The curious case of peroxiredoxin-5: what its absence in aves can tell us and how it can be used.

BACKGROUND: Peroxiredoxins are ubiquitous thiol-dependent peroxidases that represent a major antioxidant defense in both prokaryotic cells and eukaryotic organisms. Among the six vertebrate peroxiredoxin isoforms, peroxiredoxin-5 (PRDX5) appears to be a particular peroxiredoxin, displaying a different catalytic mechanism, as well as a wider substrate specificity and subcellular distribution. In addition, several evolutionary peculiarities, such as loss of subcellular targeting in certain species, have been reported for this enzyme. RESULTS: Western blotting analyses of 2-cys PRDXs (PRDX1-5) failed to identify the PRDX5 isoform in chicken tissue homogenates. Thereafter, via in silico analysis of PRDX5 orthologs, we went on to show that the PRDX5 gene is conserved in all branches of the amniotes clade, with the exception of aves. Further investigation of bird genomic sequences and expressed tag sequences confirmed the disappearance of the gene, though TRMT112, a gene located closely to the 5' extremity of the PRDX5 gene, is conserved. Finally, using in ovo electroporation to overexpress the long and short forms of human PRDX5, we showed that, though the gene is lost in birds, subcellular targeting of human PRDX5 is conserved in the chick. CONCLUSIONS: Further adding to the distinctiveness of this enzyme, this study reports converging evidence supporting loss of PRDX5 in aves. In-depth analysis revealed that this absence is proper to birds as PRDX5 appears to be conserved in non-avian amniotes. Finally, taking advantage of the in ovo electroporation technique, we validate the subcellular targeting of human PRDX5 in the chick embryo and bring forward this gain-of-function model as a potent way to study PRDX5 functions in vivo.

Thioredoxin-2 Modulates Neuronal Programmed Cell Death in the Embryonic Chick Spinal Cord in Basal and Target-Deprived Conditions.

Thioredoxin-2 (Trx2) is a mitochondrial protein using a dithiol active site to reduce protein disulfides. In addition to the cytoprotective function of this enzyme, several studies have highlighted the implication of Trx2 in cellular signaling events. In particular, growing evidence points to such roles of redox enzymes in developmental processes taking place in the central nervous system. Here, we investigate the potential implication of Trx2 in embryonic development of chick spinal cord. To this end, we first studied the distribution of the enzyme in this tissue and report strong expression of Trx2 in chick embryo post-mitotic neurons at E4.5 and in motor neurons at E6.5. Using in ovo electroporation, we go on to highlight a cytoprotective effect of Trx2 on the programmed cell death (PCD) of neurons during spinal cord development and in a novel cultured spinal cord explant model. These findings suggest an implication of Trx2 in the modulation of developmental PCD of neurons during embryonic development of the spinal cord, possibly through redox regulation mechanisms.

Expression of peroxiredoxins and thioredoxins in the mouse spinal cord during embryonic development.

Reactive oxygen and nitrogen species (ROS/RNS) are natural byproducts of cellular metabolism. Although these molecules are deleterious at high concentrations, moderate levels of ROS/RNS are essential for normal cell function and take part in numerous cellular processes. The regulation of ROS/RNS is largely attended by peroxiredoxins (Prdxs) and their main reductants, thioredoxins (Trxs). Through their oxidoreductase activities, the members of the Trx/Prdx system can also affect certain cellular processes, notably many implicated in central nervous system (CNS) development. Although several studies have investigated the expression of Prdxs and Trxs in mouse, rat, and human adult CNS, few data are available concerning embryonic stages. In this work, we use immunofluorescence analyses to study the distribution of these enzymes during prenatal mouse spinal cord development. Our results highlight several patterns that contrast with available data for the adult. Indeed, Prdx1, Prdx4, and Prdx6, which are expressed in glial cells in the adult CNS, present clear neuronal localization in mouse spinal cord during embryonic development. Additionally, Prdx1, Prdx2, and to a lesser extent Prdx4, Prdx6, and Trx1 are localized mainly in the nucleus of neural cells. Finally, we identified a consistent, intense expression of all Prdxs and Trxs in groups of cells located in ventral regions of the spinal cord that express motor neuronal markers. These striking expression patterns suggest novel functions of these enzymes at these stages and offer clues to the role of the Trx/Prdx system during embryonic development of the spinal cord.