Hair grows from stem cells residing in hair follicles.
During aging, the capability of hair follicles to grow hair is successively lost, leading to hair thinning and ultimately hair loss.
In a new study, researchers found a novel mechanism by which hair follicles lose their regenerative capabilities.
The research was conducted by a team from the University of Tokyo and elsewhere.
Hair follicles are mini-organs from which new hair constantly grows. The basis for new hair growth is the proper function of hair follicle stem cells (HFSCs).
HFSCs undergo cyclic symmetric and asymmetric cell divisions (SCDs and ACDs). SCDs generate two identical cells that go on to have the same fate, while ACDs generate a differentiating cell and a self-renewing stem cell.
The combination ensures that the stem cell population continues to exist, yet how those contribute to the loss of HFSC function due to aging is not yet completely understood.
In the study, the team aimed to understand how stem cell division plays into hair growth during aging.
To achieve their goal, they examined stem cell division in HFSCs in young and aged mice by employing two different types of assays.
Strikingly, the researchers were able to show that while HFSCs in young mice underwent typical symmetric and asymmetric cell divisions to regenerate hair follicles, during aging they adopted an atypical senescent type of asymmetric cell division.
But why does the mode of cell division change so drastically during aging? To answer this question, the researchers focused on a class of proteins that connect the cells to the extracellular matrix.
The researchers found that during aging, HFSCs become exhausted and lost (leading to hair thinning and hair loss) over time.
These are striking results that show how hair follicles lose their ability to regenerate hair over time.
The results may contribute to the development of new approaches to regulate organ aging and aging-associated diseases.
One author of the study is Emi Nishimura.
The study is published in Nature Aging.
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