Abstract
The isocitrate dehydrogenase (IDH) enzymes were initially identified as essential components of the Krebs cycle. IDH mutations were thought to be incompatible with cell survival. However, 90% of glioblastomas were recently shown to be associated with somatic mutations in these enzymes, indicating a possible role for IDH in promoting cellular survival in hypoxic environments. Our proteomic analysis of rats given 10 minutes of middle cerebral artery occlusion to induce transient ischemia demonstrates a significant decrease in IDH expression. We have recapitulated this decrease in an in vitro model using primary cortical neurons exposed to acute oxygen and glucose deprivation. Given the role of IDHs in energy metabolism and antioxidant production, we hypothesize that the IDHs may serve as first-line, rapid-response enzymes that regulate survival in environments of energetic or oxidative stress. In order to identify the specific events that regulate IDH enzymes, HT-22 neural cells were subjected to either a selective energetic challenge or a pure oxidative stress. In response to the non-lethal energetic challenge induced by substituting galactose for glucose, we observed increased IDH1, 2, and 3 expression and cessation of cellular proliferation. No change in expression of any IDH isoform was observed when neural cells were subjected to subtoxic oxidative stress via glutathione depletion. Taken together, these data imply that IDH expression rapidly responds to changes in energetic status, but not to oxidative stress. These data also suggest that IDH enzymes respond not only to allosteric modulation, but can also change patterns of expression in response to moderate stress in an effort to maximize ATP production and survival.