Ischemic preconditioning triggers nuclear translocation of thioredoxin and its interaction with Ref-1 potentiating a survival signal through the PI-3-kinase-Akt pathway.

Thioredoxin (Trx-1), a key mediator of cellular redox homeostasis and cell survival, is implicated in redox signaling in the ischemic myocardium. To investigate further its mechanism of action, Trx expression in rat heart was suppressed by direct injection of small hairpin RNA against Trx-1 (shRNA-Trx-1). Forty-eight hours after treatment, hearts were excised for isolated working-heart preparation. A group of hearts was preconditioned (PC) by subjecting them to four cyclic episodes of 5-min ischemia, each followed by 10 min of reperfusion. All the hearts, PC or non-PC, were subjected to 30-min ischemia followed by 2 h of reperfusion. As expected, the PC hearts exhibited improved ventricular function, reduced infarct size, and cardiomyocyte apoptosis. Also in PC hearts, an increase was noted in Trx-1 and other cardioprotective and redox-regulated proteins like Ref-1, phospho-Akt, and NF-kappaB DNA-binding activity. PC also caused nuclear translocation of Trx-1 and Ref-1 followed by their association. However, in hearts treated with shRNA-Trx 1, the cardioprotective effects of PC were abolished along with a concomitant decrease in nuclear localized Trx-1 and Ref-1, along with a decrease in phospho-Akt and NF-kappaB. These results demonstrate that PC triggers translocation of Trx-1 into the nucleus, where it becomes associated with Ref-1 and performs redox signaling through the activation of NF-kappaB and an increase in prosurvival signal inducer phospho-Akt.