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Computer model said to help explain why skin ages

June 27, 2013
Courtesy of the University of Sheffield
and World Science staff

Sci­en­tists have nev­er quite agreed on we con­stantly grow new skin and slough off the old, but some say new re­search of­fers an an­swer.

En­gi­neers and bi­ol­o­gists at the Uni­vers­ity of Shef­field in the U.K. say a new com­put­er mod­el shows the key to the pro­cess is a pop­ula­t­ion of “sleep­ing” stem cells, or pro­gen­i­tor cells, in the skin. Signs of ag­ing arise as those cells are de­pleted.

The re­search, con­ducted with the Proc­ter & Gam­ble Co., which makes skin lo­tions, and pub­lished in Na­ture Sci­en­tif­ic Re­ports, may have im­plica­t­ions for com­bat­ing the ef­fects of ag­ing and skin can­cer.

The re­search­ers de­vel­oped a com­put­er sim­ula­t­ion to cap­ture how the skin’s out­er lay­ers de­vel­op and main­tain them­selves, and used it to test the three most pop­u­lar the­o­ries of how skin cells act to re­gen­er­ate skin. Only one the­o­ry en­abled the vir­tu­al skin to still be in good shape af­ter three years, the in­ves­ti­ga­tors said.

“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 study co-author Xin­shan Li of the Uni­vers­ity of Shef­field. “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.”

The mod­el in­di­cat­ed that we grad­u­ally lose these sleep­ing stem cells over time—which would ex­plain why our abil­ity to re­gen­er­ate our 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 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 ag­ing on our skin.”

Com­put­er mod­elling of skin is help­ful be­cause lab­o­r­a­to­ry cul­tures of en­gi­neered skin are vi­a­ble for only a few weeks, and stud­ies in hu­mans are only prac­ti­cal for a few months, the sci­en­tists ex­plained.

The abil­ity to fol­low vir­tu­al skin mod­els over dec­ades may be es­pe­cially im­por­tant to skin can­cer re­search, they added. En­vi­ron­men­tal dam­age caused by UV ex­po­sure or chron­ic wound­ing can cause sleep­ing cells to har­bor the muta­t­ions that cause skin can­cers such as ba­sal cell car­ci­no­ma, a very ag­gres­sive type of skin can­cer.

“The stem cells can har­bor muta­t­ions through­out the years, but with no ef­fect if they’re still in sleep mod­e,” said Li. “How­ever, when they start to di­vide to heal a wound for ex­am­ple, this could trig­ger the can­cer.”

Oth­er parts of the body, such as the lung or gut lin­ing and the cor­nea, al­so re­gen­er­ate in the same way as our skin, ac­cord­ing to sci­en­tists. Sci­en­tists at Shef­field are look­ing at, for ex­am­ple, the heal­ing pro­cess of the lung lin­ing af­ter asth­ma at­tacks.


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Scientists have never quite agreed on we constantly grow new skin and slough off the old, but some say new research offers an answer. Engineers and biologists at the University of Sheffield in the U.K. say a new computer model shows the key to the process is a population of “sleeping” stem cells, or progenitor cells, in the skin. The research, conducted with the Procter & Gamble Co., which makes skin lotions, and published in Nature Scientific Reports—has implications for combating the effects of aging and perhaps skin cancer. The researchers developed a computer simulation to capture how the skin’s outer layers develop and maintain themselves, and used it to test the three most popular theories of how skin cells act to regenerate skin. Only one theory enabled the virtual skin to still be in good shape after three years, the investigators said. “The theory which seems to fit best said 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 study co-author Xinshan Li of the University of Sheffield. “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.” The model indicated that we gradually lose these sleeping stem cells over time—which would explain why our ability to regenerate our 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 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 aging on our skin.” Computer modelling of skin is helpful because laboratory cultures of engineered skin are viable for only a few weeks, and clinical studies in humans are only practical for a few months, the scientists explained. The ability to follow virtual skin models over decades may be especially important to skin cancer research, they added. Environmental damage caused by UV exposure or chronic wounding can cause sleeping cells to harbor the mutations that cause skin cancers such as basal cell carcinoma, a very aggressive type of skin cancer. “The stem cells can harbor mutations throughout the years, but with no effect if they’re still in sleep mode,” said Li. “However, when they start to divide to heal a wound for example, this could trigger the cancer.” Other parts of the body, such as the lung or gut lining and the cornea, also regenerate in the same way as our skin, according to scientists. Scientists at Sheffield are looking at, for example, the healing process of the lung lining after asthma attacks.