Document Type : Research Paper
Authors
1
Department of Exercise Physiology, Faculty of Humanities and Social Sciences, University of Kurdistan, Sanandaj, Iran
2
Department of Exercise Physiology, Faculty of Humanities and Social Sciences, University of Kurdistan, Sanandaj, Iran.
Abstract
Background and Purpose
Diabetic cardiomyopathy (DCM) is a serious and prevalent complication of type 2 diabetes (T2D), characterized by structural and functional alterations in the myocardium, independent of coronary artery disease or hypertension. Key pathophysiological mechanisms underlying DCM include oxidative stress, inflammation, apoptosis, and impaired cellular clearance systems. Among these, the autophagy-lysosomal pathway is a vital system for the degradation and recycling of damaged cellular components, such as defective mitochondria (mitophagy), playing a crucial role in maintaining cardiomyocyte homeostasis. The optimal function of this system depends on the health and integrity of the lysosomal organelle. Lysosomal membrane proteins, particularly Lysosome-Associated Membrane Proteins 1 and 2 (LAMP1 and LAMP2), are essential for protecting the lysosomal membrane from enzymatic degradation and for the fusion of lysosomes with autophagic vacuoles. Furthermore, the Transcription Factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy, coordinates the expression of genes related to lysosomal function and autophagic processes. Evidence indicates that in diabetic conditions, the function of this pathway is suppressed, leading to the accumulation of cellular debris and ultimately heart failure.As non-pharmacological interventions are considered complementary strategies for managing diabetic complications, exercise training has been a focus of research due to its well-known metabolic and cardiovascular benefits. Among various exercise regimens, High-Intensity Interval Training (HIIT) has gained significant interest due to its time efficiency and superior ability to induce metabolic and mitochondrial adaptations. However, the precise effects of this type of exercise on the lysosomal pathway in heart tissue under diabetic cardiomyopathy conditions are not well understood. Therefore, this study aimed to investigate the effect of an eight-week HIIT program on the expression of LAMP1, LAMP2, and TFEB proteins in the heart tissue of rats with diabetic cardiomyopathy.
Materials and Methods
This experimental study was conducted on male Wistar rats weighing approximately 200-250 grams. Type 2 diabetes was induced in rats by high-fat diet feeding followed by streptozotocin injection. Rats were randomly divided into three groups (n = 8 each): normal control (NC), diabetic control (DC, no exercise), and diabetic + HIIT.The HIIT program was performed for eight weeks, five sessions per week, on a rodent-specific treadmill. The protocol included a 5-minute warm-up and cool-down at low intensity. The main exercise session consisted of intervals of running at maximum speed (approximately 85-90% of VO₂ max) for 4 minutes, followed by active recovery periods at low intensity (approximately 50-60% of VO₂ max) for 1 minute. This cycle was repeated for 5 to 7 repetitions per session.At the end of the intervention period, the animals were fasted overnight, anesthetized, and their blood and heart tissue samples were collected. Metabolic indices, including fasting blood glucose and the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), were measured. To evaluate the expression of the target proteins, Western Blot analysis was employed. Total proteins were extracted from heart tissue, separated by electrophoresis, transferred to a membrane, and incubated with specific primary antibodies against LAMP1, LAMP2, and TFEB. The resulting signals were quantified using ImageJ software and normalized to a housekeeping protein (such as β-Actin). Finally, the data were analyzed using an independent t-test or one-way analysis of variance (ANOVA), GraphPad prisma statistical software, with a significance level set at p<0.05.
Results
The results from biochemical assessments confirmed the successful induction of the T2D model, leading to hyperglycemia and insulin resistance in the rats. Fasting blood glucose and HOMA-IR index were significantly higher in the diabetic control group compared to healthy groups. The implementation of the HIIT protocol led to a significant improvement in these metabolic indices in the exercise group compared to the sedentary diabetic control group.At the molecular level, the findings revealed that diabetes induction had a profound impact on the expression of key lysosomal proteins in the heart tissue. The expression of all three proteins LAMP1, LAMP2, and TFEB was significantly decreased in the diabetic control group compared to the healthy group (with p=0.028, p=0.021, and p=0.005, respectively).The HIIT exercise program had a significant compensatory effect on this decreased expression. The levels of these proteins in the trained group showed a remarkable increase compared to the diabetic control group. Statistical analyses confirmed a significant increase in the expression of LAMP1 (p=0.001), LAMP2 (p=0.001), and TFEB (p=0.001) following the training. Quantitatively, this increase was substantial, with protein levels rising by approximately 155%, 150%, and 187% for LAMP1, LAMP2, and TFEB, respectively, compared to the diabetic control group. These results clearly demonstrate that HIIT was able to activate the suppressed lysosomal pathway in the diabetic heart and improve cellular clearance function.
Conclusion
The findings of this study conclusively show that a period of High-Intensity Interval Training (HIIT) not only improves metabolic indices, including hyperglycemia and insulin resistance, in diabetic rats but also, by upregulating the expression of critical lysosomal proteins (LAMP1, LAMP2) and the master transcription factor governing lysosomal biogenesis (TFEB), can restore the function of the autophagy-lysosomal system in heart tissue. This molecular adaptation appears to be a potential protective mechanism of HIIT against the accumulation of cellular debris and oxidative stress in diabetic cardiomyocytes, ultimately leading to improved cardiac structure and function and the prevention or delay of diabetic cardiomyopathy progression.Therefore, HIIT can be considered an effective and promising non-pharmacological strategy to help maintain cardiac health in patients with type 2 diabetes. However, further clinical studies are essential to translate these findings to human models. Investigating complementary downstream mechanisms and the effects of exercise protocols with different intensities and durations is also recommended.
Article Message
Diabetes can lead to cardiomyopathy and impaired cardiac lysosomal function. This study investigated the effect of an eight-week HIIT program session on the levels of key proteins related to lysosomal function in the heart tissue of rats with diabetic cardiomyopathy. Our findings showed that HIIT resulted in upregulation of lysosomal markers and improved autophagy. These results suggest that HIIT may provide a protective strategy against diabetes-induced cardiac complications by improving mitochondrial clearance and reducing oxidative stress, and has significant therapeutic potential.
Ethical Considerations
This study was approved by the Ethics Committee of the University of Kurdistan under the code: IR.UOK.REC.1400.015
Authors’ Contributions
All authors contributed to the design, implementation, and writing of all parts of the present study.
Conflict of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
Acknowledgments
The authors would like to express their sincere gratitude to the University of Kurdistan, Department of Exercise Physiology for providing the necessary facilities and support to conduct this research.
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