Search

2-Cysteine (Cys) peroxiredoxins (Prxs), which include mammalian Prxs I-IV, possess two conserved Cys residues that are readily oxidized by H2O2 to form a disulfide. In the case of Prx I-III, the disulfide is reduced by thioredoxin, thus enabling these proteins to function as peroxidases. Prx IV was shown previously to be synthesized as a 31-kDa polypeptide with an NH2-terminal signal peptide that is subsequently cleaved to generate a 27-kDa form of the protein that is localized to the endoplasmic reticulum. A form of Prx IV, larger than 27 kDa revealed by immunoblot analysis was suggested to represent the unprocessed, 31-kDa form, but this larger form was detected only in spermatids of the postpubertal testis. We now show that the larger form of Prx IV (here designated Prx IV-L) detected in the testis is actually a product of alternative transcription of the Prx IV gene that is encoded by newly identified exon1Atogether with exons 2-7 that are shared with the 27-kDa form (designated Prx IV-S). Prx IV-L was detected in spermatids but not in mature sperm, it could form disulfide-linked dimers but not higher order oligomers via oxidation, and it was resistant to hyperoxidation unless additional reductant was added, suggesting that its peroxidase activity is limited in vivo. Phylogenetic analysis showed that the Prx IV-S gene is present in all vertebrates examined, whereas the Prx IV-L gene was detected only in placental mammals.Wesuggest that Prx IV-L functions as an H2O2 sensor that mediates protein thiol oxidation required for the maturation of spermatozoa in placental mammals. [ABSTRACT FROM AUTHOR]

Thioredoxin/glutathione reductase (TXNRD3) is a selenoprotein composed of thioredoxin reductase and glutaredoxin domains. This NADPH-dependent thiol oxidoreductase evolved through gene duplication within the Txnrd family, is expressed in the testes, and can reduce both thioredoxin and glutathione in vitro; however, the function of this enzyme remains unknown. To characterize the function of TXNRD3 in vivo, we generated a strain of mice bearing deletion of Txnrd3 gene. We show that these Txnrd3 knockout mice are viable and without discernable gross phenotypes, and also that TXNRD3 deficiency leads to fertility impairment in male mice. We found that Txnrd3 knockout animals exhibited a lower fertilization rate in vitro, a sperm movement phenotype, and an altered thiol redox status in sperm cells. Proteomic analyses further revealed a broad range of substrates reduced by TXNRD3 during sperm maturation, presumably as a part of sperm quality control. Taken together, these results show that TXNRD3 plays a critical role in male reproduction via the thiol redox control of spermatogenesis. [ABSTRACT FROM AUTHOR]

C/EBPα is highly expressed in liver and regulates many genes that are preferentially expressed in liver. Because C/EBPα-null mice die soon after birth, it is impossible to analyze the function of C/EBPα in the adult with this model. To address the function of C/EBPα in adult hepatocytes, liver-specific C/EBPα-null mice were produced using a floxed C/EBPα allele and the albuminCre transgene. Unlike whole body C/EBPα-null mice, mice lacking hepatic C/EBPα expression did not exhibit hypoglycemia, nor did they show reduced hepatic glycogen in adult. Expression of liver glycogen synthase, phosphoenolpyruvate carboxykinase, and glucose-6phosphatase remained at normal levels. However, these mice exhibited impaired glucose tolerance due in part to reduced expression of hepatic glucokinase, and hyperammonemia from reduced expression of hepatic carbamoyl phosphate synthase-I. These mice also had reduced serum cholesterol and steatotic livers that was exacerbated with aging. This phenotype could be explained by increased expression of hepatic lipoprotein lipase and reduced expression of microsomal triglyceride transfer protein, apolipoproteins B100, and A-IV. These data demonstrate that hepatic C/EBPα is critical for ammonia detoxification and glucose and lipid homeostasis in adult mice. [ABSTRACT FROM AUTHOR]