The Effect of Two Types of Exercise (Continuous and Intermittent) on the Expression of PP2Ac and NF-κB Genes in the Heart Tissue of Diabetic Rats

Diabetes as a chronic disease significantly contributes to the spread of physical injuries, mortality and health costs, especially as a cardiovascular risk factor it plays a significant role in mortality (1). Diabetic cardiomyopathy (DCM) is one of the most common complications in diabetic patients and often occurs independently of coronary artery disease, hypertension, or other cardiovascular disease (3). Studies have also shown that inhibition of cardiomyocyte apoptosis improves heart function in diabetic rats (8). Thus, inhibiting apoptosis is a potential therapeutic strategy for DCM. Continuous activation of the NF-κB signaling pathway causes apoptosis in high-glucose cultured cardiomyocytes (7, 9) and inhibition of this pathway improves cardiac dysfunction in diabetic rats (7). Therefore, targeted inhibition of continuous activation of NF-κB signaling may effectively treat DCM.In recent years, exercise has been used as a non-pharmacological strategy to control diabetes and its complications (11, 12). The aim of this study was to investigate the effect of two types of exercise (continuous and intermittent) on the expression of PP2Ac and NF-κB genes is the heart tissue of diabetic model rats.

In experimental research, 40 male Wistar rats were randomly divided into 5 groups, including 1) healthy control, 2) diabetic control, 3) diabetic + continuous training, 4) diabetic + periodic training, and 5) Saline group. After grouping the mice, streptozotocin (STZ) at a dose of 50 mg / kg body weight was used to make the mice diabetic, which was injected intraperitoneally to ensure that the mice were diabetic from the corner of the eye. Blood samples were taken and the glucose level, which was considered higher than 126 mg / dL, was considered.The rats of the exercise groups performed two types of continuous and intermittent exercise 5 days a week for 8 weeks. In a continuous exercise program, rats start running on a treadmill for 15 minutes at 15 meters per minute for the first week. Then the running time was increased every week by increasing the speed from 1 to 2 meters per minute for 1 to 2 minutes. In the fourth week, the speed reached 20 meters per minute and the running time reached 13 to 14 minutes, and in the eighth week, the running speed reached 28 to 29 meters per minute and the duration was 21 to 22 minutes. On the other hand, the periodic training program consisted of six sets of 2.5 minutes, with a break of four minutes between each set. It should be noted that periodic exercise was performed for 5 sessions per week. Control mice also spent eight weeks without any training.At the end of the training period, 48 hours after the last training session, with 10 to 12 hours of night fasting, the rats were anesthetized by intraperitoneal injection of a combination of ketamine and xylazine and tissue sampling was performed. Laboratory analysis of PP2Ac and NF-κB gene levels of cardiac tissue was determined using special commercial kits by real-time PCR. Descriptive statistics were used to classify the data obtained from this study. Shapirovilk test was used to determine the normality of data distribution. One-way analysis of variance was used to determine the significance of the difference between the variables and the interaction between them, and if the data were significant, the Tukey post hoc test was used to determine the location of the difference. Findings were evaluated at 95% confidence level (P≤0.05)

Induction of diabetes significantly reduced the expression of PP2Ac gene in rat heart tissue, which periodic and continuous exercise increased the expression of PP2Ac gene in heart tissue of diabetic rats compared to the diabetic control group. There was a significant increase in the expression of NF-κB gene in the heart tissue of rats, which periodic and continuous exercise led to a decrease in the expression of the NF-κB gene in the heart tissue of diabetic rats compared to the diabetic control group.

Hyperglycemia is one of the complications of diabetes that activates NF-κB by increasing the formation of ROS and AGE (18). Also, increased levels of interleukins and cytokines such as TNF-α and IL-1β in response to NF-κB activation exacerbate neuropathy and increase pain sensitivity in diabetic neuropathy (15), so the use of factors that can inhibit their production or activation, They may delay or stop the effects of diabetes. Therefore, in this study, increasing the expression of NF-κB gene in the heart tissue of diabetic rats may induce apoptosis and the development of cardiomyopathy. Continuous and intermittent exercise reduced NF-κB gene expression in diabetic heart tissue that may prevent the progression of cardiomyopathy. In line with this study, Taghiabadi et al. (2019) reported a decrease in NF-κB gene expression in the cardiac tissue of rats with hyperglycemia after 8 weeks of aerobic exercise (10). Also, one round of aerobic exercise reduced the expression and activity of NF-κB in skeletal muscle (19) and lung tissue (20) of diabetic rats. The decrease in NF-κB gene expression appears to be due to a decrease in HMGB1, AGEs, and NADPH oxidase following exercise. It has been shown that under the influence of aerobic exercise, the activity of NADPH oxidase enzyme in the heart tissue of diabetic rats (21) and the amount of AGEs in the bloodstream of elderly mice (22) are reduced. On the other hand, the reduction of HMGB1 protein has been confirmed following exercise (10, 23). Studies show that HMGB1 and AGEs activate NF-κB in different tissues of diabetic patients by binding to their receptors through different pathways (24). Cheng et al. Showed that PP2A activity participated in diabetic cardiomyocytes due to anti-apoptotic and anti-inflammatory activity of regular exercise (26). In the present study, regular intermittent and continuous exercise partially compensated for the decrease in PP2A content due to diabetes induction and brought it closer to the PP2Ac level of healthy mice. It is possible that physical activity in this way inhibits NF-κB signaling and prevents the progression of diabetes-induced cardiomyopathy. Due to the induction of diabetes, the expression of NF-κB gene and the expression of PP2Ac gene in heart tissue increased and decreased significantly, respectively. Therefore, it is possible that regular exercise can prevent the development of cardiomyopathy caused by diabetes induction by increasing the PP2Ac gene and inhibiting NF-κB signaling, and has a protective effect on the heart.