基材之物理性質於in vitro與in vivo中對調控細胞基本功能之影響甚鉅。先前實驗室發現上皮細胞培養於柔軟之collagen gel上明顯提升細胞凋亡的比率，然而於轉型細胞與纖維母細胞則無此一現象。我們認為細胞內部力學之分佈與方向，對基材硬度反應之細胞延展與存活扮演重要角色。為了印證此假說，我們將不同細胞株培養於不同軟硬度之polyacrylamide gel上，發現LLC-PK1 (上皮細胞)，HeLa (轉型細胞) 和NIH-3T3 (纖維母細胞)於不同軟硬度上，分別展現細胞特異性之延展能力與各自對基材硬度之適應範圍。在LLC-PK1中，MLC-p分布於cortical actin之中央，然而在NIH-3T3與HeLa中，MLC-p則是均勻的散佈於橫跨細胞兩端之stress fibers。為了測量奈米牛頓 (nN) 等級下之細胞內部收縮力，實驗室導入了一微米柱陣列感測器系統(microfabricated post-array-detector, mPAD)。NIH-3T3與HeLa皆展現出平行於長軸之雙方向力學分佈與較低之平均收縮力，但是LLC-PK1細胞則顯示了較高的平均收縮力但卻無特定之方向。更進一步，TGF- 誘發型態上被拉長的LLC-PK1以近乎NIH-3T3之方式，重新安排細胞內部力學分佈與方向。這些結果顯示，上皮細胞與轉型細胞或纖維母細胞支不同之處，在於其等向性之力學分佈與產生較高之收縮力。在軟性基材上，上皮細胞內等向性分佈之骨架不利於維持有效之力學結構，導致細胞於基材上延展能力降低，進而造成細胞凋亡發生。

Substrate mechanical properties play important role for the regulation of cellular function in vitro and in vivo. Previous study in our lab demonstrated that soft collagen gel induced apoptosis in epithelial cell but not in fibroblast and transformed cells. We hypothesized that the force orientation and distribution in response to substratum stiffness played important role for cell spreading and survival. In order to test the hypothesis, we cultured different cells on polyacrylamide gel with different rigidity modulus. We found that LLC-PKI (epithelia), HeLa (transformed cell) and NIH-3T3 (fibroblast) showed cell type-specific spreading ability and adaption to substratum stiffness. Immunofluorescent studies that myosin light chain phosphorylation (MLCp) was located in the center of cortical actin in LLC-PK1 cells, whereas MLCp was evenly located on stress fibers in NIH-3T3 and HeLa cells. To measure intracellular traction force in nano-Newton scale, we established micro-fabricated post array detector (mPAD). NIH-3T3 and HeLa demonstrated bi-directional force distribution with lower average force, whereas LLC-PK1 displayed higher average force without particular direction. In addition, TGF- induced elongated LLC-PK1 cells rearranged their traction forces similarly to that of NIH-3T3 cells. These findings indicate that epithelial cells orientate intracellular force in isotropy and generate higher intracellular tension than fibroblast or transformed cells. The isotropic cytoskeleton distribution in epithelial cells could be disadvantageous for maintaining mechanical force on soft substrate.

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