The requirement of extracellular signal-related protein kinase pathway in the activation of hypoxia inducible factor 1α in the developing rat brain after hypoxia-ischemia

Hypoxia inducible factor 1 alpha (HIF-1 alpha) is a key regulator of cellular oxygen homeostasis. However, the regulation of HIF-1 alpha in neonates with hypoxia-ischemia (HI) is not clear. Under normoxic conditions, the extracellular signal-related protein kinase (ERK) pathway has been shown to be involved in the activation of HIF-1 alpha in cell lines. Therefore, we hypothesized that the ERK pathway is involved in the activation of HIF-1 alpha and its target genes in the developing rat brain following HI. To test this hypothesis, we set up an HI model by ligating the right common carotid artery followed by hypoxia using postnatal day 10 rats. Rat brains from HI and sham controls were collected to detect the expression of HIF-1 alpha, its target gene, vascular endothelial growth factor (VEGF), and ERK using immunohistochemistry, Western blot analysis, and RT-PCR. We found that the expression of HIF-1 alpha protein was significantly upregulated at 4 h and peaked at 8 h after HI compared with sham controls. Accordingly, VEGF was similarly upregulated. However, the expression of total ERK (Erk1/2) had no obvious changes. Even though the phosphorylated form of ERK, p-Erk1/2, was upregulated and peaked at 4 h after HI, it is earlier than that seen in HIF-1 alpha expression. Furthermore, the induction of HIF-1 alpha protein, but not its mRNA, could be significantly inhibited by Erk1/2 pathway specific inhibitor, U0126. Our findings suggest that Erk1/2 pathway is involved in the regulation of HIF-1 alpha and VEGF in the developing rat brain after HI. The Erk1/2 pathway may work as a potential target for therapeutic intervention in neonates with HI.