The effect of eight weeks of high-intensity interval training on hypertrophy-related proteins in the heart tissue of male rats with type 2 diabetes

Extended abstract
Background and Aim: Diabetes is a major health concern characterized by elevated  high blood glucose levels resulting from either insufficient insulin production by pancreatic cells or impaired insulin utilization by body tissues. One of the primary causes of mortality in individuals with diabetes is  cardiovascular complications, such as heart damage due to atherosclerosis and diabetes-related cardiomyopathy. Increasing physical activity and improving dietary habits in the form of low-calorie diets are particularly important for the control of type 2 diabetes. Regular exercise training is widely recognized as a non-pharmacological strategy and an adjunct therapy for heart failure. Researchers report that cardiovascular, muscular, and metabolic adaptations following exercise in healthy and diseased populations are dependent on exercise intensity, and that the beneficial effects of high intensity interval training (HIIT) are more evident than those of continuous endurance training for cardioprotection. Therefore, the present study aimed to investigate the effect of HIIT on changes in the levels of phosphatidylinositol-3 kinases (PI3K)/ protein kinase B (AKT)/ mammalian target of rapamycin (mTOR) signaling pathway proteins associated with physiological and pathological hypertrophy in the heart tissue of mice with type 2 diabetes.
Materials and Methods: Forty male Wistar rats, (eight weeks old, weighing 191±16 g) were obtained from the faculty of veterinary medicine, Shahid Chamran university of Ahvaz. The rats were housed in polycarbonate rodent cages (five rats per cage) at a temperature of 22±2 °C, a humidity of 45±5%, and a 12:12 light-dark cycle. After a one-week acclimation period, the rats were randomly assigned to four groups (n=10 per group): healthy control, healthy exercise, diabetic control, and diabetic exercise. Diabetes was induced in the diabetic groups through a combination of dietary manipulation and streptozotocin (STZ) administration. Subsequently, the exercise groups performed a HIIT program for eight weeks, consisting of five sessions per week based on maximum running speed. The maximum running speed of the rats was reassessed every two weeks, and the training protocol for the subsequent period was adjusted accordingly to ensure the application of the overload principle. Forty-eight hours after the last training session, all rats were anesthetized by intraperitoneal injection of a combination of Ketamine (80 mg/kg of body weight) and Xylazine (10 mg/kg of body weight). Then, the heart tissue was removed from the animal’s body, washed with normal saline, and immediately frozen at -70°C for protein measurement. The normality of data distribution was assessed using the Shapiro–Wilk test, and homogeneity of variances was verified using Levene’s test. Changes in body weight and blood glucose levels were analyzed using two-way analysis of variance (ANOVA). One-way ANOVA followed by Tukey’s post hoc test was used to evaluate differences between groups. Statistical significance was set at p<0.05. Data analysis was performed using SPSS software (version 25) and Microsoft Excel (2016).
Findings: The results of the two-way ANOVA test showed that the body weight in the diabetic groups increased significantly following the initiation of the high-fat diet and prior to streptozotocin (STZ) injection (p=0.001 for both groups). However, a significant reduction in body weight was observed at the end of the HIIT program in both diabetic groups (p=0.001). Furthermore, after completion of the HIIT program, the body weight of rats in the diabetic control group was significantly lower than that of the other groups (p=0.001 for all comparisons).
Blood glucose levels in the diabetic groups increased significantly one week after STZ injection (p=0.001 for both groups). However, following the HIIT intervention, blood glucose levels in the diabetic exercise group decreased significantly compared to the levels measured one week after STZ injection (p=0.001).
The results of one-way ANOVA showed that the mean levels of PI3K, AKT, and mTOR proteins in rat heart tissue were significantly different between the different groups (p=0.001, p=0.001, and p=0.003, respectively) (Table 1). According to the results of Tukey’s post hoc test, the relative levels of PI3K, AKT, and mTOR proteins in the diabetic control group were significantly reduced compared to the healthy control group (p=0.001 for all); while the levels of these proteins in the diabetic exercise group were significantly increased compared to the diabetic control group (p=0.03, p=0.009, and p=0.04, respectively).
Conclusion: The findings suggest that eight weeks of HIIT may improve cardiac remodeling in type 2 diabetes by upregulating the protein expression of PI3K, AKT, and mTOR in heart tissue. Activation of this signaling pathway appears to shift pathological hypertrophy toward a more physiological form and may reduce apoptosis in cardiomyocytes. Furthermore, the hypoglycemic effects of HIIT may indirectly influence downstream molecular pathways involved in fibrosis and extracellular matrix remodeling. Adaptive responses in cardiac cells may vary depending on the type, intensity, and duration of exercise, as peak changes in certain signaling proteins often occur during or shortly after the final training session. In this context, two possibilities can be considered: first, that the response of hypertrophy-related proteins is transient and time-dependent; and second, that the underlying mechanisms are influenced by exercise intensity and modality, suggesting that different training protocols elicit distinct molecular and structural adaptations in the diabetic heart. Evidence suggests that regular HIIT can positively regulate the PI3K/AKT/mTOR signaling axis while suppressing pathological pathways. In addition, reductions in hyperglycemia and inhibition of pro-apoptotic signaling may decrease the expression of genes associated with cardiac fibrosis and dysfunction. Since the molecular and genetic adaptations induced by HIIT may differ from those resulting from continuous or resistance training, specific cellular signaling pathways and gene expression profiles are likely activated depending on the exercise protocol. Therefore, regular HIIT appears to be an effective non-pharmacological strategy for managing type 2 diabetes and its associated cardiac complications. It may attenuate pathological cardiac remodeling while promoting physiological hypertrophy. These findings also highlight the importance of targeted exercise interventions as safe, cost-effective, and non-pharmacological approaches for the prevention and management of diabetic cardiomyopath
Ethical Considerations: This study received ethical approval from the Research Ethics Committee of Shahid Chamran University of Ahvaz (Ethical Code: EE/1401.1.2.24.222048/scu.ac.ir). The research was conducted using the minimum number of rats necessary and adhered to optimal laboratory animal conditions (12:12 light-dark cycle, 45±5% relative humidity, and 22±2 °C temperature). Non-invasive and low-pain methods, minimizing distress, were employed. All researchers completed mandatory training courses on animal handling and ethical principles.
Compliance with ethical guideline: Alternative methods to animal experimentation were considered whenever feasible, and laboratory procedures were designed to minimize pain and suffering.
Funding: This article is not sponsored.
Conflicts of interest: There is no conflict of interest.