Progenitor Cells in Hair Loss - Bernstein Medical - Center for Hair Restoration
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Following some new research on stem cells, and their relationship with androgenetic alopecia (genetic hair loss), an article on stem cells and the way they organize hair growth was published in the April 29th issue of the journal Science.

At issue is not the conversion of hair follicle stem cells into the progenitor cells that stimulate hair growth, as with the prior research, but the ways in which large numbers of stem cells coordinate the cycle of hair growth over thousands of hair follicles. How do all of those hair follicle stem cells know when to grow hair, and how do they know what their “neighbor” hair follicles are doing?

The researchers studied hair growth patterns in rabbits and mice and discovered that certain types of molecules, which were previously known to act as a signaling mechanism for stem cells in maintaining an individual hair follicle’s growth cycle, were also important in enabling large groups of stem cells to coordinate their activity.

The scientists found that hair stem cells coordinate their regeneration with each other with the aid of a pair of molecular activator WNT and inhibitor BMP. When WNT and BMP signals are used repetitively among a population of thousands of hair follicles across the entire skin surface, complex regenerative hair growth behavior emerges via the process of self-organization.

Perhaps more importantly, they found that the stem cell communication pathway present in rabbits and mice is far more robust than in men and women.

“When each human hair follicle wants to regenerate, it can only count on itself; it’s not getting help from other follicles,” Chuong said. “But when a rabbit hair follicle regenerates, it can count on two inputs: its own activation, and the activation signal from its neighbors. Rabbits have a very active hair growth, and that is essential for their survival in the wild.”

The article suggests that if there was a way to manage that process in humans, or “turn back on” the stem cell communication process in human hair follicles, then a treatment could be developed which would substantially increase the number of hair follicles that produce healthy hair.

Read a summary of this new research at ScienceDaily.com.

For more discussion on recent research, visit the Hair Cloning topic.

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We recently discussed ground-breaking research that pointed to the important differences between stem cells and progenitor cells in the development of common baldness, or androgenetic alopecia (AGA).

In the March/April 2011 issue of Hair Transplant Forum International, we see a review of that research and another indication of the importance of this research in achieving the goal of being able to clone human hair.

It is now well established that, in each hair cycle, stem cells divide and generate progenitor cells, and that these progenitor cells stimulate the growth of the hair follicle. In conducting the experiment, the scientists’ original hypothesis was that the number of stem cells would be lower in scalp samples from bald areas than areas of scalp with hair. Surprisingly, they found that the stem cells were present in both samples. However, they found that the number of progenitor cells in the samples with hair was significantly higher in comparison to the bald samples. These findings suggest that it is not a reduced number of stem cells that leads to AGA, but the decreased conversion of stem cells into progenitor cells.

The research also suggests that the conversion of stem cells to progenitor cells may be the crucial mechanism that, when disrupted, leads to miniaturization of hair follicles, and common baldness. If there was a way to prevent the breakdown of stem cell conversion to progenitor cells, that could, in theory, stop the process of miniaturization and prevent androgenetic alopecia from occurring.

The study’s results and the review in the hair restoration journal indicate that, while a great deal of research must still be conducted, the scientific community is zeroing in on the cause of, and a potential cure for, genetic hair loss which has affected men and women for millennia.

For further reading on this exciting topic, here are some links:

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Research published in the January 2011 issue of the Journal of Clinical Investigation (Vol. 121, issue 1) reveals another breakthrough in the medical community’s understanding of the causes of — and possible cure for — androgenetic alopecia, or common male pattern baldness. The new research shows that the presence of a certain type of cell, called progenitor cells, is significantly reduced in men with common baldness compared to men who are not bald.

An article on AOL, which calls these “faulty” stem cells the root of hair loss in men, sheds light on the findings:

Using cell samples from men having hair transplants, a team led by University of Pennsylvania dermatologist Dr. George Cotsarelis compared follicles from portions of bald scalp to follicles from scalp areas with hair.

They learned that on the same person, the bald patches had an equal number of stem cells as the patches with hair. But they did find a difference: the areas of bald scalp had a significantly lower number of a more mature type of cell, called a progenitor cell.

That finding suggests that stem cells in parts of the head without hair have malfunctioned, losing their ability to convert into progenitor cells. ((AOL, “Scientists Trace Root of Male Hair Loss to Faulty Stem Cells,” January 5th 2011))

The study showed that, contrary to conventional wisdom, it is not the total “number” of stem cells that causes hair loss. In fact, the scientists’ original hypothesis was that, “the miniaturization of the hair follicle seen in [androgenetic alopecia] may result from loss of hair follicle stem cells.” That hypothesis turned out to be inaccurate. Instead, the authors of the study indicate that the findings:

…Support the notion that a defect in conversion of hair follicle stem cells to progenitor cells plays a role in the pathogenesis of [androgenetic alopecia]. ((J Clin Invest. doi:10.1172/JCI44478.))

The study’s results suggest that further research into the mechanism for the conversion of hair follicle stem cells to progenitor cells is warranted. If scientists can devise a way to correct that mechanism, then, in theory, stem cells in men who are predisposed to have androgenetic alopecia can be converted to progenitor cells at a normal rate. That correction would, in theory, eliminate that person’s susceptibility to the hair follicle miniaturization which causes hair loss, and would effectively cure his male pattern baldness.

Progenitor Cells vs. Stem Cells

Compared to stem cells, progenitor cells are further along in the process of differentiating into their target tissue, in this case mature hair follicles. Whereas stem cells are pluripotent, meaning that they can differentiate into a number of types of cells, progenitor cells are already committed to a specific cell line. Another important difference between stem cells and progenitor cells is that stem cells can replicate indefinitely, whereas progenitor cells can only divide a limited number of times.

For further reading on this stem cells and the causes of hair loss, here are some links:

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