Scientists have never exactly agreed on how the sloughing of old and growth of new skin works, but new research may provide the answer. Engineers and biologists at the University of Sheffield have shown how a recent theory — that skin has ‘sleeping’ stem cells which can be woken when required — best explains how our skin constantly regrows. The research — conducted in collaboration with The Procter & Gamble Company (P&G), and published in Nature Scientific Reports — has implications for combating the effects of ageing and perhaps even skin cancer.
The Sheffield/P&G team developed an ‘in silico’ (computer) model of human skin biology, capturing how the outer layers of the skin are developed and maintained over time. This ‘virtual’ skin was then used to test the three most popular theories of how skin cells function to regenerate over a 3-year period.
When the simulation was run according to two of the theories, the virtual skin failed to fully regenerate. Only one theory enabled the virtual skin to still be in good shape after three years, as Dr Xinshan Li (University of Sheffield Faculty of Engineering) and Dr Arun Upadhyay (P&G) explained in their research.
‘The theory which seems to fit best says that skin has a population of ‘sleeping’ stem cells, which sit in the lowest layer of the skin, but don’t constantly divide to make new cells,’ said Dr Li.
‘However, these sleeping cells can be called into action if the skin is damaged, or if the numbers of other types of more mature skin cells decrease, ensuring that the skin can be constantly regenerated under all conditions.’
The model showed that we gradually lose these sleeping stem cells over time, which would explain why our ability to regenerate skin reduces as we age.
‘Each time we wake up these cells, to heal a wound or replenish stocks of other cells, a few of them don’t go back into sleep mode, so the population slowly reduces,’ said Dr Li. ‘This explains why older skin is slower to heal and in part why our skin changes as we age. By understanding this mechanism better, it might be possible to find ways to combat the effects of ageing on our skin.’
Computer modelling of skin biology is the latest step in the evolution of skin science. It allows scientists to project the activity of tissues that are difficult to follow in live systems for extended periods. The ability to follow virtual skin models over decades may be especially important to skin cancer research. Environmental damage caused by UV exposure or chronic wounding can cause sleeping cells to harbour the mutations which cause skin cancers.