a role in the cardiac response to PAF. Methods: The negative inotropic effect of PAF was studied ex vivo, in isolated electrically driven atria and in Langendorff-perfused whole hearts derived from wild-type and PI3Kγ-null mice. Postischemic recovery of contractility was analyzed in normal and mutant whole hearts subjected to 30 min of ischemia and 40 min of reperfusion in the presence or absence of a PAF receptor antagonist. Results: While wild-type hearts stimulated with PAF showed increased nitric oxide (NO) production and a consequent decreased cardiac contractility, PI3Kγ-null hearts displayed reduced phosphorylation of nitric oxide synthase 3 (NOS3), blunted nitric oxide production and a complete protection from the PAF-induced negative inotropism. In addition, Langendorff-perfused PI3Kγ-null hearts showed a better contractile recovery after ischemia/reperfusion, a condition where PAF is known to be an important player in depressing contractility. In agreement with a role of PI3Kγ in this PAF-mediated signaling, postischemic contractile recovery in PI3Kγ-null mice appeared overlapping with that of normal hearts treated with the PAF receptor antagonist WEB 2170. Conclusion: These data indicate a novel PAF-dependent signaling pathway that, involving PI3Kγ and NOS3, contributes to postischemic contractile depressio

Protection from angiotensin II–mediated vasculotoxic and hypertensive response in mice lacking PI3Kγ

Hypertension affects nearly 20% of the population in Western countries and strongly increases the risk for cardiovascular diseases. In the pathogenesis of hypertension, the vasoactive peptide of the renin-angiotensin system, angiotensin II and its G protein–coupled receptors (GPCRs), play a crucial role by eliciting reactive oxygen species (ROS) and mediating vessel contractility. Here we show that mice lacking the GPCR-activated phosphoinositide 3-kinase (PI3K)γ are protected from hypertension that is induced by administration of angiotensin II in vivo. PI3Kγ was found to play a role in angiotensin II–evoked smooth muscle contraction in two crucial, distinct signaling pathways. In response to angiotensin II, PI3Kγ was required for the activation of Rac and the subsequent triggering of ROS production. Conversely, PI3Kγ was necessary to activate protein kinase B/Akt, which, in turn, enhanced L-type Ca2+ channel–mediated extracellular Ca2+ entry. These data indicate that PI3Kγ is a key transducer of the intracellular signals that are evoked by angiotensin II and suggest that blocking PI3Kγ function might be exploited to improve therapeutic intervention on hypertension

Phosphoinositide 3-kinase gamma gene knockout impairs postischemic neovascularization and endothelial progenitor cell functions

OBJECTIVE: We evaluated whether phosphatidylinositol 3-kinase γ (PI3Kγ) plays a role in reparative neovascularization and endothelial progenitor cell (EPC) function. METHODS AND RESULTS: Unilateral limb ischemia was induced in mice lacking the PI3Kγ gene (PI3Kγ(−/−)) or expressing a catalytically inactive mutant (PI3Kγ(KD/KD)) and wild-type controls (WT). Capillarization and arteriogenesis were reduced in PI3Kγ(−/−) ischemic muscles resulting in delayed reperfusion compared with WT, whereas reparative neovascularization was preserved in PI3Kγ(KD/KD). In PI3Kγ(−/−) 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. PI3Kγ is constitutively expressed by WT EPCs, with expression levels being upregulated by hypoxia. PI3Kγ(−/−) 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 PI3Kγ(−/−) EPCs. PI3Kγ(KD/KD) EPCs showed reduced Akt phosphorylation, but constitutive activation of eNOS and preserved proliferation, survival, and migration. CONCLUSIONS: We newly demonstrated that PI3Kγ modulates angiogenesis, arteriogenesis, and vasculogenesis by mechanisms independent from its kinase activity