Key Growth Factors in Platelet-Rich Plasma

I have mentioned platelet-rich plasma (PRP) in a dozen or so posts on this blog over the past three years. The positive effect of PRP on hair growth is somewhat controversial. However, there is no controversy when it comes to the fact that PRP contains numerous concentrated growth factors (GFs). And many of these growth factors are known to at least modestly benefit hair thickness as well as hair quantity.

PRP Growth Factors
Platelet-Rich Plasma (PRP) Growth Factors.

In the past I have briefly discussed some of the key growth factors that are highly concentrated in PRP. I think it is worth having a separate post here that discusses all of them in a bit more detail. There is a good chance that I am still missing things, so any corrections and suggestions are welcome via the comments.

It should be noted that even many non-PRP related hair loss products target one or more of the below listed growth factors in order to stimulate hair growth. There is a good chance that both PRP as well as hair loss products that contain some of the below growth factors make existing hair stronger. It is probably unlikely that such products ever bring back hair that has been lost for a long time.

Growth Factors in Platelet-Rich Plasma

The key growth factors in PRP that are supposedly beneficial to hair growth are:

  • Insulin-Like Growth Factor 1 (IGF-1).
  • Fibroblast Growth Factor (FGF).
  • Platelet-Derived Growth Factor (PDGF).
  • Vascular Endothelial Growth Factor (VEGF).
  • Epidermal Growth Factor (EGF).
  • Transforming Growth Factor Beta (TGF-β).
  • Nerve Growth Factor (NGF).

IGF-1

I start with the growth hormone insulin-like growth factor 1 (IGF-1) because I have already covered it a few times before.

  • Promotion of IGF-1 expression is one of the main considerations behind Shiseido’s bestselling adenosine based products.
  • US-based Follicept was targeting IGF-1 delivery in its hair loss product, prior to the company’s demise.
  • Adipose-derived stem cells (ADSCs — an exciting recent development in the hair loss world) are rich in various growth factors, including IGF-1.
  • Last year, an important and widely publicized study found that topical application of oleuropein (derived from the leaves of olive drupes) induces hair growth in mice. According to the study findings, oleuropein-treated mouse skin showed substantial upregulation of IGF-1.

FGF

I list fibroblast growth factor (FGF) next because I have also covered it many times on this blog before. There are 22 types of FGFs numbered FGF-1 through FGF-22. A significant number of these influence hair growth. I may write an entire detailed post on FGFs at some point in the future. I have covered some of the key ones on this blog before, in particular FGF-5, which discourages hair growth and has to be inhibited. Australian company Cellmid’s Evolis line of products claims to inhibit FGF-5.

Note that PRP does not inhibit growth factors. So it is more relevant for the purposes of this post to discuss some of the FGFs that promote hair growth. It seems like the main ones are FGF-1, FGF-2, FGF-7, FGF-9 and FGF-10. Evidence for three of those (FGF-1, FGF-2 and FGF-10) and their positive effects on hair is found in an important 2014 study from China. Fibroblast growth factors stimulate hair growth through β-Catenin and Shh expression.

Note that “hair cell regeneration” or variations of that term are mentioned a number of times in this study, even if in mice.  PRP is said to increase FGF-2 concentration levels. Interestingly, when I interviewed Dr. Malcolm Xing last year, he mentioned that FGF-2 is the preferred growth factor used at this clinic for his work purposes.

FGF-9 has become an especially important growth factor in large part due to the work of the renowned Dr. George Cotsarelis, who holds a patent titled “Fibroblast growth factor-9 promotes hair follicle regeneration after wounding“. Dr. Cotsarelis is also a co-author of a 2013 paper that concludes: “The importance of FGF-9 in hair follicle regeneration suggests that it could be used therapeutically in humans“.

Finally, FGF-7 (also called keratinocyte growth factor, or KGF) is required for hair growth. The well known researcher Dr. Elaine Fuchs co-authored an important study on FGF-7, hair development and wound healing all the way back in 1995. Moreover, Histogen’s Hair Stimulating Complex product is focusing on KGF as one of the key growth factors to be injected in human scalps.

PDGF

Platelet-derived growth factor (PDGF) is a key growth factor involved in blood vessel formation. A 2006 study from Japan found that “PDGF isoforms induce and maintain anagen phase of murine hair follicles“. Adipose-derived stem cells (ADSCs) are rich in various growth factors, including  PDGF, and are increasingly utilized in the hair loss world.

VEGF

Besides hair growth, vascular endothelial growth factor (VEGF) is also involved in blood vessel formation. A 2001 study concluded that “normal hair growth and size are dependent on VEGF-induced perifollicular angiogenesis”. Note that Shiseido’s adenosine based shampoo also promotes the expression of VEGF. The previously discussed adipose-derived stem cells are also rich in various growth factors including  VEGF.

Also, one of the ways in which Minoxidil works to grow hair is via the upregulation of VEGF. Moreover, Histogen’s Hair Stimulating Complex product is focusing on VEGF as one of the key growth factors to be injected in human scalps.

A number of studies have examined natural and synthetic products that increase VEGF and their impact on scalp hair. For example, in 2018, Japanese researchers found that water-soluble chicken egg yolk peptides stimulate hair growth through induction of VEGF production.

EGF

Epidermal growth factor (EGF) promotes cell growth, proliferation and differentiation. A 2003 study from Hong Kong concluded that EGF functions as a biological switch that is “turned on and off in hair follicles at the beginning and end of the anagen phase of the hair cycle“.

TGF-β

Transforming growth factor beta (TGF-β) is a cytokine protein growth factor. From the brief research I did, it seems like TGF-β actually adversely impacts hair growth!  e.g., see here, here and here. So I am not sure if this growth factor in PRP benefits hair.  Will update this if I find out more.

NGF

There seem to be mixed opinions on the impact of nerve growth factor (NGF) on the hair cycle in any significant manner. A 2006 study suggests both anagen-promoting and catagen-promoting effects of NGF on the hair cycle. Another study, also from 2006, seems to also find different effects of NGF on the hair cycle.

JAK-STAT Signaling Jump Starts the Hair Cycle

Over the past few years, I have discussed the janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway a number of times.  It has become of increasing importance in the hair loss world ever since JAK inhibitors were first shown to cure alopecia areata (AA) in 2014.  Even prior to that development, there had always been some interest in the JAK-STAT signaling pathway and its relationship to the hair follicle cycle.

However, since 2014, research in this area seems to have multiplied significantly.  In 2015, I discussed Dr. Angela Christiano, Dr. Claire Higgins et al’s groundbreaking paper titled “Pharmacologic inhibition of JAK-STAT signaling promotes hair growth“.

Now, in the latest (November 2016) issue of Journal of Investigative Dermatology, Columbia University’s Dr. Angela Christiano, Dr. Etienne Wang and Dr. Sivan Harel have published a new paper titled “JAK-STAT signaling jump starts the hair cycle“.  Thanks to the commentator in the last post who notified us about this.

However, it should be noted that this paper does not pertain to any new study or research by Dr. Christiano!  Instead, it is largely an analysis by the Columbia University team of a study/paper that was published earlier this year by Dr. Julien Legrand and his team at The University of Queensland.  This study from Australia was titled “STAT5 activation in the dermal papilla Is important for hair follicle growth phase Induction“.  The conclusion of that paper was that “STAT5 activation acts as a mesenchymal switch to trigger natural anagen entry in postdevelopmental hair follicle cycling“.  STAT5 is an acronym for signal transducer and activator of transcription 5.

Dr. Christiano’s team raises some interesting points in their analysis, especially the fact that while Dr. Legrand’s research has shown that JAK/STAT5 signaling in the dermal papilla is required for anagen onset in the murine (mice) hair cycle, other researchers have shown that JAK inhibition is able to induce the transition of telogen to anagen in wild-type mice.  This contradiction highlights the complexity  and still yet to be fully understood nature of JAK-STAT signaling in the various stem cell niches of the hair follicle.

Dr. Christiano continues to believe that topical JAK inhibitors could work to treat regular male pattern hair loss via the following quotes:

“Targeting the JAK-STAT pathway might be a potential treatment for nonimmune alopecias”.

“Further work in this exciting area may uncover novel pathways that control hair follicle stem cell quiescence and activation.  Targeting
these pathways pharmacologically may facilitate the discovery of new therapies to treat various forms of alopecia”.

“In our recent study (Note: its the one I mentioned earlier from 2015) we found that in wild-type mice, topical application (rather than systemic treatment) with JAK inhibitors was required to trigger the telogen-to-anagen transition, possibly due to a requirement for high threshold local concentrations of the drug in the hair follicle.  Further, we found that the timing of topical treatment was crucial: treatment induced hair growth only if administered after 8.5 weeks, during late telogen“.

Nothing groundbreaking in this development, but it seems like the University of Queensland based Australian team of researchers is important enough to warrant inclusion in my global map of hair loss research centers.  One of the co-authors (Dr. Kiarash Khosrotehrani) of their paper specifically mentions research interest in “hair follicle biology, cycling and regeneration” in his biography page.