Adipocyte-specific ETB receptor overexpression induces obesity, insulin resistance, and dyslipidemia in high-fat diet-fed female mice

Abstract

In rodent models of diet-induced obesity, a metabolic syndrome-like phenotype develops that is more pronounced in males compared to females. Our lab reported that endothelin-1 (ET-1) is increased in visceral adipose of high-fat diet-fed (HFD) mice where it inhibits adiponectin production through activation of the ET-1 type B receptor (ET_B). Further, adipocyte-specific knockout of ET_B improves insulin sensitivity in HFD-fed male mice. We report that males produce significantly more ET-1 with higher expression of ET_B in visceral adipose compared to females. We hypothesized that adipocyte-specific overexpression of the ET_B receptor (adET_BOX) would abolish or attenuate protection against HFD observed in female mice. The data indicate that female adET_BOX mice placed on HFD for 10 weeks had increased adiposity compared to floxed controls, while no detectable difference was observed between adET_BOX and floxed controls fed NMD. Compared to NMD floxed control mice, insulin tolerance was impaired in adET_BOX fed either NMD or HFD. Finally, HFD-fed adET_BOX had exacerbated dyslipidemia and insulin intolerance compared to floxed controls. These data indicate that reduced ET-1 signaling on adipocytes at least partially mediates protection against HFD-induced metabolic disease in female mice.

Keywords: adipose; endothelin; insulin resistance; obesity; sex differences.

FIGURE 1

Female mice have significantly reduced adipocyte expression of ET_B receptor. (a) ET‐1, (b) ET_B receptor, and (c) ET_A receptor mRNA expression in visceral (gonadal) adipose tissue of male and female C57Bl6 mice fed NMD or HFD for 10 weeks. Data were analyzed using a two‐way ANOVA with Tukey's post hoc test for individual groups. Data are expressed as mean ± SD. p Values represent results from multiple comparisons post hoc analysis.

FIGURE 2

Body weight and fat mass are significantly increased by overexpression of ET_B receptor by adipocytes in female mice. (a) Body weight (grams), (b) fat mass (percent of body weight), and (c) lean mass (percent of body weight) in female floxed control or adET_BOX mice fed NMD or HFD after 8 weeks of NMD or HFD. Data were analyzed by two‐way ANOVA with post hoc Tukey's post hoc test to compare each group. Data are expressed as mean ± SD. p Values represent results from multiple comparisons post hoc analysis. ANOVA tables: 2a, p _Interaction < 0.001, p _gen < 0.001, p _diet < 0.001; 2b, p _Interaction = 0.0008, p _gen < 0.0001, p _diet < 0.0001; 2c, p _Interaction = 0.97, p _gen = 0.79, p _diet = 0.0007.

FIGURE 3

Female adET_BOX receptor overexpression mice. (a) Plasma insulin concentration and (b) fasting blood glucose from female floxed control or adET_BOX mice fed NMD or HFD for 10 weeks. (c) Insulin tolerance test (ITT) and (d) Area under the curve (AUC) followed by (e) oral glucose tolerance test (OGTT) and (f) OGTT AUC. ITT and GTT were performed between 8 and 10 weeks of NMD or HFD feeding per methods. Insulin, fasting glucose, and AUC were analyzed using a two‐way ANOVA with post hoc Tukey's test between individual groups. Data are expressed as mean ± SD. p Values represent results from multiple comparisons post hoc analysis. ANOVA results: ITT p _time < 0.0001, p _gen = 0.03, p _diet < 0.001, p _{time × gen × diet}. GTT p _time < 0.0001, p _gen = 0.22, p _diet <0.0001, p _{time × gen × diet} = 0.94.

FIGURE 4

Adipocyte ET_B overexpression in female mice increases dyslipidemia following feeding. Plasma concentration of (a) cholesterol, (b) high‐density lipoprotein (HDL), (c) low‐density lipoprotein (LDL), (d) nonesterified free fatty acids (NEFA), and (e) triglycerides in female floxed control or adET_BOX mice fed NMD or HFD for 10 weeks. Statistical analyses were performed by two‐way ANOVA with Tukey's post hoc test between individual groups. Data are expressed as mean ± SD. p Values represent results from multiple comparisons post hoc analysis. ANOVA tables: 4a, p _Interaction = 0.016, p _gen < 0.012, p _diet < 0.0001; 4b, p _Interaction = 0.058, p _gen < 0.037, p _diet < 0.0001; 4c, p _Interaction = 0.096, p _gen < 0.03, p _diet < 0.0001; 4d, p _Interaction = 0.57, p _gen < 0.079, p _diet < 0.0001; 4e, p _Interaction = 0.75, p _gen < 0.075, p _diet < 0.0001.