Silencing Astrocyte Elevated Gene-1 during Calcium Signaling and Glutamate Excitotoxicity

Purpose: During central nervous system (CNS) injury or infection, astrocytes undergo inflammatory and functional changes, ultimately regulating cognitive impairment. Among these devastating changes is the downregulation of excitatory amino acid transporter 2 (EAAT2). EAAT2 is critical for glutamate uptake in synaptic clefts, so when downregulated, results in glutamate excitotoxicity. Our previous studies highlighted astrocyte elevated gene-1 (AEG-1) overexpression as a novel modulator of EAAT2 repression during HIV-1 associated neuroinflammation. Additionally, elevated AEG-1 levels are evident in several cancers, neurodegeneration, oxidative stress, and aging. AEG-1 cooperates in several cell signaling pathways mediating cell development, inflammation, proliferation, differentiation, metabolism, apoptosis, and autophagy. While AEG-1 is ubiquitously expressed, levels are higher in muscle-dominated organs and endocrine glands, suggesting a role of AEG-1 in calcium associated signaling. Furthermore, we have shown AEG-1 to have a direct interaction with the calcium-binding chaperone calnexin. Both calcium and glutamate are prominent CNS signaling molecules reported to be dysregulated during conditions AEG-1 is often upregulated. However, the role of AEG-1 in calcium signaling has not yet been explored. Materials & Methods: AEG-1 specific siRNA was used to isolate AEG-1 dependent outcomes. Astrocyte activation was measured via morphological staining and cytokine ELISA. EAAT2 protein and mRNA expression were examined in conjunction with functional glutamate clearance assay to correlate potential glutamate excitotoxicity. Calcium signaling was measured by live cell confocal microscopy using a genetically encoded calcium sensor. Results: AEG-1 siRNA significantly decreased protein and mRNA expression of AEG-1 compared to non-specific siRNA. Preliminary studies for calcium signaling required standardization and suggest a decreased calcium response when AEG-1 is knocked down. Additional investigations are still in progress. Conclusion: The current study focuses on investigating how AEG-1 regulates calcium signaling and astrocyte activation in connection with glutamate excitotoxicity. These findings will help better understand AEG-1 mediated dysregulation of astrocyte function, possibly identifying a novel therapeutic target for cognitive impairment.