Hypoxic preconditioning up-regulates glucose transport activity and glucose transporter (GLUT1 and GLUT3) gene expression after acute anoxic exposure in the cultured rat hippocampal neurons and astrocytes

Hypoxic preconditioning has been shown to increase the hypoxic tolerance of brain neurons. However, the mechanism underlying the increased hypoxic tolerance has not been well elucidated. Since anaerobic glycolysis is the only pathway for a vertebrate cell to produce energy under anoxic conditions, which needs a large amount of glucose, we hypothesize that glucose transport, the rate-limiting step for glucose metabolism, plays a critical role in the hypoxic tolerance induced by hypoxic preconditioning. In this study, the effects of hypoxic preconditioning on glucose transport activity and the gene expression of two major forms of glucose transporters (GLUT1 and GLUT3) in the brain were investigated in cultured rat hippocampal neurons and astrocytes. The neuronal and astroglial cultures were preconditioned for 6 days by intermittently exposing the cells to sublethal hypoxic gas mixture (1% O2/10% CO2/89% N2) for 20 min each day. 24 h after the last hypoxic exposure, the cells were exposed to a lethal anoxic gas mixture (10% CO2/90% N2) for 6 h and the uptake rate of [3H] 2-deoxyglucose (2-DG) and the levels of GLUT1 and GLUT3 glucose transporter mRNAs in the cells were examined immediately after anoxic exposure. The neurons and astrocytes preconditioned with hypoxia showed higher 2-DG uptake rates than the non-preconditioned cells. Compatible with the change in 2-DG uptake, hypoxic preconditioning also increased GLUT1 mRNA levels in the astrocytes and GLUT1 and GLUT3 mRNA levels in the neurons. The neurons preconditioned by hypoxia displayed increased anoxic tolerance. However, when glucose uptake in the neurons was blocked by cytochalasin B, the anoxic tolerance was almost abolished. These results suggest that glucose transport is critical to neuronal survival during anoxic exposure and the increased glucose transport activity is probably one of the important mechanisms for the enhanced hypoxic tolerance induced by hypoxic preconditioning.