Tumor Necrosis Factor and Lymphotoxin in Regulation of Intestinal Inflammation
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ISSN 0006-2979, Biochemistry (Moscow), 2016, Vol. 81, No. 11, pp. 1309-1325. © Pleiades Publishing, Ltd., 2016. Original Russian Text © E. О. Gubernatorova, A. V. Tumanov, 2016, published in Biokhimiya, 2016, Vol. 81, No. 11, pp. 1559-1577. REVIEW Tumor Necrosis Factor and Lymphotoxin in Regulation of Intestinal Inflammation E. О. Gubernatorova1 and A. V. Tumanov1,2* 1Institute of Molecular Biology, Russian Academy of Sciences, 119991 Moscow, Russia; E-mail: [email protected] 2University of Texas Health Science Center, Department of Microbiology, Immunology, and Molecular Genetics, San Antonio, TX 78229, USA Received July 3, 2016 Revision received August 16, 2016 Abstract—Ulcerative colitis and Crohn’s disease are the major forms of inflammatory bowel disease. Cytokines of the tumor necrosis factor (TNF) family play an important role in the regulation of intestinal inflammation. In this review, we discuss the function of key cytokines of this family – TNF and lymphotoxin (LT) – in mucosal healing, IgA production, and in control of innate lymphoid cells (ILCs), novel regulators of mucosal homeostasis in the gut. TNF plays a central role in the pathogenesis of inflammatory bowel diseases (IBD). LT regulates group 3 of ILCs and IL-22 production and protects the epithelium against damage by chemicals and mucosal bacterial pathogens. In addition, we discuss major mouse models employed to study the mechanism of intestinal inflammation, their advantages and limitations, as well as application of TNF blockers in the therapy for IBD. DOI: 10.1134/S0006297916110092 Key words: tumor necrosis factor, lymphotoxin, intestinal inflammation, inflammatory bowel disease, mouse models CYTOKINES OF TNF SUPERFAMILY pairs) are expressed by immune system cells [1]. Some receptors belonging to this cytokine family, for instance, Tumor Necrosis Factor (TNF), lymphotoxin (LT), TNFR1, are able to activate mechanisms of cell death, and LIGHT (homologous to lymphotoxin, exhibits whereas others (LTβR) predominantly promote cell sur- inducible expression and competes with HSV glycopro- vival and inflammation [2]. Most ligands of the TNF tein D for binding to herpesvirus entry mediator, a recep- superfamily are membrane-associated trimeric mole- tor expressed on T-lymphocytes, TNFSF14) are key cules. However, upon activation of certain metallopro- cytokines of the TNF superfamily that perform various teinases, trimers may be converted into soluble form. For functions in mammalian biology. Most ligands and recep- instance, metalloproteinase TACE (TNF-alpha convert- tors of the TNF superfamily (over 40 ligand–receptor ing enzyme) releases the extracellular TNF moiety [3]. Intracellular parts of receptors do not contain kinase domains and are unable to bind tyrosine kinase. Thus, Abbreviations: CD, Crohn’s disease; DCs, dendritic cells; DSS, dextran sulfate sodium; FDA, Food and Drug Administration signaling is realized by means of adapter molecules. of USA; FDC, follicular dendritic cells; GALT, gut-associated Several receptors of the TNF family, such as TNFR1 and lymphoid tissue; IBD, inflammatory bowel disease; IFN, inter- Fas, contain death domains within their cytoplasmic feron; IL, interleukin; ILCs, innate lymphoid cells; LIGHT, regions, which are able to activate and recruit caspase homologous to lymphotoxin, exhibits inducible expression and precursors and to induce apoptosis. Another feature of competes with HSV glycoprotein D for binding to herpesvirus these molecules is their composition of three subunits entry mediator, a receptor expressed on T-lymphocytes (anoth- that determines signaling stereochemistry. Thus, the list- er name: tumor necrosis factor superfamily member 14, ed unique structural attributes determine the connection TNFSF14); LT, lymphotoxin; LT R, membrane lymphotoxin β between cytokines of the TNF superfamily and signal receptor; MHC, major histocompatibility complex; MNP, mononuclear phagocytes; TACE, TNF-alpha converting transduction pathways in cell proliferation, differentia- enzyme; TNBS, 2,4,6-trinitrobenzenesulfonic acid; TNF, tion, and survival [1, 2]. This is why possible use of tumor necrosis factor; TNFR, tumor necrosis factor receptor; cytokines of the TNF superfamily and their inhibitors in UC, ulcerative colitis. therapy for various autoimmune diseases and cancer is * To whom correspondence should be addressed. actively studied in recent years [4]. 1309 1310 GUBERNATOROVA, TUMANOV The main ligand–receptor interactions in the macrophages, NK cells, and DCs, can also interact with TNF/LT system as well as producer and responding cells LTβR [3]. In addition to LTβR, LIGHT can interact with are presented in the Fig. 1. TNF and TNFR are widely herpes virus entry mediator (HVEM) receptor, which is produced. Membrane lymphotoxin is an LTβ2LTα1 het- also a ligand for receptors belonging to another cytokine erotrimer that is predominantly located on lymphocytes. family, CD160 and BTLA (B and T lymphocyte attenua- LTβR receptor for the membrane lymphotoxin, in turn, is tor) [9]. This complex system of ligands and receptors in expressed in epithelial and stromal cells, dendritic cells the TNF cytokine family provides selectivity of interac- (DCs), and macrophages, but it is absent on lymphocytes tion and signal transduction between various immune sys- [3, 5]. This expression pattern for LT and LTβR provides tem cells and implies involvement of compensatory interaction of LT-producing lymphocytes – cells with mechanisms. stromal microenvironment – that is important for lymph The best-studied function of LT and LTβR is their node development and maintenance of lymphoid organ participation in lymphoid organ development, such as structure [3, 6]. Recent studies have demonstrated that lymph nodes and Peyer’s patches, and in maintenance of LTα1β2 has two LTβR binding sites with different affini- proper spleen white pulp architecture [6, 10]. However, it ties, and LTβR dimerizes upon LTα1β2 binding. This was later shown that LT function is broader and not dimerization is required for efficient signal transduction restricted to lymphoid organs and protection against [7]. Soluble LTα3 homotrimer does not bind LTβR, but it infections. Thus, it was found that LT plays an important interacts with TNFR1 and TNFR2, and, similarly to role in maintenance of lipid homeostasis and liver regen- TNF, it is able to stimulate development of various eration. It also regulates inflammation and commensal inflammatory reactions. In contrast to TNFR1, which is gut microbiota, proliferation, and tumor transformation constantly expressed in all cells, TNFR2 expression is [11-17]. In addition to maintenance of lymphoid organ more selective and inducible [8]. It is known that mem- structure, TNF also participates in defense against infec- brane TNF has higher affinity for TNFR2 compared to tions, regulation of inflammation, and autoimmune dis- the soluble TNF [8]. Another TNF family ligand, eases [18-20]. Therefore, LT, TNF, and LIGHT form an LIGHT (TNFSF14), mainly expressed on T cells, integral signaling network that is required for efficient innate and adaptive immune responses. We will further review mechanisms of TNF and LT participation in regu- Global T-, B-, NK-cells, ILC – T cells, DC, expression innate lymphoid cells macrophages lation of intestinal homeostasis and describe mouse mod- els widely used in studying the mechanisms of intestinal inflammation. EXPERIMENTAL ANIMAL MODELS FOR INTESTINAL INFLAMMATION The intestine is a sophisticated organ containing dif- ferent cell types that contact the “outer” environment and are constantly interacting with commensal microbio- ta. Revealing mechanisms involved in intestinal inflam- mation and damage is an important step in developing therapeutic strategies and prevention of disease. It is beyond doubt that the most reliable data can only be obtained during analysis of samples from patients who suffer from various diseases. However, sampling size, eth- ical issues related to utilization of human samples, and Global Epithelial and stromal cells, DC, T cells, genetic heterogeneity in the group significantly restrict expression DC, monocytes epithelial cells, macrophages human research trials. Therefore, studying pathogenesis Inflammation Modification of the gastrointestinal tract requires developing complex and activation of lymphoid T cell survival of immune microenvironment, experimental models on animals that are devoid of such system DC maturation drawbacks as sampling limitation and genetic hetero- geneity. At the same time, human diseases should be Fig. 1. Ligands and receptors of the TNF/LT family. The main lig- reproduced in these animals with maximum likeness [21- and–receptor interactions and producer cells are indicated with 23]. Advantages in the genetic engineering field and well- arrows. The dashed line indicates action sites for metallopro- teinases (MMP), whose activity converts membrane-bound ligand studied genome make mice the most-used object in mod- into a soluble form. DcR3 is a receptor-trap for LIGHT (found in eling immune processes, including those involved in some human tumors). intestinal inflammation [24]. Modeling disorders in mice BIOCHEMISTRY (Moscow) Vol. 81 No. 11 2016 TNF AND LT CYTOKINES IN REGULATION OF INTESTINAL INFLAMMATION 1311 gives a number of advantages, such as simplicity of trols in the same cage is recommended. If this is impossi- genome and microbiome manipulations, and fast genera- ble, microbiota composition is balanced before the exper- tion change.