Cellular traction forces are contractile forces that depend on the material/substrate stiffness and play essential roles in sensing mechanical environments and regulating cell morphology and function. Traction forces are primarily generated by the actin cytoskeleton and transmitted to the substrate through focal adhesions. The cell nucleus is also believed to be involved in the regulation of this type of force; however, the role of the nucleus in cellular traction forces remains unclear. In this study, we explored the effects of nucleus-actin filament coupling on cellular traction forces in human dermal fibroblasts cultured on substrates with varying stiffness (5, 15, and 48 kPa). To investigate these effects, we transfected the cells with a dominant-negative Klarsicht/ANC-1/Syne homology (DN-KASH) protein that was designed to displace endogenous linker proteins and disrupt nucleus-actin cytoskeleton connections. The force that exists between the cytoskeleton and the nucleus (nuclear tension) was also evaluated with a fluorescence resonance energy transfer (FRET)-based tension sensor. We observed a biphasic change in cellular traction forces with a peak at 15 kPa, regardless of DN-KASH expression, that was inversely correlated with the nuclear tension. In addition, the relative magnitude and distribution of traction forces in nontreated wild-type cells were similar across different stiffness conditions, while DN-KASH-transfected cells exhibited a different distribution pattern that was impacted by the substrate stiffness. These results suggest that the nucleus-actin filament coupling play a homeostatic role by maintaining the relative magnitude of cellular traction forces in fibroblasts under different stiffness conditions.

细胞牵引力是取决于材料/基底刚度的收缩力，在传感机械环境和调节细胞形态和功能方面发挥着重要作用。牵引力主要由肌动蛋白细胞骨架产生并通过粘着斑传递至基底。细胞核也被认为参与了这种力的调节。然而，细胞核在细胞牵引力中的作用仍不清楚。在这项研究中，我们探讨了核-肌动蛋白丝耦合对在不同硬度（5、15 和 48 kPa）的基质上培养的人真皮成纤维细胞的细胞牵引力的影响。为了研究这些影响，我们用显性失活 Klarsicht/ANC-1/Syne 同源 (DN-KASH) 蛋白转染细胞，该蛋白旨在取代内源性连接蛋白并破坏细胞核-肌动蛋白细胞骨架连接。还使用基于荧光共振能量转移 (FRET) 的张力传感器评估了细胞骨架和细胞核之间存在的力（核张力）。我们观察到细胞牵引力的双相变化，峰值为 15 kPa，无论 DN-KASH 表达如何，这与核张力呈负相关。此外，未经处理的野生型细胞中牵引力的相对大小和分布在不同硬度条件下相似，而 DN-KASH 转染细胞表现出受基质硬度影响的不同分布模式。这些结果表明，核-肌动蛋白丝耦合通过在不同硬度条件下维持成纤维细胞中细胞牵引力的相对大小来发挥稳态作用。