1. Introduction

Apoptosis is a biologically active and reversible process that plays a key role in regulating the balance between cell growth and death in various tissues, especially the myocardium. This process begins with the compression and fragmentation of chromatins and the condensation of the cellular cytoplasm and ends with the crumpling of the cell nucleus and membranes and the production of vacuoles containing apoptotic particles [1-3]. Apoptosis occurs through the intracellular and extracellular pathways [1, 2, 4]. 

The internal pathway, as the most important pathway for apoptosis, is associated with changes in mitochondrial permeability and release of apoptotic agents. Molecular events of apoptosis are determined by the balance between pre- and anti-apoptotic specific regulatory proteins. In the meantime, Bax and Bcl2 proteins are involved as major proteins in the formation of apoptosis and mitochondrial apoptotic messages. The aim of the present study was to investigate the effect of 8 weeks of High-Intensity Interval Training (HIIT) with and without calorie restriction on gene expression of caspase-3 and caspase-9 proteins in male rats.

2. Materials and Methods

The present research was an experimental study performed in a field and laboratory method in which the effect of 8 weeks of high-intensity interval training with and without calorie restriction on gene expression of caspase-3 and caspase-9 proteins in male rats was investigated. Considering the suitable conditions of the animal model for the present study, 30 two-month-old male Wistar rats were purchased from the Pasteur Institute of Iran. After familiarizing the rats with the laboratory environment, they were divided into five groups of six (“basic control”, “control”, “calorie restriction”, “exercise”, and “exercise and calorie restriction”) (Table 1).

In order to control the baseline variables and to determine the reference group, the “baseline control” group underwent surgery at the beginning of the research period using the specified laboratory method. All rats were placed on a treadmill for 14 days under a training program.

The subjects in the “control” and “exercise” groups freely used standard food and water during the study period. To determine the amount of food consumed by the “calorie restriction” and “exercise” groups, along with the application of calorie restriction to them, the amount of food consumed by the other subjects was measured daily and the restricted groups received 50% of the food consumed by the other groups.

3. Results

The results of one-way ANOVA showed that there was a significant difference between the expression of myocardial caspase-3 protein in male rats (P=0.001). Also, the results of Tukey post hoc test showed that the “basic control” and “control” groups had a significant increase in the expression of myocardial caspase-3 protein compared to the “exercise and calorie restriction” and “exercise” groups (P<0.05). The results of one-way ANOVA showed that there was a significant difference between the expression rate of myocardial caspase-9 protein in male rats (P=0.001). 

Also, the results of Tukey post hoc test showed that the “basic control”, “control” and “calorie restriction” groups had a significant increase in the expression of myocardial caspase-9 protein compared to the “exercise and calorie restriction” and “exercise” groups (P<0.05). On the other hand, the “exercise” group had a significant decrease in the expression of myocardial caspase-9 protein compared to the “exercise and calorie restriction” group (P<0.05) (Figures 1 and 2).

4. Discussion

Although the exact mechanisms of exercise-induced apoptosis are unclear, there are many possible hypotheses that need further investigation. One of the important hypotheses in this regard is that during exercise, muscle metabolism increases, which leads to the production of ROS [5]. High quantities of ROS can produce oxidative damage and thus lead to apoptosis via the internal pathway [15].

It has been reported that a significant decrease in caspase-3 protein expression following aerobic exercise was associated with a decrease in pre-apoptotic factors such as Bax protein expression and Bax to Bcl2 ratio as well as a significant increase in Bcl2 anti-apoptotic protein. This decrease in mitochondrial apoptotic potential following aerobic exercise in elderly rats may be associated with decreased release of apoptotic agents such as cytochrome c and Apaf1 into skeletal muscle, which significantly reduced caspase-3 expression [14].

In the internal pathway, mitochondria and endoplasmic reticulum play a major role in this process, in which the role of mitochondria in apoptosis is the most important and have been focused in many studies [5, 16, 17]. Under stressful conditions, factors such as glucocorticoids, ROS, nitrogen monoxide, chemotherapy drugs, radiation, reduced growth stimulants, and cytokines cause changes in mitochondrial permeability by causing stress; and cytochrome c which is located in the inner membrane of the mitochondria and interstitial space, is released into the cytosol and binds to apoptosis-activating protease factor 1 (Apaf-1) inside the release cytosol to form a compound called dATP. This compound then induces apoptosis by activating procaspase-9, caspase-9, and caspase-3 [18]. The most important step in controlling this pathway is the release of cytochrome c. Cell death pathway inhibitory proteins such as Bcl-2 and Bcl-XL inhibit the release of cytochrome c and thus play a role [19].

5. Conclusion

According to the results, it seems that high-intensity interval exercise with and without calorie restriction provides the necessary adaptations to inhibit or stop apoptosis caused by aerobic exercise. In addition, in this study, the contribution of caspase-8, especially caspase-6, and even bad protein as pathways for possible interactions was not investigated. Therefore, activation of caspase-3 might have originated externally, which was one of the limitations of the present study.

Ethical Considerations

Compliance with ethical guidelines

The protocol of this study was approved by the Medical Committee of Sanandaj University of Medical Sciences (Code: IR.MYK.REC.1397.5022).

Funding

The present paper was extracted from the PhD. thesis of the first author, Department of Exercise Physiology, School of Physical Education and Sport Sciences, Sanandaj Branch, Islamic Azad University. 

Authors' contributions

All authors contributed in preparing this article.

Conflicts of interest

 The authors declared no conflict of interest.

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