第三型乙型轉化生長因子調控肺泡細胞發育機制之探討

Abstract

藉由先前發現的無血清培養原代培養系統，可以取得一群能形成細胞群聚、自我增生且具有分化成肺泡第一型表皮細胞能力的肺部前驅幹細胞 (mPSCs)，肺部前驅幹細胞會表現Oct-4、SSEA-1以及Sca-1這些代表細胞具有多能性之轉錄因子，同時還會表現柯薩奇病毒和腺病毒受體(CAR)，因此可藉由流式細胞儀將CAR陽性之細胞分選、純化。肺部前驅幹細胞在分化系統的培養環境下，最明顯的變化為肺泡第一型表皮細胞表面標誌的表現以及細胞型態的變化。但是分化的機轉能然未知。透過第三型乙型轉化生長因子(TGF-β3)基因剃除鼠的動物模型，觀察到發育不完全的肺泡、肺部前驅幹細胞不正常堆疊在支氣管壁上以及鮮少肺泡第一型表皮細胞表現。藉由基因剃除鼠模型的線索，我們利用肺部前驅幹細胞分化成肺泡第一型表皮細胞的分化模型，來探討肺部前驅幹細胞分化的機轉。實驗中觀察到，肺部前驅幹細胞在分化的過程中會分泌第三型乙型轉化生長因子，並且活化下游的分子Smad3。除此之外，轉錄因子Snail1的表現量會增加，並調控cdc42、rac-1以及細胞骨架相關蛋白的表現量，進而調控細胞型態之變化。因此推測第三型乙型轉化生長因子會驅動肺部前驅幹細胞的分化。

In previous study which published in 2006, reported a selective serum-free culture system for primary neonatal mice pulmonary cells. An special population cells, mPSCs, could be enriched through the culture system, which expresses the markers of stem cells, such as octamer-binding transcription factor-4 (Oct-4), stage specific embryonic antigen-1 (SSEA-1) and stem cell antigen-1 (Sca-1). The mPSCs are also coxsackievirus and adenovirus receptor (CAR) - positive. Therefore, the mPSCs could be purified by fluorescence-activated cell sorting (FACS). During the differentiation process, the surface marker of type-I pneumocyte and the morphology transforming were changed dramatically. But the mechanism was still unknown. Meanwhile, the transforming growth factor-beta 3 (TGF-β3) knockout mice model, the retard developing lung, the abnormal accumulation of CAR-positive cells and poor development of alveolar type-I pneumocytes, provided the clue of differentiation. Therefore, we used the model of mPSCs differentiation into alveolar type-I pneumocyte to study the biological function of TGF-β3 in the developing lung. The secreted TGF-β3 in the culture system was increased during differentiation and the downstream signaling molecular, Smad3, was activated. Further, the small G protein, cdc42 and rac-1, mediate the cytoskeleton remodeling via snail1 pathway. We supposed that the differentiation process of mPSCs to alveolar type-I pneumocytes was initiated by TGF-β3.