Researchers have published studies on the Greenland shark (Somniosus microcephalus), examining its genome and eye function to understand the genetic and biological mechanisms associated with its long lifespan, which is estimated to reach up to 400 years.
The Greenland sharkâs genome and pristine eyes may hold the key to understanding extreme longevity, potentially offering new pathways for human aging and retinal health research.
Genome Sequencing and Key Findings
A team led by Shigeharu Kinoshita at the University of Tokyo sequenced nearly the entire genome (96.7%) of a Greenland shark. The sequencing revealed several genetic adaptations that may contribute to the shark's longevity and resistance to cancer:
Histone modifications: Unique amino acid substitutions in linker histone proteins were identified, which may stabilize chromatin and reduce the accumulation of DNA damage.
Gene family expansion: Expanded gene families related to immune responses and DNA repair pathways were found. This suggests efficient damage repair and immune regulation may play roles in longevity and cancer resistance.
Ferritin gene expansion: An increase in ferritin genes was observed, suggesting enhanced control of iron metabolism and limitation of oxidative stress, potentially restricting ferroptosis.
Eye Function and Retinal Health
A separate study, published in Nature Communications, examined the eyes of 10 deceased Greenland sharks estimated to be between 100 and 134 years old. The study found that the sharks' eyes remain fully functional with minimal deterioration over time.
Key observations include:
- The sharks' eyes, measuring 5-6 centimeters in diameter, contain only rod cells, optimized for dim light vision, resulting in black-and-white perception with limited resolution.
- Despite parasitic copepods (Ommatokoita elongata) attaching to the corneas, the sharks' ability to detect light, contrast, and movement is not significantly hindered.
- The retinas of the studied eyes were found to be in pristine condition with no signs of degeneration.
Lead study author Lily Fogg and senior author Dorota Skowronska-Krawczyk identified that specific DNA repair genes, ERCC1 and ERCC4, may contribute to the long-term health of the shark's retina.
Expert Perspectives
"Features linked to immune enhancement, cancer resistance, DNA repair, and chromatin stability may explain the shark's lifespan," said Dorota Skowronska-Krawczyk (University of California, Irvine), though she noted that functional studies are still needed.
Aaron MacNeil (Dalhousie University) expressed skepticism regarding the 400-year age estimate for the shark, suggesting it may be too high, while acknowledging the sharks are at least 200 years old.
Visual neuroscientist Patricia Jusuf noted that the same DNA repair genes identified in the shark are involved in human DNA repair pathways, and that malfunctions in these genes in mammals are linked to premature aging.
Potential Biomedical Applications
According to Kinoshita, the genome findings indicate that extreme longevity involves coordinated changes across multiple biological systems, including genome stability, iron metabolism, immune function, and stress resistance. This may inform research on human aging and age-related diseases.
Regarding eye health, the absence of retinal degeneration in aged Greenland sharks suggests these DNA repair pathways could be important for maintaining retinal health. Researchers indicated this could offer avenues for addressing age-related retinal degeneration, macular degeneration, and retinitis pigmentosa, conditions that affect over 200 million people globally.
Future Research Directions
Researchers have indicated plans to study other "sleeper shark" species, including the southern sleeper shark (Somniosus antarcticus) and Pacific sleeper shark (Somniosus pacificus), for additional genetic insights that could have biomedical applications.
Previous research has also suggested that the shark's metabolism remains stable throughout its life, which may contribute to its longevity.