Loss of Keratin 76 in Thymic Epithelial Cells affects Skin Tissue Self-Antigens presentation in the Thymus and disrupts T cell tolerance

角蛋白是上皮细胞表达的细胞骨架蛋白，包括髓样胸腺上皮细胞（mTECs）。最近的研究发现角蛋白在调节免疫中的作用（Hobbs et al., 2015）。角化蛋白76 （Keratin76, Krt76）在口腔、鳞状胃和胸腺上皮细胞中表达，并在口腔癌和胃癌中发挥免疫调节作用（Sequeira et al., 2018）。Krt76-/-成年小鼠表现出慢性炎症表型，然而，尚不清楚表达Krt76的胸腺上皮细胞（TECs）如何与免疫系统相互作用并调节免疫系统。我的目的是研究胸腺中Krt76的特异性缺失如何影响T细胞的发育，并证明其在与细胞成分沟通以调节胸腺内皮肤特异性组织自抗原（TSAs）表达中的作用。我们发现Krt76在其他终末分化的mTEC标记物和人类和小鼠Hassall's小体中共表达，Hassall's小体是一种独特的胸腺结构，功能不明。我们将胎儿Krt76-/-胸腺移植到胸腺裸鼠的肾囊中，证实了成年Krt76-/-炎症表型是由胸腺中特异性的Krt76破坏驱动的。根据Michelson等人最近的研究，我们假设Krt76+ TECs可能负责tsa的表达（Cell 2022）。他们发表的数据集分析表明，Krt76+ mtec表达了特定的皮肤TSAs。此外，我们对Krt76-/-胸腺进行了scrna测序，研究了Krt76-/-胸腺的细胞和分子差异，并评估了调节这些变化的分子机制。此外，流式细胞术和免疫组织化学分析显示，年轻成年Krt76-/-小鼠外周的效应T细胞数量较高，但时间点较早。我们的研究结果证实，胸腺中的角蛋白可以影响T细胞的成熟，特别是通过引发T细胞特异性地对抗皮肤TSAs。这项研究强调了角蛋白在严格调节的免疫过程中的基本作用。这项研究将Krt76+ tec与皮肤免疫稳态直接联系起来，这可能成为未来治疗干预的主要新靶点。”

"Keratins are cytoskeletal proteins expressed in epithelial cells, including medullary thymic epithelial cells (mTECs). Recent studies have uncovered a role for keratins in regulating immunity (Hobbs et al., 2015). Keratin76 (Krt76) is expressed in epithelial cells of the oral cavity, squamous stomach and thymus, and was shown to play an immunomodulatory role in oral and gastric cancer (Sequeira et al., 2018). Krt76-/- adult mice display a chronic inflammation phenotype, however, it remains unclear how thymic epithelial cells (TECs) expressing Krt76 are interacting with and regulating the immune system.I aim to investigate how loss of Krt76 specifically in the thymus impacts T cell development and demonstrate its role in communicating with cellular components to regulate the expression of skin-specific tissue self-antigens (TSAs) within the thymus. We identified co-expression of Krt76 amongst other terminally differentiated mTEC markers and in human and mice Hassall's Corpuscles, unique thymic structures with an unclear function. We transplanted foetal Krt76-/- thymi into the renal capsule of athymic nude mice which confirmed that adult Krt76-/- inflammatory phenotype was driven by Krt76 disruption specifically in the thymus. We hypothesised that Krt76+ TECs may be responsible for the expression of TSAs, based on the recent study by Michelson et al. (Cell 2022). Analysis of their published dataset indicated expression of specific skin TSAs by Krt76+ mTECs. Additionally, we carried out scRNA-seq of Krt76-/- thymi to investigate the cellular and molecular differences in the Krt76-/- thymi, and assessed the molecular mechanisms regulating these changes. Additionally, flow cytometry and immunohistochemistry analysis revealed higher numbers of effector T cells in the periphery of young adult Krt76-/- mice, but not at earlier timepoints. Our results confirm that keratins in the thymus can impact the maturation of T cells, in particular by priming T cells specifically against skin TSAs. This study highlights the fundamental role of keratins in tightly regulated immunological processes. This study places Krt76+ TECs in direct communication with skin immune homeostasis, which could present as a major new target for future therapeutic interventions."