Inhibitory role of peroxiredoxin II (Prx II) on cellular senescence

Exercise, healthy ageing, and the potential role of small extracellular vesicles

Extracellular vesicles (EVs) can be released from most cells in the body and act as intercellular messengers transferring information in their cargo to affect cellular function. A growing body of evidence suggests that a subset of EVs, referred to here as 'small extracellular vesicles' (sEVs), can accelerate or slow the processes of ageing and age-related diseases dependent on their molecular cargo and cellular origin. Continued exploration of the vast complexity of the sEV cargo aims to further characterise these systemic vehicles that may be targeted to ameliorate age-related pathologies. Marked progress in the development of mass spectrometry-based technologies means that it is now possible to characterise a significant proportion of the proteome of sEVs (surface and cargo) via unbiased proteomics. This information is vital for identifying biomarkers and the development of sEV-based therapeutics in the context of ageing. Although exercise and physical activity are prominent features in maintaining health in advancing years, the mechanisms responsible are unclear. A potential mechanism by which plasma sEVs released during exercise could influence ageing and senescence is via the increased delivery of cargo proteins that function as antioxidant enzymes or inhibitors of senescence. These have been observed to increase in sEVs following acute and chronic exercise, as identified via independent interrogation of high coverage, publicly available proteomic datasets. Establishing tropism and exchange of functionally active proteins by these processes represents a promising line of enquiry in implicating sEVs as biologically relevant mediators of the ageing process.

Peroxiredoxin 2 deficiency does not affect insulin resistance and oxidative stress in high-fat diet-fed obese mice

OBJECTIVE

To examine if peroxiredoxin 2 (Prx2) deficiency aggravates high-fat diet-induced insulin resistance.

MATERIAL AND METHODS

Insulin sensitivity was measured in Prx2 knockout (KO) and wild-type (WT) littermates using the hyperinsulinemic-euglycemic clamp.

RESULTS

Whole body glucose turnover, glucose uptake, and levels of glucose transporter 4 (Glut4) protein in the skeletal muscle were found to be lower. This was followed by increased expression of oxidative stress markers in Prx2 KO mice than that in WT mice in the control diet group. Although, a 12-week high-fat diet induced insulin resistance and enhanced oxidative stress in both genotypes, there was no difference between WT and Prx2 KO mice with respect to insulin sensitivity and the level of oxidative stress markers. Accordingly, the levels of phosphorylated Akt and Glut4 were similar between the two genotypes.

CONCLUSION

These results suggest that Prx2 does not affect high-fat diet-induced oxidative stress and insulin resistance in mice.

Deletion of Peroxiredoxin II Inhibits the Growth of Mouse Primary Mesenchymal Stem Cells Through Induction of the G0/G1 Cell-cycle Arrest and Activation of AKT/GSK3β/β-Catenin Signaling

BACKGROUND/AIM

Dermal mesenchymal stem cells (DMSCs) are pluripotent stem cells found in the skin which maintain the thickness of the dermal layer and participate in skin wound healing.

MATERIALS AND METHODS

The MTT assay was performed to detect cell proliferation and cell-cycle progression and cell-surface markers were assessed by flow cytometry. The levels of proteins in related signaling pathways were detected by western blotting assay and the translocation of β-catenin into the nucleus were detected by immunofluorescence. Red oil O staining was performed to examine the differentiational ability of DMSCs.

RESULTS

Knockout of PRDX2 inhibited DMSC cell growth, and cell-cycle arrest at G₀/G₁ phase; p16, p21 and cyclin D1 expression levels in Prdx2 knockout DMSCs were significantly increased. Furthermore, AKT phosphorylation were significantly increased in Prdx2 knockout DMSCs, GSK3β activity were inhibited, result in β-Catenin accumulated in the nucleus.

CONCLUSION

In conclusion, these results demonstrated that PRDX2 plays a pivotal role in regulating the proliferation of DMSCs, and this is closely related to the AKT/glycogen synthase kinase 3 beta/β-catenin signaling pathway.

Knockout Mouse Models for Peroxiredoxins

Peroxiredoxins (PRDXs) are members of a highly conserved peroxidase family and maintain intracellular reactive oxygen species (ROS) homeostasis. The family members are expressed in most organisms and involved in various biological processes, such as cellular protection against ROS, inflammation, carcinogenesis, atherosclerosis, heart diseases, and metabolism. In mammals, six PRDX members have been identified and are subdivided into three subfamilies: typical 2-Cys (PRDX1, PRDX2, PRDX3, and PRDX4), atypical 2-Cys (PRDX5), and 1-Cys (PRDX6) subfamilies. Knockout mouse models of PRDXs have been developed to investigate their in vivo roles. This review presents an overview of the knockout mouse models of PRDXs with emphases on the biological and physiological changes of these model mice.

Effects of Peroxiredoxin 2 in Neurological Disorders: A Review of its Molecular Mechanisms

Oxidative stress and neuroinflammation are closely related to the pathological processes of neurological disorders. Peroxiredoxin 2 (Prdx2) is an abundant antioxidant enzyme in the central nervous system. Prdx2 reduces the production of reactive oxygen species and participates in regulating various signaling pathways in neurons by catalyzing hydrogen peroxide (H₂O₂), thereby protecting neurons against oxidative stress and an inflammatory injury. However, the spillage of Prdx2, as damage-associated molecular patterns, accelerates brain damage after stroke by activating an inflammatory response. The post-translational modifications of Prdx2 also affect its enzyme activity. This review focuses on the effects of Prdx2 and its molecular mechanisms in various neurological disorders.

Redox Balance Keepers and Possible Cell Functions Managed by Redox Homeostasis in Trypanosoma cruzi

The toxicity of oxygen and nitrogen reactive species appears to be merely the tip of the iceberg in the world of redox homeostasis. Now, oxidative stress can be seen as a two-sided process; at high concentrations, it causes damage to biomolecules, and thus, trypanosomes have evolved a strong antioxidant defense system to cope with these stressors. At low concentrations, oxidants are essential for cell signaling, and in fact, the oxidants/antioxidants balance may be able to trigger different cell fates. In this comprehensive review, we discuss the current knowledge of the oxidant environment experienced by T. cruzi along the different phases of its life cycle, and the molecular tools exploited by this pathogen to deal with oxidative stress, for better or worse. Further, we discuss the possible redox-regulated processes that could be governed by this oxidative context. Most of the current research has addressed the importance of the trypanosomes' antioxidant network based on its detox activity of harmful species; however, new efforts are necessary to highlight other functions of this network and the mechanisms underlying the fine regulation of the defense machinery, as this represents a master key to hinder crucial pathogen functions. Understanding the relevance of this balance keeper program in parasite biology will give us new perspectives to delineate improved treatment strategies.

Peroxiredoxin2 Deficiency Aggravates Aging-Induced Insulin Resistance and Declines Muscle Strength

This study examined the role of peroxiredoxin2 (Prx2) in aging-induced insulin resistance and reduction in skeletal muscle function in young (2-month-old) and old (24-month-old) Prx2 knockout (KO) and wild-type mice. Plasma insulin levels increased with aging in Prx2 KO mice but not in wild-type mice. Insulin sensitivity in the whole-body and skeletal muscle as assessed with the hyperinsulinemic-euglycemic clamp was lower in Prx2 KO mice than in wild-type mice in the old group but was not significantly different between the two genotypes in the young group. Insulin-induced activation of intracellular signaling molecules was also suppressed in old Prx2 KO mice compared to their wild-type littermates. Oxidative stress, inflammation, and p53 expression levels in skeletal muscle were higher in Prx2 KO mice than in wild-type mice in the old group but were not different between the two genotypes in the young group. p53 expression was negatively correlated with skeletal muscle insulin sensitivity in old mice. Skeletal muscle mass was similar between the two genotypes but grip strength was reduced in old Prx2 KO mice compared to old wild-type mice. These results suggest that Prx2 plays a protective role in aging-induced insulin resistance and declines in muscle strength by suppressing oxidative stress.

Peroxiredoxin II negatively regulates BMP2-induced osteoblast differentiation and bone formation via PP2A Cα-mediated Smad1/5/9 dephosphorylation

Peroxiredoxin II (Prx II), an antioxidant enzyme in the Prx family, reduces oxidative stress by decreasing the intracellular ROS levels. Osteoblast differentiation is promoted by bone morphogenetic protein 2 (BMP2), which upregulates the expression of osteoblast differentiation marker genes, through Smad1/5/9 phosphorylation. We found that Prx II expression was increased by a high dose of lipopolysaccharide (LPS) but was not increased by a low dose of LPS. Prx II itself caused a decrease in the osteogenic gene expression, alkaline phosphatase (ALP) activity, and Smad1/5/9 phosphorylation induced by BMP2. In addition, BMP2-induced osteogenic gene expression and ALP activity were higher in Prx II knockout (KO) cells than they were in wild-type (WT) cells. These inhibitory effects were mediated by protein phosphatase 2A Cα (PP2A Cα), which was increased and is known to induce the dephosphorylation of Smad1/5/9. The overexpression of Prx II increased the expression of PP2A Cα, and PP2A Cα was not expressed in Prx II KO cells. Moreover, PP2A Cα reduced the level of BMP2-induced osteogenic gene expression and Smad1/5/9 phosphorylation. LPS inhibited BMP2-induced Smad1/5/9 phosphorylation and the suppressed phosphorylation was restored by the PP2A inhibitor okadaic acid (OA). Bone phenotype analyses using microcomputed tomography (μCT) revealed that the Prx II KO mice had higher levels of bone mass than the levels of the WT mice. We hypothesize that Prx II has a negative role in osteoblast differentiation through the PP2A-dependent dephosphorylation of Smad1/5/9.

An antioxidant enzyme actively works to reduce bone synthesis under oxidative stress conditions in order to protect bone cells from damage and cell death. Bone is generated by cells called osteoblasts, which differentiate from stem cells. In osteoporosis and diabetes, excessive reactive oxygen species (ROS) within cells can disrupt osteoblast differentiation. South Korean researchers led by Eun-jung Kim at Kyungpook National University, Daegu, and Won-Gu Jang at Daegu University, Gyeongbuk, have shown that an antioxidant enzyme, peroxiredoxin II (PrxII), helps regulate bone formation under oxidative stress. The team generated PrxII-deficient mice and compared them with healthy normal mice. Under oxidative stress conditions, the mice had higher bone mass and higher expression of genes related to bone formation than the normal mice. PrxII limits osteoblast differentiation during elevated ROS by influencing associated protein activity and signalling pathways.

Highly Purified Human Extracellular Vesicles Produced by Stem Cells Alleviate Aging Cellular Phenotypes of Senescent Human Cells

Extracellular vesicles (EVs), including exosomes and microvesicles, mediate intercellular communications and exert various biological activities via delivering unique cargos of functional molecules such as RNAs and proteins to recipient cells. Previous studies showed that EVs produced and secreted by human mesenchymal stem cells (MSCs) can substitute intact MSCs for tissue repair and regeneration. In this study, we examined properties and functions of EVs from human induced pluripotent stem cells (iPSCs) that can be cultured infinitely under a chemically defined medium free of any exogenous EVs. We collected and purified EVs secreted by human iPSCs and MSCs. Purified EVs produced by both stem cell types have similar sizes (∼150 nm in diameter), but human iPSCs produced 16‐fold more EVs than MSCs. When highly purified iPSC‐EVs were applied in culture to senescent MSCs that have elevated reactive oxygen species (ROS), human iPSC‐EVs reduced cellular ROS levels and alleviated aging phenotypes of senescent MSCs. Our discovery reveals that EVs from human stem cells can alleviate cellular aging in culture, at least in part by delivering intracellular peroxiredoxin antioxidant enzymes. stem cells2019;37:779–790

The Multifaceted Impact of Peroxiredoxins on Aging and Disease

SIGNIFICANCE

Peroxiredoxins (Prxs), a family of thiol-associated peroxidases, are purported to play a major role in sensing and managing hydrogen peroxide concentrations and transducing peroxide-derived signals. Recent Advances: Prxs can act as detoxifying factors and impart effects to cells that can be either sparing or suicidal. Advances have been made to address the qualitative changes in Prx function in response to quantitative changes in the signal level and to understand how Prx activity could be affected by their own substrates. Here we rationalize the basis for both positive and negative effects on signaling pathways and cell physiology, summarizing data from model organisms, including invertebrates.

CRITICAL ISSUES

Resolving the relationship between the promiscuous behavior of reactive oxygen species and the specificity of Prxs toward different targets in redox-sensitive signaling pathways is a key area of research. Attempts to understand Prx function and underlying mechanisms were conducted in vitro or in vivo under nonphysiological conditions, leaving the physiological relevance yet to be defined. Other issues: Why despite the high degree of homology and similarities in subcellular and tissue distribution between Prxs do they display differential effects on signaling? How is the specificity of post-translational protein modifications determined? Other than chaperone-like activity, how do hyperoxidized Prxs function?

FUTURE DIRECTIONS

Genetic models with mutated catalytic and resolving cysteines should be further exploited to dissect the functional significance of individual Prxs in their different states together with their alternative reducing partners. Such an analysis may then be extended to help identify Prx-specific targets.

The acute stresses role of the atypical 2-cys peroxiredoxin PmPrx5 in black tiger shrimp (Penaeus monodon) from biological immunity and environmental toxicity stress

As a unique atypical 2-Cys Peroxiredoxin (Prx) of the Prx-like superfamily, Peroxiredoxin5 (Prx5) possesses special properties, such as its enzymatic mechanism, wide subcellular distribution and high affinity for peroxides and peroxynitrite. Prx5 plays a crucial role in oxidative stress, immune responses, cell apoptosis, proliferation, differentiation, intracellular signaling, the modulation of gene expression, ecdysis, etc. In this paper, we obtained a full-length Prx5 cDNA sequence (designated PmPrx5) from black tiger shrimp (P. monodon). The full-length PmPrx5 cDNA sequence was 1686 bp containing a 5' untranslated region (UTR) of 76 bp with two nucleotide sequences (AAA), a 3' UTR of 1040 bp with a poly (A) tail and two canonical polyadenylation signal sequences (AATAAA), and an open reading frame of 570 bp encoding 189 amino acid residues with a predicted molecular mass of 20 kDa and a theoretical isoelectric point of 6.29. Phylogenetic trees and multiple sequence alignment showed that the PmPrx5 had strong homology with Prx5 proteins from other species, such as similarity with Palaemon carinicauda (69%) and Macrobrachium rosenbergii (69%), containing the highly conserved functional domain. PmPrx5 mRNA was ubiquitously detected in all tested tissues. After P. monodon was exposed to pathogenic bacteria, osmotic pressure, acidity and alkalinity and the heavy metal, the mRNA expression of PmPrx5 in the gills and hepatopancreas was significantly enhanced (P < 0.01) because of the immune response and declined with heavy metal copper and cadmium challenges as time progressed. The recombinant PmPrx5 protein purified in E. coli (DE3) was further confirmed to exhibit antioxidant activity and antibacterial properties to a certain extent using a bacterial growth inhibition test in both liquid and solid cultures in vitro. E. coli transformed with pRSET-PmPrx5 were dramatically protected in response to metal toxicity stress. Thus, PmPrx5 may be developed as a potential therapeutic drug against pathogenic bacteria and as a biomarker for pollutant levels. This work offers useful clues to further explore the functional mechanism of Prx5 in marine shrimp immunity.

Proteomic analyses reveal that ginsenoside Rg3(S) partially reverses cellular senescence in human dermal fibroblasts by inducing peroxiredoxin

Background

The cellular senescence of primary cultured cells is an irreversible process characterized by growth arrest. Restoration of senescence by ginsenosides has not been explored so far. Rg3(S) treatment markedly decreased senescence-associated β-galactosidase activity and intracellular reactive oxygen species levels in senescent human dermal fibroblasts (HDFs). However, the underlying mechanism of this effect of Rg3(S) on the senescent HDFs remains unknown.

Methods

We performed a label-free quantitative proteomics to identify the altered proteins in Rg3(S)-treated senescent HDFs. Upregulated proteins induced by Rg3(S) were validated by real-time polymerase chain reaction and immunoblot analyses.

Results

Finally, 157 human proteins were identified, and variable peroxiredoxin (PRDX) isotypes were highly implicated by network analyses. Among them, the mitochondrial PRDX3 was transcriptionally and translationally increased in response to Rg3(S) treatment in senescent HDFs in a time-dependent manner.

Conclusion

Our proteomic approach provides insights into the partial reversing effect of Rg3 on senescent HDFs through induction of antioxidant enzymes, particularly PRDX3.

Peroxiredoxin 2 deficiency accelerates age-related ovarian failure through the reactive oxygen species-mediated JNK pathway in mice

Reactive oxygen species (ROS) produced in biological reactions have been shown to contribute to ovarian aging. Peroxiredoxin 2 (Prx2) is an antioxidant enzyme that protects cells by scavenging ROS; however, its effect on age-related, oxidative stress-associated ovarian failure has not been reported. Here, we investigated its role in age-related ovarian dysfunction and 4-vinylcyclohexene diepoxide (VCD)-induced premature ovarian failure using Prx2-deficient mice. Compared to those in wildtype (WT) mice, serum levels of anti-Müllerian hormone, 17β-estradiol, and progesterone and numbers of follicles and corpora lutea were significantly lower in 18-month-old Prx2^-/- mice. Moreover, levels of Bax, cytochrome c, cleaved caspase-3, and phosphorylated JNK proteins were higher and numbers of apoptotic (terminal deoxynucleotidyl transferase dUTP nick end labeling-positive) cells were considerably greater in 18-month-old Prx2^-/- ovaries than WT ovaries. Furthermore, the effects of the ovarian toxicant VCD in significantly enhancing ROS levels and apoptosis through activation of JNK-mediated apoptotic signaling were more pronounced in Prx2^-/- than WT mouse embryonic fibroblasts. Expression of the steroidogenic proteins StAR, CYP11A1, and 3β-HSD and serum levels of 17β-estradiol and progesterone were also reduced to a greater extent in Prx2^-/- mice than WT mice after VCD injection. This reduced steroidogenesis was rescued by addition of the Prx mimic ebselen or JNK inhibitor SP600125. This constitutes the first report that Prx2 deficiency leads to acceleration of age-related or VCD-induced ovarian failure by activation of the ROS-induced JNK pathway. These findings suggest that Prx2 plays an important role in preventing accelerated ovarian failure by inhibiting ROS-induced JNK activation.

Beyond ROS clearance: Peroxiredoxins in stress signaling and aging

Antioxidants were long predicted to have lifespan-promoting effects, but in general this prediction has not been well supported. While some antioxidants do seem to have a clear effect on longevity, this may not be primarily as a result of their role in the removal of reactive oxygen species, but rather mediated by other mechanisms such as the modulation of intracellular signaling. In this review we discuss peroxiredoxins, a class of proteinaceous antioxidants with redox signaling and chaperone functions, and their involvement in regulating longevity and stress resistance. Peroxiredoxins have a clear role in the regulation of lifespan and survival of many model organisms, including the mouse, Caenorhabditis elegans and Drosophila melanogaster. Recent research on peroxiredoxins - in these models and beyond - has revealed surprising new insights regarding the interplay between peroxiredoxins and longevity signaling, which will be discussed here in detail. As redox signaling is emerging as a potentially important player in the regulation of longevity and aging, increased knowledge of these fascinating antioxidants and their mode(s) of action is paramount.

Peroxiredoxin I participates in the protection of reactive oxygen species-mediated cellular senescence

Peroxiredoxin I (Prx I) plays an important role as a reactive oxygen species (ROS) scavenger in protecting and maintaining cellular homeostasis; however, the underlying mechanisms are not well understood. Here, we identified a critical role of Prx I in protecting cells against ROS-mediated cellular senescence by suppression of p16^INK4a expression. Compared to wild-type mouse embryonic fibroblasts (WT-MEFs), Prx I^−/− MEFs exhibited senescence-associated phenotypes. Moreover, the aged Prx I^−/− mice showed an increased number of cells with senescence associated-β-galactosidase (SA-β-gal) activity in a variety of tissues. Increased ROS levels and SA-β-gal activity, and reduction of chemical antioxidant in Prx I^−/− MEF further supported an essential role of Prx I peroxidase activity in cellular senescence that is mediated by oxidative stress. The up-regulation of p16^INK4a expression in Prx I^−/− and suppression by overexpression of Prx I indicate that Prx I possibly modulate cellular senescence through ROS/p16^INK4a pathway.

Peroxiredoxin 2 regulates PGF2α-induced corpus luteum regression in mice by inhibiting ROS-dependent JNK activation

Luteal regression is a natural and necessary event to regulate the reproductive process in all mammals. Prostaglandin F2α (PGF2α) is the main factor that causes functional and structural regression of the corpus luteum (CL). It is well known that PGF2α-mediated ROS generation is closely involved in luteal regression. Peroxiredoxin 2 (Prx2) as an antioxidant enzyme plays a protective role against oxidative stress-induced cell death. However, the effect of Prx2 on PGF2α-induced luteal regression has not been reported. Here, we investigated the role of Prx2 in functional and structural CL regression induced by PGF2α-mediated ROS using Prx2-deficient (-/-) mice. We found that PGF2α-induced ROS generation was significantly higher in Prx2-/- MEF cells compared with that in wild-type (WT) cells, which induced apoptosis by activating JNK-mediated apoptotic signaling pathway. Also, PGF2α treatment in the CL derived from Prx2-/- mice promoted the reduction of steroidogenic enzyme expression and the activation of JNK and caspase3. Compared to WT mice, serum progesterone levels and luteal expression of steroidogenic enzymes decreased more rapidly whereas JNK and caspase3 activations were significantly increased in Prx2-/- mice injected with PGF2α. However, the impaired steroidogenesis and PGF2α-induced JNK-dependent apoptosis were rescued by the addition of the antioxidant N-acetyl-L-cysteine (NAC). This is the first study to demonstrate that Prx2 deficiency ultimately accelerated the PGF2α-induced luteal regression through activation of the ROS-dependent JNK pathway. These findings suggest that Prx2 plays a crucial role in preventing accelerated luteal regression via inhibition of the ROS/JNK pathway.

Cardiac Cell Senescence and Redox Signaling

Aging is characterized by a progressive loss of the ability of the organism to cope with stressors and to repair tissue damage. As a result, chronic diseases, including cardiovascular disease, increase their prevalence with aging, underlining the existence of common mechanisms that lead to frailty and age-related diseases. In this frame, the progressive decline of the homeostatic and reparative function of primitive cells has been hypothesized to play a major role in the evolution of cardiac pathology to heart failure. Although initially it was believed that reactive oxygen species (ROS) were produced in an unregulated manner as a byproduct of cellular metabolism, causing macromolecular damage and aging, accumulating evidence indicate the major role played by redox signaling in physiology. Aim of this review is to critically revise evidence linking ROS to cell senescence and aging and to provide evidence of the primary role played by redox signaling, with a particular emphasis on the multifunctional protein APE1/Ref in stem cell biology. Finally, we will discuss evidence supporting the role of redox signaling in cardiovascular cells.

Redox Regulating Enzymes and Connected MicroRNA Regulators Have Prognostic Value in Classical Hodgkin Lymphomas

There are no previous studies assessing the microRNAs that regulate antioxidant enzymes in Hodgkin lymphomas (HLs). We determined the mRNA levels of redox regulating enzymes peroxiredoxins (PRDXs) I–III, manganese superoxide dismutase (MnSOD), nuclear factor erythroid-derived 2-like 2 (Nrf2), and Kelch-like ECH-associated protein 1 (Keap1) from a carefully collected set of 41 classical HL patients before receiving any treatments. The levels of redoxmiRs, miRNAs known to regulate the above-mentioned enzymes, were also assessed, along with CD3, CD20, and CD30 protein expression. RNAs were isolated from freshly frozen lymph node samples and the expression levels were analyzed by qPCR. mir23b correlated inversely with CD3 and CD20 expressions (p = 0.00076; r = −0.523 and p = 0.0012; r = −0.507) and miR144 with CD3, CD20, and CD30 (p = 0.030; r = −0.352, p = 0.041; r = −0.333 and p = 0.0032; r = −0.47, resp.). High MnSOD mRNA levels associated with poor HL-specific outcome in the patients with advanced disease (p = 0.045) and high miR-122 levels associated with worse HL-specific survival in the whole patient population (p = 0.015). When standardized according to the CD30 expression, high miR212 and miR510 predicted worse relapse-free survival (p = 0.049 and p = 0.0058, resp.). In conclusion, several redoxmiRs and redox regulating enzyme mRNA levels associate with aggressive disease outcome and may also produce prognostic information in classical HL.

Dimeric peroxiredoxins are druggable targets in human Burkitt lymphoma

Burkitt lymphoma is a fast-growing tumor derived from germinal center B cells. It is mainly treated with aggressive chemotherapy, therefore novel therapeutic approaches are needed due to treatment toxicity and developing resistance. Disturbance of red-ox homeostasis has recently emerged as an efficient antitumor strategy. Peroxiredoxins (PRDXs) are thioredoxin-family antioxidant enzymes that scavenge cellular peroxides and contribute to red-ox homeostasis. PRDXs are robustly expressed in various malignancies and critically involved in cell proliferation, differentiation and apoptosis. To elucidate potential role of PRDXs in lymphoma, we studied their expression level in B cell-derived primary lymphoma cells as well as in cell lines. We found that PRDX1 and PRDX2 are upregulated in tumor B cells as compared with normal counterparts. Concomitant knockdown of PRDX1 and PRDX2 significantly attenuated the growth rate of lymphoma cells. Furthermore, in human Burkitt lymphoma cell lines, we isolated dimeric 2-cysteine peroxiredoxins as targets for SK053, a novel thiol-specific small-molecule peptidomimetic with antitumor activity. We observed that treatment of lymphoma cells with SK053 triggers formation of covalent PRDX dimers, accumulation of intracellular reactive oxygen species, phosphorylation of ERK1/2 and AKT and leads to cell cycle arrest and apoptosis. Based on site-directed mutagenesis and modeling studies, we propose a mechanism of SK053-mediated PRDX crosslinking, involving double thioalkylation of active site cysteine residues. Altogether, our results suggest that peroxiredoxins are novel therapeutic targets in Burkitt lymphoma and provide the basis for new approaches to the treatment of this disease.

Total peroxiredoxin expression is associated with survival in patients with follicular lymphoma

Redox state-regulating enzymes may have roles in chemoresistance and also in lymphomagenesis, but there have been only a limited number of studies on this topic in lymphomas. Our aim was to assess expression of the redox state-regulating enzymes peroxiredoxins (Prxs) I-VI and thioredoxin (Trx) and the oxidative stress marker nitrotyrosine in follicular lymphomas (FLs). We immunohistochemically assessed Prxs I-VI, Trx and nitrotyrosine in a cohort of 76 histologically confirmed, untreated FLs. We also studied the localisation of Prxs I, II, III, V and VI by means of immunoelectron microscopy (IEM). Immunohistochemistry results were correlated with disease-specific survival (DSS), progression-free survival (PFS), overall survival (OS) and clinical prognostic factors. When all Prx expression intensities were grouped as a single variable, we discovered that high total Prx intensity correlated with favourable DSS (p = 0.024) and OS (p = 0.035) but not with PFS. No deaths due to lymphoma were recorded amongst patients with high total Prx expression during the median follow-up period of 7.6 years. IEM results were in line with earlier ones demonstrating wide subcellular localisation of Prx isoenzymes. In conclusion, our results demonstrate an association between high total Prx expression and prolonged survival and suggest that Prxs may have a protective role in FL that cannot be compensated by other antioxidant mechanisms.

Peroxiredoxin II promotes hepatic tumorigenesis through cooperation with Ras/Forkhead box M1 signaling pathway

The current study was carried out to define the involvement of Peroxiredoxin (Prx) II in progression of hepatocellular carcinoma (HCC) and the underlying molecular mechanism(s). Expression and function of Prx II in HCC was determined using H-ras(G12V)-transformed HCC cells (H-ras(G12V)-HCC cells) and the tumor livers from H-ras(G12V)-transgenic (Tg) mice and HCC patients. Prx II was upregulated in H-ras(G12V)-HCC cells and H-ras(G12V)-Tg mouse tumor livers, the expression pattern of which highly similar to that of forkhead Box M1 (FoxM1). Moreover, either knockdown of FoxM1 or site-directed mutagenesis of FoxM1-binding site of Prx II promoter significantly reduced Prx II levels in H-ras(G12V)-HCC cells, indicating FoxM1 as a direct transcription factor of Prx II in HCC. Interestingly, the null mutation of Prx II markedly decreased the number and size of tumors in H-ras(G12V)-Tg livers. Consistent with this, knockdown of Prx II in H-ras(G12V)-HCC cells reduced the expression of cyclin D1, cell proliferation, anchorage-independent growth and tumor formation in athymic nude mice, whereas overexpression of Prx II increased or aggravated the tumor phenotypes. Importantly, the expression of Prx II was correlated with that of FoxM1 in HCC patients. The activation of extracellular signal-related kinase (ERK) pathway and the expression of FoxM1 and cyclin D1 were highly dependent on Prx II in H-ras(G12V)-HCC cells and H-ras(G12V)-Tg livers. Prx II is FoxM1-dependently-expressed antioxidant in HCC and function as an enhancer of Ras(G12V) oncogenic potential in hepatic tumorigenesis through activation of ERK/FoxM1/cyclin D1 cascade.

Tuning of peroxiredoxin catalysis for various physiological roles

Peroxiredoxins (Prxs) make up an ancient family of enzymes that are the predominant peroxidases for nearly all organisms and play essential roles in reducing hydrogen peroxide, organic hydroperoxides, and peroxynitrite. Even between distantly related organisms, the core protein fold and key catalytic residues related to its cysteine-based catalytic mechanism have been retained. Given that these enzymes appeared early in biology, Prxs have experienced more than 1 billion years of optimization for specific ecological niches. Although their basic enzymatic function remains the same, Prxs have diversified and are involved in roles such as protecting DNA against mutation, defending pathogens against host immune responses, suppressing tumor formation, and--for eukaryotes--helping regulate peroxide signaling via hyperoxidation of their catalytic Cys residues. Here, we review the current understanding of the physiological roles of Prxs by analyzing knockout and knockdown studies from ∼25 different species. We also review what is known about the structural basis for the sensitivity of some eukaryotic Prxs to inactivation by hyperoxidation. In considering the physiological relevance of hyperoxidation, we explore the distribution across species of sulfiredoxin (Srx), the enzyme responsible for rescuing hyperoxidized Prxs. We unexpectedly find that among eukaryotes appearing to have a "sensitive" Prx isoform, some do not contain Srx. Also, as Prxs are suggested to be promising targets for drug design, we discuss the rationale behind recently proposed strategies for their selective inhibition.

The Enzymatic Antioxidant System of Human Spermatozoa

The ejaculated spermatozoon, as an aerobic cell, must fight against toxic levels of reactive oxygen species (ROS) generated by its own metabolism but also by other sources such as abnormal spermatozoa, chemicals and toxicants, or the presence of leukocytes in semen. Mammalian spermatozoa are extremely sensitive to oxidative stress, a condition occurring when there is a net increase in ROS levels within the cell. Opportunely, this specialized cell has a battery of antioxidant enzymes (superoxide dismutase, peroxiredoxins, thioredoxins, thioredoxins reductases, and glutathione s-transferases) working in concert to assure normal sperm function. Any impairment of the antioxidant enzymatic activities will promote severe oxidative damage which is observed as plasma membrane lipid peroxidation, oxidation of structural proteins and enzymes, and oxidation of DNA bases that lead to abnormal sperm function. Altogether, these damages occurring in spermatozoa are associated with male infertility. The present review contains a description of the enzymatic antioxidant system of the human spermatozoon and a reevaluation of the role of its different components and highlights the necessity of sufficient supply of reducing agents (NADPH and reduced glutathione) to guarantee normal sperm function.

Peroxiredoxins: hidden players in the antioxidant defence of human spermatozoa

Spermatozoon is a cell with a precious message to deliver: the paternal DNA. Its motility machinery must be working perfectly and it should be able to acquire fertilizing ability in order to accomplish this mission. Infertility touches 1 in 6 couples worldwide and in half of the cases the causes can be traced to men. A variety of conditions such as infections of the male genital tract, varicocele, drugs, environmental factors, diseases, smoking, etc., are associated with male infertility and a common feature among them is the oxidative stress in semen that occurs when reactive oxygen species (ROS) are produced at high levels and/or when the antioxidant systems are decreased in the seminal plasma and/or spermatozoa. ROS-dependent damage targets proteins, lipids, and DNA, thus compromising sperm function and survival. Elevated ROS in spermatozoa are associated with DNA damage and decreased motility. Paradoxically, ROS, at very low levels, regulate sperm activation for fertilization. Therefore, the regulation of redox signaling in the male reproductive tract is essential for fertility. Peroxiredoxins (PRDXs) play a central role in redox signaling being both antioxidant enzymes and modulators of ROS action and are essential for pathological and physiological events. Recent studies from our lab emphasize the importance of PRDXs in the protection of spermatozoa as infertile men have significant low levels of PRDXs in semen and with little enzymatic activity available for ROS scavenging. The relationships between sperm DNA damage, motility and lipid peroxidation and high levels of thiol-oxidized PRDXs suggest the enhanced susceptibility of spermatozoa to oxidative stress and further support the importance of PRDXs in human sperm physiology. This review aims to characterize PRDXs, hidden players of the sperm antioxidant system and highlight the central role of PRDXs isoforms in the protection against oxidative stress to assure a proper function and DNA integrity of human spermatozoa.

Modulation of the peroxiredoxin system by cytokines in insulin-producing RINm5F cells: down-regulation of PRDX6 increases susceptibility of beta cells to oxidative stress

Peroxiredoxins are a family of six antioxidant enzymes (PRDX1-6), and may be an alternative system for the pancreatic beta cells to cope with oxidative stress. This study investigated whether the main diabetogenic pro-inflammatory cytokines or the anti-inflammatory cytokine IL-4 modulate PRDXs levels and putative intracellular pathways important for this process in the insulin-producing RINm5F cells. RINm5F cells expressed significant amounts of PRDX1, PRDX3 and PRDX6 enzymes. Only PRDX6 was modulated by cytokines, showing both mRNA and protein down-regulation following incubation of RINm5F cells with TNF-alpha and IFN-gamma but not with IL-1beta. Separately IFN-gamma or TNF-alpha decreased PRDX6 protein but not mRNA levels. The blockage of the JNK signalling and of the calpains and proteasome proteolysis systems restored PRDX6 protein levels. IL-4 alone did not modulate PRDXs levels. However, pre/co-incubation with IL-4 substantially prevented the decrease in PRDX6 induced by pro-inflammatory cytokines. Knockdown of PRDX6 increased susceptibility of RINm5F cells to the deleterious effects of pro-inflammatory cytokines and to oxidative stress. These results show that, from the PRDXs significantly expressed in RINm5F cells, only PRDX6 is modulated by the diabetogenic cytokines IFN-gamma and TNF-alpha. This PRDX6 down-regulation depends on the calpain and proteasome systems and JNK signalling. PRDX6 is an important enzyme for protection against oxidative stress and the interaction between pro- and anti-inflammatory cytokines might be important to determine the antioxidant capacity of the cells.

Hyperoxidized peroxiredoxin 2 interacts with the protein disulfide- isomerase ERp46

Prx (peroxiredoxin) 2 protects cells from deleterious oxidative damage. It catalyses the breakdown of hydroperoxides through a highly reactive cysteine residue and has been linked to chaperone activity that promotes cell survival under conditions of oxidative stress. It may also be involved in redox signalling by binding to other proteins. In the present study we have searched for binding partners of Prx2 in H2O2-treated Jurkat and human umbilical vein endothelial cells and discovered that the hyperoxidized form selectively co-precipitated with the protein disulfide-isomerase ERp46. Mutant analyses revealed that loss of the peroxidative cysteine residue of Prx2 also facilitated complex formation with ERp46, even without H2O2 treatment, whereas the resolving cysteine residue of Prx2 was indispensible for the interaction to occur. The complex involved a stable non-covalent interaction that was disassociated by the reduction of intramolecular disulfides in ERp46, or by disruption of the decameric structure of hyperoxidized Prx2. This is the first example of a protein interaction dependent on the hyperoxidized status of a Prx.

Prolonged expression of senescence markers in mice exposed to gamma-irradiation

Although ionizing radiation is known to induce cellular senescence in vitro and in vivo, its long-term in vivo effects are not well defined. In this study, we examined the prolonged expression of senescence markers in mice irradiated with single or fractionated doses. C57BL/6 female mice were exposed to 5 Gy of γ-rays in single or 5, 10, 25 fractions. At 2, 4, and 6 months after irradiation, senescence markers including mitochondrial DNA (mtDNA) common deletion, p21, and senescence-associated β-galactosidase (SA β-gal) were monitored in the lung, liver, and kidney. Increases of mtDNA deletion were detected in the lung, liver, and kidney of irradiated groups. p21 expression and SA β-gal staining were also increased in the irradiated groups compared to the non-irradiated control group. Increases of senescence markers persisted up to 6 months after irradiation. Additionally, the extent of mtDNA deletion and the numbers of SA β-gal positive cells were greater as the number of radiation fractions increased. In conclusion, our results showed that ionizing radiation, especially that delivered in fractions, can cause the persistent upregulation of senescence marker expression in vivo. This should be considered when dealing with chronic normal tissue injuries caused by radiation therapy or radiation accidents.

Caffeoylquinic acid-rich purple sweet potato extract, with or without anthocyanin, imparts neuroprotection and contributes to the improvement of spatial learning and memory of SAMP8 mouse

The effects of caffeoylquinic acid (CQA)-rich purple sweet potato (PSP) extract, with (PSPEa) or without (PSPEb) anthocyanin, on the improvement of spatial learning and memory of senescence-accelerated prone mouse strain (SAMP) 8 was determined. SAMP8 was treated with 20 mg/kg/day of PSPEa or PSPEb for 30 days. The effect on spatial learning and memory and the molecular mechanism of this effect were determined in vivo (SAMP8) and in vitro (SH-SY5Y cells). PSPEa or PSPEb reduced the escape latency time of SAMP8 by 17.0 ± 8.0 and 14.2 ± 5.8 s (P < 0.01), respectively. PSPEa administration induced an overexpression of antioxidant-, energy metabolism-, and neuronal plasticity-related proteins in the brain of SAMP8. Additionally, PSPEa and PSPEb increased the cell viability by 141.6 and 133% as compared to Aβ1-42-treated cells. These findings suggest that PSP rich in CQA derivatives with or without anthocyanidine had a neuroprotective effect on mouse brain and can improve the spatial learning and memory of SAMP8.

Role for Prdx1 as a specific sensor in redox-regulated senescence in breast cancer

Recent studies suggest that Peroxiredoxin 1 (Prdx1), in addition to its known H₂O₂-scavenging function, mediates cell signaling through redox-specific protein-protein interactions. Our data illustrate how Prdx1 specifically coordinates p38MAPK-induced signaling through regulating p38MAPKα phosphatases in an H₂O₂ dose-dependent manner. MAPK phosphatases (MKP-1 and/or MKP-5), which are known to dephosphorylate and deactivate the senescence-inducing MAPK p38α, belong to a group of redox-sensitive phosphatases (protein tyrosine phosphatases) characterized by a low pKa cysteine in their active sites. We found that Prdx1 bound to both MKP-1 and MKP-5, but dissociated from MKP-1 when the Prdx1 peroxidatic cysteine Cys52 was over-oxidized to sulfonic acid, which in turn resulted in MKP-1 oxidation-induced oligomerization and inactivity toward p38MAPKα. Conversely, over-oxidation of Prdx1-Cys52 was enhancing in the Prdx1:MKP-5 complex with increasing amounts of H₂O₂ concentrations and correlated with a protection from oxidation-induced oligomerization and inactivation of MKP-5 so that activation toward p38MAPK was maintained. Further examination of this Prdx1-specific mechanism in a model of reactive oxygen species-induced senescence of human breast epithelial cells revealed the specific activation of MKP-5, resulting in decreased p38MAPKα activity. Taken together, our data suggest that Prdx1 orchestrates redox signaling in an H₂O₂ dose-dependent manner through the oxidation status of its peroxidatic cysteine Cys52.

Mouse Models of Oxidative Stress Indicate a Role for Modulating Healthy Aging

Aging is a complex process that affects every major system at the molecular, cellular and organ levels. Although the exact cause of aging is unknown, there is significant evidence that oxidative stress plays a major role in the aging process. The basis of the oxidative stress hypothesis is that aging occurs as a result of an imbalance between oxidants and antioxidants, which leads to the accrual of damaged proteins, lipids and DNA macromolecules with age. Age-dependent increases in protein oxidation and aggregates, lipofuscin, and DNA mutations contribute to age-related pathologies. Many transgenic/knockout mouse models over expressing or deficient in key antioxidant enzymes have been generated to examine the effect of oxidative stress on aging and age-related diseases. Based on currently reported lifespan studies using mice with altered antioxidant defense, there is little evidence that oxidative stress plays a role in determining lifespan. However, mice deficient in antioxidant enzymes are often more susceptible to age-related disease while mice overexpressing antioxidant enzymes often have an increase in the amount of time spent without disease, i.e., healthspan. Thus, by understanding the mechanisms that affect healthy aging, we may discover potential therapeutic targets to extend human healthspan.

Peroxiredoxin 2 deficiency exacerbates atherosclerosis in apolipoprotein E-deficient mice

RATIONALE

Peroxiredoxin 2 (Prdx2), a thiol-specific peroxidase, has been reported to regulate proinflammatory responses, vascular remodeling, and global oxidative stress.

OBJECTIVE

Although Prdx2 has been proposed to retard atherosclerosis development, no direct evidence and mechanisms have been reported.

METHODS AND RESULTS

We show that Prdx2 is highly expressed in endothelial and immune cells in atherosclerotic lesions and blocked the increase of endogenous H(2)O(2) by atherogenic stimulation. Deficiency of Prdx2 in apolipoprotein E-deficient (ApoE(-/-)) mice accelerated plaque formation with enhanced activation of p65, c-Jun, JNKs, and p38 mitogen-activated protein kinase; and these proatherogenic effects of Prdx2 deficiency were rescued by administration of the antioxidant ebselen. In bone marrow transplantation experiments, we found that Prdx2 has a major role in inhibiting atherogenic responses in both vascular and immune cells. Prdx2 deficiency resulted in increased expression of vascular adhesion molecule-1, intercellular adhesion molecule-1, and monocyte chemotactic protein-1, which led to increased immune cell adhesion and infiltration into the aortic intima. Compared with deficiency of glutathione peroxidase 1 or catalase, Prdx2 deficiency showed a severe predisposition to develop atherosclerosis.

CONCLUSIONS

Prdx2 is a specific peroxidase that inhibits atherogenic responses in vascular and inflammatory cells, and specific activation of Prdx2 may be an effective means of antiatherogenic therapy.

Premature aging with impaired oxidative stress defense in mice lacking TR4

Early studies suggest that TR4 nuclear receptor is a key transcriptional factor regulating various biological activities, including reproduction, cerebella development, and metabolism. Here we report that mice lacking TR4 (TR4(-/-)) exhibited increasing genome instability and defective oxidative stress defense, which are associated with premature aging phenotypes. At the cellular level, we observed rapid cellular growth arrest and less resistance to oxidative stress and DNA damage in TR4(-/-) mouse embryonic fibroblasts (MEFs) in vitro. Restoring TR4 or supplying the antioxidant N-acetyl-l-cysteine (NAC) to TR4(-/-) MEFs reduced the DNA damage and slowed down cellular growth arrest. Focused qPCR array revealed alteration of gene profiles in the DNA damage response (DDR) and anti-reactive oxygen species (ROS) pathways in TR4(-/-) MEFs, which further supports the hypothesis that the premature aging in TR4(-/-) mice might stem from oxidative DNA damage caused by increased oxidative stress or compromised genome integrity. Together, our finding identifies a novel role of TR4 in mediating the interplay between oxidative stress defense and aging.

Cdk5: mediator of neuronal development, death and the response to DNA damage

In the central nervous system, cyclin-dependent kinase 5 (Cdk5), an unusual member of the Cdk family, is implicated in the regulation of various physiological processes ranging from neuronal survival, migration and differentiation, to synaptogenesis, synaptic plasticity and neurotransmission. Dysregulation of this kinase has been demonstrated to play a critical role in the pathogenic process of neurodegenerative disorders. DNA damage is emerging as an important pathological component in various neurodegenerative conditions. In this review, we discuss the recent progress regarding the regulation and roles of Cdk5 under physiological conditions, and its dysregulation under pathological conditions, especially in neuronal death mediated by DNA damage.

ROS/Epac1-mediated Rap1/NF-kappaB activation is required for the expression of BAFF in Raw264.7 murine macrophages

B-cell activating factor (BAFF) plays a role for the maturation and the maintenance of B cells. Lipopolysaccharide (LPS) activates toll-like receptor 4 (TLR4)-dependent signal transduction, which resulted in BAFF expression through nuclear factor kappa B (NF-κB) activation. Here, we investigated whether BAFF expression could be regulated by p65 phosphorylation through the production of reactive oxygen species (ROS) or cyclic AMP (cAMP) in Raw264.7 murine macrophages. mBAFF expression was reduced by ROS scavengers and it was increased by dibutyl-cAMP, a cAMP analogue. mBAFF expression and mBAFF promoter activity were increased by co-transfection of p65 but they were reduced by p65-small interference (si) RNA. Serine (Ser) 276 phosphorylation of p65 was increased by LPS-mediated PKA activation or by the treatment with forskolin, adenylate cyclase activator and dibutyl-cAMP. In contrast, p65 phosphorylation at Ser276 was decreased by ROS scavengers. H(2)O(2) increased intracellular cAMP concentration, significantly. While no increase in p65 phosphorylation at Ser276 was detected by the treatment with H(2)O(2), CREB and p65 phosphorylation at Ser133 and Ser536 was observed, respectively. It implicates that p65 phosphorylation at Ser276 is independent of ROS-induced cAMP production. As another cAMP effector protein was cAMP-responsive guanine nucleotide exchange factor (Epac), a Rap GDP exchange factor, NF-κB was activated by the treatment with 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (CPT) that is an activator to Epac. Epac1-mediated Rap1 was activated by the treatment with H(2)O(2) but it was inhibited by ROS scavengers. CPT induced p65 phosphorylation at both Ser276 and Ser536. CPT also increased not only mBAFF expression but mBAFF promoter activity. Data demonstrate that TLR4-mediated mBAFF expression was resulted from the crosstalk of p65 phosphorylation at Ser536 and Ser276 through ROS- and/or cAMP-mediated signal transduction. It suggests for the first time that ROS/Epac1-mediated Rap1/NF-κB pathway could be required for BAFF expression.

Peroxiredoxin 2 inhibits granulosa cell apoptosis during follicle atresia through the NFKB pathway in mice

Peroxiredoxin 2 (PRDX2) has been known to act as an antioxidant enzyme whose main function is H(2)O(2) reduction in cells. We aimed to study the expression patterns of PRDX2 in mouse ovaries and explore the function of this protein in apoptosis of granulosa cells (GCs). We found that the expression of the PRDX2 protein in atretic follicle GCs was markedly higher than in healthy follicle GCs. In vitro, the transfection of siRNA targeting the Prdx2 gene inhibited the proliferation and induced the apoptosis of primary cultured GCs. Furthermore, suppression of PRDX2 resulted in the augmentation of endogenous H(2)O(2), and the ability to eliminate the exogenous H(2)O(2) was attenuated. The expression of PRDX2 and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB), whose activity was inhibited by binding to IKB, increased in GCs treated with various concentrations of H(2)O(2) for 30 min. However, no significant change in cytoplasmic IKB expression was observed. At 2 h after treatment with H(2)O(2), nuclear NFKB expression level was reduced, cytoplasmic IKB expression was increased, and PRDX2 expression was unchanged. Silencing of the Prdx2 gene caused early changes in NFKB and IKB expression in the primary cultured GCs compared to that in control cells. Taken together, these data suggest that PRDX2 plays an important role in inhibiting apoptosis in GCs and that PRDX2 actions may be related to the expression of NFKB and IKB.

Distinct gene signature revealed in white blood cells, CD4(+) and CD8(+) T cells in (NZBx NZW) F1 lupus mice after tolerization with anti-DNA Ig peptide

Tolerizing mice polygenically predisposed to lupus-like disease (NZB/NZW F1 females) with a peptide mimicking anti-DNA IgG sequences containing MHC class I and class II T cell determinants (pConsensus, pCons) results in protection from full-blown disease attributable in part to the induction of CD4(+)CD25(+)Foxp3+ and CD8(+)Foxp3+ regulatory T cells. We compared 45 000 murine genes in total white blood cells (WBC), CD4(+) T cells, and CD8(+) T cells from splenocytes of (NZBxNZW) F1 lupus-prone mice tolerized with pCons vs untreated naïve mice and found two-fold or greater differential expression for 448 WBC, 174 CD4, and 60 CD8 genes. We identified differentially expressed genes that played roles in the immune response and apoptosis. Using real-time PCR, we validated differential expression of selected genes (IFI202B, Bcl2, Foxp3, Trp-53, CCR7 and IFNar1) in the CD8(+)T cell microarray and determined expression of selected highly upregulated genes in different immune cell subsets. We also determined Smads expression in different immune cell subsets, including CD4(+) T cells and CD8(+) T cells, to detect the effects of TGF-beta, known to be the major cytokine that accounts for the suppressive capacity of CD8(+) Treg in this system. Silencing of anti-apoptotic gene Bcl2 or interferon genes (IFI202b and IFNar1 in combination) in CD8(+) T cells from tolerized mice did not affect the expression of the other selected genes. However, silencing of Foxp3 reduced expression of Foxp3, Ifi202b and PD1-all of which are involved in the suppressive capacity of CD8(+) Treg in this model.

Proteomic identification of overexpressed PRDX 1 and its clinical implications in ovarian carcinoma

Ovarian carcinoma is the most lethal gynecological malignancy in worldwide. The discovery of reliable marker for early detection of ovarian carcinoma is critical for increasing patient's survival because high mortality rate is associated with late diagnosis of this tumor. In the present study, we performed comparative analysis of whole proteomes between serous borderline tumor and serous carcinoma to identify a useful biomarker for the early diagnosis and progression of ovarian carcinoma. Nine proteins were significantly overexpressed in ovarian serous carcinomas compared to borderline tumors. After validation with Western blotting and immunohistochemical analysis, prdx 1 was found to be the strongest overexpressed protein in malignant ovarian tumors among the selected proteins. In addition, the high level of prdx 1 expression (>50% positive cancer cells) was significantly correlated with poor overall survival in ovarian serous carcinomas. On a multivariate cox analysis, the relative risk of death was 8.74 in patients with serous carcinomas showing >50% of prdx 1-positive cancer cells. Our results suggest that prdx 1 may be a useful diagnostic and prognostic biomarker in ovarian carcinoma, especially serous carcinoma.

The cell cycle is a redox cycle: linking phase-specific targets to cell fate

Reactive oxygen species (ROS) regulate the strength and duration of signaling through redox-dependent signal transduction pathways via the cyclic oxidation/reduction of cysteine residues in kinases, phosphatases, and other regulatory factors. Signaling circuits may be segregated in organelles or other subcellular domains with distinct redox states, permitting them to respond independently to changes in the oxidation state of two major thiol reductants, glutathione and thioredoxin. Studies in yeast, and in complex eukaryotes, show that oscillations in oxygen consumption, energy metabolism, and redox state are intimately integrated with cell cycle progression. Because signaling pathways play specific roles in different phases of the cell cycle and the hierarchy of redox-dependent regulatory checkpoints changes during cell cycle progression, the effects of ROS on cell fate vary during the cell cycle. In G1, ROS stimulate mitogenic pathways that control the activity of cyclin-dependent kinases (CDKs) and phosphorylation of the retinoblastoma protein (pRB), thereby regulating S-phase entry. In response to oxidative stress, Nrf2 and Foxo3a promote cell survival by inducing the expression of antioxidant enzymes and factors involved in cell cycle withdrawal, such as the cyclin-dependent kinase inhibitor (CKI) p27. In S phase, ROS induce S-phase arrest via PP2A-dependent dephosphorylation of pRB. In precancerous cells, unconstrained mitogenic signaling by activated oncogenes induces replication stress in S phase, which activates the DNA-damage response and induces cell senescence. A number of studies suggest that interactions of ROS with the G1 CDK/CKI network play a fundamental role in senescence, which is considered a barrier to tumorigenesis. Adaptive responses and loss of checkpoint proteins such as p53 and p16(INK4a) allow tumor cells to tolerate constitutive mitogenic signaling and enhanced production of ROS, leading to altered redox status in many fully transformed cells. Alterations in oxidant and energy metabolism of cancer cells have emerged as fertile ground for new therapeutic targets. The present challenge is to identify redox-dependent targets relevant to each cell cycle phase, to understand how these targets control fate decisions, and to describe the mechanisms that link metabolism to cell cycle progression.

Inhibition of thioredoxin reductase 1 by caveolin 1 promotes stress-induced premature senescence

Thioredoxin reductase 1 (TrxR1) is an important antioxidant enzyme that controls cellular redox homeostasis. By using a proteomic-based approach, here we identify TrxR1 as a caveolar membrane-resident protein. We show that caveolin 1, the structural protein component of caveolae, is a TrxR1-binding protein by demonstrating that the scaffolding domain of caveolin 1 (amino acids 82-101) binds directly to the caveolin-binding motif (CBM) of TrxR1 (amino acids 454-463). We also show that overexpression of caveolin 1 inhibits TrxR activity, whereas a lack of caveolin 1 activates TrxR, both in vitro and in vivo. Expression of a peptide corresponding to the caveolin 1 scaffolding domain is sufficient to inhibit TrxR activity. A TrxR1 mutant lacking the CBM, which fails to localize to caveolae and bind to caveolin 1, is constitutively active and inhibits oxidative-stress-mediated activation of the p53/p21(Waf1/Cip1) pathway and induction of premature senescence. Finally, we show that caveolin 1 expression inhibits TrxR1-mediated cell transformation. Thus, caveolin 1 links free radicals to activation of the p53/p21(Waf1/Cip1) pathway and induction of cellular senescence by acting as an endogenous inhibitor of TrxR1.

Redox-regulated chaperones

Redox regulation of stress proteins, such as molecular chaperones, guarantees an immediate response to oxidative stress conditions. This review focuses on the two major classes of redox-regulated chaperones, Hsp33 in bacteria and typical 2-Cys peroxiredoxins in eukaryotes. Both proteins employ redox-sensitive cysteines, whose oxidation status directly controls their affinity for unfolding proteins and therefore their chaperone function. We will first discuss Hsp33, whose oxidative stress-induced disulfide bond formation triggers the partial unfolding of the chaperone, which, in turn, leads to the exposure of a high-affinity binding site for unfolded proteins. This rapid mode of activation makes Hsp33 essential for protecting bacteria against severe oxidative stress conditions, such as hypochlorite (i.e., bleach) treatment, which leads to widespread protein unfolding and aggregation. We will compare Hsp33 to the highly abundant eukaryotic typical 2-Cys peroxiredoxin, whose oxidative stress-induced sulfinic acid formation turns the peroxidase into a molecular chaperone in vitro and presumably in vivo. These examples illustrate how proteins use reversible cysteine modifications to rapidly adjust to oxidative stress conditions and demonstrate that redox regulation plays a vital role in protecting organisms against reactive oxygen species-mediated cell death.

Peroxiredoxin 5 confers protection against oxidative stress and apoptosis and also promotes longevity in Drosophila

Peroxiredoxin 5 is a distinct isoform of the peroxiredoxin gene family. The antioxidative and anti-apoptotic functions of peroxiredoxin 5 have been extensively demonstrated in cell culture experiments. In the present paper, we provide the first functional analysis of peroxiredoxin 5 in a multicellular organism, Drosophila melanogaster. Similar to its mammalian, yeast or human counterparts, dPrx5 (Drosophila peroxiredoxin 5) is expressed in several cellular compartments, including the cytosol, nucleus and the mitochondrion. Global overexpression of dPrx5 in flies increased resistance to oxidative stress and extended their life span by up to 30% under normal conditions. The dprx5(-/-) null flies were comparatively more susceptible to oxidative stress, had higher incidence of apoptosis, and a shortened life span. TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) analysis revealed that the dprx5(-/-) null mutant had discernible tissue-specific apoptotic patterns, similar to those observed in control flies exposed to paraquat. In addition, apoptosis was particularly notable in oenocytes. During development the dPrx5 levels co-varied with ecdysone pulses, suggesting inter-relationship between ecdystreroids and dPrx5 expression. The importance of dPrx5 for development was further underscored by the embryonic lethal phenotype of progeny derived from the dprx5(-/-) null mutant. Results from the present study suggest that the antioxidant and anti-apoptotic activities of dPrx5 play a critical role in development and aging of the fly.

Decreasing peroxiredoxin II expression decreases glutathione, alters cell cycle distribution, and sensitizes glioma cells to ionizing radiation and H(2)O(2)

Glioblastomas are notorious for their resistance to ionizing radiation and chemotherapy. We hypothesize that this resistance to ionizing radiation is due, in part, to alterations in antioxidant enzymes. Here, we show that rat and human glioma cells overexpress the antioxidant enzyme peroxiredoxin II (Prx II). Glioma cells in which Prx II is decreased using shRNA exhibit increased hyperoxidation of the remaining cellular Prxs, suggesting that the redox environment is more oxidizing. Of interest, decreasing Prx II does not alter other antioxidant enzymes (i.e., catalase, GPx, Prx I, Prx III, CuZnSOD, and MnSOD). Analysis of the redox environment revealed that decreasing Prx II increased intracellular reactive oxygen species in 36B10 cells; extracellular levels of H(2)O(2) were also increased in both C6 and 36B10 cells. Treatment with H(2)O(2) led to a further elevation in intracellular reactive oxygen species in cells where Prx II was decreased. Decreasing Prx II expression in glioma cells also reduced clonogenic cell survival following exposure to ionizing radiation and H(2)O(2). Furthermore, lowering Prx II expression decreased intracellular glutathione and resulted in a significant decline in glutathione reductase activity, suggesting a possible mechanism for the observed increased sensitivity to oxidative insults. Additionally, decreasing Prx II expression increased cell cycle doubling times, with fewer cells distributed to S phase in C6 glioma cells and more cells redistributed to the most radiosensitive phase of the cell cycle, G2/M, in 36B10 glioma cells. These findings support the hypothesis that inhibiting Prx II sensitizes glioma cells to oxidative stress, presenting Prxs as potential therapeutic targets.

Differential protein expression during aging in ventricular myocardium of Fischer 344 x Brown Norway hybrid rats

The aging heart undergoes well characterized structural changes associated with functional decline, though the underlying mechanisms are not understood. The aim of this study was to determine to what extent ventricular myocardial protein expression was altered with age and which proteins underwent protein nitration. Fischer 344 x Brown Norway F1 hybrid (FBN) rats of four age groups were used, 4, 12, 24, and 34 months. Differential protein expression was determined by 2-DE and proteins were identified by peptide mass fingerprinting. Altered protein nitration with age was assessed by immunoblotting. Over 1000 protein spots per sample were detected, and 255 were found to be differentially expressed when all aged groups were compared to young rats (4 months) (p0.05). A strong positive correlation between differential protein expression and increasing age (p=0.03, R(2)=0.997) indicated a progressive, rather than abrupt, change with age. Of 46 differentially expressed proteins identified, seventeen have roles in apoptosis, ten in hypertrophy, seven in fibrosis, and three in diastolic dysfunction, aging-associated processes previously reported in both human and FBN rat heart. Protein expression alterations detected here could have beneficial effects on cardiac function; thus, our data indicate a largely adaptive change in protein expression during aging. In contrast, differential protein nitration increased abruptly, rather than progressively, at 24 months of age. Altogether, the results suggest that differential myocardial protein expression occurs in a progressive manner during aging, and that a proteomic-based approach is an effective method for the identification of potential therapeutic targets to mitigate aging-related myocardial dysfunction.

Proteome analysis of aflatoxin B1-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) and functional identification of candidate protein peroxiredoxin II

In order to explore the proteins responsible for hepatocellular carcinoma (HCC), aflatoxin B(1)-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) was analyzed with 2-DE and MS. By comparing HCC samples with their own precancerous biopsies and HCC-surrounding tissues, a group of candidate proteins that differentially expressed in HCC were obtained. Peroxiredoxin (Prx) II, one of the candidates with distinct alteration, was further investigated and validated. Western blot and RT-PCR assays confirmed the overexpression of Prx II in both tree shrew and human HCC tissues. RNA interference for silencing Prx II was employed subsequently to explore the function and underlying mechanism of Prx II on liver cancer cell line Hep3B. Results showed the cell proliferation and clone formation decreased obviously when Prx II expression was inhibited, while the flow cytometer analysis showed the percentage of cell apoptosis enhanced. Inhibition of Prx II expression also obviously increased the generation of ROS and malondialdehyde, both are the products from peroxidation. These results imply the important role of Prx II in hepatocarcinogenesis, possibly through its function in regulating peroxidation and hereby to provide a favorable microenvironment for cancer cell surviving and progressing.