表皮生長因子誘導血管平滑肌細胞巢蛋白之表現

Abstract

動脈硬化發生時，於動脈新內層 (neo-intima)有新內層平滑肌細胞增生，而新內層的平滑肌細胞不同正常成熟血管平滑肌細胞，會失去收縮能力，並有了增生、移動能力和分泌大量胞外基質，此血管新內層之平滑肌型態的特異是一個重要的課題。巢蛋白是一類中間絲蛋白，專一表現在肌肉和神經的幹細胞。而本研究利用大鼠主動脈血管平滑肌細胞當做實驗材料，並以免疫螢光染色方法發現有分泌型特徵的血管平滑肌細胞會表現巢蛋白；而將細胞培養於去除血清之培養液中，血管平滑肌細胞會分化為具有收縮型平滑肌細胞的特徵，然而巢蛋白的表現明顯減弱。這個結果也暗示了巢蛋白是分泌型血管平滑肌細胞的標誌蛋白。為了要找出調節巢蛋白表現的胞外因子，利用免疫螢光染色對細胞培養的血管平滑肌細胞來做研究，結果顯示，在細胞培養中，表皮生長因子可誘導巢蛋白表現。進一步做訊息傳遞分析，顯示出表皮生長因子主要藉由活化Ras-Raf-ERK訊息路徑來誘導巢蛋白的再表現。而這是第一個研究指出在血管平滑肌細胞中，巢蛋白可藉由胞外的生長因子刺激調節。

During the progression of atherosclerosis, vascular smooth muscle cells (VSMCs) are observed in the arterial neo-intima where they proliferate. The neo-intimal smooth muscle cells are different from the mature VSMCs in that they lack of the contraction abilities, but display the characteristics of proliferation, migration, as well as the ability to secrete a large amount of extra-cellular matrix. The formation of this special phenotype of VSMCs in the neo-intima layer is a key event during the atherosclerosis. Nestin is a intermediate filament (IF) protein specifically expressed in myogenic and neural stem cells. In this study, we showed that nestin is expressed in primary cultures of rat aortic VSMCs that represent the synthetic phenotype and its expression diminished in those cells upon differentiation to the contractile phenotype after serum deprivation.These results suggested that nestin is a marker of synthetic VSMCs. To identify the extracellular factors that regulate nestin expression, immunofluorescence microscopy was used. Results showed that epidermal growth factor (EGF) induced nestin expression in serum-deprived primary cultures of VSMCs. Furthermore, signaling analyses revealed that the EGF-induced nestin re-expression is mediated through the activation of the Ras-Raf-ERK signaling axis. This is the first report showing that nestin expression is regulated by the extracellular growth factors in VSMCs.