State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
Mol Med Rep. 2013 Oct;8(4):1155-62. doi: 10.3892/mmr.2013.1654. Epub 2013 Aug 27.
To investigate the mechanism of cartilage degradation induced by overloading in the temporomandibular joint (TMJ), the effect of cyclic mechanical compressive stress on the activity of plasminogen activator (PA) and the expression of the predominant components of the PA system were analyzed in cultured mandibular condylar chondrocytes (MCCs) in rats. MCCs were exposed to cyclic mechanical compressive stress (2000, 4000 and 6000 µ strain) at 0.5 Hz by a four‑point bending system. The activity of PA was determined by hydrolysis of the chromogenic substrate H‑D-Val-Leu-Lys‑pNA (S‑2251). The mRNA and protein expression levels of urokinase‑type PA (uPA), tissue‑type PA (tPA), uPA receptor (uPAR) and PA inhibitor 1 (PAI‑1) were detected by qPCR and western blot analysis, respectively. Cyclic mechanical stress at 4000 and 6000 µ strain induced the expression of uPA, tPA and uPAR, and increased the activity of PA. Furthermore, cyclic mechanical stress at 6000 µ strain also inhibited the expression of PAI‑1. Analysis of pericellular proteolytic activity demonstrated that PA functioned as the active enzyme in excessive mechanical stress responsiveness (e.g., 4000 and 6000 µ strain) largely via uPAR, not PAI‑1. Cyclic mechanical stress at 2000 µ strain induced the expression of tPA and PAI‑1; however, it did not change the activity of PA. These results suggested that the mechanical induction of uPA, tPA and uPAR upregulated PA activity, which may provide a proteolytic environment of extracellular matrix components and subsequently contribute to the cartilage degradation in TMJ osteoarthritis.
为了研究颞下颌关节（TMJ）超负荷导致软骨降解的机制，本研究在大鼠下颌髁状突软骨细胞（MCC）中分析了循环机械压缩应力对纤溶酶原激活物（PA）活性和 PA 系统主要成分表达的影响。MCC 采用四点弯曲系统在 0.5 Hz 下承受循环机械压缩应力（2000、4000 和 6000 µ应变）。通过水解发色底物 H-D-Val-Leu-Lys-pNA（S-2251）测定 PA 活性。采用 qPCR 和 Western blot 分析分别检测尿激酶型 PA（uPA）、组织型 PA（tPA）、uPA 受体（uPAR）和 PA 抑制剂 1（PAI-1）的 mRNA 和蛋白表达水平。4000 和 6000 µ应变的循环机械应力诱导 uPA、tPA 和 uPAR 的表达，并增加 PA 的活性。此外，6000 µ应变的循环机械应力还抑制了 PAI-1 的表达。细胞周隙蛋白水解活性分析表明，PA 在过度机械应激反应中作为活性酶（例如 4000 和 6000 µ应变）主要通过 uPAR 而不是 PAI-1 发挥作用。2000 µ应变的循环机械应力诱导 tPA 和 PAI-1 的表达；然而，它并没有改变 PA 的活性。这些结果表明，uPA、tPA 和 uPAR 的机械诱导上调了 PA 活性，这可能为细胞外基质成分的蛋白水解环境提供了条件，随后导致 TMJ 骨关节炎中的软骨降解。
