Extracellular cysteine/cystine redox potential controls lung fibroblast proliferation and matrix expression through upregulation of transforming growth factor-beta

Fibroblasts-Warriors at the Intersection of Wound Healing and Disrepair

Wound healing is triggered by inflammation elicited after tissue injury. Mesenchymal cells, specifically fibroblasts, accumulate in the injured tissues, where they engage in tissue repair through the expression and assembly of extracellular matrices that provide a scaffold for cell adhesion, the re-epithelialization of tissues, the production of soluble bioactive mediators that promote cellular recruitment and differentiation, and the regulation of immune responses. If appropriately deployed, these processes promote adaptive repair, resulting in the preservation of the tissue structure and function. Conversely, the dysregulation of these processes leads to maladaptive repair or disrepair, which causes tissue destruction and a loss of organ function. Thus, fibroblasts not only serve as structural cells that maintain tissue integrity, but are key effector cells in the process of wound healing. The review will discuss the general concepts about the origins and heterogeneity of this cell population and highlight the specific fibroblast functions disrupted in human disease. Finally, the review will explore the role of fibroblasts in tissue disrepair, with special attention to the lung, the role of aging, and how alterations in the fibroblast phenotype underpin disorders characterized by pulmonary fibrosis.

Role of pulmonary epithelial arginase-II in activation of fibroblasts and lung inflammaging

Elevated arginases including type-I (Arg-I) and type-II isoenzyme (Arg-II) are reported to play a role in aging, age-associated organ inflammaging, and fibrosis. A role of arginase in pulmonary aging and underlying mechanisms are not explored. Our present study shows increased Arg-II levels in aging lung of female mice, which is detected in bronchial ciliated epithelium, club cells, alveolar type 2 (AT2) pneumocytes, and fibroblasts (but not vascular endothelial and smooth muscle cells). Similar cellular localization of Arg-II is also observed in human lung biopsies. The age-associated increase in lung fibrosis and inflammatory cytokines, including IL-1β and TGF-β1 that are highly expressed in bronchial epithelium, AT2 cells, and fibroblasts, are ameliorated in arg-ii deficient (arg-ii^-/- ) mice. The effects of arg-ii^-/- on lung inflammaging are weaker in male as compared to female animals. Conditioned medium (CM) from human Arg-II-positive bronchial and alveolar epithelial cells, but not that from arg-ii^-/- cells, activates fibroblasts to produce various cytokines including TGF-β1 and collagen, which is abolished by IL-1β receptor antagonist or TGF-β type I receptor blocker. Conversely, TGF-β1 or IL-1β also increases Arg-II expression. In the mouse models, we confirmed the age-associated increase in IL-1β and TGF-β1 in epithelial cells and activation of fibroblasts, which is inhibited in arg-ii^-/- mice. Taken together, our study demonstrates a critical role of epithelial Arg-II in activation of pulmonary fibroblasts via paracrine release of IL-1β and TGF-β1, contributing to pulmonary inflammaging and fibrosis. The results provide a novel mechanistic insight in the role of Arg-II in pulmonary aging.

Cysteine-Mediated Extracellular Electron Transfer of Lysinibacillus varians GY32

Microbial extracellular electron transfer (EET) is essential in many natural and engineering processes. Compared with the versatile EET pathways of Gram-negative bacteria, the EET of Gram-positive bacteria has been studied much less and is mainly limited to the flavin-mediated pathway. Here, we investigate the EET pathway of a Gram-positive filamentous bacterium Lysinibacillus varians GY32. Strain GY32 has a wide electron donor spectrum (including lactate, acetate, formate, and some amino acids) in electrode respiration. Transcriptomic, proteomic, and electrochemical analyses show that the electrode respiration of GY32 mainly depends on electron mediators, and c-type cytochromes may be involved in its respiration. Fluorescent sensor and electrochemical analyses demonstrate that strain GY32 can secrete cysteine and flavins. Cysteine added shortly after inoculation into microbial fuel cells accelerated EET, showing cysteine is a new endogenous electron mediator of Gram-positive bacteria, which provides novel information to understand the EET networks in natural environments. IMPORTANCE Extracellular electron transport (EET) is a key driving force in biogeochemical element cycles and microbial chemical-electrical-optical energy conversion on the Earth. Gram-positive bacteria are ubiquitous and even dominant in EET-enriched environments. However, attention and knowledge of their EET pathways are largely lacking. Gram-positive bacterium Lysinibacillus varians GY32 has extremely long cells (>1 mm) and conductive nanowires, promising a unique and enormous role in the microenvironments where it lives. Its capability to secrete cysteine renders it not only an EET pathway to respire and survive, but also an electrochemical strategy to connect and shape the ambient microbial community at a millimeter scale. Moreover, its incapability of using flavins as an electron mediator suggests that the common electron mediator is species-dependent. Therefore, our results are important to understanding the EET networks in natural and engineering processes.

The profibrotic and senescence phenotype of old lung fibroblasts is reversed or ameliorated by genetic and pharmacological manipulation of Slc7a11 expression

Increased senescence and expression of profibrotic genes in old lung fibroblasts contribute to disrepair responses. We reported that primary lung fibroblasts from old mice have lower expression and activity of the cystine transporter Slc7a11/xCT than cells from young mice, resulting in changes in both the intracellular and extracellular redox environments. This study examines the hypothesis that low Slc7a11 expression in old lung fibroblasts promotes senescence and profibrotic gene expression. The levels of mRNA and protein of Slc7a11, senescence markers, and profibrotic genes were measured in primary fibroblasts from the lungs of old (24 mo) and young (3 mo) mice. In addition, the effects of genetic and pharmacological manipulation of Slc7a11 were investigated. We found that decreased expression of Slc7a11 in old cells was associated with elevated markers of senescence (p21, p16, p53, and β-galactosidase) and increased expression of profibrotic genes (Tgfb1, Smad3, Acta2, Fn1, Col1a1, and Col5a1). Silencing of Slc7a11 in young cells replicated the aging phenotype, whereas overexpression of Slc7a11 in old cells decreased expression of senescence and profibrotic genes. Young cells were induced to express the senescence and profibrotic phenotype by sulfasalazine, a Slc7a11 inhibitor, whereas treatment of old cells with sulforaphane, a Slc7a11 inducer, decreased senescence without affecting profibrotic genes. Like aging cells, idiopathic pulmonary fibrosis fibroblasts show decreased Slc7a11 expression and increased profibrotic markers. In short, old lung fibroblasts manifest a profibrotic and senescence phenotype that is modulated by genetic or pharmacological manipulation of Slc7a11.

Donor factors and risk of primary graft dysfunction and mortality post lung transplantation: A proposed conceptual framework

Lung transplantation remains a therapeutic option in end-stage lung disease. However, despite advances in the field, early allograft function can be compromised by the development of primary graft dysfunction (PGD); this being the leading cause of morbidity and mortality immediately following the lung transplant procedure. Several recipient factors have been associated with increased risk of PGD, but less is known about donor factors. Aging, tobacco, and chronic alcohol use are donor factors implicated, but how these factors promote PGD remains unclear. Herein, we discuss the available clinical data that link these donor factors with outcomes after lung transplantation, and how they might render the recipient susceptible to PGD through a two-hit process.

Sexually dimorphic and brain region-specific transporter adaptations in system xc- null mice

System x_c^- is a heterodimeric amino acid antiporter that, in the central nervous system, is best known for linking the import of L-cystine (CySS) with the export of L-glutamate for the production and maintenance of cellular glutathione (GSH) and extracellular glutamate levels, respectively. Yet, mice that are null for system x_c^- are healthy, fertile, and, morphologically, their brains are grossly normal. This suggests other glutamate and/or cyst(e)ine transport mechanisms may be upregulated in compensation. To test this, we measured the plasma membrane expression of Excitatory Amino Acid Transporters (EAATs) 1-3, the Alanine-Serine-Cysteine-Transporter (ASCT) 1, the sodium-coupled neutral amino acid transporter (SNAT) 3 and the L Amino Acid Transporter (LAT) 2 in striatum, hippocampus and cortex of male and female mice using Western Blot analysis. Present results demonstrate brain region and transporter-specific changes occurs in female system x_c^- null mice with increased expression of EAAT1 and ASCT1 occurring in the striatum and cortex, respectively, and decreased SNAT 3 expression in cortex. In male system x_c^- null brain, only SNAT3 was altered significantly - increasing in the cortex, but decreasing in the striatum. Total levels of GSH and CyS were similar to that found in age and sex-matched littermate control mice, however, reductions in the ratio of reduced to oxidized GSH (GSH/GSSG) - a hallmark of oxidative stress - were found in all three brain regions in female system x_c^- null mice, whereas this occurred exclusively in the striatum of males. Protein levels of Superoxide dismutase (SOD) 1 were reduced, whereas SOD2 was enhanced in the hippocampus of male x_c^- null mice only. Finally, striatal vulnerability to 3-nitropropionic acid (3-NP)-mediated oxidative stress in either sex showed no genotype difference, although 3-NP was more toxic to female mice of either genotype, as evidenced by an increase in moribundity as compared to males.

Redox States of Protein Cysteines in Pathways of Protein Turnover and Cytoskeleton Dynamics Are Changed with Aging and Reversed by Slc7a11 Restoration in Mouse Lung Fibroblasts

Slc7a11 is the key component of system X_c⁻, an antiporter that imports cystine (CySS) and exports glutamate. It plays an important role in cellular defense against oxidative stress because cysteine (Cys), reduced from CySS, is used for and limits the synthesis of glutathione (GSH). We have shown that downregulation of Slc7a11 is responsible for oxidation of extracellular Cys/CySS redox potential in lung fibroblasts from old mice. However, how age-related change of Slc7a11 expression affects the intracellular redox environment of mouse lung fibroblasts remains unexplored. The purpose of this study is to evaluate the effects of aging on the redox states of intracellular proteins and to examine whether Slc7a11 contributes to the age-dependent effects. Iodoacetyl Tandem Mass Tags were used to differentially label reduced and oxidized forms of Cys residues in primary lung fibroblasts from young and old mice, as well as old fibroblasts transfected with Slc7a11. The ratio of oxidized/reduced forms (i.e., redox state) of a Cys residue was determined via multiplexed tandem mass spectrometry. Redox states of 151 proteins were different in old fibroblasts compared to young fibroblasts. Slc7a11 overexpression restored redox states of 104 (69%) of these proteins. Ingenuity Pathway Analysis (IPA) showed that age-dependent Slc7a11-responsive proteins were involved in pathways of protein translation initiation, ubiquitin-proteasome-mediated degradation, and integrin-cytoskeleton-associated signaling. Gene ontology analysis showed cell adhesion, protein translation, and organization of actin cytoskeleton were among the top enriched terms for biological process. Protein-protein interaction network demonstrated the interactions between components of the three enriched pathways predicted by IPA. Follow-up experiments confirmed that proteasome activity was lower in old cells than in young cells and that upregulation of Slc7a11 expression by sulforaphane restored this activity. This study finds that aging results in changes of redox states of proteins involved in protein turnover and cytoskeleton dynamics, and that upregulating Slc7a11 can partially restore the redox states of these proteins.

Impact of sex, age and diet on the cysteine/cystine and glutathione/glutathione disulfide plasma redox couples in mice

Age, sex and diet are well-established risk factors for several diseases. In humans, each of these variables has been linked to differences in plasma redox potentials (E_h) of the glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) redox couples. Mice have been very useful for modeling human disease processes, but it is unknown if age, sex and diet affect redox couples in mice as they do in humans. The purpose of the present study was to examine the effects of these factors on plasma redox potentials in C57BL/6J mice. We found that age had no effect on either redox couple in either sex. Plasma E_h Cys/CySS and E_h GSH/GSSG were both more oxidized (more positive) in females than in males. A 24-hour fast negated the sex differences in both redox potentials by oxidizing both redox couples in male mice, while having no effect on E_h Cys/CySS and a smaller effect on E_h GSH/GSSG in female mice. A diet with excess sulfur amino acids reduced the plasma E_h Cys/CySS in females to a level comparable to that seen in male mice. Thus, sex-specific differences in plasma E_h Cys/CySS could be normalized by two different dietary interventions. Some of these findings are consistent with reported human studies, while others are not. Most strikingly, mice do not exhibit age-dependent oxidation of plasma redox potentials. Care must be taken when designing and interpreting mouse studies to investigate redox regulation in humans.

Synthesis of Potent Cytotoxic Epidithiodiketopiperazines Designed for Derivatization

We describe our design, synthesis, and chemical study of a set of functional epidithiodiketopiperazines (ETPs) and evaluation of their activity against five human cancer cell lines. Our structure-activity relationship-guided substitution of ETP alkaloids offers versatile derivatization while maintaining potent anticancer activity, offering exciting opportunity for their use as there are no examples of complex and potently anticancer (nM) ETPs being directly used as conjugatable probes or warheads. Our synthetic solutions to strategically designed ETPs with functional linkers required advances in stereoselective late-stage oxidation and thiolation chemistry in complex settings, including the application of novel reagents for dihydroxylation and cis-sulfidation of diketopiperazines. We demonstrate that complex ETPs equipped with a strategically substituted azide functional group are readily derivatized to the corresponding ETP-triazoles without compromising anticancer activity. Our chemical stability studies of ETPs along with cytotoxic evaluation of our designed ETPs against A549, DU 145, HeLa, HCT 116, and MCF7 human cancer cell lines provide insights into the impact of structural features on potency and chemical stability, informing future utility of ETPs in chemical and biological studies.

S-protected thiolated hyaluronic acid: In-situ crosslinking hydrogels for 3D cell culture scaffold

The purpose of this study was to synthesize S-protected thiolated hyaluronic acid (HA) and to evaluate its potential for 3D cell culture scaffold. S-protected thiolated HA was synthesized by the covalent attachment of N-acetyl-S-((3-((2,5-dioxopyrrolidin-1-yl)oxy)-3-oxopropyl)thio)cysteine hydrazide ligand to the HA. Hydrogels were characterized for texture, swelling behavior and rheological properties. Furthermore, the potential of S-protected thiolated HA hydrogels as a scaffold for tissue engineering was evaluated by cell proliferation studies with Caco-2 and NIH 3T3 cells. It showed enhanced cohesion upon addition of N-acetyl cysteine (NAC). Dynamic viscosity of S-protected thiolated HA hydrogel was increased up to 19.5-fold by addition of NAC and 10.1-fold after mixing with mucus. Furthermore, Caco-2 and NIH 3T3 cells encapsulated into hydrogels proliferated in-vitro. As this novel S-protected thiolated HA is stable towards oxidation and forms highly cohesive gels when getting into contact with endogenous thiols due to disulfide-crosslinking, it is a promising tool for 3D cell culture scaffold.

An engineered enzyme that targets circulating lactate to alleviate intracellular NADH:NAD+ imbalance

An elevated intracellular NADH:NAD+ ratio, or 'reductive stress', has been associated with multiple diseases, including disorders of the mitochondrial electron transport chain. As the intracellular NADH:NAD+ ratio can be in near equilibrium with the circulating lactate:pyruvate ratio, we hypothesized that reductive stress could be alleviated by oxidizing extracellular lactate to pyruvate. We engineered LOXCAT, a fusion of bacterial lactate oxidase (LOX) and catalase (CAT), which irreversibly converts lactate and oxygen to pyruvate and water. Addition of purified LOXCAT to the medium of cultured human cells with a defective electron transport chain decreased the extracellular lactate:pyruvate ratio, normalized the intracellular NADH:NAD+ ratio, upregulated glycolytic ATP production and restored cellular proliferation. In mice, tail-vein-injected LOXCAT lowered the circulating lactate:pyruvate ratio, blunted a metformin-induced rise in blood lactate:pyruvate ratio and improved NADH:NAD+ balance in the heart and brain. Our study lays the groundwork for a class of injectable therapeutic enzymes that alleviates intracellular redox imbalances by directly targeting circulating redox-coupled metabolites.

Plasma cysteine/cystine and glutathione/glutathione disulfide redox potentials in HIV and COPD patients

Chronic obstructive pulmonary disease (COPD) is prevalent in patients infected with HIV. The purpose of this study was to test the hypothesis that systemic oxidation correlates with loss of lung function in subjects with COPD, and that HIV infection can contribute to creating such an environment. Subjects were recruited at the University of Louisville in the following groups: HIV-infected (n = 36), COPD (n = 32), HIV and COPD (n = 28), and uninfected controls with normal lung function (n = 34). HIV infection was assessed by viral load and CD4 cell counts. Pulmonary function was determined by spirometry, and plasma was collected for measurement of cysteine (Cys), cystine (CySS), glutathione (GSH) and GSH disulfide (GSSG) by HPLC followed by estimation of redox potentials (E_h) using the Nernst equation. Results showed that patients with COPD had more oxidized plasma E_h Cys/CySS than patients with normal lung function, but plasma E_h GSH/GSSG was unaltered. In addition, there was a correlation between the extent of plasma E_h Cys/CySS oxidation and loss of lung function, and this correlation remained even after correcting for age, sex, race and body mass index. HIV infection per se was not associated with increased oxidation of plasma E_h Cys/CySS, but plasma E_h Cys/CySS was more oxidized in patients with lower CD4-positve T cell counts. In patients with both HIV infection and COPD, there was a significant correlation between CD4 cell counts and lung function. Thus, systemic oxidation correlated with decreased lung function in subjects with COPD and decreased CD4 counts in subjects infected with HIV. Thus, factors contributing to plasma E_h Cys/CySS may represent novel mechanisms underlying the increased prevalence of COPD in people living with HIV.

Proteogenomic landscape of squamous cell lung cancer

How genomic and transcriptomic alterations affect the functional proteome in lung cancer is not fully understood. Here, we integrate DNA copy number, somatic mutations, RNA-sequencing, and expression proteomics in a cohort of 108 squamous cell lung cancer (SCC) patients. We identify three proteomic subtypes, two of which (Inflamed, Redox) comprise 87% of tumors. The Inflamed subtype is enriched with neutrophils, B-cells, and monocytes and expresses more PD-1. Redox tumours are enriched for oxidation-reduction and glutathione pathways and harbor more NFE2L2/KEAP1 alterations and copy gain in the 3q2 locus. Proteomic subtypes are not associated with patient survival. However, B-cell-rich tertiary lymph node structures, more common in Inflamed, are associated with better survival. We identify metabolic vulnerabilities (TP63, PSAT1, and TFRC) in Redox. Our work provides a powerful resource for lung SCC biology and suggests therapeutic opportunities based on redox metabolism and immune cell infiltrates.

Squamous cell lung cancer has dismal prognosis due to the dearth of effective treatments. Here, the authors perform an integrated proteogenomic analysis of the disease, revealing three proteomics-based subtypes and suggesting potential therapeutic opportunities.

The Aging Lung and Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is one of many clinical syndromes that are associated with aging, and is increasing in both incidence and prevalence with the rapid rise in aging populations world-wide. There is accumulating data on how the biology of aging may influence the susceptibility to lung fibrosis in the elderly. In this review, we explore some of the known "hallmarks of aging," including telomere attrition, genomic instability, epigenetic alterations, loss of proteostasis, cellular senescence and mitochondrial dysfunction in the pathobiology of IPF. Additionally, we discuss age-associated alterations in extracellular matrix that may contribute to the development and/or progression of IPF.

Beneficial effects of ascorbic acid to treat lung fibrosis induced by paraquat

Paraquat (PQ) is one of the most widely employed herbicides that is used worldwide and it causes severe toxic effects in humans and animals. A PQ exposition can lead to pulmonary fibrosis (PF) and the mechanisms seem to be linked to oxidative stress, although other pathways have been suggested. Antioxidants can be useful as a therapy, although interventions with this kind of system are still controversial. Hence, this study has investigated the role of ascorbic acid (vitamin C) post-treatment on PQ-induced PF in male C57/BL6 mice. Pulmonary fibrosis was induced by a single PQ injection (10mg/kg; i.p.). The control group received a PQ vehicle. Seven days after the PQ or vehicle injections, the mice received vitamin C (150 mg/kg, ip, once a day) or the vehicle, over the following 7 days. Twenty-four hours after the last dose of vitamin C or the vehicle, the mice were euthanized and their bronchoalveolar lavage fluid (BALF) and their lungs were collected. The data obtained showed that vitamin C reduced the cellular recruitment, the secretion of IL-17 –a cytokine involved in neutrophils migration, TGF-β–a pro-fibrotic mediator and the collagen deposition. Moreover, vitamin C elevated the superoxide dismutase (SOD) and catalase levels, both antioxidant enzymes, but it did not alter the tracheal contractile response that was evoked by methacholine. Therefore, the researchers have highlighted the mechanisms of vitamin C as being non-invasive and have suggested it as a promising tool to treat lung fibrosis when it is induced by a PQ intoxication.

Clair WH, St. Clair DK. Redox Paradox: A Novel Approach to Therapeutics-Resistant Cancer

SIGNIFICANCE

Cancer cells that are resistant to radiation and chemotherapy are a major problem limiting the success of cancer therapy. Aggressive cancer cells depend on elevated intracellular levels of reactive oxygen species (ROS) to proliferate, self-renew, and metastasize. As a result, these aggressive cancers maintain high basal levels of ROS compared with normal cells. The prominence of the redox state in cancer cells led us to consider whether increasing the redox state to the condition of oxidative stress could be used as a successful adjuvant therapy for aggressive cancers. Recent Advances: Past attempts using antioxidant compounds to inhibit ROS levels in cancers as redox-based therapy have met with very limited success. However, recent clinical trials using pro-oxidant compounds reveal noteworthy results, which could have a significant impact on the development of strategies for redox-based therapies.

CRITICAL ISSUES

The major objective of this review is to discuss the role of the redox state in aggressive cancers and how to utilize the shift in redox state to improve cancer therapy. We also discuss the paradox of redox state parameters; that is, hydrogen peroxide (H2O2) as the driver molecule for cancer progression as well as a target for cancer treatment.

FUTURE DIRECTIONS

Based on the biological significance of the redox state, we postulate that this system could potentially be used to create a new avenue for targeted therapy, including the potential to incorporate personalized redox therapy for cancer treatment.

Implications of plasma thiol redox in disease

Thiol groups are crucially involved in signaling/homeostasis through oxidation, reduction, and disulphide exchange. The overall thiol pool is the resultant of several individual pools of small compounds (e.g. cysteine), peptides (e.g. glutathione), and thiol proteins (e.g. thioredoxin (Trx)), which are not in equilibrium and present specific oxidized/reduced ratios. This review addresses mechanisms and implications of circulating plasma thiol/disulphide redox pools, which are involved in several physiologic processes and explored as disease biomarkers. Thiol pools are regulated by mechanisms linked to their intrinsic reactivity against oxidants, concentration of antioxidants, thiol-disulphide exchange rates, and their dynamic release/removal from plasma. Major thiol couples determining plasma redox potential (Eh) are reduced cysteine (CyS)/cystine (the disulphide form of cysteine) (CySS), followed by GSH/disulphide-oxidized glutathione (GSSG). Hydrogen peroxide and hypohalous acids are the main plasma oxidants, while water-soluble and lipid-soluble small molecules are the main antioxidants. The thiol proteome and thiol-oxidoreductases are emerging investigative areas given their specific disease-related responses (e.g. protein disulphide isomerases (PDIs) in thrombosis). Plasma cysteine and glutathione redox couples exhibit pro-oxidant changes directly correlated with ageing/age-related diseases. We further discuss changes in thiol-disulphide redox state in specific groups of diseases: cardiovascular, cancer, and neurodegenerative. These results indicate association with the disease states, although not yet clear-cut to yield specific biomarkers. We also highlight mechanisms whereby thiol pools affect atherosclerosis pathophysiology. Overall, it is unlikely that a single measurement provides global assessment of plasma oxidative stress. Rather, assessment of individual thiol pools and thiol-proteins specific to any given condition has more solid and logical perspective to yield novel relevant information on disease risk and prognosis.

Age-dependent oxidation of extracellular cysteine/cystine redox state (Eh(Cys/CySS)) in mouse lung fibroblasts is mediated by a decline in Slc7a11 expression

Aging is associated with progressive oxidation of the extracellular environment. The redox state of human plasma, defined by the concentrations of cysteine (Cys) and cystine (CySS), becomes more oxidized as we age. Recently, we showed that fibroblasts isolated from the lungs of young and old mice retain this differential phenotype; old cells produce and maintain a more oxidizing extracellular redox potential (E_h(Cys/CySS)) than young cells. Microarray analysis identified down-regulation of Slc7a11, the light subunit of the CySS/glutamate transporter, as a potential mediator of age-related oxidation in these cells. The purpose of the present study was to investigate the mechanistic link between Slc7a11 expression and extracellular E_h(Cys/CySS). Sulforaphane treatment or overexpression of Slc7a11 was used to increase Slc7a11 in lung fibroblasts from old mice, and sulfasalazine treatment or siRNA-mediated knock down was used to decrease Slc7a11 in young fibroblasts. Slc7a11 mRNA levels were measured by real-time PCR, Slc7a11 activity was determined by measuring the rate of glutamate release, Cys, CySS, glutathione (GSH) and its disulfide (GSSG) were measured by HPLC, and E_h(Cys/CySS) was calculated from the Nernst equation. The results showed that both E_h(Cys/CySS) and E_h(GSH/GSSG) were more oxidized in the conditioned media of old cells than in young cells. Up-regulation of Slc7a11 via overexpression or sulforaphane treatment restored extracellular E_h(Cys/CySS) in cultures of old cells, whereas down-regulation reproduced the oxidizing E_h(Cys/CySS) in young cells. Only sulforaphane treatment was able to increase total GSH and restore E_h(GSH/GSSG), whereas overexpression, knock down and sulfasalazine had no effect on these parameters. In addition, inhibition of GSH synthesis with buthionine sulfoximine had no effect on the ability of cells to restore their extracellular redox potential in response to an oxidative challenge. In conclusion, our study reveals Slc7a11 is the key regulator of age-dependent changes in extracellular E_h(Cys/CySS) in primary mouse lung fibroblasts, and its effects are not dependent on GSH synthesis.

Redox theory of aging: implications for health and disease

Genetics ultimately defines an individual, yet the phenotype of an adult is extensively determined by the sequence of lifelong exposures, termed the exposome. The redox theory of aging recognizes that animals evolved within an oxygen-rich environment, which created a critical redox interface between an organism and its environment. Advances in redox biology show that redox elements are present throughout metabolic and structural systems and operate as functional networks to support the genome in adaptation to environmental resources and challenges during lifespan. These principles emphasize that physical and functional phenotypes of an adult are determined by gene-environment interactions from early life onward. The principles highlight the critical nature of cumulative exposure memories in defining changes in resilience progressively during life. Both plasma glutathione and cysteine systems become oxidized with aging, and the recent finding that cystine to glutathione ratio in human plasma predicts death in coronary artery disease (CAD) patients suggests this could provide a way to measure resilience of redox networks in aging and disease. The emerging concepts of cumulative gene-environment interactions warrant focused efforts to elucidate central mechanisms by which exposure memory governs health and etiology, onset and progression of disease.

Cadmium stimulates myofibroblast differentiation and mouse lung fibrosis

Increasing evidence suggests that Cd at levels found in the human diet can cause oxidative stress and activate redox-sensitive transcription factors in inflammatory signaling. Following inflammation, tissue repair often involves activation of redox-sensitive transcription factors in fibroblasts. In lungs, epithelial barrier remodeling is required to restore gas exchange and barrier function, and aberrant myofibroblast differentiation leads to pulmonary fibrosis. Contributions of exogenous exposures, such as dietary Cd, to pulmonary fibrosis remain incompletely defined. In the current study, we tested whether Cd activates fibrotic signaling in human fetal lung fibroblasts (HFLF) at micromolar and submicromolar Cd concentrations that do not cause cell death. Exposure of HFLF to low-dose Cd (≤1.0μM) caused an increase in stress fibers and increased protein levels of myofibroblast differentiation markers, including α-smooth muscle actin (α-SMA) and extra-domain-A-containing fibronectin (ED-A-FN). Assay of transcription factor (TF) activity using a 45-TF array showed that Cd increased activity of 12 TF, including SMAD2/3/4 (mothers against decapentaplegic homolog) signaling differentiation and fibrosis. Results were confirmed by real-time PCR and supported by increased expression of target genes of SMAD2/3/4. Immunocytochemistry of lungs of mice exposed to low-dose Cd (0.3 and 1.0mg/L in drinking water) showed increased α-SMA protein level with lung Cd accumulation similar to lung Cd in non-smoking humans. Together, the results show that relatively low Cd exposures stimulate pulmonary fibrotic signaling and myofibroblast differentiation by activating SMAD2/3/4-dependent signaling. The results indicate that dietary Cd intake could be an important variable contributing to pulmonary fibrosis in humans.

Autophagy and mitochondrial dysfunction in adjuvant-arthritis rats treatment with resveratrol

Resveratrol is a polyphenol derivatives which exhibits a pro-apoptotic effect in a variety of human cancers by triggering mitochondria apoptosis pathway and autophagy. However, there are scarcely reports on its apoptosis-promoting effect in abnormal proliferation fibroblast-like synoviocytes (FLSs). In this study, we investigated the underlying mechanism and apoptosis-inducing effects of resveratrol on the abnormal proliferation of FLSs in adjuvant-arthritis (AA) rats. Since using resveratrol for 12 days resulted in a significant decreasing the swelling degree of the paw, reducing malondialdehyde (MDA) content and enhancing superoxide dismutase (SOD) activity, antioxidant capacity, glutathione peroxidase and glutathione reductase ratio in AA rats. Moreover, we found that 5 μMH₂O₂ could increase cells viability, Beclin1, LC3A/B, MnSOD, SIRT3 protein expression in FLSs. But, resveratrol could reverse these effects by changing mitochondrial membrane potential (Δψm) to promote mitochondrial reactive oxygen species (mtROS) generation in 5 μMH₂O₂-treatment FLSs. These results suggest that oxidative stress existed in AA rats. Resveratrol could suppress oxidative stress in AA rats and increase mtROS production by reducing autophagy protein Beclin1, LC3A/B and oxidative stress protein MnSOD to promoted the apoptosis of FLSs. Thus, targeting of mtROS may be a crucial mechanism of resveratrol confers patients with rheumatoid arthritis.

Differential Regulation of the Extracellular Cysteine/Cystine Redox State (EhCySS) by Lung Fibroblasts from Young and Old Mice

Aging is associated with progressive oxidation of plasma cysteine (Cys)/cystine (CySS) redox state, expressed as E_hCySS. Cultured cells condition their media to reproduce physiological E_hCySS, but it is unknown whether aged cells produce a more oxidized extracellular environment reflective of that seen in vivo. In the current study, we isolated primary lung fibroblasts from young and old female mice and measured the media E_hCySS before and after challenge with Cys or CySS. We also measured expression of genes related to redox regulation and fibroblast function. These studies revealed that old fibroblasts produced a more oxidizing extracellular E_hCySS than young fibroblasts and that old fibroblasts had a decreased capacity to recover from an oxidative challenge due to a slower rate of reduction of CySS to Cys. These defects were associated with 10-fold lower expression of the Slc7a11 subunit of the xCT cystine-glutamate transporter. Extracellular superoxide dismutase (Sod3) was the only antioxidant or thiol-disulfide regulating enzyme among 36 examined that was downregulated in old fibroblasts by more than 2-fold, but there were numerous changes in extracellular matrix components. Thus, aging fibroblasts not only contribute to remodeling of the extracellular matrix but also have a profound effect on the extracellular redox environment.

Thiol-Disulfide Exchange Reactions in the Mammalian Extracellular Environment

Disulfide bonds represent versatile posttranslational modifications whose roles encompass the structure, catalysis, and regulation of protein function. Due to the oxidizing nature of the extracellular environment, disulfide bonds found in secreted proteins were once believed to be inert. This notion has been challenged by the discovery of redox-sensitive disulfides that, once cleaved, can lead to changes in protein activity. These functional disulfides are twisted into unique configurations, leading to high strain and potential energy. In some cases, cleavage of these disulfides can lead to a gain of function in protein activity. Thus, these motifs can be referred to as switches. We describe the couples that control redox in the extracellular environment, examine several examples of proteins with switchable disulfides, and discuss the potential applications of disulfides in molecular biology.

Lung extracellular matrix and redox regulation

Pulmonary fibrosis affects millions worldwide and, even though there has been a significant investment in understanding the processes involved in wound healing and maladaptive repair, a complete understanding of the mechanisms responsible for lung fibrogenesis eludes us, and interventions capable of reversing or halting disease progression are not available. Pulmonary fibrosis is characterized by the excessive expression and uncontrolled deposition of extracellular matrix (ECM) proteins resulting in erosion of the tissue structure. Initially considered an 'end-stage' process elicited after injury, these events are now considered pathogenic and are believed to contribute to the course of the disease. By interacting with integrins capable of signal transduction and by influencing tissue mechanics, ECM proteins modulate processes ranging from cell adhesion and migration to differentiation and growth factor expression. In doing so, ECM proteins help orchestrate complex developmental processes and maintain tissue homeostasis. However, poorly controlled deposition of ECM proteins promotes inflammation, fibroproliferation, and aberrant differentiation of cells, and has been implicated in the pathogenesis of pulmonary fibrosis, atherosclerosis and cancer. Considering their vital functions, ECM proteins are the target of investigation, and oxidation-reduction (redox) reactions have emerged as important regulators of the ECM. Oxidative stress invariably accompanies lung disease and promotes ECM expression directly or through the overproduction of pro-fibrotic growth factors, while affecting integrin binding and activation. In vitro and in vivo investigations point to redox reactions as targets for intervention in pulmonary fibrosis and related disorders, but studies in humans have been disappointing probably due to the narrow impact of the interventions tested, and our poor understanding of the factors that regulate these complex reactions. This review is not meant to provide a comprehensive review of this field, but rather to highlight what has been learned and to raise interest in this area in need of much attention.

Potential Role of the Gut/Liver/Lung Axis in Alcohol-Induced Tissue Pathology

Both Alcoholic Liver Disease (ALD) and alcohol-related susceptibility to acute lung injury are estimated to account for the highest morbidity and mortality related to chronic alcohol abuse and, thus, represent a focus of intense investigation. In general, alcohol-induced derangements to both organs are considered to be independent and are often evaluated separately. However, the liver and lung share many general responses to damage, and specific responses to alcohol exposure. For example, both organs possess resident macrophages that play key roles in mediating the immune/inflammatory response. Additionally, alcohol-induced damage to both organs appears to involve oxidative stress that favors tissue injury. Another mechanism that appears to be shared between the organs is that inflammatory injury to both organs is enhanced by alcohol exposure. Lastly, altered extracellular matrix (ECM) deposition appears to be a key step in disease progression in both organs. Indeed, recent studies suggest that early subtle changes in the ECM may predispose the target organ to an inflammatory insult. The purpose of this chapter is to review the parallel mechanisms of liver and lung injury in response to alcohol consumption. This chapter will also explore the potential that these mechanisms are interdependent, as part of a gut-liver-lung axis.

Cystic fibrosis-related oxidative stress and intestinal lipid disorders

SIGNIFICANCE

Cystic fibrosis (CF) is the most common lethal genetic disorder in the Caucasian people. It is due to the mutation of cystic fibrosis transmembrane conductance regulator (CFTR) gene located on the long arm of the chromosome 7, which encodes for CFTR protein. The latter, an adenosine triphosphate binding cassette, is a transmembrane chloride channel that is also involved in glutathione transport. As glutathione/glutathione disulfide constitutes the most important pool of cellular redox systems, CFTR defects could thus disrupt the intracellular redox balance. Resulting multisystemic diseases are essentially characterized by a chronic respiratory failure, a pancreatic insufficiency, an essential fatty acid deficiency (EFAD), and inadequate levels of antioxidant vitamins.

RECENT ADVANCES

The pathophysiology of CF is complex; however, several mechanisms are proposed, including oxidative stress (OxS) whose implication is recognized and has been clearly demonstrated in CF airways.

CRITICAL ISSUES

Little is known about OxS intrinsic triggers and its own involvement in intestinal lipid disorders. Despite the regular administration of pancreatic supplements, high-fat high-calorie diets, and antioxidant fat-soluble vitamins, there is a persistence of steatorrhea, EFAD, and harmful OxS. Intriguingly, several trials with elevated doses of antioxidant vitamins have not yielded significant improvements.

FUTURE DIRECTIONS

The main sources and self-maintenance of OxS in CF should be clarified to improve treatment of patients. Therefore, this review will discuss the potential sources and study the mechanisms of OxS in the intestine, known to develop various complications, and its involvement in intestinal lipid disorders in CF patients.

Reactive oxygen species and redox compartmentalization

Reactive oxygen species (ROS) formation and signaling are of major importance and regulate a number of processes in physiological conditions. A disruption in redox status regulation, however, has been associated with numerous pathological conditions. In recent years it has become increasingly clear that oxidative and reductive modifications are confined in a spatio-temporal manner. This makes ROS signaling similar to that of Ca(2+) or other second messengers. Some subcellular compartments are more oxidizing (such as lysosomes or peroxisomes) whereas others are more reducing (mitochondria, nuclei). Moreover, although more reducing, mitochondria are especially susceptible to oxidation, most likely due to the high number of exposed thiols present in that compartment. Recent advances in the development of redox probes allow specific measurement of defined ROS in different cellular compartments in intact living cells or organisms. The availability of these tools now allows simultaneous spatio-temporal measurements and correlation between ROS generation and organelle and/or cellular function. The study of ROS compartmentalization and microdomains will help elucidate their role in physiology and disease. Here we will examine redox probes currently available and how ROS generation may vary between subcellular compartments. Furthermore, we will discuss ROS compartmentalization in physiological and pathological conditions focusing our attention on mitochondria, since their vulnerability to oxidative stress is likely at the basis of several diseases.

Thrombin promotes proliferation of human lung fibroblasts via protease activated receptor-1-dependent and NF-κB-independent pathways

Acute and chronic respiratory diseases are associated with abnormal coagulation regulation and fibrolysis. However, the detailed mechanism by which coagulation regulation and fibrolysis affect the occurrence and development of lung diseases remain to be elucidated. Protease activated receptor-1 (PAR-1), a major high-affinity thrombin receptor, and nuclear factor kappa B (NF-κB), a transcription factor, are involved in cell survival, differentiation, and proliferation. We have investigated the potential mechanism of thrombin-induced fibroblast proliferation and roles of PAR-1 and NF-κB signalling in this process. The effect of thrombin on proliferation of human pulmonary fibroblasts (HPF) was assessed by 5-bromo-2-deoxyuridine (BrdU) incorporation assay. The expression of PAR1 and NF-κB subunit p65 protein was detected by Western blot. Nuclear translocation of p65 was examined by laser scanning confocal microscopy. We show that thrombin significantly increased proliferation of HPF as determined by induction of BrdU-positive incorporation ratio. Induced PAR1 protein expression was also seen in HPF cells treated with thrombin. However, thrombin had no significant effect on expression and translocation of NF-κB p65 in HPF cells. The results indicate that, by increasing protein expression and interacting with PAR1, thrombin promotes HPF proliferation. NF-κB signalling appears to play no role in this process.

Suppression of nuclear factor erythroid 2-related factor 2 via extracellular signal-regulated kinase contributes to bleomycin-induced oxidative stress and fibrogenesis

Pulmonary fibrosis is a serious and irreversible lung injury with obscure etiologic mechanisms and no effective treatment to date. This study explored a crucial link between oxidative stress and pulmonary fibrogenesis, focusing on nuclear factor erythroid 2-related factor 2 (Nrf2), a core transcription factor in antioxidative regulation systems. Treatment of C57 BL/6 mice with bleomycin increased fibroblast viability and collagen production and significantly downregulated Nrf2. In addition, prominent oxidative stress was indicated by changes in superoxide dismutase, catalase activity, and glutathione and thiobarbituric acid-reactive substance levels. In a cell-based model, bleomycin suppressed Nrf2 activation via extracellular signal-related kinase phosphorylation, enhancing intracellular reactive oxygen species in lung fibroblasts and stimulating abnormal cell proliferation and collagen secretion. To confirm this novel mechanism of bleomycin-induced fibrogenesis, we attempted to upregulate Nrf2 and related antioxidant proteins in bleomycin-treated fibroblasts using a putative Nrf2 activator, caffeic acid phenethyl ester, and the results showed that bleomycin-induced fibroblast proliferation and collagen content were attenuated through improved redox balance. Collectively, these results disclose a potential regulatory mechanism in pulmonary fibrosis that will aid the development of new therapies.

Nicotinic acetylcholine receptors are sensors for ethanol in lung fibroblasts

BACKGROUND

Chronic ethanol (EtOH) abuse in humans is known to independently increase the incidence of and mortality due to acute lung injury in at-risk individuals. However, the mechanisms by which EtOH affects lung cells remain incompletely elucidated. In earlier work, we reported that EtOH increased the expression in lung fibroblasts of fibronectin, a matrix glycoprotein implicated in lung injury and repair. This effect was blocked by α-bungarotoxin, a neurotoxin that binds certain nicotinic acetylcholine receptors (nAChRs) thereby implicating nAChRs in this process. Here, we examine the identity of these receptors.

METHODS

Mouse lung fibroblasts were stimulated with EtOH (60 mM) or acetylcholine (100 to 500 μM) and evaluated for the expression of fibronectin and nAChRs. Inhibitors to nAChRs or the antioxidant N-acetyl cysteine (NAC) were used to assess changes in fibronectin expression. Animals exposed to EtOH for up to 6 weeks were used to evaluate the expression of nAChRs in vivo.

RESULTS

First, in EtOH-treated fibroblasts, we observed increased expression of α4 and α9 nAChR subunits. Second, we found that acetylcholine, a natural ligand for nAChRs, mimicked the effects of EtOH. Dihydro-β-erythroidin hydrobromide, a competitive inhibitor of α4 nAChR, blocked the increase in fibronectin expression and cell proliferation. Furthermore, EtOH-induced fibronectin expression was inhibited in cells silenced for α4 nAChR. However, EtOH-treated cells showed increased α-bungarotoxin binding suggesting that α4 nAChR mediates the effects of EtOH via a ligand-independent pathway. Knowing there are several important cysteine residues near the ligand-binding site of α4 nAChRs, we tested the antioxidant NAC and found that it too blocked the induction of fibronectin expression by EtOH. Also, fibroblasts exposed to oxidant stress showed increased fibronectin expression that was blocked with α-bungarotoxin. Finally, we showed increased expression of α4 nAChRs in the lung tissue of mice and rats exposed to EtOH suggesting a role for these receptors in vivo.

CONCLUSIONS

Altogether, our observations suggest that α4 nAChRs serve as sensors for EtOH-induced oxidant stress in lung fibroblasts, thereby revealing a new mechanism by which EtOH may affect lung cells and tissue remodeling and pointing to nAChRs as potential targets for intervention.

Molecular and cellular mechanisms of pulmonary fibrosis

Pulmonary fibrosis is a chronic lung disease characterized by excessive accumulation of extracellular matrix (ECM) and remodeling of the lung architecture. Idiopathic pulmonary fibrosis is considered the most common and severe form of the disease, with a median survival of approximately three years and no proven effective therapy. Despite the fact that effective treatments are absent and the precise mechanisms that drive fibrosis in most patients remain incompletely understood, an extensive body of scientific literature regarding pulmonary fibrosis has accumulated over the past 35 years. In this review, we discuss three broad areas which have been explored that may be responsible for the combination of altered lung fibroblasts, loss of alveolar epithelial cells, and excessive accumulation of ECM: inflammation and immune mechanisms, oxidative stress and oxidative signaling, and procoagulant mechanisms. We discuss each of these processes separately to facilitate clarity, but certainly significant interplay will occur amongst these pathways in patients with this disease.

Glutathione redox control of asthma: from molecular mechanisms to therapeutic opportunities

Asthma is a chronic inflammatory disorder of the airways associated with airway hyper-responsiveness and airflow limitation in response to specific triggers. Whereas inflammation is important for tissue regeneration and wound healing, the profound and sustained inflammatory response associated with asthma may result in airway remodeling that involves smooth muscle hypertrophy, epithelial goblet-cell hyperplasia, and permanent deposition of airway extracellular matrix proteins. Although the specific mechanisms responsible for asthma are still being unraveled, free radicals such as reactive oxygen species and reactive nitrogen species are important mediators of airway tissue damage that are increased in subjects with asthma. There is also a growing body of literature implicating disturbances in oxidation/reduction (redox) reactions and impaired antioxidant defenses as a risk factor for asthma development and asthma severity. Ultimately, these redox-related perturbations result in a vicious cycle of airway inflammation and injury that is not always amenable to current asthma therapy, particularly in cases of severe asthma. This review will discuss disruptions of redox signaling and control in asthma with a focus on the thiol, glutathione, and reduced (thiol) form (GSH). First, GSH synthesis, GSH distribution, and GSH function and homeostasis are discussed. We then review the literature related to GSH redox balance in health and asthma, with an emphasis on human studies. Finally, therapeutic opportunities to restore the GSH redox balance in subjects with asthma are discussed.

Targeting TGFβ superfamily ligand accessory proteins as novel therapeutics for chronic lung disorders

Dysregulation of the transforming growth factor β (TGFβ) pathway has been implicated to underlie a number of disease indications including chronic lung disorders such as asthma, chronic obstructive pulmonary disease (COPD), interstitial pneumonias, and pulmonary arterial hypertension (PAH). Consequently, the pharmaceutical industry has devoted significant resources in the pursuit of TGFβ pathway inhibitors that target the cognate type I and II receptors and respective ligands. The progress of these approaches has been painfully slow, due in part to dose-limiting safety issues that result from the antagonism of a pathway that is responsible for regulating many fundamental biological processes including immune surveillance and cardiovascular responses. These disappointments have led many in the field to conclude that modulating the TGFβ pathway for chronic indications with a sufficient safety window using conventional approaches may be extremely difficult to achieve. Here we review the rationale and limitations of the use of TGFβ pathway inhibitors in chronic lung disorders and the possibility of targeting TGFβ superfamily ligand accessory proteins to allow rheostatic regulation of signaling to achieve efficacy while maintaining a sufficient therapeutic index.

Regulation of prostate cancer cell invasion by modulation of extra- and intracellular redox balance

Recent metabolic profiles of human prostate cancer tissues showed a significant increase in cysteine (Cys) and a significant decrease in reduced glutathione (GSH) during cancer progression from low- to high-grade Gleason scores. Cys is primarily localized extracellularly, whereas GSH is present mostly inside the cell. We hypothesized that extra- or intracellular redox state alterations differentially regulate cell invasion in PC3 prostate carcinoma cells versus PrEC normal prostate epithelial cells. Cells were exposed to media with calculated Cys/CySS redox potentials (E(h)CySS) ranging from -60 to -180mV. After 3h exposure to a reducing extracellular redox state (E(h)CySS=-180mV), matrix metalloprotease (MMP), gelatinase, and NADPH oxidase activities increased, correlating with increases in cell invasion, cell migration, and extracellular hydrogen peroxide levels in PC3 cells but not PrECs. Knockdown of NADPH oxidase or MMP with silencing RNAs during cultivation with E(h)CySS=-180mV medium significantly decreased PC3 cell invasion. Modulation of extra- and intracellular redox states by exposure of PC3 cells to Cys/CySS-free medium (approx E(h)CySS=-87mV) containing 500μMN-acetylcysteine resulted in a more reducing intracellular redox state and a significant decrease in cell invasive ability. The decrease in PC3 cell invasion induced by these conditions correlated with a decrease in MMP activity. Our studies demonstrated that an extracellular redox state that was more reducing than a physiologic microenvironment redox state increased PC3 cancer cell invasive ability, whereas an intracellular redox environmental that was more reducing than an intracellular physiologic redox state inhibited PC3 cell invasive ability.

Thiols stabilize cobblestone morphology of cultured mesothelial cells

Cellular thiols including GSH (glutathione) and L-Cys (L-cysteine) are essential for cell signalling, growth and differentiation. L-Cys is derived from the extracellular thiol pool and is the rate-limiting compound for intracellular GSH biosynthesis. The present study investigated the effect of thiol-supplemented medium on cell growth, phenotype and total GSH of cultured hPMCs (human peritoneal mesothelial cells). Cells were cultured in medium M199 supplemented with 2% serum, with 'plus' or without 'minus' L-Cys and compared with medium supplemented with either β-ME (β-mercaptoethanol) (0.25 mmol/l) or the receptor tyrosine kinase ligand EGF (epidermal growth factor, 100 ng/ml). β-ME produced a disproportionate increase in total GSH compared with L-Cys and other thiols tested [(procysteine (2-oxothiazolidine-4-carboxylic acid) or NAC (N-acetyl-L-cysteine)], while growth and morphology were identical. Cell behaviour of primary hPMCs is characterized by the transition of fibroblastoid to cobblestone morphology during early passage. L-Cys and β-ME promoted a rapid MET (mesenchymal-to-epithelial transition) within 3 days of culture, confirmed by the presence of cobblestone cells, intact organelles, abundant microvilli, primary cilia and cortical actin. In contrast, EGF produced a biphasic response consisting of delayed growth and retention of a fibroblastoid morphology. During a rapid log phase of growth, MET was accompanied by rapid catch-up growth. Thiols may stabilize the epithelial phenotype by engaging redox-sensitive receptors and transcription factors that modulate differentiation. These data may benefit researchers working on thiol-mediated cell differentiation and strategies to regenerate damage to serosal membranes.

Redox-proteomics of the effects of homogentisic acid in an in vitro human serum model of alkaptonuric ochronosis

Alkaptonuria (AKU) is a rare inborn error of metabolism associated with a deficient activity of homogentisate 1,2-dioxygenase (HGO), an enzyme involved in tyrosine and phenylalanine metabolism. Such a deficiency leads to the accumulation of homogentisic acid (HGA) and its oxidized/polymerized products in connective tissues, where melanin-like pigments accumulate (ochronosis). Ochronosis involves especially joints, where an ochronotic arthropathy develops. Little is known on the molecular mechanisms leading to ochronosis and ochronotic arthropathy in AKU. Previous works of ours showed that HGA in vitro propagates oxidative stress through its conversion into benzoquinone acetate (BQA). We hence used an in vitro model consisting of human serum treated with HGA and evaluated the activities of glutathione related anti-oxidant enzymes and levels of compounds indexes of oxidative stress. Proteomics and redox-proteomics were used to identify oxidized proteins and proteins more likely able to bind BQA. Overall, we found that the production of ochronotic pigment in HGA-treated serum is accompanied by lipid peroxidation, decreased activity of the enzyme glutathione peroxidase and massive depletion of thiol groups, together with increased protein carbonylation and thiol oxidation. We also found that BQA was likely to bind carrier proteins and naturally abundant serum proteins, eventually altering their chemico-physical properties. Concluding, our work points towards a critical importance of thiol compounds in counteracting HGA- and BQA- mediated stress in AKU, so that future research for disease biomarkers and pharmacological treatments for AKU and ochronosis will be more easily addressed.

Extracellular cysteine (Cys)/cystine (CySS) redox regulates metabotropic glutamate receptor 5 activity

Extracellular cysteine (Cys)/cystine (CySS) redox potential (E(h)) has been shown to regulate diverse biological processes, including enzyme catalysis, gene expression, and signaling pathways for cell proliferation and apoptosis, and is sensitive to aging, smoking, and other host factors. However, the effects of extracellular Cys/CySS redox on the nervous system remain unknown. In this study, we explored the role of extracellular Cys/CySS E(h) in metabotropic glutamate receptor 5 (mGlu5) activation to understand the mechanism of its regulation of nerve cell growth and activation. We showed that the oxidized Cys/CySS redox state (0 mV) in C6 glial cells induced a significant increase in mGlu5-mediated phosphorylation of extracellular signal-regulated kinase (ERK), blocked by an inhibitor of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (MEK), U0126, a nonpermeant alkylating agent, 4-acetamide-4'-maleimidylstilbene-2,2'-disulfonic acid (AMS), and a specific mGlu5 antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), respectively. ERK phosphorylation under oxidized extracellular Cys/CySS E(h) was confirmed in mGlu5-overexpressed human embryonic kidney 293 (HEK293) cells. Oxidized extracellular Cys/CySS E(h) also stimulated the generation of intracellular reactive oxygen species (ROS) involved in the phosphorylation of ERK by mGlu5. Moreover, activation of mGlu5 by oxidized extracellular Cys/CySS E(h) was found to affect expression of NF-κB and inducible nitric oxide synthase (iNOS). The results also showed that extracellular Cys/CySS E(h) involved in the activation of mGlu5 controlled cell death and cell activation in neurotoxicity. In addition, plasma Cys/CySS E(h) was found to be associated with the process of Parkinson's disease (PD) in a rotenone-induced rat model of PD together with dietary deficiency and supplementation of sulfur amino acid (SAA). The effects of extracellular Cys/CySS E(h) on SAA dietary deficiency in the rotenone-induced rat model of PD was almost blocked by MPEP pretreatment, further indicating that oxidized extracellular Cys/CySS E(h) plays a role in mGlu5 activity. Taken together, the results indicate that mGlu5 can be activated by extracellular Cys/CySS redox in nerve cells, which possibly contributes to the process of PD. These in vitro and in vivo findings may aid in the development of potential new nutritional strategies that could assist in slowing the degeneration of PD.

Angiotensin II increases periostin expression via Ras/p38 MAPK/CREB and ERK1/2/TGF-β1 pathways in cardiac fibroblasts

AIMS

Angiotensin II (AngII) is involved in extracellular matrix (ECM) accumulation contributing to heart failure. Periostin, a 90 kDa ECM protein, is a key regulator of cardiac fibrosis, and its expression is significantly higher in failing hearts. We determined the modulatory effect of AngII on periostin level and explored the possible signal transduction mechanism.

METHODS AND RESULTS

AngII (400 ng/kg/min) or normal saline was infused subcutaneously for 28 days into rats; AngII antagonism was with losartan (10 mg/kg/day orally). AngII infusion induced cardiac fibrosis and increased periostin expression, which was attenuated by losartan. In cultured adult rat cardiac fibroblasts, AngII promoted the mRNA and protein expression of periostin. AngII provoked activation of cAMP response element-binding protein (CREB), and CREB small interfering RNA (siRNA) suppressed AngII-induced periostin expression. Inhibition of p38 mitogen-activated protein kinase (p38 MAPK) with SB202190 attenuated AngII-induced CREB activation and periostin expression. Transfection with Ras guanyl-releasing protein 1 siRNA or RasN17 dominant-negative plasmid prevented AngII-induced p38 MAPK phosphorylation and periostin expression. Transforming growth factor (TGF)-β1 antibody decreased the stimulatory effect of AngII on periostin expression. The extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor PD98059 attenuated AngII-induced TGF-β1 expression, Smad2/3 nuclear accumulation, and periostin expression.

CONCLUSION

The activation of the Ras/p38 MAPK/CREB pathway is required for AngII-induced periostin expression. ERK1/2 also participates in AngII-induced periostin expression by regulating TGF-β1/Smad signalling.

Cysteine/cystine redox signaling in cardiovascular disease

Extracellular thiol/disulfide redox environments are highly regulated in healthy individuals. The major thiol/disulfide redox couple in human plasma is cysteine (Cys) and its disulfide form, cystine (CySS). Oxidation of this redox couple, measured as a more positive steady-state redox potential (E(h)), is associated with risk factors for cardiovascular disease (CVD), including aging, smoking, obesity, and alcohol abuse. Rodent and vascular cell studies show that the extracellular redox state of Cys/CySS (E(h)CySS) can play a vital role in controlling CVD through proinflammatory signaling. This inflammatory signaling is regulated by cell-surface protein redox state and involves mitochondrial oxidation, nuclear factor-κB activation, and elevated expression of genes for monocyte recruitment to endothelial cells. Gene array and proteomics studies reveal the global nature of redox effects, and different cell types, e.g., endothelial cells, monocytes, fibroblasts, and epithelial cells, show cell-specific redox responses with different phenotypic traits, e.g., proliferation and apoptosis, which can contribute to CVD. The critical nature of the proinflammatory redox signaling and cell biology associated with E(h)CySS supports the use of plasma levels of Cys, CySS, and E(h)CySS as key indicators of vascular health. Plasma redox-state-based pharmacologic interventions to control or improve E(h)CySS may be effective in preventing CVD onset or progression.

Redox sensing: orthogonal control in cell cycle and apoptosis signalling

Living systems have three major types of cell signalling systems that are dependent upon high-energy chemicals, redox environment and transmembranal ion-gating mechanisms. Development of integrated systems biology descriptions of cell signalling require conceptual models incorporating all three. Recent advances in redox biology show that thiol-disulphide redox systems are regulated under dynamic, nonequilibrium conditions, progressively oxidized with the life cycle of cells and distinct in terms of redox potentials amongst subcellular compartments. This article uses these observations as a basis to distinguish 'redox-sensing' mechanisms, which are more global biologic redox control mechanisms, from 'redox signalling', which involves conveyance of discrete activating or inactivating signals. Both redox sensing and redox signalling use sulphur switches, especially cysteine (Cys) residues in proteins which are sensitive to reversible oxidation, nitrosylation, glutathionylation, acylation, sulfhydration or metal binding. Unlike specific signalling mechanisms, the redox-sensing mechanisms provide means to globally affect the rates and activities of the high-energy, ion-gating and redox-signalling systems by controlling sensitivity, distribution, macromolecular interactions and mobility of signalling proteins. Effects mediated through Cys residues not directly involved in signalling means redox-sensing control can be orthogonal to the signalling mechanisms. This provides a capability to integrate signals according to cell cycle and physiologic state without fundamentally altering the signalling mechanisms. Recent findings that thiol-disulphide pools in humans are oxidized with age, environmental exposures and disease risk suggest that redox-sensing thiols could provide a central mechanistic link in disease development and progression.

Redox compartmentalization and cellular stress

Mammalian cells are highly organized to optimize function. For instance, oxidative energy-producing processes in mitochondria are sequestered away from plasma membrane redox signalling complexes and also from nuclear DNA, which is subject to oxidant-induced mutation. Proteins are unique among macromolecules in having reversible oxidizable elements, 'sulphur switches', which support dynamic regulation of structure and function. Accumulating evidence shows that redox signalling and control systems are maintained under kinetically limited steady states, which are highly displaced from redox equilibrium and distinct among organelles. Mitochondria are most reducing and susceptible to oxidation under stressed conditions, while nuclei are also reducing but relatively resistant to oxidation. Within compartments, the glutathione and thioredoxin systems serve parallel and non-redundant functions to maintain the dynamic redox balance of subsets of protein cysteines, which function in redox signalling and control. This organization allows cells to be poised to respond to cell stress but also creates sites of vulnerability. Importantly, disruption of redox organization is a common basis for disease. Research tools are becoming available to elucidate details of subcellular redox organization, and this development highlights an opportunity for a new generation of targeted antioxidants to enhance and restore redox signalling and control in disease prevention.

An oxidized extracellular oxidation-reduction state increases Nox1 expression and proliferation in vascular smooth muscle cells via epidermal growth factor receptor activation

OBJECTIVE

To examine the effect of an oxidized extracellular oxidation-reduction (redox) state (E(h)) on the expression of NADPH oxidases in vascular cells.

METHODS AND RESULTS

The generation of reactive oxygen species by NADPH oxidase (Nox)-based NADPH oxidases activates redox-dependent signaling pathways and contributes to the development of "oxidative stress" in vascular disease. An oxidized plasma redox state is associated with cardiovascular disease in humans; however, the cellular mechanisms by which the extracellular redox state may cause disease are not known. Aortic segments and cultured aortic smooth muscle cells were exposed to E(h) between -150 mV (reduced) and 0 mV (oxidized) by altering the concentration of cysteine and its disulfide, cystine, the predominant redox couple in plasma. A more oxidized E(h) increased the expression of Nox1 and resulted in Nox1-dependent proliferation of smooth muscle cells. Oxidized E(h) rapidly induced epidermal growth factor receptor phosphorylation via shedding of epidermal growth factor-like ligands from the plasma membrane and caused extracellular signal-regulated kinase 1/2-dependent phosphorylation of the transcription factors activating transcription factor-1 and cAMP-response element-binding protein. Inhibition of epidermal growth factor receptor or extracellular signal-regulated kinase 1/2 activation, or addition of small interference RNA to activating transcription factor-1, prevented the increase in Nox1 expression.

CONCLUSIONS

Our results identify a novel mechanism by which extracellular oxidative stress increases expression and activity of Nox1 NADPH oxidase and contributes to vascular disease.

Redox metabolism and malignancy

Redox balance underlies cellular homeostasis. Cancer initiation and progression has been linked to the disruption of redox balance and oxidative stress. Recent findings exemplify the distinctive roles of intracellular and extracellular redox state in the etiology and maintenance of oxidative stress associated with malignancy and metastasis. Within these compartments, redox sensitive cysteines play a crucial role in regulating cell signaling events that act to promote the malignant phenotype via the activation of survival pathways, disruption of cell-death signaling, and increases in cell proliferation. New approaches that aim to accurately evaluate subcellular and microenvironment redox potential may be useful in developing cancer diagnostics and therapeutics.

Redox clamp model for study of extracellular thiols and disulfides in redox signaling

Extracellular thiol/disulfide redox environments are highly regulated in healthy individuals and become oxidized in disease. This oxidation affects the function of cell surface receptors, ion channels, and structural proteins. Downstream signaling due to changes in extracellular redox potential can be studied using a redox clamp in which thiol and disulfide concentrations are varied to obtain a series of controlled redox potentials. Previous applications of this approach show that cell proliferation, apoptosis, and proinflammatory signaling respond to extracellular redox potential. Furthermore, gene expression and proteomic studies reveal the global nature of redox effects, and different cell types, for example, endothelial cells, fibroblasts, monocytes, and epithelial cells, show cell-specific redox responses. Application of the redox clamp to studies of different signaling pathways could enhance the understanding of redox transitions in many aspects of normal physiology and disease.

Oxidation of plasma cysteine/cystine and GSH/GSSG redox potentials by acetaminophen and sulfur amino acid insufficiency in humans

Variations in plasma sulfur amino acid (SAA) pools are associated with disease risks, but little information is available about the factors affecting plasma SAA pools. Drug metabolism by glutathione (GSH) and sulfate conjugation can, in principle, represent a quantitatively important burden on SAA supply. The present study was designed to determine whether therapeutic doses of acetaminophen (APAP) alter SAA metabolism in healthy human adults. A double-blind, crossover design incorporating four treatment periods with diets providing 100% of the recommended dietary allowance (RDA) for SAA without or with APAP (15 mg/kg) and 0% RDA for SAA without or with APAP, in randomized order. After a 3-day equilibration period, chemically defined diets with 100 or 0% RDA for SAA were given for 2 complete days. On day 3, APAP or placebo was given in two successive doses (6-h interval), and timed plasma samples were collected. With SAA intake at 100% RDA, APAP administration oxidized the plasma cysteine/cystine redox potential (E(h)CySS) but not the plasma GSH/GSSG redox potential (E(h)GSSG). The extent of oxidation caused by APAP was similar to that seen with 0% SAA and no APAP. However, APAP administration with 0% SAA did not cause further oxidation beyond APAP or 0% SAA alone. In contrast, an oxidation of the plasma E(h)GSSG was apparent for SAA insufficiency only with APAP. The results suggest a need to evaluate possible effects of APAP in association with SAA insufficiency as a contributing factor in disease risk.

Inhibition of apoptotic signalling in spermine-treated vascular smooth muscle cells by a novel glutathione precursor

CKD (chronic kidney disease) is a public health problem, mediated by haemodynamic and non-haemodynamic events including oxidative stress. We investigated the effect of two GSH (glutathione) precursors, NAC (N-acetylcysteine) and cystine as the physiological carrier of cysteine in GSH with added selenomethionine (F1) in preventing spermine (uraemic toxin)-induced apoptosis in cultured human aortic VSMC (vascular smooth muscle cells). VSMCs exposed to spermine (15 microM) with or without antioxidants (doses 50, 100, 200 and 500 microg/ml) were assessed for apoptosis, JNK (c-Jun-NH2-terminal kinase) activation and iNOS (inducible nitric oxide synthase) induction and activation of intrinsic pathway signalling. Spermine exposure resulted in activation of JNK and iNOS induction and apoptosis. NAC and F1 (dose range 50-500 microg/ml) attenuated spermine-induced acceleration of VSMC apoptosis but only F1 (at 200 and 500 microg/ml) maintained spermine-induced apoptosis at control levels. Spermine-induced JNK activation was prevented by 200 microg/ml of both NAC and F1, while iNOS induction was blocked only by F1. Notably, the adverse effects of spermine on BAX/BCL-2 ratio, cytochrome c release and caspase activation was fully attenuated by F1. In conclusion, F1 was more effective than NAC in preventing spermine-induced apoptosis and downstream changes in related signal transduction pathways in VSMCs. Further studies are needed to examine the effect of these compounds in preventing CKD-associated vascular disease.

Postprandial cysteine/cystine redox potential in human plasma varies with meal content of sulfur amino acids

Few data are available on plasma redox responses to sulfur amino acid (SAA) loads. In this study, we had 2 aims: to determine whether the SAA content of a meal affected postprandial plasma cysteine (Cys), cystine (CySS), or redox potential (E(h)CySS) in humans and whether SAA intake level (adequate or inadequate) in the days preceding the meal challenge affected these postprandial levels. Eight healthy individuals aged 18-36 y were equilibrated for 3 d to adequate SAA, fed chemically defined meals without SAA for 5 d (inadequate SAA) and then fed isoenergetic, isonitrogenous meals with adequate SAA for 5 d. On the first and last days with the chemically defined meals, a morning meal containing 60% of the daily food intake was given, and plasma Cys, CySS, and E(h)CySS were determined over an 8-h postprandial time course. Following equilibration to adequate intake, provision of the meal with SAA resulted in increased plasma Cys and CySS concentrations and more reduced plasma E(h)CySS compared with the postprandial values following the same meal without SAA. Equilibration to inadequate SAA intake for the days preceding the meal challenge did not affect this response. The magnitude of the difference in postprandial plasma E(h)CySS (10 mV) due to meal content of SAA was comparable to those which alter physiologic signaling and/or are associated with disease risk. Consequently, the SAA content of meals could affect physiologic signaling and associated disease mechanisms in the postprandial period by changes in Cys, CySS, or E(h)CySS.

Mitochondrial energetics and therapeutics

Mitochondrial dysfunction has been linked to a wide range of degenerative and metabolic diseases, cancer, and aging. All these clinical manifestations arise from the central role of bioenergetics in cell biology. Although genetic therapies are maturing as the rules of bioenergetic genetics are clarified, metabolic therapies have been ineffectual. This failure results from our limited appreciation of the role of bioenergetics as the interface between the environment and the cell. A systems approach, which, ironically, was first successfully applied over 80 years ago with the introduction of the ketogenic diet, is required. Analysis of the many ways that a shift from carbohydrate glycolytic metabolism to fatty acid and ketone oxidative metabolism may modulate metabolism, signal transduction pathways, and the epigenome gives us an appreciation of the ketogenic diet and the potential for bioenergetic therapeutics.