Even a low dose of tamoxifen profoundly induces adipose tissue browning in female mice

Abstract

Background: Tamoxifen-inducible Cre/lox site-specific recombination technology has been widely used to generate conditional transgenic mice. As an estrogen receptor ligand, tamoxifen itself potentially affects energy metabolism, which may confound interpretation of data especially in metabolic studies. Considering sexual dimorphism, in this study, the effects of low-dose tamoxifen administration on energy metabolism, and browning of adipose tissues in female and male mice were investigated.

Methods: Female and male C57/BL6 mice were injected with tamoxifen oil solution (i.p.) and then housed at both room temperature (23 ± 2 °C) and cold environment (6 ± 1 °C). Serum, brown and white adipose tissues were obtained, and the effects of tamoxifen administration on energy metabolism and the browning of adipose tissues were evaluated.

Results: At 25 mg/kg body weight (BDW), tamoxifen administration for 3 alternative days decreased the percentage of inguinal and gonadal white adipose tissue weights in female mice accompanied by the up-regulation of thermogenesis in adipose tissues. In contrast, this dosage of tamoxifen did not induce noticeable changes in the energy metabolism and thermogenesis of adipose tissue in male mice under room temperature. Consistently, under cold stimulus, substantial browning of adipose tissues was observed in female mice injected with tamoxifen (50 mg/kg BDW, single injection) but not in male mice. Two-way ANOVA tests also demonstrated significant interactions between tamoxifen treatment and gender on the expression of thermogenic markers in adipose tissues.

Conclusion: Tamoxifen, even at a low dose, remarkably increases thermogenesis in adipose tissues of female mice; meanwhile, such a low dose could be used in male mice for inducing gene recombination without confounding the interpretation of data related to metabolism and thermogenesis of adipose tissues.

Figure 1.

Effects of tamoxifen administration on body composition, serum metabolic parameters, and histological structure of fat tissues in both genders of mice under room temperature. A, body weight. B-C, fat index (ratio of fat tissues weight to the whole-body weight) of BAT, ingWAT and gonWAT of female (B) and male mice (C). D-F, serum insulin (D), glucose (E), and free fatty acid (F) levels. G-H, representative H&E staining and percentage distribution of adipocyte diameters for ingWAT (G) and gonWAT (H) sections of female mice. I-J, representative H&E staining and percentage distribution of adipocyte diameters for ingWAT (I) and gonWAT (J) sections of male mice. *p<0.05, ** p<0.01. Data are expressed as mean ± SEM (n=6).

Figure 2.

Effects of tamoxifen administration on browning of adipose tissues in female mice under room temperature. A, C, E, mRNA expression of thermogenic and adipogenic genes in BAT (A), ingWAT (C), and gonWAT (E). B, D, F, representative images of immunoblotting and arbitrary units for UCP1 and Cytochrome C (Cyt C) in BAT (B), ingWAT (D), and gonWAT (F). *p<0.05, ** p<0.01. Data are expressed as mean ± SEM (n=6).

Figure 3.

Effects of tamoxifen administration on body composition, serum metabolic parameters, body temperature, and histological structure of fat tissues in both genders of mice under cold environment. A, body weight. B-C, fat index (ratio of fat tissues weight to the whole-body weight) of BAT, ingWAT, and gonWAT of female (B) and male mice (C). D-F, serum insulin (D), glucose (E), and free fatty acid (F) levels. G-H, body temperature changes of male (G) and female (H) mice after exposed at cold environment. I-J, representative H&E staining and percentage distribution of adipocyte diameters for ingWAT and gonWAT sections of male (I) and female (J) mice. *p<0.05, ** p<0.01. Data are expressed as mean ± SEM (n=6).

Figure 4.

Effects of tamoxifen administration on browning of adipose tissues in female mice under cold environment. A, C, E, mRNA expression of thermogenic and adipogenic genes in BAT (A), ingWAT (C), and gonWAT (E). B, D, F, Representative images of immunoblotting and arbitrary units for UCP1 and Cytochrome C (Cyt C) in BAT (B), ingWAT (D), and gonWAT (F). *p<0.05, **p<0.01. Data are expressed as mean ± SEM (n=6).

Figure 5.

Effects of tamoxifen administration on mRNA expression of thermogenic and adipogenic genes in BAT (A), ingWAT (B), and gonWAT (C) of male mice. *p<0.05, ** p<0.01. Data are expressed as mean ± SEM (n=6).