Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition
Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition
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DOI：
10.1073/pnas.0901462106
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发表时间：
2009-06-30
影响因子：
11.1
通讯作者：
Fredberg, J. J.
中科院分区：
文献类型：
--
作者：
Zhou, E. H.;Trepat, X.;Fredberg, J. J.
细胞在不同应力和变形模式下的机械鲁棒性对其存活和功能至关重要。在张力下，机械刚性由细胞骨架网络提供;随着应力的增加，该网络变硬，提供增加的抗变形性。然而，细胞还必须抵抗压缩，这将不可避免地发生，每当细胞体积减少，在生物学上重要的过程，如脱水和凋亡。在压力下，单个细丝可以弯曲，从而降低刚度并削弱细胞骨架网络。然而，细胞内空间挤满了可以抵抗压缩的大分子和细胞器。描述其行为的一个简单的图片是胶体颗粒;胶体表现出粘度随着体积分数的增加而急剧增加，最终经历玻璃化转变并成为固体。我们调查的后果，这2个竞争的影响，并表明，作为一个细胞是由高渗应力压缩，它变得越来越刚性。尽管这种硬化行为在一定程度上取决于细胞类型、起始条件、分子马达和细胞骨架的贡献，但其对固体体积分数的依赖在每种情况下都是指数的。这种普遍的行为表明，压缩引起的网络弱化被拥挤引起的细胞质硬化所压倒。我们还表明，压缩显着减缓细胞内的松弛过程。刚度的增加，结合松弛过程的减缓，使人想起胶体悬浮液的玻璃化转变，但只有当由可变形颗粒组成时。我们的工作提供了一种手段来探测压缩下的细胞质的物理性质，并导致跨细胞类型的通用结果。
Mechanical robustness of the cell under different modes of stress and deformation is essential to its survival and function. Under tension, mechanical rigidity is provided by the cytoskeletal network; with increasing stress, this network stiffens, providing increased resistance to deformation. However, a cell must also resist compression, which will inevitably occur whenever cell volume is decreased during such biologically important processes as anhydrobiosis and apoptosis. Under compression, individual filaments can buckle, thereby reducing the stiffness and weakening the cytoskeletal network. However, the intracellular space is crowded with macromolecules and organelles that can resist compression. A simple picture describing their behavior is that of colloidal particles; colloids exhibit a sharp increase in viscosity with increasing volume fraction, ultimately undergoing a glass transition and becoming a solid. We investigate the consequences of these 2 competing effects and show that as a cell is compressed by hyperosmotic stress it becomes progressively more rigid. Although this stiffening behavior depends somewhat on cell type, starting conditions, molecular motors, and cytoskeletal contributions, its dependence on solid volume fraction is exponential in every instance. This universal behavior suggests that compression-induced weakening of the network is overwhelmed by crowding-induced stiffening of the cytoplasm. We also show that compression dramatically slows intracellular relaxation processes. The increase in stiffness, combined with the slowing of relaxation processes, is reminiscent of a glass transition of colloidal suspensions, but only when comprised of deformable particles. Our work provides a means to probe the physical nature of the cytoplasm under compression, and leads to results that are universal across cell type.