Targeting fibroblast growth factor-inducible-14 signaling protects from chronic relapsing experimental autoimmune encephalomyelitis

Fn14 and TNFR2 as regulators of cytotoxic TNFR1 signaling

Tumor necrosis factor (TNF) receptor 1 (TNFR1), TNFR2 and fibroblast growth factor-inducible 14 (Fn14) belong to the TNF receptor superfamily (TNFRSF). From a structural point of view, TNFR1 is a prototypic death domain (DD)-containing receptor. In contrast to other prominent death receptors, such as CD95/Fas and the two TRAIL death receptors DR4 and DR5, however, liganded TNFR1 does not instruct the formation of a plasma membrane-associated death inducing signaling complex converting procaspase-8 into highly active mature heterotetrameric caspase-8 molecules. Instead, liganded TNFR1 recruits the DD-containing cytoplasmic signaling proteins TRADD and RIPK1 and empowers these proteins to trigger cell death signaling by cytosolic complexes after their release from the TNFR1 signaling complex. The activity and quality (apoptosis versus necroptosis) of TNF-induced cell death signaling is controlled by caspase-8, the caspase-8 regulatory FLIP proteins, TRAF2, RIPK1 and the RIPK1-ubiquitinating E3 ligases cIAP1 and cIAP2. TNFR2 and Fn14 efficiently recruit TRAF2 along with the TRAF2 binding partners cIAP1 and cIAP2 and can thereby limit the availability of these molecules for other TRAF2/cIAP1/2-utilizing proteins including TNFR1. Accordingly, at the cellular level engagement of TNFR2 or Fn14 inhibits TNFR1-induced RIPK1-mediated effects reaching from activation of the classical NFκB pathway to induction of apoptosis and necroptosis. In this review, we summarize the effects of TNFR2- and Fn14-mediated depletion of TRAF2 and the cIAP1/2 on TNFR1 signaling at the molecular level and discuss the consequences this has in vivo.

TWEAK and TNFα, Both TNF Ligand Family Members and Multiple Sclerosis-Related Cytokines, Induce Distinct Gene Response in Human Brain Microvascular Endothelial Cells

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the TNF ligand family involved in various diseases including brain inflammatory pathologies such as multiple sclerosis. It has been demonstrated that TWEAK can induce cerebrovascular permeability in an in vitro model of the blood-brain barrier. The molecular mechanisms playing a role in TWEAK versus TNFα signaling on cerebral microvascular endothelial cells are not well defined. Therefore, we aimed to identify gene expression changes in cultures of human brain microvascular endothelial cells (hCMEC/D3) to address changes initiated by TWEAK exposure. Taken together, our studies highlighted that gene involved in leukocyte extravasation, notably claudin-5, were differentially modulated by TWEAK and TNFα. We identified differential gene expression of hCMEC/D3 cells at three timepoints following TWEAK versus TNFα stimulation and also found distinct modulations of several canonical pathways including the actin cytoskeleton, vascular endothelial growth factor (VEGF), Rho family GTPases, and phosphatase and tensin homolog (PTEN) pathways. To our knowledge, this is the first study to interrogate and compare the effects of TWEAK versus TNFα on gene expression in brain microvascular endothelial cells.

Reverse Signaling of Tumor Necrosis Factor Superfamily Proteins in Macrophages and Microglia: Superfamily Portrait in the Neuroimmune Interface

The tumor necrosis factor (TNF) superfamily (TNFSF) is a protein superfamily of type II transmembrane proteins commonly containing the TNF homology domain. The superfamily contains more than 20 protein members, which can be released from the cell membrane by proteolytic cleavage. Members of the TNFSF function as cytokines and regulate diverse biological processes, including immune responses, proliferation, differentiation, apoptosis, and embryogenesis, by binding to TNFSF receptors. Many TNFSF proteins are also known to be responsible for the regulation of innate immunity and inflammation. Both receptor-mediated forward signaling and ligand-mediated reverse signaling play important roles in these processes. In this review, we discuss the functional expression and roles of various reverse signaling molecules and pathways of TNFSF members in macrophages and microglia in the central nervous system (CNS). A thorough understanding of the roles of TNFSF ligands and receptors in the activation of macrophages and microglia may improve the treatment of inflammatory diseases in the brain and periphery. In particular, TNFSF reverse signaling in microglia can be exploited to gain further insights into the functions of the neuroimmune interface in physiological and pathological processes in the CNS.

Regulation of Neuroinflammation: What Role for the Tumor Necrosis Factor-Like Weak Inducer of Apoptosis/Fn14 Pathway?

Observed in many central nervous system diseases, neuroinflammation (NI) proceeds from peripheral immune cell infiltration into the parenchyma, from cytokine secretion and from oxidative stress. Astrocytes and microglia also get activated and proliferate. NI manifestations and consequences depend on its context and on the acute or chronic aspect of the disease. The tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 pathway has been involved in chronic human inflammatory pathologies such as neurodegenerative, autoimmune, or malignant diseases. New data now describe its regulatory effects in tissues or fluids from patients with neurological diseases. In this mini-review, we aim to highlight the role of TWEAK/Fn14 in modulating NI in multiple sclerosis, neuropsychiatric systemic lupus erythematosus, stroke, or glioma. TWEAK/Fn14 can modulate NI by activating canonical and non-canonical nuclear factor-κB pathways but also by stimulating mitogen-activated protein kinase signaling. These downstream activations are associated with (i) inflammatory cytokine, chemokine and adhesion molecule expression or release, involved in NI propagation, (ii) matrix-metalloproteinase 9 secretion, implicated in blood–brain barrier disruption and tissue remodeling, (iii) astrogliosis and microgliosis, and (iv) migration of tumor cells in glioma. In addition, we report several animal and human studies pointing to TWEAK as an attractive therapeutic target.

TWEAK mediates inflammation in experimental atopic dermatitis and psoriasis

Atopic dermatitis (AD) and psoriasis are driven by alternate type 2 and type 17 immune responses, but some proteins might be critical to both diseases. Here we show that a deficiency of the TNF superfamily molecule TWEAK (TNFSF12) in mice results in defective maintenance of AD-specific T helper type 2 (Th2) and psoriasis-specific Th17 cells in the skin, and impaired expression of disease-characteristic chemokines and cytokines, such as CCL17 and TSLP in AD, and CCL20 and IL-19 in psoriasis. The TWEAK receptor, Fn14, is upregulated in keratinocytes and dermal fibroblasts, and TWEAK induces these cytokines and chemokines alone and in synergy with the signature T helper cytokines of either disease, IL-13 and IL-17. Furthermore, subcutaneous injection of recombinant TWEAK into naive mice induces cutaneous inflammation with histological and molecular signs of both diseases. TWEAK is therefore a critical contributor to skin inflammation and a possible therapeutic target in AD and psoriasis.

Death Ligands and Autoimmune Demyelination

Death ligands induce apoptosis, which is a cell suicide program leading mainly to selective elimination of an organism's useless cells. Importantly, the dying cell is an active participant in its own demise (“cellular suicide”). Under physiological conditions, apoptosis is most often found during normal cell turnover and tissue homeostasis, embryogenesis, induction and maintenance of immune tolerance, development of the nervous system, and endocrine-dependent tissue atrophy. However, apoptotic processes have also been suggested to contribute to the pathology of the autoimmune demyelinating disease multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis. Here, apoptosis plays a double role. On one hand, impaired apoptosis may result in increased numbers or persistence of activated myelinspecific T cells. On the other hand, local tissue damage involves apoptosis of oligodendrocytes and neurons, leading to the clinical symptoms. In this article, an overview is given of the current knowledge of the roles of apoptosis-mediating and immune regulatory death ligands of the tumor necrosis factor (TNF) family (TNF, lymphotoxin-beta, OX40L [CD134L], CD154 [CD40L], CD95L, CD70 [CD27L], CD153 [CD30L], 4-1BBL [CD137L], TRAIL, TWEAK, BAFF, GITRL) in the pathogenesis of MS and of their implications for related therapeutic strategies.

Role of Tumor Necrosis Factor Superfamily in Neuroinflammation and Autoimmunity

Tumor necrosis factor superfamily (TNFSF) molecules play an important role in the activation, proliferation, differentiation, and migration of immune cells into the central nervous system (CNS). Several TNF superfamily molecules are known to control alloimmunity, autoimmunity, and immunity. Development of transgenic and gene knockout animals, and monoclonal antibodies against TNFSF molecules have increased our understanding of individual receptor-ligand interactions, and their intracellular signaling during homeostasis and neuroinflammation. A strong clinical association has been observed between TNFSF members and CNS autoimmunity such as multiple sclerosis and also in its animal model experimental autoimmune encephalomyelitis. Therefore, they are promising targets for alternative therapeutic options to control autoimmunity. Although, TNFSF ligands are widely distributed and have diverse functions, we have restricted the discussions in this review to TNFSF receptor-ligand interactions and their role in the pathogenesis of neuroinflammation and CNS autoimmunity.

The TWEAK-Fn14 system as a potential drug target

Fibroblast growth factor-inducible 14 (Fn14) is a member of the tumour necrosis factor (TNF) receptor family that is induced in a variety of cell types in situations of tissue injury. Fn14 becomes activated by TNF-like weak inducer of apoptosis (TWEAK), a typical member of the TNF ligand family. TWEAK is constitutively expressed by monocytes and some tumour cell lines and also shows cytokine inducible expression in various other cell types. Fn14 activation results in stimulation of signalling pathways culminating in the activation of NFκB transcription factors and various MAPKs but might also trigger the PI3K/Akt pathway and GTPases of the Rho family. In accordance with its tissue damage-associated expression pattern and its pleiotropic proinflammatory signalling capabilities, the TWEAK-Fn14 system has been implicated in a huge number of pathologies. The use of TWEAK- and Fn14-knockout mice identified the TWEAK-Fn14 system as a crucial player in muscle atrophy, cerebral ischaemia, kidney injury, atherosclerosis and infarction as well as in various autoimmune scenarios including experimental autoimmune encephalitis, rheumatoid arthritis and inflammatory bowel disease. Moreover, there is increasing preclinical evidence that Fn14 targeting is a useful option in tumour therapy. Based on a discussion of the signalling capabilities of TWEAK and Fn14, this review is focused on two major issues. On the one hand, on the molecular and cellular basis of the TWEAK/Fn14-related pathological outcomes in the aforementioned diseases and on the other hand, on the preclinical experience that have been made so far with TWEAK and Fn14 targeting drugs.

TWEAK/Fn14 Axis-Targeted Therapeutics: Moving Basic Science Discoveries to the Clinic

The TNF superfamily member TWEAK (TNFSF12) is a multifunctional cytokine implicated in physiological tissue regeneration and wound repair. TWEAK is initially synthesized as a membrane-anchored protein, but furin cleavage within the stalk region can generate a secreted TWEAK isoform. Both TWEAK isoforms bind to a small cell surface receptor named Fn14 (TNFRSF12A) and this interaction stimulates various cellular responses, including proliferation and migration. Fn14, like other members of the TNF receptor superfamily, is not a ligand-activated protein kinase. Instead, TWEAK:Fn14 engagement promotes Fn14 association with members of the TNFR associated factor family of adapter proteins, which triggers activation of various signaling pathways, including the classical and alternative NF-κB pathways. Numerous studies have revealed that Fn14 gene expression is significantly elevated in injured tissues and in most solid tumor types. Also, sustained Fn14 signaling has been implicated in the pathogenesis of cerebral ischemia, chronic inflammatory diseases, and cancer. Accordingly, several groups are developing TWEAK- or Fn14-targeted agents for possible therapeutic use in patients. These agents include monoclonal antibodies, fusion proteins, and immunotoxins. In this article, we provide an overview of some of the TWEAK/Fn14 axis-targeted agents currently in pre-clinical animal studies or in human clinical trials and discuss two other potential approaches to target this intriguing signaling node.

A further TWEAK to multiple sclerosis pathophysiology

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a member of the TNF super family that controls many cellular activities including proliferation, migration, differentiation, apoptosis, and inflammation by binding to fibroblast growth factor-inducible 14 (Fn14), a highly inducible cell surface receptor. Recent studies have indicated that TWEAK-Fn14 axis signaling may contribute to chronic autoimmune diseases. TWEAK expression via microglia in cortical lesions, presence of TWEAK(+) macrophages in inflamed leptomeninges, and absence of TWEAK/Fn14 expression in healthy brain implicates importance of this pathway in pathogenesis of multiple sclerosis lesions. TWEAK-Fn14 axis blockade has also shown promise in various multiple sclerosis animal models. Stimulation of the TWEAK/Fn14 pathway can result in activation of both canonical and noncanonical NF-κB signaling and could also stimulate mitogen-activated protein kinase (MAPK) signaling pathways. Here, we have reviewed evidence of the possible role of TWEAK-Fn14 axis in pathophysiology of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) via neuroinflammation, tissue remodeling, blood-brain barrier (BBB) disruption, neurodegeneration, and astrogliosis.

Fibroblast growth factor inducible (Fn14)-specific antibodies concomitantly display signaling pathway-specific agonistic and antagonistic activity

BACKGROUND

Fn14 is a therapeutic target in various diseases.

RESULTS

Anti-Fn14 antibodies activate the alternative NFκB pathway but not other Fn14-related activities induced by soluble or membrane-bound TWEAK. FcγR-bound anti-Fn14 antibodies, however, activate the full spectrum of Fn14-associated activities.

CONCLUSION

Anti-Fn14 antibodies elicit agonistic activities differing from those of the natural Fn14 ligand TWEAK.

SIGNIFICANCE

These findings influence the rationale of designing Fn14-targeted therapies. The Fn14-specific monoclonal antibodies PDL192 and P4A8, which are under consideration in clinical trials, showed no agonistic activity with respect to IL8 production and cell death induction. However, oligomerization with protein G or binding to Fcγ receptors converted both anti-Fn14 antibodies into potent agonists. TNF-like weak inducer of apoptosis (TWEAK), the ligand of Fn14, occurs naturally in two forms with partly different signaling capabilities, as a membrane-bound ligand and as a soluble trimeric molecule. Although membrane TWEAK strongly triggers all Fn14-associated pathways, soluble TWEAK predominately triggers the alternative nuclear factor κB (NFκB) pathway and enhances TNF-induced cell death but has only a poor effect on the classical NFκB pathway and chemokine production. Thus, the oligomerized and FcγR-bound anti-Fn14 mAbs mimicked the activity of membrane TWEAK. Notably, both anti-Fn14 antibodies significantly triggered p100 processing, the hallmark of the alternative NFκB pathway, and therefore resembled soluble TWEAK. In contrast to the latter, however, the anti-Fn14s showed no effect on TNF receptor 1-induced cell death and P4A8 even blocked the corresponding TWEAK response. Thus, we showed that Fn14 antibodies display an alternative NFκB pathway-specific agonistic activity but fail to phenocopy other activities of soluble TWEAK, whereas oligomerized or FcγR-bound Fn14 antibodies fully mimic the activity of membrane TWEAK. In view of the trivalent nature of the TWEAK-Fn14 interaction, this suggests that the alternative NFκB pathway is uniquely responsive already to Fn14 dimerization enabling antibodies to elicit an unnatural response pattern distinct from that of the naturally occurring Fn14 ligands.

Amelioration of autoimmune neuroinflammation by the fusion molecule Fn14·TRAIL

Background

Multiple sclerosis (MS) is a, T cell-mediated autoimmune disease, the management of which remains challenging. The recently described fusion protein, Fn14·TRAIL, combining the extracellular domain of Fn14 (capable of blocking the pro-inflammatory TWEAK ligand) fused to the extracellular domain of the TRAIL ligand (capable of sending apoptotic signals through its receptors on activated inflammatory cells) was designed to modulate the immune system as an anti-inflammatory agent. The present study explores the efficacy of this purified protein as an anti-inflammatory agent, using the animal model of MS - experimental autoimmune encephalomyelitis (EAE).

Methods

EAE was induced by myelin oligodendrocyte glycoprotein (MOG). Fn14·TRAIL or vehicle were injected daily for 4 to 16 days, at different time points after disease induction. Animals were examined daily and evaluated for EAE clinical signs. Lymphocytes were analyzed for ex vivo re-stimulation, cytokine secretion, transcription factor expression and subtype cell analysis. Spinal cords were checked for inflammatory foci. The Mann- Whitney rank sum test, Student’s t-test or ANOVA were used for statistical analysis.

Results

Significant improvement of EAE in the group treated with Fn14·TRAIL was noted from day 6 of disease onset and lasted until the end of follow-up (day 40 from disease induction), even in animals treated for 4 days only. Clinical improvement was linked to decreased lymphocyte infiltrates in the central nervous system (CNS) and to decreased Th1 and Th17 responses and to increased number of T- regulatory in the treated mice. No liver or kidney toxicity was evident. In vitro assays established the ability of Fn14·TRAIL to induce apoptosis of T cell lines expressing TRAIL receptors and TWEAK.

Conclusions

In this study we established the potency of Fn14·TRAIL, a unique fusion protein combining two potentially functional domains, in inhibiting the clinical course of EAE, even when given for a short time, without apparent toxicity. These findings make Fn14·TRAIL a highly promising agent to be used for targeted amelioration of neuro-inflammatory processes, as well as other autoimmune pathologies.

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

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

Inhibition of SLPI ameliorates disease activity in experimental autoimmune encephalomyelitis

Background

The secretory leukocyte protease inhibitor (SLPI) exerts wide ranging effects on inflammatory pathways and is upregulated in EAE but the biological role of SLPI in EAE, an animal model of multiple sclerosis is unknown

Methods

To investigate the pathophysiological effects of SLPI within EAE, we induced SLPI-neutralizing antibodies in mice and rats to determine the clinical severity of the disease. In addition we studied the effects of SLPI on the anti-inflammatory cytokine TGF-β.

Results

The induction of SLPI neutralizing antibodies resulted in a milder disease course in mouse and rat EAE. SLPI neutralization was associated with increased serum levels of TGF-β and increased numbers of FoxP3+ CD4+ T cells in lymph nodes. In vitro, the addition of SLPI significantly decreased the number of functional FoxP3+ CD25^hi CD4+ regulatory T cells in cultures of naive human CD4+ T cells. Adding recombinant TGF-β to SLPI-treated human T cell cultures neutralized SLPI's inhibitory effect on regulatory T cell differentiation.

Conclusion

In EAE, SLPI exerts potent pro-inflammatory actions by modulation of T-cell activity and its neutralization may be beneficial for the disease.

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.

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.

Is there another possible approach to inhibit wear particles-induced inflammatory osteolysis?

Periprosthetic osteolysis can lead to aseptic loosening of components, massive bone loss that renders revision surgery substantially more complex. Recent researches had been demonstrated the biological cascade of events that was initiated by particulate debris and involved in proinflammatory cytokine production and osteoclastogenesis, finally resulted in periprosthetic bone loss. Recent advances in our understanding of cellular and molecular mechanisms of periprosthetic bone loss had highlighted cytokine release and osteoclasts function controlled by numerous intracellular signaling pathway, one of which was TNF-like weak inducer of apoptosis (TWEAK) binding FGF-inducible molecule 14 (Fn14). TWEAK and/or Fn14 inhibition can diminish joint inflammation, synovial angiogenesis, as well as cartilage and bone erosion. At present there were no approved nonoperative treatments for periprosthetic osteolysis. Specific inhibition or blockade of signaling pathway, however, may be one of potential methods to treat periprosthetic osteolysis. As the implant interface cells were located in the closed joint space, intra-articular injection of some proteins or antibodies to block TWEAK/Fn14 signaling pathway was accessible as local administration to avoid systemic side effect. We hypothesized that local administration of some proteins or antibodies to block TWEAK/Fn14 signaling pathway could inhibit wear particles-induced inflammatory osteolysis. In our opinion, specific signaling pathway blockage may be with promising future prospects for effective therapeutic interventions in humans.

Proinflammatory effect of TWEAK/Fn14 interaction in human retinal pigment epithelial cells

PURPOSE

To investigate the expression and function of fibroblast growth factor-inducible 14 (Fn14) in human retinal pigment epithelial cells.

METHODS

A human retinal pigment epithelial cell line (RPE cells: ARPE-19) was used. Expression of Fn14 protein was assessed by flow cytometry. An antibody array and ELISA were used to detect chemokines and cytokines in the supernatant of RPE cells cultured with or without stimulation by TWEAK and/or TGF-beta(1). To explore the mechanism by which TWEAK stimulates RPE cells, we investigated phosphorylation of MAP kinase in TWEAK-stimulated cells. We also investigated whether TWEAK induced the migration of RPE cells by performing an in vitro wound assay.

RESULTS

RPE cells showed constitutive surface expression of Fn14 protein. FGF, VEGF, and TGF-beta(1) did not induce Fn14 expression by RPE cells. TWEAK increased the production of IL-8 and MCP-1 by RPE cells via Fn14, and TGF-beta(1) augmented TWEAK-induced production of these chemokines. TWEAK induced the phosphorylation of MAP kinase in RPE cells and promoted the migration of these cells via MAP kinase.

CONCLUSION

TWEAK/Fn14 interaction may have proinflammatory effects in RPE cells.

The Decoy Receptor 3 (DcR3, TNFRSF6B) suppresses Th17 immune responses and is abundant in human cerebrospinal fluid

The Decoy Receptor 3 (DcR3) is known to compete with the signalling receptors of the Fas ligand (FasL), LIGHT and the TNF-like molecule 1A (TL1A). The primary aim of this study was to provide insights into the role of DcR3 in the modulation of myelin-specific encephalitogenic autoimmune T cell responses. Treatment of PLP-specific lymph node cells with DcR3.Fc protein resulted in a suppression of IFN-g and IL-17, in a reduced proportion of Th17 cells and in a decrease of encephalitogenicity. The Th17 response promoting cytokines IL-6 and IL-23 were suppressed by DcR3.Fc as well. DcR3.Fc-treatment of CD4+ T cells with a defective FasL did not influence the production of IL-17 indicating that DcR3 suppresses IL-17 production by disruption of Fas-FasL interactions. We identified high concentrations of DcR3 in the cerebrospinal fluid (CSF) of patients with various neurological disease states while almost no DcR3 was detected in corresponding serum samples. In conclusion, DcR3 modulates CNS-autoimmunity by interfering with Th17 responses via blockade of Fas-FasL interaction. The anti-inflammatory properties and high DcR3 concentrations in the CSF warrant further investigations in the expression pattern and the function of DcR3 within the CNS.

TNF-like weak inducer of apoptosis (TWEAK) induces inflammatory and proliferative effects in human kidney cells

Members of the TNF-ligand and receptor superfamilies are important in the pathogenesis of lupus nephritis, a major cause of mortality and morbidity in SLE. TWEAK, a member of the TNF-ligand superfamily, is markedly increased in urine from patients with active lupus nephritis, and urinary TWEAK levels significantly correlate with renal disease activity. To support a possible role of TWEAK in the pathogenesis of lupus nephritis and other inflammatory nephritides, we examined the effects of TWEAK in human kidney mesangial cells, podocytes and tubular cells, following our demonstration of the presence of the TWEAK receptor Fn14 on these cells. We found that TWEAK induces human kidney cells to express multiple inflammatory mediators, including RANTES, MCP-1, IP-10, MIP-1alpha, ICAM-1, and VCAM-1. Cytokine production is mediated through NF-kappaB activation, and is inhibited by anti-TWEAK monoclonal antibodies. TWEAK stimulated chemokines induced migration of human PBMC, particularly monocytes/macrophages. Furthermore, we found that TWEAK promotes kidney infiltration of inflammatory cells, and stimulates proliferation of kidney cells in vitro and in vivo. Thus, TWEAK may play an important pathogenic role in the development of glomerulonephritis by promoting a local inflammatory environment and inducing kidney cell proliferation. Blocking TWEAK/Fn14 interactions may be a promising therapeutic target in immune-mediated renal diseases.

Fn14-TRAIL, a chimeric intercellular signal exchanger, attenuates experimental autoimmune encephalomyelitis

Hallmarks of the pathogenesis of autoimmune encephalomyelitis include perivascular infiltration of inflammatory cells into the central nervous system, multifocal demyelination in the brain and spinal cord, and focal neuronal degeneration. Optimal treatment of this complex disease will ultimately call for agents that target the spectrum of underlying pathogenic processes. In the present study, Fn14-TRAIL is introduced as a unique immunotherapeutic fusion protein that is designed to exchange and redirect intercellular signals within inflammatory cell networks, and, in so doing, to impact multiple pathogenic events and yield a net anti-inflammatory effect. In this soluble protein product, a Fn14 receptor component (capable of blocking the pro-inflammatory TWEAK ligand) is fused to a TRAIL ligand (capable of inhibiting activated, pathogenic T cells). Sustained Fn14-TRAIL expression was obtained in vivo using a transposon-based eukaryotic expression vector. Fn14-TRAIL expression effectively prevented chronic, nonremitting, paralytic disease in myelin oligodendrocyte glycoprotein-challenged C57BL/6 mice. Disease suppression in this model was reflected by decreases in the clinical score, disease incidence, nervous tissue inflammation, and Th1, Th2, and Th17 cytokine responses. Significantly, the therapeutic efficacy of Fn14-TRAIL could not be recapitulated simply by administering its component parts (Fn14 and TRAIL) as soluble agents, either alone or in combination. Its functional pleiotropism was manifest in its additional ability to attenuate the enhanced permeability of the blood-brain barrier that typically accompanies autoimmune encephalomyelitis.

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

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

Vaccines for multiple sclerosis: progress to date

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS, characterized pathologically by a perivascular infiltrate consisting predominantly of T cells and macrophages. Although its aetiology remains unknown, several lines of evidence support the hypothesis that autoimmune mechanisms play a major role in the development of the disease. Several widely used disease-modifying agents are approved for the treatment of MS. However, these agents are only partially effective and their ability to attenuate the more progressive phases of the disease is not clear at this time. Therefore, there is a need to develop improved treatment options for MS. This article reviews the role of several novel, selective vaccine strategies that are currently under investigation, including: (i) T-cell vaccination (TCV); (ii) T-cell receptor (TCR) peptide vaccination; (iii) DNA vaccination; and (iv) altered peptide ligand (APL) vaccination. The administration of attenuated autoreactive T cells induces regulatory networks to specifically suppress pathogenic T cells in MS, a strategy named TCV. The concept of TCV was based on the experience of vaccination against aetiological agents of infectious diseases in which individuals are purposely exposed to an attenuated microbial pathogen, which then instructs the immune system to recognize and neutralize it in its virulent form. In regard to TCV, attenuated, pathogenic T cells are similarly used to instruct the immune system to recognize and neutralize disease-inducing T cells. In experimental allergic encephalomyelitis (EAE), an animal model for MS, pathogenic T cells use a strikingly limited number of variable-region elements (V region) to form TCR specific for defined autoantigens. Thus, vaccination with peptides directed against these TCR structures may induce immunoregulatory mechanisms, thereby preventing EAE. However, unlike EAE, myelin-reactive T cells derived from MS patients utilize a broad range of different V regions, challenging the clinical utility of this approach. Subsequently, the demonstration that injection of plasmid DNA encoding a reporter gene into skeletal muscle results in expression of the encoded proteins, as well as in the induction of immune responses in animal models of autoimmunity, was explored as another strategy to re-establish self-tolerance. This approach has promise for the treatment of MS and, therefore, warrants further investigation. APLs are molecules in which the native encephalitogenic peptides are modified by substitution(s) of one or a few amino acids critical for contact with the TCR. Depending on the substitution(s) at the TCR contact residues of the cognate peptide, an APL can induce immune responses that can protect against or reverse EAE. However, the heterogeneity of the immune response in MS patients requires further study to determine which patients are most likely to benefit from APL therapy. Other potential approaches for vaccines in MS include vaccination against axonal growth inhibitors associated with myelin, use of dendritic cells pulsed with specific antigens, and active vaccination against proinflammatory cytokines. Overall, vaccines for MS represent promising approaches for the treatment of this devastating disease, as well as other autoimmune diseases.

Soluble TWEAK is markedly elevated in hemophagocytic lymphohistiocytosis

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a newly identified monocyte derived cytokine, which has weak apoptosis inducing function against sensitive tumor cell lines in vitro. Also, TWEAK has been reported to have proangiogenic and proinflammatory activities in vivo. However, its functions in pathological situation remain to be elucidated. Here, we analyzed soluble TWEAK in serum of 24 patients with hemophagocytic lymphohistiocytosis (HLH) in combination with interferon-gamma (IFN-gamma) and killer-specific secretory protein of 37 kDa (Ksp37). Soluble TWEAK was not detected in serum of healthy individuals. Soluble TWEAK was markedly elevated in all six primary HLH patients and 12 of 18 secondary HLH patients. Serum IFN-gamma, which is an only known mediator to stimulate TWEAK production in monocyte in vitro, was not elevated despite elevated serum TWEAK in three of six primary HLH patients, although IFN-gamma was markedly elevated in other cases. Ksp37 was only slightly increased in HLH patients. These results indicate that TWEAK may be involved in pathogenesis of HLH and is useful as a clinical marker.

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

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

TWEAK binding to the Fn14 cysteine-rich domain depends on charged residues located in both the A1 and D2 modules

TWEAK [TNF (tumour necrosis factor)-like weak inducer of apoptosis] is a member of the TNF superfamily of cytokines. TWEAK binds with high affinity to a single TNF receptor super-family member, Fn14 (fibroblast growth factor-inducible 14). This interaction can stimulate a variety of biological responses, depending on the cell type analysed. The murine Fn14 extracellular region is only 53 amino acids in length and primarily consists of a CRD (cysteine-rich domain) containing three disulphide bonds. In the present study, we investigated whether TWEAK binding to this CRD was dependent on selected evolutionarily conserved amino acid residues by using a site-specific mutagenesis approach and several different ligand-binding assays. Our results indicate that three residues within the predicted Fn14 CRD A1 module (Asp45, Lys48 and Met50) and one residue within the predicted D2 module (Asp62) are each critical for high-affinity TWEAK binding. Mutation of the three charged polar residues Asp45, Lys48 and Asp62 had the greatest deleterious effect, suggesting that electrostatic interactions between TWEAK and Fn14 residues may be particularly important for complex formation or stability. To determine whether the four critical residues were likely to be located on the Fn14 CRD surface, we made an Fn14 homology model based on a previously derived X-ray structure for the B-cell maturation antigen receptor, which also contains only one CRD. This model revealed that each of these critical residues were in areas of the receptor that are potentially capable of interacting with TWEAK. These results indicate that the TWEAK-Fn14 interaction is highly dependent on multiple Fn14 residues located in both CRD modules.

Intraovarian tumor necrosis factor-related weak inducer of apoptosis/fibroblast growth factor-inducible-14 ligand-receptor system limits ovarian preovulatory follicles from excessive luteinization

In addition to gonadotropins, many ovarian paracrine factors are crucial for optimal follicle rupture, oocyte maturation, and luteinization. Based on DNA microarray analyses, we found that transcripts for the fibroblast growth factor-inducible-14 (Fn14) receptor are increased after LH/human chorionic gonadotropin (hCG) treatment of gonadotropin-primed immature mice or rats. Fn14 is the cognate receptor for TNF-related weak inducer of apoptosis (TWEAK), a TNF superfamily member. TWEAK transcripts also were detected in the ovary; however, their levels were not regulated by gonadotropins. In situ hybridization analyses indicated that the Fn14 receptor is expressed in the granulosa and cumulus cells of preovulatory follicles and, to a lesser extent, in theca cells. In contrast, in situ hybridization analyses revealed that TWEAK is primarily expressed in theca cells. In cultured granulosa cells pretreated with hCG to induce Fn14 receptor expression, treatment with TWEAK suppressed progesterone synthesis without accompanying changes in cAMP production. Furthermore, intrabursal injection of TWEAK suppressed ovarian progesterone content in gonadotropin-primed rats. In contrast, preovulatory follicles cultured in the presence of the Fn14 decoy, a recombinant protein containing the ligand-binding domain of Fn14, led to increases in progesterone production, presumably by antagonizing the actions of endogenous TWEAK. Likewise, ip injection of the Fn14 decoy enhanced serum progesterone levels with accompanying increases in transcript levels for several key steroidogenic enzymes. The present findings demonstrate a suppressive role of the TWEAK/Fn14 signaling system in the ovary. Following gonadotropin induction of ovulation, Fn14 is induced and could protect preovulatory follicles from excessive luteinization.

Antigen-specific therapies in multiple sclerosis: going beyond proteins and peptides

Multiple sclerosis (MS) is a complex immune-mediated disease resulting largely from an autoimmune attack against components of central nervous system myelin, including several proteins and lipids. Knowledge about the details of this anomalous immune response has come mostly from studies in the animal model experimental autoimmune encephalomyelitis (EAE). In this model, it has been possible to prevent and effectively treat established disease through several antigen-specific therapeutic strategies, which have included administration of whole myelin or myelin proteins by various routes, random copolymers consisting of the main major histocompatability complex (MHC) and T-cell receptor (TCR) contact amino acid residues, altered peptide ligands of dominant myelin epitopes in which one or more residues are selectively substituted, and lately DNA vaccination encoding self-myelin antigens. However, there have been difficulties in making successful transitions from animal models to human clinical trials, due either to lack of efficacy or unforeseen complications. Despite these problems, antigen-specific therapies have retained their attraction for clinicians and scientists alike, and hopefully the upcoming generation of agents--including altered peptide ligands and DNA vaccines--will benefit from the increasing knowledge about this disease and surmount existing difficulties to make an impact in the treatment of multiple sclerosis.

Anti-TWEAK monoclonal antibodies reduce immune cell infiltration in the central nervous system and severity of experimental autoimmune encephalomyelitis

TWEAK is a member of the TNF family, constitutively expressed in the central nervous system (CNS), with pro-inflammatory, proliferative or apoptotic effects depending upon cell types. Its receptor, Fn14, is expressed in CNS by endothelial cells, reactive astrocytes and neurons. We showed that TWEAK and Fn14 mRNA expression increased in spinal cord during experimental autoimmune encephalomyelitis (EAE). We investigated the role of TWEAK during EAE using neutralizing anti-TWEAK antibody in myelin oligodendrocyte glycoprotein (MOG) induced EAE in C57BL/6 mice. We observed a reduction of disease severity and leukocyte infiltration when mice were treated after the priming phase.