Repeated sense of hunger leads to the development of visceral obesity and metabolic syndrome in a mouse model

Abstract

Obesity-related disorders, especially metabolic syndrome, contribute to 2.8 million deaths each year worldwide, with significantly increasing morbidity. Eating at regular times and proper food quantity are crucial for maintaining a healthy status. However, many people in developed countries do not follow a regular eating schedule due to a busy lifestyle. Herein, we show that a repeated sense of hunger leads to a high risk of developing visceral obesity and metabolic syndrome in a mouse model (both 3-week and 6-week-old age, 10 mice in each group). The ad libitum (AL) group (normal eating pattern) and the food restriction (FR) group (alternate-day partially food restriction by given only 1/3 of average amount) were compared after 8-week experimental period. The total food consumption in the FR group was lower than in the AL group, however, the FR group showed a metabolic syndrome-like condition with significant fat accumulation in adipose tissues. Consequently, the repeated sense of hunger induced the typical characteristics of metabolic syndrome in an animal model; a distinct visceral obesity, hyperlipidemia, hyperglycemia and hepatic steatosis. Furthermore, we found that specifically leptin, a major metabolic hormone, played a major role in the development of these pathological disorders. Our study indicated the importance of regular eating habits besides controlling calorie intake.

Figure 1. Food intake and body weight.

(A) Food intake was monitored daily. (B) The body weight was measured twice weekly. Each point represents the mean ± standard deviation (SD; n = 10). *p<0.05, **p<0.01 compared with the AL group.

Figure 2. Fat pad weight and histological findings of adipose tissues.

(A) The fat pads were weighed from visceral adipose tissue (VAT), retroperitoneal adipose tissue (RAT) and epididymal adipose tissue (EAT). Data are expressed as means ± SD (n = 10). *p<0.05, **p<0.01 compared with the AL group. (B) After hematoxylin and eosin (H&E) staining, the histological differences of adipose tissues were examined under a microscope (Scale bars: 40 µm).

Figure 3. Serum protein levels of metabolic and proinflammatory mediators.

(A) The protein levels of resistin, adiponectin and leptin as well as (B) ghrelin, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in serum were analyzed by ELISA. Data are expressed as means ± SD (n = 10). *p<0.05, **p<0.01 compared with the AL group.

Figure 4. Gene expression levels in visceral adipose tissue (VAT).

(A) The mRNA expression levels of fatty acid synthase (FAS), sterol regulatory element-binding protein-1c (SREBP-1c) and interleukin-6 (IL-6) as well as (B) resistin, adiponectin and leptin were determined using qRT-PCR analysis. Data are expressed as means ± SD (n = 10, fold change relative to the AL group). *p<0.05, **p<0.01 compared with the AL group.

Figure 5. Gene expression levels in skeletal muscles.

The mRNA levels of glucose transporter 4 (GLUT4), AMP-activated protein kinase (AMPK) and proliferator-activated receptor alpha (PPARα) were determined using qRT-PCR analysis. Data are expressed as means ± SD (n = 10, fold change relative to AL group). *p<0.05 compared with the AL group.

Figure 6. Measurement of hepatic steatosis.

(A) Hepatic triglycerides and cholesterol were measured using commercially available kits. Data are expressed as means ± SD (n = 10, respectively). *p<0.05, **p<0.01 compared with the AL group. (B) Hepatic tissues were evaluated using Oil Red O staining and the histological differences were examined under a microscope (Scale bars: 40 µm).

Figure 7. Gene expression levels in the liver.

The mRNA levels of sterol regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS), proliferator-activated receptor gamma (PPARγ), stearoyl-CoA desaturase-1 (SCD-1), proliferator-activated receptor alpha (PPARα) and AMP-activated protein kinase (AMPK) were determined using qRT-PCR. Data are expressed as means ± SD (n = 10, fold change relative to the AL group). *p<0.05, **p<0.01 compared with the AL group.

Figure 8. Protein and gene expression levels in the brain.

(A) Proopiomelanocortin (POMC) activity was analyzed by Western blotting (n = 5). (B) The mRNA levels of POMC and neuropeptide Y (NPY) as well as (C) melanocortin receptor-4 (MC4R) and agouti-gene related protein (AgRP) were determined using qRT-PCR. Data are expressed as means ± SD (n = 5, fold change relative to the AL group). *p<0.05 compared with the AL group.

Figure 9. Graphical summary of the metabolic syndrome by a repeated hunger sense.