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Histone deacetylase 4/5 (HDAC4/5) are essential for regulating metabolic gene expression; AMPKα2 regulates HDAC4/5 activity and the expression of MuRF1 during exercise. In this study, we used wild-type and AMPKα2−/− mice to explore the potential regulatory relationship between AMPKα2 and HDAC4/5 expression during exercise. Firstly, we fed C57BL/6J mice with high-fat diet for 8 weeks to assess the effects of high-fat diet on skeletal muscle metabolism and HDAC4/5 expression. We then performed a 6-week treadmill exercise on both wild-type and AMPKα2−/− mice. After exercise, the expressions of HDAC4/5 were examined in both gastrocnemius and soleus. The citrate synthase activity and proteins involved in skeletal muscle oxidative process were assessed. To determine the relationship of HDAC4/5 and skeletal muscle oxidative capacity, citrate synthase activity was assessed after silencing HDAC4/5. Moreover, HDAC5 ubiquitination and the association of MuRF1 to HDAC5 were also investigated. Our results showed that 6-week exercise increased the skeletal muscle oxidative capacity and decreased HDAC4/5 expression only in soleus. HDAC5 silencing increased C2C12 cell oxidative capacity. Proteasome inhibition by MG132 abolished exercise-induced HDAC5 degradation mediated by MuRF1–ubiquitin–proteasome system. However, the ubiquitin–proteasome system (UPS) did not dominantly account for exercise-induced HDAC4 degradation. Exercise upregulated MuRF1–HDAC5 association in wild-type mice but not in AMPKα2−/− mice. Our results revealed that 6-week exercise increased the skeletal muscle oxidative capacity and promoted HDAC5 degradation in soleus through the UPS, MuRF1-mediated HDAC5 ubiquitination. Although AMPKα2 played a partial role in regulating MuRF1 expression and HDAC5 ubiquitination, exercise-induced HDAC5 degradation did not fully depend on AMPKα2.

Neuronal regeneration and functional recovery are severely compromised following traumatic brain injury (TBI). Treatment options, including cell transplantation and drug therapy, have been shown to benefit TBI, although the underlying mechanisms remain elusive. In this study, neural stem cells (NSCs) are transplanted into TBI-challenged mice, together with olfactory ensheathing cells (OECs) or followed by valproic acid (VPA) treatment. Both OEC grafting and VPA treatment facilitate the differentiation of NSCs into neurons (including endogenous and exogenous neurons) and significantly attenuate neurological functional defects in TBI mice. Combination of NSCs with OECs or VPA administration leads to overt improvement in axonal regeneration, synaptogenesis, and synaptic plasticity in the cerebral cortex in TBI-challenged mice, as shown by retrograde corticospinal tract tracing, electron microscopy, growth-associated protein 43 (GAP43), and synaptophysin (SYN) analyses. However, these beneficial effects of VPA are reversed by local delivery of N-methyl-D-aspartate (NMDA) into tissues surrounding the injury epicenter in the cerebral cortex, accompanied by a pronounced drop in axons and synapses in the brain. Our findings reveal that increased axonal regeneration and synaptogenesis evoked by cell grafting and VPA fosters neural repair in a murine model of TBI. Moreover, VPA-induced neuroprotective roles are antagonized by exogenous NMDA administration and its concomitant decrease in the number of neurons of local brain, indicating that increased neurons induced by VPA treatment mediate axonal regeneration and synaptogenesis in mice after TBI operation. Collectively, this study provides new insights into NSC transplantation therapy for TBI.

Skeletal muscle insulin resistance (IR) is closely linked to hyperglycemia and metabolic disorders. Regular exercise enhances insulin sensitivity in skeletal muscle, but its underlying mechanisms remain unknown. Sestrin3 (SESN3) is a stress-inducible protein that protects against obesity-induced hepatic steatosis and insulin resistance. Regular exercise training is known to increase SESN3 expression in skeletal muscle. The purpose of this study was to explore whether SESN3 mediates the metabolic effects of exercise in the mouse model of high-fat diet (HFD)-induced IR. SESN3

With exercise, white adipose tissues (WAT) are readily convertible to a "brown-like" state, altering from lipid-storing to energy-catabolizing function, which counteracts obesity and increases insulin sensitivity. Sestrin2 (SESN2) is a stress-inducible protein that can regulate the cold-induced increase of uncoupling protein 1 (UCP1), which is paramount for the thermogenic capacity of brown-like WAT. This study aimed to elucidate the necessity of SESN2 in mediating exercise-induced browning of WAT.We used 8-week, male wild-type and SESN2 knockout C57BL/6J mice to explore the potential role of SESN2 in the exercise-induced WAT browning process. Over a 3-week intervention (sedentary versus treadmill exercise, normal chow versus 60% high-fat diet), we examined the exercise-induced alterations of the browning phenotype in different depots of white fat. In vitro, 3T3-L1 pre-adipocytes and primary adipocytes were used to determine the potential mechanism.Our data revealed that SESN2 was required for the exercise-induced subcutaneous WAT (scWAT) browning. This may be mediated by higher fibronectin type III domain containing 5 (FNDC5) contents in scWAT locally, rather than skeletal muscle FNDC5 expression and circulating serum irisin levels. SESN2 ablation significantly impaired the exercise-improved glucose metabolism, where browning of scWAT may serve as an essential pathway. Moreover, SESN2 ablation significantly attenuated the exercise-promoted respiratory exchange ratio and indexes of energy metabolism (oxygen uptake and energy expenditure).Taken together, our results provided evidence that SESN2 is a key integrating factor in driving the diverse metabolic benefits conferred by aerobic exercise.

The health benefits of exercise have attracted substantial attention, because regular exercise can strengthen muscles and improve endurance. Physical activity is an integral part of an overall healthy lifestyle, which helps protect against chronic diseases, such as obesity, insulin resistance and type 2 diabetes. In consideration of the differences in duration, intensity, and type of activity of exercise, it is likely to involve different signaling pathways and bring different benefits in different tissues. Here we review our growing knowledge of exercise training adaptations and regulation in cellular processes related to energy metabolism, aging and autophagy, and many important findings remain to be discovered.

SESN2 and JNK are emerging powerful stress-inducible proteins in regulating lipid metabolism. The aim of this study was to determine the underlying mechanism of SESN2/JNK signaling in exercise to improve lipid disorder induced by high-fat diet (HFD). Our data showed that HFD and SESN2 knockout resulted in abnormalities including elevated body weight, increased fat mass, serum total cholesterol, lipid biosynthesis related proteins, and a concomitant increase of pJNK-Thr183/Tyr185. The above changes were reversed by exercise training. SESN2 silencing or JNK inhibition in palmitate-treated C2C12 further confirmed that SESN2 and JNK play a vital role in lipid biosynthesis. Rescue experiment further demonstrated that SESN2 reduced lipid biosynthesis through inhibition of JNK. SESN2/JNK signaling axis regulates lipid biosynthesis in both animal and cell models with abnormalities of lipid metabolism induced by HFD or palmitate treatment. This study provided evidence that exercise ameliorated lipid metabolic disorder induced by HFD feeding or by SESN2 knockout. SESN2 may improve lipid metabolism through inhibition JNK expression in skeletal muscle cells, providing a molecular mechanism that may represent an attractive target for the treatment of lipid disorder. Novelty: Exercise improved lipid disorder induced by HFD feeding and SESN2 knockout. SESN2 and JNK play a vital role in lipid biosynthesis in vivo and in vitro. SESN2 suppressed JNK to improve lipid metabolism in skeletal muscle cells.

Sarcopenia, the age-related loss of skeletal muscle mass and function, contributes to high morbidity and mortality in the older population. Regular exercise is necessary to avoid the initiation and progression of sarcopenia, in which the underlying molecular mechanism is still not clear. Our data revealed that the outcomes induced by sarcopenia, including muscle mass and strength loss, decreased cross-sectional area of gastrocnemius fiber, chronic inflammation, and increased dysfunctional mitochondria, were reversed by regulation exercise. Knockout or silencing of Sestrin2 (Sesn2) resulted in imbalanced mitochondrial fusion and fission, mitochondrial biogenesis, and mitophagy damage in vivo and in vitro, which was attenuated by aerobic exercise or overexpression of Sesn2. Moreover, we found that the effects of Sesn2 on mitochondrial function are dependent on AMP-activated protein kinase α2 (AMPKα2). This study indicates that aerobic exercise alleviates the negative effects resulting from sarcopenia via the Sesn2/AMPKα2 pathway and provides new insights into the molecular mechanism by which the Sesn2/AMPKα2 signaling axis mediates the beneficial impact of exercise on sarcopenia.

Exercise training increases insulin sensitivity. Over the past decades, considerable progress has been made in understanding the molecular basis for this important effect of physical exercise. However, the underlying mechanism is still not fully described. Recent studies have revealed that the stress responsive protein family Sestrins (SESNs) may play an important role in improving insulin sensitivity of skeletal muscle under exercise training. In this study, we aim to better understand the relationship between SESNs and AMPK in response to exercise training and the possible mechanism by which SESNs mediate glucose metabolism. We used wild type, AMPKα2+/− and AMPKα2−/− C57BL/6 mice to reveal the pathway by which 6 weeks of exercise training induced SESNs. We explored the mechanism through which SESNs regulated glucose metabolism in vitro by overexpressing or inhibiting SESNs, and inhibiting AMPK or autophagy in myotubes. We found that a 6-week exercise training regime improved oxidative metabolism, activated the insulin signaling pathway and increased the level of SESN2 and SESN3 in an AMPKα2-dependent manner. Overexpression of SESN3 or SESN2 and SESN3 together increased glucose uptake, activated the insulin signaling pathway, and promoted GLUT4 translocation in myotubes. Although inhibition of SESNs had no effect on glucose uptake, SESNs could reverse reduced glucose uptake following autophagy inhibition, and may be downstream effectors of AMPK responses in myotubes. Taken together our data show that SESNs are induced by AMPKα2 after exercise training, and SESNs, specifically SESN3, play a key role in exercise training-mediated glucose metabolism in skeletal muscle.

Titin serves important functions in skeletal muscle during exercise, and posttranslational modifications of titin participate in the regulation of titin-based sarcomeric functions. Scriptaid has exercise-like effects through the inhibition of HDAC and regulatory acetylation of proteins. However, it remains mostly unclear if exercise could result in titin’s acetylation and whether Scriptaid could regulate acetylation of titin. We treated C57BL/6 mice with 6-wk treadmill exercise and 6-wk Scriptaid administration to explore Scriptaid’s effects on mice exercise capacity and whether Scriptaid administration/exercise could induce titin’s acetylation modification. An exercise endurance test was conducted to explore their effects on mice exercise capacity, and proteomic studies were conducted with gastrocnemius muscle tissue of mice from different groups to explore titin’s acetylation modification. We found that Scriptaid and exercise did not change titin’s protein expression, but they did induce acetylation modification changes of titin. In total, 333 acetylated lysine sites were identified. Exercise changed the acetylation levels of 33 lysine sites of titin, whereas Scriptaid changed acetylation levels of 31 titin lysine sites. Exercise treatment and Scriptaid administration shared 11 lysine sites. In conclusion, Scriptaid increased exercise endurance of mice by increasing the time mice spent running to fatigue. Acetylation is a common type of posttranslational modification of titin, and exercise/Scriptaid changed the acetylation levels of titin and titin-interacting proteins. Most importantly, titin may be a mediator through which Scriptaid and exercise modulate the properties and functions of exercise-induced skeletal muscle at the molecular level. NEW & NOTEWORTHY Scriptaid administration increased mouse exercise endurance. Acetylation is another type of posttranslational modification of titin. Scriptaid/exercise changed acetylation levels of titin and titin-interacting proteins. Titin may mediate exercise-induced skeletal muscle properties and functions.

Impaired insulin-stimulated glucose uptake in skeletal muscle serves a critical role in the development of insulin resistance (IR), whereas the precise mechanism of the process remains unknown. Recently, the evolutionarily conserved, stress-inducible protein Sestrin2 (Sesn2) has been proposed to play a protective role against obesity-induced IR and diabetes. Activation of Sesn2 may activate AMP-activated protein kinase (AMPK) accompanied by suppression of mammalian target of rapamycin (mTOR), which may ultimately lead to autophagy induction. In view of the potential protective effects of autophagy on the physiological and the pathological regulatory processes via the regulation of energy homeostasis and metabolism, we investigated the effects of Sesn2 on the components of the insulin signaling pathway and insulin-stimulated glucose uptake in palmitate-induced insulin-resistant C2C12 myotubes. We showed that Sesn2 effectively restored the impaired insulin signaling. Moreover, autophagic activity decreased in response to palmitate, whereas Sesn2 significantly reversed the palmitate-suppressed autophagic signaling in this context. Our findings further revealed that Sesn2-induced autophagy contributed to restore the impaired insulin signaling through the activation of AMPK signal. Even in the presence of palmitate, Sesn2 up-regulation maintained insulin sensitivity and glucose metabolism via AMPK-dependent autophagic activation.

Activation of AMP-activated protein kinase (AMPK) has been viewed as an important target for the treatment of insulin resistance. Here, by proteomic analysis, we found that expression of heat shock protein beta-1 (HSPB1) was induced by the AMP analog 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside in palmitate-induced insulin-resistant cells. Overexpression of AMPKα2, or activation of AMPKα via acute/chronic exercise training, increased HSPB1 expression in the skeletal muscle. In AMPKα2-/- mice, HSPB1 expression was downregulated in the quadriceps muscles. Exercise did not increase HSPB1 expression in AMPKα2-/- mice. Moreover, overexpression of HSPB1 enhanced insulin sensitivity in palmitate-induced insulin-resistant cells and restored metabolic phenotypes associated with defective AMPK. Finally, HSPB1 was required for AMPK-mediated activation of the class IIa histone deacetylases and glucose uptake in the skeletal muscle. Our results demonstrate that AMPK-mediated HSPB1 expression enhanced insulin sensitivity in the skeletal muscle.

The composition and activity of the gut microbiota depend on the host genome, nutrition, and lifestyle. Exercise and sodium butyrate (NaB) exert metabolic benefits in both mice and humans. However, the underlying mechanisms have not been fully elucidated. This study aimed to examine the effect of exercise training and dietary supplementation of butyrate on the composition of gut microbiota and whether the altered gut microbiota can stimulate differential production of short-chain fatty acids (SCFAs), which promote the expression of SESN2 and CRTC2 to improve metabolic health and protect against obesity. C57BL/6J mice were used to study the effect of exercise and high-fat diet (HFD) with or without NaB on gut microbiota. Bacterial communities were assayed in fecal samples using pyrosequencing of 16S rRNA gene amplicons. Western blot was performed using relevant antibodies to detect the protein expressions in liver and HepG2 cell extracts. Exercise and butyrate administration significantly reversed metabolic dysfunctions induced by HFD (P P = 0.001). Exercise and butyrate supplementation significantly inhibited the relative abundance of lipopolysaccharide-producing phyla (P = 0.001). SESN2 and CRTC2 expression in the liver of mice were significantly increased after exercise (P P

Objective Obesity is becoming increasingly prevalent and is an important contributor to the worldwide burden of diseases. It is widely accepted that exercise training is beneficial for the prevention and treatment of obesity. However, the underlying mechanism by which exercise training improving skeletal muscle lipid metabolism is still not fully described. Sestrins (Sestrin1-3) are highly conserved stress-inducible protein. Concomitant ablation of Sestrin2 and Sestrin3 has been reported to provoke hepatic mTORC1/S6K1 activation and insulin resistance even without nutritional overload and obesity, implicating that Sestrin2 and Sestrin3 have an important homeostatic function in the control of mammalian glucose and lipid metabolism. Our previous results demonstrated that physical exercise increased Sestrin2 expression in murine skeletal muscle, while the role of Sestrin2 in regulating lipid metabolism remains unknown. SH2 domain containing inositol 5-phosphatase (SHIP2) acts as a negative regulator of the insulin signaling both in vitro and in vivo. An increased expression of SHIP2 inhibits the insulin-induced Akt activation, glucose uptake, and glycogen synthesis in 3T3-L1 adipocytes, L6 myotubes and tissues of animal models. Alterations of SHIP2 expression and/or enzymatic function appear to have a profound impact on the development of insulin resistance. However, the regulatory function of SHIP2 in lipid metabolism after exercise remains unclear. It has been reported that SHIP2 modulated lipid metabolism through regulating the activity of c-Jun N-terminal kinase (JNK) and Sterol regulatory element-binding protein-1 (SREBP-1). JNK is a subclass of mitogen-activated protein kinase (MAPK) signaling pathway in mammalian cells and plays a crucial role in metabolic changes and inflammation associated with a high-fat diet. Inhibition of JNK reduces lipid deposition and proteins level of fatty acid de novo synthesis in liver cells. It has been reported that Sestrin2 regulated the phosphorylation of JNK, however the underlying mechanism remains unclear. SREBP-1 is important in regulating cholesterol biosynthesis and uptake and fatty acid biosynthesis, and SREBP-1 expression produces two different isoforms, SREBP-1a and SREBP-1c. SREBP-1c is responsible for regulating the genes required for de novo lipogenesis and its expression is regulated by insulin. SREBP-1a regulates genes related to lipid and cholesterol production and its activity is regulated by sterol levels in the cell. Altogether, the purpose of this study was to explore the effect and underlying mechanism of Sestrin2 on lipid accumulation after exercise training. Methods Male wild type and SESN2−/− mice were divided into normal chow (NC) and high-fat diet (HFD) groups to create insulin resistance mice model. After 8 weeks the IR model group was then divided into HFD sedentary control and HFD exercise groups (HE). Mice in HE group underwent 6-week treadmill exercise to reveal the effect of exercise training on lipid metabolism in insulin resistance model induced by HFD. We explored the mechanism through which Sestrin2 regulated lipid metabolism in vitro by supplying palmitate, overexpressing or inhibiting SESNs, SHIP2 and JNK in myotubes. Results We found that 6-week exercise training decreased body weight, BMI and fat mass in wild type and SESN2-/- mice after high-fat diet (HFD) feeding. And exercise training decreased the level of plasma glucose, serum insulin, triglycerides and free fatty acids in wild type but not in Sestrin2-/- mice. Lipid droplet in skeletal muscle was also decreased in wild type but did not in Sestrin2-/- mice. Moreover, exercise training increased the proteins expression involved in fatty acid oxidation and decreased the proteins which related to fatty acid de novo synthesis. The results of oil red staining and the change of proteins related to fatty acid de novo synthesis and beta oxidation in myotubes treated with palmitate, Ad-SESN2 and siRNA-Sestrin2 were consisted with the results in vivo, which suggested that Sestrin2 was a key regulator in lipid metabolism. Exercise training increased Sestrin2 expression and reversed up-regulation of SHIP2 and pJNK induced by HFD in wild type mice but not in Sestrin2-/- mice. In parallel, overexpression of Sestrin2 decreased the level of SHIP2 and pJNK induced by palmitate while Sestrin2 knock down by siRNA-Sestrin2 treatment did not change the expression of SHIP2 and pJNK, which suggested that Sestrin2 modulated SHIP2 and JNK in the state of abnormal lipid metabolism. Inhibition of SHIP2 reduced the activity of JNK, increased lipid accumulation and the proteins of fatty acid synthesis after palmitate treatment and over expression of Sestrin2, which suggest that Sestrin2 modulated lipid metabolism through SHIP2/JNK pathway. Conclusions Sestrin2 plays an important role in improving lipid metabolism after exercise training, and Sestrin2 regulates lipid metabolism by SHIP2-JNK pathway in skeletal muscle.

Abnormal glucose metabolism induces various metabolic disorders such as insulin resistance and type 2 diabetes. Regular exercise improved glucose uptake and enhanced glucose oxidation by increasing GLUT4 transcription in skeletal muscle. However, the regulatory mechanisms of GLUT4 transcription in response to exercise are poorly understood. AMPK is a sensor of exercise and upstream kinase of class II HDACs that act as transcriptional repressors. We used 6-week treadmill exercise or one single-bout exercise wild type or AMPKα2-/- C57BL/6J mice to explore how HDACs regulate GLUT4 transcription and the underlying molecular mechanisms mediated by AMPK in the physiologic process of exercise. We demonstrate that regular physical exercise significantly enhanced GLUT4 transcription by inactivating HDAC4/5 in skeletal muscle by ChIP experiment. HDAC4 coordinately regulated with HDAC5 represses transcriptional activity of GLUT4 promoter in C2C12 myotubes by Luciferase assay. If either HDAC4 or HDAC5 is silenced via RNAi technology, the functional compensation by the other will occur. In addition, a single-bout of exercise decreased HDAC4/5 activity in skeletal muscle of wild type but not in AMPKα2-/- mice, suggesting an AMPKα2-dependent manner. Those findings provide new insight into the mechanisms responsible for AMPKα2-dependent regulation of GLUT4 transcription after exercise.

Aim Muscle-type carnitine palmitoyltransferase 1 (CPT1b) plays an important role in skeletal muscle mitochondrial fatty acid β-oxidation. A myocyte-specific enhancer factor (MEF2) site that binds MEF2A in the promoter of Cpt1b has been identified. The aim of this study is to determine whether Cpt1b expression is regulated by MEF2 in response to exercise training. Methods Twelve male, 14-week-old C57BL/6 mice underwent 6 weeks of treadmill exercise at 12 m min−1, for 60 min day−1, 5 days week−1. Quadriceps muscles were analysed by real-time PCR, Western blot, chromatin immunoprecipitation. Results The binding of MEF2A to the Cpt1b promoter was elevated in the quadriceps muscle of mice after 6-week aerobic exercise intervention. The repressor partner of MEF2, histone deacetylase 5 (HDAC5), binding to the Cpt1b promoter was decreased by exercise training. In C2C12 myoblast, MEF2A overexpression increased the Cpt1b mRNA expression and the Cpt1b promoter transcriptional activity, which were suppressed by HDAC5. Moreover, exercise training induced MEF2A hyperacetylation, which is strongly associated with its enhanced DNA-binding ability. The binding of both HDAC5 and histone deacetylase 3 (HDAC3) to MEF2A was decreased by exercise training. Overexpression of HDAC5 decreased exogenous MEF2A acetylation level with an increased binding of endogenous HDAC3 to MEF2A. Finally, the phosphorylation levels of HDAC5 Ser259 and Ser498 were increased by exercise training. Exercise training decreased the abundance of HDAC5 in the nucleus while increasing its abundance in the cytoplasm. Conclusion Our results indicated that exercise-induced CPT1b expression was at least in part mediated by HDAC5/MEF2A interaction.

Exercise training may decrease insulin resistance (IR) and increase glucose tolerance. However, the adaptive responses in skeletal muscle at the molecular and genetic level have not been clearly understood. Here we used oligonucleotide microarray analysis to dissect the effects of high-fat diet (HFD) and regular aerobic exercise on global gene expression in the skeletal muscle of C57BL/6 mice. C57BL/6 male mice (n = 40) were fed with normal chow (n = 20) and HFD (n = 20) for 8 weeks. The animals were then divided into 1 of 4 intervention groups: groups of mice fed with normal chow and HFD accompanied with 6-week treadmill running (60 min/d) at 75% maximum oxygen consumption (NE and HE) and their sedentary control groups (NC and HC). Oligonucleotide microarray was applied to analyze the effect of aerobic exercise and HFD at the transcriptional level, and selected genes were confirmed by real-time polymerase chain reaction. Our data showed that 6 weeks of aerobic exercise improved the plasma lipid profile and reversed the glucose intolerance induced by HFD. A set of 503 genes was differentially expressed in samples of HC mice as compared with those of the NC group. Forty of those genes were identified as involved in the process of aerobic exercise ameliorating IR by comparing the changes in expression profiles between the HE and HC groups. These changes include genes involved in metabolism, defense, and inflammation and genes of unknown function. Aerobic exercise training is able to ameliorate IR of mice maintained with HFD. The biochemical pathways involved in ameliorating IR identified in this study may represent potential targets for the treatment of IR.

Objective Exercise has beneficial effects on human health, including protection against metabolic disorders such as diabetes. However, the cellular mechanisms underlying the metabolic effects of exercise are not completely understood. We know that autophagy plays an important role in maintaining cellular homeostasis. In this study, we aimed to better understand the metabolic effects of autophagy in skeletal muscle and the role of Sestrins/AMPK in mediating the beneficial effects of physical exercise through autophagy. Material/methods We used wild type and AMPKα2−/− C57BL/6 mice as animal models to elucidate the role of AMPK in autophagy activation and the metabolism-promoting effects of acute and regular exercise. C2C12 myotubes were used to study the metabolic effects of autophagy in vitro. Results Autophagy promotes glucose uptake in skeletal muscle. A single bout of exercise increased the activity of autophagy in the skeletal muscle of wild type mice but not of AMPKα2−/− mice. This difference was associated with increased amounts of both Sestrin2 and Sestrin3 coimmunoprecipitated with AMPKα2. Long-term physical exercise significantly increased the basal level of muscle autophagy and protein expression of Sestrin2 and Sestrin3 in both normal chow and high-fat diet-fed mice. Conclusion We believe that exercise-induced AMPK and Sestrins interaction may be involved in the beneficial metabolic effects of exercise by activating autophagy. This interaction provides a molecular mechanism that is a potential target in metabolic syndromes.

Aerobic exercise has beneficial effects on both weight control and skeletal muscle insulin sensitivity through a number of specific signaling proteins. To investigate the targets by which exercise exerts its effects on insulin resistance, an approach of proteomic screen was applied to detect the potential different protein expressions from skeletal muscle of insulin-resistant mice after prolonged aerobic exercise training and their sedentary controls. Eighteen C57BL/6 mice were divided into two groups: 6 mice were fed normal chow (NC) and 12 mice were fed high-fat diet (HFD) for 10 weeks to produce an IR model. The model group was then subdivided into HFD sedentary control (HC, n = 6) and HFD exercise groups (HE, n = 6). Mice in HE group underwent 6 weeks of treadmill running. After 6 weeks, mice were sacrificed and skeletal muscle was dissected. Total protein (n = 6, each group) was extracted and followed by citrate synthase, 2D proteome profile analysis and immunoblot. Fifteen protein spots were altered between the NC and HC groups and 23 protein spots were changed between the HC and HE groups significantly. The results provided an array of changes in protein abundance in exercise-trained skeletal muscle and also provided the basis for a new hypothesis regarding the mechanism of exercise ameliorating insulin resistance.

The crosstalk between mTORC1/S6K1 signaling and AMPK is emerging as a powerful and highly regulated way to gauge cellular energy and nutrient content. The aim of the current study was to determine the mechanism by which exercise training reverses lipid-induced insulin resistance and the role of AMPK/mTOR/S6K1 signaling axis in mediating this response in skeletal muscle. Our results showed that high-fat feeding resulted in decreased glucose tolerance, which was associated with decreased Akt expression and increased intramuscular triglyceride deposition in the skeletal muscle of C57BL/6 mice. Impairments in lipid metabolism were accompanied by increased total protein and phosphorylation of S6K1, SREBP-1c cleavage, and decreased AMPK phosphorylation. Exercise training reversed these impairments, resulting in improved serum lipid profiles and glucose tolerance. C2C12 myotubes were exposed to palmitate, resulting in an increased insulin-dependent Akt Ser473 phosphorylation, associated with a significant increase in the level of phosphorylation of S6K1 on T389. All these changes were reversed by activation of AMPK. Consistent with this, inhibition of AMPK by compound C induced an enhanced phosphorylation of both S6K1 and Akt, and silencing of S6K1 with siRNA showed no effect on Akt phosphorylation in both the absence and presence of palmitate cultured myotubes. In addition, compound C led to an elevated SREBP-1c cleavage but was blocked by S6K1 siRNA. In summary, exercise training inhibits SREBP-1c cleavage through AMPK/mTOR/S6K1 signaling, resulting in decreased intramyocellular lipid accumulation. Our results provide new insights into the mechanism by which AMPK/mTOR/S6K1 signaling axis mediates the physiological process of exercise-induced insulin sensitization.