title: Differential expression of nitric oxide synthases in human scalp epidermal and hair follicle pigmentary units: implications for regulation of melanogenesis.
abstract: BACKGROUND
  Nitric oxide (NO) is a ubiquitous gaseous lipophilic molecule generated from the conversion of L-arginine to L-citrulline by the NO synthases (NOSs). Ultraviolet radiation (UVR)-induced NO production appears to stimulate epidermal melanogenesis. However, given their relative protection from UVR, it is unclear whether NO plays a similar role in hair bulb melanocytes.
  
  
  OBJECTIVE
  We aimed to identify the expression profiles of the NOS isoforms endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS) and of phosphorylated eNOS and nitrotyrosine within the epidermal and follicular melanin units of normal human haired scalp during the hair growth cycle.
  
  
  METHODS
  This study employed single and double immunohistochemical and immunofluorescence staining techniques using haired scalp from 10 healthy individuals (six women and four men).
  
  
  RESULTS
  Melanocytes in the basal layer of the epidermis expressed eNOS, nNOS and nitrotyrosine. By contrast, melanogenically active melanocytes of the anagen hair bulb were wholly negative for these markers. However, other follicular melanocytes not actively involved in pigment production, including undifferentiated melanocytes located in the outer root sheath and melanocytes surviving the apoptosis-driven hair follicle (HF) regression during catagen/telogen, expressed eNOS, nNOS and nitrotyrosine. While iNOS was only weakly expressed in the basal layer of the human epidermis, it was highly expressed in keratinocytes of the inner root sheath (IRS), where it colocalized with trichohyalin, a differentiation-associated protein of the IRS that requires enzyme-catalysed conversion of arginine to citrulline.
  
  
  CONCLUSIONS
  The NOS isoforms and nitrotyrosine are differentially expressed in different cutaneous melanocyte subpopulations. Results of this study suggest a possible role for eNOS, nNOS, iNOS and nitrotyrosine in melanocyte biology, particularly with respect to melanogenesis and melanocyte survival during HF regression. Another example of possible NO involvement in HF biology is the postsynthetic modification of trichohyalin in differentiating keratinocytes of the IRS. These results suggest that NO may influence several aspects of HF biology.
authors.affiliation: Department of Biomedical Sciences, School of Life Sciences, University of Bradford, Bradford BD7 1DP, UK.
authors.forename: H M
authors.initials: HM
authors.lastname: Sowden
authors.forename: K M
authors.initials: KM
authors.lastname: Naseem
authors.forename: D J
authors.initials: DJ
authors.lastname: Tobin
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005455:Fluorescent Antibody Technique / Q000379:methods; D006197:Hair / Q000254:growth & development; D018859:Hair Follicle / Q000201:enzymology*; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D015603:Keratinocytes / Q000201:enzymology; D008297:Male; D008543:Melanins / Q000378:metabolism; D008544:Melanocytes / Q000201:enzymology*; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010766:Phosphorylation; D012535:Scalp / Q000201:enzymology*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
chemical_list: D008543:Melanins; D009419:Nerve Tissue Proteins; C002744:3-nitrotyrosine; D014443:Tyrosine; C496320:NOS1 protein, human; C496319:NOS2 protein, human; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III