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1.  TWEAK and its receptor Fn14 in the synovium of patients with rheumatoid arthritis compared to psoriatic arthritis and its response to tumour necrosis factor blockade 
Annals of the Rheumatic Diseases  2009;69(1):301-304.
Objective:
To investigate the expression of tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor inducible 14 (Fn14) in the inflamed synovium of patients with arthritis, as TWEAK blockade has been observed to have a beneficial effect in an animal model of rheumatoid arthritis (RA).
Methods:
Synovial tissue (ST) biopsies were obtained from 6 early, methotrexate-naive patients with RA as well as 13 patients with RA and 16 patients with psoriatic arthritis (PsA) who were matched for treatment and disease duration. Serial ST samples were obtained from a separate cohort of 13 patients with RA before and after infliximab treatment. TWEAK and Fn14 expression was evaluated by immunohistochemistry and digital image analysis.
Results:
TWEAK and Fn14 were clearly expressed in ST of patients with RA and PsA. TWEAK expression was significantly higher in RA (sub)lining samples compared to PsA (p = 0.005 and p = 0.014, respectively), but Fn14 expression was comparable. Double immunofluorescence showed TWEAK and Fn14 expression on fibroblast-like synoviocytes and macrophages, but not T cells. Of interest, persistent TWEAK and Fn14 expression was found after anti-TNF therapy.
Conclusions:
TWEAK and Fn14 are abundantly expressed in the inflamed synovium of patients with RA and PsA. This raises the possibility that blocking TWEAK/Fn14 signalling could be of therapeutic benefit in inflammatory arthritis.
doi:10.1136/ard.2008.090548
PMCID: PMC2789939  PMID: 19147618
2.  Functional Expression of TWEAK and the Receptor Fn14 in Human Malignant Ovarian Tumors: Possible Implication for Ovarian Tumor Intervention 
PLoS ONE  2013;8(3):e57436.
The aim of this current study was to investigate the expression of the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) in human malignant ovarian tumors, and test TWEAK’s potential role on tumor progression in cell models in-vitro. Using immunohistochemistry (IHC), we found that TWEAK and its receptor Fn14 were expressed in human malignant ovarian tumors, but not in normal ovarian tissues or in borderline/benign epithelial ovarian tumors. High levels of TWEAK expression was detected in the majority of malignant tumors (36 out of 41, 87.80%). Similarly, 35 out of 41 (85.37%) malignant ovarian tumors were Fn14 positive. In these malignant ovarian tumors, however, TWEAK/Fn14 expression was not corrected with patients’ clinical subtype/stages or pathological features. In vitro, we demonstrated that TWEAK only inhibited ovarian cancer HO-8910PM cell proliferation in combination with tumor necrosis factor-α (TNF-α), whereas either TWEAK or TNF-α alone didn’t affect HO-8910PM cell growth. TWEAK promoted TNF-α production in cultured THP-1 macrophages. Meanwhile, conditioned media from TWEAK-activated macrophages inhibited cultured HO-8910PM cell proliferation and invasion. Further, TWEAK increased monocyte chemoattractant protein-1 (MCP-1) production in cultured HO-8910PM cells to possibly recruit macrophages. Our results suggest that TWEAK/Fn14, by activating macrophages, could be ovarian tumor suppressors. The unique expression of TWEAK/Fn14 in malignant tumors indicates that it might be detected as a malignant ovarian tumor marker.
doi:10.1371/journal.pone.0057436
PMCID: PMC3587594  PMID: 23469193
3.  Urinary TWEAK as a biomarker of lupus nephritis: a multicenter cohort study 
Arthritis Research & Therapy  2009;11(5):R143.
Introduction
TNF-like weak inducer of apoptosis (TWEAK) has been implicated as a mediator of chronic inflammatory processes via prolonged activation of the NF-κB pathway in several tissues, including the kidney. Evidence for the importance of TWEAK in the pathogenesis of lupus nephritis (LN) has been recently introduced. Thus, TWEAK levels may serve as an indication of LN presence and activity.
Methods
Multicenter cohorts of systemic lupus erythematosus (SLE) patients and controls were recruited for cross-sectional and longitudinal analysis of urinary TWEAK (uTWEAK) and/or serum TWEAK (sTWEAK) levels as potential biomarkers of LN. The performance of TWEAK as a biomarker for nephritis was compared with routinely used laboratory tests in lupus patients, including anti-double stranded DNA antibodies and levels of C3 and C4.
Results
uTWEAK levels were significantly higher in LN patients than in non-LN SLE patients and other disease control groups (P = 0.039). Furthermore, uTWEAK was better at distinguishing between LN and non-LN SLE patients than anti-DNA antibodies and complement levels, while high uTWEAK levels predicted LN in SLE patients with an odds ratio of 7.36 (95% confidence interval = 2.25 to 24.07; P = 0.001). uTWEAK levels peaked during LN flares, and were significantly higher during the flare than at 4 and 6 months prior to or following the flare event. A linear mixed-effects model showed a significant association between uTWEAK levels in SLE patients and their disease activity over time (P = 0.008). sTWEAK levels, however, were not found to correlate with the presence of LN or the degree of nephritis activity.
Conclusions
High uTWEAK levels are indicative of LN, as opposed to non-LN SLE and other healthy and disease control populations, and reflect renal disease activity in longitudinal follow-up. Thus, our study further supports a role for TWEAK in the pathogenesis of LN, and provides strong evidence for uTWEAK as a candidate clinical biomarker for LN.
doi:10.1186/ar2816
PMCID: PMC2787265  PMID: 19785730
4.  Therapeutic potential of the TWEAK/Fn14 pathway in intractable gastrointestinal cancer 
Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the TNF superfamily. It has been suggested that it plays a pivotal role in various physiological and pathological conditions due to its proinflammatory properties. Fibroblast growth-inducible 14 (Fn14) has been identified as a TWEAK receptor. A number of studies have suggested that TWEAK-Fn14 interaction results in the promotion of apoptosis, cell growth as well as angiogenesis. Although recent studies have indicated that TWEAK and Fn14 are expressed in a number of tumor lines and tissues, the therapeutic potential of this pathway has yet to be elucidated. This study investigated the potential of TWEAK and Fn14 in esophageal and pancreatic cancer as novel molecular targets for anti-cancer therapy. TWEAK and Fn14 protein expression was evaluated in 43 patients with esophageal cancer and 51 patients with pancreatic cancer by immunohistochemistry. As a result, either TWEAK or Fn14 expression was observed in 58.1% of the cases with esophageal cancer and 74.5% of the cases with pancreatic cancer. Furthermore, TWEAK/Fn14 gene expression was identified in the majority of the human esophageal and pancreatic cancer cell lines. Therapeutic efficacies of blocking TWEAK and Fn14 were evaluated by tumor growth inhibition assay in TWEAK- and Fn14-expressing human esophageal and pancreatic cancer cell lines. Coculture with anti-TWEAK or -Fn14 mAb was found to induce a 22–65% cell growth inhibition of these cells. Finally, the significant therapeutic effect of targeting this pathway under in vivo physiological conditions was confirmed using a murine gastrointestinal cancer model. In conclusion, the TWEAK/Fn14 pathway may be functional and critical in intractable gastrointestinal cancers. Therefore, TWEAK and/or Fn14 may be novel molecular targets for anti-cancer therapy.
doi:10.3892/etm.2010.181
PMCID: PMC3440634  PMID: 22977477
esophageal cancer; pancreatic cancer; tumor necrosis factor-like weak inducer of apoptosis; fibroblast growth-inducible 14; molecular target therapy
5.  A Bioinformatics Resource for TWEAK-Fn14 Signaling Pathway 
Journal of Signal Transduction  2012;2012:376470.
TNF-related weak inducer of apoptosis (TWEAK) is a new member of the TNF superfamily. It signals through TNFRSF12A, commonly known as Fn14. The TWEAK-Fn14 interaction regulates cellular activities including proliferation, migration, differentiation, apoptosis, angiogenesis, tissue remodeling and inflammation. Although TWEAK has been reported to be associated with autoimmune diseases, cancers, stroke, and kidney-related disorders, the downstream molecular events of TWEAK-Fn14 signaling are yet not available in any signaling pathway repository. In this paper, we manually compiled from the literature, in particular those reported in human systems, the downstream reactions stimulated by TWEAK-Fn14 interactions. Our manual amassment of the TWEAK-Fn14 pathway has resulted in cataloging of 46 proteins involved in various biochemical reactions and TWEAK-Fn14 induced expression of 28 genes. We have enabled the availability of data in various standard exchange formats from NetPath, a repository for signaling pathways. We believe that this composite molecular interaction pathway will enable identification of new signaling components in TWEAK signaling pathway. This in turn may lead to the identification of potential therapeutic targets in TWEAK-associated disorders.
doi:10.1155/2012/376470
PMCID: PMC3357548  PMID: 22649723
6.  Expression of TweakR in breast cancer and preclinical activity of enavatuzumab, a humanized anti-TweakR mAb 
Background
The receptor for the cytokine TWEAK (TweakR) is a cell surface member of the tumor necrosis factor receptor superfamily with diverse biological roles. TNFRSF family members are appealing therapeutic targets in oncology due to their aberrant expression and function in tumor cells. The goal of the current study was to examine the potential of TweakR as a therapeutic target in breast cancer.
Methods
Expression of TweakR in primary breast cancer tissues and metastases was characterized using immunohistochemistry. To determine the functional relevance of TweakR, breast cancer cell lines were treated in vitro and in vivo with enavatuzumab, a humanized mAb against TweakR.
Results
Overexpression of TweakR was observed in infiltrating tumors compared to normal adjacent breast tissues, and strong staining of TweakR was observed in all subtypes of invasive ductal breast cancer. In addition, a positive correlation of TweakR and HER2 expression and co-localization were observed, irrespective of ER status. TweakR expression was also observed in bone metastasis samples from primary breast cancer but rarely in benign tumors. Enavatuzumab inhibited the in vitro growth of TweakR-expressing breast cancer cell lines, and this activity was augmented by cross-linking the mAb. In addition, enavatuzumab significantly inhibited the in vivo growth of multiple breast cancer xenograft models including a model of metastasis.
Conclusions
TweakR is highly expressed in all subtypes of invasive ductal breast cancer, and enavatuzumab administration exhibited a dose-dependent inhibition of primary tumor growth and lung metastasis and enhanced the antitumor activity of several chemotherapy agents currently used to treat breast cancer. These data provide the rationale to evaluate enavatuzumab as a potential therapy for the treatment of breast cancer.
Electronic supplementary material
The online version of this article (doi:10.1007/s00432-012-1332-x) contains supplementary material, which is available to authorized users.
doi:10.1007/s00432-012-1332-x
PMCID: PMC3549414  PMID: 23073510
TweakR; Antibody; Breast cancer; Fn14
7.  Is TWEAK a Biomarker for Autoimmune/Chronic Inflammatory Diseases? 
The TWEAK/Fn14 pathway is now well-known for its involvement in the modulation of inflammation in various human autoimmune/chronic inflammatory diseases (AICID) including lupus, rheumatoid arthritis, and multiple sclerosis. A panel of data is now available concerning TWEAK expression in tissues or biological fluids of patients suffering from AICID, suggesting that it could be a promising biological marker in these diseases. Evidences from several teams support the hypothesis that blocking TWEAK/Fn14 pathway is an attractive new therapeutic lead in such diseases and clinical trials with anti-TWEAK-blocking antibodies are in progress. In this mini-review we discuss the potential use of TWEAK quantification in AICD management in routine practice and highlight the challenge of standardizing data collection to better estimate the clinical utility of such a biological parameter.
doi:10.3389/fimmu.2013.00489
PMCID: PMC3873518  PMID: 24409182
TWEAK; biomarker; auto-immunity; disease monitoring; serum levels; urinary levels
8.  Reduced circulating sTWEAK levels are associated with metabolic syndrome in elderly individuals at high cardiovascular risk 
Background
The circulating soluble TNF-like weak inducer of apoptosis (sTWEAK) is a cytokine that modulates inflammatory and atherogenic reactions related to cardiometabolic risk. We investigated the association between sTWEAK levels and metabolic syndrome (MetS) and its components in older subjects at high cardiovascular risk.
Methods
Cross-sectional analysis of 452 non-diabetic individuals (men and women aged 55–80 years) at high cardiovascular risk. MetS was defined by AHA/NHLBI and IDF criteria. Logistic regression analyses were used to estimate odds ratios (ORs) for MetS and its components by tertiles of serum sTWEAK concentrations measured by ELISA.
Results
sTWEAK concentrations were lower in subjects with MetS than in those without. In gender- and age-adjusted analyses, subjects in the lowest sTWEAK tertile had higher ORs for overall MetS [1.71 (95% CI, 1.07-2.72)] and its components abdominal obesity [2.01 (1.15-3.52)], hyperglycemia [1.94 (1.20-3.11)], and hypertriglyceridemia [1.73 (1.05-2.82)] than those in the upper tertile. These associations persisted after controlling for family history of diabetes and premature coronary heart disease, lifestyle, kidney function and other MetS components. sTWEAK concentrations decreased as the number of MetS components increased. Individuals in the lowest vs the upper sTWEAK tertile had an increased risk of disclosing greater number of MetS features. Adjusted ORs for individuals with 2 vs ≤1, 3 vs ≤1, and ≥4 vs ≤ 1 MetS components were 2.60 (1.09-6.22), 2.83 (1.16-6.87) and 6.39 (2.42-16.85), respectively.
Conclusion
In older subjects at high cardiovascular risk, reduced sTWEAK levels are associated with MetS: abdominal obesity, hypertriglyceridemia and hyperglycemia are the main contributors to this association.
doi:10.1186/1475-2840-13-51
PMCID: PMC3974038  PMID: 24565471
sTWEAK; Metabolic syndrome; Cardiovascular risk; Biomarkers; Insulin resistance
9.  TWEAK/Fn14 interaction regulates RANTES production, BMP-2-induced differentiation, and RANKL expression in mouse osteoblastic MC3T3-E1 cells 
Tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a member of the TNF family, is a multifunctional cytokine that regulates cell growth, migration, and survival principally through a TWEAK receptor, fibroblast growth factor-inducible 14 (Fn14). However, its physiological roles in bone are largely unknown. We herein report various effects of TWEAK on mouse osteoblastic MC3T3-E1 cells. MC3T3-E1 cells expressed Fn14 and produced RANTES (regulated upon activation, healthy T cell expressed and secreted) upon TWEAK stimulation through PI3K-Akt, but not nuclear factor-κB (NF-κB), pathway. In addition, TWEAK inhibited bone morphogenetic protein (BMP)-2-induced expression of osteoblast differentiation markers such as alkaline phosphatase through mitogen-activated protein kinase (MAPK) Erk pathway. Furthermore, TWEAK upregulated RANKL (receptor activation of NF-κB ligand) expression through MAPK Erk pathway in MC3T3-E1 cells. All these effects of TWEAK on MC3T3-E1 cells were abolished by mouse Fn14-Fc chimera. We also found significant TWEAK mRNA or protein expression in osteoblast – and osteoclast-lineage cell lines or the mouse bone tissue, respectively. Finally, we showed that human osteoblasts expressed Fn14 and induced RANTES and RANKL upon TWEAK stimulation. Collectively, TWEAK/Fn14 interaction regulates RANTES production, BMP-2-induced differentiation, and RANKL expression in MC3T3-E1 cells. TWEAK may thus be a novel cytokine that regulates several aspects of osteoblast function.
doi:10.1186/ar2038
PMCID: PMC1779446  PMID: 16945157
10.  Nrf2 Protects Against TWEAK-mediated Skeletal Muscle Wasting 
Scientific Reports  2014;4:3625.
Skeletal muscle (SM) regeneration after injury is impaired by excessive inflammation. Particularly, the inflammatory cytokine tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a potent inducer of skeletal muscle wasting and fibrosis. In this study we investigated the role of Nrf2, a major regulator of oxidative stress defence, in SM ischemia/reperfusion (I/R) injury and TWEAK induced atrophy. We explored the time-dependent expression of TWEAK after I/R in SM of Nrf2-wildtype (WT) and knockout (KO) mice. Nrf2-KO mice expressed significant higher levels of TWEAK as compared to WT mice. Consequently, Nrf2-KO mice present an insufficient regeneration as compared to Nrf2-WT mice. Moreover, TWEAK stimulation activates Nrf2 in the mouse myoblast cell line C2C12. This Nrf2 activation inhibits TWEAK induced atrophy in C2C12 differentiated myotubes. In summary, we show that Nrf2 protects SM from TWEAK-induced cell death in vitro and that Nrf2-deficient mice therefore have poorer muscle regeneration.
doi:10.1038/srep03625
PMCID: PMC3887379  PMID: 24406502
11.  TNF-Like Weak Inducer of Apoptosis (TWEAK) Promotes Beta Cell Neogenesis from Pancreatic Ductal Epithelium in Adult Mice 
PLoS ONE  2013;8(8):e72132.
Aim/Hypothesis
The adult mammalian pancreas has limited ability to regenerate in order to restore adequate insulin production from multipotent progenitors, the identity and function of which remain poorly understood. Here we test whether the TNF family member TWEAK (TNF-like weak inducer of apoptosis) promotes β-cell neogenesis from proliferating pancreatic ductal epithelium in adult mice.
Methods
C57Bl/6J mice were treated with Fc-TWEAK and pancreas harvested at different time points for analysis by histology and immunohistochemistry. For lineage tracing, 4 week old double transgenic mice CAII-CreERTM: R26R-eYFP were implanted with tamoxifen pellet, injected with Fc-TWEAK or control Ig twice weekly and analyzed at day 18 for TWEAK-induced duct cell progeny by costaining for insulin and YFP. The effect of TWEAK on pancreatic regeneration was determined by pancytokeratin immunostaining of paraffin embedded sections from wildtype and TWEAK receptor (Fn14) deficient mice after Px.
Results
TWEAK stimulates proliferation of ductal epithelial cells through its receptor Fn14, while it has no mitogenic effect on pancreatic α- or β-cells or acinar cells. Importantly, TWEAK induces transient expression of endogenous Ngn3, a master regulator of endocrine cell development, and induces focal ductal structures with characteristics of regeneration foci. In addition, we identify by lineage tracing TWEAK-induced pancreatic β-cells derived from pancreatic duct epithelial cells. Conversely, we show that Fn14 deficiency delays formation of regenerating foci after Px and limits their expansion.
Conclusions/Interpretation
We conclude that TWEAK is a novel factor mediating pancreatic β-cell neogenesis from ductal epithelium in normal adult mice.
doi:10.1371/journal.pone.0072132
PMCID: PMC3753348  PMID: 23991053
12.  Expression of tumor necrosis factor-like weak inducer of apoptosis and fibroblast growth factor-inducible 14 in patients with polymyositis and dermatomyositis 
Introduction
The aim of this study was to investigate the expression of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) in patients with polymyositis (PM) and dermatomyositis (DM), and their relation to clinical manifestations.
Methods
Serum levels of TWEAK were detected in 98 PM/DM patients and 37 healthy controls by using the ELISA method. Total RNA isolated from fresh-frozen muscle tissue samples of 36 PM/DM patients and 10 healthy controls were used for analyzing the mRNA levels of TWEAK and Fn14 by quantitative reverse transcription polymerase chain reaction (RT-PCR). Immunofluorescence staining of TWEAK and Fn14 was conducted on muscle biopsy specimens from 23 PM/DM patients and seven healthy controls.
Results
Serum levels of TWEAK were significantly decreased in the PM/DM patients compared to those in the healthy controls (P < 0.001), and serum TWEAK levels negatively correlated with serum CD163 levels in PM/DM patients (r = -0.49, P < 0.001). The expression of Fn14 mRNA was significantly increased in the muscle tissue of PM/DM patients than in the muscle tissue of healthy controls (P < 0.01), whereas the expression of TWEAK mRNA in PM/DM patients was not statistically different from that of the healthy controls (P > 0.05). Fn14 mRNA levels in muscle tissue positively correlated with muscle disease activity (r = 0.512, P < 0.01). Patients with oropharyngeal dysphagia had significantly higher Fn14 mRNA levels than patients without oropharyngeal dysphagia (P < 0.05). The results of immunofluorescence staining showed that 19 out of 23 PM/DM patients were TWEAK-positive, and 20 out of 23 PM/DM patients were Fn14-positive. No detectable expressions of TWEAK or Fn14 were observed in the healthy controls.
Conclusions
TWEAK-Fn14 axis may be involved in the pathogenesis of PM/DM. Further understanding of TWEAK-Fn14 function in PM/DM may help to define therapeutic targets for PM/DM.
doi:10.1186/ar4454
PMCID: PMC3978894  PMID: 24467773
13.  TNF-Like Weak Inducer of Apoptosis Aggravates Left Ventricular Dysfunction after Myocardial Infarction in Mice 
Mediators of Inflammation  2014;2014:131950.
Background. TNF-like weak inducer of apoptosis (TWEAK) has recently been shown to be potentially involved in adverse cardiac remodeling. However, neither the exact role of TWEAK itself nor of its receptor Fn14 in this setting is known. Aim of the Study. To analyze the effects of sTWEAK on myocardial function and gene expression in response to experimental myocardial infarction in mice. Results. TWEAK directly suppressed the expression of PGC-1α and genes of oxidative phosphorylation (OXPHOS) in cardiomyocytes. Systemic sTWEAK application after MI resulted in reduced left ventricular function and increased mortality without changes in interstitial fibrosis or infarct size. Molecular analysis revealed decreased phosphorylation of PI3K/Akt and ERK1/2 pathways associated with reduced expression of PGC-1α and PPARα. Likewise, expression of OXPHOS genes such as atp5O, cycs, cox5b, and ndufb5 was also reduced. Fn14 −/− mice showed significantly improved left ventricular function and PGC-1α levels after MI compared to their respective WT littermates (Fn14 +/+). Finally, inhibition of intrinsic TWEAK with anti-TWEAK antibodies resulted in improved left ventricular function and survival. Conclusions. TWEAK exerted maladaptive effects in mice after myocardial infarction most likely via direct effects on cardiomyocytes. Analysis of the potential mechanisms revealed that TWEAK reduced metabolic adaptations to increased cardiac workload by inhibition of PGC-1α.
doi:10.1155/2014/131950
PMCID: PMC3945977
14.  Fibroblast growth factor inducible 14 (Fn14) is expressed in the lower genital tract and may play a role in amplifying inflammation during infection 
TNF-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) cytokine superfamily which regulates a number of cellular responses, including inflammation and proliferation. TWEAK is primarily secreted by phagocytic cells and its receptor, fibroblast growth factor-inducible 14 (Fn14), is expressed on non-lymphoid cells, including epithelial, endothelial and mesenchymal cells. The TWEAK/Fn14 pathway is highly conserved from an evolutionary standpoint, and has been shown to play a role in tissue regeneration and inflammation in the liver, kidney, lung and skeletal muscle. We hypothesized that TWEAK/Fn14 might have a physiological role in regulating infection-induced inflammation in the lower female genital tract. To test this hypothesis, we examined expression of the receptor Fn14 in relevant cells and tissue. Receptor function was tested by treating cells with recombinant TWEAK, with and without other known pro-inflammatory stimuli. Flow cytometric analysis of vaginal and cervical epithelial cells revealed that Fn14 was highly expressed at the cell surface. We also detected both Fn14 and TWEAK in whole cervical tissue by RT-PCR. Treatment of vaginal and cervical epithelial cells with recombinant TWEAK led to a weak induction of the chemokine IL-8. However, TWEAK potentiated the effects of IL-1ß, the TLR2 ligand Pam3CysSK4, and live Neisseria gonorrhoeae in a synergistic manner. These data reveal a novel pathway for regulation of microbial-induced inflammation in the female reproductive tract and suggest that interference with the TWEAK/Fn14 pathway might be an approach to abrogate excessive infection-induced inflammation caused by sexually transmitted pathogens.
doi:10.1016/j.jri.2009.09.009
PMCID: PMC2814934  PMID: 19963275
Innate Immunity; Epithelial Cells; Cytokine Receptors
15.  TWEAK/Fn14 and Non-Canonical NF-kappaB Signaling in Kidney Disease 
The incidence of acute kidney injury (AKI) and chronic kidney disease (CKD) is increasing. However, there is no effective therapy for AKI and current approaches only slow down, but do not prevent progression of CKD. TWEAK is a TNF superfamily cytokine. A solid base of preclinical data suggests a role of therapies targeting the TWEAK or its receptor Fn14 in AKI and CKD. In particular TWEAK/Fn14 targeting may preserve renal function and decrease cell death, inflammation, proteinuria, and fibrosis in mouse animal models. Furthermore there is clinical evidence for a role of TWEAK in human kidney injury including increased tissue and/or urinary levels of TWEAK and parenchymal renal cell expression of the receptor Fn14. In this regard, clinical trials of TWEAK targeting are ongoing in lupus nephritis. Nuclear factor-kappa B (NF-κB) activation plays a key role in TWEAK-elicited inflammatory responses. Activation of the non-canonical NF-κB pathway is a critical difference between TWEAK and TNF. TWEAK activation of the non-canonical NF-κB pathways promotes inflammatory responses in tubular cells. However, there is an incomplete understanding of the role of non-canonical NF-κB activation in kidney disease and on its contribution to TWEAK actions in vivo.
doi:10.3389/fimmu.2013.00447
PMCID: PMC3857575  PMID: 24339827
acute kidney injury; fibrosis; inflammation; kidney; lupus nephritis; podocyte; proteinuria
16.  PGC1α Plays a Critical Role in TWEAK–Induced Cardiac Dysfunction 
PLoS ONE  2013;8(1):e54054.
Background
Inflammatory cytokines play an important role in the pathogenesis of heart failure. We have recently found the cytokine TWEAK (tumor necrosis factor (TNF)-like weak inducer of apoptosis), a member of the TNF superfamily, to be increased in patients with cardiomyopathy and result in the development of heart failure when overexpressed in mice. The molecular mechanisms underlying TWEAK-induced cardiac pathology, however, remain unknown.
Methodology and Critical Finding
Using mouse models of elevated circulating TWEAK levels, established through intravenous injection of adenovirus expressing TWEAK or recombinant TWEAK protein, we find that TWEAK induces a progressive dilated cardiomyopathy with impaired contractile function in mice. Moreover, TWEAK treatment is associated with decreased expression of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC1α) and genes required for mitochondrial oxidative phosphorylation, which precede the onset of cardiac dysfunction. TWEAK-induced downregulation of PGC1α requires expression of its cell surface receptor, fibroblast growth factor-inducible 14 (Fn14). We further find that TWEAK downregulates PGC1α gene expression via the TNF receptor-associated factor 2 (TRAF2) and NFκB signaling pathways. Maintaining PGC1α levels through adenoviral-mediated gene expression is sufficient to protect against TWEAK-induced cardiomyocyte dysfunction.
Conclusion
Collectively, our data suggest that TWEAK induces cardiac dysfunction via downregulation of PGC1α, through FN14-TRAF2-NFκB-dependent signaling. Selective targeting of the FN14-TRAF2-NFκB-dependent signaling pathway or augmenting PGC1α levels may serve as novel therapeutic strategies for cardiomyopathy and heart failure.
doi:10.1371/journal.pone.0054054
PMCID: PMC3546975  PMID: 23342071
17.  TUMOR NECROSIS FACTOR-LIKE WEAK INDUCER OF APOPTOSIS (TWEAK) AND FIBROBLAST GROWTH FACTOR-INDUCIBLE 14 (Fn14) MEDIATE CEREBRAL ISCHEMIA-INDUCED POLY(ADP-RIBOSE) POLYMERASE-1 ACTIVATION AND NEURONAL DEATH 
Neuroscience  2010;171(4):1256-1264.
Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fibroblast growth factor-inducible 14 (Fn14) are expressed in neurons. Here we demonstrate that TWEAK induces a dose-dependent increase in neuronal death and that this effect is independent of TNF-α and mediated by NF-κB pathway activation. Incubation with TWEAK induces apoptotic cell death in wild-type (Wt) but not in Fn14 deficient (Fn14−/−) neurons. Intracerebral injection of TWEAK induces accumulation of poly(ADP-ribose) polymers (PAR) in Wt but not in Fn14−/− mice. Exposure to oxygen-glucose deprivation (OGD) conditions increases TWEAK and Fn14 mRNA expression in Wt neurons, and decreases cell survival in Wt but not in Fn14−/− or TWEAK deficient (TWEAK−/−) neurons. Experimental middle cerebral artery occlusion (MCAO) increases the expression of TWEAK and Fn14 mRNA and active caspase-3, and the cleavage of poly(ADP-ribose)polymerase-1 with accumulation of PAR in the ischemic area in Wt but not Fn14−/− mice. Together, these results suggest a model where in response to hypoxia/ischemia the interaction between TWEAK and Fn14 in neurons induces PARP-1 activation with accumulation of PAR polymers and cell death via NF-κB pathway activation. This is a novel pathway for hypoxia/ischemia-induced TWEAK-mediated cell death and a potential therapeutic target for ischemic stroke.
doi:10.1016/j.neuroscience.2010.10.029
PMCID: PMC2991428  PMID: 20955770
Cerebral ischemia; Tumor necrosis factor-like weak inducer of apoptosis (TWEAK); Fibroblast growth factor-inducible 14 (Fn14); Poly(ADP-ribose)polymerase-1 (PARP-1); Poly(ADP-ribose) polymers (PAR)
18.  The TWEAK-Fn14 System: Breaking the Silence of Cytokine-Induced Skeletal Muscle Wasting 
Current Molecular Medicine  2012;12(1):3-13.
The occurrence of skeletal muscle atrophy, a devastating complication of a large number of disease states and inactivity/disuse conditions, provides a never ending quest to identify novel targets for its therapy. Proinflammatory cytokines are considered the mediators of muscle wasting in chronic diseases; however, their role in disuse atrophy has just begun to be elucidated. An inflammatory cytokine, tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), has recently been identified as a potent inducer of skeletal muscle wasting. TWEAK activates various proteolytic pathways and stimulates the degradation of myofibril protein both in vitro and in vivo. Moreover, TWEAK mediates the loss of skeletal muscle mass and function in response to denervation, a model of disuse atrophy. Adult skeletal muscle express very low to minimal levels of TWEAK receptor, Fn14. Specific catabolic conditions such as denervation, immobilization, or unloading rapidly increase the expression of Fn14 in skeletal muscle which in turn stimulates the TWEAK activation of various catabolic pathways leading to muscle atrophy. In this article, we have discussed the emerging roles and the mechanisms of action of TWEAK-Fn14 system in skeletal muscle with particular reference to different models of muscle atrophy and injury and its potential to be used as a therapeutic target for prevention of muscle loss.
doi:10.2174/156652412798376107
PMCID: PMC3257753  PMID: 22082477
Denervation; disuse; inflammation; MuRF1; NF-kappa B; skeletal muscle; TWEAK.
19.  Proinflammatory activity of TWEAK on human dermal fibroblasts and synoviocytes: blocking and enhancing effects of anti-TWEAK monoclonal antibodies 
Arthritis Research  2001;4(2):126-133.
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-γ-inducible protein-10 (IP-10) in culture supernatant of fibroblasts and synoviocytes. In combination with TNF or IL-1β, 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-1β 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-1β 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-1α, 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.
PMCID: PMC83846  PMID: 11879548
chemokines; cytokines; metalloproteinases; rheumatoid arthritis; TNF
20.  TWEAK Promotes Peritoneal Inflammation 
PLoS ONE  2014;9(3):e90399.
Peritoneal dialysis (PD) is complicated by peritonitis episodes that cause loss of mesothelium and eventually sclerosing peritonitis. An improved understanding of the molecular contributors to peritoneal injury and defense may increase the therapeutic armamentarium to optimize peritoneal defenses while minimizing peritoneal injury. There is no information on the expression and function of the cytokine TWEAK and its receptor Fn14 during peritoneal injury. Fn14 expression and soluble TWEAK levels were measured in human PD peritoneal effluent cells or fluids with or without peritonitis. Fn14 expression was also analyzed in peritoneal biopsies from PD patients. Actions of intraperitoneal TWEAK were studied in mice in vivo. sTWEAK levels were increased in peritoneal effluent in PD peritonitis. Effluent sTWEAK levels correlated with the number of peritoneal macrophages (r = 0.491, p = 0.002). Potential TWEAK targets that express the receptor Fn14 include mesothelial cells and macrophages, as demonstrated by flow cytometry of peritoneal effluents and by analysis of peritoneal biopsies. Peritoneal biopsy Fn14 correlated with mesothelial injury, fibrosis and inflammation, suggesting a potential deleterious effect of TWEAK/Fn14. In this regard, intraperitoneal TWEAK administration to mice promoted peritoneal inflammation characterized by increased peritoneal effluent MCP-1, Fn14 and Gr1+ macrophages, increased mesothelial Fn14, MCP-1 and CCL21 expression and submesothelial tissue macrophage recruitment. Taken together these data suggest that the TWEAK/Fn14 system may promote inflammation and tissue injury during peritonitis and PD.
doi:10.1371/journal.pone.0090399
PMCID: PMC3944020  PMID: 24599047
21.  Soluble TWEAK independently predicts atherosclerosis in renal transplant patients 
BMC Nephrology  2013;14:144.
Background
Cardiovascular risk is increased in the early stages of chronic kidney disease (CKD) and also found to be ongoing in renal transplant (Rtx) patients. As a sign of atherosclerosis, increased carotid intima-media thickness (CIMT) has been widely accepted as a strong predictor of cardiovascular disease (CVD) and mortality in CKD patients. A novel markers, soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) and neutrophil-to-lymphocyte ratio (NLR) were introduced as potential markers in inflammatory disorders including CKD. The role of Rtx in terms of atherogenesis is still unclear. We aimed to investigate the relationship between sTWEAK, NLR and CIMT in Rtx patients without overt CVD and to compare these results with those obtained from healthy subjects.
Methods
Cross-sectional analysis in which CIMT measurements, NLR and serum TWEAK levels were assessed in 70 Rtx patients (29 females; mean age, 40.6 ± 12.4 years) and 25 healthy subjects (13 females, mean age; 37.4±8.8 years).
Results
sTWEAK levels were significantly decreased (p=0.01) and hs-CRP, NLR and CIMT levels of Rtx patients were significantly increased compared to healthy subjects (p<0.0001, p=0.001, p<0.0001, respectively). sTWEAK was also found to be decreased when eGFR was decreased (p=0.04 between all groups). CIMT was positively correlated with sTWEAK and NLR in Rtx patients (r=0.81, p<0.0001 and r=0.33, p=0.006, respectively). sTWEAK was also positively correlated with NLR (r=0.37, p=0.002). In the multivariate analysis only sTWEAK was found to be an independent variable of increased CIMT.
Conclusion
sTWEAK might have a role in the pathogenesis of ongoing atherosclerosis in Rtx patients.
doi:10.1186/1471-2369-14-144
PMCID: PMC3711729  PMID: 23849432
sTWEAK; Neutrophil-to-lymphocyte ratio; Carotid intima-media thickness; Renal transplantation
22.  Involvement of Tweak in Interferon γ–Stimulated Monocyte Cytotoxicity 
The Journal of Experimental Medicine  2000;192(9):1373-1380.
TWEAK, a new member of the tumor necrosis factor (TNF) family, induces cell death in some tumor cell lines, but its physiological functions are largely unknown. In this study, we investigated the expression and function of TWEAK in human peripheral blood mononuclear cells (PBMCs) by using newly generated anti–human TWEAK mAbs. Although freshly isolated PBMCs expressed no detectable level of TWEAK on their surfaces, a remarkable TWEAK expression was rapidly observed on monocytes upon stimulation with interferon (IFN)-γ but not with IFN-α or lipopolysaccharide. Cytotoxic activity of IFN-γ–stimulated monocytes against human squamous carcinoma cell line HSC3 was inhibited partially by anti-TWEAK mAb alone and almost completely by combination with anti-TRAIL (TNF-related apoptosis-inducing ligand) mAb. These results revealed a novel pathway of monocyte cytotoxicity against tumor cells that is mediated by TWEAK and potentiated by IFN-γ.
PMCID: PMC2193363  PMID: 11067885
TWEAK; TRAIL; IFN-γ; monocyte; cytotoxicity
23.  TWEAK/Fn14 Signaling Is Required for Liver Regeneration after Partial Hepatectomy in Mice 
PLoS ONE  2014;9(1):e83987.
Background & Aims
Pro-inflammatory cytokines are important for liver regeneration after partial hepatectomy (PH). Expression of Fibroblast growth factor-inducible 14 (Fn14), the receptor for TNF-like weak inducer of apoptosis (TWEAK), is induced rapidly after PH and remains elevated throughout the period of peak hepatocyte replication. The role of Fn14 in post-PH liver regeneration is uncertain because Fn14 is expressed by liver progenitors and TWEAK-Fn14 interactions stimulate progenitor growth, but replication of mature hepatocytes is thought to drive liver regeneration after PH.
Methods
To clarify the role of TWEAK-Fn14 after PH, we compared post-PH regenerative responses in wild type (WT) mice, Fn14 knockout (KO) mice, TWEAK KO mice, and WT mice treated with anti-TWEAK antibodies.
Results
In WT mice, rare Fn14(+) cells localized with other progenitor markers in peri-portal areas before PH. PH rapidly increased proliferation of Fn14(+) cells; hepatocytic cells that expressed Fn14 and other progenitor markers, such as Lgr5, progressively accumulated from 12–8 h post-PH and then declined to baseline by 96 h. When TWEAK/Fn14 signaling was disrupted, progenitor accumulation, induction of pro-regenerative cytokines, hepatocyte and cholangiocyte proliferation, and over-all survival were inhibited, while post-PH liver damage and bilirubin levels were increased. TWEAK stimulated proliferation and increased Lgr5 expression in cultured liver progenitors, but had no effect on either parameter in cultured primary hepatocytes.
Conclusions
TWEAK-FN14 signaling is necessary for the healthy adult liver to regenerate normally after acute partial hepatectomy.
doi:10.1371/journal.pone.0083987
PMCID: PMC3886973  PMID: 24416188
24.  Exogenous Administration of a Recombinant Variant of TWEAK Impairs Healing after Myocardial Infarction by Aggravation of Inflammation 
PLoS ONE  2013;8(11):e78938.
Background
Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are upregulated after myocardial infarction (MI) in both humans and mice. They modulate inflammation and the extracellular matrix, and could therefore be important for healing and remodeling after MI. However, the function of TWEAK after MI remains poorly defined.
Methods and results
Following ligation of the left coronary artery, mice were injected twice per week with a recombinant human serum albumin conjugated variant of TWEAK (HSA-Flag-TWEAK), mimicking the activity of soluble TWEAK. Treatment with HSA-Flag-TWEAK resulted in significantly increased mortality in comparison to the placebo group due to myocardial rupture. Infarct size, extracellular matrix remodeling, and apoptosis rates were not different after MI. However, HSA-Flag-TWEAK treatment increased infiltration of proinflammatory cells into the myocardium. Accordingly, depletion of neutrophils prevented cardiac ruptures without modulating all-cause mortality.
Conclusion
Treatment of mice with HSA-Flag-TWEAK induces myocardial healing defects after experimental MI. This is mediated by an exaggerated neutrophil infiltration into the myocardium.
doi:10.1371/journal.pone.0078938
PMCID: PMC3823964  PMID: 24244389
25.  TWEAK Affects Keratinocyte G2/M Growth Arrest and Induces Apoptosis through the Translocation of the AIF Protein to the Nucleus 
PLoS ONE  2012;7(3):e33609.
The soluble TNF-like weak inducer of apoptosis (TWEAK, TNFSF12) binds to the fibroblast growth factor-inducible 14 receptor (FN14, TNFRSF12A) on the cell membrane and induces multiple biological responses, such as proliferation, migration, differentiation, angiogenesis and apoptosis. Previous reports show that TWEAK, which does not contain a death domain in its cytoplasmic tail, induces the apoptosis of tumor cell lines through the induction of TNFα secretion. TWEAK induces apoptosis in human keratinocytes. Our experiments clearly demonstrate that TWEAK does not induce the secretion of TNFα or TRAIL proteins. The use of specific inhibitors and the absence of procaspase-3 cleavage suggest that the apoptosis of keratinocytes follows a caspase- and cathepsin B-independent pathway. Further investigation showed that TWEAK induces a decrease in the mitochondrial membrane potential of keratinocytes. Confocal microscopy showed that TWEAK induces the cleavage and the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus, thus initiating caspase-independent apoptosis. Moreover, TWEAK induces FOXO3 and GADD45 expression, cdc2 phosphorylation and cdc2 and cyclinB1 degradation, resulting in the arrest of cell growth at the G2/M phase. Finally, we report that TWEAK and FN14 are normally expressed in the basal layer of the physiological epidermis and are greatly enhanced in benign (psoriasis) and malignant (squamous cell carcinoma) skin pathologies that are characterized by an inflammatory component. TWEAK might play an essential role in skin homeostasis and pathology.
doi:10.1371/journal.pone.0033609
PMCID: PMC3306430  PMID: 22438963

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