中文摘要：

目的：：观察流体静压力作用下Rac1信号通路对大鼠骨髓间充质干细胞（ BMSCs）增殖、细胞骨架改建及成软骨向分化的影响。方法：体外分离培养大鼠BMSCs,并随机分为对照组、Rac1激动剂组、Rac1拮抗剂组、压力组、Rac1激动剂＋压力组、Rac1拮抗剂＋压力组；其中各压力组均置于细胞加载装置中施加90 kPa流体静压力,每天1 h,其他各组常规条件下进行培养。分别对各组细胞处理后,采用流式细胞仪检测细胞周期、共聚焦显微镜观察细胞骨架、Real-time PCR检测成软骨标志基因（ Sox9、Aggrecan、Col-ⅡmRNA）的表达水平。结果：流体静压力下BMSCs中DNA合成期的细胞比例及细胞增殖指数显著高于对照组（P≤0.05）,且该过程依赖Rac1活性；而Rac1在流体静压力导致的细胞骨架光密度值升高（P≤0.05）的过程中呈负调控作用；流体静压力可促BMSCs中成软骨标志基因的表达量显著升高（P≤0.05）,该过程依赖Rac1活性。结论：Rac1在流体静压力导致的细胞周期启动、骨架装配及成软骨分化的过程中均具有调控作用。

英文摘要：

AIM：To study the role of Racl signal pathway in chondrogenic transduction of bone marrow mes-enchymal stem cells （ BMSCs） under hydrostatic pressure. METHODS： BMSCs were isolated and cultured in vitro. The cells were then randomly divided into control group, Rac1agonist group, Rac1antagonist group, hydrostatic pres-sure group, hydrostatic pressure plus Aac1 agonist group and pressure plus Aac1 antagonist group. Cell cycle was ex-amined by flow-cytometry and cytoskeleton was observed by confocal microscopy. mRNA expression of Sox9, Aggrecan and Col-Ⅱ were detected by real-time PCR. RESULTS： Under hydrostatic pressure, S-phase fraction and the cell proliferation index of BMSCs were significantly higher than those in the control group （P≤0. 05） in a Rac1-dependent way. However, activation of the Rac1 pathway blocked F-actin cytoskeleton assembly which induced by hydrostatic pressure. The significant increase of chondrogenic marker mRNA expression in chondrogenic differentiation induced by hydrostatic pressure （P≤0. 05） was dependent on the activity of Rac1. CONCLUSION：Rac1 plays an important role in the start of the BMSCs cell cycle, cytoskeleton assembly and chondrogenic differentiation under mechanical pressure.