Age-related epithelial defects limit thymic function and regeneration [single cell; Foxn1LacZ]

The thymus is essential for establishing adaptive immunity yet undergoes age-related involution that leads to compromised immune responsiveness. The thymus is also extremely sensitive to acute insult and although capable of regeneration, this capacity declines with age for unknown reasons. We applied single-cell and spatial transcriptomics, lineage-tracing and advanced imaging to define age-related changes in non-hematopoietic stromal cells and discovered the emergence of two atypical thymic epithelial cell (TEC) states. These age-associated (aa)TECs formed high-density peri-medullary epithelial clusters that were devoid of thymocytes; an accretion of non-productive thymic tissue that worsened with age, exhibited features of epithelial-to-mesenchymal transition (EMT), and was associated with downregulation of FOXN1. Interaction analysis revealed that the emergence of aaTEC drew tonic signals from other functional TEC populations at baseline acting as a sink for TEC growth factors. Following acute injury, aaTEC expanded substantially, further perturbing trophic regeneration pathways and correlating with defective repair of the involuted thymus. These findings therefore define a unique feature of thymic involution linked to immune aging and could have implications for developing immune boosting therapies in older individuals. Single cell RNA-seq profiles of CD45- thymic cells from Foxn1 LacZ mock and mutant 6-month-old mice at steady state.胸腺是建立适应性免疫的关键器官，却会发生年龄相关性萎缩，进而引发免疫应答受损。胸腺对急性损伤也极为敏感：尽管具备再生潜能，但该能力会随年龄增长逐渐衰退，具体机制迄今尚未明确。本研究采用单细胞与空间转录组学、谱系示踪及先进成像技术，对非造血基质细胞的年龄相关变化进行系统解析，发现了两种非典型胸腺上皮细胞（thymic epithelial cell, TEC）状态的产生。这些年龄相关（age-associated, aa）TEC形成了无胸腺细胞定植的高密度髓周上皮簇——此类无功能胸腺组织的积聚随年龄增长而加重，且呈现上皮间质转化（epithelial-to-mesenchymal transition, EMT）特征，同时伴随FOXN1的表达下调。相互作用分析显示，aaTEC会接收来自其他功能性TEC群体的基础持续性信号，成为TEC生长因子的消耗池。在急性损伤后，aaTEC会大幅扩增，进一步干扰营养再生通路，并与萎缩胸腺的修复缺陷密切相关。综上，本研究明确了与免疫衰老相关的胸腺萎缩的独特特征，该发现或可为老年群体的免疫增强疗法开发提供思路。本数据集包含稳态下6月龄Foxn1-LacZ假处理组与突变组小鼠的CD45阴性胸腺细胞的单细胞RNA测序（single cell RNA-seq）谱。