Post-Transcriptional Regulation of Interleukin-7 Receptor Expression

IL-7受体的表达和信号对传统T细胞至关重要，但IL-7受体在先天T细胞中的作用尚不清楚。具体地说，不变NKT(INKT)细胞对IL-7的要求仍不清楚，iNKT是胸腺来源的效应T细胞群体，在炎症和癌症中发挥强大的调节作用。我们最近已经将我们的研究从传统的ab T细胞扩展到IL-7在iNKT细胞中的作用，并且我们记录了以前不被认可的对iNKT细胞稳态的IL-7的要求。对iNKT细胞的传统观点认为，这种T细胞群主要依赖IL-15信号来维持其生存和维持，而IL-7在这一过程中只起到很小的作用。使用IL-15缺陷小鼠和成年胸腺切除小鼠，植入IL-7或IL-15释放的渗透泵，我们现在证明，控制周围组织中iNKT细胞的动态平衡的是IL-7，而不是IL-15(Park JY等，2022，Cell Reports)。这些结果对成熟的iNKT细胞表达IL-7R提出了新的要求，从而扩大了IL-7在T细胞生物学中的作用。其他先天类T细胞，如MAIT细胞、PLZF+Gd T细胞和胸腺先天CD8 T细胞是否也需要IL-7R的表达和信号来维持其稳态尚不清楚，但我们打算在未来的研究中解决这些问题。沿着这些思路，我们还评估了IL-7在非淋巴组织中的ab T细胞上的作用，包括肝、肺和小肠上皮(SI)。SI上皮内淋巴细胞(IELs)相当于体内最大的T细胞储存库，它们被认为在维持肠道的免疫监视和静止方面发挥着关键作用。在这里，我们发现，SI IEL对生存的细胞因子需求不同，因此它们大多独立于IL-7，也不能对IL-7做出反应。目前，SI IEL T细胞IL-7非依赖性内稳态的分子基础是我们正在解决的一个主要问题，我们正在检验SI上皮微环境将提供这些生存线索的假设。在这方面，我们最近报道了Foxp3 Treg细胞，它们需要IL-2来生存和发挥效应功能，一旦它们进入SI上皮，就可以免除它们对IL-2的要求(Prakhar P.等，2021，JCI Insights)。总的来说，这些结果表明，不同组织对细胞因子的作用和需求不同，在评估给定细胞因子的个体作用时，需要考虑组织环境。最后，我们启动了一系列关于IL-7受体表达调控机制的新研究，其中我们还讨论了IL-7R表达的表观遗传学方面。具体地说，我们正在评估染色质重塑锌指转录因子Ikfz1(Ikfz1)作为控制IL-7ra基因座可及性的新调节因子的作用。因此，我们发现Ikfz1在胸腺T细胞发育的早期和外周T细胞的生存/动态平衡中控制IL-7ra的表达。为了进一步了解Ikaros如何在细胞因子受体调控中发挥作用，特别是对IL-7ra的表达，我们培育了一系列Ikfz1条件基因敲除小鼠，其中Ikfz1-Flox小鼠与CD2-Cre重组酶转基因小鼠或CD4-Cre转基因小鼠杂交。同时，我们还建立了Ikfz1转基因小鼠，以测试在IL-7R信号背景下Ikfz1过表达对T细胞生成和动态平衡的影响。在IL-7R表达的背景下分析这些小鼠的T细胞发育和分化目前正在研究中。

IL-7 receptor expression and signaling is ciritical for conventional T cells, but the role of IL-7 receptor in innate-like T cells is less well understood. Specifically, the IL-7 requirement for invariant NKT (iNKT) cells, which is a thymus-derived population of effector T cells that plays potent regulatory roles in inflammation and cancer, has remained unclear. We have recently expanded our studies from conventional ab T cells into the role of IL-7 in iNKT cells, and we documented a previously unappreciated requirement for IL-7 in iNKT cell homeostasis. The conventional view on iNKT cells has been that this T cell population is mostly dependent on IL-15 signaling for their survival and maintenance, and that IL-7 only plays a minor role in this process. Using IL-15-deficient mice and employing adult thymectomized mice that were implanted with either IL-7- or IL-15-releasing osmotic pumps, we now demonstrated that it is IL-7, and not IL-15, that controls the homeostasis of iNKT cells in peripheral tissues (Park JY et al., 2022, Cell Reports). These results establish a new requirement for IL-7R expression on mature iNKT cells, thus expanding the role of IL-7 in T cell biology. Whether other innate-like T cells, such as MAIT cells, PLZF+ gd T cells, and thymic innate CD8 T cells also require IL-7R expression and signaling for their homeostasis is not clear to us, but we aim to address these issues in our future studies. Along these lines, we have also assessed the role of IL-7 on ab T cells in non-lymphoid tissues, including the liver, lung, and the epithelium of the small intestine (SI). The SI intra-epithelial lymphocytes (IELs) correspond to the largest reservoir of T cells in the body, and they are considered to play critical roles in maintaining immune surveillance and quiescence in the gut. Here, we found that SI IELs differ in their cytokine requirement for survival, so that they are mostly independent of IL-7, and they also cannot respond to IL-7. The molecular basis of the IL-7-independent homeostasis of SI IEL T cells is currently a major question that we are addressing in this project, and we are testing the hypothesis that the SI epithelial microenvironment would be providing these survival cues. In this regard, we recently reported that Foxp3 Treg cells, which need IL-2 for their survival and effector function, are exempt from their IL-2 requirement once they enter the SI epithelium (Prakhar P. et al., 2021, JCI Insights). Collectively, these results indicated that the role and requirement for cytokines differ depending on the tissue, and that the tissue environment needs to be taken into account when assessing the individual role of a given cytokine. Finally, we have initiated a series of new studies on the regulatory mechanisms of IL-7 receptor expression where we also address the epigenetic aspect of IL-7R expression. Specifically, we are assessing a role for the chromatin remodeling zinc finger transcription factor Ikaros (Ikfz1) as a novel regulator of controlling the accessibility of IL-7Ra gene locus. As such, we found that Ikfz1 controls IL-7Ra expression during the early T cell development in the thymus and in the survival/homeostasis of peripheral T cells. To further understand how Ikaros contributes to cytokine receptor regulation in general, and specifically to IL-7Ra expression, we have generated a series of Ikfz1-conditional knock out mice whereby Ikfz1-floxed mice were crossed with CD2-Cre recombinase transgenic mice or CD4-Cre transgenic mice, among others. In parallel, we also generated Ikfz1 transgenic mice to test the effect of Ikfz1 overexpression on T cell generation and homeostasis in the context of IL-7R signaling. Analyzing the T cell development and differentiation of these mice in context of IL-7R expression is currently under investigation.