题记：看到这个标题让人兴奋，原来我们人类的肝脏是这么年轻有为！在人体中肝脏的工作艰巨且繁重，但值得庆幸的是进化赋予了它特殊的功能——不断更新，因此，肝脏永远充满活力。也因此，肝脏具有了再生功能（肝脏是唯一一个再被切掉部分后还能生长完好的器官）。随着科学技术的发展和进步，我们是否可以相信或期待：我们人类的其他器官也能像肝脏一样不断更新和再生呢！

Constant Renewal: Your Liver Is Just Under Three Years Old

不断更新：你的肝脏还不到三岁

https://scitechdaily.com/images/Human-Liver-Cells.jpg?ezimgfmt=ng:webp/ngcb1/rs:device/rscb1-1

Human liver is composed of cells with different amounts of DNA. Most of the cells have just two copies of DNA, as the cell indicated with a white arrow. Some cells accumulate more sets of DNA, like the ones indicated with yellow arrows. Those various types of cells renew differently. Credit: Paula Heinke
人类肝脏由具有不同数量 DNA 的细胞组成。 大多数细胞只有两个 DNA 拷贝，如白色箭头所示的细胞。 一些细胞会积累更多的 DNA 组，如黄色箭头所示。 这些不同类型的细胞以不同的方式更新。图片来源：保拉•海因克
Using retrospective radiocarbon birth dating, an international team of scientists shows that the human liver stays young throughout life and is on average less than three years old.
使用可追溯性放射性碳出生日期，一个国际科学家团队表明，人类肝脏在整个生命中都保持年轻，平均不到三岁。
As one of the major organs of the body, the liver performs many essential biological functions. Almost all the blood in a person’s body passes through the liver, where waste products, worn-out cells, and toxins are filtered. It also produces bile, a solution that helps digest fats and eliminate waste products. Those are just a couple of the major duties it performs — more ore than 500 vital functions have been identified with the liver.
作为人体的主要器官之一，肝脏具有许多重要的生物学功能。人体内几乎所有的血液都通过肝脏，在那里过滤掉废物、磨损的细胞和毒素。 它还产生胆汁，这是一种有助于消化脂肪和消除废物的解决方案。 这些只是它执行的主要职责中的几项，已确定肝脏有超过 500 种重要功能。
The liver is an essential organ that takes care of detoxifying our bodies. It is prone to injury because it is constantly exposed to toxic substances. To overcome this, the liver has a unique capacity among organs to regenerate itself after damage. Because a lot of the body’s ability to heal and regenerate itself decreases as we age, scientists were wondering if the liver’s capacity to renew also diminishes with age.
肝脏是我们身体排毒的重要器官。它很容易受伤，因为它经常暴露在有毒的物质中。为了克服这一点，肝脏在器官中具有独特的在损伤后自我再生的能力。 因为随着年龄的增长，身体的许多自我修复和再生能力都会下降，科学家们想知道肝脏的更新能力是否也会随着年龄的增长而下降。
The nature of liver renewal in humans also remained a mystery. The animal models provided contradictory answers. “Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover. It was clear to us that if we want to know what happens in humans, we need to find a way to directly assess the age of human liver cells,” says Dr. Olaf Bergmann, research group leader at the Center for Regenerative Therapies Dresden (CRTD) at TU Dresden.
人类肝脏更新的性质也仍然是一个谜。 动物模型提供了相互矛盾的答案。 “一些研究指出肝细胞寿命长的可能性，而另一些则显示出持续的更新。我们很清楚，如果我们想知道人类的肝脏发生了什么，我们需要找到一种方法来直接评估人类肝细胞的年龄，” 德累斯顿工业大学德累斯顿再生治疗中心(CRTD)的研究小组负责人奥拉夫•伯格曼博士说。
The Human Liver Remains a Young Organ
The interdisciplinary team of biologists, physicists, mathematicians, and clinicians led by Dr. Bergmann analyzed the livers of multiple individuals who died at ages between 20 and 84 years old. Surprisingly, the team showed that the liver cells of all subjects were more or less the same age.
人类肝脏仍然是一个年轻的器官
由 Bergmann 博士领导的由生物学家、物理学家、数学家和临床医生组成的跨学科团队分析了多名死于 20 至 84 岁的人的肝脏。 令人惊讶的是，该团队显示所有受试者的肝细胞年龄大致相同。

https://scitechdaily.com/images/Liver-Human-Body-Anatomy-777x518.jpg?ezimgfmt=rs:720x480/rscb1/ng:webp/ngcb1

Location of the liver in the human body.
人体中肝脏的位置
“No matter if you are 20 or 84, your liver stays on average just under three years old,” explains Dr. Bergmann. The results show that the adjustment of liver mass to the needs of the body is tightly regulated through the constant replacement of liver cells and that this process is maintained even in older people. This ongoing liver cell replacement is important for various aspects of liver regeneration and cancer formation. 
“无论您是 20 岁还是 84 岁，您的肝脏平均年龄都不到 3 岁，”伯格曼博士解释说。 结果表明，通过肝细胞的不断更换，肝脏质量对身体需要的调整受到严格调节，即使在老年人中也能维持这一过程。这种正在进行的肝细胞替代对于肝脏再生和癌症形成的各个方面都很重要。
Liver Cells with More DNA Renew Less
However, not all the cells in our liver are that young. A fraction of cells can live up to 10 years before renewing itself. This subpopulation of liver cells carries more DNA than the typical cells. “Most of our cells have two sets of chromosomes, but some cells accumulate more DNA as they age. In the end, such cells can carry four, eight, or even more sets of chromosomes,” explains Dr. Bergmann.
具有更多 DNA 的肝细胞更新更少
然而，并非我们肝脏中的所有细胞都那么年轻。 一小部分细胞在自我更新之前可以存活长达 10 年。这种肝细胞亚群比典型的细胞携带更多的 DNA。“我们的大多数细胞都有两组染色体，但有些细胞随着年龄的增长会积累更多的 DNA。 最后，这些细胞可以携带四组、八组甚至更多组染色体，”伯格曼博士解释说。
“When we compared typical liver cells with the cells richer in DNA, we found fundamental differences in their renewal. Typical cells renew approximately once a year, while the cells richer in DNA can reside in the liver for up to a decade,” says Dr. Bergmann. “As this fraction gradually increases with age, this could be a protective mechanism that safeguards us from accumulating harmful mutations. We need to find out if there are similar mechanisms in chronic liver disease, which in some cases can turn into cancer.”
“当我们将典型的肝细胞与富含 DNA 的细胞进行比较时，我们发现它们的更新存在根本差异。典型的细胞大约每年更新一次，而富含 DNA 的细胞可以在肝脏中存活长达十年，”Bergmann 博士说。 “随着这一比例随着年龄的增长而逐渐增加，这可能是一种保护机制，可以保护我们免于积累有害突变。我们需要找出慢性肝病是否有类似的机制，在某些情况下会变成癌症。”
Lessons from the Nuclear Fallout
Determining the biological age of human cells is a massive technical challenge, as methods commonly used in animal models cannot be applied to humans.
核辐射的教训
确定人体细胞的生物学年龄是一项巨大的技术挑战，因为动物模型中常用的方法不能应用于人类。
Dr. Bergmann’s group specializes in retrospective radiocarbon birth dating and uses the technique to assess the biological age of human tissues. Carbon is a chemical element that is ubiquitous and forms the backbone of life on Earth. Radiocarbon is one of a variety of types of carbon. It appears naturally in the atmosphere. Plants incorporate it through photosynthesis, in the same way as typical carbon, and pass it on to animals and humans. Radiocarbon is weakly radioactive and unstable. These characteristics are taken advantage of in archeology to determine the age of ancient samples.
Bergmann 博士的小组专门研究可追溯性放射性碳出生日期，并使用该技术评估人体组织的生物学年龄。碳是一种无处不在的化学元素，是地球上生命的支柱。放射性碳是多种碳中的一种。 它自然地出现在大气中。植物通过光合作用吸收它，就像典型的碳一样，并将其传递给动物和人类。 放射性碳具有弱放射性且不稳定。 这些特征在考古学中被用来确定古代样品的年龄。

https://scitechdaily.com/images/Human-Liver-Model-777x518.jpg?ezimgfmt=rs:720x480/rscb1/ng:webp/ngcb1

Human liver model. 人类肝脏模型
“Archeologists have used the decay of radiocarbon successfully for many years to assess the age of specimens, one example being dating of the shroud of Turin,” says Dr. Bergmann. “The radioactive decay of radiocarbon is very slow. It provides enough resolution for archeologists but it is not useful for determining the age of human cells. Nevertheless, we can still take advantage of the radiocarbon in our research.”
“多年来，考古学家成功地利用放射性碳的衰变来评估标本的年龄，其中一个例子是都灵裹尸布的年代测定，”伯格曼博士说。 “放射性碳的放射性衰变非常缓慢。 它为考古学家提供了足够的分辨率，但对确定人体细胞的年龄没有用处。 尽管如此，我们仍然可以在研究中利用放射性碳。”
The aboveground nuclear tests carried out in the 1950s introduced massive amounts of radiocarbon into the atmosphere, into the plants, and into the animals. As a result, cells formed in this period have higher amounts of radiocarbon in their DNA.
上世纪50 年代进行的地上核试验将大量放射性碳引入大气、植物和动物体内。 因此，在此期间形成的细胞 DNA 中的放射性碳含量较高。
Following the official ban of aboveground nuclear testing in 1963, the amounts of atmospheric radiocarbon started to drop and so did the amounts of radiocarbon incorporated into the animal DNA. The values of atmospheric and cellular radiocarbon correspond to each other very well.
在 1963 年官方禁止进行地上核试验之后，大气中放射性碳的含量开始下降，动物 DNA 中的放射性碳含量也开始下降。大气和细胞放射性碳的值非常吻合。
“Even though these are negligible amounts that are not harmful, we can detect and measure them in tissue samples. By comparing the values to the levels of atmospheric radiocarbon, we can retrospectively establish the age of the cells,” explains Dr. Bergmann.
“即使这些是无害的微不足道的量，我们也可以在组织样本中检测和测量它们。 通过将这些值与大气放射性碳的水平进行比较，我们可以追溯确定细胞的年龄，”Bergmann 博士解释说。
Unparalleled Insights Directly From the Source
The Bergmann group also explores the mechanisms that drive the regeneration of other tissues considered as static, such as the brain or the heart. The team has previously used their expertise in retrospective radiocarbon birth dating to show that the formation of new brain and heart cells is not limited to prenatal time but continues throughout life. Currently, the group is investigating whether new human heart muscle cells can still be generated in people with chronic heart disease.
直接从源头获得无与伦比的洞察力
Bergmann 小组还探索了驱动其他被认为是静态的组织（例如大脑或心脏）再生的机制。该团队之前利用他们在可追溯性放射性碳出生约会方面的专业知识表明，新的大脑和心脏细胞的形成不仅限于产前时间，而且会持续一生。 目前，该小组正在研究是否仍然可以在患有慢性心脏病的人身上产生新的人类心肌细胞。
“Our research shows that studying cell renewal directly in humans is technically very challenging but it can provide unparalleled insights into the underlying cellular and molecular mechanisms of human organ regeneration,” concludes Dr. Bergmann.
“我们的研究表明，直接在人体中研究细胞更新在技术上非常具有挑战性，但它可以为人体器官再生的潜在细胞和分子机制提供无与伦比的见解，”Bergmann 博士总结道。