Thioredoxin Reductase Deficiency Potentiates Oxidative Stress, Mitochondrial Dysfunction and Cell Death in Dopaminergic Cells

Abstract

Mitochondria are considered major generators of cellular reactive oxygen species (ROS) which are implicated in the pathogenesis of neurodegenerative diseases such as Parkinson’s disease (PD). We have recently shown that isolated mitochondria consume hydrogen peroxide (H2O2) in a substrate- and respiration-dependent manner predominantly via the thioredoxin/peroxiredoxin (Trx/Prx) system. The goal of this study was to determine the role of Trx/Prx system in dopaminergic cell death. We asked if pharmacological and lentiviral inhibition of the Trx/Prx system sensitized dopaminergic cells to mitochondrial dysfunction, increased steady-state H2O2 levels and death in response to toxicants implicated in PD. Incubation of N27 dopaminergic cells or primary rat mesencephalic cultures with the Trx reductase (TrxR) inhibitor auranofin in the presence of sub-toxic concentrations of parkinsonian toxicants paraquat; PQ or 6-hydroxydopamine; 6OHDA (for N27 cells) resulted in a synergistic increase in H2O2 levels and subsequent cell death. shRNA targeting the mitochondrial thioredoxin reductase (TrxR2) in N27 cells confirmed the effects of pharmacological inhibition. A synergistic decrease in maximal and reserve respiratory capacity was observed in auranofin treated cells and TrxR2 deficient cells following incubation with PQ or 6OHDA. Additionally, TrxR2 deficient cells showed decreased basal mitochondrial oxygen consumption rates. These data demonstrate that inhibition of the mitochondrial Trx/Prx system sensitizes dopaminergic cells to mitochondrial dysfunction, increased steady-state H2O2, and cell death. Therefore, in addition to their role in the production of cellular H2O2 the mitochondrial Trx/Prx system serve as a major sink for cellular H2O2 and its disruption may contribute to dopaminergic pathology associated with PD.

RA Differentiation Enhances Dopaminergic Features, Changes Redox Parameters, and Increases Dopamine Transporter Dependency in 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Cells

“…Cellular resistance to H 2 O 2 in the neuronal phenotype can be explained by the elevated basal antioxidant capacity. Since the RA-induced differentiation decreases levels of TrxR and GSH, this may suggests a role of these antioxidants in 6-OHDA detoxification, as previously described (SotoOtero et al 2000;Lopert et al 2012). Hence, the resistance to 6-OHDA found in undifferentiated cells can be explained, at least in part, by the high GSH levels presented in the tumoral phenotype.…”

“…The H 2 O 2 detoxification in neuronal cells is catalyzed primarily by thioredoxin and glutathione systems, which are the most important antioxidants in the brain (Lopert et al 2012;Garcia-Garcia et al 2012), hence we found that both models mimic the oxidative neuronal profile.…”

Post-translational Activation of Glutamate Cysteine Ligase with Dimercaprol

“…LDH activity was measured in media and cell lysates collected in a Tris/NaCl lysis buffer containing 0.1% Triton (v/v), as described previously (85). Activity was measured spectrophotometrically at 30°C as the amount of pyruvate consumed, by monitoring the decrease in absorbance because of NADH oxidation at 340 nm.…”

A unique thioredoxin reductase plays defensive roles against oxidative, nitrosative and nutritional stresses in Schizosaccharomyces pombe

“…Yeast cells lacking TrxR have reduced abilities to detoxify oxidants and to repair oxidative damage (Carmel-Harel et al, 2001). Disruption of TrxR elevates oxidative stress, mitochondrial dysfunction, and cell death in dopaminergic cells (Lopert et al, 2012). TrxR inhibitors cause growth inhibition and apoptosis in various cancer cells, indicating a relationship between TrxR inactivation and apoptosis or inhibition of cell growth (Zhao et al, 2005).…”