Removal of Epididymal Visceral Adipose Tissue Prevents Obesity-Induced Multi-organ Insulin Resistance in Male Mice

Figures

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  Figure 1.. VAT removal prevents high-fat diet (HFD)-induced weight gain. (A) Overall study design (see the details in Materials and Methods). At 8 to 9 months of age, C57BL/6J male mice were assigned to sham operation and epididymal visceral adipose tissue (VAT) removal operation groups. Mice were fed either a regular-chow diet (RCD) or HFD after surgery. Body weight was measured in sham and VAT-removed (VAT-R) mice before surgery and 2 months after RCD (n = 5-6 per group) (B) and HFD feeding (n = 11-12 per group) (C). (D) Tissue weight of VAT, omental AT, and inguinal subcutaneous adipose tissue (SAT) were determined 3 months after HFD feeding (n = 5-12 per group). Whole-body oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient (RQ) were evaluated in 12- to 13-month-old sham and VAT-R mice under RCD (E) and HFD (F) conditions (n = 4 per group). Values are means ± SEM. Data were analyzed by 1-way analysis of variance with the Tukey’s post-hoc test (B and C) and Student’s unpaired t-test (D). *P < 0.05.

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  Figure 2.. VAT removal prevents obesity-induced insulin resistance. Insulin tolerance tests (ITTs) and intraperitoneal glucose tolerance tests (IPGTTs) were conducted in 12- to 13-month-old mice under RCD (n = 4-6 per group) and HFD conditions (n = 11 per group). (A) After a 4-h fasting period, mice were intraperitoneally injected with insulin (0.75 U/kg body weight), and blood glucose concentration was measured. (B) The area under the curves (AUC) during the ITTs were determined. (C) After overnight fasting, mice were intraperitoneally injected with dextrose (2 g/kg body weight) and blood glucose concentration was measured. (D) The area under the curves (AUC) during the IPGTTs were determined. Plasma insulin concentrations before (0 min) and 30 min after the intraperitoneal injection of glucose (E) and fold-increase in plasma insulin concentration (F) were determined in HFD-fed mice (n = 6–7 per group). Fasting blood glucose (G) and insulin (H) concentrations were evaluated in sham and VAT-R mice under RCD (n = 5-6 per group) and HFD conditions (n = 10-12 per group). Values are means ± SEM. #Analysis of variance revealed a significant group × time interaction (P < 0.05). Data were analyzed…

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  Figure 3.. VAT removal enhances insulin signaling in SAT, liver, and skeletal muscle. (A) Insulin signaling in subcutaneous adipose tissue (SAT), liver, and skeletal muscle were evaluated in HFD-fed sham and VAT-R mice (n = 3-4 per group). Mice were intraperitoneally injected with phosphate-buffered saline (−) or insulin (10 U/kg body weight) following a 4-h fasting. After 15 min, mice were sacrificed and tissue samples were collected. Phosphorylated AKT (p-AKT) on Serine473 (S473) and Threonine308 (T308) and total AKT protein were evaluated by Western blot. Densitometric analyses of p-AKT S473 (B) and p-AKT T308 (C) relative to total AKT. Values are means ± SEM. Data were analyzed by 1-way analysis of variance with the Tukey’s post-hoc test. *P < 0.05.

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  Figure 4.. VAT removal improves plasma lipid profiling under HFD condition. Twelve- to 13-month-old sham and VAT-R mice were fasted overnight and plasma concentrations of total cholesterol (TC) (A), triglyceride (TG) (B), and free fatty acids (FFA) (C) in sham and VAT-R mice under RCD (n = 5-6 per group) and HFD conditions (n = 10-11 per group) were measured. Values are means ± SEM. *Data were analyzed by Student’s unpaired t-test (P < 0.05).

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  Figure 5.. VAT removal prevents HFD-induced hepatosteatosis. (A) Hepatic TG content in 12- to 13-month-old sham and VAT-R mice under RCD (n = 5 per group) and HFD conditions (n = 5–7 per group). (B) Liver weight in HFD-fed sham and VAT-R mice (n = 5-7 per group). (C) Representative hematoxylin and eosin staining images of liver from HFD-fed sham and VAT-R mice. Liver fat content (%) (D) and NAFLD activity score (NAS) (E) were determined by analyzing the hematoxylin- and eosin-stained section (n = 5-7 per group). Values are means ± SEM. *Data were analyzed by Student’s unpaired t-test (P < 0.05).

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  Figure 6.. Effects of VAT removal on key adipokines. Plasma concentrations of IL-6 (A), leptin (B), and adiponectin (C) were determined in 12- to 13-month-old sham and VAT-R mice under RCD and HFD conditions (n = 5-7 per group). (D) Western blot analysis of phosphorylated AMPK on Threonine172 (p-AMPK T172) and total AMPK in liver obtained from HFD-fed sham and VAT-R mice (n = 6-7 per group). Densitometric analysis of p-AMPK normalized to total AMPK is shown. Values are means ± SEM. *Data were analyzed by Student’s unpaired t-test (P < 0.05).

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  Figure 7.. Effects of VAT removal on gene expression profiling in liver and SAT. RNA-sequencing of liver (A and B) and SAT (C and D) obtained from sham and VAT-R mice under a HFD condition (n = 5 per group). (A and C) Volcano plots of RNA-seq data with log2-fold change (FC) (X-axis) and -log10-P-value (Y-axis). Up- and downregulated differentially expressed genes (DEGs) between HFD-fed sham and VAT-R mice are shown as red and blue dots, respectively. (B and D) The DAVID Bioinformatics Resources identified biological pathways significantly enriched with DEGs. The top 10 Gene Ontology terms ranked by fold-enrichment are shown.

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  Figure 8.. Systemic metabolic benefits induced by prophylactic VAT removal. The present study demonstrates prophylactic VAT removal prevents obesity and its related systemic metabolic abnormalities, such as insulin resistance, hepatosteatosis, inflammation, and oxidative stress. The alterations in adipose tissue-derived adipokine and FFA likely explain the mechanism of the systemic metabolic benefits induced by prophylactic VAT removal.