PDF(Pubmed)
Abstract：
Pulmonary surfactant is essential for maintaining proper lung function. Alveolar epithelial type II (AE2) cells secrete surfactants via lamellar bodies (LBs). In tidal loading during each breath, the physiological cyclic stretching of AE2 cells promotes surfactant secretion. Excessive stretching inhibits surfactant secretion, which is considered to contribute to the development of lung damage. However, its precise mechanism remains unknown. This study tested whether actin polymerization and intracellular transport are required for pulmonary surfactant secretion and the association of actin polymerization and transport in identical human AE2-derived A549 cells using live-cell imaging, not in the bulk cells population. We found that overstretching approximately doubled actin polymerization into filaments (F-actin) and suppressed LB secretion by half in the fluorescent area ratio, compared with physiological stretching (F-actin: 1.495 vs 0.643 (P < 0.01); LB: 0.739 vs 0.332 (P < 0.01)). An inhibitor of actin polymerization increased LB secretion. Intracellular tracking using fluorescent particles revealed that cyclic stretching shifted the particle motion perpendicularly to the direction of stretching according to the orientation of the F-actin (proportion of perpendicular axis motion prior particle: 0h 40.12 % vs 2h 63.13 % (P < 0.01)), and particle motion was restricted over time in the cells subjected to overstretching, indicating that overstretching regulates intracellular transport dynamics (proportion of stop motion particle: 0h 1.01 % vs 2h 11.04 % (P < 0.01)). These findings suggest that overstretching changes secretion through the cytoskeleton: overstretching AE2 cells inhibits pulmonary surfactant secretion, at least through accelerating actin polymerization and decreasing intracellular trafficking, and the change in actin orientation would modulate intracellular trafficking.
摘要：
肺表面活性剂对于维持适当的肺功能至关重要。肺泡上皮II型（AE2）细胞通过层状体（LB）分泌表面活性剂。在每次呼吸的潮汐负荷中，AE2细胞的生理循环拉伸促进表面活性剂分泌。过度拉伸会抑制表面活性剂的分泌，这被认为有助于肺损伤的发展。然而,其确切机制尚不清楚。这项研究使用活细胞成像测试了在相同的人AE2衍生的A549细胞中，肺表面活性物质分泌是否需要肌动蛋白聚合和细胞内转运，以及肌动蛋白聚合和转运的关联。不在批量细胞群体中。我们发现，过度拉伸大约使肌动蛋白聚合成丝（F-肌动蛋白）加倍，并在荧光面积比中将LB分泌抑制了一半，与生理拉伸相比（F-肌动蛋白：1.495vs0.643（P<0.01）；LB：0.739vs0.332（P<0.01））。肌动蛋白聚合抑制剂增加LB分泌。使用荧光颗粒的细胞内跟踪显示，循环拉伸根据F-肌动蛋白的方向将颗粒运动垂直于拉伸方向移动（在粒子之前的垂直轴运动比例：0h40.12％vs2h63.13％（P<0.01）），随着时间的推移，粒子运动在过度拉伸的细胞中受到限制，表明过度拉伸调节细胞内运输动力学(停止运动粒子的比例:0h1.01%vs2h11.04%(P<0.01))。这些发现表明，过度拉伸会改变通过细胞骨架的分泌：过度拉伸AE2细胞会抑制肺表面活性物质的分泌，至少通过加速肌动蛋白聚合和减少细胞内运输，肌动蛋白取向的变化会调节细胞内的运输。
