PRDX6 Inhibits Neurogenesis through Downregulation of WDFY1-Mediated TLR4 Signal

Impaired neurogenesis has been associated with several brain disorders, such as Alzheimer's disease (AD) and Parkinson's disease (PD). The role of peroxiredoxin 6 (PRDX6) in neurodegenerative diseases is very controversial. To demonstrate the role of PRDX6 in neurogenesis, we compared the neurogenesis ability of PRDX6-overexpressing transgenic (Tg) mice and wild-type mice and studied the involved molecular mechanisms. We showed that the neurogenesis of neural stem cells (NSCs) and the expression of the marker protein were lower in PRDX6 Tg-mice than in wild-type mice. To determine the factors involved in PRDX6-related neural stem cell impairment, we performed a microarray experiment. We showed that the expression of WDFY1 was dramatically decreased in PRDX6-Tg mice. Moreover, WDFY1 siRNA decreases the differentiation ability of primary neural stem cells. Interestingly, WDFY1 reportedly recruits the signaling adaptor TIR-domain-containing adapter-inducing interferon-β (TRIF) to toll-like receptors (TLRs); thus, we showed the relationship among TLRs, PRDX6, and WDFY1. We showed that TLR4 was dramatically reduced in PRDX6 Tg mice, and reduced TLR4 expression and neurogenesis was reversed by the introduction of WDFY1 plasmid in the neural stem cells from PRDX6 Tg mice. This study indicated that PRDX6 inhibits the neurogenesis of neural precursor cells through TLR4-dependent downregulation of WDFY1 and suggested that the inhibitory effect of PRDX6 on neurogenesis play a role in the development of neurodegenerative diseases in the PRDX6 overexpressing transgenic mice.

Genetic inactivation of the phospholipase A2 activity of peroxiredoxin 6 in mice protects against LPS-induced acute lung injury

Peroxiredoxin 6 (Prdx6) is a multifunctional enzyme that serves important antioxidant roles by scavenging hydroperoxides and reducing peroxidized cell membranes. Prdx6 also plays a key role in cell signaling by activating the NADPH oxidase, type 2 (Nox2) through its acidic Ca2+-independent phospholipase A2 (aiPLA2) activity. Nox2 generation of O2·-, in addition to signaling, can contribute to oxidative stress and inflammation such as during sepsis-induced acute lung injury (ALI). To evaluate a possible role of Prdx6-aiPLA2 activity in the pathophysiology of ALI associated with a systemic insult, wild-type (WT) and Prdx6-D140A mice, which lack aiPLA2 but retain peroxidase activity were administered intraperitoneal LPS. LPS-treated mutant mice had increased survival compared with WT mice while cytokines in lung lavage fluid and lung VCAM-1 expression, nitrotyrosine levels, PMN infiltration, and permeability increased in WT but not in mutant mice. Exposure of mouse pulmonary microvascular endothelial cells in primary culture to LPS promoted phosphorylation of Prdx6 and its translocation to the plasma membrane and increased aiPLA2 activity as well as increased H2O2 generation, nitrotyrosine levels, lipid peroxidation, NF-κB nuclear localization, and nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome assembly; these effects were not seen in Nox2 null cells, Prdx6-D140A cells, or WT cells pretreated with MJ33, an inhibitor of aiPLA2 activity. Thus aiPLA2 activity is needed for Nox2-derived oxidant stress associated with LPS exposure. Since inactivation of aiPLA2 reduced mortality and prevented lung inflammation and oxidative stress in this animal model, the aiPLA2 activity of Prdx6 could be a novel target for prevention or treatment of sepsis-induced ALI.

Ginkgolic Acid Rescues Lens Epithelial Cells from Injury Caused by Redox Regulated-Aberrant Sumoylation Signaling by Reviving Prdx6 and Sp1 Expression and Activities

Sumoylation is a downstream effector of aging/oxidative stress; excess oxidative stress leads to dysregulation of a specificity protein1 (Sp1) and its target genes, such as Peroxiredoxin 6 (Prdx6), resulting in cellular damage. To cope with oxidative stress, cells rely on a signaling pathway involving redox-sensitive genes. Herein, we examined the therapeutic efficacy of the small molecule Ginkgolic acid (GA), a Sumoylation antagonist, to disrupt aberrant Sumoylation signaling in human and mouse lens epithelial cells (LECs) facing oxidative stress or aberrantly expressing Sumo1 (small ubiquitin-like modifier). We found that GA globally reduced aberrant Sumoylation of proteins. In contrast, Betulinic acid (BA), a Sumoylation agonist, augmented the process. GA increased Sp1 and Prdx6 expression by disrupting the Sumoylation signaling, while BA repressed the expression of both molecules. In vitro DNA binding, transactivation, Sumoylation and expression assays revealed that GA enhanced Sp1 binding to GC-boxes in the Prdx6 promoter and upregulated its transcription. Cell viability and intracellular redox status assays showed that LECs pretreated with GA gained resistance against oxidative stress-driven aberrant Sumoylation signaling. Overall, our study revealed an unprecedented role for GA in LECs and provided new mechanistic insights into the use of GA in rescuing LECs from aging/oxidative stress-evoked dysregulation of Sp1/Prdx6 protective molecules.

Functional role of peroxiredoxin 6 in the eye

Peroxiredoxin 6 (Prdx6) is the only mammalian 1-Cys member of the Prdx family, a group of enzymes which share the ability to reduce peroxides. In addition to its peroxidase function, Prdx6 also demonstrates phospholipase A₂ and lysophosphatidylcholine acyl transferase (LPCAT) activities. These enzymatic activities play an important role in regenerating oxidized membrane phospholipids and maintaining an appropriate balance of intracellular reactive oxygen species. Development of clinical pathologies, including those within the eye, have been linked to dysregulation of Prdx6 function. Interplay between external stressors like exposure to UV light, transforming growth factor β (TGF-β), and hyperglycemia in conjunction with diminished Prdx6 levels and loss of redox balance is associated with cellular changes in a variety of ophthalmic pathologies including cataracts, glaucoma, and retinal degeneration. Many of these cellular abnormalities can be rescued through supplementation with exogenous Prdx6. Additionally, corneal endothelial cells have been found to express high levels of Prdx6 in the plasma membrane. These findings highlight the importance of Prdx6 as an essential regulator of oxidative stress in the eye.

Sumoylation-deficient Prdx6 repairs aberrant Sumoylation-mediated Sp1 dysregulation-dependent Prdx6 repression and cell injury in aging and oxidative stress

Progressive deterioration of antioxidant response in aging is a major culprit in the initiation of age-related pathobiology induced by oxidative stress. We previously reported that oxidative stress leads to a marked reduction in transcription factor Sp1 and its mediated Prdx6 expression in lens epithelial cells (LECs) leading to cell death. Herein, we examined how Sp1 activity goes awry during oxidative stress/aging, and whether it is remediable. We found that Sp1 is hyper-Sumoylated at lysine (K) 16 residue in aging LECs. DNA binding and promoter assays revealed, in aging and oxidative stress, a significant reduction in Sp1 overall binding, and specifically to Prdx6 promoter. Expression/overexpression assay revealed that the observed reduction in Sp1-DNA binding activity was connected to its hyper-Sumoylation due to increased reactive oxygen species (ROS) and Sumo1 levels, and reduced levels of Senp1, Prdx6 and Sp1. Mutagenesis of Sp1 at K16R (arginine) residue restored steady-state, and improved Sp1-DNA binding activity and transactivation potential. Extrinsic expression of Sp1K16R increased cell survival and reduced ROS levels by upregulating Prdx6 expression in LECs under aging/oxidative stress, demonstrating that Sp1K16R escapes the aberrant Sumoylation processes. Intriguingly, the deleterious processes are reversible by the delivery of Sumoylation-deficient Prdx6, an antioxidant, which would be a candidate molecule to restrict aging pathobiology.

Nrf2-Mediated Antioxidant Defense and Peroxiredoxin 6 Are Linked to Biosynthesis of Palmitic Acid Ester of 9-Hydroxystearic Acid

Fatty acid esters of hydroxy fatty acids (FAHFAs) are lipid mediators with promising antidiabetic and anti-inflammatory properties that are formed in white adipose tissue (WAT) via de novo lipogenesis, but their biosynthetic enzymes are unknown. Using a combination of lipidomics in WAT, quantitative trait locus mapping, and correlation analyses in rat BXH/HXB recombinant inbred strains, as well as response to oxidative stress in murine models, we elucidated the potential pathway of biosynthesis of several FAHFAs. Comprehensive analysis of WAT samples identified ∼160 regioisomers, documenting the complexity of this lipid class. The linkage analysis highlighted several members of the nuclear factor, erythroid 2 like 2 (Nrf2)-mediated antioxidant defense system (Prdx6, Mgst1, Mgst3), lipid-handling proteins (Cd36, Scd6, Acnat1, Acnat2, Baat), and the family of flavin containing monooxygenases (Fmo) as the positional candidate genes. Transgenic expression of Nrf2 and deletion of Prdx6 genes resulted in reduction of palmitic acid ester of 9-hydroxystearic acid (9-PAHSA) and 11-PAHSA levels, while oxidative stress induced by an inhibitor of glutathione synthesis increased PAHSA levels nonspecifically. Our results indicate that the synthesis of FAHFAs via carbohydrate-responsive element-binding protein-driven de novo lipogenesis depends on the adaptive antioxidant system and suggest that FAHFAs may link activity of this system with insulin sensitivity in peripheral tissues.

Sulforaphane reactivates cellular antioxidant defense by inducing Nrf2/ARE/Prdx6 activity during aging and oxidative stress

Upon oxidative stress and aging, Nrf2 (NFE2-related factor2) triggers antioxidant defense genes to defends against homeostatic failure. Using human(h) or rat(r) lens epithelial cells (LECs) and aging human lenses, we showed that a progressive increase in oxidative load during aging was linked to a decline in Prdx6 expression. DNA binding experiments using gel-shift and ChIP assays demonstrated a progressive reduction in Nrf2/ARE binding (-357/-349) of Prdx6 promoter. The promoter (-918) with ARE showed a marked reduction in young vs aged hLECs, which was directly correlated to decreased Nrf2/ARE binding. A Nrf2 activator, Sulforaphane (SFN), augmented Prdx6, catalase and GSTπ expression in dose-dependent fashion, and halted Nrf2 dysregulation of these antioxidants. SFN reinforced Nrf2/DNA binding and increased promoter activities by enhancing expression and facilitating Nrf2 translocalization in nucleus. Conversely, promoter mutated at ARE site did not respond to SFN, validating the SFN-mediated restoration of Nrf2/ARE signaling. Furthermore, SFN rescued cells from UVB-induced toxicity in dose-dependent fashion, which was consistent with SFN's dose-dependent activation of Nrf2/ARE interaction. Importantly, knockdown of Prdx6 revealed that Prdx6 expression was prerequisite for SFN-mediated cytoprotection. Collectively, our results suggest that loss of Prdx6 caused by dysregulation of ARE/Nrf2 can be attenuated through a SFN, to combat diseases associated with aging.

Peroxiredoxin 6 expression is inversely correlated with nuclear factor-κB activation during Clonorchis sinensis infestation

Clonorchis sinensis is a carcinogenic human liver fluke. Its infection promotes persistent oxidative stress and chronic inflammation environments in the bile duct and surrounding liver tissues owing to direct contact with worms and their excretory-secretory products (ESPs), provoking epithelial hyperplasia, periductal fibrosis, and cholangiocarcinogenesis. We examined the reciprocal regulation of two ESP-induced redox-active proteins, NF-κB and peroxiredoxin 6 (Prdx6), during C. sinensis infection. Prdx6 overexpression suppressed intracellular free-radical generation by inhibiting NADPH oxidase2 and inducible nitric oxide synthase activation in the ESP-treated cholangiocarcinoma cells, substantially attenuating NF-κB-mediated inflammation. NF-κB overexpression decreased Prdx6 transcription levels by binding to two κB sites within the promoter. This transcriptional repression was compensated for by other ESP-induced redox-active transcription factors, including erythroid 2-related factor 2 (Nrf2), hypoxia inducible factor 1α (HIF1α), and CCAAT/enhancer-binding protein β (C/EBPβ). Distribution of immunoreactive Prdx6 and NF-κB was distinct in the early stages of infection in mouse livers but shared concomitant localization in the later stages. The intensity and extent of their immunoreactive staining in infected mouse livers are proportional to lesion severity and infection duration. The constitutive elevations of Prdx6 and NF-κB during C. sinensis infection may be associated with more severe persistent hepatobiliary abnormalities mediated by clonorchiasis.

Characterization of a 1-cysteine peroxiredoxin from big-belly seahorse (Hippocampus abdominalis); insights into host antioxidant defense, molecular profiling and its expressional response to septic conditions

1-cysteine peroxiredoxin (Prx6) is an antioxidant enzyme that protects cells by detoxifying multiple peroxide species. This study aimed to describe molecular features, functional assessments and potential immune responses of Prx6 identified from the big-belly seahorse, Hippocampus abdominalis (HaPrx6). The complete ORF (666 bp) of HaPrx6 encodes a polypeptide (24 kDa) of 222 amino acids, and harbors a prominent peroxiredoxin super-family domain, a peroxidatic catalytic center, and a peroxidatic cysteine. The deduced amino acid sequence of HaPrx6 shares a relatively high amino acid sequence similarity and close evolutionary relationship with Oplegnathus fasciatus Prx6. The purified recombinant HaPrx6 protein (rHaPrx6) was shown to protect plasmid DNA in the Metal Catalyzed Oxidation (MCO) assay and, together with 1,4-Dithiothreitol (DTT), protected human leukemia THP-1 cells from extracellular H2O2-mediated cell death. In addition, quantitative real-time PCR revealed that HaPrx6 mRNA was constitutively expressed in 14 different tissues, with the highest expression observed in liver tissue. Inductive transcriptional responses were observed in liver and kidney tissues of fish after treating them with bacterial stimuli, including LPS, Edwardsiella tarda, and Streptococcus iniae. These results suggest that HaPrx6 may play an important role in the immune response of the big-belly seahorse against microbial infection. Collectively, these findings provide structural and functional insights into HaPrx6.

Expression of Peroxiredoxins and Pulmonary Surfactant Protein A Induced by Silica in Rat Lung Tissue

Silicosis is one of the most serious occupational diseases in China and dates back to centuries ago. In this study, we successfully established a rat model of silicosis by intratracheal silica injection for 28 days and determined hydroxyproline levels to evaluate collagen metabolism in lung homogenates. Oxidative stress status was evaluated by detecting catalase and glutathione peroxidase activities. Expression levels of peroxiredoxins (Prx I and Prx VI) were detected by Western blotting. Pulmonary surfactant protein A (SP-A) levels in rat serum and lung tissue were analyzed by ELISA, and SP-A and Prx expression levels in lung tissues were detected by immunohistochemistry. The results suggest that Prx proteins may be involved in pulmonary fibrosis induced by silica. Downregulation of SP-A expression caused due to silica is an important factor in the occurrence and development of silicosis.

[Knockdown of PRDX6 in microglia reduces neuron viability after OGD/R injury]

Objective To observe the effects of peroxiredoxin 6 (PRDX6) knockdown in the microglia on neuron viability after oxygen-glucose deprivation and reoxygenation (OGD/R). Methods Microglia was treated with lentivirus PRDX6-siRNA and Ca(2+)-independent phospholipase A2 (iPLA2) inhibitor, 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33). Twenty-four hours later, it was co-cultured with primary neuron to establish the microglia-neuron co-culture OGD/R model. According to the different treatment of microglia, the cells were divided into normal group, OGD/R group, negative control-siRNA treated OGD/R group, PRDX6-siRNA treated OGD/R group and PRDX6-siRNA combined with MJ33 treated OGD/R group. Western blot analysis and real-time quantitative PCR were respectively performed to detect PRDX6 protein and mRNA levels after knockdown of PRDX6 in microglia. The iPLA2 activity was measured by ELISA. MTS and lactate dehydrogenase (LDH) assay were used to measure neuron viability and cell damage. The oxidative stress level of neuron was determined by measuring superoxide dismutase (SOD) and malonaldehyde (MDA) content. Results In PRDX6-siRNA group, neuron viability was inhibited and oxidative stress damage was aggravated compared with OGD/R group. In PRDX6-siRNA combined with MJ33 group, cell viability was promoted and oxidative stress damage was alleviated compared with PRDX6-siRNA group. Conclusion PRDX6 in microglia protects neuron against OGD/R-induced injury, and iPLA2 activity has an effect on PRDX6.

Peroxiredoxin 6 (Prdx6) supports NADPH oxidase1 (Nox1)-based superoxide generation and cell migration

Nox1 is an abundant source of reactive oxygen species (ROS) in colon epithelium recently shown to function in wound healing and epithelial homeostasis. We identified Peroxiredoxin 6 (Prdx6) as a novel binding partner of Nox activator 1 (Noxa1) in yeast two-hybrid screening experiments using the Noxa1 SH3 domain as bait. Prdx6 is a unique member of the Prdx antioxidant enzyme family exhibiting both glutathione peroxidase and phospholipase A2 activities. We confirmed this interaction in cells overexpressing both proteins, showing Prdx6 binds to and stabilizes wild type Noxa1, but not the SH3 domain mutant form, Noxa1 W436R. We demonstrated in several cell models that Prdx6 knockdown suppresses Nox1 activity, whereas enhanced Prdx6 expression supports higher Nox1-derived superoxide production. Both peroxidase- and lipase-deficient mutant forms of Prdx6 (Prdx6 C47S and S32A, respectively) failed to bind to or stabilize Nox1 components or support Nox1-mediated superoxide generation. Furthermore, the transition-state substrate analogue inhibitor of Prdx6 phospholipase A2 activity (MJ-33) was shown to suppress Nox1 activity, suggesting Nox1 activity is regulated by the phospholipase activity of Prdx6. Finally, wild type Prdx6, but not lipase or peroxidase mutant forms, supports Nox1-mediated cell migration in the HCT-116 colon epithelial cell model of wound closure. These findings highlight a novel pathway in which this antioxidant enzyme positively regulates an oxidant-generating system to support cell migration and wound healing.

Peroxiredoxin 6 homodimerization and heterodimerization with glutathione S-transferase pi are required for its peroxidase but not phospholipase A2 activity

Peroxiredoxin 6 (Prdx6) is a unique 1-Cys member of the peroxiredoxin family with both GSH peroxidase and phospholipase A2 (PLA2) activities. It is highly expressed in the lung where it plays an important role in antioxidant defense and lung surfactant metabolism. Glutathionylation of Prdx6 mediated by its heterodimerization with GSH S-transferase π (πGST) is required for its peroxidatic catalytic cycle. Recombinant human Prdx6 crystallizes as a homodimer and sedimentation equilibrium analysis confirmed that this protein exists as a high affinity dimer in solution. Based on measurement of molecular mass, dimeric Prdx6 that was oxidized to the sulfenic acid formed a sulfenylamide during storage. After examination of the dimer interface in the crystal structure, we postulated that the hydrophobic amino acids L145 and L148 play an important role in homodimerization of Prdx6 as well as in its heterodimerization with πGST. Oxidation of Prdx6 also was required for its heterodimerization. Sedimentation equilibrium analysis and the Duolink proximity ligation assay following mutation of the L145 and L148 residues of Prdx6 to Glu indicated greatly decreased dimerization propensity reflecting the loss of hydrophobic interactions between the protein monomers. Peroxidase activity was markedly reduced by mutation at either of the Leu sites and was essentially abolished by the double mutation, while PLA2 activity was unaffected. Decreased peroxidase activity following mutation of the interfacial leucines presumably is mediated via impaired heterodimerization of Prdx6 with πGST that is required for reduction and re-activation of the oxidized enzyme.

Impaired Lysosomal Integral Membrane Protein 2-dependent Peroxiredoxin 6 Delivery to Lamellar Bodies Accounts for Altered Alveolar Phospholipid Content in Adaptor Protein-3-deficient pearl Mice

The Hermansky Pudlak syndromes (HPS) constitute a family of disorders characterized by oculocutaneous albinism and bleeding diathesis, often associated with lethal lung fibrosis. HPS results from mutations in genes of membrane trafficking complexes that facilitate delivery of cargo to lysosome-related organelles. Among the affected lysosome-related organelles are lamellar bodies (LB) within alveolar type 2 cells (AT2) in which surfactant components are assembled, modified, and stored. AT2 from HPS patients and mouse models of HPS exhibit enlarged LB with increased phospholipid content, but the mechanism underlying these defects is unknown. We now show that AT2 in the pearl mouse model of HPS type 2 lacking the adaptor protein 3 complex (AP-3) fails to accumulate the soluble enzyme peroxiredoxin 6 (PRDX6) in LB. This defect reflects impaired AP-3-dependent trafficking of PRDX6 to LB, because pearl mouse AT2 cells harbor a normal total PRDX6 content. AP-3-dependent targeting of PRDX6 to LB requires the transmembrane protein LIMP-2/SCARB2, a known AP-3-dependent cargo protein that functions as a carrier for lysosomal proteins in other cell types. Depletion of LB PRDX6 in AP-3- or LIMP-2/SCARB2-deficient mice correlates with phospholipid accumulation in lamellar bodies and with defective intraluminal degradation of LB disaturated phosphatidylcholine. Furthermore, AP-3-dependent LB targeting is facilitated by protein/protein interaction between LIMP-2/SCARB2 and PRDX6 in vitro and in vivo Our data provide the first evidence for an AP-3-dependent cargo protein required for the maturation of LB in AT2 and suggest that the loss of PRDX6 activity contributes to the pathogenic changes in LB phospholipid homeostasis found HPS2 patients.

Identification and molecular characterization of peroxiredoxin 6 from Japanese eel (Anguilla japonica) revealing its potent antioxidant properties and putative immune relevancy

Peroxiredoxins (Prdx) are thiol specific antioxidant enzymes that play a pivotal role in cellular oxidative stress by reducing toxic peroxide compounds into nontoxic products. In this study, we identified and characterized a peroxiredoxin 6 counterpart from Japanese eel (Anguilla japonica) (AjPrdx6) at molecular, transcriptional and protein level. The identified full-length coding sequence of AjPrdx6 (669 bp) coded for a polypeptide of 223 aa residues (24.9 kDa). Deduced protein of AjPrdx6 showed analogy to characteristic structural features of 1-cysteine peroxiredoxin sub-family. According to the topology of the generated phylogenetic reconstruction AjPrdx6 showed closest evolutionary relationship with Salmo salar. As detected by Quantitative real time PCR (qPCR), AjPrdx6 mRNA was constitutively expressed in all the tissues examined. Upon the immune challenges with Edwardsiella tarda, lipopolysaccharides and polyinosinic:polycytidylic acid, expression of AjPrdx6 mRNA transcripts were significantly induced. The general functional properties of Prdx6 were confirmed using purified recombinant AjPrdx6 protein by deciphering its potent protective effects on cultured vero cells (kidney epithelial cell from an African green monkey) against H2O2-induced oxidative stress and protection against oxidative DNA damage elicited by mixed function oxidative (MFO) system. Altogether, our findings suggest that AjPrdx6 is a potent antioxidant protein in Japanese eels and its putative immune relevancy in pathogen stress mounted by live-bacteria or pathogen associated molecular patterns (PAMPs).

The Expression of Porcine Prdx6 Gene Is Up-Regulated by C/EBPβ and CREB

Peroxiredoxin6 (Prdx6) is one of the peroxiredoxin (Prdxs) family members that play an important role in maintaining cell homeostasis. Our previous studies demonstrated that Prdx6 was significantly associated with pig meat quality, especially meat tenderness. However, the transcriptional regulation of porcine Prdx6 remains unclear. In this study, we determined the transcription start site (TSS) of porcine Prdx6 gene by 5' rapid-amplification of cDNA ends (5' RACE). Several regulatory elements including CCAAT/enhancer-binding proteinβ (C/EBPβ), Myogenic Differentiation (MyoD), cAMP response element binding protein (CREB), stimulating protein1 (Sp1) and heat shock factor (HSF) binding sites were found by computational analyses together with luciferase reporter system. Overexpression and RNA interference experiments showed that C/EBPβ or CREB could up-regulate the expression of porcine Prdx6 gene at both mRNA and protein level. Electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation assays (ChIP) confirmed that C/EBPβ and CREB could interact with Prdx6 promoter. Immuoprecipitation results also showed that C/EBPβ could interact with Prdx6 in vivo. Taken together, our findings identified C/EBPβ and CREB as the important regulators of porcine Prdx6 gene expression, and offered clues for further investigation of Prdx6 gene function.

Critical role of peroxiredoxin 6 in the repair of peroxidized cell membranes following oxidative stress

Phospholipids are a major structural component of all cell membranes; their peroxidation represents a severe threat to cellular integrity and their repair is important to prevent cell death. Peroxiredoxin 6 (Prdx6), a protein with both GSH peroxidase and phospholipase A(2) (PLA(2)) activity, plays a critical role in antioxidant defense of the lung and other organs. We investigated the role of Prdx6 in the repair of peroxidized cell membranes in pulmonary microvascular endothelial cells (PMVEC) and isolated mouse lungs treated with tert-butyl hydroperoxide and lungs from mice exposed to hyperoxia (100% O(2)). Lipid peroxidation was evaluated by measurement of thiobarbituric acid reactive substances, oxidation of diphenyl-1-pyrenylphosphine, or ferrous xylenol orange assay. The exposure dose was varied to give a similar degree of lipid peroxidation at the end of exposure in the different models. Values for lipid peroxidation returned to control levels within 2 h after oxidant removal in wild-type PMVEC and perfused lungs but were unchanged in Pxdx6 null preparations. An intermediate degree of repair was observed with PMVEC and lungs that expressed only C47S or D140A mutant Prdx6; the former mutant does not have peroxidase activity, while the latter loses its PLA(2) activity. Prdx6 null mice showed markedly delayed recovery from lipid peroxidation during 20 h observation following exposure to hyperoxia. Thus, Prdx6 plays a critical role in the repair of peroxidized phospholipids in cell membranes and the recovery of lung cells from peroxidative stress; the peroxidase and PLA(2) activity each contribute to the recovery process.

Advancing age increases sperm chromatin damage and impairs fertility in peroxiredoxin 6 null mice

Due to socioeconomic factors, more couples are choosing to delay conception than ever. Increasing average maternal and paternal age in developed countries over the past 40 years has raised the question of how aging affects reproductive success of males and females. Since oxidative stress in the male reproductive tract increases with age, we investigated the impact of advanced paternal age on the integrity of sperm nucleus and reproductive success of males by using a Prdx6(-/-) mouse model. We compared sperm motility, cytoplasmic droplet retention sperm chromatin quality and reproductive outcomes of young (2-month-old), adult (8-month-old), and old (20-month-old) Prdx6(-/-) males with their age-matched wild type (WT) controls. Absence of PRDX6 caused age-dependent impairment of sperm motility and sperm maturation and increased sperm DNA fragmentation and oxidation as well as decreased sperm DNA compaction and protamination. Litter size, total number of litters and total number of pups per male were significantly lower in Prdx6(-/-) males compared to WT controls. These abnormal reproductive outcomes were severely affected by age in Prdx6(-/-) males. In conclusion, the advanced paternal age affects sperm chromatin integrity and fertility more severely in the absence of PRDX6, suggesting a protective role of PRDX6 in age-associated decline in the sperm quality and fertility in mice.

PRDX6 promotes tumor development via the JAK2/STAT3 pathway in a urethane-induced lung tumor model

Peroxiredoxin 6 (PRDX6) is a bifunctional protein with both glutathione peroxidase (GPx) and iPLA2 activities. Even though several pathophysiological functions have been studied, the definitive role of PRDX6 in tumor growth is not clear. Here, we compared carcinogen-induced tumor growth in PRDX6-transgenic (Tg) mice and non-Tg mice to evaluate the roles of PRDX6 in lung tumor development. Urethane (1g/kg)-induced tumor incidence in PRDX6-Tg mice was significantly higher compared to non-Tg mice. In the tumors of PRDX6-Tg mice, the activation of JAK2/STAT3 and STAT3 DNA binding were also increased, accompanied by increased GPx and iPLA2 activities. PRDX6 was colocalized with JAK2 in tumor tissues and lung cancer cells and also showed physical interaction with JAK2. We found that increasing levels of PRDX6 increase the activation of the JAK2/STAT3 pathway. Furthermore, PRDX6-Tg mice showed altered cytokine levels in the tumors, especially leading to increased CCL5 levels. We validated that the activation of JAK2 was also decreased in lung tumors of CCR5(-/-) mice, and CCL5 increased the JAK2/STAT3 pathway in the lung cancer cells. Thus, our findings suggest that PRDX6 promotes lung tumor development via its mediated and CCL5-associated activation of the JAK2/STAT3 pathway.

Peroxiredoxin 6, a novel player in the pathogenesis of diabetes

Enhanced oxidative stress contributes to the pathogenesis of diabetes and its complications. Peroxiredoxin 6 (PRDX6) is a key regulator of cellular redox balance, with the peculiar ability to neutralize peroxides, peroxynitrite, and phospholipid hydroperoxides. In the current study, we aimed to define the role of PRDX6 in the pathophysiology of type 2 diabetes (T2D) using PRDX6 knockout (-/-) mice. Glucose and insulin responses were evaluated respectively by intraperitoneal glucose and insulin tolerance tests. Peripheral insulin sensitivity was analyzed by euglycemic-hyperinsulinemic clamp, and molecular tools were used to investigate insulin signaling. Moreover, inflammatory and lipid parameters were evaluated. We demonstrated that PRDX6(-/-) mice developed a phenotype similar to early-stage T2D caused by both reduced glucose-dependent insulin secretion and increased insulin resistance. Impaired insulin signaling was present in PRDX6(-/-) mice, leading to reduction of muscle glucose uptake. Morphological and ultrastructural changes were observed in islets of Langerhans and livers of mutant animals, as well as altered plasma lipid profiles and inflammatory parameters. In conclusion, we demonstrated that PRDX6 is a key mediator of overt hyperglycemia in T2D glucose metabolism, opening new perspectives for targeted therapeutic strategies in diabetes care.

Antioxidant effects of lipophilic tea polyphenols on diethylnitrosamine/phenobarbital-induced hepatocarcinogenesis in rats

BACKGROUND

The purpose of the present study was to compare the antioxidant potential of lipophilic tea polyphenols (LTP) against the one of naturally-occurring water-soluble green tea polyphenols (GTP) in a two-stage model of diethylnitrosamine (DEN)/phenobarbital (PB)-induced hepatocarcinogenesis in Sprague-Dawley rats.

MATERIALS AND METHODS

GTP/LTP was given 5-times weekly by oral gavage with tea polyphenols equivalent to 0-, 40- and 400-mg/kg of body weight/day. GTP/LTP treatment was started 2 weeks prior to the initiation of DEN and continued for 30 weeks.

RESULTS

Histopathological and electron microscopic examination of liver tissue confirmed the protective effect of LTP on DEN/PB-induced liver damage and pre-carcinogenesis. LTP treatment significantly increased total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) activity in liver tissues. Immunohistochemical detection of cellular nuclear factor erythroid-2-related factor-2 (Nrf2) and peroxiredoxin-6 (P6) indicated a down-regulation in Nrf2 and up-regulation of P6 expression in the liver of LTP-supplemented rats.

CONCLUSION

The present study provides evidence for the first time, that LTP exerts significant antioxidant effects on DEN/PB-induced liver damage and hepatocarcinogenesis through elevating T-AOC levels, enhancing GSH-Px activity and inducing P6 expression in rat liver tissues.

Ligustilide ameliorates neuroinflammation and brain injury in focal cerebral ischemia/reperfusion rats: involvement of inhibition of TLR4/peroxiredoxin 6 signaling

Blocking TLR4/peroxiredoxin (Prx6) signaling is proposed to be a novel therapeutic strategy for ischemic stroke because extracellular Prx6 released from ischemic cells may act as an endogenous ligand for TLR4 and initiate destructive immune responses in ischemic brain. Our previous studies showed that ligustilide (LIG) exerted antineuroinflammatory and neuroprotective effects against ischemic insult, but the underlying mechanisms remain unclear. This study investigated whether the TLR4/Prx6 pathway is involved in the protective effect of LIG against postischemic neuroinflammation and brain injury induced by transient middle cerebral artery occlusion (MCAO) in rats. Intraperitoneal LIG administration (20 and 40 mg/kg/day) at reperfusion onset after MCAO resulted in a reduction of brain infarct size and improved neurological outcome over 72 h. LIG-induced neuroprotection was accompanied by improvement of neuropathological alterations, including neuron loss, astrocyte and microglia/macrophage activation, neutrophil and T-lymphocyte invasion, and regulation of inflammatory mediators expression. Moreover, LIG significantly inhibited the expression and extracellular release of Prx6 and activation of TLR4 signaling, reflected by decreased TLR4 expression, extracellular signal-regulated kinase 1/2 phosphorylation, and transcriptional activity of NF-κB and signal transducer and activator of transcription 3 in the ischemic brain. Our results demonstrate that LIG may provide an early and direct neuroprotection by inhibiting TLR4/Prx6 signaling and subsequent immunity and neuroinflammation after cerebral ischemia. These findings support the translational potential of blocking TLR4/Prx6 signaling for the treatment of ischemic stroke.

PRDX6 promotes lung tumor progression via its GPx and iPLA2 activities

PRDX6 is a bifunctional protein with both glutathione peroxidase (GPx) and calcium-independent phospholipase A2 (iPLA2) activities, which are concomitantly increased with the expression of PRDX6. PRDX6 promoted lung tumor growth in an in vivo allograft model. Herein, we further studied the vital roles in tumor progression of PRDX6 in lung cancer using nude mice bearing PRDX6-overexpressing lung cancer cells. Nude mice xenografted with PRDX6 showed increases in tumor size and weight compared to control mice. Histopathological and Western blotting examination demonstrated that expression of proliferating cell nuclear antigen, vascular endothelial growth factor, metalloproteinases 2 and 9, and cyclin-dependent kinases accompanied by increased iPLA2 and GPx activities were increased in the tumor tissues of PRDX6-overexpressing nude mice. In tumor tissues of PRDX6-overexpressing mice, the activation of mitogen-activated protein kinases and AP-1 DNA binding were also increased. The growth of lung cancer cell lines (A549 and NCI-H460) was enhanced by the increase in iPLA2 and GPx activities of PRDX6. In addition, mutant PRDX6 (C47S) attenuated PRDX6-mediated p38, ERK1/2, and AP-1 activities as well as its enzyme activities in the A549 and NCI-H460 lines. Furthermore, tumor growth and p38, ERK1/2, and AP-1 activities were also inhibited in nude mice bearing mutant PRDX6 (C47S) compared to PRDX6. Therefore, our findings indicate that PRDX6 promotes lung tumor growth via increased glutathione peroxidase and iPLA2 activities.

Protein and miRNA profiling of radiation-induced skin injury in rats: the protective role of peroxiredoxin-6 against ionizing radiation

Radiation-induced skin injury is a serious concern during radiotherapy. However, the molecular mechanism underlying the pathogenesis of radiation-induced skin injury has not been extensively reported. Most biological functions are performed and regulated by proteins and noncoding RNAs, including microRNAs (miRNAs). The interplay between mRNA and miRNA has been implicated in disease initiation and progression. Technical advances in genomics and proteomics have enabled the exploration of the etiology of diseases and have the potential to broaden our understanding of the molecular pathogenesis of radiation-induced skin injury. In this study, we compared the protein and miRNA expression in rat skin irradiated with a 45-Gy electron beam with expression from adjacent normal tissues. We found 24 preferentially expressed proteins and 12 dysregulated miRNAs in irradiated skin. By analyzing the protein and miRNA profiles using bioinformatics tools, we identified a possible interaction between miR-214 and peroxiredoxin-6 (PRDX-6). Next, we investigated the expression of PRDX-6 and the consequences of its dysregulation. PRDX-6 is suppressed by radiation-inducible miR-214 and is involved in the pathogenesis of radiation-induced skin injury. Overexpression of PRDX-6 conferred radioresistance on cells, decreased cell apoptosis, and preserved mitochondrial integrity after radiation exposure. In addition, in vivo transfection with PRDX-6 reduced radiation-induced reactive oxygen species and the malondialdehyde concentration and ameliorated radiation-induced skin damage in rats. Our present findings illustrate the molecular changes during radiation-induced skin injury and the important role of PRDX-6 in ameliorating this damage in rats.

Anti-cancer effect of thiacremonone through down regulation of peroxiredoxin 6

Thiacremonone (2, 4-dihydroxy-2, 5-dimethyl-thiophene-3-one) is an antioxidant substance as a novel sulfur compound generated from High-Temperature-High-Pressure-treated garlic. Peroxiredoxin 6 (PRDX6) is a member of peroxidases, and has glutathione peroxidase and calcium-independent phospholipase A2 (iPLA2) activities. Several studies have demonstrated that PRDX6 stimulates lung cancer cell growth via an increase of glutathione peroxidase activity. A docking model study and pull down assay showed that thiacremonone completely fits on the active site (cys-47) of glutathione peroxidase of PRDX6 and interacts with PRDX6. Thus, we investigated whether thiacremonone inhibits cell growth by blocking glutathione peroxidase of PRDX6 in the human lung cancer cells, A549 and NCI-H460. Thiacremonone (0-50 μg/ml) inhibited lung cancer cell growth in a concentration dependent manner through induction of apoptotic cell death accompanied by induction of cleaved caspase-3, -8, -9, Bax, p21 and p53, but decrease of xIAP, cIAP and Bcl2 expression. Thiacremonone further inhibited glutathione peroxidase activity in lung cancer cells. However, the cell growth inhibitory effect of thiacremonone was not observed in the lung cancer cells transfected with mutant PRDX6 (C47S) and in the presence of dithiothreitol and glutathione. In an allograft in vivo model, thiacremonone (30 mg/kg) also inhibited tumor growth accompanied with the reduction of PRDX6 expression and glutathione peroxidase activity, but increased expression of cleaved caspase-3, -8, -9, Bax, p21 and p53. These data indicate that thiacremonone inhibits tumor growth via inhibition of glutathione peroxidase activity of PRDX6 through interaction. These data suggest that thiacremonone may have potentially beneficial effects in lung cancer.