Impaired cross-talk between the thioredoxin and glutathione systems is related to ASK-1 mediated apoptosis in neuronal cells exposed to mercury

Abstract

Mercury (Hg) compounds target both cysteine (Cys) and selenocysteine (Sec) residues in peptides and proteins. Thus, the components of the two major cellular antioxidant systems – glutathione (GSH) and thioredoxin (Trx) systems – are likely targets for mercurials. Hg exposure results in GSH depletion and Trx and thioredoxin reductase (TrxR) are prime targets for mercury. These systems have a wide-range of common functions and interaction between their components has been reported. However, toxic effects over both systems are normally treated as isolated events.To study how the interaction between the glutathione and thioredoxin systems is affected by Hg, human neuroblastoma (SH-SY5Y) cells were exposed to 1 and 5 μM of inorganic mercury (Hg2+), methylmercury (MeHg) or ethylmercury (EtHg) and examined for TrxR, GSH and Grx levels and activities, as well as for Trx redox state. Phosphorylation of apoptosis signalling kinase 1 (ASK1), caspase-3 activity and the number of apoptotic cells were evaluated to investigate the induction of Trx-mediated apoptotic cell death. Additionally, primary cerebellar neurons from mice depleted of mitochondrial Grx2 (mGrx2D) were used to examine the link between Grx activity and Trx function.Results showed that Trx was affected at higher exposure levels than TrxR, especially for EtHg. GSH levels were only significantly affected by exposure to a high concentration of EtHg. Depletion of GSH with buthionine sulfoximine (BSO) severely increased Trx oxidation by Hg. Notably, EtHg-induced oxidation of Trx was significantly enhanced in primary neurons of mGrx2D mice. Our results suggest that GSH/Grx acts as backups for TrxR in neuronal cells to maintain Trx turnover during Hg exposure, thus linking different mechanisms of molecular and cellular toxicity. Finally, Trx oxidation by Hg compounds was associated to apoptotic hallmarks, including increased ASK-1 phosphorylation, caspase-3 activation and increased number of apoptotic cells.

Sevoflurane preconditioning induces tolerance to brain ischemia partially via inhibiting thioredoxin-1 nitration

“…3 b, rats pre-treated with sevoflurane had better post-ischemic behavioral outcomes than those with oxygen vehicle (11 [ 10 , 13 ] vs. 9 [ 8 , 9 ], P < 0.05). However, this amelioration in neurological scoring was reversed by the 3-N-Trx-1 (8 [ 7 , 8 ] vs. 11 [ 10 , 13 ], P < 0.05), but not hTrx-1 (11 [ 10 , 13 ] vs. 12 [ 10 , 14 ], P > 0.05). 3-N-Trx-1 group and hTrx-1 group also showed significant difference in behavioral scores.…”

“…Intraperitoneal administration of recombinant human Trx-1 (hTrx-1) protected brain damage from ischemic stroke [ 7 ], while reducing the level of Trx-1 by small interfering RNA deteriorated the cerebral injury [ 8 ]. In addition, the anti-apoptosis effect of Trx-1could be realized by interacting with apoptosis-regulating kinase-1 signaling [ 9 , 10 ] .The recent studies have also authenticated that nitrative modification inactivated Trx-1 after heart ischemia, which resulted in myocardial apoptosis [ 11 ].…”

Small molecule inhibitors of mammalian thioredoxin reductase as potential anticancer agents: An update

“…Reduced Trxs perform most functions of the thioredoxin system via interacting with various downstream proteins to form oxidized Trxs, and the disulfide bridge in the active site of oxidized Trxs must be regenerated to a dithiol form by TrxRs. Although, the glutathione system has been reported to act as a backup to maintain Trxs in a reduced state, TrxRs are still considered as the primary reductases in reducing the oxidized Trxs in vivo, and thus the functions of the thioredoxin system are heavily determined by the activity of TrxRs (Figure ).…”

Identification of phenazine analogue as a novel scaffold for thioredoxin reductase I inhibitors against Hep G2 cancer cell lines

“…At the begining of the protein profiles of the downstream protein molecules, ASK1, a member of mitogen-activated protein kinase (MAPK) family, was chosen as the first molecule to be investigated, which is not only combined to reduce Trx1 directly but also can induce apoptosis in cancer cells at free molecule status 25 . Since reduced Trx1, but not the oxided Trx1 is known to bind with ASK-1 to repress its activities 26 , we firstly obtained the potein levels of ASK-1 before and after treated with CPUL1 by western blot analysis. In agreement with this, increased levels (1.6 folds) of ASK1 were found in HepG2 cells after exposed to 4 µM of CPUL1 for 24 h (Figure 3(A,B)), which is consistent with the increased oxidation levels of Trx1 previously observed in Figure 2(D).…”