Mittal Nikhil, Michels Etienne B, Massey Andrew E, Qiu Yunxiu, Royer-Weeden Shaina P, Smith Bryan R, Cartagena-Rivera Alexander X, Han Sangyoon J
Department of Biomedical Engineering, Michigan Technological University, Houghton, MI, USA.
Health Research Institute, Michigan Technological University, Houghton, MI, USA.
Commun Mater. 2024;5. doi: 10.1038/s43246-024-00444-0. Epub 2024 Jan 15.
The stiffness of the extracellular matrix induces differential tension within integrin-based adhesions, triggering differential mechanoresponses. However, it has been unclear if the stiffness-dependent differential tension is induced solely by myosin activity. Here, we report that in the absence of myosin contractility, 3T3 fibroblasts still transmit stiffness-dependent differential levels of traction. This myosin-independent differential traction is regulated by polymerizing actin assisted by actin nucleators Arp2/3 and formin where formin has a stronger contribution than Arp2/3 to both traction and actin flow. Intriguingly, despite only slight changes in F-actin flow speed observed in cells with the combined inhibition of Arp2/3 and myosin compared to cells with sole myosin inhibition, they show a 4-times reduction in traction than cells with myosin-only inhibition. Our analyses indicate that traditional models based on rigid F-actin are inadequate for capturing such dramatic force reduction with similar actin flow. Instead, incorporating the F-actin network's viscoelastic properties is crucial. Our new model including the F-actin viscoelasticity reveals that Arp2/3 and formin enhance stiffness sensitivity by mechanically reinforcing the F-actin network, thereby facilitating more effective transmission of flow-induced forces. This model is validated by cell stiffness measurement with atomic force microscopy and experimental observation of model-predicted stiffness-dependent actin flow fluctuation.
细胞外基质的刚度会在基于整合素的黏附中诱导不同的张力，从而引发不同的机械反应。然而，尚不清楚这种依赖于刚度的差异张力是否仅由肌球蛋白活性诱导产生。在此，我们报告，在缺乏肌球蛋白收缩性的情况下，3T3成纤维细胞仍能传递依赖于刚度的不同水平的牵引力。这种不依赖于肌球蛋白的差异牵引力由肌动蛋白成核因子Arp2/3和formin辅助的肌动蛋白聚合调节，其中formin对牵引力和肌动蛋白流动的贡献比Arp2/3更强。有趣的是，尽管与仅抑制肌球蛋白的细胞相比，同时抑制Arp2/3和肌球蛋白的细胞中观察到的F-肌动蛋白流动速度仅有轻微变化，但它们的牵引力却比仅抑制肌球蛋白的细胞降低了4倍。我们的分析表明，基于刚性F-肌动蛋白的传统模型不足以捕捉在类似肌动蛋白流动情况下如此显著的力降低现象。相反，纳入F-肌动蛋白网络的粘弹性特性至关重要。我们包含F-肌动蛋白粘弹性的新模型表明，Arp2/3和formin通过机械增强F-肌动蛋白网络来提高刚度敏感性，从而促进流动诱导力的更有效传递。该模型通过原子力显微镜进行的细胞刚度测量以及对模型预测的依赖于刚度的肌动蛋白流动波动的实验观察得到了验证。
