Addressing the Role of Mitochondrial Thioredoxin Reductase and xCT in the Maintenance of Redox Homeostasis

The thioredoxin system, along with the glutathione (GSH)-dependent system, is critically involved in the maintenance of the intracellular redox balance. The thioredoxin dependent system consists of thioredoxin reductases, thioredoxins and thioredoxin-dependent peroxidases. The mitochondrial thioredoxin reductase (Txnrd2) is an important component of the mitochondrial antioxidant system. Using Txnrd2 null cells we show that Txnrd2−/− cells produced more ROS, and were highly susceptible to different prooxiditans and GSH depletion. Administration of various antioxidants, such as NAC, GSH and α-Toc, reverted the phenotyp of the Txnrd2−/− cells. The up-regulation of the mitochondrial peroxiredoxins Prx III and Prx V and sulfiredoxin transcripts in Txnrd2−/− cells could be a compensatory mechanism for loss of Txnrd2. However, under oxidative stress, Txnrd2−/− cells showed higher amount of overoxidation of Prx I and PrxII/PrxIII indicating that in absence of Txnrd2 ROS scavenging efficiency of Trx2-Prx system is greatly compromised. Oxidative stress has been implicated in cardiovascular diseases, including infarction and heart failure. Disruption of Txnrd2 leads to perturbed heart development and embryonic lethality in mice. Heart-specific Txnrd2 disruption causes post-natal death due to biventricular dilatation of the heart and mitochondrial aberrations of cardiomyocytes. Additional evidence for a possible involvement of Txnrd2 in the pathogenesis of cardiac diseases came form the study of the patients suffering from dialated cardiomyopathy (DCM). By DNA sequence analysis of these samples, we found two novel mutations (Ala59Thr and Gly375Arg) in TXNRD2. Stable expression of murine Txnrd2 harboring these two mutations in Txnrd2−/− cells showed a dominant negative effect and were unable to rescue the cells from GSH depletion. Our data strongly suggest that the mutations found in a small percentage of DCM cases might be due to loss of Txnrd2 functions. The cellular redox balance is maintained by thioredoxin- and GSH-dependent system along with Cys/(Cys)2-cycle which is a distinct redox node of major importance. Previous study in the lab showed that the essential requirement of GSH can be bypassed by the Cys/(Cys)2-cycle. To gain further insights into the role of the thioredoxin system being a driving force for the Cys/(Cys)2-cycle, xCT was overexpressed in Txnrd2−/− fibroblasts. xCT overexpression rescued the Txnrd2−/− cells form GSH depletion. This suggests that the (Cys)2/Cys redox cycle is functional and intact even in the absence of GSH and/or mitochondrial thioredoxin reductase. In a parallel study, we found that cytosolic thioredoxin reductase (Txnrd1) is the driving force behind the Cys/(Cys)2 redox cycle. xCT epression provided growth advantages in culture conditions. In order to recapitulate our findings in vivo, we generated xCT knock-in mice, in which xCT expression can be induced in a spatio-temporal manner by tamoxifen. To our great surprise, overexpression of xCT in mice resulted in adverse effects like atrophy of spleen, thymus and testis, defective erythropoiesis and ultimately death after 5 weeks of induction. Detailed analysis of the bone marrow revealed that although there is an increase in the hematopoietic stem cell population, xCT overexpression leads to impaired erythropoiesis. The observed paradox with xCT overexpression could be due to glutamate-mediated toxicity or impaired redox balance

Differences in attitudes of operators and managers on risk management of pressure equipment

Objectives. Previous research indicates that models for risk assessment of pressure equipment have not sufficiently or adequately integrated indicators of human factors and organizational factors. Methods. The goal of this article is to check the differences in attitudes of operators and managers engaged in the area of pressure equipment risk management. A questionnaire was designed and data were then collected from 253 operators and managers working with the same pressure equipment in Serbia. By applying a paired t test, differences in their attitudes were checked for issues described by the constructs of communication (COM), potentially hazardous materials and equipment (PHME), process safety (PS), safety and health at work (SHW), organizational change management (OCM), maintenance/inspection (MI) procedures, human error (HE), trainings and competences of employees for crisis situations (TCECS) and conducting research after accidents (CRAA). Results. It is statistically evident that the coincidence of attitudes accounted for less than 20% of questions. The highest coincidence is shown for PHME and TCECS, where one-half of the dimensions of the given constructs indicate that there are no statistically significant differences. Conclusions. The differences found could be used as an explanation for high-risk levels of pressure equipment exploitation and how they influence it