皮肤细胞至肝细胞快捷方式

StephenW

The Scientist


Skin-to-Liver Cell Shortcut

Researchers use an adapted reprogramming technique to generate hepatocytes for the repopulation of an injured mouse liver.

By Abby Olena | February 23, 2014



Human fibroblast-derived hepatocytesMILAD REZVANI
Scientists have differentiated human induced pluripotent stem cells (iPSCs) into hepatocytes in a dish, but faced challenges using these cells therapeutically. Most iPSC-derived liver cells do not adequately proliferate after transplantation or function exactly like adult hepatocytes do. Now, researchers from the University of California, San Francisco (UCSF), have differentiated human hepatocytes with a modified technique that bypasses pluripotency, and used these cells to repopulate a mouse liver. Their work was published in Nature today (February 23).

“I really like this paper. It’s a step forward in the field,” said Alejandro Soto-Gutiérrez, an assistant professor of pathology from the University of Pittsburgh, who was not involved in the work. “The concept is reprogramming, but with a shortcut, which is really cool.”

The team isolated human fibroblasts and transduced them with retroviruses expressing three stemness factors: OCT4, SOX2, and KLF4. The researchers grew the transduced cells in the presence of growth factors and small molecules to encourage reprogramming into endoderm. “We divert the cells on their path to pluripotency,” explained coauthor Holger Willenbring, an associate professor of surgery at UCSF. “We still take advantage of what is intrinsic to reprogramming, that the cells are becoming very plastic; they’ve become flexible in what kind of cell type they can be directed towards.”

The authors called these cells induced multipotent progenitor cells (iMPCs), which they later differentiated into endodermal progenitor cells (iMPC-EPCs). They used small molecules and growth factors to increase iMPC-EPC colony size while maintaining the cells in an endodermal state. The researchers then cultured the cells with factors and small molecules known to promote hepatocyte differentiation, generating iMPC-Hepatocytes (Heps). Upon transplantation into a mouse model of liver injury, the iMPC-Hep population continued to proliferate at least nine months after transplantation. And the cells matured, displaying a gene expression profile similar to that of typical adult hepatocytes. Transplantation of iMPC-Heps also increased the survival of a mouse model of chronic liver failure about as efficiently as transplantation of adult hepatocytes did.

“It is a breakthrough for us because it’s the first time that we’ve seen a cell that can actually repopulate a mouse’s liver,” said Willenbring. He speculated that the cells generated using this reprogramming shortcut may be better able to repopulate the liver because starting with an iMPC—rather than an iPSC—eliminates some steps along the path to generating hepatocytes. The power of this model is that the cells can functionally mature, while still retaining the ability to proliferate, which are both prerequisites for therapeutic applications, he added.

But before the technique enters the clinic, there is still work to be done. “The key to all of this is trying to generate cells that are identical to adult liver cells,” said Stephen Duncan, a professor of cell biology at Medical College of Wisconsin, who was not involved in the study. “You really need these cells to take on all of the functions of a normal liver cell.” Duncan explained that liver cells taken directly from a human adult might be able to repopulate the liver in this same mouse model at levels close to 90 percent.

Willenbring and his colleagues saw repopulation levels of 2 percent by iMPC-Heps, which is still better than the 0.05 percent repopulation typically accomplished by hepatocytes derived from iPSCs or embryonic stem cells. “As good as this is, the field will need greater levels of expansion,” said Ken Zaret of the Institute for Regenerative Medicine at the University of Pennsylvania, who did not participate in the work. “But the question is: What is limiting the proliferative capacity of the cells?”

Zaret explained that it is not yet clear whether some aspect of how the cells were programmed that differed from how they normally develop could have an impact on how well the population expands after transplantation. “There still is a ways to go,” he said, “but [the authors] were able to show much better long term repopulation with human cells in the mouse model than other groups have.”

S. Zhu et al., “Mouse liver repopulation with hepatocytes generated from human fibroblasts,” Nature, doi:10.1038/nature13020, 2014.

StephenW

科学家


皮肤对肝细胞快捷方式

研究人员使用一种适应重编程技术来生成肝细胞的一个损伤小鼠肝脏的再增殖。

由艾比奥莱娜| 2014年2月23日



人成纤维细胞衍生的hepatocytesMILAD REZVANI
科学家们已经分化的人类诱导多能干细胞（ iPS细胞），成菜肝细胞，但治疗上使用这些细胞所面临的挑战。大多数源自iPSC的肝细胞不充分移植或功能完全一样的成人肝细胞后做增殖。现在，研究人员从美国加州大学旧金山分校（UCSF ） ，已分化的人类肝细胞用改良的技术，绕过多能性，并用这些细胞重新填充小鼠肝脏。他们今天的工作发表在自然（ 2月23日） 。

“我真的很喜欢这个文章。这是向前迈进了一步领域， “亚历杭德罗·索托 - 古铁雷斯，病理来自美国匹兹堡大学的助理教授，没有参与的工作谁说。 “这个概念是重新编程，但有一个捷径，这是真的很酷。 ”

该研究小组分离出人类成纤维细胞和转导他们逆转录病毒表达3干性因素： OCT4 ， SOX2 ， KLF4和。研究人员在生长因子和小分子，以鼓励重新编程成内胚层的存在下生长的转导细胞。 “我们转移他们的路径，多能性细胞，解释说：”合著者霍尔格Willenbring ，手术在加州大学旧金山分校的副教授。 “我们还是好好利用一下是内在的重新编程，使细胞变得非常的塑料，他们已经在什么样的细胞类型，他们可以对定向松动。 ”

作者称，这些细胞诱导多能祖细胞（ iMPCs ） ，他们后来分化为内胚层祖细胞（ IMPC - EPCs）的。它们用于小分子和生长因子增加IMPC -EPC菌落大小，同时保持细胞的内胚层的状态。然后，研究人员培养的细胞被称为促进肝细胞分化因子和小分子，生成IMPC -肝细胞（ HEPS ） 。一旦移植到肝损伤的小鼠模型中， IMPC -喉癌人口继续移植后增殖至少9个月。将细胞成熟，显示类似于典型的成年肝细胞的基因表达图谱。 IMPC - HEPS移植也增加了慢性肝功能衰竭的小鼠模型中的存活有关的效率，因为成年肝细胞的移植一样。

“这是一个突破，为我们，因为这是第一次，我们已经看到，实际上可以重新填充一个老鼠的肝细胞， ” Willenbring说。他推测，使用这个快捷方式重新编程产生的细胞可能能够更好地重新填充的肝脏，因为开始与IMPC ，而不是IPSC的，消除了沿路径的一些步骤来生成肝细胞。这种模式的强大之处在于细胞可以在功能成熟，同时仍保留增殖的能力，这两者都是先决条件治疗应用，他补充说。

但该技术进入临床之前，还有很多工作要做。 “的关键，所有这一切都是试图生成细胞是相同的成人肝细胞， ”斯蒂芬说邓肯，细胞生物学威斯康星医学院的教授，没有参与这项研究说谁。 “你真的需要这些细胞承担所有的正常肝细胞的功能。 ”邓肯解释说，直接从一个人成年采取肝细胞也许能以接近90 ％的水平，以重新填充肝脏在这同一个小鼠模型。

Willenbring和他的同事们看到了2％的再增殖水平由IMPC - HEPS ，这仍比通常通过从iPS细胞或胚胎干细胞来源的肝细胞的0.05 ％的再增殖更好。 “作为好，因为这是，该领域将扩展需要更高水平”的再生医学研究所在宾夕法尼亚大学的，谁没有参加工作的Ken Zaret说。 “但问题是：是什么限制了细胞的增殖能力？ ”

Zaret解释说，目前尚不清楚如何将细胞编程，从他们通常如何发展差异的某些方面是否能对人口移植后有多好し影响。 “目前仍然是很长的路要走， ”他说，“但[作者]能够显示更好的长期​​复育与人体细胞在小鼠模型比其他群体有。 ”

，S. Zhu等人， “鼠标肝复育与人成纤维细胞产生的肝细胞， ”自然， DOI ： 10.1038/nature13020 ， 2014年。