In previous preclinical studies, low (non-burning) doses of UV radiation (UVR) limited weight gain and metabolic dysfunction in mice fed with a high-fat diet. Here, we explored the effects of low-dose UVR on physical activity and food intake and mechanistic pathways in interscapular brown adipose tissue (iBAT). Young adult C57Bl/6J male mice, housed as individuals, were fed a high-fat diet and exposed to low-dose UVR (sub-oedemal, 1 kJ/m2 UVB, twice-a-week) or ‘mock’ treatment, with or without running wheel access (2 h, for ‘moderate’ physical activity) immediately after phototherapy. There was no difference in distance run in mice exposed to UVR or mock-treated over 12 weeks of exposure to running wheels (P = 0.14). UVR (alone) did not significantly affect food intake, adiposity, or signs of glucose dysfunction. Access to running wheels increased food intake (after 10 weeks, P ≤ 0.02) and reduced gonadal white adipose tissue and iBAT mass (P ≤ 0.03). Body weight and hepatic steatosis were lowest in mice exposed to UVR with running wheel access. In the iBAT of mice exposed to UVR and running wheels, elevated Atgl, Cd36, Fasn, Igf1, Pparγ, and Ucp1 mRNAs and reduced CD11c on F4-80 + MHC class II+ macrophages were observed, while renal Sglt2 mRNA levels were increased, compared to high-fat diet alone (P ≤ 0.03). Blood levels of 25-hydroxyvitamin D were not increased by exposure to UVR and/or access to running wheels. In conclusion, when combined with physical activity, low-dose UVR may more effectively limit adiposity (specifically, body weight and hepatic steatosis) and modulate metabolic and immune pathways in iBAT.
Supplementary Table 1 A supplementary table (n=1) for Allemann et al (Low-dose UV light and running wheels together increase brown adipose tissue activity).
Supplementary Figure 1: Low-dose UVR and access to running wheels increased Sglt2 mRNA in kidneys of mice fed a high-fat diet (individually housed). Four-week old male C57Bl/6J male mice were fed a low-fat diet (LFD) for 4 weeks. At 8 weeks of age, mice were separated into one of 5 treatment groups: 1) LFD; 2) High-fat diet (HFD); 3) HFD with UVR (UVR); 4) HFD with physical activity (PA); or, 5) HFD with UVR and physical activity (UVR + PA). After 12 weeks of treatment, mRNAs were quantified in kidney via real-time PCR, specifically those for Sglt2, Tnf, and Il6. Data are shown as mean + SD (n=4-5/treatment); *p<0.05 (one-way ANOVA with Tukey’s post-hoc).