FoxO1 haploinsufficiency protects against high-fat diet-induced insulin resistance with enhanced peroxisome proliferator-activated receptor gamma activation in adipose tissue - PubMed (original) (raw)

. 2009 Jun;58(6):1275-82.

doi: 10.2337/db08-1001. Epub 2009 Mar 16.

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FoxO1 haploinsufficiency protects against high-fat diet-induced insulin resistance with enhanced peroxisome proliferator-activated receptor gamma activation in adipose tissue

Jane J Kim et al. Diabetes. 2009 Jun.

Abstract

Objective: Forkhead box O (FoxO) transcription factors represent evolutionarily conserved targets of insulin signaling, regulating metabolism and cellular differentiation in response to changes in nutrient availability. Although the FoxO1 isoform is known to play a key role in adipogenesis, its physiological role in differentiated adipose tissue remains unclear.

Research design and methods: In this study, we analyzed the phenotype of FoxO1 haploinsufficient mice to investigate the role of FoxO1 in high-fat diet-induced obesity and adipose tissue metabolism.

Results: We showed that reduced FoxO1 expression protects mice against obesity-related insulin resistance with marked improvement not only in hepatic insulin sensitivity but also in skeletal muscle insulin action. FoxO1 haploinsufficiency also resulted in increased peroxisome proliferator-activated receptor (PPAR)gamma gene expression in adipose tissue, with enhanced expression of PPARgamma target genes known to influence metabolism. Moreover, treatment of mice with the PPARgamma agonist rosiglitazone caused a greater improvement in in vivo insulin sensitivity in FoxO1 haploinsufficient animals, including reductions in circulating proinflammatory cytokines.

Conclusions: These findings indicate that FoxO1 proteins negatively regulate insulin action and that their effect may be explained, at least in part, by inhibition of PPARgamma function.

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Figures

FIG. 1.

FIG. 1.

Metabolic characterization of HFD-fed Foxo1+/− mice. Metabolic features of 10-month-old male mice after 24 weeks of a HFD (wild type n = 10; Foxo1+/− n = 14). A and B: Whole-blood glucose and plasma insulin during intraperitoneal glucose tolerance testing. C and D: Insulin tolerance testing. Animals were fasted for 6 and 4 h before GTTs and ITTs, respectively. Results are represented as both absolute glucose values and percent glucose decrease from basal. Values represent mean glucose ± SE. *P < 0.05 for Foxo1+/− versus wild-type. E: Mice were weighed at the initiation of the HFD and then at 4-week intervals up to 28 weeks of HFD duration. Values represent mean body weight of at least 15 mice per genotype ± SE. ■, wild type; ○, Foxo1+/−.

FIG. 2.

FIG. 2.

Improved liver and skeletal muscle insulin sensitivity in Foxo1+/− mice. Hyperinsulinemic-euglycemic clamp studies were performed in 10-month-old male mice after 26 weeks of a HFD (wild type n = 4; Foxo1+/− n = 5). Foxo1+/− mice show increased GIRs. A: Decreased basal hepatic glucose output (Foxo1+/− 5.94 ± 1.93 vs. wild type 11.82 ± 1.95 mg/kg/min, P < 0.05) and improved insulin-stimulated hepatic glucose suppression (B) when compared with wild-type littermates. Foxo1+/− mice also demonstrate enhanced total Rd (C) and IS-GDR (D). Values represent the means ± SE. *P < 0.05.

FIG. 3.

FIG. 3.

Insulin action in liver and muscle of Foxo1+/− mice. A and B: Enhanced signaling through the PI3K pathway in Foxo1+/− and wild-type (WT) mice was determined by measuring Akt activity after insulin injection into the inferior vena cava. Representative blots from quadriceps muscle and liver are shown. The intensity of bands corresponding to phospho-Akt (pAkt) was corrected by total Akt levels to obtain relative measures of Akt phosphorylation between samples. Quantitation of results from three independent experiments is shown. C: Glut4 gene expression in skeletal muscle. Relative mRNA amounts of Glut4 from quadriceps and gastrocnemius muscle of HFD-fed Foxo1+/− and wild-type mice were measured using real-time PCR. D and E: Liver gene expression analysis. Relative mRNA amounts of genes controlling gluconeogenesis and lipogenesis were measured in fasted mice using a 16-gene microarray platform (wild type n = 4; Foxo1+/− n = 6). Values represent the means ± SE. *P < 0.05. The same cohort of HFD-fed Foxo1+/− and wild-type mice was used for all of the above experiments. RNA samples were isolated from fasting mice before insulin injection. AU, arbitrary units.

FIG. 4.

FIG. 4.

Adipose tissue characteristics of HFD-fed Foxo1+/− mice. A and B: Average cell size of adipocytes from epididymal fat (wild type n = 6; Foxo1+/− n = 8). Representative photomicrographs are represented. Scale bars represent 100 μm. C: Epididymal adipose fat pads were isolated and weighed in HFD-fed wild-type and Foxo1+/− mice. Each bar represents individual means ± SE. *P < 0.03. D–G: Gene expression studies were performed on white adipose tissue of HFD-fed animals using real-time PCR to measure relative amounts of PPARγ and PPARγ target genes. Data represent means ± SE of RNA samples (n = 5 mice per genotype). *P < 0.05. AU, arbitrary units. ■, wild type; □, Foxo1+/−.

FIG. 5.

FIG. 5.

Effect of TZD treatment on in vivo glucose homeostasis and insulin sensitivity in Foxo1+/− mice. A: Body weights of male mice were measured at initiation of rosiglitazone treatment and every 4 weeks up to 8 weeks of age (wild-type HFD + TZD n = 8; Foxo1+/− HFD + TZD n = 10). B: Glucose tolerance testing (1 g/kg dextrose i.p.) was performed on mice after 5 weeks of combined HFD and TZD (wild-type HFD + TZD n = 8; Foxo1+/− HFD + TZD n = 10) and compared with GTT results from mice after 5 weeks of the HFD alone (wild-type HFD n = 10; Foxo1+/− HFD n = 14). Values represent mean glucose ± SE. C and D: Insulin tolerance testing (0.35 unit/kg insulin i.p.) was conducted on mice after 5 weeks of combined HFD and TZD (HFD + TZD wild type n = 8; HFD Foxo1+/− + TZD n = 10) and compared with GTT results from mice after 5 weeks of the HFD alone (HFD wild type n = 10; HFD Foxo1+/− n = 14). Results are represented as both absolute glucose values and percent glucose decrease from basal. Glucose curves from both GTT and ITT were significantly different between TZD-treated Foxo1+/− and wild-type mice (P < 0.04) and between TZD-treated Foxo1+/− mice compared with mice fed a HFD alone (P < 0.001). ○, HFD Foxo1+/−; ■, HFD wild type; ○, HFD + TZD Foxo1+/−; ■, HFD + TZD wild type. E and F: Liver gene expression studies conducted in TZD-treated Foxo1+/− mice used a programmed microarray technique to measure genes that influence both hepatic glucose production and fatty acid synthesis. Relative mRNA values are reported as means ± SE. *P < 0.05. AU, arbitrary units. ■, FD + TZD wild type; ▨, HFD + TZD Foxo1+/−.

FIG. 6.

FIG. 6.

Cytokine and adipokine profiling in TZD-treated Foxo1+/− mice. A and B: Average size of adipocytes from epididymal fat (wild type n = 4; Foxo1+/− n = 5). Representative photomicrographs are represented. Scale bars represent 100 μm. C–E. Multiplexed bead immunoassay techniques were used to measure circulating cytokine and adipokine levels in HFD-fed animals in the presence or absence of TZD. Proinflammatory serum cytokines (tumor necrosis factor-α [TNF-α], IL-6, and monocyte chemoattractant protein 1 [MCP-1]) are significantly reduced in TZD-treated Foxo1+/− mice. Although serum adiponectin levels are lower in HFD-fed Foxo1+/− compared with HFD-fed wild-type, FoxO1 haploinsufficiency is associated with higher elevations in serum adiponectin after TZD treatment. In contrast, serum leptin values decrease to a greater extent in TZD-treated Foxo1+/− animals. These serum cytokine and adipokine data are also presented in numeric form in Table 1. Values are reported as means ± SE. *P < 0.05. ■, HFD wild type; □, HFD Foxo1+/−; ▩, HFD + TZD wild type; ▨, HFD + TZD Foxo1+/−.

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