Age-related epithelial defects limit thymic function and regeneration [single cell; Foxn1Lin]

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 lineage trace and wild type 20-month-old mice at steady state.胸腺对于适应性免疫的建立至关重要，却会发生年龄相关性萎缩，进而导致免疫应答受损。胸腺同时对急性损伤极为敏感；尽管具备再生能力，但该能力随年龄增长逐渐衰退，具体机制尚不明确。本研究采用单细胞及空间转录组学、谱系示踪与先进成像技术，对非造血基质细胞的年龄相关变化进行系统性解析，发现了两种非典型胸腺上皮细胞（thymic epithelial cell, TEC）状态的出现。这些年龄相关性（aa）胸腺上皮细胞（TEC）会形成无胸腺细胞分布的高密度髓周上皮簇；这类非功能性胸腺组织的堆积随年龄增长而加重，呈现上皮间质转化（epithelial-to-mesenchymal transition, EMT）特征，且伴随FOXN1表达下调。相互作用分析显示，在稳态条件下，aaTECs会从其他功能性TEC群体接收持续信号，成为TEC生长因子的“消耗池”。在遭受急性损伤后，aaTECs会大幅扩增，进一步干扰营养再生通路，且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，或可为老年人群的免疫增强疗法开发提供理论参考。本数据集包含稳态下来自Foxn1谱系示踪小鼠与20月龄野生型小鼠的CD45阴性胸腺细胞的单细胞RNA测序（single-cell RNA-seq）图谱。