نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Extended Abstract
Background and Aim: Maintaining mitochondrial function is essential for preserving cellular homeostasis. Mitochondrial quality control depends on the coordinated regulation of mitochondrial biogenesis, dynamics, and mitophagy. The selective removal of damaged mitochondrial components requires their segregation from the mitochondrial network through mitochondrial fission, a process is regulated by two key proteins: mitochondrial fission protein 1 (Fis1) and dynamin-related protein 1 (Drp1). While maintaining quality depends on the removal of dysfunctional mitochondria, the synthesis of new mitochondria is equally important. Mitochondrial fusion, on the other hand, is mediated by fusion proteins such as mitofusin 1 and 2 (Mfn1/2) and optic atrophy 1 (Opa1). Mitochondrial function declines rapidly during periods of skeletal muscle disuse and is characterized by increased mitochondrial fission accompanied by reduced fusion and biogenesis. Although endurance exercise has been shown to increase PGC-1α gene expression in the soleus muscle of male rats, most existing studies have focused on continuous aerobic exercise, with very few investigating interval training. Given the importance of these processes in skeletal muscle function and the modulation of cellular energy charge by exercise, it is necessary to investigate how these regulatory processes are altered by moderate-intensity interval training (MIT). Specifically, it remains unclear whether the duration and nature of MIT over an eight-week period can induce adaptations in mitophagy and mitochondrial dynamics genes to maintain high mitochondrial function. Therefore, the present study aimed to investigate the effects of eight weeks of MIT on the expression of key genes regulating mitochondrial fission and fusion in the soleus muscle of male rats.
Materials and Methods: In this experimental study, twelve male Wistar rats (mean weight: 180±20 g; age: 7–8 weeks) were obtained from the laboratory animal farm of the Pasteur Institute of Babol. The animals were randomly assigned to two groups (n=6): the control group and the MIT group. Prior to the intervention, the rats underwent a one-week acclimation period to the laboratory environment and the treadmill. The experimental protocol was approved by the Ethics Committee of Hakim Sabzevari University (Approval No. IR.HSU.AEC.1401.017). Prior to the initiating the training program, an incremental exercise test to exhaustion was conducted to determine the maximal running speed of the rats. The mean maximal speed of the MIT group was subsequently used to prescribe the training protocol. The MIT group completed an eight-week treadmill training program, five days per week. The training program consisted of two phases: an active phase at 60–65% of maximal speed (six 4-minute bouts) and an active recovery phase at 30% of maximal speed (six 2-minute bouts). Following the final exercise session, rats were anesthetized via intramuscular injection of ketamine (75 mg/kg) and xylazine (10 mg/kg). The soleus muscle was harvested, immediately frozen in liquid nitrogen, and subsequently stored at −80∘C. For gene expression analysis, 50 mg of soleus muscle tissue was used for RNA extraction. Tissue lysis and homogenization were performed using TRIzol reagent (Yekta Tajhiz Azma, Iran) and a tissue homogenizer. RNA concentration and purity were assessed using a PicoDrop device at 260/280 and 260/230 ratios. Complementary DNA (cDNA) was synthesized using a commercial reverse transcription kit (SinaGene, Iran) according to the manufacturer’s instructions. Primers were designed using the online Primer-BLAST tool, with β-Actin serving as the internal control. Gene expression levels of PGC-1α, Opa1, Fis1, Drp1, and Mfn1,2 were quantified via PCR. Data are presented as mean±SD. Normality was assessed using the Shapiro-Wilk test, and inter-group differences were analyzed using the independent t-test (p<0.05). Statistical analyses were performed using GraphPad Prism software (version 9).
Findings: Changes in body weight were evaluated following the eight-week moderate-intensity interval training (MIT) intervention. Independent t-test revealed a significant reduction in body weight in the MIT group compared to the control group. Regarding the gene expression of mitochondrial fission markers in the soleus muscle, MIT led to a significant downregulation of Drp1 and Fis1 expression relative to the control group (p<0.01). Furthermore, MIT significantly increased the expression of Mfn1, Mfn2, and PGC-1α genes compared to the control group (p=0.01, p=0.007, and p=0.03, respectively). However, no significant change was observed in the relative expression of the Opa1 gene compared to the control group (p=0.21, Figure 1).
Conclusion: The findings of the present study demonstrate that the implementation of MIT protocols leads to the structural and functional remodeling of mitochondria within skeletal muscles. Our results indicate that these exercises modulate the equilibrium between fusion and fission processes, thereby enhancing mitochondrial network integrity. Specifically, the upregulation of fusion markers (Mfn1/2) and the master regulator PGC-1α, coupled with the downregulation of fission genes (Fis1/Drp1), creates a favorable environment for augmented biogenesis and improved mitochondrial quality control. These molecular adaptations likely facilitate enhanced cellular capacity for managing metabolic stress and preserving energy reserves. In essence, the ability of MIT to shift the mitochondrial dynamic toward a pro-fusion phenotype may serve as an adaptive mechanism to counteract the detrimental effects of physical inactivity or muscular atrophy. Although further studies are warranted to investigate the effects of different exercise intensities and training durations on mitochondrial remodeling and the regulation of additional genes involved in mitochondrial structure and function, this research underscores the high potential of interval training in optimizing mitochondrial dynamics and enhancing muscular metabolic health.
Ethical Considerations: The experimental procedures were approved by the Ethics Committee of Hakim Sabzevari University (Approval code: IR.HSU.AEC.1401.017).
Compliance with ethical guideline: Ethical guidelines for working with laboratory animals were strictly followed, including provisions for adequate food, water, and appropriate housing conditions.
Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conflicts of interest: The authors hereby declare that they have no conflicts of interest related to this study.
کلیدواژهها English
