MOLECULAR MECHANISM OF MORPHOLOGICAL RESPONSE TO MECHANICAL STIMULI IN ENDOTHELIAL CELLS

内皮细胞呈纺锤形，纵方向与血管平行。这种特殊的形状和排列对于防止细胞被血流剥离是非常重要的。然而，培养的内皮细胞不显示这种形状和排列。那么内皮细胞产生这种适应性特征的机制是什么呢？众所周知，脉动血流对细胞施加的机械应力，如剪切应力和周期性的周向拉伸，足以在内皮细胞中诱导这种形态反应。本项目的最终目标是了解内皮细胞机械诱导形态反应的潜在分子机制。特别是我们的目标是证明我们的分子级联假设：周期性拉伸*机械敏感通道的激活*细胞内钙动员*应力纤维和力粘附的重组*形态变化。在第一年，我们集中研究了级联的早期部分，发现细胞内钙离子的动员是由钙渗透的机械敏感离子通道的激活所介导的，这是形态学响应的必要条件。第二年，我们分析了钙动员后细胞形态变化与细胞骨架重组的关系。应力纤维（f -肌动蛋白束）的重组过程可分为三个步骤：先前存在的f -肌动蛋白纤维的聚解*与拉伸轴垂直的新肌动蛋白细丝的形成*肌动蛋白纤维的延伸和捆绑。细胞的形态变化伴随着细胞骨架重组的最后一步，这需要钙的动员。事实上，在这一步骤中发生了局灶黏附蛋白的钙依赖性酪氨酸磷酸化。当这种磷酸化被药物抑制时，细胞骨架重组和形态学反应都被完全抑制。激酶和GTP结合蛋白在分子级联中的作用仍有待解决。少

Endothelial cells exhibit spindle like shape aligning their longtude parallel with vessel running. This peculiar shape and alignment is isgnificant to prevent the cells from being pealed off by blood flow. However, cultured endothelial cells do not show such shape and alignment. Then what mechanisms do bring about such an adaptive feature in endothelial cells? It is known that mechanical stresses onto the cells, like shear stress and periodic circumferential stetch, by pulsative blood flow are enough to induce such a morphological response in endothelial cells. The altimate goal of this project is to know the inderlying molecular mechanism in mechanically induced morphological response of endothlial cells. Partcularly we aimed to prove our hypothesis on the molecular cascade : periodic stretch*activation of mechanosensitive channels*intracellular Ca-mobilization*reorganization of stress fibers and forcal adhesion*morphological change.In the first year we concentrated on the early part … More of the cascade, and found that intacellular Ca-mobilization mediated by the activation of Ca-permeable mechanosensitive ion channels is necessary for the morphological response. In the second year we analyzed the relationship between the cell morphological change and the cytoskeletal reoganization following Ca-mobilization. The reoganization process of stress fibers (bundle of F-actins) could be disected into three steps : depolimerization of pre-exisiting F-actin fibers*formation of new actin filaments perpendicuraly to stretch axis*elongation and bundling of actin fibers. Morphological change of the cells proceeded concomitant with the last step of cytoskeletal reoganization that requires Ca-mobilization. In fact Ca-dependent tyrosine phosphorylation of focal adhesion proteins occured during this step. When this phosphorylation was inhibited by drugs, both the cytoskeletal reoganization and the morphological response was completely inhibited. Involvement of kinases and GTP binding proteins in the molecular cascade remains to be solved. Less