Baldness and follicle stem cells
Hair grows from stem cells located in the hair follicles. During aging, the hair follicles gradually lose their ability to give hair growth, which leads to their thinning and loss. In a new study, a team from Tokyo Medical and Dental University and the University of Tokyo has identified a new mechanism by which hair follicles lose their regenerative abilities.
The basis for the growth of new hair is the proper function of the stem cells of the hair follicles. They undergo cyclic symmetrical and asymmetric cell divisions. Symmetrical cell division generates two identical cells with the same functions, while asymmetric division generates a differentiating cell and a self-renewing stem cell. The combination of these types of division preserves the stem cell population. For proper functioning, symmetrical and asymmetric cell divisions must be in balance. As soon as stem cells are more often exposed to one of them or even deviate from the typical process of cell division of any type, the functions of hair follicles suffer.
A team of researchers led by Amy Nishimura studied the division of stem cells in hair follicles in young and old mice using two different types of analysis: determining the fate of cells and analyzing the direction of cell division. In the first case, the hair follicle stem cells were labeled with a fluorescent protein so that they could be monitored for a long time. In the second case, the direction of cell division was determined, that is, the future of daughter cells. The researchers were able to show that the stem cells of the hair follicles of young mice underwent typical symmetrical and asymmetric cell divisions, while in older animals they chose an atypical type of asymmetric cell division.
But why does the mechanism of cell division change so dramatically during aging? To answer this question, the researchers focused on the semidesmosome proteins that connect cells to the extracellular matrix. It is already known that specific proteins of the extracellular matrix give cells polarity, that is, the ability to sense their position in a given space. The researchers found that during the aging process, both semi-chromosomal proteins and polarity proteins are destabilized, which leads to the formation of aberrantly differentiating cells during the division of hair follicle stem cells. As a result, their stock is not replenished and is lost over time – this leads to thinning and hair loss.
Diagram of different types of hair follicle stem cell divisions (HFSC). Young HFSCs undergo symmetrical and asymmetric division, generating, among other things, new stem cells. Old HFSCs provoke instability of semidesmosomes, including COL17A1 collagen, and undergo stress disruption of asymmetric division, which leads to a gradual decrease in the number of HFSCs.
Thus, hair follicles lose their ability to regenerate hair with age due to a gradual decrease in the number of stem cells. The results of the study may help in the development of new methods for regulating the aging of organs and aging-related diseases.
Article by H.Matsumura et al. Distinct types of stem cell divisions determine organ regeneration and aging in hair follicles is published in the journal Nature Aging.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on TMDU: The bald truth – altered cell divisions cause hair thinning.