Aerobic Exercise Modulates Lipo-Toxicity Genes Expression in Cardiac Tissue of Obese Rats Induced with High-Fat and Fructose Diet

Abstract

Background:

Obesity stands as a significant contributor to physical disability and is associated with a range of health issues, particularly cardiovascular diseases. This study aims to explore the impact of aerobic exercise on the expression levels of lipo-toxicity genes within the cardiac tissue of obese male rats that have been subjected to a diet high in fat and fructose.

Materials and Methods:

Twenty-four male Wistar rats were randomly divided into three groups (n = 8 rats): 2 months of standard diet, 2 months of high-fat diet containing fructose (60% fat and 25% fructose diet), and aerobic exercise group (consumed 60% fat food containing 25% fructose; in addition, from the eighth week to the end of the research period, they performed continuous aerobic exercise with an average intensity of 15 m/min for 30 min on a treadmill). At the end of the study, the anthropometrical parameters and markers of obesity and also genes expression of peroxisome proliferator-activated receptor alpha (PPARα), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), pyruvate dehydrogenase kinase 4 (PDK4), and mast cell protease-1 (mCPT1) were measured using the real-time polymerase chain reaction technique. One-way analysis of variance and Tukey’s post hoc test were used for statistical analysis.

Results:

The expression level of PPARα, PGC1-α, PDK4, and mCPT1 genes in the cardiac tissue of obese rats was significantly lower than that of the healthy control group. Also, the gene expression level of PGC1-α, PDK4, and mCPT1 significantly decreases, whereas the gene expression level of the PPARα increased in the exercise group compared to the obese groups.

Conclusion:

It seems that aerobic exercise can modulate the expression of PPARα, PGC1-α, PDK4, and mCPT1 genes and improve fat metabolism in cardiac tissue samples. It is suggested that aerobic exercise can be useful for obese patients with cardiovascular problems.

INTRODUCTION

The global prevalence of obesity, insulin resistance, and diabetes has reached epidemic proportions. Obesity not only diminishes life expectancy but also elevates the risk of stroke and coronary artery disease, while contributing to a range of adverse health outcomes, including cancer, accelerated aging, cardiovascular diseases, and various other pathological conditions. Furthermore, it leads to the abnormal accumulation of fat in numerous non-adipose tissues, including the pancreas, kidneys, blood vessels, liver, skeletal muscles, and cardiac structures.[1,2]

Mitochondrial dysfunction has emerged as a crucial contributor to the progression of chronic metabolic disorders linked to insulin resistance. It is essential to recognize, however, that this dysfunction can occur independently of high blood sugar levels, often triggered by factors such as lipotoxicity, oxidative stress, or inflammation. Mitochondria are the primary source of reactive oxygen species (ROS) within cells, generated through the respiratory chain complexes. The oxidative stress and inflammation induced by dietary factors are further intensified by advanced glycation end products (AGEs), which encompass a wide range of compounds. The concentration of AGEs in the body is determined not only by their internal production but also by external sources. The interaction between glucose and free amino groups, particularly those found in lysine or arginine, initiates the formation of Schiff bases, which then undergo a complex series of reactions. Obesity-related lipotoxic cardiomyopathy is characterized by an increase in cardiac fat, resulting in alterations to myocardial structure and function. This condition is closely linked to abnormal lipid metabolism, which ultimately facilitates the excessive entry of fatty acids into oxidative pathways. Such changes in cellular signaling contribute to mitochondrial dysfunction and promote increased rates of apoptosis.[3]

Peroxisome proliferator-activated receptors (PPARs) belong to the class I superfamily of nuclear hormone receptors and are categorized into three distinct isoforms: α, β, and γ. These isoforms can be stimulated by both endogenous ligands, including fatty acids, and synthetic pharmaceutical compounds. PPARs play a crucial role in the regulation of lipid metabolism across several tissues, including the heart, skeletal muscle, liver, and adipose tissue.[4,5] Elevated expression of the peroxisome proliferator-activated receptor alpha (PPARα) gene has been demonstrated to enhance fatty acid metabolism within the skeletal muscle of Zucker ZDF rats. In the cardiovascular system, PPARα inhibits the pyruvate oxidation pathway while promoting fatty acid oxidation (FAO) through its influence on the expression of the Pyruvate dehydrogenase kinase 4 (PDK4) gene. The PDK4 gene is typically expressed at high levels in various tissues that have significant energy requirements, including the heart, skeletal muscle, liver, kidney, pancreatic islets, and lactating mammary glands. The expression of PDK4 is generally stimulated in response to increased levels of free fatty acids (FFAs) in the blood, a condition often observed during periods of starvation.[6] This process is, to some extent, influenced by PPARα along with various other mechanisms. The activator family of PPAR receptors contributes to a greater level of organization. Among these receptors, PPAR coactivator 1α (PGC-1α) is the most extensively researched. It is proposed that the pathways governing the expression of nuclear-encoded factors related to mitochondria converge on PGC-1α, leading to its designation as a master regulator of mitochondrial biogenesis.[7]

Research has indicated that physical activity enhances the reduced expression of lipotoxicity-related genes, likely attributable to the function of this molecule in the metabolism and regulation of fatty acids.[8,9] Considering the role of lipotoxicity genes in fat metabolism in the cardiovascular system, it seems necessary to investigate its changes during physical activity in obese rats. Accordingly, the aim of the current experiment was to evaluate the effect of aerobic exercise on the level of lipotoxic genes such as PPARα, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), PDK4, and mast cell protease-1 (MCPT1) in the cardiac tissue of obese male rats induced by high-fat/fructose diet.

MATERIALS AND METHODS

The current research involved male Wistar rats as the subjects. A total of 24 male Wistar rats, each 8 weeks old and weighing approximately 300 ± 11.3 g, were sourced from the Laboratory Animal Breeding Center at Jundishapur University of Medical Sciences in Ahvaz, Iran. The environmental conditions within the animal housing facility were meticulously regulated, maintaining a temperature of approximately 22°C ± 2°C and a relative humidity level ranging from 40% to 60%. Additionally, the light–dark cycle was consistently monitored and controlled using an electronic regulator, ensuring a 12-h light and 12-h dark period.

Animal grouping

Following a 2-week acclimatization period to the new laboratory setting, during which the subjects were provided with a standard diet comprising 20% of calories from fat, 20% from protein, and 60% from carbohydrates (yielding 1.3 kcal/g), the rats were subsequently assigned to one of three groups (n = 8) through random selection. One group continued on the standard diet for a duration of 8 weeks, while another group was placed on a high-fat diet enriched with fructose for the same period. Upon completion of the 8 weeks, all rats were transitioned to a high-calorie diet consisting of 60% fat and 25% fructose. The study identified two specific categories: the obese group, which maintained a diet of 60% fat and 25% fructose throughout the entire research duration, and the obese plus aerobic exercise group, which followed the same dietary regimen while also engaging in aerobic exercise from the eighth week until the conclusion of the study, thereby progressing to the subsequent phases of the research.

High-fat diet

This feed is specifically formulated to promote obesity. The composition of a typical rodent diet includes a 60% high-fat diet, which derives 60% of its caloric content from fat, providing 2.5 kcal/g of energy, predominantly sourced from 90% processed animal fat, with an additional 10% soybean oil incorporated into the standard rodent feed. This feed was manufactured by Royan Biotech Company located in Isfahan. To produce 100 kg of 60% high-fat pellets, a mixture of 45 kg of standard pellet powder and 30 kg of animal fat—obtained from melting cow tail along with soybean oil—was processed into standard pellets. This formulation effectively meets the caloric and energy requirements necessary for inducing obesity.[10]

High-fructose diet

To create a 25% volumetric solution of fructose, the formula of 100 times the solution volume in milliliters divided by the soluble volume in milliliters equals the volume percentage was applied. Consequently, 250 mL of fructose liquid was dissolved in 750 mL of water to achieve the desired 25% concentration. This 25% fructose solution was prepared on a daily basis and made readily accessible in 500 mL bottles, specifically for use with laboratory animals.[11]

Aerobic exercise protocol

The endurance training regimen was conducted over a period of 8 weeks. In this investigation, a protocol characterized by moderate to high training intensity was implemented, incorporating progressive increases in both intensity and duration while adhering to the principle of gradual overload, as outlined in the research by Chang Huan et al. (2011). Consequently, both the obese exercise groups and the healthy exercise control group engaged in treadmill workouts five times a week for the duration of the study. All training sessions were scheduled at the conclusion of the animals’ sleep cycle, specifically between 16:00 and 18:00 in the evening. The treadmill exercise commenced at a speed of 10 m/min for 10 min during the first week, followed by 10 m/min for 20 min in the second week. In the third week, the speed was increased to 14–15 m/min for 20 min, and in the fourth week, it was maintained at 14–15 m/min for 30 min From the fifth to the eighth week, the speed was further elevated to 17–18 m/min for 30 min. To ensure that the adaptations reached a uniform state, all training variables were standardized during the final week of the protocol.[12]

Approval of obesity induction

To validate the induction of obesity, a high-calorie diet consisting of 60% fat and 25% fructose was administered to the rats over a period of 8 weeks. Following this duration, anthropometric and nutritional assessments were conducted across all groups to ascertain the presence of obesity. Weight changes among the subjects were monitored weekly on a designated day, allowing for the compilation of weight charts for each group throughout the study. Additionally, the rats were weighed immediately after anesthesia and prior to dissection. The abdominal circumference (AC) was measured in centimeters at the widest point just in front of the hind leg, while the chest circumference (TC) was recorded in centimeters just behind the forelimb. The ratio of AC to chest circumference (AC/T) was calculated by dividing the AC by the chest circumference. Furthermore, body length was measured in centimeters from the tip of the nose to the anus.[13]

Body mass index

Body weight in grams divided by the length of the body from the nose to the anus to the power of two in centimeters was calculated as the body mass index (BMI).[14]

Lee index

Lee’s index was calculated as an index of body composition in rodents using the cube root formula of body weight in grams divided by body length from nose to anus in centimeters.[14]

Lipo-toxicity genes expression

To assess gene expression, all rats were anesthetized using a combination of Ketamine and Xylazine at a dosage of 90/10 mg/kg. Subsequently, cardiac tissue samples were collected, and after undergoing centrifugation, the supernatant was utilized for RNA isolation employing the Parstous total RNA isolation kit (Iran), following the manufacturer’s guidelines. The synthesis of complementary DNA (cDNA) was then carried out using Quantitect Reverse Transcriptase. A real-time polymerase chain reaction (RT-PCR) was conducted to quantify the expression levels of the target genes, specifically PPARα, PGC1α, PDK4, and MCPT1, with glyceraldehyde 3-phosphate dehydrogenase serving as the control gene, utilizing the RT-PCR Real-Time method. The primers used for this process were as follows [Table 1].

Table 1.

The sequences of the applied primers in this study

Genes	Reverse	Forward
GAPDH	5ʹ-TTCTTGTGCAGTGCCAGCCTCGTC-3ʹ	5ʹ-TAGGAACACGGAAGGCCATGCCAG-3ʹ
PPARα	5ʹ-ATGAGCACGGAAAGCATGATCCGA-3ʹ	5ʹ-CCAAAGTAGACCTGCCCGGACTC-3ʹ
MCPT1	5ʹ-CTACAGGGTTTCATCCAGGATC-3ʹ	5ʹ-CCACATCAGCAATCATCCTCTG-3ʹ
PDK4	5ʹ-CCAGTTGCCTTCTTGGGACTGATG-3ʹ	5ʹ-ATTTTCTGACCACAGTGAGGAATG-3ʹ
PGC1-α	5ʹ-ATGGCAACTGTCCCTGAACTCAACT-3ʹ	5ʹ-CAGGACAGGTATAGATTCAACCCCTT-3ʹ

GAPDH=Glyceraldehyde 3-phosphate dehydrogenase, PPARα=Peroxisome proliferator-activated receptor alpha, PGC1-α=Peroxisome proliferator-activated receptor gamma coactivator 1-alpha, PDK4=Pyruvate dehydrogenase kinase 4, MCPT1=Mast cell protease-1

Oil Red histopathology evaluation

To evaluate cardiac histopathology, the cardiac sections underwent staining using the Oil Red protocol. Subsequently, the nuclei were counterstained with hematoxylin. The stained samples were then examined using an Olympus microscope.[15]

Statistical analysis

The obtained results were analyzed using GraphPad Prism version 8.00 (GraphPad Software, La Jolla California USA). One-way analysis of variance, followed by Tukey’s post hoc test, was used, and data were expressed as mean ± standard error of mean. Finally, P < 0.05 considered as the level of significance.

RESULTS

Effect of high-fat/fructose diet and exercise on obesity indexes

As shown in Table 2, the weight in the obesity group is significantly higher than control in response to high-fat and fructose diet. On the other hand, in the rat group with exercise, the weight is significantly lower than the obesity group. Moreover, evaluation of other indexes such as Lee, BMI, and abdominal/chest circumference shows that in the high-fat/fructose diet group, the values are significantly higher than control rats and exercise caused to improve in all anthropometrical parameters compared to the obese rats.

Table 2.

Anthropometrical parameters of obesity in all groups including control, obesity, and obesity plus exercise

Indexes	Group	Mean±SEM	P	t
Weight (gr)	Control	297.9±5.8	0.001	6.79
	Obese	401.7±0.4
	Exercise	294.10±0.7	0.001	5.529
BMI (gr/Cm2)	Control	0.44±0.069	0.02	3.345
	Obese	0.671±0.065
	Exercise	0.44±0.026	0.035	3.12
Lee Index (gr2/3/cm)	Control	0.26±0.081	0.046	2.635
	Obese	0.319±0.043
	Exercise	0.26±0.068	0.037	1.75
Abdominal/chest circumference (cm)	Control	1.33±0.072	0.048	2.611
	Obese	1.36±0.033
	Exercise	1.43±0.023	0.039	1.98

One-way ANOVA analysis was done and the data expressed as mean±SEM. SEM=Standard error of mean. ANOVA=Analysis of variance, SEM=Standard error of mean, BMI=Body mass index

Effect of high-fat/fructose diet and exercise on lipotoxicity genes expression

As shown in Figure 1, the results of the statistical analysis revealed that the level of PPARα gene expression in the cardiac tissue of obese rats was significantly lower than that of the control group (P ≤ 0.001). Also, a significant difference was observed in the expression levels of the PPARα gene between the obese groups compared to the exercise group [Figure 1a] (P ≤ 0.01). Also, the expression level of PGC1-α gene in the cardiac tissue of obese rats was significantly lower than the control group (P ≤ 0.001). Furthermore, the expression level of PDK4 gene in the cardiac tissue of obese rats was significantly higher than the control group [Figure 1b] (P ≤ 0.001). A significant difference was shown in the expression levels of PDK4 gene between the obese group compared to the exercise and control groups (P ≤ 0.01). Also, the expression level of mCPT 1 gene in the cardiac tissue of obese rats was significantly higher than the control rats [Figure 1c] (P ≤ 0.001). A remarkable decrease was shown in the expression levels of the mCPT 1 gene between the obese groups compared to the exercise and control groups; on the other hand, the expression level of the mCPT 1 gene was higher in the exercise rats compared to the control group [Figure 1d] (P ≤ 0.01).

Figure 1.

Effects of obesity and exercise on PPARα (a), PGC1-α (b), PDK4 (c), and MCPT1 (d) genes expression in cardiac tissues. Data are presented as mean ± SEM, analyzed by one-way analysis of variance followed by Tukey’s post hoc test. * = significant at P < 0.05, ^#Versus obese group *** = significant at P< 0.001, ## = significant at P < 0.01, ### = significant at P < 0.001. SEM = Standard error of mean, PPARα = Peroxisome proliferator-activated receptor alpha, PGC1-α = Peroxisome proliferator-activated receptor gamma coactivator 1-alpha, PDK4 = Pyruvate dehydrogenase kinase 4, MCPT1 = Mast cell protease-1

Effect of high-fat/fructose diet and exercise on cardiac histopathology

In order to evaluate the effect of obesity and exercise on lipid deposition in cardiac tissue, Oil Red O staining was done. As shown in Figure 2, in cardiac tissue of normal rats, there are no lipid droplets, although large orange-red lipid droplets were shown in the cardiac tissues of obese rats (P ≤ 0.001). However, exercise reduced lipid deposition in the cardiac tissue compared to the obese group (P ≤ 0.01).

Figure 2.

The comparison effect of obesity and exercise on cardiac histopathology (a) and lipid droplet (b). Data are presented as mean ± SEM; analyzed by one-way analysis of variance followed by Tukey’s post hoc test. * = significant at P < 0.05, ^# = significant at P < 0.05, ^*** = significant at P < 0.001, ^## = significant at P < 0.01. SEM = Standard error of mean

DISCUSSION

The examination of the impact of a diet rich in fats and fructose on the development of obesity in male rats revealed a significant increase in various anthropometric measurements, such as weight, BMI, Lee’s index, and the ratio of AC to chest circumference, when compared to healthy rats.

Previous studies have indicated that diets high in fatty acids contribute to weight gain and increased body fat, primarily due to their appealing taste and high caloric content.[16] Different rat breeds exhibit varying responses to this dietary regimen, and factors such as age and sex also influence how these diets contribute to obesity. Notably, younger and male rats tend to be more susceptible to metabolic diseases associated with obesity. Numerous studies have established a connection between high-fat food consumption and the onset of obesity, elevated plasma cholesterol levels, and the emergence of metabolic disorders. Research conducted by Matias et al. demonstrated that a fat-rich diet can induce obesity in animals that resembles human obesity, primarily due to an increase in body fat.[17,18] In a separate investigation, it was discovered that the intake of saturated fatty acids may contribute to increased fat storage due to the resynthesis of new triglycerides (TG). An elevation in the proportion of fat within the daily diet creates a disparity between lipid consumption and its oxidation, resulting in an increase in fat tissue mass characterized by both hypertrophy and hyperplasia. Consequently, this leads to a rise in the processes of lipolysis and FAO. Thus, the expansion of adipose tissue will trigger the stimulation of lipid oxidation.[19,20]

The findings of this study indicated that the expression of the PPARα gene in the cardiac tissue of obese rats was markedly lower when compared to the control group. These results are consistent with the observations made by Paul et al. in 2015 as well as those reported by Nakamura and Sadoshima in 2020 and Sankaralingam et al., in 2015.[21,22]

The cardiac system demands substantial energy owing to its continuous contractile function. FAO serves as the primary energy source for the heart. In typical physiological conditions, the cardiac system is capable of utilizing a range of substrates, including carbohydrates, ketones, lactate, and certain amino acids, to facilitate energy production.[23] The heart’s metabolic system is intricately structured to meet the energy requirements of its daily functions. Its remarkable adaptability allows the myocardium to respond swiftly to fluctuations in energy needs. Under typical circumstances, the cardiac system primarily utilizes the chemical energy found in FFAs, accounting for 60%–90% of its energy supply, along with pyruvate derived from glucose and lactate, which contributes 10%–40% to its adenosine triphosphate (ATP) production.[24] However, in cases of diabetes or obesity, the heart’s metabolic flexibility diminishes, resulting in an increased reliance on FAO for energy.[25] Studies indicate that in obese rats subjected to a high-fat diet, this overdependence on FAO correlates with a significant decline in glucose oxidation. The interplay between fatty acid and glucose oxidation negatively regulates glucose oxidation, further inhibiting its utilization.[26] Cardiac PPARα serves as a crucial regulator of FAO within the heart, playing a significant role in the modulation of gene expression related to fatty acid metabolism. In studies involving PPARα-deficient rats, there was a notable reduction in the expression levels of genes that encode proteins essential for sarcolemma transport, such as fatty acid translocase (FAT), CD36, and fatty acid transport protein 1. Furthermore, research conducted by Karwi et al.[27] in 2021 demonstrated that PPARα is instrumental in regulating acyl-CoA oxidase, the enzyme responsible for initiating the FAO process. Overall, PPARα is integral to the regulation of energy metabolism in the body, influencing processes such as fatty acid transport, oxidation, and ketogenesis.[28] PPARα and ∆ PPAR signaling pathways are engaged in the adult heart, promoting a standard metabolic profile that sustains elevated levels of high-energy phosphates through mitochondrial FAO and glucose metabolism. The activation of PPARα signaling enhances the transport of fatty acids into cells, stimulates lipogenesis, and supports both mitochondrial and peroxisomal oxidation processes. In contrast, ∆PPAR signaling primarily promotes the transport of fatty acids and glucose into cells, mitochondrial oxidation, the generation of new mitochondria, and mechanisms that inhibit ROS. Collectively, these findings strongly indicate that the upregulation of PPARα plays a crucial role in facilitating mitochondrial fatty acid metabolism in the context of diabetic and obese cardiomyopathy.[29]

The lipid-lowering effects of PPARα may be mediated through several mechanisms, including the regulation of FAO metabolism and a decrease in the production of very low-density lipoprotein (VLDL). PPARα and its ligands are known to downregulate the expression of genes responsible for the hydrolysis of TG and high-density lipoprotein (HDL) within the bloodstream. Additionally, PPARα influences the expression of genes that are involved in HDL production, thereby regulating lipoprotein lipase (LPL) activity. This regulation helps to maintain HDL levels by restoring its size and composition, primarily through the enhanced transfer of unesterified cholesterol to HDL.[30] Experimental investigations utilizing animal models of metabolic disorders have demonstrated that the activation of PPARα offers protection against vascular complications by exerting anti-inflammatory, anti-atherogenic, and antioxidant effects. Furthermore, PPARα plays a significant role in regulating oxidative responses, cellular regeneration, and inflammation within the cardiac system, particularly in the context of ischemia/reperfusion injury, hypertrophy, and fibrosis.[31]

The findings of this study indicate that the expression level of the PGC1-α gene in the cardiac tissue of obese rats is significantly lower when compared to the control group. These results are consistent with the research conducted by Kulikova et al., Cheng et al., and Teixeira et al., which demonstrated that a reduction in PGC-1α within white adipose tissue is linked to obesity-related disruptions in overall metabolism.[32,33,34] This suggests that PGC-1α and β play crucial roles in the regulation of mitochondrial mass, oxygen consumption, and respiratory efficiency. Furthermore, the depletion of PGC-1α is frequently observed as a characteristic feature of cardiac disorders in various rodent models exhibiting cardiac hypertrophy or failure.[35]

PGC-1α and PGC-1β are predominantly found in tissues characterized by high oxidative capacity, including the heart, brown adipose tissue, kidneys, and slow-twitch skeletal muscle. The expression of the coactivator PGC-1α can be significantly induced at the transcriptional level through the activation of various upstream signaling pathways. Studies involving the overexpression of PGC-1α in cardiomyocytes, both in cell culture and in vivo, have demonstrated a marked increase in FAO.[36] The PPAR family of transcription factors is integral to this process as fatty acids and their metabolic byproducts serve as low to moderate affinity ligands for PPARs, potentially relaying information regarding the intracellular lipid environment to influence gene regulation. In cardiac cells, PGC-1α interacts with PPARα, leading to the activation of several genes essential for fatty acid metabolism, including CD36, CPT1b, and PDK4, which inhibits the transport of pyruvate to mitochondria, as well as inducing MCAD, a key enzyme in the oxidation of medium-chain β-fatty acids.[37]

The findings of the current study indicate that an 8-week regimen of moderate-intensity aerobic exercise led to an increase in PGC1-α levels within the cardiac tissue of rats. Additionally, this research demonstrates that engaging in aerobic activity has effectively diminished the expression of MCP-1 in the cardiac tissue of these animals.

During prolonged physical activity, the hormones epinephrine, norepinephrine, and glucagon play a crucial role in promoting the mobilization of fatty acids from TG stored in adipose tissue, while insulin acts to inhibit this process. Epinephrine and glucagon interact with their respective receptors located in the lipid membrane, which activates adenylyl cyclase to generate cyclic AMP (cAMP). The increase in cAMP levels subsequently activates cAMP-dependent protein kinase, leading to the phosphorylation of hormone-sensitive lipase (HSL) and perilipin on the surface of lipid droplets. The phosphorylation of perilipin enhances the activity of adipose triglyceride lipase, resulting in an increased availability of diacylglycerol (DAG) substrates for HSL.[38] HSL then catalyzes the hydrolysis of DAG into FFAs and monoacylglycerol (MAG), with the latter being further broken down by MAG lipase. The released FFAs migrate to the plasma membrane, where they associate with adipose fatty acid-binding protein, exit the adipocyte, and subsequently bind to serum albumin in the bloodstream. Additionally, physical activity stimulates the expression of LPL on the endothelial cells of skeletal muscle, facilitating further lipid metabolism.[38] Increased activity of LPL enhances the hydrolysis of TG from triglyceride-rich lipoproteins, including chylomicrons and VLDLs. This process results in the release of FFA, glycerol, free cholesterol, and free phospholipids. The esterified cholesterol is incorporated into the core of HDL particles, contributing to elevated levels of plasma HDL cholesterol.[39] The FFAs released from lipoproteins and through lipid lipolysis are subsequently liberated from albumin and transported into cells via specific fatty acid transport mechanisms, including FAT (FAT/CD36), plasma membrane-associated fatty acid binding proteins, and other transport systems that facilitate fatty acid uptake into myocytes.[40]

The findings of this study indicated that the expression level of the PDK4 gene in the cardiac tissue of obese rats was markedly elevated compared to the control group. This heightened expression of PDK4 suggests a systematic metabolic transition from utilizing glucose to relying on fatty acids as the main source of energy.

The cardiovascular system possesses a remarkable ability to metabolize a variety of substrates for the generation of ATP, which serves as a crucial source of chemical energy. This metabolic adaptability enables the heart to effectively adjust to ongoing fluctuations in energy demands and the availability of nutrients.[41] While the heart can utilize a range of nutrients, it exhibits a preferential utilization pattern, with fatty acids and ketone bodies being prioritized over glucose. The PDK4 gene is predominantly expressed in high-energy-demand tissues, such as the cardiovascular system, skeletal muscle, liver, kidneys, pancreatic islets, and lactating mammary glands. In these tissues, the expression of PDK4 is typically stimulated in response to elevated levels of FFAs in the bloodstream. This regulatory process is partially influenced by PPARα, along with other mechanisms, leading to the upregulation of PDK4 through the modulation of PPARα.[42]

The findings from the current experiment indicate that the induction of obesity in rats through a diet high in fat and fructose influenced the expression of genes associated with lipotoxicity. Notably, moderate-intensity aerobic exercise was found to enhance the expression of PPARα, PGC1α, PDK4, and MCPT1 genes within the cardiac tissue of the rats, which appears to mitigate cardiac injury. Consequently, it is proposed that aerobic exercise may serve as an effective preventive or therapeutic approach to alleviate the complications associated with obesity and related cardiovascular issues.

CONCLUSION

This research examines the impact of a diet high in fats and fructose on the progression of obesity, revealing notable increases in anthropometric measurements when compared to healthy control groups. The findings indicate significant reduced expression of the PPARα gene in the cardiac tissue of obese rats, which suggests a decline in FAO and metabolic flexibility typically regulated by PPARα. Additionally, the expression of the PGC-1α gene was found to be considerably diminished in obese rats, highlighting the essential role of this coactivator in mitochondrial functionality and energy metabolism. Engaging in moderate-intensity aerobic exercise can boost the expression of PPARα, PGC-1α, PDK4, and other pertinent genes within cardiac tissue, thereby alleviating cardiac damage and indicating a possible therapeutic strategy for addressing cardiovascular issues related to obesity. In summary, the results emphasize the intricate relationship between lipotoxic genes expression and physical activity in the management of obesity and its associated metabolic effects.

Limitations

The current research is subject to certain limitations. Primarily, the duration of 8 weeks on a high-fat diet may not have been sufficient to induce significant cardiac damage. Nevertheless, it has been demonstrated that comparable durations of high-fat diet exposure can lead to detrimental effects at both the molecular and cellular levels, as evidenced by the findings of the current study.

Ethics approval and consent to participate

This study approved by Ethics Committee with the code IR.IAU.AHVAZ.REC.1401.149.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.