Reactive oxygen species and Wnt signalling crosstalk patterns mouse extraembryonic endoderm

Non-thermal atmospheric pressure plasma activates Wnt/β-catenin signaling in dermal papilla cells

There is an unmet need for novel, non-pharmacological therapeutics to treat alopecia. Recent studies have shown the potential biological benefits of non-thermal atmospheric pressure plasma (NTAPP), including wound healing, angiogenesis, and the proliferation of stem cells. We hypothesized that NTAPP might have a stimulatory effect on hair growth or regeneration. We designed an NTAPP-generating apparatus which is applicable to in vitro and in vivo experiments. The human dermal papilla (DP) cells, isolated fresh hair follicles, and mouse back skin were exposed with the NTAPP. Biological outcomes were measured using RNA-sequencing, RT-PCR, Western blots, and immunostaining. The NTAPP treatment increased the expression levels of Wnt/β-catenin pathway-related genes (AMER3, CCND1, LEF1, and LRG1) and proteins (β-catenin, p-GSK3β, and cyclin D1) in human DP cells. In contrast, inhibitors of Wnt/β-catenin signaling, endo-IWR1 and IWP2, attenuated the levels of cyclin D1, p-GSK3β, and β-catenin proteins induced by NTAPP. Furthermore, we observed that NTAPP induced the activation of β-catenin in DP cells of hair follicles and the mRNA levels of target genes of the β-catenin signaling pathway (CCND1, LEF1, and TCF4). NTAPP-treated mice exhibited markedly increased anagen induction, hair growth, and the protein levels of β-catenin, p-GSK3β, p-AKT, and cyclin D1. NTAPP stimulates hair growth via activation of the Wnt/β-catenin signaling pathway in DP cells. These findings collectively suggest that NTAPP may be a potentially safe and non-pharmacological therapeutic intervention for alopecia.

A Positive Feed Forward Loop between Wnt/β-Catenin and NOX4 Promotes Silicon Dioxide-Induced Epithelial-Mesenchymal Transition of Lung Epithelial Cells

Silicosis is a chronic fibrotic lung disease caused by the accumulation of silica dust in the distal lung. Canonical Wnt signaling and NADPH oxidase 4 (NOX4) have been demonstrated to play a crucial role in the pathogenesis of pulmonary fibrosis including silicosis. However, the underlying mechanisms of crosstalk between these two signalings are not fully understood. In the present study, we aimed to explore the interaction of Wnt/β-catenin and NOX4 of human epithelial cells in response to an exposure of silica dust. Results demonstrated an elevated expression of key components of Wnt/β-catenin signaling and NOX4 in the lungs of silicon dioxide- (SiO₂-) induced silicosis mice. Furthermore, the activated Wnt/β-catenin and NOX4 signaling are accompanied by an inhibition of cell proliferation, an increase of ROS production and cell apoptosis, and an upregulation of profibrogenic factors in BEAS-2B human lung epithelial cells exposed to SiO₂. A mechanistic study further demonstrated that the Wnt3a-mediated activation of canonical Wnt signaling could augment the SiO₂-induced NOX4 expression and reactive oxygen species (ROS) production but reduced glutathione (GSH), while Wnt inhibitor DKK1 exhibited an opposite effect to Wnt3a. Vice versa, an overexpression of NOX4 further activated SiO₂-induced Wnt/β-catenin signaling and NFE2-related factor 2 (Nrf2) antioxidant response along with a reduction of GSH, whereas the shRNA-mediated knockdown of NOX4 showed an opposite effect to NOX4 overexpression. These results imply a positive feed forward loop between Wnt/β-catenin and NOX4 signaling that may promote epithelial-mesenchymal transition (EMT) of lung epithelial cells in response to an exposure of silica dust, which may thus provide an insight into the profibrogenic role of Wnt/β-catenin and NOX4 crosstalk in lung epithelial cell injury and pathogenesis of silicosis.

Age-related declines in α-Klotho drive progenitor cell mitochondrial dysfunction and impaired muscle regeneration

While young muscle is capable of restoring the original architecture of damaged myofibers, aged muscle displays a markedly reduced regeneration. We show that expression of the "anti-aging" protein, α-Klotho, is up-regulated within young injured muscle as a result of transient Klotho promoter demethylation. However, epigenetic control of the Klotho promoter is lost with aging. Genetic inhibition of α-Klotho in vivo disrupted muscle progenitor cell (MPC) lineage progression and impaired myofiber regeneration, revealing a critical role for α-Klotho in the regenerative cascade. Genetic silencing of Klotho in young MPCs drove mitochondrial DNA (mtDNA) damage and decreased cellular bioenergetics. Conversely, supplementation with α-Klotho restored mtDNA integrity and bioenergetics of aged MPCs to youthful levels in vitro and enhanced functional regeneration of aged muscle in vivo in a temporally-dependent manner. These studies identify a role for α-Klotho in the regulation of MPC mitochondrial function and implicate α-Klotho declines as a driver of impaired muscle regeneration with age.

Metabolic profile and differentiation potential of extraembryonic endoderm-like cells

Glucose metabolism has a crucial role for providing substrates required to generate ATP and regulate the epigenetic landscape. We reported that F9 embryonal carcinoma stem-like cells require cytosolic reactive oxygen species to differentiate into extraembryonic endoderm; however, mitochondrial sources were not examined. To extend these studies, we examined the metabolic profile of early and late-passage F9 cells, and show that their ability to differentiate is similar, even though each population has dramatically different metabolic profiles. Differentiated early-passage cells relied on glycolysis, while differentiated late-passage cells transitioned towards oxidative phosphorylation (OXPHOS). Unexpectedly, electron transport chain protein stoichiometry was disrupted in differentiated late-passage cells, whereas genes encoding mitofusion 1 and 2, which promote mitochondrial fusion and favor OXPHOS, were upregulated in differentiated early-passage cells. Despite this, early-passage cells cultured under conditions to promote glycolysis showed enhanced differentiation, whereas promoting OXPHOS in late-passage cells showed a similar trend. Further analysis revealed that the distinct metabolic profiles seen between the two populations is largely associated with changes in genomic integrity, linking metabolism to passage number. Together, these results indicate that passaging has no effect on the potential for F9 cells to differentiate into extraembryonic endoderm; however, it does impact their metabolic profile. Thus, it is imperative to determine the molecular and metabolic status of a stem cell population before considering its utility as a therapeutic tool for regenerative medicine.

Glutathione peroxidase 4 inhibits Wnt/β-catenin signaling and regulates dorsal organizer formation in zebrafish embryos

The Wnt/β-catenin signaling pathway plays pivotal roles in axis formation during embryogenesis and in adult tissue homeostasis. Glutathione peroxidase 4 (GPX4) is a selenoenzyme and participates in the reduction of peroxides. Its synthesis depends on the availability of the element selenium. However, the roles of GPX4 in vertebrate embryonic development and underlying mechanisms are largely unknown. Here, we show that maternal loss of zebrafish gpx4b promotes embryonic dorsal organizer formation, whereas overexpression of gpx4b inhibits the development of the dorsal organizer. Depletion of human GPX4 and zebrafish gpx4b (GPX4/gpx4b) increases, while GPX4/gpx4b overexpression decreases, Wnt/β-catenin signaling in vivo and in vitro Functional and epistatic studies showed that GPX4 functions at the Tcf/Lef level, independently of selenocysteine activation. Mechanistically, GPX4 interacts with Tcf/Lefs and inhibits Wnt activity by preventing the binding of Tcf/Lefs to the promoters of Wnt target genes, resulting in inhibitory action in the presence of Wnt/β-catenin signaling. Our findings unravel GPX4 as a suppressor of Wnt/β-catenin signals, suggesting a possible relationship between the Wnt/β-catenin pathway and selenium via the association of Tcf/Lef family proteins with GPX4.

Regulation of stem-like cancer cells by glutamine through β-catenin pathway mediated by redox signaling

Background

Cancer stem cells (CSCs) are thought to play an important role in tumor recurrence and drug resistance, and present a major challenge in cancer therapy. The tumor microenvironment such as growth factors, nutrients and oxygen affect CSC generation and proliferation by providing the necessary energy sources and growth signals. The side population (SP) analysis has been used to detect the stem-like cancer cell populations based on their high expression of ABCG2 that exports Hoechst-33342 and certain cytotoxic drugs from the cells. The purpose of this research is to investigate the effect of a main nutrient molecule, glutamine, on SP cells and the possible underlying mechanism(s).

Methods

Biochemical assays and flow cytometric analysis were used to evaluate the effect of glutamine on stem-like side population cells in vitro. Molecular analyses including RNAi interfering, qRT-PCR, and immunoblotting were employed to investigate the molecular signaling in response to glutamine deprivation and its influence on tumor formation capacity in vivo.

Results

We show that glutamine supports the maintenance of the stem cell phenotype by promoting glutathione synthesis and thus maintaining redox balance for SP cells. A deprivation of glutamine in the culture medium significantly reduced the proportion of SP cells. L-asparaginase, an enzyme that catalyzes the hydrolysis of asparagine and glutamine to aspartic acid and glutamate, respectively, mimics the effect of glutamine withdrawal and also diminished the proportion of SP cells. Mechanistically, glutamine deprivation increases intracellular ROS levels, leading to down-regulation of the β-catenin pathway.

Conclusion

Glutamine plays a significant role in maintaining the stemness of cancer cells by a redox-mediated mechanism mediated by β-catenin. Inhibition of glutamine metabolism or deprivation of glutamine by L-asparaginase may be a new strategy to eliminate CSCs and overcome drug resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0623-x) contains supplementary material, which is available to authorized users.

NOX1 and NOX4 are required for the differentiation of mouse F9 cells into extraembryonic endoderm

Mouse F9 cells differentiate to primitive endoderm (PrE) when treated with retinoic acid (RA). Differentiation is accompanied by increased reactive oxygen species (ROS) levels, and while treating F9 cells with antioxidants attenuates differentiation, H₂O₂ treatment alone is sufficient to induce PrE. We identified the NADPH oxidase (NOX) complexes as candidates for the source of this endogenous ROS, and within this gene family, and over the course of differentiation, Nox1 and Nox 4 show the greatest upregulation induced by RA. Gata6, encoding a master regulator of extraembryonic endoderm is also up-regulated by RA and we provide evidence that NOX1 and NOX4 protein levels increase in F9 cells overexpressing Gata6. Pan-NOX and NOX1-specific inhibitors significantly reduced the ability of RA to induce PrE, and this was recapitulated using a genetic approach to knockdown Nox1 and/or Nox4 transcripts. Interestingly, overexpressing either gene in untreated F9 cells did not induce differentiation, even though each elevated ROS levels. Thus, the data suggests that ROS produced during PrE differentiation is dependent in part on increased NOX1 and NOX4 levels, which is under the control of GATA6. Furthermore, these results suggest that the combined activity of multiple NOX proteins is necessary for the differentiation of F9 cells to primitive endoderm.

Developmental Drift and the Role of Wnt Signaling in Aging

Population aging is a public health problem affecting the majority of the developed world. As populations age, the incidence of degenerative diseases increases exponentially, leading to large increases in public spending on healthcare. Here we summarize recent findings on the developmental drift theory of aging, and the links that have been established between aging and the Wnt signaling pathways. We focus on insights derived from model organisms connecting the evolutionary basis of aging and the link to developmental programming.

Protective Effect of Ginsenoside Rg1 on Hematopoietic Stem/Progenitor Cells through Attenuating Oxidative Stress and the Wnt/β-Catenin Signaling Pathway in a Mouse Model of d-Galactose-induced Aging

Stem cell senescence is an important and current hypothesis accounting for organismal aging, especially the hematopoietic stem cell (HSC). Ginsenoside Rg1 is the main active pharmaceutical ingredient of ginseng, which is a traditional Chinese medicine. This study explored the protective effect of ginsenoside Rg1 on Sca-1⁺ hematopoietic stem/progenitor cells (HSC/HPCs) in a mouse model of d-galactose-induced aging. The mimetic aging mouse model was induced by continuous injection of d-gal for 42 days, and the C57BL/6 mice were respectively treated with ginsenoside Rg1, Vitamin E or normal saline after 7 days of d-gal injection. Compared with those in the d-gal administration alone group, ginsenoside Rg1 protected Sca-1⁺ HSC/HPCs by decreasing SA-β-Gal and enhancing the colony forming unit-mixture (CFU-Mix), and adjusting oxidative stress indices like reactive oxygen species (ROS), total anti-oxidant (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-px) and malondialdehyde (MDA). In addition, ginsenoside Rg1 decreased β-catenin and c-Myc mRNA expression and enhanced the phosphorylation of GSK-3β. Moreover, ginsenoside Rg1 down-regulated advanced glycation end products (AGEs), 4-hydroxynonenal (4-HNE), phospho-histone H2A.X (r-H2A.X), 8-OHdG, p16(Ink4a), Rb, p21(Cip1/Waf1) and p53 in senescent Sca-1⁺ HSC/HPCs. Our findings indicated that ginsenoside Rg1 can improve the resistance of Sca-1⁺ HSC/HPCs in a mouse model of d-galactose-induced aging through the suppression of oxidative stress and excessive activation of the Wnt/β-catenin signaling pathway, and reduction of DNA damage response, p16(Ink4a)-Rb and p53-p21(Cip1/Waf1) signaling.

High glucose and hyperglycemic sera from type 2 diabetic patients impair DC differentiation by inducing ROS and activating Wnt/β-catenin and p38 MAPK

Type 2 is the type of diabetes with higher prevalence in contemporary time, representing about 90% of the global cases of diabetes. In the course of diabetes, several complications can occur, mostly due to hyperglycemia and increased reactive oxygen species (ROS) production. One of them is represented by an increased susceptibility to microbial infections and by a reduced capacity to clear them. Therefore, knowing the impact of hyperglycemia on immune system functionality is of utmost importance for the management of the disease. In this study, we show that medium containing high glucose reduced the in-vitro differentiation of monocytes into functional DCs and their activation mediated by PAMPs or DAMPs. Most importantly, the same effects were mediated by the hyperglycemic sera derived by type 2 diabetic patients, mimicking a more physiologic condition. DC dysfunction caused by hyperglycemia may be involved in the inefficient control of infections observed in diabetic patients, given the pivotal role of these cells in both the innate and adaptive immune response. Searching for the molecular mechanisms underlying DC dysfunction, we found that canonical Wnt/β-catenin and p38 MAPK pathways were activated in the DCs differentiated either in the presence of high glucose or of hyper-glycemic sera. Interestingly, the activation of these pathways and the DC immune dysfunction were partially counteracted by the anti-oxidant quercetin, a flavonoid already known to exert several beneficial effects in diabetes.

Controlling Redox Status for Stem Cell Survival, Expansion, and Differentiation

Reactive oxygen species (ROS) have long been considered as pathological agents inducing apoptosis under adverse culture conditions. However, recent findings have challenged this dogma and physiological levels of ROS are now considered as secondary messengers, mediating numerous cellular functions in stem cells. Stem cells represent important tools for tissue engineering, drug screening, and disease modeling. However, the safe use of stem cells for clinical applications still requires culture improvements to obtain functional cells. With the examples of mesenchymal stem cells (MSCs) and pluripotent stem cells (PSCs), this review investigates the roles of ROS in the maintenance of self-renewal, proliferation, and differentiation of stem cells. In addition, this work highlights that the tight control of stem cell microenvironment, including cell organization, and metabolic and mechanical environments, may be an effective approach to regulate endogenous ROS generation. Taken together, this paper indicates the need for better quantification of ROS towards the accurate control of stem cell fate.

Cytotoxin-induced NADPH oxides activation: roles in regulation of cell death

Numerous studies have shown that a variety of cytotoxic agents can activate the NADPH oxidase system and induce redox-dependent regulation of cellular functions. Cytotoxin-induced NADPH oxidase activation may either exert cytoprotective actions (e.g., survival, proliferation, and stress tolerance) or cause cell death. Here we summarize the experimental evidence showing the context-dependent dichotomous effects of NADPH oxidase on cell fate under cytotoxic stress conditions and the potential redox signaling mechanisms underlying this phenomenon. Clearly, it is difficult to create a unified paradigm on the toxicological implications of NADPH oxidase activation in response to cytotoxic stimuli. We suggest that interventional strategies targeting the NADPH oxidase system to prevent the adverse impacts of cytotoxins need to be contemplated in a stimuli- and cell type-specific manner.

Hypoxia enhances differentiation of mouse embryonic stem cells into definitive endoderm and distal lung cells

We investigated the effects of hypoxia on spontaneous (SP)- and activin A (AA)-induced definitive endoderm (DE) differentiation of mouse embryonic stem cells (mESCs) and their subsequent differentiation into distal pulmonary epithelial cells. SP differentiation for 6 days of mESCs toward endoderm at hypoxia of 1% O2, but not at 3% or 21% (normoxia), increased the expression of Sox17 and Foxa2 by 31- and 63-fold above maintenance culture, respectively. Treatment of mESCs with 20 ng/mL AA for 6 days under hypoxia further increased the expression of DE marker genes Sox17, Foxa2, and Cxcr4 by 501-, 1,483-, and 126-fold above maintenance cultures, respectively. Transient exposure to hypoxia, as short as 24 h, was sufficient to enhance AA-induced endoderm formation. The involvement of hypoxia-inducible factor (HIF)-1α and reactive oxygen species (ROS) in the AA-induced endoderm enrichment was assessed using HIF-1α(-/-) mESCs and the ROS scavenger N-acetylcysteine (NAC). Under SP conditions, HIF-1α(-/-) mESCs failed to increase the expression of endodermal marker genes but rather shifted toward ectoderm. Hypoxia induced only a marginal potentiation of AA-induced endoderm differentiation in HIF-1α(-/-) mESCs. Treatment of mESCs with AA and NAC led to a dose-dependent decrease in Sox17 and Foxa2 expression. In addition, the duration of exposure to hypoxia in the course of a recently reported lung differentiation protocol resulted in differentially enhanced expression of distal lung epithelial cell marker genes aquaporin 5 (Aqp5), surfactant protein C (Sftpc), and secretoglobin 1a1 (Scgb1a1) for alveolar epithelium type I, type II, and club cells, respectively. Our study is the first to show the effects of in vitro hypoxia on efficient formation of DE and lung lineages. We suggest that the extent of hypoxia and careful timing may be important components of in vitro differentiation bioprocesses for the differential generation of distal lung epithelial cells from pluripotent progenitors.

IGF antagonizes the Wnt/β-Catenin pathway and promotes differentiation of extra-embryonic endoderm

Mouse F9 teratocarcinoma cells are an established model for the differentiation of extra-embryonic endoderm (ExEn). Primitive endoderm, parietal and visceral endoderm can be generated by stimulation of F9 cells with retinoic acid and dibutyryl cyclic adenosine monophosphate. Here we show that Wnt/β-Catenin signaling is down-regulated during ExEn differentiation in F9 cells and that the inhibition of the Wnt pathway promotes differentiation of the three extra-embryonic endoderm lineages. Wnt inhibition is achieved through the IGF pathway, which is up-regulated during differentiation. IGF signaling antagonizes the Wnt pathway by stimulating transcription of axin2 and by stabilizing Axin1 protein. Both Axin1 and Axin2 are components of the β-Catenin destruction complex and act as intra-cellular inhibitors of the Wnt/β-Catenin pathway. The data presented reveal a mechanism which restricts pluripotency of undifferentiated cells and directs them toward extra-embryonic lineages.

Oxidative DNA damage induces the ATM-mediated transcriptional suppression of the Wnt inhibitor WIF-1 in systemic sclerosis and fibrosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by extensive visceral organ and skin fibrosis. SSc patients have increased production of autoreactive antibodies and Wnt signaling activity. We found that expression of the gene encoding Wnt inhibitor factor 1 (WIF-1) was decreased in fibroblasts from SSc patient biopsies. WIF-1 deficiency in SSc patient cells correlated with increased abundance of the Wnt effector β-catenin and the production of collagen. Knocking down WIF-1 in normal fibroblasts increased Wnt signaling and collagen production. WIF-1 loss and DNA damage were induced in normal fibroblasts by either SSc patient immunoglobulins or oxidative DNA-damaging agents, such as ultraviolet light, hydrogen peroxide, or bleomycin. The DNA damage checkpoint kinase ataxia telangiectasia mutated (ATM) mediated WIF-1 silencing through the phosphorylation of the transcription factor c-Jun, which in turn activated the expression of the gene encoding activating transcription factor 3 (ATF3). ATF3 and c-Jun were recruited together with histone deacetylase 3 (HDAC3) to the WIF-1 promoter and inhibited WIF-1 expression. Preventing the accumulation of reactive oxygen species or inhibiting the activation of ATM, c-Jun, or HDACs restored WIF-1 expression in cultured SSc patient cells. Trichostatin A, an HDAC inhibitor, prevented WIF-1 loss, β-catenin induction, and collagen accumulation in an experimental fibrosis model. Our findings suggest that oxidative DNA damage induced by SSc autoreactive antibodies enables Wnt activation that contributes to fibrosis.

Ca2+-mediated mitochondrial reactive oxygen species metabolism augments Wnt/β-catenin pathway activation to facilitate cell differentiation

Emerging evidence suggests that reactive oxygen species (ROS) can stimulate the Wnt/β-catenin pathway in a number of cellular processes. However, potential sources of endogenous ROS have not been thoroughly explored. Here, we show that growth factor depletion in human neural progenitor cells induces ROS production in mitochondria. Elevated ROS levels augment activation of Wnt/β-catenin signaling that regulates neural differentiation. We find that growth factor depletion stimulates the release of Ca(2+) from the endoplasmic reticulum stores. Ca(2+) subsequently accumulates in the mitochondria and triggers ROS production. The inhibition of mitochondrial Ca(2+) uptake with simultaneous growth factor depletion prevents the rise in ROS metabolism. Moreover, low ROS levels block the dissociation of the Wnt effector Dishevelled from nucleoredoxin. Attenuation of the response amplitudes of pathway effectors delays the onset of the Wnt/β-catenin pathway activation and results in markedly impaired neuronal differentiation. Our findings reveal Ca(2+)-mediated ROS metabolic cues that fine-tune the efficiency of cell differentiation by modulating the extent of the Wnt/β-catenin signaling output.

Redox regulation of canonical Wnt signaling affects extraembryonic endoderm formation

Retinoic acid (RA) induces mouse F9 cells to form primitive endoderm (PrE) and increased levels of reactive oxygen species (ROS) accompany differentiation. ROS are obligatory for differentiation and while H2O2 alone induces PrE, antioxidants attenuate the response to RA. Evidence shows that ROS can modulate the Wnt/β-catenin pathway and in this study, we show that extraembryonic endoderm formation is dependent on the redox state of nucleoredoxin (NRX). In undifferentiated F9 cells, NRX interacted with dishevelled 2 (Dvl2) and while this association was enhanced under reduced conditions, it decreased following H2O2 treatment. Depleting NRX levels caused morphological changes like those induced by RA, while increasing protein kinase A activity further induced these PrE cells to parietal endoderm. Reduced NRX levels also correlated to an increase in T-cell-factors-lymphoid enhancer factors-mediated transcription, indicative of canonical Wnt signaling. Together these results indicate that a mechanism exists whereby NRX maintains canonical Wnt signaling in the off state in F9 cells, while increased ROS levels lift these constraints. Dvl2 no longer bound to NRX is now positioned to prime the Wnt pathway(s) required for PrE formation.

Molecular chaperones and proteostasis regulation during redox imbalance

Free radicals originate from both exogenous environmental sources and as by-products of the respiratory chain and cellular oxygen metabolism. Sustained accumulation of free radicals, beyond a physiological level, induces oxidative stress that is harmful for the cellular homeodynamics as it promotes the oxidative damage and stochastic modification of all cellular biomolecules including proteins. In relation to proteome stability and maintenance, the increased concentration of oxidants disrupts the functionality of cellular protein machines resulting eventually in proteotoxic stress and the deregulation of the proteostasis (homeostasis of the proteome) network (PN). PN curates the proteome in the various cellular compartments and the extracellular milieu by modulating protein synthesis and protein machines assembly, protein recycling and stress responses, as well as refolding or degradation of damaged proteins. Molecular chaperones are key players of the PN since they facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of unfolded, misfolded, or non-native proteins. Therefore, the expression and the activity of the molecular chaperones are tightly regulated at both the transcriptional and post-translational level at organismal states of increased oxidative and, consequently, proteotoxic stress, including ageing and various age-related diseases (e.g. degenerative diseases and cancer). In the current review we present a synopsis of the various classes of intra- and extracellular chaperones, the effects of oxidants on cellular homeodynamics and diseases and the redox regulation of chaperones.

•

Free radicals originate from various sources and at physiological concentrations are essential for the modulation of cell signalling pathways.

•

Abnormally high levels of free radicals induce oxidative stress and damage all cellular biomolecules, including proteins.

•

Molecular chaperones facilitate folding of nascent polypeptides, as well as holding, folding, and/or degradation of damaged proteins.

•

The expression and the activity of chaperones during oxidative stress are regulated at both the transcriptional and post-translational level.

Glutathione peroxidase mimic ebselen improves glucose-stimulated insulin secretion in murine islets

AIMS

Glutathione peroxidase (GPX) mimic ebselen and superoxide dismutase (SOD) mimic copper diisopropylsalicylate (CuDIPs) were used to rescue impaired glucose-stimulated insulin secretion (GSIS) in islets of GPX1 and(or) SOD1-knockout mice.

RESULTS

Ebselen improved GSIS in islets of all four tested genotypes. The rescue in the GPX1 knockout resulted from a coordinated transcriptional regulation of four key GSIS regulators and was mediated by the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α)-mediated signaling pathways. In contrast, CuDIPs improved GSIS only in the SOD1 knockout and suppressed gene expression of the PGC-1α pathway.

INNOVATION

Islets from the GPX1 and(or) SOD1 knockout mice provided metabolically controlled intracellular hydrogen peroxide (H2O2) and superoxide conditions for the present study to avoid confounding effects. Bioinformatics analyses of gene promoters and expression profiles guided the search for upstream signaling pathways to link the ebselen-initiated H2O2 scavenging to downstream key events of GSIS. The RNA interference was applied to prove PGC-1α as the main mediator for that link.

CONCLUSION

Our study revealed a novel metabolic use and clinical potential of ebselen in rescuing GSIS in the GPX1-deficient islets and mice, along with distinct differences between the GPX and SOD mimics in this regard. These findings highlight the necessities and opportunities of discretional applications of various antioxidant enzyme mimics in treating insulin secretion disorders. REBOUND TRACK: This work was rejected during standard peer review and rescued by Rebound Peer Review (Antioxid Redox Signal 16: 293-296, 2012) with the following serving as open reviewers: Regina Brigelius-Flohe, Vadim Gladyshev, Dexing Hou, and Holger Steinbrenner.

Oxidative stress and pulmonary fibrosis

Oxidative stress is implicated as an important molecular mechanism underlying fibrosis in a variety of organs, including the lungs. However, the causal role of reactive oxygen species (ROS) released from environmental exposures and inflammatory/interstitial cells in mediating fibrosis as well as how best to target an imbalance in ROS production in patients with fibrosis is not firmly established. We focus on the role of ROS in pulmonary fibrosis and, where possible, highlight overlapping molecular pathways in other organs. The key origins of oxidative stress in pulmonary fibrosis (e.g. environmental toxins, mitochondria/NADPH oxidase of inflammatory and lung target cells, and depletion of antioxidant defenses) are reviewed. The role of alveolar epithelial cell (AEC) apoptosis by mitochondria- and p53-regulated death pathways is examined. We emphasize an emerging role for the endoplasmic reticulum (ER) in pulmonary fibrosis. After briefly summarizing how ROS trigger a DNA damage response, we concentrate on recent studies implicating a role for mitochondrial DNA (mtDNA) damage and repair mechanisms focusing on 8-oxoguanine DNA glycosylase (Ogg1) as well as crosstalk between ROS production, mtDNA damage, p53, Ogg1, and mitochondrial aconitase (ACO2). Finally, the association between ROS and TGF-β1-induced fibrosis is discussed. Novel insights into the molecular basis of ROS-induced pulmonary diseases and, in particular, lung epithelial cell death may promote the development of unique therapeutic targets for managing pulmonary fibrosis as well as fibrosis in other organs and tumors, and in aging; diseases for which effective management is lacking. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.