Effect of a Single Bout of Exercise on Autophagy Regulation in Skeletal Muscle of High-Fat High-Sucrose Diet-Fed Mice

Effects of gallic acid and physical training on liver damage, force, and anxiety in obese mice: Hepatic modulation of Sestrin 2 (SESN2) and PGC-α expression

Obesity and overweight are multifactorial diseases affecting more than one-third of the world's population. Physical inactivity contributes to a positive energy balance and the onset of obesity. Exercise combined with a balanced diet is an effective non-pharmacological strategy to improve obesity-related disorders. Gallic acid (GA), is a natural endogenous polyphenol found in a variety of fruits, vegetables, and wines, with beneficial effects on energetic homeostasis. The present study aims to investigate the effects of exercise training on obese mice supplemented with GA. Animal experimentation was performed with male Swiss mice divided into five groups: ST (standard control), HFD (obese control), HFD + GA (GA supplement), HFD + Trained (training), and HFD + GA + Trained (GA and training). The groups are treated for eight weeks with 200 mg/kg/body weight of the feed compound and, if applicable, physical training. The main findings of the present study show that GA supplementation improves liver fat, body weight, adiposity, and plasma insulin levels. In addition, animals treated with the GA and a physical training program demonstrate reduced levels of anxiety. Gene expression analyses show that Sesn2 is activated via PGC-1α independent of the GATOR2 protein, which is activated by GA in the context of physical activity. These data are corroborated by molecular docking analysis, demonstrating the interaction of GA with GATOR2. The present study contributes to understanding the metabolic effects of GA and physical training and demonstrates a new hepatic mechanism of action via Sestrin 2 and PGC-1α.

Autophagy and Exercise: Current Insights and Future Research Directions

Autophagy is a cellular process by which proteins and organelles are degraded inside the lysosome. Exercise is known to influence the regulation of autophagy in skeletal muscle. However, as gold standard techniques to assess autophagy flux in vivo are restricted to animal research, important gaps remain in our understanding of how exercise influences autophagy activity in humans. Using available datasets, we show how the gene expression profile of autophagy receptors and ATG8 family members differ between human and mouse skeletal muscle, providing a potential explanation for their differing exercise-induced autophagy responses. Furthermore, we provide a comprehensive view of autophagy regulation following exercise in humans by summarizing human transcriptomic and phosphoproteomic datasets that provide novel targets of potential relevance. These newly identified phosphorylation sites may provide an explanation as to why both endurance and resistance exercise lead to an exercise-induced reduction in LC3B-II, while possibly divergently regulating autophagy receptors, and, potentially, autophagy flux. We also provide recommendations to use ex vivo autophagy flux assays to better understand the influence of exercise, and other stimuli, on autophagy regulation in humans. This review provides a critical overview of the field and directs researchers towards novel research areas that will improve our understanding of autophagy regulation following exercise in humans.

A single bout of exhaustive treadmill exercise increased AMPK activation associated with enhanced autophagy in mice skeletal muscle

Previous studies reported inconsistent findings on autophagy activation in skeletal muscles after acute exercise. In this study, we investigated the effect of a single bout of exhaustive treadmill exercise on AMPK and autophagy activations in mice gastrocnemius muscle in vivo. Male ICR/CD-1 mice were randomly divided into the control and exercise groups. The later was subjected to a single bout of exhaustive treadmill exercise. Changes of AMPK, phosphorylation of AMPKThr172 (pAMPKThr172 ), and autophagy markers including Beclin1, LC3II/LC3I and p62 mRNA and protein expressions in gastrocnemius muscle at different times (0, 6, 12, 24 h) after the exercise were analysed by quantitative real-time PCR and western blot. Our results demonstrated that a single bout of exhaustive treadmill exercise significantly induced AMPK content and AMPK activity at 0, 6 and 12 h after the exercise, and changed the expressions of autophagy markers at different time points in the recovery period, respectively. Moreover, we observed positive correlations between expressions of LC3II/LC3I ratio and pAMPKThr172 or AMPK, and a negative correlation between expressions of p62 and AMPK or pAMPKThr172 . In conclusion, a single bout of exhaustive treadmill exercise in mice caused a prolonged activation of AMPK and improved autophagy in the gastrocnemius muscle. The regulation of autophagic markers were related to enhanced AMPK activity. The findings indicate that acute exercise enhanced AMPK-related autophagy activation may be the underlying molecular mechanism that regulates cellular energy metabolism during exercise.

Exercise and Training Regulation of Autophagy Markers in Human and Rat Skeletal Muscle

Autophagy is a key intracellular mechanism by which cells degrade old or dysfunctional proteins and organelles. In skeletal muscle, evidence suggests that exercise increases autophagosome content and autophagy flux. However, the exercise-induced response seems to differ between rodents and humans, and little is known about how different exercise prescription parameters may affect these results. The present study utilised skeletal muscle samples obtained from four different experimental studies using rats and humans. Here, we show that, following exercise, in the soleus muscle of Wistar rats, there is an increase in LC3B-I protein levels immediately after exercise (+109%), and a subsequent increase in LC3B-II protein levels 3 h into the recovery (+97%), despite no change in Map1lc3b mRNA levels. Conversely, in human skeletal muscle, there is an immediate exercise-induced decrease in LC3B-II protein levels (−24%), independent of whether exercise is performed below or above the maximal lactate steady state, which returns to baseline 3.5 h following recovery, while no change in LC3B-I protein levels or MAP1LC3B mRNA levels is observed. SQSTM1/p62 protein and mRNA levels did not change in either rats or humans following exercise. By employing an ex vivo autophagy flux assay previously used in rodents we demonstrate that the exercise-induced decrease in LC3B-II protein levels in humans does not reflect a decreased autophagy flux. Instead, effect size analyses suggest a modest-to-large increase in autophagy flux following exercise that lasts up to 24 h. Our findings suggest that exercise-induced changes in autophagosome content markers differ between rodents and humans, and that exercise-induced decreases in LC3B-II protein levels do not reflect autophagy flux level.

EFFECTS OF EXHAUSTIVE EXERCISE AND CONTUSION ON AUTOPHAGY-RELATED FACTORS IN SKELETAL MUSCLE OF RATS

ABSTRACT Objective: To study the effects of exhaustive exercise and contusion on autophagy-related factors Beclin1, LC3 and PINK1 expression in the skeletal muscle of rats. Methods: Forty-two male SD rats were randomly divided into 7 groups, 6 rats in each group: C, D0, D24, D48, E0, E24, and E48. Each group of rats was killed and dissected at the different respective time points specified above. The whole quadriceps femoris of the left hind limbs were removed and divided into two parts, one for mRNAs of Beclin1, LC3 and PINK1 by real-time fluorescent quantitative PCR, and the other for LC3 protein by Western blotting. Results: Compared with group C, the contents of Beclin1 mRNA, PINK1 mRNA, and LC3 mRNA in the immediate exhaustive exercise group (E0) were significantly reduced p<0.01. However, the levels of PINK1 mRNA, LC3 mRNA, and LC3 protein in skeletal muscle cells increased significantly in the 48 hours after exhaustion (E48) p<0.05, suggesting that cell autophagy had an increasing trend during the recovery period. Meanwhile, compared with the C group, the contents of Beclin1 mRNA, PINK1 mRNA, and LC3 mRNA in the immediate blunt contusion group (D0) increased significantly p<0.01 and were followed by a downward trend. Conclusion: Generally, there were differences between the blunt contusion and exhausted exercise models at each recovery phase. The gene expression of the autophagy-related factors was not high in the early exhaustive exercise recovery phase and subsequently followed an upward trend. But the above factors increased significantly in the immediate and early recovery phases after blunt contusion. Injury from blunt contusion may be more severe than exhaustive exercise-induced-injury, so the autophagy starts earlier according to the changes in autophagy-related factors. Level of evidence III; Therapeutic studies investigating the results of treatment.

The Effects of Exercise and Restriction of Sugar-Sweetened Beverages on Muscle Function and Autophagy Regulation in High-Fat High-Sucrose-Fed Obesity Mice

BACKGROUND

Autophagy maintains muscle mass and healthy skeletal muscles. Several recent studies have associated sugar-sweetened beverage (SSB) consumption with diseases. We investigated whether muscle dysfunction due to obesity could be restored by SSB restriction (SR) alone or in combination with exercise (EX) training.

METHODS

Obese mice were subjected to SR combined with treadmill EX. Intraperitoneal glucose tolerance test, grip strength test, hanging time test, and body composition analysis were performed. Triglyceride (TG) and total cholesterol (TC) serum concentrations and TG concentrations in quadriceps muscles were analyzed. Western blot and reverse transcription-quantitative polymerase chain reaction helped analyze autophagy-related protein and mRNA expression, respectively.

RESULTS

SR alone had no significant effect on fasting blood glucose levels, glucose tolerance, and muscle function. However, it had effect on serum TC, serum TG, and BCL2 interacting protein 3 expression. SR+EX improved glucose tolerance and muscle function and increased serum TC utilization than SR alone. SR+EX reduced P62 levels, increased glucose transporter type 4 and peroxisome proliferator-activated receptor γ coactivator-1α protein expression, and improved grip strength relative to the high-fat and high-sucrose liquid (HFHS) group, and this was not observed in the HFHS+EX group.

CONCLUSION

SR induced mitophagy-related protein expression in quadriceps, without affecting muscle function. And, the combination of SR and EX activated mitophagy-related proteins and improved muscle function.

Differential Protein Metabolism and Regeneration in Gastrocnemius Muscles in High-fat Diet Fed Mice and Pre-hibernation Daurian Ground Squirrels: A Comparison between Pathological and Healthy Obesity

We focused on pathological obesity induced by excessive fat intake (nutritional obesity) in non-hibernator and healthy obesity due to pre-hibernation (PRE) fat storage in hibernator to study the effects of different types of obesity on skeletal muscle protein metabolism and cell regeneration. Kunming mice were fed with high-fat diet for 3 months to construct a pathological obesity model. Daurian ground squirrels fattened naturally before hibernation were used as a healthy obesity model. Body weight, adipose tissue wet weight, gastrocnemius muscle wet weight, muscle fiber cross-sectional area (CSA) and fiber type distribution were measured. The protein expression levels related to protein degradation (MuRF-1, atrogin-1, calpain1, calpain2, calpastatin, desmin, troponin T, Beclin-1, LC3-II), protein synthesis (P-Akt, P-mTORC1, P-S6K1, P-4E-BP1) and cell regeneration (MyoD, myogenin, myostatin) were detected by Western blot. As a result, the body weight and adipose tissue wet weight were both significantly increased in high fat obese (OB) mice and pre-hibernation fat (PRE) ground squirrels. The muscle wet weight, ratio of muscle wet weight to body weight, and muscle fiber CSA were significantly decreased, while the percentage of MHC I fiber isoform was significantly increased in gastrocnemius muscle of OB mice compared with the control (CON) group. The protein expression levels of P-Akt, P-mTORC1, P-4E-BP1 and myogenin were significantly decreased, while those of calpain1, calpain2, MuRF-1 and myostatin were significantly increased in the OB mice. In the ground squirrels, the muscle wet weight, muscle fiber CSA and percentage of MHC I fiber isoform all showed no change in the gastrocnemius muscle in the PRE group compared with the summer active (SA) group. The protein expression levels of P-Akt, P-mTORC1, P-S6K1 and MyoD were significantly increased, while those of Beclin-1 and LC3-II were significantly decreased in the PRE ground squirrels. This study demonstrated that the decrease in protein expression levels in the Akt/mTOR pathway (P-Akt, P-mTORC1 and P-4E-BP1) and cell regeneration (myogenin) and the increase in protein expression levels of the calpain pathway (calpain1 and calpain2) and ubiquitin-proteasome pathway (MuRF-1) were involved in the mechanism of muscle atrophy in gastrocnemius muscle of the pathologically obese Kunming mice induced by high-fat diet. In contrast, the increased protein expression levels of the Akt/mTOR pathway (P-Akt, P-mTORC1 and P-S6K1) and cell regeneration (MyoD), and the decreased protein expression levels of the autophagy lysosomal pathway (Beclin-1 and LC3-II) were involved in the mechanism of anti-atrophy in gastrocnemius muscle of the healthy obese ground squirrels fattened before hibernation.

The effects of diet composition and chronic obesity on muscle growth and function

Diet-induced obesity (DIO) is associated with glucose intolerance, insulin resistance (IR), and an increase in intramyocellular lipids (IMCL), which may lead to disturbances in glucose and protein metabolism. To this matter, it has been speculated that chronic obesity and elevated IMCL may contribute to skeletal muscle loss and deficits in muscle function and growth capacity. Thus, we hypothesized that diets with elevated fat content would induce obesity and insulin resistance, leading to a decrease in muscle mass and an attenuated growth response to increased external loading in adult male mice. Male C57BL/6 mice (8 wk of age) were subjected to five different diets, namely, chow, low-dat-diet (LFD), high-fat-diet (HFD), sucrose, or Western diet, for 28 wk. At 25 wk, HFD and Western diets induced a 60.4% and 35.9% increase in body weight, respectively. Interestingly, HFD, but not Western or sucrose, induced glucose intolerance and insulin resistance. Measurement of isometric torque (ankle plantar flexor and ankle dorsiflexor muscles) revealed no effect of DIO on muscle function. At 28 wk of intervention, muscle area and protein synthesis were similar across all diet groups, despite insulin resistance and increased IMCL being observed in HFD and Western diet groups. In response to 30 days of functional overload, an attenuated growth response was observed in only the HFD group. Nevertheless, our results show that DIO alone is not sufficient to induce muscle atrophy and contractile dysfunction in adult male C57BL/6 mice. However, diet composition does have an impact on muscle growth in response to increased external loading.NEW & NOTEWORTHY The effects of diet-induced obesity on skeletal muscle mass are complex and dependent on diet composition and diet duration. The present study results show that chronic exposure to high levels of fatty acids does not affect muscle mass, contractile function, or protein synthesis in obese C57BL/6 mice compared with the consumption of chow. Obesity did result in a delay in load-induced growth; however, only a 45% HFD resulted in attenuated growth following 30 days of functional overload.