Hypoxic preconditioning involves system Xc − regulation in mouse neural stem cells

Abstract

In animals, hypoxic preconditioning has been used as a form of neuroprotection. The exact mechanism involved in neuroprotective hypoxic preconditioning has not been described, yet could be valuable for possible neuroprotective strategies. The overexpression of the cystine-glutamate exchanger, system Xc −, has been demonstrated as being neuroprotective (Shih, Erb et al. 2006). Here, using immunohistochemistry, we demonstrate that C57BL/6 mice exposed to hypoxia showed an increase in system Xc − expression, with the highest level of intensity in the hippocampus. Western Blot analysis also showed an almost 2-fold increase in system Xc − protein in hypoxia-exposed versus control mice. The mRNA for the regulatory subunit of system Xc −, xCT, and the xCT/actin ratio were also increased under hypoxic conditions. Experiments using hypoxia-inducible factor (HIF-1α) siRNA showed a statistically significant decrease in HIF-1α and system Xc − expression. Under hypoxic conditions, system Xc − activity, as determined by cystine uptake, increased 2-fold. Importantly, hypoxic preconditioning was attenuated in neural stem cells by pharmacological inhibition of system Xc − activity with S4-carboxyphenylglycine. These data provide the first evidence of hypoxic regulation of the cystine glutamate exchanger system Xc −.