Human adipocytes are capable of melanin biosynthesis, which is elevated in obesity

Manpreet Randhawa, Tom Huff, Julio Valencia, Zobair Younossi, Vikas Chandhoke, Vincent J. Hearing, Ancha Baranova

This is a collaborative project between:

Molecular and Microbiology Department, College of Science,George Mason University, Fairfax, VA

Translational Reseach Institute, Inova Hospital, VA

Pigment Cell Division, NCI, NIH

This study was published in: FASEB J. 2009 Mar;23(3):835-43.

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.

This research has been supported by a grant from the Thomas F. Jeffress and Kate Miller Jeffress Memorial Trust and by the Intramural Research Program of the National Cancer Institute at NIH . A.B. and M.R. are grateful to Shobha M. Gowder for initial technical assistance with the project and F. Otaizo for the help with the first round of RT-PCR experiments.

The study is currently being extended in order to check whether induction of the melanigenesis in the adipose could be used as therapeutical intervention in obese and overweight individulas aimed at the prevention of co-morbidities.

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This paper has been also reviewed by Prof. Shosuke Ito in the Commentary: Melanin seem to be everywhere in the body, but for what? published in Pigment Cell Melanoma Res. 2009 Feb;22(1):12-3.