Mitochondrial GSH Systems in CA1 Pyramidal Cells and Astrocytes React Differently during Oxygen-Glucose Deprivation and Reperfusion.

Abstract

Pyramidal cells and astrocytes have differential susceptibility to oxygen-glucose deprivation and reperfusion (OGD-RP). It is known that excessive reactive oxygen species (ROS) in mitochondria initiates cell death, while glutathione (GSH) is one of the major defenses against ROS. Although it is known that astrocytes contain a higher concentration of GSH than neurons, and that astrocytes can provide neurons with GSH, we are unaware of a detailed and quantitative examination of the dynamic changes in the mitochondrial GSH system in the two cell types during OGD-RP. Here, we determined mitochondrial membrane potential and the degrees of oxidation of the mitochondrially targeted roGFP-based sensors for hydrogen peroxide (OxDP) and GSH (OxDG). We also developed a method to estimate the mitochondrial GSH (mGSH) concentration in single cells in the CA1 region of organotypic hippocampal slice cultures at several time-points during OGD-RP. We find that mitochondrial membrane potential drops in pyramidal cells during OGD while it is relatively stable in astrocytes. In both types of cell, the mitochondrial membrane potential decreases during RP. During OGD-RP, mitochondrial peroxide levels are the same. Astrocytic mGSH is more than four times higher than pyramidal cell mGSH (3.2 vs 0.7 mM). Astrocytic mGSH is drained from mitochondria during OGD, whereas in pyramidal cells it remains fairly constant. OxDGSH prior to and during OGD is lower (less oxidized) in pyramidal cells than in astrocytes, but the two nearly converge during RP. The larger changes of redox status in the GSH system in pyramidal cells than astrocytes is an upstream sign of the higher mortality of the pyramidal cells after facing an insult. The pattern of [mGSH] changes in the two cell types could be recognized as another mechanism by which astrocytes protect neurons from transient, extreme conditions.