Abstract 17373: Decreased Levels of Inorganic Polyphosphates Prevent Opening of the Mitochondrial Permeability Transition Pore in Ischemia-Reperfusion Injury
Introduction: Minimizing reperfusion injury (RI) is a principal clinical strategy to reduce myocardial damage following myocardial infarction. At the molecular level opening of the mitochondrial permeability transition pore (mPTP) is a central event leading to RI. Recent clinical trials suggest that the use of the mPTP inhibitor cyclosporin A (CsA) significantly reduces infarct size in human patients. We previously showed that decreased levels of inorganic polyphosphates (polyP) in cardiac mitochondria prevent opening of mPTP induced by Ca overload.
Aim: We investigated the role of mitochondrial polyP for mPTP opening under conditions of RI.
Methods: Using cultured rabbit ventricular myocytes we decreased polyP levels by adenoviral expression of a mitochondrially targeted polyP hydrolyzing enzyme (PPX). RI was induced by exposing cells to glucose-free Tyrode solution containing 20 mM 2-deoxyglucose and 2 mM NaCN, pH 6.4, followed by perfusion with standard Tyrode solution. Calcein red and TMRM were used to measure mPTP opening and mitochondrial membrane potential (Δψm), respectively.
Results: PPX expressing cells with depleted polyP levels (PPX cells) exhibited a significantly smaller decrease in calcein red fluorescence following RI, indicative of decreased opening of the mPTP (ctrl: -25±1%, n=20; PPX: -16±3%, n=14; p≤0.01). CsA, a blocker of the mPTP, reduced calcein red release from mitochondria in control cells (ctrl+CsA: -20±1%, n=9; p≤0.05). Δψm measurements showed that polyP depletion lessened the degree of Δψm depolarization induced by RI (ctrl: -75±5%, n=9; PPX: -48±9%, n=8; p≤0.01). Δψm depolarization in control cells was diminished to the same level seen in PPX cells by CsA (ctrl+CsA: -49±4%, n=8; p≤0.01). Remarkably, CsA did not further improve protection against mPTP opening in PPX cells, suggesting that reduction of polyP levels is sufficient to prevent mPTP opening in RI.
Conclusion: Decreasing polyP levels in cardiac myocytes protects against mPTP opening during RI. Our results indicate that polyP is a previously unrecognized essential mediator of mPTP activity and cell death following RI. We suggest that polyP reduction will be a very promising novel strategy for RI treatment.
- © 2010 by American Heart Association, Inc.