How does a cell know when to stop dividing?
Cells stop dividing through built-in emergency brakes that respond to damage, stress, or viruses. This system is protective in the short term, but when chronically activated it can cause damage itself.
A cell does not simply divide without limit. When it encounters damaged DNA, an energy shortage, or excessive oxidative stress, it can apply a kind of emergency brake: a permanent halt to division called senescence. This protects the tissue by preventing damaged cells from passing their errors on to daughter cells.
That emergency brake has a downside. In the short term the standstill is useful, but when too many cells remain in this state for a long time they accumulate in tissues. They then secrete signalling molecules that damage surrounding cells. As a result, accumulated senescent cells are associated with diseases such as atherosclerosis, joint degeneration, and cancer. The same pattern is well documented in kidney damage: a temporary halt to division protects the kidney during acute injury, but if that halt lasts too long it actually contributes to permanent kidney disease.
The cell has multiple checkpoints in its division cycle, and each checkpoint can respond to different signals. Some viruses, such as cytomegalovirus, actively force a cell to stop at a specific checkpoint so that the virus can replicate its own genetic material. Replication stress, in which the machinery that copies DNA is damaged by reactive oxygen species, leads to arrest at a different point.
In cancer research this mechanism is used as a point of attack. Experimental compounds, including a derivative of a plant acid and an extract from liquorice, can force cancer cells to stop dividing and subsequently die. Plant-derived alkaloids also block the division of colorectal cancer cells in laboratory research. This has been demonstrated exclusively in cell culture and in animal models; whether it works in humans has not yet been investigated.
All claims are based on two to four published studies per sub-topic. The basic biological mechanism (senescence) has moderate support from human and animal research. The cancer-related applications are exclusively preclinical.
Why do some cells stop dividing as you age?
Cells stop dividing as a protection against damage and cancer, but the accumulation of such stopped cells contributes over the years to inflammation and age-related diseases. Drugs that target this are promising in animal research, but are not yet ready for use outside clinical studies.
What is the difference between cell division and cellular ageing?
Cell division and cellular ageing are two sides of the same biological story: every division costs a small piece of telomere, and once those are used up, the cell stops dividing permanently. That distinction is well established and forms the basis of much research into ageing.
Why do cells lose their ability to repair themselves over time?
Cells lose their repair capacity through a combination of declining energy stores, impaired DNA repair and the accumulation of 'burned-out' cells that secrete inflammatory substances. These are well-supported mechanisms, although it is still too early to act on them through supplements or therapies.
What do zombie cells do to your ageing?
Zombie cells accumulate as you age and accelerate ageing through inflammatory signals; how to tackle them is promising but still very much under investigation.
Can meditation do anything about ageing at the cellular level?
There are cautious indications that meditation favourably influences the activity of the telomere-repairing enzyme, but whether this truly keeps your cells younger has not yet been convincingly proven. Meditation for stress reduction has a considerably stronger evidence base in any case, and an indirect effect on cellular ageing via that pathway is plausible.
Do my stem cells run out as I get older?
Your stem cells do indeed decline with age: they repair tissue less effectively and become partly exhausted. Regular exercise, good sleep and not overeating are the best-supported ways to slow this process.