p67(phox) terminates the phospholipase A(2)-derived signal for activation of NADPH oxidase (NOX2)

Peroxiredoxin 6 Regulates Glutathione Peroxidase 1-Medited Glutamine Synthase Preservation in the Hippocampus of Chronic Epilepsy Rats

Clasmatodendrosis (an autophagic astroglial degeneration) plays an important role in the regulation of spontaneous seizure duration but not seizure frequency or behavioral seizure severity in chronic epilepsy rats. Recently, it has been reported that N-acetylcysteine (NAC), a precursor to glutathione (GSH), attenuates clasmatodendritic degeneration and shortens spontaneous seizure duration in chronic epilepsy rats, although the underlying mechanisms of its anti-convulsive effects are not fully understood. To elucidate this, the present study was designed to investigate whether NAC affects astroglial glutamine synthase (GS) expression mediated by GSH peroxidase 1 (GPx1) and/or peroxiredoxin 6 (Prdx6) in the epileptic hippocampus. As compared to control animals, GS and GPx1 expressions were upregulated in reactive CA1 astrocytes of chronic epilepsy rats, while their expressions were significantly decreased in clasmatodendritic CA1 astrocytes and reactive astrocytes within the molecular layer of the dentate gyrus. Prdx6 expression was increased in reactive CA1 astrocytes as well as clasmatodendritic CA1 astrocytes. In the molecular layer of the dentate gyrus, Prdx6 expression levels were similar to those in control animals. NAC ameliorated clasmatodendrosis through the increment of GS and GPx1 expressions, while it abolished Prdx6 upregulation. 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) alleviated clasmatodendrosis by enhancing GPx1 and GS expressions in clasmatodendritic CA1 astrocytes without changing the Prdx6 level. NAC or MJ33 did not affect GS, GPx1 and Prdx6 expression in astrocytes within the molecular layer of the dentate gyrus. These findings indicate that upregulated aiPLA2 activity of Prdx6 may abolish GPx1-mediated GS preservation and lead to clasmatodendrosis in CA1 astrocytes, which would extend spontaneous seizure duration due to impaired glutamate-glutamine conversion regulated by GS. Therefore, the present data suggest that aiPLA2 activity of Prdx6 in astrocytes may be one of the upstream effectors of seizure duration in the epileptic hippocampus.

Sp1-Mediated Prdx6 Upregulation Leads to Clasmatodendrosis by Increasing Its aiPLA2 Activity in the CA1 Astrocytes in Chronic Epilepsy Rats

Clasmatodendrosis is an autophagic astroglial degeneration (a non-apoptotic (type II) programmed cell death) whose underlying mechanisms are fully understood. Peroxiredoxin-6 (Prdx6), the “non-selenium glutathione peroxidase (NSGPx)”, is the only member of the 1-cysteine peroxiredoxin family. Unlike the other Prdx family, Prdx6 has multiple functions as glutathione peroxidase (GPx) and acidic calcium-independent phospholipase (aiPLA2). The present study shows that Prdx6 was upregulated in CA1 astrocytes in chronic epilepsy rats. 2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) and N-acetylcysteine (NAC, a precursor of glutathione) ameliorated clasmatodendrosis accompanied by reduced Prdx6 level in CA1 astrocytes. Specificity protein 1 (Sp1) expression was upregulated in CA1 astrocyte, which was inhibited by mithramycin A (MMA). MMA alleviated clasmatodendrosis and Prdx6 upregulation. Sp1 expression was also downregulated by CDDO-Me and NAC. Furthermore, 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) attenuated clasmatodendrosis without affecting Prdx6 expression. All chemicals shortened spontaneous seizure duration but not seizure frequency and behavioral seizure severity in chronic epilepsy rats. Therefore, our findings suggest that Sp1 activation may upregulate Prdx6, whose aiPLA2 activity would dominate over GPx activity in CA1 astrocytes and may lead to prolonged seizure activity due to autophagic astroglial degeneration.

The anti-oxidant enzyme, Prdx6 might have cis-acting regulatory sequence(s)

Peroxiredoxin 6 (Prdx6) is a ubiquitously expressed 1-cysteine Peroxiredoxin found throughout all phyla. In mammals, under different physiological conditions, it has evolved from a peroxidase to a multifunctional enzyme. Among the mammalian Prdx6's, human and rat Prdx6's are the most extensively studied. Our study revealed that human and rat Prdx6's exhibit differences in their peroxidase activity. These two Prdx6's have only 8% difference in their primary sequence (with 19 amino acids) with no apparent modification at any of the key conserved residues. In the present communication, we have investigated the roles of thermodynamics, structure and internal flexibility of Prdx6 to account for the difference in their peroxidase activity. We discovered that these amino acid variations have led to structural alterations in human Prdx6 so that it shows enhanced intrinsic dynamics (or flexibility) than the rat protein. We could also identify the gain of intrinsic dynamics of the catalytic site in human Prdx6 due to relocation of an important active site residue (R132) to the loop region as the most plausible reason for high catalytic activity in the human protein as compared to rat variant. Since it is the thioredoxin fold that upholds the peroxidase function, certain structural alteration in the Prdx6 structure might help to regulate the efficiency of thioredoxin folds. Our results hint that Prdx6 might have a cis-acting regulatory sequence(s).

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.

Regulation of NADPH Oxidases by G Protein-Coupled Receptors

SIGNIFICANCE

G protein-coupled receptors (GPCR) are the largest group of cell surface receptors, which link cells to their environment. Reactive oxygen species (ROS) can act as important cellular signaling molecules. The family of NADPH oxidases generates ROS in response to activated cell surface receptors. Recent Advances: Various signaling pathways linking GPCRs and activation of NADPH oxidases have been characterized.

CRITICAL ISSUES

Still, a more detailed analysis of G proteins involved in the GPCR-mediated activation of NADPH oxidases is needed. In addition, a more precise discrimination of NADPH oxidase activation due to either upregulation of subunit expression or post-translational subunit modifications is needed. Also, the role of noncanonical modulators of NADPH oxidase activation in the response to GPCRs awaits further analyses.

FUTURE DIRECTIONS

As GPCRs are one of the most popular classes of investigational drug targets, further detailing of G protein-coupled mechanisms in the activation mechanism of NADPH oxidases as well as better understanding of the link between newly identified NADPH oxidase interaction partners and GPCR signaling will provide new opportunities for improved efficiency and decreased off target effects of therapies targeting GPCRs.

The Role of Peroxiredoxin 6 in Cell Signaling

Peroxiredoxin 6 (Prdx6, 1-cys peroxiredoxin) is a unique member of the peroxiredoxin family that, in contrast to other mammalian peroxiredoxins, lacks a resolving cysteine and uses glutathione and π glutathione S-transferase to complete its catalytic cycle. Prdx6 is also the only peroxiredoxin capable of reducing phospholipid hydroperoxides through its glutathione peroxidase (Gpx) activity. In addition to its peroxidase activity, Prdx6 expresses acidic calcium-independent phospholipase A₂ (aiPLA₂) and lysophosphatidylcholine acyl transferase (LPCAT) activities in separate catalytic sites. Prdx6 plays crucial roles in lung phospholipid metabolism, lipid peroxidation repair, and inflammatory signaling. Here, we review how the distinct activities of Prdx6 are regulated during physiological and pathological conditions, in addition to the role of Prdx6 in cellular signaling and disease.

The phospholipase A2 activity of peroxiredoxin 6

Peroxiredoxin 6 (Prdx6) is a Ca²⁺-independent intracellular phospholipase A₂ (called aiPLA₂) that is localized to cytosol, lysosomes, and lysosomal-related organelles. Activity is minimal at cytosolic pH but is increased significantly with enzyme phosphorylation, at acidic pH, and in the presence of oxidized phospholipid substrate; maximal activity with phosphorylated aiPLA₂ is ∼2 µmol/min/mg protein. Prdx6 is a "moonlighting" protein that also expresses glutathione peroxidase and lysophosphatidylcholine acyl transferase activities. The catalytic site for aiPLA₂ activity is an S32-H26-D140 triad; S32-H26 is also the phospholipid binding site. Activity is inhibited by a serine "protease" inhibitor (diethyl p-nitrophenyl phosphate), an analog of the PLA₂ transition state [1-hexadecyl-3-(trifluoroethyl)-sn-glycero-2-phosphomethanol (MJ33)], and by two naturally occurring proteins (surfactant protein A and p67^phox), but not by bromoenol lactone. aiPLA₂ activity has important physiological roles in the turnover (synthesis and degradation) of lung surfactant phospholipids, in the repair of peroxidized cell membranes, and in the activation of NADPH oxidase type 2 (NOX2). The enzyme has been implicated in acute lung injury, carcinogenesis, neurodegenerative diseases, diabetes, male infertility, and sundry other conditions, although its specific roles have not been well defined. Protein mutations and animal models are now available to further investigate the roles of Prdx6-aiPLA₂ activity in normal and pathological physiology.

Phagocyte NADPH oxidase, oxidative stress and lipids: Anti- or pro ageing?

The role of NADPH oxidase in ageing is debated because of the dual roles of free radicals, toxic though necessary. In this paper we summarize some results about two aspects linked to the regulation of the activity of phagocyte NADPH oxidase (Nox2), encountered frequently in elderly people: inflammation and hypercholesterolemia. In the presence of a high amount of reactive oxygen species (ROS) created by itself or by any other source, the enzyme activity is mostly lowered. Oxidation of the membrane and/or of one of the cytosolic partners could be responsible for this loss of activity. However using a cell free system, we had also shown that a low amount of ROS could activate this enzyme. Similarly, cholesterol has a similar dual role, either activating or inhibiting. In in vitro cell free system with neutrophil membranes from healthy donors, the addition, as well as the removal of cholesterol, diminishes the Nox2 activity. The activity of Nox2 is lowered in neutrophils of untreated hypercholesterolemic patients. Finally oxysterols (25-hydroxy-cholesterol or 5α, 6α - epoxy-cholesterol) do not induce effects different from that of non-oxidized cholesterol. These findings are in agreement with the Janus role of NADPH oxidase, the main source of non-mitochondrial ROS.

Peroxiredoxin 6 mediates Gαi protein-coupled receptor inactivation by cJun kinase

Inactivation of opioid receptors limits the therapeutic efficacy of morphine-like analgesics and mediates the long duration of kappa opioid antidepressants by an uncharacterized, arrestin-independent mechanism. Here we use an iterative, discovery-based proteomic approach to show that following opioid administration, peroxiredoxin 6 (PRDX6) is recruited to the opioid receptor complex by c-Jun N-terminal kinase (JNK) phosphorylation. PRDX6 activation generates reactive oxygen species via NADPH oxidase, reducing the palmitoylation of receptor-associated Gαi in a JNK-dependent manner. Selective inhibition of PRDX6 blocks Gαi depalmitoylation, prevents the enhanced receptor G-protein association and blocks acute analgesic tolerance to morphine and kappa opioid receptor inactivation in vivo. Opioid stimulation of JNK also inactivates dopamine D2 receptors in a PRDX6-dependent manner. We show that the loss of this lipid modification distorts the receptor G-protein association, thereby preventing agonist-induced guanine nucleotide exchange. These findings establish JNK-dependent PRDX6 recruitment and oxidation-induced Gαi depalmitoylation as an additional mechanism of Gαi-G-protein-coupled receptor inactivation.

Opioid receptors are important modulators of nociceptive pain. Here the authors show that opioid receptor activation recruits peroxiredoxin 6 (PRDX6) to the receptor-Gαi complex by c-Jun N-terminal kinase, resulting in Gαi depalmitoylation and enhanced receptor-Gαi association.

Phospholipase A2 of Peroxiredoxin 6 Plays a Critical Role in Cerebral Ischemia/Reperfusion Inflammatory Injury

Microglia-mediated inflammation is an important step in the progression of cerebral ischemia/reperfusion injury and the associated production of receptors of immunomoudulation, including Toll-like receptors (TLRs). Peroxiredoxin 6 (Prdx6) has been demonstrated as the endogenous antioxidant protein for its peroxidase properties. However, the role of the independent phospholipase A2 (iPLA2) activity of Prdx6 in stroke has not been well studied. In this study, we evaluated whether blocking the calcium-iPLA2 activity of Prdx6 using siRNA and inhibitors (1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol, MJ33) would have a critical effect on inflammatory brain damage. We conducted oxygen-glucose deprivation (OGD)/recovery (R) in vitro and middle cerebral artery occlusion (MCAO) in vivo in a microglia/neuron co-culture system and in rats. In vitro, we found that Prdx6-iPLA2 activity was associated with the secretion of neurotoxic inflammatory mediators interleukin1β (IL-1β), interleukin-17 (IL-17) and interleukin-23 (IL-23) and elevated expression of Toll-like receptor 2/4 (TLR2/4), leading to the formation of nuclear factor-kappa B (NF-κB), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in microglial cells. In vivo, combined treatment with Prdx6-iPLA2 activity inhibitor MJ33 showed a greater diminution in neurologic deficits, cerebral infarction, brain water content and inflammatory molecules than Prdx6-siRNA treatment alone. Our findings provide new insight into Prdx6-iPLA2 function in the brain. Inhibition of Prdx6-iPLA2 activity by gene therapy and/or pharmacology may constitute a promising new therapeutic approach to the treatment of stroke.

Peroxiredoxin 6 in the repair of peroxidized cell membranes and cell signaling

Peroxiredoxin 6 represents a widely distributed group of peroxiredoxins that contain a single conserved cysteine in the protein monomer (1-cys Prdx). The cys when oxidized to the sulfenic form is reduced with glutathione (GSH) catalyzed by the π isoform of GSH-S-transferase. Three enzymatic activities of the protein have been described:1) peroxidase with H2O2, short chain hydroperoxides, and phospholipid hydroperoxides as substrates; 2) phospholipase A2 (PLA2); and 3) lysophosphatidylcholine acyl transferase (LPCAT). These activities have important physiological roles in antioxidant defense, turnover of cellular phospholipids, and the generation of superoxide anion via initiation of the signaling cascade for activation of NADPH oxidase (type 2). The ability of Prdx6 to reduce peroxidized cell membrane phospholipids (peroxidase activity) and also to replace the oxidized sn-2 fatty acyl group through hydrolysis/reacylation (PLA2 and LPCAT activities) provides a complete system for the repair of peroxidized cell membranes.

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.

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.

Ageing-induced changes in the redox status of peripheral motor nerves imply an effect on redox signalling rather than oxidative damage

Ageing is associated with loss of skeletal muscle fibres, atrophy of the remaining fibres and weakness. These changes in muscle are accompanied by disruption of motor neurons and neuromuscular junctions although the direct relationship between the nerve and muscle degeneration is not understood. Oxidative changes have been implicated in the mechanisms leading to age-related loss of muscle mass and in degeneration of the central nervous system, but little is known about age-related changes in oxidation in specific peripheral nerves that supply muscles that are affected by ageing. We have therefore examined the sciatic nerve of old mice at an age when loss of tibialis anterior muscle mass and function is apparent. Sciatic nerve from old mice did not show a gross increase in oxidative damage, but electron paramagnetic resonance (EPR) studies indicated an increase in the activity of superoxide and/or peroxynitrite in the nerves of old mice at rest that was further exacerbated by electrical stimulation of the nerve to activate muscle contractions. Proteomic analyses indicated that specific redox-sensitive proteins are increased in content in the nerves of old mice that may reflect an adaptation to regulate the increased superoxide/peroxynitrite and maintain redox homoeostasis. Analysis of redox active cysteines showed some increase in reversible oxidation in specific proteins in nerves of old mice, but this was not universally seen across all redox-active cysteines. Detailed analysis of the redox-active cysteine in one protein in the nerve of old mice that is key to redox signalling (Peroxiredoxin 6, Cys 47) showed a minor increase in reversible oxidation that would be compatible with a change in its redox signalling function. In conclusion, the data presented indicate that sciatic nerve from old mice does not show a gross increase in oxidative damage similar to that seen in the TA and other muscles that it innervates. Our results indicate an adaptation to increased oxidation with minor changes in the oxidation of key cysteines that may contribute to defective redox signalling in the nerve.

Roles of peroxiredoxins in cancer, neurodegenerative diseases and inflammatory diseases

Peroxiredoxins (PRDXs) are antioxidant enzymes, known to catalyze peroxide reduction to balance cellular hydrogen peroxide (H₂O₂) levels, which are essential for cell signaling and metabolism and act as a regulator of redox signaling. Redox signaling is a critical component of cell signaling pathways that are involved in the regulation of cell growth, metabolism, hormone signaling, immune regulation and variety of other physiological functions. Early studies demonstrated that PRDXs regulates cell growth, metabolism and immune regulation and therefore involved in the pathologic regulator or protectant of several cancers, neurodegenerative diseases and inflammatory diseases. Oxidative stress and antioxidant systems are important regulators of redox signaling regulated diseases. In addition, thiol-based redox systems through peroxiredoxins have been demonstrated to regulate several redox-dependent process related diseases. In this review article, we will discuss recent findings regarding PRDXs in the development of diseases and further discuss therapeutic approaches targeting PRDXs. Moreover, we will suggest that PRDXs could be targets of several diseases and the therapeutic agents for targeting PRDXs may have potential beneficial effects for the treatment of cancers, neurodegenerative diseases and inflammatory diseases. Future research should open new avenues for the design of novel therapeutic approaches targeting PRDXs.

Optimal ROS Signaling Is Critical for Nuclear Reprogramming

Efficient nuclear reprogramming of somatic cells to pluripotency requires activation of innate immunity. Because innate immune activation triggers reactive oxygen species (ROS) signaling, we sought to determine whether there was a role of ROS signaling in nuclear reprogramming. We examined ROS production during the reprogramming of doxycycline (dox)-inducible mouse embryonic fibroblasts (MEFs) carrying the Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc [OSKM]) into induced pluripotent stem cells (iPSCs). ROS generation was substantially increased with the onset of reprogramming. Depletion of ROS via antioxidants or Nox inhibitors substantially decreased reprogramming efficiency. Similarly, both knockdown and knockout of p22(phox)-a critical subunit of the Nox (1-4) complex-decreased reprogramming efficiency. However, excessive ROS generation using genetic and pharmacological approaches also impaired reprogramming. Overall, our data indicate that ROS signaling is activated early with nuclear reprogramming, and optimal levels of ROS signaling are essential to induce pluripotency.

A novel lysophosphatidylcholine acyl transferase activity is expressed by peroxiredoxin 6

The phospholipase A2(PLA2) activity of peroxiredoxin (Prdx)6 has important physiological roles in the synthesis of lung surfactant and in the repair of peroxidized cell membranes. These functions require the activity of a lysophospholipid acyl transferase as a critical component of the phospholipid remodeling pathway. We now describe a lysophosphatidylcholine acyl transferase (LPCAT) activity for Prdx6 that showed a strong preference for lysophosphatidylcholine (LPC) as the head group and for palmitoyl CoA in the acylation reaction. The calculated kinetic constants for acylation wereKm18 μM andVmax30 nmol/min/mg protein; theVmaxwas increased 25-fold by phosphorylation of the protein whileKmwas unchanged. Study of recombinant protein in vitro and in mouse pulmonary microvascular endothelial cells infected with a lentiviral vector construct indicated that amino acid D31 is crucial for LPCAT activity. A linear incorporation of labeled fatty acyl CoA into dipalmitoyl phosphatidylcholine (PC) indicated that LPC generated by Prdx6 PLA2activity remained bound to the enzyme for the reacylation reaction. Prdx6 is the first LPCAT enzyme with demonstrated cytoplasmic localization. Thus, Prdx6 is a complete enzyme comprising both PLA2and LPCAT activities for the remodeling pathway of PC synthesis or for repair of membrane lipid peroxidation.

Binding sites for interaction of peroxiredoxin 6 with surfactant protein A

Peroxiredoxin 6 (Prdx6) is a bifunctional enzyme with peroxidase and phospholipase A2 (PLA2) activities. This protein participates in the degradation and remodeling of internalized dipalmitoylphosphatidylcholine (DPPC), the major phospholipid component of lung surfactant. We have shown previously that the PLA2 activity of Prdx6 is inhibited by the lung surfactant-associated protein called surfactant protein A (SP-A) through direct protein-protein interaction. Docking of SPA and Prdx6 was modeled using the ZDOCK (zlab.bu.edu) program in order to predict molecular sites for binding of the two proteins. The predicted peptide sequences were evaluated for binding to the opposite protein using isothermal titration calorimetry and circular dichroism measurement followed by determination of the effect of the SP-A peptide on the PLA2 activity of Prdx6. The sequences 195EEEAKKLFPK204.in the Prdx6 helix and 83DEELQTELYEIKHQIL99 in SP-A were identified as the sites for hydrophobic interaction and H(+)-bonding between the 2 proteins. Treatment of mouse endothelial cells with the SP-A peptide inhibited their recovery from lipid peroxidation associated with oxidative stress indicating inhibition of Prdx6 activity by the peptide in the intact cell.

Close teamwork between Nrf2 and peroxiredoxins 1 and 6 for the regulation of prostaglandin D2 and E2 production in macrophages in acute inflammation

Inflammation is a complex biological self-defense reaction triggered by tissue damage or infection by pathogens. Acute inflammation is regulated by the time- and cell type-dependent production of cytokines and small signaling molecules including reactive oxygen species and prostaglandins. Recent studies have unveiled the important role of the transcription factor Nrf2 in the regulation of prostaglandin production through transcriptional regulation of peroxiredoxins 1 and 6 (Prx1 and Prx6) and lipocalin-type prostaglandin D synthase (L-PGDS). Prx1 and Prx6 are multifunctional proteins important for cell protection against oxidative stress, but also work together to facilitate production of prostaglandins E2 and D2 (PGE2 and PGD2). Prx1 secreted from cells under mild oxidative stress binds Toll-like receptor 4 and induces NF-κB activation, important for the expression of cyclooxygenase-2 and microsomal PGE synthase-1 (mPGES-1) expression. The activated MAPKs p38 and ERK phosphorylate Prx6, leading to NADPH oxidase-2 activation, which contributes to production of PGD2 by hematopoietic prostaglandin D synthase (H-PGDS). PGD2 and its end product 15-deoxy-∆(12,14)-prostaglandin J2 (15d-PGJ2) activate Nrf2 thereby forming a positive feedback loop for further production of PGD2 by L-PGDS. Maintenance of cellular glutathione levels is an important role of Nrf2 not only for cell protection but also for the synthesis of prostaglandins, as mPGES-1 and H-PGDS require glutathione for their activities. This review is aimed at describing the functions of Prx1 and Prx6 in the regulation of PGD2 and PGE2 production in acute inflammation in macrophages and the importance of 15d-PGJ2 as an intrinsic Nrf2 activator.