Abstract 1532: Ischemic Preconditioning Triggers Nuclear Translocation of Thioredoxin and its Interaction with REF-1 Potentiating a Survival Signal through PI-3-KINASE-AKT Pathway
Thioredoxin (Trx-1), a key modulator of intracellular redox homeostasis, has recently been attributed to cardioprotection in the ischemic myocardium. However, the molecular mechanism by which thioredoxin system contributes towards this process is largely unknown. To determine the mechanism of action of Trx in the myocardium, a group of rat hearts was injected with shRNA against Trx-1 (Trx-shRNA) while control rats received either the empty vector or saline. Also a group of hearts was preconditioned (PC) by subjecting them to four cyclic episodes of brief periods of ischemia-reperfusion. Forty-eight hours after the injection, hearts were excised for isolated heart preparation. 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, there was an induction of a number of cardioprotective and redox responsive proteins such as Trx-1, Ref-1; increased phosphorylation of Akt and increased NFkB activity. The cardioprotective effects of PC were abolished in hearts injected with Trx-shRNA with concurrent attenuation of those cardiopro-tective markers. Western analysis and Immunohistochemistry further revealed that in PC hearts Trx is translocated from cytosolic to nuclear compartment where it associates with redox effector factor 1 (Ref-1). Such translocation of Trx was abrogated in hearts injected with Trx-shRNA. Since Ref-1 plays a pivotal role in modulating gene regulatory and DNA repair activities in the nucleus, association of Trx-1 with Ref-1 presumably initiates sequence of gene regulatory events leading to the activation of NFkB and phosphorylation of Akt thereby rendering cardioprotection.