The Mitochondrial Thioredoxin Is Required For Liver Development In Zebrafish

Thioredoxins (Trxs) maintain the balance of cellular redox status to prevent cells from oxidative stresses and also have a crucial role in the apoptosis, neuroprotection and inflammatory reaction. All Trxs have a canonical CXXC catalytic motif and reduce substrate proteins with the action of NAPDH and TrxR. Protein de-nitrosylation and trans-nitrosylation by cytosolic and mitochondrial Trxs were proposed in recent report. Trx2is a redox protein located in mitochondria. Mitochondria are the energy factories of the cells and Electron transfer and oxidative phosphorylation occur in mitochondria. Oxidative stress can induce apoptosis by the release of cytochrome c and other apoptotic factors from the mitochondria. A loss of the mitochondrial membrane potential will induce cell death irreversibly. So, normal mitochondrial function is essential to cell growth. Trx2plays an essential role in scavenging increased ROS (reactive oxygen species) in mitochondria. The anti-apoptotic function of Trx2has been persistently focusing on. Overexpression of Trx2in143B cells protect against TBH (tert butyl hydroperoxide)-induced cell cytotoxicity. In human HEK-293cells, Trx2can protect cells from etoposide-induced cell death and increased mitochondrial membrane potential. Trx2conditional knockout in chicken DT40cell caused an elevated ROS levels and apoptosis.Little is known about the contribution of Trx2during embryogenesis. The absence of mitochondrial thioredoxin2caused massive apoptosis and early embryonic lethality in homozygous mice. To Trx2(+/-) heterozygous mice, increased oxidative damage were found to DNA, protein and lipid in liver although the mice were fertile and had no gross defect. Under oxidative stress, the liver of heterozygous mice showed increased more apoptosis compare to wt livers. Also a lower ATP production and increased H2O2levels existed in heterozygous mice because of impared mitochondrial fuction. So, we performed Trx2knockdown in zebrafish to thoroughly investigate the role of Trx2during liver development. First we performed RT-PCR and in situ with zebrafish embryos and found that Trx2spcecially expressed in zebrafish liver. Then we conducted Trx2knockdown in zebrafish by two morphanlinos and found Trx2knockdown in zebrafish could induce severe liver cell death but little effect on cell proliferation. Moreover, Trx2knockdown led to a defect in denitrosylation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In HepG2, the increase of S-nitrosylated GAPDH triggered by Trx2knockdown promoted the nuclear translocation of GAPDH and then the acetylation of p53which activates the apoptosis related genes, such as bax and puma. We also found increased bax and puma in vivo. Here, we propose a novel mechanism of cell death induced by Trx2konck-down and it suggests that Trx2play an important role in the eary liver development.