Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin–ligand bonds are separated by more than a few tens of nanometres. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model, in which individual integrin–ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds support our model. Our results provide a general framework for how cells sense spatial and physical information at the nanoscale, precisely tuning the range of conditions at which they form adhesions and activate transcriptional regulation.

中文翻译：

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力加载解释了细胞对配体的空间感测

细胞可以通过单个整合素蛋白和细胞膜内更大的含有整合素的粘附复合物来感知细胞外基质 (ECM) 分子的密度和分布。这种空间感应在各种正常和病理环境中驱动细胞活动。先前对刚性玻璃表面细胞的研究表明，ECM 配体的空间感应发生在纳米尺度上，当单个整合素-配体键分开超过几十纳米时，整合素聚集和随后的粘着斑形成会受损。因此，有人提出这种大小的交联“适配器”蛋白可能会将整联蛋白连接到肌动蛋白细胞骨架，充当直接感知配体间距的分子标尺。这里，我们开发了可以控制和改变 ECM 配体刚性和纳米级分布的凝胶。我们发现增加配体之间的间距会促进低刚性基材上粘着斑的生长，但会导致更刚性基材上的粘着力崩溃。此外，无序配体分布会大大增加粘附增长，但会降低粘附崩溃的刚性阈值。粘着斑的生长和塌陷分别反映在转录调节蛋白 YAP 的核或细胞质定位上。我们不是通过直接感知配体间距，而是通过使用扩展的计算分子离合器模型来解释这些发现，其中单个整合素-ECM 键（分子离合器）通过招募额外的整合素来响应力载荷，达到最大值。这会产生更多的离合器，在它们之间重新分配整体力，并减少每个离合器的力负载。在高刚性和高配体间距下，达到最大募集，防止进一步的力重新分配并导致粘附崩溃。细胞牵引力和肌动蛋白流速的测量支持我们的模型。我们的研究结果为细胞如何在纳米尺度上感知空间和物理信息提供了一个通用框架，精确地调整了它们形成粘附和激活转录调控的条件范围。防止进一步的力重新分布并导致粘附力崩溃。细胞牵引力和肌动蛋白流速的测量支持我们的模型。我们的研究结果为细胞如何在纳米尺度上感知空间和物理信息提供了一个通用框架，精确地调整了它们形成粘附和激活转录调控的条件范围。防止进一步的力重新分布并导致粘附力崩溃。细胞牵引力和肌动蛋白流速的测量支持我们的模型。我们的研究结果为细胞如何在纳米尺度上感知空间和物理信息提供了一个通用框架，精确地调整了它们形成粘附和激活转录调控的条件范围。