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

The relationships between serum sTWEAK, FGF-23 levels, and carotid atherosclerosis in renal transplant patients

BACKGROUND

Cardiovascular disease is the main cause of mortality after renal transplantation. Soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) and fibroblast growth factor-23 (FGF-23) are two novel molecules that have been associated with atherosclerosis in different populations. In this cross-sectional study, we investigated the associations between sTWEAK, FGF-23, and carotid artery intima-media thickness (CA-IMT) in renal transplant patients.

METHODS

A total of 117 renal transplant patients were studied. CA-IMT was determined by B-mode Doppler ultrasonography. Serum sTWEAK and FGF-23 were measured by a commercially available enzyme-linked immunosorbent assay (ELISA).

RESULTS

Mean age was 39.6 ± 9.6 years and 51% of the patients were male. Mean sTWEAK level was 595 ± 225 pg/mL (158-1140), FGF-23 level was 92 ± 123 RU/mL (9.6-1006), and CA-IMT level was 0.62 ± 0.11 mm (0.40-0.98). sTWEAK level was positively correlated with CA-IMT. There was no association between sTWEAK and FGF-23 levels. FGF-23 was also associated with CA-IMT. In adjusted models using linear regression analysis, only age and serum TWEAK levels were predictors for CA-IMT.

CONCLUSION

There is a positive correlation between CA-IMT and sTWEAK, but not with FGF-23 levels in renal transplant patients.

Relationship of Intrarenal Gene Expression and the Histological Class of Lupus Nephritis — A Study on Repeat Renal Biopsy

Objective.

To study the role of tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK)/Fn14 and the interferon-inducible protein (IP-10)/CXCR3 axis in lupus nephritis (LN).

Methods.

We studied 113 patients with LN who had had repeat renal biopsies. Glomerular and tubulointerstitial messenger RNA expression of TWEAK, Fn14, IP-10, and CXCR3 were quantified.

Results.

Glomerular Fn14 expression decreased when changed from proliferative or mixed nephritis to membranous nephropathy (p = 0.016), and increased when changed from membranous to proliferative or mixed nephritis (p = 0.0006). On the other hand, tubulointerstitial TWEAK expression decreased when changed from proliferative or mixed nephritis to membranous nephropathy (p = 0.004), and increased when changed from membranous nephropathy to proliferative nephritis (p = 0.010). Tubulointerstitial IP-10 expression decreased when changed from proliferative or mixed nephritis to membranous nephropathy (p < 0.0001). Histological activity index correlated significantly with the glomerular expression of Fn14 (r = 0.421, p < 0.0001) and tubulointerstitial expression of TWEAK (r = 0.413, p < 0.0001) and IP-10 (r = 0.472, p < 0.0001).

Conclusion.

Glomerular Fn14 and tubulointerstitial TWEAK and IP-10 expression appeared to have consistent changes in relation to the histological class of LN and correlated with the histological activity index. Our findings suggest a specific role of these genes in the pathogenesis of LN.

The role of TWEAK/Fn14 in cardiac remodeling

The pathophysiological basis of heart failure is cardiac remodeling, a process that comprises structural and functional changes including cardiomyocyte proliferation, hypertrophy, necrosis, apoptosis, autophagy, interstitial fibrosis, contractile dysfunction and ventricular dilatation. Accumulating evidence demonstrate that tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is involved in the process by binding its receptor fibroblast growth factor-inducible molecule 14 (Fn14). In this review, we will discuss the potential role of the TWEAK/Fn14 axis in cardiac remodeling, elucidate its possible mechanisms and explore new therapeutic targets for heart failure.

Role of TWEAK in lupus nephritis: a bench-to-bedside review

There is significant unmet need in the treatment of lupus nephritis (LN) patients. In this review, we highlight the role of the TWEAK/Fn14 pathway in mediating key pathologic processes underlying LN involving both glomerular and tubular injury, and thus the potential for renal protection via blockade of this pathway. The specific pathological mechanisms of TWEAK - namely promoting inflammation, renal cell proliferation and apoptosis, vascular activation and fibrosis - are described, with supporting data from animal models and in vitro systems. Furthermore, we detail the translational relevance of these mechanisms to clinical readouts in human LN. We present the opportunity for an anti-TWEAK therapeutic as a renal protective agent to improve efficacy relative to current standard of care treatments hopefully without increased safety risk, and highlight a phase II trial with BIIB023, an anti-TWEAK neutralizing antibody, designed to assess efficacy in LN patients. Taken together, targeting the TWEAK/Fn14 axis represents a potential new therapeutic paradigm for achieving renal protection in LN patients.

Resistin: functional roles and therapeutic considerations for cardiovascular disease

Resistin, originally described as an adipocyte-specific hormone, has been suggested to be an important link between obesity, insulin resistance and diabetes. Although its expression was initially defined in adipocytes, significant levels of resistin expression in humans are mainly found in mononuclear leukocytes, macrophages, spleen and bone marrow cells. Increasing evidence indicates that resistin plays important regulatory roles apart from its role in insulin resistance and diabetes in a variety of biological processes: atherosclerosis and cardiovascular disease (CVD), non-alcoholic fatty liver disease, autoimmune disease, malignancy, asthma, inflammatory bowel disease and chronic kidney disease. As CVD accounts for a significant amount of morbidity and mortality in patients with diabetes and without diabetes, it is important to understand the role that adipokines such as resistin play in the cardiovascular system. Evidence suggests that resistin is involved in pathological processes leading to CVD including inflammation, endothelial dysfunction, thrombosis, angiogenesis and smooth muscle cell dysfunction. The modes of action and signalling pathways whereby resistin interacts with its target cells are beginning to be understood. In this review, the current knowledge about the functions and pathophysiological implications of resistin in CVD development is summarized; clinical translations, therapeutic considerations and future directions in the field of resistin research are discussed.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Resistin: functional roles and therapeutic considerations for cardiovascular disease

Resistin, originally described as an adipocyte-specific hormone, has been suggested to be an important link between obesity, insulin resistance and diabetes. Although its expression was initially defined in adipocytes, significant levels of resistin expression in humans are mainly found in mononuclear leukocytes, macrophages, spleen and bone marrow cells. Increasing evidence indicates that resistin plays important regulatory roles apart from its role in insulin resistance and diabetes in a variety of biological processes: atherosclerosis and cardiovascular disease (CVD), non-alcoholic fatty liver disease, autoimmune disease, malignancy, asthma, inflammatory bowel disease and chronic kidney disease. As CVD accounts for a significant amount of morbidity and mortality in patients with diabetes and without diabetes, it is important to understand the role that adipokines such as resistin play in the cardiovascular system. Evidence suggests that resistin is involved in pathological processes leading to CVD including inflammation, endothelial dysfunction, thrombosis, angiogenesis and smooth muscle cell dysfunction. The modes of action and signalling pathways whereby resistin interacts with its target cells are beginning to be understood. In this review, the current knowledge about the functions and pathophysiological implications of resistin in CVD development is summarized; clinical translations, therapeutic considerations and future directions in the field of resistin research are discussed.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

TWEAK/Fn14 promotes the proliferation and collagen synthesis of rat cardiac fibroblasts via the NF-кB pathway

We wished to elucidate a potential role of the tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible molecule 14 (Fn14) axis in myocardial fibrosis. Stimulation of neonatal rat cardiac fibroblasts (CFs) with TWEAK could increase CFs numbers and collagen synthesis. Conversely, when CFs were pretreated with siRNA against Fn14, induction of cell proliferation and collagen synthesis by TWEAK were inhibited. Pretreatment with TWEAK on CFs induced activation of the nuclear factor-kappaB (NF-кB) pathway and subsequently increased the production of metalloproteinase-9 (MMP-9). Cell treatment with siRNA against Fn14 led to inhibition of the NF-кB pathway. Additionally, after stimulation of cell with ammonium pyrrolidine dithiocarbamate, cell proliferation and collagen synthesis induced by NF-кB and the upregulation of MMP-9 production were inhibited. The present study suggested that the TWEAK/Fn14 axis increased cell proliferation and collagen synthesis by activating the NF-кB pathway and increasing MMP-9 activity. This axis may be important for regulating myocardial fibrosis.

Tumor necrosis factor-like weak inducer of apoptosis increases CC chemokine ligand 20 production in interleukin 1β-stimulated human gingival fibroblasts

CC chemokine ligand 20 (CCL20) is related to T-helper (Th)-17 cell migration, and Th17 cells play important roles in exacerbation in periodontal disease. However, the effect of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) on CCL20 production is unknown. In this study, we examined the mechanisms of TWEAK in combination with interleukin (IL)-1β-induced CCL20 production in human gingival fibroblasts (HGFs). TWEAK alone did not induce CCL20 production in HGFs. However, TWEAK enhanced CCL20 expression from IL-1β-stimulated HGFs in a dose-dependent manner. Inhibitors of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK), protein kinase B (Akt), and nuclear factor κB (NF-κB) significantly inhibited CCL20 production in TWEAK and IL-1β-stimulated HGFs. Western blot analysis revealed that phosphorylations of ERK, Akt, and inhibitor of NF-κB were enhanced in TWEAK and IL-1β-treated HGFs. These data suggest that TWEAK is positively related to Th17 cell migration in periodontally diseased tissues to enhance CCL20 production in IL-1β-stimulated HGFs.

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

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

TWEAK in inclusion-body myositis muscle: possible pathogenic role of a cytokine inhibiting myogenesis

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 exert pleiotropic effects, including regulation of myogenesis. Sporadic inclusion-body myositis (IBM) is the most common muscle disease of the elderly population and leads to severe disability. IBM mesoangioblasts, different from mesoangioblasts in other inflammatory myopathies, display a myogenic differentiation defect. The objective of the present study was to investigate TWEAK-Fn14 expression in IBM and other inflammatory myopathies and explore whether TWEAK modulation affects myogenesis in IBM mesoangioblasts. TWEAK, Fn14, and NF-κB expression was assessed by immunohistochemistry and Western blot in cell samples from both muscle biopsies and primary cultures. Mesoangioblasts isolated from samples of IBM, dermatomyositis, polymyositis, and control muscles were treated with recombinant human TWEAK, Fn14-Fc chimera, and anti-TWEAK antibody. TWEAK-RNA interference was performed in IBM and dermatomyositis mesoangioblasts. TWEAK levels in culture media were determined by enzyme-linked immunosorbent assay. In IBM muscle, we found increased TWEAK-Fn14 expression. Increased levels of TWEAK were found in differentiation medium from IBM mesoangioblasts. Moreover, TWEAK inhibited myogenic differentiation of mesoangioblasts. Consistent with this evidence, TWEAK inhibition by Fn14-Fc chimera or short interfering RNA induced myogenic differentiation of IBM mesoangioblasts. We provide evidence that TWEAK is a negative regulator of human mesoangioblast differentiation. Dysregulation of the TWEAK-Fn14 axis in IBM muscle may induce progressive muscle atrophy and reduce activation and differentiation of muscle precursor cells.

Transcriptome signature of resistance exercise adaptations: mixed muscle and fiber type specific profiles in young and old adults

This investigation examined the effects of acute resistance exercise (RE), progressive resistance training (PRT), and age on the human skeletal muscle Transcriptome. Two cohorts of young and old adults [study A: 24 yr, 84 yr (n = 28); study B: 25 yr, 78 yr (n = 36)] were studied. Vastus lateralis biopsies were obtained pre- and 4 h post-RE in conjunction with the 1st and 36th (last) training session as part of a 12-wk PRT program in study A, whereas biopsies were obtained in the basal untrained state in study B. Additionally, the muscle fiber type specific (MHC I and MHC IIa) Transcriptome response to RE was examined in a subset of young and old women from study A. Transcriptome profiling was performed using HG U133 Plus 2.0 Arrays. The main findings were 1) there were 661 genes affected by RE during the 1st and 36th training bout that correlated with gains in muscle size and strength with PRT (termed the Transcriptome signature of resistance exercise adaptations); 2) the RE gene response was most pronounced in fast-twitch (MHC IIa) muscle fibers and provided additional insight into the skeletal muscle biology affected by RE; 3) skeletal muscle of young adults is more responsive to RE at the gene level compared with old adults and age also affected basal level skeletal muscle gene expression. These skeletal muscle Transcriptome findings provide further insight into the molecular basis of sarcopenia and the impact of resistance exercise at the mixed muscle and fiber type specific level.

Serum TNF-related and weak inducer of apoptosis levels in septic shock patients

Capillary permeability is a tightly regulated feature of microcirculation in all organ beds. In sepsis, this feature is fundamentally altered. We have previously reported elevated levels of angiopoietin-2 in patients with septic shock, and have investigated tumor necrosis factor (TNF)-related and weak inducer of apoptosis (TWEAK), which mediates both angiogenesis and inflammation, in those patients. Enzyme-linked immunoassay was used to measure serum TWEAK levels in 20 patients with septic shock, all of whom were treated by direct hemoperfusion with a polymyxin B-immobilized fiber column (DHP-PMX), and in 20 non-septic controls. The TWEAK levels were higher in patients with septic shock (192.8 ± 230.5 pg/mL) than in controls (84.1 ± 28.7 pg/mL, P = 0.043). Between 11 survivors and 10 non-survivors, there was no significant difference in the serum TWEAK levels before the DHP-PMX therapy. During DHP-PMX therapy, however, the serum TWEAK levels were significantly increased in non-survivors (142.2 ± 88.1 pg/mL to 399.0 ± 307.1 pg/mL, P = 0.022). There was a significant correlation between the serum TWEAK levels and white blood cell counts (r = 0.393, P < 0.001), platelet counts (r = 0.418, P < 0.001), or serum CRP levels (r = 0.259, P = 0.029), but there was no correlation between the serum TWEAK levels and blood pressure. The serum TWEAK levels were also correlated with the ratio of angiopoietin-2 to -1 (r = 0.464, P < 0.001). TWEAK may be a suitable marker of disease severity and mortality in septic patients, and TWEAK levels may be associated with vascular permeability via angiopoietin balance.

Interleukin-13 damages intestinal mucosa via TWEAK and Fn14 in mice-a pathway associated with ulcerative colitis

BACKGROUND & AIMS

TWEAK, a member of the tumor necrosis factor (TNF) superfamily, promotes intestinal epithelial cell injury and signals through the receptor Fn14 following irradiation-induced tissue damage and during development of colitis in mice. Interleukin (IL)-13, an effector of tissue damage in similar models, has been associated with the pathogenesis of ulcerative colitis (UC). We investigated interactions between TWEAK and IL-13 following mucosal damage in mice.

METHODS

We compared patterns of gene expression in intestinal tissues from wild-type and TWEAK knockout mice following γ-irradiation. Intestinal explants from these mice were used to detect cell damage induced by IL-13 and TNF-α. Levels of messenger RNA for IL-13, TWEAK, and Fn14 were measured in mucosal samples from patients with UC.

RESULTS

Based on gene expression analysis, TWEAK mediates γ-irradiation-induced epithelial cell cycle arrest and apoptosis. However, TWEAK alone did not induce damage or apoptosis of primary intestinal epithelial cells. On the other hand, exogenous IL-13 activated caspase-3 in naïve intestinal explants; this process required TWEAK, Fn14, and secretion of endogenous TNF-α which was mediated by ADAM17. Conversely, activation of caspase by exogenous TNF-α required IL-13, TWEAK, and Fn14. In mucosa from patients with UC, messenger RNA levels of IL-13, TWEAK, and Fn14 increased with level of disease severity.

CONCLUSIONS

IL-13-induced damage of intestinal epithelial cells requires TWEAK, its receptor (Fn14), and TNF-α. IL-13, TNF-α, TWEAK, and Fn14 could perpetuate and aggravate intestinal inflammation in patients with UC.

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.

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.

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.

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.

The inflammatory cytokines TWEAK and TNFα reduce renal klotho expression through NFκB

Proinflammatory cytokines contribute to renal injury, but the downstream effectors within kidney cells are not well understood. One candidate effector is Klotho, a protein expressed by renal cells that has antiaging properties; Klotho-deficient mice have an accelerated aging-like phenotype, including vascular injury and renal injury. Whether proinflammatory cytokines, such as TNF and TNF-like weak inducer of apoptosis (TWEAK), modulate Klotho is unknown. In mice, exogenous administration of TWEAK decreased expression of Klotho in the kidney. In the setting of acute kidney injury induced by folic acid, the blockade or absence of TWEAK abrogated the injury-related decrease in renal and plasma Klotho levels. TWEAK, TNFα, and siRNA-mediated knockdown of IκBα all activated NFκB and reduced Klotho expression in the MCT tubular cell line. Furthermore, inhibition of NFκB with parthenolide prevented TWEAK- or TNFα-induced downregulation of Klotho. Inhibition of histone deacetylase reversed TWEAK-induced downregulation of Klotho, and chromatin immunoprecipitation showed that TWEAK promotes RelA binding to the Klotho promoter, inducing its deacetylation. In conclusion, inflammatory cytokines, such as TWEAK and TNFα, downregulate Klotho expression through an NFκB-dependent mechanism. These results may partially explain the relationship between inflammation and diseases characterized by accelerated aging of organs, including CKD.

Development of an Fn14 agonistic antibody as an anti-tumor agent

TWEAK, a TNF family ligand with pleiotropic cellular functions, was originally described as capable of inducing tumor cell death in vitro. TWEAK functions by binding its receptor, Fn14, which is up-regulated on many human solid tumors. Herein, we show that intratumoral administration of TWEAK, delivered either by an adenoviral vector or in an immunoglobulin Fc-fusion form, results in significant inhibition of tumor growth in a breast xenograft model. To exploit the TWEAK-Fn14 pathway as a therapeutic target in oncology, we developed an anti-Fn14 agonistic antibody, BIIB036. Studies described herein show that BIIB036 binds specifically to Fn14 but not other members of the TNF receptor family, induces Fn14 signaling, and promotes tumor cell apoptosis in vitro. In vivo, BIIB036 effectively inhibits growth of tumors in multiple xenograft models, including colon (WiDr), breast (MDA-MB-231), and gastric (NCI-N87) tumors, regardless of tumor cell growth inhibition response observed to BIIB036 in vitro. The anti-tumor activity in these cell lines is not TNF-dependent. Increasing the antigen-binding valency of BIB036 significantly enhances its anti-tumor effect, suggesting the contribution of higher order cross-linking of the Fn14 receptor. Full Fc effector function is required for maximal activity of BIIB036 in vivo, likely due to the cross-linking effect and/or ADCC mediated tumor killing activity. Taken together, the anti-tumor properties of BIIB036 validate Fn14 as a promising target in oncology and demonstrate its potential therapeutic utility in multiple solid tumor indications.

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.

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.

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.

Mst1/2 signalling to Yap: gatekeeper for liver size and tumour development

The mechanisms controlling mammalian organ size have long been a source of fascination for biologists. These controls are needed to both ensure the integrity of the body plan and to restrict inappropriate proliferation that could lead to cancer. Regulation of liver size is of particular interest inasmuch as this organ maintains the capacity for regeneration throughout life, and is able to regain precisely its original mass after partial surgical resection. Recent studies using genetically engineered mouse strains have shed new light on this problem; the Hippo signalling pathway, first elucidated as a regulator of organ size in Drosophila, has been identified as dominant determinant of liver growth. Defects in this pathway in mouse liver lead to sustained liver overgrowth and the eventual development of both major types of liver cancer, hepatocellular carcinoma and cholangiocarcinoma. In this review, we discuss the role of Hippo signalling in liver biology and the contribution of this pathway to liver cancer in humans.

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.

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.

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.

Tumor necrosis factor-like weak inducer of apoptosis is a mitogen for liver progenitor cells

Liver progenitor cells (LPCs) represent the cell compartment facilitating hepatic regeneration during chronic injury while hepatocyte-mediated repair mechanisms are compromised. LPC proliferation is frequently observed in human chronic liver diseases such as hereditary hemochromatosis, fatty liver disease, and chronic hepatitis. In vivo studies have suggested that a tumor necrosis factor family member, tumor necrosis factor-like weak inducer of apoptosis (TWEAK), is promitotic for LPCs; whether it acts directly is not known. In our murine choline-deficient, ethionine-supplemented (CDE) model of chronic liver injury, TWEAK receptor [fibroblast growth factor-inducible 14 (Fn14)] expression in the whole liver is massively upregulated. We therefore set out to investigate whether TWEAK/Fn14 signaling promotes the regenerative response in CDE-induced chronic liver injury by mitotic stimulation of LPCs. Fn14 knockout (KO) mice showed significantly reduced LPC numbers and attenuated inflammation and cytokine production after 2 weeks of CDE feeding. The close association between LPC proliferation and activation of hepatic stellate cells in chronic liver injury prompted us to investigate whether fibrogenesis was also modulated in Fn14 KO animals. Collagen deposition and expression of key fibrogenesis mediators were reduced after 2 weeks of injury, and this correlated with LPC numbers. Furthermore, the injection of 2-week-CDE-treated wildtype animals with TWEAK led to increased proliferation of nonparenchymal pan cytokeratin-positive cells. Stimulation of an Fn14-positive LPC line with TWEAK led to nuclear factor kappa light chain enhancer of activated B cells (NFkappaB) activation and dose-dependent proliferation, which was diminished after targeting of the p50 NFkappaB subunit by RNA interference.

CONCLUSION

TWEAK acts directly and stimulates LPC mitosis in an Fn14-dependent and NFkappaB-dependent fashion, and signaling via this pathway mediates the LPC response to CDE-induced injury and regeneration.

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.

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.

Full-length, membrane-anchored TWEAK can function as a juxtacrine signaling molecule and activate the NF-kappaB pathway

Tumor necrosis factor (TNF) family members are initially synthesized as type II transmembrane proteins, but some of these proteins are substrates for proteolytic enzymes that generate soluble cytokines with biological activity. TWEAK (TNF-like weak inducer of apoptosis), a member of the TNF family, is a multifunctional cytokine that acts via binding to a cell surface receptor named Fn14 (fibroblast growth factor-inducible 14). Studies conducted to date indicate that TWEAK-producing cells can co-express both membrane-anchored and soluble TWEAK isoforms, but there is little information on TWEAK proteolytic processing. Also, it is presently unclear whether membrane-anchored TWEAK, like soluble TWEAK, is biologically active. Here we show that full-length human TWEAK is processed intracellularly by the serine protease furin and identify TWEAK amino acid residues 90-93 as the predominant furin recognition site. In addition, we report that full-length, membrane-anchored TWEAK can bind the Fn14 receptor on neighboring cells and activate the NF-kappaB signaling pathway. Thus, TWEAK can act in a juxtacrine manner to initiate cellular responses, and this property may be important for TWEAK function during physiological wound repair and disease pathogenesis.

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

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.

The quest for liver progenitor cells: a practical point of view

Many chronic liver diseases can lead to hepatic dysfunction with organ failure. At present, orthotopic liver transplantation represents the benchmark therapy of terminal liver disease. However this practice is limited by shortage of donor grafts, the need for lifelong immunosuppression and very demanding state-of-the-art surgery. For this reason, new therapies have been developed to restore liver function, primarily in the form of hepatocyte transplantation and artificial liver support devices. While already offered in very specialized centers, both of these modalities still remain experimental. Recently, liver progenitor cells have shown great promise for cell therapy, and consequently they have attracted a lot of attention as an alternative or supportive tool for liver transplantation. These liver progenitor cells are quiescent in the healthy liver and become activated in certain liver diseases in which the regenerative capacity of mature hepatocytes and/or cholangiocytes is impaired. Although reports describing liver progenitor cells are numerous, they have not led to a consensus on the identity of the liver progenitor cell. In this review, we will discuss some of the characteristics of these cells and the different ways that have been used to obtain these from rodents. We will also highlight the challenges that researchers are facing in their quest to identify and use liver progenitor cells.

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 proinflammatory 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 Pam(3)CysSK(4), 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.

Tumor Necrosis Factor–Like Weak Inducer of Apoptosis (TWEAK) Enhances Vascular and Renal Damage Induced by Hyperlipidemic Diet in ApoE-Knockout Mice

Objective— Tumor necrosis factor–like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily of cytokines. TWEAK binds and activates the Fn14 receptor, and may regulate apoptosis, inflammation, and angiogenesis, in different pathological conditions. We have evaluated the effect of exogenous TWEAK administration as well as the role of endogenous TWEAK on proinflammatory cytokine expression and vascular and renal injury severity in hyperlipidemic ApoE-knockout mice.

Methods and Results— ApoE −/− mice were fed with hyperlipidemic diet for 4 to 10 weeks, then randomized and treated with saline (controls), TWEAK (10 μg/kg/d), anti-TWEAK neutralizing mAb (1000 μg/kg/d), TWEAK plus anti-TWEAK antibody (10 μg TWEAK +1000 μg anti-TWEAK/kg/d), or nonspecific IgG (1000 μg/kg/d) daily for 9 days. In ApoE −/− mice, exogenous TWEAK administration in ApoE −/− mice induced activation of NF-κB, a key transcription factor implicated in the regulation of the inflammatory response, in vascular and renal lesions. Furthermore, TWEAK treatment increased chemokine expression (RANTES and MCP-1), as well as macrophage infiltration in atherosclerotic plaques and renal lesions. These effects were associated with exacerbation of vascular and renal damage. Conversely, treatment of ApoE −/− mice with an anti-TWEAK blocking mAb decreased NF-κB activation, proinflammatory cytokine expression, macrophage infiltration, and vascular and renal injury severity, indicating a pathological role for endogenous TWEAK. Finally, in murine vascular smooth muscle cells or tubular cells, either ox-LDL or TWEAK treatment increased expression and secretion of both RANTES and MCP-1. Furthermore, ox-LDL and TWEAK synergized for induction of MCP-1 and RANTES expression and secretion.

Conclusion— Our results suggest that TWEAK exacerbates the inflammatory response associated with a high lipid–rich diet. TWEAK may be a novel therapeutic target to prevent vascular and renal damage associated with hyperlipidemia.

Fn14-Fc Fusion Protein Regulates Atherosclerosis in ApoE −/− Mice and Inhibits Macrophage Lipid Uptake In Vitro

Objective— TWEAK is a multifunctional cytokine belonging to the tumor necrosis factor superfamily and binds to the receptor Fn14. TWEAK and Fn14 are expressed in atherosclerotic plaques in areas rich in macrophages and foam cells. We investigated the role of TWEAK/Fn14 interactions in ApoE −/− mice and bone marrow–derived macrophages in vitro.

Methods and Results— ApoE −/− mice were treated with TWEAK-inhibiting fusion protein, Fn14-Fc, in an early (5 to 17 weeks of age) or delayed (17 to 29 weeks of age) setting. In the aortic arch, Fn14-Fc as compared to control treatment resulted in advanced plaques which were smaller (early treatment), fewer (delayed treatment), lower in fibrotic content (early and delayed treatment), and exhibited an increased macrophage content and smaller macrophage size (delayed treatment). There were no differences in apoptosis in atherosclerotic plaques after Fn14-Fc versus control Ab treatment. However, blocking TWEAK resulted in less macrophage uptake of modified lipids in vitro.

Conclusions— Fn14-Fc fusion protein treatment did not prevent lesion initiation but inhibited some features of plaque progression and induced a unique advanced plaque phenotype with increased macrophage content and smaller macrophage size, which may be attributable to reduced lipid uptake. These findings indicate that TWEAK/Fn14 interactions regulate atherosclerosis and mediate lipid uptake in macrophages.

TWEAK is a positive regulator of cardiomyocyte proliferation

AIMS

Proliferation of mammalian cardiomyocytes stops during the first weeks after birth, preventing the heart from regenerating after injury. Recently, several studies have indicated that induction of cardiomyocyte proliferation can be utilized to regenerate the mammalian heart. Thus, it is important to identify novel factors that can induce proliferation of cardiomyocytes. Here, we determine the effect of TNF-related weak inducer of apoptosis (TWEAK) on cardiomyocytes, a cytokine known to regulate proliferation in several other cell types.

METHODS AND RESULTS

Stimulation of neonatal rat cardiomyocytes with TWEAK resulted in increased DNA synthesis, increased expression of the proliferative markers Cyclin D2 and Ki67, and downregulation of the cell cycle inhibitor p27KIP1. Importantly, TWEAK stimulation resulted also in mitosis (H3P), cytokinesis (Aurora B), and increased cardiomyocyte numbers. Loss of function experiments revealed that re-induction of proliferation was dependent on tumour necrosis factor receptor superfamily member 12A (FN14) signalling. Downstream signalling was mediated through activation of extracellular signal-regulated kinases and phosphatidylinositol 3-kinase as well as inhibition of glycogen synthase kinase-3beta. In contrast to neonatal cardiomyocytes, TWEAK had no effect on adult rat cardiomyocytes due to developmental downregulation of its receptor FN14. However, adenoviral expression of FN14 enabled efficient induction of cell cycle re-entry in adult cardiomyocytes after TWEAK stimulation.

CONCLUSION

Our data establish TWEAK as a positive regulator of cardiomyocyte proliferation.

Adipocytes as immune cells: differential expression of TWEAK, BAFF, and APRIL and their receptors (Fn14, BAFF-R, TACI, and BCMA) at different stages of normal and pathological adipose tissue development

Adipose tissue represents a rich source of multipotent stem cells. Mesenchymal cells, isolated from this source, can differentiate to other cell types in vitro and therefore can be used for a number of regenerative therapies. Our view of adipose tissue has recently changed, establishing adipocytes as new members of the immune system, as they produce a number of proinflammatory cytokines (such as IL-6 and TNFalpha and chemokines, in addition to adipokines (leptin, adiponectin, resistin) and molecules associated with the innate immune system. In this paper, we report the differential expression of TNF-superfamily members B cell activating factor of the TNF Family (BAFF), a proliferation inducing ligand (APRIL), and TNF-like weak inducer of apoptosis (TWEAK) in immature-appearing and mature adipocytes and in benign and malignant adipose tissue-derived tumors. These ligands act through their cognitive receptors, BAFF receptor, transmembrane activator and calcium signal-modulating cyclophilic ligand (TACI), B cell maturation Ag (BCMA), and fibroblast growth factor-inducible 14 (Fn14), which are also expressed in these cells. We further report the existence of functional BCMA, TACI, and Fn14 receptors and their ligands BAFF, APRIL, and TWEAK on adipose tissue-derived mesenchymal cells, their interaction modifying the rate of adipogenesis. Our data integrate BAFF, APRIL, and TWEAK and their receptors BCMA, TACI, and Fn14 as novel potential mediators of adipogenesis, in addition to their specific role in immunity, and define immature and mature adipocytes as source of immune mediators.