Matsuda N, Yokoyama K, Takeshita S, Watanabe M
Laboratory of Cell and Stress Biology, JST at Nagasaki, Omura, Japan.
Arch Oral Biol. 1998 Dec;43(12):987-97. doi: 10.1016/s0003-9969(98)00079-x.
The periodontal ligament (PDL) contains precursor cells for osteoblasts and cementoblasts. It has been shown that epidermal growth factor (EGF) inhibits dexamethasone-induced differentiation and up-regulates EGF-receptor (EGF-R) expression, whereas EGF-R is down-regulated in the course of differentiation. Thus it was suggested that EGF and its receptors act as a negative regulator of osteoblastic differentiation in PDL cells. In order to investigate further this hypothesis, human PDL cells were now used to elucidate the role of EGF and EGF-R in their proliferation and differentiation under mechanical stress-loaded conditions in vitro, as the PDL regularly receives mechanical stress from occlusal forces. As a model of mechanical stress, a cyclic stretch of 9 or 18% elongation was applied to the cells with a Flexercell cell-strain unit system. Alkaline phosphatase activity and osteocalcin mRNA expression were significantly induced by loading cyclic stretch for more than 4 days, whereas stretch slightly inhibited cell proliferation. Visualization of the actin stress fibres of the cells by rhodamine phalloidin revealed that approx. 10% of the total number of cells had become aligned perpendicularly to the direction of the stretch. The effects of stretch on alkaline phosphatase activity and cell proliferation were totally abolished by the presence of 10 ng/ml EGF. Western blotting of EGF-R protein demonstrated that stretch-induced differentiation accompanied the decreased expression of EGF-R protein in the cells. However, the amount of tyrosine-phosphorylated EGF-R upon EGF stimulation was restored to the control level in stretched cells. These results suggest that the EGF/EGF-R system acts as a negative regulator of differentiation of PDL cells regardless of the type of differentiation stimuli. Also, interaction between mechanical stress and the EGF/EGF-R system may participate in the osteoblastic differentiation of PDL cells and thereby regulate the source of cementoblasts and osteoblasts.
牙周韧带（PDL）含有成骨细胞和牙骨质细胞的前体细胞。研究表明，表皮生长因子（EGF）可抑制地塞米松诱导的分化并上调表皮生长因子受体（EGF-R）的表达，而EGF-R在分化过程中表达下调。因此，有人提出EGF及其受体作为PDL细胞中成骨细胞分化的负调节因子。为了进一步研究这一假设，由于PDL经常受到咬合力的机械应力，现在使用人PDL细胞来阐明EGF和EGF-R在体外机械应力加载条件下其增殖和分化中的作用。作为机械应力的模型，使用Flexercell细胞拉伸装置系统对细胞施加9%或18%伸长的循环拉伸。加载循环拉伸超过4天后，碱性磷酸酶活性和骨钙素mRNA表达明显诱导，而拉伸轻微抑制细胞增殖。用罗丹明鬼笔环肽对细胞的肌动蛋白应力纤维进行可视化显示，约10%的细胞总数已垂直于拉伸方向排列。10 ng/ml EGF的存在完全消除了拉伸对碱性磷酸酶活性和细胞增殖的影响。EGF-R蛋白的蛋白质印迹表明，拉伸诱导的分化伴随着细胞中EGF-R蛋白表达的降低。然而，在拉伸细胞中，EGF刺激后酪氨酸磷酸化的EGF-R量恢复到对照水平。这些结果表明，无论分化刺激的类型如何，EGF/EGF-R系统都作为PDL细胞分化的负调节因子。此外，机械应力与EGF/EGF-R系统之间的相互作用可能参与PDL细胞的成骨细胞分化，从而调节牙骨质细胞和成骨细胞的来源。
