By studying mice, researchers found that stem cells in the fatty layer of the skin send signals that trigger hair growth, and suggest the discovery could lead to new treatments for reversing baldness. The Yale researchers write about their study in the 2 September issue of Cell.
Senior author Valerie Horsley, assistant professor of molecular, cellular and developmental biology, told the press that:
“If we can get these fat cells in the skin to talk to the dormant stem cells at the base of hair follicles, we might be able to get hair to grow again.”
The skin of a mammal is a complex organ comprising many types of cell in various layers. Also, while it looks like it’s not doing much, inside these layers there is enormous dynamic activity, but it is stable, because the cells signal to each other to ensure a homeostatic balance between processes of growth, death and regeneration of different types of tissue.
One such process is the generation of hair. Hair grows because stem cells in the follicle roots receive signals that jump start the fairly complex cycle of hair regeneration, growth and gathering of cells to push out through the follicle, to resting and anchoring the hair to the skin, to death of the follicle and hardening the protein coat surrounding the hair shaft.
Without the jump starting signals the cells that generate hair remain dormant, but they are still there, even in men with male pattern baldness, said the researchers. Scientists have known for some time that the follicle stem cells need to receive signals from elsewhere in the skin for the hair generation cycle to initiate, but until this study, it was not clear which part of the skin actually sends the signals.
Horsley and colleagues noticed that when hair dies, the layer of fat that makes up most of the thickness of the skin on the scalp gets thinner. When hair growth begins, the layer of fat thickens: this process is called adipogenesis (literally the creation of new fat cells).
By studying mice they found that adipose precursor cells, a type of stem cell that is involved in the making of new fat cells, were essential for hair growth to occur in the mice. Immature fat cells, in fact, appear to be “necessary and sufficient for hair follicle regeneration”, they discovered, and these cells express a molecule called PDGF (platelet derived growth factor) to promote hair regeneration.
“Functional analysis of adipocyte lineage cells in mice with defects in adipogenesis and in transplantation experiments revealed that intradermal adipocyte lineage cells are necessary and sufficient to drive follicular stem cell activation,” write the researchers.
Horsley and colleagues are now trying to discover what other signals the adipose precursor stem cell send that may also regulate hair growth, and whether these same signals regulate hair growth in humans.
Funds from the National Institutes of Health and the Connecticut Stem Cell Research Program helped pay for the study.
Written by Catharine Paddock PhD