Glutathionylation chemistry promotes interleukin-1 beta-mediated glycolytic reprogramming and pro-inflammatory signaling in lung epithelial cells.

Glycolysis is a well-known process by which metabolically active cells, such as tumor or immune cells meet their high metabolic demands. Previously, our laboratory has demonstrated that in airway epithelial cells, the pleiotropic cytokine, interleukin-1 beta (IL1B) induces glycolysis and that this contributes to allergic airway inflammation and remodeling. Activation of glycolysis is known to increase NADPH reducing equivalents generated from the pentose phosphate pathway, linking metabolic reprogramming with redox homeostasis. In addition, numerous glycolytic enzymes are known to be redox regulated. However, whether and how redox chemistry regulates metabolic reprogramming more generally remains unclear. In this study, we employed a multi-omics approach in primary mouse airway basal cells to evaluate the role of protein redox biochemistry, specifically protein glutathionylation, in mediating metabolic reprogramming. Our findings demonstrate that IL1B induces glutathionylation of multiple proteins involved in metabolic regulation, notably in the glycolysis pathway. Cells lacking Glutaredoxin-1 (Glrx), the enzyme responsible for reversing glutathionylation, show modulation of multiple metabolic pathways including an enhanced IL1B-induced glycolytic response. This was accompanied by increased secretion of thymic stromal lymphopoietin (TSLP), a cytokine important in asthma pathogenesis. Targeted inhibition of glycolysis prevented TSLP release, confirming the functional relevance of enhanced glycolysis in cells stimulated with IL1B. Collectively, data herein point to an intriguing link between glutathionylation chemistry and glycolytic reprogramming in epithelial cells and suggest that glutathionylation chemistry may represent a therapeutic target in pulmonary pathologies with perturbations in the glycolysis pathway.

Pyruvate Kinase M2 Promotes Expression of Proinflammatory Mediators in House Dust Mite-Induced Allergic Airways Disease.

Asthma is a chronic disorder characterized by inflammation, mucus metaplasia, airway remodeling, and hyperresponsiveness. We recently showed that IL-1-induced glycolytic reprogramming contributes to allergic airway disease using a murine house dust mite model. Moreover, levels of pyruvate kinase M2 (PKM2) were increased in this model as well as in nasal epithelial cells from asthmatics as compared with healthy controls. Although the tetramer form of PKM2 converts phosphoenolpyruvate to pyruvate, the dimeric form of PKM2 has alternative, nonglycolysis functions as a transcriptional coactivator to enhance the transcription of several proinflammatory cytokines. In the current study, we examined the impact of PKM2 on the pathogenesis of house dust mite-induced allergic airways disease in C57BL/6NJ mice. We report, in this study, that activation of PKM2, using the small molecule activator, TEPP46, augmented PKM activity in lung tissues and attenuated airway eosinophils, mucus metaplasia, and subepithelial collagen. TEPP46 attenuated IL-1ß-mediated airway inflammation and expression of proinflammatory mediators. Exposure to TEPP46 strongly decreased the IL-1ß-mediated increases in thymic stromal lymphopoietin (TSLP) and GM-CSF in primary tracheal epithelial cells isolated from C57BL/6NJ mice. We also demonstrate that IL-1ß-mediated increases in nuclear phospho-STAT3 were decreased by TEPP46. Finally, STAT3 inhibition attenuated the IL-1ß-induced release of TSLP and GM-CSF, suggesting that the ability of PKM2 to phosphorylate STAT3 contributes to its proinflammatory function. Collectively, these results demonstrate that the glycolysis-inactive form of PKM2 plays a crucial role in the pathogenesis of allergic airways disease by increasing IL-1ß-induced proinflammatory signaling, in part, through phosphorylation of STAT3.

Dysregulation of Pyruvate Kinase M2 Promotes Inflammation in a Mouse Model of Obese Allergic Asthma.

Obesity is a risk factor for the development of asthma and represents a difficult-to-treat disease phenotype. Aerobic glycolysis is emerging as a key feature of asthma, and changes in glucose metabolism are linked to leukocyte activation and adaptation to oxidative stress. Dysregulation of PKM2 (pyruvate kinase M2), the enzyme that catalyzes the last step of glycolysis, contributes to house dust mite (HDM)-induced airway inflammation and remodeling in lean mice. It remains unclear whether glycolytic reprogramming and dysregulation of PKM2 also contribute to obese asthma. The goal of the present study was to elucidate the functional role of PKM2 in a murine model of obese allergic asthma. We evaluated the small molecule activator of PKM2, TEPP46, and assessed the role of PKM2 using conditional ablation of the Pkm2 allele from airway epithelial cells. In obese C57BL/6NJ mice, parameters indicative of glycolytic reprogramming remained unchanged in the absence of stimulation with HDM. Obese mice that were subjected to HDM showed evidence of glycolytic reprogramming, and treatment with TEPP46 diminished airway inflammation, whereas parameters of airway remodeling were unaffected. Epithelial ablation of Pkm2 decreased central airway resistance in both lean and obese allergic mice in addition to decreasing inflammatory cytokines in the lung tissue. Lastly, we highlight a novel role for PKM2 in the regulation of glutathione-dependent protein oxidation in the lung tissue of obese allergic mice via a putative IFN-γ-glutaredoxin1 pathway. Overall, targeting metabolism and protein oxidation may be a novel treatment strategy for obese allergic asthma.

Dysregulation of the glutaredoxin/S-glutathionylation redox axis in lung diseases.

Glutathione is a major redox buffer, reaching millimolar concentrations within cells and high micromolar concentrations in airways. While glutathione has been traditionally known as an antioxidant defense mechanism that protects the lung tissue from oxidative stress, glutathione more recently has become recognized for its ability to become covalently conjugated to reactive cysteines within proteins, a modification known as S-glutathionylation (or S-glutathiolation or protein mixed disulfide). S-glutathionylation has the potential to change the structure and function of the target protein, owing to its size (the addition of three amino acids) and charge (glutamic acid). S-glutathionylation also protects proteins from irreversible oxidation, allowing them to be enzymatically regenerated. Numerous enzymes have been identified to catalyze the glutathionylation/deglutathionylation reactions, including glutathione S-transferases and glutaredoxins. Although protein S-glutathionylation has been implicated in numerous biological processes, S-glutathionylated proteomes have largely remained unknown. In this paper, we focus on the pathways that regulate GSH homeostasis, S-glutathionylated proteins, and glutaredoxins, and we review methods required toward identification of glutathionylated proteomes. Finally, we present the latest findings on the role of glutathionylation/glutaredoxins in various lung diseases: idiopathic pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease.

IL-1/inhibitory κB kinase ε-induced glycolysis augment epithelial effector function and promote allergic airways disease.

BACKGROUND: Emerging studies suggest that enhanced glycolysis accompanies inflammatory responses. Virtually nothing is known about the relevance of glycolysis in patients with allergic asthma. OBJECTIVES: We sought to determine whether glycolysis is altered in patients with allergic asthma and to address its importance in the pathogenesis of allergic asthma. METHODS: We examined alterations in glycolysis in sputum samples from asthmatic patients and primary human nasal cells and used murine models of allergic asthma, as well as primary mouse tracheal epithelial cells, to evaluate the relevance of glycolysis. RESULTS: In a murine model of allergic asthma, glycolysis was induced in the lungs in an IL-1-dependent manner. Furthermore, administration of IL-1ß into the airways stimulated lactate production and expression of glycolytic enzymes, with notable expression of lactate dehydrogenase A occurring in the airway epithelium. Indeed, exposure of mouse tracheal epithelial cells to IL-1ß or IL-1α resulted in increased glycolytic flux, glucose use, expression of glycolysis genes, and lactate production. Enhanced glycolysis was required for IL-1ß- or IL-1α-mediated proinflammatory responses and the stimulatory effects of IL-1ß on house dust mite (HDM)-induced release of thymic stromal lymphopoietin and GM-CSF from tracheal epithelial cells. Inhibitor of κB kinase ε was downstream of HDM or IL-1ß and required for HDM-induced glycolysis and pathogenesis of allergic airways disease. Small interfering RNA ablation of lactate dehydrogenase A attenuated HDM-induced increases in lactate levels and attenuated HDM-induced disease. Primary nasal epithelial cells from asthmatic patients intrinsically produced more lactate compared with cells from healthy subjects. Lactate content was significantly higher in sputum supernatants from asthmatic patients, notably those with greater than 61% neutrophils. A positive correlation was observed between sputum lactate and IL-1ß levels, and lactate content correlated negatively with lung function. CONCLUSIONS: Collectively, these findings demonstrate that IL-1ß/inhibitory κB kinase ε signaling plays an important role in HDM-induced glycolysis and pathogenesis of allergic airways disease.

The stress protein heat shock cognate 70 (Hsc70) inhibits the Transient Receptor Potential Vanilloid type 1 (TRPV1) channel.

BACKGROUND: Specialized cellular defense mechanisms prevent damage from chemical, biological, and physical hazards. The heat shock proteins have been recognized as key chaperones that maintain cell survival against a variety of exogenous and endogenous stress signals including noxious temperature. However, the role of heat shock proteins in nociception remains poorly understood. We carried out an expression analysis of the constitutively expressed 70 kDa heat-shock cognate protein, a member of the stress-induced HSP70 family in lumbar dorsal root ganglia from a mouse model of Complete Freund's Adjuvant-induced chronic inflammatory pain. We used immunolabeling of dorsal root ganglion neurons, behavioral analysis and patch clamp electrophysiology in both dorsal root ganglion neurons and HEK cells transfected with Hsc70 and Transient Receptor Potential Channels to examine their functional interaction in heat shock stress condition. RESULTS: We report an increase in protein levels of Hsc70 in mouse dorsal root ganglia, 3 days post Complete Freund's Adjuvant injection in the hind paw. Immunostaining of Hsc70 was observed in most of the dorsal root ganglion neurons, including the small size nociceptors immunoreactive to the TRPV1 channel. Standard whole-cell patch-clamp technique was used to record Transient Receptor Potential Vanilloid type 1 current after exposure to heat shock. We found that capsaicin-evoked currents are inhibited by heat shock in dorsal root ganglion neurons and transfected HEK cells expressing Hsc70 and TRPV1. Blocking Hsc70 with matrine or spergualin compounds prevented heat shock-induced inhibition of the channel. We also found that, in contrast to TRPV1, both the cold sensor channels TRPA1 and TRPM8 were unresponsive to heat shock stress. Finally, we show that inhibition of TRPV1 depends on the ATPase activity of Hsc70 and involves the rho-associated protein kinase. CONCLUSIONS: Our work identified Hsc70 and its ATPase activity as a central cofactor of TRPV1 channel function and points to the role of this stress protein in pain associated with neurodegenerative and/or metabolic disorders, including aging.

Targeting the transient receptor potential vanilloid type 1 (TRPV1) assembly domain attenuates inflammation-induced hypersensitivity.

The transient receptor potential channel vanilloid type 1 (TRPV1) is a non-selective cation channel expressed in sensory neurons of the dorsal root and trigeminal ganglia. TRPV1 is a polymodal channel activated by noxious heat, capsaicin, and protons. As a sensor for noxious stimuli, TRPV1 channel has been described as a key contributor to pain signaling. To form a functional channel, TRPV1 subunits must assemble into tetramers, and several studies have identified the TRPV1 C terminus as an essential element in subunit association. Here we combined biochemical assays with electrophysiology and imaging-based bimolecular fluorescence complementation (BiFC) and bioluminescence resonance energy transfer (BRET) in live cells to identify a short motif in the C-terminal tail of the TRPV1 subunit that governs channel assembly. Removing this region through early truncation or targeted deletion results in loss of subunit association and channel function. Importantly, we found that interfering with TRPV1 subunit association using a plasma membrane-tethered peptide attenuated mechanical and thermal hypersensitivity in two mouse models of inflammatory hyperalgesia. This represents a novel mechanism to disrupt TRPV1 subunit assembly and hence may offer a new analgesic tool for pain relief.

The glutathione S-transferase Gstt1 drives survival and dissemination in metastases.

Identifying the adaptive mechanisms of metastatic cancer cells remains an elusive question in the treatment of metastatic disease, particularly in pancreatic cancer (pancreatic adenocarcinoma, PDA). A loss-of-function shRNA targeted screen in metastatic-derived cells identified Gstt1, a member of the glutathione S-transferase superfamily, as uniquely required for dissemination and metastasis, but dispensable for primary tumour growth. Gstt1 is expressed in latent disseminated tumour cells (DTCs), is retained within a subpopulation of slow-cycling cells within existing metastases, and its inhibition leads to complete regression of macrometastatic tumours. This distinct Gstt1high population is highly metastatic and retains slow-cycling phenotypes, epithelial-mesenchymal transition features and DTC characteristics compared to the Gstt1low population. Mechanistic studies indicate that in this subset of cancer cells, Gstt1 maintains metastases by binding and glutathione-modifying intracellular fibronectin, in turn promoting its secretion and deposition into the metastatic microenvironment. We identified Gstt1 as a mediator of metastasis, highlighting the importance of heterogeneity and its influence on the metastatic tumour microenvironment.

Glutaredoxin attenuates glutathione levels via deglutathionylation of Otub1 and subsequent destabilization of system xC.

Glutathione (GSH) is a critical component of the cellular redox system that combats oxidative stress. The glutamate-cystine antiporter, system xC-, is a key player in GSH synthesis that allows for the uptake of cystine, the rate-limiting building block of GSH. It is unclear whether GSH or GSH-dependent protein oxidation [protein S-glutathionylation (PSSG)] regulates the activity of system xC-. We demonstrate that an environment of enhanced PSSG promotes GSH increases via a system xC--dependent mechanism. Absence of the deglutathionylase, glutaredoxin (GLRX), augmented SLC7A11 protein and led to significant increases of GSH content. S-glutathionylation of C23 or C204 of the deubiquitinase OTUB1 promoted interaction with the E2-conjugating enzyme UBCH5A, leading to diminished ubiquitination and proteasomal degradation of SLC7A11 and augmentation of GSH, effects that were reversed by GLRX. These findings demonstrate an intricate link between GLRX and GSH via S-glutathionylation of OTUB1 and system xC- and illuminate a previously unknown feed-forward regulatory mechanism whereby enhanced GSH protein oxidation augments cellular GSH.

S-Glutathionylation-Controlled Apoptosis of Lung Epithelial Cells; Potential Implications for Lung Fibrosis.

Glutathione (GSH), a major antioxidant in mammalian cells, regulates several vital cellular processes, such as nutrient metabolism, protein synthesis, and immune responses. In addition to its role in antioxidant defense, GSH controls biological processes through its conjugation to reactive protein cysteines in a post-translational modification known as protein S-glutathionylation (PSSG). PSSG has recently been implicated in the pathogenesis of multiple diseases including idiopathic pulmonary fibrosis (IPF). Hallmarks of IPF include repeated injury to the alveolar epithelium with aberrant tissue repair, epithelial cell apoptosis and fibroblast resistance to apoptosis, and the accumulation of extracellular matrix and distortion of normal lung architecture. Several studies have linked oxidative stress and PSSG to the development and progression of IPF. Additionally, it has been suggested that the loss of epithelial cell homeostasis and increased apoptosis, accompanied by the release of various metabolites, creates a vicious cycle that aggravates disease progression. In this short review, we highlight some recent studies that link PSSG to epithelial cell apoptosis and highlight the potential implication of metabolites secreted by apoptotic cells.

Glutathione-S-transferase P promotes glycolysis in asthma in association with oxidation of pyruvate kinase M2.

BACKGROUND: Interleukin-1-dependent increases in glycolysis promote allergic airways disease in mice and disruption of pyruvate kinase M2 (PKM2) activity is critical herein. Glutathione-S-transferase P (GSTP) has been implicated in asthma pathogenesis and regulates the oxidation state of proteins via S-glutathionylation. We addressed whether GSTP-dependent S-glutathionylation promotes allergic airways disease by promoting glycolytic reprogramming and whether it involves the disruption of PKM2. METHODS: We used house dust mite (HDM) or interleukin-1ß in C57BL6/NJ WT or mice that lack GSTP. Airway basal cells were stimulated with interleukin-1ß and the selective GSTP inhibitor, TLK199. GSTP and PKM2 were evaluated in sputum samples of asthmatics and healthy controls and incorporated analysis of the U-BIOPRED severe asthma cohort database. RESULTS: Ablation of Gstp decreased total S-glutathionylation and attenuated HDM-induced allergic airways disease and interleukin-1ß-mediated inflammation. Gstp deletion or inhibition by TLK199 decreased the interleukin-1ß-stimulated secretion of pro-inflammatory mediators and lactate by epithelial cells. 13C-glucose metabolomics showed decreased glycolysis flux at the pyruvate kinase step in response to TLK199. GSTP and PKM2 levels were increased in BAL of HDM-exposed mice as well as in sputum of asthmatics compared to controls. Sputum proteomics and transcriptomics revealed strong correlations between GSTP, PKM2, and the glycolysis pathway in asthma. CONCLUSIONS: GSTP contributes to the pathogenesis of allergic airways disease in association with enhanced glycolysis and oxidative disruption of PKM2. Our findings also suggest a PKM2-GSTP-glycolysis signature in asthma that is associated with severe disease.

Glutaredoxin deficiency promotes activation of the transforming growth factor beta pathway in airway epithelial cells, in association with fibrotic airway remodeling.

S-glutathionylation of reactive protein cysteines is a post-translational event that plays a critical role in transducing signals from oxidants into biological responses. S-glutathionylation can be reversed by the deglutathionylating enzyme glutaredoxin (GLRX). We have previously demonstrated that ablation of Glrx sensitizes mice to the development of parenchymal lung fibrosis(1). It remains unclear whether GLRX also controls airway fibrosis, a clinical feature relevant to asthma and chronic obstructive pulmonary disease, and whether GLRX controls the biology of airway epithelial cells, which have been implicated in the pathophysiology of these diseases. In the present study we utilized a house dust mite (HDM) model of allergic airway disease in wild type (WT) and Glrx-/- mice on a C57BL/6 background prone to develop airway fibrosis, and tracheal basal stem cells derived from WT mice, global Glrx-/- mice, or bi-transgenic mice allowing conditional ablation of the Glrx gene. Herein we show that absence of Glrx led to enhanced HDM-induced collagen deposition, elevated levels of transforming growth factor beta 1 (TGFB1) in the bronchoalveolar lavage, and resulted in increases in airway hyperresponsiveness. Airway epithelial cells isolated from Glrx-/- mice or following conditional ablation of Glrx showed spontaneous increases in secretion of TGFB1. Glrx-/- basal cells also showed spontaneous TGFB pathway activation, in association with increased expression of mesenchymal genes, including collagen 1a1 and fibronectin. Overall, these findings suggest that GLRX regulates airway fibrosis via a mechanism(s) that involve the plasticity of basal cells, the stem cells of the airways.

TRPV1 promotes opioid analgesia during inflammation.

Pain and inflammation are inherently linked responses to injury, infection, or chronic diseases. Given that acute inflammation in humans or mice enhances the analgesic properties of opioids, there is much interest in determining the inflammatory transducers that prime opioid receptor signaling in primary afferent nociceptors. Here, we found that activation of the transient receptor potential vanilloid type 1 (TRPV1) channel stimulated a mitogen-activated protein kinase (MAPK) signaling pathway that was accompanied by the shuttling of the scaffold protein ß-arrestin2 to the nucleus. The nuclear translocation of ß-arrestin2 in turn prevented its recruitment to the µ-opioid receptor (MOR), the subsequent internalization of agonist-bound MOR, and the suppression of MOR activity that occurs upon receptor desensitization. Using the complete Freund's adjuvant (CFA) inflammatory pain model to examine the role of TRPV1 in regulating endogenous opioid analgesia in mice, we found that naloxone methiodide (Nal-M), a peripherally restricted, nonselective, and competitive opioid receptor antagonist, slowed the recovery from CFA-induced hypersensitivity in wild-type, but not TRPV1-deficient, mice. Furthermore, we showed that inflammation prolonged morphine-induced antinociception in a mouse model of opioid receptor desensitization, a process that depended on TRPV1. Together, our data reveal a TRPV1-mediated signaling pathway that serves as an endogenous pain-resolution mechanism by promoting the nuclear translocation of ß-arrestin2 to minimize MOR desensitization. This previously uncharacterized mechanism may underlie the peripheral opioid control of inflammatory pain. Dysregulation of the TRPV1-ß-arrestin2 axis may thus contribute to the transition from acute to chronic pain.

Peroxiredoxins and Beyond; Redox Systems Regulating Lung Physiology and Disease.

Significance: The lung is a unique organ, as it is constantly exposed to air, and thus it requires a robust antioxidant defense system to prevent the potential damage from exposure to an array of environmental insults, including oxidants. The peroxiredoxin (PRDX) family plays an important role in scavenging peroxides and is critical to the cellular antioxidant defense system. Recent Advances: Exciting discoveries have been made to highlight the key features of PRDXs that regulate the redox tone. PRDXs do not act in isolation as they require the thioredoxin/thioredoxin reductase/NADPH, sulfiredoxin (SRXN1) redox system, and in some cases glutaredoxin/glutathione, for their reduction. Furthermore, the chaperone function of PRDXs, controlled by the oxidation state, demonstrates the versatility in redox regulation and control of cellular biology exerted by this class of proteins. Critical Issues: Despite the long-known observations that redox perturbations accompany a number of pulmonary diseases, surprisingly little is known about the role of PRDXs in the etiology of these diseases. In this perspective, we review the studies that have been conducted thus far to address the roles of PRDXs in lung disease, or experimental models used to study these diseases. Intriguing findings, such as the secretion of PRDXs and the formation of autoantibodies, raise a number of questions about the pathways that regulate secretion, redox status, and immune response to PRDXs. Future Directions: Further understanding of the mechanisms by which individual PRDXs control lung inflammation, injury, repair, chronic remodeling, and cancer, and the importance of PRDX oxidation state, configuration, and client proteins that govern these processes is needed.

Reducing protein oxidation reverses lung fibrosis.

Idiopathic pulmonary fibrosis is characterized by excessive deposition of collagen in the lung, leading to chronically impaired gas exchange and death1-3. Oxidative stress is believed to be critical in this disease pathogenesis4-6, although the exact mechanisms remain enigmatic. Protein S-glutathionylation (PSSG) is a post-translational modification of proteins that can be reversed by glutaredoxin-1 (GLRX)7. It remains unknown whether GLRX and PSSG play a role in lung fibrosis. Here, we explored the impact of GLRX and PSSG status on the pathogenesis of pulmonary fibrosis, using lung tissues from subjects with idiopathic pulmonary fibrosis, transgenic mouse models and direct administration of recombinant Glrx to airways of mice with existing fibrosis. We demonstrate that GLRX enzymatic activity was strongly decreased in fibrotic lungs, in accordance with increases in PSSG. Mice lacking Glrx were far more susceptible to bleomycin- or adenovirus encoding active transforming growth factor beta-1 (AdTGFB1)-induced pulmonary fibrosis, whereas transgenic overexpression of Glrx in the lung epithelium attenuated fibrosis. We furthermore show that endogenous GLRX was inactivated through an oxidative mechanism and that direct administration of the Glrx protein into airways augmented Glrx activity and reversed increases in collagen in mice with TGFB1- or bleomycin-induced fibrosis, even when administered to fibrotic, aged animals. Collectively, these findings suggest the therapeutic potential of exogenous GLRX in treating lung fibrosis.