UV Irradiation Increases Appetite and Prevents Body Weight Gain through the Upregulation of Norepinephrine in Mice.

UV irradiation of the human skin downregulates lipid synthesis and adipokine production in subcutaneous fat. Recent evidence has suggested that UV exposure limits body weight gain in mouse models of obesity. However, the relationship between norepinephrine and UV irradiation has not been previously reported. Chronic UV exposure stimulated food intake but prevented body weight gain. Leptin, an appetite-suppressing hormone, was significantly reduced in the serum of the UV-irradiated mice. In contrast, UV irradiation induced browning of subcutaneous white adipose tissues without increasing physical activity. Notably, UV irradiation significantly increased norepinephrine levels, and the inhibition of norepinephrine production reversed the effects of chronic UV irradiation on food intake and body weight gain. In conclusion, chronic UV irradiation induces norepinephrine release, resulting in the stimulation of food intake due to the downregulation of leptin levels, but it prevents weight gain by inducing the browning process and elevating energy expenditure.