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

Studies of binding of tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) to fibroblast growth factor inducible 14 (Fn14)

To perform highly sensitive cellular binding studies with TNF-like weak inducer of apoptosis (TWEAK), we developed a bioluminescent variant of soluble TWEAK (GpL-FLAG-TNC-TWEAK) by fusing it genetically to the C terminus of the luciferase of Gaussia princeps (GpL). Equilibrium binding studies on human (HT1080 and HT29) and murine (Renca and B16) cell lines at 37 °C revealed high affinities of human TWEAK from 53 to 112 pm. The dissociation rate constant of the TWEAK-Fn14 interaction was between 0.48×10(-3) s(-1) (HT29) and 0.58×10(-3) s(-1) (HT1080) for the human molecules, and the association rate constant obtained was 3.3×10(6) m(-1) s(-1) for both cell lines. It has been shown previously that oligomerization of soluble TWEAK trimers results in enhanced Fn14-mediated activation of the classical NFκB pathway. Binding studies with GpL-FLAG-TNC-TWEAK trimers oligomerized by help of a FLAG tag-specific antibody gave no evidence for a major increase in Fn14 occupancy by oligomerized ligand despite strongly enhanced induction of the NFκB target IL8. Thus, aggregated complexes of soluble TWEAK and Fn14 have a higher intrinsic activity to stimulate the classical NFκB pathway and qualitatively differ from isolated trimeric TWEAK-Fn14 complexes. Furthermore, determination of IL8 induction as a function of occupied activated receptors revealed that the intrinsic capability of TNFR1 to stimulate the classical NFκB pathway and IL8 production was ∼100-fold higher than Fn14. Thus, although ∼25 activated TNFR1 trimers were sufficient to trigger half-maximal IL8 production, more than 2500 cell-bound oligomerized TWEAK trimers were required to elicit a similar response.

The tumor necrosis factor superfamily of cytokines in the inflammatory myopathies: potential targets for therapy

The idiopathic inflammatory myopathies (IM) represent a heterogeneous group of autoimmune diseases, of which dermatomyositis (DM), polymyositis (PM), and sporadic inclusion body myositis (IBM) are the most common. The crucial role played by tumor necrosis factor alpha (TNFα) in the IM has long been recognized. However, so far, 18 other members of the TNF superfamily have been characterized, and many of these have not yet received the attention they deserve. In this paper, we summarize current findings for all TNF cytokines in IM, pinpointing what we know already and where current knowledge fails. For each TNF family member, possibilities for treating inflammatory diseases in general and the IM in particular are explored.

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.

Impact of soluble TWEAK and CD163/TWEAK ratio on long-term cardiovascular mortality in patients with peripheral arterial disease

AIM

Soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) has recently been introduced as a potential mediator of cardiovascular disease. We examined the associations between sTWEAK, its scavenger receptor sCD163, sCD163/sTWEAK ratio and risk for long-term all-cause and cardiovascular mortality in patients with lower-extremity peripheral arterial disease (PAD).

METHODS

sTWEAK and sCD163 serum levels were measured retrospectively in a cohort of 295 patients with symptomatic PAD followed for 6.1±2.1 years. The endpoints were defined as all-cause or cardiovascular death. The relationship between sTWEAK, sCD163 levels, sCD163/sTWEAK ratio, and times to fatal outcome was examined by Cox proportional hazards analysis.

RESULTS

sTWEAK levels were significantly lower (672 (IQR 515; 872)pg/ml vs. 814 (IQR 673; 957)pg/ml, p < 0.0001), and sCD163/sTWEAK ratio significantly higher (0.91 (IQR 0.63; 1.37) vs. 0.77 (IQR 0.55; 1.12), p = 0.008) in patients with critical limb ischemia (CLI) on admission as compared with those with intermittent claudication (IC). During follow-up, 80 (27%) patients died, hereof 33 (11.5%) of cardiovascular causes. Cox regression analysis revealed that an increase of 100 pg/ml of baseline sTWEAK were associated with a decreased risk for all cause [adjusted hazard ratio (HR) 0.89 (95%CI (0.80-0.99)), p = 0.043] and cardiovascular mortality [adjusted HR 0.83 (95% CI (0.69-0.99)), p = 0.038]. The patients with lower sTWEAK concentrations had a higher risk for cardiovascular death being more than two times as great as patients in the two upper tertiles (adjusted HR 2.2, 95% CI (1.06-4.87), p = 0.035). Similarly, the risk of cardiovascular death was 3-fold increased for patients in the upper tertile of sCD163/sTWEAK ratio as comparing with the patients in two lower tertiles (adjusted HR 3.04, 95% CI (1.44-6.43), p = 0.004). The model including sCD163/sTWEAK ratio have shown a significant improvement in accuracy of cardiovascular death prediction (the area under ROC curve 0.79 (0.72-0.86) vs. 0.84 (0.78-0.90), p = 0.019).

CONCLUSIONS

Decreased sTWEAK concentration, and increased sCD163/sTWEAK ratio were significantly and independently associated with long-term cardiovascular mortality in patients with lower-extremity PAD.

Molecular structure and characterization of the cytokine TWEAK and its receptor Fn14 in bovine

Full-length cDNA encoding TWEAK and Fn14 from bovine was isolated. We used bioinformatics to analyze the gene structure, function, evolutionary relationships, and predicted three-dimensional structure of proteins and binding sites. Real-time quantitative PCR (Q-PCR) analysis revealed that both TWEAK and Fn14 are constitutively expressed in various tissues in bovine. Bovine TWEAK and Fn14 interaction analysis by yeast two-hybrid. Our results suggest that the TWEAK-Fn14 pathway is evolutionarily highly conserved. It will be helpful for investigation on the biological role of the TWEAK/Fn14 system in this important animal model. Furthermore, it provides insight into the molecular evolution of the emerging TWEAK and Fn14 families.

DHA reduces the atrophy-associated Fn14 protein in differentiated myotubes during coculture with macrophages

Macrophages are an important component of muscle where they are involved in complex processes such as repair, regeneration and hypertrophy. We recently reported that macrophage numbers increase in the muscle of obese patients, suggesting that muscle-resident macrophages could be involved in the development of muscle insulin resistance that is associated with obesity. Coculture of activated macrophages with human muscle cells impairs insulin signaling and induces atrophy signaling pathways in the human muscle cells; this is exacerbated by the addition of palmitic acid. In this study, we tested the hypothesis that docosahexaenoic acid (DHA), a polyunsaturated fatty acid that has anti-inflammatory properties, would have the opposite effect of palmitic acid on muscle-macrophage cocultures. Surprisingly, DHA did not stimulate insulin signaling in human muscle myotubes that were cocultured with fibroblasts or macrophages. However, DHA inhibited Fn14, the TNF-like weak inducer of apoptosis receptor that increases the expression of the muscle-specific ubiquitin ligase MuRF-1 (muscle ring-finger protein-1). DHA treatment also increased the apparent molecular mass of MuRF-1 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, suggesting that DHA causes MuRF-1 to be posttranslationally modified. In conclusion, these results suggest that DHA may have a beneficial effect on muscle mass in humans by inhibiting the induction of Fn14 by infiltrating macrophages.

Gene expression of TWEAK/Fn14 and IP-10/CXCR3 in glomerulus and tubulointerstitium of patients with lupus nephritis

AIM

The role of the tumour necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 and interferon-inducible protein (IP-10)/CXCR3 axis in the pathogenesis of lupus nephritis were studied.

METHODS

The mRNA expression of TWEAK, Fn14, IP-10 and CXCR3 were quantified in the glomerulus and tubulointerstitium of 42 patients with lupus nephritis (LN group) and 10 healthy controls.

RESULTS

As compared to controls, LN patients had higher glomerular expression of TWEAK and Fn14, but glomerular CXCR3 expression was lower in the LN group. Similarly, the LN group had higher tubulointerstitial expression of TWEAK and Fn14, but lower tubulointerstitial expression of CXCR3, than controls. Glomerular TWEAK expression of class V nephritis was significantly higher than class IV nephritis. Glomerular expression of CXCR3 significantly correlated with proteinuria (r = -0.532; P = 0.019), whereas tubulointerstitial CXCR3 significantly correlated with serum creatinine (r = -0.447; P = 0.029).

CONCLUSION

In patients with lupus nephritis, there is an increase in intra-renal expression of TWEAK and Fn14, and a decrease in CXCR3 expression. Intra-renal expression of CXCR3 correlates with proteinuria and renal function. Our findings suggest that the TWEAK/Fn14 and IP-10/CXCR3 axis may contribute to the pathogenesis of lupus nephritis.

Overexpression of Fn14 promotes androgen-independent prostate cancer progression through MMP-9 and correlates with poor treatment outcome

Fibroblast growth factor-inducible 14 (Fn14), a transmembrane receptor binding to the multifunctional cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK), is known to modulate many cellular activities including cancer progression. Here, we demonstrated the significant role of Fn14 in invasion, migration and proliferation of androgen-independent prostate cancer (AIPC) cells. Fn14 and its ligand TWEAK were highly expressed in two AIPC cell lines, DU 145 and PC-3, whereas expression was weak in androgen-sensitive LNCaP cells. Fn14 knockdown using small-interfering RNAs attenuated migration, invasion and proliferation and enhanced apoptosis in the AIPC cell lines. Both forced overexpression of Fn14 by stable Fn14 complementary DNA transfection to PC-3 cells (PC-3/Fn14) and ligand activation by recombinant TWEAK in PC-3 cells enhanced invasion. Fn14 was shown to modulate expression of matrix metalloproteinase (MMP)-9, and MMP-9 mediated the invasive potential influenced by Fn14 in PC-3 cells. In vivo, subcutaneous xenografts of PC-3/Fn14 grew significantly faster than xenograft of PC-3/Mock, and the invasive capacity in PC-3/Fn14 was found to be higher than that of PC-3/Mock as evaluated in an invasion model of the diaphragm. Furthermore, the messenger RNA expressions of MMP-9 in PC-3/Fn14 xenografts were significantly higher than those in PC-3/Mock xenografts. Clinically, high expression of Fn14 was significantly associated with higher prostate-specific antigen recurrence rate in patients who underwent radical prostatectomy. In conclusion, the overexpression of Fn14 may contribute to multiple malignant cellular phenotypes associated with prostate cancer (PCa) progression, in part via MMP-9. TWEAK-Fn14 signaling may be a novel therapeutic target of PCa.

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.

Low TWEAK expression is correlated to the progression of squamous cervical carcinoma

OBJECTIVE

To investigate the correlation of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its specific receptor fibroblast growth factor-inducible immediate-early response protein 14 (Fn14) to cervical carcinogenesis by examining TWEAK/Fn14 expression levels or locations in different cervical tissues and cells.

METHODS

TWEAK/Fn14 mRNA expressions were detected by quantitative real-time PCR in total of 120 cervical samples including normal, precancerous and cancerous tissues, while protein expressions were detected by immunofluorescent staining and western blot in both tissues and cell lines. Correlation between TWEAK expression levels to cancer progression and clinicopathologic features was statistically analyzed.

RESULTS

The TWEAK expression was significantly decreased while Fn14 expression was increased in carcinoma and cervical intraepithelial neoplasm (CIN) specimens compared with that in normal control specimens. A similar trend of TWEAK/Fn14 expression was also observed in cervical cell lines. In addition, TWEAK expression decreased further along with the interstitial depth of invasion (P<0.05) and tumor grade (P<0.05), suggesting that TWEAK acts rather on local cancer tissue infiltration.

CONCLUSION

TWEAK/Fn14 pathway may play a role in the development of squamous cervical carcinoma, in which the reduced level of TWEAK could promote the progression and invasion of cervical cancer. An increase in Fn14 may reflect a compensatory response to decreased TWEAK and may provide a novel therapeutic target for human cervical cancer treatment or a biomarker for cervical cancer diagnosis.

The expression of BAFF, APRIL and TWEAK is altered in eczema skin but not in the circulation of atopic and seborrheic eczema patients

The TNF family cytokines BAFF (B-cell activating factor of the TNF family) and APRIL (a proliferation-inducing ligand) are crucial survival factors for B-cell development and activation. B-cell directed treatments have been shown to improve atopic eczema (AE), suggesting the involvement of these cytokines in the pathogenesis of AE. We therefore analyzed the expression of these TNF cytokines in AE, seborrheic eczema (SE) and healthy controls (HC). The serum/plasma concentration of BAFF, APRIL and a close TNF member TWEAK (TNF-like weak inducer of apoptosis) was measured by ELISA. The expression of these cytokines and their receptors in skin was analyzed by quantitative RT-PCR and immunofluorescence. Unlike other inflammatory diseases including autoimmune diseases and asthma, the circulating levels of BAFF, APRIL and TWEAK were not elevated in AE or SE patients compared with HCs and did not correlate with the disease severity or systemic IgE levels in AE patients. Interestingly, we found that the expression of these cytokines and their receptors was altered in positive atopy patch test reactions in AE patients (APT-AE) and in lesional skin of AE and SE patients. The expression of APRIL was decreased and the expression of BAFF was increased in eczema skin of AE and SE, which could contribute to a reduced negative regulatory input on B-cells. This was found to be more pronounced in APT-AE, the initiating acute stage of AE, which may result in dysregulation of over-activated B-cells. Furthermore, the expression levels of TWEAK and its receptor positively correlated to each other in SE lesions, but inversely correlated in AE lesions. These results shed light on potential pathogenic roles of these TNF factors in AE and SE, and pinpoint a potential of tailored treatments towards these factors in AE and SE.

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.

Development and characterization of a potent immunoconjugate targeting the Fn14 receptor on solid tumor cells

TNF-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor (FGF)-inducible 14 (Fn14) are a TNF superfamily ligand-receptor pair involved in many cellular processes including proliferation, migration, differentiation, inflammation, and angiogenesis. The Fn14 receptor is expressed at relatively low levels in normal tissues, but it is known to be dramatically elevated in a number of tumor types, including brain and breast tumors. Thus, it seems to be an excellent candidate for therapeutic intervention. We first analyzed Fn14 expression in human tumor cell lines. Fn14 was expressed in a variety of lines including breast, brain, bladder, skin, lung, ovarian, pancreatic, colon, prostate, and cervical cancer cell lines. We then developed an immunoconjugate containing a high-affinity anti-Fn14 monoclonal antibody (ITEM-4) conjugated to recombinant gelonin (rGel), a highly cytotoxic ribosome-inactivating N-glycosidase. Both ITEM-4 and the conjugate were found to bind to cells to an equivalent extent. Confocal microscopic analysis showed that ITEM4-rGel specifically and rapidly (within 2 hours) internalized into Fn14-positive T-24 bladder cancer cells but not into Fn14-deficient mouse embryonic fibroblasts. Cytotoxicity studies against 22 different tumor cell lines showed that ITEM4-rGel was highly cytotoxic to Fn14-expressing cells and was 8- to 8 × 10(4)-fold more potent than free rGel. ITEM4-rGel was found to kill cells by inducing apoptosis with high-mobility group box 1 protein release. Finally, ITEM4-rGel immunoconjugate administration promoted long-term tumor growth suppression in nude mice bearing T-24 human bladder cancer cell xenografts. Our data support the use of an antibody-drug conjugate approach to selectively target and inhibit the growth of Fn14-expressing tumors.

Cysteine tagging for MS-based proteomics

Amino acid-tagging strategies are widespread in proteomics. Because of the central role of mass spectrometry (MS) as a detection technique in protein sciences, the term "mass tagging" was coined to describe the attachment of a label, which serves MS analysis and/or adds analytical value to the measurements. These so-called mass tags can be used for separation, enrichment, detection, and quantitation of peptides and proteins. In this context, cysteine is a frequent target for modifications because the thiol function can react specifically by nucleophilic substitution or addition. Furthermore, cysteines present natural modifications of biological importance and a low occurrence in the proteome that justify the development of strategies to specifically target them in peptides or proteins. In the present review, the mass-tagging methods directed to cysteine residues are comprehensively discussed, and the advantages and drawbacks of these strategies are addressed. Some concrete applications are given to underline the relevance of cysteine-tagging techniques for MS-based proteomics.

TWEAK-Fn14 as a mediator of acute kidney injury

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (TWEAK-Fn14), are widely expressed and are involved in both injury and repair. Hotta et al. now demonstrate an important role for Fn14 in the common clamp ischemia model of acute kidney injury. Their data suggest paracrine and autocrine effects in which TWEAK produced by tubule cells feeds back on them via upregulated Fn-14 receptors expressed downstream in the proximal tubule.

TWEAK induces apoptosis through a death-signaling complex comprising receptor-interacting protein 1 (RIP1), Fas-associated death domain (FADD), and caspase-8

The tumor necrosis factor (TNF) superfamily member TNF-like weak inducer of apoptosis (TNFSF12, CD255) (TWEAK) can stimulate apoptosis in certain cancer cells. Previous studies suggest that TWEAK activates cell death indirectly, by inducing TNFα-mediated autocrine signals. However, the underlying death-signaling mechanism has not been directly defined. Consistent with earlier work, TWEAK assembled a proximal signaling complex containing its cognate receptor FN14, the adaptor TRAF2, and cellular inhibitor of apoptosis protein 1 (cIAP1). Neither the death domain adaptor Fas-associated death domain nor the apoptosis-initiating protease caspase-8 associated with this primary complex. Rather, TWEAK induced TNFα secretion and TNF receptor 1-dependent assembly of a death-signaling complex containing receptor-interacting protein 1 (RIP1), FADD, and caspase-8. Knockdown of RIP1 by siRNA prevented TWEAK-induced association of FADD with caspase-8 but not formation of the FN14-TRAF2-cIAP1 complex and inhibited apoptosis activation. Depletion of the RIP1 E3 ubiquitin ligase cIAP1 enhanced assembly of the RIP1-FADD-caspase-8 complex and augmented cell death. Conversely, knockdown of the RIP1 deubiquitinase CYLD inhibited these functions. Depletion of FADD, caspase-8, BID, or BAX and BAK but not RIP3 attenuated TWEAK-induced cell death. Pharmacologic inhibition of the NF-κB pathway or siRNA knockdown of RelA attenuated TWEAK induction of TNFα and association of RIP1 with FADD and caspase-8. These results suggest that TWEAK triggers apoptosis by promoting assembly of a RIP1-FADD-caspse-8 complex via autocrine TNFα-TNFR1 signaling. The proapoptotic activity of TWEAK is modulated by cIAP1 and CYLD and engages both the extrinsic and intrinsic signaling pathways.

TWEAK and Fn14 expression in the pathogenesis of joint inflammation and bone erosion in rheumatoid arthritis

INTRODUCTION

TNF-like weak inducer of apoptosis (TWEAK) has been proposed as a mediator of inflammation and bone erosion in rheumatoid arthritis (RA). This study aimed to investigate TWEAK and TWEAK receptor (Fn14) expression in synovial tissue from patients with active and inactive rheumatoid arthritis (RA), osteoarthritis (OA) and normal controls and assess soluble (s)TWEAK levels in the synovial fluids from patients with active RA and OA. Effects of sTWEAK on osteoclasts and osteoblasts were investigated in vitro.

METHODS

TWEAK and Fn14 expression were detected in synovial tissues by immunohistochemistry (IHC). Selected tissues were dual labelled with antibodies specific for TWEAK and lineage-selective cell surface markers CD68, Tryptase G, CD22 and CD38. TWEAK mRNA expression was examined in human peripheral blood mononuclear cells (PBMC) sorted on the basis of their expression of CD22. sTWEAK was detected in synovial fluid from OA and RA patients by ELISA. The effect of sTWEAK on PBMC and RAW 264.7 osteoclastogenesis was examined. The effect of sTWEAK on cell surface receptor activator of NF Kappa B Ligand (RANKL) expression by human osteoblasts was determined by flow cytometry.

RESULTS

TWEAK and Fn14 expression were significantly higher in synovial tissue from all patient groups compared to the synovial tissue from control subjects (P < 0.05). TWEAK was significantly higher in active compared with inactive RA tissues (P < 0.05). TWEAK expression co-localised with a subset of CD38+ plasma cells and with CD22+ B-lymphocytes in RA tissues. Abundant TWEAK mRNA expression was detected in normal human CD22+ B cells. Higher levels of sTWEAK were observed in synovial fluids isolated from active RA compared with OA patients. sTWEAK did not stimulate osteoclast formation directly from PBMC, however, sTWEAK induced the surface expression of RANKL by human immature, STRO-1+ osteoblasts.

CONCLUSIONS

The expression of TWEAK by CD22+ B cells and CD38+ plasma cells in RA synovium represents a novel potential pathogenic pathway. High levels of sTWEAK in active RA synovial fluid and of TWEAK and Fn14 in active RA tissue, together with the effect of TWEAK to induce osteoblastic RANKL expression, is consistent with TWEAK/Fn14 signalling being important in the pathogenesis of inflammation and bone erosion in RA.

Soluble TWEAK and PTX3 in nondialysis CKD patients: impact on endothelial dysfunction and cardiovascular outcomes

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) conveys high mortality rates. Soluble TNF-like weak inducer of apoptosis (sTWEAK) and long pentraxin 3 (PTX3) are predictors of mortality in dialysis patients and determinants of endothelial dysfunction. Now, we hypothesize that both sTWEAK and PTX3 act as biomarkers of cardiovascular outcomes in nondialysis CKD patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Cross-sectional analysis in which flow-mediated dilation (FMD) and intima-media thickness (IMT) were assessed in 257 nondialysis stage 1 to 5 CKD patients (mean age, 52 ± 12 years; 130 men), together with biochemical measurements and sTWEAK and PTX3 assessments. Patients were followed for cardiovascular outcomes.

RESULTS

PTX3 and IMT increased, whereas FMD and sTWEAK decreased across CKD stages (P<0.001 for all). Both PTX3 and sTWEAK appeared as strong determinants of FMD in multivariate analysis. The univariate associations of sTWEAK and PTX3 with IMT were dependent on estimated GFR. After a median of 39 months (range, 2 to 43 months), 22 fatal and 57 nonfatal cardiovascular events occurred. In a Cox model excluding PTX3, decreasing sTWEAK concentration was associated with increased risk of cardiovascular events independently of basic confounders (age, gender, estimated GFR, C reactive protein, diabetes, and cardiovascular comorbidity) and FMD. In a model excluding sTWEAK, circulating levels of PTX3 were directly associated with cardiovascular outcomes independently of basic confounders, but this association was lost after adjustment for FMD.

CONCLUSIONS

Both PTX3 and sTWEAK levels associated with the endothelial dysfunction observed with progressive kidney failure. Additionally, both biomarkers impacted the predictability of cardiovascular outcomes.

TWEAK appears as a modulator of endometrial IL-18 related cytotoxic activity of uterine natural killers

Background

TWEAK (Tumor necrosis factor like WEAK inducer of apoptosis) is highly expressed by different immune cells and triggers multiple cellular responses, including control of angiogenesis. Our objective was to investigate its role in the human endometrium during the implantation window, using an ex-vivo endometrial microhistoculture model. Indeed, previous results suggested that basic TWEAK expression influences the IL-18 related uNK recruitment and local cytotoxicity.

Methodology/Principal Findings

Endometrial biopsies were performed 7 to 9 days after the ovulation surge of women in monitored natural cycles. Biopsies were cut in micro-pieces and cultured on collagen sponge with appropriate medium. Morphology, functionality and cell death were analysed at different time of the culture. We used this ex vivo model to study mRNA expressions of NKp46 (a uNK cytotoxic receptor) and TGF-beta1 (protein which regulates uNK cytokine production) after adjunction of excess of recombinant IL-18 and either recombinant TWEAK or its antibody. NKp46 protein expression was also detailed by immunohistochemistry in selected patients with high basic mRNA level of IL-18 and either low or high mRNA level of TWEAK. The NKp46 immunostaining was stronger in patients with an IL-18 over-expression and a low TWEAK expression, when compared with patients with both IL-18 and TWEAK high expressions. We did not observe any difference for TWEAK expression when recombinant protein IL-18 or its antibody was added, or conversely, for IL-18 expression when TWEAK or its antibody was added in the culture medium. In a pro-inflammatory environment (obtained by an excess of IL-18), inhibition of TWEAK was able to increase significantly NKp46 and TGF-beta1 mRNA expressions.

Conclusions/Significance

TWEAK doesn't act on IL-18 expression but seems to control IL-18 related cytotoxicity on uNK cells when IL-18 is over-expressed. Thus, TWEAK appears as a crucial physiological modulator to prevent endometrial uNK cytotoxicity in human.

Elevation of human tumor necrosis factor-like weak inducer of apoptosis in peripheral blood mononuclear cells is correlated with disease activity and lupus nephritis in patients with systemic lupus erythematosus

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a recently identified proinflammatory cytokine of the TNF superfamily. Studies have indicated that TWEAK plays an important role in renal, vascular injury and immune disease. The aim of this study was to explore the expression of the TWEAK in peripheral blood mononuclear cells (PBMCs) and analyze the correlation between TWEAK and disease activity and renal damage of SLE. The expression of TWEAK in PBMCs was determined by RT-PCR and western blot. SLE disease activity was evaluated by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) 2000 score. Next were analyzed the correlations of TWEAK mRNA and protein to serum IL-10, MCP-1 and some laboratory parameters of SLE disease activity. Subjects comprised 48 patients with SLE including 25 patients with renal damage and 23 without, 20 patients with rheumatoid arthrithis (RA) and 15 healthy controls. The results showed that TWEAK expressions in PBMCs from SLE patients were significantly higher than that in RA patients or healthy controls, especially higher in those patients with renal disease. Elevated production of TWEAK is correlated positively and significantly with SLEDAI, proteinuria, serum anti-dsDNA, IL-10 and MCP-1, but inversely associated with serum complements. Our results suggested that TWEAK in PBMCs is positively related to SLE disease activity and might be involved in the pathogenesis of SLE.

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.

Soluble TWEAK plasma levels predict expansion of human abdominal aortic aneurysms

OBJECTIVES

Diminished soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) concentrations are associated with cardiovascular diseases. We have analyzed sTWEAK levels and its relation with expansion rate in subjects with abdominal aortic aneurysm (AAA).

METHODS

sTWEAK levels were measured by ELISA.

RESULTS

sTWEAK concentrations were diminished in small AAA (≤ 5 cm; 353 ± 12 pg/mL; n = 25, p = 0.03) and large AAA (>5 cm; 315 ± 21 pg/mL; n = 18, p = 0.004) compared with healthy subjects (411 ± 22 pg/mL; n=27). Moreover, sTWEAK concentrations were negatively associated with AAA size (r = -0.4; p = 0.008). sTWEAK was also negatively associated with AAA expansion rate with 5 years of follow-up (n = 79, r = -0.263; p = 0.031). Multivariate regression analysis revealed that sTWEAK levels were independently associated with AAA growth rate (β = -0.208; p = 0.046).

CONCLUSIONS

sTWEAK plasma levels were decreased in subjects with AAA and were independently related with AAA expansion rate indicating that this protein could be a novel diagnostic and prognostic biomarker of AAA.

TWEAK regulates proliferation and differentiation of adult neural progenitor cells

The cytokine TWEAK is expressed in the brain and is induced in cerebral ischemia and other brain disorders. TWEAK regulates proliferation and differentiation of progenitor cells but its effect on adult neural progenitor cells is still unknown. Therefore, we investigated the proliferation of neural progenitor cells from the subventricular zone of adult mice in response to TWEAK treatment. TWEAK inhibited proliferation of neural progenitor cells through its membrane receptor Fn14. The reduced proliferation was not due to cell death. By using a reporter assay we found that TWEAK activated the transcription factor NF-κB in adult neural progenitor cells. Blockade of NF-κB signaling reversed the inhibition of cell proliferation by TWEAK. In addition, TWEAK induced neuronal differentiation of neural progenitor cells and lowered the expression of hes1, a transcription factor that prevents neuronal differentiation. In adult mice deficient of the TWEAK receptor Fn14, neurogenesis was reduced in the subventricular zone. In conclusion, our data show that TWEAK regulates adult neurogenesis in the subventricular zone by binding to the membrane receptor Fn14 and activating NF-κB.

Tumor necrosis factor-like weak inducer of apoptosis and fibroblast growth factor-inducible 14 mediate cerebral ischemia-induced poly(ADP-ribose) polymerase-1 activation and neuronal death

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 tumor necrosis factor alpha (TNF-α) and mediated by nuclear factor-kappa B (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 (PARP-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.

Regulation of tumor necrosis factor-like weak inducer of apoptosis receptor protein (TWEAKR) expression by Kaposi's sarcoma-associated herpesvirus microRNA prevents TWEAK-induced apoptosis and inflammatory cytokine expression

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is the causative agent of KS, the second most common AIDS-associated malignancy. KSHV expresses at least 18 different mature microRNAs (miRNAs) during latency. To identify cellular targets of KSHV miRNAs, we have analyzed a previously reported series of microarrays examining changes in cellular gene expression in the presence of KSHV miRNAs. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) receptor (TWEAKR) was among the most consistently and robustly downregulated genes in the presence of KSHV miR-K12-10a (miR-K10a). Results from luciferase assays with reporter plasmids containing the 3' untranslated region (UTR) of TWEAKR suggest a targeting of TWEAKR by miR-K10a. The mutation of two predicted miR-K10a recognition sites within the 3' UTR of TWEAKR completely disrupts inhibition by miR-K10a. The expression of TWEAKR was downregulated in cells transfected with miR-K10a as well as during de novo KSHV infection. In a KS tumor-derived endothelial cell line, the downregulation of TWEAKR by miR-K10a resulted in reduced levels of TWEAK-induced caspase activation. In addition, cells transfected with miR-K10a showed less induction of apoptosis by annexin V staining and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays. Finally, the downregulation of TWEAKR by miR-K10a in primary human endothelial cells resulted in a decrease in levels of expression of the proinflammatory cytokines interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) in response to TWEAK. These results identify and validate an important cellular target of KSHV miRNAs. Furthermore, we demonstrate that a viral miRNA protects cells from apoptosis and suppresses a proinflammatory response, which may have significant implications in the complex context of KS lesions.

Differences in the predictive value of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in advanced ischemic and non-ischemic heart failure

OBJECTIVE

To assess the prognostic value of the pro-apoptotic, but also cell growth-inducing molecule soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) in heart failure (HF).

METHODS

We assayed sTWEAK levels in 351 patients with advanced HF (non-ischemic: 130, ischemic: 221). During a median follow-up of 4.9 years, 195 patients (56%) died.

RESULTS

sTWEAK concentrations were associated with extended survival in patients with non-ischemic (P=0.022), but not with ischemic HF (P=0.82). The inverse association in non-ischemic HF remained significant in a multivariable Cox regression model (P=0.025) with a hazard ratio of 0.40 (95% confidence interval: 0.21-0.77) comparing the third to the first tertile (P=0.007).

CONCLUSION

Low sTWEAK levels independently predict mortality in advanced non-ischemic HF. sTWEAK-induced proliferation of cardiomyocytes may explain its impact on suvival. The different prognostic value of sTWEAK in ischemic and non-ischemic HF may point towards distinct pathogenic pathways determining the course of disease.

Genetic ablation of TWEAK augments regeneration and post-injury growth of skeletal muscle in mice

Impairment in the regeneration process is a critical determinant for skeletal muscle wasting in chronic diseases and degenerative muscle disorders. Inflammatory cytokines are known to cause significant muscle wasting, however, their role in myofiber regeneration is less clear. In this study we have investigated the role of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in skeletal muscle regeneration in vivo. Our results show that expression levels of TWEAK and its receptor Fn14 are significantly increased in skeletal muscles of mice after injury. Genetic deletion of TWEAK increased the fiber cross-sectional area and levels of embryonic isoform of myosin heavy chain in regenerating tibial anterior muscle. Conversely, muscle-specific transgenic overexpression of TWEAK reduced the fiber cross-sectional area and levels of the embryonic myosin heavy chain in regenerating muscle. TWEAK induced the expression of several inflammatory molecules and increased interstitial fibrosis in regenerating muscle. Genetic ablation of TWEAK suppressed, whereas overexpression of TWEAK increased, the activation of nuclear factor-kappa B without affecting the activation of Akt or p38 kinase in regenerating myofibers. Primary myoblasts from TWEAK-null mice showed enhanced differentiation in vitro, whereas myoblasts from TWEAK-Tg mice showed reduced differentiation compared with wild-type mice. Collectively, our study suggests that TWEAK negatively regulates muscle regeneration and that TWEAK is a potential therapeutic target to enhance skeletal muscle regeneration in vivo.

Soluble and transmembrane TNF-like weak inducer of apoptosis differentially activate the classical and noncanonical NF-kappa B pathway

TNF-like weak inducer of apoptosis, TWEAK, is a typical member of the TNF ligand family. Thus, it is initially expressed as a type II transmembrane protein from which a soluble variant can be released by proteolytic processing. In this study, we show that membrane TWEAK is superior to soluble variant of TWEAK (sTWEAK) with respect to the activation of the classical NF-kappaB pathway, whereas both TWEAK variants are potent inducers of TNFR-associated factor-2 depletion, NF-kappaB-inducing kinase accumulation and p100 processing, hallmarks of activation of the noncanonical NF-kappaB pathway. Like other soluble TNF ligands with a poor capability to activate their corresponding receptor, sTWEAK acquires an activity resembling those of the transmembrane ligand by oligomerization or cell surface-immobilization. Blockade of the Fn14 receptor inhibited NF-kappaB signaling irrespective of the TWEAK form used for stimulation, indicating that the differential activities of the two TWEAK variants on classical and noncanonical NF-kappaB signaling is not related to the use of different receptors.

IAPs: from caspase inhibitors to modulators of NF-kappaB, inflammation and cancer

The realization that alterations in inhibitor of apoptosis (IAP) proteins are found in many types of human cancer and are associated with chemoresistance, disease progression and poor prognosis, has sparked a worldwide frenzy in the development of small pharmacological inhibitors of IAPs. The development of such inhibitors has radically changed our knowledge of the signalling processes that are regulated by IAPs. Recent studies indicate that IAPs not only regulate caspases and apoptosis, but also modulate inflammatory signalling and immunity, mitogenic kinase signalling, proliferation and mitosis, as well as cell invasion and metastasis.

Highly conserved transcriptional responses to mechanical ventilation of the lung

Cross-species analysis of microarray data has shown improved discriminating power between healthy and diseased states. Computational approaches have proven effective in deciphering the complexity of human disease by identifying upstream regulatory elements and the transcription factors that interact with them. Here we used both methods to identify highly conserved transcriptional responses during mechanical ventilation, an important therapeutic treatment that has injurious side effects. We generated control and ventilated whole lung samples from the premature baboon model of bronchopulmonary dysplasia (BPD), processed them for microarray, and combined them with existing whole lung oligonucleotide microarray data from 85 additional control samples from mouse, rat, and human and 19 additional ventilated samples from mouse and rat. Of the 2,531 orthologs shared by all 114 samples, 60 were modulated by mechanical ventilation [false discovery rate (FDR)-adjusted q value (q(FDR)) = 0.005, ANOVA]. These included transcripts encoding the transcription factors ATF3 and FOS. Because of compelling known roles for these transcription factors, we used computational methods to predict their targets in the premature baboon model of BPD, which included elastin (ELN), gastrin-releasing polypeptide (GRP), and connective tissue growth factor (CTGF). This approach identified highly conserved transcriptional responses to mechanical ventilation and may facilitate identification of therapeutic targets to reduce the side effects of this valuable treatment.

Methods and potential biomarkers for the evaluation of endothelial dysfunction in chronic kidney disease: a critical approach

The impressive cardiovascular morbidity and mortality of chronic kidney disease (CKD) patients is attributable in a significant proportion to endothelial dysfunction (ED), arterial stiffness, and vascular calcifications. Abnormal vascular reactivity in these patients is more pronounced compared with other high-risk populations, but remains undiagnosed in the usual clinical setting. We briefly review the most important causes and risk factors of ED, oxidative stress, and inflammation related to arterial stiffness. We describe the main methods of ED investigation and the importance of using potential biomarkers together with classic techniques for a more comprehensive assessment of this condition. These methods include evaluation of: forearm blood flow by plethysmography, skin microcirculation by laser Doppler, and flow-mediated vasodilation by Doppler ultrasound imaging. Applanation tonometry is an easy-to-handle tool that allows a clinically reliable assessment of arterial stiffness and is also useful in quantifying endothelium-dependent and -independent vascular reactivity. We also discuss the diagnostic and therapeutic impact of new markers of ED in the CKD population. Improvement of endothelial function is an important challenge for clinical practice, and there are relatively few therapeutical strategies available. Therefore, a combined biomarker and bedside investigational approach could be a starting point for developing optimal therapeutic tools.

Genetics vs. entropy: longevity factors suppress the NF-kappaB-driven entropic aging process

Molecular studies in model organisms have identified potent longevity genes which can delay the aging process and extend the lifespan. Longevity factors promote stress resistance and cellular survival. It seems that the aging process itself is not genetically programmed but a random process involving the loss of molecular fidelity and subsequent accumulation of waste products. This age-related increase in cellular entropy is compatible with the disposable soma theory of aging. A large array of host defence systems has been linked to the NF-kappaB system which is an ancient signaling pathway specialized to host defence, e.g. functioning in immune system. Emerging evidence demonstrates that the NF-kappaB system is activated during aging. Oxidative stress and DNA damage increase with aging and elicit a sustained activation of the NF-kappaB system which has negative consequences, e.g. chronic inflammatory response, increase in apoptotic resistance, decline in autophagic cleansing, and tissue atrophy, i.e. processes that enhance the aging process. We will discuss the role of NF-kappaB system in the pro-aging signaling and will emphasize that several longevity factors seem to be inhibitors of NF-kappaB signaling and in that way they can suppress the NF-kappaB-driven entropic host defence catastrophe.

Mechanism of endothelial dysfunction in chronic kidney disease

Endothelium is the largest organ in the body strategically located between the wall of blood vessels and the blood stream. The human body contains approximately 10(13) endothelial cells weighing approximately 1kg, and covering a surface area of 4000 to 7000m(2) equivalent to the soccer playground. Hypertension and shear stress, inflammation, diabetes-associated factors such as advanced glycated end products, and uremic toxins are some of the prevalent risk factors of endothelial dysfunction in chronic kidney disease. In renal failure endothelial dysfunction and atherosclerosis are almost universal, as well as cardiovascular complications. Endothelial cell damage or injury is invariably associated with such clinical conditions as thrombosis, hypertension, renal failure and atherosclerosis and may be also responsible for accelerated atherosclerosis in patients with chronic renal failure. Traditional risk factor cannot explain the high prevalence and incidence of cardiovascular disease in chronic kidney disease, therefore other non-traditional risk factors such as endothelial dysfunction, oxidative stress or insulin resistance have increasingly been studied. In this review paper mechanism of endothelial dysfunction, including the role of nitric oxide pathway, adipocytokines and hemodialysis-induced endothelial dysfunction is discussed.

Neuroprotective effect of Fn14 deficiency is associated with induction of the granulocyte-colony stimulating factor (G-CSF) pathway in experimental stroke and enhanced by a pathogenic human antiphospholipid antibody

Using a transgenic mouse model of ischemic stroke we checked for a possible interaction of antiphospholipid antibodies (aPL) which often cause thromboses as well as central nervous system (CNS) involvement under non-thrombotic conditions and the TWEAK/Fn14 pathway known to be adversely involved in inflammatory and ischemic brain disease. After 7 days, infarct volumes were reduced in Fn14 deficient mice and were further decreased by aPL treatment. This was associated with strongest increase of the endogenous neuroprotective G-CSF/G-CSF receptor system. This unexpected beneficial action of aPL is an example for a non-thrombogenic action and the double-edged nature of aPL.

The interaction between tumor necrosis factor-like weak inducer of apoptosis and its receptor fibroblast growth factor-inducible 14 promotes the recruitment of neutrophils into the ischemic brain

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are expressed in endothelial cells and perivascular astrocytes. Here, we show that TWEAK induces a dose-dependent increase in the expression of the chemokine monocyte chemoattractant protein-1 (MCP-1) in astrocytes, and that this effect is mediated by its interaction with Fn14 via nuclear factor-kappaB pathway activation. Exposure to oxygen-glucose deprivation (OGD) conditions increases TWEAK and Fn14 mRNA expression in wild-type (Wt) astrocytic cultures. Likewise, incubation under OGD conditions induces the expression of MCP-1 in Wt astrocytes but not in astrocytes deficient on either TWEAK (TWEAK(-/-)) or Fn14 (Fn14(-/-)). We also found that TWEAK induces the passage of neutrophils to the abluminal side of an in vitro model of the blood-brain barrier. Our earlier studies indicate that cerebral ischemia increases the expression of TWEAK and Fn14 in the endothelial cell-basement membrane-astrocyte interface. Here, we report that middle cerebral artery occlusion increases the expression of MCP-1 and the recruitment of neutrophils into the ischemic tissue in Wt but not in TWEAK(-/-) or Fn14(-/-) mice. These novel results indicate that during cerebral ischemia, the interaction between TWEAK and Fn14 leads to the recruitment of leukocytes into the ischemic tissue.

Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 during cardiac remodelling in rats

AIM

Accumulating evidence supports the concept that proinflammatory cytokines play an essential role in the failing heart. We examined the concomitant tumour necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 expression in myocytes in vitro as well as in vivo in cardiac remodelling.

METHODS

We assessed TWEAK and its receptor Fn14 expression in response to angiotensin (Ang) II, myocardial infarction (MI) as well as to local adenovirus-mediated p38 gene transfer in vivo. The effect of various hypertrophic factors and mechanical stretch was studied in neonatal rat ventricular myocyte cell culture.

RESULTS

Ang II increased Fn14 levels from 6 h to 2 weeks, the greatest increase in mRNA levels being observed at 6 h (6.3-fold, P < 0.001) and protein levels at 12 h (4.9-fold, P < 0.01). TWEAK mRNA and protein levels remained almost unchanged during Ang II infusion. Likewise, a rapid and sustained elevation of Fn14 mRNA and protein levels in the left ventricle was observed after experimental MI. Moreover, local p38 gene transfer increased Fn14 mRNA and protein but not TWEAK levels. Fn14 immunoreactive cells were mainly proliferating non-myocytes in the inflammation area while TWEAK immunoreactivity localized to cardiomyocytes and endothelial cells of the coronary arteries. Hypertrophic agonists and lipopolysaccharide increased Fn14 but not TWEAK gene expression in neonatal rat myocytes, while mechanical stretch upregulated Fn14 and downregulated TWEAK gene expression.

CONCLUSIONS

In conclusion, the cardiac TWEAK/Fn14 pathway is modified in response to myocardial injury, inflammation and pressure overload. Furthermore, our findings underscore the importance of Fn14 as a mediator of TWEAK/Fn14 signalling in the heart and a potential target for therapeutic interventions.

Combined therapy with renin-angiotensin system and calcium channel blockers in type 2 diabetic hypertensive patients with proteinuria: effects on soluble TWEAK, PTX3, and flow-mediated dilation

BACKGROUND AND OBJECTIVES

Soluble TNF-like weak inducer of apoptosis (sTWEAK) and long pentraxin-3 (PTX3) concentrations have been associated with endothelial function in patients with chronic kidney disease (CKD). This study tested the hypothesis that the improvement in endothelial function after initiation of angiotensin II receptor blocker (valsartan), calcium channel blocker (amlodipine) therapy, or a combination of both is directly linked to the normalization of sTWEAK and PTX3.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One-hundred-eight diabetic CKD stage I patients with hypertension (56% men, 46.7+/-5.3 years) were allocated to a 12-week intervention with amlodipine (10 mg/d), valsartan (160 mg/d), or their combination. Plasma levels of sTWEAK, PTX3, and flow-mediated dilation (FMD) were studied during the interventions.

RESULTS

All treatment strategies effectively increased FMD and reduced proteinuria, confirming a more prone reduction with the combined therapy. These improvements were followed by significant PTX3 reductions. Valsartan alone and in combination with amlodipine achieved significant incremental raises in sTWEAK plasma levels. More importantly, the changes observed in sTWEAK (beta=0.25, P=0.006) or PTX3 (beta=-0.24, P=0.007) plasma levels were independently associated with the improvement in ultrasonographically measured FMD.

CONCLUSIONS

This study shows that treatment with antihypertensive drugs improves FMD and normalizes proteinuria, PTX3, and sTWEAK in diabetic CKD stage I patients with hypertension. The improvement in FMD was independently associated with PTX3 and sTWEAK normalization. Two surrogate biomarkers of endothelial function are therefore identified with potential as therapeutic targets. The study was registered in clinicaltrials.gov as NCT00921570.

The TWEAK-Fn14 system is a critical regulator of denervation-induced skeletal muscle atrophy in mice

The TNF-related cytokine TWEAK promotes skeletal muscle atrophy that is associated with classical disuse syndromes.

Skeletal muscle atrophy occurs in a variety of clinical settings, including cachexia, disuse, and denervation. Inflammatory cytokines have been shown to be mediators of cancer cachexia; however, the role of cytokines in denervation- and immobilization-induced skeletal muscle loss remains unknown. In this study, we demonstrate that a single cytokine, TNF-like weak inducer of apoptosis (TWEAK), mediates skeletal muscle atrophy that occurs under denervation conditions. Transgenic expression of TWEAK induces atrophy, fibrosis, fiber-type switching, and the degradation of muscle proteins. Importantly, genetic ablation of TWEAK decreases the loss of muscle proteins and spared fiber cross-sectional area, muscle mass, and strength after denervation. Expression of the TWEAK receptor Fn14 (fibroblast growth factor–inducible receptor 14) and not the cytokine is significantly increased in muscle upon denervation, demonstrating an unexpected inside-out signaling pathway; the receptor up-regulation allows for TWEAK activation of nuclear factor κB, causing an increase in the expression of the E3 ubiquitin ligase MuRF1. This study reveals a novel mediator of skeletal muscle atrophy and indicates that the TWEAK–Fn14 system is an important target for preventing skeletal muscle wasting.

Biomarkers for lupus nephritis: a critical appraisal

Kidney disease is one of the most serious manifestations of systemic lupus erythematosus (SLE). Despite the improvement in the medical care of SLE in the past two decades, the prognosis of lupus nephritis remains unsatisfactory. Besides exploring more effective but less toxic treatment modalities that will further improve the remission rate, early detection and treatment of renal activity may spare patients from intensive immunosuppressive therapies and reduce renal damage. Conventional clinical parameters such as creatinine clearance, proteinuria, urine sediments, anti-dsDNA, and complement levels are not sensitive or specific enough for detecting ongoing disease activity in the lupus kidneys and early relapse of nephritis. Thus, novel biomarkers are necessary to enhance the diagnostic accuracy and sensitivity of lupus renal disease, prognostic stratification, monitoring of treatment response, and detection of early renal flares. This paper reviews promising biomarkers that have recently been evaluated in longitudinal studies of lupus nephritis.

Molecular characterization of the canine cytokine TWEAK (CD255) and its receptor, Fn14 (CD266)

TWEAK is a member of the tumor necrosis factor superfamily. The interaction of TWEAK with its receptor Fn14 regulates multiple cellular responses, including stimulation of proliferation, migration, apoptosis, angiogenesis, and induction of proinflammatory cytokines. This paper reports for the first time the molecular cloning of dog TWEAK and Fn14. The open reading frame (ORF) of dog TWEAK is 750bp, its genomic DNA consists of seven exons and six introns and is approximately 10kb in size by computer-assisted analysis. Sequence similarity at the amino acid level between dog TWEAK and human or mouse was 95 and 92%, respectively. The ORF of dog Fn14 contains 390bp. Sequence similarity at the amino acid level between dog Fn14 and human, or mouse, or frog was 95, 93 and 64%, respectively. Real-time quantitative PCR analysis revealed that both TWEAK and Fn14 are constitutively expressed in various tissues in dog. Furthermore, we verified dTWEAK interacted with dFn14 by yeast two-hybrid assay. Our results suggest that the TWEAK-Fn14 pathway is evolutionarily highly conserved. It will be helpful for investigation on the biological role of the TWEAK/Fn14 system in this important animal model. Furthermore, it provides insight into the molecular evolution of the emerging TWEAK and Fn14 families.