The nuclear orphan receptor Nr4a2 induces Foxp3 and regulates differentiation of CD4+ T cells.
Bottom Line: Regulatory T cells (Tregs) have a central role in maintaining immune homoeostasis through various mechanisms.Nr4a2 binds to regulatory regions of Foxp3, where it mediates permissive histone modifications.Nr4a2-deficeint Tregs are prone to lose Foxp3 expression and have attenuated suppressive ability both in vitro and in vivo.
Affiliation: Department of Microbiology and Immunology, Keio University School of Medicine, Tokyo 160-8582, Japan.Show MeSH
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Mentions: Next, we analysed the roles of Nr4a2 in Tregs by breeding Nr4a2-floxed mice with Foxp3YFP-Cre mice3637 to knockout Nr4a2 specifically in Tregs. We confirmed the specific deletion of Nr4a2 in Tregs (Supplementary Fig. S6a). Nr4a2fl/flFoxp3YFP-Cre mice were apparently normal, disease free and without differences in the activation status of CD4+ T cells (Supplementary Fig. S6b). In the first experiment, we compared the relative sizes of Nr4a2-sufficient and Nr4a2-deficient Tregs population in Nr4a2+/+Foxp3YFP-Cre/+, heterozygous Nr4a2fl/+Foxp3YFP-Cre/+ and homozygous Nr4a2fl/flFoxp3YFP-Cre/+ females (foxp3 is on X chromosome). The YFP+/YFP– ratio in Nr4a2+/+Foxp3YFP-Cre/+ mice was near 1:1 in both thymus and periphery (Fig. 6a,b). However, in Nr4a2fl/flFoxp3YFP-Cre/+ mice, ratios of YFP+/YFP− were suboptimal (∼0.3 in thymus and ∼0.1 in periphery, Fig. 6a,b), indicating that Tregs were not properly maintained on deletion of Nr4a2. The YFP+/YFP− ratio in Nr4a2fl/+Foxp3YFP-Cre/+ mice was near ∼0.8 in thymus, and ∼0.4 in periphery, indicating that Tregs are not properly maintained even by the heterozygous deletion of Nr4a2 (Fig. 6b). Importantly, the ratio of YFP+/YFP− in Nr4a2fl/flFoxp3YFP-Cre/+ mice decreased with age (Supplementary Fig. S6c), supporting the idea that the disequilibrium is caused by the accelerated reduction of the Nr4a2-deficient Tregs in the periphery, rather than the reduced positive selection of Tregs in the thymus. Another possibility which could explain this disequilibrium might be reduced export of Nr4a2-deficient Tregs, although we think it less probable, because the reduced export is expected to result in an increase in the number of Nr4a2-deficient Tregs in the thymus. Deletion of Nr4a1 did not affect the YFP+/YFP− ratio in Tregs (Fig. 6a,b and Supplementary Fig. S6d), indicating that Nr4a1 does not contribute to Treg homoeostasis; this corresponds well with the observation that Nr4a1-transduction did not induce Foxp3 (Fig. 3a). The CpG methylation status of CNS2, an important determinant of Treg lineage stability, was not perturbed in Nr4a2fl/flLck-Cre+ mice (Supplementary Fig. S6e), suggesting that Nr4a2 is not essential for the demethylation of CNS2 during nTreg development. This was consistent with our forced expression study (Fig. 2d).
Affiliation: Department of Microbiology and Immunology, Keio University School of Medicine, Tokyo 160-8582, Japan.