Category Archives: Progenitor Cells

CD200, CD34, Progenitor Cells, Sox9

Partially Bald Regions of the Scalp Retain Progenitor Cells

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To end the year 2025, I leave you with some good news. At least for those who have some hair left in various parts of their scalp.

In 2011, a famous study from the US found that balding people still have intact hair follicle stem cells. However, they have a defect in the conversion of these stem cells into active progenitor cells (which were markedly depleted in bald scalps per the study findings). Among the authors of this report were the world renowned hair loss researchers Dr. Luis Garza and Dr. George Cotsarelis.

But now a new study from India has found that partially bald areas of the scalp retain most of their progenitor cells. Perhaps this bodes well for upcoming new hair growth treatments (such as Breezula and PP405) kick-starting the hair growth cycle all over the scalp in those who are not severely bald.

Note that in rare instances, even those who are at Norwood 5-7 levels of baldness have regained long-lost hair. Hair loss and hair loss reversal are still not close to being fully understood.

Partially Bald Regions of the Scalp Retain Progenitor Cells

The above new November 2025 Indian study found that partially bald areas of the scalps of men suffering from androgenic alopecia (AGA) retain bulge hair follicle progenitor cells. The ten patients in the study were all male Indians.

The authors mention that previous studies (see next section) have mostly focused on fully bald areas. But the hair follicles in partially bald areas of AGA sufferers were not characterized till now when it comes to the status of stem cell and progenitor cell populations.

Key quote:

“Quantification of CD34+ and Sox9+ cells revealed that the number of progenitor cells is not significantly reduced in the partially bald area compared to the hair follicles of the occipital unaffected area.”

In the below first image from the study, you can see the green and blue streaks showing how progenitor cells (CD34 and Sox9) still exist in partially bald regions in the front of scalps. Almost to the same extent as in the occipital non-balding areas of the volunteers’ scalps.

Progenitor Cells in a Partially Bald Scalp.
Progenitor cells are still intact in partially bald regions of the scalp.

In contrast, fully bald regions of the volunteers’ scalps show no remaining CD34 or Sox9 progenitor cells. Note the absence of any green or blue lines in the top left section of the below image.

Progenitor Cells in Fully Bald Scalps.
Progenitor cells are entirely destroyed in fully bald regions of the scalp.

Bald Scalps Retain Hair Follicle Stem Cells but Lose Progenitor Cells

The news is very significant, and we need to go back in time to learn why. As I mentioned at the beginning of the post, In 2011, a team of US researchers from University of Pennsylvania School of Medicine found that:

“Bald scalp in men with androgenetic alopecia retains hair follicle stem cells, but lacks CD200-rich and CD34-positive hair follicle progenitor cells.”

So AGA is not characterized by the loss of follicular stem cells as was thought by many scientists. Rather, it is a defect in the conversion of these stem cells into active progenitor cells, which in turn leads to hair follicle miniaturization. This news was huge at the time and I have mentioned these findings a number of times in the past.

Another study from Egypt in 2015 confirmed these findings by concluding that follicular stem cells are still present in both men and women suffering from pattern hair loss.

On a related note, a Chinese study from 2020 found that vascular endothelial growth factor (VEGF) can protect CD200-rich and CD34-positive hair follicle stem cells from androgen induced apoptosis.

For those who are interested, the below image from this 2020 study from Poland is instructive. It depicts the location of hair follicle bulge stem cells in relation to the dermal papilla (DP), sebaceous gland, sweat gland, epidermis, dermis and adipose layer of the skin.

Hair Follicle Bulge Stem Cells
Hair follicle bulge stem cells.

Other Changes in the Scalps of Hair Loss Sufferers

Over the years, I have covered numerous studies that analyze various changes that happen to the scalps of people who are suffering from hair loss.

Perhaps the three biggest findings that I can recall are that:

  1. Balding scalps have fewer fat cells and become thinner and tighter as fibrosis sets in. Not surprisingly, the transplantation of adipose-derived stem cells into balding heads has seen significant interest over the past decade.
  2. The arrector pili muscles get slowly destroyed in balding scalps. Albeit a fraction of these muscles may continue to exist even in entirely bald regions of the scalp.
  3. The balding scalp shows increased Prostaglandin D2 (PGD2) levels and decreased Prostaglandin E2 (PGE2) levels.

And now we can add progenitor cell population changes to this list.

Ear Hair Cells, Frequency Therapeutics, Progenitor Cells, Wnt/Beta-Catenin

Ear Hair Cell Regeneration and Frequency Therapeutics

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Update: April 19, 2022 — Scientists from Harvard Medical School have managed to regenerate inner ear hair cells that enable hearing (h/t “Rali”). They claim to have moved closer to a gene therapy solution for sensorineural hearing loss, although no human clinical trials have started as yet.

The research team was led by Dr. Zheng-Yi Chen. They reported creating a drug-like cocktail of different molecules that successfully regenerated hair cells in a mouse model by reprogramming a series of genetic pathways within the inner ear. The full study was published on April 17, 2023 in PNAS.

Note that the team identified and used a combination (cocktail) of drug-like molecules that was composed of small molecules and siRNAs. Make sure to read my past related posts on siRNA as well as on creating the ultimate hair loss drug cocktail.

Frequency Therapeutics

Update: April 21, 2023 — Frequency Therapeutics phase IIb clinical trial results for FX-322 have been officially posted. A total of 142 adult patients were involved, 72 of whom got the placebo. The remaining 70 got a single intratympanic injection of FX-322 (laduviglusib 0.628 mg/sodium valproate 17.72 mg) into their hearing loss affected ear.

In February, the company announced that these trials did not succeed and the company’s stock price subsequently collapsed.

Update: March 29, 2022 — Update on MIT spinout Frequency Therapeutics and its drug candidate that stimulates inner ear hair cell growth.

February 21, 2017

An interesting new article titled “Drug treatment could combat hearing loss” seems to have little bearing with scalp hair loss. However, hearing loss is usually caused by permanent damage to many of the 15,000 hair cells in each inner ear. Regenerating those with this new drug therapy could also indicate a similar potential for regenerating scalp hair cells.

In the article, the author discusses a new paper that is published in the February 21 issue of Cell Reports. In fact, the findings of this paper are so important that the cover page of the journal has a photo taken directly from the research. Note that the lead scientists are also working on this technology via a new company called Frequency Therapeutics.

Ear Hair Cell Growth

Ear Hair Follicle Regeneration

In this paper, a team of scientists (from MIT, Brigham and Women’s Hospital, and Massachusetts Eye and Ear) have found a way to regenerate tiny inner ear hair follicles via a drug combination treatment.

This combination is a two step process where in the first step, a combination of drugs expands the progenitor cell population. In the second step, another combination of drugs induces the new cells to differentiate into hair cells.

In one variation of the experiment, the second step was not even necessary because “once the progenitor cells were formed, they were naturally exposed to signals that stimulated them to become mature hair cells”.

I am pretty certain that I have read articles in the past about ear hair cell regeneration. I might even have mentioned one or two of them in passing on this blog before. However, this particular article and associated study warranted its own separate post and stuck out for two key reasons:

  1. The researchers succeeded in regenerating mouse ear hair cells via creating new progenitor cells. This is quite astounding to me because in regular scalp hair loss, scientists have found that hair is not lost due to the death of hair cells, but rather, due to the death of progenitor cells. So if these scientists can create new progenitor cells in the ear that lead to ear hair regeneration, I do not see how they can not try to use the same method to create new progenitor cells in the scalp.
  2. The researchers accomplished their potentially ground breaking achievement via stimulating the Wnt signaling pathway. I have discussed that pathway numerous times on this blog in the past, since it seems to be crucial for scalp hair growth. Moreover, well known company Samumed’s hair loss drug is targeting that same pathway.

Will ear hair cell research and findings become applicable towards scalp hair cell research? I really hope so, and this new work is encouraging due to the involvement of the Wnt/Beta-Catenin pathway.