Sex hormones have pervasive effects on thymic epithelial cells

The goal of our study was to evaluate at the systems-level, the effect of sex hormones on thymic epithelial cells (TECs). To this end, we sequenced the transcriptome of cortical and medullary TECs (cTECs and mTECs) from three groups of 6 month-old mice: males, females and males castrated at four weeks of age. In parallel, we analyzed variations in the size of TEC subsets in those three groups between 1 and 12 months of age. We report that sex hormones have pervasive effects on the transcriptome of TECs: the number of differentially expressed genes was 1,440 in cTECs and 1,783 in mTECs. Sexual dimorphism was particularly conspicuous in cTECs. Male cTECs displayed low proliferation rates that correlated with low expression of Foxn1 and its main targets. Furthermore, male cTECs expressed relatively low levels of genes instrumental in thymocyte expansion (e.g., Dll4) and positive selection (Psmb11 and Ctsl). Nevertheless, cTECs were more abundant in males than females. Accumulation of cTECs in males correlated with differential expression of genes regulating cell survival and cell differentiation. Unexpectedly, we observed that female and male sex hormones repressed promiscuous gene expression in mTECs. Since sex hormones did not affect the expression of Aire per se, they must impinge on the activity of unidentified regulator(s) of promiscuous gene expression in mTECs. The sexual dimorphism of TECs highlighted here may be mechanistically linked to the well-recognized sex differences in susceptibility to infections and autoimmune diseases. Overall design: Cortical and medullary thymic epithelial cells from 6 month-old male, female and castrated male mice were sequenced in 3 replicates (but only 2 replicates for castrated male mTECs).

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Patenaude J, Perreault C