Abstract 3300: C-Jun N-terminal Kinase Protects the Heart From Brief Ischemia by Activating Akt and Blocking Mitochondrial Death Channels
INTRODUCTION: JNK is activated by ischemia-reperfusion (I/R) and has been shown to promote death or protection in different models of I/R. The reasons for the differences are not known. In vivo studies have shown that specific JNK inhibitors can reduce infarct size by 50% or more during AMI.
HYPOTHESIS: JNK promotes death or survival depending on the duration of ischemia prior to reperfusion.
METHODS: Cardiac injury was quantified in mouse and pig hearts subjected to 5 or 20-min (mouse) and 10-min (pig) of ischemia respectively and 2h, 24h or 3 weeks reperfusion ± JNK inhibitors. Hearts were analyzed by Evans blue and TTC staining, TUNEL staining of sections, western blots of extracted proteins, echocardiography and MRI.
RESULTS: Minimal infarction was present when wild type mouse hearts were subjected to 5-min ischemia, whereas 20-min ischemia produced a 33±3% LV infarct and 34±9% apoptotic index in the AAR (n=6). JNK inhibition during 20-min I/R decreased infarction to 18±4% with a parallel decrease of apoptotic index to 14% (n=6; p<0.01). Five minutes of ischemia in the presence of JNK inhibitor SP600125 produced 31±3% infarction and 39% apoptotic index of wild type mouse; transgenic JNK −/− mice also sustained 33±7% infarction after 5min ischemia-24h reperfusion (n=4). Pig hearts subjected 10-min ischemia-2h reperfusion displayed stunning but no infarction; infusion of the cell-permeant JNK inhibitor peptide DJNKi-1 before and during 10-min ischemia produced apical infarction and increased apoptosis (37±8%; n=3) at 2h reperfusion. Echocardiography and MRI of mouse hearts after 3 weeks revealed extensive remodeling cause by 20-min ischemia or 5-min ischemia with JNK inhibitor. Ejection fractions decreased from 78±11% to 46±8% (20-min; n=6, p<0.05)) and 53±9% (5min ischemia + JNK inhibitor; n=6, p<0.05). Western analyses indicated a 4-fold increase in the phosphorylation of Akt at Thr-450, a target for JNK, during reperfusion after 5-min compared with 20-min ischemia. These effects were sensitive to inhibition of GSK3β by lithium or SB216763.
CONCLUSION: JNK protects selectively against short episodes of ischemia by activating Akt, inhibiting GSK3β and blocking mitochondrial death channels. JNK is essential to allow ischemic preconditioning.