To survive wintry months in the American Northeast, hardy amphibians, fish, and bloodsucking ticks have antifreeze proteins that help prevent tissue damage. And now, researchers show that this frostbite protection could be transferred to mammals—specifically mice, for starters. The findings were published in PLOS ONE this week.
For ectotherms that can’t regulate their internal body temperature, antifreeze proteins prevent cold damage by limiting the growth of ice crystals from water molecules in the body. Ice needles inflict a lot of damage to tissue. Previous work have identified an antifreeze glycoprotein called IAFGP in blacklegged ticks (Ixodes scapularis), and these proteins even serve their cold protective function in experiments with fruit flies.
This time, a Yale team led by Erol Fikrig wanted to see if the antifreeze glycoprotein—when expressed by genetically engineered mice—could protect mammal cells and living mammals from cold shock and frostbite, respectively. After introducing the tick antifreeze protein into mice, the team stored mouse skin samples at 4 degrees Celsius for four days. The team also dipped the tails of these transgenic mice who could produce antifreeze glycoproteins into a liquid bath of minus 22 degrees Celsius for seven days.
Turns out, “if you put an antifreeze protein into warm-blooded animals, it does elicit antifreeze activity and it can protect the animal from frostbite,” Fikrig says in a news release. The skin samples showed reduced cell death and even increased in number after cold storage compared with control cells. And the live transgenic mice showed increased temperature resistance: 60 percent of the treated mice showed no visible sign of frostbite, compared to only 11 percent of control mice. Their tails also showed fewer signs of a gangrenous inflammation consistent with frostbite damage.
If tick-derived antifreeze would work well in other mammals, these might help extend the amount of time donated organs could spend in cold storage before the actual transplant surgery. But it might be a while. "Our study doesn't address the question of how we'd deliver the protein," Fikrig tells the Washington Post. "We're using transgenic mice, and we're obviously not going to put this gene into people." Maybe one day this antifreeze could help people with cold sensitivity due to autoimmune disorders like scleroderma.
