Tryptophan catabolites in the regulation of immune cell differentiation and function

A major challenge for the treatment of immune-mediated inflammatory diseases is to understand factors which determine the balance between pro- and anti-inflammatory activity of lymphoid and myeloid subsets. Several tryptophan catabolites (kynurenines) have been shown to modulate immune cell function and we have shown that the first enzyme of the kynurenine pathway, indoleamine-2,3-dioxygenase (IDO), inhibits the development of arthritis [1]and atherosclerosis [2]in animal models along with a suppression of Th17 cells. Thus, administration of kynurenine improved symptoms whereas the elimination of IDO exacerbated them. Indeed, it has previously been reported that regulatory T(Treg) cells are defectivein RAand we showed that this defect is caused by down-regulation of CTLA-4 on Treg cells, resulting in an inability to activate the KP [3]. Other catabolites, such as 3-hydroxy-anthranilic acid (3HAA),can potentiate the reduction by IDO-positive dendritic cells of IFN-ɣ production by T cells, with an increased production of the anti-inflammatory cytokine, IL-10. IDO activation and kynurenine catabolites also promote the generation of FoxP3+CD4+CD25+Treg cells which induce IDO expression in dendritic cells which further promotes Treg cell responses. The aim of the project is to understand the regulation of immune cell function by kynurenines in the context of inflammatory disease.

The project will investigate: (a) the efficacy of ligands acting on Dicarboxylic Amino Acid Receptors [DAARs, responding to N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate]; (b) the activity of tryptophan catabolites in the kynurenine pathway known to act on these receptors in the nervous system; (c) the existence of interactions (synergistic or antagonistic) between these compounds; (d) the involvement of related receptors such as aryl hydrocarbon receptors (AHR), hydroxy-carboxylate receptors or GPR35 sites; (e) the effects of test compounds on the viability and functionality of leukocytes bearing the above receptors (differentiation, proliferation, apoptosis, chemotaxis); (f) the effects of selected compounds on disease activity in animal models
The results will contribute to understanding cellular functions underlying the generation, maintenance and resolution of inflammatory conditions. T cells and monocytes will be isolated from human blood and exposed to recognised DAAR ligands and compounds from the oxidative metabolism of tryptophan, including kynurenine, kynurenic acid, 3-hydroxykynurenine, 3-hydroxy-anthranilic acid (3HAA), cinnabarinic acid, picolinic acid and quinolinic acid. Functional changes in the activity of these cells will be examined as follows: a) proliferation, as measured by incorporation of bromodeoxyuridine.; b) differentiation into functionally distinct subsets (e.g. Th1, Th2, Th17 or Treg cells); c) spontaneous migration; d) chemotaxis; e) cytokine expression

TRAINING OPPORTUNITIES
The Kennedy Institute is a world-renowned research centre and is housed in a brand new state-of-the-art research facility. Students will use a variety of in vitromolecular and cellular methods (e.g. RT-PCR, FACS, Western blotting, ELISAs, cell migration assays), as well as in vivomodels (e.g. collagen-Induced Arthritis). Receptor silencing or modification using siRNA or CRISPR modifications will be used for more detailed analysis of receptor function. A core curriculum of lectures will be taken in the first term to provide a solid foundation in a broad range of subjects including musculoskeletal biology, inflammation, epigenetics, translational immunology, data analysis and the microbiome. Students will attend regular seminars within the department and those relevant in the wider University. Students will be expected to present data regularly in lab meetings and departmental seminars,and to attend external conferences to present their research globally. Students will have access to various courses run by the Medical Sciences Division Skills Training Team and other departments.