The effect of eight weeks of high intensity interval training and moderate continuous training on PGC-1α and ERRα gene expression in subcutaneous adipose tissue of male rats

PGC-1α is involved in their activation by binding to transcription factors, including ERRα. PGC-1α and ERRα work together to transcribe genes involved in energy metabolism (13), including genes involved in processes such as brown adipocyte differentiation, adipogenesis and mitochondrial biogenesis (8), and activation of carbohydrate and fat oxidation enzymes(9), mitochondrial respiration (10), upregulation of gene expression VEGF (vascular endothelial growth factor) and other growth factors of angiogenesis (11), thermogenesis and antioxidant effects (12). Therefore, the levels of PGC-1α and ERRα in adipose tissue can have beneficial effects on systemic metabolism and can be considered as an important goal in the treatment of diseases (18, 20). Although the beneficial effects of exercise on adipose tissue and metabolic activity are well known, however, the effect of different exercise intensities on the expression of these two genes in subcutaneous adipose tissue is less known. In previous have not found any study that examined the expression of these two genes simultaneously in subcutaneous adipose tissue following of exercise. Therefore, the aim of this study was to investigate the response of PGC-1α and ERRα factors to high-intensity interval training (HIIT) and moderate-intensity continuous training (MIT) in the subcutaneous adipose tissue of healthy male rats.

In the present experimental study, 24 healthy male rats with average weight 237± 33 g were randomly divided into 3 groups of 8: 8-week control, High-Intensity Interval Training (HIIT) and Moderate Intensity Training (MIT). HIIT and MIT participated in training programs for 8 weeks. Rats in the control group did not participate in any exercise program. The HIIT training protocol consisted of 4 intense alternations with 4 minutes of running at 90 to 100% VO2max and 30 m / min and 4 intense alternations with 3 minutes running at 50 to 60% VO2max at 20 m / min  which lasted a total of 38 minutes and included 10 minutes of warm-up and 28 minutes of main body training. The MIT protocol started in the first week with 20 minutes of main body training and a speed of 20 meters per minute and with the gradual increase of training time in the following weeks, from the fifth week, the time of the main body of training increased to 30 minutes. The speed was constant throughout the training period and the training was performed at 65% of the maximum oxygen consumption and was accompanied by 5 minutes of warm-up and 5 minutes of cooling The control group along with 2 training groups were anesthetized after 8 weeks of training and 24 hours after the last training session and 12 hours of fasting with xylazine and ketamine injection and adipose tissue in their groin area were removed. The sample tissue of each animal was immediately immersed in a liquid nitrogen solution in a tube and the samples were kept in the laboratory until the experiments evaluating the amount of gene expression changes in the -80 ° C freezer. RT-PCR was used to measure gene expression. PCR amplification was assessed by evaluating the amplification curve and melting peak. In this study, GAPDH gene was used an internal control. Shapiro-Wilk  test was used to determine the normality of data distribution and Leven test was used to examine the homogeneity of variances. Due to the normal distribution of variables, One-way analysis of variance statistical test was used to determine the significance and differences between groups and then Tukey post hoc test was used at a significance level of P <0.05.

8 weeks of HIIT and MIT trainings increased the expression of PGC-1α gene in comparison with the control group (P ≤ 0.001). However, no significant difference was observed in PGC-1α gene expression between HIIT and MIT groups (P = 0.514). 8 weeks of HIIT trainings increased the expression of ERRα gene in comparison with the control group (P ≤ 0.001). However, no significant difference was observed in the expression of ERRα gene between the MIT group and the control group despite a 104% increase compared to the control group (P = 0.052). Also, there was no significant difference in the expression of ERRα gene between HIIT and MIT groups (P = 0.062). The results of the present study showed an increase in the expression of PGC-1α and ERRα genes in the subcutaneous adipose tissue of male rats after eight weeks of HIIT and MIT training compared to the control group. Comparison between HIIT group and control group in PGC-1α and ERRα gene expression showed an increase of 278 and 206%, respectively. Comparison between MIT training group and control group in PGC-1α and ERRα gene expression also showed an increase of 190 and 104%, respectively, although the difference between MIT group and control was not significant (P = 0.052).

The results of the present study showed that high-intensity interval training (HIIT) compared to moderate-intensity continuous training (MIT) significantly increased the expression of PGC-1α and ERRα genes in subcutaneous adipose tissue. Therefore, increased expression of both genes studied in subcutaneous adipose tissue is traceable factor, but HIIT exercises are probably more effective due to their higher intensity. The dramatic increase in these two factors following HIIT and MIT trainings can be a valuable result because the cooperation and cross-activation of PGC-1α  with ERRα regulate underlying metabolic processes such as brown adipocyte differentiation, adipogenesis and mitochondrial biogenesis, and angiogenesis. Considering the health-related beneficial effects of increasing these two factors following previous research on the one hand and significantly increasing the expression of both genes in HIIT and MIT exercises, the use of both training methods as a suitable solution to maintain health is suggested. HIIT exercises seem to be more practical in practice due to the shorter time to perform.