Genomic analysis of ischemic preconditioning in adult rat hippocampal slice cultures.

Understanding endogenous mechanisms of neuroprotection may have important clinical applications. It is well established that brain tissue becomes more resistant to ischemic injury following a sublethal ischemic insult. This process, called ischemic preconditioning (IPC), can be induced in adult rat hippocampal slice cultures by a brief oxygen-glucose deprivation (OGD) [Hassen, G.W., Tian, D., Ding, D., Bergold, P.J., 2004. A new model of ischemic preconditioning using young adult hippocampal slice cultures. Brain Res. Brain Res. Protoc. 13, 135-143]. We have analyzed the changes in gene expression brought about by IPC in this model in order to understand the mechanisms involved. Total RNA was isolated at different time points following a brief OGD (3, 6 and 12 h) and used to probe genome-wide expression microarrays. Genes were identified that were significantly up- or down-regulated relative to controls. We placed genes that were differentially expressed into statistically significant groups based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) terms. Genes involved in signal transduction, transcription, and oxidative phosphorylation are differentially expressed at each time point. The analysis demonstrates that alterations in signaling pathways (TGF-beta, Wnt, MAPK, ErbB, Toll-like receptor, JAK-STAT, VEGF) consistently accompany IPC. RT-PCR was used to confirm that members of these signaling pathways are regulated as predicted by the microarray analysis. We verified that protein translation following OGD is necessary for IPC. We also found that blocking the NMDA receptor during OGD does not significantly inhibit IPC in this model or produce large changes in gene expression. Our data thus suggests that changes in signaling pathways and their down-stream targets play an important role in triggering endogenous neuroprotection.