Expression of TWEAK and Its Receptor Fn14 in the Multiple Sclerosis Brain: Implications for Inflammatory Tissue Injury

Identification of oxidative stress signatures of lung adenocarcinoma and prediction of patient prognosis or treatment response with single-cell RNA sequencing and bulk RNA sequencing data

Lung adenocarcinoma (LUAD), the most common subtype of lung cancer globally, has seen improved prognosis with advancements in diagnostic, surgical, radiotherapy, and molecular therapy techniques, while its 5-year survival rate remains low. Molecular biomarkers provide prognostic value. Oxidative stress factors, such as reactive nitrogen species and ROS, are crucial in various stages of tumor progression, influencing cell transformation, proliferation, angiogenesis, and metastasis. ROS demonstrate dual roles, affecting tumor cells, hypoxia sensitivity, and the microenvironment. Comprehensive analysis of oxidative stress in LUAD has not been conducted to date. Therefore, we systematically investigated the regulatory patterns of oxidative stress in LUAD based on oxidative stress-related genes and correlated these patterns with cellular infiltration characteristics of the tumor immune microenvironment. The model utilizes single-factor Cox analysis to screen key differential genes with prognostic value and employs least absolute shrinkage and selection operator (LASSO) penalized Cox regression analysis to construct a prognostic-related prediction model. Ten candidate genes were selected based on this model. The risk score was constructed using the coefficients and expression levels of these ten genes. Furthermore, the impact of this risk score on overall survival (OS) was determined. Two genes with the most significant differential expression, SFTPB and S100P, were selected through qRT-PCR. Cell experiments including CCK-8, Edu, transwell assays confirmed their effects on lung cancer cells growth, consistent with the results of bioinformatics analysis. These findings suggested that this model held potential clinical value for evaluating the prognosis of lung adenocarcinoma.

Characterizing neuroinflammation and identifying prenatal diagnostic markers for neural tube defects through integrated multi-omics analysis

BACKGROUND

Neural Tube Defects (NTDs) are congenital malformations of the central nervous system resulting from the incomplete closure of the neural tube during early embryonic development. Neuroinflammation refers to the inflammatory response in the nervous system, typically resulting from damage to neural tissue. Immune-related processes have been identified in NTDs, however, the detailed relationship and underlying mechanisms between neuroinflammation and NTDs remain largely unclear. In this study, we utilized integrated multi-omics analysis to explore the role of neuroinflammation in NTDs and identify potential prenatal diagnostic markers using a murine model.

METHODS

Nine public datasets from Gene Expression Omnibus (GEO) and ArrayExpress were mined using integrated multi-omics analysis to characterize the molecular landscape associated with neuroinflammation in NTDs. Special attention was given to the involvement of macrophages in neuroinflammation within amniotic fluid, as well as the dynamics of macrophage polarization and their interactions with neural cells at single-cell resolution. We also used qPCR assay to validate the key TFs and candidate prenatal diagnostic genes identified through the integrated analysis in a retinoic acid-induced NTDs mouse model.

RESULTS

Our analysis indicated that neuroinflammation is a critical pathological feature of NTDs, regulated both transcriptionally and epigenetically within central nervous system tissues. Key alterations in gene expression and pathways highlighted the crucial role of STATs molecules in the JAK-STAT signaling pathway in regulating NTDs-associated neuroinflammation. Furthermore, single-cell resolution analysis revealed significant polarization of macrophages and their interaction with neural cells in amniotic fluid, underscoring their central role in mediating neuroinflammation associated with NTDs. Finally, we identified a set of six potential prenatal diagnostic genes, including FABP7, CRMP1, SCG3, SLC16A10, RNASE6 and RNASE1, which were subsequently validated in a murine NTDs model, indicating their promise as prospective markers for prenatal diagnosis of NTDs.

CONCLUSIONS

Our study emphasizes the pivotal role of neuroinflammation in the progression of NTDs and underlines the potential of specific inflammatory and neural markers as novel prenatal diagnostic tools. These findings provide important clues for further understanding the underlying mechanisms between neuroinflammation and NTDs, and offer valuable insights for the future development of prenatal diagnostics.

MAP3K19 Affects TWEAK-Induced Response in Cultured Bronchial Epithelial Cells and Regulates Allergic Airway Inflammation in an Asthma Murine Model

The mitogen-activated protein kinase (MAPK) signaling pathway is involved in the epithelial-mesenchymal transition (EMT) and asthma; however, the role of mitogen-activated protein kinase kinase kinase 19 (MAP3K19) remains uncertain. Therefore, we investigated the involvement of MAP3K19 in in vitro EMT and ovalbumin (OVA)-induced asthma murine models. The involvement of MAP3K19 in the EMT and the production of cytokines and chemokines were analyzed using a cultured bronchial epithelial cell line, BEAS-2B, in which MAP3K19 was knocked down using small interfering RNA. We also evaluated the involvement of MAP3K19 in the OVA-induced asthma murine model using Map3k19-deficient (MAP3K19-/-) mice. Transforming growth factor beta 1 (TGF-β1) and tumor necrosis factor-like weak inducer of apoptosis (TWEAK) induced the MAP3K19 messenger RNA (mRNA) expression in the BEAS-2B cells. The knockdown of MAP3K19 enhanced the reduction in E-cadherin mRNA and the production of regulated upon activation normal T cell express sequence (RANTES) via stimulation with TWEAK alone or with the combination of TGF-β1 and TWEAK. Furthermore, the expression of MAP3K19 mRNA was upregulated in both the lungs and tracheas of the mice in the OVA-induced asthma murine model. The MAP3K19-/- mice exhibited worsened eosinophilic inflammation and an increased production of RANTES in the airway epithelium compared with the wild-type mice. These findings indicate that MAP3K19 suppressed the TWEAK-stimulated airway epithelial response, including adhesion factor attenuation and RANTES production, and suppressed allergic airway inflammation in an asthma mouse model, suggesting that MAP3K19 regulates allergic airway inflammation in patients with asthma.

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.

Cytokines and Inflammation in Meniere Disease

Meniere disease (MD) is a rare set of conditions associated with the accumulation of endolymph in the cochlear duct and the vestibular labyrinth with a decrease of endocochlear potential. It is considered a chronic inflammatory disorder of the inner ear with a multifactorial origin. The clinical syndrome includes several groups of patients with a core phenotype: sensorineural hearing loss, episodes of vertigo, and tinnitus with a non-predictable course. Genetic factors and the innate immune response seem to play a central role in the pathophysiology of the condition. Autoimmune MD should be diagnosed if a patient fulfills the diagnostic criteria for MD and one of the following autoimmune disorders: autoimmune thyroid disease, psoriasis, autoimmune arthritis, ankylosing spondylitis, or systemic lupus erythematosus. We summarize the evidence to support autoimmune MD as an endophenotype in bilateral MD associated with the allelic variant rs4947296 and nuclear factor-kappa B (NF-κB)-mediated inflammation, the role of cytokines (particularly interleukin-1β and tumor necrosis factor-α) in defining a subset of patients with autoinflammation, and the potential role of cytokines as biomarkers to distinguish between patients with MD and vestibular migraine. Finally, we also introduce a list of potential drugs that could regulate the immune response in MD with potential for repurposing in clinical trials.

Dynamic Responses of Microglia in Animal Models of Multiple Sclerosis

Microglia play an essential role in maintaining central nervous system (CNS) homeostasis, as well as responding to injury and disease. Most neurological disorders feature microglial activation, a process whereby microglia undergo profound morphological and transcriptional changes aimed at containing CNS damage and promoting repair, but often resulting in overt inflammation that sustains and propagates the neurodegenerative process. This is especially evident in multiple sclerosis (MS), were microglial activation and microglia-driven neuroinflammation are considered key events in the onset, progression, and resolution of the disease. Our understanding of microglial functions in MS has widened exponentially in the last decade by way of new tools and markers to discriminate microglia from other myeloid populations. Consequently, the complex functional and phenotypical diversity of microglia can now be appreciated. This, in combination with a variety of animal models that mimic specific features and processes of MS, has contributed to filling the gap of knowledge in the cascade of events underlying MS pathophysiology. The purpose of this review is to present the most up to date knowledge of the dynamic responses of microglia in the commonly used animal models of MS, specifically the immune-mediated experimental autoimmune encephalomyelitis (EAE) model, and the chemically-induced cuprizone and lysolecithin models. Elucidating the spectrum of microglial functions in these models, from detrimental to protective, is essential to identify emerging targets for therapy and guide drug discovery efforts.

Serum tumor necrosis factor-like weak inducer of apoptosis levels are elevated in schizophrenia

OBJECTIVE

The purpose of this study was to assess serum Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) concentrations to determine whether changes in patients with schizophrenia could have etiopathogenetic importance. Since very little research has addressed the connection between the inflammatory marker TWEAK and schizophrenia, we wanted to examine alterations of TWEAK and investigate the possible correlation between clinical symptomatology and serum concentrations.

METHODS

A total of 45 schizophrenia patients and 40 healthy controls were included in this study. The Positive Symptom Assessment scale and the Negative Symptom Assessment scale were administered to determine symptom severity. Venous blood samples were collected and serum TWEAK levels were measured.

RESULTS

Serum TWEAK levels were significantly higher in the schizophrenia group than the control group, independently of potential confounders, including sex, age, body mass index and smoking status.

CONCLUSION

The results indicate that TWEAK is elevated in schizophrenia patients, which could deepen our understanding of the role of inflammation in the pathogenesis of schizophrenia.

TWEAK/Fn14 axis in respiratory diseases

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

High fat diet consumption results in mitochondrial dysfunction, oxidative stress, and oligodendrocyte loss in the central nervous system

Metabolic syndrome is a key risk factor and co-morbidity in multiple sclerosis (MS) and other neurological conditions, such that a better understanding of how a high fat diet contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. Results demonstrate that modeling metabolic dysfunction in mice with chronic high fat diet (HFD) consumption promotes loss of oligodendrocyte progenitors across the brain and spinal cord. A number of transcriptomic and metabolomic changes in ER stress, mitochondrial dysfunction, and oxidative stress pathways in HFD-fed mouse spinal cords were also identified. Moreover, deficits in TCA cycle intermediates and mitochondrial respiration were observed in the chronic HFD spinal cord tissue. Oligodendrocytes are known to be particularly vulnerable to oxidative damage, and we observed increased markers of oxidative stress in both the brain and spinal cord of HFD-fed mice. We additionally identified that increased apoptotic cell death signaling is underway in oligodendrocytes from mice chronically fed a HFD. When cultured under high saturated fat conditions, oligodendrocytes decreased both mitochondrial function and differentiation. Overall, our findings show that HFD-related changes in metabolic regulators, decreased mitochondrial function, and oxidative stress contribute to a loss of myelinating cells. These studies identify HFD consumption as a key modifiable lifestyle factor for improved myelin integrity in the adult central nervous system and in addition new tractable metabolic targets for myelin protection and repair strategies.

Cryptotanshinone Attenuates Airway Remodeling by Inhibiting Crosstalk Between Tumor Necrosis Factor-Like Weak Inducer of Apoptosis and Transforming Growth Factor Beta 1 Signaling Pathways in Asthma

The study is to investigate the effect of cryptotanshinone (CTS) on airway remodeling and the possible mechanism. Male BALB/c mice were pretreated with CTS or dexamethasone 30 min before nebulized inhalation of ovalbumin (OVA). CTS significantly inhibited OVA-induced increases of eosinophils and neutrophils infiltration of bronchoalveolar lavage fluids (BALFs), reduced airway resistance in asthmatic mice, decreased the accumulation of inflammatory cells, the hyperplasia of goblet cells and the deposition of collagen in asthmatic mice lung tissue, as well as markedly attenuated the leakage of inflammatory cells and the level of OVA-specific immunoglobulin E in BALFs. CTS also inhibited the expressions of alpha-smooth muscle actin, tumor necrosis factor-like weak inducer of apoptosis (TWEAK), Fn14, transforming growth factor (TGF)-β1, Smad4, and phosphorylation of Smad2/3 and STAT3 (Tyr705). In comparison to TWEAK inhibitor or TWEAK small interfering RNA (siRNA), which were used to inhibit TWEAK/STAT3 signaling pathways, CTS caused a similar effect as them on airway remodeling. Additionally, CTS also played a similar role as the TGF-β1 inhibitor or TGF-β1 siRNA in TGF-β1/STAT3 signaling pathways in airway remodeling. The anti-inflammatory effects of CTS against OVA-induced airway remodeling may be through inhibiting STAT3, which further suppresses TWEAK and TGF-β1 signaling cross talk in asthma. CTS may be a promising therapeutic reagent for asthma treatment.

A single molecule assay for ultrasensitive detection of Fn14 in human serum

Fibroblast growth factor inducible-14 (Fn14) is a receptor protein that plays an important role in the progression of cancer and some other diseases. Here, an ultrasensitive assay was developed for the detection of Fn14 based on a digital sandwich enzyme-linked immunosorbent bead-based assay (dELISA). Beads containing a single immunocomplex are loaded into microwells (~46 fL) and produce fluorescence through enzyme-catalyzed reactions in extremely small volumes. By measuring the number of fluorescent microwells in arrays arranged on a circular Disc, the concentration of Fn14 was determined. To obtain better performance for Fn14 detection, assay conditions including reagent concentrations and measurement parameters were optimized and 44 different antibody pairs were screened. The detection range of Fn14 is 1.26 pg/mL to 3683 pg/mL with a lower detection limit of 0.32 pg/mL, which is much lower than that of conventional ELISAs. In addition, the total operation of this assay is automated and only takes approximately an hour to accomplish. Furthermore, this assay was successfully applied to the determination of spiked Fn14 in serum samples with satisfactory performance.

The contribution of astrocytes to the neuroinflammatory response in multiple sclerosis and experimental autoimmune encephalomyelitis

Neuroinflammation is the coordinated response of the central nervous system (CNS) to threats to its integrity posed by a variety of conditions, including autoimmunity, pathogens and trauma. Activated astrocytes, in concert with other cellular elements of the CNS and immune system, are important players in the modulation of the neuroinflammatory response. During neurological disease, they produce and respond to cellular signals that often lead to dichotomous processes, which can promote further damage or contribute to repair. This occurs also in multiple sclerosis (MS), where astrocytes are now recognized as key components of its immunopathology. Evidence supporting this role has emerged not only from studies in MS patients, but also from animal models, among which the experimental autoimmune encephalomyelitis (EAE) model has proved especially instrumental. Based on this premise, the purpose of the present review is to summarize the current knowledge of astrocyte behavior in MS and EAE. Following a brief description of the pathological characteristics of the two diseases and the main functional roles of astrocytes in CNS physiology, we will delve into the specific responses of this cell population, analyzing MS and EAE in parallel. We will define the temporal and anatomical profile of astroglial activation, then focus on key processes they participate in. These include: (1) production and response to soluble mediators (e.g., cytokines and chemokines), (2) regulation of oxidative stress, and (3) maintenance of BBB integrity and function. Finally, we will review the state of the art on the available methods to measure astroglial activation in vivo in MS patients, and how this could be exploited to optimize diagnosis, prognosis and treatment decisions. Ultimately, we believe that integrating the knowledge obtained from studies in MS and EAE may help not only better understand the pathophysiology of MS, but also uncover new signals to be targeted for therapeutic intervention.

High levels of serum soluble TWEAK are associated with neuroinflammation during multiple sclerosis

Background

Inflammation and demyelination are the main processes in multiple sclerosis. Nevertheless, to date, blood biomarkers of inflammation are lacking. TWEAK, a transmembrane protein that belongs to the TNF ligand family, has been previously identified as a potential candidate.

Methods

Twenty-eight patients (9 males, 19 females) were prospectively included after a first clinical episode suggestive of multiple sclerosis and clinically followed during 3 years. Fifty-seven healthy controls were also included. TWEAK serum levels and MRI exams including magnetization transfer imaging were performed at baseline, 6- and 12-month follow-up.

Results

TWEAK serum levels were significantly increased in the patient group (mean baseline = 1086 ± 493 pg/mL, mean M6 = 624 ± 302 pg/mL and mean M12 = 578 ± 245 pg/mL) compared to healthy controls (mean = 467 ± 177 pg/mL; respectively p < 0.0001, 0.01 and 0.06). Serum levels of soluble TWEAK were significantly increased during relapses, compared to time periods without any relapse (respectively 935 ± 489 pg/mL and 611 ± 292 pg/mL, p = 0.0005). Moreover, patients presenting at least one gadolinium-enhanced CNS lesion at baseline (n = 7) displayed significantly increased serum TWEAK levels in comparison with patients without any gadolinium-enhanced lesion at baseline (n = 21) (respectively 1421 ± 657 pg/mL vs 975 ± 382 pg/mL; p = 0.02). Finally, no correlation was evidenced between TWEAK serum levels and the extent of brain tissue damage assessed by magnetization transfer ratio.

Conclusions

The present study showed that TWEAK serum levels are increased in MS patients, in relation to the disease activity. This simple and reproducible serum test could be used as a marker of ongoing inflammation, contributing in the follow-up and the care of MS patients. Thus, TWEAK is a promising serum marker of the best window to perform brain MRI, optimizing the disease control in patients.

Sputum TWEAK expression correlates with severity and degree of control in non-eosinophilic childhood asthma

BACKGROUND

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is known to play a role in the pathogenesis of various inflammatory diseases. However, no study has been performed on childhood asthma.

METHODS

Ninety-five children with asthma and 78 controls aged 5-18 years were included. Sputum induction, pulmonary function test (PFT), and methacholine challenge test were performed. The subjects were divided into the eosinophilic airway (EA) and non-EA (NEA) groups based on sputum analysis and into the high and low TWEAK groups according to the TWEAK cutoff level (263.0 pg/mL). TWEAK in induced sputum supernatant was measured through enzyme-linked immunosorbent assay.

RESULTS

Children with asthma had higher TWEAK levels than healthy controls (493.0 [157.1-904.3] vs 118.2 (67.5-345.5) pg/mL, P < .001). Sputum TWEAK levels were significantly correlated with PFT parameters reflecting airway obstruction. This association was particularly prominent in subjects with NEA inflammation. Significant differences in FEF_25-75 (maximum mid-expiratory flow, % predicted; P = .017), AX (reactance area; P < .001), R5-R20 (difference between resistance at 5 and 20 Hz; P = .025), and X5 (reactance at 5 Hz, % predicted; P < .001) were noted between the high and low TWEAK groups within the NEA group. Sputum TWEAK level also showed significant positive correlations with asthma severity (r = .358, P = .001) and control status (r = .470, P < .001), distinctively in subjects with NEA inflammation.

CONCLUSIONS

Airway TWEAK may play a role in small airway inflammation especially in children with non-eosinophilic asthma.

Regulation of Fn14 Receptor and NF-κB Underlies Inflammation in Meniere's Disease

Meniere’s disease (MD) is a rare disorder characterized by episodic vertigo, sensorineural hearing loss, tinnitus, and aural fullness. It is associated with a fluid imbalance between the secretion of endolymph in the cochlear duct and its reabsorption into the subarachnoid space, leading to an accumulation of endolymph in the inner ear. Epidemiological evidence, including familial aggregation, indicates a genetic contribution and a consistent association with autoimmune diseases (AD). We conducted a case–control study in two phases using an immune genotyping array in a total of 420 patients with bilateral MD and 1,630 controls. We have identified the first locus, at 6p21.33, suggesting an association with bilateral MD [meta-analysis leading signal rs4947296, OR = 2.089 (1.661–2.627); p = 1.39 × 10⁻⁰⁹]. Gene expression profiles of homozygous genotype-selected peripheral blood mononuclear cells (PBMCs) demonstrated that this region is a trans-expression quantitative trait locus (eQTL) in PBMCs. Signaling analysis predicted several tumor necrosis factor-related pathways, the TWEAK/Fn14 pathway being the top candidate (p = 2.42 × 10⁻¹¹). This pathway is involved in the modulation of inflammation in several human AD, including multiple sclerosis, systemic lupus erythematosus, or rheumatoid arthritis. In vitro studies with genotype-selected lymphoblastoid cells from patients with MD suggest that this trans-eQTL may regulate cellular proliferation in lymphoid cells through the TWEAK/Fn14 pathway by increasing the translation of NF-κB. Taken together; these findings suggest that the carriers of the risk genotype may develop an NF-κB-mediated inflammatory response in MD.

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.

How Mouse Macrophages Sense What Is Going On

Macrophages are central to both innate and adaptive immunity. With few exceptions, macrophages are the first cells that sense trouble and respond to disturbances in almost all tissues and organs. They sense their environment, inhibit or kill pathogens, take up apoptotic and necrotic cells, heal tissue damage, and present antigens to T cells. Although the origins (yolk sac versus monocyte-derived) and phenotypes (functions, gene expression profiles, surface markers) of macrophages vary between tissues, they have many receptors in common that are specific to one or a few molecular species. Here, we review the expression and function of almost 200 key macrophage receptors that help the macrophages sense what is going on, including pathogen-derived molecules, the state of the surrounding tissue cells, apoptotic and necrotic cell death, antibodies and immune complexes, altered self molecules, extracellular matrix components, and cytokines, including chemokines.

Immune responses to non-tumor antigens in the central nervous system

The central nervous system (CNS), once viewed as an immune-privileged site protected by the blood-brain barrier (BBB), is now known to be a dynamic immunological environment through which immune cells migrate to prevent and respond to events such as localized infection. During these responses, endogenous glial cells, including astrocytes and microglia, become highly reactive and may secrete inflammatory mediators that regulate BBB permeability and recruit additional circulating immune cells. Here, we discuss the various roles played by astrocytes, microglia, and infiltrating immune cells during host immunity to non-tumor antigens in the CNS, focusing first on bacterial and viral infections, and then turning to responses directed against self-antigens in the setting of 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.

Regulation of fibroblast growth factor-inducible 14 (Fn14) expression levels via ligand-independent lysosomal degradation

Fibroblast growth factor-inducible 14 (Fn14) is a highly inducible cytokine receptor that engages multiple intracellular signaling pathways, including nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK). Fn14 expression is regulated by several cytokines and growth factors, and Fn14 is transiently up-regulated after injury. In contrast, in states of chronic inflammatory disease and in some solid tumors, Fn14 is persistently up-regulated. However, the post-translational regulation of Fn14 expression has not been directly investigated. Thus, we examined Fn14 proteostasis in the presence and absence of the Fn14 ligand TNF-like weak inducer of apoptosis (TWEAK). Similar to other TNF receptor superfamily members, we found that TWEAK induces Fn14 internalization and degradation. Surprisingly, we also observed rapid, TWEAK-independent, constitutive Fn14 internalization and turnover. Fn14 levels are maintained in cell culture by ongoing synthesis and trafficking of the receptor, leading to subsequent down-regulation by lysosomal degradation. Unexpectedly, the extracellular domain of Fn14 is necessary and sufficient for constitutive turnover. Based on these findings, we propose a model in which constitutive down-regulation of Fn14 facilitates dynamic regulation of Fn14 protein levels and prevents spontaneous or inappropriate receptor signaling.

Pericytes and adaptive angioplasticity: the role of tumor necrosis factor-like weak inducer of apoptosis (TWEAK)

The TNF superfamily member TWEAK has emerged as a pleiotropic cytokine that regulates many cellular functions that include immune/inflammatory activity, angiogenesis, cell proliferation, and fate. TWEAK through its inducible receptor, FGF-inducible molecule 14 (Fn14), can induce both beneficial and deleterious activity that has a profound effect on cell survival. Thus it is highly likely that TWEAK and Fn14 expressed by cells of the neurovascular unit help regulate and maintain vascular and tissue homeostasis. In this chapter we discuss the expression of TWEAK and Fn14 signaling in the cerebral microvascular pericyte. Pericytes are a highly enigmatic population of microvascular cells that are important in regulatory pathways that modulate physiological angiogenesis in response to chronic mild hypoxic stress. A brief introduction will identify the microvascular pericyte. A more detailed discussion of pericyte TWEAK signaling during adaptive angioplasticity will follow.

Is TWEAK a Biomarker for Autoimmune/Chronic Inflammatory Diseases?

The TWEAK/Fn14 pathway is now well-known for its involvement in the modulation of inflammation in various human autoimmune/chronic inflammatory diseases (AICID) including lupus, rheumatoid arthritis, and multiple sclerosis. A panel of data is now available concerning TWEAK expression in tissues or biological fluids of patients suffering from AICID, suggesting that it could be a promising biological marker in these diseases. Evidences from several teams support the hypothesis that blocking TWEAK/Fn14 pathway is an attractive new therapeutic lead in such diseases and clinical trials with anti-TWEAK-blocking antibodies are in progress. In this mini-review we discuss the potential use of TWEAK quantification in AICD management in routine practice and highlight the challenge of standardizing data collection to better estimate the clinical utility of such a biological parameter.

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.

BAFF, APRIL, TWEAK, BCMA, TACI and Fn14 proteins are related to human glioma tumor grade: immunohistochemistry and public microarray data meta-analysis

Gliomas are common and lethal tumors of the central nervous system (CNS). Genetic alterations, inflammatory and angiogenic processes have been identified throughout tumor progression; however, treatment still remains palliative for most cases. Biological research on parameters influencing cell survival, invasion and tumor heterogeneity identified several cytokines interfering in CNS inflammation, oxidative stress and malignant transformation, including TNF-superfamily (TNFSF) members. In this report we performed a meta-analysis of public gene-array data on the expression of a group of TNFSF ligands (BAFF, APRIL, TWEAK) and their receptors (BAFF-R, TACI, BCMA, Fn14) in gliomas. In addition, we investigated by immunohistochemistry (IHC) the tumor cells' expression of these ligands and receptors in a series of 56 gliomas of different grade. We show that in IHC, BAFF and APRIL as well as their cognate receptors (BCMA, TACI) and Fn14 expression correlate with tumor grade. This result was not evidenced in micro-arrays meta-analysis. Finally, we detected for the first time Fn14, BAFF, BCMA and TACI in glioma-related vascular endothelium. Our data, combined with our previous report in glioma cell lines, suggest a role for these receptors and ligands in glioma biology and advance these molecules as potential markers for the classification of these tumors to the proliferative, angiogenic or stem-like molecular subtype.

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.

Crystal structure of human TWEAK in complex with the Fab fragment of a neutralizing antibody reveals insights into receptor binding

The tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a multifunctional cytokine playing a key role in tissue regeneration and remodeling. Dysregulation of TWEAK signaling is involved in various pathological processes like autoimmune diseases and cancer. The unique interaction with its cognate receptor Fn14 makes both ligand and receptor promising targets for novel therapeutics. To gain insights into this important signaling pathway, we determined the structure of soluble human TWEAK in complex with the Fab fragment of an antibody selected for inhibition of receptor binding. In the crystallized complex TWEAK is bound by three Fab fragments of the neutralizing antibody. Homology modeling shows that Fab binding overlaps with the putative Fn14 binding site of TWEAK. Docking of the Fn14 cysteine rich domain (CRD) to that site generates a highly complementary interface with perfectly opposing charged and hydrophobic residues. Taken together the presented structure provides new insights into the biology of TWEAK and the TWEAK/Fn14 pathway, which will help to optimize the therapeutic strategy for treatment of related cancer types and autoimmune diseases.

B-cell enrichment and Epstein-Barr virus infection in inflammatory cortical lesions in secondary progressive multiple sclerosis

Gray matter lesions are thought to play a key role in the progression of disability and cognitive impairment in multiple sclerosis (MS) patients, but whether gray matter damage is caused by inflammation or secondary to axon loss in the white matter, or both, is not clear. In an analysis of postmortem brain samples from 44 cases of secondary progressive MS, 26 cases were characterized by meningeal inflammation with ectopic B-cell follicles and prominent gray matter pathology; subpial cortical lesions containing dense perivascular lymphocytic infiltrates were present in 11 of these cases. Because intracortical immune infiltrates were enriched in B-lineage cells and because we have shown previously that B cells accumulating in the MS brain support an active Epstein-Barr virus (EBV) infection, we investigated evidence of EBV in the infiltrated cortical lesions. Cells expressing EBV-encoded small RNA and plasma cells expressing EBV early lytic proteins (BZLF1, BFRF1) were present in all and most of the intracortical perivascular cuffs examined, respectively. Immunohistochemistry for CD8-positive cells, granzyme B, perforin, and CD107a indicated cytotoxic activity toward EBV-infected plasma cells that was consistently observed in infiltrated cortical lesions, suggesting active immune surveillance. These findings indicate that both meningeal and intraparenchymal inflammation may contribute to cortical damage during MS progression, and that intracortical inflammation may be sustained by an EBV-driven immunopathologic response, similar to findings in white matter lesions and meninges.

TWEAK/Fn14 pathway modulates properties of a human microvascular endothelial cell model of blood brain barrier

BACKGROUND

The TNF ligand family member TWEAK exists as membrane and soluble forms and is involved in the regulation of various human inflammatory pathologies, through binding to its main receptor, Fn14. We have shown that the soluble form of TWEAK has a pro-neuroinflammatory effect in an animal model of multiple sclerosis and we further demonstrated that blocking TWEAK activity during the recruitment phase of immune cells across the blood brain barrier (BBB) was protective in this model. It is now well established that endothelial cells in the periphery and astrocytes in the central nervous system (CNS) are targets of TWEAK. Moreover, it has been shown by others that, when injected into mice brains, TWEAK disrupts the architecture of the BBB and induces expression of matrix metalloproteinase-9 (MMP-9) in the brain. Nevertheless, the mechanisms involved in such conditions are complex and remain to be explored, especially because there is a lack of data concerning the TWEAK/Fn14 pathway in microvascular cerebral endothelial cells.

METHODS

In this study, we used human cerebral microvascular endothelial cell (HCMEC) cultures as an in vitro model of the BBB to study the effects of soluble TWEAK on the properties and the integrity of the BBB model.

RESULTS

We showed that soluble TWEAK induces an inflammatory profile on HCMECs, especially by promoting secretion of cytokines, by modulating production and activation of MMP-9, and by expression of cell adhesion molecules. We also demonstrated that these effects of TWEAK are associated with increased permeability of the HCMEC monolayer in the in vitro BBB model.

CONCLUSIONS

Taken together, the data suggest a role for soluble TWEAK in BBB inflammation and in the promotion of BBB interactions with immune cells. These results support the contention that the TWEAK/Fn14 pathway could contribute at least to the endothelial steps of neuroinflammation.

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.

A homogeneous HTRF assay for the identification of inhibitors of the TWEAK-Fn14 protein interaction

The TWEAK-Fn14 pathway is upregulated in models of inflammation, autoimmune diseases, and cancer. Both TWEAK and Fn14 show increased expression also in the CNS in response to different stimuli, particularly astrocytes, microglia, and neurons, leading to activation of NF-κB and release of proinflammatory cytokines. Although neutralizing antibodies against these proteins have been shown to have therapeutic efficacy in animal models of inflammation, no small-molecule therapeutics are yet available. Here, we describe the development of a novel homogeneous time-resolved fluorescence (HTRF)-based screening assay together with several counterassays for the identification of small-molecule inhibitors of this protein-protein interaction. Recombinant HIS-TWEAK and Fn14-Fc proteins as well as FLAG-TWEAK and Fn14-FLAG proteins and an anti-Fn14 antibody were used to establish and validate these assays and to screen a library of 60 000 compounds. Two HTRF counterassays with unrelated proteins in the same assay format, an antiaggregation assay and a redox assay, were applied to filter out potential false-positive compounds. The novel assay and associated screening cascade should be useful for the discovery of small-molecule inhibitors of the TWEAK-Fn14 protein interaction.

A Bioinformatics Resource for TWEAK-Fn14 Signaling Pathway

TNF-related weak inducer of apoptosis (TWEAK) is a new member of the TNF superfamily. It signals through TNFRSF12A, commonly known as Fn14. The TWEAK-Fn14 interaction regulates cellular activities including proliferation, migration, differentiation, apoptosis, angiogenesis, tissue remodeling and inflammation. Although TWEAK has been reported to be associated with autoimmune diseases, cancers, stroke, and kidney-related disorders, the downstream molecular events of TWEAK-Fn14 signaling are yet not available in any signaling pathway repository. In this paper, we manually compiled from the literature, in particular those reported in human systems, the downstream reactions stimulated by TWEAK-Fn14 interactions. Our manual amassment of the TWEAK-Fn14 pathway has resulted in cataloging of 46 proteins involved in various biochemical reactions and TWEAK-Fn14 induced expression of 28 genes. We have enabled the availability of data in various standard exchange formats from NetPath, a repository for signaling pathways. We believe that this composite molecular interaction pathway will enable identification of new signaling components in TWEAK signaling pathway. This in turn may lead to the identification of potential therapeutic targets in TWEAK-associated disorders.

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.

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.

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.

Role of the innate immune system in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease with heterogeneous clinical presentations and course. MS is considered to be a T cell mediated disease but in recent years contribution of innate immune cells in mediating MS pathogenesis is being appreciated. In this review, we have discussed the role of various innate immune cells in mediating MS. In particular, we have provided an overview of potential anti-inflammatory or pro-inflammatory function of DCs, microglial Cells, NK cells, NK-T cells and gamma delta T cells along with their interaction among themselves and with myelin. Given the understanding of the role of the innate immune cells in MS, it is possible that immunotherapeutic intervention targeting these cells may provide a better and effective treatment.

Meningeal inflammation is not associated with cortical demyelination in chronic multiple sclerosis

Cortical demyelination can be extensive in chronic multiple sclerosis (MS) patients. Cortical lesions are not associated with lymphocyte infiltration, blood-brain barrier disruption, or complement deposition; therefore, their pathogenesis is unclear. We analyzed the extent and cellular composition of leptomeningeal inflammatory infiltrates and their relationship with cortical demyelinated lesions in brain autopsy samples from 28 chronic MS patients; samples from 6 nonneurological disease control patients were also studied. Immunohistochemistry was used to detect meningeal T cells, B cells, macrophages, mature and immature dendritic cells, T-helper cells, (activated) cytotoxic T cells, and plasma cells. Quantitative analysis revealed significant meningeal inflammation in chronic MS patients; T cells were the predominant inflammatory cells. Morphometric analysis was performed on coronal hemisphere sections of the MS cases to assess subpial demyelination; no correlation between the extent of subpial demyelination and extent of meningeal inflammation was identified. Moreover, no differences were observed in the degree or cellular composition of meningeal infiltrates in areas directly adjacent to subpial lesions compared with areas adjacent to normal-appearing gray matter in the MS cases. In addition, no follicle-like structures were found in the MS samples. Our data suggest that the occurrence of cortical lesions is not related to the presence of meningeal inflammation in a large number of chronic MS patients.