Comparative modeling of TNFRSF25 (DR3) predicts receptor destabilization by a mutation linked to rheumatoid arthritis

Conserved aging-related signatures of senescence and inflammation in different tissues and species

Increasing evidence indicates that chronic inflammation and senescence are the cause of many severe age-related diseases, with both biological processes highly upregulated during aging. However, until now, it has remained unknown whether specific inflammation- or senescence-related genes exist that are common between different species or tissues. These potential markers of aging could help to identify possible targets for therapeutic interventions of aging-associated afflictions and might also deepen our understanding of the principal mechanisms of aging. With the objective of identifying such signatures of aging and tissue-specific aging markers, we analyzed a multitude of cross-sectional RNA-Seq data from four evolutionarily distinct species (human, mouse and two fish) and four different tissues (blood, brain, liver and skin). In at least three different species and three different tissues, we identified several genes that displayed similar expression patterns that might serve as potential aging markers. Additionally, we show that genes involved in aging-related processes tend to be tighter controlled in long-lived than in average-lived individuals. These observations hint at a general genetic level that affect an individual’s life span. Altogether, this descriptive study contributes to a better understanding of common aging signatures as well as tissue-specific aging patterns and supplies the basis for further investigative age-related studies.

A variant of death-receptor 3 associated with rheumatoid arthritis interferes with apoptosis-induction of T cell

Rheumatoid arthritis (RA) is a chronic polyarthritis of unknown etiology. To unravel the molecular mechanisms in RA, we performed targeted DNA sequencing analysis of patients with RA. This analysis identified a variant of the death receptor 3 (DR3) gene, a member of the family of apoptosis-inducing Fas genes, which contains four single-nucleotide polymorphisms (SNPs) and a 14-nucleotide deletion within exon 5 and intron 5. We found that the deletion causes the binding of splicing regulatory proteins to DR3 pre-mRNA intron 5, resulting in a portion of intron 5 becoming part of the coding sequence, thereby generating a premature stop codon. We also found that this truncated DR3 protein product lacks the death domain and forms a heterotrimer complex with wildtype DR3 that dominant-negatively inhibits ligand-induced apoptosis in lymphocytes. Myelocytes from transgenic mice expressing the human DR3 variant produced soluble truncated DR3, forming a complex with TNF-like ligand 1A (TL1A), which inhibited apoptosis induction. In summary, our results reveal that a DR3 splice variant that interferes with ligand-induced T cell responses and apoptosis may contribute to RA pathogenesis.

The TNF-family cytokine TL1A: from lymphocyte costimulator to disease co-conspirator

Originally described in 2002 as a T cell-costimulatory cytokine, the tumor necrosis factor family member TNF-like factor 1A (TL1A), encoded by the TNFSF15 gene, has since been found to affect multiple cell lineages through its receptor, death receptor 3 (DR3, encoded by TNFRSF25) with distinct cell-type effects. Genetic deficiency or blockade of TL1A-DR3 has defined a number of disease states that depend on this cytokine-receptor pair, whereas excess TL1A leads to allergic gastrointestinal inflammation through stimulation of group 2 innate lymphoid cells. Noncoding variants in the TL1A locus are associated with susceptibility to inflammatory bowel disease and leprosy, predicting that the level of TL1A expression may influence host defense and the development of autoimmune and inflammatory diseases.

Progranulin-derived Atsttrin directly binds to TNFRSF25 (DR3) and inhibits TNF-like ligand 1A (TL1A) activity

Atsttrin, a progranulin (PGRN)-derived molecule composed of three TNFR-binding domains of PGRN, binds to TNF receptors (TNFR) and is therapeutic against inflammatory arthritis. Here we screened the associations of Atsttrin and other members in TNFR subfamily, which led to the discovery of TNFRSF25 (DR3) as an additional Atsttrin-interacting member in TNFR family. Similar to TNFR1 and TNFR2, DR3 also directly bound to Atsttrin. The first three cysteine-rich domains (CRD) in the extracellular portion of DR3 were required for this interaction. Atsttrin inhibited the interaction between DR3 and its TNF-Like Ligand 1A (TL1A). In addition, Atsttrin inhibited TL1A-stimulated target gene expressions and neutralized TL1A-enhanced osteoclastogenesis in vitro. Furthermore, Atsttrin ameliorated the pathology in dextran sulfate sodium induced colitis. Taken together, these findings not only provide the new insights into Atsttrin's therapeutic action in inflammatory arthritis, but may also present Atsttrin as a novel biological agent for treating various types of diseases associated with TL1A/DR3 pathway.

Membrane trafficking of death receptors: implications on signalling

Death receptors were initially recognised as potent inducers of apoptotic cell death and soon ambitious attempts were made to exploit selective ignition of controlled cellular suicide as therapeutic strategy in malignant diseases. However, the complexity of death receptor signalling has increased substantially during recent years. Beyond activation of the apoptotic cascade, involvement in a variety of cellular processes including inflammation, proliferation and immune response was recognised. Mechanistically, these findings raised the question how multipurpose receptors can ensure selective activation of a particular pathway. A growing body of evidence points to an elegant spatiotemporal regulation of composition and assembly of the receptor-associated signalling complex. Upon ligand binding, receptor recruitment in specialized membrane compartments, formation of receptor-ligand clusters and internalisation processes constitute key regulatory elements. In this review, we will summarise the current concepts of death receptor trafficking and its implications on receptor-associated signalling events.

TL1A and DR3, a TNF family ligand-receptor pair that promotes lymphocyte costimulation, mucosal hyperplasia, and autoimmune inflammation

DR3 (TNFRSF25) is a member of the tumor necrosis factor receptor (TNFR) superfamily expressed primarily on lymphocytes and is a receptor for the TNF family cytokine TL1A (TNFSF15). DR3 costimulates T-cell activation, but it is unique among these receptors in that it signals through an intracytoplasmic death domain and the adapter protein TRADD (TNFR-associated death domain). TL1A costimulates T cells to produce a wide variety of cytokines and can promote expansion of activated and regulatory T cells in vivo. Studies in mice deficient in DR3 or TL1A or in animals treated with antibodies that block the activity of TL1A have revealed a specific role for DR3 in enhancing effector T-cell proliferation at the site of tissue inflammation in autoimmune disease models. DR3 appears to be required in autoimmune disease models dependent on a variety of different T-cell subsets and also invariant natural killer T (iNKT) cells. Chronic expression of TL1A induces a distinct interleukin-13-dependent pathology in the small intestine marked by goblet cell hyperplasia and other features associated with allergic and anti-parasitic responses. These studies suggest that TL1A may be a viable target for therapies designed to inhibit the T-cell-dependent component of diverse autoimmune diseases.

Biochemical and structural characterization of the human TL1A ectodomain

TNF-like 1A (TL1A) is a newly described member of the TNF superfamily that is directly implicated in the pathogenesis of autoimmune diseases, including inflammatory bowel disease, atherosclerosis, and rheumatoid arthritis. We report the crystal structure of the human TL1A extracellular domain at a resolution of 2.5 A, which reveals a jelly-roll fold typical of the TNF superfamily. This structural information, in combination with complementary mutagenesis and biochemical characterization, provides insights into the binding interface and the specificity of the interactions between TL1A and the DcR3 and DR3 receptors. These studies suggest that the mode of interaction between TL1A and DcR3 differs from other characterized TNF ligand/receptor complexes. In addition, we have generated functional TL1A mutants with altered disulfide bonding capability that exhibit enhanced solution properties, which will facilitate the production of materials for future cell-based and whole animal studies. In summary, these studies provide insights into the structure and function of TL1A and provide the basis for the rational manipulation of its interactions with cognate receptors.

Monocyte gene-expression profile in men with familial combined hyperlipidemia and its modification by atorvastatin treatment

AIM

The genetic origin of familial combined hyperlipidemia (FCH) is not well understood. We used microarray profiling of peripheral blood monocytes to search novel genes and pathways involved in FCH.

METHODS

Fasting plasma for determination of lipid profiles, inflammatory molecules and adipokines was obtained and peripheral blood monocytes were isolated from male FCH patients basally and after 4 weeks of atorvastatin treatment. Sex-, age- and adiposity-matched controls were also studied. Gene-expression profiles were analyzed using Affymetrix Human Genome U133A 2.0 GeneChip arrays.

RESULTS

Analysis of gene expression by cDNA microarrays showed that 82 genes were differentially expressed in FCH monocytes compared with controls. Atorvastatin treatment modified the expression of 86 genes. Pathway analysis revealed the over-representation of the complement and coagulation cascades, the hematopoietic cell lineage and the arachidonic acid metabolism pathways. Changes in the expression of some genes, confirmed by real-time RT-PCR, (CD36, leucine-rich repeats and immunoglobulin-like domains-1, tissue factor pathway inhibitor 2, myeloid cell nuclear differentiation antigen, tumor necrosis factor receptor superfamily, member 25, CD96 and lipoprotein lipase), may be related to a proinflammatory environment in FCH monocytes, which is partially reversed by atorvastatin. Higher plasma levels of triglycerides and free fatty acids and lower levels of adiponectin in FCH patients could also trigger changes in gene expression that atorvastatin cannot modify.

CONCLUSION

Our results show clear differences in gene expression in FCH monocytes compared with those of matched healthy controls, some of which are influenced by atorvastatin treatment.

[TNF receptor-associated periodic syndrome (TRAPS) in Japan: clinical characterization, pathogenesis, diagnostic criteria, and treatment]

TNF receptor-associated periodic syndrome (TRAPS) is an autosomal dominant inherited disease characterized by prolonged episodes of periodic fever and localized inflammation. The hypothetical pathogenesis of TRAPS is defective TNF receptor 1 (TNFRSF1A) shedding from cell membranes in response to a stimulus including TNFalpha. This mechanism has recently been shown to account for a minor population of TRAPS patients and other mechanisms are reported to explain the disease, such as resistance to apoptosis, TNFRSF1A internalization, or TNFRSF1A misfolding and aggregation, leading to NF-kappaB activation and apoptosis. Until now 15 TRAPS patients from 5 pedigree including 5 different mutations (C30R, C30Y, T61I, C70S, C70G) had been reported in Japan. There were many sporadic cases of TRAPS without TNFRSF1A mutation in our epidemiological study. In this issue, we described the clinical characterization, pathogenesis, diagnostic criteria, and treatment of TRAPS according to our case and literature.

Death receptor-3 mediates apoptosis in human osteoblasts under narrowly regulated conditions

We previously reported that a soluble form of the TNF-family receptor death receptor-3 (DR3) is expressed in osteoblasts. DR3 regulates death or differentiation in other tissues, and DR3 ligands occur in bone, but the function of DR3 in the osteoblast was unknown. We studied the expression of DR3 and the effects crosslinking antibodies to DR3 or of natural DR3 ligands in human osteoblasts. Western analysis showed that nontransformed osteoblasts and the MG63 osteosarcoma cell line produce both soluble decoy receptor and transmembrane isoforms of DR3. Cell surface labeling showed that low and high DR3-expressing osteoblast populations occur. Verification of by cloning showed a point mutation in DR3 from MG63 cells. Activation of DR3 by antibody crosslinking or with DR3 ligands caused apoptosis in osteoblasts and in MG63 cells, but only in low-density cell cultures. In dense cultures apoptosis did not occur, but nuclear factor-kappaB nuclear translocation was observed under some conditions. Crosslinking of DR3 in high-density MG63 cultures blocked expression of bone matrix elements. DR3 activation in high-density nontransformed osteoblasts had only minor effects on cell maturation. We conclude that DR3 activation can mediate apoptosis in osteoblasts. Its activity is, however, highly restricted by its soluble ligand-binding isoform and possibly also by alternate survival signals. In the presence of survival signals, DR3 may affect cell maturation although effects on differentiation were clearly seen only in the MG63 transformed cell line.

Role of TL1A and its receptor DR3 in two models of chronic murine ileitis

TL1A is a TNF-like cytokine that binds to the death-domain receptor (DR)3 and provides costimulatory signals to activated lymphocytes. Through this interaction, TL1A induces secretion of IFN-gamma and may, therefore, participate in the development of T helper-1-type effector responses. In this study, we investigated whether interactions between TL1A and DR3 are involved in the pathogenesis of chronic murine ileitis. We demonstrate that alternative splicing of DR3 mRNA takes place during the activation of lymphocytes, which results in up-regulation of the complete/transmembrane (tm) form of DR3. Using two immunogenetically distinct animal models of Crohn's disease, we demonstrate that induction of intestinal inflammation is associated with significant up-regulation of TL1A and tm DR3 in the inflamed mucosa. In addition, within isolated lamina propria mononuclear cells from mice with inflammation, TL1A is primarily expressed on CD11c(high) dendritic cells. We also report that TL1A acts preferentially on memory CD4(+)/CD45RB(lo) murine lymphocytes by significantly inducing their proliferation, whereas it does not affect the proliferation of the naïve CD4(+)/CD45RB(hi) T helper cell subpopulation. Finally, we demonstrate that TL1A synergizes with both the cytokine-dependent IL-12/IL-18 pathway and with low-dose stimulation of the T cell receptor to significantly induce the secretion of IFN-gamma via an IL-18-independent pathway. Our results raise the possibility that interaction(s) between TL1A expressed on antigen-presenting cells and tm DR3 on lymphocytes may be of particular importance for the pathogenesis of chronic inflammatory conditions that depend on IFN-gamma secretion, including inflammatory bowel disease. Blockade of the TL1A/DR3 pathway may, therefore, offer therapeutic opportunities in Crohn's disease.

Modeling of tumor necrosis factor receptor superfamily 1A mutants associated with tumor necrosis factor receptor–associated periodic syndrome indicates misfolding consistent with abnormal function

OBJECTIVE

To investigate the effect of mutations in the tumor necrosis factor receptor superfamily 1A (TNFRSF1A) gene on the conformation and behavior of the TNFRSF1A protein. Mutations in TNFRSF1A cause the autosomal-dominant, autoinflammatory TNFR-associated periodic syndrome (TRAPS).

METHODS

The expression of recombinant TNFRSF1A was compared in SK-HEp-1 endothelial cells and HEK 293 epithelial cells stably transfected with full-length R347A or Deltasig constructs of wild-type or TRAPS-associated mutant TNFRSF1A. TNF binding was assessed in HEK 293 cell lines expressing R347A wild-type or mutant TNFRSF1A. Homology modeling of the 3-dimensional structure of the ectodomains of wild-type and mutant TNFRSF1A was performed.

RESULTS

TRAPS-associated mutant and wild-type TNFRSF1A behaved differently and had different localization properties within the cell, as a direct result of mutations in the ectodomains of TNFRSF1A. From a structural perspective, mutants with a predicted structure similar to that of the wild-type protein (e.g., R92Q) behaved similarly to wild-type TNFRSF1A, whereas forms of TNFRSF1A with mutations predicted to drastically destabilize the protein structure (e.g., cysteine mutations) showed defects in cell surface expression and TNF binding.

CONCLUSION

The results obtained from the in vitro experiments, in combination with the modeled structures, indicate that the phenotype and clinical differences between different TRAPS-associated mutants of TNFRSF1A result from different conformations of the TNFRSF1A ectodomains.