Biology:FGF5

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Short description: Mammalian protein found in Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Fibroblast growth factor 5 is a protein that in humans is encoded by the FGF5 gene.

The majority of FGF family members are glycosaminoglycan binding proteins which possess broad mitogenic and cell survival activities, and are involved in a variety of biological processes, including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth and invasion. FGF proteins interact with a family of specific tyrosine kinase receptors, a process often regulated by proteoglycans or extracellular binding protein cofactors. A number of intracellular signalling cascades are known to be activated after FGF-FGFR interaction including PI3K-AKT, PLCγ, RAS-MAPK and STAT pathways.[1]

Receptor

FGF5 is a 268 amino acid, 29.1 kDa protein, which also naturally occurs as a 123 amino acid isoform splice variant (FGF5s).[2][3] FGF5 is produced in the outer root sheath of the hair follicle as well as perifollicular macrophages, with maximum expression occurring in the late anagen phase of the hair cycle.[4][5] The receptor for FGF5, FGFR1, is largely expressed in the dermal papilla cells of the hair follicle.[4][5] The alternatively spliced isoform FGF5s, has been identified as an antagonist of FGF5 in a number of studies.[2][3][6]

Role in hair cycling

Research comparing dogs with different coat lengths has demonstrated FGF5 as a major contributing factor
Research comparing different breeds of dogs has demonstrated FGF5 as a major contributing factor in coat length.

The only described function of FGF5 in adults is in the regulation of the hair cycle. FGF5 performs a critical role in the hair cycle, where it acts as the key signalling molecule in initiating the transition from the anagen (growth) phase to the catagen (regression) phase.[7][8] Evidence of this activity was initially gathered via targeted disruption of the homolog of the FGF5 gene in mice, which resulted in a phenotype with abnormally long hair.[8]

In numerous genetic studies of long haired phenotypes of animals it has been shown that small changes in the FGF5 gene can disrupt its expression, leading to an increase in the length of the anagen phase of the hair cycle, resulting in phenotypes with extremely long hair. This has been demonstrated in many species, including cats,[9][10] dogs,[11][12] mice,[8] rabbits,[13] donkeys,[14] sheep and goats,[15] where it is often referred to as the angora mutation. Recently, CRISPR modification of goats to artificially knock out the FGF5 gene, was shown to result in higher wool yield, without any fertility or other negative effects on the goats.[16]

It has been hypothesised that, in an alternate type of mutation, positive selection for increased expression of the FGF5 protein was one of the contributing factors in the evolutionary loss of hair in cetaceans as they transitioned from the terrestrial to the aquatic environment.[17]

FGF5 also affects the hair cycle in humans. Individuals with mutations in FGF5 exhibit familial trichomegaly, a condition that involves a significant increase in the portion of anagen phase hair as well as extremely long eyelashes.[7] FGF5 has also been identified as a potentially important factor in androgenetic alopecia. In 2017, a large genome wide association study of men with early onset androgenetic alopecia identified polymorphisms in FGF5 as having a strong association with male pattern hair loss.[18]

Blocking FGF5 in the human scalp extends the hair cycle, resulting in less hair fall, faster hair growth rate and increased hair growth.[19][20] In vitro methods using engineered cell lines and FGFR1 expressing dermal papilla cells have identified a number of naturally derived botanical isolates including Sanguisorba officnalis,[19] and single molecule members of the monoterpenoid family[20] as inhibitors (blockers) of FGF5. Clinical studies have shown that topical application of formulations containing these natural extracts and molecules are beneficial in men and women experiencing hair loss.[19][20]

References

  1. ↑ "The Fibroblast Growth Factor signaling pathway". Wiley Interdisciplinary Reviews: Developmental Biology 4 (3): 215–66. 2015. doi:10.1002/wdev.176. PMID 25772309. 
  2. ↑ 2.0 2.1 "Localization of rat FGF-5 protein in skin macrophage-like cells and FGF-5S protein in hair follicle: possible involvement of two Fgf-5 gene products in hair growth cycle regulation". The Journal of Investigative Dermatology 111 (6): 963–72. December 1998. doi:10.1046/j.1523-1747.1998.00427.x. PMID 9856803. 
  3. ↑ 3.0 3.1 "Dual-mode regulation of hair growth cycle by two Fgf-5 gene products". The Journal of Investigative Dermatology 114 (3): 456–63. March 2000. doi:10.1046/j.1523-1747.2000.00912.x. PMID 10692103. 
  4. ↑ 4.0 4.1 "Fibroblast growth factor signalling in the hair growth cycle: expression of the fibroblast growth factor receptor and ligand genes in the murine hair follicle". Developmental Dynamics 205 (4): 379–86. April 1996. doi:10.1002/(SICI)1097-0177(199604)205:4<379::AID-AJA2>3.0.CO;2-F. PMID 8901049. 
  5. ↑ 5.0 5.1 "Fibroblast growth factor 5 inhibits hair growth by blocking dermal papilla cell activation". Biochemical and Biophysical Research Communications 290 (1): 169–76. January 2002. doi:10.1006/bbrc.2001.6140. PMID 11779149. 
  6. ↑ "Fibroblast growth factor 5-short (FGF5s) inhibits the activity of FGF5 in primary and secondary hair follicle dermal papilla cells of cashmere goats". Gene 575 (2 Pt 2): 393–398. January 2016. doi:10.1016/j.gene.2015.09.034. PMID 26390813. 
  7. ↑ 7.0 7.1 "FGF5 is a crucial regulator of hair length in humans". Proceedings of the National Academy of Sciences of the United States of America 111 (29): 10648–53. July 2014. doi:10.1073/pnas.1402862111. PMID 24989505. Bibcode: 2014PNAS..11110648H. 
  8. ↑ 8.0 8.1 8.2 "FGF5 as a regulator of the hair growth cycle: evidence from targeted and spontaneous mutations". Cell 78 (6): 1017–25. September 1994. doi:10.1016/0092-8674(94)90276-3. PMID 7923352. 
  9. ↑ "Mutations within the FGF5 gene are associated with hair length in cats". Animal Genetics 38 (3): 218–21. June 2007. doi:10.1111/j.1365-2052.2007.01590.x. PMID 17433015. 
  10. ↑ "Four independent mutations in the feline fibroblast growth factor 5 gene determine the long-haired phenotype in domestic cats". The Journal of Heredity 98 (6): 555–66. 2007. doi:10.1093/jhered/esm072. PMID 17767004. 
  11. ↑ "Allelic heterogeneity of FGF5 mutations causes the long-hair phenotype in dogs". Animal Genetics 44 (4): 425–31. August 2013. doi:10.1111/age.12010. PMID 23384345. 
  12. ↑ "The long and the short of it: evidence that FGF5 is a major determinant of canine 'hair'-itability". Animal Genetics 37 (4): 309–15. August 2006. doi:10.1111/j.1365-2052.2006.01448.x. PMID 16879338. 
  13. ↑ "[Correlation analysis between single nucleotide polymorphism of FGF5 gene and wool yield in rabbits]". Yi Chuan = Hereditas 30 (7): 893–9. July 2008. doi:10.3724/sp.j.1005.2008.00893. PMID 18779133. 
  14. ↑ "Two recessive mutations in FGF5 are associated with the long-hair phenotype in donkeys". Genetics, Selection, Evolution 46 (1): 65. September 2014. doi:10.1186/s12711-014-0065-5. PMID 25927731. 
  15. ↑ "[Effects of FGF5 gene on fibre traits on Inner Mongolian cashmere goats]". Yi Chuan = Hereditas 31 (2): 175–9. February 2009. doi:10.3724/sp.j.1005.2009.00175. PMID 19273426. 
  16. ↑ "Disruption of FGF5 in Cashmere Goats Using CRISPR/Cas9 Results in More Secondary Hair Follicles and Longer Fibers". PLOS ONE 11 (10): e0164640. 2016. doi:10.1371/journal.pone.0164640. PMID 27755602. Bibcode: 2016PLoSO..1164640W. 
  17. ↑ "Characterization of hairless (Hr) and FGF5 genes provides insights into the molecular basis of hair loss in cetaceans". BMC Evolutionary Biology 13: 34. February 2013. doi:10.1186/1471-2148-13-34. PMID 23394579. 
  18. ↑ "Meta-analysis identifies novel risk loci and yields systematic insights into the biology of male-pattern baldness". Nature Communications 8: 14694. March 2017. doi:10.1038/ncomms14694. PMID 28272467. Bibcode: 2017NatCo...814694H. 
  19. ↑ 19.0 19.1 19.2 "Sanguisorba Officinalis Root Extract Has FGF-5 Inhibitory Activity and Reduces Hair Loss by Causing Prolongation of the Anagen Period". Nishinihon J. Dermatology 69 (1): 81–86. 2007. doi:10.2336/nishinihonhifu.69.81. 
  20. ↑ 20.0 20.1 20.2 "Promotion of anagen, increased hair density and reduction of hair fall in a clinical setting following identification of FGF5-inhibiting compounds via a novel 2-stage process". Clinical, Cosmetic and Investigational Dermatology 10: 71–85. 2017. doi:10.2147/CCID.S123401. PMID 28280377. 

Further reading



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