Nuclear-mitochondrial cross-talk in global myocardial ischemia. A time-course analysis.

Myocardial ischemia results in early and progressive damage to mitochondrial structure and function, but the molecular events leading to these changes have not been clearly established. We hypothesized that mitochondrial dysfunction and a coordinated expression of nuclear and mitochondrial genes occur in a time-dependent manner by relating the time courses of changes in parameters of mitochondrial bioenergetics after ischemia-reperfusion. Using a Langendorff rat heart model, mitochondrial bioenergetics and protein levels were assessed at different times of ischemia and ischemia/reperfusion. Mitochondrial and nuclear gene expression (super array analysis) and mitochondrial DNA levels were evaluated after late ischemia. Ischemia induced progressive and marked decreases in complex I, III, and V activities. Reperfusion (15, 30, and 60 min) after 45 min of ischemia had little further effect on enzyme activities or respiration. Super array analysis after 45 min ischemia revealed increased levels of the proteins with more pronounced increases in the corresponding mRNAs. Expression of mitochondrial and nuclear genes involved in oxidative phosphorylation increased after 45 min of ischemia but not after reperfusion. Myocardial ischemia induces mitochondrial dysfunction and differential but coordinated expression of nuclear and mitochondrial genes in a time-dependent manner. Our observations are pertinent to the search for molecular stimuli that generate mitochondrial defects and alter mitochondrial and nuclear transcriptional responses that may impact ischemic preconditioning and cardioprotection.