Tardigrades, which are microscopic animals found across the world, have charmed countless people with their cuddly looks and steely endurance in conditions that would kill other organisms. These tiny creatures can survive intense pressures and temperatures, and even exposure to the vacuum of space, earning them a reputation as one of the hardiest species on (and occasionally off) our planet.
Now, scientists have revealed new details about how tardigrades survive near complete dehydration for long durations, even decades, which is an extraordinary superpower considering that water is the key ingredient for life. Indeed, tardigrades are nicknamed water bears because they are aquatic animals, making it all the more puzzling that they can persist without this vital substance for years at a time.
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To shed light on this superpower, researchers led by Akihiro Tanaka, a graduate student in biological sciences at the University of Tokyo, studied structures called cytoplasmic-abundant heat soluble (CAHS) proteins.
The team revealed that these proteins can form protective substances akin to gels that “contribute to the exceptional physical stability in a dehydrated state” seen in tardigrades, a finding that may have implications for human medical treatments and technologies, according to a study published in the journal PLOS Biology on Tuesday.
“Although water is essential to all life we know of, some tardigrades can live without it potentially for decades,” said Takekazu Kunieda, an associate professor at the University of Tokyo and the senior author of the study, in a statement. “The trick is in how their cells deal with this stress during the process of dehydration.”
“It’s thought that as water leaves a cell, some kind of protein must help the cell maintain physical strength to avoid collapsing in on itself,” he continued. “After testing several different kinds, we have found that cytoplasmic-abundant heat soluble (CAHS) proteins, unique to tardigrades, are responsible for protecting their cells against dehydration.”
Water loss in typically living cells causes these biological units to lose their structural integrity, making them prone to collapse, but in tardigrades, CAHS proteins take over to maintain cellular stability in a dehydrated state. When dehydrated water bears finally quench their thirst, the process reverses, as the proteins recede to make way for water’s reentry to the cell.
The researchers searched through more than 300 CAHS proteins that may help water bears endure waterless periods. The team also introduced the proteins in human cultured cells, where they displayed some limited functionality.
“Trying to see how CAHS proteins behaved in insect and human cells presented some interesting challenges,” said Tanaka in the statement. “For one thing, in order to visualize the proteins, we needed to stain them so they show up under our microscopes. However, the typical staining method requires solutions containing water, which obviously confounds any experiment where water concentration is a factor one seeks to control for. So we turned to a methanol-based solution to get around this problem.”
These new techniques could help scientists figure out new ways to preserve biological materials for long periods, which could extend the shelf life of medicines or improve access to organ transplants. But they also open yet another window into the secret mechanisms that make tardigrades some of the toughest, and most adorable, animals on the planet.
“Everything about tardigrades is fascinating,” Kunieda concluded. “The extreme range of environments some species can survive leads us to explore never-before-seen mechanisms and structures. For a biologist, this field is a gold mine.”
