科学家说，你的肝脏只有大约三岁

StephenW

科学家说，你的肝脏只有大约三岁
大卫尼尔德
2022 年 6 月 2 日

根据一项新的研究，即使我们身体的其他部分变老，人类的肝脏也会保持年轻，而且无论它所依附的人的年龄如何，平均该器官的年龄不到三年。

使用数学模型和一种称为回顾性放射性碳出生约会的技术——该技术根据 20 世纪中期核试验后在大气中飙升的碳同位素水平确定人体细胞的日期——科学家们发现，随着年龄的增长，肝脏更新在很大程度上不受影响。

这种更新是肝脏主要功能的关键，即清除体内有毒物质。这种废物清除会对器官造成伤害，但它具有在受损后自我再生的独特能力。

“无论你是 20 岁还是 84 岁，你的肝脏平均寿命不到 3 岁，”德国德累斯顿工业大学的分子生物学家 Olaf Bergmann 说。

该团队分析了 50 多名年龄在 20 至 84 岁之间的人的尸检和活检组织样本。他们发现我们的生物学通过不断更换肝细胞，在我们的一生中严格控制肝脏的质量。

""正在分析的肝细胞。 （保拉·海因克）

随着我们的身体变老，它们更新细胞和进行修复的能力降低。新研究表明，这不适用于肝细胞，即肝脏中的细胞。虽然早期的动物研究给出了相互矛盾的结果，但这里的情况要清楚得多。

然而，研究人员发现，并非所有肝细胞的更新速度都是相同的：一小部分肝细胞可以活到 10 岁。这似乎与他们携带多少组染色体有关。

除了我们的性细胞外，我们身体中的大多数细胞都携带我们整个基因组的两个副本。肝细胞是一个奇怪的例外，其中一部分细胞在顶部产生了我们整个 DNA 文库的更多副本。

“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，”伯格曼说。 “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。”

“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中是否存在类似的机制，在某些情况下可能会变成癌症。”

这是对肝脏如何运作的生物学机制的重要新见解——当然，我们对身体器官的了解越多，我们就越能更好地弄清楚如何保持它们的健康以及如何治愈它们的疾病.

研究人员还在研究其他器官，包括心脏，以了解细胞在全身更新的速度。回顾性放射性碳出生日期的相同技术可用于准确确定细胞日期并计算更新率。

这是我们目前掌握的用于确定人体组织年龄的最佳方法之一，使用大气中放射性碳的衰减率来对应人体中的痕迹。事实证明，你的器官可能没有你感觉的那么老。

“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 说。

该研究已发表在《细胞系统》上。

StephenW

Your Liver Is Only About Three Years Old, Scientists Say
DAVID NIELD
2 JUNE 2022

The human liver stays youthful even while the rest of our bodies grow old, according to new research, and on average the organ is is less than three years old, no matter what the age of the person it's attached to.

Using mathematical modeling and a technique called retrospective radiocarbon birth dating – which dates human cells based on levels of a carbon isotope that spiked in the atmosphere following mid-20th century nuclear testing – scientists have found that liver renewal is largely unaffected as we grow old.

That renewal is key to the liver's primary function, which is clearing toxic substances out of the body. This waste removal takes its toll on the organ, but it has a unique ability to regenerate itself after being damaged.

"No matter if you are 20 or 84, your liver stays on average just under three years old," says molecular biologist Olaf Bergmann from the Dresden University of Technology in Germany.

The team analyzed post-mortem and biopsy tissue samples from more than 50 individuals aged between 20 and 84 years. They found our biology maintains tight control over the mass of the liver throughout our lives, via the continual replacement of liver cells.

""Liver cells under analysis. (Paula Heinke)

As our bodies get older, they're less able to renew cells and carry out repairs. What the new study shows is that this doesn't apply to the hepatocytes, the cells in the liver. Whereas earlier animal studies had given conflicting results, here there's much more clarity.

However, not all liver cells are the same in terms of how quickly they renew: A small fraction can live to be up to 10 years old, the researchers found. This seems to be related to how many sets of chromosomes they're carrying.

Most cells in our body, aside from our sex cells, carry two copies of our entire genome. Liver cells are an odd exception, with a proportion of cells generating even more copies of our whole DNA library on top.

"When we compared typical liver cells with the cells richer in DNA, we found fundamental differences in their renewal," says Bergmann. "Typical cells renew approximately once a year, while the cells richer in DNA can reside in the liver for up to a decade."

"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."

This is an important new insight into the biological mechanisms underpinning how the liver works – and of course the more we know about the organs in the body, the better we can get at figuring out how to keep them healthy and how to cure them from disease.

The researchers are also looking at other organs, including the heart, to see how fast cells are renewed across the body. The same technique of retrospective radiocarbon birth dating can be used to accurately date cells and work out renewal rates.

It's one of the best methods we've currently got for figuring out the age of human tissue, using the decay rates of radiocarbon in the atmosphere to correspond to traces in the body. As it turns out, your organs might not be as old as you feel.

"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," says Bergmann.

The research has been published in Cell Systems.