TXN2

Abstract: Overexpression of human manganese superoxide dismutase (MnSOD) in mouse NIH/3T3 cells using an inducible retroviral system led toalterations in the mitochondrial redox state since levels of reactive oxygen species rapidly increased after induction of human MnSOD(Antioxid. Redox Signal. 6:489–500; 2004). Alterations in exogenous human MnSOD led to large increases in levels of endogenous mouseMnSOD (sod2) and thioredoxin 2 (txn2) mRNAs, but smaller increases in MnSOD and thioredoxin 2 protein expression. Tight regulation ofmitochondrial protein levels seems to be necessary for optimal cellular function, since mitochondrial antioxidant protein levels did notincrease to the same extent as antioxidant protein mRNA levels. We hypothesize that these changes in antioxidant proteins are adaptations tothe altered mitochondrial redox state elicited by MnSOD overexpression. The mitochondrial-specific antioxidant MitoQ reversed cell growthinhibition, and greatly decreased levels of endogenous sod2 and txn2 transcripts following induction of exogenous MnSOD. Elevated levelsof mouse sod2 transcripts resulted from transcriptional activation of the endogenous sod2 gene since actinomycin D prevented transcriptionof this gene. Therefore, the mitochondrial redox state appears to modulate a nuclear-driven biochemical event, i.e., transcriptional activationof a nuclear gene encoding a protein targeted to mitochondria.D 2004 Elsevier Inc. All rights reserved.

Abstract: Objective: In this study, the effects of overexpression of thioredoxin 2 (Trx2) on aging and age-related diseases were examined using Trx2 transgenic mice [Tg(TXN2)+/0]. Because our previous studies demonstrated that thioredoxin (Trx) overexpression in the cytosol (Trx1) did not extend maximum lifespan, this study was conducted to test if increased Trx2 expression in mitochondria shows beneficial effects on aging and age-related pathology. Methods: Trx2 transgenic mice were generated using a fragment of the human genome containing the TXN2 gene. Effects of Trx2 overexpression on survival, age-related pathology, oxidative stress, and redox-sensitive signaling pathways were examined in male Tg(TXN2)+/0 mice. Results: Trx2 levels were significantly higher (approximately 1.6- to 5-fold) in all of the tissues we examined in Tg(TXN2)+/0 mice compared to wild-type (WT) littermates, and the expression levels were maintained during aging (up to 22-24 months old). Trx2 overexpression did not alter the levels of Trx1, glutaredoxin, glutathione, or other major antioxidant enzymes. Overexpression of Trx2 was associated with reduced reactive oxygen species (ROS) production from mitochondria and lower isoprostane levels compared to WT mice. When we conducted the survival study, male Tg(TXN2)+/0 mice showed a slight extension (approximately 8-9%) of mean, median, and 10th percentile lifespans; however, the survival curve was not significantly different from WT mice. Cross-sectional pathological analysis (22-24 months old) showed that Tg(TXN2)+/0 mice had a slightly higher severity of lymphoma; however, tumor burden, disease burden, and severity of glomerulonephritis and inflammation were similar to WT mice. Trx2 overexpression was also associated with higher c-Jun and c-Fos levels; however, mTOR activity and levels of NFκB p65 and p50 were similar to WT littermates. Conclusions: Our findings suggest that the increased levels of Trx2 in mitochondria over the lifespan in Tg(TXN2)+/0 mice showed a slight life-extending effect, reduced ROS production from mitochondria and oxidative damage to lipids, but showed no significant effects on aging and and age-related diseases. Keywords: Thioredoxin, transgenic Mouse, oxidative stress, aging