Evaluation of hypoxia inducible factor expression in inflammatory and neurodegenerative brain models

The neuroinflammatory process is thought to contribute to the progression of neurological disorders and brain pathologies. The release of pro-inflammatory cytokines and chemokines by activated glial cells, astrocytes and microglia plays an important role in this process. However, the role of hypoxia-inducible factor-1α (HIF-1α), the key transcription factor regulating the expression of hypoxia-inducible genes, during glial activation is less known. Thus, we examined the significance of HIF-1α in three experimental models: first in an acute model of inflammation induced by pro-inflammatory cytokines TNF-α, IL-1β and IFN-γ; secondly, in a chronic model of inflammation using an APPswe/PS1dE9 (APP/PS1) transgenic mouse model of Alzheimer's disease and thirdly via the inhibition of the PI3K/AKT pathway in a model of neuronal apoptosis. During acute glial inflammation induced by in vitro administration of TNF-α, IL-1β and IFN-γ, mRNA expression levels of HIF-1α were significantly upregulated; however, this effect was blocked by SP600126, a pharmacological inhibitor of mitogen-activated protein kinases (MAPKs). These data suggest that MAPKs could be involved in HIF-1α regulation. In addition, we observed that HIF-1α is not involved in the neuronal apoptotic process mediated by PI3-kinase inhibition, which is regulated by c-Jun. Finally, we did not detect significant differences in the expression of HIF-1α mRNA in APP/PS1 mice during the course of the study (3-12 months of age). Thus, we demonstrated that HIF-1α has a prominent role in acute but not in chronic inflammatory processes, such as the one which occurs in the APP/PS1 experimental model of AD. Moreover, HIF-1α is not involved in neuronal apoptosis after PI3K/AKT inhibition.