Deletion of peroxiredoxin 6 potentiates lipopolysaccharide-induced acute lung injury in mice*:

The glycyl-l-histidyl-l-lysine-Cu2+ tripeptide complex attenuates lung inflammation and fibrosis in silicosis by targeting peroxiredoxin 6

Silicosis is the most common type of pneumoconiosis, having a high incidence in workers chronically exposed to crystalline silica (CS). No specific medication exists for this condition. GHK, a tripeptide naturally occurring in human blood and urine, has antioxidant effects. We aimed to investigate the therapeutic effect of GHK-Cu on silicosis and its potential underlying molecular mechanism. An experimental silicosis mouse model was established to observe the effects of GHK-Cu on lung inflammation and fibrosis. Moreover, the effects of GHK-Cu on the alveolar macrophages (AM) were examined using the RAW264.7 cell line. Its molecular target, peroxiredoxin 6 (PRDX6), has been identified, and GHK-Cu can bind to PRDX6, thus attenuating lung inflammation and fibrosis in silicosis mice without significant systemic toxicity. These effects were partly related to the inhibition of the CS-induced oxidative stress in AM induced by GHK-Cu. Thus, our results suggest that GHK-Cu acts as a potential drug by attenuating alveolar macrophage oxidative stress. This, in turn, attenuates the progression of pulmonary inflammation and fibrosis, which provides a reference for the treatment of silicosis.

Peroxiredoxin 6 Protects Pulmonary Epithelial Cells From Cigarette-related Ferroptosis in Chronic Obstructive Pulmonary Disease

Peroxiredoxin 6 (PRDX6) has a protective effect on pulmonary epithelial cells against cigarette smoke (CS)-induced ferroptosis. This study investigates the role of PRDX6 in the development of chronic obstructive pulmonary disease (COPD) and its possibility as a target. We observed that PRDX6 was downregulated in lung tissues of COPD patients and in CS-stimulated cells. The degradation of PRDX6 could be through the lysosomal pathway. PRDX6 deficiency exacerbated pulmonary inflammation and mucus hypersecretion in vivo. Overexpression of PRDX6 in Beas-2B cells ameliorated CS-induced cell death and inflammation, suggesting its protective role against CS-induced damage. Furthermore, PRDX6 deficiency promoted ferroptosis by adding the content of iron and reactive oxygen species, while iron chelation with deferoxamine mitigated CS-induced ferroptosis, cell death, and inflammatory infiltration both in vitro and in vivo. The critical role of PRDX6 in regulating ferroptosis suggests that targeting PRDX6 or iron metabolism may represent a promising strategy for COPD treatment.

Astragaloside IV targets PRDX6, inhibits the activation of RAC subunit in NADPH oxidase 2 for oxidative damage

BACKGROUND

Radix Astragali Mongolici, as a traditional Chinese medicine, is widely used in the treatment of qi deficiency, viral or bacterial infection, inflammation and cancer. Astragaloside IV (AST), a key active compound in Radix Astragali Mongolici, has been shown to reduce disease progression by inhibiting oxidative stress and inflammation. However, the specific target and mechanism of action of AST in improving oxidative stress are still unclear.

PURPOSE

This study aims to explore the target and mechanism of AST to improve oxidative stress, and to explain the biological process of oxidative stress.

METHODS

AST functional probes were designed to capture target proteins and combined with protein spectrum to analyze target proteins. Small molecule and protein interaction technologies were used to verify the mode of action, while computer dynamics simulation technology was used to analyze the site of interaction with the target protein. The pharmacological activity of AST in improving oxidative stress was evaluated in a mouse model of acute lung injury induced by LPS. Additionally, pharmacological and serial molecular biological approaches were used to explore the underlying mechanism of action.

RESULTS

AST inhibits PLA2 activity in PRDX6 by targeting the PLA2 catalytic triad pocket. This binding alters the conformation and structural stability of PRDX6 and interferes with the interaction between PRDX6 and RAC, hindering the activation of the RAC-GDI heterodimer. Inactivation of RAC prevents NOX2 maturation, attenuates superoxide anion production, and improves oxidative stress damage.

CONCLUSION

The findings of this research indicate that AST impedes PLA2 activity by acting on the catalytic triad of PRDX6. This, in turn, disrupts the interaction between PRDX6 and RAC, thereby hindering the maturation of NOX2 and diminishing the oxidative stress damage.

Functional Genome Analysis for Immune Cells Provides Clues for Stratification of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is caused by a combination of genetic and environmental factors. Recently, analysis of a functional genome database of genetic polymorphisms and transcriptomic data from various immune cell subsets revealed the importance of the oxidative phosphorylation (OXPHOS) pathway in the pathogenesis of SLE. In particular, activation of the OXPHOS pathway is persistent in inactive SLE, and this activation is associated with organ damage. The finding that hydroxychloroquine (HCQ), which improves the prognosis of SLE, targets toll-like receptor (TLR) signaling upstream of OXPHOS suggests the clinical importance of this pathway. IRF5 and SLC15A4, which are regulated by polymorphisms associated with SLE susceptibility, are functionally associated with OXPHOS as well as blood interferon activity and metabolome. Future analyses of OXPHOS-associated disease-susceptibility polymorphisms, gene expression, and protein function may be useful for risk stratification of SLE.

Anti-Oxidant and Pro-Oxidant Effects of Peroxiredoxin 6: A Potential Target in Respiratory Diseases

Peroxiredoxin 6 (PRDX6) is widely distributed in several organs, especially the lungs. The role of PRDX6 in oxidative stress is controversial and even contradictory, as indicated by research conducted over the past 20 years. PRDX6 has anti-oxidant or pro-oxidant effects on oxidative stress in different diseases. It can even exhibit both anti-oxidant and pro-oxidant effects in the same disease. These findings are attributed to the fact that PRDX6 is a multifunctional enzyme. The peroxidase and phospholipase A2 activity of PRDX6 is closely related to its anti-oxidant and pro-oxidant effects, which leads to the conflicting regulatory effects of PRDX6 on oxidative stress in respiratory diseases. Moreover, PRDX6 interacts with multiple redox signaling pathways to interfere with cell proliferation and apoptosis. PRDX6 has become a new target in respiratory disease research due to its important regulatory role in oxidative stress. In this paper, the role of PRDX6 in oxidative stress in respiratory diseases and the research progress in targeting PRDX6 are reviewed.

Peroxiredoxin 6 mediates the protective function of curcumin pretreatment in acute lung injury induced by serum from patients undergoing one-lung ventilation in vitro

Background

Curcumin has attracted much attention due to its wide range of therapeutic effects. In this study, we used serum collected from patients undergoing one-lung ventilation (OLV) to establish an in vitro acute lung injury (ALI) model to explore the potential protective mechanism of curcumin on ALI. Our study provides a new reference for the prevention and treatment of ALI induced by OLV.

Methods

A549 cells were treated with 20% serum from patients undergoing OLV to establish an in vitro ALI model. Curcumin, at a dose of 40 μg/ml, was administered two hours prior to this model. The levels of inflammation and oxidative stress markers were observed by Western blot, qRT–PCR, ELISA and reactive oxygen species assay. Additionally, the expression of peroxiredoxin 6 (Prdx6) and proteins involved in the NF-κB signaling pathway was evaluated.

Results

Twenty percent of serum collected from patients undergoing OLV downregulated the expression of Prdx6, leading to the activation of the NF-κB signaling pathway, which was associated with the subsequent overproduction of inflammatory cytokines and reactive oxygen species. Pretreatment with curcumin restored Prdx6 downregulation and inhibited NF-κB pathway activation by suppressing the nuclear translocation of P65, eventually reducing inflammation and oxidative stress damage in A549 cells.

Conclusions

Prdx6 mediated the protective function of curcumin by inhibiting the activation of the NF-κB pathway in ALI in vitro.

The β3/5 Integrin-MMP9 Axis Regulates Pulmonary Inflammatory Response and Endothelial Leakage in Acute Lung Injury

Background

Acute lung injury (ALI) is a severe respiratory disease with high rates of morbidity and mortality. Many mediators regarding endogenous or exogenous are involved in the pathophysiology of ALI. Here, we have uncovered the involvement of integrins and matrix metalloproteinases, as critical determinants of excessive inflammation and endothelial permeability, in the regulation of ALI.

Methods

Inflammatory cytokines were measured by quantitative real-time PCR for mRNA levels and ELISA for secretion levels. Endothelial permeability assay was detected by the passage of rhodamine B isothiocyanate-dextran. Mice lung permeability was assayed by Evans blue albumin (EBA). Western blot was used for protein level measurements. The intracellular reactive oxygen species (ROS) were evaluated using a cell-permeable probe, DCFH-DA. Intratracheal injection of lipopolysaccharide (LPS) into mice was conducted to establish the lung injury model.

Results

Exogenous MMP-9 significantly aggravated the inflammatory response and permeability in mouse pulmonary microvascular endothelial cells (PMVECs) treated by LPS, whereas knockdown of MMP-9 exhibited the opposite phenotypes. Knockdown of integrin β3 or β5 in LPS-treated PMVECs significantly downregulated MMP-9 expression and decreased inflammatory response and permeability in the presence or absence of exogenous MMP-9. Additionally, the interaction of MMP-9 and integrin β5 was impaired by a ROS scavenger, which further decreased the pro-inflammatory cytokines production and endothelial leakage in PMVECs subjected to co-treatment (LPS with exogenous MMP-9). In vivo studies, exogenous MMP-9 treatment or knockdown β3 integrin significantly decreased survival in ALI mice. Notably, knockdown of β5 integrin alone had no remarkable effect on survival, but which combined with anti-MMP-9 treatment significantly improved the survival by ameliorating excessive lung inflammation and permeability in ALI mice.

Conclusion

These findings support the β3/5 integrin-MMP-9 axis as an endogenous signal that could play a pivotal role in regulating inflammatory response and alveolar-capillary permeability in ALI.

MicroRNA-762 Modulates Lipopolysaccharide-induced Acute Lung Injury via SIRT7

Background: Inflammation and oxidative stress contribute to the pathogenesis of lipopolysaccharide (LPS)-induced acute lung injury (ALI). MicroRNA-762 (miR-762) has been implicated in the progression of inflammation and oxidative stress; however, its role in ALI remains unclear. In this study, we aim to investigate the role and underlying mechanisms of miR-762 in LPS-induced ALI. Methods: Mice were intravenously injected with miR-762 antagomir, agomir or the negative controls for 3 consecutive days and then received a single intratracheal instillation of LPS (5 mg/kg) for 12 h to establish ALI model. Adenoviral vectors were used to knock down the endogenous SIRT7 expression. Results: An increased miR-762 expression was detected in LPS-treated lungs. miR-762 antagomir significantly reduced inflammation, oxidative stress and ALI in mice, while the mice with miR-762 agomir treatment exhibited a deleterious phenotype. Besides, we found that SIRT7 upregulation was essential for the pulmonoprotective effects of miR-762 antagomir, and that SIRT7 silence completely abolished the anti-inflammatory and anti-oxidant capacities of miR-762 antagomir. Conclusion: miR-762 is implicated in the pathogenesis of LPS-induced ALI via modulating inflammation and oxidative stress, which depends on its regulation of SIRT7 expression. It might be a valuable therapeutic target for the treatment of ALI.

The Roles of Peroxiredoxin 6 in Brain Diseases

Peroxiredoxin 6 (PRDX6), the only mammalian 1-Cys member of the peroxiredoxins (PRDXs) family, has multiple functions of glutathione peroxidase (Gpx) activity, acidic calcium-independent phospholipase (aiPLA2) activity, and lysophosphatidylcholine acyl transferase (LPCAT) activity. It has been documented to be involved in redox homeostasis, phospholipid turnover, glycolipid metabolism, and cellular signaling. Here, we reviewed the characteristics of the available Prdx6 genetic mouse models and the research progresses made with regard to PRDX6 in neuropsychiatric disorders, including neurodegenerative diseases, brain aging, stroke, neurotrauma, gliomas, major depressive disorder, drug addiction, post-traumatic stress disorder, and schizophrenia. The present review highlights the important roles of PRDX6 in neuropsychiatric disorders and may provide novel insights for the development of effective pharmacological treatments and genetic therapies.

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.

Peroxiredoxin6 in Endothelial Signaling

Peroxiredoxins (Prdx) are a ubiquitous family of highly conserved antioxidant enzymes with a cysteine residue that participate in the reduction of peroxides. This family comprises members Prdx1–6, of which Peroxiredoxin 6 (Prdx6) is unique in that it is multifunctional with the ability to neutralize peroxides (peroxidase activity) and to produce reactive oxygen species (ROS) via its phospholipase (PLA₂) activity that drives assembly of NADPH oxidase (NOX2). From the crystal structure, a C47 residue is responsible for peroxidase activity while a catalytic triad (S32, H26, and D140) has been identified as the active site for its PLA₂ activity. This paradox of being an antioxidant as well as an oxidant generator implies that Prdx6 is a regulator of cellular redox equilibrium (graphical abstract). It also indicates that a fine-tuned regulation of Prdx6 expression and activity is crucial to cellular homeostasis. This is specifically important in the endothelium, where ROS production and signaling are critical players in inflammation, injury, and repair, that collectively signal the onset of vascular diseases. Here we review the role of Prdx6 as a regulator of redox signaling, specifically in the endothelium and in mediating various pathologies.

Peroxiredoxin 6 knockout aggravates cecal ligation and puncture-induced acute lung injury

BACKGROUND

The aim of present study was to investigate the effects and mechanisms of peroxiredoxin (Prdx) 6 on cecal ligation and puncture (CLP) induced acute lung injury (ALI) in mice.

METHODS

The cecal of male Prdx 6 knockout and wildtype C57BL/6J mice were ligated and perforated. Stool was extruded to ensure wound patency. Two hours, 4 h, 8 h and 16 h after stimulation, the morphology, wet/dry ratio, protein concentration in bronchial alveolar lavage fluid (BALF) were measured to evaluate lung injury. Myeloperoxidase (MPO) activity, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), total superoxide dismutase (SOD), xanthine oxidase (XOD), CuZn-SOD, total anti-oxidative capability (TAOC), glutathione peroxidase (GSH-PX), catalase (CAT) in lungs were measured by assay kits. The mRNA expression of lung tumor necrosis factor (TNF-α), interleukin (IL)-1β, and matrix metalloproteinases (MMP) 2 and 9 were tested by real-time RT-PCR. The nuclear factor (NF)-κB activity was measured by TransAM kit.

RESULTS

CLP-induced ALI was characterized by inflammation in morphology, increased wet/dry ratio, elevated protein concentration in BALF and higher level of MPO activity. The levels of H₂O₂, MDA, and XOD were significantly increased and SOD, CuZn-SOD, GSH-PX, CAT, and T-AOC were significantly decreased in lungs after CLP. The activity of NF-κB was significantly increased and subsequently, the mRNA expression of TNF-α, IL-1β and MMP2 and MMP9 were significantly increased after CLP. Those above injury parameters were more severe in Prdx 6 knockout mice than those in wildtype mice.

CONCLUSIONS

Prdx 6 knockout aggravated the CLP induced lung injury by augmenting oxidative stress, inflammation and matrix degradation partially through NF-κB pathway.

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.

Peroxiredoxin-2 plays a pivotal role as multimodal cytoprotector in the early phase of pulmonary hypertension

Pulmonary-artery-hypertension (PAH) is a life-threatening and highly invalidating chronic disorder. Chronic oxidation contributes to lung damage and disease progression. Peroxiredoxin-2 (Prx2) is a typical 2-cysteine (Cys) peroxiredoxin but its role on lung homeostasis is yet to be fully defined. Here, we showed that Prx2^-/- mice displayed chronic lung inflammatory disease associated with (i) abnormal pulmonary vascular dysfunction; and (ii) increased markers of extracellular-matrix remodeling. Hypoxia was used to induce PAH. We focused on the early phase PAH to dissect the role of Prx2 in generation of PAH. Hypoxic Prx2^-/-mice showed (i) amplified inflammatory response combined with cytokine storm; (ii) vascular activation and dysfunction; (iii) increased PDGF-B lung levels, as marker of extracellular-matrix deposition and remodeling; and (iv) ER stress with activation of UPR system and autophagy. Rescue experiments with in vivo the administration of fused-recombinant-PEP-Prx2 show a reduction in pulmonary inflammatory vasculopathy and in ER stress with down-regulation of autophagy. Thus, we propose Prx2 plays a pivotal role in the early stage of PAH as multimodal cytoprotector, targeting oxidation, inflammatory vasculopathy and ER stress with inhibition of autophagy. Collectively, our data indicate that Prx2 is able to interrupt the hypoxia induced vicious cycle involving oxidation-inflammation-autophagy in the pathogenesis of PAH.

Peroxiredoxin 6 overexpression attenuates lipopolysaccharide-induced acute kidney injury

Peroxiredoxin 6 (PRDX6) is a member of the PRDX family of antioxidant enzymes and correlated with inflammatory response. Therefore, we investigated the role of PRDX6 during lipopolysaccharide (LPS)-induced acute kidney injury. Both 3 months aged PRDX6-overexpressing transgenic mice (PRDX6 mice) and wild type (WT) mice had acute renal injury induced by intraperitoneal injection of LPS (10 mg/kg)., PRDX6 mice showed decreased mortality and renal injury following LPS challenge compared to WT mice. Furthermore, infiltration of macrophages, T-cells and neutrophils, and the number of apoptotic cells were more decreased by LPS treatment in PRDX6 mice than in WT mice. Because LPS induces reactive oxygen species (ROS) production which induces inflammation through c-Jun N-terminal Kinase (JNK) and p38 MAPK activation, we investigated ROS concentration and MAPK signaling pathway in the kidney of PRDX6 mice. As expected, LPS-induced oxidative stress was attenuated, and p38 MAPK and JNK activation was decreased in the kidney of PRDX6 mice. Inhibitory effect of PRDX6 on LPS-induced apoptosis and MAPK activation in the primary renal proximal tubular cells were overcome by treatment with PRDX6 inhibitor or hydrogen peroxide. These results suggest that PRDX6 overexpression inactivates p38 MAPK and JNK pathway through decrease LPS-induced ROS concentration in the kidney, resulting in inhibition of renal apoptosis and leukocyte infiltration and led to attenuation of LPS-induced acute kidney injury.

Peroxiredoxin-6 Negatively Regulates Bactericidal Activity and NF-κB Activity by Interrupting TRAF6-ECSIT Complex

A TRAF6-ECSIT complex is crucial for the generation of mitochondrial reactive oxygen species (mROS) and nuclear factor-kappa B (NF-κB) activation induced by Toll-like receptor 4 (TLR4). Peroxiredoxin-6 (Prdx6) as a member of the peroxiredoxin family of antioxidant enzymes is involved in antioxidant protection and cell signaling. Here, we report on a regulatory role of Prdx6 in mROS production and NF-κB activation by TLR4. Prdx6 was translocated into the mitochondria by TLR4 stimulation and Prdx6-knockdown (Prdx6^KD) THP-1 cells had increased level of mitochondrial reactive oxygen species levels and were resistant to Salmonella typhimurium infection. Biochemical studies revealed Prdx6 interaction with the C-terminal TRAF-C domain of TRAF6, which drove translocation into the mitochondria. Interestingly, Prdx6 competitively interacted with ECSIT to TRAF6 through its C-terminal TRAF-C domain, leading to the interruption of TRAF6-ECSIT interaction. The inhibitory effect was critically implicated in the activation of NF-κB induced by TLR4. Overexpression of Prdx6 led to the inhibition of NF-κB induced by TLR4, whereas Prdx6^KD THP-1 cells displayed enhanced production of pro-inflammatory cytokines including interleukin-6 and -1β, and the up-regulation of NF-κB-dependent genes induced by TLR4 stimulation. Taken together, the data demonstrate that Prdx6 interrupts the formation of TRAF6-ECSIT complex induced by TLR4 stimulation, leading to suppression of bactericidal activity because of inhibited mROS production in mitochondria and the inhibition of NF-κB activation in the cytoplasm.

Peroxiredoxin 6 suppresses Muc5ac overproduction in LPS-induced airway inflammation through H2O2-EGFR-MAPK signaling pathway

Mucus hypersecretion is a prominent mechanism in airway inflammation. Muc5ac is a major component of mucus and can be activated by reactive oxygen species (ROS). Peroxiredoxin 6 (Prdx6) highly expresses in airway epithelium and protects the airway from oxidative stress. In this study, we investigated the roles of Prdx6 in lipopolysaccharide (LPS)-induced mucin production in mice. We found that the levels of H₂O₂ and the Muc5ac mRNA were significantly increased in Prdx6 (-/-) mice compared to those in C57BL/6J mice after LPS instillation, which were markedly inhibited by epithelial growth factor receptor (EGFR) inhibitor Elrotinib. In vitro studies showed that mRNA levels of Prdx6 were decreased while H₂O₂ and Muc5ac were increased in a dose-dependent manner after LPS exposure, with significant increase in Prdx6 knockdown bronchial epithelial cells compared with those in normal epithelial cells. LPS-induced Muc5ac release was significantly inhibited by EGFR inhibitor, p38 inhibitor and JNK inhibitor, but not ERK1/2 inhibitor, indicating that the H₂O₂-EGFR-MAPK pathway is likely involved in the responses. This study indicated that Prdx6 decreased LPS-induced Muc5ac increase and played important roles in mucin hypersecretion after LPS exposure.

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.

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).

Inactivation of Peroxiredoxin 6 by the Pla Protease of Yersinia pestis

Pneumonic plague represents the most severe form of disease caused by Yersinia pestis due to its ease of transmission, rapid progression, and high mortality rate. The Y. pestis outer membrane Pla protease is essential for the development of pneumonic plague; however, the complete repertoire of substrates cleaved by Pla in the lungs is not known. In this study, we describe a proteomic screen to identify host proteins contained within the bronchoalveolar lavage fluid of mice that are cleaved and/or processed by Y. pestis in a Pla-dependent manner. We identified peroxiredoxin 6 (Prdx6), a host factor that contributes to pulmonary surfactant metabolism and lung defense against oxidative stress, as a previously unknown substrate of Pla. Pla cleaves Prdx6 at three distinct sites, and these cleavages disrupt both the peroxidase and phospholipase A2 activities of Prdx6. In addition, we found that infection with wild-type Y. pestis reduces the abundance of extracellular Prdx6 in the lungs compared to that after infection with Δpla Y. pestis, suggesting that Pla cleaves Prdx6 in the pulmonary compartment. However, following infection with either wild-type or Δpla Y. pestis, Prdx6-deficient mice exhibit no differences in bacterial burden, host immune response, or lung damage from wild-type mice. Thus, while Pla is able to disrupt Prdx6 function in vitro and reduce Prdx6 levels in vivo, the cleavage of Prdx6 has little detectable impact on the progression or outcome of pneumonic plague.

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.

NSFC spurs significant basic research progress of respiratory medicine in China

Over the years, research in respiratory medicine has progressed rapidly in China. This commentary narrates the role of the National Natural Science Foundation of China (NSFC) in supporting the basic research of respiratory medicine, summarizes the major progress of respiratory medicine in China, and addresses the main future research directions sponsored by the NSFC.

Peptide targeting and imaging of damaged lung tissue in influenza-infected mice

AIM

In this study, we investigate whether pH (low) insertion peptide (pHLIP) can target regions of lung injury associated with influenza infection.

MATERIALS & METHODS

Fluorophore-conjugated pHLIP was injected intraperitoneally into mice infected with a sublethal dose of H1N1 influenza and visualized histologically.

RESULTS

pHLIP specifically targeted inflamed lung tissues of infected mice in the later stages of disease and at sites where alveolar type I and type II cells were depleted. Regions of pHLIP-targeted lung tissue were devoid of peroxiredoxin 6, the lung-abundant antioxidant enzyme, and were deficient in pneumocytes. Interestingly, a pHLIP variant possessing mutations that render it insensitive to pH changes was also able to target damaged lung tissue.

CONCLUSION

pHLIP holds potential for delivering therapeutics for lung injury during influenza infection. Furthermore, there may be more than one mechanism that enables pHLIP variants to target inflamed lung tissue.

Traumatic brain injury induces macrophage subsets in the brain

Traumatic brain injury (TBI) elicits innate inflammatory responses that can lead to secondary brain injury. To better understand the mechanisms involved in TBI-induced inflammation, we examined the nature of macrophages responding to TBI in mice. In this model, brain macrophages were increased >20-fold the day after injury and >77-fold 4 days after injury in the ipsilateral hemisphere compared with sham controls. TBI macrophage subsets were identified by using a reporter mouse strain (YARG) that expresses eYFP from an internal ribosome entry site (IRES) inserted at the 3' end of the gene for arginase-1 (Arg1), a hallmark of alternatively activated (M2) macrophages. One day after TBI, 21 ± 1.5% of ipsilateral brain macrophages expressed relatively high levels of Arg1 as detected by yellow fluorescent protein, and this subpopulation declined thereafter. Arg1(+) cells localized with macrophages near the TBI lesion. Gene expression analysis of sorted Arg1(+) and Arg1(-) brain macrophages revealed that both populations had profiles that included features of conventional M2 macrophages and classically activated (M1) macrophages. The Arg1(+) cells differed from Arg1(-) cells in multiple aspects, most notably in their chemokine repertoires. Thus, the macrophage response to TBI initially involves heterogeneous polarization toward at least two major subsets.

Comparative proteome analysis of lung tissue from patients with idiopathic pulmonary fibrosis (IPF), non-specific interstitial pneumonia (NSIP) and organ donors

Among the idiopathic interstitial pneumonias (IIP), the two entities IPF and NSIP seem to be clinically related, but NSIP has a better outcome. The proteomic signatures which distinguish NSIP from IPF remain still elusive. We therefore performed comparative proteomic analysis of peripheral lung tissue from patients with sporadic IPF (n=14) and fibrotic NSIP (fNSIP, n=8) and organ donors (Controls, n=10), by using the 2-dimensional DIGE technique and MALDI-TOF-MS. The study revealed that the proteomic profiles of IPF and fNSIP were quite similar. Among the upregulated proteins in IPF and fNSIP were stress-induced genes involved in the ER stress-pathway, whereas downregulated proteins in IPF and fNSIP included antiapoptotic factors and antifibrotic molecules. The comparison fNSIP versus IPF indicated upregulation of subunits of the proteasome activator complex and antioxidant enzymes of the peroxiredoxin family. We conclude, that only few protein expression changes exist between IPF and fNSIP, and that epithelial ER- and oxidative stress play a major role in the pathogenesis of both diseases. In contrast to IPF, intracellular clearance of ROS and misfolded protein carbonyls seem to be enhanced in fNSIP due to enhanced expression of antioxidant acting proteins, and may explain the better outcome and survival in patients with fNSIP.

BIOLOGICAL SIGNIFICANCE

IPF and fibrotic NSIP (fNSIP) belong to the idiopathic interstitial pneumonias and are usually fatal, but fNSIP has a better outcome. In order to identify molecular mechanisms and differences between IPF and fNSIP, we herein present results of a comparative proteome analysis of IPF, fNSIP and control lung tissue. Our data including validation experiments suggest that ER stress and a general stress-response as well as the decline of antioxidant capacity in alveolar epithelium is key in the pathogenesis of IPF and fNSIP. In addition, we could observe a signature of an increased alveolar epithelial protection against oxidative and ER-stress in fNSIP as compared to IPF, which could help to explain the better outcome of fNSIP patients.

Role of CD69 in acute lung injury

AIMS

CD69 is an early activation marker in lymphocytes and an important signal transmitter in inflammatory processes. However, its role in acute lung injury (ALI) is still unknown. We used a lipopolysaccharide (LPS)-induced mouse model of ALI to study the role of macrophage-surface CD69 in this condition.

MAIN METHODS

We investigated bronchoalveolar lavage fluid (BALF) cell subpopulations, myeloperoxidase levels in lung homogenates, lung pathology, and lung oedema in CD69-deficient (CD69(-/-)) mice 24h after LPS instillation. We also determined cytokine/chemokine expression levels in BALF and macrophage culture supernatant from CD69(-/-) and wild type (WT) mice. Also, we investigated CD69, keratinocyte-derived chemokine (KC) and macrophage inflammatory protein (MIP)-2 localization in the lungs after LPS administration. Furthermore, we examined the effect of anti-CD69 antibody on LPS-induced cytokine/chemokine release from cultured macrophages.

KEY FINDINGS

Our study shows that intratracheal instillation of LPS-induced neutrophilic infiltration, histopathological changes, myeloperoxidase positivity, and oedema in the lung to a lower degree in CD69(-/-) mice than in WT mice. The immunoreactivities for CD69, KC and MIP2 were induced in the lung of WT mice instilled with LPS and were predominantly localized to the macrophages. Moreover, the cytokine/chemokine expression profile between the two genotypes of cultured macrophages in response to LPS was similar to that observed in the BALF. In addition, anti-CD69 antibody inhibited the LPS-induced cytokine/chemokine expression.

SIGNIFICANCE

These results suggest that CD69 on macrophages plays a crucial role in the progression of LPS-induced ALI and may be a potentially useful target in the therapy for ALI.