Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA.
Biophys J. 2011 Nov 2;101(9):2122-30. doi: 10.1016/j.bpj.2011.09.047. Epub 2011 Nov 1.
Circular dorsal ruffles (CDRs) are transient actin-rich ringlike structures that form on the dorsal surface of growth-factor stimulated cells. However, the dynamics and mechanism of formation of CDRs are still unknown. It has been observed that CDR formation leads to stress fibers disappearing near the CDRs. Because stress fiber formation can be modified by substrate stiffness, we examined the effect of substrate stiffness on CDR formation by seeding NIH 3T3 fibroblasts on glass and polydimethylsiloxane substrates of varying stiffnesses from 20 kPa to 1800 kPa. We found that increasing substrate stiffness increased the lifetime of the CDRs. We developed a mathematical model of the signaling pathways involved in CDR formation to provide insight into this lifetime and size dependence that is linked to substrate stiffness via Rac-Rho antagonism. From the model, increasing stiffness raised mDia1-nucleated stress fiber formation due to Rho activation. The increased stress fibers present increased replenishment of the G-actin pool, therefore prolonging Arp2/3-nucleated CDR formation due to Rac activation. Negative feedback by WAVE-related RacGAP on Rac explained how CDR actin propagates as an excitable wave, much like wave propagation in other excitable medium, e.g., nerve signal transmission.
环状背侧皱襞 (CDRs) 是一种短暂的富含肌动蛋白的环状结构，在生长因子刺激的细胞的背侧表面形成。然而，CDR 的形成的动态和机制仍然未知。已经观察到 CDR 的形成导致靠近 CDR 的应力纤维消失。由于应力纤维的形成可以通过基质的硬度来修饰，我们通过在玻璃和聚二甲基硅氧烷基质上接种 NIH 3T3 成纤维细胞来研究基质硬度对 CDR 形成的影响，这些基质的硬度从 20 kPa 到 1800 kPa 不等。我们发现，增加基质硬度会增加 CDR 的寿命。我们开发了一个涉及 CDR 形成的信号通路的数学模型，以深入了解与基质硬度相关的这种寿命和尺寸依赖性，这种依赖性是通过 Rac-Rho 拮抗作用与基质硬度联系起来的。从模型中可以看出，由于 Rho 的激活，增加的基质硬度会增加 mDia1 引发的应力纤维的形成。增加的应力纤维会增加 G-肌动蛋白池的补充，因此由于 Rac 的激活而延长了 Arp2/3 引发的 CDR 的形成。WAVE 相关 RacGAP 对 Rac 的负反馈解释了 CDR 肌动蛋白如何像其他可兴奋介质（例如神经信号传输）中的波传播一样作为可兴奋波传播。
