Intramitochondrial Zn2Â + accumulation via the Ca2Â + uniporter contributes to acute ischemic neurodegeneration

Ca2 + and Zn2 + have both been implicated in the induction of acute ischemic neurodegeneration. We recently examined changes in intracellular Zn2 + and Ca2 + in CA1 pyramidal neurons subjected to oxygen glucose deprivation (OGD), and found that Zn2 + rises precede and contribute to the onset of terminal Ca2 + rises (“Ca2 + deregulation”), which are causatively linked to a lethal loss of membrane integrity. The present study seeks to examine the specific role of intramitochondrial Zn2 + accumulation in ischemic injury, using blockers of the mitochondrial Ca2 + uniporter (MCU), through which both Zn2 + and Ca2 + appear able to enter the mitochondrial matrix. In physiological extracellular Ca2 +, treatment with the MCU blocker, Ruthenium Red (RR), accelerated the Ca2 + deregulation, most likely by disrupting mitochondrial Ca2 + buffering and thus accelerating the lethal cytosolic Ca2 + overload. However, when intracellular Ca2 + overload was slowed, either by adding blockers of major Ca2 + entry channels or by lowering the concentration of Ca2 + in the extracellular buffer, Ca2 + deregulation was delayed, and under these conditions either Zn2 + chelation or MCU blockade resulted in similar further delays of the Ca2 + deregulation. In parallel studies using the reactive oxygen species (ROS) indicator, hydroethidine, lowering Ca2 + surprisingly accelerated OGD induced ROS generation, and in these low Ca2 + conditions, either Zn2 + chelation or MCU block slowed the ROS generation. These studies suggest that, during acute ischemia, Zn2 + entry into mitochondria via the MCU induces mitochondrial dysfunction (including ROS generation) that occurs upstream of, and contributes to the terminal Ca2 + deregulation.