Research by a Stanford University team of scientists has shed new light on how and why neural stem cells (NSCs), the cells behind the generation of new neurons in the adult brain, become less active as brains age. Anne Brunet, PhD, professor of genetics, and her team developed in vitro and in vivo high-throughput CRISPR-Cas9 screening platforms and carried out a genome-wide search for genes that, when knocked out, increase the activation of neural stem cells in old mice, but not young animals.

。遗传学教授Anne Brunet博士及其团队开发了体外和体内高通量CRISPR-Cas9筛选平台，并进行了全基因组搜索，寻找基因敲除后会增加神经干细胞活化的基因。老鼠，但不是年轻动物。

Of the top gene knockouts identified, the team found that knocking out Slc2a4—which encodes the insulin-dependent GLUT4 glucose transporter—notably improved the function of old NSCs..

。。

“We first found 300 genes that had this ability—which is a lot,” emphasized Brunet, the Michele and Timothy Barakett Endowed Professor. After narrowing the candidates down to 10, “one in particular caught our attention,” Brunet said. “It was the gene for the glucose transporter known as the GLUT4 protein, suggesting that elevated glucose levels in and around old neural stem cells could be keeping those cells inactive.”.

米歇尔和蒂莫西·巴拉科特（Michele and TimothyBarakett）教授布鲁内特（Brunet）强调：“我们首先发现了300个具有这种能力的基因，这是非常多的。”。布鲁内特说，在将候选人人数缩小到10人之后，“其中一人特别引起了我们的注意”。“这是葡萄糖转运蛋白GLUT4蛋白的基因，表明旧神经干细胞内和周围葡萄糖水平升高可能会使这些细胞保持无活性。”。

The study results could point to some intriguing next steps in addressing this old neural stem cell passivity—or even stimulating neurogenesis in younger brains in need of repair— by targeting newly identified pathways that could reactivate the stem cells.

研究结果可能指出了一些有趣的下一步，通过针对新发现的可能重新激活干细胞的途径，解决这种旧的神经干细胞被动性，甚至刺激需要修复的年轻大脑的神经发生。

Brunet and colleagues described their findings in Nature, in a paper titled “CRISPR–Cas9 screens reveal regulators of ageing in neural stem cells,” in which they stated “Our work provides scalable platforms to systematically identify genetic interventions that boost the function of old NSCs, including in vivo, with important implications for countering regenerative decline during aging.”.

Brunet及其同事在《自然》杂志上发表了一篇题为“CRISPR-Cas9筛选揭示神经干细胞衰老调节因子”的论文，描述了他们的研究结果，他们在论文中表示“我们的工作提供了可扩展的平台，可以系统地识别促进旧神经干细胞功能的遗传干预措施，包括体内，对对抗衰老过程中的再生衰退具有重要意义。”。

Most neurons in the human brain last a lifetime, and for good reason. Intricate, long-term information is preserved in the complex structural relationships between their synapses. To lose the neurons would be to lose that critical information—that is, to forget. Some new neurons are still produced in the adult brain by a population of neural stem cells.

人脑中的大多数神经元都能存活一辈子，这是有道理的。错综复杂的长期信息保存在它们突触之间复杂的结构关系中。失去神经元意味着失去关键信息，即忘记。一些新的神经元仍然是由一群神经干细胞在成年大脑中产生的。

“The adult mammalian brain contains several NSC regions that give rise to newborn neurons and can repair tissue damaged by stroke or brain injuries,” the investigators stated..

研究人员表示：“成年哺乳动物的大脑包含几个神经干细胞区域，这些区域会产生新生神经元，并可以修复中风或脑损伤造成的组织。”。。

There are parts of the brain, such as the hippocampus and the olfactory bulb, where many neurons have shorter lives, where they regularly expire and may be replaced by new ones, said lead author Tyson Ruetz, PhD, a formal post-doctoral scholar in Brunet’s lab. “In these more dynamic parts of the brain, at least in young and healthy brains,” he said, “new neurons are constantly being born and the more transient neurons are replaced by new ones.”.

布鲁内特实验室的正式博士后学者、首席作者泰森·鲁茨博士说，大脑的某些部分，如海马和嗅球，许多神经元的寿命较短，经常会过期，可能会被新的神经元取代。他说：“在大脑这些更具活力的部分，至少在年轻和健康的大脑中，新的神经元不断产生，更短暂的神经元会被新的神经元取代。”。

As brains age, however, NSCs become increasingly less adept at making these new neurons, a trend that can have devastating neurological consequences, not just for memory, but also for degenerative brain diseases such as Alzheimer’s and Parkinson’s, and for recovery from stroke or other brain injury.

然而，随着大脑年龄的增长，神经干细胞越来越不擅长制造这些新神经元，这一趋势不仅会对记忆产生破坏性的神经后果，还会对阿尔茨海默氏症和帕金森氏症等退行性脑部疾病以及中风或其他脑损伤的恢复产生破坏性影响。

“Aging impairs the ability of neural stem cells (NSCs) to transition from quiescence to proliferation in the adult mammalian brain,” the team continued. “Functional decline of NSCs results in the decreased production of new neurons and defective regeneration following injury during aging.”.

“衰老削弱了成年哺乳动物大脑中神经干细胞（NSCs）从静止过渡到增殖的能力，”该团队继续说道。“神经干细胞的功能衰退导致衰老过程中新神经元的产生减少和损伤后的再生缺陷。”。

Ruetz developed a way to test genetic pathways that might be involved in new neuron production in vivo, “where the results really count,” Brunet said. To do this, Ruetz took advantage of the distance between the part of the brain where the neural stem cells are activated, the subventricular zone (SVZ), and the place the new cells proliferate and migrate to, the olfactory bulb, which is many millimeters away in a mouse brain.

布鲁内特说，鲁茨开发了一种测试体内新神经元产生可能涉及的遗传途径的方法，“结果真的很重要”。为了做到这一点，鲁茨利用了大脑中神经干细胞被激活的部分，脑室下区（SVZ）和新细胞增殖并迁移到嗅球之间的距离，嗅球在小鼠大脑中相距数毫米。

“It’s allowing us to observe three key functions of the neural stem cells,” Ruetz said. “First, we can tell they are proliferating. Second, we can see that they’re migrating to the olfactory bulb, where they’re supposed to be. And third, we can see they are forming new neurons in that site.”.

。“首先，我们可以看出它们正在增殖。其次，我们可以看到它们正在迁移到嗅球，它们应该在那里。第三，我们可以看到它们在该部位形成新的神经元。”。

To systematically identify genes that boost NSC activation as a function of age the team developed screening platforms that allowed them to investigate gene knockouts that boost NSC activation specifically in old mice. “Our genome-wide screens in primary cultures of young and old NSCs uncovered more than 300 gene knockouts that specifically restore the activation of old NSCs,” they wrote.

为了系统地鉴定随着年龄的增长而促进NSC活化的基因，该团队开发了筛选平台，使他们能够研究专门在老年小鼠中促进NSC活化的基因敲除。他们写道：“我们在年轻和老年神经干细胞原代培养物中进行的全基因组筛选发现了300多个基因敲除，这些基因敲除可以特异性地恢复老年神经干细胞的活化。”。

“One of the most consistent gene knockouts that boost old NSC function both in vitro and in vivo is Slc2a4 knockout.”.

“在体外和体内促进旧NSC功能的最一致的基因敲除之一是Slc2a4敲除。”。

By knocking out the glucose transporter genes in the SVZ, waiting several weeks, then counting the number of new neurons in the olfactory bulb, the team demonstrated that knocking out GLUT4 had an activating and proliferative effect on neural stem cells, leading to a significant increase in new neuron production in live mice.

通过敲除SVZ中的葡萄糖转运蛋白基因，等待数周，然后计算嗅球中新神经元的数量，该团队证明敲除GLUT4对神经干细胞具有激活和增殖作用，从而导致活小鼠中新神经元产生的显着增加。

“The knockout of the insulin-sensitive glucose transporter GLUT4 was consistently a top hit for both in vitro and in vivo screens, which led to a twofold increase in neurogenesis in old mice in vivo,” the investigators pointed out..

研究人员指出：“胰岛素敏感性葡萄糖转运蛋白GLUT4的敲除一直是体外和体内筛选的热门话题，这导致体内老年小鼠的神经发生增加了两倍。”。。

The glucose transporter connection “is a hopeful finding,” Brunet said. For one, it suggests not only the possibility of designing pharmaceutical or genetic therapies to turn on new neuron growth in old or injured brains, but also the possibility of developing simpler behavioral interventions, such as a low carbohydrate diet that might adjust the amount of glucose taken up by old neural stem cells.”.

布鲁内特说，葡萄糖转运蛋白的联系“是一个有希望的发现”。首先，它不仅表明有可能设计药物或基因疗法来启动旧大脑或受损大脑中新神经元的生长，而且有可能开发更简单的行为干预措施，例如低碳水化合物饮食，可以调节旧神经干细胞摄取的葡萄糖量。“。

Commenting on their collective results the team noted, “Thus, expression of the glucose transporter GLUT4 increases during aging in NSCs in vivo, and knockout of this transporter boosts NSC number and neurogenesis in old mice. Together, these data raise the possibility that the age-dependent increase in GLUT4 could be detrimental for NSC function and neurogenesis in old brains.”.

在评论他们的集体结果时，研究小组指出，“因此，葡萄糖转运蛋白GLUT4的表达在体内NSCs衰老过程中增加，而这种转运蛋白的敲除会增加老年小鼠的NSC数量和神经发生。总之，这些数据提高了GLUT4的年龄依赖性增加可能对老年大脑的NSC功能和神经发生有害的可能性。”。

The researchers found other provocative pathways worthy of follow-up studies. Genes relating to primary cilia, parts of some brain cells that play a critical role in sensing and processing signals such as growth factors and neurotransmitters, also are associated with neural stem cell activation. This finding reassured the team that their methodology was effective, partly because unrelated previous work had already discovered associations between cilia organization and neural stem cell function.

研究人员发现了其他值得后续研究的挑衅性途径。。这一发现使研究小组确信，他们的方法是有效的，部分原因是之前不相关的研究已经发现纤毛组织与神经干细胞功能之间存在关联。

It is also exciting because the association with the new leads about glucose transmission could point toward alternative avenues of treatment that might engage both pathways, Brunet said..

布鲁内特说，这也是令人兴奋的，因为与葡萄糖传播新线索的关联可能指向可能涉及两种途径的替代治疗途径。。

“There might be interesting crosstalk between the primary cilia—and their ability to influence stem cell quiescence, metabolism and function—and what we found in terms of glucose metabolism,” she noted. “The next step,” Brunet continued, “is to look more closely at what glucose restriction, as opposed to knocking out genes for glucose transport, does in living animals.”.

她指出：“初级纤毛与其影响干细胞静止、代谢和功能的能力以及我们在葡萄糖代谢方面的发现之间可能存在有趣的串扰。”。“下一步，”布鲁内特继续说，“是更仔细地研究葡萄糖限制，而不是敲除葡萄糖转运基因，在活体动物中的作用。”。

The same technique could also be applied to studies of brain damage, Ruetz pointed out. “Neural stem cells in the subventricular zone are also in the business of repairing brain tissue damage from stroke or traumatic brain injury.”

Ruetz指出，同样的技术也可以应用于脑损伤的研究。

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