2023 Impact Factor
2023 Impact Factor
The incidence of metabolic diseases, including diabetes mellitus (DM), is continuously increasing worldwide (Arroyave et al., 2020). DM is associated with insufficient insulin production and hyperglycemic conditions that lead to myopathy, cardiovascular diseases, nephropathy, and other complications (Purnamasari et al., 2022). Among these, myopathy contributes to the progression of other complications and comorbidities, accompanied by several symptoms (i.e., reduced physical capacity, weakness, and reduced skeletal muscle mass) (Bassi-Dibai et al., 2022).
Skeletal muscle, which is the largest component of the body, is an important tissue that maintains glucose homeostasis (Savikj et al., 2022). Several studies have reported that DM engages the skeletal muscle as the major tissue (Shen et al., 2022; Cea et al., 2023). Owing to this, diabetic skeletal muscle diseases, including myopathy, are common pathological conditions, and are characterized by symptoms such as reduced skeletal muscle mass and acceleration of muscle atrophy (Tariq et al., 2023). Muscle atrophy in turn weakens insulin reactions and increases blood glucose levels. Therefore, it is important to identify an effective solution for skeletal muscle atrophy in patients with DM.
Muscle atrophy leads to wasting or a reduce in muscle size owing to injury, lack of use, or disease (Bodine et al., 2023). It is characterized by several muscle alterations (e.g., myofiber shrinkage, changing fiber types, etc.) (Sartori et al., 2021). E3 ubiquitin ligases, such as muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx/atrogin-1), trigger muscle atrophy via mediating protein degradation, revealing the prime biomarkers in muscles (Bodine and Baehr, 2014). These ligases affect tumor necrosis factor-α (TNF-α) and transforming growth factor beta (TGF-β) signaling, which are overactivated in diabetic muscle and directly engage in muscle protein degradation, contributing to muscle atrophy (Orhan et al., 2021). Thus, inhibition of these two E3 ubiquitin ligases is considered an effective strategy for preventing skeletal muscle dysfunction.
Methylglyoxal (MGO) is an α-dicarbonyl metabolite from glycolysis in the human body, and a well-known causative agent of diabetic complications (Baig et al., 2017). It binds easily to proteins, lipids, and DNA to form advanced glycation end products (AGEs) (Ramasamy et al., 2006). In particular, MGO shows a critical role in mitochondrial dysfunction and inflammation, causing diabetic complications (Schalkwijk and Stehouwer, 2020). Recent studies reported that MGO is involved in the development and progression of skeletal muscle atrophy (Lai et al., 2022; Todoriki et al., 2022). It induces mitochondrial dysfunction in skeletal muscles and decreases the expressed levels of several genes associated to mitochondrial biogenesis and the glyoxalase system (Egawa et al., 2022). Moreover, it facilitates atrophy, inflammation, fibrosis, and oxidative stress in myoblasts (Todoriki et al., 2022). However, whether MGO affects skeletal muscles (e.g., gastrocnemius, plantaris, soleus, and extensor digitorum longus) and the underlying mechanisms remain unknown.
Exercise is an effective strategy for improving skeletal muscle dysfunction and a good physical activity for improving human health (Dieter and Vella, 2013). It has already been demonstrated that exercise increases insulin signaling, glucose uptake, and mitochondrial metabolism in skeletal muscles; however, a few reports have revealed that patients with diabetes who have insulin resistance have a reduced response to mitochondrial function including biogenesis after exercise (Egawa et al., 2022). Distinguishing between exercise- and non-exercised-resistance entries seem complicated. Further, few reports revealed the relationship between aerobic exercise and MGO. Besides, there are no studies on the effects of aerobic exercise on MGO-induced muscle atrophy.
In addition, numerous studies showed the muscle specific sensitivity to exercise training. For example, Egawa et al. (2022) showed that exercise adaptions such as endurance exercise enhanced more clearly in plantaris (PLA) muscle than soleus (SOL) muscle. Other studies revealed that exercise training such as running wheel increased the activities of mitochondrial functions (i.e., biogenesis, angiogenesis, aerobic enzymes) in PLA (Hyatt et al., 2019). Meanwhile, aerobic exercise by using treadmill facilitated the gastrocnemius (GCM) muscle mass than other muscles (Seo et al., 2015). Although the mechanisms underlying phenomenon is still not clear, it seems to different muscle sensitivity among various exercise types. Although the deep mechanisms underlying muscle atrophy is still not clear, it seems to be variable to sensitivity of each muscle involved depending on the type of exercise.
Thus, our work aimed to evaluate whether MGO induces muscle atrophy and to assess the ameliorative effect of aerobic exercise in an MGO-induced muscle atrophy model. We examined the effect of moderate-intensity aerobic exercise on the size and function of skeletal muscle, and other related factors in mice with MGO-induced muscle atrophy. We used mice undergoing moderate-intensity treadmill exercise with MGO treatment for 2 weeks. The designed model will be useful for evaluating the effects of MGO on exercise adaptations in skeletal muscle atrophy over a short period. This is the first trial study to reveal that MGO is a risk factor for skeletal muscle atrophy and that aerobic exercise has an ameliorative effect on this phenomenon.
Institute of Cancer Research (ICR) mice (5-weeks, male) were purchased from Orient Bio (Seongnam, Korea), fed a laboratory diet (AIN-76A), and given water ad libitum. The mice were housed for 1 week at 23 ± 1°C and a relative humidity of 55 ± 5% under a 12 h light/dark cycle. Aerobic exercise was performed on a treadmill following training adaptation for 1 week. After adaptation, each mouse was randomly divided into three groups (eight mice per group): Control (Con), MGO-treated (MGO, 60 mg/kg), and MGO-treated with exercise (MGO, 60 mg/kg). MGO (dissolved in 30% v/v glycerol in saline) was rectal injected to the experimental ICR mice for 2 weeks at a dose of 60 mg/kg. The exercise group performed aerobic exercise for 2 weeks after adaptation and was administered MGO (Scheme 1). The Animal Care Committee of the Center of Animal Care and Use at Gachon University (GU1-2022-IA0046) reviewed and approved all experimental guidelines.
Figure 1. Schematic diagram of in vivo experiments. Aerobic exercise on a treadmill was performed for 1 week. After adaptation, the mice were randomly divided into three groups (eight mice per group): Control (Con), MGO-treated (MGO, 60 mg/kg), and MGO-treated with exercise (MGO, 60 mg/kg). MGO (dissolved in 30% v/v glycerol in saline) was administered to the experimental ICR mice via rectal injection for 2 weeks at a dose of 60 mg/kg. The exercise group performed the aerobic exercise for 2 weeks after adaptation and was administered MGO.
A moderate-intensity aerobic (treadmill) exercise design (see Scheme 1) for measuring physical activity was used (Sakai et al., 2017). Briefly, each mouse was placed on a treadmill (JD-A-22, Jungdo B&P, Seoul, Korea) at a speed of 5 m/min for the first 5 min, followed by a flow-up at a speed of 10 m/min for the next 5 min, and then at a speed of 8 m/min for the last 20 min without inclination. Mice were allowed to adapt to the treadmill for 1 week, and then the above exercise was performed for 2 weeks. After 3 weeks, running time (s) and speed (m/min) were recorded manually.
The grip strength of each mouse was analyzed as maximal muscle strength (Park et al., 2023). The mice grasped a piece of green steel connected to a force gauge. Next, the tail of each mouse was then pulled from the steel graft until its forelimb released the graft. The grip strength (g) was analyzed three times, and the average value was recorded on the last day of the experiment. The mice were adapted to the grip strength meter (JD-A-22, Jungdo B&P) on the last day.
A rotarod test (JD-A-07TS, Jungdo B&P) was performed on the last day to measure the balance and coordination (Doukkali et al., 2015). The velocity of the rod (diameter: 3 cm) was set at constant speeds of 10, 15, and 20 rpm. The latency until a fall was automatically recorded using a magnetic trip plate.
The thickness of the left leg of each mouse was measured before sacrifice using electronic digital calipers (Mitutoyo, Tokyo, Japan). Wet muscle mass of the SOL, PLA, GCM, and extensor digitorum longus (EDL) muscles was analyzed. Muscles obtained from legs of sacrificed mice were quantitatively dissected and weighed. Values obtained from measuring both the right and left legs were averaged.
GCM and EDL muscles were homogenized in RIPA buffer containing protease/phosphatase inhibitor cocktails and then centrifuged at 12,000 rpm for 1 h at 4°C (Brock Symons et al., 2023). Proteins (30 µg) were separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis to measure their expression. The separated proteins were transferred to a nitrocellulose membrane and then incubated overnight at 4°C with primary antibodies against muscle atrophy, viz. F-box (MAFbx/atrogin-1, ab-168372, 1:1000, Abcam, Cambridge, UK), MuRF1 (ab-172479, 1:1000, Abcam), myosin heavy chain (MyHC, sc-376157, Santa Cruz Biotechnology, CA, USA), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH. Sc-32233; Santa Cruz Biotechnology). After incubation and rinsing with T-BST, the membrane was incubated with an HRP-conjugated secondary antibody for 1 h at room temperature (25°C). Membranes were analyzed using a ChemiDoc XRS+ imaging system (Bio-Rad, Hercules, CA, USA).
GCM and EDL muscles were fixed in 10% neutral buffered formalin for 24 h then embedded in paraffin. Four micrometer thickness sections were sliced and stained with hematoxylin and eosin (H&E) for histopathological analysis or Sirius red for analyzing collagen fibers. Changes in the muscle tissue morphology were observed at 20-40× magnification by using microscope (Olympus, Tokyo, Japan). The cross-sectional area of 100 muscle fibers from each skeletal muscle was determined using ImageJ software (National Institutes of Health, NY, USA).
The 4 μm paraffin-embedded sections were deparaffinized using xylene and rehydrated with EtOH (100% to 70%), followed by treatment with peroxidase blocker, and finally washed with PBS. Each section silde were incubated with primary antibodies, MAFbx/atrogin-1 (dilution 1:100) and MyHC (dilution 1:100) at 4°C for 1 day. In the next day, each section was incubated with secondary antibodies, rabbit and mouse IgG (dilution 1:200) for 1 h, followed by incubation with an avidin-biotin horseradish peroxidase complex (Vector Laboratories, CA, USA). The expression of MAFbx/atrogin-1 and MyHC following GCM and EDL immunoreactivity was calculating via ImageJ software (National Institutes of Health). Images were captured at 20-40× magnification by using microscope (Olympus).
All data were analyzed using GraphPad Prism 5 software (GraphPad Software, Inc., La Jolla, CA, USA) and are represented as means ± standard error of the mean (SEM). All results were analyzed using one-way or two-way analysis of variance (ANOVA). Statistical significance was set at p<0.05.
To evaluate the effect of MGO on skeletal muscle function in ICR mice, we performed several exercise tests using a treadmill, grip strength, and rotor rod. In the treadmill behavior test (Fig. 1A), the exercise group showed significantly increased running time (1697.1 ± 26.8 s, ***p<0.001) in comparison with the MGO-treated group (985.30 ± 130.01 s, ###p<0.001). In addition, we observed increased speeds in the exercise group (32.30 ± 1.28 meter/min, ##p<0.01) which were similar to those of the control group. On the last day, grip strength and rotarod tests were performed in each group. As shown in Fig. 1B, grip strength, which measures muscle strength factor, was significantly decreased in the MGO-treated group (3.36 ± 0.14 N/g, ##p<0.01), but significantly restored in the exercise group (4.12 ± 0.15 N/g, *p<0.05). Moreover, the data of the rotarod test (Fig. 1C) showed that the exercise group (173.88 ± 5.80 s, *p<0.05) significantly stayed on longer than of the MGO-treated group (109.63 ± 24.12 s). Our results indicate that MGO may be a risk factor for reduced skeletal muscle function.
Figure 2. Aerobic exercise restored atrophy in mice following MGO treatment. (A) The running time (s) and speed (m/min) were recorded after aerobic exercise on the last day. (B) The grip strength test was performed on the last day after aerobic exercise. (C) The rotarod test was performed to determine motor balance and coordination on the last day after aerobic exercise. Data are presented as mean ± SEM (n=8). #p<0.05, ##p<0.01 and ###p<0.001 vs. control group. *p<0.05, **p<0.01 and ***p<0.001 vs. MGO treated group.
To measure the effect of aerobic exercise in the MGO-induced muscle atrophy mouse model, we first measured the body weight and thickness of the calf skeletal muscle (refer to Fig. 2). The MGO-treated group (*p<0.05) did not show any loss in body weight in comparison with the control group. However, the exercise group had a significantly lower body weight than the control group (Fig. 2A), suggesting that treadmill exercise could reduce body weight in mice. Interestingly, the thickness of calf, which is essential for walking and running, was significantly decreased by MGO treatment (4.90 ± 0.11 mm, ###p<0.001); however, exercise led to an increase in calf thickness (5.70 ± 0.15 mm, *p<0.05) as shown in Fig. 2B. MGO treatment decreased calf thickness in a short period of time, indicating that MGO might be associated with metabolic muscle atrophy. Furthermore, the muscle mass of calf in exercise group (58.12 ± 5.75 mg/g, *p<0.05) that normalized to body weight significantly increased in the MGO-induced muscle atrophy mouse model, whereas the MGO-treated group significantly decreased muscle mass of calf (37.35 ± 7.11 mg/g, #p<0.05). In addition, our findings suggest that aerobic exercise may reverse MGO-induced atrophy in calf muscles. To this end, we further evaluated the mass of different types of calf muscles, including the SOL, GCM, PLA, and EDL muscles.
Figure 3. Aerobic exercise reduced body weight and restored calf thickness. (A) Changes in body weight during experiments. (B) The thickness of the left leg in mice was measured before sacrifice using electronic digital calipers. (C) Fresh calf muscle mass was analyzed. The muscles obtained from legs of sacrificed mice were quantitatively dissected and weighed. The values obtained from measuring the right and left leg muscles were averaged. Data are presented as mean ± SEM (n=8). #p<0.05 and ###p<0.001 vs. control group. *p<0.05 vs. MGO treated group.
It is well-known that aerobic exercise constantly stimulates the calf muscle including gastrocnemius (GCM), and extensor digitorum longus (EDL), which helps to improve balance and running ability (Hesse, 1999). To analyze the effect of aerobic exercise on MGO-induced atrophic alterations, we analyzed SOL, PLA, GCM, and EDL skeletal muscle mass. As shown in Fig. 3, each muscle normalized to body weight was increased following exercise (SOL, 3.99 ± 0.24 mg/g; PLA, 7.97 ± 0.24 mg/g; GCM, 52.22 ± 1.77 mg/g; EDL, 4.69 ± 0.18 mg/g) in the MGO-induced muscle atrophy mouse model, whereas the MGO-treated group showed slightly decreased muscle mass (SOL, 2.09 ± 0.08 mg/g; PLA, 5.20 ± 0.11 mg/g; GCM, 42.69 ± 1.13 mg/g; EDL, 2.85 ± 0.13 mg/g) in comparison with the control group (SOL, 2.70 ± 0.14 mg/g; PLA, 2.09 ± 0.08 mg/g; GCM, 48.55 ± 1.33 mg/g; EDL, 3.21 ± 0.21 mg/g). These results show that aerobic exercise has beneficial effects in preventing the progression of skeletal muscle atrophy via active metabolites of glucose, such as MGO.
Figure 4. Aerobic exercise increased SOL, PLA, GCM, and EDL muscle mass. Wet soleus (SOL), plantaris (PLA), gastrocnemius (GCM), and extensor digitorum longus (EDL) muscle mass was analyzed. The muscles obtained from legs of sacrificed mice were quantitatively dissected and weighed. The values obtained from measuring the right and left leg muscles were averaged. Data are presented as mean ± SEM (n=8). #p<0.05 vs. control group. **p<0.01 and ***p<0.001 vs. MGO treated group.
We first examined the expression levels of atrophic factors, including MuRF1, MAFbx/atrogin-1, and MyHC, in SOL, PLA, GCM, and EDL muscles. SOL and EDL muscles did not show any changes in protein expression levels (data not shown). Interestingly, we found that the GCM muscle, as a type I fiber, and the EDL muscle, as a type II fiber, showed related atrophic factors. Two E3 ubiquitin ligases, MuRF1 and atrogin-1, are atrophy biomarkers that are involved in skeletal muscle degradation (Bodine and Baehr, 2014). The expression levels in the GCM muscle were increased by MGO treatment, whereas the exercise group showed restored protein levels of MuRF1 (*p<0.05) and MAFbx/atrogin-1 (*p<0.05). MyHC, a sarcomeric thick filament, functions as a myosin motor molecule, and MAFbx/atrogin-1 degrades myogenic factors such as MyHC (Dablainville and Sanchez, 2019) (See Fig. 4). As shown in Fig. 4B, the expressed levels of MyHC were significantly higher in the exercise group (*p<0.05) than MGO-treated group, indicating that aerobic exercise stimulated MyHC in the EDL muscle and suppressed skeletal muscle atrophy induced by MGO.
Figure 5. Aerobic exercise decreased levels of muscle degradation factors and increased those of muscle synthesis factors in a MGO-induced muscle atrophy mouse model. (A) Protein levels of MuRF1 and MAFbx/atrogin-1 in the GCM muscle were analyzed by western blotting. (B) Protein levels of MyHC in the EDL muscle were analyzed by western blotting. GAPDH was used as a loading control. Quantification was performed using Bio-Rad Quantity software. Data are presented as mean ± SEM (n=3). ##p<0.01 vs. control group. *p<0.05 and ***p<0.001 vs. MGO treated group.
Next, we examined the effect of aerobic exercise on skeletal muscle atrophy, which showed altered atrophy factors from MGO treatment. The results of H&E staining of GCM and EDL muscles showed that treatment with MGO caused clear variations in size and arrangement of the muscles; however, the exercise group recovered from these changes (Fig. 5). The cross-sectional area of GCM and EDL muscle fibers was significantly reduced by approximately 2.5-5 folds in the MGO-treated group, comparing with control group. However, the exercise group showed a significantly increased cross-sectional area of the GCM (603.97 ± 11.66 µm2, **p<0.01) and EDL (309.89 ± 16.42 µm2, **p<0.01) muscle fibers compared to the MGO group (GCM, 457.06 ± 17.46 µm2; EDL, 185.01 ± 6.94 µm2). These results suggest that aerobic exercise restores MGO-induced decreases in muscle mass and function. To characterize fibrosis in GCM and EDL muscles, we stained each muscle section with Sirius red to investigate the collagen content (Fig. 5A, 5B). In the MGO-treated group, collagen content was significantly increased in GCM (4.95 ± 0.76%, ##p<0.01) and EDL (10.04 ± 1.74%, ##p<0.01) muscles in comparison to that of the control group (GCM, 0.89 ± 0.18%; EDL, 1.61 ± 0.71%). On the other hand, in the exercise group, collagen content of GCM (1.68 ± 0.31%, **p<0.01) and EDL (3.47 ± 0.70%, *p<0.05) muscles dramatically lower than MGO-treated group. It also appeared as if aerobic exercise suppressed fibrosis in GCM and EDL muscles in the MGO-induced muscle atrophy mouse model.
Figure 6. Aerobic exercise increased muscle myofiber size and decreased collagen accumulation in a MGO-induced muscle atrophy mouse model. (A, B) Histological analyses of GCM (A) and EDL (B) muscles including H&E and Sirius red staining were performed. Cross-sectional area and collagen contents of GCM and EDL muscles were measured using ImageJ software. Data are presented as mean ± SEM (n=3). ##p<0.01 and ###p<0.001 vs. control group. *p<0.05 and **p<0.01 vs. MGO treated group.
In the immunohistochemistry assay (Fig. 6), MAFbx/atrogin-1 protein was significantly increased in the MGO-treated group (~3-folds, ###p<0.001) compared with control group. In particular, GCM cells in the exercise group (~2-folds, ***p<0.001) strongly suppressed yellow-brown particles compared to the MGO-treated group. Meanwhile, MyHC protein of the EDL muscle in the exercise group (~4-folds, ***p<0.001) significantly increased the number of yellow-brown particles compared to that of the MGO-treated group. This finding indicates that aerobic exercise significantly downregulated the expression levels of MAFbx/atrogin-1 protein in GCM muscle and enhanced MyHC in the EDL muscle, which supported the western blotting results (refer to Fig. 4).
Figure 7. Aerobic exercise improved the levels of MAFbx/atrogin-1 in the GCM muscle and MyHC in the EDL muscle in a MGO-induced muscle atrophy mouse model. (A, B) Immunohistochemical analyses of GCM (A) and EDL (B) muscles for MAFbx/atrogin-1 and MyHC were performed, respectively. The obtained immunochemical images were quantified using ImageJ software. Data are presented as mean ± SEM (n=3). ###p<0.001 vs. control group. ***p<0.001 vs. MGO treated group.
Skeletal muscles contain 30 to 40% of total body mass and are associated with movement, energy metabolism, and respiration (Rasmussen and Phillips, 2003). Muscle mass is regulated by dynamic balances among related protein genesis, synthesis, and degradation (Bonaldo and Sandri, 2013). With these regulation processes, it is important to prevent protein degradation, which leads to decreased mass and function of muscle and results as muscle atrophy (Jhuo et al., 2023). This atrophy is a serious complication that can cause several pathological conditions, including myopathy, and increase morbidity and mortality in humans (Bassi-Dibai et al., 2022). Exercise is a typical treatment for preventing skeletal muscle atrophy; however, it is necessary to elucidate its benefits at the molecular level (Bonaldo and Sandri, 2013). Therefore, we examined the effect of moderate-intensity aerobic exercise on size and function of skeletal muscle, and its underlying molecular parameters in an animal model of atrophy.
In the present study, it investigated the effect of aerobic exercise on MGO-induced skeletal muscle atrophy. MGO, with high glucotoxicity, is a reactive dicarbonyl compound that develops into AGEs and causes DM complications such as myopathy (Lee et al., 2023). The MGO levels in the serum are higher in patients with DM than in healthy individuals (Yadav et al., 2023). This indicates that MGO might have a negative effect on skeletal muscle. We hypothesized that MGO plays a central role in increasing skeletal muscle atrophy. Interestingly, our data indicated that MGO directly and indirectly damaged skeletal muscles, including reducing OL, PLA, GCM, and EDL muscle mass (Fig. 2, 3). Under MGO treatment conditions, the ratio of GCM muscle weight to body weight decreased, and the levels of muscle fibrosis and related atrophy proteins such as MuRF and MAFbx/atrogin-1 increased (Fig. 4, 6). In addition, EDL muscles showed that treatment with MGO suppressed MyHC-related myogenesis and caused poor behavioral values on the treadmill, during grip strength, and on the rotarod system (Fig. 1, 4, 6). Based on our data, we suggest that MGO may be one of major risk factor as an endogenous molecule in human body on the induction of skeletal muscle atrophy as similar as dexamethasone, which causes muscle atrophy as an exogenous compound (Park et al., 2023). Also, MGO, as an endogenous toxic molecule, may be a key target for regulating the skeletal muscle atrophy.
Aerobic exercise is a potential intervention for accelerating the action of insulin in glucose homeostasis, whereas MGO is considered a negative factor for insulin transduction (Egawa et al., 2022). Therefore, we aimed to evaluate whether MGO induces muscle atrophy and examine the ameliorative effect of aerobic exercise using a MGO-induced muscle atrophy mouse model. Interestingly, the exercise group showed recovery of body weight/mass, muscle fiber, and MyHC protein following MGO treatment, resulting in attenuated skeletal muscle atrophy (Fig. 1-6). Exercise promotes skeletal muscle glucose uptake and is associated with insulin-stimulated glucose disposal (Rebello et al., 2023). Moreover, mitochondrial dysfunction caused by insulin resistance in skeletal muscles results in atrophy (Zhang et al., 2023). Several studies have demonstrated that exercise in diabetic models increases AKT activation and HKII expression, which are related to mitochondrial function (Nogueira-Ferreira et al., 2023). This suggests that aerobic exercise may attenuate the influence of MGO on skeletal muscle atrophy and increase mitochondrial function to mediate insulin resistance in glucose metabolic diseases.
In the skeletal muscle, the detoxification system of MGO is mainly modulated via glyoxalase-1, glyoxalase-2, and aldehyde dehydrogenase-2, metabolizing MGO to d-lactate and pyruvate (Egawa et al., 2022). In addition, the receptor of AGEs (RAGE) is related to the biological functions of MGO, which reacts with several types of proteins to produce AGEs (Yadav et al., 2023). RAGE is known to stimulate cellular dysfunction in skeletal muscles (Shen et al., 2022). Several studies have been reported that the treatment of MGO downregulates the expression levels of glyoxalase-1 and aldehyde dehyrogenase-2 in the PLA muscle, indicating that MGO may be a causative agent for stimulating muscle atrophy via dysfunction of the MGO detoxification system (Egawa et al., 2022). Also, it had reported that exercise increased the expression levels of several molecular (e.g., peroxisome proliferator-activated receptor gamma coactivator 1α, mitochondria complex proteins, glyoxalase 1 enzyme, etc.), expecting that aerobic exercise may be enhanced their molecular and restore the skeletal muscles such as GCM (Egawa et al., 2022). Also, a mechanism study that can explain the differential sensitivity of responding muscles between exercise only doing groups and exercise-doing group with MGO treatment should be conducted later.
This study showed that aerobic exercise increased the sensitivity of GCM and EDL muscles when compared to that of SOL and PLA muscles. Numerous studies have demonstrated the efficacy of treadmill exercise (Handschin et al., 2007; Kjobsted et al., 2017). For example, our results showed that aerobic exercise for 2 weeks did not attenuate atrophic factors (i.e., MuRF1, MAFbx/Atrogin-1, and MyHC) in the SOL and PLA muscles, but increased muscle mass. Previous studies have demonstrated that exercising for 8 weeks induces mitochondrial biogenesis and aerobic enzymes in PLA and SOL muscles, indicating that our designed model did not show the sensitivity of these muscles in the investigated short-term training period (Egawa et al., 2022). In spite of fact that the mechanisms underlying the resistance remain unclear, PLA and SOL muscles may demand a higher exercise intensity to show a response.
GCM is the main muscle that maintains the balance in muscle metabolism (Yang et al., 2022). A few studies have revealed that GCM muscles are contributed in the regulation of muscle metabolism in muscle atrophy models (Honda et al., 2022; Jhuo et al., 2023; Park et al., 2023). In this work, it found that aerobic exercise strongly restored decreased GCM muscle mass and increased the levels of atrophic factors (i.e., MuRF1 and MAFbx/atrogin-1) in mice with MGO-induced muscle atrophy, probably due to the regulation of protein degradation. The ubiquitin ligases MuRF1 and MAFbx/atrogin-1 are related to muscle atrophy induced by drug inducers such as dexamethasone, which contribute to muscle dysfunction (Park et al., 2023). Moreover, the upregulation of PI3K/AKT signaling in skeletal muscle is related to protein synthesis, improving the inhibition of the ubiquitin ligase-dependent proteolytic pathway (Shi et al., 2023). The mechanisms underlying the GCM muscle through exercise seem to mediate the improvement in muscle mass related to PI3K/AKT, MuRF1, and MAFbx/atrogin-1 signaling. Therefore, we plan to conduct further experiments in this field.
The EDL is also a major muscle that is classified as a type II skeletal muscle fiber (Girgenrath et al., 2005). These are fast-twitch fibers with low endurance and have been shown to occur predominantly in a glucocorticoid (GC)-induced muscle atrophy model (Jun et al., 2023). Various pathological conditions characterized by muscle atrophy are related with increased GC levels, indicating that GCs may trigger muscle atrophy (Fang et al., 1995). It was reported that GCs increase the expression levels of myostatin as a negative regulator in muscle growth, which decreases the fiber cross-sectional area and reduces myofibrillar and MyHC proteins (Smith et al., 2010). In particular, GCs disrupt insulin signaling in muscle cells (Macedo et al., 2023). In our previous work, it found that MGO slightly enhanced the levels of GC receptors, indicating that MGO can accelerate the expression of GCs and attenuate MyHCs (unpublished). Herein, we also found that aerobic exercise resulted in increased expression of MyHC protein levels in the EDL, suggesting that exercise stimulated specific muscle sensitivity in this muscle to restore skeletal muscle atrophy.
In summary, our study showed that skeletal muscle atrophy induced by treatment with MGO not only facilitated muscle mass and atrophy factors (e.g., MuRF1, MAFbx/atrogin-1, and MyHC), but also enabled muscle atrophy. Our designed in vivo model could be useful for identifying anti-muscle atrophic agents in the short term. In addition, aerobic exercise ameliorated MGO-induced muscle atrophy by increasing the sensitivity of GCM and EDL muscle functions. A mechanistic study of the role of glucose metabolism factors and GCs in the ameliorative effect of exercise on MGO-induced muscle atrophy is essential in future studies.
Taken together, we demonstrated that aerobic exercise ameliorates skeletal muscle atrophy induced by MGO and increases mass and function of skeletal muscle in GCM and EDL muscles of mice via regulating muscle protein degradation and biogenesis. Our findings suggest that aerobic exercise could be a powerful tool for regulating skeletal muscle atrophy via metabolic factors, such as MGO.
The authors declare no conflict of interest.
The authors declare no conflict of interest.
Seong-Min Hong: Conceptualization, formal analysis, data curation, methodology, writing, reviewing, and editing. Eun Yoo Lee: Conceptualization, formal analysis, data curation, and methodology. Jinho Park: Formal analysis, data curation, and methodology. Jiyoun Kim: Conceptualization, supervision, writing, reviewing, and editing and funding acquisition. Sun Yeon Kim: Conceptualization, supervision, writing, reviewing, and editing.
Funding Information
National Research Foundation of Korea Ministry of Education |
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