Sex hormones have pervasive effects on thymic epithelial cells. Mus musculus

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).

本研究的目标是在系统层面评估性激素对胸腺上皮细胞（thymic epithelial cells, TECs）的影响。为此，我们对三组6月龄小鼠的皮质胸腺上皮细胞（cortical TECs, cTECs）和髓质胸腺上皮细胞（medullary TECs, mTECs）的转录组进行了测序，三组分别为雄性小鼠、雌性小鼠，以及于4周龄时去势的雄性小鼠。同时，我们分析了这三组小鼠在1至12月龄间TEC亚群的大小变化。

本研究发现，性激素对TEC的转录组具有广泛影响：皮质胸腺上皮细胞中差异表达基因的数量为1440个，髓质胸腺上皮细胞中则为1783个。雌雄二态性在皮质胸腺上皮细胞中尤为显著。雄性皮质胸腺上皮细胞的增殖速率较低，这与Foxn1及其主要靶基因的低表达相关。此外，雄性皮质胸腺上皮细胞中参与胸腺细胞扩增（如Dll4）及阳性选择（Psmb11与Ctsl）的关键基因表达水平相对较低。尽管如此，雄性个体的皮质胸腺上皮细胞数量多于雌性。雄性皮质胸腺上皮细胞的积累与调控细胞存活及细胞分化的基因差异表达相关。

出乎意料的是，我们观察到雌性与雄性性激素均可抑制髓质胸腺上皮细胞中的异位基因表达（promiscuous gene expression）。由于性激素本身并未影响Aire的表达，因此它们必然通过作用于尚未被鉴定的髓质胸腺上皮细胞异位基因表达调控因子来发挥功能。本研究揭示的胸腺上皮细胞雌雄二态性，可能与学界公认的感染易感性及自身免疫疾病的性别差异存在机制层面的关联。

实验设计概况：对来自6月龄雄性、雌性及去势雄性小鼠的皮质与髓质胸腺上皮细胞进行转录组测序，每组设置3次生物学重复（去势雄性小鼠的髓质胸腺上皮细胞仅设置2次重复）。