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

Abstract

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 30min before induction of a 30-min transient middle cerebral artery occlusion (tMCAO). Brains were extracted after 5 and 24h of reperfusion for immunohistochemistry and Western blot analyses. The results showed that preischemic hyperglycemia significantly increased infarct volume in SOD2(-/+)mice and that HIF-1alpha protein levels were significantly reduced in ischemic core area at 5- and 24-h of reperfusion in hyperglycemic SOD2(-/+) mice. However, the HIF-1alpha 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-1alpha suppression, while hyperglycemia per se does not seem to exert its detrimental effects on ischemic brain via modulating HIF-1 pathway.

Figure 1

Microphotographs showing nuclear morphology produced by propidium iodide staining on brain sections from control, 5- and 24-hrs of reperfusion in both wild type (WT) and SOD2^−/+ mice. Arrows denote intact nuclei. Magnification 20X.

Figure 2

Western blots showing the immunointensity of HIF-1α in the striatum (A) and cortex (B) collected from wild type (WT) and SOD2^−/+ (KO) mice at 5- and 24-hrs of reperfusion. The band intensity ratio between HIF-1α and β-actin was calculated and converted to percent change. Data are expressed as Mean ±SD. *p<0.05 and **p<0.01 vs. control, #p< 0.05 and ##p<0.01 vs. WT at the same reperfusion time.