Development and Plasticity of Alveolar Type 1 Cells. Mus musculus

The alveolar type 1 (AT1) cell covers >95% of the gas exchange surface and is extremely thin to facilitate passive gas diffusion. The development of this highly specialized cell is poorly understood including fundamental questions regarding cell number and morphology. Using new molecular stereology and single cell imaging methods, we show that AT1 cells develop via a non-proliferative two-step process while maintaining proliferative potential. In the flattening step, AT1 cells remodel cell junctions and undergo molecular specification. In the folding step, AT1 cells are sculptured to match secondary septa formation, resulting in a single AT1 cell spanning multiple alveoli. AT1 cells grow in size by >10-fold, fueling most of the postnatal lung growth. Strikingly AT1 cells proliferate upon ectopic SOX2 expression and undergo stage-dependent cell fate reprogramming. These results contradict the traditional view of AT1 cells being terminally differentiated and provide insights to alveolar maturation. In this experiment, we conducted next-generation sequencing on flow-sorter AT1 cells isolated from mouse lungs ectopically expressing Sox2 under the control of the AT1-specific promoter Scnn1a versus control AT1 cells. Overall design: Two samples of Sox2-expressing AT1 cells versus two control AT1 samples.

肺泡1型（alveolar type 1, AT1）细胞覆盖了超过95%的肺部气体交换表面积，且自身极薄，以促进被动气体扩散。目前学界对这种高度特化细胞的发育机制仍知之甚少，包括细胞数量与形态等基础科学问题尚未得到解答。本研究采用新型分子体视学（molecular stereology）与单细胞成像技术，发现AT1细胞通过非增殖性两步发育过程完成成熟，且在此过程中保留增殖潜能。其中，铺展阶段中AT1细胞会重塑细胞连接并完成分子层面的特化；折叠阶段中，AT1细胞会被塑形以匹配次级肺泡隔膜的形成，最终形成单个跨越多处肺泡的AT1细胞。AT1细胞的体积可增长10倍以上，为出生后肺部的大部分生长提供了细胞基础。值得注意的是，当AT1细胞发生异位SOX2表达时会进入增殖状态，并呈现出阶段依赖性的细胞命运重编程。上述结果与“AT1细胞为终末分化细胞”的传统观点相悖，为肺泡成熟机制的研究提供了新的见解。本实验对两组经流式分选的AT1细胞（flow-sorted AT1 cells）进行了下一代测序（next-generation sequencing），这些细胞取自异位表达Sox2的小鼠肺组织，其中Sox2的表达受AT1特异性启动子Scnn1a调控，对照组则为正常AT1细胞。整体实验设计为：两组Sox2阳性AT1细胞样本，与两组对照AT1细胞样本。