Flies usually live less than 20 days, captive mice can live for 2 years, foxes can live for 10 years, gorillas can live for about 40 years... In general, the life expectancy of a species is closely related to its size. However, there are exceptions that can ignore the rules of time. What's the secret to them? What mysterious biological processes have freed them from the shackles of time?
Jellyfish are able to rejuvenate
The little Dawn Lighthouse Jellyfish (Turritopsis dohrnii) holds the secret of eternal life!
When stressed or reproduction is completed, it shrinks and degenerates to a young age, becoming a hydra attached to the seabed. This process, which is not yet clear, is called transdifferentiation, which allows cells to return to an undifferentiated state, as they were at birth, and then re-differentiate and begin a new life cycle.
"We've only found this phenomenon in juvenile jellyfish before," said Thomas Bastian, a postdoctoral fellow in marine biology at the University of Marine at The University of The Maritime in France, "and it would be a small revolution to observe it in adults as well." The team of Associate Professor Zheng Lianming of Xiamen University's School of Oceanography and Earth science ignited the trigger for this revolution: In 2015, they successfully observed the same phenomenon of differentiation and metastasis in a type of sea moon jellyfish distributed offshore China.
"There's every reason to believe that this is one of the secrets to the survival of these creatures that have survived for more than 500 million years." Thomas Bastian added.
Tardigrades are able to pause time
"If they were human, clinically we could pronounce them dead." Cédric Hubas, a lecturer at France's National Museum of Natural History, is still amazed when he talks about the tardigrades he studies (commonly known as "tardigrades").
Of the thousands of species of tardigrades that have been recorded, only 15 are clearly cryptobiotic: when their habitat deteriorates (dry, low temperatures, hypoxia), they can lose up to 99 percent of their water and shrink into a sac, like a lifeless sphere.
In this state that can be maintained for hundreds of years, the body's metabolism has stagnated. The fluid in its tissues is replaced by trehalose to maintain the cellular structure. Once the environment becomes livable again, they rehydrate and recover. "Some scientists have proposed the 'Sleeping Beauty' hypothesis: in this state, tardigrades cells do not age."
Scientists at Japan's National Polar Research Institute "resurrected" two tardigrades scientifically known as Acutuncus antarticus in 2014: they were discovered in a moss in Antarctica in 1983 and were preserved at -20°C for 30.5 years. During their resuscitation, there seems to be a unique DNA repair mechanism that kicks in at the same time.
By sequencing another species of tardigrade called Ramazzottius Varieornatu, biologists at the University of Tokyo found that a protein in its body even had the ability to repair 40% of the DNA of human cells damaged by X-ray radiation!
A slow-paced life of a cave salamander
"Because of its long lifespan, it is expected to have a slow metabolism or a high degree of antioxidant mechanism, but it is not." Yann Voituron, a physiologist at the Laboratory of Ecology of Natural and Artificial Hydrological Systems at the University of Lyon in France, points out.
To explore the secret of the longevity of this small cave-dwelling amphibian that lived for a century, he and other colleagues proposed multiple hypotheses.
The latest results show that their lifestyles are very slow, with an average daily activity time of only 5 minutes. "Our hypothesis is that because they are crammed into the cracks and do nothing, they rarely produce toxic byproducts to the body. And because there are no known predators, the cave salamander can move at a very slow speed with peace of mind, consuming very little energy.
However, these studies are still in the exploratory stage. Olivier Gillaume, a research engineer at the French Workstation in Theoretical Ecology and Experimental Ecology, said his explorations of the animal date back to 1954.
Bowhead whales are immune to cancer
Bowhead whales, which have thousands of times the number of cells in humans, are supposed to have a higher risk of cancer, yet they are insulated from them.
"We observed that they have mechanisms to repair DNA and prevent damage to their DNA as they age by regulating the cell cycle." João Pedro de Magalhães, an expert on aging at the University of Liverpool in the United Kingdom, explains why. But what are the corresponding cellular, molecular, and genetic mechanisms? "It is impossible to experiment on whales..."
The researcher said with regret that in order to get more information, he considered implanting bowhead whale genes in mice for further research.
Sea urchins are capable of regeneration throughout their lives
"We see from sea urchins that the decline of the body that accompanies aging is not inevitable." Andrea Bodnar, a biochemist at the Bermuda Marine Sciences Institute (BIOS), who specializes in aging, is convinced that sea urchins run counter to all theories of aging.
For example, the star sea urchin (Astropyga radiata) will continue to grow even if it reaches the age of 100, or the purple ball sea urchin (Strongylocentrotus purpuratus) reaches the age of 50, and will also repair their damaged appendages (ducts and spines). This is a rare superpower because most animals have a weaker ability to regenerate tissue with age.
Their secret lies in specialized stem cells in mature tissues, capable of differentiating into different types of cells and enabling tissue regeneration. "In particular, we confirmed that in the body tissues of sea urchins, the gene expression of specialized stem cells does not deteriorate with age. The next step is to understand the relevant cellular and molecular mechanisms. Andrea Bernard elaborated on his observations.
Even the Lytechinus variegatus, which has a life expectancy of only 4 years, does not seem to have undergone degeneration. "They die from predators, accidents or infectious diseases, not physiological aging." The researcher concluded in surprise. Even if they don't live long, they won't get old!
Naked mole rats fight cancer with hyaluronic acid
The "legend" was turned upside down: In March 2016, researchers at the University of Washington in the United States found two cases of cancer in naked mole rats, which have long been considered uninfected by cancer.
The rodents live up to 30 years (mice only live 2 years) and have an amazing defensive weapon to avoid tumor formation, and that is hyaluronic acid, which is used in many cosmetics. This polymer is composed of sugars and is widely present in connective tissue in living organisms.
According to the measurement results of researchers at the University of Rochester in the United States, the concentration of high molecular weight hyaluronic acid in naked mole rats is 5 times that of mice and humans. This molecule stops the cell cycle and avoids mutant cells from dividing uncontrollably after coming into contact with each other like cancer cells.
"Hyaluronic acid's role is significant, but there should be other reasons to explain resistance to cancer." Delphine del Marmol, who published her doctoral dissertation on the subject at the University of Namur School of Medicine in Belgium, said she was intrigued by the number of cellular receptors that can interact with hyaluronic acid.
"Frozen" oxidative reaction of the small-headed sleeping shark
The nearly 400-year-old small-headed sleeping shark discovered earlier is undoubtedly living evidence that low temperatures contribute to longevity.
The harsh cold environment in which it operates (the temperature of the deep waters of the Arctic Ocean does not exceed 12°C) reduces the rate of chemical reactions in its body, making it not only less susceptible to infection, but also slowing down its metabolism – that is, aging – the rate.
However, recent studies of Caenorhabditis elegans have shown that the effect of cold on longevity should also have some genetic factors: low temperature actually activates a gene in nematodes that involves oxidative stress resistance and cellular aging.
This mechanism, according to the researchers, may be applicable to the entire animal kingdom... The small-headed sleeping shark is clearly the best of them.
Written by Camille Chandès
Compiled by Chen Tianhan