Interleukin-1α deficiency reduces adiposity, glucose intolerance and hepatic de-novo lipogenesis in diet-induced obese mice

Abstract

Objective: While extensive research revealed that interleukin (IL)-1β contributes to insulin resistance (IR) development, the role of IL-1α in obesity and IR was scarcely studied. Using control, whole body IL-1α knockout (KO) or myeloid-cell-specific IL-1α-deficient mice, we tested the hypothesis that IL-1α deficiency would protect against high-fat diet (HFD)-induced obesity and its metabolic consequences.

Research design and methods: To induce obesity and IR, control and IL-1α KO mice were given either chow or HFD for 16 weeks. Glucose tolerance test was performed at 10 and 15 weeks, representing early and progressive stages of glucose intolerance, respectively. Liver and epididymal white adipose tissue (eWAT) samples were analyzed for general morphology and adipocyte size. Plasma levels of adiponectin, insulin, total cholesterol and triglyceride (TG), lipoprotein profile as well as hepatic lipids were analyzed. Expression of lipid and inflammation-related genes in liver and eWAT was analyzed. Primary mouse hepatocytes isolated from control mice were treated either with dimethyl sulfoxide (DMSO) (control) or 20 ng/mL recombinant IL-1α for 24 hours and subjected to gene expression analysis.

Results: Although total body weight gain was similar, IL-1α KO mice showed reduced adiposity and were completely protected from HFD-induced glucose intolerance. In addition, plasma total cholesterol and TG levels were lower and HFD-induced accumulation of liver TGs was completely inhibited in IL-1α KO compared with control mice. Expression of stearoyl-CoA desaturase1 (SCD1), fatty acid synthase (FASN), elongation of long-chain fatty acids family member 6 (ELOVL6), acetyl-CoA carboxylase (ACC), key enzymes that promote de-novo lipogenesis, was lower in livers of IL-1α KO mice. Treatment with recombinant IL-1α elevated the expression of ELOVL6 and FASN in mouse primary hepatocytes. Finally, mice with myeloid-cell-specific deletion of IL-1α did not show reduced adiposity and improved glucose tolerance.

Conclusions: We demonstrate a novel role of IL-1α in promoting adiposity, obesity-induced glucose intolerance and liver TG accumulation and suggest that IL-1α blockade could be used for treatment of obesity and its metabolic consequences.

Keywords: de novo lipogenesis; glucose intolerance; interleukin-1; obesity.

Figure 1

IL-1α deficiency reduced eWAT weight and adipocyte size without affecting total body weight. (A) Body weight, (B) eWAT weight, (C) eWAT histology with H&E and (D) adipocyte size quantification in male Loxp and IL-1α KO mice (6 weeks of age at start of dietary intervention) fed either regular chow or HFD (n=7–12 per group) for 16 weeks. Data are presented as mean±SE. Asterisk/dollar/Hash marks depict statistically significant differences. **p≤0.01 ***p≤0.001 to Loxp. ###p≤0.001 to chow (two-way ANOVA). $$$p≤0.001 between chow to HFD (three-way mixed design ANOVA). ANOVA, analysis of variance; H&E, hematoxylin and eosin; HFD, high-fat diet; IL, interleukin; KO, knockout.

Figure 2

IL-1α deficiency prevented the onset of HFD-induced glucose intolerance and attenuated fasting plasma insulin and adiponectin levels. GTT and glucose AUC at 10 (A) and 15 (B) weeks of HFD. Fasting plasma levels of insulin (C) and adiponectin (D) after 8 weeks of HFD. Data are presented as mean±SE. Asterisks/Hash marks depict statistically significant differences. *p≤0.05; ***p≤0.001 to Loxp. #p≤0.05 ###p≤0.001 to chow (student’s t-test or two-way ANOVA). ANOVA, analysis of variance; AUC, area under curve; GTT, glucose tolerance test; HFD, high-fat diet; IL, interleukin; KO, knockout.

Figure 3

Fasting plasma cholesterol and TG levels were lower in IL-1α KO compared with Loxp mice. Fasting total plasma cholesterol (A, upper panel) and TG (B, upper panel) levels in male Loxp and IL-1α KO mice fed either regular chow or HFD (n=7–12 per group) for 8 weeks. Analysis of the distribution of plasma lipoprotein cholesterol (A, lower panel) and TG (B, lower panel) was performed with FPLC. Blood was obtained from fasted animals and plasma samples were pooled in each group. Data are presented as mean±SE. Asterisks/Hash marks depict statistically significant differences. ***p≤0.001 to Loxp. ###p≤0.001 to chow (two-way ANOVA). ANOVA, analysis of variance; FPLC, fast protein liquid chromatography; HFD, high-fat diet; IL, interleukin; KO, knockout; TG, triglyceride.

Figure 4

IL-1α deficiency completely inhibited HFD-induced accumulation of liver TGs. Liver specimens were obtained from male Loxp and IL-1α KO mice fed either regular chow or HFD (n=7–12 per group) for 16 weeks. (A) Total lipid weight in the liver normalized to liver weight. (B) Analysis of hepatic lipids with TLC. Data are presented as mean±SE. Asterisks/Hash marks depict statistically significant differences. *p≤0.05; **p≤0.01; ***p≤0.001 to Loxp. #p≤0.05; ##p≤0.01; ###p≤0.001 to chow (two-way ANOVA). ANOVA, analysis of variance; HFD, high-fat diet; IL, interleukin; KO, knockout; TG, triglyceride; TLC, thin-layer chromatography.

Figure 5

The mRNA levels of IL-6 and TNFα in eWAT were lower in HFD-fed IL-1α KO compared with Loxp mice. The mRNA expression level of IL-1α, IL-1β, IL-6 and TNFα in eWAT (A) and liver (B) of Loxp and IL-1α KO mice-fed HFD for 16 weeks. Data are presented as mean±SE. Asterisks depict statistically significant differences. *p≤0.05; **p≤0.01 to Loxp (student’s t-test). ANOVA, analysis of variance; HFD, high-fat diet; IL, interleukin; KO. knockout; TG, triglyceride; TNF, tumor necrosis factor.

Figure 6

IL-1α deficiency lowered the expression of genes that promote hepatic DNL. (A) The mRNA expression levels of SCD1, FASN, ELOVL6, ACCα, DGAT, ChREBP, Srebpf-1c and LXR in livers of Loxp (control) and IL-1α KO mice-fed HFD for 16 weeks. (B) mRNA expression levels of ELOVL6 and FASN in primary mouse hepatocytes treated either with DMSO (control) or recombinant IL-1α for 24 hours. Data are presented as mean±SE. Asterisks depict statistically significant differences. *p≤0.05; **p≤0.01 to control mice/cells (student’s t-test). ACCα, acetyl-CoA carboxylase α; ChREBP, carbohydrate response element binding protein; DGAT, diacylglycerol acyltransferase; DMSO, dimethyl sulfoxide; DNL, de-novo lipogenesis; ELOVL6, elongation of long-chain fatty acids family member 6; FASN, fatty acid synthase; IL, interleukin; KO, knockout; LXR, liver X receptor; SCD1, stearoyl-CoA desaturase1; Srebpf-1c, sterol regulatory element-binding protein 1.