ORF39-04 - Developmental Programming of the T Cell Repertoire by Systemic Glucocorticoid Exposure

Adaptive immunity is dependent on T cells, which have a huge repertoire of unique antigen receptors (TCRs) that enable recognition and response to virtually any antigen. The diverse repertoire of TCRs is generated by random gene recombination during T cell development in the thymus, but this process inadvertently also creates autoreactivity TCRs. To prevent autoimmunity, medullary thymic epithelial cells (mTECs) expressing the transcription factor AIRE which drives promiscuous expression of tissue-specific genes and enable self-reactive T cells that react to these self-antigens to be removed by apoptosis (negative selection). mTEC expression of AIRE is increased by androgens, increasing expression of self-antigens, and results in more effective removal of autoreactive T cells and lower autoimmune risk in males than females. Early life glucocorticoid exposure has dramatic effects on lifelong risk for many immune-mediated disease, but whether an altered TCR repertoire is responsible is unknown. Given the similarity in DNA-binding motifs between the glucocorticoid receptor (GR) and androgen receptor (AR), we hypothesized that glucocorticoids directly upregulate AIRE expression to alter the TCR repertoire. We first analyzed scRNA-seq data from human and mouse thymi and found that NR3C1 (encoding the GR) is robustly expressed across all mTEC populations, especially during the maturational stages preceding and concurrent with AIRE expression. JASPAR analysis of transcription factor binding sites identified multiple putative GR bindings motifs in the human and mouse AIRE promoters, and ATAC-seq data showed that most are found in regions of accessible chromatin. We then cultured mouse thymi ex vivo and found that the addition of dexamethasone increased expression of Aire and also Fezf2, another gene involved in promiscuous thymic gene expression. Finally, oral dexamethasone treatment altered Aire protein levels in vivo. These findings demonstrated that systemic glucocorticoids upregulate Aire, and propose a novel mechanism by which early life glucocorticoid exposure may have important programming effects on the TCR repertoire and lifelong susceptibility to immune-mediated disease. Future work will directly characterize changes to the TCR repertoire, susceptibility to autoimmune disease and cancer, and whether these are modified by psychological stressors.