Abstract 103: Regulation Of Cardiac PTEN/Akt Signaling By Moderate Intra-Ischemic Therapeutic Hypothermia

Abstract

Introduction: Previous studies demonstrate a critical role for Akt in mediating cardioprotection by therapeutic hypothermia. However, the mechanism of hypothermia-induced Akt activation remains poorly understood. Akt activation is determined in part by PTEN activity and degradation. Hypothesis: We hypothesized that moderate intra-ischemic cooling activates Akt in the ischemic-reperfused heart due to enhanced PTEN degradation. Methods: Rat hearts were isolated and perfused media containing 5 mM glucose. LV function was monitored continuously by an intraventricular balloon. Rate-pressure product (RPP=heart rate x LV developed pressure) was monitored as an index of cardiac function. Hearts in the normothermic control group (I/R) were subjected to 20 min. of global, no-flow ischemia followed by reperfusion at 37 °C. In the hypothermia intervention group (I/R+TH), hearts were cooled to 30 °C at the start of ischemia and then rewarmed 10 min. after reperfusion. Coronary perfusate was collected from the pulmonary artery at preischemic baseline and 10 min. after reperfusion. Ventricular tissue was harvested at 0 or 30 min. after reperfusion for western blotting. Results: RPP was significantly higher in the I/R+TH group (n=7) compared to the I/R group (n=8) at 30 min. post-reperfusion (24,725 ± 1,112 mmHg*beats/min. vs. 18,237 ± 2,223 mmHg*beats/min., p<0.05). Coronary perfusate taurine concentration was significantly higher in the I/R group compared to the I/R+TH group at 10 min. post-reperfusion (19 ± 4 μM vs. 5 ± 1 μM, p<0.01). Akt serine473 phosphorylation was significantly higher in the I/R+TH group compared to the I/R group at 0 min. post-reperfusion (p<0.01), but significantly lower at 30 min. post-reperfusion (p<0.01). Additionally, TH enhanced total PTEN expression at 0 min. (p<0.05) and 30 min. (p<0.01) post-reperfusion without affecting the ratio of phospho-PTEN/PTEN. Conclusion: Intra-ischemic cooling was associated with temporal changes in Akt phosphorylation despite enhanced PTEN expression. Additionally, modulation of cardiac taurine release by hypothermia should be carefully considered in future studies assessing taurine as a biomarker for cardiac arrest and ischemic heart pathologies.