(肝細胞) 中科院: 多能幹細胞 多次相互轉換 新突破epithelial–mesenchymal–epithelial

與陰陽理念重合 我國科學家揭示幹細胞分化新機制 北京新浪網 (2017-05-03 21:35) 新華社北京5月3日電（記者 董瑞豐）記者3日從中國科學院獲悉，中科院廣州生物醫藥與健康研究院裴端卿和舒曉東團隊關於調控人胚胎幹細胞向肝細胞分化的機理研究取得突破，該成果為解決幹細胞在再生醫學的運用打開一扇新門窗。具有特定功能的細胞如神經元、肝細胞及胰腺β細胞等，是細胞移植及體外人類器官構建的基礎。如何大量獲得這些細胞，成為當前再生醫學研究的重要課題之一。裴端卿介紹，成熟肝臟細胞是典型的上皮細胞，可由其同屬上皮細胞的人胚胎幹細胞通過體外定向分化而獲得，在研究中，科研人員發現這兩種上皮細胞之間的命運轉換需要經過一個間充質狀態的中間階段。裴端卿說，在胚胎幹細胞分化為定型內胚層階段發生了一個名為EMT的過程，即上皮細胞向間充質細胞轉換；而隨後進一步的肝系分化成熟過程伴隨著一個名為MET的過程，即間充質細胞向上皮細胞轉換。這樣的多次相互轉換機理，與中國傳統陰陽太極理念較一致。據了解，此次研究突破相當於做了一道證明題：證明從幹細胞到肝細胞的分化，存在這個EMT/MET的過程。未來，科研人員有望通過對EMT/MET過程的分析和調控，高效、同步地獲得特定功能的細胞。同時，降低分化程度不足導致的潛在安全隱患，如成瘤性等，從而滿足再生醫學研究對細胞的需求。上述研究成果已由國際學術期刊《自然·通訊》在線發表。

A sequential EMT-MET mechanism drives the differentiation of human embryonic stem cells towards hepatocytes. Nature Communications 8, Article number: 15166 (2017) Abstract Reprogramming has been shown to involve EMT–MET; however, its role in cell differentiation is unclear. We report here that in vitro differentiation of hESCs to hepatic lineage undergoes a sequential EMT–MET with an obligatory intermediate mesenchymal phase. Gene expression analysis reveals that Activin A-induced formation of definitive endoderm (DE) accompanies a synchronous EMT mediated by autocrine TGFβ signalling followed by a MET process. Pharmacological inhibition of TGFβ signalling blocks the EMT as well as DE formation. We then identify SNAI1 as the key EMT transcriptional factor required for the specification of DE. Genetic ablation of SNAI1 in hESCs does not affect the maintenance of pluripotency or neural differentiation, but completely disrupts the formation of DE. These results reveal a critical mesenchymal phase during the acquisition of DE, highlighting a role for sequential EMT–METs in both differentiation and reprogramming. Introduction Reprogramming of somatic cells into pluripotent ones with defined factors not only provides a new way to generate functional cells for regenerative medicine, but also establishes a new paradigm for cell fate decisions. For the latter, a cell at a terminally differentiated state can be restored back to pluripotency under well-defined conditions fully observable through molecular and cellular tools. Indeed, the reprogramming process has been analysed in great detail to reveal novel insights into the mechanism of cell fate changes. Of particular interest is the acquisition of epithelial characteristics from mesenchymal mouse embryonic fibroblasts (MEFs) commonly employed as starting cells in reprogramming experiments. Termed the mesenchymal to epithelial transition (MET), we and others have described the MET as marking the earliest cellular change upon the simultaneous transduction of reprogramming factors POU5F1 (OCT4), SOX2, KLF4 and MYC or OSKM into MEFs. However, when delivered sequentially as OK+M+S, they initiate a sequential epithelial to mesenchymal transition (EMT)-MET process that drives reprogramming more efficiently than the simultaneous approach, suggesting that the switching between mesenchymal and epithelial fates underlies the reprogramming process, that is, the acquisition of pluripotency. We then speculated that such a sequential EMT–MET process might underlie cell fate decisions in other situations such as differentiation, generally viewed as the reversal of reprogramming with the loss of pluripotency. Herein, we report that a similar epithelial–mesenchymal–epithelial transition drives the differentiation of human embryonic stem cells (hESCs) towards hepatocytes. A synchronous EMT occurs during the formation of DE and DE cells are in a typical mesenchymal-like status, while further differentiation of DE to hepatocyte-like cells is accompanied by a MET. We reveal that the intermediate mesenchymal DE cells is induced by an autocrine TGFβ signalling and mediated by SNAI1. On the other hand, the neural differentiation of hESCs is not dependent on TGFβ signalling or SNAI1. Thus, EMT-related transcriptional factor such as SNAI1 participates in lineage-specific cell fate changes.