Peroxiredoxin 6 suppresses ferroptosis in lung endothelial cells

Peroxiredoxin 6 (Prdx6) repairs peroxidized membranes by reducing oxidized phospholipids, and by replacing oxidized sn-2 fatty acyl groups through hydrolysis/reacylation by its phospholipase A2 (aiPLA2) and lysophosphatidylcholine acyltransferase activities. Prdx6 is highly expressed in the lung, and intact lungs and cells null for Prdx6 or with single-point mutations that inactivate either Prdx6-peroxidase or aiPLA2 activity alone exhibit decreased viability, increased lipid peroxidation, and incomplete repair when exposed to paraquat, hyperoxia, or organic peroxides. Ferroptosis is form of cell death driven by the accumulation of phospholipid hydroperoxides. We studied the role of Prdx6 as a ferroptosis suppressor in the lung. We first compared the expression Prdx6 and glutathione peroxidase 4 (GPx4) and visualized Prdx6 and GPx4 within the lung. Lung Prdx6 mRNA levels were five times higher than GPx4 levels. Both Prdx6 and GPx4 localized to epithelial and endothelial cells. Prdx6 knockout or knockdown sensitized lung endothelial cells to erastin-induced ferroptosis. Cells with genetic inactivation of either aiPLA2 or Prdx6-peroxidase were more sensitive to ferroptosis than WT cells, but less sensitive than KO cells. We then conducted RNA-seq analyses in Prdx6-depleted cells to further explore how the loss of Prdx6 sensitizes lung endothelial cells to ferroptosis. Prdx6 KD upregulated transcriptional signatures associated with selenoamino acid metabolism and mitochondrial function. Accordingly, Prdx6 deficiency blunted mitochondrial function and increased GPx4 abundance whereas GPx4 KD had the opposite effect on Prdx6. Moreover, we detected Prdx6 and GPx4 interactions in intact cells, suggesting that both enzymes cooperate to suppress lipid peroxidation. Notably, Prdx6-depleted cells remained sensitive to erastin-induced ferroptosis despite the compensatory increase in GPx4. These results show that Prdx6 suppresses ferroptosis in lung endothelial cells and that both aiPLA2 and Prdx6-peroxidase contribute to this effect. These results also show that Prdx6 supports mitochondrial function and modulates several coordinated cytoprotective pathways in the pulmonary endothelium.

Expression and clinical role of PRDX6 in lung adenocarcinoma

OBJECTIVE

To explore the levels of expression and clinical role of peroxiredoxin 6 (PRDX6) in lung adenocarcinoma.

METHODS

This retrospective study used a series of bioinformatics methods to detect the levels of expression of and mutations in the PRDX6 gene in a range of cancers and lung adenocarcinoma. Immunohistochemistry was used to verify the levels of expression of PRDX6 protein in samples of lung adenocarcinoma compared with normal adjacent tissue. The effect of PRDX6 gene knockdown on the in vitro proliferation of a lung adenocarcinoma cell line was measured. Bioinformatics methods were used to determine the diagnostic value and impact on survival of the PRDX6 gene in patients with lung adenocarcinoma.

RESULTS

The results showed that the PRDX6 gene was highly expressed in lung adenocarcinoma and there were five mutations at different sites on the gene. PRDX6 promoted the proliferation of the lung adenocarcinoma cell line. The survival duration of lung adenocarcinoma patients with high levels of PRDX6 gene expression was significantly shorter than that of patients with low PRDX6 gene expression.

CONCLUSION

PRDX6 is highly expressed in lung adenocarcinoma and higher levels of expression of the PRDX6 gene were associated with a poorer prognosis.

PRDX6-iPLA2 aggravates neuroinflammation after ischemic stroke via regulating astrocytes-induced M1 microglia

The crosstalk between astrocytes and microglia plays a pivotal role in neuroinflammation following ischemic stroke, and phenotypic distribution of these cells can change with the progression of ischemic stroke. Peroxiredoxin (PRDX) 6 phospholipase A2 (iPLA2) activity is involved in the generation of reactive oxygen species(ROS), with ROS driving the activation of microglia and astrocytes; however, its exact function remains unexplored. MJ33, PRDX6D140A mutation was used to block PRDX6-iPLA2 activity in vitro and vivo after ischemic stroke. PRDX6T177A mutation was used to block the phosphorylation of PRDX6 in CTX-TNA2 cell lines. NAC, GSK2795039, Mdivi-1, U0126, and SB202190 were used to block the activity of ROS, NOX2, mitochondrial fission, ERK, and P38, respectively, in CTX-TNA2 cells. In ischemic stroke, PRDX6 is mainly expressed in astrocytes and PRDX6-iPLA2 is involved in the activation of astrocytes and microglia. In co-culture system, Asp140 mutation in PRDX6 of CTX-TNA2 inhibited the polarization of microglia, reduced the production of ROS, suppressed NOX2 activation, and inhibited the Drp1-dependent mitochondrial fission following OGD/R. These effects were further strengthened by the inhibition of ROS production. In subsequent experiments, U0126 and SB202190 inhibited the phosphorylation of PRDX6 at Thr177 and reduced PRDX6-iPLA2 activity. These results suggest that PRDX6-iPLA2 plays an important role in the astrocyte-induced generation of ROS and activation of microglia, which are regulated by the activation of Nox2 and Drp1-dependent mitochondrial fission pathways. Additionally, PRDX6-iPLA2 activity is regulated by MAPKs via the phosphorylation of PRDX6 at Thr177 in astrocytes.

An Increase in Peroxiredoxin 6 Expression Induces Neurotoxic A1 Astrocytes in the Lumbar Spinal Cord of Amyotrophic Lateral Sclerosis Mice Model

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease with selective degeneration of motor neurons. It has been reported that an increase in the levels of inflammatory cytokines and glial cells such as reactive astrocytes is closely involved in the pathological progression of ALS. Recently, the levels of neuropathic cytotoxic (A1) astrocytes among reactive astrocytes have reportedly increased in the central nervous system of ALS mice, which induce motor neuron degeneration through the production of inflammatory cytokines and secretion of neuropathic factors. Hence, elucidating the induction mechanism of A1 astrocytes in ALS is important to understand the mechanism of disease progression in ALS. In this study, we observed that the expression of peroxiredoxin 6 (PRDX6), a member of the peroxiredoxin family, was markedly upregulated in astrocytes of the lumbar spinal cord of SOD1G93A mice model for ALS. Additionally, when PRDX6 was transiently transfected into the mouse astrocyte cell line C8-D1A and human astrocytoma cell line U-251 MG, the mRNA expression of complement C3 (a marker for A1 astrocyte phenotype) and inflammatory cytokines was increased. Furthermore, the mRNA expression of C3 and inflammatory cytokine was increased in C8-D1A and U-251 MG cells stably expressing PRDX6, and the increased mRNA expression was significantly suppressed by MJ33 (lithium[1-hexadecoxy-3-(2,2,2-trifluoroethoxy) propan-2-yl] methyl phosphate), an inhibitor of the phospholipase A2 activity of PRDX6. Our results suggest that the expression of PRDX6 in astrocytes plays an important role in the induction of A1 astrocytes and expression of inflammatory cytokines in the ALS mice model.

Curcumin strengthens a spontaneous self-protective mechanism-SP1/PRDX6 pathway, against di-n-butyl phthalate-induced testicular ferroptosis damage

As one of the common plasticizers, di-n-butyl phthalate (DBP) has been using in various daily consumer products worldwide. Since it is easily released from products and exists in the environment for a long time, it has a lasting impact on human health, especially male reproductive health. However, the detailed mechanism of testicular damage from DBP and the protection strategy are still not clear enough. In this study, we found that DBP could induce dose-dependent ferroptosis in testicular tissue. Mechanism dissection indicates that DBP can upregulate SP1 expression, which could directly transcriptionally upregulate PRDX6, a negative regulator of ferroptosis. Overexpression of PRDX6 or adding SP1 agonist curcumin could suppress the DBP-induced ferroptosis on testicular cells. In vivo, rats were given 500 mg/kg/day DBP orally for 3 weeks; elevated levels of ferroptosis were detected in testicular tissue. When the above-mentioned doses of DBP and curcumin at a dose of 300 mg/kg/day were administered intragastrically simultaneously, the testicular ferroptosis induced by DBP was alleviated. Immunohistochemistry and quantitative real-time PCR of testis tissue showed that the expression of PRDX6 was upregulated under the action of DBP and curcumin. These findings suggest a spontaneous self-protection mechanism of testicular tissue from DBP damage by upregulating SP1 and PRDX6. However, it is not strong enough to resist the DBP-induced ferroptosis. Curcumin can strengthen this self-protection mechanism and weaken the level of ferroptosis induced by DBP. This study may help us to develop a novel therapeutic option with curcumin to protect the testicular tissue from ferroptosis and function impairment by DBP.

Prdx6 Regulates Nlrp3 Inflammasome Activation-Driven Inflammatory Response in Lens Epithelial Cells

The continuum of antioxidant response dysregulation in aging/oxidative stress-driven Nlrp3 inflammasome activation-mediated inflammatory response is associated with age-related diseases. Peroxiredoxin (Prdx) 6 is a key antioxidant that provides cytoprotection by regulating redox homeostasis. Herein, using lens epithelial cells (LECs) derived from the targeted inactivation of Prdx6 gene and aging lenses, we present molecular evidence that Prdx6-deficiency causes oxidative-driven Nlrp3 inflammasome activation, resulting in pyroptosis in aging/redox active cells wherein Prdx6 availability offsets the inflammatory process. We observed that Prdx6-/- and aging LECs harboring accumulated reactive oxygen species (ROS) showed augmented activation of Nlrp3 and bioactive inflammatory components, like Caspase-1, IL-1β, ASC and Gasdermin-D. Similar to lipopolysaccharide treatment, oxidative exposure led to further ROS amplification with increased activation of the Nlrp3 inflammasome pathway. Mechanistically, we found that oxidative stress enhanced Kruppel-like factor 9 (Klf9) expression in aging/Prdx6-/- mLECs, leading to a Klf9-dependent increase in Nlrp3 transcription, while the elimination of ROS by the delivery of Prdx6 or by silencing Klf9 prevented the inflammatory response. Altogether, our data identify the biological significance of Prdx6 as an intrinsic checkpoint for regulating the cellular health of aging or redox active LECs and provide opportunities to develop antioxidant-based therapeutic(s) to prevent oxidative/aging-related diseases linked to aberrant Nlrp3 inflammasome activation.

Protective Effects of Peroxiredoxin 6 in Pro-Inflammatory Response Model Using Raw 264.7 Macrophages

The aim of the work was to study effects of peroxiredoxin 6 (PRDX6), a recombinant antioxidant protein, on the level of pro-inflammatory responses of RAW 264.7 macrophages to endotoxin exposure. Addition of LPS to the RAW 264.7 cell culture medium expectedly increased production of TNF-α, and addition of PRDX6 led to a significant (15-20%) decrease in its production. The level of production of another pro-inflammatory cytokine, IL-1β, which was significantly activated by endotoxin, was completely normalized under the PRDX6 action. Moreover, addition of PRDX6 reduced production of reactive oxygen species (ROS) induced by endotoxin and also prevented overexpression of the iNos gene in the RAW 264.7 cells. The results showed that PRDX6 had a suppressive effect on the expression of Nrf-2 gene and production of the transcription factor NRF-2 during the first 6 h of cell cultivation. Addition of endotoxin caused activation of the NF-κB and SAPK/JNK signaling cascades, while in the presence of PRDX6, activity of these signaling cascades decreases. It is known that the pro-inflammatory response of cells caused by exposure to bacterial LPS leads to activation of apoptosis and elimination of the damaged cells. Our studies confirm this, since exposure to LPS led to activation of the expression of P53 gene, a marker of apoptosis. Peroxiredoxin 6 added within the first hours of the development of acute pro-inflammatory response suppressed the P53 gene expression, indicating protective effect of PRDX6 that reduced apoptosis in the RAW 264.7 macrophages.

The Role of Phospholipase Activity of Peroxiredoxin 6 in Its Transmembrane Transport and Protective Properties

Peroxiredoxin 6 (Prdx6) is a multifunctional eukaryotic antioxidant enzyme. Mammalian Prdx6 possesses peroxidase activity against a wide range of organic and inorganic hydroperoxides, as well as exhibits phospholipase A2 (aiPLA2) activity, which plays an important role in the reduction of oxidized phospholipids and cell membrane remodeling. Exogenous Prdx6 has recently been shown to be able to penetrate inside the cell. We hypothesized that this entry may be due to the phospholipase activity of Prdx6. Experiments using exogenous Prdx6 in three cell lines (3T3, A549, RAW 264.7) demonstrated that it is the phospholipase activity that promotes its penetration into the cell. Overoxidation of Prdx6 led to a suppression of the peroxidase activity and a 3-to-4-fold growth of aiPLA2, which enhanced the efficiency of its transmembrane transport into the cells by up to 15 times. A mutant form of Prdx6-S32A with an inactivated phospholipase center turned out to be unable to enter the cells in both the reduced and oxidized state of the peroxidase active center. Previously, we have shown that exogenous Prdx6 has a significant radioprotective action. However, the role of phospholipase activity in the radioprotective effects of Prdx6 remained unstudied. Trials with the mutant Prdx6-S32A form, with the use of a total irradiation model in mice, showed a nearly 50% reduction of the radioprotective effect upon aiPLA2 loss. Such a significant decrease in the radioprotective action may be due to the inability of Prdx6-S32A to penetrate animal cells, which prevents its reduction by the natural intracellular reducing agent glutathione S-transferase (πGST) and lowers the efficiency of elimination of peroxides formed from the effect of ionizing radiation. Thus, phospholipase activity may play an important role in the reduction of oxidized Prdx6 and manifestation of its antioxidant properties.

The role of peroxiredoxin 6 in biosynthesis of FAHFAs

Peroxiredoxin 6 (Prdx6) is a multifunctional enzyme, a unique member of the peroxiredoxin family, with an important role in antioxidant defense. Moreover, it has also been linked with the biosynthesis of anti-inflammatory and anti-diabetic lipids called fatty acid esters of hydroxy fatty acids (FAHFAs) and many diseases, including cancer, inflammation, and metabolic disorders. Here, we performed metabolomic and lipidomic profiling of subcutaneous adipose tissue from mouse models with genetically modified Prdx6. Deletion of Prdx6 resulted in reduced levels of FAHFAs containing 13-hydroxylinoleic acid (13-HLA). Mutation of Prdx6 C47S impaired the glutathione peroxidase activity and reduced FAHFA levels, while D140A mutation, responsible for phospholipase A2 activity, showed only minor effects. Targeted analysis of oxidized phospholipids and triacylglycerols in adipocytes highlighted a correlation between FAHFA and hydroxy fatty acid production by Prdx6 or glutathione peroxidase 4. FAHFA regioisomer abundance was negatively affected by the Prdx6 deletion, and this effect was more pronounced in longer and more unsaturated FAHFAs. The predicted protein model of Prdx6 suggested that the monomer-dimer transition mechanism might be involved in the repair of longer-chain peroxidized phospholipids bound over two monomers and that the role of Prdx6 in FAHFA synthesis might be restricted to branching positions further from carbon 9. In conclusion, our work linked the peroxidase activity of Prdx6 with the levels of FAHFAs in adipose tissue.

PRDX6AS1 gene polymorphisms and SLE susceptibility in Chinese populations

Background

Systemic lupus erythematosus (SLE) is a complex, multisystem autoimmune disease that is characterized by the production of autoantibodies. Although accumulated evidence suggests that the dysregulation of long non-coding RNAs (lncRNAs) is involved in the pathogenesis of SLE, the genetic contributions of lncRNA coding genes to SLE susceptibility remain largely unknown. Here, we aimed to provide more evidence for the role of lncRNA coding genes to SLE susceptibility.

Methods

The genetic association analysis was first adopted from the previous genome-wide association studies (GWAS) and was then validated in an independent cohort. PRDX6-AS1 is located at chr1:173204199-173446294. It spans a region of approximately 240 kb, and 297 single nucleotide polymorphisms (SNPs) were covered by the previous GWAS. Differential expression at the mRNA level was analyzed based on the ArrayExpress Archive database.

Results

A total of 33 SNPs were associated with SLE susceptibility, with a P<1.68×10^-4. The strongest association signal was detected at rs844649 (P=2.12×10^-6), according to the previous GWAS. Combining the results from the GWAS Chinese cohort and our replication cohort, we pursued a meta-analysis approach and found a pronounced genetic association between PRDX6-AS1 rs844649 and SLE susceptibility (p_meta=1.24×10^-13, OR 1.50, 95% CI: 1.34–1.67). The mRNA expression of PRDX6 was elevated in peripheral blood cells, peripheral blood mononuclear cells (PBMCs), and multiple cell subpopulations, such as B cells, CD4⁺ T cells, CD3⁺ cells, and monocytes in patients with SLE. The PRDX6 protein expression level was also increased in patients with SLE compared with healthy donors.

Conclusion

Our study provides new evidence that variants located in lncRNA coding genes are associated with SLE susceptibility.

Effect of Peroxiredoxin 6 on p53 Transcription Factor Level

Peroxiredoxin 6 (Prdx6) is an important antioxidant enzyme with multiple functions in the cell. Prdx6 neutralizes a wide range of hydroperoxides, participates in phospholipid metabolism and cell membrane repair, and in transmission of intracellular and intercellular signals. Disruption of normal Prdx6 expression in the cell leads to the development of pathological conditions. Decrease in the Prdx6 concentration leads to increase in oxidative damage to the cell. At the same time, hyperproduction of Prdx6 is associated with increase in antioxidant status, suppression of apoptosis, and carcinogenesis. Currently, mechanisms of carcinogenic action of peroxiredoxins are poorly understood. In this work we established that the 3-4-fold increase in Prdx6 production in mouse embryonic fibroblast 3T3 cells leads to the 4-5-fold decrease in the level of oncosuppressor p53. At the same time, hyperproduction of Prdx6 leads to the increased expression of RELA and HIF1A, which have oncogenic effects. The 3-4-fold increase in intracellular Prdx6 increases intensity of cell proliferation by 20-30%, promotes increase in antioxidant activity by 30-50%, and increases radioresistance of the transfected 3T3 cells by 30-40%. Increase of the level of intranuclear Prdx6 leads to the decrease in expression of the DNA repair genes in response to radiation, indicating decrease in the genomic DNA damage. This work discusses possible molecular mechanisms of p53 suppression during Prdx6 hyperproduction, which could be used in the development of new approaches in cancer therapy.

Circular RNA hsa_circ_0011385 contributes to cervical cancer progression through sequestering miR-149-5p and increasing PRDX6 expression

Cervical cancer (CC) is a common tumor in the female reproductive tract. Circular RNA hsa_circ_0011385 has been reported to be up-regulated in CC tissues. Nevertheless, the role and regulatory mechanism of hsa_circ_0011385 in CC are still being further verified. The levels of hsa_circ_0011385, microRNA (miR)- 149-5p, and peroxiredoxin 6 (PRDX6) mRNA in CC samples and cell lines were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Loss-of-function experiments were performed to survey the impacts of hsa_circ_0011385 inhibition on CC cell proliferation, colony formation, cycle progression, apoptosis, metastasis, invasion, and angiogenesis. Protein levels were detected by western blotting. The relationship between hsa_circ_0011385 or PRDX6 and miR-149-5p was verified by dual-luciferase reporter, RNA immunoprecipitation (RIP), and/or RNA pull-down assays. The tumorigenesis role of hsa_circ_0011385 in CC was confirmed by xenograft assay. We observed that hsa_circ_0011385 and PRDX6 were up-regulated while miR-149-5p was down-regulated in CC samples and cell lines. CC patients with high hsa_circ_0011385 expression possessed a shorter overall survival. Hsa_circ_0011385 knockdown reduced tumor growth in vivo and facilitated apoptosis, cell cycle arrest, impeded proliferation, metastasis, invasion, and angiogenesis of CC cells in vitro. Hsa_circ_0011385 could mediate PRDX6 expression through binding to miR-149-5p. MiR-149-5p silencing reversed hsa_circ_0011385 knockdown-mediated effects on CC cell angiogenesis and malignancy. PRDX6 overexpression overturned the inhibitory effects of miR-149-5p overexpression on angiogenesis and malignant behaviors of CC cells. In conclusion, hsa_circ_0011385 accelerated angiogenesis and malignant behaviors of CC cells by regulating the miR-149-5p/PRDX6 axis, manifesting that hsa_circ_0011385 might be a therapeutic target for CC.

Peroxiredoxin 6 Modulates Insulin Secretion and Beta Cell Death via a Mitochondrial Dynamic Network

In pancreatic beta cells, mitochondrial metabolism controls glucose-stimulated insulin secretion (GSIS) by ATP production, redox signaling, and calcium (Ca²⁺) handling. Previously, we demonstrated that knockout mice for peroxiredoxin 6 (Prdx6^-/- ), an antioxidant enzyme with both peroxidase and phospholipase A2 activity, develop a mild form of diabetes mellitus with a reduction in GSIS and in peripheral insulin sensitivity. However, whether the defect of GSIS present in these mice is directly modulated by Prdx6 is unknown. Therefore, the main goal of the present study was to evaluate if depletion of Prdx6 affects directly GSIS and pancreatic beta β-cell function. Murine pancreatic β-cell line (βTC6) knockdown for Prdx6 (Prdx6^KD) was employed, and insulin secretion, ATP, and intracellular Ca²⁺ content were assessed in response to glucose stimulation. Mitochondrial morphology and function were also evaluated through electron microscopy, and by testing mitochondrial membrane potential, oxygen consumption, and mitochondrial mass. Prdx6^KD cells showed a significant reduction in GSIS as confirmed by decrease in both ATP release and Ca²⁺ influx. GSIS alteration was also demonstrated by a marked impairment of mitochondrial morphology and function. These latest are mainly linked to mitofusin downregulation, which are, in turn, strictly related to mitochondrial homeostasis (by regulating autophagy) and cell fate (by modulating apoptosis). Following a pro-inflammatory stimulus (typical of diabetic subjects), and in agreement with the deregulation of mitofusin steady-state levels, we also observed an enhancement in apoptotic death in Prdx6^KD compared to control cells. We analyzed molecular mechanisms leading to apoptosis, and we further demonstrated that Prdx6 suppression activates both intrinsic and extrinsic apoptotic pathways, ultimately leading to caspase 3 and PARP-1 activation. In conclusion, Prdx6 is the first antioxidant enzyme, in pancreatic β-cells, that by controlling mitochondrial homeostasis plays a pivotal role in GSIS modulation.

Identification of peroxiredoxin 6 as a direct target of withangulatin A by quantitative chemical proteomics in non-small cell lung cancer

Peroxiredoxin 6 (PRDX6), as a bifunctional enzyme with glutathione peroxidase activity (GPx) and Ca2+-independent phospholipase A2 (iPLA2) activity, has a higher expression in various cancer cells, which leads to the increase of antioxidant properties and promotes tumorigenesis. However, only a few inhibitors of PRDX6 have been discovered to date, especially the covalent inhibitors of PRDX6. Here, we firstly identified Withangulatin A (WA), a natural small molecule, as a novel covalent inhibitor of PRDX6. SILAC-ABPP identified that WA could directly bind to PRDX6 and inactivate the enzyme activity of PRDX6 by the α, β-unsaturated ketone moiety. Moreover, WA also facilitated the generation of ROS, and inhibited the GPx and iPLA2 activities. However, WA-1, with a reduced α, β-unsaturated ketone moiety, had no significant inhibition of the GPx and iPLA2 activities. Biolayer interferometry and LC-MS/MS analysis further demonstrated the selectively covalent binding of WA to the cysteine 47 residue (Cys47) of PRDX6, while mutation of Cys47 blocked the binding of WA to PRDX6. Notably, WA-mediated cytotoxicity and inhibition of the GPx and iPLA2 activities were almost abolished by the deficiency of PRDX6. Therefore, this study indicates that WA is a novel PRDX6 covalent inhibitor, which could covalently bind to the Cys47 of PRDX6 and holds great potential in developing anti-tumor agents for targeting PRDX6.

Porcine Picornavirus 3C Protease Degrades PRDX6 to Impair PRDX6-mediated Antiviral Function

Peroxiredoxin-6 (PRDX6) is an antioxidant enzyme with both the activities of peroxidase and phospholipase A2 (PLA2), which is involved in regulation of many cellular reactions. However, the function of PRDX6 during virus infection remains unknown. In this study, we found that the abundance of PRDX6 protein was dramatically decreased in foot-and-mouth disease virus (FMDV) infected cells. Overexpression of PRDX6 inhibited FMDV replication. In contrast, knockdown of PRDX6 expression promoted FMDV replication, suggesting an antiviral role of PRDX6. To explore whether the activity of peroxidase and PLA2 was associated with PRDX6-mediated antiviral function, a specific inhibitor of PLA2 (MJ33) and a specific inhibitor of peroxidase activity (mercaptosuccinate) were used to treat the cells before FMDV infection. The results showed that incubation of MJ33 but not mercaptosuccinate promoted FMDV replication. Meanwhile, overexpression of PRDX6 slightly enhanced type I interferon signaling. We further determined that the viral 3Cpro was responsible for degradation of PRDX6, and 3Cpro-induced reduction of PRDX6 was independent of the proteasome, lysosome, and caspase pathways. The protease activity of 3Cpro was required for induction of PRDX6 reduction. Besides, PRDX6 suppressed the replication of another porcine picornavirus Senecavirus A (SVA), and the 3Cpro of SVA induced the reduction of PRDX6 through its proteolytic activity as well. Together, our results suggested that PRDX6 plays an important antiviral role during porcine picornavirus infection, and the viral 3Cpro induces the degradation of PRDX6 to overcome PRDX6-mediated antiviral function.

Lack of the peroxiredoxin 6 gene causes impaired spatial memory and abnormal synaptic plasticity

Peroxiredoxin 6 (PRDX6) is expressed dominantly in the astrocytes and exerts either neuroprotective or neurotoxic effects in the brain. Although PRDX6 can modulate several signaling cascades involving cognitive functions, its physiological role in spatial memory has not been investigated yet. This study aims to explore the function of the Prdx6 gene in spatial memory formation and synaptic plasticity. We first tested Prdx6-/- mice on a Morris water maze task and found that their memory performance was defective, along with reduced long-term potentiation (LTP) in CA3-CA1 hippocampal synapses recorded from hippocampal sections of home-caged mice. Surprisingly, after the probe test, these knockout mice exhibited elevated hippocampal LTP, higher phosphorylated ERK1/2 level, and decreased reactive astrocyte markers. We further reduced ERK1/2 phosphorylation by administering MEK inhibitor, U0126, into Prdx6-/- mice before the probe test, which reversed their spatial memory deficit. This study is the first one to report the role of PRDX6 in spatial memory and synaptic plasticity. Our results revealed that PRDX6 is necessary for maintaining spatial memory by modulating ERK1/2 phosphorylation and astrocyte activation.

KLF9 regulates PRDX6 expression in hyperglycemia-aggravated bupivacaine neurotoxicity

BACKGROUND

Neurotoxicity induced by local anesthetics (LAs) is potentially life threatening, especially for patients with underlying diseases like diabetes. The anesthetic bupivacaine (Bup) has been reported to induce neurotoxicity mediated by reactive oxygen species (ROS), which is aggravated by hyperglycemia. Krüppel-like factor 9 (KLF9), an axon growth-suppressing transcription factor, plays a key role in neuronal maturation and promotes oxidative stress. This study was designed to investigate whether and how KLF9 regulates ROS levels related to LA neurotoxicity under hyperglycemic conditions.

METHODS

Klf9/GFP ShRNA (LV Sh-Klf9) was used to achieve stable Klf9 knockdown in the SH-SY5Y cell line. KLF9-deficient and normal cells were cultured under normal or high-glucose (HG) culture conditions and then exposed to Bup. Cell viability, intracellular and mitochondrial ROS, and mitochondrial membrane potential (ΔΨm) were detected to examine the role of KLF9. Thereafter, KLF9-deficient and normal cells were pretreated with small-interfering RNA targeting peroxiredoxin 6 (siRNA-Prdx6) to determine if PRDX6 was the target protein in HG-aggravated Bup neurotoxicity.

RESULTS

The mRNA and protein levels of KLF9 were increased after Bup and hyperglycemia treatment. In addition, cell survival and mitochondrial function were significantly improved, and ROS production was decreased after Sh-Klf9 treatment compared with Sh-Ctrl. Furthermore, the expression of PRDX6 was suppressed by Bup in hyperglycemic cultures and was upregulated in the Sh-Klf9 group. Moreover, the protection provided by KLF9 deficiency for cell survival, the increase in ROS production in cells and mitochondria, and the disruption of mitochondrial function were abolished by Prdx6 knockdown.

CONCLUSIONS

The results of this study demonstrated that hyperglycemia aggravated Bup neurotoxicity by upregulating KLF9 expression, which repressed the antioxidant PRDX6 and led to mitochondrial dysfunction, ROS burst, and cell death. Understanding this mechanism may, thus, offer valuable insights for the prevention and treatment of neurotoxicity induced by LAs, especially in diabetic patients.

Identification and molecular characterization of peroxiredoxin 6 from noble scallop Chlamys nobilis revealing its potent immune response and antioxidant property

The 1-cyseine peroxiredoxin (Prx6) is an importantly antioxidant enzyme that protects cells from oxidative damage caused by excessive production of reactive oxygen species (ROS). In this study, we described the molecular characteristics of the noble scallop Chlamys nobilis peroxiredoxin 6 (designed as CnPrx6), immune responses and DNA protection activity of the recombinant protein. The complete ORF (696 bp) of CnPrx6 encoded a polypeptide (25.5 kDa) of 231 amino acids, harboring a conserved peroxidase catalytic center (⁴¹PVCTTE⁴⁶) and the catalytic triads putatively involved in peroxidase and phospholipase A2 activities. The deduced amino acid sequence of CnPrx6 shared a relatively high amino acid sequence similarity (more than 50%). The qRT-PCR revealed that the CnPrx6 mRNA was constitutively expressed in all examined tissues, with the highest expression observed in adductor. Upon immunological challenge with Vibrio parahaemolyticus, lipopolysaccharides (LPS) and polyinosinic-polycytidylic acid (Poly I:C), the expression level of CnPrx6 mRNA was significantly up-regulated (P < 0.05). Furthermore, there was a significant difference (P < 0.05) in the expression level of CnPrx6 between golden and brown scallops. The purified recombinant CnPrx6 protein protected the supercoiled plasmid DNA from metal-catalyzed ROS damage. Taken together, these results indicated that the CnPrx6 may play an important role in modulating immune responses and minimizing DNA damage in noble scallop Chlamys nobilis.

Peroxiredoxin 6 mediates acetaminophen-induced hepatocyte death through JNK activation

Acetaminophen (APAP) is one of the most frequently used drugs; however, its overdose leads to acute liver injury. Recently, studies have reported that the adduction of peroxiredoxin 6 (PRDX6), a member of the PRDX family of antioxidant enzymes, is associated with liver diseases. However, the role of PRDX6 in APAP-induced liver injury remains unclear. Here, we assessed both age-matched (about 12 weeks) PRDX6-overexpressing transgenic mice (PRDX6 mice) and wild type (WT) mice presenting acute liver injury induced by the intraperitoneal injection of APAP (500 mg/kg). Although PRDX6 is known as an antioxidant enzyme, PRDX6 mice unexpectedly demonstrated severe liver injury following APAP injection compared with WT mice. We observed that PRDX6 was hyperoxidized after APAP administration. Additionally, calcium-independent phospholipase A₂ (iPLA2) activity and lysophosphatidylcholine (LPC) levels were markedly elevated in PRDX6 mice following APAP administration. Moreover, APAP-induced JNK phosphorylation was considerably increased in the liver of PRDX6 mice. MJ33, an inhibitor of PRDX6, attenuated APAP-induced liver injury both in WT and PRDX6 mice. Notably, MJ33 reduced the APAP-induced increase in JNK activation, iPLA2 activity, and LPC levels. Although SP600125, a JNK inhibitor, abolished APAP-induced liver injury, it failed to affect the APAP-induced hyperoxidation of PRDX6, iPLA2 activity, and LPC levels. These results suggested that PRDX6 was converted to the hyperoxidized form by the APAP-induced high concentration of hydrogen peroxides. In the liver, hyperoxidized PRDX6 induced cellular toxicity via JNK activation by enhancing iPLA2 activity and LPC levels; this mechanism appears to be a one-way cascade.

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PRDX6 is hyperoxidized by ROS induced by APAP in the liver.

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Increased hyperoxidized PRDX6 by overexpression aggravates APAP-induced liver injury.

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Hyperoxidized PRDX6 enhances JNK activation via increasing its iPLA2 activity.

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MJ33, iPLA activity of PRDX6 inhibitor, inhibits APAP-induced liver injury.

Peroxiredoxin 6 modulates Toll signaling pathway and protects DNA damage against oxidative stress in red swamp crayfish (Procambarus clarkii)

Peroxiredoxin 6 (Prx6) is an important member of the peroxiredoxin family that plays critical roles in protecting host against the toxicity of oxidative stress and participates in cell signaling. Herein, we report Prx6 gene from red swamp crayfish, Procambarus clarkii. The cDNA fragment of PcPrx6 was 660 bp, encoding a 219 amino acid residues protein. The quantitative real time PCR analysis showed ubiquitous expression of PcPrx6 mRNA in the tested tissues. The challenge with peptidoglycan and Poly I:C remarkably suppressed the mRNA level of PcPrx6 in hepatopancreas at 3, 12, 48 h compared with the PBS control. However, the expression level significantly increased after 36 h of their treatment. The knockdown of PcPrx6 by small interference RNA significantly enhanced the transcript levels of Toll pathway-responsive genes at 24 h. Recombinant PcPrx6 protein was purified using affinity chromatography and analyzed for its biological role. The results revealed that the recombinant PcPrx6 protein manifested the ability to protect supercoiled DNA damage from oxidative stress elicited by mixed function oxidative assay. Altogether, PcPrx6 may have multiple functional roles in the physiology of P. clarkii, since it negatively regulates the Toll signaling transduction and protects supercoiled DNA damage from oxidative stress.

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.

Clinical significance of Keap1 and Nrf2 in oral squamous cell carcinoma

Oxidative stress has been reported to play an important role in progression and prognostication in various kinds of cancers. However, the role and clinical significance of oxidative stress markers Keap1 and Nrf2 in oral squamous cell carcinoma (OSCC) has not been elucidated. This study aimed to investigate the correlation of oxidative stress markers Keap1 and Nrf2 expression and pathological features in OSCC by using tissue microarray. Tissue microarrays containing 17 normal oral mucosa, 7 oral epithelial dysplasia and 43 OSCC specimens were studied by immunohistochemistry. The association among these proteins and pathological features were analyzed. Expression of oxidative stress markers Keap1, Nrf2, and antioxidants PPIA, Prdx6, as well as CD147 was found to increase consecutively from normal oral mucosa to OSCC, and the Keap1, Nrf2, PPIA, Prdx6, CD147 expression in OSCC were significantly higher when compared to normal oral mucosa. Expression of Keap1, Nrf2 in tumors was not found to be significantly associated with T category, lymph node metastases, and pathological grade. Furthermore, we checked the relationship among these oxidative stress markers and found that Keap1 was significantly correlated with Nrf2, Prdx6 and CD147. Significant relationship between Nrf2 and Prdx6 was also detected. Finally, we found patients with overexpression of Keap1 and Nrf2 had not significantly worse overall survival by Kaplan-Meier analysis. These findings suggest that ROS markers are associated with carcinogenesis and progression of OSCC, which may have prognostic value and could be regarded as potential therapeutic targets in OSCC.

Cathepsin E deficiency impairs autophagic proteolysis in macrophages

Cathepsin E is an endosomal aspartic proteinase that is predominantly expressed in immune-related cells. Recently, we showed that macrophages derived from cathepsin E-deficient (CatE(-/-)) mice display accumulation of lysosomal membrane proteins and abnormal membrane trafficking. In this study, we demonstrated that CatE(-/-) macrophages exhibit abnormalities in autophagy, a bulk degradation system for aggregated proteins and damaged organelles. CatE(-/-) macrophages showed increased accumulation of autophagy marker proteins such as LC3 and p62, and polyubiquitinated proteins. Cathepsin E deficiency also altered autophagy-related signaling pathways such as those mediated by the mammalian target of rapamycin (mTOR), Akt, and extracellular signal-related kinase (ERK). Furthermore, immunofluorescence microscopy analyses showed that LC3-positive vesicles were merged with acidic compartments in wild-type macrophages, but not in CatE(-/-) macrophages, indicating inhibition of fusion of autophagosome with lysosomes in CatE(-/-) cells. Delayed degradation of LC3 protein was also observed under starvation-induced conditions. Since the autophagy system is involved in the degradation of damaged mitochondria, we examined the accumulation of damaged mitochondria in CatE(-/-) macrophages. Several mitochondrial abnormalities such as decreased intracellular ATP levels, depolarized mitochondrial membrane potential, and decreased mitochondrial oxygen consumption were observed. Such mitochondrial dysfunction likely led to the accompanying oxidative stress. In fact, CatE(-/-) macrophages showed increased reactive oxygen species (ROS) production and up-regulation of oxidized peroxiredoxin-6, but decreased antioxidant glutathione. These results indicate that cathepsin E deficiency causes autophagy impairment concomitantly with increased aberrant mitochondria as well as increased oxidative stress.

Involvement of retinoic acid-induced peroxiredoxin 6 expression in recovery of noise-induced temporary hearing threshold shifts

All-trans retinoic acid (ATRA) is reported to reduce hair cell loss and hearing deterioration caused by noise-induced hearing loss (NIHL). The present study investigates the involvement of peroxiredoxin 6 (Prdx 6) in ATRA-mediated protection of temporary threshold shift of hearing. Mice fed with ATRA before or after exposure to white noise showed a faster recovery than untreated controls within 1 week, with a concomitant increase of cochlear Prdx 6 expression. Treatment of mouse auditory cells with ATRA induced Prdx 6 expression. A putative retinoic acid (RA)-response element (RARE) was identified in a murine Prdx 6 promoter region. Prdx 6 promoter activities were elevated in wild-type reporter plasmid-transfected cells, whereas no significant change in activity was in those with RARE-disrupted mutant reporter. RA receptor α (RARα) functions as a transactivator of Prdx 6 gene expression. These findings suggest that ATRA-induced Prdx 6 expression may be associated with rapid recovery from temporary NIHL.

Combustion-derived flame generated ultrafine soot generates reactive oxygen species and activates Nrf2 antioxidants differently in neonatal and adult rat lungs

BACKGROUND

Urban particulate matter (PM) has been epidemiologically correlated with multiple cardiopulmonary morbidities and mortalities, in sensitive populations. Children exposed to PM are more likely to develop respiratory infections and asthma. Although PM originates from natural and anthropogenic sources, vehicle exhaust rich in polycyclic aromatic hydrocarbons (PAH) can be a dominant contributor to the PM2.5 and PM0.1 fractions and has been implicated in the generation of reactive oxygen species (ROS).

OBJECTIVES

Current studies of ambient PM are confounded by the variable nature of PM, so we utilized a previously characterized ethylene-combusted premixed flame particles (PFP) with consistent and reproducible physiochemical properties and 1) measured the oxidative potential of PFP compared to ambient PM, 2) determined the ability of PFPs to generate oxidative stress and activate the transcription factor using in vitro and ex vivo models, and 3) we correlated these responses with antioxidant enzyme expression in vivo.

METHODS

We compared oxidative stress response (HMOX1) and antioxidant enzyme (SOD1, SOD2, CAT, and PRDX6) expression in vivo by performing a time-course study in 7-day old neonatal and young adult rats exposed to a single 6-hour exposure to 22.4 μg/m3 PFPs.

RESULTS

We showed that PFP is a potent ROS generator that induces oxidative stress and activates Nrf2. Induction of the oxidative stress responsive enzyme HMOX1 in vitro was mediated through Nrf2 activation and was variably upregulated in both ages. Furthermore, antioxidant enzyme expression had age and lung compartment variations post exposure. Of particular interest was SOD1, which had mRNA and protein upregulation in adult parenchyma, but lacked a similar response in neonates.

CONCLUSIONS

We conclude that PFPs are effective ROS generators, comparable to urban ambient PM2.5, that induce oxidative stress in neonatal and adult rat lungs. PFPs upregulate a select set of antioxidant enzymes in young adult animals, that are unaffected in neonates. We conclude that the inability of neonatal animals to upregulate the antioxidant response may, in part, explain enhanced their susceptibility to ultrafine particles, such as PFP.

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.

Using PCR-RFLP technology to teach single nucleotide polymorphism for undergraduates

Recent studies indicated that the aberrant gene expression of peroxiredoxin-6 (prdx6) was found in various kinds of cancers. Because of its biochemical function and gene expression pattern in cancer cells, the association between genetic polymorphism of Prdx6 and cancer onset is interesting. In this report, we have developed and implemented a serial experiment in molecular biology laboratory course to teach single nucleotide polymorphism (SNP) to undergraduate students majoring in molecular biology or genetics. The flanking sequence of rs4382766 was located in Prdx6 gene, which contained a restriction site of SspI, and was used as a target in this lab course. The students could mimic real research by integrating different techniques, such as database retrieving, genomic DNA isolation, PCR, and restriction enzyme assay. This serial experiment of PCR-RFLP helps students set up intact idea of molecular biology and understand the relation among individual experiments. Students were found to be more enthusiastic during the laboratory classes than those in the former curriculum.

[Impact of PAHs on the expression of PRDX in earthworm (Eisenia fetida)]

A peroxiredoxin6 (PRDX6)-like gene segment has been found in up-regulated cDNA libraries of earthworm Eisenia fetida exposed to benzo[a]pyrene(BaP). Analysis with basic local alignment search tool (BLAST) and phylogenetic analysis revealed that the gene segment contains a characteristic motif which was encoded by Cys, illustrating that this gene segment belongs to PRDX. To verify the response of PRDX in E. feitida exposed to poly aromatic hydrocarbons (PAHs), four-week pollution experiments were conducted following the methods recommended by the Organization for Economic Co-operation and Development (OECD). The results showed that the expression of PRDX was up-regulated in earthworm exposed to 1.0 mg x kg(-1) Pyrene and BaP. It was indicated that PRDX in E. fetida was the potential molecular biomarkers of antioxidative stress caused by soil contamination.