Determining the age of the oldest living cell is a fascinating scientific question. Cells are the basic building blocks of life, so understanding their longevity provides insight into the nature of organisms. Answering this question requires investigating which types of cells can live the longest and what allows them to survive for so many years.
What is a cell?
A cell is the basic structural and functional unit of life. Organisms are made up of one or more cells. Each cell contains the fundamental molecular components necessary for life: DNA, RNA, proteins, lipids, and carbohydrates. Cells carry out all of the processes needed for organisms to live, grow, and reproduce.
There are two main types of cells: prokaryotic cells and eukaryotic cells. Prokaryotic cells are simpler and smaller than eukaryotic cells. Bacteria and archaea are made up of prokaryotic cells. Eukaryotic cells are larger and more complex. They contain specialized structures called organelles that carry out different cell functions. Animals, plants, fungi, and protists are made up of eukaryotic cells.
How do cells age?
Cells age due to a variety of molecular and cellular processes:
- Damage to DNA – Environmental stressors and errors during DNA replication can cause mutations to accumulate over time.
- Shortening of telomeres – Telomeres are protective caps on the ends of chromosomes that shorten with each cell division.
- Accumulation of degraded molecules – Cellular waste products and damaged proteins build up over time.
- Impaired mitochondria – Mitochondria are the “powerhouses” of cells. Their function declines with age.
- Loss of proteostasis – The breakdown of mechanisms that regulate protein production, folding, and degradation.
- Cellular senescence – Cells permanently stop dividing after a certain number of divisions.
These age-related changes reduce cell function and viability. Cells have molecular pathways to repair damage and remove waste. However, over time the accumulation of damage outpaces repair mechanisms, leading to cell aging.
What types of cells live the longest?
Certain cell types have properties that allow them to survive for extraordinarily long periods of time. The longest-lived human cells include:
- Neurons – Most neurons in the cerebral cortex live the entire lifetime of the organism. They stop dividing early in development.
- Cardiomyocytes – Heart muscle cells generally last as long as the individual, except those damaged by heart attacks.
- Retinal cells – Many cells in the retina, including rods, cones, and ganglion cells, last a lifetime.
In addition, some long-lived model organisms provide examples of extremely durable cell types:
- Hydra stem cells – Small freshwater invertebrates called hydra appear to be immortal. Their stem cells continuously divide without signs of aging.
- Planarian stem cells – Flatworms called planarians can regenerate an entirely new body from a tiny piece of tissue due to their pluripotent stem cells.
- Lobster nerve cells – Lobsters exhibit negligible senescence and some nerve cells persist for decades.
Stem cells and non-dividing cells exhibit enhanced longevity compared to rapidly dividing cells. DNA repair mechanisms and resistance to stress also contribute to their long lifespans.
What is the oldest known cell?
Based on current evidence, the oldest known continuously living human cells are neurons in the cerebral cortex and retinal cells in the eye.
Researchers used carbon-14 generated by nuclear bomb testing during the Cold War to determine the lifespan of human cortical neurons. Atmospheric levels of carbon-14 peaked in the 1960s. By measuring the amount of carbon-14 in DNA, scientists could date the birthdate of cells. This technique found that most neocortical neurons are as old as the individual, indicating lifespans of over 90 years in some people.
Likewise, a study that measured levels of carbon-14 in retinal tissue determined that cells in the eye’s center, called the macula, are as old as the person. These retinal cells live for a lifetime.
Outside of actual aged human cells, some other extraordinarily durable cells include:
- Greenland shark eye lens cells – Estimated to be 300 to 500 years old
- Antarctic sponge stem cells – Possibly 1,000+ years old based on sponge size
- Creosote bush root cells – 11,700 years old based on carbon dating
In summary, the best available evidence points to human cortical neurons and retinal cells as the longest-living human cells, with potential lifespans over 90 years. But some non-human species possess certain cells that may remain viable for centuries or even millennia.
How do cells live so long?
The cellular properties and behaviors that allow for such incredible longevity include:
- Non-dividing state – Cells that do not divide, like many neurons, avoid shortening telomeres and accumulating replication errors.
- Stem cell potency – Pluripotent stem cells can self-renew through cell division without signs of aging.
- Low metabolism – Slow-metabolizing cells generate fewer reactive oxygen species that cause molecular damage.
- Efficient repair mechanisms – Long-lived cells invest in robust DNA and protein repair pathways.
- Resistance to stress – Adapted to withstand extreme environmental conditions like hypoxia or anoxia.
- Anti-aging molecules – Some cells produce anti-aging compounds and antioxidants.
Additionally, the post-mitotic cells in the central nervous system benefit from being located in an immunoprivileged site behind the blood-brain barrier. This limits inflammation and exposure to pathogens and toxins.
The ability to maintain genomic integrity appears especially important for cellular longevity. Neurons and stem cells are very effective at repairing DNA damage caused by aging and environmental stressors.
Do immortal cell lines exist?
There are some cell lines that appear immortal under laboratory cell culture conditions. Examples include:
- HeLa cells – Cervical cancer cells that have been dividing continuously since 1951.
- Henrietta Lacks cells – Taken without consent from Henrietta Lacks, these cancer cells proliferate indefinitely.
- HCT 116 cells – An intestinal cancer cell line cultured since the 1970s.
- 3T3 cells – Mouse fibroblast cells that have doubled over 200 times since 1962.
However, it is unclear whether these cell lines would continue dividing forever if left in the body. The culture conditions provide an artificial environment optimized for cell growth. In the body, immortal cell lines like cancers are subject to metabolic constraints, immune attacks, and contact inhibition that limit runaway expansion.
While immortalized cell lines are an important research tool, there is no clear evidence that healthy non-cancerous cells can proliferate indefinitely. Cells removed from the body and cultured in vitro do not necessarily reflect natural aging processes.
Conclusion
Based on current scientific evidence from carbon dating and other techniques, the oldest confirmed living cells are neurons and retinal cells in humans that have persisted for more than 90 years. Comparative research on long-lived animals such as sponges, sharks, and plants like creosote bushes demonstrate that certain cells may endure for centuries or millennia.
Non-dividing cells, stem cells, and cells with efficient repair mechanisms seem most apt to achieve exceptional longevity. While immortal cell lines can divide forever in laboratory cultures, cells in the body are subject to metabolic, environmental, and genetic constraints on indefinite proliferation. Understanding how the oldest cellular survivors are able to maintain viability for so long remains an intriguing avenue of aging research.