Regulatory T cell (Treg) immunosuppression is critical for maintaining immune tolerance to a diverse array of potential antigens in the intestinal mucosa. In patients with inflammatory bowel disease (IBD), chronic intestinal inflammation overwhelms local Treg function, allowing inflammation to persist. Our previous work and that of others have identified important roles for 17?-estradiol (estrogen, E2) signaling in promoting Treg differentiation and function. E2 signals through two nuclear receptors, alpha and beta (ER?, ER?), to modulate gene transcription in target cells. Although they share high sequence homology, ER? and ER? mediate distinct and often opposing functions on gene regulation. In previously published work, we showed that shifting the balance of E2 signaling towards ER? is generally pro-inflammatory, whereas shifting towards ER? is generally protective. In recent preliminary studies using IBD patient samples, we observed significantly diminished ER? expression in intestinal biopsy tissues and peripheral T cells from females with active Crohn?s disease (CD). We also found that ER?-deficient T cells are resistant to ex vivo, TGF?-dependent Treg differentiation, and that deletion of ER? in a spontaneous ileitis model (SAMP/YitFC, ?SAMP? mice) results in significant impairment of Treg transcriptional and functional responses, contributing to exacerbated inflammation. Therefore, the goal of this project is to determine the molecular and cellular mechanism(s) by which altered E2 signaling impacts Treg differentiation and function, contributing to intestinal inflammation. The mechanisms by which E2 signaling cross-talks with inflammatory signals to influence immune cell function are poorly understood. This proposal seeks to address this knowledge gap through our central hypothesis that dysregulated E2 signaling contributes to Treg transcriptional remodeling and loss-of-function, facilitating sustained intestinal inflammation in IBD.
In Aim 1, we propose to delineate the molecular mechanisms by which ER?- and ER? cross-talk with signaling downstream of TGF? in primary T cells, influencing TGF?-dependent Foxp3 expression and function.
Aim 2 will determine the functional impact of rebalancing Treg-specific E2 signaling on intestinal inflammation in vivo, testing our hypothesis that augmenting Treg-specific ER? signaling may prevent and/or rescue intestinal inflammation. Experiments will include adoptive transfer of ER?-expressing Tregs to SAMP mice, as well as in vivo assays using a T cell-dependent colitis model.
In Aim 3, we plan to determine the transcriptional and functional effects of rebalancing E2 signaling in CD patient Tregs using novel MaxCyte transfection technology, assessing ER?- and ER?-specific effects on (i) TGF?-dependent Foxp3 induction in nave T cells and (ii) ex vivo suppressive function of Tregs. Successful completion of our proposed Aims will provide key mechanistic insight into the functional impact of E2 signaling in Tregs, an under-studied area with broad applicability to numerous diseases exhibiting dysregulation of ER expression and/or activation and subsequent reductions in Treg function.
Steroid sex hormones such as 17?-estradiol (estrogen) are important regulators of immune responses. Although estrogen is generally immunoprotective, our data show that it contributes to the pathogenesis of chronic inflammatory diseases such as IBD by impairing the differentiation and function of regulatory T cells (Tregs). This project seeks to identify the mechanism(s) by which altered estrogen signaling impairs Treg- mediated immunosuppression in the chronically inflamed intestine, with the ultimate goal of developing novel approaches for the treatment of IBD.
