Metabotropic glutamate receptor 5 knockout rescues obesity phenotype in a mouse model of Huntington's disease

Abstract

Obesity represents a global health problem and is characterized by metabolic dysfunctions and a low-grade chronic inflammatory state, which can increase the risk of comorbidities, such as atherosclerosis, diabetes and insulin resistance. Here we tested the hypothesis that the genetic deletion of metabotropic glutamate receptor 5 (mGluR5) may rescue metabolic and inflammatory features present in BACHD mice, a mouse model of Huntington's disease (HD) with an obese phenotype. For that, we crossed BACHD and mGluR5 knockout mice (mGluR5^-/-) in order to obtain the following groups: Wild type (WT), mGluR5^-/-, BACHD and BACHD/mGluR5^-/- (double mutant mice). Our results showed that the double mutant mice present decreased body weight as compared to BACHD mice in all tested ages and reduced visceral adiposity as compared to BACHD at 6 months of age. Additionally, 12-month-old double mutant mice present increased adipose tissue levels of adiponectin, decreased leptin levels, and increased IL-10/TNF ratio as compared to BACHD mice. Taken together, our preliminary data propose that the absence of mGluR5 reduce weight gain and visceral adiposity in BACHD mice, along with a decrease in the inflammatory state in the visceral adipose tissue (VAT), which may indicate that mGluR5 may play a role in adiposity modulation.

Figure 1

Schematic representation of experimental design. (A) Generation of the mice lines. FVB/NJ, FVB/N-Tg (HTT*97Q) IXwy/J (BACHD) and mGluR5 KO mice (mGluR5^−/−) mice were crossed over to generate the double mutant mice (BACHD/mGluR5^−/− mice) (F1). The F2 generation containing all genotypes used in this study was obtained by crossing between F1 generation. (B) From 2 to 12 months of age, mice were weighted once a month and adiposity index was measured at 2, 6 and 12 months in all tested genotypes. Subsequently at 2, 6 and 12 months of age mice were euthanized for obtaining visceral white adipose tissues and the hypothalamus in order to perform immunologic and metabolic analysis. EAT epidydimal adipose tissue, MAT mesenteric adipose tissue, RPAT retroperitoneal adipose tissue.

Figure 2

mGluR5 genetic deletion decreases body weight in BACHD mice. (A) Body weight measurements of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice from 2 to 12 months showed an interaction effect between time and genotype (F(_30,329) = 4,302). (B–D) Body weight of all tested groups at 2, 6 and 12 months of age. Error bars represent the mean ± SEM; n = 7–11. Repeated measures ANOVA and mixed model followed by Tukey post test (A). One-Way ANOVA followed by Bonferroni (B–C), and Kruskal–Wallis followed by Dunn’s post test (D). *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.

Figure 3

mGluR5 genetic deletion reduces fat pads wet weight and adiposity indices in BACHD mice at 6 months of age. All fat pads were individually weighted, and the adiposity index was obtained by the sum of the weight of visceral adipose tissue fat pads (VAT), normalized by body weight of individual mice. (A–F) measurement of the wet weight of the epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissue of WT, mGluR5, BACHD and BACHD/mGluR5^−/− mice, at 6 and 12 months of age, left and right columns, respectively. (G, H) Adiposity index of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice from 6 and 12 months of age. Error bars represent the mean ± SEM; n = 3–8. One-Way ANOVA followed by Bonferroni post test (A, B, D, E, G), and Krustal-Wallis followed by Dunn’s post test (C, F, H). *p < 0.05, **p < 0.01, ***p < 0.001; ****p < 0.0001.

Figure 4

The deletion of mGluR5 restores adiponectin levels in the epididymal adipose tissue of BACHD mice. (A–E) Adiponectin levels in the hypothalamus, epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissues, and in the sum of visceral adipose tissues (VAT) of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice at 12 months of age. Error bars represent the mean ± SEM; n = 5–7. One-Way ANOVA followed by Bonferroni post test (A, C–E), and One-Way Welch ANOVA followed by Games-Howell’s post test (B). * p < 0.05; ** p < 0.01.

Figure 5

The absence of mGluR5 decreases leptin levels in BACHD mice at 12 months of age (A–E) Leptin levels in the hypothalamus, epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissue, and in the sum of visceral adipose tissues (VAT) of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice at 12 months of age. Error bars represent the mean ± SEM; n = 4–7. One-Way Welch ANOVA followed by Games-Howell’s post test (A–D), and Kruskal–Wallis followed by Dunn’s post test (E). * p < 0.05; ** p < 0.01.

Figure 6

mGluR5 KO mice present increased adiponectin/leptin levels in several adipose tissue. (A–E) Adiponectin/leptin ratio in the hypothalamus, epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissue, and in the sum of visceral adipose tissues (VAT) of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice, at 12 months of age. Error bars represent the mean ± SEM; n = 4–7. One-Way ANOVA followed by Bonferroni post-test (A–D) and Kruskal Wallis followed by Dunn’s post test (E). * p < 0.05; ** p < 0.01; ***p < 0.005.

Figure 7

BACHD/mGluR5^−/− mice exhibit decreased IL-4/IFN ratio in the mesenteric adipose tissue. (A–E) IL-4/IFN ratio in the hypothalamus, epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissue, and in the sum of visceral adipose tissue (VAT) of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice, at 12 months of age. Error bars represent the mean ± SEM; n = 5–7. One-Way ANOVA followed by Bonferroni's post-test (A, C), Kruskal Wallis followed by Dunn’s post test (B, E), and One-Way Welch ANOVA followed by Games-Howell’s post test (C). *p < 0.05.

Figure 8

BACHD/mGluR5^−/− mice present an increase of IL-10/TNF ratio in the EAT, and in the sum of visceral adipose tissue. (A–E) IL-10/TNF ratio in the hypothalamus, epididymal (EAT), mesenteric (MAT), retroperitoneal (RPAT) adipose tissue, and in the sum of adipose tissues (VAT) of WT, mGluR5^−/−, BACHD and BACHD/mGluR5^−/− mice at 12 months of age. Error bars represent the mean ± SEM; n = 5–7. One-Way ANOVA followed by Bonferroni post-test (A, E), and One-Way Welch ANOVA followed by Games-Howell’s post test (B, C, D). *p < 0.05.

Figure 9

Proposed mechanism of mGluR5 absence in the improvements of obesity phenotype associated to BACHD mice. BACHD mice present an obesity phenotype associated with an inflammatory disturbance in the visceral white adipose tissue, leading to alterations in the peripheral adipokines. We hypothesized that the absence of mGluR5 signaling in the BACHD/mGluR5^−/− promoting an anti-inflammatory outcome in the visceral white adipose tissue, which may be associated with the modulation of macrophage polarization and T cells, and remodeling of the visceral white adipose tissue. Furthermore, reduction of inflammatory environment can regulate adipokine profile, and improving peripheral anorexigen signaling, contributing to regulate body weight in the double mutant mice.