中間絲巢蛋白於神經膠瘤細胞與星型膠細胞的表現調控

Abstract

中間絲巢蛋白是一分子量240 kDa的中間絲蛋白成員，主要表現於神經與肌肉的幹細胞中，並且被廣泛的使用為這些細胞的分子標記。關於巢蛋白的相關研究主要集中於中樞神經系統中，目前已知巢蛋白只會短暫的表現神經發育初期，隨著神經發育的過程其表現量會逐漸遞減，當神經發育完成時，巢蛋白的表現就會終止，並且在成熟的神經元以及神經膠細胞會分別被神經絲蛋白與神經膠質微纖維酸性蛋白質所取代，但是在神經系統受傷的初期，星型膠細胞會受到刺激而重新表現巢蛋白，這些重新表現巢蛋白的稱之為反應型星型膠細胞。儘管目前有許多研究專注於反應型星型膠細胞的細胞特性，但是很少有研究在探討究竟是什麼分子透過何種機制影響星型膠細胞的巢蛋白重新表現，而這也是本篇論文的研究主題。第二型纖維母細胞生長因子是發育時期重要的細胞激素，其功能在於促進神經前驅細胞、神經膠前驅細胞以及平滑肌細胞的增生與發育，而這些細胞也正好是會表現巢蛋白的細胞。以神經膠瘤細胞作為模組的實驗中証實第二型纖維母細胞生長因子確為刺激巢蛋白表現的重要因子，並且是經由核酸與蛋白質重新合成所產生的。更進一步的訊息調控路徑檢視發現，此第二型纖維母細胞生長因子誘發巢蛋白的表現機制是透過纖維母細胞生長因子受體活化下游Ras-Raf-ERK路徑，並且牽涉到轉錄因子Sp1的活性，而在初級培養的星型膠細胞中也是此機制來調控巢蛋白之表現。本篇研究對反應型星型膠細胞之巢蛋白調控提供了新的見解，並且能作為未來研究巢蛋白在神經膠疤生成的功能之基石。

Nestin is a 240-kDa intermediate filament (IF) protein expressed mainly in neural and myogenic stem cells. The expression of nestin has primarily been studied in the central nervous system (CNS), where it is expressed transiently in CNS stem cells. During the development of the CNS, neural progenitor cells (NPCs) in the neural tube differentiate into mature neurons and glial cells, while nestin expression is down-regulated and replaced by the expression of neurofilament and glial fibrillary acidic protein (GFAP), respectively. During the early stages of CNS injury, nestin expression reappears in the injury-induced reactive astrocytes adjacent to wound regions. Although a substantial number of studies have focused on the cellular characteristics of reactive astrocytes, little is known about the factors that induce and regulate the re-expression of nestin. Fibroblast growth factor-2 (FGF-2) is an effective mitogen and is expressed in the developing nervous tissue. It stimulates the proliferation and differentiation of NPCs, glial precursor cells, and smooth muscle cells, where nestin is expressed. To assess whether FGF-2 is a potent factor that induces the re-expression of nestin, C6 glioma cells were used. The results showed that nestin expression was up-regulated by FGF-2 via de novo RNA and protein synthesis. Further signaling analyses also revealed that the FGF-2-induced nestin re-expression is mediated through the activation of the FGFR-MAPK-ERK signaling axis and the downstream transcriptional factor Sp1 in both C6 glioma cells and primary astrocytes. These findings provide new insights into the regulation of nestin in reactive astrocytes and enable further studies in understanding the function of nestin in glial scar formation.