Human hair greying is linked to a specific depletion of hair follicle melanocytes affecting both the bulb and the outer root sheath.
BACKGROUND
Although hair greying is a very common phenomenon characterized by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in humans are still unclear.


OBJECTIVE
To decipher the origin of natural hair whitening.


METHODS
Human hair melanocytes were immunohistochemically characterized at different stages of whitening.


RESULTS
Loss of hair shaft melanin was found to be associated with a decrease in both bulb melanin content and bulb melanocyte population. Although few melanocytes were present in the bulbs of grey hair, they still expressed tyrosinase and tyrosinase-related protein-1, synthesized and transferred melanins to cortical keratinocytes as seen by the presence of melanin granules. In white hair bulbs, no melanocytes could be detected either with pMel-17 or vimentin labelling. Pigmented hair follicles are known to contain inactive melanocytes in the outer root sheath (ORS), and grey and white hairs were also found to contain some of these quiescent melanocytes. However, their population was decreased compared with pigmented hair follicles, ranging from small to nil. This depletion of melanocytes in the different areas of white hairs was detected throughout the hair cycle, namely at telogen and early anagen stages. In contrast, the infundibulum and sebaceous gland of both pigmented and white hairs showed a similar distribution of melanocytes. Furthermore, other distinct cell populations located in the ORS, namely putative stem cells, Merkel cells and Langerhans cells were equivalently identified in pigmented and white hairs.


CONCLUSIONS
Thus, hair greying appears to be a consequence of an overall and specific depletion of bulb and ORS melanocytes of human hair.
Commo
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S
L'Oréal Recherche, 90 rue du général Roguet, 92583 Clichy cedex, France. scommo@rd.loreal.com
Gaillard
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O
Bernard
B A
BA
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D005260:Female; D006200:Hair Color / Q000502:physiology*; D018859:Hair Follicle / Q000166:cytology* / Q000201:enzymology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D015603:Keratinocytes / Q000502:physiology; D008297:Male; D008543:Melanins / Q000032:analysis; D008544:Melanocytes / Q000502:physiology*; D008562:Membrane Glycoproteins; D008875:Middle Aged; D014442:Monophenol Monooxygenase / Q000032:analysis; D010088:Oxidoreductases; D011506:Proteins / Q000032:analysis; D012627:Sebaceous Glands / Q000166:cytology
D008543:Melanins; D008562:Membrane Glycoproteins; D011506:Proteins; D010088:Oxidoreductases; C489799:TYRP1 protein, human; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase