Studying Chronic Exposure of Mice to Ultraviolet B Radiation

Abstract

Ultraviolet B (UVB) radiation (280-320 nm) has been recognized as a carcinogen since 1928, leading to sun exposure minimization. However, epidemiological studies suggest that sun exposure correlates with increased life expectancy and reduced incidence of cardiovascular diseases and certain cancers such as colon and endometrial cancer. UVB exposure also influences liver metabolism, protects against hepatocellular lipotoxicity, and affects metabolic health. These effects are partly due to vitamin D synthesis, though some are independent of vitamin D. Moreover, phototherapy with UVB has immunomodulatory properties and is used to treat skin conditions such as vitiligo and psoriasis while also affecting the systemic immune system. Given UVB's broad physiological effects, there are gaps in understanding the mechanism behind most of these effects. We showed that daily low-level UVB exposure enhances food-seeking behavior in male mice but not in females due to increased ghrelin secretion from skin adipocytes. In females, estrogen inhibits adipocytes' p53 activity, blocking ghrelin elevation and demonstrating a sex-dependent response to UVB radiation. Additionally, UVB-induced p53 activation in epidermal keratinocytes activates the hypothalamus-pituitary-gonadal axis, inducing sexual behavior and ovarian pro-fertility. This paper outlines a protocol for studying local and systemic effects of low UVB radiation using a C57BL/6J mouse model. Key elements include precise calibration of UVB doses, housing conditions, and careful hair removal to ensure consistent exposure. Mice are subjected to a graded UVB exposure regime over several weeks, with monitoring for health and behavioral changes. Methods for validation of radiation efficiency through pigmentation measurements are also detailed. By emphasizing calibration of UVB doses, rigorous animal care, and methodological controls, this protocol will facilitate the study of the comprehensive effects of UVB exposure, contributing to a nuanced understanding of its therapeutic benefits and risks.