1161 UV irradiation modulates appetite and body weight through upregulating norepinephrine in mice

Ultraviolet (UV) irradiation to the skin downregulates lipid synthesis and adipokine production in subcutaneous fat. Recent evidence also suggests that UV exposure limits body weight gain in obesity models. However, it is still unclear how chronic UV irradiation modulates the energy metabolism of the whole body. High fat- or normal diet-fed female C57BL/6 mice were treated with UV or sham irradiation for 12 weeks. UV exposure stimulated food intake but prevented body weight gain. Leptin, an appetite-suppressing hormone, was significantly reduced in serum, skin, and inguinal subcutaneous fat of high fat diet-fed UV-irradiated mice. Besides, UV irradiation significantly promoted the orexigenic pathway involving neuropeptide Y and agouti-related peptide in hypothalamus. Mice with UV irradiation showed browning of subcutaneous white adipose tissues and increased thermogenesis without increased physical activity. Notably, liquid chromatography/mass spectrometer analyses in the skin revealed that norepinephrine was among the most significantly increased neurotransmitters in UV-irradiated mice, and downregulation of norepinephrine production by dopamine β-hydroxylase inhibitor nepicastat reversed the effects of UV on food intake and body weight. In conclusion, chronic UV irradiation induces NE release resulting in stimulating food intake due to the downregulation of the anorexigenic hormone leptin, but preventing weight gain through the elevation of energy expenditure.