Effect of 2-week Cold-water Swimming on White Adipose Tissue Browning in Mice

Brown adipose tissue (BAT) is an important thermogenic organ and is generally induced by exercise or cold exposure via a white adipose tissue browning pathway. However, the synergic effects of exercise and cold exposure on this pathway remain unclear. Cold-water swimming, such as winter swimming which is a traditional sport in northern China and Russia, may be a potential therapeutic form of exercise in the treatment of obesity and diabetes. PURPOSE: To investigate the synergic effects of exercise and cold exposure on white adipose tissue browning in mice. METHODS: 8-week-old male ICR (Institute of Cancer Research) mice were randomly divided into 3 groups: a control group (N=6), a warm-swimming group (N=6) and a cold-swimming group (N=6). Mice in the warm-swimming and cold-swimming groups trained twice a day for 2 weeks and the duration of the exercise session was gradually increased (from 10 min to 60 min). The temperature of water was 35±2°C in the warm-swimming group and 22±2°C in the cold-swimming group. Body weight of mice in each group was recorded daily before the exercise sessions. Biomarkers of white adipose tissue browning were examined by hematoxylin and eosin (H&E) stain, western blotting and immunohistochemistry. RESULTS: After 2-weeks of swimming training, body weight was significantly lower in the cold-swimming group compared to the warm-swimming and control groups (34.4±1.0 vs. 35.3±1.4 & 37.2±1.1g, both p<0.05). And the relative cell size of white adipose tissue in the cold-swimming and warm-swimming groups decreased in compared with the control group (142±41 & 168±68 vs. 328±59%, both p<0.05). The expression of uncoupling protein-1 (UCP-1) in white adipose tissue in the cold-swimming group was higher significantly than in the warm-swimming and control groups (147±8 vs. 112±6 & 123±2%, both p<0.01), while peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1-alpha) in the warm-swimming group was higher than the control group (193±48 vs. 124±28%, p<0.05). Moreover, serum zinc finger protein-516 (ZNF-516) increased in the cold-swimming group compared to the control group (323±44 vs. 179±43%, p<0.05). CONCLUSIONS: Cold-water swimming induces white adipose tissue browning and weight loss and may be an effective form of exercise in the treatment of cardiometabolic diseases.