Division of Pulmonary, Critical Care, Sleep, and Allergy, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois.
Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois.
Biophys J. 2018 Feb 27;114(4):929-938. doi: 10.1016/j.bpj.2017.12.032.
Regulation of cell volume is a fundamental property of all mammalian cells. Multiple signaling pathways are known to be activated by cell swelling and to contribute to cell volume homeostasis. Although cell mechanics and membrane tension have been proposed to couple cell swelling to signaling pathways, the impact of swelling on cellular biomechanics and membrane tension have yet to be fully elucidated. In this study, we use atomic force microscopy under isotonic and hypotonic conditions to measure mechanical properties of endothelial membranes including membrane stiffness, which reflects the stiffness of the submembrane cytoskeleton complex, and the force required for membrane tether formation, reflecting membrane tension and membrane-cytoskeleton attachment. We find that hypotonic swelling results in significant stiffening of the endothelial membrane without a change in membrane tension/membrane-cytoskeleton attachment. Furthermore, depolymerization of F-actin, which, as expected, results in a dramatic decrease in the cellular elastic modulus of both the membrane and the deeper cytoskeleton, indicating a collapse of the cytoskeleton scaffold, does not abrogate swelling-induced stiffening of the membrane. Instead, this swelling-induced stiffening of the membrane is enhanced. We propose that the membrane stiffening should be attributed to an increase in hydrostatic pressure that results from an influx of solutes and water into the cells. Most importantly, our results suggest that increased hydrostatic pressure, rather than changes in membrane tension, could be responsible for activating volume-sensitive mechanisms in hypotonically swollen cells.
细胞体积调节是所有哺乳动物细胞的基本特性。已知多种信号通路可被细胞肿胀激活，并有助于细胞体积稳态。尽管细胞力学和膜张力已被提议将细胞肿胀与信号通路偶联，但肿胀对细胞生物力学和膜张力的影响尚未完全阐明。在这项研究中，我们在等渗和低渗条件下使用原子力显微镜测量内皮细胞膜的机械性能，包括反映亚膜细胞骨架复合物刚度的膜硬度，以及形成膜栓所需的力，反映膜张力和膜-细胞骨架附着。我们发现低渗肿胀导致内皮膜显著变硬，而膜张力/膜-细胞骨架附着没有变化。此外，正如预期的那样，F-肌动蛋白的解聚导致膜和更深的细胞骨架的细胞弹性模量急剧下降，表明细胞骨架支架的崩溃，不会消除肿胀引起的膜变硬。相反，这种肿胀引起的膜变硬会增强。我们提出，膜变硬应该归因于溶质和水流入细胞导致的静压增加。最重要的是，我们的结果表明，增加的静压而不是膜张力的变化可能是导致低渗肿胀细胞中体积敏感机制激活的原因。
