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. 2023 Oct 12;43(8):4295–4307. doi: 10.1007/s10571-023-01421-w

High Intensity Interval Training can Ameliorate Hypothalamic Appetite Regulation in Male Rats with Type 2 Diabetes: The Role of Leptin

Kayvan Khoramipour 1,✉, Maryam Hossein Rezaei 2, Elham Madadizadeh 2, Mahdieh Sadat Hosseini 3, Zahra Soltani 3, Janis Schierbauer 4, Othmar Moser 4,5
PMCID: PMC11407713  PMID: 37828299

Abstract

Disruption of leptin (LEP) signaling in the hypothalamus caused by type 2 diabetes (T2D) can impair appetite regulation. The aim of this study was to investigate whether the improvement in appetite regulation induced by high-intensity interval training (HIIT) in rats with T2D can be mediated by LEP signaling. In this study, 20 male Wister rats were randomly assigned to one of four groups: CO (non-type 2 diabetes control), T2D (type 2 diabetes), EX (non-type 2 diabetes exercise), and T2D + EX (type 2 diabetes + exercise).To induce T2D, a combination of a high-fat diet for 2 months and a single dose of streptozotocin (35 mg/kg) was administered. Rats in the EX and T2D + EX groups performed 4–10 intervals of treadmill running at 80–100% of their maximum velocity (Vmax). Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), serum levels of insulin (INS) and LEP (LEPS) as well as hypothalamic expression of LEP receptors (LEP-R), Janus kinase 2 (JAK-2), signal transducer and activator of transcription 3 (STAT-3), neuropeptide Y (NPY), agouti-related protein (AGRP), pro-opiomelanocortin cocaine (POMC), amphetamine-related transcript (CART), suppressor of cytokine signaling (SOCS3), forkhead box protein O1 (FOXO1) were assessed. ANOVA and Tukey post hoc tests were used to compare the results between the groups. The levels of LEPS and INS, as well as the levels of LEP-R, JAK-2, STAT-3, POMC, and CART in the hypothalamus were found to be higher in the T2D + EX group compared to the T2D group. On the other hand, the levels of HOMA-IR, NPY, AGRP, SOCS3, and FOXO1 were lower in the T2D + EX group compared to the T2D group (P < 0.0001). The findings of this study suggest that HIIT may improve appetite regulation in rats with T2D, and LEP signaling may play a crucial role in this improvement.

Graphical Abstract

Graphical abstract (leptin signaling in the hypothalamus), Leptin (LEP), Leptin receptor (LEP-R), Janus kinase 2 (JAK2), Signal transducer and activator of transcription 3 (STAT3), expressing Neuropeptide Y (NPY), Agouti-related protein (AGRP), anorexigenic neurons (expressing pro-opiomelanocortin cocaine (POMC), Amphetamine-related transcript (CART), suppressor of cytokine signaling (SOCS3), forkhead box protein O1 (FOXO1).graphic file with name 10571_2023_1421_Figa_HTML.jpg

Keywords: Appetite, Leptin resistance, Adipokine, Orexigenic neuron, Anorexigenic neuron, HIIT

Introduction

Appetite is regulated by a coordinated interplay between adipose tissue and the brain (Khoramipour et al. 2020; Liu et al. 2018). A primary site for appetite regulation is the hypothalamus, where interaction between orexigenic neurons (expressing Neuropeptide Y (NPY) /Agouti-related protein (AGRP) and anorexigenic neurons (expressing pro-opiomelanocortin cocaine (POMC)/Amphetamine-related transcript (CART) controls energy homeostasis (Park and Ahima 2014). Several peripheral signals have been shown to modulate the activity of orexigenic and anorexigenic neurons, with adipokines as the most important (Villano et al. 2022).

Previous studies have shown that the most critical adipokine for linking adipose tissue and the hypothalamus is leptin (LEP), an appetite hormone. LEP can cross the blood-brain barrier (BBB) and enter the hypothalamus by binding to the LEP receptor (LEP-R), which activates four cellular pathways in appetite regulation (Liu et al. 2018; Park and Ahima 2014; Ibeas et al. 2021). Among these four cellular pathways, Janus kinase 2 (JAK-2)/signal transducer and activator of transcription 3 (STAT-3) are the most effective in regulating appetite through orexigenic and anorexigenic neurons (Liu et al. 2018; Park and Ahima 2014). LEP binding to LEP-R results in receptor dimerization and JAK2 binding to LEP-R cytoplasmic part. JAK2 is a self-phosphorylating protein that phosphorylates tyrosine residuals (i.e., 985, 1077, 1138) of LEP-R. Then STAT3 binds to phosphorylated tyrosine 1138, is dimerized, and enters the nucleus. Entering the nucleus, STAT3 stimulates the expression of appetite-suppressing genes such as POMC and CART and inhibits the expression of appetite-stimulating genes such as NPY and AGRP (Sahu 2003). The suppressor of cytokine signaling (SOCS3) is the suppressor of the JAK2/STAT3 pathway, which plays a significant role in the final regulation of this pathway (Liu et al. 2017).

On the other hand, forkhead box protein O1 (FOXO1), an inhibitor of POMC gene expression, is phosphorylated by STAT3, an intermediate leptin signaling. When phosphorylated, FOXO1 exit the nucleus, and POMC gene expression could start (Sasaki and Kitamura 2010; Yang et al. 2009).

Researches have shown that disturbance in satiety processes is one of the essential factors in developing/exacerbating metabolic disorder such as type 2 diabtes (Rajabi et al. 2022), which is the cause of one-third of deaths worldwide (Ibeas et al. 2021; Zhang and Bi 2018). Over the last decade, regulating appetite has emerged as a key focus of scientific research (Ibeas et al. 2021; Zhang and Bi 2018; Lyu et al. 2022).

Exercise has been shown to regulate appetite by improving LEP signaling (Ruegsegger and Booth 2017). Studies have shown that chronic exercise training improves LEP signaling in the hypothalamus, increases energy consumption, and decreases appetite in obese rats (Kadoglou et al. 2007; Bahrami and Saremi 2011); however, Ruppel et al. (Ropelle et al. 2010) showed that long-term low-intensity aerobic exercise did not affect LEP signaling in the hypothalamus of obese rats. In addition, Kang et al. (2013). He at., concluded in their metanalysis that HIIT could influence human appetite by increasing the levels of peptide tyrosine tyrosine (PYY), pancreatic polypeptide or glucagon-like peptide 1 (GLP-1) which suppress food intake (He et al. 2018a, b). Another study was also reported reduced ghrelin in diabetic participants after 12 weeks of HIIT (Afrasyabi et al. 2019).

These findings suggest that exercise intensity might play a vital role when assessing the interplay of appetited regulation and exercise. Based on these previous findings, we hypothesized that high-intensity interval training (HIIT) could improve LEP signaling in the hypothalamus due to the high intensity, aerobic recovery phases, and its interval nature, thereby increasing POMC and CART and reducing the NPY and AGRP genes expression in the hypothalamus. The present study aimed to determine the effect of HIIT on appetite regulation in the hypothalamus of rats with type 2 diabetes with a particular focus on LEP signaling.

Material and Method

Animal Care

Twenty male Wistar rats with mean body mass of 200 ± 10.25 g at the age of 8 weeks were purchased from the Kerman University of Medical Sciences animal farm. The animals were kept at standardized laboratory conditions with a mean temperature of 22 ± 1.4 °C, a humidity of 50 ± 4%, and a day night cycle (1:1) in the polycarbonate cage with free access to water and rodent chow (Faradamzarin Esfahan, Iran). Experimental procedures were approved by the Committee standards care of the animal at Kerman University of Medical Sciences (IR.UK.REC.1400.007). After familiarizing with the laboratory environment, the animals were randomly assigned to four group (5 rats per group): non-type 2 diabetes control (CO), type 2 diabetes control (T2D), non-type 2 diabetes exercise (EX), and type 2 diabetes + exercise (T2D + EX). The water and food intake were recorded weekly and the body weight and blood glucose were recorded mounthly.

Type 2 Diabetes Inducing

Prior to the start of the exercise intervention, the type 2 diabetes groups (T2D and T2D + EX) were fed a for two months high-fat diet (HFD) which included the following ingredients: 60% fat (245 g Lard and 25 g Soybean oil), 20% carbohydrate (125 g Lodex 10 and 72.8 g Sucrose), 19% protein (200 g Casein and 3 g Cysteine) (Table 1) (Lee et al. 2019; Shimizu et al. 2017). Followingly, after 12 h of fasting, the animals received a single dose of streptozotocin (STZ, 35 mg kg−1) intraperitoneally. Three days after injection, the animals’ blood glucose was measured (Eliza et al. 2009). Fasting blood glucose (FBG) above 300 mg/dL was considered a criterion for diabetic rats (Speisman et al. 2013).

Table 1.

High-fat and regular diet ingredients

Diet ingredients Fat (%) Carbohydrate (%) Protein (%) Fiber/mineral/vitamin (%) Total energy
Regular diet 10 70 19 1 341 Cal/100 g or 1432 J/100 g
High-fat diet 60 20 19 1 429 Cal/100 g or 1802 J/g
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The American institute of nutrition standards (cat. no. D12492; Research Diets, Inc., New Brunswick, USA)

Exercise Protocol

All rats underwent a 5 days familiarization period (i.e. running for 10 min once a day with a speed of 8 m/min) and we selected runner rats for the training groups. At the end of the familiarization period, an incremental test was performed to measure the maximum velocity (Vmax) in the EX and T2D + EX groups. Afterwards, the rats in EX and EX + T2D performed a high-intensity interval training (HIIT) program at 80–100% Vmax 5 days a week for 8 weeks with 4–10 intervals per training session. The exercise protocol was deigned in our lab (we named it K1 protocol) which has been described fully in our previous publication (Rajizadeh et al. 2023; Khoramipour et al. 2023; Rezaei et al. 2023; Orumiyehei et al. 2022; Ebrahimnezhad et al. 2023).

Serum and Tissue Sampling

Fourtyeight hours after the last training session, the rats were anesthetized using ketamine (80 mg/kg( and xylazine )10 mg/kg). Blood samples were taken from the animal’s heart, and hypothalamus tissues were harvested. The hypothalamus was washed in PBS solution. An ultrasonic homogenizer performed homogenization in RIPA buffer solution with protease inhibitor on ice. The homogenate was centrifuged at 4 °C at 13.000 rpm for 20 min, and the supernatant was kept at − 80 °C (Basereh et al. 2017; Rahmaty et al. 2015; Bejeshk et al. 2022).

Western Blotting Methods

To evaluate the concentrations of LEP-R (sc-8391, SANTA CRUZ BIOTECHNOLOGY, INC), JAK2 (sc-390,539, SANTA CRUZ BIOTECHNOLOGY, INC), STAT3 (678,002, United States), POMC (ab32893, United States), AGRP (sc-518,077, SANTA CRUZ BIOTECHNOLOGY, INC) ,CART (sc-293,241, SANTA CRUZ BIOTECHNOLOGY, INC), NPY (sc-133,080, SANTA CRUZ BIOTECHNOLOGY, INC), FOXO1 (sc-374,427, SANTA CRUZ BIOTECHNOLOGY, INC), SOCS3 (sc-518,020, SANTA CRUZ BIOTECHNOLOGY, INC) we used Western blotting method. The total protein concentration in the hypothalamus samples was measured by the Lowry method, while bovine serum albumin was used as standard. After matching the concentrations, 40 µg of protein from each sample was mixed with a buffer sample. Then electrophoresed was performed for 75 min using 11% SDSPAGE gel. After that, the proteins separated in the gel were transferred to PVDF paper. The membrane was then incubated in 2% block solution overnight (at 4 °C). In the next step, the membrane was quenched four times each washed with TBST solution for 5 min and incubated for 3 h with the initial antibody (concentration 1.200) for each of the mentioned proteins. Then, the membrane was exposed to a secondary antibody (with a concentration of 1.1000) for 1 h. In the next step, immune detection was recorded using Chemi Doc XRS + imaging system (Bio-Rad Company, USA) and analyzed by ImageJ software. β-actin was used as a control (Frankenberg et al. 2017).

ELISA Method

The ELISA method used to measure LEP-S, INS-S and INS-H concentration. According to the manufacturer’s instructions, serum and tissue leptin and insulin were assayed using relevant kits. Leptin (Rat ELISA Kit, Eastbiopharm, Beijing, China) and insulin (Rat ELISA Kit, Eastbiopharm, Beijing, China) (Frankenberg et al. 2017; MAGALHÃES et al. 2019).

Calculation of Insulin Resistance

The homeostasis model assessment (HOMA) was used to assess insulin resistance (HOMA-IR). HOMA-IR scores were calculated using the following formula: HOMA-IR = [(fasting glucose (mmol/L) × fasting insulin (µU/mL)/22.5] (Sims-Robinson et al. 2010).

Statistical Analysis

Normality and homogeneity of variances were assessed using Shapiro–Wilk and Leven tests respectively. One-way ANOVA was used to compare the variables, and the Tukey test was used to determine the significant differences between the groups. All data are reported as mean ± standard deviation (SD). The level of significance was set at P ≤ 0.05. Then Data analysis was performed using Graph Pad Prism software version 9. The authors were blinded to the experimental protocol while performing the experiments and the statistical analysis.

Results

Vmax

To show the effectiveness of the HIIT protocol, rats’ Vmax was re-measured every 2 weeks. The statistical analysis showed that Vmax was significantly increased in both EX and T2D + EX groups during the training period (P < 0.01). In addition, Vmax in the EX was higher than the T2D + EX group in the weeks 7 (P < 0.001) and 9 (P < 0.0001) (Fig. 1).

Fig. 1.

Fig. 1

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Rats’ Vmax in EX and T2D + EX groups (n = 5 in each group) which was measured every 2 weeks with increamental test. *significant different with week 1 (P < 0.01), ****(P < 0.0001) and ***(P < 0.001) significant difference between T2D + Ex and Ex groups

Food Intake, Water Intake, Blood Glucose and Body Weight Changes

Water and food intake did not show significant different in the begning (week 0). However, from week 3 to week 16, water intake was found to be significantly higher in T2D and T2D + EX groups as compared to the other groups (P < 0.01). In addition, after strating exercise (week 8), T2D + EX group showed higher water intake than T2D group (P < 0.001). From week 1 to week 16, there was a notable increase in food intake among the T2D and T2D + EX groups in comparison to the other groups, as evidenced by a significant upward trend (P < 0.001). Following the commencement of exercise at week 8, the T2D + EX group demonstrated a greater intake of food compared to the T2D group (P < 0.001).

We measured FBG to ensure our diabetes induction protocol. Our results showed that FBG was significantly increased after diabetes induction (week 8) compared with basline (week 0) in T2D and T2D + EX groups (P < 0.0001), with no significant difference between these groups. But after 8 weels of HIIT (week 16), T2D + EX group showed lower FBG compared to T2D (P < 0.001).

Subsequent to the induction of diabetes at week 8, there was a significant increase in the weight of rats in both the T2D and T2D + EX groups (P < 0.0001). Following 8 weeks of HIIT (week 16), there was a significant decrease in the weight of rats in both the T2D and T2D + EX groups (P < 0.0001). The T2D group showed a greater reduction in weight compared to the T2D + EX group (P < 0.0001, as shown in Fig. 2) which may highlight the beneficial effect of HIIT in perserving the muscle weight while reducing the body fat.

Fig. 2.

Fig. 2

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Water intake (A), food intake in callories (B), food intake in grams (C), Fasting blood glucose (D), body weight (E) in all groups (n = 5 in each group). We measured these parameters before the high-fat diet (month 0), after the high-fat diet and STZ injection (month 2), and 48 h after the 8 week HIIT program (month 4). FBG: fasting blood glucose, CO control, T2D type 2 diabetes, EX exercise, and T2D + EX Type 2 diabetes + exercise. *significant difference between T2D and T2D + EX with other groups, #significant difference between T2D + EX with other groups

LEP and Insulin Levels in Serum and HOMA-IR in the Hypothalamus

Our results showed that after 8 weeks of HIIT, LEP (f3,16 = 164.2, P < 0.0001) and insulin (f3,16 = 32.27, P < 0.0001) levels in serum was significantly different bwetween groups. EX (P < 0.001) increased and T2D (P < 0.0001) decreased LEP levels in serum. In addition, the T2D + EX group showed higher LEP levels (P < 0.0001) in serum than the T2D group. Serum insulin (INS-S) level was significantly different in CO from T2D group (P < 0.0001). In addition, T2D + EX showed significantly higher levels of INS-S levels compared to the T2D group (P < 0.0001). Furthermore, we measured Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) which showed significant difference between groups (f3,16 = 159.1, P < 0.0001). Our results showed that T2D had higher HOMA-IR than CO group (P < 0.0001), however, no significant difference was found between EX and CO groups. In addition, a significant difference was shown between T2D and T2D + EX groups (P < 0.0001, Fig. 3).

Fig. 3.

Fig. 3

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LEP-S (A) INS-S (B), HOMA-IR (C) in all groups (n = 5 in each group). LEP-S serum leptin, LEP-H hypothalamus leptin, INS-S insulin level in serum, INS-H insulin level in hypothalamus, HOMA-IR homeostatic model assessment for insulin resistance. CO control, T2D type 2 diabetes, EX exercise, and T2D + EX type 2 diabetes + exercise. ****P < 0.0001, ***(P < 0.001), **(P < 0.01), *(P < 0.05)

LEP-R, JAK2, STAT3

We showed that hypothalamus LEP-R levels were significantly different between groups (f3,16 = 154.4, P < 0.0001). Furthermore, EX group showed higher (P < 0.0001) and T2D showed lower (P < 0.0001) LEP-R levels compared to CO group. T2D + EX also showed higher levels of LEP-R compared to T2D (P < 0.0001). After passing the blood brain barier (BBB), LEP binds to its receptor and increases phosphorylated JAK2 and STAT3. Phosphorylated JAK-2 (f3,16 = 21.67, P < 0.0001) and STAT3 (f3,16 = 29.61, P < 0.0001) levels in the hypothalamus showed a significant difference between groups. Phosphorylated JAK-2 and STAT3 levels were significantly higher and lower in EX and T2D compared to Co group respectively (P < 0.0001). In addition, their levels were higher in T2D + EX compared to the T2D group (P < 0.0001, Fig. 4).

Fig. 4.

Fig. 4

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LEP-R (A), JAK2 (B), P-JAK2 (C), STAT3 (D), P-STAT3 (E) levels in the hypothalamus in all groups (n = 5 in each group). LEP-R leptin receptor, JAK-2 Janus kinase 2, P-JAK-2 Janus kinase 2 phosphorylated, STAT-3 signal transducer and activator of transcription 3, P-STAT-3 signal transducer and activator of transcription 3 phosphorylated. CO control, T2D type 2 diabetes, EX exercise, and T2D + EX type 2 diabetes + exercise. ****P < 0.0001, ***(P < 0.001), **(P < 0.01), *(P < 0.05)

Anorexigenic and Orexigenic Neuropeptides

POMC (f3,16 = 69.25, P < 0.0001) and CART (f3,16 = 21.85, P < 0.0001) levels in the hypothalamus showed a significant difference between groups. POMC (P < 0.0001) and CART (P < 0.05) levels were higher in EX but lower (P < 0.01) in T2D group compared to CO group. In addition, T2D showed lower levels of POMC and CART compared to T2D + EX group (P < 0.01). NPY (f3,16 = 33.26, P < 0.0001) and AGRP (f3,16 = 22.23, P < 0.0001) levels in the hypothalamus showed a significant difference between groups with lower levels in EX (P < 0.01) and higher levels in T2D (P < 0.001) than CO group. In addition, T2D showed higher levels of NPY and AGRP compared to T2D + EX group (P < 0.0001, Fig. 5).

Fig. 5.

Fig. 5

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POMC (A), CART (B), NPY (C) and AGRP (D) levels in the hypothalamus in all groups (n = 5 in each group). CO control, T2D type 2 diabetes, EX exercise, and T2D + EX type 2 diabetes + exercise. POMC pro-opiomelanocortin cocaine, CART amphetamine-related transcript, NPY Neuropeptide Y, AGRP Agouti-related protein. ****P < 0.0001, ***(P < 0.001), **(P < 0.01), *(P < 0.05)

SOCS3 and FOXO1

Our results showed that SOCS3 (f3,16 = 46.65, P < 0.0001) and FOXO1 (f3,16 = 23.64, P < 0.0001) levels in the hypothalamus were difference between groups. SOCS3 (P < 0.0001) and FOXO1 (P < 0.05)showed lower levels in EX group but higher (P < 0.01) levels in T2D compared to CO group. Furthermore, T2D showed higher levels of both (i.e. SOCS3 and FOXO1) compared to T2D + EX group (P < 0.0001, Fig. 6).

Fig. 6.

Fig. 6

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FOXO1 (A), SOCS3 (B) levels in the hypothalamus in all groups (n = 5 in each group). CO control, T2D type 2 diabetes, EX exercise, and T2D + EX type 2 diabetes + exercise. FOXO1 forkhead box protein O1, SOCS3 suppressor of cytokine signaling. ****P < 0.0001, ***(P < 0.001), **(P < 0.01), *(P < 0.05)

Discussion

In the present study, we investigated the effect of an 8 week HIIT on LEP signaling in the hypothalamus of type 2 diabetic rats. Our data showed that T2D decreased INS, LEPS and LEP-R disruting JAK2/STAT3 pathway. The final outcome is decrease POMC, and CART neuropeptides and increase HOMA-IR, SOCS3, FOXO1, NPY, and AGRP levels in the hypothalamus. However, HIIT increased INS and LEPS, as well as LEP-R in the hypothalamus of type 2 diabetic rats. In addition, HIIT increased hypothalamic levels of p-JAK2, p-STAT3, POMC, and CART in T2D + EX group compared to T2D. This increase was accompanied by decreased HOMA-IR, SOCS3, FOXO1, NPY, and AGRP levels in the hypothalamus.

Deacreased INS and increased HOMA-IR in T2D group confirmed our diabetic induction method. In addition, water intake showed significant increased in T2D groups. In instances where blood glucose levels are elevated, the body stimulates the kidneys to produce more urine, aiding in the elimination of excess glucose. The frequent urination that results from this process is a common symptom of diabetes, which can lead to increased thirst and subsequent consumption of water (MAGALHÃES et al. 2019). Furthermore, it is possible that HIIT could lead to dehydration, thereby causing an increase in water intake among the EX and T2D + EX groups.

Our findings indicated that T2D has a detrimental impact on the levels of INS and LEP in the bloodstream, as well as on the expression of their respective receptors in the hypothalamus. Previous studies (Oquendo et al. 2022; D’souza et al. 2016; Lima et al. 2013; Morioka et al. 2013) has shown that there is a positive correlation between LEP levels and beta-cell function, as well as insulin secretion. This is consistent with our findings of lower INS-S levels. Furthermore, our study confirmed the presence of insulin resistance (IR) resulting from diabetes, as evidenced by a higher HOMA-IR in the T2D group. This IR subsequently leads to leptin resistance (LR), as indicated by decreased levels LEP-R in the hypothalamus. These findings are consistent with reports of previous studies (Platt et al. 2016; Cernea et al. 2018; El-Haschimi et al. 2000; Peng et al. 2021).

Activation of the LEP signaling pathway in the hypothalamus requires the phosphorylation of JAK and STAT proteins through binding to LEP-R (Park and Ahima 2014). However, T2D inhibits the phosphorylation and activation of JAK and STAT, disrupting appetite regulation, energy expenditure, and food intake (Platt et al. 2016). This blockade of LEP signaling through inactivation of JAK and STAT could result in the increase in LEP secretion, which may exacerbate hypothalamic LR (Wauters et al. 2003). Garzon et al. found that T2D increased the levels of dephosphorylated JAK2 and STAT3, leading to an increase in the expression of NPY and AGRP genes and a decrease in the expression of POMC and CART genes (Gurzov et al. 2016).

Furthermore, T2D results in an increase in SOCS3, which is an inhibitor of JAK/STAT signaling. This increase in SOCS3 reduces the inhibitory effect of STAT3 on FOXO1 (Liu et al. 2017; Yang et al. 2009), leading to an increase in the levels of orexigenic neuropeptides (i.e. NPY, AGRP) and a decrease in the levels of anorexigenic neuropeptides (i.e. POMC, CART) as FOXO1 exits the nucleus (Yang et al. 2009). Consistent with this, food intake was higher in T2D and T2D + EX compared to other groups.

Interestingly, we observed weight loss in the T2D group. In addition to IR, diabetes disrupts glucose absorption, which may explain why despite increased food intake, body weight decreased in the T2D group (Platt et al. 2016; Cernea et al. 2018; El-Haschimi et al. 2000; Peng et al. 2021).

In line with our results, many studies (Kang et al. 2013; Peng et al. 2021; Park et al. 2005) have demonstrated that exercise training can increase LEP-R expression in the hypothalamus, thereby reducing LR. This hypothesis is supported by the fact that decreased HOMA-IR is strongly correlated with a reduction in LR, likely due to the link between IR and LR. (Peng et al. 2021; Wauters et al. 2003; Oliveira et al. 2010). In addition, improving central LR via the regulation of IR could potentially aid in reducing the progression of diabetes (Peng et al. 2021; Moonishaa et al. 2017; Fischer et al. 2002; Zhao et al. 2011). Increased LEP secretion and LEP-R levels stimulate LEP signaling in the hypothalamus, which is initiated by JAK2 (Park and Ahima 2014; Kang et al. 2013). The phosphorylated JAK2 can phosphorylate and activate STAT3, the main stimulator of orexigenic neurons and a vital inhibitor of anorexigenic neurons (Park and Ahima 2014; Zhao et al. 2011). He et al. (2018a, b) reported decreased orexigenic neuropeptides (i.e., NPY and AGRP) and an increased anorexigenic neuropeptide (i.e., POMC) after ten sessions of HIIT. Other studies reported the same results (Park and Ahima 2014; Liu et al. 2017; Kang et al. 2013; Zhao et al. 2011).

On the other hand, it was observed that HIIT decreased the inhibitor of the JAK2/STAT3 (i.e., SOCS3), reinforcing the JAK2/STAT3 pathway and subsequently decreasing appetite (Liu et al. 2017; Kang et al. 2013).

In addition, HIIT decreased FOXO1 in the nucleus, thus eliminating its inhibitory effects on anorexigenic neuropeptides. Our findings are consistent with a study by Pauli et al., in which acute exercise (two 3 h exercise bouts separated by a 45 min rest period) was found to decrease the levels of dephosphorylated FOXO1 and increase the levels of phosphorylated FOXO1. The researchers suggested that reducing the activity of FOXO1 is crucial for LEP-mediated appetite regulation and can help to restore control over food intake in individuals with metabolic disorders (Pauli et al. 2015).

Conclusion

Our study demonstrated that 8 weeks of high-intensity interval training (HIIT) couldincrease the serum level of LEP as well as the expression of LEPR in the hypothalamus and therby improve the LEP signalling in the hypothalamus. This could finally lead to decreases the expression of NPY and AGRP and increases the expression POMC and CART, amilorating appetite regulation. Further research is warranted in the field, hoping that our research will inspire others working in humans.

Limitations and Suggestions Propective Studies

We had started by 10 rats in each group but due to mortality during T2D induction and 8 weeks HIIT, we ended up with 5 animals per group. The low number of animals in each group could affect the results. We used young adult rats in a rapid growth period that could potentially affect the results. In addition, we did not measure the fat mass which could affect the amount of LEP secretion. Using LEPR inhibitor in the perspective studies could also assure us that the observed results could be attribute to LEPR. Other appetite regulations signaling such as PI3K/AKT pathway, need to be investigated in the prospective studies. In addition, we suggest assessing LEP concentration in the cerebrospinal fluid (CSF) as an index of BBB permeability to LEP in the prespective studies.

Acknowledgements

We would like to thanks Mohammad Amin Rajizadeh and Abbas Bejeshk for their help and support.

Abbreviations

AGRP

Agouti-related protein

CART

Amphetamine-related transcript

CON

Non-type 2 diabetes control

EX

Non-type 2 diabetes exercise

FOXO1

Forkhead box protein O1

HIIT

High-intensity interval training

INS-S

Serum insulin levels

INS-H

Hypothalamus insulin

JAK-2

Janus kinase 2

LEP

Leptin

NPY

Neuropeptide Y

POMC

Pro-opiomelanocortin cocaine

SOCS3

Suppressor of cytokine signaling

STAT-3

Signal transducer and activator of transcription 3

T2D

Type 2 diabetes

T2D + EX

Type 2 diabetes + exercise

Vmax

Maximum velocity

Author Contributions

Conceptualization, KK; methodology, KK; software, MH; validation, MH; formal analysis, ZS; investigation, MH; resources, EM.; data curation, ZS ; writing—original draft preparation, EM; writing—review and editing, KK; visualization, ZS; supervision, KK; project administration, KK; funding acquisition, KK.

Funding

This research was supported by neuroscience research center, Kerman University of Medical Scinces (Project No: 400000089).

Data Availability

Data that support the findings of this study are available at Kerman University of Medical Scinces.

Declarations

Conflict of interest

No conflicts of interest, financial or otherwise, are declared by the authors.

Footnotes

Publisher’s Note

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References

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Associated Data

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Data Availability Statement

Data that support the findings of this study are available at Kerman University of Medical Scinces.

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