Abstract：
Mechanical stress and the stiffness of the extracellular matrix are key drivers of tissue development and homeostasis. Aberrant mechanosensation is associated with a wide range of pathologies, including osteoarthritis. Matrix (or substrate) stiffness plays a major role in cell spreading, adhesion, proliferation, and differentiation. However, how specific cells sense substrate stiffness still remains unclear. The primary cilium is an essential cellular organelle that senses and integrates mechanical and chemical signals from the extracellular environment. We hypothesized that the primary cilium dynamically alters its length and position to fine-tune cell mechanosignaling based on substrate stiffness alone. We used a hydrogel system of varying substrate stiffness to examine the role of stiffness on cilia frequency, length, and centriole position as well as cell and nuclei area over time. Contrary to other cell types, we show that chondrocyte primary cilia shorten on softer substrates, demonstrating tissue-specific mechanosensing that is aligned with the tissue stiffness the cells originate from. We further show that stiffness determines centriole positioning to either the basal or apical membrane during attachment and spreading, with centrioles positioned toward the basal membrane on stiffer substrates. These phenomena are mediated by force generation actin-myosin stress fibers in a time-dependent manner. Finally, we show on stiff substrates that primary cilia are involved in tension-mediated cell spreading. We propose that substrate stiffness plays a role in cilia positioning, regulating cellular responses to external forces, and maybe a key driver of mechanosignaling-associated diseases.
摘要：
机械应力和细胞外基质的硬度是组织发育和稳态的关键驱动因素。异常的机械感觉与广泛的病理有关，包括骨关节炎.基质(或底物)刚度在细胞铺展中起主要作用，附着力,扩散,和差异化。然而,特定细胞如何感知底物硬度仍不清楚。初级纤毛是感知和整合来自细胞外环境的机械和化学信号的重要细胞器。我们假设初级纤毛会动态改变其长度和位置，从而仅基于底物刚度来微调细胞机械信号。我们使用了不同基质刚度的水凝胶系统来检查刚度对纤毛频率的作用，长度,和中心粒位置以及细胞和细胞核的面积随着时间的推移。与其他细胞类型相反，我们显示软骨细胞初级纤毛在较软的基质上缩短，证明与细胞起源的组织硬度一致的组织特异性机械传感。我们进一步表明，在附着和扩散过程中，刚度决定了中心粒定位到基底膜或根尖膜，中心粒位于较硬的基底上的基底膜。这些现象由力产生肌动蛋白-肌球蛋白应力纤维以时间依赖性方式介导。最后,我们在坚硬的基质上显示，初级纤毛参与张力介导的细胞扩散。我们建议基底刚度在纤毛定位中起作用，调节细胞对外力的反应，也许是机械信号相关疾病的关键驱动因素。
