Hydrogen Sulfide Promotes Tet1- and Tet2-Mediated Foxp3 Demethylation to Drive Regulatory T Cell Differentiation and Maintain Immune Homeostasis

Abstract

SUMMARY Regulatory T (Treg) cells are essential for maintenance of immune homeostasis. Here we found that hydrogen sulfide (H2S) was required for Foxp3+ Treg cell differentiation and function, and that H2S deficiency led to systemic autoimmune disease. H2S maintained expression of methylcytosine dioxygenases Tet1 and Tet2 by sulfhydrating nuclear transcription factor Y subunit beta (NFYB) to facilitate its binding to Tet1 and Tet2 promoters. Transforming growth factor-β (TGF-β)-activated Smad3 and interleukin-2 (IL-2)-activated Stat5 facilitated Tet1 and Tet2 binding to Foxp3. Tet1 and Tet2 catalyzed conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in Foxp3 to establish a Treg cell-specific hypomethylation pattern and stable Foxp3 expression. Consequently, Tet1 and Tet2 deletion led to Foxp3 hypermethylation, impaired Treg cell differentiation and function, and autoimmune disease. Thus, H2S promotes Tet1 and Tet2 expression, which are recruited to Foxp3 by TGF-β and IL-2 signaling to maintain Foxp3 demethylation and Treg cell-associated immune homeostasis.

Vitamin C Facilitates Demethylation of the Foxp3 Enhancer in a Tet-Dependent Manner

“…1). However, a high dose (100 mg/ml) of vitamin C induced CNS2 demethylation in Tet2 2/2 and in WT iTregs (data not shown), implying that other Tet proteins, such as Tet1 (31) and Tet3 (50), could be substituted for Tet2 in vitamin C-rich environments. These results led us to hypothesize that the overexpression of Tet2 could make vitamin C redundant and induce CNS2 demethylation without vitamin C. We introduced the plasmid encoding FLAG-tagged mouse Tet2 into WT CD8 2 thymocytes (DN and CD4SP), sorted GFP 2 CD25 2 CD4SP cells, and then cultured under the iTreg condition for 5 d. GFP + CD25 + iTregs were sorted again and used for the demethylation study.…”

“…Furthermore, CNS2 is demethylated in tTregs expressing Foxp3 stably, but it is fully methylated in activated T cells or iTregs expressing Foxp3 transiently (18,29). CNS2 demethylation has been reported to occur within the thymus during the developmental stages and achieved through an active DNA oxidation process including ten-eleven-translocation (Tet) family (30,31). However, the underlying mechanism of the epigenetic regulation of CNS2 is still elusive.…”

Mutations in 5-methylcytosine oxidase TET2 and RhoA cooperatively disrupt T cell homeostasis

“…Tregs are well known for their immunosuppressive role: they downregulate effector T cell function, maintain tolerance to self-antigens, and prevent autoimmune disease (37). TET2 depletion in mice has been previously shown to reduce Foxp3 gene expression, with a subsequent decrease in Tregs (38)(39)(40). Our in vitro-directed T cell differentiation study further confirmed this (Supplemental Figure 3F).…”

5-Hydroxymethylcytosine (5hmC), or How to Identify Your Favorite Cell

“…In line with this, 5hmC changes are overrepresented in highly transcribed genes. For example, chromatin-accessible-regions are associated with T cell [36,44] and induced natural killers (iNK) T cell development [45], Treg FoxP3 activation [46,47], B cell identity genes [39,41], or Bcl6 binding sites in T follicular helper (Tfh) cells [48] (Figure 2 and Table 1). During mast cell development, it was shown that Tet2 knockout caused differential 5hmC levels in genes enriched with leukocyte differentiation and proliferation, malignant transformation, and mast cell-related processes [40].…”