Hair Follicle Dermal Stem Cell - Bernstein Medical - Center for Hair Restoration
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Scientific research is often the quintessential example of taking something apart to learn how it works. A team of researchers has used that age-old technique to unwind the complex process by which embryonic cells organize into functional skin that includes “organoids” like hair follicles. By untangling this biological mystery, they were able to develop a model that could potentially lead to hair regeneration treatments and other advances in regenerative medicine. The study — “Self-organization process in newborn skin organoid formation inspires strategy to restore hair regeneration of adult cells” — was published in the August 22nd, 2017 issue of the journal PNAS. ((Lei M, Schumacher LJ, et al. Self-organization process in newborn skin organoid formation inspires strategy to restore hair regeneration of adult cells. Proceedings of the National Academy of Sciences. 114. 201700475. 10.1073/pnas.1700475114.))

Background

Scientists have long known that embryonic cells organize and form bodily organs like the heart, liver, and skin, but understanding the details behind this spontaneous process of “self-organization” was a challenge. It has been understood that the DNA code produces chemicals that enable “cross-talk” between cells as they go through several stages in forming 3-dimensional, functional organs. But what these stages represented, and which specific molecules were involved in this communication, needed to be understood.

The Study

The researchers set out with two goals in mind: 1) to describe the conditions that enable a group of cells to self-organize into skin organs and 2) to describe transplant techniques that allow these skin organs to grow normal, functional hairs.

To achieve their first goal, the researchers started with populations of individual “dissociated” epidermal and dermal cells from newborn mice. They then combined these cells in a 3-D cell drop and observed the cells’ interactions. At every stage, they measured how the cells behaved and which proteins and molecules were present to promote or inhibit certain processes. The dissociated cells self-organized into functional skin through a complex 5-stage process:

  • Stage 1: Cells form aggregations
  • Stage 2: Aggregates form cysts
  • Stage 3: Cysts fuse to form epidermal “planes”
  • Stage 4: Small epidermal planes merge to form a larger, multi-layered plane of embryonic skin
  • Stage 5: Embryonic skin forms “placode” structures that can develop into hair follicles

When the Stage 5 cultured skin was transplanted to the back of a hairless mouse, it grew robust hair follicles.

Self-organization process in newborn skin organoid formation inspires strategy to restore hair regeneration of adult cells
(A) The experiment design. (B) Images showing the self-organization process. (C) Diagram of the stages of new skin formation. (D) Robust hair regeneration seen with cells from newborn mice but not adults. (E) Adult cells form only small aggregates. (F) Aggregate size with cells from newborn mice vs. adults. (G) Schematic showing how self-organization in adult cells stops before growth is complete. Image c/o PNAS

With a better understanding of these processes using embryonic cells, they went about attempting to induce this same process in adult mouse skin cells. Adult cells on their own formed only a few small aggregates which did not grow. To confirm the significance of newborn dermal cells and the chemicals that cause them to self-organize, the researchers experimented by first combining newborn dermal cells and adult epidermal cells and then combining newborn epidermal cells and adult dermal cells. The population that contained newborn dermal cells formed numerous hairs, while the population with newborn epidermal cells formed very few hairs.

Findings

  • Researchers identified several different classes of molecules that are required to induce the transitions between the various stages of skin development
  • The transition periods were not discrete events, but instead occurred over time and were dependent on the presence of the “communication” molecules
  • Inhibiting or promoting the key communication molecules can suppress or accelerate the phase transition process
  • Adding the communication molecules to adult cell cultures at the appropriate times can induce the adult cells to form functional skin complete with a robust number of hair follicles
  • It is both the progression of the phases and the presence of the molecular signals that, together, form the key to self-organization

Conclusion

The researchers behind this study sought to achieve two complicated tasks: to explain how cells self-organize and to induce self-organization in cells which had lost that capability. Only through painstaking experimentation were they able to untangle some of the mystery behind how these embryonic cells transform from a group of individual cells into fully-formed skin complete with hair follicles. This effort paid off, as they were able to apply the newfound knowledge to populations of adult cells. The capability to induce robust hair follicle growth in adult skin is a significant achievement.

For now, we must be content that the adult skin that was cultured in the lab needed to be grafted onto a healthy host. Next steps would be to determine how to use the same or similar process to induce hair follicle growth directly in the skin. Much more research must be done in that regard. However, the implications of this technique for the field of regenerative medicine may be substantial, as scientists explore the ability to regenerate not only skin organs but other body organs in the future.

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Hair follicle aging is driven by transepidermal elimination of stem cells via COL17A1 proteolysis
Researchers show how the normal hair cycle (left) is disrupted by DNA damage (center),
resulting in age-induced hair follicle miniaturization (right)

We have known for decades that the incidence of male pattern baldness increases with age. New research published in the February 2016 edition of the journal Science has shed light on why this is the case. Researchers examining the role of hair follicle stem cells (HFSC) in the hair growth cycle have found that accumulated DNA damage in these cells results in the depletion of a key signaling protein and the progressive miniaturization of the hair follicle (and eventual hair loss). ((Matsumura H, Mohri Y, Binh NT, et al. Hair follicle aging is driven by transepidermal elimination of stem cells via COL17A1 proteolysis. Science. 2016 Feb: Vol. 351, Issue 6273, p. 613.)) The study represents a breakthrough in our understanding of the cell aging process and could open new pathways for the treatment of not only hair loss but other age-related conditions as well.

Background: The Hair Growth Cycle

At any point in time, a hair follicle exists in one of three phases:

  • Anagen Phase – this is the “growth” phase in which the hair follicle is actively producing living hair. Anagen can last from two to seven years.
  • Catagen Phase – this is a short transitional phase in which hair growth stops, the middle of the follicle constricts, and the bottom of the follicle begins to form the “club.” The follicle also separates from the bloodstream. Catagen lasts two to three weeks.
  • Telogen Phase – this is the “resting” phase in which the clubbed hair detaches from the dermal papilla and is susceptible to falling out. Telogen lasts three to four months before hair follicle stem cells initiate a new anagen (growth) phase and the cycle repeats.

Stem Cells and the Hair Cycle

Normally, hair follicle stem cells (HFSC) perpetuate the hair cycle by initiating a new anagen (growth) phase after the telogen (resting) phase. But HFSC, like all cells, age over time. Included in this aging process is damage to DNA strands inside these cells due to spontaneous errors in DNA replication or those due to exposure to sunlight and other insults. While it has been well understood that hair follicle miniaturization occurs as a person ages and that damage to genetic material contributes to the process, the exact mechanism that ties cell aging to the disruption of the normal hair cycle was unknown. The recent study examines miniaturization from cell aging and distinguishes it from miniaturization caused by the effects of DHT.

Results of the Study

The key finding in this new research is that as hair follicle stem cells (HFSC) accumulate genetic damage over time, their store of a signaling protein called COL17A1 is depleted. The depletion of this key protein forces HFSC to differentiate into a common type of skin cell called a keratinocyte. By differentiating into keratinocytes, the population of HFSC gradually shrinks, there are fewer HFSC to initiate the anagen (growth) phase, and the telogen (resting) phase is extended. With a gradually longer telogen phase and shorter anagen phase, the follicle progressively miniaturizes. Eventually, the hair-producing follicle disappears leaving a bald scalp and the keratinocytes, which no longer serve a purpose in the hair growth cycle, are ejected from the skin.1 Click here to view the graphic that illustrates this process.

The authors of the study suggest that restoring COL17A1 levels, or halting their depletion, may prevent this aging-induced hair follicle miniaturization from occurring.1

With perhaps much broader significance, the study confirms the tight linkage between the instability of genetic material in stem cells (that can be due to environmental factors) and the shrinkage and functional decline seen in many organs as they age.

Conclusion

Progressive hair loss is a pervasive problem for males as they age. However, current treatments deal, exclusively, with hormone-induced miniaturization. The discovery of the mechanism behind age-induced miniaturization may result in a new avenue for the treatment of hair loss. More research into methods of boosting levels, or preventing the depletion, of COL17A1 may yield a hair loss therapy that targets this cause of hair loss.

Further, developing a better understanding of the cell aging process may open up new avenues of research into the causes of, and potential solutions to, the age-induced decline of major organs in the body.

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Image c/o Science

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New research published in the journal PLoS One found that embryonic stem cells can be used to form a type of cell that induces new hair follicle growth, and that these cells promote robust hair growth when implanted into mice.

Background

Dermal Papilla (DP) cells play a role in new hair follicle formation and in the growth of new hair. Because of this role, it was hoped that DP cells grown in the laboratory (i.e., grown in culture) could form the basis of a treatment for genetic hair loss. However, it turned out that these cultured DP cells lost their hair follicle-inducing potential too quickly to be useful in treating hair loss.

New Research

Now, however, new research has found that human embryonic stem cells (hESCs) can generate cells that are functionally equivalent to DP cells. ((Gnedeva K, Vorotelyak E, Cimadamore F, Cattarossi G, Giusto E, Terskikh V.V, Terskikh A.V. Derivation of hair-inducing cell from human pluripotent stem cells. PLoS One. 2015 Jan 21;10(1)) Like DP cells, these functionally equivalent cells can induce hair follicle formation just as readily as DP cells. But more significantly, unlike cultured DP cells, they do not lose their potential to induce hair follicle formation when grown in the laboratory. This discovery represents an important advance in developing a hair cloning technique to cure pattern baldness.

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New research published in the journal Developmental Cell has confirmed the importance of dermal sheath stem cells in maintaining the hair growth cycle. ((Rahmani W, et al. Hair Follicle Dermal Stem Cells Regenerate the Dermal Sheath, Repopulate the Dermal Papilla, and Modulate Hair Type. Dev Cell. 2014 Dec 8;31(5):543-58.)) These cells, located around the lower portion of growing follicles, form the basis of an experimental treatment, being developed by Replicel Life Sciences, Inc., to regenerate hair-producing follicles. If successful, the treatment will be a game-changer for the hair restoration industry.

Colony of self-renewing dermal sheath cellsColony of self-renewing dermal sheath cells

The study, published in December 2014, sought to confirm what had been indirect evidence of a type of stem cell residing in the dermal sheath (DS) that was said to replenish dermal papilla (DP) cells. The authors of the study suggest that they now have definitive evidence that new DP cells are derived from stem cells in the dermal sheath “cup” (DSC). This development clarifies the relationship between the DS and the DP and confirms that DSC cells play a critical role in hair follicle regeneration by repopulating the dermal papilla cells at the end of the telogen (resting) phase of the normal hair cycle.

Importance of the Dermal Sheath Cup Cells

The number of dermal papilla (DP) cells in a hair follicle has been found to be a determining factor as to when the anagen (growth) phase of the hair cycle is initiated. ((Chi W, Wu E, Morgan BA, et al. (2013). Dermal papilla cell number specifies hair size, shape and cycling and its reduction causes follicular decline. Development 140, 1676–1683.)) The gradual loss of DP cells over time results in a longer delay in the onset of the anagen phase; a longer telogen (resting) phase; and a hair follicle that shrivels and eventually disappears. This process, called miniaturization, plays out over multiple hair cycles and has been shown to be the primary contributor to androgenetic alopecia and eventual baldness. ((Randall VA. (2008). Androgens and hair growth. Dermatol. Ther. 21, 314–328.))

While dermal sheath cup (DSC) stem cells are known to be long-lived and self-renewing, it is not fully understood how they replicate or why the pool of DSC cells becomes depleted over time. We do know, however, that the gradual loss of DSC cells results in a failure to produce the necessary number of DP cells. And without enough DP cells to trigger the anagen phase, the follicle begins to miniaturize. It is clear that maintaining the population of DSC cells after each iteration of the hair cycle is very important in preserving and maintaining healthy and mature terminal hairs.

Replicel Reacts to the Study

The new data confirming the importance of the dermal sheath cup (DSC) cells was celebrated by researchers and executives at Replicel Life Sciences, Inc., who have been studying this issue for over a decade. Replicel is set to start phase II clinical trials of RCH-01, their proprietary treatment for androgenetic alopecia.

In the RCH-01 treatment, cloned DSC cells are injected into balding areas of the scalp where they are expected to reverse miniaturization and regenerate healthy, hair-producing follicles. Phase I trials of RCH-01, the results of which were published in 2012, showed that the treatment could produce promising results and that it was safe to administer. Six months after patients were treated with RCH-01, overall hair density increased by an average of 11.8% in ten patients out of 16. In two patients, overall hair density increased by more than 19%. There were no significant adverse safety events recorded. ((Lortkipanidze, N. Safety and Efficacy Study of Human Autologous Hair Follicle Cells to Treat Androgenetic Alopecia. In Clinicaltrials.gov. Retrieved July 26, 2012.)) Phase II clinical trials are set to begin in 2015, with data collection continuing for 39 months.

Through a 2013 agreement with Replicel, Japanese cosmetics giant Shiseido may introduce RCH-01 into the Asian market as early as 2018.

Image c/o Developmental Cell 31, 543–558, December 8, 2014 ª2014 Elsevier Inc.

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Scientists have known that dermal papilla (DP) cells trigger hair follicle regeneration, a mechanism that protects hair follicles against injury, disease and aging. They have also known that hair loss is associated with the gradual depletion and atrophy of DP cells. But what they did not know is how DP cells were maintained inside healthy hair follicles.

New research has shown that the hair follicle dermal stem cell plays a direct role in maintaining these hair growth inducing DP cells. ((Rahmani W., Abbasi S., Hagner A., Raharjo E., Kumar R., Hotta A., Magness S., Metzger D., Biernaskie J. (2014), Hair follicle dermal stem cells regenerate the dermal sheath, repopulate the dermal papilla, and modulate hair type. Dev Cell, Dec 8;31(50:543-58). ))

This discovery sets the stage for the development of new drugs designed to target these dermal stem cells in order to “replenish or rejuvenate the DP cells that are responsible for inducing hair growth,” says Jeff Biernaskie, PhD, one of the researchers.

Such drugs could be useful for repairing hair follicles damaged by disease or injury, or by medical treatments, specifically chemotherapy and/or radiation therapy. The development of such drugs, however, could be at least a decade or more out.

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