Influences of childhood exercise on adipose tissue browning in OLETF rats

Abstract

Exercise promotes mitochondrial uncoupling in brown adipose tissue (BAT), which results in browning and accelerated energy metabolism. Because obesity leads to mitochondrial dysfunction with consequential impaired uncoupling, exercise-induced adipose tissue browning could be inhibited in genetic predisposition to obesity. The purpose of the present study was to investigate the influences of childhood exercise in spontaneous obesity animals focusing on adipose tissue browning. Four-week-old male Otsuka Long-Evans Tokushima fatty (OLETF, 88 ± 4 g body weight) rats and age-matched male Long-Evans Tokushima Otsuka (LETO, 82 ± 4 g body weight) rats were used as spontaneous obesity animals and non-obesity animals, respectively. All rats were divided into the exercise or non-exercise groups. The 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 weeks of age. Food and water were provided ad libitum. Transverse sections were obtained from interscapular BAT and stained with hematoxylin and eosin for histological observation. In addition, the expression levels of uncoupling protein 1 (UCP1) in BAT were measured by western blotting. White adipocytes with unilocular lipid droplet were widely observed in the BAT of OLETF rats. The enlarged white adipocytes were rarely observed in OLETF rats of the exercise group. Although there were no significant differences in the expression level of UCP1 among the experimental groups, the levels were obviously different between OLETF rats in the exercise group. Total food intake during 12 h of voluntary wheel running was lower in the rat with the high UCP1 expression than in the low expression. Total running distance was higher in the rat with high UCP1 expression than in the low expression. Therefore, higher ratio of the total running distance to total food intake was shown in the OLETF rat with higher UCP1 expression. Exercise in childhood shrank the adipocytes in the BAT, suggesting the effectiveness to prevent pediatric obesity. Additionally, exercise-induced UCP1 expression could depend on the ratio of exercise to food intake.