Loening A M, James I E, Levenston M E, Badger A M, Frank E H, Kurz B, Nuttall M E, Hung H H, Blake S M, Grodzinsky A J, Lark M W
Center for Biomedical Engineering, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge 02139, USA.
Arch Biochem Biophys. 2000 Sep 15;381(2):205-12. doi: 10.1006/abbi.2000.1988.
A bovine cartilage explant system was used to evaluate the effects of injurious compression on chondrocyte apoptosis and matrix biochemical and biomechanical properties within intact cartilage. Disks of newborn bovine articular cartilage were compressed in vitro to various peak stress levels and chondrocyte apoptotic cell death, tissue biomechanical properties, tissue swelling, glycosaminoglycan loss, and nitrite levels were quantified. Chondrocyte apoptosis occurred at peak stresses as low as 4.5 MPa and increased with peak stress in a dose-dependent manner. This increase in apoptosis was maximal by 24 h after the termination of the loading protocol. At high peak stresses (>20 MPa), greater than 50% of cells apoptosed. When measured in uniaxial confined compression, the equilibrium and dynamic stiffness of explants decreased with the severity of injurious load, although this trend was not significant until 24-MPa peak stress. In contrast, the equilibrium and dynamic stiffness measured in radially unconfined compression decreased significantly after injurious stresses of 12 and 7 MPa, respectively. Together, these results suggested that injurious compression caused a degradation of the collagen fibril network in the 7- to 12-MPa range. Consistent with this hypothesis, injurious compression caused a dose-dependent increase in tissue swelling, significant by 13-MPa peak stress. Glycosaminoglycans were also released from the cartilage in a dose-dependent manner, significant by 6- to 13-MPa peak stress. Nitrite levels were significantly increased above controls at 20-MPa peak stress. Together, these data suggest that injurious compression can stimulate cell death as well as a range of biomechanical and biochemical alterations to the matrix and, possibly, chondrocyte nitric oxide expression. Interestingly, chondrocyte programmed cell death appears to take place at stresses lower than those required to stimulate cartilage matrix degradation and biomechanical changes. While chondrocyte apoptosis may therefore be one of the earliest responses to tissue injury, it is currently unclear whether this initial cellular response subsequently drives cartilage matrix degradation and changes in the biomechanical properties of the tissue.
采用牛软骨外植体系统评估损伤性压缩对完整软骨内软骨细胞凋亡以及基质生化和生物力学特性的影响。将新生牛关节软骨圆盘在体外压缩至不同的峰值应力水平，并对软骨细胞凋亡性细胞死亡、组织生物力学特性、组织肿胀、糖胺聚糖损失和亚硝酸盐水平进行定量分析。软骨细胞凋亡在低至4.5MPa的峰值应力时就会发生，并随着峰值应力呈剂量依赖性增加。这种凋亡增加在加载方案终止后24小时达到最大值。在高峰值应力（>20MPa）时，超过50%的细胞发生凋亡。在单轴受限压缩中测量时，外植体的平衡和动态刚度随损伤性负荷的严重程度而降低，尽管直到24MPa的峰值应力时这种趋势才显著。相比之下，在径向无受限压缩中测量的平衡和动态刚度分别在12MPa和7MPa的损伤性应力后显著降低。这些结果共同表明，损伤性压缩在7至12MPa范围内导致胶原纤维网络降解。与该假设一致，损伤性压缩导致组织肿胀呈剂量依赖性增加，在13MPa的峰值应力时显著。糖胺聚糖也以剂量依赖性方式从软骨中释放出来，在6至13MPa的峰值应力时显著。在20MPa的峰值应力时，亚硝酸盐水平显著高于对照组。这些数据共同表明，损伤性压缩可刺激细胞死亡以及基质的一系列生物力学和生化改变，并且可能刺激软骨细胞一氧化氮表达。有趣的是，软骨细胞程序性细胞死亡似乎发生在低于刺激软骨基质降解和生物力学变化所需的应力水平。因此，虽然软骨细胞凋亡可能是对组织损伤的最早反应之一，但目前尚不清楚这种初始细胞反应是否随后驱动软骨基质降解和组织生物力学特性的变化。
