Abstract 155: Thioredoxin 1 Is Persistently Oxidized (inactive) In Failing Hearts, Due To Lower Trx1 Reductase Expression/activity And Nadph Bioavailability.
The thioredoxin 1 (Trx1) system, consisting of Trx1, Trx1 reductase (TrxR1) and NADPH is a major contributor to antioxidant defenses and redox signaling in the heart and most other tissues.The active site of Trx1 becomes oxidized and must be regenerated by TrxR1 using electrons from NADPH. Although Trx1 expression is up-regulated in human congestive heart failure (CHF), persistent oxidative stress is evident in this syndrome. We hypothesized that the other components of the thioredoxin system may be impaired in CHF, resulting in an overall decrease in its function. To test this, mice overexpressing Gαq (Gαq), displaying severe cardiomyopathy, were compared to FVBN mice (WT) in terms of Trx1 and TrxR1 levels (western blot), NADPH levels (HPLC) and Trx1 redox state (redox WB). In addition, the redox state of glutathione was assessed by HPLC. In Gαq hearts, a 10-fold increase in Trx1 protein was evident as compared to WT (from 24 ± 5 to 266 ± 50 A.U., n=15). In contrast, there was a 44% decrease in TrxR1 protein level (from 101 ± 8 to 57 ± 7 A.U. in Gαq, p<0.005). Also NADPH declined in Gαq from 13.5 ± 1.3 to 4 ± 0.3 nmol/g wet weight (p<0.005). Accordingly, the fraction of the Trx1 pool that was in the oxidized (inactive) form increased 2-fold in Gαq hearts. Glutathione, the other major thiol antioxidant, was also more oxidized in failing hearts; reduced glutathione (GSH) dropped from 1121 ± 93 to 682 ± 32 nmol/g wet weight (p=0.013, n=5) while oxidized glutathione (GSSG) rose from 10.4 ± 0.8 to 56 ± 3 nmol/g wet weight (p<0.0005). Our data show for the first time that the Trx1 system is markedly impaired in failing hearts. These changes stem from loss of TrxR1 and lack of NADPH bioavailability, resulting in lower levels of active Trx1. Thus, enhancing TrxR1 signal may represent an additional strategy to re-establish a proper redox balance in the CHF heart, in order to counter maladaptive remodeling and cardiac dysfunction.