TWEAK/Fn14 pathway promotes a T helper 2-type chronic colitis with fibrosis in mice

Intestinal Stromal Cells in the Turmoil of Inflammation and Defective Connective Tissue Remodeling in Inflammatory Bowel Disease

In steady state, intestinal subepithelial myofibroblasts form a thin layer below the basement membrane. Unlike the rest of the stromal cells in the lamina propria, they express tensile proteins, guide epithelial regeneration, and sense luminal microbiota. Upon inflammation in inflammatory bowel disease (IBD), they express activation markers, accept trophic signaling by infiltrating neutrophils and macrophages, and are activated by cytokines from helper T cells to produce a narrow spectrum of cytokines and a wider spectrum of chemokines, attract cells of innate and adaptive immunity, orchestrate inflammatory responses, and qualitatively and quantitatively modify the extracellular matrix. Thus, beyond being structural tissue components, they assume active roles in the pathogenesis of complicated IBD. Discrimination between myofibroblasts and fibroblasts may be an oversimplification in light of single-cell sequencing data unveiling the complexity of multiple phenotypes of stromal cells with distinct roles and plasticity. Spatial transcriptomics revealed distinct phenotypes by histologic localization and, more intriguingly, the assembly of mucosal neighborhoods that support spatially distinct functions. Current IBD treatments target inflammation but fail in fibrostenotic or fistulizing disease. Baseline and recent findings on stromal cells, molecules, and pathways involved in disrupted extracellular matrix homeostasis are reviewed to provide relevant pharmacologic targets.

Mechanisms of norcantharidin against renal tubulointerstitial fibrosis

Renal tubulointerstitial fibrosis (RTIF) is a common feature and inevitable consequence of all progressive chronic kidney diseases, leading to end-stage renal failure regardless of the initial cause. Although research over the past few decades has greatly improved our understanding of the pathophysiology of RTIF, until now there has been no specific treatment available that can halt the progression of RTIF. Norcantharidin (NCTD) is a demethylated analogue of cantharidin, a natural compound isolated from 1500 species of medicinal insect, the blister beetle (Mylabris phalerata Pallas), traditionally used for medicinal purposes. Many studies have found that NCTD can attenuate RTIF and has the potential to be an anti-RTIF drug. This article reviews the recent progress of NCTD in the treatment of RTIF, with emphasis on the pharmacological mechanism of NCTD against RTIF.

Gut microbiota modulation and effects of a diet enriched in apple pomace on inflammation in a DSS-induced colitis mouse model

Certain types of soluble dietary fibre, such as pectin and pectic oligosaccharides from different sources, have demonstrated protective effects against inflammation in DSS-induced colitis mouse models. In this work, we have evaluated the impact of a diet enriched in apple pomace (AP-diet), an agricultural by-product with a significant content of pectin and that previously demonstrated prebiotic properties in human fecal batch fermentation models, on the gut microbiota composition, intestinal damage and inflammation markers in a DSS-induced colitis model. We found that the apple pomace enriched diet (AP-diet), providing a significant amount of pectin with demonstrated prebiotic properties, was associated with a slower increase in the disease activity index, translating into better clinical symptomatology of the animals. Histological damage scoring confirmed less severe damage in those animals receiving an AP-diet before and during the DSS administration period. Some serum inflammatory markers, such as TNFα, also demonstrated lower levels in the group receiving the AP-diet, compared to the control diet. AP-diet administration is also associated with the modulation of key taxa in the colonic microbiota of animals, such as some Lachnospiraceae genera and Ruminococcus species, including commensal short chain fatty acid producers that could play a role in attenuating inflammation at the intestinal level.

TSLP/TSLPR promotes renal fibrosis by activating STAT3 in renal fibroblasts

Previous studies have demonstrated the importance of TSLP-TSLPR in inflammatory, allergic, and fibrotic diseases. However, their exact molecular mechanism in regulating renal fibrosis has not been fully explored yet. The current study identified the high expression levels of TSLP and TSLPR in human and mouse hydronephrotic tissues. In addition, immunofluorescence staining showed that TSLP was highly expressed in renal tubular cells, while TSLPR was mainly co-localized with α-SMA, a marker of fibroblasts. Knocking out TSLPR in the UUO model could alleviate the severity of renal fibrosis. Most importantly, the application of antibody blockade of TSLP reduced the fibrotic level in the UUO model. The functional analysis revealed that the hypoxic exposure could induce the overexpression of TSLP in renal tubular cells via HIF-1α. The tubular cell-derived TSLP could bind to the TSLPR of fibroblasts in a paracrine manner to activate them. Specifically, the HIF-1α/TSLP/TSLPR-axis could activate fibroblasts through the STAT3 signaling pathway. This study revealed a mechanistic interaction of HIF-1α/TSLP/TSLPR and STAT3 signaling pathways in the activation and proliferation of human and murine kidney fibroblasts; these pathways might be exploited as a therapeutic target in renal fibrosis.

Conventional and pathogenic Th2 cells in inflammation, tissue repair, and fibrosis

Type 2 helper T (Th2) cells, a subset of CD4⁺ T cells, play an important role in the host defense against pathogens and allergens by producing Th2 cytokines, such as interleukin-4 (IL-4), IL-5, and IL-13, to trigger inflammatory responses. Emerging evidence reveals that Th2 cells also contribute to the repair of injured tissues after inflammatory reactions. However, when the tissue repair process becomes chronic, excessive, or uncontrolled, pathological fibrosis is induced, leading to organ failure and death. Thus, proper control of Th2 cells is needed for complete tissue repair without the induction of fibrosis. Recently, the existence of pathogenic Th2 (Tpath2) cells has been revealed. Tpath2 cells produce large amounts of Th2 cytokines and induce type 2 inflammation when activated by antigen exposure or tissue injury. In recent studies, Tpath2 cells are suggested to play a central role in the induction of type 2 inflammation whereas the role of Tpath2 cells in tissue repair and fibrosis has been less reported in comparison to conventional Th2 cells. In this review, we discuss the roles of conventional Th2 cells and pathogenic Th2 cells in the sequence of tissue inflammation, repair, and fibrosis.

Lower Expression of TWEAK is Associated with Poor Survival and Dysregulate TIICs in Lung Adenocarcinoma

Background. Lung cancer remains the leading cause of cancer death worldwide, and the most subtype is lung adenocarcinoma (LUAD). Tumor-infiltrating immune cells (TIICs) greatly impact the prognosis of LUAD. Tumor necrosis factor–like weak inducer of apoptosis (TWEAK), signal via its receptor fibroblast growth factor-inducible 14 (Fn14), dysregulates immune cell recruitment within tumor environment, thus promoting the progression of autoimmune diseases and cancer. We aimed to explore its role in LUAD. Methods. The expression level of TWEAK was explored in Tumor Immune Estimation Resource 2.0 (TIMER2.0) and Oncomine databases. The Tumor Immune Dysfunction and Exclusion (TIDE) and Lung Cancer Explorer (LCE) databases were applied to evaluate the survival in correlation to TWEAK expression. TIICs were assessed with TIMER2.0 and TIDE datasets. The expression of TWEAK protein was detected in LUAD cell lines and also in tissue samples from LUAD patients via western blotting or combination with immunochemistry. Results. Our results showed that TWEAK was downregulated in LUAD tumors compared to normal tissues in TIMER2.0, Oncomine, cell lines, and clinical specimens. Poor survival was uncovered in lower TWEAK expression of LUAD patients in LCE ( $\text{meta}-\text{HR}=0.84$ [95% CI, 0.76-0.92]) and TCGA ( $\text{Continuous}\text{Z}=-1.97$ , $p=0.0486$ ) and GSE13213@PRECOG ( $\text{Continuous}\text{Z}=-4.25$ , $p=2.12\text{e}-5$ ) in TIDE. Multiple tumor-infiltrating immune cells (TIICs) were found closely correlated with TWEAK expression in LUAD, especially hematopoietic stem cell ( $\text{Rho}=0.505$ , $p=2.78\text{e}-33$ ), common lymphoid progenitor ( $\text{Rho}=-0.504$ , $p=3.79\text{e}-33$ ), and myeloid-derived suppressor cells (MDSCs) ( $\text{Rho}=-0.615$ , $p=1.36\text{e}-52$ ). Conclusion. Lower level of TWEAK was linked with poor survival and aberrant recruitment and phenotype of TIICs in LUAD, which might motivate immune escape and weaken the effects of immunotherapy.

TWEAK functions with TNF and IL-17 on keratinocytes and is a potential target for psoriasis therapy

[Figure: see text].

TWEAK/Fn14 axis is an important player in fibrosis

Fibrosis is a common pathological condition associated with abnormal repair after tissue injury. However, the etiology and molecular mechanisms of fibrosis are still not well-understood. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) belongs to the TNF superfamily and acts by binding to its receptor, fibroblast growth factor-inducible 14 (Fn14), thereby activating a variety of intracellular signal transduction pathways in various types of cells. Besides promoting the expression of growth factors, activation of TWEAK/Fn14 signaling after tissue injury can promote the expression of pro-inflammatory cytokines, which trigger the immune response, thereby exacerbating the injury. Severe or repetitive injury leads to a dysregulated tissue repair process, in which the TWEAK/Fn14 axis promotes the activation and proliferation of myofibroblasts, induces the secretion of the extracellular matrix, and regulates profibrotic mediators to further perpetuate and sustain the fibrotic process. In this review, we summarize the available experimental evidence on the underlying molecular mechanisms by which the TWEAK/Fn14 pathway mediates the development and progression of fibrosis. In addition, we discuss the therapeutic potential of the TWEAK/Fn14 pathway in fibrosis-associated diseases based on evidence derived from multiple models and cells from injured tissue and fibrotic tissue.

Norcantharidin protects against renal interstitial fibrosis by suppressing TWEAK-mediated Smad3 phosphorylation

AIMS

This study investigated the role and mechanism of action of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in the pathogenesis of renal interstitial fibrosis (RIF), and its involvement in the anti-RIF effect of norcantharidin (NCTD).

MAIN METHODS

Mice with unilateral ureteral obstruction and BUMPT mouse proximal tubular cells exposed to transforming growth factor (TGF)-β1 were used as in vivo and in vitro models of RIF, respectively. NCTD was administered to mice by intraperitoneal injection (0.075 mg kg^-1·day^-1). Hematoxylin-eosin and Masson's trichrome staining were performed to assess pathologic changes in the kidney. Immunohistochemistry, western blotting, and real-time PCR were performed to evaluate the expression of TWEAK and the fibrotic factors fibronectin (FN) and collagen type I (Col-I). The role of TWEAK in RIF and in the anti-RIF effect of NCTD was evaluated by TWEAK overexpression and neutralization with a specific antibody, and specific inhibitor of Mothers against decapentaplegic homolog (Smad)3 (SIS3) was used to examine the involvement of TGF-β1/Smad3 signaling.

KEY FINDINGS

TWEAK was mainly expressed in renal tubules in mice; the level was markedly elevated in both in vivo and in vitro RIF models. TWEAK overexpression in BUMPT cells increased the levels of phosphorylated Smad3, FN, and Col-I, which were reduced by treatment with SIS3. NCTD suppressed FN and Col-I expression by blocking TWEAK-mediated Smad3 phosphorylation.

SIGNIFICANCE

Upregulation of TWEAK contributes to RIF by promoting Smad3 phosphorylation, while NCTD inhibits this process.

Bacterial Quorum Sensing Molecules Promote Allergic Airway Inflammation by Activating the Retinoic Acid Response

IgE and IgG1 production in the type 2 immune response is the characteristic feature of an allergic reaction. However, whether bacterial molecules modulate IgE and IgG1 production remains obscure. Here, we demonstrate that the bacterial quorum sensing molecules acyl homoserine lactones (AHLs) induce IgE and IgG1 production by activating the RARE (retinoic acid response element) response in dendritic cells (DCs) in vivo. DC-specific knockout of the retinoic acid transcriptional factor Rara diminished the AHL-stimulated type 2 immune response in vitro. AHLs altered DC phenotype, upregulated OX40L and IFN-I signature, and promoted T helper 2 cell differentiation in vitro. Finally, AHLs activated the RARE response by inhibiting AKT phosphorylation in vitro, as the AKT agonists IGF-1 and PDGF abolished the effect of AHLs on the RARE response. This study demonstrates a mechanism by which AHLs drive allergic airway inflammation through activating retinoic acid signaling in DCs.

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Acyl homoserine lactones (AHLs) exacerbate allergic airway inflammation

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AHLs induce IgE and IgG1 production

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AHLs activate the RARE response in dendritic cells

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AHLs inhibit AKT phosphorylation

Ginkgo Flavonol Glycosides or Ginkgolides Tend to Differentially Protect Myocardial or Cerebral Ischemia-Reperfusion Injury via Regulation of TWEAK-Fn14 Signaling in Heart and Brain

Shuxuening injection (SXNI), one of the pharmaceutical preparations of Ginkgo biloba extract, has significant effects on both ischemic stroke and heart diseases from bench to bedside. Its major active ingredients are ginkgo flavonol glycosides (GFGs) and ginkgolides (GGs). We have previously reported that SXNI as a whole protected ischemic brain and heart, but the active ingredients and their contribution to the therapeutic effects remain unclear. Therefore, we combined experimental and network analysis approach to further explore the specific effects and underlying mechanisms of GFGs and GGs of SXNI on ischemia–reperfusion injury in mouse brain and heart. In the myocardial ischemia–reperfusion injury (MIRI) model, pretreatment with GFGs at 2.5 ml/kg was superior to the same dose of GGs in improving cardiac function and coronary blood flow and reducing the levels of lactate dehydrogenase and aspartate aminotransferase in serum, with an effect similar to that achieved by SXNI. In contrast, pretreatment with GGs at 2.5 ml/kg reduced cerebral infarction area and cerebral edema similarly to that of SXNI but more significantly compared with GFGs in cerebral ischemia–reperfusion injury (CIRI) model. Network pharmacology analysis of GFGs and GGs revealed that tumor necrosis factor-related weak inducer of apoptosis (TWEAK)–fibroblast growth factor-inducible 14 (Fn14) signaling pathway as an important common mechanism but with differential targets in MIRI and CIRI. In addition, immunohistochemistry and enzyme linked immunosorbent assay (ELISA) assays were performed to evaluate the regulatory roles of GFGs and GGs on the common TWEAK–Fn14 signaling pathway to protect the heart and brain. Experimental results confirmed that TWEAK ligand and Fn14 receptor were downregulated by GFGs to mitigate MIRI in the heart while upregulated by GGs to improve CIRI in the brain. In conclusion, our study showed that GFGs and GGs of SXNI tend to differentially protect brain and heart from ischemia–reperfusion injuries at least in part by regulating a common TWEAK–Fn14 signaling pathway.

FN14 Signaling Plays a Pathogenic Role in a Mouse Model of Experimental Autoimmune Myocarditis

BACKGROUND

The pathogenesis of inflammatory cardiomyopathy is affected by the activation of autoimmune-mediated cascades. To study these cascades, we developed an experimental model of troponin I (TnI)-induced autoimmune myocarditis (EAM). One factor playing a pivotal role in the context of autoimmune disorders is the receptor fibroblast growth factor-inducible 14 (FN14). Thus, the impact of FN14 in the development of autoimmune myocarditis was investigated.

METHODS AND RESULTS

TnI-immunization led to a significantly increased myocardial FN14 mRNA and protein expression in wild-type (wt) mice. To investigate the precise role of FN14 in EAM, FN14 knockout (ko) and wt littermates were immunized with TnI or control buffer. The animals were evaluated for cardiac parameters and indicators of myocardial injury. FN14 deficiency resulted in better cardiac performance, less myocardial inflammation, fibrosis, and cardiac damage. A lower myocardial mRNA expression of inflammatory cytokines and chemokines as well as their receptors could be demonstrated in TnI-immunized FN14ko compared to wt mice also immunized with TnI. Western blot analysis revealed a contribution of nuclear factor kappa-light-chain-enhancer of activated B cells to FN14-induced signaling cascades.

CONCLUSIONS

In the pathogenesis of autoimmune myocarditis, the inflammatory response to cardiac injury is attenuated in FN14ko mice. Thus, inhibition of FN14 in patients might represent a novel therapeutic strategy in the treatment of inflammatory cardiomyopathy.

TWEAK/Fn14 Is Overexpressed in Crohn's Disease and Mediates Experimental Ileitis by Regulating Critical Innate and Adaptive Immune Pathways

BACKGROUND & AIMS

Crohn's disease (CD) is a debilitating inflammatory disorder that affects more than 1.6 million people in North America alone. Members of the tumor necrosis factor superfamily are key regulators of intestinal inflammation; specifically, tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (Fn14), are involved in normal and pathologic tissue remodeling. Our aim was to determine the role of TWEAK/Fn14 in CD and a murine model of CD-like ileitis (ie, SAMP1/YitFc [SAMP] strain).

METHODS

SAMP mice deficient in Fn14 (SAMP × Fn14-/-) were developed and a detailed time-course study was performed evaluating ileal tissues by histology and stereomicroscopy, as well as quantitative polymerase chain reaction and NanoString technology (Seattle, WA). Reciprocal bone marrow chimeras were generated to assess the relevance of Fn14 in hematopoietic vs nonhematopoietic compartments. Surgically resected intestinal tissues and mucosal biopsy specimens from patients with CD, ulcerative colitis, and healthy controls were analyzed for the expression of TWEAK/Fn14 by quantitative polymerase chain reaction, Western blot, immunohistochemistry, and immunofluorescence.

RESULTS

SAMP × Fn14-/- showed a marked decrease in ileitis severity at 20 weeks of age compared with SAMP WT controls. Bone marrow chimeras showed that Fn14 was required in both hematopoietic and nonhematopoietic compartments for ileitis to develop. Transcriptome data showed multiple cellular pathways regulated by Fn14 signaling. Finally, increased expression of TWEAK and Fn14 was observed in tissue lesions from CD patients compared with ulcerative colitis and healthy controls.

CONCLUSIONS

TWEAK/Fn14 are up-regulated in CD, and also mediate experimental CD-like ileitis, by regulation of multiple innate and adaptive cellular pathways. Therefore, TWEAK/Fn14 may represent a novel therapeutic target for the treatment of small intestinal inflammation in CD.

Flagellin-mediated activation of IL-33-ST2 signaling by a pathobiont promotes intestinal fibrosis

Intestinal fibrosis is a severe complication in patients with Crohn's disease (CD). Unfortunately, the trigger leading to the development of intestinal fibrosis in the context of CD remains elusive. Here, we show that colonization by a CD-associated pathobiont adherent-invasive Escherichia coli (AIEC) promotes the development of intestinal fibrosis. Exogenously inoculated AIEC strain LF82 and commensal E. coli HS were gradually eradicated from the intestine in healthy mice. In Salmonella- or dextran sodium sulfate-induced colitis models, AIEC exploited inflammation and stably colonize the gut. Consequently, persistent colonization by AIEC LF82 led to substantial fibrosis. In contrast, commensal E. coli HS was unable to derive a growth advantage from inflammation, thereby failing to colonize the inflamed intestine or promote intestinal fibrosis. AIEC colonization potentiated the expression of the IL-33 receptor ST2 in the intestinal epithelium, which is crucial for the development of intestinal fibrosis. The induction of ST2 by AIEC LF82 was mediated by flagellin, as the ΔfliC mutant failed to induce ST2. These observations provide novel insights into pathobiont-driven intestinal fibrosis and can lead to the development of novel therapeutic approaches for the treatment of intestinal fibrosis in the context of CD that target AIEC and/or its downstream IL-33-ST2 signaling.

Combination of TWEAK and TGF-β1 induces the production of TSLP, RANTES, and TARC in BEAS-2B human bronchial epithelial cells during epithelial-mesenchymal transition

AIM OF THE STUDY

In patients with asthma, chronic inflammatory processes and the subsequent remodeling of the airways contribute to the symptoms and the pathophysiological changes. Epithelial-mesenchymal transition (EMT) is thought to play an important role in tissue remodeling. Previous reports show that tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a cytokine of the TNF superfamily, exerts pro-inflammatory effects, and enhances transforming growth factor (TGF)-β-induced EMT in bronchial epithelial cells. In this study, we investigated the TWEAK-induced cytokine and chemokine production in the human bronchial epithelial cell line BEAS-2B during EMT.

MATERIALS AND METHODS

Quantitative real-time RT-PCR, enzyme-linked immunosorbent assays, western blotting, and immunohistochemistry were used to define the production of cytokines and chemokines.

RESULTS

We found that TWEAK increases mRNA and protein levels of thymic stromal lymphopoietin (TSLP), monocyte chemoattractant protein -1 (MCP-1), regulated upon activation normal T cell express sequence (RANTES), and IL-8 in BEAS-2B bronchial epithelial cells. Moreover, co-treatment with TWEAK and TGF-β1 induces not only features of EMT but also enhances the production of TSLP and RANTES. Thymus- and activation-regulated chemokines (TARC) production is induced by the co-treatment of TWEAK and TGF-β1 but not by TWEAK or TGF-β1 stimulation alone. Furthermore, the increased mRNA expression of TSLP and RANTES after co-treatment with TWEAK and TGF-β1 is prevented by inhibitors of Smad-independent signaling pathways.

CONCLUSIONS

In the present study, we have revealed a novel mechanism for the production of asthma-related cytokines and chemokines in EMT driven by the co-stimulation with TWEAK and TGF-β1. We conclude that cellular EMT processes caused by TWEAK and TGF-β1 may contribute to chronic airway inflammation and remodeling.

Tnfrsf12a-Mediated Atherosclerosis Signaling and Inflammatory Response as a Common Protection Mechanism of Shuxuening Injection Against Both Myocardial and Cerebral Ischemia-Reperfusion Injuries

Shuxuening injection (SXNI) is a widely prescribed herbal medicine of Ginkgo biloba extract (EGB) for cerebral and cardiovascular diseases in China. However, its curative effects on ischemic stroke and heart diseases and the underlying mechanisms remain unknown. Taking an integrated approach of RNA-seq and network pharmacology analysis, we compared transcriptome profiles of brain and heart ischemia reperfusion injury in C57BL/6J mice to identify common and differential target genes by SXNI. Models for myocardial ischemia reperfusion injury (MIRI) by ligating left anterior descending coronary artery (LAD) for 30 min ischemia and 24 h reperfusion and cerebral ischemia reperfusion injury (CIRI) by middle cerebral artery occlusion (MCAO) for 90 min ischemia and 24 h reperfusion were employed to identify the common mechanisms of SXNI on both cerebral and myocardial ischemia reperfusion. In the CIRI model, ischemic infarct volume was markedly decreased after pre-treatment with SXNI at 0.5, 2.5, and 12.5 mL/kg. In the MIRI model, pre-treatment with SXNI at 2.5 and 12.5 mL/kg improved cardiac function and coronary blood flow and decreased myocardial infarction area. Besides, SXNI at 2.5 mL/kg also markedly reduced the levels of LDH, AST, CK-MB, and CK in serum. RNA-seq analysis identified 329 differentially expressed genes (DEGs) in brain and 94 DEGs in heart after SXNI treatment in CIRI or MIRI models, respectively. Core analysis by Ingenuity Pathway Analysis (IPA) revealed that atherosclerosis signaling and inflammatory response were top-ranked in the target profiles for both CIRI and MIRI after pre-treatment with SXNI. Specifically, Tnfrsf12a was recognized as an important common target, and was regulated by SXNI in CIRI and MIRI. In conclusion, our study showed that SXNI effectively protects brain and heart from I/R injuries via a common Tnfrsf12a-mediated pathway involving atherosclerosis signaling and inflammatory response. It provides a novel knowledge of active ingredients of Ginkgo biloba on cardio-cerebral vascular diseases in future clinical application.

Biomeasures and mechanistic modeling highlight PK/PD risks for a monoclonal antibody targeting Fn14 in kidney disease

Discovery of the upregulation of fibroblast growth factor-inducible-14 (Fn14) receptor following tissue injury has prompted investigation into biotherapeutic targeting of the Fn14 receptor for the treatment of conditions such as chronic kidney diseases. In the development of monoclonal antibody (mAb) therapeutics, there is an increasing trend to use biomeasures combined with mechanistic pharmacokinetic/pharmacodynamic (PK/PD) modeling to enable decision making in early discovery. With the aim of guiding preclinical efforts on designing an antibody with optimized properties, we developed a mechanistic site-of-action (SoA) PK/PD model for human application. This model incorporates experimental biomeasures, including concentration of soluble Fn14 (sFn14) in human plasma and membrane Fn14 (mFn14) in human kidney tissue, and turnover rate of human sFn14. Pulse-chase studies using stable isotope-labeled amino acids and mass spectrometry indicated the sFn14 half-life to be approximately 5 hours in healthy volunteers. The biomeasures (concentration, turnover) of sFn14 in plasma reveals a significant hurdle in designing an antibody against Fn14 with desired characteristics. The projected dose (>1 mg/kg/wk for 90% target coverage) derived from the human PK/PD model revealed potential high and frequent dosing requirements under certain conditions. The PK/PD model suggested a unique bell-shaped relationship between target coverage and antibody affinity for anti-Fn14 mAb, which could be applied to direct the antibody engineering towards an optimized affinity. This investigation highlighted potential applications, including assessment of PK/PD risks during early target validation, human dose prediction and drug candidate optimization.

Type 2 immunity in tissue repair and fibrosis

Type 2 immunity is characterized by the production of IL-4, IL-5, IL-9 and IL-13, and this immune response is commonly observed in tissues during allergic inflammation or infection with helminth parasites. However, many of the key cell types associated with type 2 immune responses - including T helper 2 cells, eosinophils, mast cells, basophils, type 2 innate lymphoid cells and IL-4- and IL-13-activated macrophages - also regulate tissue repair following injury. Indeed, these cell populations engage in crucial protective activity by reducing tissue inflammation and activating important tissue-regenerative mechanisms. Nevertheless, when type 2 cytokine-mediated repair processes become chronic, over-exuberant or dysregulated, they can also contribute to the development of pathological fibrosis in many different organ systems. In this Review, we discuss the mechanisms by which type 2 immunity contributes to tissue regeneration and fibrosis following injury.

Lipopolysaccharide Upregulated Intestinal Epithelial Cell Expression of Fn14 and Activation of Fn14 Signaling Amplify Intestinal TLR4-Mediated Inflammation

TLR4 in intestinal epithelial cells has been shown both inflammatory and homeostatic roles following binding of its cognate ligand lipopolysaccharide (LPS). TWEAK-Fn14 axis plays an important role in pathologies caused by excessive or abnormal inflammatory responses. This study aimed to evaluate potential cross-talk between TLR4 and TWEAK/Fn14 system in porcine small intestinal epithelial cells. Our in vivo results showed that, compared with the age-matched normal control piglets, increased expression of Fn14 in epithelium and decreased TWEAK expression in lamina propria were detected in the small intestinal of piglets stimulated with LPS. Consistent with this finding, treatment with LPS increased the expression of Fn14 and TLR4 while decreased TWEAK expression in porcine small intestinal epithelial cell lines SIEC02. Interestingly, modulating Fn14 activation using agonistic anti-Fn14 decreased TLR4-mediated TNF-α production by SIEC02. In addition, pretreatment of LPS-stimulated SIEC02 with recombinant TWEAK protein suppresses the expression of Fn14 and TNF-α and inhibits the negative impact of LPS on the tight junctional protein occludin expression. In conclusion, this study demonstrates that the TWEAK-independent Fn14 activation augments TLR4-mediated inflammatory responses in the intestine of piglets. Furthermore, the TWEAK-dependent suppression of Fn14 signaling may play a role in intestinal homeostasis.

Immune and myodegenerative pathomechanisms in inclusion body myositis

Inclusion Body Myositis (IBM) is a relatively common acquired inflammatory myopathy in patients above 50 years of age. Pathological hallmarks of IBM are intramyofiber protein inclusions and endomysial inflammation, indicating that both myodegenerative and inflammatory mechanisms contribute to its pathogenesis. Impaired protein degradation by the autophagic machinery, which regulates innate and adaptive immune responses, in skeletal muscle fibers has recently been identified as a potential key pathomechanism in IBM. Immunotherapies, which are successfully used for treating other inflammatory myopathies lack efficacy in IBM and so far no effective treatment is available. Thus, a better understanding of the mechanistic pathways underlying progressive muscle weakness and atrophy in IBM is crucial in identifying novel promising targets for therapeutic intervention. Here, we discuss recent insights into the pathomechanistic network of mutually dependent inflammatory and degenerative events during IBM.

Disruption of the TWEAK/Fn14 pathway prevents 5-fluorouracil-induced diarrhea in mice

AIM

To clarify the roles of TWEAK and its receptor Fn14 in 5-fluorouracil (5-FU)-induced diarrhea.

METHODS

Diarrhea was induced in wild-type (WT), Fn14 knockout (KO), and IL-13 receptor (IL-13R)α1 KO BALB/c mice using a single injection of 5-FU. Histological analysis, cytokine analysis, and flow cytometry was performed on ileal tissues and cells. Murine colon carcinoma-bearing mice were co-treated with an anti-TWEAK antibody and 5-FU. Embryonic fibroblast response to cytokines was also analyzed.

RESULTS

5-FU induced high Fn14 expression in epithelial cells. The severity of 5-FU-induced diarrhea was lower in Fn14 KO mice compared with WT mice. Administration of anti-TWEAK antibody reduced 5-FU-induced diarrhea without affecting the antitumor effects of 5-FU in vivo. 5-FU-induced expression of IL-13, IL-17A, TNF-α, and IFN-γ in the ileum was Fn14 dependent. The severity of 5-FU-induced diarrhea was lower in IL-13Rα1 KO mice, indicating major role for IL-13 signaling via IL-13Rα1 in pathogenesis. We found that IL-13Rα2, an IL-13 neutralizing/cell protective receptor, was strongly induced by IL-33 in vitro and in vivo. IL-13Rα2 was upregulated in the ileum of 5-FU-treated Fn14 KO mice. Thus, the deletion of Fn14 upregulated IL-13Rα2 expression, which reduced IL-13 expression and activity.

CONCLUSION

Disruption of the TWEAK/Fn14 pathway affects several interconnected pathways, including those associated with IL-13, IL-33, and IL-13Rα2, to attenuate 5-FU-induced intestinal side effects.

Inhibitor of Apoptosis Protein-1 Regulates Tumor Necrosis Factor-Mediated Destruction of Intestinal Epithelial Cells

BACKGROUND AND AIMS

Tumor necrosis factor (TNF) is a cytokine that promotes inflammation and contributes to pathogenesis of inflammatory bowel diseases. Unlike other cells and tissues, intestinal epithelial cells undergo rapid cell death upon exposure to TNF, by unclear mechanisms. We investigated the roles of inhibitor of apoptosis proteins (IAPs) in the regulation of TNF-induced cell death in the intestinal epithelium of mice and intestinal organoids.

METHODS

RNA from cell lines and tissues was analyzed by quantitative polymerase chain reaction, protein levels were analyzed by immunoblot assays. BIRC2 (also called cIAP1) was expressed upon induction from lentiviral vectors in young adult mouse colon (YAMC) cells. YAMC cells, the mouse colon carcinoma cell line MC38, the mouse macrophage cell line RAW 264.7, or mouse and human organoids were incubated with second mitochondrial activator of caspases (Smac)-mimetic compound LCL161 or recombinant TNF-like weak inducer of apoptosis (TNFSF12) along with TNF, and cell death was quantified. C57BL/6 mice with disruption of Xiap, Birc2 (encodes cIAP1), Birc3 (encodes cIAP2), Tnfrsf1a, or Tnfrsf1b (Tnfrsf1a and b encode TNF receptors) were injected with TNF or saline (control); liver and intestinal tissues were collected and analyzed for apoptosis induction by cleaved caspase 3 immunohistochemistry. We also measured levels of TNF and alanine aminotransferase in serum from mice.

RESULTS

YAMC cells, and mouse and human intestinal organoids, died rapidly in response to TNF. YAMC and intestinal crypts expressed lower levels of XIAP, cIAP1, cIAP2, and cFLIP than liver tissue. Smac-mimetics reduced levels of cIAP1 and XIAP in MC38 and YAMC cells, and Smac-mimetics and TNF-related weak inducer of apoptosis increased TNF-induced cell death in YAMC cells and organoids-most likely by sequestering and degrading cIAP1. Injection of TNF greatly increased levels of cell death in intestinal tissue of cIAP1-null mice, compared with wild-type C57BL/6 mice, cIAP2-null mice, or XIAP-null mice. Excessive TNF-induced cell death in the intestinal epithelium was mediated TNF receptor 1.

CONCLUSIONS

In a study of mouse and human cell lines, organoids, and tissues, we found cIAP1 to be required for regulation of TNF-induced intestinal epithelial cell death and survival. These findings have important implications for the pathogenesis of TNF-mediated enteropathies and chronic inflammatory diseases of the intestine.

Serum soluble TWEAK levels are decreased in treatment naive noncirrhotic chronic hepatitis B patients

The mechanisms underlying hepatic inflammation and fibrogenesis in chronic hepatitis B (CHB) are complex and several cytokines are involved. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily which also acts as a cytokine. This study was conducted to evaluate serum soluble TWEAK (sTWEAK) levels in noncirrhotic CHB patients.Fifty-two treatment naive CHB patients and 30 healthy controls were included in the study and serum sTWEAK concentrations were measured using commercially available ELISA kits.Mean serum sTWEAK concentration was significantly lower in CHB group than healthy controls (189.6 ± 63.3 pg/mL in CHB group and 297.6 ± 61.5 pg/mL in control group, P < 0.001). According to the degree of necroinflammation in liver biopsies mean sTWEAK concentrations were found to be 168.14 ± 51.51, 206.96 ± 58.51, and 223.62 ± 78.88 pg/mL in patients with mild, moderate, and severe inflammation, respectively, and the difference between groups was statistically significant (P = 0.022). sTWEAK concentration was also found to be significantly higher in patients with advanced fibrosis in liver biopsy samples (169.59 ± 52.02 and 211.17 ± 68.22 pg/mL in patients with mild and advanced fibrosis, respectively, P = 0.016). Receiver operating characteristic (ROC) curves were obtained in CHB group to differentiate patients with advanced fibrosis from patients with mild fibrosis. Area under curve (AUC) was 0.676 (95% Cl; 0.526-0.825) for sTWEAK and for the specified cut-off value of 213.67 pg/mL sensitivity and specificity were 60% and 81.4%, respectively. ROC curve for sTWEAK to differentiate patients with severe inflammation revealed an AUC of 0.664 (95% Cl; 0.450-0.878). A cut-off value of 243.27 pg/mL yielded 54.5% sensitivity and 82.9% specificity.Serum sTWEAK concentration is decreased in treatment naive CHB patients. Further studies with simultaneous determination of circulating sTWEAK concentrations and TWEAK and factor-inducible 14 (Fn14) expressions in the liver biopsy samples would clarify the exact association of TWEAK/Fn14 pathway in the pathogenesis of CHB.

Soluble Fn14 Is Detected and Elevated in Mouse and Human Kidney Disease

The cytokine TWEAK and its cognate receptor Fn14 are members of the TNF/TNFR superfamily and are upregulated in tissue injury to mediate local tissue responses including inflammation and tissue remodeling. We found that in various models of kidney disease, Fn14 expression (mRNA and protein) is upregulated in the kidney. These models include: lupus nephritis mouse models (Nephrotoxic serum Transfer Nephritis and MRL.Faslpr/lpr), acute kidney injury models (Ischemia reperfusion injury and Folic acid injury), and a ZSF-1 diabetic nephropathy rat model. Fn14 expression levels correlate with disease severity as measured by disease histology. We have also shown for the first time the detection of soluble Fn14 (sFn14) in the urine and serum of mice. Importantly, we found the sFn14 levels are markedly increased in the diseased mice and are correlated with disease biomarkers including proteinuria and MCP-1. We have also detected sFn14 in human plasma and urine. Moreover, sFn14 levels, in urine are significantly increased in DN patients and correlated with proteinuria and MCP-1 levels. Thus our data not only confirm the up-regulation of Fn14/TWEAK pathway in kidney diseases, but also suggest a novel mechanism for its regulation by the generation of sFn14. The correlation of sFn14 levels and disease severity suggest that sFn14 may serve as a potential biomarker for both acute and chronic kidney diseases.

Can exercise affect the course of inflammatory bowel disease? Experimental and clinical evidence

The inflammatory bowel disease (IBD) consisting of Crohn's disease (CD) and ulcerative colitis (UC) are defined as idiopathic, chronic and relapsing intestinal disorders occurring in genetically predisposed individuals exposed to environmental risk factors such as diet and microbiome changes. Since conventional drug therapy is expensive and not fully efficient, there is a need for alternative remedies that can improve the outcome in patients suffering from IBD. Whether exercise, which has been proposed as adjunct therapy in IBD, can be beneficial in patients with IBD remains an intriguing question. In this review, we provide an overview of the effects of exercise on human IBD and experimental colitis in animal models that mimic human disease, although the information on exercise in human IBD are sparse and poorly understood. Moderate exercise can exert a beneficial ameliorating effect on IBD and improve the healing of experimental animal colitis due to the activity of protective myokines such as irisin released from working skeletal muscles. CD patients with higher levels of exercise were significantly less likely to develop active disease at six months. Moreover, voluntary exercise has been shown to exert a positive effect on IBD patients' mood, weight maintenance and osteoporosis. On the other hand, depending on its intensity and duration, exercise can evoke transient mild systemic inflammation and enhances pro-inflammatory cytokine release, thereby exacerbating the gastrointestinal symptoms. We discuss recent advances in the mechanism of voluntary and strenuous exercise affecting the outcome of IBD in patients and experimental animal models.

Fn14, a Downstream Target of the TGF-β Signaling Pathway, Regulates Fibroblast Activation

Fibrosis, the hallmark of human injuries and diseases such as serious burns, is characterized by excessive collagen synthesis and myofibroblast accumulation. Transforming growth factor-β (TGF-β), a potent inducer of collagen synthesis, has been implicated in fibrosis in animals. In addition to TGF-β, fibroblast growth factor-inducible molecule 14 (Fn14) has been reported to play an important role in fibrotic diseases, such as cardiac fibrosis. However, the function and detailed regulatory mechanism of Fn14 in fibrosis are unclear. Here, we investigated the effect of Fn14 on the activation of human dermal fibroblasts. In normal dermal fibroblasts, TGF-β signaling increased collagen production and Fn14 expression. Furthermore, Fn14 siRNA blocked extracellular matrix gene expression; even when TGF-β signaling was activated by TGF-β1, fibroblast activation remained blocked in the presence of Fn14 siRNA. Overexpressing Fn14 increased extracellular matrix gene expression. In determining the molecular regulatory mechanism, we discovered that SMAD4, an important TGF-β signaling co-mediator, bound to the Fn14 promoter and activated Fn14 transcription. Taken together, these results indicate that the TGF-β signaling pathway activates Fn14 expression through the transcription factor SMAD4 and that activated Fn14 expression increases extracellular matrix synthesis and fibroblast activation. Therefore, Fn14 may represent a promising approach to preventing the excessive accumulation of collagen or ECM in skin fibrosis.

Blocking TWEAK-Fn14 interaction inhibits hematopoietic stem cell transplantation-induced intestinal cell death and reduces GVHD

Inhibition of the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible 14 (Fn14) system reduces intestinal cell death and disease development in several models of colitis. In view of the crucial role of TNF and intestinal cell death in graft-versus-host disease (GVHD) and the ability of TWEAK to enhance TNF-induced cell death, we tested here the therapeutic potential of Fn14 blockade on allogeneic hematopoietic cell transplantation (allo-HCT)-induced intestinal GVHD. An Fn14-specific blocking human immunoglobulin G1 antibody variant with compromised antibody-dependent cellular cytotoxicity (ADCC) activity strongly inhibited the severity of murine allo-HCT-induced GVHD. Treatment of the allo-HCT recipients with this monoclonal antibody reduced cell death of gastrointestinal cells but neither affected organ infiltration by donor T cells nor cytokine production. Fn14 blockade also inhibited intestinal cell death in mice challenged with TNF. This suggests that the protective effect of Fn14 blockade in allo-HCT is based on the protection of intestinal cells from TNF-induced apoptosis and not due to immune suppression. Importantly, Fn14 blockade showed no negative effect on graft-versus-leukemia/lymphoma (GVL) activity. Thus, ADCC-defective Fn14-blocking antibodies are not only possible novel GVL effect-sparing therapeutics for the treatment of GVHD but might also be useful for the treatment of other inflammatory bowel diseases where TNF-induced cell death is of relevance.

Moderate exercise training attenuates the severity of experimental rodent colitis: the importance of crosstalk between adipose tissue and skeletal muscles

Although progress has been recently made in understanding of inflammatory bowel diseases (IBD), their etiology is unknown apart from several factors from adipose tissue and skeletal muscles such as cytokines, adipokines, and myokines were implicated in the pathogenesis of ulcerative colitis. We studied the effect high-fat diet (HFD; cholesterol up to 70%), low-fat diet (LFD; cholesterol up to 10%), and the normal diet (total fat up to 5%) in rats with TNBS colitis forced to treadmill running exercise (5 days/week) for 6 weeks. In nonexercising HFD rats, the area of colonic damage, colonic tissue weight, the plasma IL-1β, TNF-α, TWEAK, and leptin levels, and the expression of IL-1β-, TNF-α-, and Hif1α mRNAs were significantly increased and a significant fall in plasma adiponectin and irisin levels was observed as compared to LFD rats. In HFD animals, the exercise significantly accelerated the healing of colitis, raised the plasma levels of IL-6 and irisin, downregulated the expression of IL-1β, TNF-α, and Hif1α, and significantly decreased the plasma IL-1β, TNF α, TWEAK, and leptin levels. We conclude that HFD delays the healing of colitis in trained rats via decrease in CBF and plasma IL-1β, TNF-α, TWEAK, and leptin levels and the release of protective irisin.

TWEAK and the progression of renal disease: clinical translation

Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) activates the fibroblast growth factor-inducible-14 (Fn14) receptor. TWEAK has actions on intrinsic kidney cells and on inflammatory cells of potential pathophysiological relevance. The effects of TWEAK in tubular cells have been explored in most detail. In cultured murine tubular cells TWEAK induces the expression of inflammatory cytokines, downregulates the expression of Klotho, is mitogenic, and in the presence of sensitizing agents promotes apoptosis. Similar actions were observed on glomerular mesangial cells. In vivo TWEAK actions on healthy kidneys mimic cell culture observations. Increased expression of TWEAK and Fn14 was reported in human and experimental acute and chronic kidney injury. The role of TWEAK/Fn14 in kidney injury has been demonstrated in non-inflammatory compensatory renal growth, acute kidney injury and chronic kidney disease of immune and non-immune origin, including hyperlipidaemic nephropathy, lupus nephritis (LN) and anti-GBM nephritis. The nephroprotective effect of TWEAK or Fn14 targeting in immune-mediated kidney injury is the result of protection from TWEAK-induced injury of renal intrinsic cells, not from interference with the immune response. A phase I dose-ranging clinical trial demonstrated the safety of anti-TWEAK antibodies in humans. A phase II randomized placebo-controlled clinical trial exploring the efficacy, safety and tolerability of neutralizing anti-TWEAK antibodies as a tissue protection strategy in LN is ongoing. The eventual success of this trial may expand the range of kidney diseases in which TWEAK targeting should be explored.

Pathological activation of canonical nuclear-factor κB by synergy of tumor necrosis factor α and TNF-like weak inducer of apoptosis in mouse acute colitis

Tumor necrosis factor (TNF)-α is a major effector in various inflammatory conditions. TNF-like weak inducer of apoptosis (TWEAK) is a member of the TNF superfamily that promotes inflammatory tissue damage through its receptor, FGF-inducible molecule 14 (Fn14). Since both TWEAK and TNF-α have been shown to mediate pathological responses through inter-dependent or independent pathways by in vitro, the potential interplay of these pathways was investigated in a mouse colitis model. Acute colitis was induced by rectal injection of trinitrobenzene sulfonic acid (TNBS), with administration of control IgG, TNF receptor (TNFR)-Ig chimeric protein, anti-TWEAK monoclonal antibody, or the combination of TNFR-Ig and anti-TWEAK antibody. On day 4, disease severity was evaluated and gene expression profiling was analyzed using whole colon tissue. NF-κB activation was investigated with Western blot. Levels of transcript of TWEAK, Fn14 and NF-κB-related molecules were measured in purified colon epithelial cells (ECs). As a result, activation of the canonical (p50/RelA), but not noncanonical (p100/RelB)-mediated pathway was the hallmark of inflammatory responses in this model. Inflammation induced upregulation of Fn14 only in ECs but not in other cell types. Combination treatment of TNFR-Ig and anti-TWEAK antibody synergistically reduced disease severity in comparison with the control antibody or single agent treatment. Gene expression profile of the colon indicated downregulation of canonical NF-κB pathway with combination treatment. In conclusion, synergistic activation of canonical NF-κB by TWEAK and TNF-α is critical for the induction of inflammatory tissue damage in acute inflammation.

The role of physical exercise in inflammatory bowel disease

We reviewed and analyzed the relationship between physical exercise and inflammatory bowel disease (IBD) which covers a group of chronic, relapsing, and remitting intestinal disorders including Crohn's disease (CD) and ulcerative colitis. The etiology of IBD likely involves a combination of genetic predisposition and environmental risk factors. Physical training has been suggested to be protective against the onset of IBD, but there are inconsistencies in the findings of the published literature. Hypertrophy of the mesenteric white adipose tissue (mWAT) is recognized as a characteristic feature of CD, but its importance for the perpetuation of onset of this intestinal disease is unknown. Adipocytes synthesize proinflammatory and anti-inflammatory cytokines. Hypertrophy of mWAT could play a role as a barrier to the inflammatory process, but recent data suggest that deregulation of adipokine secretion is involved in the pathogenesis of CD. Adipocytokines and macrophage mediators perpetuate the intestinal inflammatory process, leading to mucosal ulcerations along the mesenteric border, a typical feature of CD. Contracting skeletal muscles release biologically active myokines, known to exert the direct anti-inflammatory effects, and inhibit the release of proinflammatory mediators from visceral fat. Further research is required to confirm these observations and establish exercise regimes for IBD patients.

Role of the TWEAK-Fn14-cIAP1-NF-κB Signaling Axis in the Regulation of Myogenesis and Muscle Homeostasis

Mammalian skeletal muscle maintains a robust regenerative capacity throughout life, largely due to the presence of a stem cell population known as “satellite cells” in the muscle milieu. In normal conditions, these cells remain quiescent; they are activated upon injury to become myoblasts, which proliferate extensively and eventually differentiate and fuse to form new multinucleated muscle fibers. Recent findings have identified some of the factors, including the cytokine TNFα-like weak inducer of apoptosis (TWEAK), which govern these cells’ decisions to proliferate, differentiate, or fuse. In this review, we will address the functions of TWEAK, its receptor Fn14, and the associated signal transduction molecule, the cellular inhibitor of apoptosis 1 (cIAP1), in the regulation of myogenesis. TWEAK signaling can activate the canonical NF-κB signaling pathway, which promotes myoblast proliferation and inhibits myogenesis. In addition, TWEAK activates the non-canonical NF-κB pathway, which, in contrast, promotes myogenesis by increasing myoblast fusion. Both pathways are regulated by cIAP1, which is an essential component of downstream signaling mediated by TWEAK and similar cytokines. This review will focus on the seemingly contradictory roles played by TWEAK during muscle regeneration, by highlighting the interplay between the two NF-κB pathways under physiological and pathological conditions. We will also discuss how myogenesis is negatively affected by chronic conditions, which affect homeostasis of the skeletal muscle environment.

The TWEAK-Fn14 pathway: a potent regulator of skeletal muscle biology in health and disease

TNF-like weak inducer of apoptosis (TWEAK), a TNF superfamily ligand, and its bona fide receptor, the TNF receptor superfamily member fibroblast growth factor-inducible 14 (Fn14), represent a pivotal axis for shaping both physiological and pathological tissue responses to acute or chronic injury and disease. In recent years significant advances have been made in delineating the prominent role of TWEAK-Fn14 dyad in regulating skeletal muscle mass and metabolism. Also emerging from the broad study of tissue injury in skeletal muscle and other organs is the role of the TWEAK-Fn14 pathway in promoting fibrosis. This review article highlights recent advancements toward understanding how the TWEAK-Fn14 pathway regulates the response to various skeletal muscle insults and, more broadly, engages multiple mechanisms to drive tissue fibrosis.