Abstract 1010: Endogenous Mitochondrial, But Not Cytosolic Thioredoxin Reductase Protects Against Myocardial Ischemia-reperfusion Injury
Excessive reactive oxygen species (ROS) formation during postischemic reperfusion injury of the heart contributes to tissue injury and functional deterioration of the heart. Besides glutathione, thioredoxin (Txn) is an important enzyme for ROS reduction. Two isoforms of thioredoxin-regenerating enzymes are known in the heart, cytosolic Txn-reductase 1 (Txnrd1) and mitochondrial Txnrd2. Heart specific deletion of Txnrd1 results in viable mice strains, while heart specific deletion Txnrd2 results in 100% neonatal death. To circumnavigate this restriction, we generated an inducible heart specific cre-mediated Txnrd2-knock out mouse, allowing for a 70% reduction of heart specific Txnrd2-activity tamoxifen-induction (Kiermayer et al., Genesis 2007). Methods: After 5 weeks of tamoxifen and 4 weeks regular diet, a 90 minutes LAD-occlusion (ischemia =I) was followed by 24 hours or 14 days of reperfusion (R) in wildtype (WT), Txnrd1 −/ − (KO-1) and Txnrd2-/lox(Tg[aMHC-MERCreMER]) (KO-2) mice (n = 8 per group). Left ventricular (LV) functional reserve was analysed invasively using Millar tip catheter with increasing concentration of norepinephrine (NE). Furthermore, infarct size in relation to the left ventricle was analysed planimetrically after histological staining ex vivo after 14d of I/R. Results: 24h after I/R, LV developed pressure (LVDP) was significantly impaired WT controls (82,3 ± 2mmHg* vs. 101 ± 2mmHg in sham group). Whereas KO-1 animals did not display a further loss of LV function (79 ± 3mmHg), KO-2 animals suffered from further reduction of LVDP (71,6 ± 3mmHg, p<0,05 vs. WT). Application of N-acetyl-cysteine (N-Ac, 15μMol i.p.) antagonized the KO-2 specific loss of LV-function (82,3 ± 2mmHg). After 14 days of I/R the size of LV-infarction increased in KO-2 animals (25 ± 2,5%*) compared to KO-1 (20 ± 4%) or WT-controls (19 ± 1,3%, n=5, *p<0,05 vs. WT). Summary: Here we show for the first time that mitochondrial, but not cytosolic thioredoxin reductase is essential for protective ROS-scavenging in myocardial ischemia and reperfusion in vivo.