Fairness of skin correlates with diminished epidermal expression of eumelanin, the brown/black pigment responsible for dark complexion. Instead, there is preferential expression of pheomelanin, a sulfated blonde/red melanin species that is soluble and has poor UV-blocking abilities. Persons with high levels of pheomelanin and low levels of eumelanin in the skin have little basal protection from UV radiation, and therefore suffer the highest incidence of UV-mediated skin damage and skin cancer. To delineate the relationship between UV exposure and pigmentation and develop novel pigment-based UV protective strategies, we have developed a mouse model of """"""""humanized skin"""""""" with inducible pigmentation. Like in humans, the fair-skinned phenotype in our animal model is caused by defective signaling in melanocytes by the melanocortin-1 receptor (MC1R), a protein that mediates adenylate cyclase activation and cAMP generation when bound by its natural ligand, melanocyte stimulating hormone (MSH). Similar to fair- skinned humans who tend to burn rather than tan after sunlight exposure, our fair-skinned animals demonstrate heightened UV sensitivity and failure to tan adaptively. Using this novel mouse model, we study melanin induction by forskolin, a labdane diterpenoid that directly activates adenylate cyclase and promotes intracellular accumulation of cAMP. By topically applying root extract from the C. forskohlii plant (the natural source of forskolin) to the skin, we can induce the production of UV-protective eumelanin by chemically circumventing the defective cAMP signaling associated with the mutant MC1R. Using our animal model, we will directly modulate cAMP signaling and melanin levels to clarify the protective effects of C. forskohlii extract against UV-mediated skin damage. We hypothesize that pharmacologic up- regulation of cAMP in the skin will protect against UV-mediated damage by promoting eumelanin synthesis and by enhancing the repair of UV-induced DNA photolesions. To address our hypothesis, we propose three specific aims: i) Characterize the role of MC1R function in UV-mediated oxidative damage, and determine whether pharmacologic replacement of MC1R function protects against oxidative UV injury;ii) Delineate the impact of MC1R function in the repair of UV-induced DNA lesions;and iii) Determine whether molecular bypass of MC1R function by cAMP up-regulation enhances repair following UV exposure. Our goal is to develop the novel approach of UV protection by sunless tanning based on topical administration of this root extract or small molecule derivatives. Our research strategy will provide a substantial foundation on which we can develop UV-protective strategies to prevent, rather than treat, skin cancer.

Public Health Relevance

Our goals are to (1) understand how UV irradiation damages skin of different pigment types;(2) devise natural pigment-based strategies that protect against UV-mediated skin damage;and (3) effectively prevent skin cancer. Using unique transgenic mice that mimic human skin, we will measure DNA damage and repair in UV- exposed skin, and explore mitigation of this damage and enhancement of repair. Our proposed research includes both in vivo and in vitro analyses of UV effects in whole skin and in melanocytes derived from our animal model, respectively.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Exploratory/Developmental Grants (R21)
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Chemo/Dietary Prevention Study Section (CDP)
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Umar, Asad
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University of Kentucky
Internal Medicine/Medicine
Schools of Medicine
United States
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Jarrett, Stuart G; Wolf Horrell, Erin M; Christian, Perry A et al. (2014) PKA-mediated phosphorylation of ATR promotes recruitment of XPA to UV-induced DNA damage. Mol Cell 54:999-1011
Scott, Timothy L; Christian, Perry A; Kesler, Melissa V et al. (2012) Pigment-independent cAMP-mediated epidermal thickening protects against cutaneous UV injury by keratinocyte proliferation. Exp Dermatol 21:771-7
Scott, Timothy L; Wakamatsu, Kazumasa; Ito, Shosuke et al. (2009) Purification and growth of melanocortin 1 receptor (Mc1r)- defective primary murine melanocytes is dependent on stem cell factor (SFC) from keratinocyte-conditioned media. In Vitro Cell Dev Biol Anim 45:577-83
Vanover, Jillian C; Spry, Malinda L; Hamilton, Laura et al. (2009) Stem cell factor rescues tyrosinase expression and pigmentation in discreet anatomic locations in albino mice. Pigment Cell Melanoma Res 22:827-38
Spry, Malinda L; Vanover, Jillian C; Scott, Timothy et al. (2009) Prolonged treatment of fair-skinned mice with topical forskolin causes persistent tanning and UV protection. Pigment Cell Melanoma Res 22:219-29