Characterization of the effects of cannabinoid receptor deletion on energy metabolism in female C57BL mice

Abstract

Background: Despite the evidence that energy balance is regulated differently in females and that the endocannabinoid system is sexually dimorphic, previous studies on the endocannabinoid system and energy balance predominantly used male models. Here, we characterize the effects of cannabinoid receptor deletion on body weight gain and glucose metabolism in female C57BL mice.

Methods: Female mice lacking the cannabinoid-1 receptor (CB1R^-/-), cannabinoid-2 receptor (CB2R^-/-), or both receptors (CB1R^-/-/CB2R^-/-) and wild-type (WT) mice were fed with a low (LFD; 10% of calories from fat) or high-fat diet (HFD; 45% of calories from fat) for six weeks.

Results: Female WT mice fed with HFD gained significantly more weight than WT mice fed with LFD (p < 0.001). Similar pattern was observed for CB2^/- mice fed with HFD compared to CB2R^-/- mice fed with LFD (p < 0.001), but not for CB1R^-/- fed with HFD vs. LFD (p = 0.22) or CB1R^-/-/CB2R^-/- fed with HFD vs. LFD (p = 0.96). Comparing the 4 groups on LFD, weight gain of CB1R^-/- mice was greater than all other genotypes (p < 0.05). When fed with HFD, the deletion of CB1R alone in females did not attenuate weight gain compared to WT mice (p = 0.72). Female CB1R^-/-/CB2R^-/- mice gained less weight than WT mice when fed with HFD (p = 0.007) despite similar food intake and locomotor activity, potentially owing to enhanced thermogenesis in the white adipose tissue. No significant difference in weight gain was observed for female CB2R^-/- and WT mice on LFD or HFD. Fasting glucose, however, was higher in CB2R^-/- mice fed with LFD than all other groups (p < 0.05).

Conclusion: The effects of cannabinoid receptor deletion on glucose metabolism in female mice were similar to previously published findings on male mice, yet the effects on body weight gain and thermogenesis were attenuated in CB1R^-/- mice.

Keywords: body weight; cannabinoids; female; glucose metabolism; thermogenesis.

Figure 1

Body weight gain of female mice lacking the cannabinoid receptors Arrows indicate the comparison with WT mice. (A) Body weight gain of female mice on LFD for 6 weeks (n = 16-24/group). Repeated measure ANOVA F_genotype = 9.7; p <0.001. (B) Body weight gain of female mice on HFD for 6 weeks (n = 14-25/group). Repeated measure ANOVA F_genotype = 4.9; p = 0.004. (C) Change in body fat mass of female mice when fed with LFD for 6 weeks (n = 9-23/group). One-way ANOVA: F = 2.2, p = 0.09. (D) Change in body fat mass of female mice when fed with HFD for 6 weeks (n = 13-23/group). One-way ANOVA: F = 4.5, p = 0.006.

Figure 2

Food intake and locomotion of female mice lacking the cannabinoid receptors. Arrows indicate the comparison with WT mice. (A) Food intake of female mice for 108 hours on LFD (n = 3-6/group). One-way ANOVA for light cycle: F = 9.0, p = 0.001; for dark cycle: F = 13.8, p < 0.001. (B) Food intake of female mice for 108 hours on HFD (n = 4-6/group). One-way ANOVA for light cycle: F = 14.5, p < 0.001; for dark cycle: F = 8.1, p = 0.003. (C) Locomotion of female mice for 108 hours on LFD (n = 4-6/group). One-way ANOVA for light cycle: F = 6.7, p = 0.004; for dark cycle: F = 11.8, p <0.001. (D) Locomotion of female mice for 108 hours on HFD (n = 3-6/group). One-way ANOVA for light cycle: F = 23.3, p < 0.001; for dark cycle: F = 2.5, p = 0.10.

Figure 3

Respiratory exchange ratio (RER) and heat production of female mice lacking the cannabinoid receptors. Arrows indicate the comparison with WT mice. (A) RER of female mice for 108 hours on LFD (n = 4-6/group). One-way ANOVA for light cycle: F = 15.9, p <0.001; for dark cycle: F = 15.8, p <0.001. (B) RER of female mice for 108 hours on HFD (n = 4-6/group). One-way ANOVA for light cycle: F = 34.6, p <0.001; for dark cycle: F = 58.6, p <0.001. (C) Heat production of female mice for 108 hours on LFD (n = 4-6/group). One-way ANOVA for light cycle: F = 3.0, p = 0.06; for dark cycle: F = 6.2, p = 0.007. (D) Heat production of female mice for 108 hours on HFD (n = 4-6/group). One-way ANOVA for light cycle: F = 7.2, p = 0.004; for dark cycle: F = 5.7, p = 0.009.

Figure 4

Glucose metabolism of female mice lacking the cannabinoid receptors Arrows indicate the comparison with WT mice. (A) Fasting blood glucose of female mice when fed with LFD for 6 weeks (n = 12-25/group). One way-ANOVA = 5.3; p = 0.002. (B) Fasting blood glucose of female mice when fed with HFD for 6 weeks (n = 9-19/group). One way-ANOVA = 0.9; p = 0.5 (C) Fasting blood insulin of female mice when fed with LFD for 6 weeks (n = 3-11/group). One way-ANOVA = 0.7; p = 0.6. (D) Fasting blood insulin of female mice when fed with HFD for 6 weeks (n = 5-8/group). One way-ANOVA = 6.7; p = 0.002 (E, G) Blood glucose levels of female LFD mice after intrapertonial injection of D-glucose solution (2 g/kg; n = 5-9). Area under the curve one way-ANOVA F = 3.8; p = 0.03. (F, H) Blood glucose levels of female HFD mice after intrapertonial injection of D-glucose solution (2 g/kg; n = 6-9). Area under the curve one way-ANOVA F = 3.0; p = 0.05.

Figure 5

Expression of thermogensis genes in adipose tissue of female mice lacking the cannabinoid receptors Arrows indicate the comparison with WT mice. (A) Relative expression of UCP1 (One way-ANOVA = 4.4; p = 0.01; n = 7-13/group) and COX8B (One way-ANOVA = 11.2; p < 0.001; n = 7-17/group) in the WAT of female mice fed with LFD for 6 weeks. (B) Relative expression of UCP1 (One way-ANOVA = 5.0; p = 0.001; n = 6-13/group) and COX8B (One way-ANOVA = 0.9; p = 0.46; n = 7-14/group) in the WAT of female mice fed with HFD for 6 weeks. (C) Relative expression of UCP1 (One way-ANOVA = 3.9; p = 0.02; n = 6-16/group) and COX8B (One way-ANOVA = 2.1; p = 0.12; n = 5-16/group) in the BAT of female mice fed with LFD for 6 weeks. (D) Relative expression of UCP1 (One way-ANOVA = 5.4; p = 0.004; n = 8-11/group) and COX8B (One way-ANOVA = 0.1; p = 0.96; n = 8-11/group) in the BAT of female mice fed with HFD for 6 weeks.

Figure 6

Expression of CB1R and CB2R genes in adipose tissue and liver of female mice Arrows indicate the comparison with WT mice. (A) Relative expression of CB1R in WAT (LFD n = 8-10/group; HFD n = 5-10/group) (B) Relative expression of CB1R in BAT (LFD n = 5-6/group; HFD n = 10-11/group) (C) Relative expression of CB1R in liver (LFD n = 8-13/group; HFD n = 7-13/group) (D) Relative expression of CB2R in WAT (LFD n = 8/group; HFD n = 8-11/group) (E) Relative expression of CB2R in BAT (LFD n = 9-13/group; HFD n = 6-10/group) (F) Relative expression of CB2R in liver (LFD n = 8-13/group; HFD n = 7-14/group).