# Mechanisms of delayed ischemia/reperfusion evoked ROS generation in the hippocampal CA1 zone of adult mouse brain slices

## TL;DR

This study explores how reactive oxygen species (ROS) are produced in the brain after reperfusion following ischemia, identifying mitochondrial hyperpolarization and zinc accumulation as key contributors.

## Contribution

The study identifies mitochondrial hyperpolarization and Zn2+ accumulation as novel mechanisms contributing to delayed ROS production after reperfusion.

## Key findings

- OGD evokes a two-stage ROS production: an initial increase during OGD and a delayed burst after reperfusion.
- Mitochondrial hyperpolarization shortly after OGD contributes to the delayed ROS burst.
- Zn2+ chelation reduces the late ROS surge, supporting a role for mitochondrial Zn2+ accumulation.

## Abstract

ROS overproduction is an important contributor to delayed ischemia/reperfusion induced neuronal injury, but relevant mechanisms remain poorly understood. We used oxygen-glucose deprivation (OGD)/reperfusion in mouse hippocampal slices to investigate ROS production in the CA1 pyramidal cell layer during and after transient ischemia. OGD evoked a 2-stage increase in ROS production: 1st – an abrupt increase in ROS generation starting during OGD followed by a marked slowing; and 2nd – a sharp ROS burst starting ~ 40 min after reperfusion. We further found that a slight mitochondrial hyperpolarization occurs shortly after OGD termination. Consequently, we showed that administration of low dose FCCP or of FTY720 (both of which cause mild, ~ 10%, mitochondrial depolarization), markedly diminished the delayed ROS burst, suggesting that mitochondrial hyperpolarization contributes to ROS production after reperfusion. Zn2+ chelation after OGD withdrawal also substantially decreased the late surge of ROS generation– in line with our prior studies indicating a critical contribution of Zn2+ entry into mitochondria via the mitochondrial Ca2+ uniporter (MCU) to mitochondrial damage after OGD. Thus, reperfusion-induced mitochondria hyperpolarization and mitochondrial Zn2+ accumulation both contribute to mitochondrial ROS overproduction after ischemia. As these events occur after reperfusion, they may be amenable to therapeutic interventions.