Downregulated Expression of Peroxiredoxin 4 in Granulosa Cells from Polycystic Ovary Syndrome

Peroxiredoxin 4 (PRDX4), a member of Peroxiredoxin (PRDX) family, is a typical 2-Cys PRDX. PRDX4 monitors the oxidative burden within cellular compartment and reduces hydrogen peroxide and alkyl hydroperoxide related to oxidative stress and apoptosis. Antioxidant, like PRDX4, may promote follicle development and participate in the pathophysiology of PCOS. In our previous study, we found that PRDX4 was expressed in mice oocyte cumulus oophorus complex, and that PRDX4 could be associated with follicle development. In this study, we explored the expression of PRDX4 in human follicles and possible role of PRDX4 in PCOS pathophysiology. Our data showed that PRDX4 was mainly expressed in granulosa cells in human ovaries. When compared to control group, both PRDX4 mRNA level and protein level decreased in PCOS group. The lowered levels of PRDX4 may relate to oxidative stress in the pathophysiologic progress of PCOS. Furthermore, expression of PRDX4 in the granulosa cells of in vivo or in vitro matured follicles was higher than that in immatured follicles, which suggested that PRDX4 may have a close relationship with follicular development. Altogether, our findings may provide new clues of the pathophysiologic mechanism of PCOS and potential therapeutic strategy using antioxidant, like PRDX4.     

Antioxidant enzyme peroxiredoxin 5 is upregulated in degenerative human tendon

Peroxiredoxin 5 (PRDX5) is a novel thioredoxin peroxidase recently identified in a variety of human cells and tissues, which is considered to play an important role in oxidative stress protection mechanisms. However, little is known about its expression in tendon degeneration, a common and disabling condition that primarily affects older people, in which oxidative stress may be implicated. The present study demonstrated that normal human tendon expresses PRDX5 and its expression is significantly increased in degenerative tendon. In addition, we have localized PRDX5 to fibroblasts in normal tendon and to both fibroblasts and endothelial cells in degenerate tendon. The differential expression of PRDX5 in normal and degenerate tendon shows that a thioredoxin peroxidase with antioxidant properties is upregulated under pathophysiological conditions and suggests that oxidative stress may be involved in the pathogenesis of tendon degeneration. PRDX5 may play a protective role against oxidative stress during this pathophysiological process.     

Oxidative protein folding by an endoplasmic reticulum-localized peroxiredoxin

Endoplasmic reticulum (ER) oxidation 1 (ERO1) transfers disulfides to protein disulfide isomerase (PDI) and is essential for oxidative protein folding in simple eukaryotes such as yeast and worms. Surprisingly, ERO1-deficient mammalian cells exhibit only a modest delay in disulfide bond formation. To identify ERO1-independent pathways to disulfide bond formation, we purified PDI oxidants with a trapping mutant of PDI. Peroxiredoxin IV (PRDX4) stood out in this list, as the related cytosolic peroxiredoxins are known to form disulfides in the presence of hydroperoxides. Mouse embryo fibroblasts lacking ERO1 were intolerant of PRDX4 knockdown. Introduction of wild-type mammalian PRDX4 into the ER rescued the temperature-sensitive phenotype of an ero1 yeast mutation. In the presence of an H(2)O(2)-generating system, purified PRDX4 oxidized PDI and reconstituted oxidative folding of RNase A. These observations implicate ER-localized PRDX4 in a previously unanticipated, parallel, ERO1-independent pathway that couples hydroperoxide production to oxidative protein folding in mammalian cells.     

Crystal structure of human peroxiredoxin 5, a novel type of mammalian peroxiredoxin at 1.5 A resolution

The peroxiredoxins define an emerging family of peroxidases able to reduce hydrogen peroxide and alkyl hydroperoxides with the use of reducing equivalents derived from thiol-containing donor molecules such as thioredoxin, glutathione, trypanothione and AhpF. Peroxiredoxins have been identified in prokaryotes as well as in eukaryotes. Peroxiredoxin 5 (PRDX5) is a novel type of mammalian thioredoxin peroxidase widely expressed in tissues and located cellularly to mitochondria, peroxisomes and cytosol. Functionally, PRDX5 has been implicated in antioxidant protective mechanisms as well as in signal transduction in cells. We report here the 1.5 A resolution crystal structure of human PRDX5 in its reduced form. The crystal structure reveals that PRDX5 presents a thioredoxin-like domain. Interestingly, the crystal structure shows also that PRDX5 does not form a dimer like other mammalian members of the peroxiredoxin family. In the reduced form of PRDX5, Cys47 and Cys151 are distant of 13.8 A although these two cysteine residues are thought to be involved in peroxide reductase activity by forming an intramolecular disulfide intermediate in the oxidized enzyme. These data suggest that the enzyme would necessitate a conformational change to form a disulfide bond between catalytic Cys47 and Cys151 upon oxidation according to proposed peroxide reduction mechanisms. Moreover, the presence of a benzoate ion, a hydroxyl radical scavenger, was noted close to the active-site pocket. The possible role of benzoate in the antioxidant activity of PRDX5 is discussed.     

Nrf2b, novel zebrafish paralog of oxidant-responsive transcription factor NF-E2-related factor 2 (NRF2)

NF-E2-related factor 2 (NRF2; also called NFE2L2) and related NRF family members regulate antioxidant defenses by activating gene expression via antioxidant response elements (AREs), but their roles in embryonic development are not well understood. We report here that zebrafish (Danio rerio), an important developmental model species, possesses six nrf genes, including duplicated nrf1 and nrf2 genes. We cloned a novel zebrafish nrf2 paralog, nrf2b. The predicted Nrf2b protein sequence shares several domains with the original Nrf2 (now Nrf2a) but lacks the Neh4 transactivation domain. Zebrafish-human comparisons demonstrate conserved synteny involving nrf2 and hox genes, indicating that nrf2a and nrf2b are co-orthologs of human NRF2. nrf2a and nrf2b displayed distinct patterns of expression during embryonic development; nrf2b was more highly expressed at all stages. Embryos in which Nrf2a expression had been knocked down with morpholino oligonucleotides were more sensitive to tert-butylhydroperoxide but not tert-butylhydroquinone, whereas knockdown of Nrf2b did not affect sensitivity of embryos to either chemical. Gene expression profiling by microarray identified a specific role for Nrf2b as a negative regulator of several genes, including p53, cyclin G1, and heme oxygenase 1, in embryos. Nrf2a and Nrf2b exhibited different mechanisms of cross-talk with the Ahr2 signaling pathway. Together, these results demonstrate distinct roles for nrf2a and nrf2b, consistent with subfunction partitioning, and identify a novel negative regulatory role for Nrf2b during development. The identification of zebrafish nrf2 co-orthologs will facilitate new understanding of the multiple roles of NRF2 in protecting vertebrate embryos from oxidative damage.