Oxygen-Glucose Deprivation Increases NR4A1 Expression and Promotes Its Extranuclear Translocation in Mouse Astrocytes

Hypoxic-ischemic brain injury induces metabolic dysfunction that ultimately leads to neuronal cell death. Astrocytes, a type of glial cell, play a key role in brain metabolism; however, their response to hypoxic-ischemic brain injury is not fully understood. Microglia were removed from murine primary mixed glial cultures to enrich astrocytes. Next, we explored genes whose expression is altered following oxygen-glucose deprivation using a microarray. Microarray analysis revealed that the expression of Nr4a1 and Nr4a3 is markedly increased in astrocyte-enriched cultures after 15 h of oxygen-glucose deprivation. The expression of both Nr4a1 and Nr4a3 was regulated by HIF-1α. At the protein level, NR4A1 was translocated from the nucleus to the cytoplasm following oxygen-glucose deprivation and co-localized with mitochondria in apoptotic cells; however, its localization was restored to the nucleus after reoxygenation. Oxygen-glucose deprivation causes an increase in NR4A1 mRNA in astrocytes as well as its nuclear to cytoplasmic transfer. Furthermore, reoxygenation enhances NR4A1 transcription and promotes its nuclear translocation.