Hyperglycemia-enhanced ischemic brain damage in mutant manganese SOD mice is associated with suppression of HIF-1α

Both preischemic hyperglycemia and reduction of manganese superoxide dismutase activity are known to enhance neuronal death induced by transient cerebral ischemia. Transcriptional factor hypoxia-inducible factor 1 (HIF-1) regulates multiple downstream genes that modulate cell metabolism, survival, death, angiogenesis, hematopoiesis, and other functions. The objectives of this study were to determine (i) whether hyperglycemia is able to increase ischemic brain damage in mutant manganese superoxide dismutase (SOD2) mice and (ii) whether the reduction of SOD2 activity has a profound effect on HIF-1 protein expression under hyperglycemic ischemic condition. Both wild type and mutant SOD deficient (SOD2−/+) mice were induced to hyperglycemia 30 min before induction of a 30-min transient middle cerebral artery occlusion (tMCAO). Brains were extracted after 5 and 24 h of reperfusion for immunohistochemistry and Western blot analyses. The results showed that preischemic hyperglycemia significantly increased infarct volume in SOD2−/+mice and that HIF-1α protein levels were significantly reduced in ischemic core area at 5- and 24-h of reperfusion in hyperglycemic SOD2−/+ mice. However, the HIF-1α protein levels were not significantly decreased in hyperglycemic wild type animals subjected to stroke. The results suggest that the increased brain damage observed in hyperglycemic SOD2−/+ mice is associated with HIF-1α suppression, while hyperglycemia per se does not seem to exert its detrimental effects on ischemic brain via modulating HIF-1 pathway.