Webster Kevin D, Ng Win Pin, Fletcher Daniel A
Biophysics Graduate Group, University of California, Berkeley, California; Department of Bioengineering, University of California, Berkeley, California.
Department of Bioengineering, University of California, Berkeley, California; University of California Berkeley/University of California San Francisco Graduate Group in Bioengineering, Berkeley, California.
Biophys J. 2014 Jul 1;107(1):146-55. doi: 10.1016/j.bpj.2014.04.051.
Adherent cells generate forces through acto-myosin contraction to move, change shape, and sense the mechanical properties of their environment. They are thought to maintain defined levels of tension with their surroundings despite mechanical perturbations that could change tension, a concept known as tensional homeostasis. Misregulation of tensional homeostasis has been proposed to drive disorganization of tissues and promote progression of diseases such as cancer. However, whether tensional homeostasis operates at the single cell level is unclear. Here, we directly test the ability of single fibroblast cells to regulate tension when subjected to mechanical displacements in the absence of changes to spread area or substrate elasticity. We use a feedback-controlled atomic force microscope to measure and modulate forces and displacements of individual contracting cells as they spread on a fibronectin-patterned atomic-force microscope cantilever and coverslip. We find that the cells reach a steady-state contraction force and height that is insensitive to stiffness changes as they fill the micropatterned areas. Rather than maintaining a constant tension, the fibroblasts altered their contraction force in response to mechanical displacement in a strain-rate-dependent manner, leading to a new and stable steady-state force and height. This response is influenced by overexpression of the actin crosslinker α-actinin, and rheology measurements reveal that changes in cell elasticity are also strain- rate-dependent. Our finding of tensional buffering, rather than homeostasis, allows cells to transition between different tensional states depending on how they are displaced, permitting distinct responses to slow deformations during tissue growth and rapid deformations associated with injury.
贴壁细胞通过肌动蛋白-肌球蛋白收缩产生力量来移动、改变形状并感知周围环境的力学特性。尽管机械扰动可能会改变张力，但人们认为它们能与周围环境保持一定的张力水平，这一概念被称为张力稳态。有人提出，张力稳态失调会导致组织紊乱，并促进癌症等疾病的发展。然而，张力稳态是否在单细胞水平上起作用尚不清楚。在这里，我们直接测试单个成纤维细胞在不改变铺展面积或底物弹性的情况下受到机械位移时调节张力的能力。我们使用反馈控制的原子力显微镜来测量和调节单个收缩细胞在纤连蛋白图案化的原子力显微镜悬臂和盖玻片上铺展时的力和位移。我们发现，当细胞填充微图案区域时，它们会达到一个对刚度变化不敏感的稳态收缩力和高度。成纤维细胞不是维持恒定的张力，而是以应变率依赖的方式响应机械位移来改变其收缩力，从而导致新的稳定稳态力和高度。这种反应受肌动蛋白交联蛋白α-辅肌动蛋白过表达的影响，流变学测量表明细胞弹性的变化也是应变率依赖的。我们发现的是张力缓冲而非稳态，这使得细胞能够根据其位移方式在不同的张力状态之间转换，从而对组织生长过程中的缓慢变形以及与损伤相关的快速变形做出不同反应。
