McAndrews Kathleen M, McGrail Daniel J, Quach Nhat D, Dawson Michelle R
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Phys Biol. 2014 Aug 26;11(5):056004. doi: 10.1088/1478-3975/11/5/056004.
The mechanical properties within the cell are regulated by the organization of the actin cytoskeleton, which is linked to the extracellular environment through focal adhesion proteins that transmit force. Chemical and mechanical stimuli alter the organization of cytoskeletal actin, which results in changes in cell shape, adhesion, and differentiation. By combining particle-tracking microrheology and traction force cytometry, we can monitor the mechanical properties of the actin meshwork and determine how changes in the intracellular network contribute to force generation. In this study, we investigated the effects of chemical (differentiation factors) and mechanical (substrate rigidity) stimuli important in mesenchymal stem cell (MSC) differentiation on the intracellular mechanics and traction stress generation. We found the presence of adipogenic factors resulted in stiffening of the actin meshwork regardless of substrate rigidity. In contrast, these factors increased traction stresses on hard substrates, which was associated with increased expression of contractility genes. Furthermore, MSCs cultured on hard substrates expressed both adipogenic and osteogenic markers indicative of mixed differentiation. On hard substrates, heterogeneity in the local elastic modulus-traction stress correlation was also increased in response to adipogenic factors, indicating that these mechanical properties may be reflective of differences in the level of MSC differentiation. These results suggest intracellular rheology and traction stress generation are spatially regulated and contribute insight into how single cell mechanical forces contribute to MSC differentiation.
细胞内的力学特性由肌动蛋白细胞骨架的组织来调节,肌动蛋白细胞骨架通过传递力的粘着斑蛋白与细胞外环境相连。化学和机械刺激会改变细胞骨架肌动蛋白的组织,进而导致细胞形状、粘附和分化的变化。通过结合粒子追踪微流变学和牵引力细胞术,我们可以监测肌动蛋白网络的力学特性,并确定细胞内网络的变化如何影响力的产生。在本研究中,我们调查了间充质干细胞(MSC)分化过程中重要的化学(分化因子)和机械(基质硬度)刺激对细胞内力学和牵引力产生的影响。我们发现,无论基质硬度如何,脂肪生成因子的存在都会导致肌动蛋白网络变硬。相比之下,这些因子会增加硬基质上的牵引力,这与收缩性基因表达增加有关。此外,在硬基质上培养的间充质干细胞表达了表明混合分化的脂肪生成和成骨标记物。在硬基质上,局部弹性模量与牵引力相关性的异质性也因脂肪生成因子而增加,这表明这些力学特性可能反映了间充质干细胞分化水平的差异。这些结果表明,细胞内流变学和牵引力的产生在空间上受到调节,有助于深入了解单细胞机械力如何促进间充质干细胞的分化。