Clare E. Bryant

The IUPHAR/BPS Guide to PHARMACOLOGY in 2018: updates and expansion to encompass the new guide to IMMUNOPHARMACOLOGY

Abstract The IUPHAR/BPS Guide to PHARMACOLOGY (GtoPdb, www.guidetopharmacology.org) and its precursor IUPHAR-DB, have captured expert-curated interactions between targets and ligands from selected papers in pharmacology and drug discovery since 2003. This resource continues to be developed in conjunction with the International Union of Basic and Clinical Pharmacology (IUPHAR) and the British Pharmacological Society (BPS). As previously described, our unique model of content selection and quality control is based on 96 target-class subcommittees comprising 512 scientists collaborating with in-house curators. This update describes content expansion, new features and interoperability improvements introduced in the 10 releases since August 2015. Our relationship matrix now describes ∼9000 ligands, ∼15 000 binding constants, ∼6000 papers and ∼1700 human proteins. As an important addition, we also introduce our newly funded project for the Guide to IMMUNOPHARMACOLOGY (GtoImmuPdb, www.guidetoimmunopharmacology.org). This has been ‘forked’ from the well-established GtoPdb data model and expanded into new types of data related to the immune system and inflammatory processes. This includes new ligands, targets, pathways, cell types and diseases for which we are recruiting new IUPHAR expert committees. Designed as an immunopharmacological gateway, it also has an emphasis on potential therapeutic interventions.

Therapeutic Targeting of Toll-Like Receptors for Infectious and Inflammatory Diseases and Cancer

Since first being described in the fruit fly Drosophila melanogaster, Toll-like receptors (TLRs) have proven to be of great interest to immunologists and investigators interested in the molecular basis to inflammation. They recognize pathogen-derived factors and also products of inflamed tissue, and trigger signaling pathways that lead to activation of transcription factors such as nuclear factor-κB and the interferon regulatory factors. These in turn lead to induction of immune and inflammatory genes, including such important cytokines as tumor necrosis factor-α and type I interferon. Much evidence points to a role for TLRs in immune and inflammatory diseases and increasingly in cancer. Examples include clear roles for TLR4 in sepsis, rheumatoid arthritis, ischemia/reperfusion injury, and allergy. TLR2 has been implicated in similar pathologic conditions and also in systemic lupus erythematosus (SLE) and tumor metastasis. TLR7 has also been shown to be important in SLE. TLR5 has been shown to be radioprotective. Recent advances in our understanding of signaling pathways activated by TLRs, structural insights into TLRs bound to their ligands and antagonists, and approaches to inhibit TLRs (including antibodies, peptides, and small molecules) are providing possiblemeans by which to interfere with TLRs clinically. Here we review these recent advances and speculate about whether manipulating TLRs is likely to be successful in fighting off different diseases.

Assembly and localization of Toll-like receptor signalling complexes

Signal transduction by the Toll-like receptors (TLRs) is central to host defence against many pathogenic microorganisms and also underlies a large burden of human disease. Thus, the mechanisms and regulation of signalling by TLRs are of considerable interest. In this Review, we discuss the molecular basis for the recognition of pathogen-associated molecular patterns, the nature of the protein complexes that mediate signalling, and the way in which signals are regulated and integrated at the level of allosteric assembly, post-translational modification and subcellular trafficking of the components of the signalling complexes. These fundamental molecular mechanisms determine whether the signalling output leads to a protective immune response or to serious pathologies such as sepsis. A detailed understanding of these processes at the molecular level provides a rational framework for the development of new drugs that can specifically target pathological rather than protective signalling in inflammatory and autoimmune disease.

Molecular mechanisms involved in inflammasome activation

Germline-encoded pattern recognition receptors (PRRs) sense microbial or endogenous products released from damaged or dying cells and trigger innate immunity. In most cases, sensing of these signals is coupled to signal transduction pathways that lead to transcription of immune response genes that combat infection or lead to cell death. Members of the NOD-like receptor (NLR) family assemble into large multiprotein complexes, termed inflammasomes. Inflammasomes do not regulate transcription of immune response genes, but activate caspase-1, a proteolytic enzyme that cleaves and activates the secreted cytokines interleukin-1beta and interleukin-18. Inflammasomes also regulate pyroptosis, a caspase-1-dependent form of cell death that is highly inflammatory. Here, we review exciting recent developments on the role of inflammasome complexes in host defense and the discovery of a new DNA sensing inflammasome, and describe important progress made in our understanding of how inflammasomes are activated. Additionally, we highlight how dysregulation of inflammasomes contributes to human disease.

Ovarian follicular cells have innate immune capabilities that modulate their endocrine function.

Oestrogens are pivotal in ovarian follicular growth, development and function, with fundamental roles in steroidogenesis, nurturing the oocyte and ovulation. Infections with bacteria such as Escherichia coli cause infertility in mammals at least in part by perturbing ovarian follicle function, characterised by suppression of oestradiol production. Ovarian follicle granulosa cells produce oestradiol by aromatisation of androstenedione from the theca cells, under the regulation of gonadotrophins such as FSH. Many of the effects of E. coli are mediated by its surface molecule lipopolysaccharide (LPS) binding to the Toll-like receptor-4 (TLR4), CD14, MD-2 receptor complex on immune cells, but immune cells are not present inside ovarian follicles. The present study tested the hypothesis that granulosa cells express the TLR4 complex and LPS directly perturbs their secretion of oestradiol. Granulosa cells from recruited or dominant follicles are exposed to LPS in vivo and when they were cultured in the absence of immune cell contamination in vitro they produced less oestradiol when challenged with LPS, although theca cell androstenedione production was unchanged. The suppression of oestradiol production by LPS was associated with down-regulation of transcripts for aromatase in granulosa cells, and did not affect cell survival. Furthermore, these cells expressed TLR4, CD14 and MD-2 transcripts throughout the key stages of follicle growth and development. It appears that granulosa cells have an immune capability to detect bacterial infection, which perturbs follicle steroidogenesis, and this is a likely mechanism by which ovarian follicle growth and function is perturbed during bacterial infection.

The molecular basis of the host response to lipopolysaccharide

Lipopolysaccharide (LPS), which is produced by Gram-negative bacteria, is a powerful activator of innate immune responses. LPS binds to the proteins Toll-like receptor 4 (TLR4) and MD2 to activate pro-inflammatory signalling pathways. The TLR4–MD2 receptor complex is crucial for the host recognition of Gram-negative bacterial infection, and pathogens have devised many strategies to evade or manipulate TLR4–MD2 activity. The TLR4–MD2 signalling pathway is therefore potentially an important therapeutic target. This Progress article focuses on recent exciting data that have revealed the structural basis of TLR4–MD2 recognition of LPS.

A dimer of the toll-like receptor 4 cytoplasmic domain provides a specific scaffold for the recruitment of signalling adaptor proteins

The Toll-like receptor 4 (TLR4) is a class I transmembrane receptor expressed on the surface of immune system cells. TLR4 is activated by exposure to lipopolysaccharides derived from the outer membrane of Gram negative bacteria and forms part of the innate immune response in mammals. Like other class 1 receptors, TLR4 is activated by ligand induced dimerization, and recent studies suggest that this causes concerted conformational changes in the receptor leading to self association of the cytoplasmic Toll/Interleukin 1 receptor (TIR) signalling domain. This homodimerization event is proposed to provide a new scaffold that is able to bind downstream signalling adaptor proteins. TLR4 uses two different sets of adaptors; TRAM and TRIF, and Mal and MyD88. These adaptor pairs couple two distinct signalling pathways leading to the activation of interferon response factor 3 (IRF-3) and nuclear factor κB (NFκB) respectively. In this paper we have generated a structural model of the TLR4 TIR dimer and used molecular docking to probe for potential sites of interaction between the receptor homodimer and the adaptor molecules. Remarkably, both the Mal and TRAM adaptors are strongly predicted to bind at two symmetry-related sites at the homodimer interface. This model of TLR4 activation is supported by extensive functional studies involving site directed mutagenesis, inhibition by cell permeable peptides and stable protein phosphorylation of receptor and adaptor TIR domains. Our results also suggest a molecular mechanism for two recent findings, the caspase 1 dependence of Mal signalling and the protective effects conferred by the Mal polymorphism Ser180Leu.

Bacterial lipopolysaccharide induces an endocrine switch from prostaglandin F2α to prostaglandin E2 in bovine endometrium

Escherichia coli infection of the endometrium causes uterine disease after parturition and is associated with prolonged luteal phases of the ovarian cycle in cattle. Termination of the luteal phase is initiated by prostaglandin F(2alpha) (PGF) from oxytocin-stimulated endometrial epithelial cells. Compared with normal animals, the peripheral plasma of animals with E. coli infection of the endometrium had higher concentrations of lipopolysaccharide (LPS) and prostaglandin E(2) (PGE) but not PGF. Endometrial explants accumulated predominantly PGE in the culture medium in response to LPS, and this effect was not reversed by oxytocin. Endometrial cells expressed the Toll-like receptor 4/CD14/MD-2 receptor complex necessary to detect LPS. Epithelial and stromal cells treated with LPS had higher steady-state media concentrations of PGE rather than PGF. Arachadonic acid is liberated from cell membranes by phospholipase 2 (PLA2) enzymes and converted to prostaglandins by synthase enzymes. Treatment of epithelial and stromal cells with LPS did not change the levels of PGE or PGF synthase enzymes. However, LPS stimulated increased levels of PLA2 group VI but not PLA2 group IV C immunoreactive protein in epithelial cells. Endometrial cells expressed the E prostanoid 2 and E prostanoid 4 receptors necessary to respond to PGE, which regulates inflammation as well as being luteotropic. In conclusion, LPS detection by endometrial cells stimulated the accumulation of PGE rather than PGF, providing a mechanism to explain prolonged luteal phases in animals with uterine disease, and this PGE may also be important for regulating inflammatory responses in the endometrium.

Inflammasome activation causes dual recruitment of NLRC4 and NLRP3 to the same macromolecular complex

Significance The nucleotide-binding oligomerization domain-like receptor (NLR) family members, NLRC4 and NLRP3, activate the inflammasome to provide host defenses against infection. The precise molecular constituents of an inflammasome are unknown; however, it is believed that receptor-specific complexes containing apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) and caspase-1 are formed. Here, we used confocal and superresolution microscopy to show that in macrophages infected with Salmonella Typhimurium, a pathogen that activates two distinct NLRs, ASC forms an outer ring-like structure that comprises NLRC4, NLRP3, caspase-1, caspase-8, and pro–IL-1β within the same macromolecular complex. These results suggest that the inflammasome is a highly dynamic macromolecular protein complex capable of recruiting different NLRs and effectors to coordinate inflammasome responses to infection. Pathogen recognition by nucleotide-binding oligomerization domain-like receptor (NLR) results in the formation of a macromolecular protein complex (inflammasome) that drives protective inflammatory responses in the host. It is thought that the number of inflammasome complexes forming in a cell is determined by the number of NLRs being activated, with each NLR initiating its own inflammasome assembly independent of one another; however, we show here that the important foodborne pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) simultaneously activates at least two NLRs, whereas only a single inflammasome complex is formed in a macrophage. Both nucleotide-binding domain and leucine-rich repeat caspase recruitment domain 4 and nucleotide-binding domain and leucine-rich repeat pyrin domain 3 are simultaneously present in the same inflammasome, where both NLRs are required to drive IL-1β processing within the Salmonella-infected cell and to regulate the bacterial burden in mice. Superresolution imaging of Salmonella-infected macrophages revealed a macromolecular complex with an outer ring of apoptosis-associated speck-like protein containing a caspase activation and recruitment domain and an inner ring of NLRs, with active caspase effectors containing the pro–IL-1β substrate localized internal to the ring structure. Our data reveal the spatial localization of different components of the inflammasome and how different members of the NLR family cooperate to drive robust IL-1β processing during Salmonella infection.

Toll-Like Receptor 4 and MYD88-Dependent Signaling Mechanisms of the Innate Immune System Are Essential for the Response to Lipopolysaccharide by Epithelial and Stromal Cells of the Bovine Endometrium

ABSTRACT Infection of the bovine endometrium with Gram-negative bacteria commonly causes uterine disease. Toll-like receptor 4 (TLR4) on cells of the immune system bind Gram-negative bacterial lipopolysaccharide (LPS), stimulating the secretion of the proinflammatory cytokines interleukin 1B (IL1B) and IL6, and the chemokine IL8. Because the endometrium is the first barrier to infection of the uterus, the signaling cascade triggered by LPS and the subsequent expression of inflammatory mediators were investigated in endometrial epithelial and stromal cells, and the key pathways identified using short interfering RNA (siRNA) and biochemical inhibitors. Treatment of endometrial cells with ultrapure LPS stimulated an inflammatory response characterized by increased IL1B, IL6, and IL8 mRNA expression, and IL6 protein accumulation in epithelial cells, and by increased IL1B and IL8 mRNA expression, and IL6 and IL8 protein accumulation in stromal cells. Treatment of endometrial cells with LPS also induced the degradation of IKB and the nuclear translocation of NFKB, as well as rapid phosphorylation of mitogen-activated protein kinase 3/1 (MAPK3/1) and MAPK14. Knockdown of TLR4 or its signaling adaptor molecule, myeloid differentiation factor 88 (MYD88), using siRNA reduced the inflammatory response to LPS in epithelial and stromal cells. Biochemical inhibition of MAPK3/1, but not JNK or MAPK14, reduced LPS-induced IL1B, IL6, and IL8 expression in endometrial cells. In conclusion, epithelial and stromal cells have an intrinsic role in innate immune surveillance in the endometrium, and in the case of LPS this recognition occurs via TLR4- and MYD88-dependent cell signaling pathways.