The effects of exercise and cold exposure on mitochondrial biogenesis in skeletal muscle and white adipose tissue.
PURPOSE
The purpose of this study was to determine whether exercise or/and cold exposure regulate mitochondria biogenesis-related gene expression in soleus and inguinal adipose tissue of mice.


METHODS
Forty ICR 5-week old male mice were divided into four groups: thermoneutrality-untrained (23 ± 1 °C in room temperature, n=10), cold-water immersion (24 ± 1 °C, n=10), exercise in neutral temperature (34 ± 1 °C, n=10), and exercise in cold temperature (24 ± 1 °C, n=10). The mice performed swimming exercise (30 min to 60 min, 5 times) for 8 weeks. After 8 weeks, we confirmed mitochondrial biogenesis-related gene expression changes for peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), nuclear respiratory factors 1 (NRF1), and mitochondrial transcription factor A (Tfam) in soleus muscle and inguinal adipose tissue, and the related protein expression in soleus muscle.


RESULTS
In soleus muscle, PGC-1α expression significantly increased in response to cold exposure (p = 0.006) and exercise (p = 0.05). There was also significant interaction between exercise and cold exposure (p = 0.005). Only exercise had a significant effect on NRF1 relative expression (p=0.001). Neither cold exposure nor the interaction showed significant effects (p = 0.1222 and p = 0.875, respectively). Relative Tfam expression did not show any significant effect from exercise. In inguinal adipose tissue, relative PGC-1α expression did not significantly change in any group. NRF1 expression showed a significant change from exercise (p = 0.01) and cold exposure (p = 0.011). There was also a significant interaction between exercise and cold exposure (p = 0.000). Tfam mRNA expression showed a significant effect from exercise (p=0.000) and an interaction between exercise and cold exposure (p=0.001). Only temperature significantly affected PGC-1α protein levels (p=0.045). Neither exercise nor the interaction were significant (p = 0.397 and p = 0.292, respectively). NRF1 protein levels did not show a significant effect in any experimental treatments. Tfam protein levels showed a significant effect in the exercise group (p=0.012), but effects of neither cold exposure nor the interaction were significant (p = 0.085 and p=0.374, respectively).


CONCLUSION
Exercise and cold exposure promoted increased expression of mitochondrial biogenesis- related genes in soleus muscle. Only cold exposure had a significant effect on PGC-1α protein expression and only exercise had a significant effect on Tfam protein expression. In inguinal adipose tissue, there was interaction between exercise and cold exposure in expression of mitochondrial biogenesis-related genes.
['Chung|Nana|N|', 'Park|Jonghoon|J|', 'Lim|Kiwon|K|']
Exercise Cold exposure Mitochondrial biogenesis PGC-1α Tfam NRF-1