Continual Cell Deformation Induced via Attachment to Oriented Fibers Enhances Fibroblast Cell Migration

Fibroblast migration is critical to the wound healing process. In vivo, migration occurs on fibrillar substrates, and previous observations have shown that a significant time lag exists before the onset of granulation tissue. We therefore conducted a series of experiments to understand the impact of both fibrillar morphology and migration time. Substrate topography was first shown to have a profound influence. Fibroblasts preferentially attach to fibrillar surfaces, and orient their cytoplasm for maximal contact with the fiber edge. In the case of en-mass cell migration out of an agarose droplet, fibroblasts on flat surfaces emerged with an enhanced velocity, v = 52μm/h, that decreases to the single cell value, v = 28μm/h within 24 hours and remained constant for at least four days. Fibroblasts emerging on fibrillar surfaces emerged with the single cell velocity, which remained constant for the first 24 hours and then increased reaching a plateau with more than twice the initial velocity within the next three days. The focal adhesions were distributed uniformly in cells on flat surfaces, while on the fibrillar surface they were clustered along the cell periphery. Furthermore, the number of focal adhesions for the cells on the flat surfaces remained constant, while it decreased on the fibrillar surface during the next three days. The deformation of the cell nuclei was found to be 50% larger on the fiber surfaces for the first 24 hours. While the mean deformation remained constant on the flat surface, it increased for the next three days by 24% in cells on fibers. On the fourth day, large actin/myosin fibers formed in cells on fibrillar surfaces only and coincided with a change from the standard migration mechanism involving extension of lamellipodia, and retraction of the rear, to one involving strong contractions oriented along the fibers and centered about the nucleus.

成纤维细胞（fibroblast）的迁移对伤口愈合过程至关重要。在体内环境中，细胞迁移发生于纤维状底物之上，既往研究观察到肉芽组织形成前存在显著的时间滞后现象。为此，我们开展了一系列实验，以探究纤维状基底形貌与迁移时间二者的共同影响。研究首先证实基底形貌具有显著调控作用：成纤维细胞更倾向于黏附于纤维状表面，并对胞质进行定向排布，以最大化与纤维边缘的接触面积。在琼脂糖微滴释放的群体细胞迁移实验中，平坦表面上的成纤维细胞初始迁移速度提升至52μm/h，随后在24小时内降至单细胞迁移速度28μm/h，并至少持续四天保持稳定。而纤维状表面上迁出的成纤维细胞，初始迁移速度即为单细胞水平，并在最初24小时内保持恒定；随后速度逐渐升高，在后续三天内达到初始速度两倍以上的平台期。平坦表面上的细胞其黏着斑（focal adhesion）分布均匀，而纤维状表面上的黏着斑则沿细胞周边聚集。此外，平坦表面细胞的黏着斑数量保持恒定，而纤维状表面细胞的黏着斑数量在后续三天内逐渐减少。研究还发现，前24小时内纤维表面上的细胞核变形量较平坦表面高出50%。平坦表面细胞的平均细胞核变形量保持稳定，而纤维表面细胞的该数值在后续三天内升高了24%。至第四天，仅纤维状表面上的细胞形成了粗大的肌动蛋白/肌球蛋白纤维，此时细胞迁移机制也发生转变：从依赖片状伪足（lamellipodia）延展与尾部回缩的经典模式，转变为沿纤维方向定向、以细胞核为中心的强收缩模式。