Life lies in stillness? A breakthrough in the secret of human blood clots lies in the hibernation of bears!

Although humans often regard themselves as the "most intelligent creatures on earth", compared with other creatures living on the earth, the human body always exhibits some "fragile" characteristics - lacking hard "armor" and aggressive organs, organs such as the eyes, neck, and body systems such as the respiratory system and digestive system may have serious impacts on health even if they suffer minor damages... Even just sitting in a car or plane for more than ten hours will make the human body start to feel uncomfortable, and the risk of blood clots will increase accordingly.

In the "winter months when you can't wake up", facing the "ultimate temptation" of the quilt, many people sighed, "It would be great if humans could hibernate, too." The ideal is beautiful, but unfortunately, the fragile human body does not allow this fantasy to come true. In fact, no matter how tired or sleepy you are, if humans try to sleep for as long as other hibernating animals, their bodies will suffer from problems such as blood clots, muscle atrophy, bone loss, and bedsores. This makes us wonder, what kind of "talent" do hibernating animals rely on to "sleep soundly"? How do they avoid the risk of blood clots caused by long-term relative stillness?

Now, an article published in Science has given the answer to this question. Taking bears that hibernate for up to half a year as the research subjects, the research members found that the hibernating bears produced less of a protein that helps blood coagulation, so the bears do not form fatal blood clots when hibernating.

The same bear before hibernation in October (left) and after hibernation in April of the following year (right)

The secret of sleeping for half a year

Feed yourself, carefully choose a safe cave, hide well, and fall asleep. Hibernation is an effective survival strategy for bears, which can help them successfully survive the winter when food is scarce and the climate is cold. When hibernating, bears will enter a "low energy consumption" state, not eating, drinking, or excreting; after hibernating for about half a year, bears do not have any health problems due to not eating or excreting for a long time. On the contrary, they can maintain their body functions and immunity, and quickly restore vitality and appetite, all thanks to the magical and complex regulatory mechanism inside their bodies. The secret of why bears do not form blood clots when hibernating is an important part of this regulatory mechanism.

Bear digging a hole for hibernation

Tobias Petzold and Manuela Thienel, two cardiologists from the University of Munich in Germany, collaborated with other researchers to study hibernating Swedish brown bears. In order to compare the similarities and differences in various data in the blood of bears in different seasons, the research team began to fly helicopters over Sweden and Scandinavia in the summer to look for brown bears. After anesthesia, the researchers quickly collected samples and put GPS collars on the bears; in the following two winters, the researchers trudged through the snow with the "guidance" of the signal, found hibernating brown bears wearing GPS collars and collected blood samples. After comparison, they found seasonal differences in the bears' blood-in the summer, a protein called HSP47 was abundant in the bears' blood, but in the winter, this protein almost disappeared.

The research team found the hibernating bears and quickly collected blood samples on site

HSP47 is not a "strange" protein for relevant researchers. In previous studies, scientists found that, among other functions, this protein is also present on the surface of platelets involved in thrombosis, helping blood cells stick together. When blood clots form in wounds, they stop the body from bleeding and help the wound heal; however, when blood coagulates in veins and cannot dissolve naturally, fatal thrombi can form. Specifically, HSP47 on platelets can activate neutrophils to form a "net" that captures proteins, pathogens and cells; platelets with less HSP47 are less likely to attract and bind to infection-fighting white blood cells, neutrophils, which is a key step in thrombosis. In other words, because hibernating bears produce less HSP47, their blood is less likely to form these "nets", so the blood of hibernating bears is not easy to coagulate and form thrombi during hibernation, which is the secret of bears being able to sleep peacefully.

Inspiration for mankind

It is understood that HSP47 is not only present in bears, but also in humans. Does this mean that humans also have the possibility of hibernation? Before answering this ultimate question, the researchers turned their attention to patients with spinal cord injuries who were in a "similar situation" to the hibernating bears. Like the hibernating bears, they do not seem to have blood clots despite being immobile for a long time. After testing HSP47 in patients with spinal cord injuries, the researchers found that these people had relatively less HSP47 than other people with greater mobility, proving that their bodies reduced the production of this protein after being immobilized, thereby reducing their risk of blood clots.

On this basis, they further introduced healthy volunteers as a control group and let the volunteers rest in bed for 27 days. The test results after the end of the experiment showed that the level of HSP47 in the volunteers decreased over time; in other words, HSP47 can be downregulated by the relative stillness of the human body, thereby preventing thrombosis by weakening the activation of immune cells. As the research members said, HSP47 seems to play the same role in bears and humans. This work shows that mammals evolved this coagulation mechanism a long time ago; at the same time, this is also a potential new mechanism for preventing thrombosis, which can help cancer, surgery and trauma patients who are at greater risk of thrombosis.

Hibernating brown bears, like people with chronic mobility impairments, have an internal mechanism to resist blood clots

What's more exciting is that this research result also allows researchers to see the great prospects of developing new anti-thrombotic drugs. Venous thromboembolism mainly includes deep vein thrombosis and pulmonary embolism, which are the main causes of human morbidity and mortality. Although there are several drugs that are widely used to prevent thrombosis, the common feature of these drugs is that they are all associated with the risk of bleeding, which may even be life-threatening in severe cases. By studying the ability of brown bears to hibernate, it will not only help humans use new "problem-solving ideas" to develop anti-thrombotic drugs with fewer side effects; on this basis, it may also achieve the prevention and protection of people with a high incidence of thrombosis, and help humans solve the public health problems of obesity and overweight. Not only that, this research also points to the stars and the sea. In an era when "human beings must go to space to seek a new home in order to survive", humans urgently need to study new technologies that can ensure that astronauts can maintain healthy vital signs during long-term space travel or hibernation. With the exploration of the mysteries of bear hibernation, perhaps in the near future, humans can turn the space travel described in science fiction works into reality.