Abstract 14440: PI3Kα Deletion in Cardiomyocytes Causes Maintained Mitochondrial Membrane Potential and Blocks Necrotic Cell Death in Ischemia/Reperfusion Injury
Introduction: PI3K signaling is associated with protection in ischemia/reperfusion (IR) injury. However, PI3Kα dominant negative (PI3KαDN) with reduced PI3Kα in the heart has enhanced IR recovery. Activation of Akt and ERK1/2 are potential mechanisms of this phenotype through mitochondrial protection.
Hypothesis: Loss of PI3Kα in multiple models improves IR recovery by protecting mitochondrial membrane potential and cell membrane integrity.
Methods: Murine models include PI3KαDN and PI3Kαflx/flx /αMHC-Cre treated with tamoxifen, (40mg/kg/day*2 days p.o.) (TAM+Cre). Langendorff-perfused hearts were subjected to 30min ischemia and 40min reperfusion. For live tissue imaging of cell death and mitochondrial membrane potential (ΔΨ), TMRE (100nM), Hoechst (500nM) and Sytox Green (1 μM) are perfused. The Akt inhibitor MK2206 (1μM) and MEK1/2inhibitor MEK-162 (100nM) are included in select groups.
Results: PI3KαDN heart rate pressure product (RPP) recovery to 17,332±2,486 mmHg/min is not significantly reduced with Akt inhibition 14,940±2,486 mmHg/min or MEK inhibition 16,283±4,301 mmHg/min. Inducible PI3Kα deletion (TAM+Cre) caused IR protection compared to no-Cre littermates: 14,057±2,235 vs. 3,390±1,121 mmHg/min (RPP recovery). Post IR control hearts show evidence of necrotic cell death and lost mitochondria function that is attenuated in TAM+Cre and PI3KαDN : Sytox positive nuclei are 9±2% and 15±2% respectively and 59±8% for controls. Using live tissue imaging post IR, we showed mitochondrial ΔΨ TMRE staining was 2.6±0.3 and 3.5±0.5 fold higher than controls respectively. Investigating potential mediators of necrosis, RIP1 and 3 were increased in PI3KαDN at baseline and minimally detectible in post IR hearts; Bax and Bak were increased in PI3KαDN and were localized to mitochondrial fractions in both control and PI3KαDN post IR hearts, suggesting that these pathways cannot explain the PI3KαDN/TAM+Cre phenotypes.
Conclusions: Impaired PI3Kα function causes IR protection with reduced necrosis and maintained mitochondrial ΔΨ, which is not dependent on Akt or ERK1/2 activation. These findings have important implications since PI3Kα has predominantly been considered a pro-survival pathway.
Author Disclosures: B.A. McLean: None. P. Zhabyeyev: None. X. Chen: None. A. Haromy: None. B. Vanhaesebroeck: None. E.D. Michelakis: None. G.Y. Oudit: None.
- © 2016 by American Heart Association, Inc.