Secretion of pulmonary surfactant in the alveoli of the lungs is essential to maintain lung function. Stretching of alveoli during lung inflation is the main trigger for surfactant secretion. Yet, the molecular mechanisms how mechanical distension of alveoli results in surfactant secretion are still elusive. The alveolar epithelium consists of alveolar epithelial type I (ATI) and surfactant secreting type II (ATII) cells. ATI, but not ATII cells, express caveolae, small plasma membrane invaginations that can respond to plasma membrane stresses and serve mechanotransductive roles. Within this study, we investigated the role of caveolae as mechanosensors in the alveolus. We generated a human caveolin‐1 knockout ATI cell (hAELVicav−/−) using CRISPR/Cas9. Wildtype (hAELViwt) and hAELVicav−/− cells grown on flexible membranes responded to increasing stretch amplitudes with rises in intracellular Ca2+. The response was less frequent and started at higher stretch amplitudes in hAELVicav−/− cells. Stretch‐induced Ca2+‐signals depended on Ca2+‐entry via piezo1 channels, localized within caveolae in hAELViwt and primary ATI cells. Ca2+‐entry via piezo1 activated pannexin‐1 hemichannels resulting in ATP release from ATI cells. ATP release was reduced in hAELVicav−/− cells. In co‐cultures resembling the alveolar epithelium, released ATP stimulated Ca2+ signals and surfactant secretion from neighboring ATII cells when co‐cultured with hAELViwt but not hAELVicav−/− cells. In summary, we propose that caveolae in ATI cells are mechanosensors within alveoli regulating stretch‐induced surfactant secretion from ATII cells.

中文翻译：

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机械拉伸激活肺泡 I 型细胞小窝中的压电 1 以触发 ATP 释放和旁分泌刺激肺泡 II 型细胞分泌表面活性剂

肺泡中肺表面活性物质的分泌对于维持肺功能至关重要。肺膨胀期间肺泡的伸展是表面活性剂分泌的主要触发因素。然而，肺泡的机械扩张如何导致表面活性剂分泌的分子机制仍然难以捉摸。肺泡上皮由肺泡上皮 I 型 (ATI) 和表面活性剂分泌型 II (ATII) 细胞组成。ATI，但不是 ATII 细胞，表达小窝，小质膜内陷，可以响应质膜应力并发挥机械传导作用。在这项研究中，我们调查了小窝作为机械传感器在肺泡中的作用。我们使用 CRISPR/Cas9 生成了人类小窝蛋白 1 敲除 ATI 细胞（hAELVicav-/-）。生长在柔性膜上的野生型 (hAELViwt) 和 hAELVicav-/- 细胞对随着细胞内 Ca2+ 升高而增加的拉伸幅度作出反应。在 hAELVicav-/- 细胞中，响应频率较低，并以较高的拉伸幅度开始。拉伸诱导的 Ca2+ 信号依赖于通过 piezo1 通道进入的 Ca2+，定位于 hAELViwt 和原代 ATI 细胞的小窝内。Ca2+通过piezo1进入激活pannexin-1半通道，导致ATI细胞释放ATP。hAELVicav-/- 细胞中的 ATP 释放减少。在类似于肺泡上皮的共培养物中，当与 hAELViwt 而非 hAELVicav-/- 细胞共培养时，释放的 ATP 会刺激 Ca2+ 信号和邻近 ATII 细胞的表面活性剂分泌。总之，