Skin epidermal keratinocyte p53 induces food uptake upon UV exposure

Abstract

Introduction: The first cells affected by UVB exposure are epidermal keratinocytes, and p53, the genome guardian, is activated in these cells when skin is exposed to UVB. UVB exposure induces appetite, but it remains unclear whether p53 in epidermal keratinocytes plays a role in this appetite stimulation.

Results: Here we found that food intake was increased following chronic daily UVB exposure in a manner that depends on p53 expression in epidermal keratinocytes. p53 conditional knockout in epidermal keratinocytes reduced food intake in mice upon UVB exposure.

Methods: To investigate the effects of p53 activation following UVB exposure, mice behavior was assessed using the staircase, open-field, elevated-plus maze, and conditioned-place preference tests. In addition to effects on appetite, loss of p53 resulted in anxiety-related behaviors with no effect on activity level.

Discussion: Since skin p53 induces production of β-endorphin, our data suggest that UVB-mediated activation of p53 results in an increase in β-endorphin levels which in turn influences appetite. Our study positions UVB as a central environmental factor in systemic behavior and has implications for the treatment of eating and anxiety-related disorders.

Keywords: UVB exposure; anxiety-related behaviors; conditioned-place preference; epidermal keratinocytes; food intake motivation; mice; p53 activation.

Figure 1

UVB exposure increases food intake. (A) Experimental scheme for the open field test. C57BL/6 J male mice were habituated for 1 week followed by daily mock irradiation (control) or 50 mJ/cm² UVB exposure for 5 weeks. At the end of the fifth week, the animals were subjected to the CPP test. The total duration of the CPP test was 9 days. (B) Preference ratios, calculated by dividing the cumulative time spent in side A by the cumulative time spent on sides (A,B) of the CPP arena, during pre-conditioning (Day 0) and post-conditioning (Day 9) (n ≥ 22 mice per group). Data for individuals are plotted as dots, and means ± SEM are shown as a bar graph. Significance was evaluated by two-way ANOVA for conditioning as a source of variation (***p < 0.0001) and by Tukey’s multiple comparison for pre-conditioning vs. post-conditioning (**p < 0.01, *p < 0.05). Statistical details are provided in Supplementary Table S1. (C) Average food pellets consumed in 15-min CPP test session by control and UVB-treated mice on days 2, 4, 6, and 8. Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Two-tailed unpaired t-tests were performed (*p < 0.05). (D,E) Average distance traveled (in cm) and (E) total activity time (in %) during the CPP test. (n ≥ 22 mice per group). Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Significance was evaluated by two-way ANOVA for conditioning as a source of variation (***p < 0.0001) and Tukey’s multiple comparison for pre-conditioning vs. post-conditioning (*p < 0.05). Statistical details are provided in Supplementary Table S1.

Figure 2

p53 knockout in epidermal keratinocytes have significant but modest effects on UVB-induced reward food intake. (A) Experimental scheme for the open field and staircase test. Wild-type mice and mice with conditional knockout of p53 in keratinocytes were habituated for 1 week followed by daily mock irradiation or 50 mJ/cm² UVB exposure for 5 weeks. At the end of the fifth week, the animals were deprived of food for 22 h and then subjected to the staircase and open field tests. (B) Number of attempts (left) and the eating scores (right) for the control and UVB-treated male mice during the staircase test. (n ≥ 10 mice per group). Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Significance was determined by two-way ANOVA analysis with student’s t-test. Details are given in Supplementary Table S2. (C) Food pellets consumed, total distance traveled (CM), time spent in center (s), total activity (%), velocity (cm/s), and time spent in periphery (s) for the control and UVB-treated male mice during the open-field test (n ≥ 11 mice per group). Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Significance was determined by two-way ANOVA analysis with Tukey’s multiple comparison (for total distance traveled, time spent in center, total activity, velocity, and time spent in periphery) and student’s t-test (for the food pellets consumed). Details are given in Supplementary Table S2. Bottom: Representative heat maps for a mouse from each group. *Represents p-value < 0.05.

Figure 3

p53 knockout in skin epidermal keratinocytes induces anxiety-related behavior. (A) Experimental scheme for the open field test. Wild-type mice and p53-knockout mice were habituated for 1 week followed by control⁻UVB exposure for five weeks. At the end of the fifth week, the animals were starved for 22 h and then subjected to the open field test and elevated-plus maze test. (B) Total distance traveled (CM), total activity (%), time spent in the center (S), and the velocity (cm/s) in the arena were determined (n = 11 mice per group). Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Details of the statistical analyses are given in Supplementary Table S3. Bottom: Representative heat maps for males (left) and females (right) from each group. (C) Total frequency/number of visits in closed and open arms (n), activity, time spent in center (s), and velocity (cm/s) during the elevated-plus maze test. Determined (n = 11 mice per group). Data for individuals are plotted as dots and means ± SEM are shown as a bar graph. Details of the statistical analyses are given in Supplementary Table S3. Bottom: Representative heat maps for males from each group. *Represents p-value < 0.05.