Indoleamine 2,3-Dioxygenase and Metabolites Protect Murine Lung Allografts and Impair the Calcium Mobilization of T Cells

Abstract

The enzyme indoleamine 2,3-dioxygenase (IDO) converts tryptophan into kynurenine metabolites that suppress effector T-cell function. In this study, we investigated IDO and its metabolite, 3-hydroxyanthranilic acid (3HAA), in regulating lung allograft rejection, using a murine orthotopic lung transplant model with a major mismatch (BALB/c donor and C57BL6 recipient). IDO was overexpressed in murine donor lungs, using an established nonviral (polyethylenimine carrier)-based gene transfer approach, whereas 3HAA was delivered daily via intraperitoneal injection. Increased IDO expression or its metabolite, 3HAA, resulted in a remarkable therapeutic effect with near normal lung function and little acute rejection, approximately A1, compared with A3 in untreated allografts (grading based on International Society for Heart and Lung Transplantation guidelines). We found that a high IDO environment for 7 days in lung allografts resulted in impaired T-cell activation, the production of multiple effector cytokines (IL-2, IL-4, IL-5, IL-6, IFN-g, TNF-a, IL-12, and IL-13), and the generation of effector memory T cells (CD62L lo CD44 hi phenotype). In isolated murine splenocytes, we observed that IDO/3HAA impaired T-cell receptor (TCR)-mediated T-cell activation, and more importantly, a decrease of intracellular calcium, phospholipase C-g1 phosphorylation, and mitochondrial mass was evident. This work further illustrates the potential role of a high IDO environment in lung transplantation, and that the high IDO environment directly impairs TCR activation via the disruption of calcium signaling.Keywords: 3-hydroxyanthranilic acid; lung allograft rejection; nonviral gene transfer Lung transplantation is a well-accepted therapy for patients with endstage lung disease that is not amenable to other medical or surgical therapies. Unfortunately, acute cellular rejection (ACR) is a common complication in lung transplant recipients, despite current immunosuppressive protocols (1). ACR is problematic because it is the major risk factor for the development of bronchiolitis obliterans, believed to be the manifestation of chronic rejection, and ACR necessitates the augmentation of immune suppression, leading to increased mortality and morbidity (2). The difficulties with bronchiolitis obliterans and frequent rejections result in relatively poor outcomes for lung transplantation, compared with the transplants of other solid organs (1).Indoleamine 2,3-dioxygenase (IDO) is an inducible enzyme that promotes tryptophan (Trp) catabolism, and has been shown to involve immune modulating activities (3). By increasing IDO activity, an environment is generated with reduced Trp and an increase in its metabolic products, resulting in the modification of dendritic cell function and the inhibition of T-cell activation and proliferation. Consistent with this concept, our laboratory previously showed that an increase in IDO within rat lung allografts resulted in less rejection, transplant-mediated injury, and impaired CD8 cell function (4-6).In the pre...

Role of indoleamine 2,3-dioxygenase in health and disease

“…In turn, Tregs can (D) further induce IDO1 expression in APCs via the binding of CTLA-4 to CD80/86 [99]. (E) Active IDO1 in APC can also directly inhibit the function of effector T-cells by promoting Th2 cell polarisation [237,238], induce defective TCR activation [241], clonal anergy [225], as well as cell cycle arrest and apoptosis in effector T-cells [230]. Notably, this suppression of T-cell function is not confined to the classic αβ T-cell subtype, but also applies to γ δ T-cells and invariant NKT cells [159,237].…”

“…The above findings therefore indicate that IDO1-catalysed LTrp depletion, the synthesis of Kyn pathway metabolites and the activation of AhR and other signalling pathways control the activation status, phenotype and viability of T-cells, B-cells and NK cells in various ways including: (i) induction of cell cycle arrest in T-cells and induction of cell death in T-cells, B-cells and NK cells [51,[229][230][231], (ii) impairment of NK cell-mediated killing by preventing the up-regulation of the activating receptors NKp46 and NKG2D [115], (iii) Th2 polarisation of invariant NKT cells [237], (iv) apoptosis of Th1 cells but not Th2 cells [238], (v) interfering with glucose metabolism in effector T-cells to inhibit proliferation [239,240], (vi) defective TCR activation via the interruption of Ca 2+ signalling [241], (vii) down-regulation of the ζ -chain in the TCR complex on CD8 + T-cells [232], (viii) acquisition and maintenance of an immunosuppressive Foxp3 + Treg (rather than a pro-inflammatory Th17) phenotype by naïve CD4 + T-cells [232,[242][243][244] involving the IDO1-and Kyn/AhRdependent blockade of the down-regulation of the Eos transcription factor (necessary for reprogramming of Tregs into Th17 inflammatory helper-like cells) [245], and (ix) direct activation of the suppressor activity of Foxp3 + Tregs involving the PD-1 (programmed cell death 1)/PD-L (programmed cell death ligand) pathway [226].…”

“…Protective [102,294,295] Mouse kidney transplant model Protective [298] Rat and mouse liver transplant model Protective [299], not involved [305] Mouse corneal transplant model Protective [300,304] Rat and mouse lung transplant models Protective [207,241] Rat and mouse cardiac transplant model Protective [301][302][303] Mouse bone marrow transplant model Protective [306,307] Mouse skin transplant model Protective [310] Chimaeric humanised mouse model of graft arteriosclerosis Rat monocrotaline-induced pulmonary hypertension Protective [54] Angiotensin II-induced vascular constriction in rats Protective [41] Angiotensin II-induced vascular constriction in mice Protective [54], harmful [183] LPS-induced endotoxaemia Protective [182] Cataracts Mice overexpressing human IDO1 in the lens Harmful [591] Bone remodelling Wild-type mice Protective [592,593] maintenance of self-tolerance under normal conditions. However, numerous studies with Ido1 gene-deficient mice or IDO1 inhibitors reveal that the enzyme plays an important role in the establishment of acquired immune tolerance upon exposure to new or foreign antigens.…”

“…Furthermore, liver allografts, which tend to be well-tolerated in mice, are rejected following 1-MT treatment [299]. Providing further support for a beneficial role of IDO1 and the Kyn pathway, overexpression of IDO1 or administration of 3-HK or 3-HAA in animal models of allogeneic corneal, lung or cardiac transplants are able to prolong graft survival, attenuate allograft injury and are associated with decreased antigen-specific and non-specific T-cell responses [207,241,[300][301][302][303][304], although IDO1 overexpression in liver allografts did not prevent ultimate transplant rejection in mice [305].…”

Emerging Concepts on Inhibitors of Indoleamine 2,3-Dioxygenase in Rheumatic Diseases

“…Finally, kynurenine may modulate in vivo T-cell function in cooperation with other L-tryptophan metabolites, such as 3-hydroxykynurenine and 3-hydroxyanthranilic acid [67]. Finally, IDO and its metabolites may decrease intracellular calcium, phospholipase C-1 phosphorylation, and mitochondrial mass, leading to impaired Tcell activation, as shown in a mouse model of lung transplantation [68].…”