Down-regulated expression of TWEAK mRNA in acute and chronic inflammatory pathologies

TWEAK/Fn14 signalling driven super-enhancer reprogramming promotes pro-metastatic metabolic rewiring in triple-negative breast cancer

Triple Negative Breast Cancer (TNBC) is the most aggressive breast cancer subtype suffering from limited targeted treatment options. Following recent reports correlating Fibroblast growth factor-inducible 14 (Fn14) receptor overexpression in Estrogen Receptor (ER)-negative breast cancers with metastatic events, we show that Fn14 is specifically overexpressed in TNBC patients and associated with poor survival. We demonstrate that constitutive Fn14 signalling rewires the transcriptomic and epigenomic landscape of TNBC, leading to enhanced tumour growth and metastasis. We further illustrate that such mechanisms activate TNBC-specific super enhancers (SE) to drive the transcriptional activation of cancer dependency genes via chromatin looping. In particular, we uncover the SE-driven upregulation of Nicotinamide phosphoribosyltransferase (NAMPT), which promotes NAD+ and ATP metabolic reprogramming critical for filopodia formation and metastasis. Collectively, our study details the complex mechanistic link between TWEAK/Fn14 signalling and TNBC metastasis, which reveals several vulnerabilities which could be pursued for the targeted treatment of TNBC patients.

Status of TWEAK DNA methylation and mRNA expression in systemic lupus erythematosus

OBJECTIVE

Draw upon research into the serum concentration, mRNA expression, and DNA methylation of TNF-like weak inducer of apoptosis (TWEAK) in the peripheral blood of systemic lupus erythematosus patients and healthy controls in an attempt to investigate the epigenetics associated with TWEAK in the pathogenesis of systemic lupus erythematosus (SLE).

METHODS

A total of 178 SLE patients (SLE group) and 131 sex-age matched healthy controls (HC group) were recruited. Enzyme-linked immunosorbent assays (ELISA) was used to detect serum protein concentration of TWEAK. TWEAK mRNA expression was analyzed by Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Methylation levels of the promotor of TWEAK were measured using quantitative DNA methylation analysis on the MassARRAY spectrometry.

RESULTS

Serum TWEAK concentrations were not statistically significant in SLE patients and HCs. Nevertheless, serum TWEAK concentrations were significantly lower in patients with renal involvement when compared to those without it. Serum TWEAK concentrations were reduced in clinically active patients (SLEDAI ≥ 10) compared with clinically stable patients (SLEDAI < 10). It was also significantly associated with SLEDAI. Compared with the HC group, the TWEAK mRNA expression in the SLE group was significantly lower. The global DNA methylation levels of TWEAK in the SLE group were observed to be significantly higher than the HC group. SLE patients with renal involvement, and the clinically active patients had higher TWEAK global methylation as well as exhibited variation in certain CpG island methylation. Furthermore, TWEAK methylation negatively correlated with TWEAK mRNA expression.

CONCLUSION

This study suggests that TWEAK DNA methylation is a valuable as a focus for epigenetic studies because of it potentially influencing TWEAK gene expression in SLE patients. Aberrant DNA methylation of TWEAK may be involved in the initiation and development of SLE.

A potential fate decision landscape of the TWEAK/Fn14 axis on stem and progenitor cells: a systematic review

Stem and progenitor cells (SPCs) possess self-remodeling ability and differentiation potential and are responsible for the regeneration and development of organs and tissue systems. However, the precise mechanisms underlying the regulation of SPC biology remain unclear. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) acts on miscellaneous cells via binding to fibroblast growth factor-inducible 14 (Fn14) and exerts pleiotropic functions in the regulation of divergent stem cell fates. TWEAK/Fn14 signaling can regulate the proliferation, differentiation, and migration of multiple SPCs as well as tumorigenesis in certain contexts. Although TWEAK’s roles in modulating multiple SPCs are sparsely reported, the systemic effector functions of this multifaceted protein have not been fully elucidated. In this review, we summarized the fate decisions of TWEAK/Fn14 signaling on multiple stem cells and characterized its potential in stem cell therapy.

The TWEAK/Fn14/CD163 axis-implications for metabolic disease

TWEAK (tumor necrosis factor-like weak inducer of apoptosis) is a member of the TNF superfamily that controls a multitude of cellular events including proliferation, migration, differentiation, apoptosis, angiogenesis, and inflammation. TWEAK control of these events is via an expanding list of intracellular signalling pathways which include NF-κB, ERK/MAPK, Notch, EGFR and AP-1. Two receptors have been identified for TWEAK - Fn14, which targets the membrane bound form of TWEAK, and CD163, which scavenges the soluble form of TWEAK. TWEAK appears to elicit specific events based on the receptor to which it binds, tissue type in which it is expressed, specific extrinsic conditions, and the presence of other cytokines. TWEAK signalling is protective in healthy tissues, but in chronic inflammatory states become detrimental to the tissue. Consistent data show a role for the TWEAK/FN14/CD163 axis in metabolic disease, chronic autoimmune diseases, and acute ischaemic stroke. Low circulating concentrations of soluble TWEAK are predictive of poor cardiovascular outcomes in those with and without diabetes. This review details the current understanding of the TWEAK/Fn14/CD163 axis as one of the chief regulators of immune signalling and its cell-specific role in metabolic disease development and progression.

Pro-Inflammatory and B Cell Regulating Capacities of TWEAK in Rainbow Trout (Oncorhynchus mykiss)

Tumor necrosis factor (TNF)-like weak inducer of apoptosis or TWEAK is a member of the TNF superfamily involved in the regulation of many biological processes. In mammals, TWEAK has been shown to play a role in some autoimmune or inflammatory conditions, but its immune role is not yet clearly defined. In teleost fish, although a few studies have identified homologues to mammalian TWEAK, their biological effects have never been investigated. In the current study, we have studied the transcriptional regulation of two TWEAK homologues (TWEAK 1 and 2) identified in rainbow trout (Oncorhynchus mykiss) throughout different tissues, in response to parasitic or viral infections, or in head kidney (HK) leukocytes stimulated with different stimuli. Although the transcription of both homologues was modulated when HK leukocytes were exposed to several immune stimuli, only TWEAK 1 was significantly modulated upon pathogenic exposure. Thus, we performed a characterization of the functions exerted by this cytokine in HK leukocytes. Recombinant TWEAK 1 strongly up-regulated the transcription of pro-inflammatory genes and antimicrobial peptides in HK leukocytes, with differential transcriptional effects in IgM⁺ B cells, IgM^- lymphocytes and myeloid cells. TWEAK 1 also increased the survival and promoted the differentiation of B cells in HK leukocyte cultures. Our results demonstrate that in teleost fish, TWEAK 1 is involved in the response to different types of pathogens, through the modulation of antimicrobial and pro-inflammatory genes in different leukocytes subsets. Furthermore, a role for TWEAK as a B cell differentiation factor has also been established in rainbow trout.

TWEAK/Fn14 axis in respiratory diseases

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a well known multifunctional cytokine extensively distributed in cell types and tissues. Accumulating evidence has shown that TWEAK binding to the receptor factor-inducible 14 (Fn14) participates in diverse pathologic processes including cell proliferation and death, angiogenesis, carcinogenesis and inflammation. Interestingly, alterations of intracellular signaling cascades are correlated to the development of respiratory disease. Recently, a several lines of evidence suggests that TWEAK in lung tissues are closely associated with these signaling pathways. In this review, we explore if TWEAK could provide a novel therapeutic strategy for managing respiratory disease in general and pulmonary arterial hypertension (PAH), obstructive sleep apnea syndrome (OSAS), asthma, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and non-small cell lung cancer (NSCLC), specifically.

Inverse Relationship between Plasma Tumor Necrosis Factor-Like Weak Inducer of Apoptosis and Carotid Intima-Media Thickness among Patients Undergoing Hemodialysis and Peritoneal Dialysis

BACKGROUND/AIMS

This study aimed to investigate the level of soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) and its correlation with micro-inflammation and atherosclerosis in continuous ambulatory peritoneal dialysis (PD) patients.

METHODS

This retrospective study involved 23 healthy subjects (control group), 23 hemodialysis (HD) patients (HD group) and 26 PD patients (PD group). Serum biochemical measurements and sTWEAK assessments were tested. The association between intima-media thickness (IMT) and sTWEAK concentrations was evaluated.

RESULTS

The TWEAK level was lower in PD (155.16 ± 3.69 pg/mL, p < 0.001) and the HD group (150.16 ± 7.23 pg/mL, p < 0.001) than that in the control group (193.05 ± 5.36 pg/mL), with no significant difference between the PD group and the HD group. In the PD and HD groups, sTWEAK was significant negatively correlated with CPR, fibrinogen, and white blood cell (p < 0.05). Besides, compared to lower sTWEAK concentration end-stage renal disease (ESRD) patients (no >161.9 pg/mL), patients who had a higher level of sTWEAK (>161.9 pg/mL) had a lower IMT (0.97 ± 0.04 vs. 0.84 ± 0.03 cm, p = 0.029). After adjusted for sex, age, hypertension, diabetes, duration of dialysis, triglyceride, total cholesterol, low-density lipoprotein, and serum glucose, sTWEAK (B = -0.002, r = 0.015) and CRP (B = 0.022, r = 0.015) were independent risk factors for the IMT of ESRD patients.

CONCLUSION

Plasma TWEAK is inversely associated with carotid IMT among patients undergoing HD and PD.

Increased Serum Concentrations of TNF-Like Weak Inducer of Apoptosis Predict Higher 28-Day Mortality in Patients with Sepsis

We performed the current study to explore potential predictive value of serum Tumor Necrosis Factor- (TNF-) like weak inducer of apoptosis (TWEAK) concentrations for 28-day mortality in patients with sepsis. Adult septic patients (age≥18 years) admitted to a general ICU between November 2016 and October 2017 were consecutively included in our prospective observational study. TWEAK concentrations were detected in septic patients and healthy controls. Dynamic changes of TWEAK concentrations between 1st day and 3rd day of admission to ICU (ΔTWEAK concentrations) were also measured. A total of 79 septic patients were included and 19 of them (24.1%) died after a follow-up period of 28 days. We identified arterial lactate, NT-proBNP, and male gender as independent factors for 28-day mortality of patients with sepsis. The serum levels of TWEAK were significantly lower in septic patients compared to controls (417.4 ± 196.7 pg/ml versus 1243.8 ± 174.3 pg/ml, p<0.001). We found a positive correlation between TWEAK concentrations and SOFA score (Spearman correlation coefficient 0.235, p=0.037). Area under the receiver operating characteristic curve (AUROC) of ΔTWEAK concentrations for 28-day mortality was 0.754 (95% CI 0.645-0.844). We also evaluated the diagnostic performance of combinative index (ΔTWEAK concentrations and lactate) and obtained an AUROC of 0.860 (95% CI 0.763-0.928). In conclusion, our study found lower TWEAK concentrations in septic patients than those in healthy controls. Furthermore, the increased TWEAK concentrations during disease process predict higher 28-day mortality in septic patients. Dynamic changes of TWEAK should be an important supplement for current prognostic markers.

Soluble TWEAK may predict carotid atherosclerosis in treated HIV infection

BACKGROUND

Soluble Tumor Necrosis Factor Weak Inducer of Apoptosis (sTWEAK) has been proposed as a novel biomarker of cardiovascular disease risk. This study compares levels of sTWEAK, sCD163 and the sCD163/sTWEAK ratio in HIV-infected and uninfected patients and their associations with cardiovascular and inflammatory factors.

METHODS

The data for our analysis come from 274 HIV-infected adults and 59 controls. HIV participants were on stable antiretroviral therapy (ART). Wilcoxon-Mann-Whitney tests were used for comparing markers between HIV-infected participants with HIV viral load <50 copies/mL (aviremic group), HIV-infected participants with detectable viremia (HIV-1 RNA ≥50 copies/mL; viremic group) and HIV negative participants. Multivariable quantile regression analyses were used to assess associations of sTWEAK and sCD163 with other markers of inflammation and carotid intima-media thickness (cIMT).

RESULTS

Overall, 74% of participants were male; 59% were African-Americans; median age was 40 years and CD4 595 cells/mm3. Overall, HIV-infected participants had reduced sTWEAK and increased sCD163 levels compared to HIV-uninfected participants (p = 0.0001 for both markers). In addition, these biomarkers were significantly different between HIV-infected viremic and aviremic patients (p ≤ 0.01 for both markers). In multivariable models, sTWEAK and sCD163 in aviremic patients were significantly correlated with common carotid artery IMT (p ≤ 0.05). In HIV-infected aviremic participants, sTWEAK and sCD163 were both associated with IL-6, CD14 + CD16 + monocytes (p ≤ 0.02); additionally, sCD163 was associated with D-dimer- (β = -69.5, 0.05), VCAM (β = 72.4, p = 0.05), TNF RI (β = 91.1, p < 0.01), and TNF RII (β = 87.8, p < 0.01).

CONCLUSIONS

HIV-infected participants showed increased systemic inflammatory and monocyte activation markers. Soluble CD163 and sTWEAK levels were associated with carotid intima-media thickness.

Lipopolysaccharide Upregulated Intestinal Epithelial Cell Expression of Fn14 and Activation of Fn14 Signaling Amplify Intestinal TLR4-Mediated Inflammation

TLR4 in intestinal epithelial cells has been shown both inflammatory and homeostatic roles following binding of its cognate ligand lipopolysaccharide (LPS). TWEAK-Fn14 axis plays an important role in pathologies caused by excessive or abnormal inflammatory responses. This study aimed to evaluate potential cross-talk between TLR4 and TWEAK/Fn14 system in porcine small intestinal epithelial cells. Our in vivo results showed that, compared with the age-matched normal control piglets, increased expression of Fn14 in epithelium and decreased TWEAK expression in lamina propria were detected in the small intestinal of piglets stimulated with LPS. Consistent with this finding, treatment with LPS increased the expression of Fn14 and TLR4 while decreased TWEAK expression in porcine small intestinal epithelial cell lines SIEC02. Interestingly, modulating Fn14 activation using agonistic anti-Fn14 decreased TLR4-mediated TNF-α production by SIEC02. In addition, pretreatment of LPS-stimulated SIEC02 with recombinant TWEAK protein suppresses the expression of Fn14 and TNF-α and inhibits the negative impact of LPS on the tight junctional protein occludin expression. In conclusion, this study demonstrates that the TWEAK-independent Fn14 activation augments TLR4-mediated inflammatory responses in the intestine of piglets. Furthermore, the TWEAK-dependent suppression of Fn14 signaling may play a role in intestinal homeostasis.

Acute dietary fat intake initiates alterations in energy metabolism and insulin resistance

BACKGROUND

Dietary intake of saturated fat is a likely contributor to nonalcoholic fatty liver disease (NAFLD) and insulin resistance, but the mechanisms that initiate these abnormalities in humans remain unclear. We examined the effects of a single oral saturated fat load on insulin sensitivity, hepatic glucose metabolism, and lipid metabolism in humans. Similarly, initiating mechanisms were examined after an equivalent challenge in mice.

METHODS

Fourteen lean, healthy individuals randomly received either palm oil (PO) or vehicle (VCL). Hepatic metabolism was analyzed using in vivo 13C/31P/1H and ex vivo 2H magnetic resonance spectroscopy before and during hyperinsulinemic-euglycemic clamps with isotope dilution. Mice underwent identical clamp procedures and hepatic transcriptome analyses.

RESULTS

PO administration decreased whole-body, hepatic, and adipose tissue insulin sensitivity by 25%, 15%, and 34%, respectively. Hepatic triglyceride and ATP content rose by 35% and 16%, respectively. Hepatic gluconeogenesis increased by 70%, and net glycogenolysis declined by 20%. Mouse transcriptomics revealed that PO differentially regulates predicted upstream regulators and pathways, including LPS, members of the TLR and PPAR families, NF-κB, and TNF-related weak inducer of apoptosis (TWEAK).

CONCLUSION

Saturated fat ingestion rapidly increases hepatic lipid storage, energy metabolism, and insulin resistance. This is accompanied by regulation of hepatic gene expression and signaling that may contribute to development of NAFLD.REGISTRATION. ClinicalTrials.gov NCT01736202.

FUNDING

Germany: Ministry of Innovation, Science, and Research North Rhine-Westfalia, German Federal Ministry of Health, Federal Ministry of Education and Research, German Center for Diabetes Research, German Research Foundation, and German Diabetes Association. Portugal: Portuguese Foundation for Science and Technology, FEDER - European Regional Development Fund, Portuguese Foundation for Science and Technology, and Rede Nacional de Ressonância Magnética Nuclear.

Estrogen-induced expression of tumor necrosis factor-like weak inducer of apoptosis through ERα accelerates the progression of lupus nephritis

OBJECTIVES

Oestrogens have been shown to play key roles in the pathogenesis of SLE. The aim of this study was to investigate the roles and mechanisms of 17β-estradiol (E2) in TNF-like weak inducer of apoptosis (TWEAK) expression in LN.

METHODS

Peripheral blood mononuclear cells (PBMCs) obtained from LN patients were used for in vitro experiments, while female MRL/lpr and MRL/MpJ mice were used for in vivo studies. E2, ICI 182 780 [estrogen receptor (ER)-selective antagonist], methyl-piperidino-pyrazole (MPP, ERα-selective modulator), lentivirus (LV)-TWEAK-short hairpin RNA (shRNA) and LV-control-shRNA treatments were used in this study.

RESULTS

TWEAK mRNA expression in PBMCs was significantly increased following E2 treatment and downregulated after incubation with ICI 182 780 or MPP. Compared with sham-operated MRL/lpr mice, ovariectomized mice, treated with dimethyl sulphoxide vehicle alone, showed lower expression levels of renal TWEAK mRNA and protein. The expression of both mRNA and protein in ovariectomized mice was upregulated after E2 treatment and downregulated after ICI 182 780 or MPP co-treatment. Severe renal damage was observed in E2-treated ovariectomized mice, as were higher serum levels of IL-6, compared with dimethyl sulphoxide vehicle-treated ovariectomized mice. Co-treatment with LV-TWEAK-shRNA reversed these changes, and LV-control-shRNA treatment had no effect on them.

CONCLUSION

Our results demonstrated that E2 plays an important role in the upregulation of TWEAK expression in LN, most likely through an ERα-dependent pathway, causing kidney damage. This provides a novel insight into the mechanisms of the E2-TWEAK signalling pathway in LN.

Serum Levels of TNF Receptor Ligands Are Dysregulated in Sepsis and Predict Mortality in Critically Ill Patients

Introduction

TNF superfamily members, including TNF-related weak inducer of apoptosis (TWEAK) and Glucocorticoid-Induced TNFR-Related Protein Ligand (GITRL) have been described as serum based biomarkers for inflammatory and immune mediated diseases. However, up to now the role of TWEAK and GITRL has not been analyzed in critical illness and sepsis.

Methods

GITRL and TWEAK serum concentrations were measured in 121 critically ill patients (84 fulfilled with septic disease), in comparison to 50 healthy controls. Results were correlated with clinical data.

Results

Serum levels of TWEAK and GITRL were strongly decreased in critically ill patients compared with healthy controls. Concentrations of TWEAK (but not GITRL) were further decreased in patients with sepsis and correlated with routinely used markers of inflammation and bacterial infection such as C-reactive protein, procalcitonin and Interleukin-6. Notably, we failed to detect a correlation to other TNFR ligands such as TNF or APRIL. Finally, TWEAK levels of the upper quartile of the cohort were prognostic for mortality during ICU treatment.

Conclusion

TWEAK and GITRL levels were lower in intensive care unit medical patients. Levels of TWEAK were further decreased in septic patients, and alterations in TWEAK concentrations were linked to an unfavorable outcome. Together with recently published results on other TNFR ligands, these data indicate specific functions of the different TNFR ligands in septic diseases.

TWEAK-Fn14 Cytokine-Receptor Axis: A New Player of Myocardial Remodeling and Cardiac Failure

Tumor necrosis factor (TNF) has been firmly established as a pathogenic factor in heart failure, a significant socio-economic burden. In this review, we will explore the role of other members of the TNF/TNF receptor superfamily (TNFSF/TNFRSF) in cardiovascular diseases (CVDs) focusing on TWEAK and its receptor Fn14, new players in myocardial remodeling and heart failure. The TWEAK/Fn14 pathway controls a variety of cellular activities such as proliferation, differentiation, and apoptosis and has diverse biological functions in pathological mechanisms like inflammation and fibrosis that are associated with CVDs. Furthermore, it has recently been shown that the TWEAK/Fn14 axis is a positive regulator of cardiac hypertrophy and that deletion of Fn14 receptor protects from right heart fibrosis and dysfunction. We discuss the potential use of the TWEAK/Fn14 axis as biomarker for CVDs as well as therapeutic target for future treatment of human heart failure based on supporting data from animal models and in vitro studies. Collectively, existing data strongly suggest the TWEAK/Fn14 axis as a potential new therapeutic target for achieving cardiac protection in patients with CVDs.

Expression of tumor necrosis factor-like weak inducer of apoptosis in human middle ear cholesteatoma

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) was recently identified as a member of the TNF superfamily of structurally related cytokines. It regulates TNF-α and numerous cellular responses. We investigated whether TWEAK is upregulated in human middle ear cholesteatoma compared to the skin of the normal external auditory canal (EAC). The expression of TWEAK was analyzed using reverse transcription-polymerase chain reaction, Western blotting and immunohistochemical staining. TWEAK expression was correlated with that of TNF-α as determined by Western blotting. The expression of TWEAK and TNF-α protein was stronger in cholesteatoma tissue than in EAC skin. TWEAK was expressed to a greater degree in the suprabasal layer in the cholesteatoma than in EAC skin. The expression of TWEAK was correlated more closely with single-stranded DNA than Ki-67 immunohistochemically. These findings imply that TWEAK plays an important role in modulating TNF-α expression and apoptosis in cholesteatoma.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) mediates p38 mitogen-activated protein kinase activation and signal transduction in peripheral blood mononuclear cells from patients with lupus nephritis

Forty-two patients with systemic lupus erythematosus (SLE), including 26 patients with renal damage and 16 without, and 20 healthy controls were included in the study. The isolated peripheral blood mononuclear cells (PBMCs) were treated with a p38 inhibitor (SB203580) or anti-tumor necrosis factor-like weak inducer of apoptosis (TWEAK) mAb, with or without phytohemagglutinin/phorbol myristate acetate (PHA/PMA) stimulation. Western blot experiments were used to evaluate the protein expression of TWEAK and p38 MAPK in PBMCs .Next, the contents of interleukin-10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) in the supernatant were measured by ELISA. The results showed that expression of TWEAK protein in PBMCs from lupus nephritis patients was significantly higher than that from SLE patients without renal damage and healthy controls. PHA/PMA simulation could upregulate the productions of TWEAK and p-p38MAPK in PBMCs from patients with SLE. Anti-TWEAK mAb treatment downregulated both TWEAK and p-p38 MAPK expression in PBMCs, as well as IL-10 and MCP-1 in the supernatant; SB203580 had the same effect on cytokine production in PBMC, but had no effect on the expression of TWEAK. Our results suggested that TWEAK-p38 MAPK-IL-10, MCP-1 signaling pathway in PBMC played an important pathogenic role in lupus nephritis.

Tumor necrosis factor-like weak inducer of apoptosis and its potential roles in lupus nephritis

INTRODUCTION

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a recently identified proinflammatory cytokine of the TNF superfamily that functions through binding to Fn14 receptor in target cells. TWEAK has multiple biological activities. Studies show that TWEAK plays an important role in immune inflammatory diseases. Recent work has revealed that TWEAK may play an important role in the pathogenesis of kidney damage, including in systemic lupus erythematosus (SLE), where its concentration in urine was correlated with the level of activity of lupus nephritis (LN).

OBJECTIVE

The major focus of this review is to discuss the recent studies on TWEAK and its possible role in the pathogenesis of LN, and the therapeutic potential of modulating this pathway in LN.

RESULTS AND CONCLUSION

TWEAK plays a key role in the pathogenesis of LN through activation of multiple down-signaling pathway, inducing proinflammatory cytokines and chemokines, affecting cell proliferation/apoptosis and inducing renal IgG deposition. TWEAK blockade may be a novel therapeutic approach to reducing renal damage in SLE.

TWEAK/Fn14 pathway: an immunological switch for shaping tissue responses

Our immune system performs the vital function of recognizing and eliminating invading pathogens and malignancies. There is an increasing appreciation that the immune system also actively mediates tissue responses under both physiological and pathological conditions, significantly impacting the inflammatory, fibrogenic, and regenerative components. Likewise, there is a growing understanding of how epithelial, endothelial, and other non-hematopoietic tissue cell types actively contribute to the interplay that shapes tissue responses. While much of the molecular basis underlying the immune regulation of tissue responses remains to be delineated, the tumor necrosis factor (TNF) superfamily ligand/receptor pair of TNF-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor-inducible molecule 14 (Fn14) has now emerged as a key piece of this puzzle. In this review, we first discuss how the usually 'dormant' TWEAK/Fn14 pathway becomes activated specifically in injury and disease contexts. We then summarize how TWEAK-mediated Fn14 signaling triggers a wide range of activities in tissue parenchymal and stromal cells as well as progenitor cells. Finally, we review recent experimental evidence that further supports the functional dichotomy of TWEAK/Fn14 activation in physiological versus pathological tissue responses and its potential therapeutic implications. Whereas transient TWEAK/Fn14 activation promotes productive tissue responses after injury, excessive or persistent TWEAK/Fn14 activation drives pathological tissue responses, leading to progressive damage and degeneration.

Expression of human tumor necrosis factor-like weak inducer of apoptosis in patients with systemic lupus erythematosus

The aim of this study was to compare the mRNA and serum expression of tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) in patients with systemic lupus erythematosus (SLE) and healthy controls. Sixty-two SLE patients and 15 healthy controls were recruited in the study. TWEAK messenger RNA (mRNA) expression in peripheral blood mononuclear cells (PBMCs) from 33 of 62 patients was detected by relative quantification RT-PCR. TWEAK concentrations in the sera of all 62 patients were measured by ELISA. TWEAK mRNA expressions in PBMCs were decreased in SLE patients compared with healthy controls. Lower TWEAK mRNA expression was also found in the active SLE patients when compared to inactive ones. However, there was no significant difference between patients with lupus nephritis (LN) and those without. The level of serum TWEAK (sTWEAK) in SLE patients was increased when compared to healthy controls. In addition, the sTWEAK level was higher in SLE patients with vasculitis than those without vasculitis, and so was in comparison between patients with and without headache. Nevertheless, no significant differences were found between active SLE patients and inactive patients, or between LN patients and non-LN SLE patients. In this study, patients with SLE express low levels of TWEAK mRNA but high levels of sTWEAK. Additionally, sTWEAK level was associated with several clinical manifestations of SLE, indicating that TWEAK may play a complex role in SLE.

Expression of TWEAK in normal human skin, dermatitis and epidermal neoplasms: association with proliferation and differentiation of keratinocytes

BACKGROUND

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) has been implicated in the pathogenesis of various inflammatory pathologies and cancer. We aimed to investigate its expression in normal human skin, inflammatory skin diseases and epidermal neoplasms.

METHODS

Immunohistochemistry for TWEAK was performed in samples of healthy skin, plaque psoriasis, lichen planus, prurigo nodularis, discoid lupus erythematosus, lichen sclerosus, seborrheic keratosis, common warts, actinic keratosis, Bowen's disease, keratoacanthoma and basal and squamous cell carcinoma. Double immunofluorescence was used to investigate co-localization of TWEAK with cytokeratin-10 and proliferating cell nuclear antigen (PCNA).

RESULTS

TWEAK was robustly expressed in the epidermis of healthy skin and decreased in inflammatory conditions, both in the context of epidermal hyperplasia and atrophy. Decreased TWEAK immunoreactivity was regularly observed in common warts, actinic keratosis and Bowen's disease, particularly in areas of marked proliferation as evidenced by PCNA-positive nuclei. In squamous cell carcinoma, expression of TWEAK ranged from strong to completely absent, and it mostly corresponded with the expression of cytokeratin-10. TWEAK was absent in keratoacanthoma and basal cell carcinoma.

CONCLUSIONS

TWEAK is a constitutively expressed epidermal protein whose downregulation might be an early indicator of disturbed differentiation or pathologic proliferation of keratinocytes that accompany inflammatory and neoplastic skin diseases.

TWEAK, a multifunctional cytokine in kidney injury

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a cytokine of the TNF superfamily that activates the Fn14 receptor. TWEAK may regulate cell proliferation, cell death, cell differentiation, and inflammation. TWEAK and Fn14 are constitutively present in the kidney. Sources of TWEAK and Fn14 include intrinsic renal cells and infiltrating leukocytes. Basal Fn14 expression is low, but Fn14 is greatly upregulated during kidney injury. TWEAK contributes to kidney inflammation promoting chemokine secretion by renal cells through canonical and non-canonical NFκB activation. TWEAK also promotes tubular cell proliferation. However, TWEAK induces mesangial and tubular cell apoptosis under proinflammatory conditions. These data indicate that TWEAK is a multifunctional cytokine in the kidney, the actions of which are modulated by the cell microenvironment. Confirmation of the role of TWEAK in kidney injury came from functional studies in experimental animal models. The TWEAK/Fn14 pathway contributed to cell death and interstitial inflammation during acute kidney injury, to glomerular injury in lupus nephritis, to hyperlipidemia-associated kidney injury, and to tubular cell hyperplasia following unilateral nephrectomy. Circulating soluble TWEAK (sTWEAK) levels are a potential biomarker of adverse outcomes in chronic kidney disease and urinary sTWEAK is a potential biomarker of lupus nephritis activity. The available evidence suggests that TWEAK may provide diagnostic information and be a therapeutic target in renal injury. Its role in human kidney disease should be further explored.

Decreased soluble TWEAK levels predict an adverse prognosis in patients with chronic stable heart failure

AIMS

Tumour necrosis factor (TNF)-like weak inducer of apoptosis (sTWEAK) is a multifunctional cytokine that has recently been implicated in cardiovascular disease. The aim of this study was to define the plasma levels of sTWEAK in patients with stable chronic heart failure and evaluate the possibility of a prognostic impact of sTWEAK.

METHODS AND RESULTS

sTWEAK levels in plasma samples from 364 patients with systolic heart failure were compared with 36 control patients. The median levels of sTWEAK in heart failure patients were significantly lower than those of the control group (217 pg/mL, interquartile range 136-311 vs. 325 pg/mL, interquartile range 250-394 pg/mL). Moreover, sTWEAK levels were lower in patients with ischaemic cardiomyopathy vs. dilated cardiomyopathy and correlated significantly with functional NYHA class. Patients with plasma levels below a ROC-derived cut-off value of 227 pg/mL had a significantly higher mortality rate after 4 years. Upon univariate and multivariate analyses, sTWEAK levels below 227 pg/mL emerged as an independent predictor of subsequent death.

CONCLUSION

In contrast to other cytokines shown to be increased in heart failure patients, plasma levels of sTWEAK are significantly reduced in chronic stable heart failure. In addition, lower plasma levels of sTWEAK predict an adverse prognosis independent of established risk markers such as NT-proBNP.

Circulating sTWEAK improves the prediction of coronary artery disease

OBJECTIVES

Decreased concentrations of circulating soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) were recently reported to be associated with atherosclerosis, but there are still no data concerning its predictive performance.

DESIGN AND METHODS

The current cross-sectional study investigates the potential of the novel atherosclerotic biomarker for the prediction of coronary artery disease (CAD). Serum sTWEAK was measured by ELISA in 76 CAD patients and 82 CAD-free subjects.

RESULTS

Serum sTWEAK concentrations were significantly lower in the patients (534.5+/-110.9 microg/L) than in the controls (688.1+/-150.0 microg/L, p<0.001), even after adjusting for different confounders (p<0.001). The areas under ROC curves (AUC)s calculated for logistic regression models that included different known risk factors were significantly increased when sTWEAK was added to the corresponding model (p=0.011-0.035).

CONCLUSIONS

The measurement of serum sTWEAK concentrations improves the prediction of CAD based on existing biomarkers.

Use of serum biomarkers in a diagnostic test for irritable bowel syndrome

BACKGROUND

Currently, no single serum biomarker can reliably differentiate irritable bowel syndrome (IBS) from other functional gastrointestinal disorders or organic diseases of the gastrointestinal tract.

AIM

To develop and validate a diagnostic test using serum biomarkers to detect IBS.

METHODS

Ten serum biomarkers were selected from a potential panel of 140 for their ability to differentiate IBS from non-IBS disease in blood samples from patients with IBS, other gastrointestinal disorders and healthy volunteers. A predictive modelling tool was developed to assess patterns and relationships among the 10 serum biomarkers that best differentiated IBS patients from healthy controls and patients with non-IBS gastrointestinal disease. This model was tested in a different cohort of patients and healthy controls (n = 516) to determine the predictive accuracy of differentiating IBS from non-IBS.

RESULTS

The sensitivity and specificity of the 10-biomarker algorithm for differentiating IBS from non-IBS was 50% and 88% respectively. The positive predictive value was 81%, and the negative predictive value was 64% at 50% IBS prevalence in the validation cohort. Overall accuracy was 70%.

CONCLUSIONS

Assessing serum biomarker patterns can differentiate IBS from non-IBS with reasonable sensitivity and specificity. Assessing serum biomarkers in an overall diagnostic strategy may allow earlier diagnosis and treatment for patients with IBS.

Additive effects of soluble TWEAK and inflammation on mortality in hemodialysis patients

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) is characterized by an exceptionally high mortality rate, primarily due to cardiovascular disease. Reduced soluble TNF-like weak inducer of apoptosis (sTWEAK) plasma levels have been reported both in patients with subclinical atherosclerosis and CKD.

DESIGN, PARTICIPANTS, & MEASUREMENTS

A cross-sectional study was conducted in 218 prevalent patients (121 men; 63 +/- 14 yr) undergoing hemodialysis (HD). sTWEAK levels in relation with the patients' outcome were studied.

RESULTS

sTWEAK plasma levels were 208 [(165 to 272) pg/ml, median interquartile range], significantly lower than healthy controls (P < 0.0001). sTWEAK was negatively associated with inflammatory markers, such as C-reactive protein and IL-6. Overall mortality was assessed after an average follow-up of 31 mo, during which 81 patients died. After controlling for potential confounding variables, patients in the upper tertile of sTWEAK plasma levels had an increased risk of cardiovascular and all-cause mortality. A significant interaction effect between sTWEAK and IL-6 levels was found [synergy index: 2.19 (0.80, 5.93)]. Thus, the association of sTWEAK with mortality was strongest in patients with inflammation (defined as IL-6 > 7.0 pg/ml), in whom high sTWEAK strongly predicted cardiovascular and all-cause mortality. These results were confirmed in a second cohort of HD patients.

CONCLUSIONS

The concurrent presence of elevated sTWEAK plasma concentrations and an inflammatory environment have additive effects on mortality in HD patients. Further studies on the potential different role of sTWEAK in health and disease are warranted.

The TWEAK-Fn14 cytokine-receptor axis: discovery, biology and therapeutic targeting

TWEAK is a multifunctional cytokine that controls many cellular activities including proliferation, migration, differentiation, apoptosis, angiogenesis and inflammation. TWEAK acts by binding to Fn14, a highly inducible cell-surface receptor that is linked to several intracellular signalling pathways, including the nuclear factor-kappaB (NF-kappaB) pathway. The TWEAK-Fn14 axis normally regulates various physiological processes, in particular it seems to play an important, beneficial role in tissue repair following acute injury. Furthermore, recent studies have indicated that TWEAK-Fn14 axis signalling may contribute to cancer, chronic autoimmune diseases and acute ischaemic stroke. This Review provides an overview of TWEAK-Fn14 axis biology and summarizes the available data supporting the proposal that both TWEAK and Fn14 should be considered as potential targets for the development of novel therapeutics.

TWEAK/Fn14 interactions are instrumental in the pathogenesis of nephritis in the chronic graft-versus-host model of systemic lupus erythematosus

TNF-like weak inducer of apoptosis (TWEAK), a member of the TNF superfamily, is a prominent inducer of proinflammatory cytokines in vitro and in vivo. We previously found that kidney cells display the TWEAK receptor Fn14, and that TWEAK stimulation of mesangial cells and podocytes induces a potent proinflammatory response. Several of the cytokines up-regulated in the kidney in response to TWEAK are instrumental in Lupus nephritis; we therefore hypothesized that TWEAK/Fn14 interactions may be important in the cascade(s) leading to renal damage in systemic Lupus erythematosus. In this study, we analyzed the effects of Fn14 deficiency in the chronic graft-vs-host model of SLE, and the benefits of treatment with an anti-TWEAK mAb in this mouse model. We found that anti-nuclear Ab titers were no different between C57BL/6 Fn14 wild-type and deficient mice injected with alloreactive bm12 splenocytes. However, kidney disease was significantly less severe in Fn14 knockout mice. Furthermore, kidney IgG deposition, IL-6, MCP-1, RANTES, and IP-10, as well as macrophage infiltration, were significantly decreased in Fn14-deficient mice with induced lupus. Similarly, mice with induced Lupus treated with an anti-TWEAK neutralizing mAb had significantly diminished kidney expression of IL-6, MCP-1, IL-10, as well as proteinuria, but similar autoantibody titers, as compared with control-treated mice. We conclude that TWEAK is an important mediator of kidney damage that acts by promoting local inflammatory events, but without impacting adaptive immunity in this experimental LN model. Thus, TWEAK blockade may be a novel therapeutic approach to reduce renal damage in SLE.

TWEAKing tissue remodeling by a multifunctional cytokine: role of TWEAK/Fn14 pathway in health and disease

First described as a weak apoptosis inducer, the TNF superfamily ligand TWEAK has since emerged as a cytokine that regulates multiple cellular responses, including proinflammatory activity, angiogenesis and cell proliferation, suggesting roles in inflammation and cancer. More recently TWEAK's ability to regulate progenitor cell fate was elucidated. Experiments using genetic overexpression and pathway inhibition or deficiency in mice indicate that TWEAK coordinates inflammatory and progenitor cell responses in settings of acute injury through its highly inducible receptor, FGF-inducible molecule 14 (Fn14), establishing the pathway's physiological role in facilitating acute tissue repair. In contrast, in chronic inflammatory disease models characterized by persistent TWEAK/Fn14 activation, TWEAK functions as a novel pathogenic mediator by amplifying inflammation, promoting tissue damage and potentially impeding endogenous repair mechanisms. Herein we aim not only to review the multifaceted functions of this emerging pathway, but also propose a conceptual framework for TWEAK/Fn14 pathway function in health and disease, supported by studies employing TWEAK and Fn14 deficient mice and anti-TWEAK blocking mAbs in acute injury and inflammatory disease settings. In addition to a perspective of the biology, we discuss potential therapeutic strategies targeting this pathway for the treatment of tissue injury, chronic inflammatory diseases and cancer.

Proinflammatory effects of tumour necrosis factor-like weak inducer of apoptosis (TWEAK) on human gingival fibroblasts

Tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a member of the TNF family, is a multi-functional cytokine that regulates cellular proliferation, angiogenesis, inflammation and apoptosis. In this study, we investigated TWEAK expression in periodontally diseased tissues and the effect of TWEAK on human gingival fibroblasts (HGF). Reverse transcription-polymerase chain reaction (RT-PCR) analysis and immunohistochemistry revealed that TWEAK and the TWEAK receptor, fibroblast growth factor-inducible 14 (Fn14), mRNA and protein were expressed in periodontally diseased tissues. HGF expressed Fn14 and produced interleukin (IL)-8 and vascular endothelial growth factor (VEGF) production upon TWEAK stimulation in a dose-dependent manner. The IL-8 and VEGF production induced by TWEAK was augmented synergistically by simultaneous stimulation with transforming growth factor (TGF)-beta1 or IL-1beta. IL-1beta and TGF-beta1 enhanced Fn14 expression in a dose-dependent manner. Moreover, TWEAK induced intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression on HGF in a dose-dependent manner. The ICAM-1 expression induced by TWEAK was augmented by TGF-beta1. On the other hand, the TWEAK-induced VCAM-1 expression was inhibited by TGF-beta1. Phosphatidylinositol 3-kinase (PI3K) and nuclear factor-kappaB (NF-kappaB) inhibitor inhibit both ICAM-1 and VCAM-1 expression induced by TWEAK. However, mitogen-activated protein kinase (MEK) and c-Jun NH2-terminal kinase (JNK) inhibitor enhanced only VCAM-1 expression on HGF. These results suggest that TWEAK may be involved in the pathophysiology of periodontal disease. Moreover, in combination with IL-1beta or TGF-beta1, TWEAK may be related to the exacerbation of periodontal disease to induce proinflammatory cytokines and adherent molecules by HGF.

Identification of soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) as a possible biomarker of subclinical atherosclerosis

OBJECTIVES

Assessment of vascular risk in asymptomatic patients and the response to medical therapy is a major challenge for prevention of cardiovascular events. Our aim was to identify proteins differentially released by healthy versus atherosclerotic arterial walls, which could be found in plasma and serve as markers of atherosclerosis.

METHODS AND RESULTS

We have analyzed supernatants obtained from cultured human carotid plaques and healthy arteries by surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry ProteinChip System. Surface-enhanced laser-desorption/ionization analysis unveiled an 18.4-kDa peak released in lower amount by carotid plaques than normal endarteries. This protein was identified as soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK). To confirm that sTWEAK was the protein of interest, Western blot and enzyme-linked immunosorbent assay were performed. Both techniques confirmed that sTWEAK levels were decreased in carotid plaque supernatants. Subsequent measurement of sTWEAK in plasma showed a reduced concentration in subjects with carotid stenosis (N=30) compared with healthy subjects matched by sex and age (N=28) (P<0.001). Furthermore, in a test population of 106 asymptomatic subjects, we showed that sTWEAK concentrations negatively correlated with the carotid intima-media thickness (r=-0.4; P<0.001), an index of subclinical atherosclerosis.

CONCLUSIONS

These results suggest that sTWEAK could be a potential biomarker of atherosclerosis.

Urinary TWEAK and the activity of lupus nephritis

The TNF superfamily cytokine TWEAK induces mesangial cells, podocytes, and endothelial cells to secrete pro-inflammatory chemokines including MCP-1, IP-10 and RANTES, which are crucial in the pathogenesis of lupus nephritis (LN). As TWEAK regulates the secretion of these inflammatory mediators, we studied whether urinary TWEAK (uTWEAK) levels might be predictive and/or diagnostic in LN. In a cross-sectional study of a large, multi-center cohort of systemic lupus erythematosus (SLE) patients, uTWEAK levels were higher in patients with active as compared to never or non-active nephritis (median (IQR): 16.3 (9.9-23.0) versus 5.5 (2.3-16.8) pg/mg creatinine, p=0.001), and levels of uTWEAK correlated with the renal SLE disease activity index (rSLEDAI) score (r=0.405, p<0.001). uTWEAK levels were higher in patients undergoing a flare as compared to patients with chronic stable disease (11.1 (8.1-18.2) and 5.2 (2.3-15.3) pg/mg creatinine, respectively; p=0.036). Moreover, uTWEAK levels were significantly higher in patients undergoing a renal flare, as opposed to a non-renal flare (12.4 (9.1-18.2) and 5.2 (3.0-11.9) pg/mg creatinine, respectively; p=0.029). An accurate, non-invasive method to repeatedly assess kidney disease in lupus would be very helpful in managing these often challenging patients. Our study indicates that urinary TWEAK levels may be useful as a novel biomarker in LN.

Involvement of TNF-Like Weak Inducer of Apoptosis in the Pathogenesis of Collagen-Induced Arthritis

TNF-like weak inducer of apoptosis (TWEAK) is a type II membrane protein belonging to the TNF family that regulates apoptotic cell death, cellular proliferation, angiogenesis, and inflammation. However, the role of TWEAK in the pathogenesis of rheumatoid arthritis (RA) remains unclear. In this study, we have investigated the effect of neutralizing anti-TWEAK mAb on the development of collagen-induced arthritis (CIA), a well-established murine model of RA. Administration of anti-TWEAK mAb significantly ameliorated paw swelling, synovial hyperplasia, and infiltration of inflammatory cells. The levels of proinflammatory chemokines such as MCP-1 and MIP-2 in serum and knee joints were reduced by this treatment. Consistently, recombinant TWEAK enhanced the proliferation of MCP-1 and MIP-2 production by synovial cells from CIA mice in vitro. Histological examination also revealed that the treatment with anti-TWEAK mAb suppressed the development of small vessels in synovial tissues. These results indicated anti-inflammatory and antiangiogenic effects of the TWEAK blockade in CIA, which may be also beneficial for the treatment of RA.

TWEAK and Fn14: New molecular targets for cancer therapy?

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) superfamily of structurally related cytokines. Full-length, membrane-anchored TWEAK can be found on the surface of many cell types and a smaller, biologically active form, generated via proteolytic processing, has also been detected in the extracellular milieu. TWEAK acts via binding to a recently identified TNF receptor superfamily member named fibroblast growth factor-inducible 14 (Fn14). It has been demonstrated that TWEAK binding to the Fn14 receptor, or constitutive Fn14 overexpression, activates the nuclear factor-kappaB signaling pathway, which is known to play an important role in immune and inflammatory processes, oncogenesis, and cancer therapy resistance. In this article, we review recent studies indicating that TWEAK and Fn14 may be potential regulators of human tumorigenesis.

Tumor necrosis factor-like weak inducer of apoptosis-induced neurodegeneration

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) family of cytokines. It has proangiogenic and proinflammatory properties in vivo and induces cell death in tumor cell lines. TWEAK effects are mediated by the membrane receptor Fn14. In a systematic search for genes regulated in a murine stroke model with the tag-sequencing technique massively parallel signature sequencing, we have identified TWEAK as an induced gene. After 24 hr of focal cerebral ischemia in vivo or oxygen glucose deprivation in primary cortical neurons, both TWEAK and its receptor Fn14 were significantly upregulated. TWEAK induced cell death in primary neurons. Transfection of a nuclear factor (NF)-kappaB-luciferase fusion gene demonstrated that TWEAK stimulated transcriptional activity of NF-kappaB through Fn14 and the IkappaB kinase. Inhibition of NF-kappaB reduced TWEAK-stimulated neuronal cell death, suggesting that NF-kappaB mediates TWEAK-induced neurodegeneration at least in part. Intraperitoneal injection of a neutralizing anti-TWEAK antibody significantly reduced the infarct size after 48 hr of permanent cerebral ischemia. In summary, our data show that TWEAK induces neuronal cell death and is involved in neurodegeneration in vivo.

TNF-related weak inducer of apoptosis receptor, a TNF receptor superfamily member, activates NF-kappa B through TNF receptor-associated factors

TNF-related weak inducer of apoptosis (TWEAK) is a member of the TNF ligand family that induces angiogenesis in vivo. The TWEAK receptor (TweakR) is a recently identified member of the TNF receptor (TNFR) superfamily and is expressed on smooth muscle cells (SMCs) and endothelial cells (ECs). In this report we identify the TNF receptor-associated factor (TRAF) family of signal transducers as important components of TweakR-mediated NF-kappa B activation. Coimmunoprecipitation experiments suggested potential interactions between the cytoplasmic tail of TweakR with TRAFs 1, 2, 3, and 5. Dominant negative forms of TRAF2 and TRAF5 substantially inhibited TweakR-mediated NF-kappa B activation, suggesting a role of TRAFs in regulating smooth muscle and endothelial cell function. Using alanine-scanning analysis, we defined a TRAF-binding motif, PIEET, in TweakR that mediates TRAF binding and NF-kappa B activation. Furthermore, TweakR mutations within the TRAF-binding motif abolished TweakR-stimulated SMC migration, revealing a role for TRAFs in TweakR-induced activation events.

TWEAK, a member of the TNF superfamily, is a multifunctional cytokine that binds the TweakR/Fn14 receptor

The cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK) was initially described as a member of the tumor necrosis factor (TNF) superfamily in 1997. TWEAK is a cell surface-associated type II transmembrane protein, but a smaller, biologically active form can also be shed into the extracellular milieu. There is one receptor currently known to bind TWEAK with physiological affinity, and it is a type I transmembrane protein that is referred to in the literature as either TWEAK receptor (TweakR) or fibroblast growth factor-inducible 14 (Fn14). TweakR/Fn14 is the smallest member of the TNF receptor (TNFR) superfamily described to date, and it appears to signal via recruitment of several different TNFR-associated factors. TWEAK has multiple biological activities, including stimulation of cell growth and angiogenesis, induction of inflammatory cytokines, and under some experimental conditions, stimulation of apoptosis. In this report, we summarize the results from recent studies focused on the TWEAK cytokine. Although these studies have contributed a significant amount of new information, numerous questions still remain regarding the role of TWEAK in both normal physiology and the pathogenesis of human disease.

TWEAK is expressed by glial cells, induces astrocyte proliferation and increases EAE severity

TWEAK is a new TNF family member with proinflammatory and proliferative effects on different cell types, mediated by the recently identified Fn14 receptor. TWEAK expression was analyzed on mouse microglial cells and astrocytes. Both cell types express TWEAK mRNA. Astrocytes expressed Fn14 and proliferated in the presence of rTWEAK. TWEAK mRNA is expressed in normal CNS and its steady state level increases in spinal cord during EAE. Finally, EAE severity is enhanced in soluble TWEAK-overexpressing transgenic mice. These results support the contention that TWEAK is involved in CNS inflammation.

Proinflammatory activity of TWEAK on human dermal fibroblasts and synoviocytes: blocking and enhancing effects of anti-TWEAK monoclonal antibodies

Human tumour necrosis factor (TNF)-like weak inducer of apoptosis (hTWEAK) and two anti-hTWEAK mAbs were tested for their ability to elicit or block inflammatory responses in cultured human dermal fibroblasts and synoviocytes. Incubation with hTWEAK increased the production of prostaglandin E2, matrix metalloproteinase-1 (MMP-1), IL-6, and the chemokines IL-8, RANTES (regulated on activation, normal T expressed and secreted) and interferon-gamma-inducible protein-10 (IP-10) in culture supernatant of fibroblasts and synoviocytes. In combination with TNF or IL-1beta, hTWEAK further stimulated the secretion of prostaglandin E2, MMP-1, IL-6 and IL-8 up to fourfold, and IP-10 and RANTES up to 70-fold compared to TNF or IL-1beta alone. An anti-hTWEAK mAb, BCB10, blocked the effects of hTWEAK, whereas hTWEAK crosslinked by the anti-hTWEAK mAb, BEB3, further stimulated the inflammatory response of fibroblasts and synoviocytes. The anti-hTWEAK mAbs were ineffective in blocking or increasing the responses of TNF or IL-1beta and blocking anti-TNF mAb was ineffective in preventing the responses to TWEAK. These results were also confirmed at the RNA level for MMP-1, macrophage chemoattractant protein-1, RANTES, macrophage inflammatory protein-1alpha, IP-10 and IL-8. TWEAK in synergism with IL-1 and TNF may be an additional cytokine that plays a role in destructive chronic arthritic diseases.

A novel TNF receptor family member binds TWEAK and is implicated in angiogenesis

TWEAK is a member of the TNF ligand family that induces angiogenesis in vivo. We report cloning of a receptor for TWEAK (TweakR) from a human umbilical vein endothelial cell (HUVEC) library. The mature form of TweakR has only one hundred and two amino acids and six cysteine residues in its extracellular region. Five different assays demonstrate TWEAK-TweakR binding, and the interaction affinity constant (Kd) is within a physiologically relevant range of 2.3 +/- 0.1 nM. The TweakR cytoplasmic domain binds TRAFs 1, 2, and 3. Cross-linking of TweakR induces HUVEC growth, and mRNA levels are upregulated in vitro by a variety of agents and in vivo following arterial injury. Soluble TweakR inhibits endothelial cell migration in vitro and corneal angiogenesis in vivo.