Influences of exercise and detraining during childhood on brown adipose tissue in OLETF rats

Abstract

Brown adipose tissue (BAT) oxidizes lipids to fuel thermogenesis. However, the activity declines in obesity due to brown‐to‐white conversion in BAT. Because the properties of adipose tissue are determined before adult, childhood exercise could prevent brown‐to‐white conversion and maintain metabolic activity of BAT in future. The purpose of the present study was to investigate histological influences of childhood exercise and detraining in BAT of genetic predisposition to obesity. Four‐week‐old male Long‐Evans Tokushima Otsuka (LETO) rats and age‐matched male Otsuka Long‐Evans Tokushima fatty (OLETF) rats were used as non‐obesity animals and spontaneous obesity animals, respectively. OLETF rats were divided into the non‐exercise sedentary (OLETF Sed) or exercise groups. OLETF rats in the exercise group were further divided into subgroups according to exercise age. OLETF rats in the exercise groups were placed in the cages with a running wheel for 12 h (20:00 to 8:00) daily from 4 to 6 (OLETF Ex 4‐6 w) or 10 to 12 (OLETF Ex 10‐12 w) weeks of age (i.e. the OLETF Ex 4‐6 w group: exercise from 4 to 6‐week‐old, detraining from 6 to 12‐week‐old; the OLETF Ex 10‐12 w group: non‐exercise from 4 to 10‐week‐old, exercise from 10 to 12‐week‐old). Food and water were provided ad libitum. At 12‐week‐old, transverse sections were obtained from interscapular BAT and stained with hematoxylin and eosin for histological observation. The results at 12‐week‐old were shown below. The wet weights of interscapular BAT were significantly higher in the OLETF Sed group than in LETO rats. The values were significantly lower in the OLETF Ex 10‐12 w group than in the OLETF Sed group. There were no significant differences for the weights between the OLETF Ex 4‐6 w and OLETF Sed groups. Histological observation revealed conversion of brown adipocytes to white‐like unilocular cells in both LETO and OLETF rats. In LETO rats, the white‐like unilocular cells were located uniformly in the fat lobule. In OLETF rats, enlarged white‐like unilocular cells were also observed in the peripheral zone of the lobule. There were no significant differences for the diameters of white‐like unilocular cells located in the central zone of the lobule among the experimental groups. The densities of white‐like unilocular cells located in the central zone of the lobule were significantly lower in the OLETF Ex 10‐12 w group than in the other groups. There were no significant differences for the densities among LETO rats, the OLETF Sed, and OLETF Ex 4‐6 w groups. Childhood Exercise immediately inhibited brown‐to‐white conversion in the BAT and decreased the mass. However, the effectiveness did not be maintained for a long time. These results suggested that chronic exercise is required to maintain adipose tissue browning in genetic predisposition to obesity.