GATA3, HDAC6, and BCL6 Regulate FOXP3+ Treg Plasticity and Determine Treg Conversion into Either Novel Antigen-Presenting Cell-Like Treg or Th1-Treg

Abstract

We conducted an experimental database analysis to determine the expression of 61 CD4+ Th subset regulators in human and murine tissues, cells, and in T-regulatory cells (Treg) in physiological and pathological conditions. We made the following significant findings: (1) adipose tissues of diabetic patients with insulin resistance upregulated various Th effector subset regulators; (2) in skin biopsy from patients with psoriasis, and in blood cells from patients with lupus, effector Th subset regulators were more upregulated than downregulated; (3) in rosiglitazone induced failing hearts in ApoE-deficient (KO) mice, various Th subset regulators were upregulated rather than downregulated; (4) aortic endothelial cells activated by proatherogenic stimuli secrete several Th subset-promoting cytokines; (5) in Treg from follicular Th (Tfh)-transcription factor (TF) Bcl6 KO mice, various Th subset regulators were upregulated; whereas in Treg from Th2-TF GATA3 KO mice and HDAC6 KO mice, various Th subset regulators were downregulated, suggesting that Bcl6 inhibits, GATA3 and HDAC6 promote, Treg plasticity; and (6) GATA3 KO, and Bcl6 KO Treg upregulated MHC II molecules and T cell co-stimulation receptors, suggesting that GATA3 and BCL6 inhibit Treg from becoming novel APC-Treg. Our data implies that while HDAC6 and Bcl6 are important regulators of Treg plasticity, GATA3 determine the fate of plastic Tregby controlling whether it will convert in to either Th1-Treg or APC-T-reg. Our results have provided novel insights on Treg plasticity into APC-Treg and Th1-Treg, and new therapeutic targets in metabolic diseases, autoimmune diseases, and inflammatory disorders.

Keywords: APC-like Treg; CD4+ FOXP3+ regulatory T cells; CD4+ T helper subset differentiation; Th1-like Treg; metabolic cardiovascular diseases.

Figure 1

A novel working hypothesis: CD4+ T helper (Th) subset regulators are differentially expressed in normal tissues in physiological conditions; and Th subset regulator expression are modulated in various diseases and mutant mice (Th25 information is limited; therefore, Th25 is not included in this figure).

Figure 2

Flow chart of database mining strategy and two parts of data organization. (A) Presents the key questions addressed by this study. (B) Determining the expression of Th subset regulators in tissues under physiological conditions. (C) Determining the expression of Th subset regulators under pathological conditions.

Figure 3

Our newly proposed “tissue pyramid” model. We constructed a tissue pyramid based on the variety of Th subset regulators expressed in tissues.

Figure 4

The composition of Th subsets in human tissues are different. Treg regulators are dominant in brain, eye, lymph nodes, and muscle: Th17 regulators are dominant in adrenal gland, cervix, umbilical cord, and uterus have no physiologically resident Th activities.

Figure 5

The Venn diagram analysis. The Venn diagram shows that Treg plasticity regulators Gata3, Blc6, and Hdac6 shre Th1 pathway and Th differentiation pathways.

Figure 6

A novel hypothesis. Functional interaction between Treg-specific transcription factor Foxp3 and other transcription factors and/or master genes such as Gata3, Bcl6 and Hdac6 to maintain Treg identity and prevent Treg from losing the immune-suppressing activity and the conversion to APC-like Treg. Bcl6 deficiency upregulate expression of MHC class II molecules and T cell co-stimulators in Treg. This transformation of Treg to APC-Treg deliver T cell activation signal 1 via MHC class II/antigen epitope complex and T cell activation signal 2 via co-stimulation receptors LIGHT, 4-1BBL, CD48, B7-1 (CD80) and CD112. This may potentially promote inflammation and immune responses.

Figure 7

Newly proposed Treg stability/plasticity model: In order to maintain Treg stability, Treg need to express high level of FOXP3, HDAC6 and low levels of BCL6. GATA3 levels determine whether plastic T-reg will diverge in to Th1-Treg or APC-Treg lineage. When GATA3 expression is diminished in presence of high HDAC6 and low BCL6 levels, plastic T-reg tend to covert in to APC-Treg. However, when GATA3 expression is increased with high levels of HDAC6 and low Bcl6, T-reg convert in to Th1-Treg. Increased plasticity of T-reg weakens its immunosuppressive function and may facilitate inflammation and autoimmune reactions.