Abstract 460: Thioredoxin-1 and Its Interaction Partners Control Apoptosis in the Endothelium
In the endothelium, defense against oxidative stress as well as inhibition of apoptosis is mainly mediated by thioredoxin-1 (Trx-1). Trx-1 protein levels are reduced in aged endothelial cells (EC) in vitro and in vivo, leading to increased apoptosis sensitivity. Apoptosis is dependent on (i) cytoskeletal changes resulting in formation of stress fibers (thick bundles of actin), (ii) activation of caspase-3 and (iii) the redox status of the cell. The mechanisms how Trx-1 protects EC against apoptosis are not completely understood, but could involve protein-protein interactions.
We identified three proteins interacting with Trx-1: γ-actin, the p17 subunit of Caspase-3 and the AP-endonuclease 1/redox factor 1 (APEX1). We could show that H2O2-induced stress fiber formation in EC was prevented by exogenously applied or overexpressed Trx-1. Moreover, the interaction between Trx-1 and non-polymerized γ-actin precluded Trx-1 degradation, suggesting a mutual protection of both proteins. Secondly, we observed that Trx-1 overexpression reduces apoptosis induction by the p17 subunit of Caspase-3 in EC. This was corroborated by the identification of a disulfide bridge-dependent interaction of Trx-1 with cysteine 163 in p17 preventing association with the second subunit, p12, which is essential for full activation of Caspase-3. However, interaction of Trx-1 with other proteins is not necessarily dependent on disulfide bridge formation. We could demonstrate that APEX1 can protect EC against apoptosis. Interestingly, we found that Trx-1 and APEX1 associate with each other even after mutation of 3 (APEX1) or 2 (Trx-1) cysteines with the same efficiency as the wildtype proteins. It is conceivable that this interaction is required for the protective effect of APEX1.
Taken together, our data demonstrate the importance of Trx-1 in maintaining endothelial cell integrity mediated by interaction with other proteins, and that apoptosis protection of EC is not only due to its anti-oxidative capacity. Loss of Trx-1 in senescent EC therefore importantly contributes to the increased apoptosis sensitivity observed in during aging.
- © 2012 by American Heart Association, Inc.