Distinct mPTP activation mechanisms in ischaemia-reperfusion: contributions of Ca², ROS, pH, and inorganic polyphosphate.

Seidlmayer, Lea K.; Juettner, Vanessa V.; Kettlewell, Sarah; Pavlov, Evgeny V.; Blatter, Lothar A.; Dedkova, Elena N.

Aims The mitochondrial permeability transition pore (mPTP) plays a central role for tissue damage and cell death during ischaemia- reperfusion (I/R). We investigated the contribution of mitochondrial inorganic polyphosphate (polyP), a potent activator of Ca2 -induced mPTP opening, towards mPTP activation and cardiac cell death in I/R. Methods and results A significant increase in mitochondrial free calcium concentration ([Ca2 ]m), reactive oxygen species (ROS) generation, mitochondrial membrane potential depolarization (DCm), and mPTP activity, but no cell death, was observed after 20 min of ischaemia. The [Ca2 ]m increase during ischaemiawas partially prevented by the mitochondrial Ca2 uniporter (MCU) inhibitor Ru360 and completely abolished by the combination of Ru360 and the ryanodine receptor type 1 blocker dantrolene, suggesting two complimentary Ca2 uptake mechanisms. In the absence of Ru360 and dantrolene, mPTP closing by polyP depletion or CSA decreased mitochondrial Ca2 uptake, suggesting that during ischaemia Ca2 can enter mitochondria through mPTP. During reperfusion, a burst of endogenous polyP production coincided with a decrease in [Ca2 ]m, a decline in superoxide generation, and an acceleration of hydrogen peroxide (H2O2) production. An increase in H2O2 correlated with restoration of mitochondrial pHm and an increase in cell death. mPTP opening and cell death on reperfusionwere prevented by antioxidants Trolox and MnTBAP [Mn (III) tetrakis (4-benzoic acid) porphyrin chloride]. Enzymatic polyP depletion did not affect mPTP opening during reperfusion, but increased ROS generation and cell death, suggesting that polyP plays a protective role in cellular stress response. Conclusions Transient Ca2 /polyP-mediated mPTP opening during ischaemia may serve to protect cells against cytosolic Ca2 overload, whereas ROS/pH-mediated sustained mPTP opening on reperfusion induces cell death.

ISCHEMIA; INORGANIC compounds; REACTIVE oxygen species; CELL death; RYANODINE receptors; ANTIOXIDANTS

Cardiovascular Research, 2015, Vol 106, Issue 2, p237

0008-6363

Academic Journal

10.1093/cvr/cvv097