The eyes and hearts of these deep-sea sharks use biological tricks to keep them functioning
Greenland sharks reveal new secrets about fighting aging.
In the deep, dark waters of the Arctic and North Atlantic, these ghostly giants – who can live for centuries – have discovered some tips for long-term survival. Some of their organs may be resistant to the ravages of age, while others appear resistant to tissue damage that accumulates over time, recent studies suggest.
The results offer some insight into how these sharks manage to live longer than all other vertebrates on the planet. This work could one day lead to therapies to treat aging organs in humans, says Lily Fogg, a biologist at the University of Basel in Switzerland. It’s “the ultimate goal of the dream,” she says.
Scientists believe that Greenland sharks (Dreamy microcephaly) can survive more than four hundred years. “They’re these huge, ancient grandfather sharks,” says Fogg. But it’s unclear how their bodies continue to navigate decade after decade.
Fogg’s team studied the animals’ eyeballs. No one knew whether sharks had great vision, let alone whether that vision deteriorated over time. The common idea was that sharks were either severely visually impaired or completely blind, Fogg says. She and her colleagues examined eye tissue from 10 Greenland sharks, some about 150 years old. The animals had all the cellular and molecular tools to see in the dim light of the deep seathe team reported on January 5 in Natural communications.
The fabric also seemed to have avoided the typical wear and tear of aging. This may be due to increased activity of DNA repair mechanisms in the eyes, says Fogg. This machinery repairs damage that can lead to cell death and tissue degeneration. A previous study of the Greenland shark genome also found enhanced DNA repair functionreported physiologist Alessandro Cellerino and colleagues.
The anti-aging strategy at work in the eyeballs, however, may not occur in all of the Greenland shark’s organs. Researchers studying the animal’s heart have discovered that it appears to collect the typical elements scars and stress in this era of tattoos on our tissues, scientists reported December 23 on bioRxiv.org. “We expected the opposite,” says Cellerino, of the Ecole Normale Supérieure in Pisa, Italy.
His team dissected and examined the hearts of six Greenland sharks. Researchers found organs peppered with stubborn scars that accumulated as the animals aged. In humans, this scar tissue is a sign of cardiovascular disease. This stiffens the heart, making it more difficult to pump blood efficiently. The sharks’ hearts also showed signs of cellular damage, such as energy-producing mitochondria being broken down and introduced into the cells’ recycling centers.
Yet, according to Cellerino, despite the scars and other damage, the sharks’ hearts still appear to function. They can continue to pump even in the face of damage that would cause other animals’ hearts to give out. Researchers aren’t sure why, but they think shark tissues may produce protective hormones that help the heart cope with age-related injuries.
Environmentalist Catherine Macdonald says she is not surprised by the two papers’ findings. “Any animal with such a long lifespan will need the ability to both repair and maintain itself,” says Macdonald, of the University of Miami. She wants to learn more about how shark eyes and hearts work in living animals. This is difficult to study in a shark that can dive up to 2,200 meters below the ocean surface. But a better understanding of what underlies these animals’ extended lifespans could offer clues to the mysteries of aging in humans, she says.
Yet Macdonald doesn’t see immediate applications for human health. And this new work certainly doesn’t mean consumers should jump on shark-based anti-aging trends, she says. “We don’t need to go out and start drinking Greenland shark blood.”
