Phosphatidylinositol-3-Kinase Gamma Plays a Central Role in Blood-Brain Barrier Dysfunction in Acute Experimental Stroke

Background and Purpose-Phosphoinositide 3-kinase (PI3K)-gamma is linked to inflammation and oxidative stress. This study was conducted to investigate the role of the PI3K gamma in the blood-brain barrier dysfunction and brain damage induced by focal cerebral ischemia/reperfusion. Methods-Wild-type and PI3K gamma knockout mice were subjected to middle cerebral artery occlusion (60 minutes) followed by reperfusion. Evans blue leakage, brain edema, infarct volumes, and neurological deficits were examined. Oxidative stress, neutrophil infiltration, and matrix metallopeptidase-9 were assessed. Activation of nuclear factor-kappa B and expression of proinflammatory and pro-oxidative genes were studied. Results-PI3K gamma deficiency significantly reduced blood-brain barrier permeability and brain edema formation, which were time-dependently correlated with preventing the degradation of the tight junction protein, claudin-5, and the basal lamina protein, collagen IV, and the phosphorylation of myosin light chain in brain microvessels. PI3K gamma deficiency suppressed ischemia/reperfusion-induced nuclear factor-kappa B p65 (Ser536) phosphorylation and the expression of the pro-oxidant enzyme NADPH oxidase (Nox1, Nox2, and Nox4) and proinflammatory adhesion molecules (E-and P-selectin, intercellular adhesion molecule-1) at different time points. These molecular changes were associated with significant inhibition of oxidative stress (superoxide production and malondialdehyde content), neutrophil infiltration, and matrix metallopeptidase-9 expression/activity in PI3K gamma knockout mice. Eventually, PI3K gamma deficiency significantly reduced infarct volumes and neurological scores at 24 hours after ischemia/reperfusion. Conclusions-Our results provide the first direct demonstration that PI3K gamma plays a significant role in ischemia/reperfusion-induced blood-brain barrier disruption and brain damage. Future studies need to explore PI3K gamma as a potential target for stroke therapy. (Stroke. 2011; 42: 2033-2044.)