title: Evidence for the ectopic synthesis of melanin in human adipose tissue.
abstract: Melanin is a common pigment in animals. In humans, melanin is produced in melanocytes, in retinal pigment epithelium (RPE) cells, in the inner ear, and in the central nervous system. Previously, we noted that human adipose tissue expresses several melanogenesis-related genes. In the current study, we confirmed the expression of melanogenesis-related mRNAs and proteins in human adipose tissue using real-time polymerase chain reaction and immunohistochemical staining. TYR mRNA signals were also detected by in situ hybridization in visceral adipocytes. The presence of melanin in human adipose tissue was revealed both by Fontana-Masson staining and by permanganate degradation of melanin coupled with liquid chromatography/ultraviolet/mass spectrometry determination of the pyrrole-2,3,5-tricarboxylic acid (PTCA) derivative of melanin. We also compared melanogenic activities in adipose tissues and in other human tissues using the L-[U-(14)C] tyrosine assay. A marked heterogeneity in the melanogenic activities of individual adipose tissue extracts was noted. We hypothesize that the ectopic synthesis of melanin in obese adipose may serve as a compensatory mechanism that uses its anti-inflammatory and its oxidative damage-absorbing properties. In conclusion, our study demonstrates for the first time that the melanin biosynthesis pathway is functional in adipose tissue.
authors.affiliation: Molecular Biology and Microbiology Department and Center for the Study of Genomics in Liver Diseases, College of Science, George Mason University, Manassas, VA, USA.
authors.forename: Manpreet
authors.initials: M
authors.lastname: Randhawa
authors.forename: Tom
authors.initials: T
authors.lastname: Huff
authors.forename: Julio C
authors.initials: JC
authors.lastname: Valencia
authors.forename: Zobair
authors.initials: Z
authors.lastname: Younossi
authors.forename: Vikas
authors.initials: V
authors.lastname: Chandhoke
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
authors.forename: Ancha
authors.initials: A
authors.lastname: Baranova
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D002853:Chromatography, Liquid / Q000379:methods; D005786:Gene Expression Regulation / Q000502:physiology; D006197:Hair / Q000737:chemistry; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D008543:Melanins / Q000032:analysis / Q000096:biosynthesis*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism
chemical_list: D008543:Melanins; D008562:Membrane Glycoproteins; D010088:Oxidoreductases; C489799:TYRP1 protein, human; C064056:tyrosinase-related protein-1; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase