Homogeneous organ reconstruction can greatly reduce the risk of immune rejection and even eradicate the disease.
Regardless of ancient and modern times, immortality has always been the ultimate desire of mankind. It is the core of myths and legends and one of the most popular elements in science fiction. So, is it really possible for future human beings to achieve immortality?
Before answering this question, we need to answer another question: Why is the life span of human beings limited?
Before the 1860s, it was believed that vertebrate cells had the ability to divide indefinitely. Until 1961, the discovery of American microbiologist Leonardo Hayflick broke people’s illusions. Through experimental observation, Hayflick found that there is an upper limit of 40 to 60 divisions of normal cells in vitro. This upper limit is also known as the Hayflick limit.
In the 1970s, scientist Elizabeth Blackburn and others discovered the telomere structure at the end of chromosomes. Telomeres can protect chromosomes and ensure the stability of gene replication, but telomeres lose part of each time they replicate. When the lost telomeres reach the limit, the cell no longer divides. The discovery of telomeres perfectly explained the Hayflick limit.
Does telomerase achieve unlimited cell division?
Elizabeth Blackburn and others discovered telomerase that can repair telomeres. The Hayflick limit of different cells is limited by the length of the cell’s telomeres and the ability to repair. The Hayflick limit of pancreatic islet cells is only more than ten times, while the Hayflick limit of hematopoietic stem cells can reach more than 100 times.
After entering the 21st century, the study of telomeres has become a hot field in biology. In 2009, Elizabeth Blackburn and others were awarded the Nobel Prize in Physiology or Medicine. Can the Hayflick limit be broken by using telomerase to repair telomeres?
On May 23, 2016, a Russian cryonics company used a dummy to conduct a freezing experiment
The answer is certain. The reason why embryonic stem cells and germ cells can divide indefinitely is the repair of telomeres by telomerase. But in normal cells, if telomerase is too active, it will cause cancer. The reason why cancer cells can divide indefinitely also lies in the infinite repair of telomeres by telomerase.
/ Nanotechnology will inevitably affect the continuity of consciousness after repairing the brain. /
Can we break the Hayflick limit without increasing the incidence of cancer? This is feasible. Around 2000, researchers introduced exogenous telomerase to repair cell chromosomal telomeres (ectopic expression), creating an immortal cell line without cancer. The ectopic expression of telomerase has broad application prospects and may even provide a solid foundation for human immortality technology in the future.
Telomerase molecular structure
In the distant future, it is not impossible to use the ectopic expression of telomerase to achieve immortality. Among invertebrates, many animals have unlimited theoretical life spans, such as lobsters that have unlimited telomere repair capabilities.
Ice crystals challenge human freezing
Whether in legends or science fiction stories, there are always characters who have lived for centuries. In science fiction movies such as “Planet of the Apes” and “Alien”, there are always stories of astronauts crossing over long time and space through hibernation or freezing technology.
Compared to the hibernation technology that only exists in the future or science fiction movies, the one that is closer to us is the human body freezing. Cryonics is a hotly discussed and controversial topic in recent years. But the beginning of actual freezing technology originated from the freezing experiment of rodents by British scientist James Lovelock in the 1850s.
In 1955, some mice were revived after being frozen for a short period of time, but they died after 4 to 7 days. During the experiment, people also discovered that there are many obstacles to freezing technology. Among these obstacles, the destructive power of ice crystals in cells is particularly lethal.
In 1963, the Oak Ridge National Laboratory in the United States found that during freezing, if the rate of temperature reduction is controlled slow enough, the cells can be drained of sufficient water, thereby avoiding freezing in the cells.
On January 12, 1967, the first cryonics experiment began. In the 1970s, mankind developed a speed controlled slow freezing technology. While adding the cryoprotectant, the scientists controlled the temperature decrease rate to 1°C/min, achieving a perfect freezing effect at the cell level, making the freezing technology truly developed to the practical stage.
3D printed brain
Speed controlled slow freezing technology is widely used in freezing oocytes, skin, blood products, embryos, sperm, stem cells, and related frontier fields. But at this time, freezing technology still stays at the cellular level.
In the 1980s, vitrification technology began to be introduced into cryopreservation. In 1999, vitrification began to be used for the preservation of oocytes. After entering the 21st century, a medical company successfully vitrified rabbit kidneys and completed non-destructive transplantation after rewarming.
The vitrification technology is more advanced than the controlled speed slow freezing technology, which can minimize the damage of the cell tissue during freezing. Vitrification technology at the organ level has gradually matured and is getting closer and closer to clinical application.
Vitrification technology has also been used in human freezing. In 2015, Ms. Du Hong, one of the editors of “Three Body”, died of pancreatic cancer. She entrusted the American scientific research institution Alcor to freeze her head. So she became the first person to freeze the human body in China.
The technique used by Alcor to preserve Ms. Du Hong’s head is the preservation of vitrification. 50 years later, is there any possibility of Ms. Du Hong’s resurrection? The answer may not be optimistic.
The current cryonics cases, without exception, are all cryonics performed after clinical death. To make the possibility of awakening higher, unless live freezing. But even if it breaks through the moral and legal restrictions, the possibility of a living body freezing and resurrection still faces great challenges.
Before the human body is frozen, all blood will be replaced with cryoprotectants. Although cryoprotectants are conducive to the realization of vitrification technology, they are also toxic to cells, and long-term storage can cause irreversible damage to cells.
In addition, there are all kinds of radiation in the universe. These radiations can cause damage to DNA, even with perfect cryopreservation technology, the time limit for resurrection cannot exceed 1,000 years. Moreover, it is difficult for people with vitrification to completely avoid the formation of ice crystals when thawing, which will cause further damage to the cells.
In addition to starting with freezing technology, when the future of nanotechnology develops to a certain level, it is theoretically possible to use nanorobots to repair the brain.
But after nanotechnology repairs the brain, it will inevitably affect the continuity of consciousness. When a brain is damaged by 10%, it will retain 90% of its original consciousness after being repaired by nanotechnology in the future, and we can barely call it the original person. But if 90% is damaged and only 10% remains after repair, is he (she) still the same person?
The clone is knocking on the door?
If the cryo-resurrection technology is still some way away from landing, then organ reconstruction is within reach of human beings.
Compared with organ donation, reconstructed organ technology can truly solve the shortage of human organ transplants. Homogeneous organ reconstruction can greatly reduce the risk of immune rejection and even eradicate the disease.
One of the most popular and promising organ reconstruction technologies at present is therapeutic cloning. In 2013, a research team has mastered the technology of cloning human embryos to isolate stem cells. In 2018, Chinese researchers successfully cloned two primates-two crab-eating macaques.
As the time to break technical barriers is getting closer, only legal and moral hazards will limit human cloning in the future. At that time, the difficulty of cloning humans may be easier than cultivating organs alone. A series of social problems may also occur.
In addition to cloning technology, organs can also be cultivated through induced pluripotent stem cells. In 2006, a research team from Kyoto University in Japan induced somatic mouse cells and transformed them into pluripotent stem cells, marking that the technology is truly feasible.
But compared to direct cloning, induced pluripotent stem cells are often longer and less effective. The induction of mouse cells takes 1 to 2 weeks, while human cells need 3 to 4 weeks, with an efficiency of only 0.01% to 0.1%. In addition, the induction of pluripotent stem cells from the donor can also lead to a higher risk of cancer.
/ The difficulty of 3D printing organ technology mainly lies in the construction of organ blood vessels. /
It was not until 2008, after the breakthrough in related technologies, that the research of induced pluripotent stem cells had more hopes for breakthroughs. At present, induced pluripotent stem cell technology is actively exploring in the direction of organ regeneration. For example, a research team in Japan is trying to cultivate human organs in pigs through induced pluripotent stem cell technology.
Although Japan’s research frontier in this area is bold, it is still far away from clinical application.
Among all the reconstructed organ technologies, the closest to clinical application may be 3D organ printing. 3D organ printing uses biocompatible plastic as a scaffold to print the corresponding stem cells, and then transfer them to the incubator to grow the corresponding organs.
Although 3D printing technology was invented in 1984, it was not until 1990, with the application of nanotechnology and the development of bioactive material technology, that the technology began to enter the medical field, and there was “3D organ printing”. the concept of.
Although this technology has been tried on heart models, blood vessel networks, and skin, so far, the only 3D printed organ that has been successfully transplanted is the bladder. The difficulty of 3D printing organ technology mainly lies in the construction of organ blood vessels.
The main function of blood vessels is to transport nutrients, oxygen and waste products, which are vital to maintaining the normal metabolism of organs. The construction of blood vessels, especially capillaries, is extremely difficult, which involves extremely complex geometric problems.
In addition to the difficulty of building blood vessels, the source of stem cells for 3D organ printing is also a problem. Not all stem cells from patient organs can be used. Of course, in the near future, therapeutic cloning technology and induced pluripotent stem cell technology are mature enough to provide a sufficient source of stem cells for 3D organ printing.
At that time, organ regeneration technology will enter the era of full-scale technological explosion.