Department of Orthopedics, University of Zurich, Balgrist University Hospital, Zurich, Switzerland.
Integr Biol (Camb). 2013 Jun;5(6):865-76. doi: 10.1039/c3ib20282h.
The mechanical coupling between adherent cells and their substrates is a major driver of downstream behavior. This coupling relies on the formation of adhesion sites and actin bundles. How cells generate these elements remains only partly understood. A potentially important mechanism, the length threshold maturation (LTM), has previously been proposed to regulate adhesion maturation and actin bundle stabilization tangential to the leading edge. The LTM describes the process by which cells integrate lamellar myosin forces to trigger adhesion maturation. These forces, cumulated over the length of an actin bundle, are balanced at the anchoring focal complexes. When the bundle length exceeds a certain threshold, the distributed lamellar forces become sufficient to trigger the stabilization of the bundle and its adhesions. In this continuing study, we experimentally challenge the LTM for the first time, by seeding cells on micropatterned substrates with various non-adhesive gaps designed to selectively trigger the LTM. While stable actin bundles were observed on all patterns, their lengths were almost exclusively above 3 μm or 4 μm depending on the cell type. Furthermore, the frequency with which gaps were bridged increased nearly as a step function with increasing gap width, indicating a substrate dependent behavioral switch. These combined observations point strongly to LTM with a threshold above 3 μm. We thus experimentally confirm with two cell types our previous theoretical work postulating the existence of a length dependent threshold mechanism that triggers adhesion maturation and actin bundle stabilization.
黏附细胞与其基质之间的机械偶联是下游行为的主要驱动力。这种偶联依赖于黏附位点和肌动蛋白束的形成。细胞如何产生这些元素仍不完全清楚。一个潜在的重要机制，即长度阈值成熟（LTM），此前已被提出用于调节黏附成熟和沿前缘稳定肌动蛋白束。LTM 描述了细胞整合片状肌球蛋白力以触发黏附成熟的过程。这些力在肌动蛋白束的长度上累积，并在锚定的焦点复合物处达到平衡。当束长超过一定阈值时，分布的片状力足以触发束及其黏附的稳定。在这项持续的研究中，我们首次通过在具有各种非黏附间隙的微图案化基板上播种细胞来实验性地挑战 LTM，这些间隙旨在选择性地触发 LTM。虽然在所有图案上都观察到稳定的肌动蛋白束，但它们的长度几乎都在 3 μm 或 4 μm 以上，具体取决于细胞类型。此外，随着间隙宽度的增加，间隙被桥接的频率几乎呈阶跃函数增加，表明存在依赖于基质的行为开关。这些综合观察结果强烈指向 LTM，其阈值大于 3 μm。因此，我们用两种细胞类型实验证实了我们之前的理论工作，该工作假设存在一种长度依赖性的阈值机制，该机制触发黏附成熟和肌动蛋白束的稳定。
