Adipose-specific ablation of Nrf2 transiently delayed high-fat diet-induced obesity by altering glucose, lipid and energy metabolism of male mice

Abstract

Nuclear factor E2-related factor 2 (NRF2) is a well-known master controller of the cellular adaptive antioxidant and detoxification response. Recent studies demonstrated altered glucose, lipid and energy metabolism in mice with a global Nrf2 knockout. In the present study, we aim to determine the effects of an adipose-specific ablation of Nrf2 (ASAN) on diet-induced obesity (DIO) in male mice. The 6-week-old adipose-specific Nrf2 knockout (NK) and its Nrf2 control (NC) mice were fed with either control diet (CD) or high-fat diet (HFD) for 14 weeks. NK mice exhibited transiently delayed body weight (BW) growth from week 5 to week 11 of HFD feeding, higher daily physical activity levels and preferential use of fat over carbohydrates as a source of energy at week 8 of the CD-feeding period. After 14 weeks of feeding, NK mice showed comparable results with NC mice with respect to the overall BW and body fat content, but exhibited reduced blood glucose, reduced number but increased size of adipocytes, accompanied with elevated expression of many genes and proteins in the visceral fat related to glucose, lipid and energy metabolism (e.g. Fgf21, Pgc1a). These results indicated that NRF2 is an important mediator for glucose, lipid and energy metabolism in adipose tissue, and ASAN could have beneficial effect for prevention of DIO during the early development of mice.

Keywords: Adipose tissue; adipose-specific ablation of Nrf2; diet-induced obesity; glucose and lipid and energy metabolism; nuclear factor E2-related factor 2 (NRF2).

Figure 1

Confirmation of Nrf2 knockout in the fat tissues of mice. A: Relative protein level of NRF2 in the SF and VF of NC and NK mice. B: Representative figure of the NRF2 protein expression in 3 samples of the SF and VF of NC and NK mice. Bars represent mean ± SEM, n = 6/group. *Different from NC-SF, P<0.05; #Different from NC-VF, P<0.05).

Figure 2

ASAN transiently delayed body weight (BW) growth of mice under HFD conditions. (A) Changes in the BW of NC and NK mice were measured following a 14-week period of CD or HFD feeding in mice 6-20 weeks of age. At the end of the 14-week CD/HFD feeding periods, the BW (B), body fat (C) and muscle mass (D) of NC and NK mice were measured. Bars represent mean ± SEM, n = 6/group. *Different from NK-HFD at a time, P<0.05; #Different from NC-CD, P<0.05; ##Different from NK-CD, P<0.05).

Figure 3

Increased energy expenditure resulting from ASAN in mice. The respiratory exchange ratio (RER, VCO₂/VO₂) (A) and the daily physical activity level (B) of NC and NK mice were measured at week 8 of CD/HFD feeding for 1 week using an Oxymax system. Bars represent mean ± SEM, n = 4/group. *NK-CD different from NC-CD at a time, P<0.05; #NK-HFD different from NC-HFD at a time, P<0.05.

Figure 4

ASAN enhanced the glucose removal under HFD conditions. The plasma concentrations of total cholesterol (A), free fatty acid (B), LEPTIN (C) and ADIPONECTIN (D) were measured using ELISA. The intraperitoneal glucose tolerance test was performed using mice challenged with 0.5 mg/g of BW of D-(+)-glucose (E). Bars represent mean ± SEM, n = 6/group. *Different from NC-CD at a time, P<0.05; **Different from NK-CD at a time, P<0.05; #NK-HFD different from NC-HFD at a time, P<0.05.

Figure 5

ASAN caused white adipocyte hypertrophy. A: H&E staining of adipocyte. B: The image quantification of the average size of adipocytes in both the SF and VF of NK mice compared with NC mice in response to CD/HFD feeding, scale bar = 200 µm. Bars represent mean ± SEM, n = 6/group. *Different from NC-CD of SF, P<0.05; #Different from NC-CD of VF, P<0.05.

Figure 6

Diet and ASAN altered mRNA and protein expression of genes in the VF of mice. (A) mRNA level of Igf1, Igf1r, Dlk1, Fgf21, Pgc1a, Pparg, Cebpa, Insr, El, Hsl, Mgl, Lpl and (B) protein level of DLK1, PPARG, CEBPA in the VF of mice were analyzed. Abbreviation of genes: Cebpa, CCAAT/enhancer binding protein alpha; Dlk1, delta-like 1 homolog (Drosophila); El, endothelial lipase; Fgf21, fibroblast growth factor 21; Hsl, hormone-sensitive lipase; Igf1, insulin-like growth factor 1; Igf1r, insulin-like growth factor 1 receptor; Insr, insulin receptor; Lpl, lipoprotein lipase; Mgl, monoacylglycerol lipase; Pgc1a, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; Pparg, peroxisome proliferator-activated receptor gamma. Bars represent mean ± SEM, n = 6/group. *Different from NC-CD, P<0.05; **Different from NC-HFD, P<0.05; #Different from NK-CD P<0.05.

Figure 7

A proposed model of Nrf2 function in adipose tissues in the regulation of glucose, lipid and energy metabolism based on the present study.