Sexually dimorphic effects of angiopoietin-like 2 on energy metabolism and hypothalamic neuropeptide regulation

Abstract

Background: Adipokines regulate body weight and metabolism by targeting the hypothalamus, influencing feeding, energy expenditure (EE) and insulin sensitivity. Angiopoietin-like 2 (Angptl2) is a pro-inflammatory adipokine linking obesity to insulin resistance. Both Angptl2 and its receptor are expressed in the central nervous system. Yet, the contribution of Angptl2 to the regulation of energy metabolism and relevant hypothalamic neuropeptides in male and female mice is unknown. We aim at determining the impact of Angptl2 knockdown (KD) on energy balance, nutrient partitioning and hypothalamic responses to a standard (STD) or high-fat diet (HFD) in mice.

Methods: Three-month-old male and female Angptl2-KD mice and wildtype (WT) littermates were fed 16 weeks either a STD or a HFD. Body weight, food consumption and insulin sensitivity were assessed along with measurements of EE, respiratory exchange ratio (RER) and locomotor activity. We quantified the expression of Angptl2 and its receptors itga5, mag and pirb in the medio-basal hypothalamus (MBH) of WT mice, and MBH neuropeptide Y (NPY), agouti-related neuropeptide (AgRP) and proopiomelanocortin (POMC) gene expression in both KD and control fasting mice.

Results: Lack of Angptl2 reduced food intake in males on both diets, and in females on HFD. In KD males, this anorexigenic effect was associated with lower body weight, increased EE, improved insulin sensitivity and lower hypothalamic orexigenic NPY expression compared to controls. Female Angptl2-KD mice however, exhibited unaltered body weight, EE and insulin sensitivity, and elevated NPY, AgRP and MC4R expression compared to controls. Fasting caused an increase in the MBH of mag expression in males and females but Angptl2 expression only in female mice.

Conclusions: Angptl2 KD improved diet-induced obesity and associated metabolic dysfunction in male mice. The lack of similar changes in female mice and divergent MBH neuropeptide profile suggest that sex-dependent mechanisms underly the anabolic effects of this proinflammatory adipokine.

Fig. 1. Body weight, food intake and adipose and liver mass in male and female Angptl2-KD and control mice on STD or HFD.

Angptl2 mRNA expression in the MBH of WT and Angptl2-KD male (A) and female (G) mice exposed to STD or HFD. Weekly body weight (B, H) and final body after 16 weeks of diet (C, I), cumulative food intake (D, J), adipose tissue weight (E, K) and liver weight (F, L) in males and females. N = 12 mice per group; Two-way ANOVA (genotype X diet); Sidak’s post hoc test. *p < 0.05 Angptl2-KD vs. WT mice; ^‡p < 0.05 HFD vs. STD.

Fig. 2. Glucose homeostasis in male and female Angptl2-KD and control mice on STD or HFD.

Glycemia in male (A–C) and female (D–F) Angptl2-KD mice (vs. WT controls) during an ITT after 16 weeks of STD vs. HFD. A, D Fasting glycemia, B, E glycemia during insulin tolerance test (ITT) and C, F total AUC of glycemia during ITT in WT and Angptl2-KD mice. N = 7–10 mice per group; Two-way ANOVA (genotype X diet); Sidak’s post hoc test. *p < 0.05 Angptl2-KD vs. WT mice; ^‡p < 0.05 HFD vs. STD.

Fig. 3. Metabolic parameters in male and female Angptl2-KD and control mice on STD or HFD.

Respiratory exchange ratio (A, G) and its quantification (D, J), energy expenditure (B, H, E, K) and locomotor activity (C, I and F, L) measured over 12 h, in WT (open bars) and Angptl2-KD (filled bars) males (in blue) and females (in red) mice exposed to STD or HFD for 16 weeks. Data are mean ± SEM of 5 mice/groups on STD for both sexes; and mean ± SEM of 4-5 male and 2-6 female WT and KD mice on HFD; Two-way ANOVA, Sidak’s post hoc test. *p < 0.05 Angptl2-KD vs. WT mice; ^‡p < 0.05 HFD vs. STD.

Fig. 4. Gene expression in the medio-basal hypothalamus in male and female Angptl2-KD and control mice.

Gene expression of Angptl2 (A, B) and its receptors: Itga5 (C, D), Pirb (E, F) and Mag (G, H), in MBH of WT male (in blue) and female (in red) mice, fed with a STD or fasted for 16 h. Data are mean ± SEM of n = 4-6 male and n = 8 female mice. *p < 0.05 vs. fed mice, unpaired-t test. POMC (I, J), NPY (K, L), AgRP (M, N) and Mc4r (O, P) mRNA expression in the MBH. Data are mean ± SEM of n = 4/6 male (in blue) WT (open bars) and 6/4 Angptl2-KD (filled bars) mice, on STD/HFD respectively; and mean ± SEM of n = 5/6 female (in red) WT and 6/6 Angptl2-KD mice, on STD/HFD respectively; Two-way ANOVA (genotype X diet); Sidak’s post hoc test. *p < 0.05 Angptl2-KD vs. WT; ^‡p < 0.05 HFD vs. STD.