Department of Bioengineering, Rice University, P.O. Box 1892, Houston, TX 77251-1892, USA.
Biomech Model Mechanobiol. 2010 Apr;9(2):153-62. doi: 10.1007/s10237-009-0166-1. Epub 2009 Jul 31.
Articular chondrocytes experience a variety of mechanical stimuli during daily activity. One such stimulus, direct shear, is known to affect chondrocyte homeostasis and induce catabolic or anabolic pathways. Understanding how single chondrocytes respond biomechanically and morphologically to various levels of applied shear is an important first step toward elucidating tissue level responses and disease etiology. To this end, a novel videocapture method was developed in this study to examine the effect of direct shear on single chondrocytes, applied via the controlled lateral displacement of a shearing probe. Through this approach, precise force and deformation measurements could be obtained during the shear event, as well as clear pictures of the initial cell-to-probe contact configuration. To further study the non-uniform shear characteristics of single chondrocytes, the probe was positioned in three different placement ranges along the cell height. It was observed that the apparent shear modulus of single chondrocytes decreased as the probe transitioned from being close to the cell base (4.1 +/- 1.3 kPa), to the middle of the cell (2.6 +/- 1.1 kPa), and then near its top (1.7 +/- 0.8 kPa). In addition, cells experienced the greatest peak forward displacement (approximately 30% of their initial diameter) when the probe was placed low, near the base. Forward cell movement during shear, regardless of its magnitude, continued until it reached a plateau at ~35% shear strain for all probe positions, suggesting that focal adhesions become activated at this shear level to firmly adhere the cell to its substrate. Based on intracellular staining, the observed height-specific variation in cell shear stiffness and plateau in forward cell movement appeared to be due to a rearrangement of focal adhesions and actin at higher shear strains. Understanding the fundamental mechanisms at play during shear of single cells will help elucidate potential treatments for chondrocyte pathology and loading regimens related to cartilage health and disease.
关节软骨在日常活动中会经历各种机械刺激。其中一种刺激，即直接剪切，已知会影响软骨细胞的内稳态，并诱导分解代谢或合成代谢途径。了解单个软骨细胞如何对各种施加的剪切水平在生物力学和形态学上做出响应，是阐明组织水平响应和疾病病因的重要第一步。为此，本研究开发了一种新的视频捕获方法，通过控制剪切探针的侧向位移来检查直接剪切对单个软骨细胞的影响。通过这种方法，可以在剪切事件期间获得精确的力和变形测量值，以及初始细胞与探针接触配置的清晰图片。为了进一步研究单个软骨细胞的非均匀剪切特性，将探针放置在细胞高度的三个不同位置范围内。观察到，随着探针从靠近细胞基底（4.1 +/- 1.3 kPa）过渡到细胞中部（2.6 +/- 1.1 kPa），然后靠近细胞顶部（1.7 +/- 0.8 kPa），单个软骨细胞的表观剪切模量逐渐降低。此外，当探针放置在靠近基底的低处时，细胞经历的最大向前位移峰值（约为其初始直径的 30%）。无论其大小如何，在剪切过程中细胞向前运动都会持续，直到在所有探针位置达到约 35%剪切应变的平台，这表明在该剪切水平下焦点粘连被激活，从而将细胞牢固地附着在其基质上。基于细胞内染色，观察到的细胞剪切刚度的高度特异性变化和向前细胞运动的平台似乎是由于在较高的剪切应变下焦点粘连和肌动蛋白的重新排列。了解单个细胞在剪切过程中起作用的基本机制将有助于阐明针对软骨细胞病理学和与软骨健康和疾病相关的加载方案的潜在治疗方法。
