The role of TLR4/NF-κB signaling in the radioprotective effects of exogenous Prdx6

Dicarbonyl-Modified Low-Density Lipoproteins Are Key Inducers of LOX-1 and NOX1 Gene Expression in the Cultured Human Umbilical Vein Endotheliocytes

Expression of LOX-1 and NOX1 genes in the human umbilical vein endotheliocytes (HUVECs) cultured in the presence of low-density lipoproteins (LDL) modified with various natural dicarbonyls was investigated for the first time. It was found that among the investigated dicarbonyl-modified LDLs (malondialdehyde (MDA)-modified LDLs, glyoxal-modified LDLs, and methylglyoxal-modified LDLs), the MDA-modified LDLs caused the greatest induction of the LOX-1 and NOX1 genes, as well as of the genes of antioxidant enzymes and genes of proapoptotic factors in HUVECs. Key role of the dicarbonyl-modified LDLs in the molecular mechanisms of vascular wall damage and endothelial dysfunction is discussed.

Peroxiredoxin 5 overexpression decreases oxidative stress and dopaminergic cell death mediated by paraquat

Peroxiredoxins (Prdxs) are thiol-dependent enzymes that scavenge peroxides. Previously, we found that Prdxs were hyperoxidized in a Parkinson's disease model induced by paraquat (PQ), which led to their inactivation, perpetuating reactive oxygen species (ROS) formation. Herein, we evaluated the redox state of the typical 2-Cys-Prx subgroup. We found that PQ induces ROS compartmentalization in different organelles, reflected by the 2-Cys-Prdx hyperoxidation pattern detected by redox eastern blotting. 2-Cys Prdxs are most vulnerable to hyperoxidation, while atypical 2-Cys Peroxiredoxin 5 (Prdx5) is resistant and is expressed in multiple organelles, such as mitochondria, peroxisomes, and cytoplasm. Therefore, we overexpressed human Prdx5 in the dopaminergic SHSY-5Y cell line using the adenoviral vector Ad-hPrdx5. Prdx5 overexpression was confirmed by western blotting and immunofluorescence (IF) and effectively decreased PQ-mediated mitochondrial and cytoplasmic ROS assessed with a mitochondrial superoxide indicator and DHE through IF or flow cytometry. Decreased ROS mediated by Prdx5 in the main subcellular compartments led to overall cell protection against PQ-induced cell death, which was demonstrated by flow cytometry using Annexin V labeling and 7-AAD. Therefore, Prdx5 is an attractive therapeutic target for PD, as its overexpression protects dopaminergic cells from ROS and death, which warrants further experimental animal studies for its subsequent application in clinical trials.

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.

Radiation-induced NF-κB activation is involved in cochlear damage in mice via promotion of a local inflammatory response

The radiation-induced inflammatory response is involved in radiation damage to the cochlea and causes sensorineural hearing loss (SNHL). NF-κB, as the master switch of the inflammatory response, regulates the expression of many inflammation-related genes and thus the inflammatory response. Therefore, in this study we used a mouse model to determine whether radiation-induced NF-κB activation is involved in damage to the cochlea and to investigate the underlying mechanism. Eventually, we found that NF-κB was activated after radiation of the cochleae and the activation reached a maximum at 2-6 h after radiation. And morphological analysis showed severe damage to the cochleae after radiation, but this damage was significantly ameliorated by JSH-23 (an inhibitor of NF-κB) pretreatment. Along with these morphological changes, the expression levels of proinflammatory molecules (including proinflammatory cytokines IL-6, TNF-α, COX-2 and inflammation-related proteins VCAM-1, MIP-1β) in the cochlear tissues were significantly increased after radiation, but were significantly decreased by JSH-23 pretreatment compared to radiation alone. Therefore, these results indicated that radiation-induced NF-κB activation was involved in damage to the cochleae and resultant SNHL via its promotion of the inflammatory response mediated by overexpression of some proinflammatory molecules in cochlear tissues, and inhibition of radiation-induced NF-κB was conducive to preventing such damage.

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.

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.

Surface modification of fibroblasts with peroxiredoxin-1-loaded polymeric microparticles increases cell mobility, resistance to oxidative stress and collagen I production

Modification of the cell surface with artificial nano- and microparticles (also termed "cellular backpacks") containing biologically active payloads usually enables drug targeting via harnessing intrinsic cell tropism to the sites of injury. In some cases, using cells as delivery vehicles leads to improved pharmacokinetics due to extended circulation time of cell-immobilized formulations. Another rationale for particle attachment to cells is augmentation of desirable cellular functions and cell proliferation in response to release of the particle contents. In this study, we conjugated poly(lactic-co-glycolic acid) (PLGA) microparticles loaded with multifunctional antioxidant enzyme peroxiredoxin-1 (Prx1) to the surface of fibroblasts. The obtained microparticles were uniform in size and demonstrated sustained protein release. We found that the released Prx1 maintains its signaling activity resulting in macrophage activation, as indicated by TNFα upregulation and increase in ROS generation. Functionalization of fibroblasts with PLGA/Prx1 microparticles via EDC/sulfo-NHS coupling reaction did not affect cell viability but increased cell migratory properties and collagen I production. Moreover, PLGA/Prx1 backpacks increased resistance of fibroblasts to oxidative stress and attenuated cell senescence. In summary, we have developed a novel approach of fibroblast modification to augment their biological properties, which can be desirable for wound repair, cosmetic dermatology, and tissue engineering.

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.

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.

Peroxiredoxin 6 protects irradiated cells from oxidative stress and shapes their senescence-associated cytokine landscape

Cellular senescence is a complex stress response defined as an essentially irreversible cell cycle arrest mediated by the inhibition of cell cycle-specific cyclin dependent kinases. The imbalance in redox homeostasis and oxidative stress have been repeatedly observed as one of the hallmarks of the senescent phenotype. However, a large-scale study investigating protein oxidation and redox signaling in senescent cells in vitro has been lacking. Here we applied a proteome-wide analysis using SILAC-iodoTMT workflow to quantitatively estimate the level of protein sulfhydryl oxidation and proteome level changes in ionizing radiation-induced senescence (IRIS) in hTERT-RPE-1 cells. We observed that senescent cells mobilized the antioxidant system to buffer the increased oxidation stress. Among the antioxidant proteins with increased relative abundance in IRIS, a unique 1-Cys peroxiredoxin family member, peroxiredoxin 6 (PRDX6), was identified as an important contributor to protection against oxidative stress. PRDX6 silencing increased ROS production in senescent cells, decreased their resistance to oxidative stress-induced cell death, and impaired their viability. Subsequent SILAC-iodoTMT and secretome analysis after PRDX6 silencing showed the downregulation of PRDX6 in IRIS affected protein secretory pathways, decreased expression of extracellular matrix proteins, and led to unexpected attenuation of senescence-associated secretory phenotype (SASP). The latter was exemplified by decreased secretion of pro-inflammatory cytokine IL-6 which was also confirmed after treatment with an inhibitor of PRDX6 iPLA2 activity, MJ33. In conclusion, by combining different methodological approaches we discovered a novel role of PRDX6 in senescent cell viability and SASP development. Our results suggest PRDX6 could have a potential as a drug target for senolytic or senomodulatory therapy.

•

SILAC-iodoTMT is a powerful tool to quantify redox imbalance in IRIS.

•

Senescence in hTERT-RPE-1 cells is not accompanied by bulk cysteine oxidation.

•

Antioxidant proteins are upregulated in senescent hTERT-RPE-1 cells.

•

PRDX6 silencing affects redox homeostasis and viability of senescent cells.

•

PRDX6 silencing alters secretome of senescent RPE-1 cells and suppresses IL-6.

Peroxiredoxin 6 Applied after Exposure Attenuates Damaging Effects of X-ray Radiation in 3T3 Mouse Fibroblasts

Although many different classes of antioxidants have been evaluated as radioprotectors, none of them are in widespread clinical use because of their low efficiency. The goal of our study was to evaluate the potential of the antioxidant protein peroxiredoxin 6 (Prdx6) to increase the radioresistance of 3T3 fibroblasts when Prdx6 was applied after exposure to 6 Gy X-ray. In the present study, we analyzed the mRNA expression profiles of genes associated with proliferation, apoptosis, cellular stress, senescence, and the production of corresponding proteins from biological samples after exposure of 3T3 cells to X-ray radiation and application of Prdx6. Our results suggested that Prdx6 treatment normalized p53 and NF-κB/p65 expression, p21 levels, DNA repair-associated genes (XRCC4, XRCC5, H2AX, Apex1), TLR expression, cytokine production (TNF-α and IL-6), and apoptosis, as evidenced by decreased caspase 3 level in irradiated 3T3 cells. In addition, Prdx6 treatment reduced senescence, as evidenced by the decreased percentage of SA-β-Gal positive cells in cultured 3T3 fibroblasts. Importantly, the activity of the NRF2 gene, an important regulator of the antioxidant cellular machinery, was completely suppressed by irradiation but was restored by post-irradiation Prdx6 treatment. These data support the radioprotective therapeutic efficacy of Prdx6.

Role of Innate Immunity and Oxidative Stress in the Development of Type 1 Diabetes Mellitus. Peroxiredoxin 6 as a New Anti-Diabetic Agent

The review discusses information on the development of type 1 diabetes mellitus (T1D) as a systemic autoimmune and inflammatory disease. Focus of the review is on the role of innate immune system, including activation of some signaling cascades, cytokine response, and activity of the Toll-like receptors in the development of T1D. Dysfunction of innate immunity is the cause of the attack of pancreatic beta cells by the host T-lymphocytes, which leads to the death of pancreatic beta cells that produce insulin. Lack of insulin causes hyperglycemia and the need for lifelong injections of insulin in patients with T1D, which, nevertheless, does not exclude damage to many organs and tissues, given particular vulnerability of the blood vessels under conditions of hyperglycemia. The review discusses the role of oxidative stress as a factor that plays a major role in damage of vascular system and pancreatic tissue during the development of T1D. Considering high sensitivity of pancreatic beta cells to the action of reactive oxygen species (ROS), the possibility of using antioxidants for reducing the level of pathological consequences in the course of T1D development is discussed. New information on anti-diabetic activity of the exogenous antioxidant enzyme peroxiredoxin 6, which is capable of penetrating cells, activating insulin production in beta cells, reducing ROS levels, as well as decreasing activation of some signaling cascades, production of pro-inflammatory cytokines, and expression of Toll-like receptors in beta cells and in immune cells during T1D development is discussed.

Role of Glutathione Peroxidases and Peroxiredoxins in Free Radical-Induced Pathologies

In this review, we discuss the pathogenesis of some socially significant diseases associated with the development of oxidative stress, such as atherosclerosis, diabetes, and radiation sickness, as well as the possibilities of the therapeutic application of low-molecular-weight natural and synthetic antioxidants for the correction of free radical-induced pathologies. The main focus of this review is the role of two phylogenetically close families of hydroperoxide-reducing antioxidant enzymes peroxiredoxins and glutathione peroxidases - in counteracting oxidative stress. We also present examples of the application of exogenous recombinant antioxidant enzymes as therapeutic agents in the treatment of pathologies associated with free-radical processes and discuss the prospects of the therapeutic use of exogenous antioxidant enzymes, as well as the ways to improve their therapeutic properties.

Hydroperoxide-Reducing Enzymes in the Regulation of Free-Radical Processes

The review presents current concepts of the molecular mechanisms of oxidative stress development and describes main stages of the free-radical reactions in oxidative stress. Endogenous and exogenous factors of the oxidative stress development, including dysfunction of cell oxidoreductase systems, as well as the effects of various external physicochemical factors, are discussed. The review also describes the main components of the antioxidant defense system and stages of its evolution, with a special focus on peroxiredoxins, glutathione peroxidases, and glutathione S-transferases, which share some phylogenetic, structural, and catalytic properties. The substrate specificity, as well as the similarities and differences in the catalytic mechanisms of these enzymes, are discussed in detail. The role of peroxiredoxins, glutathione peroxidases, and glutathione S-transferases in the regulation of hydroperoxide-mediated intracellular and intercellular signaling and interactions of these enzymes with receptors and non-receptor proteins are described. An important contribution of hydroperoxide-reducing enzymes to the antioxidant protection and regulation of such cell processes as growth, differentiation, and apoptosis is demonstrated.