STRETCH-INDUCED CELL MORPHOGENEISI : MOLECULAR MECHANISM OF DIRECTIONSENSITIVITY AND POLARITY FORMATION

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，培养的内皮细胞不表现出这样的形状和排列，已知的是，对细胞的机械应力，如剪切应力和周期性的圆周拉伸，脉动血流足以诱导内皮细胞的这种形态。也有人认为细胞骨架和粘附分子参与了这种形态的形成。该项目的最终目标是阐明拉伸诱导内皮细胞形态发生中的信号级联，并了解细胞中二维极性形成的分子机制。利用Ca^<2+>成像、膜片钳、生化和分子生物学技术，我们可以确定拉伸诱导形态发生的主要信号级联：<单轴周期性拉伸* SA通道激活*细胞内C_amobilization* calcinyrin激活*酪氨酸激酶src激活*黏附蛋白酪氨酸磷酸化*应力纤维和强制黏附的重组*形态改变>。然而，由于拉伸激活的Ca^<2+>的增加在空间上是均匀的，这可能不是细胞极性的原因。另一方面，酪氨酸磷酸化的蛋白质倾向于分布在细胞的细长部分。因此，可能有另一种信号机制从粘附斑块（整合素）流向细胞内空间，直接施加机械力。该机制可能与前一种信号机制一起，通过调控局灶黏附蛋白的酪氨酸磷酸化来促进细胞极性的形成。我们项目的下一步应该是证明这个假设。

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 a shape and alignment, It is known that mechanical stresses onto the cells, like shear stress and periodic circumferential stretch, by pulsative blood flow are enough to induce such a morphology in endothelial cells. It has been also suggested that cytoskeletons and adhesion molecules contribute to this morphogenesis. The altimate goal of this project is to elucidate the signaling cascade in the stretchOinduced morphogenesis in cultured endothelial cells and to understand the molecular mechanism underlying the formation of two dimensional polarity in the cell. Using Ca^<2+>imaging, patch clamp, biochemical and molecular biological techniques, we could identify the major signaling cascade in the stretch-induced morphogenesis as follows : <uniaxial periodic stretch* activation of SA channels* intracellular C_amobilization* activation of calcinyrin* activation of tyrosine kinase, src, * tyrosine phosphorylation of adhesion proteins* reorganization of stress fibers and forcal adhesion* morphological change>. However, as the stretch activated Ca^<2+> increase was spatially uniform, this may not be the cause of the cell polarity. On the other hand, tyrosine phosphorylated proteins favored to distribute at the elongating portion of the cell. Hence, it is possible that there is another signaling mechanism flowing from adhesion plaque (integrin), upon which mechanical forces are directly imposed, to intracellular space. This mechanism may along with the former signaling mechanism contribute to the formation of the cell polarity through the regulation of tyrosine phosphorylation of focal adhesion proteins. Next step of our project should be to prove this hypothesis.