Nobody likes the thought of getting older, but it seems like an inevitable part of life. Most species grow, develop, and repair damage to their bodies up to some point in adulthood. After this, the body becomes less able to repair itself and slowly begins to accumulate damage.
But that doesn’t seem to apply to lobsters. They continue to grow throughout their exceptionally long lives – the oldest known lobsters caught weighed over nine kilograms and are estimated to be 120 to 140 years old.
Lobsters don’t die of old age. Instead, they end up on the seafood buffet or die of exhaustion during moulting – the process by which they swap shells as they grow larger.
Our cells have a “biological clock”
To understand why lobsters are so long-lived, we must first understand the aging process.
We are made up of cells that contain DNA – the genetic code that directs our body to carry out all the functions necessary for life. The linear strands of DNA are bundled into structures called “chromosomes”. Each chromosome contains telomeres, which are caps on the ends of DNA strands to protect them from damage. The telomeres are like the plastic tips on the ends of shoelaces that prevent fraying. Without telomeres, DNA can become damaged and alter the genetic code, which can affect a cell’s ability to function properly.
“You have to be able to protect the information in your genes, in your DNA,” said Dr. Ashwin Unnikrishnan, Head of the Molecular Mechanisms Laboratory in the Leukemia Laboratory at UNSW Medicine & Health. “Cells have engineered a solution to this problem by adding these features called telomeres. These are essentially repeating units of DNA that do not encode information per se, but can be eroded while protecting the information within the chromosome.”
Each cell in our body has a finite lifespan and must renew itself by dividing into two “daughter cells”. Before a cell divides, it must copy its DNA, which means that two copies of the DNA are available—one for each daughter cell. Each time the DNA is copied in the cell, the telomeres get shorter.
“Every time the cell divides, there is a small erosion of the telomeres. When it reaches a certain critical length, the cell can no longer divide,” said Dr. Unnikrishnan.
Telomere length is a “biological clock” that determines how many divisions a cell can make. Eventually, the remaining telomere is too short and the DNA is vulnerable to damage. At this point the cell stops dividing and either self-destructs or becomes inactive. As humans (and most other species) age, many of our cells reach this stage, which means our bodies break down and eventually stop functioning.
The secret of lobster longevity
Lobsters have exceptional lifespans due to an enzyme called ‘telomerase’ in many of their cells. Telomerase restores the length of telomeres and increases the number of divisions a cell can undergo before it dies or becomes inactive. This allows the cells to keep dividing and allows lobsters to keep growing and repairing their bodies – hence their very long lifespans.
Humans only have an active telomerase in certain special cells, such as stem cells, which can renew itself over a very long period of time. Other cells in our body that don’t contain the so-called “immortality enzyme” have a limited lifespan before the telomeres are exhausted.
Will we see telomerase-based therapies soon?
This leads us to the inevitable question: Could humans be using telomerase to slow down our biological clock and live longer? Well, don’t be so hasty about your telomerase treatment—there’s a link between telomerase activity and cancer.
“My main reason why I am skeptical about this strategy is this [telomerase] is not normally expressed in most adult cells. But it’s often “turned on” in cancer cells…it helps maintain cancer’s “immortality,” said Dr. Lindsay Wu, Head of the Aging Research Laboratory at UNSW Medicine & Health.
Unlike normal adult cells, cancer cells often activate the telomerase enzyme. Telomerase is constantly repairing their DNA, allowing them to divide many times without being controlled by a “biological clock”.
The complex relationship between telomeres, aging and cancer needs to be better understood before telomerase could possibly ever be used in a therapeutic setting. For now, lobsters will be laughing at us from the bottom of the ocean while we take our third nap of the day and (again) forget where we left the car keys.