Unregulated hair growth from overactive stem cells leads to premature greying and hair thinning in mice
Stem cells are essential if you want to grow any new hair, but at any one time many hair follicles are in a dormant, or quiescent state. This means only a portion of hair is growing at any one time, and it turns out this quiescence may be important in preserving hair thickness and colour.
"In an earlier study, my lab showed that when mice age, the old fat in their skin produces higher levels of a secreted signal, called BMP. This signal acts as a molecular brake on the hair follicle stem cells, causing them to spend much longer times in quiescence"
A new study had observed that in aging mice hair stem cells are influenced by an increased in a signalling molecule called BMP. BMP regulates stem cell behaviour and leads to more time spend in a quiescent state. The researchers initially believed that circumventing this block might restore hair, and so they knocked out a specific gene FOXC1 that is normally activated by BMP.
When they did this hair did indeed grow more rapidly as a result of constant stem cell activation, but the accelerated growth unexpectedly had a downside; greying and sparser hair. It seems that carefully pacing hair growth cycling had a beneficial effect on maintaining healthy hair growth, and that this pacing also helped to preserve melanocyte activity - maintaining hair colour for longer. This suggests that a loss of quantity and quality of stem cells in these bulges has a knock on effect, and that perhaps implantation or correction of these zones may one day restore hair growth and colour.
"Hair follicle stem cells influence the behavior of melanocyte stem cells, which co-inhabit the bulge niche. Thus, when the numbers of hair follicle stem cells declined with age, so too did the numbers of melanocyte stem cells, resulting in premature greying of whatever hairs were left"
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