Project description:The orphan chemoattractant receptor GPR15 is important for homing T lymphocytes to the large intestine, thereby maintaining intestinal immune homeostasis. However, the molecular mechanisms underlying the regulation of GPR15 expression remain elusive. Here we show a central role of the aryl hydrocarbon receptor (Ahr) in promoting GPR15 expression both in mice and human, thus gut homing of T lymphocytes. Mechanistically, Ahr directly binds to open chromatin regions of the Gpr15 locus to enhance its expression. Ahr transcriptional activity in directing GPR15 expression was modulated by two transcription factors, Foxp3 and RORγt, both of which are expressed preferentially by gut Tregs in vivo. Specifically, Foxp3 interacted with Ahr and enhanced Ahr DNA binding at the Gpr15 locus, thereby promoting GPR15 expression. In contrast, RORγt plays an inhibitory role at least in part by competing with Ahr binding to the Gpr15 locus. Our findings thus demonstrate a key role for Ahr in regulating Treg intestinal homing under the steady state and during inflammation, and the importance of Ahr-RORγt-Foxp3 axis in regulating gut homing receptor GPR15 expression by lymphocytes.
Project description:Foxp3-expressing regulatory (Treg) T cells are essential for immunological tolerance, where loss of this transcription factor leads to uncontrolled T cell responses and their associated clinical presentation of systemic autoimmunity in mice and humans. Importantly, Foxp3+ Tregs result from different origins and are either generated in the thymus (tTreg) or from conventional CD4+ T cells in the periphery (pTreg). In addition, Treg cells may adopt specific effector Treg phenotypes, reflecting the diversity of functional demands in the different tissues of the body. Here, we report that Foxp3+ T cells expressing the Th17 master transcription factor, RORγt, represent a stable effector Treg lineage that is specifically enriched in intestinal organs and gut-associated lymphoid tissues in mice possessing a complex microbial microflora. Simultaneous expression of Foxp3 and RORγt promotes the transcription of both Treg- and Th17-associated genes in Foxp3+RORγt+ T cells; however, epigenetic profiling of the Treg-specific demethylated region (TSDR) and other Treg-associated genes revealed a high degree of similarity between conventional Tregs and Foxp3+RORγt+ T cells, indicating that these cells have a stable regulatory, rather than inflammatory, function. Indeed, adoptive transfer of Foxp3+RORγt+ T cells in the context of T cell transfer colitis not only confirmed their Treg function and lineage stability in vivo, it also revealed a significantly enhanced regulatory capacity as compared to RORγt+ Treg cells. Thus, our data suggest that RORγt expression in Tregs is essential for optimal regulation of gut-specific immune responses, which renders them an important effector Treg lineage in the intestinal system.
Project description:T helper 17 and Regulatory T cells (Th17 and Treg, respectively) are two well-described lymphocyte subsets with opposing actions. The divergent fates of Th17 and Treg cells are accounted for, at least in part, by molecular antagonism that occurs between their respective specific transcription factors, RORγt and Foxp3. An imbalance between Th17 and Treg cells may lead to tissue inflammation and is associated with certain types of autoimmunity. In order to understand the heterogeneity and dynamics of the differentiation process, we studied Th17/Treg cell differentiation of naïve cells in vitro, using RORγtGFPFoxp3RFP dual-reporter mouse. Flow cytometry revealed the consistent emergence of a population of double positive RORγt+Foxp3+ (DP) cells during the early stages of Th17 cell differentiation. These DP cells are closely related to RORγt+ single positive (SPR) cells in terms of global gene expression. Nevertheless, for some genes, DP cells share an expression pattern with Foxp3+ single positive (SPF) Treg cells, most importantly by reducing IL17 levels. Using time-lapse microscopy, we could delineate the expression dynamics of RORγt and Foxp3 at a clonal level. While the RORγt expression level elevates early during differentiation, Foxp3 rises later and is more stable upon environmental changes. These distinct expression profiles are independent of each other. During differentiation and proliferation, individual cells transit between SPR, DP, and SPF states. Nevertheless, the differentiation of sister cells within a clone progeny was highly correlated. We further demonstrated that sorted SPR and DP populations were not significantly affected by changes in their environment, suggesting that the correlated fate decision emerged at early time points, before the first division. Overall, this study provides the first quantitative analysis of differentiation dynamics during the generation of DP RORγt+Foxp3+ cells. Characterizing these dynamics and the differentiation trajectory could provide a profound understanding and be used to better define the distinct fates of T cells, critical mediators of the immune response.
Project description:Th17 cells are potent mediators in autoimmune diseases and RORγt is required for their development. Recent studies have shown that RORγt+ Treg cells in the gut regulate intestinal inflammation by inhibiting effector T cell function. In the current study, we report that RORγt+ Treg cells were also found in lymph nodes following immunization. Not only distinct from intestinal RORγt+ Treg in their transcriptomes, peripheral RORγt+ Treg cells were derived from Foxp3+ thymic Treg cells, in an antigen-specific manner. Development of these RORγt+ Treg cells, coined as T regulatory 17 (Tr17) cells, depended on IL-6/Stat3 signaling. Tr17 cells showed suppressive activity against antigen-specific effector T cells in vitro. In addition, Tr17 cells efficiently inhibited myelin-specific Th17 cell-mediated CNS auto-inflammation in a passive EAE model. Collectively, our study demonstrates Tr17 cells as effector Treg cells that potentially restrict autoimmunity.
Project description:Group 3 innate lymphoid cells (ILC3) are defined by the expression of RORγt, which is selectively required for their development. The lineage-specified progenitor cells of human ILC3 and their developmental site after birth remain undefined. Here we identified a novel population of human CD34+ hematopoietic progenitor cells (HPC) expressing RORγt and sharing with ILC3 a distinct transcriptional signature. RORγt+ CD34+ HPC were located in tonsils and intestinal lamina propria (LP) and selectively differentiated towards ILC3. Conversely, RORγt- CD34+ HPC displayed commitment potential for both ILC3 and NK cells and the differentiation fate towards these two cell lineages was determined by cytokine and aryl hydrocarbon receptor (AhR) signaling. Thus, we propose that RORγt+ CD34+ cells represent human lineage-specified progenitors of IL-22+ ILC3 and that tonsils as well as intestinal LP might be preferential sites of their differentiation.
Project description:Foxp3 is the master transcription factor for the regulatory T cells (Tregs). Alternative splicing of human Foxp3 results in the expression of two isoforms: the full-length and an exon 2-deleted protein. Here, AlphaFold2 predictions and in vitro experiments demonstrate that the N-terminal domain of Foxp3 inhibits DNA binding by moving toward the C-terminus and that this movement is mediated by exon 2. Consequently, we find Foxp3∆2-bearing tTregs in the peripheral lymphoid organ are less sensitive to TCR due to the enhanced binding of Foxp3∆2 to the Batf promoter and are unsusceptible to IL-2. In contrast, among RORγt+ pTregs in the large intestine, Foxp3∆2 pTregs express much more RORγt-related genes conferring a competitive advantage. Together, our results reveal that alternative splicing of exon 2 generates a constitutively active form of Foxp3, which plays a differential role in regulating tTregs and pTregs homeostasis.
Project description:RORγt is a transcription factor required for T helper 17 (Th17) cell development. We identified three RORγt-specific inhibitors that suppress Th17 cell responses including Th17 cell-mediated autoimmune disease. We systemically characterized RORγt binding data in the presence and absence of drug with corresponding whole-transcriptome sequencing for wild-type and RORγt-deficient cells. RORγt is central in a densely interconnected regulatory network, acting both as a direct activator of genes important for Th17 cell differentiation and as a direct repressor of genes from other T-cell lineages. The three inhibitors identified here reversed both of these modes of action, but to varying extents and through distinct mechanisms. Whereas one inhibitor displaced RORγt from its target-loci, the two more potent inhibitors affected transcription predominantly without removing DNA-binding. Our work illustrates the power of a system-scale analysis of transcriptional regulation to characterize potential therapeutic compounds that inhibit pathogenic Th17 cells and suppress autoimmunity. DNA binding of RORγt in WT Th17 cells and under chemical perturbations of RORγt; Additional data is included for epitope-tagged exogenous RORγt in EL4 cells (a murine lymphoma cell line)
Project description:RORγt is a transcription factor required for T helper 17 (Th17) cell development. We identified three RORγt-specific inhibitors that suppress Th17 cell responses including Th17 cell-mediated autoimmune disease. We systemically characterized RORγt binding data in the presence and absence of drug with corresponding whole-transcriptome sequencing for wild-type and RORγt-deficient cells. RORγt is central in a densely interconnected regulatory network, acting both as a direct activator of genes important for Th17 cell differentiation and as a direct repressor of genes from other T-cell lineages. The three inhibitors identified here reversed both of these modes of action, but to varying extents and through distinct mechanisms. Whereas one inhibitor displaced RORγt from its target-loci, the two more potent inhibitors affected transcription predominantly without removing DNA-binding. Our work illustrates the power of a system-scale analysis of transcriptional regulation to characterize potential therapeutic compounds that inhibit pathogenic Th17 cells and suppress autoimmunity. Transcriptional profiling of Th17 cells under chemical perturbations of RORγt, DMSO, and knockout of RORγt. It includes repeats for all the data in GSE56018, plus one additional condition.