Oxidative stress promotes ligand-independent and enhanced ligand-dependent tumor necrosis factor receptor signaling

TNF receptors: Structure-function relationships and therapeutic targeting strategies

Tumor necrosis factor receptors (TNFR1 and TNFR2) play key roles in mediating inflammatory response and cell death signaling, which are associated with autoimmune disorders, neurodegenerative diseases, and cancers. The structure-function relationships of TNF receptors and their ligands determine the activation or inhibition of downstream signaling pathways. Available crystal structures have provided critical insights into the therapeutic targeting strategies of TNF receptors and their signaling networks. In this review, we discuss the potential of targeting receptor-ligand and receptor-receptor interactions in a competitive manner as well as perturbing receptor conformational dynamics through an allosteric mechanism to modulate TNF receptor signaling. We propose that conformational states of TNF receptors can act as a molecular switch in determining their functions and are important therapeutic targets. The knowledge of the structure-function relationships of TNF receptors can be applied to translational high-throughput drug screening and design of novel receptor-specific modulators with enhanced pharmacological properties.

Serum proteome profiling of plateau acclimatization in men using Olink proteomics approach

Plateau acclimatization involves adaptive changes in the body's neurohumoral regulation and metabolic processes due to hypoxic conditions at high altitudes. This study utilizes Olink targeted proteomics to analyze serum protein expression differences in Han Chinese individuals acclimatized for 6 months-1 year at 4500 and 5300 m altitudes, compared to those residing at sea level. The objective is to elucidate the proteins' roles in tissue and cellular adaptation to hypoxia. We identified 54 metabolism-related differentially expressed proteins (DEPs) in the serum of the high-altitude group versus the sea-level group, comprising 20 significantly upregulated and 34 downregulated proteins. Notably, 2 proteins were upregulated and 11 downregulated at both 4500 and 5300 m altitudes. The top three protein correlations among DEPs included CRKL with CA13, RNASE3 with NADK, and NADK with APEX1, alongside APLP1 with CTSH, CTSH with SOST, and CTSH with NT-proBNP in inverse correlations. KEGG enrichment analysis indicated significant DEP involvement in various metabolic pathways, particularly those associated with hypoxic cellular metabolism like glycolysis/gluconeogenesis and the HIF-1 signaling pathway. Correlation with clinical phenotypes showed positive associations of SOST, RNASE3, CA13, NADK, and CRKL with SaO2 and negative correlations with Hemoglobin and Hematocrit; ALDH1A1 positively correlated with Triglyceride; and SDC4 inversely correlated with Uric acid levels. This study provides insights into specific DEPs linked to metabolic adaptations in high-altitude acclimatized individuals, offering a foundation for understanding acclimatization mechanisms and potential therapeutic targets.

Reactive oxygen species activate the Drosophila TNF receptor Wengen for damage-induced regeneration

Tumor necrosis factor receptors (TNFRs) control pleiotropic pro-inflammatory functions that range from apoptosis to cell survival. The ability to trigger a particular function will depend on the upstream cues, association with regulatory complexes, and downstream pathways. In Drosophila melanogaster, two TNFRs have been identified, Wengen (Wgn) and Grindelwald (Grnd). Although several reports associate these receptors with JNK-dependent apoptosis, it has recently been found that Wgn activates a variety of other functions. We demonstrate that Wgn is required for survival by protecting cells from apoptosis. This is mediated by dTRAF1 and results in the activation of p38 MAP kinase. Remarkably, Wgn is required for apoptosis-induced regeneration and is activated by the reactive oxygen species (ROS) produced following apoptosis. This ROS activation is exclusive for Wgn, but not for Grnd, and can occur after knocking down Eiger/TNFα. The extracellular cysteine-rich domain of Grnd is much more divergent than that of Wgn, which is more similar to TNFRs from other animals, including humans. Our results show a novel TNFR function that responds to stressors by ensuring p38-dependent regeneration.

Peptide-based allosteric inhibitor targets TNFR1 conformationally active region and disables receptor-ligand signaling complex

Tumor necrosis factor (TNF) receptor 1 (TNFR1) plays a pivotal role in mediating TNF induced downstream signaling and regulating inflammatory response. Recent studies have suggested that TNFR1 activation involves conformational rearrangements of preligand assembled receptor dimers and targeting receptor conformational dynamics is a viable strategy to modulate TNFR1 signaling. Here, we used a combination of biophysical, biochemical, and cellular assays, as well as molecular dynamics simulation to show that an anti-inflammatory peptide (FKCRRWQWRMKK), which we termed FKC, inhibits TNFR1 activation allosterically by altering the conformational states of the receptor dimer without blocking receptor-ligand interaction or disrupting receptor dimerization. We also demonstrated the efficacy of FKC by showing that the peptide inhibits TNFR1 signaling in HEK293 cells and attenuates inflammation in mice with intraperitoneal TNF injection. Mechanistically, we found that FKC binds to TNFR1 cysteine-rich domains (CRD2/3) and perturbs the conformational dynamics required for receptor activation. Importantly, FKC increases the frequency in the opening of both CRD2/3 and CRD4 in the receptor dimer, as well as induces a conformational opening in the cytosolic regions of the receptor. This results in an inhibitory conformational state that impedes the recruitment of downstream signaling molecules. Together, these data provide evidence on the feasibility of targeting TNFR1 conformationally active region and open new avenues for receptor-specific inhibition of TNFR1 signaling.

Association between syndecan-4 and subclinical atherosclerosis in ankylosing spondylitis

BACKGROUND

Despite advances in the diagnosis and treatment of ankylosing spondylitis (AS), the risk of cardiovascular complications in AS patients is still higher than in the general population. Macrophages are at the intersection of the basic pathogenetic processes of AS and atherosclerosis. Although syndecan-4 (SDC4) mediates a variety of biological processes, the role of SDC4 in macrophage-mediated atherogenesis in AS patients remains unclear. Herein, we aimed to investigate the role of SDC4 in subclinical atherosclerosis in AS patients.

METHODS

Subjects were selected from eligible AS patients and control subjects without a prior history of AS who were referred to the rheumatology outpatient clinics. All participants' past medical records and clinical, and demographic characteristics were scanned. In addition, carotid intima-media thickness (CIMT) measurement and disease activity index measurement were applied to all patients.

RESULTS

According to our data, serum SDC4 level was significantly higher among AS patients compared with the control group (6.7 [1.5-35.0] ng/mL vs 5.1 [0.1-12.5] ng/mL, P < .001). The calculated CIMT was also significantly higher in AS patients than in the control group (0.6 [0.3-0.9] mm vs 0.4 (0.2-0.7), P < .001]. Additionally, serum C-reactive protein level and SDC4 level were independent predictors of AS and strongly associated with CIMT. Linear regression analysis showed that serum SDC4 level was the best predictor of CIMT (P = .004).

CONCLUSION

Our data indicate that serum SDC4 levels provide comprehensive information about the clinical activity of the disease and subclinical atherosclerosis in AS patients.

Continuous monitoring of postirradiation reoxygenation and cycling hypoxia using electron paramagnetic resonance imaging

Reoxygenation has a significant impact on the tumor response to radiotherapy. With developments in radiotherapy technology, the relevance of the reoxygenation phenomenon in treatment efficacy has been a topic of interest. Evaluating the reoxygenation in the tumor microenvironment throughout the course of radiation therapy is important in developing effective treatment strategies. In the current study, we used electron paramagnetic resonance imaging (EPRI) to directly map and quantify the partial oxygen pressure (pO2 ) in tumor tissues. Human colorectal cancer cell lines, HT29 and HCT116, were used to induce tumor growth in female athymic nude mice. Tumors were irradiated with 3, 10, or 20 Gy using an x-ray irradiator. Prior to each EPRI scan, magnetic resonance imaging (MRI) was performed to obtain T2-weighted anatomical images for reference. The differences in the mean pO2 were determined through two-tailed Student's t-test and one-way analysis of variance. The median pO2 60 min after irradiation was found to be lower in HCT116 than in HT29 (9.1 ± 1.5 vs. 14.0 ± 1.0 mmHg, p = 0.045). There was a tendency for delayed and incomplete recovery of pO2 in the HT29 tumor when a higher dose of irradiation (10 and 20 Gy) was applied. Moreover, there was a dose-dependent increase in the hypoxic areas (pO2  < 10 mmHg) 2 and 24 h after irradiation in all groups. In addition, an area that showed pO2 fluctuation between hypoxia and normoxia (pO2  > 10 mmHg) was also identified surrounding the region with stable hypoxia, and it slightly enlarged after recovery from acute hypoxia. In conclusion, we demonstrated the reoxygenation phenomenon in an in vivo xenograft model study using EPRI. These findings may lead to new knowledge regarding the reoxygenation process and possibilities of a new radiation therapy concept, namely, reoxygenation-based radiation therapy.

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

Genotoxicity-Stimulated and CYLD-Driven Malignant Transformation

Oxidative stress, which can cause DNA damage, can both activate TNF-R1 directly in the absence of TNF stimulation and phosphorylate c-Abl, thus promoting its cytoplasmic translocation. Persistent cytoplasmic localization of c-Abl has been associated with cellular transformation. c-Abl phosphorylates OTULIN at tyrosine 56, thereby disrupting its relationship with LUBAC. OTULIN-released LUBAC interacts with SPATA2 and is recruited to the TNF-R1sc, facilitating SPATA2-CYLD interaction. All these interactions are required for the activation of IKKβ to stimulate NF-κB transcriptional activity following genotoxic stress. IKKβ also induces the critical phosphorylation of CYLD at serine 568 to increase its deubiquitinating (DUB) activity required for the termination of signaling cascades. Contrary to the widespread belief that CYLD is an absolute tumor suppressor, CYLD initiates and terminates NF-κB activity by alternately using its oncoprotein and tumor suppressor activities, respectively. If IKKβ fails to achieve the DUB activity-inducing phosphorylation at serine 568, CYLD would operate in a sustained mode of oncogenic activity. The resulting dysregulated NF-κB activation and other accompanying pathologies will disrupt cellular homeostasis in favor of transformation.

A reduction of Syndecan-4 in macrophages promotes atherosclerosis by aggravating the proinflammatory capacity of macrophages

BACKGROUND

Cardiovascular diseases (CVDs) are a significant cause of mortality worldwide and are characterized by severe atherosclerosis (AS) in patients. However, the molecular mechanism of AS formation remains elusive. In the present study, we investigated the role of syndecan-4 (SDC4), a member of the syndecan family, in atherogenesis.

METHODS AND RESULTS

The expression of SDC4 decreased in mouse severe AS models. Moreover, knockout of SDC4 accelerated high-cholesterol diets (HCD)-induced AS in ApoE^-/- mice. Mechanistically, the decrease of SDC4 increased macrophage proinflammatory capacity may be through the PKCα-ABCA1/ABCG1 signaling pathway.

CONCLUSION

These findings provide evidence that SDC4 reduction links macrophages and inflammation to AS and that SDC4 in macrophages provides a therapeutic target for preventing AS formation.

Naltrexone-Induced Cardiac Function Improvement is Associated With an Attenuated Inflammatory Response and Lipid Perioxidation in Volume Overloaded Rats

In previous studies, upregulation of myocardial opioid receptors as well as the precursors of their endogenous ligands were detected in the failing heart due to chronic volume overload. Moreover, opioid receptor blockade by naltrexone improved left ventricular function. In parallel, inflammatory processes through cytokines have been confirmed to play an important role in the pathogenesis of different forms of heart failure. Thus, the present study examined the systemic and myocardial inflammatory response to chronic volume overload and its modulation by chronic naltrexone therapy. Chronic volume overload was induced in male Wistar rats by applying an infrarenal aortocaval fistula (ACF) for 28 days during which the selective opioid receptor antagonist naltrexone (n = 6) or vehicle (n = 6) were administered via a subcutaneously implanted Alzet minipump. The ultrastructural, morphometric and hemodynamic characterization of ACF animals were performed using an intraventricular conductance catheter in vivo and electron microscopy in vitro. Co-localization of mu-, delta- and kappa-opioid receptor subtypes (MOR, DOR, and KOR respectively) with the voltage gated L-type Ca2+ channel (Cav1.2), the ryanodine receptor (RyR), and mitochondria in cardiomyocytes as well as IL-6, IL-12, TNF-alpha, and Malondialdehyde (MDA) were determined using double immunofluorescence confocal microscopy, RT-PCR and ELISA, respectively. In rat left ventricular myocardium, three opioid receptor subtypes MOR, DOR, and KOR colocalized with Cav1.2, RyR and mitochondria suggesting a modulatory role of the excitation-contraction coupling. In rats with ACF-induced volume overload, signs of heart failure and myocardial ultrastructural damage, chronic naltrexone therapy improved cardiac function and reversed the systemic and myocardial inflammatory cytokine expression as well as lipid peroxidation. In conclusion, antagonism of the cardiodepressive effects of the myocardial opioid system does not only improve left ventricular function but also blunts the inflammatory response and lipid peroxidation.

T-Cell Repertoire in Tumor Radiation: The Emerging Frontier as a Radiotherapy Biomarker

Simple Summary

Radiotherapy constitutes an essential component of the treatment for malignant disease. Besides its direct effect on cancer cells, namely, DNA damage and cell death, ionizing irradiation also mediates indirect antitumor effects that are mostly mediated by the immune system. Investigations into the processes underlying the interaction between radiotherapy and the immune system have uncovered mechanisms that can be exploited to promote the antitumor efficacy of radiotherapy both locally in the irradiated primary tumor and also at distant lesions in non-irradiated tumors. Because of its capacity to stimulate antitumor immunity, radiotherapy is also applied in combination with immune-checkpoint-inhibition-based immunotherapy. This review discusses the important pathways that govern the synergistic interactions between ionizing radiation and antitumor immune reactivity. Unravelling these involved mechanisms is mandatory for the successful application of anticancer radiotherapy and immunotherapy. We also place emphasis on the need for biomarkers that will aid in the selection of patients most likely to benefit from such combined treatments.

Abstract

Radiotherapy (RT) is a therapeutic modality that aims to eliminate malignant cells through the induction of DNA damage in the irradiated tumor site. In addition to its cytotoxic properties, RT also induces mechanisms that result in the promotion of antitumor immunity both locally within the irradiation field but also at distant tumor lesions, a phenomenon that is known as the “abscopal” effect. Because the immune system is capable of sensing the effects of RT, several treatment protocols have been assessing the synergistic role of radiotherapy combined with immunotherapy, collectively referred to as radioimmunotherapy. Herein, we discuss mechanistic insights underlying RT-based immunomodulation, which also enhance our understanding of how RT regulates antitumor T-cell-mediated immunity. Such knowledge is essential for the discovery of predictive biomarkers and for the improvement of clinical trials investigating the efficacy of radio-immunotherapeutic modalities in cancer patients.

Immunotherapy and Radiation Therapy in Renal Cell Carcinoma

BACKGROUND

The management of renal cell carcinoma is rapidly evolving and immunotherapy, mostly consisting of immune checkpoint inhibitors, is revolutionizing the treatment scenario of metastatic patients. Novel fractionation schedules of radiotherapy, consisting of high doses in few fractions, can overcome the radioresistance of this tumor. Localized radiotherapy is associated with a systemic effect, known as the abscopal effect. This effect mediated by the immune system can be enhanced associating radiotherapy with immunotherapy.

OBJECTIVE

In this review, we explore the role of radiotherapy and immunotherapy in RCC, the rationale of combining these strategies and the on-going clinical trials investigating combinations of these two treatment modalities.

CONCLUSION

Combining immunotherapy and radiotherapy has a strong rationale and pre-clinical studies support their association because it can overcome the immunosuppression of the tumor microenvironment and increase the anti-tumor immune response. More clinical evidence, deriving from onclinical trials, are needed to prove the efficacy and safety of these treatments combined.

Radiation-induced eosinophils improve cytotoxic T lymphocyte recruitment and response to immunotherapy

The efficacy of cancer immunotherapy is dictated by CD8⁺ T cell infiltration and the nature of the tumor microenvironment (TME). By inflaming the TME to favor CD8⁺ T cell immunity, radiation is now widely considered as a neoadjuvant for immunomodulation. Here, we observed that local irradiation enhances the infiltration of intratumoral eosinophils, and depletion of eosinophil dampens CD8⁺ T cell infiltration and diminishes the anti-tumor effectiveness of radiation. Retrospectively, we identified a strong correlation between eosinophilia and survival benefit in radiation-treated cancer patients. Experimentally, we further show that radiation enhances the intratumoral infiltration of adoptive transferred T cells therapy, bolstering eosinophils by intravenous interleukin-5 administration promotes the efficacy of radiation-induced abscopal effect. Together, these results suggest that eosinophil mobilization can be considered as a mechanistically relevant biomarker for predicting the effectiveness of pre-immunotherapy radiation, as well as a new strategy to enhance T cell-mediated immunotherapy against cancers.

Radiation therapy-induced reactive oxygen species specifically eliminates CD19+IgA+ B cells in nasopharyngeal carcinoma

Purpose

Nasopharyngeal carcinoma (NPC) is one of the most common head and neck cancers and is thought to be related to the mucosal immune system. Radiation therapy (RT) is the primary treatment for NPC due to the high radiosensitivity of cancer cells. However, little is known about the impact of RT on the mucosal immune system.

Patients and methods

In this study, the expression of immune markers CD19, CD24, CD27, CD8, and IgA before and after RT, were analyzed using flow cytometry. Cytokines were assessed using the enzyme-linked immunosorbent assay. Reactive oxygen species (ROS) was assayed by flow cytometry and fluorescence staining using 2ʹ,7ʹ -dichlorofluorescein diacetate.

Results

We found that primary NPC patients had a significant increase in CD19⁺CD138⁻IgA⁺ B cells, which was then decreased after RT. Interestingly, the changes in CD19⁺CD138⁻IgA⁺ B cell frequency was accompanied by corresponding frequency changes in cytotoxic T cells (CTL), which are powerful anti-tumor lymphocytes. Mechanistically, we found that ROS release during RT specifically eliminated CD19⁺CD138⁻IgA⁺ B cells.

Conclusion

These findings suggest that RT may regulate the immune system and opens up new avenues for the utilization of immune-radiotherapy in NPC.

Cardioprotective effect of caffeic acid phenethyl ester on cardiac contusion following blunt chest trauma in rats

We investigated the effects of caffeic acid phenethyl ester (CAPE) on cardiac damage after blunt chest injury. Forty male adult Wistar albino rats were divided into four groups; control, cardiac contusion, cardiac contusion + CAPE, and CAPE. CAPE, 10 mmol/kg, was administered intraperitoneally for 7 days following cardiac contusion. Heart tissue and blood were obtained at the end of the experimental period. Cardiac histopathology was determined using hematoxylin & eosin (H & E) staining. Expression of tumor necrosis factor-alpha (TNF-α) in cardiomyocytes was determined using immunohistochemistry. Cardiac apoptosis was determined using the TUNEL method. Serum creatine kinase (CK), creatine kinase-muscle/brain (CK-MB) and lactate dehydrogenase (LDH) levels were determined using spectrophotometric methods. The serum cardiac troponin I (C-TI) level was measured using the ELISA method. Myofibril loss was detected in the cardiomyocytes of the cardiac contusion group. Increased apoptosis and TNF-α expression were observed in the cardiac contusion group compared to the control group. Increased CK, CK-MB, LDH and C-TI levels were found in the cardiac contusion group. We found that CAPE administration improved myocardial function. Compared to the cardiac contusion group, CK, CK-MB, LDH and C-TI levels decreased significantly in the cardiac contusion + CAPE group. Administration of CAPE significantly inhibited apoptosis and cardiac TNF-α expression. Our findings demonstrate the therapeutic effects of CAPE for cardiac contusion damage after blunt chest trauma.

Anti-inflammatory Action of Metformin with Respect to CX3CL1/CX3CR1 Signaling in Human Placental Circulation in Normal-Glucose Versus High-Glucose Environments

Upregulation of chemokine CX3CL1 and its receptor CX3CR1 occurs in the diabetic human placenta. Metformin, an insulin-sensitizing biguanide, is used in the therapy of diabetic pregnancy. By preventing the activation of NF-κB, metformin exhibits anti-inflammatory properties. We examined the influence of hyperglycemia (25 mmol/L glucose; HG group; N = 36) on metformin-mediated effects on CX3CL1 and TNF-α production by placental lobules perfused extracorporeally. Additionally, CX3CR1 expression and contents of CX3CR1, TNF-α receptor 1 (TNFR1), and NF-κB proteins in the placental tissue were evaluated. Placentae perfused under normoglycemia (5 mmol/L glucose; NG group; N = 36) served as the control. Metformin (2.5 and 5.0 mg/L; subgroups B and C) lowered the production of CX3CL1 and TNF-α in a dose-dependent and time-dependent manner. Hyperglycemia did not weaken the strength of these metformin effects. Moreover, CX3CL1 levels after perfusion with 5.0 mg/L metformin were reduced by 33.28 and 33.83% (at 120 and 150 min, respectively) in the HG-C subgroup versus 24.98 and 23.66% in the NG-C subgroup, which indicated an augmentation of the metformin action over time in hyperglycemia. CX3CR1 expression was significantly higher in the HG-B and HG-C subgroups compared to that in the NG-B and NG-C subgroups. Increased CX3CR1 protein content in the placental lysates was observed in subgroups B and C. The two higher metformin concentrations significantly decreased the levels of NF-κBp65 protein content in both groups. However, the decrease was significantly stronger in hyperglycemia. TNFR1 upregulation in the HG group was not affected by metformin. Further studies on metformin therapy during pregnancy are needed, including safety issues.

Large-Scale Analysis of Redox-Sensitive Conditionally Disordered Protein Regions Reveals Their Widespread Nature and Key Roles in High-Level Eukaryotic Processes

Recently developed quantitative redox proteomic studies enable the direct identification of redox-sensing cysteine residues that regulate the functional behavior of target proteins in response to changing levels of reactive oxygen species. At the molecular level, redox regulation can directly modify the active sites of enzymes, although a growing number of examples indicate the importance of an additional underlying mechanism that involves conditionally disordered proteins. These proteins alter their functional behavior by undergoing a disorder-to-order transition in response to changing redox conditions. However, the extent to which this mechanism is used in various proteomes is currently unknown. Here, a recently developed sequence-based prediction tool incorporated into the IUPred2A web server is used to estimate redox-sensitive conditionally disordered regions at a large scale. It is shown that redox-sensitive conditional disorder is fairly widespread in various proteomes and that its presence strongly correlates with the expansion of specific domains in multicellular organisms that largely rely on extra stability provided by disulfide bonds or zinc ion binding. The analyses of yeast redox proteomes and human disease data further underlie the significance of this phenomenon in the regulation of a wide range of biological processes, as well as its biomedical importance.

White light emitting diode suppresses proliferation and induces apoptosis in hippocampal neuron cells through mitochondrial cytochrome c oxydase-mediated IGF-1 and TNF-α pathways

Light emitting diode (LED) light has been tested to treat traumatic brain injury, neural degenerative diseases and psychiatric disorders. Previous studies indicate that blue LED light affects cell proliferation and apoptosis in photosensitive cells and cancer cells. In this study, we demonstrate that white LED light exposure impaired proliferation and induced apoptosis in HeLa and HT-22 hippocampal neural cells, but not C2C12 cells. Furthermore, the mechanisms underlying the effect of white LED light exposure on HT-22 cells were elucidated. In HeLa and HT-22 cells, white LED light activated mitochondrial cytochrome c oxidase (Cco), in association with enhanced ATP synthase activity and elevated intracellular ATP concentration. Also, reactive oxygen species (ROS) and nitric oxide (NO) production were increased, accompanied by higher calcium concentration and lower mitochondrial membrane potential. HT-22 cells exposed to white LED light for 24h showed reduced viability, with higher apoptotic rate and a cell cycle arrest at G0/G1 phase. Concurrently, the mRNA expression and the concentration of IGF-1 were decreased, while that of TNF-α were increased, in light-exposed cells, which was supported by the luciferase activity of both gene promoters. The down-stream mitogen-activated protein kinase (MAPK), AKT/mTOR pathways were inhibited, in association with an activation of apoptotic caspase 3. N-Acetylcysteine, a ROS scavenger, protected the cells from LED light-induced cellular damage, with rescued cell viability and restored mRNA expression of IGF-1 and TNF-α. Our data demonstrate that white LED light suppresses proliferation and induces apoptosis in hippocampal neuron cells through mitochondrial Cco/ROS-mediated IGF-1 and TNF-α pathways.

High Glucose Level Disturbs the Resveratrol-Evoked Curtailment of CX3CL1/CX3CR1 Signaling in Human Placental Circulation

Hyperglycemia-induced hyperactivity of chemokine CX3CL1 (fractalkine) occurs in the human placenta. Anti-inflammatory/antioxidant activities of resveratrol (3,5,4'-trihydroxy-trans-stilbene) are related to the modulation of chemokine CX3CL1 and its receptor, CX3CR1, signaling pathways. We examined the influence of high glucose (25 mmol/L glucose; HG group; N = 36) on resveratrol-mediated effects on CX3CL1 and TNF-α production by the placental lobule, CX3CR1 expression and contents of CX3CR1, TNF-α receptor 1 (TNFR1), and NF-κB proteins in placental tissue. The placental lobules perfused under normoglycemic conditions formed the control NG group (N = 36). Resveratrol (50 and 100 μM; subgroups B and C) administered into the perfusion fluid lowered the production of both CX3CL1 and TNF-α. The reductions in CX3CL1 levels were more evident in the NG group. CX3CR1 expression was significantly higher in the NG subgroups B and C compared to the HG subgroups B and C (385.2 and 426.5% versus 199.3 and 282.4%, resp.). An increase in CX3CR1 protein content in placental lysates was observed in the NG subgroups B and C. Also, resveratrol significantly decreased NF-κBp65 protein content only in the NG group, not affecting hyperglycemia-elicited TNFR1 upregulation. In conclusion, euglycemia assures optimal effects of resveratrol pertaining to CX3CL1/CX3CR1 signaling in the placenta. Future studies on resveratrol are needed, especially those including maternal-fetal risk assessments.

Piecing it together: Unraveling the elusive structure-function relationship in single-pass membrane receptors

The challenge of crystallizing single-pass plasma membrane receptors has remained an obstacle to understanding the structural mechanisms that connect extracellular ligand binding to cytosolic activation. For example, the complex interplay between receptor oligomerization and conformational dynamics has been, historically, only inferred from static structures of isolated receptor domains. A fundamental challenge in the field of membrane receptor biology, then, has been to integrate experimentally observable dynamics of full-length receptors (e.g. diffusion and conformational flexibility) into static structural models of the disparate domains. In certain receptor families, e.g. the ErbB receptors, structures have led somewhat linearly to a putative model of activation. In other families, e.g. the tumor necrosis factor (TNF) receptors, structures have produced divergent hypothetical mechanisms of activation and transduction. Here, we discuss in detail these and other related receptors, with the goal of illuminating the current challenges and opportunities in building comprehensive models of single-pass receptor activation. The deepening understanding of these receptors has recently been accelerated by new experimental and computational tools that offer orthogonal perspectives on both structure and dynamics. As such, this review aims to contextualize those technological developments as we highlight the elegant and complex conformational communication between receptor domains. This article is part of a Special Issue entitled: Interactions between membrane receptors in cellular membranes edited by Kalina Hristova.

Death Receptor 5 Networks Require Membrane Cholesterol for Proper Structure and Function

Death receptor 5 (DR5) is an apoptosis-inducing member of the tumor necrosis factor receptor superfamily, whose activity has been linked to membrane cholesterol content. Upon ligand binding, DR5 forms large clusters within the plasma membrane that have often been assumed to be manifestations of receptor co-localization in cholesterol-rich membrane domains. However, we have recently shown that DR5 clusters are more than just randomly aggregated receptors. Instead, these are highly structured networks held together by receptor dimers. These dimers are stabilized by specific transmembrane helix-helix interactions, including a disulfide bond in the long isoform of the receptor. The complex relationships among DR5 network formation, transmembrane helix dimerization, membrane cholesterol, and receptor activity has not been established. It is unknown whether the membrane itself plays an active role in driving DR5 transmembrane helix interactions or in the formation of the networks. We show that cholesterol depletion in cells does not inhibit the formation of DR5 networks. However, the networks that form in cholesterol-depleted cells fail to induce caspase cleavage. These results suggest a potential structural difference between active and inactive networks. As evidence, we show that cholesterol is necessary for the covalent dimerization of DR5 transmembrane domains. Molecular simulations and experiments in synthetic vesicles on the DR5 transmembrane dimer suggest that dimerization is facilitated by increased helicity in a thicker bilayer.

Association Between Tumor Necrosis Factor-α and Diabetic Peripheral Neuropathy in Patients with Type 2 Diabetes: a Meta-Analysis

Tumor necrosis factor-α (TNF-α) is a cell signaling protein involved in systemic inflammation, and is also an important cytokine in the acute phase reaction. Several studies suggested a possible association between TNF-α and diabetic peripheral neuropathy (DPN) in type 2 diabetic patients, but no accurate conclusion was available. A systematic review and meta-analysis of observational studies was performed to comprehensively assess the association between serum TNF-α levels and DPN in type 2 diabetic patients. We searched Pubmed, Web of Science, Embase, and China Biology Medicine (CMB) databases for eligible studies. Study-specific data were combined using meta-analysis. Fourteen studies were finally included into the meta-analysis, which involved a total of 2650 participants. Meta-analysis showed that there were obviously increased serum TNF-α levels in DPN patients compared with type 2 diabetic patients without DPN (standard mean difference [SMD] = 1.203, 95 % CI 0.795-1.611, P < 0.001). There were also obviously increased levels of serum TNF-α in diabetic patients with DPN when compared with healthy controls (SMD = 2.364, 95 % CI 1.333-3.394, P < 0.001). In addition, there were increased serum TNF-α levels in painful DPN patients compared with painless DPN patients (SMD = 0.964, 95 % CI 0.237-1.690, P = 0.009). High level of serum TNF-α was significantly associated with increased risk of DPN in patients with type 2 diabetes (odds ratio [OR] = 2.594, 95 % CI 1.182-5.500, P = 0.017). Increased serum levels of TNF-α was not associated with increased risk of painful DPN in patients with type 2 diabetes (OR = 2.486, 95 % CI 0.672-9.193, P = 0.172). Sensitivity analysis showed that there was no obvious change in the pooled estimates when omitting single study by turns. Type 2 diabetic patients with peripheral neuropathy have obviously increased serum TNF-α levels than type 2 diabetic patients without peripheral neuropathy and healthy controls, and high level of serum TNF-α may be associated with increased risk of peripheral neuropathy independently. Further prospective cohort studies are needed to assess the association between TNF-α and DPN.

The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence

Radiotherapy plays a central part in curing cancer. For decades, most research on improving treatment outcomes has focused on modulating radiation-induced biological effects on cancer cells. Recently, we have better understood that components within the tumour microenvironment have pivotal roles in determining treatment outcomes. In this Review, we describe vascular, stromal and immunological changes that are induced in the tumour microenvironment by irradiation and discuss how these changes may promote radioresistance and tumour recurrence. We also highlight how this knowledge is guiding the development of new treatment paradigms in which biologically targeted agents will be combined with radiotherapy.

TNF-α-induced cardiomyocyte apoptosis contributes to cardiac dysfunction after coronary microembolization in mini-pigs

This experimental study was designed to clarify the relationship between cardiomyocyte apoptosis and tumour necrosis factor-alpha (TNF-α) expression, and confirm the effect of TNF-α on cardiac dysfunction after coronary microembolization (CME) in mini-pigs. Nineteen mini-pigs were divided into three groups: sham-operation group (n = 5), CME group (n = 7) and adalimumab pre-treatment group (n = 7; TNF-α antibody, 2 mg/kg intracoronary injection before CME). Magnetic resonance imaging (3.0-T) was performed at baseline, 6th hour and 1 week after procedure. Cardiomyocyte apoptosis was detected by cardiac-TUNEL staining, and caspase-3 and caspase-8 were detected by RT-PCR and immunohistochemistry. Furthermore, serum TNF-α, IL-6 and troponin T were analysed, while myocardial expressions of TNF-α and IL-6 were detected. Both TNF-α expression (serum level and myocardial expression) and average number of apoptotic cardiomyocyte nuclei were significantly increased in CME group compared with the sham-operation group. Six hours after CME, left ventricular end-systolic volume (LVESV) was increased and the left ventricular ejection fraction (LVEF) was decreased in CME group. Pre-treatment with adalimumab not only significantly improved LVEF after CME (6th hour: 54.9 ± 2.3% versus 50.4 ± 3.9%, P = 0.036; 1 week: 56.7 ± 4.2% versus 52.7 ± 2.9%, P = 0.041), but also suppressed cardiomyocyte apoptosis and the expression of caspase-3 and caspase-8. Meanwhile, the average number of apoptotic cardiomyocytes nuclei was inversely correlated with LVEF (r = −0.535, P = 0.022). TNF-α-induced cardiomyocyte apoptosis is likely involved in cardiac dysfunction after CME. TNF-α antibody therapy suppresses cardiomyocyte apoptosis and improves early cardiac function after CME.

Silencer of death domains controls cell death through tumour necrosis factor-receptor 1 and caspase-10 in acute lymphoblastic leukemia

Resistance to apoptosis remains a significant problem in drug resistance and treatment failure in malignant disease. NO-aspirin is a novel drug that has efficacy against a number of solid tumours, and can inhibit Wnt signaling, and although we have shown Wnt signaling to be important for acute lymphoblastic leukemia (ALL) cell proliferation and survival inhibition of Wnt signaling does not appear to be involved in the induction of ALL cell death. Treatment of B lineage ALL cell lines and patient ALL cells with NO-aspirin induced rapid apoptotic cell death mediated via the extrinsic death pathway. Apoptosis was dependent on caspase-10 in association with the formation of the death-inducing signaling complex (DISC) incorporating pro-caspase-10 and tumor necrosis factor receptor 1 (TNF-R1). There was no measurable increase in TNF-R1 or TNF-α in response to NO-aspirin, suggesting that the process was ligand-independent. Consistent with this, expression of silencer of death domain (SODD) was reduced following NO-aspirin exposure and lentiviral mediated shRNA knockdown of SODD suppressed expansion of transduced cells confirming the importance of SODD for ALL cell survival. Considering that SODD and caspase-10 are frequently over-expressed in ALL, interfering with these proteins may provide a new strategy for the treatment of this and potentially other cancers.

Tumor necrosis factor receptor-associated periodic syndrome as a model linking autophagy and inflammation in protein aggregation diseases

Autophagy prevents cellular damage by eliminating insoluble aggregates of mutant misfolded proteins, which accumulate under different pathological conditions. Downregulation of autophagy enhances the inflammatory response and thus represents a possible common pathogenic event underlying a number of autoinflammatory syndromes, such as tumor necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS). The pathogenesis of other monogenic or complex disorders that display symptoms of excessive inflammation also involve the autophagy pathway. Studies have shown that TRAPS-associated TNFRSF1A mutations induce cytoplasmic retention of the TNFR1 receptor, defective TNF-induced apoptosis, and production of reactive oxygen species (ROS). Furthermore, autophagy impairment may account for the pathogenic effects of TNFRSF1A mutations, thus inducing inflammation in TRAPS. In this review, we summarize the molecular interactions and functional links between autophagy with regard to nuclear factor-kappa B activation, ROS production, and apoptosis. Furthermore, we propose a complex interplay of these pathways as a model to explain the relationship between mutant protein misfolding and inflammation in genetically determined and aggregation-prone diseases. Accordingly, autophagy function should be investigated in all diseases showing an inflammatory component, and for which the molecular pathogenesis is still unclear.

Comparative reactivity of the myeloperoxidase-derived oxidants hypochlorous acid and hypothiocyanous acid with human coronary artery endothelial cells

In the immune response, hypohalous acids are generated by activated leukocytes via the release of myeloperoxidase and the formation of H2O2. Although these oxidants have important bactericidal properties, they have also been implicated in causing tissue damage in inflammatory diseases, including atherosclerosis. Hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN) are the major oxidants formed by myeloperoxidase under physiological conditions, with the ratio of these oxidants dependent on diet and smoking status. HOCl is highly reactive and causes marked cellular damage, but few data are available on the effects of HOSCN on mammalian cells. In this study, we have compared the actions of HOCl and HOSCN on human coronary artery endothelial cells (HCAEC). HOCl reacts rapidly with the cells, resulting in extensive cell death by both apoptosis and necrosis, with necrosis dominating at higher oxidant doses. In contrast, HOSCN is consumed more slowly, with cell death occurring only by apoptosis. Exposure of HCAEC to HOCl and HOSCN induces changes in mitochondrial membrane permeability, which, in the case of HOSCN, is associated with mitochondrial release of proapoptotic factors, including cytochrome c, apoptosis-inducing factor, and endonuclease G. With each oxidant, apoptosis appears to be caspase-independent, with the inactivation of caspases 3/7 observed, and pretreatment of the cells with the caspase inhibitor Z-VAD-fmk having no effect on the extent of cell death. Loss of cellular thiols, depletion of glutathione, and the inactivation of thiol-dependent enzymes, including glyceraldehyde-3-phosphate dehydrogenase, were seen with both oxidants, though to a much greater extent with HOCl. The ability of myeloperoxidase-derived oxidants to induce endothelial cell apoptosis may contribute to the formation of unstable lesions in atherosclerosis. The results with HOSCN may be particularly significant for smokers, who have elevated plasma levels of SCN(-), the precursor of this oxidant.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Autophagy contributes to inflammation in patients with TNFR-associated periodic syndrome (TRAPS)

OBJECTIVES

Tumour necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS) is caused by TNFRSF1A mutations, known to induce intracellular retention of the TNFα receptor 1 (TNFR1) protein, defective TNFα-induced apoptosis, and production of reactive oxygen species. As downregulation of autophagy, the main cellular pathway involved in insoluble aggregate elimination, has been observed to increase the inflammatory response, we investigated whether it plays a role in TRAPS pathogenesis.

METHODS

The possible link between TNFRSF1A mutations and inflammation in TRAPS was studied in HEK-293T cells, transfected with expression constructs for wild-type and mutant TNFR1 proteins, and in monocytes derived from patients with TRAPS, by investigating autophagy function, NF-κB activation and interleukin (IL)-1β secretion.

RESULTS

We found that autophagy is responsible for clearance of wild-type TNFR1, but when TNFR1 is mutated, the autophagy process is defective, probably accounting for mutant TNFR1 accumulation as well as TRAPS-associated induction of NF-κB activity and excessive IL-1β secretion, leading to chronic inflammation. Autophagy inhibition due to TNFR1 mutant proteins can be reversed, as demonstrated by the effects of the antibiotic geldanamycin, which was found to rescue the membrane localisation of mutant TNFR1 proteins, reduce their accumulation and counteract the increased inflammation by decreasing IL-1β secretion.

CONCLUSIONS

Autophagy appears to be an important mechanism in the pathogenesis of TRAPS, an observation that provides a rationale for the most effective therapy in this autoinflammatory disorder. Our findings also suggest that autophagy could be proposed as a novel therapeutic target for TRAPS and possibly other similar diseases.

A protein disulfide isomerase/thioredoxin-1 complex is physically attached to exofacial membrane tumor necrosis factor receptors: overexpression in chronic lymphocytic leukemia cells

AIMS

The 3D structures and functions of cysteine-rich receptors such as tumor necrosis factor receptors (TNFRs) are redox-modulated by dithiol-disulfide exchange. TNFR superfamily members participate in growth regulation in B-cell chronic lymphocytic leukemia (CLL), and tissue stromal cells interact with leukemia cells, profoundly affecting their viability via release of redox-active components, including cysteine, thioredoxin-1 (Trx1), and Trx reductase. Trx1 was previously shown to enhance release of TNF, which acts as an autocrine/paracrine growth factor in CLL. The nature of the mechanism is not known, however. Here, we investigated whether Trx1 and protein disulfide isomerase (PDI), a chaperone and Trx-family member, may interact with TNFRs.

RESULTS

We found direct physical association between PDI and TNFR1 or TNFR2 by coclustering and affinity isolation. PDI (57 kDa) formed covalent/reduction-sensitive 69-kDa complexes with Trx1 (12 kDa) in a majority of CLL cell samples, detected at low levels only in control B-cells. Functionally, the TNF/TNFR signaling via the nuclear factor kappa B-driven autocrine loop was disrupted in a dose-dependent fashion by PDI-inhibitors bacitracin, anti-PDI, or anti-Trx1 antibodies, resulting in reduced viability. PDI was significantly overexpressed in immunoglobulin heavy-chain variable (IGHV) unmutated versus mutated CLL (p=0.0102), and amplified TNF release was observed in the former group.

INNOVATION

This study points out a previously unrecognized physical and functional association of TNFRs with the redox-active proteins PDI and Trx1.

CONCLUSION

We describe here a new level of TNF regulation, in which membrane TNFRs are redox controlled at the exofacial surface by PDI/Trx1. These findings shed new light on the observed survival benefit in CLL B-cells exerted by TNFR-superfamily ligands and point at potential therapeutic strategies.

Involvement of X-box binding protein 1 and reactive oxygen species pathways in the pathogenesis of tumour necrosis factor receptor-associated periodic syndrome

OBJECTIVES

To investigate convergence of endoplasmic reticulum stress pathways and enhanced reactive oxygen species (ROS) production, due to intracellular retention of mutant tumour necrosis factor receptor 1 (TNFR1), as a disease mechanism in TNFR-associated periodic syndrome (TRAPS).

METHODS

Peripheral blood mononuclear cells from patients with TRAPS (n=16) and healthy controls (HC) (n=22) were studied alongside HEK293T cells expressing wild type-TNFR1 or TRAPS-associated mutations. Unfolded protein response (UPR)-associated proteins (protein kinase-like endoplasmic reticulum kinase, PERK), phosphorylated-PERK (p-PERK), phosphorylated inositol-requiring enzyme 1α (p-IRE1α) and spliced X-box binding protein 1 (sXBP1)) were measured by flow cytometry. XBP1 splicing and UPR-associated transcript expression were assessed by reverse transcription PCR/quantitative real-time PCR. ROS levels were measured using CM-H(2)DCFDA and MitoSOX Red in patients' monocytes or HEK293T cells by flow cytometry.

RESULTS

Mutant TNFR1-expressing HEK293T cells had increased TNFR1 expression associated with intracellular aggregation. TRAPS patients had increased sXBP1 transcripts (p<0.01) compared with HC. Raised p-PERK protein was seen, indicative of an UPR, but other UPR-associated transcripts were normal. Increased ROS levels were observed in TRAPS monocytes compared with HCs (p<0.02); these increased further upon IL-6 stimulation (p<0.01). Lipopolysaccharide-stimulated peripheral blood mononuclear cells of patients with TRAPS, but not HCs, demonstrated increased sXBP1 levels (p<0.01), which were reduced by antioxidant treatment (p<0.05).

CONCLUSIONS

Patients with TRAPS have evidence of increased sXBP1 and PERK expression but without other signs of classical UPR, and also with high ROS generation that may contribute to the pro-inflammatory state associated with TRAPS. The authors propose a non-traditional XBP1 pathway with enhanced sXBP1 as a novel disease-contributing mechanism in TRAPS.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces death receptor 5 networks that are highly organized

Recent evidence suggests that TNF-related apoptosis-inducing ligand (TRAIL), a death-inducing cytokine with anti-tumor potential, initiates apoptosis by re-organizing TRAIL receptors into large clusters, although the structure of these clusters and the mechanism by which they assemble are unknown. Here, we demonstrate that TRAIL receptor 2 (DR5) forms receptor dimers in a ligand-dependent manner at endogenous receptor levels, and these receptor dimers exist within high molecular weight networks. Using mutational analysis, FRET, fluorescence microscopy, synthetic biochemistry, and molecular modeling, we find that receptor dimerization relies upon covalent and noncovalent interactions between membrane-proximal residues. Additionally, by using FRET, we show that the oligomeric structure of two functional isoforms of DR5 is indistinguishable. The resulting model of DR5 activation should revise the accepted architecture of the functioning units of DR5 and the structurally homologous TNF receptor superfamily members.

The role of tumour necrosis factor-α and tumour necrosis factor receptor signalling in inflammation-associated systemic genotoxicity

Chronic inflammatory diseases are characterised by systemically elevated levels of tumour necrosis factor (TNF)-α, a proinflammatory cytokine with pleiotropic downstream effects. We have previously demonstrated increased genotoxicity in peripheral leukocytes and various tissues in models of intestinal inflammation. In the present study, we asked whether TNF-α is sufficient to induce DNA damage systemically, as observed in intestinal inflammation, and whether tumour necrosis factor receptor (TNFR) signalling would be necessary for the resultant genotoxicity. In the wild-type mice, 500 ng per mouse of TNF-α was sufficient to induce DNA damage to multiple cell types and organs 1-h post-administration. Primary splenic T cells manifested TNF-α-induced DNA damage in the absence of other cell types. Furthermore, TNFR1(-/-)TNFR2(-/-) mice demonstrated decreased systemic DNA damage in a model of intestinal inflammation and after TNF-α injection versus wild-type mice, indicating the necessity of TNFR signalling. Nuclear factor (NF)-κB inhibitors were also able to decrease damage induced by TNF-α injection in wild-type mice. When TNF-α administration was combined with interleukin (IL)-1β, another proinflammatory cytokine, DNA damage persisted for up to 24 h. When combined with IL-10, an anti-inflammatory cytokine, decreased genotoxicity was observed in vivo and in vitro. TNF-α/TNFR-mediated signalling is therefore sufficient and plays a large role in mediating DNA damage to various cell types, subject to modulation by other cytokines and their mediators.

Mitogen-activated protein kinases in mammalian oxidative stress responses

All aerobic organisms are exposed to oxidative stress during their lifetime and are required to respond appropriately for maintenance of their survival and homeostasis. Sustained exposure to oxidative stress has devastating effects in organisms, and, not surprisingly, oxidative stress has been implicated in numerous human diseases. Therefore, an understanding of how mammals respond to oxidative stress is crucial both biologically and clinically. Intracellular signaling pathways, which are activated in response to excessive oxygen radicals, play essential roles in overcoming oxidative stress. The mitogen-activated protein kinase (MAPK) signaling pathways are involved in diverse physiological processes, and are critical for induction of oxidative stress responses. In this review, we will discuss the physiological roles of MAPKs in oxidative stress, the upstream signaling pathways leading to MAPK activation, their regulation, and the MAPK downstream substrates, with a focus on mammalian systems.

A mammalian monothiol glutaredoxin, Grx3, is critical for cell cycle progression during embryogenesis

Glutaredoxins (Grxs) have been shown to be critical in maintaining redox homeostasis in living cells. Recently, an emerging subgroup of Grxs with one cysteine residue in the putative active motif (monothiol Grxs) has been identified. However, the biological and physiological functions of this group of proteins have not been well characterized. Here, we characterize a mammalian monothiol Grx (Grx3, also termed TXNL2/PICOT) with high similarity to yeast ScGrx3/ScGrx4. In yeast expression assays, mammalian Grx3s were localized to the nuclei and able to rescue growth defects of grx3grx4 cells. Furthermore, Grx3 inhibited iron accumulation in yeast grx3gxr4 cells and suppressed the sensitivity of mutant cells to exogenous oxidants. In mice, Grx3 mRNA was ubiquitously expressed in developing embryos, adult tissues and organs, and was induced during oxidative stress. Mouse embryos absent of Grx3 grew smaller with morphological defects and eventually died at 12.5 days of gestation. Analysis in mouse embryonic fibroblasts revealed that Grx3(-/-) cells had impaired growth and cell cycle progression at the G(2) /M phase, whereas the DNA replication during the S phase was not affected by Grx3 deletion. Furthermore, Grx3-knockdown HeLa cells displayed a significant delay in mitotic exit and had a higher percentage of binucleated cells. Therefore, our findings suggest that the mammalian Grx3 has conserved functions in protecting cells against oxidative stress and deletion of Grx3 in mice causes early embryonic lethality which could be due to defective cell cycle progression during late mitosis.

TNFα in myocardial ischemia/reperfusion, remodeling and heart failure

TNFα is crucially involved in the pathogenesis and progression of myocardial ischemia/reperfusion injury and heart failure. The formation and release of TNFα and its downstream signal transduction cascade following activation of its two receptor subtypes are characterized. Myocardial TNFα and TNF receptor activation have an ambivalent role in myocardial ischemia/reperfusion injury and protection from it. Excessive TNFα expression and subsequent cardiomyocyte TNF receptor type 1 stimulation induce contractile dysfunction, hypertrophy, fibrosis and cell death, while a lower TNFα concentration and subsequent cardiomyocyte TNF receptor type 2 stimulation are protective. Apart from its concentration and receptor subtype, the myocardial action of TNFα depends on the duration of its exposure and its localization. While detrimental during sustained ischemia, TNFα contributes to ischemic preconditioning protection, no matter whether it is the first, second or third window of protection, and both TNF receptors are involved in the protective signal transduction cascade. Finally, the available clinical attempts to antagonize TNFα in cardiovascular disease, notably heart failure, are critically discussed.

Reactive oxygen species in TNFalpha-induced signaling and cell death

TNFalpha is a pleotropic cytokine that initiates many downstream signaling pathways, including NF-kappaB activation, MAP kinase activation and the induction of both apoptosis and necrosis. TNFalpha has shown to lead to reactive oxygen species generation through activation of NADPH oxidase, through mitochondrial pathways, or other enzymes. As discussed, ROS play a role in potentiation or inhibition of many of these signaling pathways. We particularly discuss the role of sustained JNK activation potentiated by ROS, which generally is supportive of apoptosis and "necrotic cell death" through various mechanisms, while ROS could have inhibitory or stimulatory roles in NF-kappaB signaling.

Aging-related atherosclerosis is exacerbated by arterial expression of tumor necrosis factor receptor-1: evidence from mouse models and human association studies

Aging is believed to be among the most important contributors to atherosclerosis, through mechanisms that remain largely obscure. Serum levels of tumor necrosis factor (TNF) rise with aging and have been correlated with the incidence of myocardial infarction. We therefore sought to determine whether genetic variation in the TNF receptor-1 gene (TNFR1) contributes to aging-related atherosclerosis in humans and whether Tnfr1 expression aggravates aging-related atherosclerosis in mice. With 1330 subjects from a coronary angiography database, we performed a case-control association study of coronary artery disease (CAD) with 16 TNFR1 single-nucleotide polymorphisms (SNPs). Two TNFR1 SNPs significantly associated with CAD in subjects >55 years old, and this association was supported by analysis of a set of 759 independent CAD cases. In multiple linear regression analysis, accounting for TNFR1 SNP rs4149573 significantly altered the relationship between aging and CAD index among 1811 subjects from the coronary angiography database. To confirm that TNFR1 contributes to aging-dependent atherosclerosis, we grafted carotid arteries from 18- and 2-month-old wild-type (WT) and Tnfr1(-/-) mice into congenic apolipoprotein E-deficient (Apoe(-/-)) mice and harvested grafts from 1 to 7 weeks post-operatively. Aged WT arteries developed accelerated atherosclerosis associated with enhanced TNFR1 expression, enhanced macrophage recruitment, reduced smooth muscle cell proliferation and collagen content, augmented apoptosis and plaque hemorrhage. In contrast, aged Tnfr1(-/-) arteries developed atherosclerosis that was indistinguishable from that in young Tnfr1(-/-) arteries and significantly less than that observed in aged WT arteries. We conclude that TNFR1 polymorphisms associate with aging-related CAD in humans, and TNFR1 contributes to aging-dependent atherosclerosis in mice.

Links between innate immunity and normal tissue radiobiology

The body senses "danger" from "damaged self" molecules through members of the same receptor superfamily it uses for microbial "non-self", triggering canonical signaling pathways that lead to the generation of acute inflammatory responses. For this reason, the biology of normal tissue responses to moderate and clinically relevant doses of radiation is inextricably connected to innate immunity. The complex sequence of inflammatory events that ensues causes further cell and tissue damage to eliminate potential invaders but also leads to cytoprotective responses that limit the spread of damage and to wound healing through tissue regeneration or replacement. These sequential processes are orchestrated through multiple feedback control mechanisms involving cyclical production of free radicals and cytokines that are common to both radiation and immune signaling. This requires a concerted effort by resident tissue and inflammatory cell types, with macrophages apparently leading the way. The initial response to moderate doses of radiation therefore feeds into a pro-inflammatory paradigm whose eventual outcome is critically dependent upon the properties of the immune cells that are involved in tissue damage, regeneration and repair and that are in part under genetic influence. Importantly, these canonical pathways provide targets for interventions aimed at modifying normal tissue radiation responses. In this review, we examine areas of intersection between innate immunity and normal tissue radiobiology.

Minireview: Won't get fooled again: the nonmetabolic roles of peroxisome proliferator-activated receptors (PPARs) in the heart

The peroxisome proliferator-activated receptor (PPAR) transcription factors are nuclear receptors initially identified for their key role in regulating metabolic processes. Recent studies designed to identify the role of PPARalpha, -beta, and -gamma in vivo uncovered extrametabolic roles that may be less well known in the heart. In this review, we describe what is known about these extrametabolic roles of PPARs, including regulation of cardiac inflammation, extracellular matrix remodeling, oxidative stress, and regulation of cardiac hypertrophy. Lastly, we discuss the emerging role of PPARs in cell cycle regulation and angiogenesis in noncardiac systems that may be applicable to heart biology. Although this review primarily discusses the extrametabolic role of PPARalpha, the most studied PPAR isoform in the heart, we highlight where possible what is known about the unique and overlapping roles of the PPAR isoforms in terms of metabolic function.

Electrophysiology of reactive oxygen production in signaling endosomes

Endosome trafficking and function require acidification by the vacuolar ATPase (V-ATPase). Electrogenic proton (H+) transport reduces the pH and creates a net positive charge in the endosomal lumen. Concomitant chloride (Cl-) influx has been proposed to occur via ClC Cl-=H+ exchangers. This maintains charge balance and drives Cl- accumulation, which may itself be critical to endosome function. Production of reactive oxygen species (ROS) in response to cytokines occurs within specialized endosomes that form in response to receptor occupation. ROS production requires an NADPH oxidase (Nox) and the ClC-3 Cl-=H+ exchanger. Like the V-ATPase, Nox activity is highly electrogenic, but separates charge with an opposite polarity (lumen negative). Here we review established paradigms of early endosomal ion transport focusing on the relation between the V-ATPase and ClC proteins. Electrophysiologic constraints on Nox-mediated vesicular ROS production are then considered. The potential for ClC-3 to participate in charge neutralization of both proton (V-ATPase) and electron (Nox) transport is discussed. It is proposed that uncompensated charge separation generated by Nox enzymatic activity could be used to drive secondary transport into negatively charged vesicles. Further experimentation will be necessary to establish firmly the biochemistry and functional implications of endosomal ROS production.