Astrocytes protect neurons from nitric oxide toxicity by a glutathione‐dependent mechanism

TLDR

Nitric oxide contributes to neuronal death in cerebral ischemia and other conditions, and astrocytes are strategically positioned to shield neurons because their processes surround most neurons. The study examined whether astrocytes can limit nitric‑oxide neurotoxicity using a cortical co‑culture system. Astrocyte‑coated dialysis membranes were placed over neuronal cultures to create a removable astrocyte layer, and the system was tested by comparing glutamate‑induced death (cleared by astrocytes) versus NMDA‑induced death, as well as by exposing co‑cultures to NO donors with astrocytes either normal or glutathione‑depleted by buthionine sulfoximine. The astrocyte layer increased glutamate LD50 four‑fold but had no effect on NMDA toxicity, and neurons exposed to NO donors with glutathione‑depleted astrocytes showed a two‑fold increase in death, indicating that astrocytes protect neurons from NO toxicity via a glutathione‑dependent mechanism.

Abstract

Nitric oxide (NO) contributes to neuronal death in cerebral ischemia and other conditions. Astrocytes are anatomically well positioned to shield neurons from NO because astrocyte processes surround most neurons. In this study, the capacity of astrocytes to limit NO neurotoxicity was examined using a cortical co‐culture system. Astrocyte‐coated dialysis membranes were placed directly on top of neuronal cultures to provide a removable astrocyte layer between the neurons and the culture medium. The utility of this system was tested by comparing neuronal death produced by glutamate, which is rapidly cleared by astrocytes, and N ‐methyl‐ d ‐aspartate (NMDA), which is not. The presence of an astrocyte layer increased the LD 50 for glutamate by approximately four‐fold, but had no effect on NMDA toxicity. Astrocyte effects on neuronal death produced by the NO donors S ‐nitroso‐ N ‐acetyl penicillamine and spermine NONOate were examined by placing these compounds into the medium of co‐cultures containing either a control astrocyte layer or an astrocyte layer depleted of glutathione by prior exposure to buthionine sulfoximine. Neurons in culture with the glutathione‐depleted astrocytes exhibited a two‐fold increase in cell death over a range of NO donor concentrations. These findings suggest that astrocytes protect neurons from NO toxicity by a glutathione‐dependent mechanism.