抑制PTB单个基因可以将多种细胞直接转化为产生多巴胺的神经元

2020/7/28 11:04:43 本站原创 佚名 【字体:

廖联明   编译

几十年来,美国加州大学圣地亚哥医学院的傅教授和他的团队研究了一种名为PTB的蛋白,这种蛋白以结合RNA和调控细胞中基因的打开关闭而闻名。为了研究PTB蛋白的作用,科学家经常操纵细胞以减少PTB蛋白的量,然后观察其结果。

几年前,傅教授实验室的一位博士后研究员采用了一种方法,这种方法运用siRNA技术,使结缔组织细胞(即成纤维细胞)中的PTB基因沉默。但这是一个单调乏味的过程,需要一遍又一遍地重复进行。他对此感到厌倦,并说服傅教授,他们应该使用不同的技术来创造一种永久缺乏PTB的稳定细胞系。起初,博士后也抱怨过细胞系,因为这样细胞生长得太慢了。

但几周后,他注意到一些奇怪的事情--成纤维细胞所剩无几。取而代之的是,几乎整个培养皿都长满了神经元。

通过这种偶然的方式,研究小组发现,仅抑制或敲除一个基因,即编码PTB的基因,就可以将几种类型的小鼠细胞直接转化为神经元。

最近,傅教授和他实验室的另一位博士后研究员Hao Qian博士将这一发现向前推进了一大步,将这种方法应用于帕金森氏症和其他神经退行性疾病,日后这可能是一种新的方法。仅仅是抑制小鼠PTB的治疗方法,就可以将天然星形胶质细胞(大脑的星形支持细胞)转化为产生神经递质多巴胺的神经元。结果,小鼠的帕金森症状消失了。

 这项研究发表在2020624日的《自然》杂志上。

加州大学圣地亚哥医学院细胞和分子医学系特聘教授傅教授说:世界各地的研究人员在实验室尝试了许多种产生神经元的方法,比如:使用干细胞或其他方法,这样我们就可以更好地研究它们,以及用它们来代替神经退行性疾病中丢失的神经元。他还说到:我们能以一种相对简单的方式产生如此多的神经元,这一事实令人大吃一惊。

有几种不同的方法可以在小鼠身上模拟帕金森病。在这种情况下,研究人员应用了一种类似多巴胺的分子来损伤产生多巴胺的神经元。结果,小鼠失去了产生多巴胺的神经元,并出现了类似帕金森病的症状,如运动缺陷。

治疗的原理是这样的:研究人员研发了一种携带反义寡核苷酸序列的非传染性病毒-一种人造DNA片段,专门与编码PTBRNA结合,从而将其降解,阻止其转化为功能蛋白,并刺激神经元发育。

研究人员将PTB反义寡核苷酸治疗直接应用于小鼠的中脑,中脑负责调节运动控制和反馈行为,以及帕金森氏症患者大脑中通常失去产生多巴胺的神经元的部分。对照组小鼠接受空病毒或无关反义序列的模拟处理。

在接受治疗的小鼠中,一小部分星形胶质细胞转化为神经元,使神经元的数量增加了约30%。多巴胺水平恢复到与正常小鼠相当的水平。更重要的是,神经元的生长,并将它们的突触伸展到大脑的其他部分。对照组小鼠多巴胺水平无变化。

通过两种不同的肢体运动和反应评定,接受治疗的小鼠在接受一次治疗后的三个月内恢复正常,并在其余生中完全没有帕金森氏症的症状。相比之下,对照组小鼠没有任何改善。

该研究的研究者、加州大学圣地亚哥医学院神经科学特聘教授、医学博士William Mobley说:我对我所看到的感到震惊。这种治疗神经退行性变的全新策略给患者带来了希望,即使是那些晚期疾病的患者,也有可能得到帮助。

当然,老鼠不是人,他提醒说。研究小组使用的模型并不能完美地再现帕金森氏症的所有基本特征。但傅教授说,这项研究提供了治疗的理论证据

下一步,研究小组计划优化他们的方法,并在通过基因改变模拟帕金森氏症的小鼠模型中测试该方法。他们还为PTB反义寡核苷酸治疗申请了专利,以便在人体上进行试验。

傅教授说:我的梦想是通过临床试验,验证这种方法是治疗帕金森氏症的方法,但也包括许多其他神经元丢失的疾病,如阿尔茨海默氏症、亨廷顿氏病和中风。傅教授说:如果我们能以PTB为靶点来纠正大脑其他部分的缺失,来治疗遗传性大脑缺陷,会怎么样?

  我打算用我之后的职业生涯来解答这些问题。

 

Journal Reference:

 

Hao Qian, Xinjiang Kang, Jing Hu, Dongyang Zhang, Zhengyu Liang, Fan Meng, Xuan Zhang, Yuanchao Xue, Roy Maimon, Steven F. Dowdy, Neal K. Devaraj, Zhuan Zhou, William C. Mobley, Don W. Cleveland, Xiang-Dong Fu. Reversing a model of Parkinson’s disease with in situ converted nigral neurons. Nature, 2020; 582 (7813): 550 DOI: 10.1038/s41586-020-2388-4

 

 原文:

Inhibiting a single gene converts many cell types directly into dopamine-producing neurons

 

For decades, Fu and his team at University of California San Diego School of Medicine studied a protein called PTB, which is well known for binding RNA and influencing which genes are turned "on" or "off" in a cell. To study the role of a protein like PTB, scientists often manipulate cells to reduce the amount of that protein, and then watch to see what happens.

Several years ago, a postdoctoral researcher working in Fu's lab was taking that approach, using a technique called siRNA to silence the PTB gene in connective tissue cells known as fibroblasts. But it's a tedious process that needs to be performed over and over. He got tired of it and convinced Fu they should use a different technique to create a stable cell line that's permanently lacking PTB. At first, the postdoc complained about that too, because it made the cells grow so slowly.

 

But then he noticed something odd after a couple of weeks -- there were very few fibroblasts left. Almost the whole dish was instead filled with neurons.

 

In this serendipitous way, the team discovered that inhibiting or deleting just a single gene, the gene that encodes PTB, transforms several types of mouse cells directly into neurons.

 

More recently, Fu and Hao Qian, PhD, another postdoctoral researcher in his lab, took the finding a big step forward, applying it in what could one day be a new therapeutic approach for Parkinson's disease and other neurodegenerative diseases. Just a single treatment to inhibit PTB in mice converted native astrocytes, star-shaped support cells of the brain, into neurons that produce the neurotransmitter dopamine. As a result, the mice's Parkinson's disease symptoms disappeared.

 

The study is published June 24, 2020 in Nature.

 

"Researchers around the world have tried many ways to generate neurons in the lab, using stem cells and other means, so we can study them better, as well as to use them to replace lost neurons in neurodegenerative diseases," said Fu, who is a Distinguished Professor in the Department of Cellular and Molecular Medicine at UC San Diego School of Medicine. "The fact that we could produce so many neurons in such a relatively easy way came as a big surprise."

 

There are several different ways to mimic Parkinson's disease in mice. In this case, the researchers applied a dopamine look-a-like molecule to poison neurons that produce dopamine. As a result, the mice lose dopamine-producing neurons and develop symptoms similar to Parkinson's disease, such as movement deficiencies.

 

The treatment works like this: The researchers developed a noninfectious virus that carries an antisense oligonucleotide sequence -- an artificial piece of DNA designed to specifically bind the RNA coding for PTB, thus degrading it, preventing it from being translated into a functional protein and stimulating neuron development.

 

The researchers administered the PTB antisense oligonucleotide treatment directly to the mouse's midbrain, which is responsible for regulating motor control and reward behaviors, and the part of the brain that typically loses dopamine-producing neurons in Parkinson's disease. A control group of mice received mock treatment with an empty virus or an irrelevant antisense sequence.

 

In the treated mice, a small subset of astrocytes converted to neurons, increasing the number of neurons by approximately 30 percent. Dopamine levels were restored to a level comparable to that in normal mice. What's more, the neurons grew and sent their processes into other parts of brain. There was no change in the control mice.

 

By two different measures of limb movement and response, the treated mice returned to normal within three months after a single treatment, and remained completely free from symptoms of Parkinson's disease for the rest of their lives. In contrast, the control mice showed no improvement.

 

"I was stunned at what I saw," said study co-author William Mobley, MD, PhD, Distinguished Professor of Neurosciences at UC San Diego School of Medicine. "This whole new strategy for treating neurodegeneration gives hope that it may be possible to help even those with advanced disease."

 

Of course, mice aren't people, he cautioned. The model the team used doesn't perfectly recapitulate all essential features of Parkinson's disease. But the study provides a proof of concept, Fu said.

 

Next, the team plans to optimize their methods and test the approach in mouse models that mimic Parkinson's disease through genetic changes. They have also patented the PTB antisense oligonucleotide treatment in order to move forward toward testing in humans.

 

"It's my dream to see this through to clinical trials, to test this approach as a treatment for Parkinson's disease, but also many other diseases where neurons are lost, such as Alzheimer's and Huntington's diseases and stroke," Fu said. "And dreaming even bigger -- what if we could target PTB to correct defects in other parts of the brain, to treat things like inherited brain defects?

 

"I intend to spend the rest of my career answering these questions."

  

相关阅读: