Huntsman Cancer Institute, Departments of Biology and Oncological Sciences, Salt Lake City, UT, USA.
Biophys J. 2012 Nov 21;103(10):2082-92. doi: 10.1016/j.bpj.2012.09.038. Epub 2012 Nov 20.
Actin stress fibers (SFs) are load-bearing and mechanosensitive structures. To our knowledge, the mechanisms that enable SFs to sense and respond to strain have not been fully defined. Acute local strain events can involve a twofold extension of a single SF sarcomere, but how these dramatic local events affect the overall SF architecture is not believed to be understood. Here we have investigated how SF architecture adjusts to episodes of local strain that occur in the cell center. Using fluorescently tagged zyxin to track the borders of sarcomeres, we characterize the dynamics of resting sarcomeres and strain-site sarcomeres. We find that sarcomeres flanking a strain site undergo rapid shortening that directly compensates for the strain-site extension, illustrating lateral communication of mechanical information along the length of a stress fiber. When a strain-site sarcomere extends asymmetrically, its adjacent sarcomeres exhibit a parallel asymmetric shortening response, illustrating that flanking sarcomeres respond to strain magnitude. After extension, strain-site sarcomeres become locations of new sarcomere addition, highlighting mechanical strain as a trigger of sarcomere addition and revealing a, to our knowledge, novel type of SF remodeling. Our findings provide evidence to suggest SF sarcomeres act as strain sensors and are interconnected to support communication of mechanical information.
肌动蛋白应力纤维 (SFs) 是承载负荷和对机械敏感的结构。据我们所知，SFs 感知和响应应变的机制尚未完全定义。急性局部应变事件可能涉及单个 SF 肌节的两倍延伸，但这些剧烈的局部事件如何影响 SF 的整体结构尚不清楚。在这里，我们研究了 SF 结构如何适应细胞中心发生的局部应变事件。我们使用荧光标记的黏着斑蛋白（zyxin）来跟踪肌节的边界，以研究静止肌节和应变部位肌节的动力学。我们发现，应变部位周围的肌节会迅速缩短，直接补偿了应变部位的延伸，这说明了机械信息在 SF 长度上的横向传递。当应变部位的肌节不对称延伸时，其相邻的肌节会表现出平行的不对称缩短反应，这表明相邻的肌节会对应变幅度做出反应。延伸后，应变部位的肌节成为新肌节添加的位置，这突出了机械应变作为肌节添加的触发因素，并揭示了一种，据我们所知，新型的 SF 重塑。我们的研究结果提供了证据，表明 SF 肌节充当应变传感器，并相互连接以支持机械信息的传递。
