Figure 1.

Threshold of hypoxia recognition of primary astrocytes and brain microvascular endothelial cells (BMEC) in vitro. HIF-1α protein expression was detected by Western blotting in primary astrocytes (A) and primary BMECs (B) treated with 21%, 9%, 7%, 5%, 3%, or 1% O₂ for 12 h. β-actin served as a loading control. The optical density of HIF-1α band was normalized to that of β-actin, and quantification was performed from two to three independent experiments. Data are shown as mean ± S.E.M. *P<0.05, **P<0.01, ***P<0.001 vs. control group (21% O₂).